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. Overall design: 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)细胞生长与存活依赖于能量产生与代谢物合成之间的精密平衡。本研究发现，一种被命名为CIIlow的替代性线粒体复合物II（mitochondrial complex II，简称CII）组装体，可在生物能量应激下作为代谢物生物合成的检查点，细胞通过调控DNA合成与细胞周期进程来抑制能量利用。CIIlow的缺失会导致能量利用与代谢物合成失衡，这一点可通过从头嘧啶合成通路的恢复以及S期细胞周期阻滞的解除得到证实。体外实验进一步通过对散发性、SDHA及SDHB突变患者的副神经节瘤组织的分析得到验证。本研究揭示了线粒体内一种全新的核心复合物，其可通过感知能量可获得性对细胞代谢进行稳态调控，而SDHA是该复合物的核心分子。实验设计：将亲本MDA-MB-231（简称MDA_）细胞（生物学重复2份）与SDHB敲除（SDH_）细胞（生物学重复3份），以及额外敲低SDHA的SDHB敲除细胞（SH1_，生物学重复3份）进行对比分析。