INCA, a Novel Human Caspase Recruitment Domain Protein That Inhibits Interleukin-1β Generation*

Using in silico methods for screening the human genome for new caspase recruitment domain (CARD) proteins, we have identified INCA (Inhibitory CARD) as a protein that shares 81% identity with the prodomain of caspase-1. The INCA gene is located on chromosome 11q22 between the genes of COP/Pseudo-ICE and ICEBERG, two other CARD proteins that arose from caspase-1 gene duplications. We show that INCA mRNA is expressed in many tissues. INCA is specifically upregulated by interferon-γ in the monocytic cell lines THP-1 and U937. INCA physically interacts with procaspase-1 and blocks the release of mature IL-1β from LPS-stimulated macrophages. Unlike COP/Pseudo-ICE and procaspase-1, INCA does not interact with RIP2 and does not induce NF-κB activation. Our data show that INCA is a novel intracellular regulator of procaspase-1 activation, involved in the regulation of pro-IL-1β processing and its release during inflammation.