Lecture 11: Signalling for LifeDeath

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Lecture 11 Signalling for Life/Death

• Describe the eukaryotic cell cycle and the
  purpose of checkpoints.
• Describe the role of cyclins and cyclin-dependent
  kinases in cell cycle progression.
• Describe the role of the protein, pRb and the
  consequence if it is defective.
• Describe the central role of p53 in signaling DNA
  damage and its sequelae for cell cycle arrest and
  DNA repair.
• Describe the three classes of growth factors and
  their receptors. Identify common elements and
  differences.
• 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.
• Identify proteins of the signal transduction
  cascade that can cause unregulated growth if they
  are mutated (oncogenes).
• Compare and contrast the roles and prevalence of
  tumor suppressor genes and oncogenes in the
  etiopathology of cancer.
• Discuss the concept of Loss of Heterozygosity
  (LOH) in the penetrance of tumor suppressor gene
  mutations.

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Describe the eukaryotic cell cycle and the
purpose of checkpoints.
Diploid
R point (starvation)
START G1/S transition
Most physiological growth arrest occurs here, as
most cells in the body are 2n.
G2/M transition
Tetraploid
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2) Describe the role of cyclins (A, D and E) and
cyclin-dependent kinases (cdc2, CDK2 and CDK4) in
cell cycle progression.
CDK4/cyclin D/PCNA needed for R transit
CDK2/cyclins E and A are needed for G1/S transit
PCNA proliferating cell nuclear antigen
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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
If Rb is defective (loss of function), E2F will
be unregulated and retinoblastoma will occur. Rb
is a tumor suppressor.
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2) Describe the central role of p53 in signaling
DNA damage and its sequelae for cell cycle arrest
and DNA repair.
DNA damage
DNA repair
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ATM
4b
GADD-45
2
p53
p21WAF
3
0
G1/S Arrest
Ubiquitin- Mediated Degradation
4a
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
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5) Describe the three classes of growth factors
and their receptors. Identify common elements
and differences.

• Epidermal growth factor EGF, FGF, NGF (FGF
  fibroblast growth factor NGFnerve growth
  factor)
• 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

• Type II (IGF and insulin) receptors are dimers
  all the time
• Ligands are different

Differences
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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.

• EGF
• EGF-R
• Tyrosine kinase (receptor/nonreceptor)
• SH2 (SHC)
• Grb-2
• SOS
• Ras (G protein)
• Raf (S/T kinase)
• MAP kinase cascade
• Nuclear transcription factors

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6) Identify proteins of the signal transduction
cascade that can cause unregulated growth if they
are mutated (gain of function) (oncogenes).

• Growth factors (EGF, FGF, PDGF)
• Growth factor-R (EGF-R, NGF-R)
• non-receptor tyrosine kinase (src, abl)
• G protein (Ras)
• S/T kinase (Raf)
• Nuclear transcription factors (myc)

abl can be inhibited by Gleevek.
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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.

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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 gt60 of all
  cancers).