β-HPV 8E6 Dysregulates the Hippo Signaling Pathway and Induces Aneuploidy

Abstract

ABSTRACTBeta genus human papillomaviruses (β-HPVs) are associated with cutaneous squamous cell carcinomas (cSCCs) in a subset of immunocompromised patients. Although β-HPVs are not necessary for tumor maintenance, they are hypothesized to destabilize the genome in the early stages of cancer development. Supporting this idea, β-HPV’s 8E6 protein attenuates p53 accumulation after failed cytokinesis. This paper identifies the mechanism of this abatement. We show β-HPV 8E6 dysregulates the Hippo signaling pathway (HP). It increases pro-proliferative gene expression, enhances TEAD activity and promotes cell growth. β-HPV 8E6 also reduces LATS activation and p53-mediated apoptosis following unsuccessful division of mitotic cells. These phenotypes are dependent on β-HPV 8E6 binding and destabilizing a cellular histone acetyltransferase, p300. Despite circumventing apoptosis, β-HPV 8E6 caused increased senescence after unsuccessful cytokinesis. We linked this lack of growth to the viral protein’s inability to prevent cytoplasmic sequestration of the HP transcription factor, YAP. We also show that increased telomerase reverse transcriptase activity (a common alteration in cSCCs) acts synergistically with β-HPV 8E6 to promote cellular proliferation after abortive cytokinesis. While β-HPV 8E6 promoted aneuploidy on its own, this genome destabilization is amplified in cells that do not divide after mitosis. Although our group and others have previously described inhibition of DNA repair, to the best of our knowledge this marks the first time that a β-HPV protein has been connected to chromosome level changes in the cellular genome. This represents a substantial escalation in the known genome destabilizing properties likely to occur during a β-HPV infection.IMPORTANCEThere is mounting evidence that β-HPVs contribute to cSCCs development in immunocompromised populations. They may also augment UV’s mutagenic potential, increasing cancer risk in the general population. We demonstrate that β-HPV 8E6 dysregulates the Hippo signaling pathway (HP). HP regulates cell growth and apoptosis in response to a myriad of stimuli, including failed cytokinesis. β-HPV 8E6 attenuates phosphorylation of the HP kinase, LATS, decreasing some but not all downstream signaling events. This allows binucleated cells to avoid apoptosis, however they succumb to senescence. We show that β-HPV 8E6 synergizes with a common cSCC mutation (telomerase activation) to avoid both apoptosis and senescence. We did not find any telomerase immortalized β-HPV 8E6 expressing cells that were not aneuploid after aberrant cytokinesis. This represents a substantial escalation in β-HPV E6’s known mutagenic potential.