Bradykinin-induced IL-6 expression through bradykinin B2 receptor, phospholipase C, protein kinase Cδ and NF-κB pathway in human synovial fibroblasts

Abstract

Bradykinin (BK) is an inflammatory mediator, and shows elevated levels in regions of severe injury and inflammatory diseases. It has been shown to induce interleukin-6 (IL-6) expression in inflammatory responses in rheumatoid arthritis. We investigated the signaling pathway involved in IL-6 production caused by BK in synovial fibroblasts. BK caused concentration- and time-dependent increases in IL-6 production. By using pharmacological inhibitors or genetic inhibition of the BK receptor, siRNA revealed that B2 but not B1 BK receptors are involved in BK-mediated up-regulation of IL-6. BK-mediated IL-6 production was attenuated by phospholipase C inhibitor (U73122), protein kinase Cδ inhibitor (rottlerin), NF-κB inhibitor (PDTC), IκB protease inhibitor (TPCK) and NF-κB inhibitor peptide. Stimulation of synovial fibroblasts with BK activated IκB kinase α/β (IKK α/β), IκBα phosphorylation, IκBα degradation, p65 phosphorylation at Ser 276, p65 and p50 translocation from the cytosol to the nucleus and κB-luciferase activity. BK mediated an increase of IKK α/β and IκBα phosphorylation, κB-luciferase activity and p65 and p50 binding to the NF-κB element was inhibited by B2 BK receptor antagonist (HOE140), U73122 and rottlerin. Our results suggest that BK increased IL-6 production in synovial fibroblasts via the B2 BK receptor/PI-PLC/PKCδ/and NF-κB signaling pathway.