No abstract

Procaspase-9 contains an NH 2 -terminal caspase-associated recruitment domain (CARD), which is essential for direct association with Apaf-1 and activation. Procaspase-1 also contains an NH 2 -terminal CARD domain, suggesting that its mechanism of activation, like that of procaspase-9, involves association with an Apaf-1-related molecule. Here we describe the identification of a human Apaf-1-related protein, named Ipaf that contains an NH 2 -terminal CARD domain, a central nucleotidebinding domain, and a COOH-terminal regulatory leucine-rich repeat domain (LRR). Ipaf associates directly and specifically with the CARD domain of procaspase-1 through CARD-CARD interaction. A constitutively active Ipaf lacking its COOH-terminal LRR domain can induce autocatalytic processing and activation of procaspase-1 and caspase-1-dependent apoptosis in transfected cells. Our results suggest that Ipaf is a specific and direct activator of procaspase-1 and could be involved in activation of caspase-1 in response to pro-inflammatory and apoptotic stimuli.

We report here the identification and functional characterization of two new human caspase recruitment domain (CARD) molecules, termed Pseudo-interleukin-1b converting enzyme (ICE) and ICEBERG. Both proteins share a high degree of homology, reaching 92% and 53% identity, respectively, to the prodomain of caspase-1/ICE. Interestingly, both Pseudo-ICE and ICEBERG are mapped to chromosome 11q22 that bears caspases-1, -4-and -5 genes, all involved in cytokine production rather than in apoptosis. We demonstrate that Pseudo-ICE and ICEBERG interact physically with caspase-1 and block, in a monocytic cell line, the interferon-g and lipopolysaccharide-induced secretion of interleukin-1b which is a well-known consequence of caspase-1 activation. Moreover, Pseudo-ICE, but not ICEBERG, interacts with the CARD-containing kinase RICK/RIP2/CARDIAK and activates NF-kB. Our data suggest that Pseudo-ICE and ICEBERG are intracellular regulators of caspase-1 activation and could play a role in the regulation of IL-1b secretion and NF-kB activation during the pro-inflammatory cytokine response. Cell Death and Differentiation (2001) 8, 649 ± 657.