New mechanistic insight into SARM1 activation: TRIM32-mediated ubiquitination is a key lever that actuates SARM1's catalytic action, leading to axon degeneration and cell death.

Sterile alpha and TIR motif-containing protein 1 (SARM1) is an enzyme that cleaves nicotinamide adenine dinucleotide (NAD+) and plays a role in disrupting neural circuits through axon degeneration and cell death. SARM1 is activated by changes in the nicotinamide mononucleotide (NMN)/NAD+ ratio and by various post-translational modifications, but its complete regulatory mechanism remains poorly understood. Here, we report that tripartite motif-containing protein 32 (TRIM32) activates SARM1 through specific ubiquitination triggered by anticancer drug treatment. TRIM32 promotes the attachment of Lys27-linked ubiquitin chains to Lys173 and Lys375 within the ARM domain, which is an autoinhibitory region of SARM1. This ubiquitination by TRIM32 increases SARM1's NAD+-cleaving catalytic activity and enhances its ability to induce neurite degeneration and cell death. A mutant form of TRIM32 lacking the enzymatically active RING domain fails to promote SARM1 ubiquitination, and reducing TRIM32 levels decreases SARM1 ubiquitination. Additionally, ubiquitin-specific peptidase 13 (USP13), a known negative regulator of SARM1, can deubiquitinate SARM1. These findings suggest that TRIM32 is a key regulator of axon degeneration and cell death through its ubiquitination of SARM1.