tumour suppressor genes

Question 1

cell fusion technique

Answer 1

compares 2 different alleles when both are forced to be present in the same cell

Question 2

what is an experiment that proves cancer can be induced by non-viral oncogenesis

Answer 2

1. grow cancer cell and normal cell together in same dish
2. add fusing agent = sendai virus or PEG
3. membranes of cells fuse together to form a large cell with 2 different nuclei = heterokaryon
   dominant allele determines phenotype of hybrid cell
4. hybrid cell is non-tumourigenic so cancer cell is recessive

Question 3

DEFINE: loss of heterozygosity

Answer 3

starting with heterozygous phenotype and ending up with homozygous phenotype after homologous recombination/mitotic recombination

Question 4

what is the frequency of loss of heterozygosity occurring after mitotic recombination?

Answer 4

10^-5 - 10^-5

Question 5

what are mechanisms used by tumour suppressor genes to stop cancer development?

Answer 5

• directly suppress cell proliferation in response to growth-inhibitory and differentiation-inducing factors
• inhibit proliferation in response to metabolic imbalance and tissue damage

Question 6

DISEASE: neurofibromatosis

Answer 6

LOF nf1 mutation
neurofibromas that can progress to malignant neurofibrosarcomas
nf1 = GAP (GTPase activating protein) - promotes inactive state
mutant nf1 = hyperactivation of ras signalling pathway

Question 7

what are neurofibromas?

Answer 7

benign tumours around nerves in PNS

Question 8

which tumours does VHL syndrome give a predisposition to?

Answer 8

• clear cell kidney carcinomas
• pheochromocytomas = adrenal gland cell tumours
• hemangioblastomas = blood vessel tumours in cns and retina

Question 9

what is the mechanism of pVHL under normoxic conditions?

Answer 9

1. 2 proline residues in HIF1α are hydroxylated by proline hydroxylase
2. hydroxylated HIF1α binds to pVHL and other proteins
3. complex formation results in HIF1α ubiquitinated and targeted for proteosomal degradation

Question 10

what is the mechanism of pVHL under hypoxic conditions?

Answer 10

1. prolines in HIF1α are not hydroxylated because proline hydroxylase requires oxygen to function
2. HIF1α accumulates and translocates into nucleus
3. HIF1α dimerises with HIF1β and together, they activate transcription of HIF target genes promoting:
   - erythropoiesis
   - angiogenesis
   - increased glycolysis and glucose uptake

Question 11

how does mutant pVHL cause cancer?

Answer 11

point mutations in AA residues in hydrophobic pocket recognising hydroxyproline residues in HIF1α –> pVHL cannot bind to HIF1α
HIF1α accumulates
constitutive activation of HIF target genes