mechanisms of disease the myeloproliferative disordersnejmra063728

8/20/2019 Mechanisms of Disease the Myeloproliferative Disordersnejmra063728

1/15

review article

Th e n e w e n g l a n d j o u r n a l o f m ed i c i n e

n engl j med 355;23 www.nejm.org december 7, 20062452

Mechanisms of Disease

The Myeloproliferative DisordersPeter J. Campbell, F.R.A.C.P., F.R.C.P.A.,

and Anthony R. Green, F.R.C.Path., F.Med.Sci.

From the Department of Haematology,Cambridge Institute for Medical Research,University of Cambridge, Cambridge, Unit-ed Kingdom. Address reprint requests toDr. Green at the Department of Haema-tology, Cambridge Institute for MedicalResearch, Hills Rd., Cambridge CB2 2XY,United Kingdom, or at [email protected].

N Engl J Med 2006;355:2452-66.Copyright © 2006 Massachusetts Medical Society.

The myeloproliferative disorders comprise several clonal he-

matologic diseases that are thought to arise from a transformation in a he-

matopoietic stem cell. The main clinical features of these diseases are theoverproduction of mature, functional blood cells and a long clinical course. Chron-

ic myeloid leukemia (not discussed in detail here) is a myeloproliferative disorderthat is defined by its causative molecular lesion, the BCR-ABL fusion gene, whichmost commonly results from the Philadelphia translocation (Ph).1 The three main

Ph-negative myeloproliferative disorders — polycythemia vera, essential thrombocy-themia, and idiopathic myelofibrosis — are the focus of this article. Less common

conditions that are also considered myeloproliferative disorders under the classifi-cation used by the World Health Organization include systemic mastocytosis, chron-

ic eosinophilic leukemia, chronic myelomonocytic leukemia, and chronic neutro-philic leukemia.2

The cardinal features of the three main myeloproliferative disorders are an in-

creased red-cell mass in polycythemia vera, a high platelet count in essential throm-bocythemia, and bone marrow f ibrosis in idiopathic myelofibrosis (Fig. 1). These

three disorders share many characteristics, including marrow hypercellularity, apropensity to thrombosis and hemorrhage, and a risk of leukemic transformation

in the long term. The annual incidences of both polycythemia vera and essentialthrombocythemia are 1 to 3 cases per 100,000 population; myelofibrosis is less

common.3

Pathogenetic Features

Clues to Molecular Mechanisms

Polycythemia vera, a condition of “persistent and excessive hypercellularity accom-panied by cyanosis,” was recognized by Vaquez in 1892,4 and idiopathic myelofibro-sis was described at about the same time (Table 1).23 Essential thrombocythemia

was recognized in the 1930s.24 Dameshek, in 1951, was the first to appreciate theconsiderable overlap in the clinical and laboratory features of these conditions and

proposed that they, together with chronic myeloid leukemia and other rarer disor-ders, constitute a spectrum of related diseases. He coined the term “myeloprolif-

erative disorders” to embrace these related conditions.5 In 1974, a critical experi-ment showed that erythroid progenitors from the bone marrow of patients withpolycythemia vera were capable of growing in vitro in the absence of erythropoie-

tin.10 At about the same time, studies based on X-chromosome inactivation wereperformed in women with polycythemia vera or essential thrombocythemia who

carried a polymorphic variant of the X-linked G6PD gene. The results suggested thateach of these diseases originated from a clone of hematopoietic stem cells.11,25

The New England Journal of Medicine

Downloaded from nejm.org by LINO F ROJAS L on February 14, 2014. For personal use only. No other uses without permission.

Copyright © 2006 Massachusetts Medical Society. All rights reserved.


2/15


n engl j med 355;23 www.nejm.org december 7, 2006 2453

Other clues to the molecular mechanisms re-

sponsible for the myeloproliferative disorders havebeen accumulating. These include the association

of several chronic myeloid cancers with activatedtyrosine kinases (Table 2)13-18,37 and the recog-

nition of increased signaling through Janus ki-nases and signal transducers and activators oftranscription (JAK–STAT) and phosphatidylino-

sitol 3-kinase (PI3K) pathways in erythroid and

myeloid cells.21,22,54 An additional hint came with

the discovery of recurrent mitotic recombinationevents affecting chromosome 9p, resulting in the

loss of heterozygosity but a normal DNA copynumber.20

The JAK2 V617F Mutation

In 2005, several groups reported a single, acquired

point mutation in the Janus kinase 2 ( JAK2) gene

PolycythemiaVera

Peripheral BloodBone Marrow

(hematoxylin and eosin)Bone Marrow

(reticulin stain)

EssentialThrombocythemia

IdiopathicMyelofibrosis

Figure 1. Laboratory Features of Polycythemia Vera, Essential Thrombocythemia, and Idiopathic Myelofibrosis.

Polycythemia vera is characterized by an increased hematocrit in the peripheral blood (test tube on left); a hypercel-

lular marrow with increased numbers of erythroid, megakaryocytic, and granulocytic precursor cells; and a variableincrease in the number of reticulin fibers. Essential thrombocythemia is characterized by an increase in the number

of platelets in the peripheral blood and an increased number of megakaryocytes in the marrow, which tend to clus-

ter together and have hyperlobated nuclei. Idiopathic myelofibrosis is characterized by the presence of immature redand white cells (a so-called leukoerythroblastic blood film) and “teardrop” red cells, disordered cellular architecture,

dysplastic megakaryocytes, new bone formation in the marrow, and the formation of collagen fibers.





3/15



in the majority of patients with Ph-negative myelo-proliferative disorders.6-9,19 JAK2, a cytoplasmic

tyrosine kinase, is critical for instigating intracel-lular signaling by the receptors for erythropoi-etin, thrombopoietin, interleukin-3, granulocyte

colony-stimulating factor (G-CSF), and granulo-cyte–macrophage colony-stimulating factor (GM-

CSF).55,56 Mice that are deficient in Jak2 die atembryonic day 12.5, with a complete absence of

definitive ery thropoiesis,57,58 a finding that un-derscores the vital role of JAK2 as a transducer ofsignals evoked by the binding of erythropoietin

to its receptor. JAK2 binds to the erythropoietinreceptor in the endoplasmic reticulum and is

required for its cell-surface expression.59 Whenerythropoietin binds to its receptor, it provokes

a conformational change in the receptor60-62 withconsequent phosphorylation and activation of

JAK2.63 The activated JAK2 then phosphorylatesthe receptor’s cytoplasmic domain, thereby pro-moting the docking of downstream effector pro-

teins and the initiation of intracellular signalingcascades55,56 (Fig. 2A).

The JAK2 mutation in the myeloproliferativedisorders is not in the germ line but, rather, is

acquired.6-9,19 Sensitive methods demonstrate themutation in more than 95% of patients with poly-cythemia vera6,26 and in 50 to 60% of patients

with essential thrombocythemia6,26-28,31,64 or id-

iopathic myelofibrosis.6,26,29-31 A substantial pro-portion of patients with polycythemia vera or

idiopathic myelofibrosis are homozygous for the JAK2 mutation as a result of mitotic recombina-tion affecting chromosome 9p,6-9 but this phe-

nomenon is rarely detected in essential throm-bocythemia.65 The mutation is also found in a

small minority of patients with the hypereosino-philic syndrome, chronic myelomonocytic leuke-

mia, chronic neutrophilic leukemia, myelodyspla-sia, or acute myeloid leukemia,31-34,66-68 but notin patients with lymphoid or other cancers or in

those without hematologic disorders.6-9,33,34,67,69 The presence of a mutant JAK2 in some patients

with acute myeloid leukemia,33 especially olderpatients, raises the possibility that they may have

had a preceding, undiagnosed myeloproliferativedisorder. The JAK2 mutation is also found in more

than 50% of patients with otherwise unexplainedBudd–Chiari syndrome,70 which also suggests thepresence of a masked myeloproliferative disorder

in such cases.The mutation in JAK2 substitutes a bulky phe-

nylalanine for a conserved valine at position 617of the JAK2 protein (V617F). This residue is lo-

cated in the JH2, or pseudokinase, domain, whichnegatively regulates the kinase domain.71 Bio-chemical studies have shown that the JAK2 V617F

mutation causes cytokine-independent activa-

Table 1. Milestones in the History of Philadelphia-Negative Myeloproliferative Disorders and Their Relationshipwith the V617F Mutation in JAK2.*

