The potent growth factors and chemoattractants alpha-thrombin and transforming growth factor-beta1 (TGF-beta1) have both been identified at sites of arterial injury, however the interaction between these two factors has not been defined. By Northern hybridization analyses, accumulation of both a 1.9- and a 2.4-kb transcript of TGF-beta1 were detected and occurred in a time- and dose-dependent fashion following alpha-thrombin stimulation of cultured vascular smooth muscle cells (VSMC). This induction of TGF-beta1 mRNA required the proteolytic activity of thrombin and was mimicked by a thrombin-receptor-(TR)-activating peptide or TRAP (SFFLRNP). Increases in alpha-thrombin-induced TGF-beta1 message expression were insensitive to cycloheximide, but sensitive to actinomycin D. Furthermore, the induction of TGF-beta1 mRNA expression correlated with the production of latent TGF-beta1 protein in alpha-thrombin-conditioned media. In summary, alpha-thrombin stimulation of VSMC induces transcriptional activation of the TGF-beta1 gene through proteolytic activation of the cloned seven-transmembrane TR resulting in the formation of latent TGF-beta1 protein. These results demonstrate a potential mechanism whereby alpha-thrombin may modulate the vascular response to injury through TGF-beta1-dependent mechanisms.