Regulation of tissue factor pathway inhibitor expression in smooth muscle cells

Tissue factor pathway inhibitor (TFPI) is the primary physiological inhibit or that regulates tissue factor-induced blood coagulation. TFPI is thought to be synthesized, in vivo, primarily by microvascular endothelial cells. L ittle is known about how TFPI is regulated under pathophysiological conditi ons. In this study, we determined mechanisms by which TFPI expression is re gulated by human pulmonary artery smooth muscle cells (PASMC), because thes e cells contribute to remodeling of the pulmonary vasculature in disease. P ASMC in culture constitutively synthesize and secrete TFPI. Exposure of PAS MC to phorbol myristate acetate, lipopolysaccharide, tumor necrosis factor alpha, thrombin, interleukin-1, and transforming growth factor-beta had no significant effect on expression of TFPI by PASMC. By contrast, treatment o f PASMC with serum and basic fibroblast growth factor (bFGF)/heparin marked ly upregulated the expression of TFPI activity and antigen. On Western blot analysis, a protein consistent with full-length TFPI (42 kD) was identifie d in the conditioned media of PASMC, and the levels of the protein were muc h higher in the conditioned media of serum and bFGF/heparin-treated cells. Northern blot analysis showed that PASMC constitutively express TFPI mRNA, and treatment of cells with serum and bFGF/heparin had a minimal effect on the steady-state levels of TFPI mRNA. Nuclear run-on analysis did not show a significant increase in the transcriptional rate of TFPI gene in PASMC tr eated with serum or bFGF/heparin. Cycloheximide, but not actinomycin-D, tre atment inhibited the serum and bFGF/heparin-induced increase in TFPI activi ty in PASMC, In conclusion, our data demonstrate that PASMC constitutively synthesize and secrete TFPI and serum or bFGF upregulate its expression, su ggesting that growth factors that can stimulate the vessel wall in vivo mig ht locally regulate TFPI expression. Our study also suggests that control o f TFPI expression by serum or bFGF occurs via translational rather than tra nscriptional regulation. (C) 1999 by The American Society of Hematology.