Multiple Factors Interacting at the GATA Sites of the Gonadotropin-Releasing Hormone Neuron-Specific Enhancer Regulate Gene Expression

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.