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bioRxiv2020

Casein Kinase 1G2 Suppresses Necroptosis-Promoted Testis Aging by Inhibiting Receptor-Interacting Kinase 3

Casein kinases are a large family of intracellular serine/threonine kinases that control a variety of cellular signaling functions. Here we report that a member of casein kinase 1 family, casein kinase 1G2, CSNK1G2, binds and inhibits the activation of receptor-interacting kinase 3, RIP3, thereby attenuating RIP3-mediated necroptosis. The binding of CSNK1G2 to RIP3 is triggered by auto-phosphorylation at serine 211/threonine 215 sites in its C-terminal domain. CSNK1G2-knockout mice showed significantly enhanced necroptosis response and pre-maturing aging of their testis, a phenotype that was rescued by either double knockout of the RIP3 gene or feeding the animal with a RIP1 kinase inhibitor-containing diet. Moreover, CSNK1G2 is also co-expressed with RIP3 in human testis, and the necroptosis activation marker phospho-MLKL was observed in the testis of old (>80) but not young men, indicating that the testis-aging program carried out by the RIP3-mediated and CSNK1G2-attenuated necroptosis is evolutionarily conserved between mice and men.

cell biology↗

bioRxiv2020

Oxidoreductases generate hydrogen peroxide that drives iron-dependent lipid peroxidation during ferroptosis

The inhibition of antioxidant systems of glutathione peroxidase 4 (GPX4) or ferroptosis suppressor protein 1 (FSP1) causes iron-dependent peroxidation of polyunsaturated phospholipids that leads to cell death, a process known as ferroptosis. The mechanisms underlying iron-dependent lipid peroxidation are under active debate. Here, we report that two endoplasmic reticulum-residing oxidoreductases, NADPH-cytochrome P450 reductase (POR) and NADH-cytochrome b5 reductase (CYB5R1), are responsible for the iron-dependent peroxidation of polyunsaturated phospholipids and membrane disruption that executes ferroptosis. Genetic ablation of POR and CYB5R1 or mutations that eliminate PORs electron transfer activity blocked ferroptosis. In vitro enzymatic assays established that POR and CYB5R1 catalyze hydrogen peroxide production by transferring electrons from NADPH/NADH to oxygen, which is then used to carry out iron-dependent lipid peroxidation via a Fenton reaction. The lipid peroxidation reaction catalyzed by POR and CYB5R1 additively disrupts polyunsaturated phospholipid-containing liposomes. Finally, POR knockdown confers significant protective effects during concanavalin A-induced, ferroptosis-associated acute liver injury in vivo. Our study thus indicates that POR and CYB5R1 are the enzymes of the "oxidant" system that operates to contravene the antioxidant GPX4/FSP1 systems; the balance between these two systems determines cell commitment to ferroptosis.

biochemistry↗