title: Involvement of both G(q/11) and G(s) proteins in gonadotropin-releasing hormone receptor-mediated signaling in L beta T2 cells.
abstract: 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 L beta T2 pituitary gonadotrope cells. We have shown previously that GnRH activates ERK and induces the c-fos and LH beta genes in these cells. Signaling via the G(i) subfamily of G proteins was excluded, as neither ERK activation nor c-Fos and LH beta induction was impaired by treatment with pertussis toxin or a cell-permeable peptide that sequesters G beta gamma-subunits. GnRH signaling was partially mimicked by adenoviral expression of a constitutively active mutant of G alpha(q) (Q209L) and was blocked by a cell-permeable peptide that uncouples G alpha(q) from GPCRs. Furthermore, chronic activation of G alpha(q) signaling induced a state of GnRH resistance. A cell-permeable peptide that uncouples G alpha(s) from receptors was also able to inhibit ERK, c-Fos, and LH beta, 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 G alpha(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 L beta T2 cells.
authors.affiliation: Department of Medicine, University of California, San Diego, California 92093, USA.
authors.forename: Fujun
authors.initials: F
authors.lastname: Liu
authors.forename: Isao
authors.initials: I
authors.lastname: Usui
authors.forename: Lui Guojing
authors.initials: LG
authors.lastname: Evans
authors.forename: Darrell A
authors.initials: DA
authors.lastname: Austin
authors.forename: Pamela L
authors.initials: PL
authors.lastname: Mellon
authors.forename: Jerrold M
authors.initials: JM
authors.lastname: Olefsky
authors.forename: Nicholas J G
authors.initials: NJ
authors.lastname: Webster
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry; D037342:Pertussis Toxin; D010902:Pituitary Gland; D017346:Protein Serine-Threonine Kinases; D051381:Rats; D011966:Receptors, LHRH / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014357:Trypsin; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D009687:Nuclear Proteins; D010446:Peptide Fragments; D011966:Receptors, LHRH; D011993:Recombinant Fusion Proteins; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D037342:Pertussis Toxin; D017346:Protein Serine-Threonine Kinases; C087996:STK19 protein, human; D020928:Mitogen-Activated Protein Kinases; D014357:Trypsin; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019205:GTP-Binding Protein alpha Subunits, Gs; D020962:Heterotrimeric GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate