Palomino T, Sánchez-Pacheco A, Peña P, Aranda A
Instituto de Investigaciones Biomédicas, CSIC, Madrid, Spain.
FASEB J. 1998 Sep;12(12):1201-9. doi: 10.1096/fasebj.12.12.1201.
The nuclear receptors for thyroid hormone (TRs) and retinoic acid (RARs and RXRs) cooperate with the pituitary-specific transcription factor GHF-1 to activate the rat growth hormone (GH) gene. The GH promoter contains a hormone response element (HRE), which binds TR/RXR and RAR/RXR heterodimers, located close to two binding sites for GHF-1. GHF-1 inhibits binding of TR/RXR and RAR/RXR heterodimers to an isolated HRE. Similarly, the receptors inhibit binding of GHF-1 to its cognate site. These results suggest the existence of direct protein to protein interactions between the receptors and the pituitary transcription factor. This was confirmed by in vitro binding studies with GST fusion proteins, which demonstrated a strong association of GHF-1 with RXR and a weaker interaction with RAR and TR. GHF-1 and the receptor heterodimers form a ternary complex with a fragment of the rat GH promoter, which contains binding sites for both, and GHF-1 increases receptor binding to the promoter when present in limiting conditions. These results suggest that the synergistic activation of the rat GH gene involves protein-DNA interactions as well as a physical association between the nuclear receptors and the pituitary-specific transcription factor GHF-1.
甲状腺激素核受体（TRs）以及视黄酸核受体（RARs和RXRs）与垂体特异性转录因子GHF-1协同作用，以激活大鼠生长激素（GH）基因。GH启动子包含一个激素反应元件（HRE），该元件可结合TR/RXR和RAR/RXR异二聚体，其位置靠近GHF-1的两个结合位点。GHF-1可抑制TR/RXR和RAR/RXR异二聚体与分离出的HRE的结合。同样，这些受体也会抑制GHF-1与其同源位点的结合。这些结果表明，受体与垂体转录因子之间存在直接的蛋白质-蛋白质相互作用。这一点通过与GST融合蛋白进行的体外结合研究得到了证实，该研究表明GHF-1与RXR有很强的结合，而与RAR和TR的相互作用较弱。GHF-1与受体异二聚体与大鼠GH启动子的一个片段形成三元复合物，该片段包含两者的结合位点，并且在有限条件下存在时，GHF-1会增加受体与启动子的结合。这些结果表明，大鼠GH基因的协同激活涉及蛋白质-DNA相互作用以及核受体与垂体特异性转录因子GHF-1之间的物理结合。
