USP36 inhibits apoptosis by deubiquitinating cIAP1 and survivin in colorectal cancer cells

Abstract

Chemotherapeutic agents for treating colorectal cancer primarily induce apoptosis in tumor cells. The ubiquitin-proteasome system (UPS) is critical for apoptosis regulation. Deubiquitinating enzymes (DUBs) remove ubiquitin from substrates to reverse ubiquitination. Although over 100 DUB members have been discovered, the biological functions of only a small proportion of DUBs have been characterized. Here, we aimed to systematically identify the DUBs that contribute to the development of colorectal cancer. Among the DUBs, ubiquitin-specific protease 36 (USP36), is upregulated in colorectal cancer. We showed that the knockdown of USP36 induces intrinsic and extrinsic apoptosis. Through gene silencing and coimmunoprecipitation techniques, we identified survivin and cIAP1 as USP36 targets. Mechanistically, USP36 binds and removes lysine-11 (K11)-linked ubiquitin chains from cIAP1 and lysine-48 (K48)-linked ubiquitin chains from survivin to abolish protein degradation. Overexpression of USP36 disrupts the formation of the XIAP-Smac complex and promotes RIPK1 ubiquitination, validating USP36 as an inhibitor to intrinsic and extrinsic apoptosis through deubiquitinating survivin and cIAP1. Therefore, our results suggest that USP36 is involved in colorectal cancer progression and is a potential therapeutic target.