Specific induction of RGS16 (regulator of G-protein signalling 16) mRNA byprotein kinase C in CEM leukaemia cells is mediated via tumour necrosis factor alpha in a calcium-sensitive manner

The RGS (regulator of G-protein signalling) proteins are GTPase-activating proteins for activated G alpha subunits. We investigated the effects of pro tein kinase C (PKC) on RGS proteins in various T cell lines by treating the m with PMA. mRNA levels of both RGS16 and tumour necrosis factor alpha (TNF alpha) were found to be up-regulated in CEM leukaemia cells in a PKC-depen dent manner. Mezerein, a non-phorbol-ester activator of PKC, also elevated RGS16 and TNF alpha mRNA levels, while the specific PKC inhibitor Go6983 ab rogated their expression. In view of the slower kinetics of PMA-induced RGS 16 expression and the tight correlation between TNF alpha and RGS16 mRNA in duction among the cell lines studied, we suggest that activation of PKC upr egulates RGS16 via TNF alpha. Indeed, addition of recombinant TNF alpha to CEM cells rapidly stimulated RGS16 mRNA expression independently of PKC. Fu rthermore, mobilization of calcium by A23187 and thapsigargin blocked the T NF alpha -mediated induction of RGS16, which was reversed by EGTA and by th e immunosuppressants FK506 and cyclosporin A: suggesting that the calcineur in/NF-AT (nuclear factor of activated T cells) pathway may repress the up-r egulation process, Our results demonstrate for the first time that activati on of PKC induces RGS16 expression via TNF alpha in a calcium-sensitive man ner, thereby implicating RGS16 in the regulation of T cell responses to inf lammation.