HPV and the DNA Damage Response

Human papillomaviruses (HPV) are the causative agents of cervical, anal and many oral cancers. While prophylactic vaccines to prevent HPV infections have been developed, there is no effective therapeutic treatment for existing HPV lesions. It is therefore of critical importance to understand how the productive life cycle of high-risk HPVs is regulated to identify potential new therapeutic targets. HPVs infect stratified squamous epithelia and link their productive life cycles to the differentiation of the infected cell. My laboratory recently demonstrated that the amplification of HPV genomes in differentiating cells is dependent on activation of the ataxia-telangiectasia mutated (ATM) kinase pathway. In contrast, the ATM pathway has minimal effects on stable maintenance replication in undifferentiated cells. In HPV positive cells, members of the ATM pathway, such as γ−H2AX, CHK2, and NBS1, are bound to viral genomes in distinct nuclear replication foci. Our studies have shown that E7 and E1 can activate the DNA damage response in the absence of viral genome replication and that they act through the innate immune regulator, STAT-5 and Tip60 to induce the phosphorylation of ATM. Additional studies using complete viral genomes have indicate that additional viral proteins, such as E5, can also activate the DNA damage pathways. Our experiments specifically implicate homologous recombination factors in mediating HPV amplification. In addition to the ATM pathway, we recently found that both the ataxia telangiectasia and Rad3-related (ATR) pathway, which is important for repair of single strand breaks, along with the p38/MK2 factors are also critical for amplification.. Additional recent studies demonstrate that the cohesin, SMC1, is activated in HPV positive cells as part of the DNA damage response and that it forms complexes with the transcriptional insulator, CTCF, at specific sites on HPV genomes. Knockdown of either SMC1 or CTCF blocks differentia