Papillomavirus E2 Growth Suppression Mechanisms

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The human papillomaviruses (HPVs) are associated with human cervical cancer as well as some other anogenital cancers and some upper airway cancers. Over 140 different HPVs have now been identified and a subset of these have been associated with these cancers. HPVs are classified as either 'high risk1 (HPV 16, 18) or 'low risk' (HPV 6, 11), based on the clinical lesions with which they are associated and the likelihood for these lesions to progress to cancer. Approximately 90 percent of human cervical cancers harbor the DNA of a high risk HPV type from which two viral oncoproteins, E6 and E7, are invariably expressed. One characteristic of HPV related carcinogenic progression is the frequent integration of the viral genome into the human chromosome in the cancer cells in a manner that results in the loss of expression of the viral E2 gene and to high levels of E6/E7 gene expression. The loss of E2 expression is an important step in HPV associated carcinogenic progression since E2 is able to repress the E6/E7 promoter. The loss of E2 results in the derepression of E6 and E7 oncogene expression. Indeed the expression of the full length E2 protein in HPV positive cervical carcinoma cell lines results in a growth arrest and cellular senescence. The consequent loss of E6 and E7 results in the stabilization of p53 and pRB that in turn mediate cellular growth suppression. The mechanisms by which different forms of E2 mediate this repression however have not yet been established and thjs project is designed to identify genes and pathways involved in this transcriptional repression. The first aim is designed to identify genes and pathways involved in E2-mediated repression of the E6/E7 promoter utilizing a non-biased whole genome siRNA screen. The second aim will determine the mechanisms involved in the repression of the E6/E7 viral promoter. This will focus on novel transcription factors and chromatin modifiers that are revealed and validated in the screen. A third aim will identify the factors and mechanisms involved repression of HPV gene expression that is mediated by a second spliced form of E2 (known as E8AE2C) that has not been extensively studied. A final aim will explore the biologic relevance of the cellular genes identified in the E2 and E8AE2C repression screens in HPV infected epithelial cells and in human cancers.