The growth and differentiation factor bone morphogenetic protein-2 (BMP-2) 
regulates cardiac development during vertebrate embryogenesis. In cardiac 
precursor cells, BMP-2 has recently been shown to induce expression of cardiac 
transcription factors, including myocyte enhancer factor 2A (MEF-2A). The 
specific signal transduction mechanism by which BMP-2 regulates these actions is 
not known. We investigated the role of phosphatidylinositol (PI) 3-kinase in 
regulating these processes in cardiomyocyte precursor CL6 cells. BMP-2 increased 
PI 3-kinase activity in these cells in a time-dependent manner, resulting in 
increased expression of sarcomeric myosin heavy chain (MHC) and MEF-2A. 
Inhibition of PI 3-kinase abolished these actions of BMP-2, indicating the 
involvement of PI 3-kinase in these processes. Furthermore, BMP-2 stimulated 
specific protein.DNA complex formation when an MEF-2 DNA recognition element was 
used as probe. Antibody supershift assay confirmed the presence of MEF-2A in 
this protein.DNA complex. Inhibition of PI 3-kinase activity completely 
prevented the MEF-2A.DNA complex formation. BMP-2 also increased transcription 
of a reporter gene driven by an MEF-2-specific DNA element in a PI 
3-kinase-dependent manner. Ectopic expression of MEF-2A increased BMP-2 
transcription to the same extent induced by BMP-2, indicating that MEF-2A may 
participate in BMP-2 autoregulation in CL6 cells. Expression of dominant 
negative PI 3-kinase completely abolished BMP-2-induced as well as 
MEF-2A-mediated BMP-2 transcription. Furthermore expression of MEF-2A increased 
MHC expression in a PI 3-kinase-dependent manner. Together these data provide 
the first evidence that BMP-2-induced PI 3-kinase signaling regulates MEF-2A 
expression and define a mechanism of MEF-2A-dependent BMP-2 transcription.