the virtual free radical school cell signaling by oxidants: mitogen-activated protein kinases (mapk)...
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The Virtual Free Radical School
Cell Signaling by Oxidants: Mitogen-Activated Protein Kinases (MAPK) and Activator Protein – 1 (AP-1)
Brooke T. Mossman* and Maria Stern
Environmental Pathology ProgramDepartment of Pathology
College of MedicineUniversity of VermontBurlington, VT 05405
Tel: [email protected]
Cell Signaling by Oxidants
Society For Free Radical Biology and Medicine Mossman & Stern 1
Overview
Oxidants can modulate cell signaling events by modifying cell surface receptors, phosphatases and protein phosphorylation, etc. These phenomena are important in transactivation of transcription factors and activation/inactivation of gene transcription that may regulate steps in the development of disease. At least two classical signaling pathways, the Mitogen-Activated Protein Kinases (MAPK) and signaling leading to activation of NF-B, are activated by oxidants. Physiological oxidant stresses, such as asbestos, induce primarily the extracellular signal-regulated kinases (ERKs) whereas H2O2 causes activation of all three MAPK cascades. A consequence of MAPK activation is formation of Activator Protein–1 (AP-1), which binds to the promoter regions of intermediate response genes governing cell proliferation, differentiation, etc.
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Cell Signaling (In)Activation ofGene Transcription
Gene Product Biological Effect Disease•Cell Proliferation•Cell Transformation•Cell Death/Apoptosis
Importance of Cell Signaling in the Development of Proliferative Diseases such as Cancer or Fibrosis
•Protein•Transcription Factor
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Two Classical Signaling Pathways/Transcription Factors are Associated with Exposure to Oxidants:
• MAPK/AP-1 (Activator Protein-1) • NF-B * (Nuclear Factor – B)
Proliferation
Survival
Apoptosis/Death
Inflammation
Survival
Cell Cycle Control
* See Janssen-Heininger et al., Free Rad. Biol. Med. 28: 1317 – 27, 2000.
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* ERK=Extracellular Signal-Regulated Kinase* JNK=c-Jun N-terminal Kinase* p38
Stimulus
MAPK Kinase Kinase
MAPK Kinase
MAPK
Response
Growth Factors ROS / RNS
Raf
MEK1/2
ERK1/2 *
Mitogenicgrowth, differentiation
CytokinesCellular Stress
(Osmotic stress, ROS)
MEKK
MEK3 MEK4
p38 * JNK1/2 *
Stress Responses
General Schema for Mitogen-Activated Protein Kinase (MAPK) Cascade
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ROS - Induced Mitogen-Activated Protein Kinase (MAPK) Cascade
Asbestos, H2O2, & Silica *
Raf
MEK1 & MEK2
ERK1/2
ApoptosisDNA Damage
MEKK HOMOLOG
MEK3 MEK4
JNK1/2
Proliferation
p38
c-fos/c-jun
??
? ?
* See Ramos et al., Molec. Cell. Biochem. 234/235: 111-115, 2002
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ROS-Induced Stimulation of Extracellular Signal Regulated Kinases (ERK1/2)
AsbestosFibers
EGF-R
RAS
P
RAF P
MEK1/2 P
ERK ERK P
ERK P
Injury/Cell Proliferation/Survival Disease?
Cytoplasm
NucleusP
O2.-
HO.
TGACTCAACTGAGT
X CatalaseNACDeferoxamine Mesylate
SRE
The ERK family (at least 8 isoforms) are typically activated in a series of protein phosphorylation events after phosphorylation of cell surface receptors (i.e. the epidermal growth factor receptor (EGFR) or other extracellular signals. Phosphorylated members of the ERK family then function to transcriptionally regulate specific subsets of genes. For example, phosphorylated ERK2 translocates to the nucleus to phosphorylate ternary complex factor (TCF) which finds to the serum response element (SRE) of c-fos. Mossman & Stern 7
Relationships between MAPK Activation and AP-1
Stress, growth factors, cytokines, oxidants
MAPK
mRNA induction: c-fos, c-jun
Protein synthesis: c-Fos, c-Jun
AP-1 formation: Fos/Jun, Jun/Jun
OutcomeMossman & Stern 8
Formation of Activator Protein–1 (AP-1)
stimulus
early response genes
c-fos
c-jun
mRNA
mRNA
intermediate response gene
Cell Proliferation, etc.
AP-1
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Summary• Oxidants can induce MAPK.
• The MAPKs family includes extracellular signal-regulated kinases (ERKs), which are generally activated by mitogens, and c-Jun NH2 – terminal kinase (JNKs) and p38 MAPKs, both activated by cytokines and cellular stresses.
• Upon activation, JNKs and ERKs phosphorylate Jun and Fos proteins, i.e. AP-1 family members. Although p38 MAPKs do not activate AP-1 proteins directly, they can regulate jun and fos transcription by phosphorylating enhancer binding proteins (C/EBPs) binding to their promoter elements.
• By selective dimerization of AP-1 family members (Jun/Jun or Fos/Jun partners) and diverse binding specificities with the promoter regions of genes, the AP-1 transcription factor regulates gene expression important in cell injury, repair, proliferation, and differentiation.
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