Phosphate-dependent regulation of MGP in osteoblasts: role of ERK1/2 and Fra-1.
Inorganic phosphate (Pi) and the matrix Gla protein (MGP) are key regulators of bone formation. We have recently shown that Pi upregulates MGP in growth plate chondrocytes, which may represent a negative feedback loop for the control of mineralization. Osteoblasts from Fra-1-deleted mice express low levels of MGP, whereas the expression of MGP is elevated in Fra-1 transgenic osteoblasts, suggesting a role for Fra-1 in MGP expression and bone formation. In this study, we aimed at deciphering the relationships between Pi and MGP in osteoblasts to determine the molecular mechanisms involved in the Pi-dependent regulation of MGP. In MC3T3-E1 cells and primary calvaria-derived osteoblasts, Pi increased MGP and Fra-1 expression at both the mRNA and protein levels. We also found that Pi enhanced the phosphorylation of ERK1/2. U0126 (MEK1/2 inhibitor) suppressed Pi-stimulated MGP and Fra-1 expression, indicating that ERK1/2 is required for Pi-dependent regulation of MGP and Fra-1. In addition, using in vitro DNA binding and chromatin immunoprecipitation assays, we showed that Fra-1 interacts with the MGP promoter in response to Pi in MC3T3-E1 cells. Finally, we found that in fra-1 knockdown MC3T3-E1 osteoblasts, the level of MGP expression is no more significantly upregulated by Pi. We further showed that primary osteoblasts from Fra-1-deficient mice failed to exhibit a Pi-dependent stimulation of MGP expression. These data show, for the first time, that Pi regulates MGP expression in osteoblasts through the ERK1/2-Fra-1 pathway.
INSERM, U 791, Laboratoire d'Ingénierie des Tissus Ostéo-Articulaires et Dentaires, Groupe Physiopathologie des Tissus Squelettiques et Ingénierie du Cartilage, Nantes, France.
Marion
M
Julien
Solmaz
S
Khoshniat
Aline
A
Lacreusette
Maithé
M
Gatius
Aline
A
Bozec
Erwin F
EF
Wagner
Yohann
Y
Wittrant
Martial
M
Masson
Pierre
P
Weiss
Laurent
L
Beck
David
D
Magne
Jerome
J
Guicheux
D000818:Animals; D002070:Butadienes / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D016326:Extracellular Matrix Proteins / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D010006:Osteoblasts / Q000187:drug effects / Q000201:enzymology*; D010710:Phosphates / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D016760:Proto-Oncogene Proteins c-fos / Q000172:deficiency / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D000097568:Matrix Gla Protein; D000099169:Fos-Related Antigen 1
D002070:Butadienes; D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D009570:Nitriles; D010710:Phosphates; D016760:Proto-Oncogene Proteins c-fos; D034741:RNA, Small Interfering; D000097568:Matrix Gla Protein; D000099169:Fos-Related Antigen 1; C113580:U 0126