Download Signal Transduction I

Tumor Biology: Cellular and Molecular
Aspects of the Transformed Cell
Growth Factors, Receptors,
and Signal Transduction I
Rebecca Riggins
202.687.7451
[email protected]
Overview
o Peptide growth factors
o Growth factor receptors
- structure and function
o Receptor activation and its consequences
o Growth factor and receptor defects in cancer
o Targeted therapies to growth factors, receptors
o Intracellular signaling “downstream” of receptors
- key pathways: Ras/MAPK, Src, PI3K
o Intracellular signaling defects in cancer
o Targeted therapies to intracellular signaling molecules
o TNF and TRAIL
Polypeptide Growth Factors
o small peptides, or proteins
o interact specifically with a receptor on the cell surface
o secreted by multiple cell types
o most are secreted as inactive precursors that need
to be cleaved or fragmented before they can act
o some are plasma membrane-bound or found in the
extracellular matrix
o transported by blood and lymphatic systems by several
different routes…3 major ones we will discuss are
Endocrine
Paracrine
Autocrine
Endocrine:
Synthesis by
specific cells,
target
(receptor) is far
away
Intracrine
Juxtacrine
Autocrine
Paracrine
Endocrine
BLOOD VESSEL
Different modes of action for growth factors (Bafico and Aaronson, Cancer Medicine, 2002)
Paracrine:
Synthesis by
many cell types,
receptor is
nearby
Intracrine
Juxtacrine
Autocrine
Paracrine
Endocrine
BLOOD VESSEL
Different modes of action for growth factors (Bafico and Aaronson, Cancer Medicine, 2002)
Autocrine:
Synthesis by
many cell types,
receptor is
on same cell
that synthesized
the growth factor
Intracrine
Juxtacrine
CANCER!
Autocrine
Paracrine
Endocrine
BLOOD VESSEL
Different modes of action for growth factors (Bafico and Aaronson, Cancer Medicine, 2002)
GROWTH FACTOR FUNCTIONS IN
VIVO
1. Early development
2. Tissue differentiation
3. Wound healing and tissue repair
4. Immune responses
5. Stromal mediators of sex and other hormones
. Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).
GROWTH FACTOR FUNCTIONS IN
VITRO
1. Proliferation
2. Differentiation
3. Chemo-attraction
4. Cell death
5. Cell migration
. Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).
REGULATION OF GROWTH
FACTOR/RECEPTOR
INTERACTIONS
1. Determined by growth factor availability and receptor
expression levels
2. Different modes of growth factor action - autocrine,
paracrine, other
3. Secretory properties - secretory signal; proteoglycan or
serum protein binding
4. More than one member of same growth factor gene
family may act on the same receptor
5. Same growth factor may cluster more than one receptor
member of the same receptor family
6. Interactions regulated by alternative growth
factor/receptor products
. Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).
ErbB/HER Family
Epidermal Growth Factor Receptor (EGFR)
Seminars in Cancer Biology, Volume 14, Issue 4, August 2004, Pages 262-270
Other Growth Factors
o platelet-derived growth factor (PDGF)
o nerve growth factor (NGF)
o hepatocyte growth factor (HGF)
o insulin-like growth factor (IGF)
o fibroblast growth factor (FGF)
o vascular endothelial growth factor (VEGF)
o named according to what they do or where they act
o most stimulate growth, or are mitogenic
Transforming Growth Factor (TGF)-b
o subgroup of a large family…25 members
o TGF-b1 is the most studied in cancer
o in some cells, TGF-b1 is mitogenic, while in others it
actually inhibits growth
o TGF-b can cooperate with PDGF…
Smooth muscle (mesenchymal)
Keratinocyte (epithelial)
No PDGFR
TGF-b increases PDGF,
cells proliferate
