The biochemical mechanism of caspase-2 activation

Abstract

A unified model for initiator caspase activation has previously been proposed based on the biochemical analysis of caspase-8 and -9. Caspase-2 is structurally related to caspase-9, but its mechanism of activation is not known. Using an uncleavable mutant of caspase-2, we show that dimerization (and not processing) is the key event that drives initial procaspase-2 activation. Following dimerization, caspase-2 undergoes autocatalytic cleavage that promotes its stable dimerization and further enhances the catalytic activity of caspase-2. Although the caspase-2 zymogen does not require cleavage for the initial acquisition of activity, intersubunit cleavage is required to generate levels of activity required to induce cell death by overexpression. We also provide evidence that the reported disulfide bond linkage between two caspase-2 monomers is dispensable for caspase-2 dimerization. As caspase-2 does not require cleavage for its initial activation, our findings confirm caspase-2 to be a bona fide initiator caspase.

Caspase function in programmed cell death

“…Some data suggest that dimerisation of caspase-2 molecules is sufficient to mediate its activation, and recruitment of caspase-2 to large apoptosome-like complexes, such as the PIDDosome, may facilitate caspase-2 dimerisation. 98,101 It is possible that caspase-2 activation occurs by more than one mechanism. Recent data suggest that phosphorylation of caspase-2 at Ser157 by protein kinase CK2 (PKCK2) keeps it inactive.…”

Caspase-2 as a tumour suppressor

“…15,25,26 As alluded to above and discussed in a number of recent reviews, 9,27 previous studies focusing on the role of caspase-2 in apoptosis have yielded somewhat contradictory findings, questioning the significance of caspase-2 in cell Caspase-2 is synthesized as a zymogen and is activated via a dimerization-dependent, autocatalytic cleavage mechanism. 45 Caspase-2 is made up of a C-terminal catalytic domain containing the active site (Cys320) and an amino terminal CARD, which mediates proteinprotein interactions and facilitates recruitment into activation platforms. 9 Upon proximity-induced oligomerization via its CARD, caspase-2 becomes partially active.…”

“…46 Autoprocessing then occurs between the small and large subunits of the catalytic domain yielding a fully active enzyme. 45 Further processing results in removal of the N-terminal CARD, generating a fully mature tetramer. 45 Caspase-2 is also actively imported into the nucleus via a nuclear localization sequence (NLS) located in the prodomain.…”

“…45 Further processing results in removal of the N-terminal CARD, generating a fully mature tetramer. 45 Caspase-2 is also actively imported into the nucleus via a nuclear localization sequence (NLS) located in the prodomain. 7,8 Caspase-2 activation has been shown to be regulated by phosphorylation mediated by various kinases, including calcium/calmodulin-dependent protein kinase II (Ser164), 47 protein kinase CK2 (Ser157) 48 and cyclin-dependent kinase 1 (Ser340).…”

Caspase-2 is required for cell death induced by cytoskeletal disruption

“…Caspase-2 activation occurs rapidly in response to diverse apoptotic signals in most cell types (Harvey et al, 1997;Zhivotovsky and Orrenius, 2005;Kumar, 2007). The CARD plays an essential role in initial caspase-2 oligomerization/activation and the fusion of the caspase-2 prodomain to caspase-3 generates an autoactivating chimeric molecule (Butt et al, 1998;Colussi et al, 1998;Shearwin-Whyatt et al, 2001;Baliga et al, 2004). Caspase-2 can bind to the CARD-containing molecule RAIDD and data suggest that PIDD, a p53-induced death domaincontaining protein, binds RAIDD and facilitates caspase-2 activation (Shearwin-Whyatt et al, 2000;Tinel and Tschopp, 2004).…”