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.