Retroviruses and cancer.

Abstract

Retroviruses are RNA viruses that reverse-transcribe their RNA into proviral DNA. These viruses are associated with a wide variety of cancers in chickens mice, cats, and monkeys. Some retroviruses cause a specific type of cancer soon after infection in a high proportion of animals, whereas others cause various cancers late after infection in a lower proportion of animals. Highly oncogenic retroviruses are recombinants of viral and host genes. The cancers induced by these viruses are determined by the transduced host gene. Retroviruses that cause cancer at a low incidence do not contain inserted host information. Rather, they appear to cause cancer via mutation of the expression of potentially oncogenic host genes. During their normal life cycle, retroviruses integrate proviral DNA into the chromosomal DNA of their host. Integrations occur at many different sites. Most integrations are benign, but some result in cancer. Retroviral research has identified 12 potentially oncogenic host genes. Each is associated with a characteristic cancer or spectrum of cancer. Several appear to code for protein kinases that phosphorylate tyrosine residues.