Porter Tom E, Ellestad Laura E, Fay Allison, Stewart Joanna L, Bossis Ioannis
Department of Animal and Avian Sciences, University of Maryland, College Park, 20742, USA.
Endocrinology. 2006 May;147(5):2535-43. doi: 10.1210/en.2005-1534. Epub 2006 Feb 9.
GHRH stimulates GH secretion in chickens as in mammals. However, nothing is known about the chicken GHRH receptor (GHRH-R). Here we report the cDNA sequence of chicken GHRH-R. Comparison of the cDNA sequence with the chicken genome localized the GHRH-R gene to chicken chromosome 2 and indicated that the chicken GHRH-R gene consists of 13 exons. Expression of all exons was confirmed by RT-PCR amplification of pituitary mRNA. The amino acid sequence predicted by the GHRH-R cDNA is homologous to that in other vertebrates and contains seven transmembrane domains and a conserved hormone-binding domain. The predicted size of the GHRH-R protein (48.9 kDa) was confirmed by binding of (125)I-GHRH to chicken pituitary membranes and SDS-PAGE. GHRH-R mRNA was readily detected by RT-PCR in the pituitary but not in the hypothalamus, total brain, lung, adrenal, ovary, or pineal gland. Effects of corticosterone (CORT), GHRH, ghrelin, pituitary adenylate cyclase-activating peptide, somatostatin (SRIF), and TRH on GHRH-R and GH gene expression were determined in cultures of chicken anterior pituitary cells. GHRH-R and GH mRNA levels were determined by quantitative real-time RT-PCR. Whereas all treatments affected levels of GH mRNA, only CORT, GHRH, and SRIF significantly altered GHRH-R mRNA levels. GHRH-R gene expression was modestly increased by GHRH and suppressed by SRIF at 4 h, and CORT dramatically decreased levels of GHRH-R mRNA at 72 h. We conclude that adrenal glucocorticoids may substantially impact pituitary GH responses to GHRH in the chicken through modulation of GHRH-R gene expression.
与哺乳动物一样，生长激素释放激素（GHRH）可刺激鸡生长激素（GH）的分泌。然而，关于鸡的GHRH受体（GHRH-R）却一无所知。在此，我们报道鸡GHRH-R的cDNA序列。将该cDNA序列与鸡基因组进行比较，将GHRH-R基因定位到鸡的2号染色体上，表明鸡GHRH-R基因由13个外显子组成。通过垂体mRNA的逆转录聚合酶链反应（RT-PCR）扩增证实了所有外显子的表达。GHRH-R cDNA预测的氨基酸序列与其他脊椎动物的同源，包含7个跨膜结构域和一个保守的激素结合结构域。通过(125)I-GHRH与鸡垂体膜结合及十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）证实了GHRH-R蛋白的预测大小（48.9 kDa）。通过RT-PCR在垂体中很容易检测到GHRH-R mRNA，但在下丘脑、全脑、肺、肾上腺、卵巢或松果体中未检测到。在鸡垂体前叶细胞培养物中测定了皮质酮（CORT）、GHRH、胃饥饿素、垂体腺苷酸环化酶激活肽、生长抑素（SRIF）和促甲状腺激素释放激素（TRH）对GHRH-R和GH基因表达的影响。通过定量实时RT-PCR测定GHRH-R和GH mRNA水平。虽然所有处理都影响GH mRNA水平，但只有CORT、GHRH和SRIF显著改变GHRH-R mRNA水平。GHRH在4小时时适度增加GHRH-R基因表达，SRIF则抑制该表达，而CORT在72小时时显著降低GHRH-R mRNA水平。我们得出结论，肾上腺糖皮质激素可能通过调节GHRH-R基因表达，对鸡垂体GH对GHRH的反应产生重大影响。
