SUPPRESSION BY CYCLOSPORINE-A OF INTERLEUKIN 1-BETA-INDUCED EXPRESSION OF GROUP-II PHOSPHOLIPASE A(2) IN RAT RENAL MESANGIAL CELLS

1 We investigated whether cyclosporin A, a potent immunosuppressive dr ug, affects group II phospholipase A(2) (PLA(2); EC 3.1.1.4) induction in rat renal mesangial cells. 2 Previously we showed that the express ion of group II PLA(2) in rat renal mesangial cells is triggered by ex posure of the cells to inflammatory cytokines such as interleukin 1 be ta (IL-1 beta) or tumour necrosis factor alpha and agents that elevate cellular levels of cyclic AMP. Treatment of mesangial cells with IL-1 beta for 24 h induced PLA(2) activity secreted into cell culture supe rnatants by about 16 fold. Incubation of mesangial cells with cyclospo rin A inhibited IL-1 beta-induced PLA(2) section in a dose-dependent f ashion, with an IC50 value of 4.3 mu M. Cyclosporin A did not directly inhibit enzymatic activity of PLA(2). 3 Immunoprecipitation of radioa ctively labelled PLA(2) protein from mesangial cell supernatants revea led that the inhibition of PLA(2) activity is due to a suppression of PLA(2) protein levels. This effect was preceded by a reduction of PLA( 2) mRNA steady state levels, as demonstrated by Northern blot analyses of total cellular RNA isolated from stimulated mesangial cells. 4 In order to evaluate whether cyclosporin A would affect the transcription al activity of the PLA(2) gene, we performed nuclear run on transcript ion experiments and provided evidence chat the transcription rate of t he PLA(2) gene is reduced by cyclosporin A. 5 Previously we found that the nuclear transcription factor kappa B (NF kappa B) is an essential component of the IL-1 beta-dependent upregulation of PLA(2) gene tran scription. By electrophoretic mobility shift analysis, we demonstrated that cyclosporin A diminishes the formation of NF kappa B DNA-binding complexes, thus suggesting that this transcription factor is a target for cyclosporin A-mediated repression of PLA(2) gene transcription. 6 The data presented in this study strongly suggest that the cellular m echanism involved in the IL1 beta dependent transcriptional upregulati on of the PLA(2) gene in mesangial cells is a target for the action of cyclosporin A.