This document provides an overview of signal transduction and its importance in cancer. It describes how extracellular signals are transmitted into cellular responses through receptors, effectors, and second messengers. Key signaling pathways like PI3K-Akt-mTOR, Ras-MAPK, JAK-STAT, and NFκB are discussed in the context of proliferation, survival and other cancer-related processes. The document outlines how abnormal signaling contributes to cancer and how targeting important pathways is a therapeutic strategy, using examples like Gleevec for Bcr-Abl in CML and Herceptin for HER2 in breast cancer. Studying signaling in cancer involves techniques like inhibitors, antibodies and transgenic models.

1. Signal Transduction and
Cancer
SURP Program
July 7, 2009

2. Outline of Today’s Lecture
8 Signal transduction overview
8 Why important in cancer?
8 Examples of important pathways
8 How signaling is studied in the lab
8 Signal transduction pathways as
therapeutic targets
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3. What is signal transduction?
8 The process by which extracellular signals are
transmitted across the cell membrane and
converted into a cellular response (e.g. gene
expression, apoptosis…)
8 “the process by which a cell converts a signal or
stimulus into another”. (www.wikipedia.com)
8 “How cells respond to environmental stimuli”
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4. Typical Components of Signaling
Pathways
Receptor
Target
Ligand Effector/
(Stimulus) Amplification
Adaptor
of signal
proteins Second
Messengers Biological
Response
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5. Types of Signals
8 Proteins:
– Cytokines (e.g. IL-1)
– Growth factors (e.g. EGF, TGFβ)
8 Nutritional factors:
– Sugars (glucose)
– Amino Acids
– Lipids
– Vitamins
8 Hormones (e.g. adrenaline, estrogen, insulin)
8 Other:
– Stress, heat, pH, radiation, etc
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6. Signals can act in a cell-type
specific manner
Mesenchymal cells
oting
th prom (e.g. fibroblasts)
Grow
TGFβ
Grow
th inhibi
ting
Epithelial cells
Endothelial cells
Hemopoietic cells
Neural cells
8 Important to note specific context when
evaluating signaling literature!
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7. Receptors
8 Growth factors signal via receptor tyrosine kinases
(RTKs/RPTKs).
8 Transmembrane proteins, containing an extracellular
domain of several hundred AAs, short alpha helix
structured hydrophobic domain spanning the membrane,
and an intracellular catalytic domain that is highly
conserved among family members.
8 Ligand binding induces a change in conformation of
receptors, allowing dimerization and transphosphorylation
of Tyr residues.
8 Signaling intermediates are recruited to the
phosphorylated (“active”) receptor to propagate the
signal.
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8. Receptor Activation Schematic
Ligand
Molecular Biology of the Cell, Alberts et al. Ch 3 8

9. Phosphorylation and dephosphorylation
regulate the activity of many proteins
8 Kinases: Enzymes that
catalyze the removal of a
phosphate group from
ATP which is transferred
to serine, threonine or
tyrosine residues in
proteins.
– 2 classes: Ser/Thr and
Tyr kinases
8 Phosphatases: Enzymes
which catalyze the
removal of phosphate
groups from proteins
Molecular Biology of the Cell, Alberts et al. Ch 3 9

10. Effectors
8 Anchor proteins localize protein kinases
and phosphatases in particular places in
the cell
– Increases efficiency and specificity of
responses
8 Protein-protein complexes form via
interactions between specific protein
domains (e.g. SH2 domains which
recognize phospho-tyrosines)
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11. Biological outcomes
8 Changes in gene
expression
8 Regulate
translation
8 Regulate the cell
cycle
8 Migrate
8 Reorganize the
cytoskeleton
8 Initiate
angiogenesis etc
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12. Cancer and growth control
8 Normal cells respond to their environment
to maintain a balance between
proliferation, differentiation and cell death.
8 Cancer cells have defects in growth
control, leading to…
Hahn and Weinberg Cell 2000 12

