Cop, a caspase recruitment domain-containing protein and inhibitor of caspase-1 activation processing

The production of bio-active interleukin-1beta (IL-1beta), a pro-inflammatory cytokine, is mediated by activated Caspase-1. One of the known molecular mechanisms underlying pro-caspase-1 processing and activation involves binding of the Caspase-1 prodomain to a Caspase recruitment domain (CARD)-containing serine/threonine kinase known as RIP2/CARDIAK/RICK. We have identified a novel protein, COP (CARD only protein), which has a high degree of sequence identity to the Caspase-1 prodomain. COP binds to both RIP2 and the Caspase-1 prodomain and inhibits RIP2-induced Caspase-1 oligomerization. COP inhibits caspase- 1-induced IL-1beta secretion as well as lipopolysaccharide-induced IL-1beta secretion in transfected cells. Our data indicate that COP can regulate IL-1beta secretion, implying that COP may play a role in down-regulating inflammatory responses analogous to the CARD protein ICEBERG.