oncogenes

Question 1

what are foci

Answer 1

clusters of rounded cells growing on top of each other

Question 2

DEFINE: cell transformation

Answer 2

the conversion of a normal cell into a cancer cell

Question 3

what experiment proved that continuous exposure of RSV is required to both initiate and maintain transformation?

Answer 3

• use temp sensitive RSV mutants
  1. maintain at permissive temp? (37 degrees) - RSV transforms cells = mutant behaves similarly to WT
  2. shift temp to 41 degrees - protein misfolded. cells lose transformed phenotype
  3. shift to 37 degrees again - cells transformed

Question 4

what are the properties of transformed cells?

Answer 4

• more rounded morphology
• loss of contact inhibition = cells can grow over each other + form foci
• grow without attachment
• ability to proliferate in absence of mitogenic growth factors
• inability to stop proliferation in absence of growth factors
• proliferate indefinitely
• increased uptake of glucose to sustain cell proliferation
• tumourigenicity
• high saturation density

Question 5

which gene from RSV induces transformation?

Answer 5

src

Question 6

which genes code for viral constituents?

Answer 6

gag
pol
env

Question 7

what experiment proved that DNA from transformed cells carries a gene that is able to convert a normal cell into a tumourogenic cell

Answer 7

1. chemically transform mouse fibroblasts
2. extract dna from these fibroblasts or tumour cells
3. precipitate dna with calcium phosphate
4. add dna to normal mouse fibroblast
5. mouse fibroblast formed focus of morphologically transformed cells
6. inject focus into mouse —> tumour formation
   only 0.1% of dna from chemically transformed fibroblasts or tumour cells established in host genome —-> only 1 gene responsible for transformation (more likely)

Question 8

what experiment was used to find out the difference between the oncogene and proto-oncogene sequence?

Answer 8

segment recombination

1. create hybrid genes with half from proto-oncogene and other half from oncogene
2. observe if hybrid was able to transform the cells or not
3. every time fragment was found to be sufficient to transform the cells, repeat
4. narrowed the area responsible for transformation = 350bp of protein needed to transform the protein

Question 9

what is the difference between ras and c-ras?

Answer 9

G12V = glycine at position 12 substituted for valine

Question 10

how does a point mutation in ras cause cancer?

Answer 10

G12V –> GTPase activity inhibited so Ras is unable to hydrolyse GTP to GDP so is constitutively active –> constitutive activation of pathways resulting in increased cell survival, cell proliferation and invasiveness

Question 11

what are the 3 members of the myc family?

Answer 11

c-myc
n-myc
l-myc

Question 12

in which cancer does gene amplification of n-myc occur in?

Answer 12

30% of childhood neuroblastomas

10 copies of n-myc

Question 13

what are the mechanisms by which myc proto-oncogene is converted into an oncogene

Answer 13

• gene amplification
• chromosomal translocation
• pro-viral integration/insertional mutagenesis

Question 14

DEFINE: oncogene

Answer 14

gene capable of transforming a normal cell into a tumour cell

Question 15

in which cancer does chromosomal translocation of c-myc occur in?

Answer 15

Burkitt lymphoma
translocation of Ig gene promoter from chromosome 14 to chromosome 8 (where myc gene is) –> c-myc under control of highly active Ig gene promoter –> massive proliferation of lymphoid cells

Question 16

what is pro-viral integration

Answer 16

virus integrates in genome next to proto-oncogene so proto-oncogene under control of viral promoter = increased myc expression

Question 17

which virus induces leukemias?

Answer 17

ALV = avian leucosis virus

Question 18

which structural change in a receptor can lead to cancer?

Answer 18

loss of EC domain - truncated receptor

constitutively active and ligand independent signalling

Question 19

how can overexpression of a receptor lead to cancer?

Answer 19

when ligand binds, receptors dimerise -> drives signalling

many receptors present results in receptors dimerising in absence of ligand