Activation of mitogen-activated protein kinase cascades is involved in regulation of bone morphogenetic protein-2-induced osteoblast differentiation in pluripotent C2Cl2 cells

Bone morphogenetic protein (BMP)-2, a member of the transforming growth fac tor-beta (TGF-beta) superfamily, is able to induce osteoblastic differentia tion of C2C12 cells. Both Smad and mitogen-activated protein kinase (MAPK) pathways are essential components of the TGF-P superfamily signaling machin ery. Although Smads have been demonstrated to participate in the BMP-2-indu ced osteoblastic differentiation of C2C12 cells, the role of MAPK has not b een addressed. This report shows that BMP-2 activates ERK and p38, but not JNK, in C2C12 cells. Pretreatment of cells with the p38 inhibitor, SB203580 , dramatically reduced BMP-2-induced expression of the osteoblast markers a lkaline phosphatase (ALP) and osteocalcin (OC). Nevertheless, overexpressio n of MKK3, a protein kinase that phosphorylates and activates p38, failed t o induce ALP or OC expression in the absence of BMP-2, indicating that p38 activation is necessary but not sufficient for the acquisition of the osteo blast phenotype by these cells. Although ALP induction was increased slight ly in the presence of PD-98059, a selective inhibitor of the ERK cascade, t his compound significantly inhibited both steady-state and BMP-2-induced OC RNA levels. Our results indicate that p38 and ERK cascades play a crucial role in the osteoblast differentiation of C2C12 cells mediated by BMP-2. (C ) 2001 by Elsevier Science Inc. All rights reserved.