A genomic approach reveals a novel mitotic pathway in papillomavirus Carcinogenesis

More than 90% of cervical carcinomas are associated with human papillomavirus (HPV) infection. The two viral oncogenes E6 and E7 play a major role in transforming the cells by disrupting p53- and pRb-dependent cell cycle checkpoints. A hallmark of HPV-associated cervical carcinoma is loss of the expression of the viral E2 protein, often by disruption of E2-encoding gene. We showed previously that reintroduction of E2 in HPV18-associated cervical carcinoma cells induces cell cycle arrest in G₁ because of the transcriptional repression of the viral oncogenes E6 and E7 and concomitant reactivation of the p53 and pRb pathways. Here we describe global gene profiling of HeLa cells expressing different HPV18 E2 mutants to study the effects of repression of the viral oncogenes. We identified 128 genes transcriptionally regulated by the viral oncogenes in cervical carcinoma. Surprisingly, E2 repressed a subset of E2F-regulated mitotic genes in an E6/E7-dependent pathway. This was corroborated by the observation that E2 delayed mitotic progression, suggesting the involvement of a mitotic pathway in HPV carcinogenesis. These mitotic genes constitute an as yet unrecognized set of genes, which were also found deregulated in other HPV-associated cervical carcinoma cell lines and therefore represent new targets for both diagnosis and therapeutic approaches in cervical cancer.