Year Historical MilestoneRelationship Later Established with V617F

Mutation in JAK2

1892 First description of polycythemia vera4

1951 Polycythemia vera, essential thrombocythemia, and idio-pathic myelofibrosis linked as related conditions5

Mutation found in all three disorders6-9

1974 Identification of erythropoietin-independent erythroidcolonies10

Mutation associated with cytokine independenceof primary erythroid progenitors and cell lines6-9

1976 Stem-cell origin of polycythemia vera11 Mutation found in multipotent progenitors andhematopoietic stem cells6,12

1983–2003 Dysregulated tyrosine kinases found in chronic myeloidleukemia,13,14 mastocytosis,15 chronic myelomonocy-tic leukemia,16,17 and chronic eosinophilic leukemia18

Tyrosine kinase function of JAK2 constitutivelyactivated by mutation7-9,19

2002 Description of mitotic recombination involving chro-mosome 9p as the most common cytogeneticlesion in polycythemia vera20

Homozygosity of the mutation caused by mitoticrecombination of chromosome 9p6-9

2001–2004 Erythropoietin-independent growth in polycythemiavera dependent on JAK–STAT signaling21,22

STAT proteins constitutively activated by muta-tion7-9,19

2005 Description of the JAK2 V617F mutation6-9,19

* STAT denotes signal transducers and activators of transcription.





4/15



tion of JAK–STAT, PI3K, and AKT (also known

as protein kinase B) pathways, and mitogen-activated protein kinase (MAPK) and extracellular

signal-regulated kinase (ERK),7-9,19 all of which areimplicated in erythropoietin-receptor signal-

ing.22,63,72,73

The JAK2 mutation provides a unifying expla-nation for many features of the myeloprolifera-

tive disorders (Table 1), but other mutations areprobably associated with JAK2 V617F-negative

myeloproliferative disorders. One example is thepresence of an activating mutation in the throm-

bopoietin receptor (MPL) gene in approximately10% of patients with V617F-negative idiopathicmyelofibrosis.35,36 This mutation is located in a

motif that is important for keeping the receptor

inactive.74

Pathophysiological Features

Genetic Marker

The insights revealed by the foregoing molecularinvestigations are reshaping our understanding

of the pathophysiology, classification, diagnosis,and treatment of these conditions. The JAK2 mu-

tation is the first genetic marker that is directlyassociated with the pathogenesis of the myelopro-

liferative disorders, and for this reason it is a pow-erful tool for analysis of the molecular and cel-lular basis of these disorders.

Table 2. Molecular Lesions Associated with the Myeloproliferative Disorders.*

Abnormality Association

Recurrent genetic lesions

BCR-ABL Chronic myeloid leukemia (100%)1

JAK2 V617F Polycythemia vera (95%),6,26 essential thrombocythemia (50–60%),27,28 idiopathic myelofibrosis

(50–60%),29,30

and other myeloid disorders (1–5%)31-34

MPL W515K/L Idiopathic myelofibrosis (5%) and essential thrombocythemia (1%)35,36

KIT mutations Systemic mastocytosis15,37

FIP1L1–PDGFRA Chronic eosinophilic leukemia18,38

PDGFRB fusion genes Chronic myelomonocytic leukemia (rare)16

FGFR fusion genes Chronic myelomonocytic leukemia (rare)17

Other cytogenetic lesions

Trisomy 9 Amplifies JAK2 gene and associated with JAK2 V617F mutation39

Trisomy 8 Found in myeloproliferative disorders, myelodysplasia, and acute myeloid leukemias; targetgenes not identified

Trisomy 1q Caused by duplication, trisomy, or unbalanced translocations40

20q deletion Found in myeloproliferative disorders and myelodysplasia41; associated with JAK2 V617F muta-tion39 and precedes it in some cases42; target genes not identified41

5q and 7q deletions Thought to reflect changes secondary to cytotoxic therapy40; target genes not identified

13q deletion Associated with idiopathic myelofibrosis; overlap of commonly deleted region and the regionfor chronic lymphocytic leukemia40

Dysregulated genes and proteins

BCL-XL Overexpressed in polycythemia vera43 as a result of constitutive JAK–STAT signaling; antiapop-totic effects in erythroid cells44,45

NFE2 Up-regulated in JAK2-positive myeloproliferative diseases46,47; may affect erythroid differentiation48,49

PRV1 RNA levels increased in polycythemia vera50,51 but unlikely to play a direct role in disease patho-genesis since protein levels are not increased51

MPL Surface levels of protein decreased and aberrantly glycosylated in myeloproliferative disorders52,53;role in disease pathogenesis unclear

* FIP1L1 denotes FH interacting protein 1–like 1, PDGFRA platelet-derived growth-factor receptor alpha polypeptide,PDGFRB platelet-derived growth-factor receptor beta polypeptide, FGFR fibroblast growth-factor receptor, BCL-XL B-cellleukemia/lymphoma 2–like protein X long-transcript variant, NFE2 nuclear factor erythroid–derived 2, PRV1 polycythemiarubra vera 1, and MPL thrombopoietin receptor.





5/15



Mouse Models

Expression of the JAK2 V617F mutation in murinehematopoietic cells by means of a retroviral vec-

tor recapitulates the features of polycythemia vera.7,75-78 The animals have erythrocytosis andleukocytosis, and there is evolution to postpoly-

cythemic myelofibrosis.75-78

Thrombocytosis isnot a reproducible feature in these mice, perhaps

because high levels of mutant JAK2 generated bythe retroviral vector inhibit the differentiation

of megakaryocytes.76 Constitutive activation ofsignal transducers and activators of transcrip-tion 5 (STAT5), erythropoietin hypersensitivity, and

cytokine independence are al l present, as in thehuman disease. These results provide direct evi-

dence of a causal link between the mutation andthe disease.

Stem-Cell Biology

The myeloproliferative disorders arise from amutant multipotent stem cell. Analyses of pat-terns of X-chromosome inactivation in female

patients11,25,79 show a skewed pattern in myeloidcells but a balanced pattern in T cells and other

cell types,79 suggesting that some myeloid cellsin these women are clonally derived. However,

skewed patterns of X-chromosome inactivationin granulocytes have been found in older women without a myeloproliferative disorder79 and are

thought to ref lect polymorphic X-linked genes thatinfluence hematopoietic stem-cell behavior.80 Age-

related skewing limits the use of the analysis of

X-chromosome inactivation for diagnostic pur-poses, but such studies remain useful as researchtools. For example, studies of X-chromosome inac-tivation indicate that in most patients with V617F-

negative essential thrombocythemia or idiopathicmyelofibrosis, there is a dominant clone of blood

cells,26,28,81 implying that these disorders are clon-al hematologic diseases.

The presence of the JAK2 mutation in colo-nies of hematopoietic progenitor cells (grown in vitro)6,65 and in hematopoietic stem cells isolat-

ed by fluorescence-activated cell sorting12,82 provides direct evidence that polycythemia vera and

related myeloproliferative disorders arise in a mul-tipotent progenitor or stem cell. In contrast to the

normal-size myeloid stem-cell compartment inchronic myeloid leukemia,83 the stem-cell com-

partment in polycythemia vera is both expandedand characterized by preferential erythroid dif-

ferentiation.12 Taken together, the data suggestthat the JAK2 mutation affects the behavior of

hematopoietic stem cells but probably also acts

at later stages of differentiation, particularly inthe erythroid, granulocytic, and megakaryocyticlineages (Fig. 2B).

Cooperating Mutations

The JAK2 mutation explains many of the cardinal

features of the myeloproliferative disorders, asdoes the BCR-ABL fusion gene in chronic myeloid

leukemia. It seems likely that, as in chronic myeloidleukemia, leukemic transformation of the myelo-proliferative disorders reflects the acquisition of

additional mutations.84,85

Four lines of evidence suggest that cooperat-

ing mutations occur at an early stage in V617F-positive myeloproliferative disorders and can even

predate the JAK2 mutation. First, deletions of 20qand other cytogenetic abnormalities occur in 5 to

Figure 2 (facing page). Role of JAK2 in Pathway Signal-ing and Erythropoietin Binding, Stem-Cell Differentia-

tion, and Development of Homozygosity for the V617F

Mutation.

