Inactivation of the CYLD Deubiquitinase by HPV E6 Mediates Hypoxia-Induced NF-kappa B Activation

The biochemical mechanisms that underlie hypoxia-induced NF-kappa B activity have remained largely undefined. Here, we find that prolonged hypoxia-induced NF-kappa B activation is restricted to cancer cell lines infected with high-risk human papillomavirus (HPV) serotypes. The HPV-encoded E6 protein is necessary and sufficient for prolonged hypoxia-induced NF-kappa B activation in these systems. The molecular target of E6 in the NF-kappa B pathway is the CYLD lysine 63 (K63) deubiquitinase, a negative regulator of the NF-kappa B pathway. Specifically, hypoxia stimulates E6-mediated ubiquitination and proteasomal degradation of CYLD. Given the established role of NF-kappa B in human carcinogenesis, these findings provide a potential molecular/viral link between hypoxia and the adverse clinical outcomes observed in HPV-associated malignancies.