Regulation of the Ca2+channel α2δ-1 subunit expression by epidermal growth factor via the ERK/ELK-1 signaling pathway

Voltage-gated Ca 2+ (Ca V ) channels are expressed in endocrine cells where they contribute to hormone secretion. Diverse chemical messengers, including epidermal growth factor (EGF), are known to affect the expression of Ca V channels. Previous studies have shown that EGF increases Ca 2+ currents in GH3 pituitary cells by increasing the number of high voltage-activated (HVA) Ca V channels at the cell membrane, which results in enhanced prolactin (PRL) secretion. However, little is known regarding the mechanisms underlying this regulation. Here, we show that EGF actually increases the expression of the Ca V α 2 δ-1 subunit, a key molecular component of HVA channels. The analysis of the gene promoter encoding Ca V α 2 δ-1 ( CACNA2D1) revealed binding sites for transcription factors activated by the Ras/Raf/MEK/ERK signaling cascade. Chromatin immunoprecipitation and site-directed mutagenesis showed that ELK-1 is crucial for the transcriptional regulation of CACNA2D1 in response to EGF. Furthermore, we found that EGF increases the membrane expression of Ca V α 2 δ-1 and that ELK-1 overexpression increases HVA current density, whereas ELK-1 knockdown decreases the functional expression of the channels. Hormone release assays revealed that Ca V α 2 δ-1 overexpression increases PRL secretion. These results suggest a mechanism for how EGF, by activating the Ras/Raf/MEK/ERK/ELK-1 pathway, may influence the expression of HVA channels and the secretory behavior of pituitary cells.