α-Thrombin Induces Transforming Growth Factor-β1 mRNA and Protein in Cultured Vascular Smooth Muscle Cells via a Proteolytically Activated Receptor

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Abstract
The potent growth factors and chemoattractants α-thrombin and transforming growth factor-β1 (TGF-β1) 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-β1 were detected and occurred in a time- and dose-dependent fashion following α-thrombin stimulation of cultured vascular smooth muscle cells (VSMC). This induction of TGF-β1 mRNA required the proteolytic activity of thrombin and was mimicked by a thrombin-receptor-(TR)-activating peptide or TRAP (SFFLRNP). Increases in α-thrombin-induced TGF-β1 message expression were insensitive to cycloheximide, but sensitive to actinomycin D. Furthermore, the induction of TGF-β1. mRNA expression correlated with the production of latent TGF-β1 protein in α-thrombin-conditioned media. In summary, α-thrombin stimulation of VSMC induces transcriptional activation of the TGF-β1 gene through proteolytic activation of the cloned seven-transmembrane TR resulting in the formation of latent TGF-β1 protein. These results demonstrate a potential mechanism whereby α-thrombin may modulate the vascular response to injury through TGF-β1-dependent mechanisms.

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