Human papillomaviruses (HPV) are associated with nearly all cervical cancers, 20% to 30% of head and neck cancers (HNC), and other cancers. Because HNCs also arise in HPV-negative patients, this type of cancer provides unique opportunities to define similarities and differences of HPV-positive versus HPVnegative cancers arising in the same tissue.

Background:A recent review by the International Agency for Research on Cancer (IARC) updated the assessments of the > 100 agents classified as Group 1, carcinogenic to humans (IARC Monographs Volume 100, parts A–F). This exercise was complicated by the absence of a broadly accepted, systematic method for evaluating mechanistic data to support conclusions regarding human hazard from exposure to carcinogens.Objectivesand Methods: IARC therefore convened two workshops in which an international Working Group of experts identified 10 key characteristics, one or more of which are commonly exhibited by established human carcinogens.Discussion:These characteristics provide the basis for an objective approach to identifying and organizing results from pertinent mechanistic studies. The 10 characteristics are the abilities of an agent to 1) act as an electrophile either directly or after metabolic activation; 2) be genotoxic; 3) alter DNA repair or cause genomic instability; 4) induce epigenetic alterations; 5) induce oxidative stress; 6) induce chronic inflammation; 7) be immunosuppressive; 8) modulate receptor-mediated effects; 9) cause immortalization; and 10) alter cell proliferation, cell death, or nutrient supply.Conclusion:We describe the use of the 10 key characteristics to conduct a systematic literature search focused on relevant end points and construct a graphical representation of the identified mechanistic information. Next, we use benzene and polychlorinated biphenyls as examples to illustrate how this approach may work in practice. The approach described is similar in many respects to those currently being implemented by the U.S. EPA’s Integrated Risk Information System Program and the U.S. National Toxicology Program.Citation:Smith MT, Guyton KZ, Gibbons CF, Fritz JM, Portier CJ, Rusyn I, DeMarini DM, Caldwell JC, Kavlock RJ, Lambert P, Hecht SS, Bucher JR, Stewart BW, Baan R, Cogliano VJ, Straif K. 2016. Key characteristics of carcinogens as a basis for organizing data on mechanisms of carcinogenesis. Environ Health Perspect 124:713–721; http://dx.doi.org/10.1289/ehp.1509912

In many cervical cancers, human papillomavirus type 16 (HPV-16) DNA genomes are found to be integrated into the host chromosome. In this study, we demonstrate that integration of HPV-16 DNA leads to increased steady-state levels of mRNAs encoding the viral oncogenes E6 and E7. This increase is shown to result, at least in part, from an increased stability of E6 and E7 mRNAs that arise specifically from those integrated viral genomes disrupted in the 3' untranslated region of the viral early region. Further, we demonstrate that the A+U-rich element within this viral early 3' untranslated region confers instability on a heterologous mRNA. We conclude that integration of HPV-16 DNA, as occurs in cervical cancers, can result in the increased expression of the viral E6 and E7 oncogenes through altered mRNA stability.Human papillomaviruses (HPVs) are small DNA viruses that infect epithelial cells. About 70 different genotypes have been identified to date, among which only a subset are associated with cervical cancers. More than 90% of cervical cancers contain these "high-risk" HPVs . In these cancers, two viral transforming genes, E6 and E7, are consistently expressed (1). The E6 and E7 proteins have been shown to interact with and inactivate the tumor-suppressor gene products p53 and pRb, respectively (34), and to immortalize human epithelial and fibroblastic cells as well as rodent fibroblasts (2-4). In transgenic mouse systems, expression of these genes leads to tumor formation (5)(6)(7)(8). These studies have demonstrated the likely importance of E6 and E7 in cervical carcinogenesis.The viral DNA genome of HPV-16 or -18 is often found integrated into the host chromosomes in cervical cancers (9)(10)(11). This viral DNA integration has been hypothesized to result in increased expression of E6 and E7 (12). To test this hypothesis, we have isolated a series of human cervical epithelial cell populations that harbor either extrachromosomal or integrated HPV-16 DNA (35). These cell populations were derived from a parental cell population, W12, that had been established from an HPV-16-positive cervical biopsy (13).Using these reagents, we have demonstrated that HPV-16 DNA integration correlates with increased expression of the viral E7 protein and with a selective growth advantage over cells harboring extrachromosomal HPV-16 DNA (35).In the current study, we have sought to define a mechanism by which integration leads to increased expression of papillomaviral transforming genes. We demonstrate that the high levels of E7 protein seen in the integrated clones correlate with increased steady-state levels of E6-and E7-specific mRNAs, at least in part as a result of changes in their stability. This increased stability appears to be the result of the integrative The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. S1 Nuclease Mapping Analysis. The E6/E7-specific cDN...

Patients with human papillomavirus associated (HPV+) head and neck cancer (HNC) demonstrate significantly improved survival outcome compared to those with HPV− negative (HPV−) tumors. Published data examining this difference offers conflicting results to date. We systematically investigated the radiation sensitivity of all available validated HPV+ HNC cell lines and a series of HPV− HNC cell lines using in vitro and in vivo techniques. HPV+ HNCs exhibited greater intrinsic radiation sensitivity (average SF2 HPV− 0.59 vs. HPV+ 0.22, p<0.0001), corresponding with a prolonged G2/M cell cycle arrest and increased apoptosis following radiation exposure (percent change 0% vs. 85%, p=0.002). A genome-wide microarray was used to compare gene-expression 24 hours following radiation between HPV+ and HPV− cell lines. Multiple genes in TP53 pathway were upregulated in HPV+ cells (Z score 4.90), including a 4.6 fold increase in TP53 (p<0.0001). Using immortalized human tonsillar epithelial cells, increased radiation sensitivity was seen in cell expressing HPV-16 E6 despite the effect of E6 to degrade p53. This suggested that low levels of normally functioning p53 in HPV+ HNC cells could be activated by radiation, leading to cell death. Consistent with this, more complete knockdown of TP53 by siRNA resulted in radiation resistance. These results provide clear evidence, and a supporting mechanism, for increased radiation sensitivity in HPV+ HNC relative to HPV− HNC. This issue is under active investigation in a series of clinical trials attempting to de-escalate radiation (and chemotherapy) in selected patients with HPV+ HNC in light of their favorable overall survival outcome.