Adler Lior, Efrati Edna, Zelikovic Israel
Department of Physiology and Biophysics, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel.
Am J Physiol Cell Physiol. 2008 May;294(5):C1261-76. doi: 10.1152/ajpcell.00486.2007. Epub 2008 Mar 5.
Pendrin, a Cl(-)/anion exchanger encoded by the gene PDS, is highly expressed in the kidney, thyroid, and inner ear epithelia and is essential for bicarbonate secretion, iodide accumulation, and endolymph ion balance, respectively. This study aimed to define promoter regulatory elements essential for renal, thyroid, and inner ear epithelial cell-specific expression of human PDS (hPDS) and to explore the effect of ambient pH and aldosterone on hPDS promoter activity. Endogenous pendrin mRNA and protein were detected in renal HEK293, thyroid LA2, and inner ear VOT36 epithelial cell lines, but not in the fibroblast cell line, NIH3T3. A 4.2-kb hPDS 5'-flanking DNA sequence and consecutive 5'-deletion products were cloned into luciferase reporter vectors and transiently transfected into the above cell lines. Distinct differences in expression/activity of deduced positive/negative regulatory elements within the hPDS promoter between HEK293, LA2, and VOT36 cells were demonstrated, with only basal activity in NIH3T3 cells. Acidic pH (7.0-7.1) decreased and alkaline pH (7.6-7.7) increased hPDS promoter activity in transfected HEK293 and VOT36, but not in LA2 cells. Aldosterone (10(-8) M) reduced hPDS promoter activity in HEK293 but had no effect in LA2 and VOT36 cells. These pH and aldosterone-induced effects on the hPDS promoter occurred within 96-bp and 89-bp regions, respectively, which likely contain distinct response elements to these modulators. Acidic pH and aldosterone decreased, and alkaline pH increased, endogenous pendrin mRNA level in HEK293 cells. In conclusion, pendrin-mediated HCO3(-) secretion in the renal tubule and anion transport in the endolymph may be regulated transcriptionally by systemic pH and aldosterone.
Pendrin是一种由PDS基因编码的Cl⁻/阴离子交换蛋白，在肾脏、甲状腺和内耳上皮细胞中高度表达，分别对碳酸氢盐分泌、碘积累和内淋巴离子平衡至关重要。本研究旨在确定人类PDS（hPDS）在肾脏、甲状腺和内耳上皮细胞特异性表达所必需的启动子调控元件，并探讨环境pH值和醛固酮对hPDS启动子活性的影响。在肾脏HEK293、甲状腺LA2和内耳VOT36上皮细胞系中检测到内源性pendrin mRNA和蛋白，但在成纤维细胞系NIH3T3中未检测到。将一段4.2kb的hPDS 5'-侧翼DNA序列及其连续的5'-缺失产物克隆到荧光素酶报告载体中，并瞬时转染到上述细胞系中。结果表明，HEK293、LA2和VOT36细胞中hPDS启动子内推导的正/负调控元件的表达/活性存在明显差异，而NIH3T3细胞中只有基础活性。酸性pH值（7.0 - 7.1）降低，碱性pH值（7.6 - 7.7）增加转染的HEK293和VOT36细胞中hPDS启动子活性，但对LA2细胞无影响。醛固酮（10⁻⁸ M）降低HEK293细胞中hPDS启动子活性，但对LA2和VOT36细胞无影响。这些pH值和醛固酮对hPDS启动子的诱导作用分别发生在96bp和89bp区域内，这些区域可能含有对这些调节剂的不同反应元件。酸性pH值和醛固酮降低，碱性pH值增加HEK293细胞内源性pendrin mRNA水平。总之，肾小管中pendrin介导的HCO₃⁻分泌和内淋巴中的阴离子转运可能受到全身pH值和醛固酮的转录调控。
