Department of Cell Biology, Centre for Research and Advanced Studies (Cinvestav), Mexico City, Mexico.
School of Medicine FES Iztacala, National Autonomous University of Mexico (UNAM), Tlalnepantla, Mexico.
Am J Physiol Endocrinol Metab. 2020 Jul 1;319(1):E232-E244. doi: 10.1152/ajpendo.00007.2020. Epub 2020 May 5.
Voltage-gated Ca (Ca) 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 channels. Previous studies have shown that EGF increases Ca currents in GH3 pituitary cells by increasing the number of high voltage-activated (HVA) Ca 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 Caαδ-1 subunit, a key molecular component of HVA channels. The analysis of the gene promoter encoding Caαδ-1 () 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 in response to EGF. Furthermore, we found that EGF increases the membrane expression of Caαδ-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 Caαδ-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.
电压门控钙 (Ca) 通道在内分泌细胞中表达，它们有助于激素分泌。多种化学信使，包括表皮生长因子 (EGF)，已知会影响 Ca 通道的表达。先前的研究表明，EGF 通过增加细胞膜上的高电压激活 (HVA) Ca 通道的数量来增加 GH3 垂体细胞中的 Ca 电流，从而增强催乳素 (PRL) 的分泌。然而，对于这种调节的机制知之甚少。在这里，我们表明 EGF 实际上增加了 Caαδ-1 亚基的表达，Caαδ-1 是 HVA 通道的关键分子组成部分。对编码 Caαδ-1 的基因启动子的分析显示，存在转录因子结合位点，这些转录因子被 Ras/Raf/MEK/ERK 信号级联激活。染色质免疫沉淀和定点诱变表明，ELK-1 对于 EGF 响应中 Caαδ-1 的转录调控至关重要。此外，我们发现 EGF 增加了 Caαδ-1 的膜表达，而 ELK-1 的过表达增加了 HVA 电流密度，而 ELK-1 的敲低则降低了通道的功能表达。激素释放测定表明，Caαδ-1 的过表达增加了 PRL 的分泌。这些结果表明了 EGF 通过激活 Ras/Raf/MEK/ERK/ELK-1 途径来影响 HVA 通道表达和垂体细胞分泌行为的机制。
