Proteotoxic stress triggers TFEB- and TFE3-mediated autophagy and lysosomal biogenesis via non-canonical MTORC1 inactivation.

Proteotoxic stress, arising from conditions that cause misfolded protein accumulation, is closely linked to the pathogenesis of multiple diseases. Macroautophagy/autophagy activation is considered a compensatory mechanism to maintain protein homeostasis, but the underlying regulatory mechanisms remain incompletely understood. Here, we show that proteotoxic stress induced by proteasome inhibition, puromycin treatment, or polyglutamine-expanded HTT (huntingtin) expression promotes nuclear accumulation of TFEB and TFE3, key regulators of lysosomal biogenesis and autophagy. Mechanistically, TFEB activation under proteotoxic stress occurs independently of canonical MTORC1 inactivation mediated by TSC2 or ATF4. Instead, it involves non-canonical inhibition of MTORC1 via RRAG GTPases. Proteotoxic stress disrupts the RRAGC-TFEB interaction, preventing TFEB recruitment to lysosomes and subsequent MTORC1 phosphorylation. An activated RRAGC mutant rescues impaired lysosomal localization and nuclear accumulation of TFEB, while co-overexpression of FLCN and FNIP2, a GAP for RRAGC, partially restores stress-induced TFEB dephosphorylation. In addition, proteasome inhibition activates non-canonical autophagy. Deletion of