Abstract 3986: Protein-bound polysaccharide induces IL-1β via NLRP3 inflammasome activation.

Abstract

Abstract Protein-bound polysaccharide-K (PSK) is a hot water extract from Trametes Versicolor mushroom. It is widely used in Asian countries for its immune enhancing and anti-cancer potential. We have recently reported that PSK activates TLR2 and has CD8 T cell- and NK cell- dependent anti-tumor activity. PSK stimulates the production of multiple pro-inflammatory cytokines, including IL-1β, the production of which requires both TLR and inflammasome activation. The current study was undertaken to investigate the mechanism by which PSK activates inflammasome and induces IL-1β. RT-PCR and Western blot analyses showed that PSK induces pro-IL-1β in a dose- and time- dependent manner. PSK activates caspase-1 and pre-incubation with z-VAD-FMK, a caspase inhibitor, abolishes PSK-induced IL-1β. Comparison of THP-1 cells and THP-1 cells deficient for NLRP3 demonstrated that PSK-induced IL-1β production requires NLRP3 inflammasome. PSK also up-regulates the expression of NLRP3 mRNA. Further experiments were performed to investigate whether potassium efflux, reactive oxygen species (ROS) generation, or lysosomal perturbation was involved in PSK-induced NLRP3 inflammasome activation. Results showed that CA-074-Me, a cathepsin B inhibitor, significantly decreased PSK-induced IL-1β, while the production of TNF-α was not affected. Phagocytosis or ROS generation was not required for PSK-induced NLRP3 inflammasome activation. Altogether, our results suggest that PSK-induced IL-1β production is a two step process. Step 1 requires TLR2-dependent induction of pro-IL-1β and upregulation of NLRP3 expression; Step 2 involves NLRP3 inflammasome activation in a cathepsin B-dependent manner. These results provide novel insights into the mechanisms of the immune stimulatory and anti-tumor effects of PSK. Citation Format: Yi Yang, Carol Inatsuka, Mary L. Disis, Hailing Lu. Protein-bound polysaccharide induces IL-1β via NLRP3 inflammasome activation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3986. doi:10.1158/1538-7445.AM2013-3986