Cutting edge: ASC mediates the induction of multiple cytokines by Porphyromonas gingivalis via caspase-1-dependent and -independent pathways.

Porphyromonas gingivalis (Pg) is a major etiologic agent for chronic periodontitis. Tissue destruction by Pg results partly from induction of host inflammatory responses through TLR2 signaling. This work examines the role of apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC), an adaptor molecule important for TLR-mediated caspase-1 activation. Results demonstrate that ASC levels are stable upon infection of human THP1 monocytic cells with Pg but decrease after cytokine induction. Using short hairpin RNA, we demonstrate an essential role for ASC in induction of IL-1beta by TLR2, 4, and 5 agonists, live Escherichia coli, and Pg. Induction of IL-6, IL-8, IL-10, and TNF also requires ASC, but this induction is not inhibited by IL-1 receptor antagonist or caspase-1 inhibitor. Similar results in U937 indicate broad applicability of these findings. Pg-infected ASC knockdown THP1 cells exhibit reduced transcript levels and NF-kappaB activation. These results suggest a role for ASC in cytokine induction by Pg involving both caspase-1-dependent and -independent mechanisms.