Objectives:Smad3 is a specific intracellular signal molecule for transforming growth factor-beta (TGF-beta).The aim of this study was to characterize the role of Smad3 protein in mediating TGF-beta1 responses in cultured human dental pulp cells (HDPC). Methods: Endogenous Smad3 expression and modulation was evaluated by Western blot analyses. The change of intracellular location of Smad3 was determined by laser scanning confocal microscopy. Smad3 function and its role in type I collagen transcription was investigated in cotransfection experiments using promoter-luciferase reporter gene constructs. Results:The results found that HDPC expressed Smad3 protein. TGF-beta1 down-regulated Smad3 protein expression after 4 and 24 hours of treatment. Smad3 expression translocated from cytoplasm to nucleus after treatment with TGF-beta1 for 1 hour, respectively. TGF-beta1 increased the activation of an a2 (I) collagen promoter-luciferase reporter construct transfected into HDPC. This activation was inhibited by contransfection with FLAG-Smad3D, a dominant negative mutant form of Smad3 in which three C-terminal serine phosphoacceptor sites were changed to alanine residues.Conclusions: From these results, it was concluded that Smad3 was present and activated by TGF-beta1 in human dental pulp cells. The Smad3 pathway was functional in these cells and appeared to be involved in TGF-beta1-induced type I collagen transcription.

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