Polyomaviruses and Papillomaviruses

Abstract

Both polyomavirus and papillomavirus families contain a small, circular DNA genome that replicates in the nucleus of infected cells. Both family members were isolated from a wide variety of species, including humans, monkeys, hamsters, mice, and birds. Historically, both family members were grouped together to form the papovavirus family, but the genomic sequencing of viruses from each family revealed that the Papillomavirus family members are larger in size and their genome is transcribed from only one strand of the genome in the clockwise direction, whereas the expression of polyomavirus genome is bidirectional. These differences led the two families to be separated. Some family members from each group are associated with a particular disease in humans. JC virus (JCV), for example, a member of the human polyomavirus family, infects more than 70–80% of the human population worldwide, and causes a central nervous system (CNS) white matter disease – known as progressive multifocal leukoencephalopathy (PML) – in immunocompromised individuals, such as AIDS patients. In PML patients, the virus specifically infects the oligodentrocytes in the CNS, which form the myelin sheet around the axons of neuronal cells. BK virus (BKV), another human polyomavirus, is reactivated mainly in the kidneys in those individuals who are undergoing immunosuppressive therapies, such as kidney transplant patients. In those patients, BKV lytically infects the kidney epithelial cells and leads to compromises in the functioning of the organ, resulting in a medical condition described as ‘polyomavirus-associated nephropathy’ (PVAN). Simian virus 40 (SV40), a prototype of polyomaviruses, does not cause any known human disease, but has been used as a tool to understand many fundamental aspects of molecular biology and cancer, including DNA replication, transcription, RNA splicing, and cell transformation. There are reported cases suggesting that SV40 might be associated with some human tumors, as is the case for JCV and BKV. Papillomavirus family members also infect humans (human papillomavirus – HPV) and more than 100 genotypes have been isolated to date. However, two genotypes in particular, HPV-16 and HPV-18, appear to be clinically important due to their being the apparent cause of cervical cancer in women. The progression of the replication cycle of the HPV is tightly regulated by the differentiation stages of the basal epithelial cells after initial infection. In this article, we have focused our attention on the biology of the polyomaviruses and papillomaviruses, particularly JCV, BKV, SV40, mouse polyoma, and HPV.