A TRIM21-UCHL3-ITCH-SIPA1 axis promotes colorectal cancer growth and metastasis.

Dysregulation of protein ubiquitination and deubiquitination is a key mechanism driving tumor progression. However, the role of upstream regulators and post-translational mechanisms regulating signal-induced proliferation-associated 1 (SIPA1) stability in colorectal cancer (CRC) remains unclear. This study aimed to investigate novel deubiquitinases that directly bind to and stabilize SIPA1 based on its catalytic activity, along with their underlying action mechanisms. Notably, ubiquitin C-terminal hydrolase L3 (UCHL3) was identified as the novel deubiquitinase. Mechanistically, UCHL3 removed K48-linked polyubiquitin chains from SIPA1 at lysine 805, protecting it from proteasomal degradation. In contrast, the E3 ligase itchy E3 ubiquitin protein ligase (ITCH) promoted SIPA1 ubiquitination and degradation, acting antagonistically to UCHL3. Furthermore, UCHL3 enhanced CRC cell proliferation, invasion, and metastasis through a SIPA1-dependent mechanism. Interestingly, tripartite motif-containing protein 21 regulated UCHL3 post-translationally by targeting UCHL3 for proteasomal degradation. Clinically, UCHL3 and SIPA1 were found to be upregulated in CRC tissues, whereas ITCH was downregulated, with their expression correlating with poor patient prognosis. Altogether, the findings of this study reveal the novel UCHL3-ITCH-SIPA1 regulatory axis that modulates oncogenic signaling and CRC progression, offering new insights into the post-translational regulation of SIPA1 and identifying potential therapeutic targets.