TRIM21 and OTUD6A orchestrate AKT K27-linked atypical ubiquitination to modulate cancer chemoresistance.

Ubiquitination regulates various physiological and pathological processes. However, the impact of atypical AKT ubiquitination and its potential role in tumorigenesis remain unclear. Here we show that AKT is modified by K27-linked ubiquitination by the E3 ubiquitin ligase TRIM21, a process antagonized by the deubiquitinase OTUD6A. As such, TRIM21 acts as a tumor suppressor by repressing AKT activity, whereas OTUD6A counteracts AKT suppression. Mechanistically, TRIM21-mediated AKT ubiquitination disrupts SKP2-mediated or TRAF6-mediated K63 ubiquitination, thereby blocking AKT membrane localization and its kinase activity. Upon activation in response to amino acids, S6K1 directly phosphorylates and inactivates OTUD6A, enabling a negative feedback loop regulating AKT activity in a deubiquitination-dependent manner. In agreement with this model, Otud6a deficiency reduces lung tumorigenesis in a Kras-driven lung cancer mouse model and TRIM21 induction alleviates hyperactive AKT-induced tumor growth in vivo. Thus, our findings unveil a fine-tuned regulation of AKT through atypical ubiquitination and suggest the strategy for combating AKT-driven cancers by targeting the TRIM21-OTUD6A axis.