Papillomaviruses induce persistent epithelial lesions, known as papillomas. Genital papillomavirus infection is widespread and associated with the development of cervical cancer. The viral E2 proteins regulate viral transcription, replication and episomal genome maintenance.
Our aim i s to elucidate the mechanisms by which the E2 proteins control the viral life cycle. We have 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 and are retained within the nucleus. The E2 transactivation domain of E2 interacts with the host chromosomes and so we have generated mutations on potential interaction surfaces of this domain and determined which abrogate the ability of E2 to interact with chromosomes. We have also identified regions of E2 important for replication and transcriptional repression. We have shown that E2 cannot segregate plasmids with E2-binding sites in Sacchromyces cerevisiae. This assay is being used to isolate the mammalian chromosomal protein that interacts with E2 using a human cDNA library. Stability of the E2 protein is regulated by phosphorylation, which leads to ubiquination and proteasomal degradation. We show that casein kinase II is responsible for regulating E2 half-life and the resulting viral genome copy number. Phosphorylation induces a conformational change in the E2 protein that leads to its degradation. 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 and cervical cancer progression.
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