Human cervical cancer development begins with infection by the DNA tumor virus, human papillomavirus (HPV). The HPV genome encodes two oncoproteins, E6 and E7, that are required for cell immortalization, E6 causes degradation of the cell cycle checkpoint/tumor suppressor protein, p53. However, development of invasive diseases requires additional events including the activation of secondary oncogenes. In this regard, environmental carcinogens play a major role. Cigarette smoking is correlated with an enhanced risk for cervical cancer development. An active agent in cigarette smoke is the ubiquitous environmental carcinogen, benzo[a]pyrene. Metabolites of B[a]P are potent DNA mutagens. B[a]P is mutagenic in cervical cells in vitro, accumulates in cervical mucus in vivo, and ras oncogene, a known target of B[a]P, is mutated at a high frequency in cervical tumors. p53 is an important cell cycle control protein. Following DNA damage, p53 pauses cell cycle progression until DNA repair is complete. Our previous in vitro studies show that treatment with B[a]P strongly inhibits the proliferation of cultured normal cervical epithelial cells This inhibition is correlated with a large increase in p53 level. In contrast, in HPV-immortalized cells, which have low p53-immortalized cells do not significantly pause in the cell cycle. Based on these studies, we hypothesize that B[a]P should be a more potent mutagen in HPV-immortalized cells, because these cells do not pause in proliferation long enough to adequately repair DNA following B[a]P exposure. Although our in vitro results are consistent with this hypothesis, our goal is to test this hypothesis in vivo. However, work in this field has been stymied by the lack of a suitable animal model of HPV-dependent neoplasia. During the past two years, we have developed an innovative transgenic mouse model of cervical cancer, in which the mice express the HPV16 E6 and E7 oncoproteins in the cervical epithelial, and we are now ready to test our hypotheses in vivo.
In Specific Aim 1 we test the hypothesis that B[a]P treatment should increase tumor formation in HPV-immortalized cervix compared to normal cervix, and examine the tumorigenic phenotype of the cells in nude mice, in soft agar, and in microinvasion assays.
In Specific Aim 2 we hypothesize that B[a]P treatment should increase tumor formation in HPV-immortalized cervix compared to normal cervix, and examine the tumorigenic phenotype of the cells in nude mice, in soft agar, and in microinvasion assays.
In Specific Aim 3 we examine the hypothesis that in vivo B[a]P treatment should differentially increase DNA mutations in HPV-immortalized cells, and that the increased mutation rate should be correlated with reduced p53 levels. We examine the effects of B[a]P treatment on p53 level, DNA adduct formation, and mutation at the H-ras and K-ras loci. The ultimate aim of these studies is use our HPV16 E6/7 cervical neoplasia mice to provide new understanding regarding the role of environmental carcinogens (polycyclic aromatic hydrocarbons) in the genesis of cervical cancer. Use of our novel transgenic model provides an innovative approach for addressing these questions.
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