Transcriptional regulation of T-type calcium channel Ca_V3.2: Bi-directionality by early growth response 1 (Egr1) and repressor element 1 (RE-1) protein -silencing transcription factor (REST)

The pore-forming Ca²⁺ channel subunit Ca_V3.2 mediates a low voltage-activated (T-type) Ca²⁺ current (I_CaT) that contributes pivotally to neuronal and cardiac pacemaker activity. Despite the importance of tightly regulated Ca_V3.2 levels, the mechanisms regulating its transcriptional dynamics are not well understood. Here, we have identified two key factors that upand down-regulate the expression of the gene encoding Ca_V3.2 (Cacna1h). First, we determined the promoter region and observed several stimulatory and inhibitory clusters. Furthermore, we found binding sites for the transcription factor early growth response 1 (Egr1/Zif268/Krox-24) to be highly overrepresented within the Ca_V3.2 promoter region. mRNA expression analyses and dual-luciferase promoter assays revealed that the Ca_V3.2 promoter was strongly activated by Egr1 overexpression in vitro and in vivo. Subsequent chromatin immunoprecipitation assays in NG108-15 cells and mouse hippocampi confirmed specific Egr1 binding to the Ca_V3.2 promoter. Congruently, whole-cell I_CaT values were significantly larger after Egr1 overexpression. Intriguingly, Egr1-induced activation of the Ca_V3.2 promoter was effectively counteracted by the repressor element 1-silencing transcription factor (REST). Thus, Egr1 and REST can bi-directionally regulate Ca_V3.2 promoter activity and mRNA expression and, hence, the size of I_CaT. This mechanism has critical implications for the regulation of neuronal and cardiac Ca²⁺ homeostasis under physiological conditions and in episodic disorders such as arrhythmias and epilepsy.