Differential effects of protein kinase C inhibitors on chemokine production in human synovial fibroblasts

1 Rheumatoid arthritis is associated with the accumulation and activation of selected populations of inflammatory cells within the arthritic joint. One putative signal for this process is the production, by resident cells, of a group of inflammatory mediators known as the chemokines. 2 The chemokines interleukin‐8 (IL‐8), monocyte chemotactic protein‐1 (MCP‐1) and RANTES (regulated on activation normal T‐cell expressed and presumably secreted) are target‐cell specific chemoattractants produced by synovial fibroblasts in response to stimulation with interleukin‐la (IL‐1α) or tumour necrosis factor α (TNFα). The signalling pathways involved in their production are not well defined. We therefore used four different protein kinase C inhibitors to investigate the role of this kinase in the regulation of chemokine mRNA and protein expression in human cultured synovial fibroblasts. 3 The non‐selective PKC inhibitor, staurosporine (1–300 nM) significantly increased the production of IL‐1α‐induced IL‐8 mRNA and protein. A specific PKC inhibitor, chelerythrine chloride (0.1–3 μm), also caused a small concentration‐dependent increase in IL‐8 mRNA and protein production. In contrast, 3‐[1‐[3‐(amidinothio)propyl]‐3‐indoly]‐4‐(1‐methyl‐3‐indolyl)‐1H‐pyrrole‐2,5‐dione methanesul‐phonate (Ro 31–8220) and 2[1‐(3‐dimethylaminopropyl)‐1H‐indol‐3‐yl]‐3‐(1H‐indol‐3‐yl)‐maleimide (GF 109203X), two selective PKC inhibitors of the substituted bisindolylmaleimide family had a concentration‐dependent biphasic effect on IL‐1α or TNFα‐induced chemokine expression. At low concentrations they caused a stimulation in chemokine production, which was especially evident at the mRNA level. At higher concentrations both inhibited IL‐1α or TNFα‐induced chemokine mRNA and protein production. Ro 31–8220 was 10 fold more potent than GF 109203X, with an IC50 of 1.6±0.08 μm (mean±s.e.mean, n = 4) for IL‐1α induced IL‐8 production. Ro 31–8220 also inhibited the expression of IL‐1α or TNFα‐induced MCP‐1 and RANTES mRNA with a similar potency. 4 The stimulatory effect of staurosporine is discussed in relation to the known poor selectivity of this inhibitor for PKC. It is proposed that activation of an isoform of PKC, possibly PKC epsilon or zeta, which is inhibited by higher concentrations of the bisinodolylmaleimides, plays a role in the regulation of chemokine expression induced by IL‐1α or TNFα in synovial cells. 5 The inhibition of chemokine production by bisindolylmaleimide compounds heralds a n