Ca2+/calmodulin-dependent protein kinase II stimulates c-fos transcription and DNA synthesis by a Src-based mechanism in glomerular mesangial cells.

Abstract

Mesangial cell growth factors elevate intracellular free [Ca2+]i, but mechanisms linking [Ca2+]i to gene expression and DNA synthesis are unclear. This study investigated the hypothesis that Ca2+/calmodulin-dependent protein kinase II (CaMK II), which is activated by elevated [Ca2+]i, increases c-fos transcription and DNA synthesis via a Src-based mechanism. In cultured rat mesangial cells, dominant negative Src (SrcK-) blocked activation of the c-fos gene promoter by CaMK II 290, a constitutively active form of CaMK IIalpha. Activation of the c-fos promoter by CaMK II 290 was also blocked by COOH-terminal Src kinase, which phosphorylates and inactivates c-Src. A pharmacologic CaMK inhibitor, KN-93, did not block activation of the c-fos promoter by ectopically expressed v-Src. Stimulation of c-Src by endothelin-1 required CaMK II activity, further supporting the notion that CaMK II acts upstream of Src in a signaling cassette. Activation of the c-fos promoter by CaMKII290 and Src required the c-fos serum response element. Dominant negative SrcK- also blocked induction of DNA synthesis in mesangial cells by CaMK II 290. Collectively, these results suggest that in mesangial cells Src protein tyrosine kinases act downstream of CaMKII in a signaling pathway in which [Ca2+]i induces the c-fos promoter and increases DNA synthesis.