Tauber Philipp, Aichinger B, Christ C, Stindl J, Rhayem Y, Beuschlein F, Warth R, Bandulik S
Medical Cell Biology (P.T., B.A., C.C., J.S., R.W., S.B.), University of Regensburg, 93053 Regensburg, Germany; and Medizinische Klinik und Poliklinik IV (Y.R., F.B.), Ludwig-Maximilians-Universität, 80336 Munich, Germany.
Endocrinology. 2016 Jun;157(6):2489-99. doi: 10.1210/en.2015-2029. Epub 2016 Apr 1.
Adrenal aldosterone-producing adenomas (APAs) are a main cause for primary aldosteronism leading to arterial hypertension. Physiologically, aldosterone production in the adrenal gland is stimulated by angiotensin II and high extracellular potassium. These stimuli lead to a depolarization of the plasma membrane and, as a consequence, an increase of intracellular Ca(2+). Mutations of the plasma membrane Ca(2+)-ATPase ATP2B3 have been found in APAs with a prevalence of 0.6%-3.1%. Here, we investigated the effects of the APA-associated ATP2B3(Leu425_Val426del) mutation in adrenocortical NCI-H295R and human embryonic kidney (HEK-293) cells. Ca(2+) measurements revealed a higher basal Ca(2+) level in cells expressing the mutant ATP2B3. This rise in intracellular Ca(2+) was even more pronounced under conditions with high extracellular Ca(2+) pointing to an increased Ca(2+) influx associated with the mutated protein. Furthermore, cells with the mutant ATP2B3 appeared to have a reduced capacity to export Ca(2+) suggesting a loss of the physiological pump function. Surprisingly, expression of the mutant ATP2B3 caused a Na(+)-dependent inward current that strongly depolarized the plasma membrane and compromised the cytosolic cation composition. In parallel to these findings, mRNA expression of the cytochrome P450, family 11, subfamily B, polypeptide 2 (aldosterone synthase) was substantially increased and aldosterone production was enhanced in cells overexpressing mutant ATP2B3. In summary, the APA-associated ATP2B3(Leu425_Val426del) mutant promotes aldosterone production by at least 2 different mechanisms: 1) a reduced Ca(2+) export due to the loss of the physiological pump function; and 2) an increased Ca(2+) influx due to opening of depolarization-activated Ca(2+) channels as well as a possible Ca(2+) leak through the mutated pump.
肾上腺醛固酮分泌性腺瘤（APA）是导致原发性醛固酮增多症进而引发动脉高血压的主要原因。在生理状态下，肾上腺中醛固酮的产生受血管紧张素II和细胞外高钾的刺激。这些刺激导致质膜去极化，结果是细胞内Ca²⁺增加。质膜Ca²⁺ - ATP酶ATP2B3的突变在APA中被发现，其发生率为0.6% - 3.1%。在此，我们研究了APA相关的ATP2B3（Leu425_Val426del）突变在肾上腺皮质NCI - H295R细胞和人胚肾（HEK - 293）细胞中的作用。Ca²⁺测量显示，表达突变型ATP2B3的细胞中基础Ca²⁺水平更高。在细胞外Ca²⁺浓度高的条件下，细胞内Ca²⁺的这种升高更为明显，表明与突变蛋白相关的Ca²⁺内流增加。此外，具有突变型ATP2B3的细胞似乎输出Ca²⁺的能力降低，提示生理泵功能丧失。令人惊讶的是，突变型ATP2B3的表达引起了一种依赖Na⁺的内向电流，该电流使质膜强烈去极化并破坏了胞质阳离子组成。与这些发现同时出现的是，细胞色素P450家族11亚家族B多肽2（醛固酮合成酶）的mRNA表达显著增加，并且在过表达突变型ATP2B3的细胞中醛固酮产生增强。总之，APA相关的ATP2B3（Leu425_Val426del）突变至少通过两种不同机制促进醛固酮产生：1）由于生理泵功能丧失导致Ca²⁺输出减少；2）由于去极化激活的Ca²⁺通道开放以及可能通过突变泵的Ca²⁺泄漏导致Ca²⁺内流增加。
