Characterization of a new upstream GnRH receptor promoter in human ovarian granulosa-luteal cells

Abstract

GnRH has been implicated as an important local autocrine and paracrine factor in regulating ovarian function. However, to date, the transcriptional regulation of GnRH receptor (GnRHR) gene in human ovary remains poorly understood. Here we report the characterization of a new upstream promoter for the GnRHR gene in human granulosa-luteal cells. Using progressive deletion analysis, a region between nucleotide -1300 and -1018 (relative to the translation start site) was shown to exhibit the highest promoter activities in two immortalized human granulosa-luteal cell lines, SVOG-4o and SVOG-4m. Two putative CCAAT/enhancer binding protein (C/EBP) motifs and one GATA motif were identified within this region. Mutational studies showed that these three motifs cooperated synergistically to regulate GnRHR gene transcription in the granulosa cells but not in other cell types including human ovarian carcinoma OVCAR-3, human embryonic kidney-293 (HEK-293) and mouse pituitary gonadotrope-derived αT3-1 cells. Surprisingly, by competitive EMSAs, we found that an Oct-1 consensus sequence was able to inhibit protein complex formation with the distal C/EBP motif, suggesting a possible cross-talk between the Oct-1 transcription factor and this C/EBP motif. Taken together, our results strongly indicate a role of the C/EBP and GATA motifs in regulating GnRHR gene transcription in human granulosa-luteal cells and further suggest that tissue-specific expression of human GnRHR gene is mediated by differential promoter usage.