Question

Which of the following mechanisms by which a human retrovirus causes cancer in humans?

the retro virus causes over expression of the human photo - oncogene

Answer 1

One of such retrovirus in human is Rous Sarcoma virus. It has a proto oncogene called src gene. One of the mechanism is MAP Kinase pathway. In this mechanism, SH2 domains of some proteins bind to specific phosphotyrosine containing peptides of receptor Tyrosine Kinase. This SH2 domains were initially recognized in Tyrosine kinases related to Src, the oncogenic protein of Rous Sarcoma virus. In MAP Kinase pathway, GEF ( guanyl nucleotide exchange factor) has this SH2 domain.

Description of MAP Kinase pathway :

1) Growth factor binds to Tyrosine Kinase receptor and then phosphorylation occurs in Tyrosine residues of c- terminal portion.

2) GEF binds to phosphorylated Tyrosine residue with it's SH2 domain and then activates GDP bound Ras protein to GTP bound Ras .

3) Active Ras protein then activates Raf protein attached to it and then phosphorylates MEK subunit.

4) MEK subunit then phosphorylates ERK.

5) After this , active ERK translocated to the nucleus and phosphorylates ELK-1 which is bound to DNA and then SRF transcription factor is activated and transcribes the gene.

6) This particular gene responses in proliferation, differentiation and cell survival and cause cancer.