UBR5 mediates colorectal cancer chemoresistance by attenuating ferroptosis via Lys 11 ubiquitin-dependent stabilization of Smad3-SLC7A11 signaling

Chemoresistance remains a principal culprit for the treatment failure in colorectal cancer (CRC), especially for patients with recurrent or metastatic disease. Deciphering the molecular basis of chemoresistance may lead to novel therapeutic strategies for this fatal disease. Here, UBR5, an E3 ubiquitin ligase frequently overexpressed in human CRC, is demonstrated to mediate chemoresistance principally by inhibiting ferroptosis. Paradoxically, UBR5 shields oxaliplatin-activated Smad3 from proteasome-dependent degradation via Lys 11-linked polyubiquitination. This novel chemical modification of Smad3 facilitates the transcriptional repression of ATF3, induction of SLC7A11 and inhibition of ferroptosis, contributing to chemoresistance. Consequently, targeting UBR5 in combination with a ferroptosis inducer synergistically sensitizes CRC to oxaliplatin-induced cell death and control of tumor growth. This study reveals, for the first time, a major clinically relevant chemoresistance mechanism in CRC mediated by UBR5 in sustaining TGF beta-Smad3 signaling and tuning ferroptosis, unveiling its potential as a viable therapeutic target for chemosensitization.