Cell Growth, Cancer and Oncogenes
Retroviral Oncogenes
Cancer Genes in the Human Genome
Retroviral Oncogenes
We have already discussed the structure of the retroviruses in relation to retrotransposons. It was mentioned that the oncogene of those viruses transform a cell to unproliferated growth carry an oncogene in addition to the three primary genes required of all retroviruses. The figure below is the generalized structure of a retrovirus.
One of the best studied retroviruses infects chicken and is called Rous Sarcoma Virus. The oncogene found in this retrovirus is src. The product of this gene is a protein kinase that phosphorylates tyrosine residues in other proteins. The protein products of other retroviral oncogenes also regulate cell division processes and contain one of four functions.
- Growth factor receptors - One example is epidermal growth factor receptor which promotes wound healing by stimulating cell growth. Some factors function as transmembrane protein kinases that are activated by an extracellular signal. An example is v-erbB found in the Avian erythroblastosis virus that infects chicken.
- Protein kinases - These proteins alter the function of other proteins by phosphorylating specific amino acid residues. The v-src from the Rous Sarcoma virus which infects chickens is an example.
- G-proteins - These proteins bind the nucleotide GTP, and also exhibit GTPase activity. The v-H-ras oncogene of the Harvey murine sarcoma virus which infects rats is an example.
- Transcription factors - These proteins function by binding to DNA and activating transcription. An example is the v-jun oncogene of the Avian sarcoma virus that infects chickens.