In Panel A, in the absence of ligand, the erythropoietin

receptor (EPOR) binds JAK2 as an inactive dimer. In cells

with wild-type JAK2 protein, the binding of erythropoi-

etin (Epo) to its receptor induces conformational chang-es in the receptor, resulting in phosphorylation (P) of

JAK2 and the cytoplasmic tail of the receptor. This leadsto signaling through pathways made up of Janus kinas-

es and signal transducers and activators of transcrip-

tion (JAK–STAT), phosphatidylinositol 3 kinase (PI3K),and RAS and mitogen-activated protein kinase (RAS–

MAPK). In cells with the V617F mutation, the signaling

is constitutively increased, even in the absence of

erythropoietin. In Panel B, the JAK2 protein binds tomultiple cytokine receptors — EPOR, thrombopoietin

receptor (MPL), granulocyte colony-stimulating factor

receptor (G-CSFR), and probably others — that are im-portant for hematopoietic stem-cell biology and differ-

entiation. Therefore, the JAK2 protein with the V617F

mutation exerts its effects at various stages of differ-entiation and in various lineages. In Panel C, the devel-

opment of homozygosity for the V617F mutation is a

two-step process, with the initial point mutation fol-lowed by mitotic recombination of chromosome 9p be-

tween the JAK2 locus and the centromere. This results

in the loss of heterozygosity but a diploid DNA copy

number.





6/15



A

B

C

Wild-type JAK2without erythropoietin

Wild-type JAK2with erythropoietin

JAK2 with V617F mutationwithout erythropoietin

Stem cell

Progenitor cells Terminally differentiated cells

Wild-type JAK2

Red cells

Megakaryocytes

Granulocytes

EPOR

MPL

G-CSFR

Heterozygous V167F

V617F

Homozygous V167F

Point mutation Mitotic recombination

No signal

JAK2

EPOR Epo

P

PI3KRAS–MAPKSTAT

JAK2V617F

P

PPP

P

P

P

Unknownreceptor

Chromosome 9

V617F

PI3KRAS–MAPKSTAT

V617F





7/15



10% of patients with a myeloproliferative disor-

der.40 In one patient with polycythemia vera andin one with essential thrombocythemia, granulo-

cytes with the 20q deletion outnumbered V617F-positive granulocytes,42 suggesting that the 20q

deletion occurred before the JAK2 mutation. Pa-

tients with molecularly defined 20q deletions arealmost exclusively V617F-positive,39 which is con-

sistent with the presence of a cooperating geneon 20q. Second, some women with polycythemia

vera or essential thrombocythemia have moreclonally derived granulocytes (estimated by pat-

terns of X-chromosome inactivation) than JAK2-positive granulocytes.26,39,42 Although this find-ing has been interpreted as evidence of a clonal

proliferation that preceded the JAK2 mutation,such a conclusion remains controversial.39 Third,

in some patients with V617F-positive polycythe-mia vera or essential thrombocythemia that un-

dergoes leukemic transformation, the leukemiccells lack the JAK2 mutation.39 This finding isconsistent with the origin of the leukemia in a

mutant clone that preceded the JAK2 mutation,although other interpretations are possible.39

Fourth, in familial clusters of the myeloprolifera-tive disorders, the JAK2 mutation is acquired,86

which suggests that the inherited predispositionis unrelated to the JAK2 mutation.

Homozygosity for V617F

Homozygosity for the V617F mutation plays a key

role in the myeloproliferative disorders. Homozy-

gosity results from mitotic recombination (Fig.2C), with the breakpoints spread along chromo-some 9p between the JAK2 locus and the centro-mere,9 implying that there is no single fragile site

that is prone to recombination. In polycythemia vera, the prevalence of blood cells that are homo-

zygous for the JAK2 mutation increases with time,65 presumably owing to a proliferative or survival ad-

vantage of mutant progenitor cells. Homozygos-ity for V617F is associated with more marked

changes in the expression of downstream targetgenes than is heterozygosity for V617F.46 This re-flects increased signaling mediated by a double

dose of V617F, possibly combined with a loss ofinhibition by the wild-type allele.7

Homozygosity in granulocytes can be detect-ed in about 30% of patients with polycythemia

vera.6-9 However, when colonies of hematopoi-etic progenitor cells derived from such patients

were studied, approximately 90% of them were

homozygous for the V617F mutation. By contrast,homozygous progenitor colonies were not found

in essential thrombocythemia.65 This differencesuggests that V617F homozygosity promotes the

development of polycythemia vera. Since there is

substantial variation in the rate of mitotic recom-bination among persons without a myeloprolifera-

tive disorder,87 genetic and environmental factorsthat determine susceptibility to mitotic recombi-

nation may influence whether essential thrombo-cythemia or polycythemia vera develops.

Signaling Pathways

The mutant JAK2 protein activates multiple down-

stream signaling pathways with effects on genetranscription,46 apoptosis, the cell cycle, and dif-

ferentiation55,56 (Table 2). Effects on apoptosisinclude overexpression of the cell-survival protein

BCL-X in erythroid precursor cells in polycythe-mia vera,43 probably as a result of enhanced JAK–STAT signaling.44,45,72 There is also a reduction

in apoptosis induced by death receptors in JAK2 V617F-positive erythroid progenitors, an effect me-

diated through PI3K–AKT and MAPK–ERK pathways.88 With respect to the cell cycle, mutant JAK2

promotes G1/S phase transition in hematopoieticcell lines, accompanied by up-regulation of cyclinD2 and down-regulation of the inhibitor p27kip.89

Effects on erythroid differentiation may be medi-ated by nuclear factor erythroid-derived 2 (NF-E2),

which is up-regulated in polycythemia vera46,47 and

plays an important role in erythroid differentia-tion.48,49 Hematopoietic cells expressing JAK2V617F become hypersensitive to insulin-like growthfactor 1 (IGF-1), suggesting that IGF-1-receptor

signaling inf luences cellular proliferation and dif-ferentiation in these diseases.90

Wild-type JAK2 is required for intracellularprocessing and cell-surface display of the eryth-

ropoietin receptor59 and the thrombopoietin re-ceptor.91 Mutant JAK2 inf luences the display and

stability of the erythropoietin receptor on the cellsurface92 but reduces levels of cell-surface throm-bopoietin receptor (MPL) in cultured cells (Con-

stantinescu S, Vainchenker W: personal communi-cation). The latter may explain the decreased

levels and altered glycosylation of MPL in the my-eloproliferative disorders.50,52,53 It has been sug-

gested that, unlike other kinases associated withhematologic cancers, the V617F protein requires





8/15



a type-1 cytokine receptor — such as the eryth-

ropoietin receptor (EPOR), MPL, or G-CSF recep-tor — to act as a scaffold and docking site for

downstream effector proteins. Such a mechanismmay explain the involvement of the erythroid,

megakaryocyte, and granulocyte lineages in the

myeloproliferative disorders (Fig. 2B),93

but de-tailed structural and biochemical analyses are

needed to explain why residue 617 is so critical for JAK2 activation.

