A cellular mechanism to detect and alleviate reductive stress

Metazoan organisms rely on conserved stress response pathways to detect and alleviate adverse conditions and preserve their cellular integrity. Stress responses are particularly important in stem cells that provide lifetime support for tissue formation and repair, yet how these protective systems are integrated into developmental programs is poorly understood. Here, we have used myoblast differentiation to identify the E3 ligase CUL2FEM1B and its substrate FNIP1 as core components of the reductive stress response. Reductive stress, as caused by prolonged antioxidant signaling or mitochondrial inactivity, reverts the oxidation of invariant Cys residues in FNIP1 and thereby allows CUL2FEM1B to recognize its target. The ensuing proteasomal degradation of FNIP1 restores mitochondrial activity to preserve both redox homeostasis and stem cell integrity. The reductive stress response is therefore built around a ubiquitin-dependent rheostat that tunes mitochondrial activity to cellular redox needs and implicates metabolic control in the coordination of stress and developmental signaling. Overall design: RNA-seq analysis was perfomred on undiffernitataed myoblasts cells seeded at subcondluent densities, and treated with ON-TARGETplus Non-targeting Control (Horizon Discovery; D-001810-03 UGGUUUACAUGUUUUCUGA), or ON-TARGET plus siRNA siKeap1 #1 mouse (Horizon Discovery; J-041104-09 GCGCCAAUGUUGACACGGA), or ON-TARGET plus siRNA siFem1b #1 mouse (Horizon Discover;y J-065205-08 GAAGAUCAGUGCAGAAUUA, or codepletion with siKeap/siFem1b