Abstract LB-391: HDAC6 is a dual enzyme with deacetylase and E3 ligase activities for MSH2 degradation

Abstract

Abstract MSH2 is a key DNA mismatch repair (MMR) protein that functions as an MSH2/MSH6 heterodimer (MutSa) in repairing errors after DNA replication as well as sensing certain types of DNA damage. It is believed that reduction of MutSα attenuates recognition of DNA adducts which renders a declined cell cycle arrest and apoptosis upon DNA damage and subsequently leads to chemotolerance. However, the mechanisms of down-regulation of MutSa are largely unknown. Here we show that histone deacetylase 6 (HDAC6) is co-purified with MutSa in HeLa nuclear extracts. Interestingly, we have found that HDAC6 itself serves as a ubiquitin E3 ligase to promote MSH2 polyubiquitination which renders MSH2 degradation by proteasome pathway. Intriguingly, HDAC6 prefers to target MSH2 monomer over MutSa for ubiquitination and degradation. Mechanistically, HDAC6 E3 ligase activity primarily resides in the N-terminal region encompassing the previously identified deacetylase domain 1 (DAC1) whereas its deacetylase activity resides in the deacetylase domain 2 (DAC2). We also showed that HDAC6 E3 ligase activity towards acetylated MSH2 is facilitated by its deacetylase activity in vivo. MSH2 lysine 249 and 892 can be either acetylated or ubiqutinated in vivo. These data suggest that HDAC6 sequentially deacetylates and ubiquitinates MSH2 via its DAC2 and DAC1 domains to target MSH2 degradation in vivo. Moreover, cells lacking or depleted of HDAC6 exhibit elevated levels of MSH2 due to impaired ubiquitin-proteasome-mediated degradation and subsequently prolonged half-life, compared with control cells. In agreement with this, HDAC6 knockout cells display higher MMR activity compared with wild type cells. Importantly, absence or reduction of HDAC6 leads to an increased cellular sensitivity to 6-TG and MNNG, whose DNA lesions were recognized by MutSa, suggesting that HDAC6 governs MSH2-dependent cytotoxicity induced by 6-TG or MNNG. Overall, our results identified a novel ubiquitin E3 ligase activity of HDAC6 and revealed that HDAC6 plays an important role in response to genotoxic stress. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-391. doi:1538-7445.AM2012-LB-391