Protein Kinase C-independent Activation of Protein Kinase D Is Involved in BMP-2-induced Activation of Stress Mitogen-activated Protein Kinases JNK and p38 and Osteoblastic Cell Differentiation

• Published in: The Journal of biological chemistry Vol. 279; no. 1; pp. 259 - 264
• Main Authors: Lemonnier, Jérome, Ghayor, Chafik, Guicheux, Jérome, Caverzasio, Joseph
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 02-01-2004; American Society for Biochemistry and Molecular Biology
• Subjects: 3T3 Cells; Animals; Base Sequence; Bone Morphogenetic Protein 2; Bone Morphogenetic Proteins - pharmacology; Carbazoles - pharmacology; Cell Differentiation; Enzyme Activation; Enzyme Inhibitors - pharmacology; Indoles - pharmacology; Kinetics; Mice; Mitogen-Activated Protein Kinases - metabolism; Molecular Sequence Data; Osteoblasts - cytology; Osteoblasts - enzymology; p38 Mitogen-Activated Protein Kinases; Protein Kinase C - antagonists & inhibitors; Protein Kinase C - genetics; Protein Kinase C - metabolism; RNA, Messenger - genetics; Transforming Growth Factor alpha - pharmacology; Transforming Growth Factor beta
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M308665200

An important role for JNK* and p38 has recently been discovered in the differentiating effect of bone morphogenetic protein 2 (BMP-2) on osteoblastic cells. In this study, we investigated the molecular mechanism by which BMP-2 activates JNK and p38 in MC3T3-E1 osteoblastic cells. Activation of JNK and p38 induced by BMP-2 was blocked by the protein kinase C/protein kinase D (PKC/PKD) inhibitor Go6976 but not by the related compound, Go6983, a selective inhibitor of conventional PKCs. Associated with this inhibitory effect of Go6976, BMP-2 induced a selective and a dose-dependent Ser916 phosphorylation/activation of PKD, which was also blocked by Go6976. In contrast to the recently described PKC-dependent molecular mechanism involved in activation of PKD by G protein-coupled receptor agonists, BMP-2 did not induce a phosphorylation of PKD on Ser744/748. To further document an implication of PKD in activation of JNK and p38 induced by BMP-2, we constructed MC3T3-E1 cells stably expressing PKD antisense oligonucleotide (AS-PKD). In AS-PKD clones having low PKD levels, activation of JNK and p38 by BMP-2, but not of Smad1/5, was markedly impaired compared with empty vector transfected (V-PKD) cells. Analysis of osteoblastic cell differentiation in AS-PKD compared with V-PKD cells showed that mRNA and protein expressions of alkaline phosphatase and osteocalcin induced by BMP-2 were markedly reduced in AS-PKD. In conclusion, results presented in this study indicate that BMP-2 can induce activation of PKD in osteoblastic cells by a PKC-independent mechanism and that this kinase is involved in activation of JNK and p38 induced by BMP-2. Thus, this pathway, in addition to Smads, appears to be essential for the effect of BMP-2 on osteoblastic cell differentiation.