Induction of Dual Specificity Phosphatase 1 (DUSP1) by Gonadotropin-Releasing Hormone (GnRH) and the Role for Gonadotropin Subunit Gene Expression in Mouse Pituitary Gonadotroph LbetaT2 Cells1

Abstract

We examined the expression of dual specificity phosphatase 1 (DUSP1) by gonadotropin-releasing hormone (GnRH) stimulation and investigated the role of DUSP1 on gonadotropin gene expression using LbetaT2 gonadotroph cell line. DUSP1 expression was markedly increased 60 min after GnRH stimulation, and mitogen-activated protein kinase 3/1 (MAPK3/1) activation was gradually decreased after 60 min. GnRH-induced MAPK3/1 activation was completely inhibited by U0126, a MEK inhibitor, whereas GnRH-induced DUSP1 expression was partially inhibited by U0126. GnRH-induced DUSP1 induction was inhibited by triptolide, a diterpenoid triepoxide. In contrast, this compound potentiated MAPK3/1 activation. U0126 prevented GnRH-stimulated gonadotropin subunit promoter activation dose dependently, and 10 muM of U0126 reduced the effects of GnRH on the Lhb and Fshb promoters to 79.15% and 55.66%, respectively. GnRH-stimulated activation of Lhb and Fshb promoters as well as serum response factor (Srf) promoters were almost completely inhibited by triptolide, suggesting that this component had a nonspecific effect to the cells. Dusp1 siRNA reduced the expression of DUSP1 and augmented MAPK3/1 phosphorylation, but it did not increase of gonadotropin promoters. By overexpression of DUSP1, both GnRH-stimulated Lhb and Fshb promoters were significantly reduced. We have previously shown that insulin-like growth factor 1 (IGF1) increases MAPK3/1 but does not activate gonadotropin subunit promoters. IGF1 failed to induce DUSP1 expression. In addition, under pulsatile GnRH stimulation, DUSP1 expression was observed following high-frequency GnRH pulses but not following low-frequency pulses. Our study demonstrated that DUSP1, induced by GnRH, functions not only as an MAPK3/1-inactivating phosphatase but also as an important mediator in gonadotropin subunit gene expression regulation.

Induction of Dual-Specificity Phosphatase 1 (DUSP1) by Pulsatile Gonadotropin-Releasing Hormone Stimulation: Role for Gonadotropin Subunit Expression in Mouse Pituitary LbetaT2 Cells1

“…We previously demonstrated that after 12 h of exposure to GnRH pulses, DUSP1 was expressed following high-frequency pulsatile GnRH stimulation but not after low-frequency GnRH pulses [16]. Here, we again confirmed the frequency-dependent induction of DUSP1 expression by pulsatile stimulation of GnRH.…”

“…In separate experiments, we demonstrated that upon pulsatile GnRH stimulation, DUSP1 expression was observed following high-but not lowfrequency GnRH pulses [16], suggesting that DUSP1 may have physiological functions that determine GnRH pulse frequency-dependent differential stimulation of Lhb and Fshb gene expression levels in gonadotrophs.…”

“…We previously showed that DUSP1 overexpression inhibited GnRH-induced gonadotropin promoter activities in static culture [16]. When DUSP1 was present in excess, MAPK3/1 was dephosphorylated, which reduced its effect on gene expression.…”

“…Thus, DUSP1 regulates MAPK signaling and its targets through a negative feedback control mechanism [13][14][15]. In pituitary gonadotrophs, DUSP1 expression is induced by GnRH and affects MAPK3/1 activation as well as its target proteins [16].…”

Regulation of Cytokine and Chemokine Expression by the Ribotoxic Stress Response Elicited by Shiga Toxin Type 1 in Human Macrophage-Like THP-1 Cells

“…Triptolide, a diterpenoid isolated from the Chinese herb Tripterygium wilfordii hook f, has been shown to inhibit DUSP1 induction in various cell types treated with different stimuli (5,46,64). Therefore, we investigated the effect of triptolide and Stx1 treatments on MAPK activation.…”