Involvement of Both Gq/11 and Gs Proteins in Gonadotropin-releasing Hormone Receptor-mediated Signaling in LβT2 Cells

• Published in: The Journal of biological chemistry 2002-08, Vol.277 (35), p.32099-32108
• Main Authors: Liu, Fujun, Usui, Isao, Evans, Lui Guojing, Austin, Darrell A., Mellon, Pamela L., Olefsky, Jerrold M., Webster, Nicholas J.G.
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M203639200

The hypothalamic hormone gonadotropin-releasing hormone (GnRH) stimulates the synthesis and release of the pituitary gonadotropins. GnRH acts through a plasma membrane receptor that is a member of the G protein-coupled receptor (GPCR) family. These receptors interact with heterotrimeric G proteins to initiate downstream signaling. In this study, we have investigated which G proteins are involved in GnRH receptor-mediated signaling in LβT2 pituitary gonadotrope cells. We have shown previously that GnRH activates ERK and induces the c- fos and LHβ genes in these cells. Signaling via the G i subfamily of G proteins was excluded, as neither ERK activation nor c-Fos and LHβ induction was impaired by treatment with pertussis toxin or a cell-permeable peptide that sequesters Gβγ-subunits. GnRH signaling was partially mimicked by adenoviral expression of a constitutively active mutant of Gα q (Q209L) and was blocked by a cell-permeable peptide that uncouples Gα q from GPCRs. Furthermore, chronic activation of Gα q signaling induced a state of GnRH resistance. A cell-permeable peptide that uncouples Gα s from receptors was also able to inhibit ERK, c-Fos, and LHβ, indicating that both G q/11 and G s proteins are involved in signaling. Consistent with this, GnRH caused GTP loading on G s and G q/11 and increased intracellular cAMP. Artificial elevation of cAMP with forskolin activated ERK and caused a partial induction of c-Fos. Finally, treatment of Gα q (Q209L)-infected cells with forskolin enhanced the induction of c-Fos showing that the two pathways are independent and additive. Taken together, these results indicate that the GnRH receptor activates both G q and G s signaling to regulate gene expression in LβT2 cells.