Matrix GLA protein, a regulatory protein for bone morphogenetic protein-2.
Matrix GLA protein (MGP) has been identified as a calcification inhibitor in cartilage and vasculature. Part of this effect may be attributed to its influence on osteoinductive activity of bone morphogenetic protein-2 (BMP-2). To detect binding between MGP and BMP-2, we performed immunoprecipitation using MGP and BMP-2 tagged with FLAG and c-Myc. The results showed co-precipitation of BMP-2 with MGP. To quantify the effect of MGP on BMP-2 activity, we assayed for alkaline phosphatase activity and showed a dose-dependent effect. Low levels of MGP relative to BMP-2 (<1-fold excess) resulted in mild enhancement of osteoinduction, whereas intermediate levels (1-15-fold excess) resulted in strong inhibition. High levels of MGP (>15-fold excess), however, resulted in pronounced enhancement of the osteoinductive effect of BMP-2. Cross-linking studies showed that inhibitory levels of MGP abolished BMP-2 receptor binding. Immunoblotting showed a corresponding decrease in activation of Smad1, part of the BMP signaling system. Enhancing levels of MGP resulted in increased Smad1 activation. To determine the cellular localization of BMP-2 in the presence of MGP, binding assays were performed on whole cells and cell-synthesized matrix. Inhibitory levels of MGP yielded increased matrix binding of BMP-2, suggesting that MGP inhibits BMP-2 in part via matrix association. These results suggest that MGP is a BMP-2 regulatory protein.
Zebboudj
Amina F
AF
Division of Cardiology, Department of Medicine, UCLA School of Medicine, Los Angeles, California 90095-1679, USA.
Imura
Minori
M
Boström
Kristina
K
D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000378:metabolism / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000502:physiology*; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D017077:Culture Media, Conditioned; D004268:DNA-Binding Proteins / Q000378:metabolism; D016326:Extracellular Matrix Proteins; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D015398:Signal Transduction / Q000502:physiology; D051785:Smad Proteins; D051898:Smad1 Protein; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta; D000097568:Matrix Gla Protein
D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D002135:Calcium-Binding Proteins; D017077:Culture Media, Conditioned; D004268:DNA-Binding Proteins; D016326:Extracellular Matrix Proteins; D051785:Smad Proteins; D051898:Smad1 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D000097568:Matrix Gla Protein; C525718:BMP2 protein, human; C525719:Bmp2 protein, mouse; C497399:SMAD1 protein, human; C497401:Smad1 protein, mouse