Lecture 11: Signalling for Life/Death
1) Describe the eukaryotic cell cycle and the purpose of checkpoints.
2) Describe the role of cyclins and cyclin-dependent kinases in cell
cycle progression.
3) Describe the role of the protein, pRb and the consequence if it is
defective.
4) Describe the central role of p53 in signaling DNA damage and its
sequelae for cell cycle arrest and DNA repair.
5) Describe the three classes of growth factors and their receptors.
Identify common elements and differences.
6) Diagram the intracellular cascade of signaling events that begin with
binding of epidermal growth factor (EGF) to the EGF receptor and
culminate in activation of transcription.
7) Identify proteins of the signal transduction cascade that can cause
unregulated growth if they are mutated (oncogenes).
8) Compare and contrast the roles and prevalence of tumor suppressor
genes and oncogenes in the etiopathology of cancer.
9) Discuss the concept of Loss of Heterozygosity (LOH) in the
penetrance of tumor suppressor gene mutations.
1) Describe the eukaryotic cell cycle and the purpose of
checkpoints.
DNA nucleus
cell
Two Diploid
Daughter Cells
Diploid
G1 Phase
(M)
Mitosis
G2/M
transition
G2
Phase
S Phase
DNA Replication
Tetraploid
R point
(starvation)
START
G1/S transition
Most physiological
growth arrest
occurs here, as
most cells in the
body are 2n.
2) Describe the role of cyclins (A, D and E) and cyclindependent kinases (cdc2, CDK2 and CDK4) in cell
cycle progression.
CDK4/cyclin D/PCNA
needed for R transit
R point
cdc2 needed for
G2/M transit
G1 phase
Start
PCNA
CDK2/cyclins E
and A are needed
for G1/S transit
PCNA = proliferating cell nuclear antigen
2) Describe the role of the retinoblastoma protein, pRb
and the consequence if it is defective.
pRb-Phos
pRb-E2F
complex
active E2F
CDK4 action
G1 phase
Start Genes
PCNA
If Rb is defective
(loss of function),
E2F will be
unregulated and
retinoblastoma will
occur.
Rb is a tumor
suppressor.
2) Describe the central role of p53 in signaling DNA damage and its
sequelae for cell cycle arrest and DNA repair.
ATM
2
UbiquitinMediated
Degradation
0
1
DNA
damage
p53
DNA repair
4b GADD-45
3
p21WAF
4a
G1/S
Arrest
G1 phase
PCNA
If p53 is defective
(loss of function),
the cell cycle can
proceed in spite of
DNA damage, and
mutations will
accumulate.
GADD = growth arrest & DNA damage inducible
5) Describe the three classes of growth factors and their
receptors. Identify common elements and differences.
I.
Epidermal growth factor: EGF, FGF, NGF (FGF=
fibroblast growth factor; NGF=nerve growth factor)
II.
III.
Insulin like growth factor: Insulin, IGF-1, IGF-2
A. Platelet-derived growth factor: [no other examples]
Common:
• Receptors on cell surface.
• Receptors active as dimers
• Receptors have intracellular
tyrosine kinase activity
• Phosphorylated receptors attract
SH2 proteins
Differences:
•Type II (IGF and insulin) receptors
are dimers all the time
•Ligands are different
6) Diagram the intracellular cascade of signaling events that begin
with binding of epidermal growth factor (EGF) to the EGF
receptor and culminate in activation of transcription.
1. EGF
2. EGF-R
3. Tyrosine kinase
(receptor/nonreceptor)
4.
5.
6.
7.
8.
9.
SH2 (SHC)
Grb-2
SOS
Ras (G protein)
Raf (S/T kinase)
MAP kinase
cascade
10. Nuclear
transcription
factors
cTK
(abl)
GRB
-2
SOS
ras
raf
MAP kinase
“cascade”
Phosphorylation
of transcription
factors
Induction of immediate
early genes (START)
6) Identify proteins of the signal transduction cascade that can cause
unregulated growth if they are mutated (gain of function) (oncogenes).
1. Growth factors
(EGF, FGF, PDGF)
2. Growth factor-R
(EGF-R, NGF-R)
3. non-receptor
tyrosine kinase
(src, abl*)
4. G protein (Ras)
5. S/T kinase (Raf)
6. Nuclear
transcription
factors (myc)
*abl can be
inhibited by
Gleevek.
cTK
(abl)
GRB
-2
SOS
ras
raf
MAP kinase
“cascade”
Phosphorylation
of transcription
factors
Induction of immediate
early genes (START)
8) Compare and contrast the roles and prevalence of tumor
suppressor genes and oncogenes in the etiopathology of cancer.
• Proto-oncogenes genes are normal cellular proteins
involved in positive regulation of proliferation.
Unregulated growth occurs from: gain-of-function
mutation of proto-oncogene resulting in oncogene.
• Tumor suppressors are normal cellular proteins that are
involved in negative regulation of proliferation.
Unregulated growth occurs from a loss-of-function
mutation of the tumor suppressor, and usually requires loss
of both alleles.
9) Discuss the concept of Loss of Heterozygosity
(LOH) in the penetrance of tumor suppressor genes.
• Loss-of-function mutations are more common
than are gain of function, yet both alleles must be
inactivated. Hence, a major mechanism for loss
of tumor suppression is loss of heterozygosity.
• The most common mutations in cancers are:
ras oncogene [gain or loss of function?]
p53 tumor suppressor gene [what is consequence?]
(ras and p53 are each mutated in >60% of all
cancers).