Insulin augments GnRH-stimulated LHβ gene expression by Egr-1

Previous studies have shown that insulin augments GnRH-stimulated LH synthesis and release from primary gonadotrophs. In this study, regulation of LHβ gene expression by GnRH and insulin was examined in LβT2 cells. Endogenous LHβ mRNA is stimulated 2.4-fold by insulin alone, 2.6-fold by GnRH alone, and 4.7-fold by insulin together with GnRH. This effect of insulin, like GnRH, mapped to sequences -140 to +1 in the mouse LHβ gene. Insulin together with GnRH stimulates activity of an LHβ-reporter gene 7.1-fold; whereas, GnRH alone or insulin alone stimulates the reporter activity 2.8- and 3.1-fold, respectively. Blocking the binding of Egr-1 to sequences -51 to -42 in the LHβ gene inhibits effects of insulin and GnRH. Insulin together with GnRH increases Egr-1 mRNA levels and total Egr-1 binding to LHβ DNA. These findings indicate that insulin may impact regulation of the reproductive axis at the level of the pituitary.