Graphical AbstractHighlights d HMCES senses abasic sites in ssDNA and forms a covalent DNA-protein crosslink d HMCES shields the abasic site from TLS polymerases and endonucleases d HMCES is a suicide enzyme and the DPC is ubiquitylated and degraded d HMCES is conserved in all domains of life and loss results in genetic instability In BriefAn enzyme conserved from bacteria to eukaryotes can covalently bind to abasic sites in single-stranded DNA to shield them and prevent genomic instability.

Human papillomaviruses (HPV) activate the ataxia telangiectasia mutated (ATM)-dependent DNA damage response to induce viral genome amplification upon epithelial differentiation. Our studies show that along with members of the ATM pathway, HPV proteins also localize factors involved in homologous DNA recombination to distinct nuclear foci that contain HPV genomes and cellular replication factors. These studies indicate that HPV activates the ATM pathway to recruit repair factors to viral genomes and allow for efficient replication.

Human papillomaviruses (HPVs) are the causative agents of over 98% of cervical cancers, which are the second most common cancers in women worldwide (53). Over 120 HPV types have been identified, and about 30% of HPVs infect the genital epithelia. These genital HPV types are further classified as either high risk (e.g., HPV16, -18, -31, and -35) or low risk (e.g., HPV6 and -11) according to their association with genital cancers (25, 30). The high-risk HPVs are causative agents of cervical cancers and are associated with cancers of the vulva, vagina, anus, and penis as well as the oral cavity. Prior to the development of cancers, HPVs establish persistent infections in the genital tract that successfully evade immune clearance (3,25,30).HPVs infect stratified epithelia and establish their doublestranded DNA genomes as episomes that are replicated in a differentiation-dependent manner (28). During their productive life cycles, these viruses escape host innate immune surveillance as well the adaptive responses through mechanisms that are not fully understood. HPV genomes encode approximately six early genes and two late genes. The E5, E6, and E7 oncoproteins play important roles in regulating the productive life cycle as well as contributing to immune evasion and development of anogenital cancers (28). The high-risk E6 proteins form complexes with the cellular E3 ubiquitin ligase E6-associated protein (E6AP) and p53, resulting in p53 degradation (6,17,23,45). E6 also binds to p300 (36) and blocks p53 acetylation (13), which further inhibits p53 function. E6AP may mediate other cellular events such as activation of expression of the catalytic subunit of telomerase, hTert, and other less-characterized substrates (16,24,50). The E7 proteins bind to members of the retinoblastoma protein (Rb) tumor suppressor family (11), resulting in constitutive activation of the E2F family of transcription factors (33), which are critical for host cell cycle progression and differentiation. The binding of E5 to the B cell receptor-associated protein 31 (BAP31) suggests a potential negatively regulatory role of E5 on the interferon (IFN)-inducible trafficking of major histocompatibility complex (MHC) class I proteins (38).The first line of host defense against viral infections is the innate immune response, which includes the IFN and Janus kinase-signal transducer and activator of transcription (JAK/ STAT) pathways (1). The JAK/STAT pathway transmits information from extracellular interferon (5) through kinases to activate expression of over a hundred genes mediated through the translocation of STAT proteins to the nucleus (39, 48). The activation of this pathway involves the phosphorylation and homodimerization of STAT-1 or the heterodimerization of STAT-1 and STAT-2 (44). In cells that stably maintain HPV genomes, the expression of many IFN-inducible genes, such as the myxovirus resistance and protein A gene (MXA, also known as MX1) and 2Ј-5Ј-oligoadenylate synthetase 2 (OAS2), was previously shown by microarray analysis to be suppr...

Infection by human papillomaviruses (HPV) leads to the formation of benign lesions, warts, and in some cases, cervical cancer. The formation of these lesions is dependent upon increased expression of proangiogenic factors. Angiogenesis is linked to tissue hypoxia through the activity of the oxygen-sensitive hypoxia-inducible factor 1a (HIF-1a). Our studies indicate that the HPV E7 protein enhances HIF-1 transcriptional activity whereas E6 functions to counteract the repressive effects of p53. Both high-and low-risk HPV E7 proteins were found to bind to HIF-1a through a domain located in the N-terminus. Importantly, the ability of E7 to enhance HIF-1 activity mapped to the C-terminus and correlated with the displacement of the histone deacetylases HDAC1, HDAC4, and HDAC7 from HIF-1a by E7. Our findings describe a novel role of the E7 oncoprotein in activating the function of a key transcription factor mediating hypoxic responses by blocking the binding of HDACs.

High-risk human papillomaviruses (HPVs) activate the ataxia telangiectasia mutated-dependent (ATM) DNA damage response as well as the ataxia telangiectasia mutated-dependent DNA-related (ATR) pathway in the absence of external DNA damaging agents for differentiation-dependent genome amplification. Through the use of comet assays and pulsed-field gel electrophoresis, our studies showed that these pathways are activated in response to DNA breaks induced by the viral proteins E6 and E7 alone and independently of viral replication. The majority of these virally induced DNA breaks are present in cellular DNAs and only minimally in HPV episomes. Treatment of HPV-positive cells with inhibitors of both ATM and ATR leads to the generation of DNA breaks and the fragmentation of viral episomes, indicating that DNA breaks are introduced into HPV genomes. These breaks, however, are rapidly repaired through the preferential recruitment of homologous recombination repair enzymes, such as RAD51 and BRCA1, to viral genomes at the expense of cellular DNAs. When HPV-positive cells are treated with hydroxyurea, this recruitment of RAD51 and BRCA1 to viral genomes is greatly enhanced with little recruitment to damaged cellular DNAs and with retention of the ability of viral genomes to amplify. Overall, our studies demonstrated that human papillomaviruses induce breaks into cellular and viral DNAs and that the preferential repair of these lesions in viral episomes leads to genome amplification.