TECPR1 is activated by damage-induced sphingomyelin exposure to mediate noncanonical autophagy

Cells use noncanonical autophagy, also called conjugation of ATG8 to single membranes (CASM), to label damaged intracellular compartments with ubiquitin-like ATG8 family proteins in order to signal danger caused by pathogens or toxic compounds. CASM relies on E3 complexes to sense membrane damage, but so far, only the mechanism to activate ATG16L1-containing E3 complexes, associated with proton gradient loss, has been described. Here, we show that TECPR1-containing E3 complexes are key mediators of CASM in cells treated with a variety of pharmacological drugs, including clinically relevant nanoparticles, transfection reagents, antihistamines, lysosomotropic compounds, and detergents. Interestingly, TECPR1 retains E3 activity when ATG16L1 CASM activity is obstructed by the Salmonella Typhimurium pathogenicity factor SopF. Mechanistically, TECPR1 is recruited by damage-induced sphingomyelin (SM) exposure using two DysF domains, resulting in its activation and ATG8 lipidation. In vitro assays using purified human TECPR1-ATG5-ATG12 complex show direct activation of its E3 activity by SM, whereas SM has no effect on ATG16L1-ATG5-ATG12. We conclude that TECPR1 is a key activator of CASM downstream of SM exposure.

Automated summary

Cells use noncanonical autophagy, called CASM, to label damaged intracellular compartments with ATG8 family proteins to signal danger. TECPR1-containing E3 complexes are key mediators of CASM activated by various drugs. TECPR1 retains E3 activity when ATG16L1 CASM activity is obstructed by SopF and is activated by damage-induced SM exposure.