(1)cell signaling

7/27/2019 (1)Cell Signaling

1/31

"Receptor-ligand interactions

- cell signaling, adhesion,

motility, cell migration"

Patricia Zuk, PhD

Research Director

Regenerative Bioengineering and Repair(REBAR) Lab

Department of Surgery

David Geffen School of Medicine at UCLA


2/31

No cell lives in isolation

survival depends on an elaborateintercellular communication network that

coordinates growth, differentiation andmetabolism

cells adjacent to one another frequentlycommunicate through cell-cell contact

other forms of communication coverlarger distances = extracellular signalingmolecules


3/31

Extracellular Signalling

signaling molecules are released by signaling cells

the signal is called the ligand

the ligand binds to its specific receptoron a target cell

this ligand-receptor interaction induces a conformational orshape-change in the receptor

produces a specific response - called the cellular response

can include a vast array of compounds

e.g. small amino acid derivatives, small peptides,proteins


4/31

Cell-to-cell communication by extracellular signaling usuallyinvolves six steps

(1) synthesis of the signaling molecule by the signaling cell

(2) release of the signaling molecule by the signaling cell

(3) transport of the signal to the target cell

(4) detection of the signal by a specific receptor protein receptor-ligand specificity

(5) a change in cellular metabolism, function, or development =cel lu lar respon se

triggered by the receptor-ligand complex specific to the ligand-receptor complex

(6) removal of the signal, which usually terminates the cellularresponse degredation of ligand


5/31

Signaling molecules operate over various distances in animals

-extracellular signaling can occur over:

1. large distanc es or endocr ine sign al ing signaling molecules are called

hormones

- act on target cells distant from their site of synthesis

-usually carried through the bloodstream2. sho rt distances or paracr ine signal ing affects target cells within proximity

to the cell that synthesized the molecule

-usually mediated by neurotransmitters and some growth

factors


6/31

Signaling molecules operate over various distances in animals

-extracellular signaling can occur over:

3. no d istance or autocr ine sign al ing the signal feeds-back and affects

itself

-action of many growth factors

-these compounds generally act on themselves toregulate proliferation

-seen frequently in tumor cells

-many compounds can act through two or even three types of cell signaling

e.g. growth factors (e.g. EGF) paracrine and autocrine and endocrine

-epinephrine endocrine and paracrine


7/31

Circulating & Local Hormones

Circulat ing

hormones

act on distant targets travel in blood endocrine hormones

Local ho rmones

paracrine hormones &autocrine hormones


8/31

Hormones

two types

lipid soluble water soluble


9/31

Lipid-Soluble Hormones

-lipid-soluble hormones can easily

enter a cell by diffusing through the

plasma membrane

-PROBLEM: how do they travel in the

water-based blood??-SOLUTION: they are carried by

carrier-proteins

-these hormones then enter their

target cell where they result in a

specific cellular effect or response


10/31

Water-soluble Hormones

-water soluble hormones can easily travel within the blood

-PROBLEM: how do they enter a cell and result in a cellular response??

-SOLUTION: binding to specific cell-surface receptors

-this binding activates the receptor and results in a series of cellular events called

the second messenger system


11/31

Lipid-soluble Hormones

Steroids lipids derived from cholesterol in SER different functional groups attached tocore of structure provide uniqueness interact with specific intracellular

receptors (within the cell) to turnspecific genes on or off

effective for hours or days

Thyro id hormones tyrosine ring plus attached iodines arelipid-soluble

activate enzymes involved in thecatabolism of fats and glucose

help set our basal metabolic rate Retinoids

vitamin A derivatives have dramatic effects on proliferationand differentiation plus cellular death(i.e. apoptosis)


12/31

Water-soluble Hormones

Am ino acid der ivat ives,

small pept ides andprotein hormones modified amino acids or

amino acids put together serotonin, melatonin,

histamine, epinephrine

larger peptide hormones insulin and glucagon

Eicosanoids

derived from arachidonicacid(fatty acid) prostaglandins or

leukotrienes

prostaglandins despite beinglipidphilic bind to cell

surface receptors


13/31

Action of Lipid-Soluble Hormones

Hormone diffusesthrough phospholipid

bilayer & into cell

Binds to receptor

turning on/off specific

genes

New mRNA is formed

& directs synthesis ofnew proteins

New protein alters

cells activity


14/31

Action of Water-Soluble Hormones

Can not diffuse through plasma

membrane Hormone receptors are integral

membrane proteins

act as first messenger Receptor protein activates G-protein in

membrane G-protein activates adenylate cyclase to

convert ATP to cAMP in the cytosol

Cyclic AMP is the 2nd messenger

Activates kinases in the cytosol to

speed up/slow down physiological

responses

Phosphodiesterase inactivates cAMP

quickly

Cell response is turned off unless

new hormone molecules arrive


15/31

Cell-surface receptors belong to four major classes

GPCRsare involved in a range of signaling pathways, includinglight detection, odorant detection, and detection of certainhormones and neurotransmitters

