Mice deficient in IL-1 beta-converting enzyme are defective in production of mature IL-1 beta and resistant to endotoxic shock

Molecular cloning and pro-apoptotic activity of ICErelII and ICErelIII, members of the ICE/CED-3 family of cysteine proteases

Cysteine proteases related to mammalian interleukin-1 beta-converting enzyme (ICE) and the nematode cell death abnormal ced-3 gene product have been implicated in the effector mechanism of apoptotic cell death. Two novel members of this new family of ICE/CED-3-related proteases, designated ICErel-II and ICErel-III, were cloned from human monocytic cells. Both were highly homologous to human ICE (52% identical) and CED-3 (25% identical) and both contained the absolutely conserved pentapeptide sequence Gln-Ala-Cys-Arg-Asp containing the catalytic cysteine residue. Other structural motifs that were comparable with ICE suggest that ICErel-II and ICErel-III are also synthesized as larger proenzymes which are proteolytically processed to form heterodimeric active enzymes. Pro-interleukin-1 beta processing activity could not be detected in cells transfected with ICErel-II or ICErel-III, but pro-domain-less truncated forms of ICErel-II and ICErel-III were capable of effectively inducing fibroblast apoptosis. ICErel-II and ICErel-III may, therefore, participate in proteolytic events culminating in the apoptotic death of human cells.

Identification and characterization of ICH-2, a novel member of the interleukin-1 beta-converting enzyme family of cysteine proteases

Interleukin-1 beta converting enzyme (ICE) is a cytoplasmic cysteine protease required for generating the bioactive form of the interleukin-1 beta cytokine from its inactive precursor. We report the identification of ICH-2, a novel human gene encoding a member of the ICE cysteine protease family, and characterization of its protein product. ICH-2 mRNA is widely expressed in human tissues in a pattern similar to, but distinct from, that of ICE. Overexpression of ICH-2 in insect cells induces apoptosis. Purified ICH-2 is functional as a protease in vitro. A comparison of the inhibitor profiles and substrate cleavage by ICH-2 and ICE shows that the enzymes share catalytic properties but may differ in substrate specificities, suggesting that the two enzymes have different functions in vivo.

Yama/CPP32 beta, a mammalian homolog of CED-3, is a CrmA-inhibitable protease that cleaves the death substrate poly(ADP-ribose) polymerase

Although the mechanism of mammalian apoptosis has not been elucidated, a protease of the CED-3/ICE family is anticipated to be a component of the death machinery. Several lines of evidence predict that this protease cleaves the death substrate poly(ADP-ribose) polymerase (PARP) to a specific 85 kDa form observed during apoptosis, is inhibitable by the CrmA protein, and is distinct from ICE. We cloned a ced-3/ICE-related gene, designated Yama, that encodes a protein identical to CPP32 beta. Purified Yama was a zymogen that, when activated, cleaved PARP to generate the 85 kDa apoptotic fragment. Cleavage of PARP by Yama was inhibited by CrmA but not by an inactive point mutant of CrmA. Furthermore, CrmA blocked cleavage of PARP in cells undergoing apoptosis. We propose that Yama may represent an effector component of the mammalian cell death pathway and suggest that CrmA blocks apoptosis by inhibiting Yama.

Cytokine-processing enzymes. Stopping the cuts

The recently discovered enzymes that process the precursors of inflammatory cytokines are good targets for the design of new anti-inflammatory therapeutic agents.

ICE-like proteases in apoptosis

The discovery of structural and functional similarities between the product of the nematode cell-death gene ced-3 and mammalian interleukin-1 beta-converting enzyme (ICE) is providing important insights into the molecular mechanism of apoptosis. This article summarizes the current knowledge of ICE and its homologues, and how these may be involved in regulating apoptosis.