8 Oncogenes of DNA Tumor Viruses: Papovaviruses

Abstract

I. INTRODUCTION
The papovavirus family includes the polyomaviruses (notably polyoma and SV40) and the papillomaviruses. Polyoma was discovered in 1953 by Ludwik Gross, who noted that extracts from leukemic mice sometimes caused salivary gland tumors. Subsequently, the virus was shown to cause a wide variety of tumors, and the name “polyoma” was proposed by Stewart and Eddy in 1958 to reflect this unusual property.

SV40 was discovered in 1960 by Sweet and Hilleman during a search for contaminants of polio vaccines prepared from monkey cell cultures. The presence of SV40 originally was missed because the virus did not cause pronounced cytopathic effect in cultures of rhesus monkey cells, the most common source for vaccine production.

Papillomas (warts) occur in many species of animals. The first papillomavirus to be well characterized was isolated from cottontail rabbits by Shope in 1933. A variety of papillomaviruses have been isolated from human warts, and some of them have been implicated in the progression of benign warts to malignant tumors. Work with these viruses has been hampered by the lack of cell-culture systems in which the viruses will multiply. However, recombinant DNA techniques have allowed much to be learned about the organization and expression of the viral genomes and the functions of the proteins they encode.

Many transforming retroviruses arose because of the incorporation of cellular genetic information into viral genomes. In contrast, the oncogenes of papovaviruses and other DNA tumor viruses seem not to be closely related to cellular genes. Presumably, their transforming potential...