Many different mammalian cell-surface receptors includingGPCRs are coupled to a trimeric signal-transducing G protein

made of an alpha, beta and gamm asubunit complex

Ligand binding activates the receptor, which activates the Gprotein, which activates an effector enzym eto generate an

in t racel lu lar second messenger e.g. adenyly l c yclaseconverts ATP to cAMP

depending on regulation at the effector enzyme this pathwaycan be either activated or inhibited

by the type of G protein activated by the hormone-receptorcomplex

Gsproteins result in stimulation of the effector enzyme Giproteins result in inhibition of the effector enzyme

adenyly l cy clase (AC)


16/31

Four classes of cell-surface

receptors

-ligand binding changes the confirmation of the receptor so that specific ions flow

through it

-the resultant ion movement alters the electric potential across the plasmamembrane

-found in high numbers on neuronal plasma membranes

e.g. ligand-gated channels for sodium and potassium

-also found on the plasma membrane of muscle cells

-binding of acetylcholine results in ion movement and

eventual contraction of muscle


17/31

-lack intrinsic catalytic activity

-binding of the ligand results in the formation of a receptor dimer (2 receptors)

-this dimer than activates a class of protein called tyros ine kinases

-this activation results in the phosphorylation of downstream targets by

these tyrosine kinases (stick phosphate groups onto tyrosines withinthe target protein)

-receptors for cytokines such as XXXX, interferons (XXXXXXX)


18/31

-also called receptor tyros ine kinases OR ligand-tr iggered protein kinases

-similar to tyrosine-linked receptors - ligand binding results in formation of a dimer

-BUT: they differ from tyrosine-linked receptorsintr ins ic catalyt ic act iv i ty-means that ligand binding activates it and the activated receptor acts as a

kinase

-recognize soluble or membrane bound peptide/protein hormones that act as

growth factors

e.g. NGF, PDGF, insulin

-binding of the ligand stimulates the receptors tyrosine kinase activity,-results in phosphorylation of multiple amino acid residues within its target

such as serine and threonine residues

-this phosphorylation activates downstream targets

-its targets are generally other protein kinaseswhich phosphorylate their

own downstream targets (other kinases??)

Signal

transductionCascade


19/31

Signal transduction cascades

-the successivephosphorylation/activation ofmultiple kinases results in acascade ofphosphorylation/activation

-this cascade is frequently called as ignal-t ransdu ct ion cascade

-this cascade eventually leads to aspecific cellular response

e.g. changes in cellphysiology and/or patterns ofgene expression

-RTK pathways are involved inregulation of cell proliferation anddifferentiation, promotion of cellsurvival, and

modulation of cellular metabolism

Signal

KINASE #2

KINASE #3

TARGET

EFFECT

KINASE #1

p

p

p

p


20/31

Second messengers

produced by the activation of GPCRs and RTKs

Hormone stimulation of Gs protein-coupled receptors leads to activationof adenyly l cyc laseand synthesis of the second messenger cAMP most commonly studied second messenger cAMP does not function in signal pathways initiated by RTKs cAMP and other second messengers activate specific protein kinases (cAMP-

dependent protein kinases or PKAs)

cAMP has a wide variety of effects depending on the cell type and thedownstream PKAs and other kinases in adipocytes, increased cAMP activates a PKA that stimulates production of fatty

acids in ovarian cells another PKA will respond to cAMP by increase estrogen synthesis

second messenger systems allow for ampl i f icat ionof an extracellularsignal

one epinephine molecule can bind one GPCR this can result in the synthesis ofmultiple cAMP molecules which can go on to activate and amplified number ofPKAs

a blood level as low as 10 -10M epinephrine can raise blood glucose levels by 50%


21/31

Second messengers

other second messengers include: IP3 and DAG breakdown products of phosphotidylinositol

