1. Growth Factors, Receptors
Chapter 5
Growth Factors, Receptors
and Cancer
5. 2 ~ 5.9 -
Mar 27 & 29, 2007

2. Decisions about growth versus no-growth must be made for the welfare of the entire tissue and whole organism, not for the benefit of its individual component cells.

3. 5.2 the Src protein functions as a tyrosine kinase
A protein kinase is a kinase enzyme that modifies other proteins by chemically adding phosphate groups to them (phosphorylation).
Figure 5.5a The Biology of Cancer (© Garland Science 2007)

4. Most of the kinases in the cell are serine
/threonine kinases (add phosphate group
on serine/threonine).
More than 99% of the phosphoamino acids
in normal cells are phosphothreonine or
phosphoserine; phosphotyrosine constitutes
as little as 0.05 to 0.1% of these cells’ total
phosphoamino acids.

5. Electrophoresis can be used to resolve 3 types
of phosphoamino acids – phosphotyrosine, phosphothreonine and phosphoserine
almost no
phosphotyrosine
increased level
of phosphotyrosine
Figure 5.8 The Biology of Cancer (© Garland Science 2007)

6. Src can phosphorylate more than 50 distinct proteins (substrate) in the cell
32P-labeled ATP was added into the cell lysates
Figure 5.7a The Biology of Cancer (© Garland Science 2007)

7. A protein kinase usually phosphorylates and modifies the functional state of a number of distinct substrate proteins
Akt: AKR mouse T-cell
lymphoma (v-Akt)
PKB: protein kinase B
HIF: hypoxia-
inducible
factor
Bad: BclxL/Bcl-2
-associated
death
promoter
GSK: glycogen synthase
kinase
Figure 5.7b The Biology of Cancer (© Garland Science 2007)

8. 5.3 The epidermal growth factor receptor
(EGF-R) functions as a tyrosine kinase
- A variety of proteins involved in cell-to-cell
signaling were found and sequenced.
- The 1st of the growth factors to be discovered
was epidermal growth factor (EGF).
- EGF has mitogenic effects when applied to a
variety of epithelial cell types.
- EGF (ligand) is able to bind to a surface protein
(receptor) of the cells whose growth it stimulates.

9. Structure of the epidermis growth factor (EGF) receptor
tyrosine kinase domain
Figure 5.9a The Biology of Cancer (© Garland Science 2007)

10. Structure of tyrosine kinase receptors
IGF-1: insulin-like growth factor-1, NGF: nerve growth factor,
PDGF: platelet-derived growth factor, FGF: fibroblast growth factor,
VEGF: vascular endothelial growth factor, Eph: ephrin
Figure The Biology of Cancer (© Garland Science 2007)

11. Growth factors and their tyrosine kinase receptors
HGF: hepatocyte growth factor, SF: scatter factor
GDNF: glial cell derived neurotrophic factor
Ret: Rearranged during transfection, SCF: stem cell factor
Table 5.1 The Biology of Cancer (© Garland Science 2007)

13. 5.4 An altered growth factor receptor can function as an oncoprotein
- In 1984, the sequence of the EGF receptor was recognized to
be closely related to the sequence of a known oncogene product
v-ErbB from avian erythroblastosis virus.
Figure The Biology of Cancer (© Garland Science 2007)

14. Mutations in growth factor receptor gene can cause ligand-independent activation
Figure 5.12a The Biology of Cancer (© Garland Science 2007)

15. Tumor cells may synthesize growth factor and creates an autocrine signaling
invasive human
breast carcinoma
receptor:
EGF-R
ligand:
TGF-α
super-imposed
Figure 5.12b The Biology of Cancer (© Garland Science 2007)

16. 4.6 - In about 1/3 of glioblastomas examined, the EGF-R has been found
to be decapitated, lacking most of its extracellular domain.
In many lung cancers, the EGF-R mRNA lacks the coding sequences
carried by exons 2 through 7.
Table 5.2 The Biology of Cancer (© Garland Science 2007)

17. 5.5 A growth factor gene can become an oncogene: the case of sis
- In 1983, the B chain of platelet-derived growth factor
(PDGF) was found to be closely related in sequence
to the oncoprotein encoded by the v-sis oncogenes of
simian sarcoma virus.
- PDGF stimulates growth
of mesenchymal cells,
such as fibroblasts,
adipocytes,
smooth muscle cells,
and endothelial cells.
PDGF can also be AA or BB A B

18. Growth factors can act on cells via three ways

19. IL-6: interleukin-6, NRG: neuregulin, PRL: prolactin,
(SCLC)
IL-6: interleukin-6, NRG: neuregulin, PRL: prolactin,
TGF: transforming growth factor, GRP: gastrin releasing peptide
Table 5.3 The Biology of Cancer (© Garland Science 2007)

20. Certain lung cancers produce 3 distinct growth
factors and express their receptors:
1. transforming growth factor (TGF) - α / EGF-R
2. stem cell factor (SCF) / Kit
3. insulin-like growth factor (IGF) - 1 / IGF-1-R
- Kaposi’s sarcomas produce PDGF, TGF-β, IGF-1,
angiogenin 2 (Ang2), CCL8, CXCL11, endothelin
and express their receptors. At the same time, the
causal agent of this disease, the human herpesvirus-8
(HHV-8) produces vIL-6 and macrophage
inflammatory protein (vMIP).

21. 5.6 Transphosphorylation underlies the
operations of receptor tyrosine kinases
(RTK)
How do growth factor receptors use their tyrosine
kinase domains to emit signals in response to
ligand binding?

22. Receptor dimerization following ligand binding
Figure The Biology of Cancer (© Garland Science 2007)

23. Transphosphorylation of the EGF receptor
- EGF EGF
A431 human vulve
epidermoid carcinoma
cell line
(overexpress EGF-R) in
32PO4-containing medium
Figure The Biology of Cancer (© Garland Science 2007)

24. Why does overexpression of growth factor receptors participate in the formation of cancers ?
1. When the receptor molecules are overexpressed, their
high numbers cause them to collide frequently, and these
encounters, like the dimerization events triggered by
ligand binding, can result in trans-phosphorylation,
receptor activation, and signal emission.
2. Alternatively, excessive receptor expression may make
some cancer cells hyper-responsive to the low levels of
growth factors that may be present in their surroundings.

25. deletion amplification point mutation translocation
Table 5.2 The Biology of Cancer (© Garland Science 2007)

26. a.a. substitutions or deletions
Sidebar 5.7 Mutant forms of a single tyrosine kinase-R
may play a causal role in very different
types of cancer
c-Kit is the receptor for
stem cell factor (SCF)
SCF stimulates the formation of various types of cells in the blood (hematopoiesis), as well as the development of a variety of nonhematopoietic cell types, including melanocytes and the cells mediating gut motility.
a.a. substitutions or deletions
GIST: gastrointestinal stromal tumor
AML: acute myelogenous leukemia
Figure 5.18a The Biology of Cancer (© Garland Science 2007)

27. 5.7 Yet other types of receptors enable mammalian
cells to communicate with their environment
- Other types of receptors which contain no kinase domains
also contribute to cancer formation.
(1) When the receptors dimerize in
response to ligand binding, the
associated Janus kinases (Jaks)
phosphorylate and activate each
other.
The activated Jaks then proceed
to phosphorylate the C-terminal
tails of the receptor molecules,
thereby activating the receptors
to emit signals.
Janus : Roman god of gates
and doors 兩面神

28. Receptors with Jaks as associated tyrosine kinases
erythropoietin (EPO) receptor – regulates the development of erythrocytes.
thromboietin (TPO) receptor – controls the development of the precursors
of blood platelets, megakaryocytes.
interferon (IFN) receptor – delivers anti-viral signals.
Jak family:
Jak1, Jak2,
Jak3, Tyk2
Tyrosine kinase 2
Figure The Biology of Cancer (© Garland Science 2007)

29. (2) Transforming growth factor β (TGF-β) receptors are
heterodimers and their kinas domains phosphorylate serine
and threonine rather than tyrosine residues.
→ suppress the proli-
feration of normal
epithelial cells and
promote the
acquisition of
invasive properties
by transformed
cells
Figure The Biology of Cancer (© Garland Science 2007)

30. (3) Notch receptor: After binding ligands (NotchL, Delta, Jagged),
Notch is cleaved successively by two proteases.
One of the resulting proteolytic Notch
fragments, derived from its
cytoplasmic domain,
migrates to the nucleus,
where it functions as part
of a complex of
transcription factors that
activate expression of
responder genes.
cytoplasm
act as a transcription factor
contribute to Ras-mediated cell
transformation and
morphogenetic processes.
Figure The Biology of Cancer (© Garland Science 2007)

