Chang Hong-Wei, Wu Vin-Cent, Huang Chao-Yuan, Huang Hong-Yu, Chen Yung-Ming, Chu Tzong-Shinn, Wu Kwan-Dun, Hsieh Bor-Shen
Nephrology Division, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan.
Am J Physiol Endocrinol Metab. 2008 Mar;294(3):E622-9. doi: 10.1152/ajpendo.00657.2007. Epub 2008 Jan 2.
Aldosterone secretion is subjected to dopaminergic regulation. Our previous study showed that both human D2 and D4 dopamine receptors (D2R and D4R) modulate aldosterone secretion, but in opposing directions. The inhibitory effect of D2R is mediated by attenuating protein kinase C-micro (PKC-micro) and calcium-dependent signaling. The mechanism of D4R effect on angiotensin II (AII)-stimulated aldosterone secretion is explored in this study. Experiments were done with primary human adrenal cortical cells and human adrenocarcinoma (NCI-H295R) cells. Activation of different PKC isoforms was detected by specific phospho-PKC antibodies and PKC translocation. The role of calcium-dependent signaling was examined by measuring the cytoplasmic inositol 1,4,5-triphosphate (IP(3)) and calcium (Ca(2+)). The D4R agonist PD-168,077 enhanced AII-stimulated aldosterone synthesis and secretion as early as 30 min following exposure independently of the modulation of aldosterone synthase (CYP11B2) transcription. CYP11B2 mRNA level elevated by AII was augmented by D4R in the later period. These effects were reversed by the D4R antagonist L-745,870. AII activated PKC-alpha/betaII, -epsilon, and -micro but not PKC-delta, -theta, or -zeta/lambda of H295R cells. The D4R agonist selectively enhanced AII-stimulated PKC-epsilon phosphorylation and its translocation to the cell membrane. Furthermore, the D4R agonist enhanced the AII-stimulated elevation of intracellular IP(3) and Ca(2+). Inhibition of PKC-epsilon translocation by the PKC-epsilon-specific inhibitory peptide attenuated AII-stimulated aldosterone secretion, CYP11B2 mRNA expression, and elevation of intracellular IP(3) and Ca(2+). We conclude that D4R augmented aldosterone synthesis/secretion induced by AII. The mechanisms responsible for this augmentation are mediated through enhancing PKC-epsilon phosphorylation and Ca(2+) elevation.
醛固酮分泌受多巴胺能调节。我们之前的研究表明，人类D2和D4多巴胺受体（D2R和D4R）均调节醛固酮分泌，但作用方向相反。D2R的抑制作用是通过减弱蛋白激酶C-微（PKC-微）和钙依赖性信号传导介导的。本研究探讨了D4R对血管紧张素II（AII）刺激的醛固酮分泌的影响机制。实验在原代人肾上腺皮质细胞和人肾上腺皮质癌（NCI-H295R）细胞中进行。通过特异性磷酸化PKC抗体和PKC转位检测不同PKC同工型的激活。通过测量细胞质肌醇1,4,5-三磷酸（IP(3)）和钙（Ca(2+)）来研究钙依赖性信号传导的作用。D4R激动剂PD-168,077早在暴露后30分钟就增强了AII刺激的醛固酮合成和分泌，且与醛固酮合酶（CYP11B2）转录的调节无关。后期，D4R增强了AII升高的CYP11B2 mRNA水平。这些作用被D4R拮抗剂L-745,870逆转。AII激活了H295R细胞的PKC-α/βII、-ε和-微，但未激活PKC-δ、-θ或-ζ/λ。D4R激动剂选择性增强了AII刺激的PKC-ε磷酸化及其向细胞膜的转位。此外，D4R激动剂增强了AII刺激的细胞内IP(3)和Ca(2+)升高。PKC-ε特异性抑制肽对PKC-ε转位的抑制减弱了AII刺激的醛固酮分泌、CYP11B2 mRNA表达以及细胞内IP(3)和Ca(2+)升高。我们得出结论，D4R增强了AII诱导的醛固酮合成/分泌。这种增强作用的机制是通过增强PKC-ε磷酸化和Ca(2+)升高介导的。
