Restraint of apoptosis during mitosis through interdomain phosphorylation of caspase‐2

The apoptotic initiator caspase‐2 has been implicated in oocyte death, in DNA damage‐ and heat shock‐induced death, and in mitotic catastrophe. We show here that the mitosis‐promoting kinase, cdk1–cyclin B1, suppresses apoptosis upstream of mitochondrial cytochrome c release by phosphorylating caspase‐2 within an evolutionarily conserved sequence at Ser 340. Phosphorylation of this residue, situated in the caspase‐2 interdomain, prevents caspase‐2 activation. S340 was susceptible to phosphatase 1 dephosphorylation, and an interaction between phosphatase 1 and caspase‐2 detected during interphase was lost in mitosis. Expression of S340A non‐phosphorylatable caspase‐2 abrogated mitotic suppression of caspase‐2 and apoptosis in various settings, including oocytes induced to undergo cdk1‐dependent maturation. Moreover, U2OS cells treated with nocodazole were found to undergo mitotic catastrophe more readily when endogenous caspase‐2 was replaced with the S340A mutant to lift mitotic inhibition. These data demonstrate that for apoptotic stimuli transduced by caspase‐2, cell death is prevented during mitosis through the inhibitory phosphorylation of caspase‐2 and suggest that under conditions of mitotic arrest, cdk1–cyclin B1 activity must be overcome for apoptosis to occur.