Martini Claudia N, Romero Damian G, Yanes Licy L, Vila María del C
Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, 1428, Buenos Aires, Argentina.
Life Sci. 2007 Jun 13;81(1):19-25. doi: 10.1016/j.lfs.2007.04.020. Epub 2007 May 1.
Different cytochromes P450 are involved in steroid biosynthesis. These cytochromes have heme as the prosthetic group. We previously reported that ACTH, an activator of glucocorticoid biosynthesis in adrenal, requires heme biosynthesis for a maximal response. In the present study, we investigated the effect of ACTH, and the effect of two activators of the adrenal mineralocorticoid synthesis, endothelin-1 and low sodium diet on 5-aminolevulinate-synthase (ALA-s) mRNA. ALA-s is the rate-limiting enzyme in heme biosynthesis. It was found that infusion of rats with ACTH for 1 h caused an increase of adrenal ALA-s mRNA and activity accompanied by an increase in plasma corticosterone. CYP21, a cytochrome involved in the synthesis of both corticosterone and aldosterone, was not modified at the RNA level in adrenal glands by 1 h of ACTH infusion. Consistently, infusion of endothelin-1 for 1 h increased ALA-s mRNA and aldosterone content in adrenal gland without modifying CYP21 mRNA levels. To study if ALA-s is also regulated by the main physiological stimuli that increase adrenal mineralocorticoid secretion, we fed rats with low salt diet for 2 or 15 days. Low salt diet treatment increased adrenal gland ALA-s mRNA levels. On the other hand, the rapid stimulation of ALA-s mRNA by ACTH which acts through cyclic AMP was confirmed in H295R human adrenocortical cells, the only human adrenal cell line that has a steroid secretion pattern and regulation similar to primary cultures of adrenal cells. Our findings suggest that the acute activation of adrenal steroidogenic cytochromes by trophic hormones involves an increase in heme biosynthesis which will favor the production of active cytochromes.
不同的细胞色素P450参与类固醇生物合成。这些细胞色素以血红素作为辅基。我们之前报道过，促肾上腺皮质激素（ACTH）作为肾上腺糖皮质激素生物合成的激活剂，其最大反应需要血红素生物合成。在本研究中，我们调查了ACTH的作用，以及肾上腺盐皮质激素合成的两种激活剂内皮素-1和低钠饮食对5-氨基酮戊酸合酶（ALA-s）mRNA的影响。ALA-s是血红素生物合成中的限速酶。结果发现，给大鼠输注ACTH 1小时会导致肾上腺ALA-s mRNA和活性增加，同时血浆皮质酮水平升高。CYP21是一种参与皮质酮和醛固酮合成的细胞色素，在肾上腺中，输注ACTH 1小时后其RNA水平未发生改变。同样，输注内皮素-1 1小时会增加肾上腺中ALA-s mRNA和醛固酮含量，而不改变CYP21 mRNA水平。为了研究ALA-s是否也受增加肾上腺盐皮质激素分泌的主要生理刺激的调节，我们用低盐饮食喂养大鼠2天或15天。低盐饮食处理增加了肾上腺ALA-s mRNA水平。另一方面，在H295R人肾上腺皮质细胞中证实了ACTH通过环磷酸腺苷起作用对ALA-s mRNA的快速刺激，H295R是唯一一种具有与肾上腺细胞原代培养相似的类固醇分泌模式和调节方式的人肾上腺细胞系。我们的研究结果表明，营养激素对肾上腺类固醇生成细胞色素的急性激活涉及血红素生物合成增加，这将有利于活性细胞色素的产生。
