Lawson M A, Buhain A R, Jovenal J C, Mellon P L
Department of Reproductive Medicine, Center for Molecular Genetics, University of California, San Diego, La Jolla 92093-0674, USA.
Mol Endocrinol. 1998 Mar;12(3):364-77. doi: 10.1210/mend.12.3.0082.
Neuron-specific expression of the GnRH gene is dependent on an upstream multicomponent enhancer. This enhancer is functional in a small population of GnRH-producing hypothalamic neurons which, through the secretion of GnRH, mediates central nervous system control of reproductive function. GnRH enhancer function requires activation by the GATA family of transcription factors that act through tandem consensus GATA-binding motifs, GATA-A and GATA-B. Here we show that two newly identified DNA-binding factors, termed GBF-A1/A2 and GBF-B1, bind the GnRH enhancer at sites overlapping the GATA factor-binding motifs. In vitro bindings of GATA, GBF-A1/A2, and GBF-B1 to the GnRH enhancer sequences are independent. Specific mutation of either the consensus GATA motif or the GBF-B1 site of GATA-B does not alter binding of the overlapping factor in vitro. Utilizing a GnRH-expressing neuronal cell line as a model system, we show by transient transfection that GBF-B1 is necessary for enhancer activity and independently activates the GnRH promoter. Transactivation of the GnRH enhancer in GT1 cells and in NIH 3T3 cells by GATA-4 is modulated by GBF-B1 binding, suggesting GBF-B1 interferes with GATA factor binding through a steric mechanism.
促性腺激素释放激素（GnRH）基因的神经元特异性表达依赖于一个上游多组分增强子。该增强子在一小群产生GnRH的下丘脑神经元中发挥作用，这些神经元通过分泌GnRH介导中枢神经系统对生殖功能的控制。GnRH增强子功能需要由GATA转录因子家族激活，该家族通过串联共有GATA结合基序GATA - A和GATA - B起作用。在这里，我们表明两个新鉴定的DNA结合因子，称为GBF - A1/A2和GBF - B1，在与GATA因子结合基序重叠的位点结合GnRH增强子。GATA、GBF - A1/A2和GBF - B1与GnRH增强子序列的体外结合是相互独立的。GATA - B的共有GATA基序或GBF - B1位点的特异性突变在体外不会改变重叠因子的结合。利用表达GnRH的神经元细胞系作为模型系统，我们通过瞬时转染表明GBF - B1是增强子活性所必需的，并且能独立激活GnRH启动子。GBF - B1的结合调节了GATA - 4在GT1细胞和NIH 3T3细胞中对GnRH增强子的反式激活，这表明GBF - B1通过空间位阻机制干扰GATA因子的结合。
