Confinement of caspase-12 proteolytic activity to autoprocessing.
Caspase-12 is a dominant-negative regulator of caspase-1 (IL-1beta-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.
Roy
Sophie
S
Department of Cardiovascular Diseases, Apoptosis Research Group, Merck Research Laboratories, 126 East Lincoln Avenue, Rahway, NJ 07065-0900, USA.
Sharom
Jeffrey R
JR
Houde
Caroline
C
Loisel
Thomas P
TP
Vaillancourt
John P
JP
Shao
Wei
W
Saleh
Maya
M
Nicholson
Donald W
DW
D000818:Animals; D001224:Aspartic Acid / Q000235:genetics / Q000378:metabolism; D020170:Caspase 1 / Q000378:metabolism; D053454:Caspase 12 / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D061945:Caspase Inhibitors; D002384:Catalysis; D002460:Cell Line; D006801:Humans; D015394:Molecular Structure; D010802:Phylogeny; D011480:Protease Inhibitors / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D013379:Substrate Specificity
D061945:Caspase Inhibitors; D011480:Protease Inhibitors; D001224:Aspartic Acid; D053454:Caspase 12; D020170:Caspase 1