No abstract

In humans, the genes for gonadotropin-releasing hormones (GnRH I and GnRH II) have the same modular structure, harboring three introns and four exons. The exons encode a precursor polypeptide consisting of a signaling peptide, the GnRH decapeptide, and the GnRH-associated peptide (GAP) with unknown function [1]. The promoter region of the human (h)GnRH II gene is located at the 5¢ flanking region, the untranslated exon 1, intron 1, and exon 2. The locations of exon 1, intron 1 and exon 2 are )793 ⁄ )750 (relative to the +1 translation start codon ATG), )749 ⁄ )8 and )7 to +154, respectively.Despite Gonadotropin-releasing hormone (GnRH) I and II are hypothalamic decapeptides with pivotal roles in the development of reproductive competence and regulation of reproductive events. In this study, transcriptional regulation of the human GnRH II gene was investigated. By scanning mutation analysis coupled with transient promoter assays, the motif at )641 ⁄ )636 (CATGCC, designated GII-Sil) was identified as a repressor element. Mutation of this motif led to full restoration of promoter activity in TE671 medulloblastoma and JEG-3 placenta choriocarcinoma cells. Supershift and chromatin immunoprecipitation assays showed in vitro and in vivo binding of NF-jB subunit p65 and the retinoic acid receptors, RARa and RXRa, to the promoter sequences. Over-expression of these protein factors indicated that p65 is a potent repressor, and the RARa ⁄ RXRa heterodimer is involved in the differential regulation of the GnRH II gene in neuronal and placental cells. This was confirmed by quantitative real-time PCR. Treatment of cells with the RARa ⁄ RXRa ligands, all-trans retinoic acid and 9-cis-retinoic acid, reduced and increased GnRH II gene expression in TE671 and JEG-3 cells, respectively. Taken together, these data demonstrate the differential roles of NF-jB p65 and RARa ⁄ RXRa, interacting with the same sequence in the promoter of the human GnRH II gene to influence gene expression in a cell-specific manner.

Secretin is a peptide hormone playing multiple functions in the brain-gut axis. In this report, we investigated, by promoter analysis, the potential function of the variable of tandem repeats (VNTR), located at the 5' upstream region of the human secretin gene, and we demonstrated for the first time that this VNTR could downregulate transcription of the human secretin gene in a promoter-specific manner. The efficiency of VNTR in silencing the promoter was found to be directly related the number of repetitive units residing within. We also showed the deoxyribonucleic acid sequence as well as the length polymorphism of the VNTR of 76 Chinese individuals. These results collectively suggest that VNTR could potentially be a functional regulator to control the expression of the human secretin gene in different individuals.