The papillomaviruses are small DNA viruses that induce persistent benign epithelial lesions. In some cases these lesions can progress to malignant carcinomas, the most notable of which is cervical cancer. The viral E1 and E2 genes regulate viral transcription and replication and our objective has been to understand the mechanisms by which they control the viral life cycle. The E2 transactivator protein is required for viral transcriptional regulation, DNA replication and stable episomal maintenance of viral genomes. We have shown that papillomavirus genomes and the E2 transactivator protein are associated with cellular chromosomes in dividing cells. This would ensure that viral genomes are segregated to daughter cells in approximately equal numbers. We have determined the regions of the E2 protein important for this association. We have also characterized how the functions of the E2 protein are regulated by protein phosphorylation. In the majority of carcinomas, papillomavirus genomes are found integrated into cellular chromosomes such that the E1 and/or E2 genes are disrupted. This has led to the hypothesis that disruption of the E1 and E2 regulatory functions is a critical step in progression to a carcinoma. To study the mechanism of this progression we have developed a system in which we can efficiently isolate keratinocyte cells containing human papillomavirus genomes that replicate independent of the E1 and E2 gene functions. This system is being used to determine the role of the E1 and E2 regulatory functions in keratinocyte growth and differentiation.
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