Papillomaviruses are small DNA viruses that induce persistent epithelial lesions, known as warts or papillomas. Genital papillomavirus infection is widespread and in some cases these lesions can progress to malignant cervical carcinomas. The viral E2 proteins regulate viral transcription, replication and episomal genome maintenance.
Our aim i s to understand in detail the mechanisms by which the E2 proteins control the viral life cycle. We have previously shown that papillomavirus genomes and the E2 transactivator protein interact with cellular mitotic chromosomes in dividing cells. This ensures that viral genomes are properly segregated to daughter cells. We have determined that the transactivation domain of E2 is sufficient for interaction with chromosomes.We have shown that the E2 proteins are phosphorylated and that mutations one of the major phosphorylation sites results in an E2 protein with an extended half-life and a virus with a greatly increased copy number. We have also determined that E2 is ubiquinated and degraded by the proteasome pathway. E2 phosphorylation regulates protein stability and viral genome copy number.In most cervical cancers, papillomavirus DNA is found integrated into cellular chromosomes instead of replicating episomally. This integration disrupts the E1 and/or E2 genes and this has led to the hypothesis that disruption of these regulatory functions is a critical step in malignant progression. To study the mechanism of this progression we have developed a system to immortalize primary human keratinocyte cells containing hybrid papillomavirus genomes that are maintained episomally in the absence of 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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