Disease Evolution

The evolution of the myeloproliferative disor-ders into other forms is poorly understood. Anincrease in reticulin fibrosis may occur with time

in patients with polycythemia vera94 or essentialthrombocythemia,95,96 and in some of them a

syndrome indistinguishable from idiopathic my-elofibrosis develops.97 The stromal cells and fi-

broblasts responsible for the increased fibro-sis, angiogenesis, and formation of new bone donot derive from the myeloproliferative clone. They

therefore represent a polyclonal reaction to cyto-kines — including transforming growth factor β

(TGF-β), basic fibroblast growth factor (bFGF),and vascular endothelial growth factor (VEGF)

— produced by megakaryocytes, monocytes, orboth from the myeloproliferative clone.98 Mousemodels of myelofibrosis suggest that excessive

MPL signaling,99 activation of nuclear factor κB(NF-κB),100 and low levels of the globin transcrip-

tion factor 1 (GATA-1)101 also contribute to cyto-

kine secretion and the development of reticulinfibrosis. In V617F-positive human disease, exces-sive MPL signaling may be particularly relevant,since the JAK2 protein is a key component of sig-

nal transduction from the MPL receptor.102

Acute myeloid leukemia develops in a small

minority of patients with a myeloproliferative dis-order, but transformation to acute lymphoblas-

tic leukemia is extremely rare.94,103 Leukemictransformation can occur without exposure to

cytoreductive therapy, but the incidence of thistransformation increases after exposure to somecytoreductive agents103 and probably reflects ac-

quisition of additional genetic lesions. The devel-opment of acute myeloid leukemia in the absence

of the JAK2 mutation in patients with a V617F-positive myeloproliferative disorder demonstrates

that mutant JAK2 is not necessarily involved inleukemic transformation.39

Molecular Classification

Prospective27,104 and retrospective28,64,105 studiesof essential thrombocythemia have shown that the

V617F mutation divides the disease into biologi-cally distinct subtypes. V617F-positive thrombo-

cythemia resembles polycythemia vera. In contrastto V617F-negative essential thrombocythemia,V617F-positive thrombocythemia typically shows

higher levels of hemoglobin and white cells, amore cellular bone marrow, an increased risk of

venous thrombosis and transformation to poly-cythemia vera, and greater sensitivity to hy-

droxyurea.27 These features suggest that V617F-positive thrombocythemia is a forme fruste of

polycythemia vera, with the degree of erythro-cytosis influenced by factors such as low ironstores, low erythropoietin levels, sex, and homo-

zygosity for V617F.27 V617F-negative patients, who

have a more isolated thrombocytosis, can pres-ent with features of a bona fide myeloprolifera-tive disorder, such as splenomegaly, cytogenetic

abnormalities, megakaryocyte dysplasia, a sus-ceptibility to leukemia or myelofibrosis,27 andclonal hematopoiesis.26,28,81 Fifty patients with

V617F-negative essential thrombocythemia re-mained V617F-negative for more than 6 years,

indicating that this disorder is distinct from, andnot an early “pre- JAK2” phase of, V617F-positive

thrombocythemia.39

V617F-positive patients with idiopathic myelo-fibrosis had a reduced transfusion requirement

and greater white-cell counts than did patients without the mutation,29 analogous to the higher

hemoglobin levels and white-cell counts in pa-tients with V617F-positive essential thrombo-

cythemia. In this study, but not in a second,30 theV617F mutation was independently associated with poor survival.29

These results lay the foundation for a molecu-lar classification of the myeloproliferative disor-

ders (Fig. 3). This classification is likely to evolveas additional genetic lesions are identif ied with-

in the JAK2 V617F-negative category. The similari-ties between V617F-positive essential thrombo-cythemia and polycythemia suggest considerable

overlap between these conditions. They may forma phenotypic continuum in which the degree of

initial erythrocytosis or thrombocytosis dependson physiological or genetic modif iers.27

The accelerated phase of a myeloproliferative





9/15



disorder is analogous to the accelerated phase of

chronic myeloid leukemia and is probably spurredby the acquisition of additional genetic changes.

In the myeloproliferative disorders, the acceler-ated phase would encompass not only the trans-formation of polycythemia vera or essential throm-

bocythemia into myelofibrosis, but also a rising white-cell count, increased blasts in the blood,

and neutropenia or thrombocytopenia.94 It is im-portant to distinguish transformation to myelo-

fibrosis from histologic detection of increasedlevels of reticulin. The former is a clinical syn-drome indicating a biologic change within the

myeloproliferative clone, whereas the latter may

accompany chronic-phase polycythemia vera oressential thrombocythemia, with the degree of

fibrosis reflecting an interplay between the dura-tion of the disease and physiological or geneticmodifiers.

The disorder that is currently termed idiopathicmyelofibrosis is clinically indistinguishable from

the transformation of polycythemia vera or es-sential thrombocythemia to myelofibrosis,30,95

and the diagnostic criteria for the two conditionsare similar.95,104,106 At least some patients whoreceive the diagnosis of idiopathic myelofibrosis

Myeloproliferative disorders

Chronic myeloidleukemia

BCR-ABL JAK2 V617F Unknown mutation

JAK2-positivethrombocythemia

JAK2-positivepolycythemia

JAK2-negativemyeloproliferative disorder

Accelerated phase

Blast crisis Leukemictransformation

myelofibrosis

cytopenias

increasing blasts

increasing white cells

Chronic phase Chronic phase Chronic phase

Accelerated phase Accelerated phase

Leukemictransformation

Figure 3. Classification of the Myeloproliferative Disorders on the Basis of Molecular Pathogenetic Characteristics.

Chronic myeloid leukemia is defined by the BCR-ABL fusion gene and characterized by three stages of disease pro-

gression, from the chronic phase through the accelerated phase to blast crisis. Analogously, JAK2-positive thrombo-

cythemia and polycythemia have overlapping phenotypes in the chronic phase and can progress to an accelerated

phase, which is manifested as myelofibrosis or other complications. Leukemic transformation can also occur. JAK2-negative disease follows similar patterns of progression. The disorder that is currently called idiopathic myelofibro-

sis or agnogenic myeloid metaplasia is clinically indistinguishable from the myelofibrotic transformation of polycy-themia vera or essential thrombocythemia. Therefore, this disorder may be an accelerated phase of polycythemia

vera or thrombocythemia. Many patients with polycythemia vera who do not have the V617F mutation have other

JAK2 mutations, and therefore truly JAK2-negative polycythemia vera is probably extremely rare.





10/15



probably are in the accelerated phase of previ-

ously unrecognized polycythemia vera or essen-tial thrombocythemia.

Diagnosis

Until recently, robust tools for the diagnosis ofthe myeloproliferative disorders have been lack-

ing. Criteria for the diagnosis of polycythemia vera are mostly modifications of 20-year-old stan-

dards from the Polycythemia Vera Study Group.107 The available tests are expensive, not universally

available, and lacking in sensitivity and specific-ity. They include a determination of red-cell massto distinguish true erythrocytosis from relative

polycythemia, identification of erythropoietin-independent erythroid colonies in vitro, cytoge-

netic analysis of bone marrow cells, testing oferythropoietin levels, ultrasonography of the

spleen, and testing for the overexpression of poly-cythemia rubra vera 1 (PRV1). There are no universally accepted diagnostic tests for essential

thrombocythemia.108,109

Testing for the JAK2 V617F mutation is now

widely available and promises to simplify thediagnostic workup. Allele-specific polymerase-

chain-reaction (PCR) assay,6,27,110 pyrosequenc-ing,31,66 restriction-enzyme digestion,6,110 andreal-time PCR 26 are all sufficiently sensitive to

detect the presence of a heterozygous mutationin as few as 5 to 10% of cells. These assays have

low rates of false positive results, making them

useful diagnostic tools.Proposed diagnostic criteria for V617F-posi-

tive and V617-negative myeloproliferative disor-ders are outlined in Tables 3 and 4, respectively.

The JAK2 mutation is not associated with causesof an absolute erythrocytosis other than polycy-

themia vera.7,9,31,111,112 Therefore, in the absenceof a coexisting secondary erythrocytosis, the pres-

ence of the JAK2 mutation in a patient with anincreased red-cell mass is sufficient for the di-

agnosis of polycythemia vera. In this situation,the role of analysis of the red-cell mass is mainlyto distinguish polycythemia vera from essential

thrombocythemia. However, this distinction isbecoming arbitrary, given the clinical and biologic

similarities between the two conditions.27,28,64,105 Therefore, in patients with the JAK2 mutation,

analysis of the red-cell mass is likely to becomeobsolete. Erythropoietin levels do not distinguishbetween polycythemia vera and V617F-positive

essential thrombocythemia27 and therefore haveminimal use in patients with the JAK2 mutation.Cytogenetic studies in patients with the JAK2 mu-tation generally do not add useful diagnostic or

prognostic information.V617F-negative polycythemia vera represents

less than 5% of all cases of polycythemia vera.6,26 In these rare cases, apparent erythrocytosis should

be excluded by analysis of the red-cell mass andsecondary erythrocytosis by measurement of eryth-ropoietin levels and oxygen saturation. Abnormal

results on cytogenetic analysis or radiologic evi-dence of splenomegaly would support the diag-

nosis of a myeloproliferative disorder.The presence of a JAK2 mutation in a patient

with thrombocytosis has a high positive predic-tive value for a myeloproliferative disorder; pa-tients with reactive or secondary thrombocytosis

and persons without a hematologic disorder areV617F-negative6-9 (Table 3). Other causes of throm-

Table 3. Proposed Diagnostic Criteria for Myeloproliferative Diseaseswith JAK2 Mutation.

