Roles of calmodulin-dependent protein kinases and phosphatase in calcium-dependent transcription of immediate early genes

Abstract

Recent studies indicate multiple mechanisms are involved in Ca2+ stimulation of gene expression. We have used cell-permeable, specific inhibitors of calmodulin-dependent protein kinases (CaM kinases) and phosphatase (calcineurin) to investigate the involvement of these enzymes in transcriptional regulation of three immediate early genes in PC12 cells stimulated with A23187 or KCl. Preincubation of PC12 cells with the CaM kinase inhibitor KN-62 blocked autophosphorylation of CaM kinase II in response to stimulation by the Ca2+ ionophore A23187. KN-62 treatment also resulted in a 60-70% inhibition of Ca(2+)-dependent transcription of c-fos, NGFI-A (zif 268), and NGFI-B (nur 77) as assessed by either Northern or nuclear run-on analyses. Preincubation with the calcineurin inhibitors FK-506 or cyclosporin A strongly enhanced expression of NGFI-A and blocked transcription of NGFI-B, but it had no significant effect on Ca(2+)-stimulated transcription of c-fos. Both FK-506 and KN-62 were specific for Ca(2+)-stimulated transcription as neither effected transcription in response to forskolin or phorbol ester (12-O-tetradecanoylphorbol-13-acetate) treatment. This is the first report of CaM kinase and calcineurin involvement in transcriptional regulation of NGFI-A and NGFI-B. Activation of CaM kinases and calcineurin, in response to elevated intracellular Ca2+, would exert antagonistic effects on transcription of NGFI-A. Since inhibition of either the kinase or phosphatase decreased transcription of NGFI-B by 60-90%, this suggests that each enzyme is necessary but not sufficient for Ca2+ stimulation. These results indicate that CaM kinases and calcineurin can mediate broad and complex regulation of Ca(2+)-stimulated gene expression.