Transcriptional Regulation of The Porcine GnRH Receptor Gene by Glucocorticoids

The binding of GnRH to its receptor results in the synthesis and secretion of the gonadotropins, as well as stimulation of the gene encoding its own receptor. Thus, the interaction between GnRH and GnRHR represents a central point for regulation of reproductive function. Glucocorticoids can alter reproduction by reducing GnRH responsiveness of gonadotropes within the anterior pituitary gland, potentially via transcriptional regulation of the GnRHR gene. Investigation of this possible mechanism, however, revealed that transcription of the murine GnRHR gene is stimulated by glucocorticoids. To determine the effect of glucocorticoids on porcine GnRHR gene expression, gonadotrope-derived αT3-1 cells were transiently transfected with a vector containing 5118 bp of 5’ flanking sequence for the porcine GnRHR gene fused to luciferase for 12 h and treated with increasing concentrations of the glucocorticoid agonist, dexamethasone (0, 1, 10, 100 and 1,000 nM) for an additional 12 h prior to harvest. Maximal induction of luciferase activity was detected at 100 nM of dexamethasone (2-fold over vehicle; P < 0.05), and this response was blocked by the glucocorticoid antagonist, mifepristone (100 pM). Deletion from 274 to 323 bp upstream of the translational start site eliminated glucocorticoid responsiveness, suggesting the presence of a GRE(s) within this region. Electrophoretic mobility shift assays (EMSA)