Thrombin stimulation of proteoglycan synthesis in vascular smooth muscle is mediated by protease-activated receptor-1 transactivation of the transforming growth factor beta type I receptor

Growth factors modify the structure of the glycosaminoglycan (GAG) chains on biglycan leading to enhanced LDL binding. G-Protein Receptor Coupled (GPCR) agonists such as thrombin, signal changes the structure of proteoglycans produced by vascular smooth muscle cells (VSMC). One component of classical GPCR signalling invokes transactivation of protein tyrosine kinase receptors such as the Epidermal Growth Factor receptor. Serine/threonine receptor growth factors such as Transforming Growth Factor-(TGF)- beta are potent activators of proteoglycan synthesis. We have used the model of proteoglycan synthesis to demonstrate that the signalling paradigm of GPCR signalling can be extended to include the transactivation of serine/threonine receptor, specifically theTGF- beta Type I receptor (T beta RI) also known as Activina??like kinase (ALK)-V. Thrombin stimulated elongation of GAG chains and increased proteoglycan core protein expression and these responses were blocked by the TI?RI antagonist, SB431542 and T beta RI siRNA knockdown, as well as several Protease Activated Receptor (PAR)-1 antagonists. The canonical downstream response to TGF- beta is increased carboxy terminal phosphorylation of the transcription factor Smad2 generating phospho-Smad2C (phosphorylation of Smad2 C-terminal region). Thrombin stimulated increased......