Alternate assembly of SDHA connects energy stress to metabolic checkpoint and DNA synthesis

Cell growth and survival depend on a delicate balance between energy production and synthesis of metabolites. We have discovered that an alternative mitochondrial complex II (CII) assembly, designated here as CIIlow, serves as a check-point for metabolite biosynthesis under bioenergetic stress, with cells suppressing their energy utilization by modulating DNA synthesis and cell cycle progression. Depletion of CIIlow leads to an imbalance in energy utilization and metabolite synthesis, as evidenced by recovery of the de novo pyrimidine pathway and unlocking cell cycle arrest from the S-phase. In vitro experiments are further corroborated by analysis of paraganglioma tissues from patients with sporadic, SDHA and SDHB mutations. These findings uncover a new core complex inside mitochondria that provides homeostatic control of cellular metabolism to reflect availability of energy, with SDHA being its central molecule. Parental MDAMB231 (MDA_) cells (duplicate) were compared with SDHB knockout (SDH_) cells (triplicate) and SDHB knockout cells with additional knockdown of SDHA (SH1_) cells (triplicate)