In cultured human dermal fibroblasts, transforming growth factor (TGF)-β induced the mRNA expression of tenascin-C (TN-C). The molecular mechanism (s) underlying this process is not presently understood. In this study, we performed serial 5′ deletion and a transient transfection analysis to define a region in the TN-C promoter mediating the inducible responsiveness to TGF-β. This region contains an atypical nucleotide recognition element for the Smad family of transcriptional regulators. A DNA affinity precipitation assay revealed that Smad2/Smad3 bound to this site in a transient and specific manner. Overexpression of Smad3 or Smad4 activated the TN-C promoter activity and superinduced the TN-C promoter activity stimulated by TGF-β. Moreover, simultaneous cotransfection of Smad3 and Smad4 activated the TN-C promoter activity in a synergistic manner. Mutation of the Smad-binding sites, the Ets-binding sites, or Sp1/3-binding sites in the TN-C promoter abrogated the TGF-β/Smad-inducible promoter activity. Immunoprecipitation analysis revealed that Smad3, Sp1, and Ets1 form a transcriptionally active complex. Furthermore, the interaction between Smads and CBP/p300 in TGF-β signaling was confirmed. These findings demonstrate the existence of a novel, functional binding element in the proximal region of the TN-C promoter mediating responsiveness to TGF-β involving Smad3/4, Sp1, Ets1, and CBP/p300.