A novel system for studying in vivo effects of tumor promoters on DNA tumor viruses.

An animal system is described that allows the analysis of the interaction of persisting hamster papovavirus (HaPV) genomes with the tumor-promoting phorbol ester TPA. In a colony of HaPV-bearing Syrian golden hamsters, extrachromosomal HaPV genomes were detected by Southern blot hybridization in DNA isolated from skin biopsies. Chronic topical treatment of hamsters with TPA resulted in a dramatic increase of viral DNA in skin cells at the site of TPA application. After finishing the TPA treatment, the amount of extrachromosomal viral DNA declined but was still enhanced more than three months thereafter. This model offers the possibility of investigating, at the molecular level, the initiating role of virus in tumorigenesis.