title: Type B gamma-aminobutyric acid receptors modulate the function of the extracellular Ca2+-sensing receptor and cell differentiation in murine growth plate chondrocytes.
abstract: Extracellular calcium-sensing receptors (CaRs) and metabotropic or type B gamma-aminobutyric acid receptors (GABA-B-Rs), two closely related members of family C of the G protein-coupled receptor superfamily, dimerize in the formation of signaling and membrane-anchored receptor complexes. We tested whether CaRs and two GABA-B-R subunits (R1 and R2) are expressed in mouse growth plate chondrocytes (GPCs) by PCR and immunocytochemistry and whether interactions between these receptors influence the expression and function of the CaR and extracellular Ca(2+)-mediated cell differentiation. Both CaRs and the GABA-B-R1 and -R2 were expressed in the same zones of the growth plate and extensively colocalized in intracellular compartments and on the membranes of cultured GPCs. The GABA-B-R1 co-immunoprecipitated with the CaR, confirming a physical interaction between the two receptors in GPCs. In vitro knockout of GABA-B-R1 genes, using a Cre-lox recombination strategy, blunted the ability of high extracellular Ca(2+) concentration to activate phospholipase C and ERK1/2, suppressed cell proliferation, and enhanced apoptosis in cultured GPCs. In GPCs, in which the GABA-B-R1 was acutely knocked down, there was reduced expression of early chondrocyte markers, aggrecan and type II collagen, and increased expression of the late differentiation markers, type X collagen and osteopontin. These results support the idea that physical interactions between CaRs and GABA-B-R1s modulate the growth and differentiation of GPCs, potentially by altering the function of CaRs.
authors.affiliation: Endocrine Research Unit, Department of Veterans Affairs Medical Center, 4150 Clement Street, San Francisco, CA 94121, USA.
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Cheng
authors.forename: Chialing
authors.initials: C
authors.lastname: Tu
authors.forename: Luis
authors.initials: L
authors.lastname: Rodriguez
authors.forename: Tsui-Hua
authors.initials: TH
authors.lastname: Chen
authors.forename: Melita M
authors.initials: MM
authors.lastname: Dvorak
authors.forename: Marta
authors.initials: M
authors.lastname: Margeta
authors.forename: Martin
authors.initials: M
authors.lastname: Gassmann
authors.forename: Bernhard
authors.initials: B
authors.lastname: Bettler
authors.forename: Dolores
authors.initials: D
authors.lastname: Shoback
authors.forename: Wenhan
authors.initials: W
authors.lastname: Chang
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D015415:Biomarkers / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology* / Q000378:metabolism*; D004789:Enzyme Activation; D045604:Extracellular Fluid / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases; D017353:Gene Deletion; D006132:Growth Plate / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000145:classification / Q000378:metabolism; D018080:Receptors, GABA-B / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014018:Tissue Distribution; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D015415:Biomarkers; C485504:Gabbr2 protein, mouse; D020033:Protein Isoforms; D044169:Receptors, Calcium-Sensing; D043562:Receptors, G-Protein-Coupled; D018080:Receptors, GABA-B; D048049:Extracellular Signal-Regulated MAP Kinases; D010738:Type C Phospholipases; D002118:Calcium