title: GPR158, an orphan member of G protein-coupled receptor Family C: glucocorticoid-stimulated expression and novel nuclear role.
abstract: Members of the large G protein-coupled receptor (GPCR) clan are implicated in many physiological and disease processes, making them important therapeutic drug targets. In the present study, we follow up on results of a pilot study suggesting a functional relationship between glucocorticoid (GC)-induced ocular hypertension and GPR158, one of three orphan members of the GPCR Family C. GC treatment increases levels of GPR158 mRNA and protein through transcriptional mechanisms, in cultured trabecular meshwork (TBM) cells derived from the eye's aqueous outflow pathway. Like treatment with GCs, transient overexpression of GPR158 stimulates cell proliferation, while siRNA knockdown of endogenous GPR158 has the opposite effect. Both endogenous and overexpressed GPR158 show an unusual subcellular localization pattern, being found almost entirely in the nucleus. However, when cells are treated with inhibitors of clathrin-mediated endocytosis, GPR158 is shifted to the plasma membrane. Mutation of a bipartite nuclear localization signal (NLS) in the 8(th) helix also shifts GPR158 out of the nucleus, but in this case the protein is found in vesicles localized in the cytoplasm. These results suggest that newly synthesized GPR158 first traffics to the plasma membrane, where it rapidly undergoes endocytosis and translocation to the nucleus. Significantly, mutation of the NLS abrogates GPR158-mediated enhancement of cell proliferation, indicating a functional requirement for nuclear localization. GPR158 overexpression upregulates levels of the cell cycle regulator cyclin D1, but mutation of the NLS reverses this. Overexpression of GPR158 enhances the barrier function of a TBM cell monolayer, which is associated with an increase in the levels of tight junction proteins ZO-1 and occludin, similar to reported studies on GC treatment. Regulated paracellular permeability controls aqueous outflow facility in vivo. Since GCs stimulate GPR158 expression, the result is consistent with a role for elevation of GPR158 expression in GC-induced ocular hypertension.
authors: Institute for Genetic Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America. nitinpat@usc.edu
authors: Nitin
authors: N
authors: Patel
authors: Tatsuo
authors: T
authors: Itakura
authors: Jose M
authors: JM
authors: Gonzalez
authors: Stephen G
authors: SG
authors: Schwartz
authors: M Elizabeth
authors: ME
authors: Fini
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D049109:Cell Proliferation; D002966:Clathrin / Q000378:metabolism; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects / Q000235:genetics; D005123:Eye / Q000378:metabolism; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D009154:Mutation / Q000187:drug effects / Q000235:genetics; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism; D062793:Occludin / Q000235:genetics / Q000378:metabolism; D009798:Ocular Hypertension / Q000235:genetics / Q000378:metabolism; D010865:Pilot Projects; D021381:Protein Transport / Q000187:drug effects / Q000235:genetics; D043562:Receptors, G-Protein-Coupled / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics; D062826:Zonula Occludens-1 Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D002966:Clathrin; D005938:Glucocorticoids; D019913:Nuclear Localization Signals; C568985:OCLN protein, human; D062793:Occludin; D043562:Receptors, G-Protein-Coupled; C569042:TJP1 protein, human; D062826:Zonula Occludens-1 Protein; D019938:Cyclin D1