TGF-b inhibits
cell proliferation
Tumor Necrosis Factor (TNF)
o again, in some cells, TNF is mitogenic, but in
most it promotes cell death, or apoptosis
o this growth factor is not soluble, but is inserted into
the plasma membrane
Intracrine
Juxtacrine
Growth Factor Receptors
o all are transmembrane proteins
o 3 major features:
o extracellular domain (ectodomain)
o transmembrane region
o intracellular domain
o where, when, and
how they are expressed
determines their biological
function
Figure 5.10 The Biology of Cancer (© Garland Science 2007)
Growth Factor Receptors
o catalytic domain has kinase activity
o kinases add phosphate groups to (phosphorylate)
specific amino acids
o Receptor Tyrosine kinases phosphorylate Tyrosine
o Receptor Serine/Threonine kinases phosphorylate
Serine and/or Threonine
ATP-binding
Phospho-transferase
ATP
P
Amino Acid P
ADP
Autophosphorylation: receptor phosphorylates itself
Growth Factor Receptors
Transphosphorylation: receptor phosphorylates its
binding partner
Figure 5.15 The Biology of Cancer (© Garland Science 2007)
“Different” Growth Factor Receptors
o Some receptors have no
catalytic domain…
o TNF receptors rely instead on
other intracellular
proteins to transmit their signal
o Adhesion receptors (integrins)
also do this
Integrins bind Extracellular Matrix (ECM)
Another Example:
G protein-coupled receptors
o Have 7 transmembrane
domains
o Ligand may bind to extracellular
OR transmembrane region
(depending on receptor)
o Also do not have a catalytic
domain
GPCR - Inactive State
Figure 5.25a The Biology of Cancer (© Garland Science 2007)
GPCR – Activation Process
Figure 5.25bc The Biology of Cancer (© Garland Science 2007)
However, “classical” growth factor
receptors have catalytic domains
that must be activated
Receptor Tyrosine Kinase (RTK) Activation
o Homodimer: 2 identical receptors cluster together
o Heterodimer: 2 different receptors from the same
family cluster together
Nature Reviews Cancer, Vol. 5, May 2005, pg. 341-354
RECEPTOR ACTIVATION BY
GROWTH FACTORS
1. Growth factors induce receptor clustering
a. High affinity binding
b. Ligand mediated receptor cross-linking
c. Ligand/receptor crystal structures
2. Receptor activation by homodimer or heterodimer
formation
a. Activation requires the ability to cross-link
. Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).
Tyrosine Kinase Receptor Activation by Dimerization
EGFR
Insulin receptor
Figure 1. Ligand Binding
Stabilizes the Formation of
Activated Dimers(A) Inactive
receptor monomers (green) are in
equilibrium with inactive (green)
or active (blue) receptor dimers.
The active receptor dimers exist
in a conformation compatible
with trans-autophosphorylation
and stimulation of PTK activity
(blue). Ligand binding stabilizes
active dimer formation and hence
PTK activation.(B) Inactive
disulfide bridged insulin-receptor
(IR) dimers (green) are in
equilibrium with active dimers
(blue). Insulin binding stabilizes
the active dimeric state leading to
PTK activation.
Schlessinger J., Cell. 2000 Oct 13;103(2):211-25.
Consequences of RTK activation
GROWTH
FACTOR
PIP3
PIP3
RTK
RAS
SOS
Grb2
P
RAS
P
P
PDK1
Akt
p85
p110 PI3K
Raf
P
MEK
P
ERK
P
BAD
P
P
NF-ĸB
PROLIFERATION CELL SURVIVAL
FKHR
P
P
P
MDM2
GSK3b
p70S6K
PROTEIN SYNTHESIS
. Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).
RTK Signaling in Cancer
•
•
•
•
Autocrine Transforming Loops
Receptor Gene Amplification
Receptor Gene Mutation
Paracrine Acting Growth Factors
in Tumor Progression
. Aaronson, Growth factor and receptor tyrosine kinases. Sci. STKE 2005, tr6 (2005).
