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PYRIN-containing Apaf1-like proteins (PYPAFs) are members of the nucleotide-binding site/leucine-rich repeat (NBS/LRR) family of signal transduction proteins. We report here that PYPAF7 is a novel PYPAF protein that activates inflammatory signaling pathways. The expression of PYPAF7 is highly restricted to immune cells, and its gene maps to chromosome 19q13.4, a locus that contains a cluster of genes encoding numerous PYPAF family members. Co-expression of PYPAF7 with ASC results in the recruitment of PYPAF7 to distinct cytoplasmic loci and a potent synergistic activation of NF-B. To identify other proteins involved in PYPAF7 and ASC signaling pathways, we performed a mammalian twohybrid screen and identified pro-caspase-1 as a binding partner of ASC. Co-expression of PYPAF7 and ASC results in the synergistic activation of caspase-1 and a corresponding increase in secretion of interleukin-1␤. In addition, PYPAF1 induces caspase-1-dependent cytokine processing when co-expressed with ASC. These findings indicate that PYPAF family members participate in inflammatory signaling by regulating the activation of NF-B and cytokine processing.

The PYRIN domain is a recently identified proteinprotein interaction domain that is found at the N terminus of several proteins thought to function in apoptotic and inflammatory signaling pathways. We report here that PYPAF1 (

PYRIN-containing Apaf-1-like proteins (PYPAFs) are a recently identi¢ed family of proteins thought to function in apoptotic and in£ammatory signaling pathways. PYPAF1 and PYPAF7 proteins have been found to assemble with the PYRIN^CARD protein ASC and coordinate the activation of NF-U UB and pro-caspase-1. To determine if other PYPAF family members function in pro-in£ammatory signaling pathways, we screened ¢ve other PYPAF proteins (PYPAF2, PYPAF3, PY-PAF4, PYPAF5 and PYPAF6) for their ability to activate NF-U UB and pro-caspase-1. Co-expression of PYPAF5 with ASC results in a synergistic activation of NF-U UB and the recruitment of PYPAF5 to punctate structures in the cytoplasm. The expression of PYPAF5 is highly restricted to granulocytes and T-cells, indicating a role for this protein in in£ammatory signaling. In contrast, PYPAF2, PYPAF3, PYPAF4 and PYPAF6 failed to colocalize with ASC and activate NF-U UB. PYPAF5 also synergistically activated caspase-1-dependent cytokine processing when co-expressed with ASC. These ¢ndings suggest that PYPAF5 functions in immune cells to coordinate the transduction of pro-in£ammatory signals to the activation of NF-U UB and pro-caspase-1.