Protein kinase D mediates the synergistic effects of BMP-7 and IGF-I on osteoblastic cell differentiation

Abstract

We previously showed that exogenous insulin-like growth factor-I (IGF-I) and bone morphogenetic protein-7 (BMP-7) synergistically stimulated osteoblast differentiation in fetal rat calvaria (FRC) cells. We have now shown that BMP-7 alone and the BMP-7 and IGF-I combination synergistically stimulated protein kinase D (PKD) phosphorylation at Ser744/748 and Ser916. Transfection of FRC cells with a constitutively active PKD stimulated marker expression, while transfection with a catalytically inactive PKD did not. Moreover, Gö6976, which inhibits protein kinase C (PKC) α and β1, blocked PKD phosphorylation and the synergistic action of the BMP-7 and IGF-I combination on osteoblast differentiation, whereas Gö6983, which inhibits PKCα, β, γ, δ, and ζ, did not. Our results suggest that the FRC cell differentiation induced by BMP-7 and the BMP-7 and IGF-I combination requires stimulation of PKD activity. Our results are consistent with a novel mechanism in which combined BMP-7 and IGF-I signaling activates upstream novel PKC(s), which then phosphorylates and activates PKD, leading to enhanced osteoblast differentiation.

Keywords::

• BMP-7
• IGF-I
• PKD
• FRC cultures

Declaration of interest: This study was supported in part by Presidents Research Enhancement Fund at the University of Texas Health Science Center San Antonio. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.