(PI) produced upon activation of multiple hormone receptor types

(GPCRs and RTKs) calcium IP3 production results in the opening of calcium-channels on the plasma membrane of the ER release ofcalcium a rise in calcium in pancreatic beta cells triggers the exocytosis

of insulin a rise in intracellular calcium also triggers contraction of

muscle cells much study has been done on the binding of calcium to a

protein called calmodul inand the effect of this complex ongene expression


22/31

MAP kinase pathways

best characterized signal transduction pathway activation of RTKs by growth factors, hormones etc.. result in activation of an adaptor protein called Ras GTPase ras induces a kinase signal cascade that starts with a kinase called rac

and culminates in activation of a MAP kinase (MAPK) in between are a series of kinases that are part of the cascade MAPK activation results in translocation into the nucleus and

phosphorylate many different proteins, including transcription factors thatregulate gene expression


23/31

MAPK kinase paths

StressCytokines

StressHormonesCytokines

MitogensHormones

cdc42/rac

MEKKs

JNKK 1/2

JNK 1/2

elk

jun

ATFMAPKAP-2

HSP27

MEK 3/6

MEKKs

p38MAPK

ATF

elk

cdc42/rac then activates one of three MAPK paths:

Activation ofras/MEK/ERK path: proliferation &

differentiation

p38MAPK: stress response & apoptosis (MAPKAP-

2, HSP27)

Stress, cytokines, hormones & mitogens signal

through cdc42/rac

raf-1

MEK 1/2

ERK 1/2

elk

RSK

ras

grb2

sos

fos

JNK: stress response & proliferation (jun)

transcription

factors (nucleus)

MAPK kinase


24/31

Common signaling pathways are initiated by differentreceptors in a class

The effects of activation of GPCRsand RTKs is more complicated thana simple step-by-step cascade

Stimulation of either GPCRs orRTKs often leads to production ofmultiple second messengers, andboth types of receptors promote orinhibit production of many of thesame second messengers

in addition, RTKs can promote asignal transduction cascade thateventually acts on the same targetas the GPCR

therefore the same cellular

response may be induced bymultiple signaling pathways bydistinct mechanisms

Interaction of different signalingpathways permits fine-tuning ofcellular activities


25/31

Integrating Cells into Tissues:

Cell-Cell Adhesion and Communication

-a key event in the evolution of multicellularity is the ability for cells to adhere to one

another and be able to communicate with each other

-evolved a series ofcel l-adhesion moleculesorCAMsthat allow interaction with

each other and with the surrounding extracellular matrix (ECM)

-this results in coordinated functioning of tissues

-HOW??

-these interactions result in the activation of specific signal transduction

cascades eventually resulting in the desired cellular effect

-therefore the physical interaction of CAMs with the ECM can turn pathways on oroff cellular effect

e.g. cellular interactions with the adhesion protein b1-integrin can result in

activation of the MAPK cascade


26/31

-various classes of CAMs found on cells

1. cadherins cell-cell adhesion

-calcium dependent

e.g, E-cadherin, P-cadherin

2. Ig superfamily of CAMs cell-cell adhesion

e.g. N-CAM, V-CAM

-calcium-independent

-some are found enriched on specific cell types N-CAM

3. Integri ns major cell-matrix adhesion molecule

e.g. a1 integrin, b1 integrin


27/31

Cell-Cell adhesion: Cadherin-containing junctions

1. Adherens junction

2. Desmosome

-cadherins are a family of calcium-dependent

CAMs

-major molecules of cell-cell adhesion (homophilic)

-over 40 different are knowne.g. E or epithelial cadherin

N or neural cadherin

-tissues have specialized junctions made of cadherins

1. adher ens j un ct io n continuous band of

cadherins found in epithelial cells

-connects cells tightly and interact

with the actin portion of the cytoskeleton2. desm osomes also found in high #s in

epithelial tissues

-cells attach via cadherins connect

to protein plaques that attach to the

plasma membrane and to intermediate

filaments within the cytoskeleton


28/31

Cell Matrix

three components to the ECM

insoluble col lagens structural framework of the ECM,provides strength and resiliency

proteoglycans cushions cells adhesive matr ix proteins bind these components to

receptors on the cell surface

different combinations result in unique ECM compositionswhich can directly affect the activity of the cells

the interaction of ECM components with specific CAMs (i.e.ECM receptors) can turn certain signaling paths ON or OFF

also the ECM is capable of sequestering growth factors andhormones by binding them and making them unavailable toturn cellular signaling on or off


