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

Abstract

In pituitary gonadotrophs, GnRH induces expression of the mitogen-activated protein kinases (MAPK3/1) dephosphorylating enzyme, dual-specificity phosphatase 1 (DUSP1). Here we examined DUSP1 expression levels following pulsatile GnRH stimulation of the LbetaT2 gonadotroph cells. DUSP1 expression was increased more prominently following high-frequency (every 30 min) GnRH pulse stimulation (7.02- ± 1.47-fold) than low-frequency (every 120 min) GnRH pulses (2.68- ± 0.09-fold). With high-frequency GnRH pulses, DUSP1 expression increased by 2.89- ± 0.32-fold 2 h after GnRH pulse initiation (four 5-min pulses). DUSP1 expression was not induced following lower frequency GnRH pulses, even when the GnRH concentration was increased. Under high-frequency conditions, MAPK3/1 phosphorylation was observed 10 min after the GnRH pulse and decreased to basal levels after 25 min. However, MAPK3/1 dephosphorylation did not occur concurrently with DUSP1 expression. Overexpression of MAP3K1, a kinase upstream of MAPK3/1, increased both the Lhb and the Fshb subunit promoter activities, which could be completely inhibited by cotransfection with DUSP1-expressing vectors. Serum response factor (Srf) promoter activities induced by MAP3K1 were also prevented by DUSP1 overexpression, confirming that MAPK3/1 has an important role in gonadotropin subunit gene expression. Both high- and low-frequency GnRH pulse stimulation failed to increase the Lhb and Fshb subunit gonadotropin gene expression levels upon DUSP1 overexpression. Our study demonstrates that DUSP1 is specifically expressed following high-frequency GnRH pulses and that this effect may participate in the differential regulation of gonadotropin subunit expression in association with MAPK3/1 phosphorylation.

Growth Differentiation Factor 9 (GDF9) Forms an Incoherent Feed-forward Loop Modulating Follicle-stimulating Hormone β-Subunit (FSHβ) Gene Expression

“…Subsequently, the feedback activity of MKP1, which inactivates MAPK via dephosphorylation, was found to modulate GnRH-induced ERK activation and gonadotropin response to GnRH (34,35). Finally, MKP1 expression was shown to be predominant under high GnRH frequency compared with low GnRH frequency (36). The relationship and relative importance of these various loci which have been implicated in frequency decoding remain to be determined.…”

GnRH pulse frequency-dependent differential regulation of LH and FSH gene expression

“…Coupled with data demonstrating that mutation of the site which governs ERK MKP binding affects ERK2-GFP translocation kinetics in response to continuous, but not pulsatile, GnRH (Armstrong et al, 2010), the findings from this group argue against a major role for MKP's in mediating the decoding of the pulsatile GnRH response. Lastly, studies conducted in LβT2 cells demonstrated a significant increase in dual-specificity kinase 1 (DUSP1) after fast GnRH pulse frequencies compared to control and slow frequency stimulated samples (Purwana et al, 2011). In these LβT2 cells, overexpression of MAP3K1 induced both Fshb and Lhb subunit promoter activities, which was inhibited by cotransfection with DUSP1 expression vectors (Purwana et al, 2011).…”

Interactions between Two Different G Protein-Coupled Receptors in Reproductive Hormone-Producing Cells: The Role of PACAP and Its Receptor PAC1R

“…MAPs are a family of protein phosphatases that inactivate ERK by dephosphorylation of threonine and/or tyrosine residues [44]. MKP expression was predominantly increased following high-rather than low-frequency GnRH pulses [45]. Because MKP induced by high-frequency GnRH pulses dephosphorylates ERK, which is activated by the initial GnRH pulse, ERK phosphorylation induced by a single GnRH pulse during high-frequency GnRH pulse stimulation would return to the basal level more rapidly.…”