Experimental Cell Research 18.5 (1989) 363-372 Thrombin Mitogenic Responses and Protein Phosphorylation Are Different in Cultured Human Endothelial Cells Derived from Large and Microvessels E. DUPUY, A. BIKFALVI, F. RENDU, S. LEVY TOLEDANO, and G. TOBELEM’ INSERM U 150 and CNRS UA 334, H@ital Lariboisihe, 75475 Paris Cedex 10, France It is well established that thrombin induces various biological responses in endothelial cells derived from large vessels. However, little is known about the effects of thrombin on the microvasculature. Protein phosphorylation may be one of the mechanisms by which an extracellular stimulus initiates cellular events like proliferation. Therefore, we have com- pared the effects of either human a-thrombin or phorbol esters (TPA) on the proliferation or protein phosphorylation in endothelial cells derived from large vessels (umbilical vein, HUVEC) or microvessels (omental tissue, HOMEC). In HOMEC, thrombin did not stimulate cell proliferation and protein phosphorylation while TPA slightly reduced the cell proliferation and induced the phosphorylation of a 27-kDa protein. In contrast, in HUVEC, thrombin or TPA markedly enhanced the cell proliferation and stimulated the phosphoryla- tion of a 59-kDa protein. These data indicate that (i) endothelial cells from large and small vessels respond differently to thrombin and (ii) there is a complex and as yet unclear relationship between the proliferation and the protein phosphorylation induced by throm- bin. 0 1989 Academic Press, Inc. Thrombin, a multifunctional enzyme formed at a site of vascular injury, most probably interacts with the endothelium. It binds to endothelial cells [25] and has various biological effects, as seen in human umbilical vein endothelial cells (HUVEC) [16,24,35]. Thrombin was also found to induce the release by cultured human endothelial cells of platelet-derived growth factor-like molecule(s) [ 191 and to stimulate c-sis gene expression in vascular endothelial cells [ 1l] as well as A- and B-chain genes of platelet-derived growth factor [22]. Thrombin, therefore, appears to promote the growth of a wide variety of cells and to act synergistically with fibroblast growth factor in human endothelial cells [ 171. Stimulation of cells by growth factor hormones or known biochemical factors initiates different cellular responses which are facilitated by the generation of intracellular second messengers and mediated by protein kinase activation [32]. The interaction of thrombin with endothelial cells appeared to trigger the same second messenger generations. When HUVEC were stimulated by thrombin, prostacyclin produc- tion was closely associated with rises in the levels of intracellular calcium, and inositoltriphosphate (IP3) [15, 18, 291 and thrombin also induced vimentin phos- phorylation in these cells [4]. Little is known about the effect of thrombin on the proliferation and protein ’ To whom reprint requests should be addressed. 363 Copyright 0 1989 by Academic press, Inc. All tights of reproduction in any form reserved 0014-4827/89 SO3.00