JAK2-positive polycythemia (diagnosis requires the presence of both cri-teria)*

A1. High hematocrit (>52% in men or >48% in women) or an increased red-cell mass (>25% above predicted value)

A2. Mutation in JAK2

JAK2-positive thrombocythemia (diagnosis requires the presence of all threecriteria)

A1. Platelet count >450×109/liter


A3. No other myeloid cancer, especially JAK2-positive polycythemia, myelo-fibrosis, or myelodysplasia

JAK2-positive myelofibrosis (diagnosis requires the presence of A1 and A2and any two B criteria)

A1. Reticulin grade 3 or higher (on a 0–4 scale)


B1. Palpable splenomegaly

B2. Otherwise unexplained anemia (hemoglobin


11/15



bocytosis must be excluded in patients without

the mutation (Table 4). Cytogenetic analysis ofbone marrow is sometimes helpful in JAK2-nega-

tive thrombocythemia if it shows a clonal abnor-mality. Essential thrombocythemia has been divid-

ed into histologically distinct subgroups (labeled

“true” essential thrombocythemia, prefibrotic my-

elofibrosis, and early overt myelofibrosis) that are

thought to have differing prognoses,2,96 but it isunclear whether this histologic classification is

robust enough to be applied outside specializedcenters.

Diagnostic criteria for idiopathic myelofibro-

sis are presented inTables 3 and 4

, modified fromthe Italian Consensus Conference.113 The criteria

proposed here define a clinical syndrome in whichreticulin fibrosis of the marrow is accompanied

by specific clinical or laboratory features and canbe used for both idiopathic myelofibrosis and

transformation from preceding essential throm-bocythemia or polycythemia vera.

T reat m en t

The JAK2 mutation is reshaping how we treat themyeloproliferative disorders. Moving to a new clas-

sification could simplify therapy. In polycythe-mia vera, the hematocrit is the primary target oftherapy, but the treatment of patients with throm-

bocytosis is controversial.94,114 By contrast, in es-sential thrombocythemia, cytoreduction to nor-

malize the platelet count reduces thrombosis inhigh-risk patients,115 but the hematocrit is not a

therapeutic target. Given the many similarities be-tween JAK2-positive polycythemia and thrombo-cythemia, it seems logical to develop target levels

for both the platelet count and the hematocrit inboth conditions. The development of a unified

treatment strategy is consistent with growing evi-

dence that the increased risk of thrombosis is notexclusively caused by erythrocytosis or thrombo-cytosis but by interactions among white cells, redcells, platelets, and the endothelium. Abnormali-

ties in the activation of leukocytes and plateletsoccur in both diseases.116,117

The JAK2 mutation also affects response totreatment. Among patients with essential throm-

bocythemia, those with the V617F mutation aremore sensitive to hydroxyurea (but not to ana-

grelide) than are patients without the mutation.27 The response to therapy can now be directly moni-tored through quantification of JAK2-positive cells

in peripheral blood.118,119

An understanding of the molecular pathogen-

esis of the myeloproliferative disorders lays thefoundation for the development of novel targeted

therapies. Since JAK2 inhibitors reduce the growthof JAK2 V617F-positive cell lines and primary cellsin vitro,8,12 there is considerable interest in de-

Table 4. Proposed Diagnostic Criteria for Myeloproliferative Diseases without

JAK2 Mutation.

JAK2-negative polycythemia vera (diagnosis requires the presence of A1, A2,and A3, plus either another A criterion or two B criteria)

A1. Increased red-cell mass (>25% above predicted value) or a hematocrit≥60% in men or >56% in women

A2. Absence of mutation in JAK2

A3. No causes of secondary erythrocytosis (normal arterial oxygen saturationand no elevation of serum erythropoietin)

A4. Palpable splenomegaly

A5. Presence of acquired genetic abnormality (excluding BCR-ABL) in hema-

topoietic cells

B1. Thrombocytosis (platelets >450×109/liter)

B2. Neutrophilia (neutrophils >10×109/liter; >12.5×109/liter in smokers)

B3. Splenomegaly on radiography

B4. Endogenous erythroid colonies or low serum erythropoietin

JAK2-negative essential thrombocythemia (diagnosis requires the presenceof all five criteria)*

A1. Platelet count >600×109/liter on two occasions at least 1 mo apart


A3. No reactive cause for thrombocytosis

A4. Normal ferritin (>20 µg/liter)

A5. No other myeloid disorder, especially chronic myeloid leukemia, myelofi-brosis, polycythemia vera, or myelodysplasia

JAK2-negative idiopathic myelofibrosis (diagnosis requires the presence ofA1, A2, A3, and any two B criteria)

A1. Reticulin grade 3 or higher (on a 0–4 scale)


A3. Absence of BCR-ABL fusion gene

B1. Palpable splenomegaly

B2. Otherwise unexplained anemia (hemoglobin


12/15



veloping compounds for clinical use. Such agents

hold particular promise for the treatment of pa-tients whose disease is in the accelerated phase,

including myelofibrosis, given the lack of satisfac-tory treatments currently available. These agents

may also prove to be useful for reducing the risk

of vascular events or long-term disease evolutionin chronic-phase disease. With an eye to the suc-

cess of imatinib in the treatment of chronic my-

eloid leukemia, we hope the next decade will see

the development of well-tolerated, therapeutic JAK2 inhibitors.

No potential conflict of interest relevant to this article wasreported.

We thank Gary Gilliland, William Vainchenker, Radek Skoda,Ruben Mesa, Tiziano Barbui, Wendy Erber, Claire Harr ison, and

Mary Frances McMullin for their construct ive comments on themanuscript, and Wendy Erber for providing some of the lightmicrographs in Figure 1.

References

Goldman JM, Melo JV. Chronic my-eloid leukemia — advances in biology andnew approaches to treatment. N Engl J Med2003;349:1451-64.

Pierre R, Imbert M, Thiele J, Vardiman JW, Brunning RD, Flandrin G. Chronic my-eloproliferative diseases. In: Jaffe ES, Har-ris NL, Stein H, Vardiman JW, eds. WorldHealth Organization classification of tu-mours: pathology and genetics of tumoursof haemopoietic and lymphoid tissues.

Lyon, France: IARC Press, 2001:61-73. Johansson P, Kutti J, Andreasson B, et

al. Trends in the incidence of chronic Phila-delphia chromosome negative (Ph-) myelo-proliferative disorders in the city of Gote-borg, Sweden, during 1983-99. J InternMed 2004;256:161-5.

Vaquez H. Sur une forme speciale decyanose s’accompagnant d’hyperglobulieexcessive et persistante. C R Soc Biol (Par-is) 1892;44:384-8.

Dameshek W. Some speculations onthe myeloproliferative syndromes. Blood1951;6:372-5.

Baxter EJ, Scott LM, Campbell PJ, et al.Acquired mutation of the tyrosine kinase

JAK2 in human myeloprolifer ative disor-

ders. Lancet 2005;365:1054-6. [Erratum,Lancet 2005;366:122.]

James C, Ugo V, Le Couedic JP, et al.A unique clonal JAK2 mutat ion leading toconstitutive signaling causes polycythae-mia vera. Nature 2005;434:1144-8.

Levine RL, Wadleigh M, Cools J, et al.Activating mutation in the tyrosine kinase

JAK2 in polycythemia vera, essential throm-bocythemia, and myeloid metaplasia withmyelofibrosis. Cancer Cell 2005;7:387-97.

Kralovics R, Passamonti F, Buser AS,et al. A gain-of-function mutat ion of JAK2 in myeloproliferative disorders. N Engl JMed 2005;352:1779-90.

Prchal JF, Axelrad AA. Bone-marrowresponses in polycythemia vera. N Engl JMed 1974;290:1382.

Adamson JW, Fialkow PJ, Murphy S,Prchal JF, Steinmann L. Polycythemia vera:stem-cell and probable clonal origin of thedisease. N Engl J Med 1976;295:913-6.

Jamieson CH, Got lib J, Durocher JA,et al. The JAK2 V617F mutation occurs inhematopoietic stem cells in polycythemia

vera and predisposes toward erythroid dif-

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

ferentiation. Proc Natl Acad Sci U S A2006;103:6224-9.

Bartram CR, de Klein A, HagemeijerA, et al. Translocat ion of c-ab1 oncogenecorrelates with the presence of a Philadel-phia chromosome in chronic myelocyticleukaemia. Nature 1983;306:277-80.

Lugo TG, Pendergast AM, Muller AJ,Witte ON. Tyrosine kinase activity andtransformation potency of bcr-abl onco-gene products. Science 1990;247:1079-82.

Buttner C, Henz BM, Welker P, SeppNT, Grabbe J. Identification of activatingc-kit mutations in adult-, but not in chi ld-hood-onset indolent mastocytosis: a pos-sible explanation for divergent clinical be-havior. J Invest Dermatol 1998;111:1227-31.

Golub TR, Barker GF, Lovett M, Gil-liland DG. Fusion of PDGF receptor betato a novel ets-like gene, tel, in chronic my-elomonocytic leukemia with t(5;12) chro-mosomal t ranslocation. Cell 1994;77:307-16.

Xiao S, Nalabolu SR, Aster JC, et al.FGFR1 is fused with a novel zinc-fingergene, ZNF198, in the t(8;13) leukaemia/lymphoma syndrome. Nat Genet 1998;

18:84-7.Cools J, DeAngelo DJ, Gotlib J, et al.

A tyrosine kinase created by fusion of thePDGFRA and FIP1L1 genes as a therapeutictarget of imatinib in idiopathic hypereo-sinophilic syndrome. N Engl J Med 2003;348:1201-14.

Zhao R, Xing S, Li Z, et al. Identifica-tion of an acquired JAK2 mutation inpolycythemia vera. J Biol Chem 2005;280:22788-92.

Kralovics R, Guan Y, Prchal JT. Ac-quired uniparental disomy of chromo-some 9p is a frequent stem cell defect inpolycythemia vera. Exp Hematol 2002;30:229-36.

Roder S, Steimle C, Meinhardt G, PahlHL. STAT3 is constitutively active in somepatients with polycythemia rubra vera.Exp Hematol 2001;29:694-702.

Ugo V, Marzac C, Teyssandier I, et al.Multiple signaling pathways are involvedin erythropoietin-independent differenti-ation of erythroid progenitors in polycy-themia vera. Exp Hematol 2004;32:179-87.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

Heuck G. Falle von Leukaemie mit ei-genthumlichen Blut-resp. Knockenmarks-befund. Virchown Archiv 1879;78:475-81.

Epstein E, Goedel A. Haemorrhagischethrombocythamie bei vascularer schrumpf-milz. Virchov’s Archiv Abtei lung 1934;293:233-47.

Fialkow PJ, Faguet GB, Jacobson RJ,Vaidya K, Murphy S. Evidence that essen-tial thrombocythemia is a clonal disor-der with origin in a multipotent stem cell.

Blood 1981;58:916-9.Levine RL, Belisle C, Wadleigh M, et

al. X-inactivation-based clonality analysisand quantitative JAK2V617F assessmentreveals a strong association between clon-alit y and JAK2V617F in PV but not ET/MMM,and identif ies a subset of JAK2V617F-neg-ative ET and MMM patients with clonalhematopoiesis. Blood 2006;107:4139-41.

Campbell PJ, Scott LM, Buck G, et al.Definit ion of subtypes of essential throm-bocythaemia and relation to polycythae-mia vera based on JAK2 V617F mutationstatus: a prospective study. Lancet 2005;366:1945-53.

Antonioli E, Guglielmelli P, PancrazziA, et al. Clinical implications of the JAK2

V617F mutation in essential thrombocy-themia. Leukemia 2005;19:1847-9.

Campbell PJ, Griesshammer M, Doh-ner K, et al. V617F mutation in JAK2 is as-sociated with poorer survival in idiopathicmyelofibrosis. Blood 2006;107:2098-100.

Tefferi A, Lasho TL, Schwager SM, etal. The JAK2(V617F) tyrosine kinase mu-tation in myelofibrosis with myeloid meta-plasia: lineage specificity and clinical cor-relates. Br J Haematol 2005;131:320-8.

Jones AV, Kreil S, Zoi K, et a l. Wide-spread occurrence of the JAK2 V617F mu-tation in chronic myeloproliferative disor-ders. Blood 2005;106:2162-8.

Steensma DP, Dewald GW, Lasho TL,et al. The JAK2 V617F activating tyrosinekinase mutation is an infrequent event inboth “atypical” myeloproliferative disor-ders and myelodysplastic syndromes. Blood2005;106:1207-9.

Scott LM, Campbell PJ, Baxter EJ, et al.The V617F JAK2 mutation is uncommonin cancers and in myeloid malignanciesother than the classic myeloproliferativedisorders. Blood 2005;106:2920-1.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32.

33.





13/15



Levine RL, Loriaux M, Huntly BJ, et al.The JAK2V617F activating mutation occursin chronic myelomonocytic leukemia andacute myeloid leukemia, but not in acutelymphoblastic leukemia or chronic lym-phocytic leukemia. Blood 2005;106:3377-9.

Pikman Y, Lee BH, Mercher T, et al.MPLW515L is a novel somatic activatingmutation in myelofibrosis with myeloidmetaplasia. PLoS Med 2006;3:e270.

Pardanani AD, Levine RL, Lasho T, etal. MPL515 mutations in myeloprolifera-tive and other myeloid disorders: a studyof 1182 patients. Blood (in press).

Longley BJ Jr, Metcalfe DD, Tharp M,et al. Activating and dominant inactivat-ing c-KIT catalytic domain mutations indistinct clinical forms of human masto-cytosis. Proc Nat l Acad Sci U S A 1999;96:1609-14.

Pardanani A, Brockman SR, Paternos-ter SF, et al. FIP1L1-PDGFRA fusion: prev-alence and clinicopathologic correlates in89 consecutive patients with moderate tosevere eosinophilia. Blood 2004;104:3038-45.

Campbell PJ, Baxter EJ, Beer PA, et al.Mutation of JAK2 in the myeloproliferativedisorders: timing, clonality studies, cyto-genetic associations and role in leukemictransformation. Blood (in press).

Bench AJ, Nacheva EP, Champion KM,Green AR. Molecular genetics and cyto-genetics of myeloproliferative disorders.Baill ieres Clin Haematol 1998;11:819-48.

Bench AJ, Nacheva EP, Hood TL, et al.Chromosome 20 deletions in myeloid ma-lignancies: reduction of the common de-leted region, generation of a PAC/BAC con-tig and identification of candidate genes.Oncogene 2000;19:3902-13.

Kralovics R, Teo SS, Li S, et al. Acquisi-tion of the V617F mutation of JAK2 isa late genetic event in a subset of patients

with myeloproliferative disorders. Blood2006;108:1377-80.

Silva M, Richard C, Benito A, Sanz C,Olalla I, Fernandez-Luna JL. Expression ofBcl-x in erythroid precursors from patients

with polycy themia vera. N Engl J Med1998;338:564-71.

Kieslinger M, Woldman I, Moriggl R,et al. Antiapoptotic activity of Stat5 re-quired during terminal stages of myeloiddifferentiation. Genes Dev 2000;14:232-44.

Socolovsky M, Nam H, Fleming MD,Haase VH, Brugnara C, Lodish HF. Ineffec-tive erythropoiesis in Stat5a(−/−)5b(−/−)mice due to decreased survival of earlyerythroblasts. Blood 2001;98:3261-73.

Kralovics R, Teo SS, Buser AS, et al.Altered gene expression in myeloprolifer-ative disorders correlates with activationof signaling by the V617F mutation of Jak2.Blood 2005;106:3374-6.

