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 Program
Department of Pathology
College of Medicine
University of Vermont
Burlington, VT 05405
Tel: 802.656.0382
Brooke.Mossman@uvm.edu
Cell Signaling by Oxidants
Society For Free Radical Biology and Medicine
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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 signalregulated 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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Importance of Cell Signaling in the Development of
Proliferative Diseases such as Cancer or Fibrosis
Cell Signaling
(In)Activation of
Gene Transcription
Gene Product
Biological Effect
•Protein
•Transcription Factor
Disease
•Cell Proliferation
•Cell Transformation
•Cell Death/Apoptosis
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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
Inflammation
Survival
Survival
Apoptosis/Death
Cell Cycle Control
* See Janssen-Heininger et al., Free Rad. Biol. Med. 28: 1317 – 27, 2000.
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General Schema
for Mitogen-Activated Protein Kinase (MAPK) Cascade
* ERK=Extracellular Signal-Regulated Kinase
* JNK=c-Jun N-terminal Kinase
* p38
Stimulus
MAPK Kinase Kinase
Growth Factors
ROS / RNS
Cytokines
Cellular Stress
(Osmotic stress, ROS)
Raf
MEKK
MAPK Kinase
MAPK
Response
MEK1/2
ERK1/2 *
Mitogenic
growth, differentiation
MEK3
MEK4
p38 *
JNK1/2 *
Stress Responses
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ROS - Induced Mitogen-Activated Protein Kinase
(MAPK) Cascade
Asbestos, H2O2, & Silica *
?
?
Raf
MEKK
MEK1 & MEK2
ERK1/2
MEK3
MEK4
p38
JNK1/2
?
Apoptosis
DNA Damage
HOMOLOG
?
c-fos/c-jun
Proliferation
* 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)
EGF-R
Asbestos
Fibers HO.
O2.-
RAS
P
P
RAF
P
MEK1/2
ERK
X
ERK
Catalase
NAC
Deferoxamine Mesylate
P
Cytoplasm
ERK
P
TGACTCA
ACTGAGT
SRE
P
Nucleus
Injury/Cell Proliferation/Survival Disease?
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.
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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
Outcome
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Formation of Activator Protein–1 (AP-1)
stimulus
early response
genes
c-fos
mRNA
c-jun
mRNA
AP-1
intermediate
response gene
Cell Proliferation, etc.
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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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