Abstract 5750: USP15 inhibits HPV16 E6 degradation and catalytically inactive USP15 has reduced inhibitive activity

Abstract

Abstract HPVs can be classified as either high-risk or low-risk depending on the transforming potential of the virus. Most cervical cancers and a significant proportion of other anogenital cancers have been associated with infection by a small number of high-risk genital HPV types. Tumorigenesis induced by high-risk genital HPVs has been linked to the expression of two viral oncoproteins, E6 and E7, which cooperate in cellular immortalization and transformation processes. HPV16 E6 is an oncoprotein that causes the development of high-risk type human papilloma virus (HPV) and induces cancers, including oropharyngeal, anal, and cervical cancers. The stability of E6 is essential for its complete function as an oncoprotein. Using the yeast two-hybrid system, we identified ubiquitin-specific protease 15 (USP15) as an HPV16 E6-interacting protein. USP15 encodes a protein that consist of 952 amino acids and functions as a deubiquitinating enzyme. Deubiquitination is an essential process that releases ubiquitin chains from ubiquitin-protein conjugates. Aberrations in the ubiquitin-proteasome system have been recently connected to the pathogenesis of several human protein degradation disorders, including cancer and neurodegenerative diseases; as such, the proteasome is now considered to be important in the mechanism of carcinogenesis. USP15 cleaves polyubiquitin chains of HPV16 E6 and/or ubiquitin precursors. Immunohistochemical analysis showed that USP15 was highly expressed in normal cervical squamous cells, and cervical cancer cells. Our results indicated that USP15 can increase the level of HPV16 E6 by inhibiting E6 degradation. USP15 dose-dependently inhibited the degradation of HPV16 E6. In contrast, catalytically inactive mutants of USP15 had a reduced inhibitory effect on E6 degradation. In particular, USP15 mutants of all three cysteine boxes and the NHL mutant of the KRF box had a drastically reduced inhibitive effect on HPV16 E6 degradation. In addition, HPV16 E6 mRNA was not induced by USP15; therefore, HPV16 E6 appears to be post-translationally regulated. These results suggest that USP15 has the ability to stabilize E6 as a deubiquitinating enzyme, and HPV16 E6 can affect biological functions as an oncoprotein in infected human cells. Citation Format: Aoi Tokuda, Masafumi Yoshimoto, Yuji Yaginuma. USP15 inhibits HPV16 E6 degradation and catalytically inactive USP15 has reduced inhibitive activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5750. doi:10.1158/1538-7445.AM2017-5750