title: Lipid raft- and protein kinase C-mediated synergism between glucocorticoid- and gonadotropin-releasing hormone signaling results in decreased cell proliferation.
abstract: Cross-talk between the glucocorticoid receptor (GR) and other receptors is emerging as a mechanism for fine-tuning cellular responses. We have previously shown that gonadotropin-releasing hormone (GnRH) ligand-independently activates the GR and synergistically modulates glucocorticoid-induced transcription of an endogenous gene in LβT2 pituitary gonadotrope precursor cells. Here, we investigated GR and GnRH receptor (GnRHR) cross-talk that involves co-localization with lipid rafts in LβT2 cells. We report that the GnRHR and a small population of the GR co-localize with the lipid raft protein flotillin-1 (Flot-1) at the plasma membrane and that the GR is present in a complex with Flot-1, independent of the presence of ligands. We found that the SGK-1 gene is up-regulated by Dex and GnRH alone, whereas a combination of both ligands resulted in a synergistic increase in SGK-1 mRNA levels. Using siRNA-mediated knockdown and antagonist strategies, we show that the gene-specific synergistic transcriptional response requires the GR, GnRHR, and Flot-1 as well as the protein kinase C pathway. Interestingly, although several GR cofactors are differentially recruited to the SGK-1 promoter in the presence of Dex and GnRH, GR levels remain unchanged compared with Dex treatment alone, suggesting that lipid raft association of the GR has a role in enhancing its transcriptional output in the nucleus. Finally, we show that Dex plus GnRH synergistically inhibit cell proliferation in a manner dependent on SGK-1 and Flot-1. Collectively the results support a mechanism whereby GR and GnRHR cross-talk within Flot-1-containing lipid rafts modulates cell proliferation via PKC activation and SGK-1 up-regulation.
authors.affiliation: From the Department of Molecular and Cell Biology, Faculty of Science and.
authors.forename: Lancelot
authors.initials: L
authors.lastname: Wehmeyer
authors.forename: Andrea
authors.initials: A
authors.lastname: Du Toit
authors.forename: Dirk M
authors.initials: DM
authors.lastname: Lang
authors.forename: Janet P
authors.initials: JP
authors.lastname: Hapgood
mesh_terms: D000818:Animals; D019556:COS Cells; D049109:Cell Proliferation / Q000187:drug effects*; D002522:Chlorocebus aethiops; D003907:Dexamethasone / Q000819:agonists / Q000494:pharmacology*; D004357:Drug Synergism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000235:genetics; D005938:Glucocorticoids / Q000819:agonists / Q000494:pharmacology*; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists / Q000494:pharmacology*; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism; D021962:Membrane Microdomains / Q000201:enzymology* / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D011493:Protein Kinase C / Q000096:biosynthesis* / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism; D011966:Receptors, LHRH / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D003907:Dexamethasone; D005938:Glucocorticoids; D007987:Gonadotropin-Releasing Hormone; D017874:Immediate-Early Proteins; D008565:Membrane Proteins; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011965:Receptors, Glucocorticoid; D011966:Receptors, LHRH; D000099184:Serum-Glucocorticoid Regulated Kinases; C106354:flotillins
keywords: Cell Proliferation; Flotillin-1; Gene Regulation; Glucocorticoid Receptor; Glucocorticoids; GnRH Receptor; Lipid Rafts; Protein Kinase C (PKC); SGK-1; Synergism