Abstract
SOS1 ablation causes specific defective phenotypes in MEFs including increased levels of intracellular ROS. We showed that the mitochondria-targeted antioxidant MitoTEMPO restores normal endogenous ROS levels, suggesting predominant involvement of mitochondria in generation of this defective SOS1-dependent phenotype. The absence of SOS1 caused specific alterations of mitochondrial shape, mass, and dynamics accompanied by higher percentage of dysfunctional mitochondria and lower rates of electron transport in comparison to WT or SOS2-KO counterparts. SOS1-deficient MEFs also exhibited specific alterations of respiratory complexes and their assembly into mitochondrial supercomplexes and consistently reduced rates of respiration, glycolysis, and ATP production, together with distinctive patterns of substrate preference for oxidative energy metabolism and dependence on glucose for survival. RASless cells showed defective respiratory/metabolic phenotypes reminiscent of those of SOS1-deficient MEFs, suggesting that the mitochondrial defects of these cells are mechanistically linked to the absence of SOS1-GEF activity on cellular RAS targets. Our observations provide a direct mechanistic link between SOS1 and control of cellular oxidative stress and suggest that SOS1-mediated RAS activation is required for correct mitochondrial dynamics and function.
Highlights
SOS1 and SOS2 are the most universal and widely expressed RASGEFs in metazoan cells [1,2,3,4,5,6,7]
Increased oxidative stress of SOS1-deficient mouse embryonic fibroblasts (MEFs) is reversed by mitochondria-targeted antioxidant MitoTEMPO We reported previously that SOS1 depletion causes specific phenotypic defects in primary MEFs, including in particular a substantial increase of intracellular ROS and oxidative stress [12, 17, 18]
KO and/or SOS1/2 DKO MEFs, of transcripts coding for intracellular catalase (CAT) [27], mitochondrial superoxide dismutase 2 (SOD2), and the extracellular SOD3 superoxide dismutase isoform [28]
Summary
SOS1 and SOS2 are the most universal and widely expressed RASGEFs (guanine nucleotide exchange factors) in metazoan cells [1,2,3,4,5,6,7]. In particular we wished to get functional insights into the mechanistic details mediating the altered redox phenotype, as well as conclusively identifying the source of the elevated ROS in SOS1-deficient fibroblasts. To this end, here we performed detailed analyses of mitochondrial morphology and function in MEFs of relevant SOS genotypes (WT, SOS1-KO, SOS2-KO, SOS1/2-DKO) and carried out functional and metabolic profiling of these SOS-devoid cells. Our observations support a specific mechanistic link between SOS1 and control of intracellular redox homeostasis and mitochondrial function, and suggest that activation of RAS proteins by SOS1 is a critical requirement for maintenance of correct mitochondrial structure, function, and respiratory/metabolic homeostasis
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