Regulatory mechanism of gene expression of peptide (SRIF and TRH) receptors

雌激素（E_2）不仅上调生长抑素（SRIF）受体的结合活性，而且增加垂体细胞中促甲状腺激素释放激素（TRH）受体的转录。本研究的目的是确定E_2调控的SRIF受体亚型，阐明E_2在转录水平上对这些肽激素受体结合活性的作用机制，并了解TRH受体基因5'侧翼区的顺式元件。结果是；(1) E_2在GH_3细胞中以不同方式上调SRIF受体亚型（SSTR1和SSTR2）的mRNA水平，而这种上调发生在没有持续蛋白合成的情况下。(2)采用竞争性逆转录聚合酶链反应（RT-PCR）获得垂体原代培养细胞中5种SRIF受体亚型mRNA水平的定量值，发现原代培养细胞中大量表达SSTR2和SSTR3 mRNA，而GH3细胞中大量表达SSTR1和SSTR2 mRNA。在原代培养细胞中，E_2主要增加SSTR2和SSTR3 mRNA水平，对SSTR1 mRNA水平影响较弱。(3)为了了解E_2对垂体肽受体的转录控制，我们确定了TRH受体5'侧区约1.1kb的核苷酸序列。虽然没有发现典型的TATA box，但发现了许多启动子元件，包括GCF，AP1, AP2，一半GRE，一半TRE共识序列。受体5'侧区没有ERE一致序列，提示E_2效应是由AP1位点介导的，可能是E_2受体与某种类型的转录因子共同作用的结果。

Estrogen (E_2) not only up-regulates the binding acitivity of Somatostatin (SRIF) receptors but also increases transcriptionally Thyrotropin-releasing hormone (TRH) receptors in the pitutary cells.The aim of this study is to determine the subtypes of SRIF receptors regulated by E_2 to elucidate the action mechanism of E_2 on the binding activity of these peptide hormone receptors at the transcriptional level, and to know the cis-elements of TRH receptor gene at 5'flanking region.The results were ; (1) E_2 up-regulated mRNA levels of SRIF recetor subtypes (SSTR1 and SSTR2) in different ways in GH_3 cells, which occurred without ongoing protein synthesis.(2) Competitive reverse transcription-polymerase chain reaction (RT-PCR) used to obtain the quantitative values of mRNA levels of 5 SRIF receptor subtypes in the pituitary primary clutured cells revealed that large amounts of SSTR2 and SSTR3 mRNA were expressed inprimary cultured cells, whereas SSTR1 and SSTR2 mRNA in GH3 cells.In primary clutured cells E_2 primarily increased the mRNA levels of SSTR2 and SSTR3, and affected weakly SSTR1 mRNA level.(3) In an attempt to understand the transciptional control of pituitary peptide receptors by E_2, we have determined the nucleotide sequence of approximately 1.1kb of 5'flanking region of the TRH receptor.Although no typical TATA box was identified, a number of promotor elements was identified, including GCF,AP1, AP2, half GRE,half TRE consensus sequences.The absence of ERE consensus sequence in the 5'flanking region of the receptor suggests that E_2 effect is mediated by the AP1 site possibly as a result of the cooperative action of E_2 receptor and a certain type of transcription factors.