Dual-regulated expression of C/EBP-alpha and BMP-2 enables differential differentiation of C2C12 cells into adipocytes and osteoblasts.

CCAAT/enhancer-binding proteins (C/EBPs) as well as bone morphogenic proteins (BMPs) play essential roles in mammalian cell differentiation in shaping adipogenic and osteoblastic lineages in particular. Recent evidence suggested that adipocytes and osteoblasts share a common mesenchymal precursor cell phenotype. Yet, the molecular details underlying the decision of adipocyte versus osteoblast differentiation as well as the involvement of C/EBPs and BMPs remains elusive. We have engineered C2C12 cells for dual-regulated expression of human C/EBP-alpha and BMP-2 to enable independent transcription control of both differentiation factors using clinically licensed antibiotics of the streptogramin (pristinamycin) and tetracycline (tetracycline) classes. Differential as well as coordinated expression of C/EBP-alpha and BMP-2 revealed that (i) C/EBP-alpha may differentiate C2C12 myoblasts into adipocytes as well as osteoblasts, (ii) BMP-2 prevents myotube differentiation, (iii) is incompetent in differentiating C2C12 into osteoblasts and (iv) even decreases C/EBP-alpha's osteoblast-specific differentiation potential but (v) cooperates with C/EBP-alpha on adipocyte differentiation, (vi) osteoblast formation occurs at low C/EBP-alpha levels while adipocyte-specific differentiation requires maximum C/EBP-alpha expression and that (vii) BMP-2 may bias the C/EBP-alpha-mediated adipocyte versus osteoblast differentiation switch towards fat cell formation. Dual-regulated expression technology enabled precise insight into combinatorial effects of two key differentiation factors involved in adipocyte/osteoblast lineage control which could be implemented in rational reprogramming of multipotent cells into desired cell phenotypes tailored for gene therapy and tissue engineering.