Thrombin stimulates proliferation of cultured rat aortic smooth muscle cells by a proteolytically activated receptor.

Abstract

Thrombin has been implicated in the stimulation of smooth muscle cell (SMC) proliferation that contributes to post angioplasty restenosis. The present studies demonstrated that human a-thrombin was a potent and efficacious mitogen for cultured rat aortic SMC, stimulating an increase in 3H-thymidine incorporation, as well as an increase in cell number at 1 to 10 nM concentration. -Thrombin, which is enzymatically active but lacks fibrinogen clotting activity, stimulated SMC mitogenesis but was -10-fold less potent than a-thrombin. In contrast, D-phenylalanyl-L-propyl-L-arginyl-chloromethyl ketonea-thrombin, which lacked enzymatic activity, had no mitogenic effect. Diisopropylfluorophosphate-a-thrombin failed to stimulate mitogenesis except at concentrations having equivalent enzymatic activity as that of a-thrombin at its threshold for mitogenesis. Thus, thrombin-induced proliferation was dependent on enzymatic activity. A 14-residue peptide (SFLLRNPNDKY-EPF) corresponding to amino acids 42 through 55 of the human thrombin receptor (Vu, T. K., D. T. Hung, V. I. Wheaton, and S. R. Coughlin, 1991. Cell. 64:1057-1068) had full efficacy in stimulating SMC proliferation. Reversing the first two amino acids of this peptide abolished mitogenic activity. Northern analysis demonstrated that SMC expressed a single mRNA species that hybridized to a labeled thrombin receptor cDNA probe. These findings indicate that a-thrombin stimulates SMC proliferation via the proteolytic activation of a receptor very similar or identical to that previously identified. (J. Clin. Invest. 1993. 91:94-98.)

The Role of Protease-Activated Receptor-1 in Bone Healing

“…Previous studies have shown that thrombin is a mitogen for many cell types, including vascular smooth muscle cells, 36,37 fibroblasts, 38,39 endothelial cells, 40 mesangial cells 41 and osteoblasts. 4 In many of these cells, proliferation is known to be mediated by PAR-1 and in osteoblasts, in particular, we have recently confirmed that proliferation is mediated by PAR-1.…”

Retroviral vector-mediated expression of hirudin by human vascular endothelial cells: implications for the design of retroviral vectors expressing biologically active proteins

“…1 Thrombin can also contribute to the development of graft neointimal hyperplasia through its action as a smooth muscle cell mitogen, a mediator of inflammation, and an agonist for the release of platelet-derived growth factor. [2][3][4][5] Hirudin, a 65-amino acid protein secreted by the salivary glands of the medicinal leech, is a potent and specific inhibitor of thrombin. 6 By blocking both the catalytic site and the anion-binding exosite of thrombin, hirudin inhibits the interaction of thrombin both with fibrinogen and with thrombin receptors that are present on the surface of platelets and vascular cells.…”

Protease activation of calcium-independent phospholipase A2 leads to neutrophil recruitment to coronary artery endothelial cells

“…Thrombin generated at sites of vascular injury is the most potent activator of blood platelets [7,8] and its action on inflammatory cells has been well characterized, serving as a chemotactic agent for monocytes [9] and a mitogenic for both lymphocytes [10] and vascular smooth muscle cells [11,12]. Thrombin activation of the vascular endothelium occurring in response to vascular injury or wounding can be beneficial in the repair process, but has the potential to mediate a prolonged inflammatory response and proliferative cellular events in the blood vessel wall, such as those that occur in atherosclerosis and restenosis [13].…”