Question

How do retroviruses without any oncogene induce tumors? How does HPV and HBV do this?

Answer 1

Retroviruses contain reverse transcriptase enzyme that convert the mRNA into cDNA. most of the retroviruses contain viral oncogenes that convert the host protooncogenes into oncogenes causing the tumors and inducing various cancers in humans. These are called as acute transforming viruses and these carry the viral oncogenes that are dirtectly introduced into host genome. In some retroviruses (human DNA tumor viruses) such as non acute retroviruses such as HPV (human papilloma virus) and HBV (hepatitis B virus), the viral long terminal repeats (LTRs) cause the transcriptional activation of protooncogenes in humans and induce the tumors.

Source: Fan, H., & Johnson, C. (2011). Insertional Oncogenesis by Non-Acute Retroviruses: Implications for Gene Therapy. Viruses, 3(4), 398–422. http://doi.org/10.3390/v3040398