Abstract
Endothelin-1 (ET-1) triggers poorly understood nuclear signaling cascades that control gene expression, cell growth, and differentiation. To better understand how ET-1 regulates gene expression, we asked whether voltage-insensitive Ca2+ channels and Ca2+/calmodulin-dependent protein kinases (CaMKs) propagate signals from ET-1 receptors to the c-fos promoter in mesangial cells. Ca2+ influx through voltage-insensitive Ca2+ channels, one of the earliest postreceptor events in ET-1 signaling, mediated induction of c-fos mRNA and activation of the c-fos promoter by ET-1. A CaMK inhibitor (KN-93) blocked activation of the c-fos promoter by ET-1. Ectopic expression of CaMKII potentiated stimulation by ET-1, providing further evidence that CaMKs contribute to c-fos promoter activation by ET-1. The c-fos serum response element was necessary but not sufficient for CaMKII to activate the c-fos promoter. Activation of the c-fos promoter by ET-1 and CaMKII also required the FAP cis element, an AP-1-like sequence adjacent to the serum response element. Thus, voltage-insensitive Ca2+ channels and CaMKs apparently propagate ET-1 signals to the c-fos promoter that require multiple, interdependent cis elements. Moreover, these experiments suggest an important role for voltage-insensitive Ca2+ channels in nuclear signal transduction in nonexcitable cells.