TRIM21 orchestrates AKT K27-linked ubiquitination to counteract cancer chemotherapeutic resistance

Ubiquitin modifications play diverse and predominant roles in virous physiological and pathological processes. However, the impact of atypical ubiquitin modification on AKT and its potential role in tumorigenesis remain largely unclear. Through systematic ubiquitin analyses, we have observed that AKT undergoes K27-linked ubiquitination to imply its negative regulation conditions. Based on the quantified mass spectrometry protein-identification assays, the E3 ubiquitin ligase TRIM21 was identified to catalyze AKT K27-linked ubiquitination, a process antagonized by the deubiquitinase OTUD6A. As such, TIRM21 acts as a tumor suppressor by repressing AKT activity, counteracted by the oncogenic protein OTUD6A. Mechanistically, TRIM21-mediated K27-linked ubiquitin disrupts SKP2/TRAF6-mediated K63-linked AKT ubiquitin, thereby blocking AKT membrane localization and kinase activity. Interestingly, activation of S6K1 in response to amino acids, directly phosphorylates and inactivates OTUD6A, enabling a negative feedback loop to regulate AKT activity in a deubiquitination-dependent manner. Moreover, Otud6a deficiency significantly reduces lung tumorigenesis in a KrasG12D-drivern lung cancer mouse model. While, pharmacological activation or AAV-based overexpression of Trim21 alleviates hyperactive AKT-induced tumor growth in vivo. Thus, our findings not only elucidate a fine-tuned regulation of AKT through atypical ubiquitin modification, but also suggest the strategy by targeting the TRIM21-OUTD6A axis for combating AKT-driven cancers.