Dual Site Phosphorylation of Caspase-7 by PAK2 Blocks Apoptotic Activity by Two Distinct Mechanisms

Caspases, the cysteine proteases that execute apoptosis, are tightly regulated via phosphorylation by a series of kinases. Although all apoptotic caspases work in concert to promote apoptosis, different kinases regulate individual caspases. Several sites of caspase-7 phosphorylation have been reported, but without knowing the molecular details, it has been impossible to exploit or control these complex interactions, which normally prevent unwanted proliferation. During dysregulation, PAK2 kinase plays an alternative anti-apoptotic role, phosphorylating caspase-7 and promoting unfettered cell growth and chemotherapeutic resistance. PAK2 phosphorylates caspase-7 at two sites, inhibiting activity using two different molecular mechanisms, before and during apoptosis. Phosphorylation of caspase-7 S30 allosterically obstructs its interaction with caspase-9, preventing intersubunit linker processing, slowing or preventing caspase-7 activation. S239 phosphorylation renders active caspase-7 incapable of binding substrate, blocking later events in apoptosis. Each of these mechanisms is novel, representing new opportunities for synergistic control of caspases and their counterpart kinases. [Display omitted] •PAK2 phosphorylation of caspase-7 inhibits activity by two distinct mechanisms•Phosphorylation of caspase-7 at S30 slows zymogen activation by upstream caspases•S30 phosphorylation interferes with caspase-7:caspase-9 interaction•Crystal structure of S239E phosphomimetic suggests substrate binding is obstructed PAK2 phosphorylates caspase-7 resulting in loss of activity, which is implicated in resistance to chemotherapeutic agents. Eron et al. decipher the molecular mechanism of phosphorylated caspase-7 inhibition at two phosphorylation sites. Phosphorylation at S30 slows initial activation while phosphorylation at S239 blocks substrate binding.