Smad protein mediated transforming growth factor β1 induction of apoptosis in the MDPC-23 odontoblast-like cell line

Objective: The function of apoptosis and its regulation in odontoblasts remain unclear. In this study, we characterize the possible role of transforming growth factor (TGF)-beta 1 in the induction of apoptosis and the molecular mechanisms that mediate TGF-beta 1-induced apoptosis in odontoblasts. Methods: Annexin V/propidium iodide staining, cell Death Detection ELISA and DNA ladder were used to examine the effect of TGF-beta 1 on apoptosis in a mouse odontoblast-like cell line, MDPC-23. Stable cell clones expressing Smad2 or Smad3 dominant negative mutants, or wild-type Smad7 were constructed to investigate the role of Smad proteins in the mediation of apoptosis by TGF-beta 1 in MDPC-23 cells. The TGF-beta 1 induced transcriptional activity in stable cell clones expressing Smad proteins was analyzed by a transient transfected TGF-beta- responsive reporter gene, p3TP-Lux. Results: TGF-beta 1 can induce apoptotic cell death in MDPC-23 cells in a dose-dependent manner. Transfection of dominant negative mutant forms of Smad2 or Smad3 blocked TGF-beta 1 -induced apoptosis; moreover, the Smad3 mutant was more efficient than the Smad2 mutant. Transfection of Smad7, an inhibitory Smad, also significantly inhibited TGF-beta 1 -induced apoptosis of these cells. Over-expression of Smad3 dominant negative mutant or Smad7 significantly inhibited TGF-beta 1 -induced transcriptional activity. Conclusion: These results suggest that Smad proteins are involved in TGF-beta 1 -induced apoptosis of odontoblast cells. (c) 2005 Elsevier Ltd. All rights reserved.