31. (4) Patched (Ptc) receptor: When the ligand Hedgehog (Hh) binds, Ptc
moves away from a 2nd membrane-spanning
protein called Smoothened (Smo).
Smoothened then
signals to a
cytoplasmic complex
that releases a
transcription factor,
and translocates to
the nucleus.
Mutant alleles of both
Ptc and Smo have been
found in the common
basal cell carcinoma of
the skin.
(functionally inert)
of transcription
Figure The Biology of Cancer (© Garland Science 2007)

32. (5) Wnt (growth factor) can activate Frizzled (Frz, the receptor)
and trigger a cascade of steps that shut down glycogen
synthase kinase-3β (GSK-3β) firing, allowing its downstream
substrate -catenin to escape degradation and to promote cell
proliferation.
(adenomatous polyposis coli)
Figure The Biology of Cancer (© Garland Science 2007)

33. Signaling through G proteins by serpentine receptors
seven-membrane-spanning
signaling through G proteins
(guanine nucleotide-binding proteins)
also called G-protein-coupled
receptors (GPCRs)
contribute to the pathogenesis of
a small number of human cancers
Figure The Biology of Cancer (© Garland Science 2007)

34. 5.8 Integrin receptors sense association between
the cell and the extracellular matrix
In the absence of attachment, many types of normal cells will activate a death program (apoptosis) that is called anoikis.
anchorage-independent growth
Figure The Biology of Cancer (© Garland Science 2007)

35. Cells are not anchored directly to the glass or plastic surface
of the dishes.
Instead, they attach to a complex network of molecules, called
extracellular matrix (ECM), which is usually found in the
spaces between cells within most tissues.
ECM is composed of glycoproteins,
including collagens, laminins,
proteoglycans, and fibronectin.
Cells are able to sense whether
or not they attach to the ECM.
Such sensing depends on
integrin receptors.
extracellular matrix
Figure The Biology of Cancer (© Garland Science 2007)

36. Integrins constitute a large family of heterodimeric
transmembrane cell
surface receptors
composed of α and β
subunits.
At least 18 α and 8 β subunits
have been identified, with a
total of 24 distinct integrins.
Figure The Biology of Cancer (© Garland Science 2007)

37. Table 5.4 The Biology of Cancer (© Garland Science 2007)

38. Integrin clustering connects ECM to cytoskeleton
(focal adhesions) and activate signaling pathways
- cell migration, proliferation and survival (anti-apoptosis)
focal adhesion
(clustered integrins,
cytoskeletons,
associated proteins)
actin fiber
Figure 5.28a The Biology of Cancer (© Garland Science 2007)

39. Organization of ECM-integrin-cytoskeleton
signals outside-in
signals inside-out
Figure 5.28b The Biology of Cancer (© Garland Science 2007)

40. 5.9 The Ras protein functions as a G protein
- The ras oncogene triggers many of the same
changes in cells which are transformed by
erbB (truncated EGF-R) or sis (PDGF-B).
- Could Ras be found somewhere downstream
of erbB and sis ?
- Do the signals emitted by EGF-R and PDGF-R
converge on some common molecule ?

41. EGF/EGFR-mediated Ras activation
SH2, SH3: Src homolog
GRB2:
growth factor receptor-
bound protein 2
Sos: son-of-sevenless

42. Sos is a guanosine exchange factor (GEF)

43. Guanosine diphosphate
Guanosine triphosphate

44. EGF/EGFR-mediated Ras activation

45. Regulation of Ras (a GTPase) activity
GEF:
guanine nucleotide
exchange
factor
Sos is a GEF, which
catalyzes conversion
of inactive GDP-bound
Ras to the active
GTP-bound form.
GAP:
GTPase-
activating
(or accelerating)
protein

46. Mammalian Ras proteins have been studied in great detail because mutants Ras proteins are associated with many types of human cancer. These mutant proteins, which bind but cannot hydrolyze GTP, are permanently in the “on” state and contribute to neoplastic transformation.
Most oncogenic, constitutively active Ras protein contain a mutation at position 12. Replacement of the normal glycine-12 with other amino acid blocks the functional binding of GAP, and in essence “lock” Ras in the active GTP-bound state.

47. The structure of the Ras protein
Figure The Biology of Cancer (© Garland Science 2007)

48. Alternative mechanisms of transformation by Ras
Figure 5.32a The Biology of Cancer (© Garland Science 2007)