29/31

Cell-matrix interactions: integrins

integrins allow connection between the extracellular matrix with the cytoskeleton of the cell also can mediate cell-cell interactions (weak)

made of an alpha and a beta subunit 17 types ofa chains, 8 types ofb chains

these ab complexes act as receptors to specific matrix components e.g. a1b1 collagen and laminin a5 b1 - fibronectin

cells will express multiple integrin types

attachment can be regulated by up- or down-regulated expression of these integrins integrins can also form very specific adhesive junctions

foca l adhesions(FN to actin) complex of more than 20 proteins can increase and decrease based on physical stress

hemidesmosomes(intermediate filaments to collagens and laminins) epithelial cells

activation of these integrins can promote cell signaling

e.g. formation and activation of focal adhesions triggers a cascade initaited by aFocal Adhesion Kinase (FAK) modulates cell growth and motility


30/31

Cell-Cell Communication: Gap Junctions

-almost all cells have specialized junctions

that allow the free passage of materials(e.g. signaling molecules) back and forth

-these junctions = gap junc t ions

-made of a channel protein called connexon

-connexons interact to form channels between

two cells

-one important compound small enough totraverse this junction is the second messenger

cAMP

-also allows passage of calcium ions and other

ions crucial to signaling (sodium, phosphate)

-these gaps are not free-swinging gates

-they actually open and close inresponse to ion concentrations

thereby restricting the flow of too

many ions

-they also exclude materials based

on size


31/31

Cell-Cell and Cell-Matrix interactions can activatesignal transduction cascades J Biomed Sci. 2006 Feb 23; Crosstalk between hepatocyte growth factor and integrin

signaling pathways.Chan PC, Chen SY, Chen CH, Chen HC

J Neurochem. 2006 Jan;96(1):148-59Fibronectin promotes brain capillary endothelial cell survival and proliferation throughalpha5beta1 and alphavbeta3 integrins via MAP kinase signalling. Wang J, Milner R.

Immunopharmacol Immunotoxicol. 2005;27(3):371-93.Interleukin-3, -5, and granulocyte macrophage colony-stimulating factor induce adhesionand chemotaxis of human eosinophils via p38 mitogen-activated protein kinase andnuclear factor kappaB. Ip WK, Wong CK, Wang CB, Tian YP, Lam CW.

Cell Commun Adhes. 2004 Sep-Dec;11(5-6):137-53.ERK signaling pathways regulate the osteogenic differentiation of human mesenchymalstem cells on collagen I and vitronectin. Salasznyk RM, Klees RF, Hughlock MK, PlopperGE.

Microsc Microanal. 2005 Jun;11(3):200-8.Cross talk between cell-cell and cell-matrix adhesion signaling pathways during heartorganogenesis: implications for cardiac birth defects.Linask KK, Manisastry S, Han M.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Chan+PC%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Chen+SY%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Chen+CH%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Chen+HC%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/utils/lofref.fcgi?PrId=3046&uid=16269008&db=pubmed&url=http://dx.doi.org/10.1111/j.1471-4159.2005.03521.xhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Wang+J%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Milner+R%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/utils/lofref.fcgi?PrId=3396&uid=16237950&db=pubmed&url=http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=0892-3973&volume=27&issue=3&spage=371http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Ip+WK%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Wong+CK%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Wang+CB%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Tian+YP%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Lam+CW%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Salasznyk+RM%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Klees+RF%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Hughlock+MK%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Plopper+GE%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Plopper+GE%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Linask+KK%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Manisastry+S%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Han+M%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Han+M%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Manisastry+S%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Linask+KK%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Plopper+GE%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Plopper+GE%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Hughlock+MK%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Klees+RF%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Salasznyk+RM%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Lam+CW%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Tian+YP%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Wang+CB%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Wong+CK%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Ip+WK%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/utils/lofref.fcgi?PrId=3396&uid=16237950&db=pubmed&url=http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=0892-3973&volume=27&issue=3&spage=371http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Milner+R%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Wang+J%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/utils/lofref.fcgi?PrId=3046&uid=16269008&db=pubmed&url=http://dx.doi.org/10.1111/j.1471-4159.2005.03521.xhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Chen+HC%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Chen+CH%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Chen+SY%22%5BAuthor%5Dhttp://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Search&itool=pubmed_Abstract&term=%22Chan+PC%22%5BAuthor%5D

(1)cell signaling

Documents