A novel MTORC2-AKT-ROS axis triggers mitofission and mitophagy-associated execution of colorectal cancer cells upon drug-induced activation of mutant KRAS

Abstract

RAS is one of the most commonly mutated oncogenes associated with multiple cancer hallmarks. Notably, RAS activation induces intracellular reactive oxygen species (ROS) generation, which we previously demonstrated as a trigger for autophagy-associated execution of mutant KRAS-expressing cancer cells. Here we report that drug (merodantoin; C1)-induced activation of mutant KRAS promotes phospho-AKT S473-dependent ROS-mediated S616 phosphorylation and mitochondrial localization of DNM1L/DRP1 (dynamin 1 like) and cleavage of the fusion-associated protein OPA1 (OPA1 mitochondrial dynamin like GTPase). Interestingly, accumulation of the outer mitochondrial membrane protein VDAC1 (voltage dependent anion channel 1) is observed in mutant KRAS-expressing cells upon exposure to C1. Conversely, silencing VDAC1 abolishes C1-induced mitophagy, and gene knockdown of either KRAS, AKT or DNM1L rescues ROS-dependent VDAC1 accumulation and stability, thus suggesting an axis of mutant active KRAS-phospho-AKT S473-ROS-DNM1L-VDAC1 in mitochondrial morphology change and cancer cell execution. Importantly, we identified MTOR (mechanistic target of rapamycin kinsase) complex 2 (MTORC2) as the upstream mediator of AKT phosphorylation at S473 in our model. Pharmacological or genetic inhibition of MTORC2 abrogated C1-induced phosphorylation of AKT S473, ROS generation and mitophagy induction, as well as rescued tumor colony forming ability and migratory capacity. Finally, increase in thermal stability of KRAS, AKT and DNM1L were observed upon exposure to C1 only in mutant KRAS-expressing cells. Taken together, our work has unraveled a novel mechanism of selective targeting of mutant KRAS-expressing cancers via MTORC2-mediated AKT activation and ROS-dependent mitofission, which could have potential therapeutic implications given the relative lack of direct RAS-targeting strategies in cancer.Abbreviations: ACTB/ß-actin: actin beta; AKT: AKT serine/threonine kinase; C1/merodantoin: 1,3-dibutyl-2-thiooxo-imidazoldine-4,5-dione; CAT: catalase; CETSA: cellular thermal shift assay; CHX: cycloheximide; DKO: double knockout; DNM1L/DRP1: dynamin 1 like; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; H₂O₂: hydrogen peroxide; HSPA1A/HSP70-1: heat shock protein family A (Hsp70) member 1A; HSP90AA1/HSP90: heat shock protein 90 alpha family class A member 1; KRAS: KRAS proto-oncogene, GTPase; MAP1LC3B/LC3B, microtubule associated protein 1 light chain 3 beta; LC3B-I: unlipidated form of LC3B; LC3B-II: phosphatidylethanolamine-conjugated form of LC3B; MAPKAP1/SIN1: MAPK associated protein 1; MAPK1/ERK2: mitogen-activated protein kinase 1; MAPK3/ERK1: mitogen-activated protein kinase 3; MFI: mean fluorescence intensity; MiNA: Mitochondrial Network Analysis; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin kinase complex 1; MTORC2: mechanistic target of rapamycin kinase complex 2; O₂.^-: superoxide; OMA1: OMA1 zinc metallopeptidase; OPA1: OPA1 mitochondrial dynamin like GTPase; RICTOR: RPTOR independent companion of MTOR complex 2; ROS: reactive oxygen species; RPTOR/raptor: regulatory associated protein of MTOR complex 1; SOD1: superoxide dismutase 1; SOD2: superoxide dismutase 2; SQSTM1/p62: sequestosome 1; VDAC1: voltage dependent anion channel 1; VDAC2: voltage dependent anion channel 2.

Keywords: AKT; DNM1L; KRAS; MTORC2; ROS; mitofission.