13. Why study signal transduction in cancer?
Nearly all proto-oncogenes are members of
signal transduction pathways involved in
regulating cell proliferation, differentiation or
apoptosis
“Signal transduction”
in title/abstract
QuickTimeª and a
decompressor
are needed to see this picture.
Total: 57037
(as of 7/6/09)
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14. What goes wrong in cancer?
8 Tumors cells
inappropriately
secrete growth
factors that activate
cognate receptors on
their cell surface -
allows signaling
independent of “true
Example: Renal cell cell-cell
carcinoma cells have an communication”
autocrine TGFα - EGFR
autocrine loop
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15. What goes wrong in cancer (2)
8 Upregulation of growth factor
receptors
8 Deletions in receptor domains
causing defects in ligand binding,
or causing constitutive
dimerization.
8 Normal cells contain
20,000-200,000 copies of EGFR;
cancers cells can contain
>1,000,000!
– Greatly increased upstream
mitogenic signaling.
Classic example: Breast cancer cells
can overexpress HER2 (an EGFR
family member)
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16. What goes wrong in cancer? (3)
8 Increase in signal transduction
– Loss of negative regulators (e.g. mutation or epigenetic
silencing of PTEN in endometrial carcinoma)
– Defects in protein turnover
– Defects in protein localization (e.g. sequestration of
p27 in to the cytoplasm in RCC)
– Novel oncogenes from chromosomal translocations
that result in constitutive activity of a kinase (e.g. Bcr-
Abl)
8 Increase in activation of transcription
– Constitutive activation of transcription factors (e.g.
STAT3)
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17. Signal transduction pathways are
targets of carcinogens
8 Carcinogen (e.g.
DMBA) causes an
activating mutation in
codon 61 of H-ras.
8 Tumor promoters like
TPA promote clonal
expansion of initiated
cells. Multiple
signaling pathways
targeted by TPA
including PI3K-Akt,
and protein kinase C.
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18. Overview of most important signal
transduction pathways in cancer
8 PI3K-Akt-mTOR SURVIVAL C
(regulate protein R
translation, cell O
growth, autophagy) S
S
8 Ras-MAPK PROLIFERATION T
8 JAK-STAT PROLIFERATION A
(anti-apoptosis, L
K
immune response)
8 NFκB INFLAMMATION
8 WNT-β-Catenin DIFFERENTIATION
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19. How signal transduction is studied
8 Cell culture studies:
– Use of inhibitors (e.g.
rapamycin, LY294002)
– Phospho-specific antibodies
– If no antibodies available,
can immunoprecipitate and
western blot with broad
phospho-tyr or phospho-
ser/thr antibodies
– In vitro kinase reactions:
determine whether a specific
kinase can phosphorylate a
given substrate in a test tube.
– Other enzyme assays which
measure products
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20. How signal transduction is studied (2)
8 In vivo studies:
– Phospho-specific
antibodies for
immunohistochemistry
– Commercially
available/custom
tissue microarrays to
look at many samples
at once
– Transgenic
/knockout mouse
models
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21. Signal tranduction as a therapeutic target
8 Traditional cytotoxic chemotherapy
has problems:
– Non-specific, unpleasant side effects --> kills
proliferating cells, even normal ones such as hair
follicles, GI epithelial cells
– Cells develop resistance mechanisms (e.g. upregulate
proteins that pump drugs out of the cells so they can
no longer accumulate)
8 Rationally designed targeted therapies that
interfere with signaling the current rage in
cancer therapeutics research.
– Ideal target = a protein not involved in normal cellular
function (Bcr-Abl example in next few slides)
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22. Determining a good drug target
8 Determine what pathways are active in your
tumor type
8 Determine whether any of these pathways are
critical for tumor survival
– “Oncogene addiction” phenomenon: Despite the fact
that tumors contain multiple genetic and epigenetic
defects, their growth/survival can often be impaired by
inactivation of a single oncogene (the “Achilles Heel”)!
8 Financially worthwhile - enough of a target
market (large enough prevalence)
8 2 examples: Bcr-Abl and HER2/neu
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23. Bcr-Abl in CML
8 Chromosomal
translocation results in
a constitutively active
tyrosine kinase.
8 Found in 95% of CML
patients
8 Signals via a multitude
of growth-promoting
pathways (PI3K, JAK-
STAT, Myc, NFκB)
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24. Gleevec
8 Gleevec is a small molecule
designed to bind to the ATP cleft
and inhibit the tyrosine kinase
activity of Bcr-Abl at low conc’s
(40nM).
– Later found to also inhibit
PDGFR and c-Kit
QuickTimeª and a
8 Successfully used so far:
decompressor
are needed to see this picture. – 98% complete response rate
in chronic phase CML
(NEJM, 2001)
– Reduce total tumor cells from
1010/1012 to 106 (minimal
residual disease)
– Now is the standard of care!
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25. HER2 as a target in breast cancer
8 Some breast cancers
(~25%) overexpress the
HER2 gene, a growth factor
receptor in the EGFR family.
8 These tumors have a worse
prognosis than non HER2-
overexpressing tumors.
8 Antibodies such as
Herceptin (trastuzumab)
have been developed to
block the aberrant mitogenic
signaling.
8 Good results are seen in
synergy with standard
therapies (chemo and
radiation)
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26. Sample of what pharma has done
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27. Take home points
8 Signal transduction is the mechanism by which cells
communicate.
8 Signal transduction networks are often bizarre in
cancer and result in an imbalance between cell
death and cell survival.
8 Multiple mechanisms are employed by cancer cells
to subvert normal regulation of proteins involved in
signaling, including gene amplification, mutations,
chromosomal translocations and epigenetic
silencing of tumor suppressors.
8 Rationally designed signaling inhibition is a relevant
therapeutic approach.
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28. Additional Resources
8 Cell Signaling Technologies website -
www.cellsignal.com (lots of signaling diagrams)
and www.phosphosite.org (information about
kinases and their substrates)
8 Science Signal Transduction Knowledge
Environment - http://stke.sciencemag.org
8 Calbiochem interactive pathways -
http://www.emdbiosciences.com/html/EMD/inter
activepathways.htm
Questions? Aalexand@mdanderson.org
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