Regulation of gene expression of a novel G-protein coupled receptor involved in growth hormone secretion

1996年，Merck研究实验室报道了一种新的G蛋白偶联受体的分子克隆，称为生长激素（GH）促分泌素受体（GHS-R），来自猪和人垂体，其结合合成的GH释放肽和非肽基GH促分泌素（GHS）。这种受体的功能是刺激和放大脉冲GH分泌，但其内源性配体仍然未知。GHS-R的发现表明，GH的分泌受三种因素的调节，一种假定的天然GHS和两种下丘脑肽，GH释放激素（GRH）和GH释放抑制激素（生长抑素）。1997年，我们利用RT-PCR和RACE技术克隆了一个大鼠垂体GHS-R的同源基因，该基因属于7跨膜G蛋白偶联受体家族，与猪和人GHS-R在氨基酸水平上的同源性为94- 95%。地高辛标记的cRNA探针原位杂交结果显示，下丘脑弓状核和腹内侧核均表达 ...更多信息 GHS-R mRNA丰富。GHRP已被证明可以刺激动物体内GRH的释放。这一发现为GHS和GHRP作用于下丘脑弓状核以刺激GRH释放从而放大GH脉冲式分泌的观点提供了形态学支持。1998年，我们尝试建立一个能够定量GHS-R mRNA水平的检测系统。可能是因为GHS-R是一种非常罕见的转录本，北方印迹法检测不到GHS-R mRNA，这使得我们开发了一种更敏感和特异的检测方法，即RNA酶保护法。用这种方法，我们成功地检测和定量大鼠GHS-R mRNA在下丘脑和垂体，发现GHS-R mRNA水平每单位总RNA约2.5倍，在内侧基底下丘脑比在垂体前叶。人重组生长激素给药5天，引起垂体中GHS-R mRNA水平的显着下降，但在下丘脑中没有。提示垂体GHS-R表达受GH负调控，其调控方式可能与下丘脑不同。少

In 1996, Merck research laboratory reported molecular cloning of a novel G-protein coupled receptor, termed growth hormone (GH) secretagogue receptor (GHS-R), from porcine and human pituitaries, that binds synthetic GH-releasing peptides and nonpeptidyl GH secretagogues (GHSs). This receptor functions in stimulating and amplifying pulsatile GH secretion although its endogenous ligand remains unknown. The discovery of GHS-R indicates that secretion of GH is regulated by three factors, a putative natural GHS and the two hypothalamic peptides, GH-releasing hormone (GRH) and GH release-inhibiting hormone (somatostatin). Using RT-PCR and a RACE protocol, we cloned a rat homolog of pituitary GHS-R in 1997, which belonged to a family of 7-transmembrane G-protein coupled receptors and showed 94-95 % homology to porcine and human GHS-Rs at amino acid level. In situ hybridization with digoxigenin-labeled cRNA probe revealed that both arcuate and ventromedial nuclei in the hypothalamus expressed … More GHS-R mRNA abundantly. GHRP has been shown to stimulate GRH release in animals. This finding provides a morphological support to the views that GHS and GHRP act on the hypothalamic arcuate nucleus to stimulate GRH release thereby amplifying GH pulsatile secretion. We then tried to set up an assay system capable of quantifying GHS-R mRNA levels in1998. Probably because of being a extremely rare transcript, GHS-R mRNA was not detected with Northern blotting, which lead us to develop a more sensitive and specific assay, i.e. RNase protection assay. With this assay we succeeded in detecting and quantitating rat GHS-R mRNA in both the hypothalamus and the pituitary and found that GHS-R mRNA levels per unit total RNA was approximately 2.5 times greater in the medial basal hypothalamus than in the anterior pituitary. Administration of human recombinant GH for 5 days caused a significant decrease on GHS-R mRNA levels in the pituitary but not in the hypothalamus. This finding suggests that GHS-R expression in the pituitaryis negatively regulated by GH and its regulation might be different from that in the hypothalamus. Less