Recent studies suggest that the elevation of intracellular cyclic adenosine monophosphate (cAMP) and the activation of the protein kinase A regulate BMP-induced osteogenesis. However the precise mechanisms underlying the enhancing effect of cAMP oil BMP2 signaling were not completely revealed. in this study we investigated the effect of elevated cAMP level and PKA activation oil the BMP2-induced osteoblastic differentiation in pluripotent C2C12 cells. Alkaline phosphatase activity and its mRNA were consistently induced by BMP2 treatment. The pretreatment of C2C12 cells with Forskolin, a cAMP generating agent, dbcAMP, an analogue of cAMP, or IBMX(3-isobutyl 1-methyl xanthine), and a nonspecific inhibitor of phosphodiesterases elicited further activation of alkaline phosphatase. Furthermore, elevated intracellular cAMP level increased BMP2-induced MKP1. On the other hand, BMP2-induced Erk phosphorylation (p44/p42) and cell proliferation were suppressed in the presence of cAMP Thus cAMP might enhance., BMP2-induced osteoblastic differentiation by a MKM1-Erk-dependent mechanism. (C) 2009 Elsevier Inc. All rights reserved.