Epigenetics of human papillomaviruses.

Human papilllomaviruses (HPVs) are common human pathogens that infect cutaneous or mucosal epithelia in which they cause warts, self-contained benign lesions that commonly regress. The HPV life cycle is intricately tied to the differentiation of the host epithelium it infects. Mucosotropic HPVs are the most common sexually transmitted pathogen known to mankind. A subset of the mucosotropic HPVs, so-called high risk HPVs, is etiologically associated with numerous cancers of the anogenital tract, most notably the cervix, as well as a growing fraction of head and neck cancers. In these cancers, the HPV genome, which normally exists an a double stranded, circular, nuclear plasmid, is commonly found integrated into the host genome and expresses two viral oncogenes, E6 and E7, that are implicated in the development and maintainance of the cancers caused by these high risk HPVs. Numerous studies, primarily on the high risk HPV16, have documented that the methylation status of the viral genome changes not only in the context of the viral life cycle but also in the context of the progressive neoplastic disease that culminates in cancer. In this article, we summarize the knowledge gained from those studies. We also provide the first analysis of available ChIP-seq data on the occupancy of both epigentically modified histones as well as transcription factors on the high risk HPV18 genome in the context of HeLa cells, a cervical cancer-derived cell line that has been the subject of extensive analyses using this technique.