Many aspects of the HPV life cycle have been characterized in cervical cell lines (W12, CIN612) and in HPV immortalized primary foreskin keratinocytes. There is now an epidemic of HPV positive oropharyngeal cancers (HPV16 is responsible for 80-90% of these); therefore increased understanding of the HPV16 life cycle in oral keratinocytes is a priority. To date there have been limited reports characterizing the HPV16 life cycle in oral keratinocytes. Using TERT immortalized "normal" oral keratinocytes (NOKs) we generated clonal cell lines maintaining the HPV16 genome as an episome, NOKs+HPV16. Organotypic raft cultures demonstrated appropriate expression of differentiation markers, E1^E4 and E2 expression along with amplification of the viral genome in the upper layers of the epithelium. Using this unique system RNA-seq analysis revealed extensive gene regulation of the host genome by HPV16; many of the changes have not been observed for HPV16 before. The RNA-seq data was validated on a key set of anti-viral innate immune response genes repressed by HPV16 in NOKs+HPV16. We show that the behavior of these NOKs+HPV16 lines is identical to HPV16 immortalized human tonsil keratinocytes with regards innate gene regulation. Finally, using The Cancer Genome Atlas (TCGA) data we examined gene expression patterns from HPV positive and negative head and neck cancers and demonstrate this innate immune gene signature set is also downregulated in HPV positive cancers versus negative. Our system provides a model for understanding HPV16 transcriptional regulation of oral keratinocytes that is directly relevant to HPV positive head and neck cancer.

Human keratinocyte immortality is genetically recessive to the normal phenotype of limited replicative lifespan and appears to require the dysfunction of p53 and the cyclin D-Cdk inhibitor p16. In order to test for the inactivation of other candidate replicative lifespan genes in the immortal cells of human tumors, we developed a series of mortal and immortal keratinocyte cultures derived from neoplastic lesions of the head and neck which were amenable to molecular genetic analysis by the loss of heterozygosity (LOH) technique. The results indicate that keratinocyte immortalization in head and neck squamous cell carcinoma (SCC-HN) development involves the inactivation of at least two further pathways to senescence and four in all. Chromosomes 1, 4 and 7 carry genes representing immortality complementation groups C, B and D respectively and immortal keratinocytes showed LOH at either 4q32-q34 between D4S1554 and D4S171 (group B) or 7q31 (group D) but never 1q25 (group C). These results tentatively suggest that the genes responsible for the immortality complementation groups encode proteins on the same pathway to senescence. In addition, all of the immortal keratinocyte lines possessed high levels of telomerase activity and a suppressor of telomerase activity has been mapped to the short arm of chromosome 3p. Five out of eight lines showed LOH at 3p21.2-p21.3, a region which may carry a gene capable of suppressing SCC-HN telomerase. However, alternative mechanisms of telomerase reactivation were also suggested by our results. None of the above genetic alterations were seen in seven senescent neoplastic keratinocyte cultures. Other loci harbouring antiproliferative genes implicated in replicative lifespan showed few or no alterations and any alterations seen were additional to those described above.

E2F integrates and coordinates cell cycle progression with the transcription apparatus through its cyclical interactions with important regulators of cellular proliferation, such as pRb, cyclins, and cdk's. Physiological E2F is a heterodimeric transcription factor composed of an E2F and a DP family member, and while E2F proteins can stimulate proliferation, certain members of the family are known to be endowed with growthinhibitory and tumor suppressor-like activity. We have investigated the product of the human mdm2 oncogene, hDM2, and report on its ability to regulate E2F-dependent apoptosis in a fashion that is independent of p53. hDM2 can prevent p53 ؊/؊ cells from entering E2F-dependent apoptosis, an outcome that is dependent upon the presence of the DP subunit. Cells rescued from apoptosis possess lower levels of E2F subunits, although the rescued cells show an increase in DNA synthesis and possess enhanced viability that reflects cooperation between E2F-DP and hMD2. Furthermore, the regulation of E2F activity correlates with an hDM2-dependent effect on the intracellular distribution of DP-1, since hDM2 causes the nuclear accumulation of DP-1. The control of E2F by hDM2 therefore has certain parallels with the targeted degradation by MDM2 of p53. However, the domains in hDM2 required for the regulation of E2F activity can be distinguished from those necessary for p53 degradation, suggesting that control of E2F and p53 by hDM2 may be mechanistically distinct. These experiments define a new level of interplay between E2F and hDM2 whereby hDM2 has a profound impact on the physiological consequences of E2F activation. They suggest that the oncogenic properties of hDM2 may in part be mediated by an antiapoptotic activity that converts E2F from a negative to a positive regulator of cell cycle progression and thereby retains E2F at a level that contributes to a continual state of growth stimulation.

The ARF protein product of the ink4a/arf locus is induced by a variety of oncogenic signals. ARF facilitates growth arrest through the p53 pathway by hindering the down-regulation of p53 activity mediated by MDM2, through the formation of a protein complex with MDM2. Here we have explored the possibility that human p14 ARF activity is integrated with growth regulating pathways other than p53, and report our results that p14 ARF can control the activity of the E2F transcription factor. p14ARF regulates E2F activity in dierent cell-types, including p53 7/7 /mdm 7/7 MEFs, thus excluding that the eects of p14 ARF are indirectly caused through MDM2 modulation. p14 ARF downregulates E2F-dependent transcription, and in cells undergoing E2F-dependent apoptosis prompts cell cycle arrest. p14 ARF possesses multiple binding domains for E2F-1, one of which resides within the N-terminal region and coincides with the regulation of E2F activity. A mutational analysis of p14 ARF indicates that the E2F-1 and MDM2 binding domains can be distinguished. These results highlight the potential interplay between p14 ARF and E2F, and establish p14 ARF as a pleiotrophic regulator of cell growth that acts by targetting at least two key pathways in the control of proliferation, namely E2F and p53.

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