Lecture 1, 3 - Hay

Question 1

*myc

Answer 1

• proto-oncogene that becomes an oncogene after it is TRANSLOCATED to a new locus
• involved in B cell proliferation -> lymphoma
• results in BYPASSING checkpoint and results in too much APOPTOSIS.
• long latency period
• bc it needs to also express Bcl2, which is anti-apoptotic. So now cancer cells can live
• Cancer needs 2 factors: bypass checkpoint (grow), avoid death

Question 2

*Investigators found that a RAS family member was activated in human tumor cells.
However, when the gene was sequenced, they did not find any activation mutation and, when expressed in normal cells, it was not activated. Further investigation showed a loss of heterozygosity (LOH) in the tumor cells in which the Ras protein was activated, and that the Ras protein is hyperactive because of this LOH. Identify the gene that was deleted by the LOH and its activity

Answer 2

LOH in PTEN protein leads to increased activity in RAS.

• PTEN, which induces cell cycle arrest
• PTEN -/- lethal, but LOH occurs when people that are +/- lose the functioning allele and go to -/-
• when you lose PTEN, PIP3 cant activate the Akt/pKB pathway. This pathway normally restricts cell proliferation and promotes apoptosis.

pathway:
GF -> Ras -> PI3K -> pip2 to pip3 via PTEN -> Akt/pKB -> cell cycle arrest, apoptosis

Question 3

*A gene with an oncogenic activity was cloned from tumor cells. Subsequent analysis of
the gene revealed that its encoded protein is a tyrosine kinase. However the cloned
oncogene differs from its normal counterpart by a point mutation.
Based on your knowledge:
a. Identify the gene
b. What is the point mutation
c. Why did the point mutation activate the tyrosine kinase

Answer 3

gene is SRC
- Mutation is at Tyr547 which causes an overactive SRC.
- This mutation is at the C terminal tail and normally interacts with SH2 domain at this locus.
Normally this locus is P to keep it off.
- in cancer, locus is mutated so that the P is shifted to the kinase, activating it.

Question 4

*Investigators have identified a mutated gene in human cancer cells that, when it was overexpressed in normal cells, exerted an oncogenic activity. However, further analysis revealed that the same gene is deleted in some human cancer cells, suggesting that it is a tumor suppressor.

a. What is the name of this tumor suppressor?
b. Why does the mutated form of this tumor suppressor exert an oncogenic activity?
c. How would you prove that it is a tumor suppressor?

Answer 4

• p53
• wild-type restricts cell proliferation.
• mutation: cant bind to DNA. growth is unrestrained
• KO: TSG, growth unrestrained.
• TSG are loss of function mutations, meaning you can test and see if a protein’s activity is lost. They also require BOTH alleles to be mutated ( 2 hit hypoth). Test a heterozygous and if its a TSG, it should still work.

Question 5

• TSG was deleted. Cells then became SENSITIVE to apoptosis due to activation of another TSG.
  a. what is the TSG that was deleted?
  b. what was the TSG that became active.
  c. how did KO of TSG1 activate TSG2?

Answer 5

a. Rb. KO Rb = p53 on!
b. tumor suppressor: p53
- wt p53 inhibits cell division and promotes apoptosis.
- When you KO or mutate p53, the cells can divide out of control and dont die.
- this is done thru the activation of p21
- controlled by MDM2 (inhibits p53) and p19ARF (activates by inhibiting MDM2)
- KO Rb, wont bind to E2F. E2F is then free to bind to p19ARF, which activates p53. Activating p53 leads to ^ apoptosis

pRb -> E2F -> p19ARF -| mdm2 -| P53 (-> apoptosis)-> p21 -> pRb

Question 6

RB

Answer 6

• inhibits cell proliferation, so when you KO both alleles, cells can proliferate out of control
• TGS, need to lose both copies (hereditary or spontaneous)
• when RB is p = apoptosis off, proteins can pass from G1 -> S.
• when RB loses p, it binds to E2F and blocks it from inhibiting p53 -> apoptosis on, cell division restricted.
• when Rb is mutated, cant bind to E2F = out of control cell proliferation.

Question 7

PTEN

Answer 7

• PTEN, which induces cell cycle arrest
• PTEN -/- lethal, but LOH occurs when people that are +/- lose the functioning allele and go to -/-
• when you lose PTEN, PIP3 cant activate the Akt/pKB pathway. This pathway normally restricts cell proliferation and promotes apoptosis.

pathway:
GF -> Ras -> PI3K -> pip2 to pip3 via PTEN -> Akt/pKB -> cell cycle arrest, apoptosis