Summary
Human vascular smooth muscle cells (SMCs) isolated from normal adult arteries were investigated for the expression of Tissue Factor (TF) procoagulant activity at their membrane surface and TF antigen in lysed cells. In growing conditions, SMCs expressed high levels of TF activity and antigen. When cells were made quiescent by 72 h of subculture in serum-poor medium, these levels fell to about one third of the initial values. Platelet-derived growth factor BB (PDGF) up-regulated in a dose-dependent manner TF expression with a significant increase (1.8 fold) within five hours. PD 98059, a specific inhibitor of mitogen-activated protein kinase (MAPK) pathway involved in cell response to PDGF, also prevented TF up-regulation. Short-term treatment by Pentoxifylline and dibutyryl cAMP also completely prevented induced TF up-regulation, but remained without effect on baseline levels of quiescent, unstimulated cells. At their effective concentrations, pentoxifylline and dibutyryl cAMP also inhibited the activation of MAPK induced by PDGF. The rapid induction of TF upon growth factor stimulation may be important in circumstances where SMCs proliferate, such as vascular events or vessel development.
