Question

Discuss how proto-oncogenes become oncogenes.

Answer 1

Transformation of protooncogenes to oncogenes occur by three mechanisms

1)Point mutations:-

Alteration occur in a single base pair in DNA

Eg:- RAS oncogene seen in bladder cancer,pancreatic adenocarcinoma

2)Chromosomal translocation

There occurs transfer of one part of chromosome carrying the protooncogene to another chromosome making it independent of growth controls.This is seen in pathogenesis of leukemia and lymphoma

Eg:- Philadelphia chromosome seen in 95% cases of chronic myeloid leukemia in which c ABL protooncogene carried in chromosome 9 is translocated to BCR of chromosome 22

3)Gene amplification

Here,there is increase in the number of copies of DNA sequences in the protooncogene so that there is over expression of gene product-oncoproteins

Eg:-ERB B1 in ovarian and breast cancer