Goerttler PS, Kreutz C, Donauer J, et

34.

35.

36.

37.

38.

39.

40.

41.

42.

43.

44.

45.

46.

47.

al. Gene expression profiling in polycy-thaemia vera: overexpression of transcrip-tion factor NF-E2. Br J Haematol 2005;129:138-50.

Labbaye C, Valtieri M, Barberi T, et al.Differential expression and functional roleof GATA-2, NF-E2, and GATA-1 in normaladult hematopoiesis. J Clin Invest 1995;95:2346-58.

Sayer MS, Tilbrook PA, Spadaccini A,et al. Ectopic expression of transcriptionfactor NF-E2 alters the phenotype of ery-throid and monoblastoid cells. J Biol Chem2000;275:25292-8.

Goerttler PS, Steimle C, Marz E, et a l.The Jak2V617F mutation, PRV-1 overexpres-sion, and EEC formation define a simi larcohort of MPD patients. Blood 2005;106:2862-4.

Klippel S, Strunck E, Busse CE, Beh-ringer D, Pahl HL. Biochemical character-ization of PRV-1, a novel hematopoietic cellsurface receptor, which is overexpressedin polycythemia rubra vera. Blood 2002;100:2441-8.

Moliterno AR, Hankins WD, Spivak JL. Impaired expression of the thrombo-poietin receptor by platelets from patients

with polycy themia vera. N Engl J Med1998;338:572-80.

Moliterno AR, Spivak JL. Posttransla-tional processing of the thrombopoietinreceptor is impaired in polycythemia vera.Blood 1999;94:2555-61.

Komura E, Chagraoui H, Mansat deMas V, et al. Spontaneous STAT5 activa-tion induces growth factor independencein idiopathic myelofibrosis: possible rela-tionship with FKBP51 overexpression. ExpHematol 2003;31:622-30.

Sandberg EM, Wallace TA, GodenyMD, Vonderlinden D, Sayeski PP. Jak2 ty-rosine kinase: a true jak of all t rades? CellBiochem Biophys 2004;41:207-32.

Kisseleva T, Bhattacharya S, Braun-stein J, Schindler CW. Signaling throughthe JAK/STAT pathway, recent advancesand future challenges. Gene 2002;285:1-24.

Neubauer H, Cumano A, Muller M, WuH, Huffstadt U, Pfeffer K. Jak2 deficiencydefines an essentia l developmental check-point in definitive hematopoiesis. Cell1998;93:397-409.

Parganas E, Wang D, Stravopodis D,et al. Jak2 is essential for signaling througha variety of cytokine receptors. Cell 1998;93:385-95.

Huang LJ, Constantinescu SN, LodishHF. The N-terminal domain of Janus ki-nase 2 is required for Golgi processingand cell surface expression of erythropoi-etin receptor. Mol Cell 2001;8:1327-38.

Remy I, Wilson IA, Michnick SW. Eryth-ropoietin receptor activation by a ligand-induced conformation change. Science1999;283:990-3.

Lu X, Gross AW, Lodish HF. Active con-

48.

49.

50.

51.

52.

53.

54.

55.

56.

57.

58.

59.

60.

61.

formation of the erythropoietin receptor:random and cysteine-scanning mutagen-esis of the extracellular juxtamembraneand transmembrane domains. J Biol Chem2006;281:7002-11.

Seubert N, Royer Y, Staerk J, et al. Ac-tive and inactive orientations of the trans-membrane and cytosolic domains of theerythropoietin receptor dimer. Mol Cell2003;12:1239-50.

Witthuhn BA, Quelle FW, Silven-noinen O, et al. JAK2 associates with theerythropoietin receptor and is tyrosinephosphorylated and activated followingstimulation with erythropoietin. Cell 1993;74:227-36.

Wolanskyj AP, Lasho TL, Schwager SM,et al. JAK2 mutation in essential throm-bocythaemia: clinical associations andlong-term prognostic relevance. Br J Hae-matol 2005;131:208-13.

Scott LM, Scott MA, Campbell PJ,Green AR. Progenitors homozygous forthe V617F JAK2 mutation occur in mostpatients with polycythemia vera but notessential thrombocythemia. Blood 2006;108:2435-7.

Jelinek J, Oki Y, Gharibyan V, et al. JAK2 mutation 1849G→T is rare in acuteleukemias but can be found in CMML, Phil-adelphia chromosome-negative CML, andmegakaryocytic leukemia. Blood 2005;106:3370-3.

Lee JW, Kim YG, Soung YH, et al. The JAK2 V617F mutation in de novo acute my-elogenous leukemias. Oncogene 2006;25:1434-6.

Frohling S, Lipka DB, Kayser S, et al.Rare occurrence of the JAK2 V617F muta-tion in AML subtypes M5, M6, and M7.Blood 2006;107:1242-3.

Melzner I, Weniger MA, Menz CK,Moller P. Absence of the JAK2 V617F acti-

vating mutation in classical Hodgkin lym-phoma and primary mediastinal B-celllymphoma. Leukemia 2006;20:157-8.

Patel RK, Lea NC, Heneghan MA, etal. Prevalence of the activating JAK2 tyro-sine kinase mutat ion V617F in the Budd-Chiari syndrome. Gastroenterology 2006;130:2031-8.

Saharinen P, Takaluoma K, Silvennoin-en O. Regulation of the Jak2 tyrosine ki-nase by its pseudokinase domain. Mol CellBiol 2000;20:3387-95.

Socolovsky M, Fallon AE, Wang S,Brugnara C, Lodish HF. Fetal anemia andapoptosis of red cell progenitors inStat5a−/−5b−/− mice: a direct role for Stat5in Bcl-X(L) induction. Cell 1999;98:181-91.

Myklebust JH, Blomhoff HK, RustenLS, Stokke T, Smeland EB. Activation ofphosphatidylinositol 3-kinase is importantfor erythropoietin-induced erythropoiesisfrom CD34(+) hematopoietic progenitorcells. Exp Hematol 2002;30:990-1000.

Staerk J, Lacout C, Sato T, Smith SO,Vainchenker W, Constantinescu SN. An

62.

63.

64.

65.

66.

67.

68.

69.

70.

71.

72.

73.

74.





14/15



amphipathic motif at the transmem-brane-cytoplasmic junction prevents au-tonomous activation of the thrombopoi-etin receptor. Blood 2006;107:1864-71.

Wernig G, Mercher T, Okabe R, LevineRL, Lee BH, Gilliland DG. Expression of

Jak2V617F causes a polycythemia vera-like disease with associated myelofibrosisin a murine bone marrow transplant mod-el. Blood 2006;107:4274-81.

Lacout C, Pisani DF, Tulliez M,Gachelin FM, Vainchenker W, Villeval JL.

JAK2V617F expression in murine hemato-poietic cells leads to MPD mimicking hu-man PV with secondary myelofibrosis.Blood 2006;108:1652-60.

Zaleskas VM, Krause DS, Lazarides K,et al. Molecular pathogenesis of polycy-themia induced in mice by JAK2 V617F.Blood 2005;106:A116. abstract.

Bumm TGP, Elsea C, Wood LG, et al. JAK2 V617F mutation induces a myelopro-liferative disorder in mice. Blood 2005;106:A116. abstract.

Gale RE. Evaluation of clonality in my-eloid stem-cell disorders. Semin Hematol1999;36:361-72.

Abkowitz JL, Taboada M, Shelton GH,Catlin SN, Guttorp P, Kiklevich JV. AnX chromosome gene regulates hemato-poietic stem cell kinetics. Proc Natl AcadSci U S A 1998;95:3862-6.

Kiladjian JJ, Elkassar N, Cassinat B, etal. Essential thrombocythemias withoutV617F JAK2 mutat ion are clonal hemato-poietic stem cell disorders. Leukemia 2006;20:1181-3.

Lasho TL, Mesa R, Gilli land DG, Tef-feri A. Mutation studies in CD3+, CD19+and CD34+ cell fractions in myeloprolif-erative disorders with homozygous JAK2(V617F) in granulocytes. Br J Haematol2005;130:797-9.

Jamieson CH, Ailles LE, Dylla SJ, et al.Granulocyte-macrophage progenitors ascandidate leukemic stem cells in blast-cri-sis CML. N Engl J Med 2004;351:657-67.

