Morishita M, Iwasaki Y, Onishi A, Asai M, Mutsuga N, Yoshida M, Oiso Y, Inoue K, Murohara T
Department of Medicine, Nagoya University Graduate School of Medicine and Hospital, Nagoya 466-8550, Japan.
J Mol Endocrinol. 2003 Dec;31(3):441-8. doi: 10.1677/jme.0.0310441.
The two hypothalamic hormones, GH-releasing hormone (GHRH) and somatostatin (SRIF), are known to regulate GH secretion. However, the effects of these hormones on GH gene expression are not completely clear, partly because of the lack of appropriate host cells maintaining the original characteristics of the somatotroph. Since MtT/S, a pure somatotroph cell line, has become available, the effects of GHRH and SRIF on GH gene transcription have been studied using a subclone of MtT/S (MtT/SGL), in which the GH gene 5'-promoter-luciferase fusion gene was stably incorporated. The expression of GHRH receptor and SRIF receptor subtypes was also studied by RT-PCR. The results showed that MtT/SGL cells intrinsically expressed the functional GHRH receptor and all of the SRIF receptor subtypes. The expression of GHRH receptor was markedly enhanced by glucocorticoid pretreatment and, in the presence of corticosterone and 3-isobutyl-1-methylxanthine, GHRH (at or above 100 pM) stimulated GH gene 5'-promoter activity in a dose-dependent manner. On the other hand, SRIF (100 nM) significantly antagonized the effect of GHRH, which was completely reversed by pretreatment with pertussis toxin (50 ng/ml). Taken together, the present data indicated that both GHRH and SRIF are involved in the transcriptional regulation of the GH gene, and that the effect of SRIF is mediated through pertussis toxin-sensitive G protein. The MtT/SGL cell line is a good in vitro model for studying the molecular mechanisms of GH gene transcription by GHRH and/or SRIF.
已知两种下丘脑激素，即生长激素释放激素（GHRH）和生长抑素（SRIF）可调节生长激素（GH）的分泌。然而，这些激素对GH基因表达的影响尚不完全清楚，部分原因是缺乏维持生长激素细胞原始特性的合适宿主细胞。自从纯生长激素细胞系MtT/S可用以来，已使用MtT/S的一个亚克隆（MtT/SGL）研究了GHRH和SRIF对GH基因转录的影响，该亚克隆中稳定整合了GH基因5'-启动子-荧光素酶融合基因。还通过逆转录聚合酶链反应（RT-PCR）研究了GHRH受体和SRIF受体亚型的表达。结果表明，MtT/SGL细胞固有地表达功能性GHRH受体和所有SRIF受体亚型。糖皮质激素预处理可显著增强GHRH受体的表达，并且在存在皮质酮和3-异丁基-1-甲基黄嘌呤的情况下，GHRH（100 pM及以上）以剂量依赖的方式刺激GH基因5'-启动子活性。另一方面，SRIF（100 nM）显著拮抗GHRH的作用，百日咳毒素（50 ng/ml）预处理可完全逆转这种作用。综上所述，目前的数据表明GHRH和SRIF均参与GH基因的转录调控，并且SRIF的作用是通过百日咳毒素敏感的G蛋白介导的。MtT/SGL细胞系是研究GHRH和/或SRIF对GH基因转录分子机制的良好体外模型。
