Confinement of caspase-12 proteolytic activity to autoprocessing

Abstract

Caspase-12 is a dominant-negative regulator of caspase-1 (IL-1β-converting enzyme) and an attenuator of cytokine responsiveness to septic infections. This molecular role for caspase-12 appears to be akin to the role of cFLIP in regulating caspase-8 in the extrinsic cell death pathway; however, unlike cFLIP/Usurpin, we demonstrate here that caspase-12 is catalytically competent. To examine these catalytic properties, rat caspase-12 was cloned, and the recombinant enzyme was used to examine the cleavage of macromolecular and synthetic fluorogenic substrates. Although caspase-12 could mediate autoproteolytic maturation of its own proenzyme, in both cis and trans , it was not able to cleave any other polypeptide substrate, including other caspase proenzymes, apoptotic substrates, cytokine precursors, or proteins in the endoplasmic reticulum that normally undergo caspase-mediated proteolysis. The dearth of potential substrates for caspase-12 also was confirmed by whole-cell diagonal-gel analysis. Autolytic cleavage within the caspase-12 proenzyme was mapped to a single site at the large–small subunit junction, ATAD 319 , and this motif was recognized by caspase-12 when incorporated into synthetic fluorogenic substrates. The specific activity of caspase-12 with these substates was several orders of magnitude lower than caspases-1 and -3, highlighting its relative catalytic paucity. In intact cells, caspase-12 autoproteolysis occurred in the inhibitory complex containing caspase-1. We propose that the proteolytic activity of caspase-12 is confined to its own proenzyme and that autocleavage within the caspase-1 complex may be a means for temporal limitation of the inhibitory effects of caspase-12 on proinflammatory cytokine maturation.

Role of the ubiquitin–proteasome system in brain ischemia: Friend or foe?

“…However, the role of this protease in neuronal demise in the ischemic brain remains to be determined. In fact, it was proposed that caspase-12 acts mainly as a dominant negative in the regulation of caspase-1 activity and the main role of the proteolytic activity of caspase-12 may be in the processing of the protease (Roy et al, 2008).…”

The endoplasmic reticulum in apoptosis and autophagy: role of the BCL-2 protein family

“…Of note, although the autocatalytic activity of caspase-12 is sufficient for subunit separation, it does not allow prodomain removal (Roy et al, 2008). Without prodomain removal, caspase-12 is capable only of self-cleavage (Roy et al, 2008), and overexpression of caspase-12 under conditions in which only autoprocessing occurs therefore does not result in apoptosis, likely due to an extremely limited substrate set prior to removal of the prodomain (Nakagawa and Yuan, 2000;Fujita et al, 2002;Kalai et al, 2003;Roy et al, 2008). Removal of the caspase-12 prodomain can be achieved through a number of mechanisms, one of which is cleavage by mcalpain.…”

Caspase-12 Dampens the Immune Response to Malaria Independently of the Inflammasome by Targeting NF-κB Signaling

“…They trigger inflammation by activating caspase-1, which cleaves pro-IL-1b and pro-IL-18 into their mature active forms. We have previously shown that a second member of the caspase-1 subfamily, caspase-12, which is catalytically inactive in humans and attenuated in rodents (6), acts as an inhibitor of both the inflammasome and NF-kB pathways (7)(8)(9). Expression of human caspase-12 is predominately confined to African descendents and is associated with dampened proinflammatory cytokine production and sepsisrelated mortality (8).…”