Figure 5.12b The Biology of Cancer (© Garland Science 2007)
Figure 5.12a The Biology of Cancer (© Garland Science 2007)
Historical Perspective
In the beginning…
o Oncogenic retroviruses caused tumors in animal
models (monkeys, chickens, etc.)
o These viruses contained transforming genes that
had nothing to do with the viral life cycle…
http://www.stanford.edu/group/nolan/index.html
Growth Factor Oncogenes
eg. PDGF
o Cancer cells, and cells in culture that were transformed
by simian sarcoma virus (SSV), were less dependent
on PDGF for growth
o PDGF-B was cloned…its sequence was very close to
that of the v-sis oncogene from SSV
o Thus, cellular PDGF-b (or c-sis-B) is a protooncogene
o Other oncogenic growth factors include the FGFs:
FGF3 – activated by mouse mammary tumor virus insertion
FGF4 – cloned from Kaposi’s sarcoma virus (skin tumors assoc.
with HIV/AIDS)
FGF5 – originally isolated from DNA of bladder tumors
Receptor Oncogenes
o v-erbB = mutated EGFR (avian erythroblastosis virus)
o v-fms = viral form of CSF-1 receptor
o v-kit = viral form of c-kit receptor
Mechanisms
o deletions, and/or insertions (v-erbB, v-kit)
o chromosomal translocation, fusions with other proteins
o “Neu” mutation of erbB2 = change of Val → Glu in
the transmembrane domain…constitutive dimerization,
activation
Table 5.1 The Biology of Cancer (© Garland Science 2007)
Table 5.2 The Biology of Cancer (© Garland Science 2007)
Table 5.3 The Biology of Cancer (© Garland Science 2007)
Receptors can be good targets:
Easy Access!
Seminars in Cancer Biology, Volume 14, Issue 4, August 2004, Pages 262-270
Targeted Therapy in Clinical Use
Nature Reviews Cancer, Vol. 5, May 2005, pg. 341-354
Understanding Targeted Therapy:
ErbB receptor family
Herceptin: anti-ErbB2
Erbitux: anti-EGFR
Iressa, Tarceva :
EGFR kinase inhibitor
Consequences of Inhibitor Action
o in vitro, these drugs can individually inhibit cell growth
and induce tumor shrinkage in mouse models
o However, cooperation between ErbB family members
in vivo means one inhibitor is usually not enough
o metastatic breast cancer, positive for ErbB2
expression…Herceptin used alone = 34% response rate
o Herceptin + cytotoxic chemotherapy drugs = better than
either drug alone…BUT there are many side effects
o in cell culture studies, Herceptin + Tarceva yield much
better response rates
UCLA Clinical Trial
o open to women with metastatic breast cancer
o must demonstrate amplified ErbB2 (excess gene copies)
o will be treated with Herceptin and Tarceva
o Phase I study: 14 patients, all received H+T…T at
various doses to determine the best
o 3 patients of 14 showed partial response or
stable disease…21%
o Phase II study: standard Herceptin + 150mg/day Tarceva
Eastern Cooperative Oncology Group
Trial
o open to women with metastatic breast cancer
o must demonstrate amplified ErbB2 (excess gene copies)
o will be treated with Herceptin and Iressa
o Phase I study: standard Herceptin + 250mg/day Iressa is
both active and well-tolerated by patients
o Phase II study: still ongoing
New Developments
o 2nd-generation tyrosine kinase inhibitors that target
BOTH EGFR and ErbB2…pan-ErbB inhibitors
ATP-binding
Phospho-transferase
Highly conserved between EGFR and ErbB2
o Canertinib, Lapatinib, others…target ATP binding site
o Lapatinib is active in breast cancer cells that have
acquired resistance to Herceptin
o In phase I/II trials, Lapatinib has also shown some effect
in patients resistant to Herceptin and Iressa
More New Developments
o blocking the interaction of receptor family members
o Pertuzumab = antibody against ErbB2, prevents
dimerization with other receptors, ie. EGFR
o This may be active in tumors without over-expressed or
amplified ErB2…currently used in trials for ovarian,
prostate, islet cell cancer
A few words about VEGF…
o VEGF interactions with its receptor are critical for
angiogenesis (formation of new blood vessels by tumors)
o anti-VEGF antibodies block the growth factor, not the
receptor
o Could be effective in treating both the primary tumor
and the metastases that develop elsewhere in the body
o Currently, Bevacizumab is approved for treatment of
metastatic colon cancer, and is undergoing phase I/II
clinical trials in breast and other cancers
On Wednesday
o Intracellular signaling “downstream” of receptors
- key pathways: Ras/MAPK, Src, PI3K
o Intracellular signaling defects in cancer
o Targeted therapies to intracellular signaling molecules
o TNF