Kim M K, McClaskey J H, Bodenner D L, Weintraub B D
Molecular and Cellular Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 1993 Nov 5;268(31):23366-75.
The human thyrotropin beta (hTSH beta) gene is inducible by various agents including thyrotropin-releasing hormone, phorbol esters, or the adenylyl cyclase activator forskolin. In this study, we have characterized the functional properties of the TGGGTCA motif at -1/+6 of the hTSH beta gene that is similar to the consensus phorbol ester response element (TRE) or the consensus cyclic AMP response element (CRE). We suggest that both protein kinases C and A as well as TRH share a common mediator which recognizes the TGGGTCA element in activating the hTSH beta promoter. Following stimulation by phorbol esters, forskolin, or TRH, the TGGGTCA-specific factor acts together with the pituitary-specific transcription factor Pit-1 (or GHF-1) bound to upstream sequences at -128 to -61 to mediate the induction of the hTSH beta promoter. The induction requires that both factors bind to their own binding sites, but Pit-1 neither increases the binding of the TGGGTCA-specific factor to its target sequences nor associates with this factor to form a heterodimer. The TGGGTCA-specific factor is present in three cell lines tested and is composed of protein(s) immunologically related to c-Jun and c-Fos but not to the CRE-binding protein, CREB. By using the hTSH beta reporter plasmids in which the TGGGTCA element is converted to consensus TRE or CRE motifs, we found that, within the context of the hTSH beta promoter, the TGGGTCA element is a more potent TRE or CRE than the consensus TRE or CRE sequences. Based upon the results of this study, we propose a model in which the TGGGTCA-specific AP-1-like factor functionally cooperates with the tissue-specific factor Pit-1 to activate the hTSH beta gene.
人促甲状腺素β（hTSHβ）基因可被多种因子诱导，包括促甲状腺激素释放激素、佛波酯或腺苷酸环化酶激活剂福斯高林。在本研究中，我们对hTSHβ基因-1/+6处的TGGGTCA基序的功能特性进行了表征，该基序类似于共有佛波酯反应元件（TRE）或共有环磷酸腺苷反应元件（CRE）。我们认为蛋白激酶C和A以及促甲状腺激素释放激素共享一种共同的介导因子，该因子在激活hTSHβ启动子时识别TGGGTCA元件。在受到佛波酯、福斯高林或促甲状腺激素释放激素刺激后，TGGGTCA特异性因子与结合在-128至-61上游序列的垂体特异性转录因子Pit-1（或GHF-1）共同作用，介导hTSHβ启动子的诱导。这种诱导要求两个因子都结合到它们各自的结合位点，但Pit-1既不增加TGGGTCA特异性因子与其靶序列的结合，也不与该因子缔合形成异二聚体。TGGGTCA特异性因子存在于所测试的三种细胞系中，由与c-Jun和c-Fos免疫相关但与CRE结合蛋白CREB无关的蛋白质组成。通过使用其中TGGGTCA元件被转换为共有TRE或CRE基序的hTSHβ报告质粒，我们发现，在hTSHβ启动子的背景下，TGGGTCA元件比共有TRE或CRE序列更有效的TRE或CRE。基于本研究结果，我们提出一个模型，其中TGGGTCA特异性AP-1样因子与组织特异性因子Pit-1在功能上协同作用以激活hTSHβ基因。
