HPV oncogenes increase viability and nuclear architecture stability in pretumoral keratinocytes exposed to UVB radiation

Ultraviolet radiation (UVR) is an environmental risk factor and a cofactor in carcinogenesis. UVB radiation (UVBR), mainly from sunlight, is a known risk factor for lip cancer and can also contribute to oral cavity cancer. Besides inducing DNA damage, UVBR can activate dormant HPV infections in the oral cavity, increasing oral carcinogenesis likelihood via HPV oncogenes. In this study, we evaluated the responses to UVBR in human keratinocytes infected with viral oncogenes of HPV-18. While UVBR induced similar levels of DNA damage in the HaCaT human keratinocyte parental cell line compared to HaCaT cells containing HPV-18 oncogenes E5, E6 and E7, the latter showed increased viability and reduced levels of apoptotic and necrotic markers in response to UVBR. Both HaCaT parental and HaCaT E5/E6/E7-18 cells showed marked alterations in the actin cytoskeleton upon UVBR, but HaCaT parental cells retained more stress fibers, while displaying deep nuclear invaginations, which were much less frequent in HaCaT E5/E6/E7-18 cells. Deep nuclear invaginations were lined by highly condensed chromatin, implying alterations in nuclear architecture that profoundly affect normal nuclear compartmentalization. Furthermore, mechanical modelling suggests that reduced nuclear invaginations in irradiated HaCaT E5/E6/E7-18 cells is related to decreased tractional stress. Our results show that HPV oncogenes confer increased viability and nuclear architecture stability to keratinocytes exposed to UVBR, which could contribute to their role in cooperating with UVBR induced carcinogenesis in the oral cavity.