8. Causes of cancer, TSGs and Oncogenes

Question 1

What is meant by the term tumour suppressor gene?

Answer 1

the normal function of these genes is inhibition of cell proliferation or repair of damaged DNA – abnormalities (of both alleles) of tumour suppressor genes can drive a normal cell towards a cancerous state

Question 2

What is meant by the term oncogenes?

Answer 2

the normal function of these genes is an increase in cell proliferation – abnormalities of only one allele of an oncogene can drive a normal cell towards a cancerous state

Question 3

What are the risk factors for cancer?

Answer 3

Old age
Environment
Genetic predisposition

Question 4

What is the loss of function of a tumour supressor gene product as a consequence of?

Answer 4

Less of the gene product being expressed

Or a mutation in the gene such that the resultant protein has reduced or a loss of function

Question 5

What is the Knudson “two hit hypothesis”

Answer 5

Requires the loss of both copies of the tumour suppressor gene

Question 6

What are example of TSGs

Answer 6

p53 gene
APC gene
Rb gene

Question 7

What is the assocaited inherited cancer syndrome for the Rb tumour suppressor gene?

Answer 7

Retinoblastoma

Question 8

What is the assocaited inherited cancer syndrome for the APC tumour suppressor gene?

Answer 8

FAP

Question 9

What is the assocaited inherited cancer syndrome for the MSH2/MLH1 tumour suppressor gene?

Answer 9

HNPCC (lynch syndrome)

Question 10

What is the assocaited inherited cancer syndrome for the BRCA1/BRCA2 tumour suppressor gene?

Answer 10

Breast cancer and ovarian cancer

Question 11

What is the assocaited inherited cancer syndrome for the p53 tumour suppressor gene?

Answer 11

Li-Fraumeni syndrome

Question 12

What is the sporadic form of the knudson hypothesis?

Answer 12

a mutation has to occur in both copies of the retinoblastoma gene, unlikely

the longer the period of time that elapses the more likely this is, but it is unlikely to occur more than in one cells. Hence tumours occur late and are unilateral.

Question 13

What is the familial form of the knudson hypothesis?

Answer 13

the child inherits from one mutant copy of the retinoblastoma gene, so only one additional mutation needed

the disease occurs earlier and also there is a high probability of it occurring in more than one cell, and thus tumours may be multi-focal and bilateral.

Question 14

What are the features of p53?

Answer 14

Altered in more than 50% of human cancers

Involves in a pathway that responds

Question 15

What are the features of p53?

Answer 15

Altered in more than 50% of human cancers
Involves in a pathway that responds to DNA damage and allows repair or apoptotic cell death
It is a transcription factor: regulates other genes

Question 16

What are the clinical features Li-Fraumeni syndrome?

Answer 16

Cancer at a young age

Development of adrenocortical carcinoma
Development of soft-tissue sarcomas
Acute leukaemias and brain tumours
Osteosarcomas
Premenopausal breast cancer is common

Question 17

What is the BRCA1 tumour supressor gene?

Answer 17

Isolated by positional cloning as one of the genes predisposing to early onset breast and ovarian c

Question 18

What is an oncogene?

Answer 18

Involved in cancer by an increased activity of the (proto)oncogene stimulating an increase in cell number

Question 19

When the does an oncogene gain its fucntion?

Answer 19

When more of the gene product being expressed
Mutation in the gene such that the resultant protein has increased function
Expression ocurring in the wrong cell type/ wrong time

Question 20

What will gaining an oncogene result in?

Answer 20

Leads to a stimulation of a critical cell process