title: Transforming growth factor-beta stimulates inorganic phosphate transport and expression of the type III phosphate transporter Glvr-1 in chondrogenic ATDC5 cells.
abstract: Members of the transforming growth factor (TGF)-beta family are important regulators of skeletal development. In this study, we investigated the effect of TGF-beta1 on inorganic phosphate (Pi) transport and on expression of the type III Pi carriers Glvr-1 and Ram-1 in murine ATDC5 chondrocytes. TGF-beta1 induced a selective, dose- and time-dependent increase in sodium-dependent Pi transport in ATDC5 cells. This response was dependent on RNA and protein synthesis and reflected a change in the maximal rate of the transport system, suggesting that TGF-beta1 induces the synthesis of new Pi carriers and their insertion into the plasma membrane. Consistently, Northern blotting analysis showed a dose-dependent increase in Glvr-1 messenger RNA expression in response to TGF-beta1, which preceded the maximal stimulation of Pi transport by several hours. Glvr-1 thus likely mediates at least part of the increase in Pi uptake induced by TGF-beta1. Ram-1 messenger RNA expression was not affected by TGF-beta1. TGF-beta1 activated the Smad signaling pathway and the mitogen-activated protein kinases ERK and p38 in ATDC5 cells. Unlike the regulation of Pi transport by receptor tyrosine kinase agonists in osteoblasts, the effect of TGF-beta1 on Pi uptake in ATDC5 cells did not involve protein kinase C or mitogen-activated protein kinases, suggesting that a specific, possibly Smad-dependent, signal mediates this response. In conclusion, TGF-beta1 stimulates Pi transport and Glvr-1 expression in chondrocytes, suggesting that, like proliferation, differentiation, and matrix synthesis, Pi handling is subject to regulation by TGF-beta3 family members in bone-forming cells.
authors.affiliation: Department of Internal Medicine, University Hospital, Geneva, Switzerland.
authors.forename: G
authors.initials: G
authors.lastname: Palmer
authors.forename: J
authors.initials: J
authors.lastname: Guicheux
authors.forename: J P
authors.initials: JP
authors.lastname: Bonjour
authors.forename: J
authors.initials: J
authors.lastname: Caverzasio
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D015152:Blotting, Northern; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D019902:Chondrocytes / Q000378:metabolism*; D004789:Enzyme Activation; D015870:Gene Expression / Q000187:drug effects*; D020935:MAP Kinase Signaling System; D051379:Mice; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D011991:Receptors, Virus / Q000235:genetics* / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D010710:Phosphates; D047428:Protein Kinase Inhibitors; D011991:Receptors, Virus; D016212:Transforming Growth Factor beta; C067981:leukemia virus receptor, gibbon ape; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases