Bone morphogenetic protein-2 (BMP-2) and transforming growth factor-β1 (TGF-β1) alter connexin 43 phosphorylation in MC3T3-E1 Cells

Northern blot analysis revealed no detectable change in the expression of Cx43 mRNA. Western blot analysis demonstrated no significant change in the expression of total Cx43 protein. However, significantly higher ratios of unphosphorylated vs. phosphorylated forms of Cx43 were detected after BMP-2 or TGF-β1 treatment. Immunofluorescence and cell protein fractionation revealed no detectable change in the localization of Cx43 between the cytosol and plasma membrane.BMP-2 and TGF-β1 do not alter expression of Cx43 at the mRNA or protein level. BMP-2 and TGF-β1 may inhibit GJIC by decreasing the phosphorylated form of Cx43 in MC3T3-E1 cells.Bone morphogenetic protein-2 (BMP-2) and transforming growth factor-β1 (TGF-β1), members of the TGF-β superfamily, play important roles in bone repair and regeneration [1-4]. BMPs, defined as osteoinductive by their ability to induce osteogenesis when implanted in extraskeletal sites, are thought to mediate the transformation of undifferentiated mesenchymal cells into bone-producing osteoblasts. BMP-2 and TGF-β1 promote osteogenesis in vivo and have been applied exogenously to accelerate healing of bony defects in various animal models [5-8].Gap junctional intercellular communication (GJIC) represents one mechanism of cell-cell communication and has been implicated in the maintenance of intercellular homeostasis and regulation of signals during embryogenesis, differentiation, growth, and regeneration [9-11]. Gap junctions have been shown by electron microscopy to exist between osteoblasts and osteocytes in homologous and heterologous cell populations [12-14]. Gap junctions are thought to be essential for maintaining skeletal integrity and coordinating repair of osseous tissue by propagating intracellular signals generated in response to soluble factors, such as epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF), or mechanical stimuli, such as cyclic stretch [15-18]. Connexins are the structural subunits of gap ju