Critical to the bacterial stringent response is the rapid relocation of resources from proliferation toward stress survival through the respective accumulation and degradation of (p)ppGpp by RelA and SpoT homologues. While mammalian genomes encode MESH1, a homologue of the bacterial (p)ppGpp hydrolase SpoT, neither (p)ppGpp nor its synthetase has been identified in mammalian cells. Here, we show that human MESH1 is an efficient cytosolic NADPH phosphatase that facilitates ferroptosis. Visualization of the MESH1–NADPH crystal structure revealed a bona fide affinity for the NADPH substrate. Ferroptosis-inducing erastin or cystine deprivation elevates MESH1, whose overexpression depletes NADPH and sensitizes cells to ferroptosis, whereas MESH1 depletion promotes ferroptosis survival by sustaining the levels of NADPH and GSH and by reducing lipid peroxidation. The ferroptotic protection by MESH1 depletion is ablated by suppression of the cytosolic NAD(H) kinase, NADK, but not its mitochondrial counterpart NADK2. Collectively, these data shed light on the importance of cytosolic NADPH levels and their regulation under ferroptosis-inducing conditions in mammalian cells.

细菌严格反应的关键是通过 RelA 和 SpoT 同源物对 (p)ppGpp 的各自积累和降解，将资源从增殖快速迁移到应激存活。虽然哺乳动物基因组编码 MESH1，它是细菌 (p)ppGpp 水解酶 SpoT 的同源物，但 (p)ppGpp 及其合成酶均未在哺乳动物细胞中被鉴定。在这里，我们表明人类 MESH1 是一种有效的胞质 NADPH 磷酸酶，可促进铁死亡。MESH1-NADPH 晶体结构的可视化揭示了对 NADPH 底物的真正亲和力。诱导铁死亡的erastin或胱氨酸剥夺会提升MESH1，其过度表达耗尽NADPH并使细胞对铁死亡敏感，而 MESH1 耗竭通过维持 NADPH 和 GSH 的水平以及通过减少脂质过氧化来促进铁死亡的存活。MESH1 耗竭造成的铁死亡保护通过抑制细胞溶质 NAD(H) 激酶 NADK 被消融，但不是其线粒体对应物 NADK2。总的来说，这些数据阐明了细胞溶质 NADPH 水平的重要性及其在哺乳动物细胞铁死亡诱导条件下的调节。