Activation of p38 mitogen-activated protein kinase and c-Jun-NH2-terminal kinase by BMP-2 and their implication in the stimulation of osteoblastic cell differentiation.
Signaling involved in osteoblastic cell differentiation remains largely unknown. This study further investigates mechanisms involved in BMP-2-induced osteoblastic cell differentiation. We report that BMP-2 can activate JNK and p38 in osteoblastic cells and provide evidences that these MAP kinases have distinct roles in regulating alkaline phosphatase and osteocalcin expression.


BACKGROUND
Bone morphogenetic protein (BMP)-2 exerts many of its biological effects through activation of the Smad pathway. Cooperative interactions between the Smads and the stress-activated protein kinase (SAPK) p38 and c-Jun-NH2-terminal kinase (JNK) pathways have recently been observed in TGF-beta signaling.


METHODS
Activation of mitogen-activated protein (MAP) kinases by BMP-2 and the role of these signaling pathways for cell differentiation induced by BMP-2 was investigated in mouse MC3T3-E1 and primary cultured calvaria-derived osteoblastic cells using immunoprecipitation, in vitro kinase assay and Western blot analysis, as well as specific MAP kinase inhibitors.


RESULTS
Associated with the rapid activation of Smads, BMP-2 barely affected extracellular-signal regulated kinase (ERK) activity, whereas it induced a transient activation of p38 and JNK. The role of p38 and JNK in mediating BMP-2-induced stimulation of osteoblastic cell differentiation was evaluated using the respective specific inhibitors SB203580 and SP600125. Inhibition of p38 by SB203580 was mainly associated with decreased alkaline phosphatase (ALP) activity, whereas inhibition of JNK by SP600125 was associated with a marked reduction in osteocalcin (OC) production induced by BMP-2. Corresponding alterations in ALP and OC mRNA levels were found in cells treated with BMP-2 and inhibitors, suggesting an implication of p38 and JNK pathways in BMP-2-induced osteoblastic cell differentiation at a transcriptional level.


CONCLUSIONS
Data presented in this study describe p38 and JNK as new signaling pathways involved in BMP-2-induced osteoblastic cell differentiation with evidences for a distinct role of each MAP kinase in the control of alkaline phosphatase and osteocalcin expression.
Guicheux
J
J
Division of Bone Diseases, Department of Geriatrics, University Hospital of Geneva, Geneva, Switzerland.
Lemonnier
J
J
Ghayor
C
C
Suzuki
A
A
Palmer
G
G
Caverzasio
J
J
D016475:3T3 Cells; D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects*; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D012886:Skull / Q000166:cytology; D016212:Transforming Growth Factor beta; D048051:p38 Mitogen-Activated Protein Kinases
D000873:Anthracenes; C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D004791:Enzyme Inhibitors; D016212:Transforming Growth Factor beta; C432165:pyrazolanthrone; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases