Transforming growth factor-β (TGF-β) signaling relies on Smad-signaling pathway controlled in part by the proteasome. Here we demonstrate that inhibition of the proteasome function in mink epithelial cells accumulates both positive and negative modulators of TGF-β signaling, phospho-Smad2 and SnoN. Inhibition of the proteasome led to abrogation of TGF-β target gene regulation in a gene-specific manner. While regulation of p15Ink4b and myc by TGF-β are lost, PAI-1 induction, previously shown to occur in a Smad3-dependent manner, was not affected by treatment of the cells with the proteasomal inhibitor MG132. The results suggest that proteasomal activity is required for TGF-β signaling in a gene-specific manner.