SDS3 is a key component of the histone deacetylase (HDAC)-dependent Sin3A co-repressor complex, serving to maintain its HDAC activity. Here, we report both exogenous and endogenous functional interaction between deubiquitinating enzyme USP17 and human SDS3 by MALDI-TOF-MS, co-immunoprecipitation assay, and GST pull-down assay. In this study, we demonstrated that SDS3 readily undergoes endogenous polyubiquitination, which is associated specifically with Lys-63-branched polyubiquitin chains and not with Lys-48-branched polyubiquitin chains. Further, we also demonstrated that USP17 specifically deubiquitinates Lys-63-linked ubiquitin chains from SDS3 and regulates its biological functions. The deubiquitinating activity of USP17 on SDS3 negatively regulates SDS3-associated HDAC activity. The constitutive expression of USP17 and its substrate SDS3 was involved in the inhibition of anchorage-independent tumor growth and blocks cell proliferation, leading to apoptosis in cervical carcinoma cells. Furthermore, we showed that USP17 and SDS3 mutually interact with each other to regulate cancer cell viability. These data support the possibility that SDS3, being a substrate of USP17, may play an important role in developing a novel therapeutic means to inhibit specific HDAC activities in cancer.Molecular processes such as phosphorylation, dephosphorylation, acetylation, deacetylation, ubiquitination, and deubiquitination of cellular proteins play an orchestrated role in coordinating homeostasis and contribute to the manifestation of physiological processes in health and disease. The process of ubiquitination is a well established event involving a complex of ubiquitin-activating enzymes (E1), ubiquitin-conjugating enzymes (E2), and ubiquitin ligase (E3) enzymes (1-4). Ubiquitination can be reversed by deubiquitinating enzymes (DUBs) 2 (3, 5). Most DUBs are cysteine proteases and consist of at least five known families: the ubiquitin C-terminal hydrolases, the ubiquitin-specific processing proteases (USP), Jab1/ Pab1/MPN domain-containing metallo-enzymes, Otu-domain ubiquitin aldehyde-binding proteins, and Ataxin-3/Josephin (3, 4, 6).USP17 was previously identified as a human ortholog of DUB-3 that is regulated by the IL-4 and IL-6 cytokines (7). Recent characterization of USP17 as a key regulator of cell proliferation has revealed its critical role in cell growth and survival (7-10). Previously, we showed that USP17 possesses two hyaluronan binding motifs (HABMs) in its C-terminal region and interacts with hyaluronan to regulate cell viability (11). However, the biological significance of these HABMs in USP17 remains to be fully understood.The Sin3 co-repressor complex has been linked to HDAC enzymatic activity by directly interacting with HDAC1 and HDAC2 within the Sin3-HDAC complex (12, 13). SDS3 is a subunit of the HDAC-dependent Sin3A co-repressor complex and exhibits a critical role in maintenance of mSin3-associated HDAC activity (14,15). It has a role in transcriptional repression, recruits HDAC activity, and enables...