Mesa RA, Powell H, Lasho T, DewaldG, McClure R, Tefferi A. JAK2(V617F) andleukemic transformation in myelofibrosis

with myeloid metaplasia. Leuk Res 2006;30:1457-60.

Mesa RA, Powell H, Lasho T, DeWaldGW, McClure R, Tefferi A. A longitudinalstudy of the JAK2(V617F) mutation in my-elofibrosis with myeloid metaplasia: analy-sis at two time points. Haematologica 2006;91:415-6.

Bellanne-Chantelot C, Chaumarel I,Labopin M, et al. Genetic and clinical im-plications of the Val617Phe JAK2 muta-tion in 72 fami lies with myeloprolifera-tive disorders. Blood 2006;108:346-52.

Holt D, Dreimanis M, Pfeiffer M, Fir-gaira F, Morley A, Turner D. Interindivid-ual variation in mitotic recombination. Am

J Hum Genet 1999;65:1423-7.Zeuner A, Pedini F, Signore M, et al.

75.

76.

77.

78.

79.

80.

81.

82.

83.

84.

85.

86.

87.

88.

Increased death receptor resistance andFLIPshort expression in polycythemia veraerythroid precursor cells. Blood 2006;107:3495-502.

Walz C, Crowley BJ, Hudon HE, et al.Activated JAK2 with the V617F point mu-tation promotes G1/S-phase transition.

J Biol Chem 2006;281:18177-83.Staerk J, Kallin A, Demoulin JB, Vain-

chenker W, Constantinescu SN. JAK1 andTyk2 activation by the homologous poly-cythemia vera JAK2 V617F mutation: cross-talk with IGF1 receptor. J Biol Chem 2005;280:41893-9.

Royer Y, Staerk J, Costuleanu M, Cour-toy PJ, Constantinescu SN. Janus kinasesaffect thrombopoietin receptor cell sur-face localizat ion and stability. J Biol Chem2005;280:27251-61.

Vainchenker W, Constantinescu SN.A unique activating mutation in JAK2(V617F) is at the origin of polycythemia

vera and allows a new classi fication ofmyeloproliferative diseases. HematologyAm Soc Hematol Educ Program 2005;195-200.

Lu X, Levine R, Tong W, et al. Expres-sion of a homodimeric type I cytokinereceptor is required for JAK2V617F-medi-ated transformation. Proc Natl Acad SciU S A 2005;102:18962-7.

Spivak JL. Polycythemia vera: myths,mechanisms, and management. Blood2002;100:4272-90.

Cervantes F, Alvarez-Larran A, TalarnC, Gomez M, Montserrat E. Myelofibro-sis with myeloid metaplasia followingessential thrombocythaemia: actuarialprobability, presenting characteristics andevolution in a series of 195 patients. Br

J Haematol 2002;118:786-90.Thiele J, Kvasnicka HM, Zankovich R,

Diehl V. Relevance of bone marrow fea-tures in the differential diagnosis betweenessential thrombocythemia and early stageidiopathic myelofibrosis. Haematologica2000;85:1126-34.

Tefferi A. Myelofibrosis with myeloidmetaplasia. N Engl J Med 2000;342:1255-65.

Idem. Pathogenesis of myelofibrosis with myeloid metaplasia. J Clin Oncol2005;23:8520-30.

Villeval JL, Cohen-Solal K, Tulliez M,et al. High thrombopoietin production byhematopoietic cells induces a fatal myelo-proliferative syndrome in mice. Blood 1997;90:4369-83.

Komura E, Tonetti C, Penard-Lacro-nique V, et al. Role for the nuclear factorkappaB pathway in transforming growthfactor-beta1 production in idiopathic my-elofibrosis: possible relationship withFK506 binding protein 51 overexpression.Cancer Res 2005;65:3281-9.

Vannucchi AM, Bianchi L, Paoletti F,et al. A pathobiologic pathway linkingthrombopoietin, GATA-1, and TGF-beta1

89.

90.

91.

92.

93.

94.

95.

96.

97.

98.

99.

100.

101.

in the development of myelofibrosis. Blood2005;105:3493-501.

James C, Ugo V, Casadevall N, Con-stantinescu SN, Vainchenker WA. JAK2mutation in myeloproliferative disorders:pathogenesis and therapeutic and scien-tif ic prospects. Trends Mol Med 2005;11:46-54.

Barbui T. The leukemia controversyin myeloproliferative disorders: is it a natu-ral progression of disease, a secondarysequela of therapy, or a combination ofboth? Semin Hematol 2004;41:Suppl 3:15-7.

Harrison CN, Campbell PJ, Buck G,et al. Hydroxyurea compared with ana-grelide in high-risk essential thrombocy-themia. N Engl J Med 2005;353:33-45.

Cheung B, Radia D, Pantelidis P, Ya-degarfar G, Harrison C. The presence ofthe JAK2 V617F mutation is associated witha higher haemoglobin and increased riskof thrombosis in essential thrombocy-thaemia. Br J Haematol 2006;132:244-5.

Marchioli R, Finazzi G, Landolfi R,et al. Vascular and neoplastic risk ina large cohort of patients with polycythe-mia vera. J Clin Oncol 2005;23:2224-32.

Berk PD, Goldberg JD, Donovan PB,Fruchtman SM, Berlin NI, Wasserman LR.Therapeutic recommendations in polycy-themia vera based on Polycythemia VeraStudy Group protocols. Semin Hematol1986;23:132-43.

Campbell PJ, Green AR. Manage-ment of polycythemia vera and essentialthrombocythemia. Hematology Am SocHematol Educ Program 2005;201-8.

Tefferi A, Murphy S. Current opinionin essential thrombocythemia: pathogen-esis, diagnosis, and management. BloodRev 2001;15:121-31.

Campbell PJ, Scott LM, Baxter EJ,Bench AJ, Green AR, Erber WN. Methodsfor the detection of the JAK2 V617F muta-tion in human myeloproliferative disor-ders. Methods Mol Med 2006;125:253-64.

Percy MJ, Jones FG, Green AR, Reilly JT, McMullin MF. The incidence of the JAK2 V617F mutation in patients with id-iopathic erythrocytosis. Haematologica2006;91:413-4.

James C, Delhommeau F, Marzac C,et al. Detection of JAK2 V617F as a firstintention diagnostic test for erythrocyto-sis. Leukemia 2006;20:350-3.

Barosi G, Ambrosetti A, Finelli C, etal. The Italian Consensus Conference ondiagnostic criteria for myelofibrosis withmyeloid metaplasia. Br J Haematol 1999;104:730-7.

McMullin MF, Bareford D, CampbellP, et al. Guidelines for the diagnosis, inves-tigation and management of polycythae-mia/erythrocytosis. Br J Haematol 2005;130:174-95.

Cortelazzo S, Finazzi G, Ruggeri M,

102.

103.

104.

105.

106.

107.

108.

109.

110.

111.

112.

113.

114.

115.





15/15



et al. Hydroxyurea for patients with es-sential thrombocythemia and a high riskof thrombosis. N Engl J Med 1995;332:1132-6.

Falanga A, Marchetti M, Vignoli A,Balducci D, Barbui T. Leukocyte-plateletinteraction in patients with essentialthrombocythemia and polycythemia vera.Exp Hematol 2005;33:523-30.

116.

Arellano-Rodrigo E, Alvarez-LarranA, Reverter JC, Villamor N, Colomer D,Cervantes F. Increased platelet and leuko-cyte activation as contributing mechanismsfor thrombosis in essential thrombocythe-mia and correlation with the JAK2 muta-tional status. Haematologica 2006;91:169-75.

Jones AV, Silver RT, Waghorn K, et al.

117.

118.

Minimal molecular response in polycythe-mia vera patients treated with imatinib orinterferon alpha. Blood 2006;107:3339-41.

Kiladjian JJ, Cassinat B, Turlure P, etal. High molecular response rate of poly-cythemia vera patients treated with pe-gylated interferon alpha-2a. Blood 2006;108:2037-40.Copyright © 2006 Massachusetts Medical Society.

119.


mechanisms of disease the myeloproliferative disordersnejmra063728

Documents