Induction of two K+ currents by complement component C5a in mouse macrophages.

Puff application of complement component C5a (5 x 10(-8) M) onto peritoneal macrophages from thioglycollate-stimulated mice induced two kinds of outward current at a holding potential of -68 mV, a slowly-rising sustained outward current and a spike-like transient outward current. Quinidine (2 x 10(-4) M) and tetraethylammonium (10(-2) M) partially suppressed both types of outward current. Charybdotoxin (2 x 10(-6) M) markedly suppressed the spike-like outward current. Reversal potentials in bath solutions of different external K+ concentrations were dependent only on K+ concentrations. The transient current was not suppressed in Ca(2+)-free EGTA-containing solution, but was completely abolished in BAPTA-containing solution. One kind of single channel responding to C5a, which has a single-channel conductance of 29 pS, was recorded from cell-attached patches. These results suggest that C5a activates a Ca(2+)-dependent and another type of K+ current.     

ADAMTS9 activation by interleukin 1β via NFATc1 in OUMS-27 chondrosarcoma cells and in human chondrocytes

ADAMTS9 is a member of the disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) genes, with aggrecan-degrading activity. It has also been characterized to be reactive and highly activated ADAMTS by IL-1β in both chondrosarcoma cells and human chondrocytes (Demircan et al. Arthritis Rheum 52:1451–1460, 2005). In order to understand the regulation of ADAMTS9 gene expression a functional 3.0 kb human ADAMTS9 promoter has been cloned and characterized. A sequence analysis of the promoter revealed the presence of putative binding sites for Nuclear Factor of Activated T cells (NFAT), which is commonly found in the ADAMTS4 and ADAMTS5 promoters. NFATc1 was up-regulated in an activated form by IL-1β in human chondrocytes. The IL-1β inducible ADAMTS9 expression was inhibited by NFAT inhibitors, FK506 and 11Arg (11R)-VIVIT. Furthermore, direct binding of NFATc1 on distal and proximal promoters of ADAMTS9 was demonstrated by a chromatin immunoprecipitation assay. Promoter-reporter assays supported those results. These findings may provide a better understanding of the regulation of ADAMTS9 expression induced by inflammatory cytokines.