Th. Welling et al., TISSUE-PLASMINOGEN ACTIVATOR INCREASES CANINE ENDOTHELIAL-CELL PROLIFERATION RATE THROUGH A PLASMIN-INDEPENDENT, RECEPTOR-MEDIATED MECHANISM, The Journal of surgical research, 66(1), 1996, pp. 36-42
Background: Tissue plasminogen activator (tPA) is elevated in cancer p
atients and is thought to promote tumor angiogenesis by facilitating e
ndothelial cell. migration through plasmin-mediated degradation of ext
racellular matrix. Due to the presence of an epidermal growth factor (
EGF)-finger domain in the tPA A-chain and the existence of an endothel
ial cell (EC) receptor that binds this domain, it was hypothesized tha
t tPA has a direct receptor-mediated effect on EC proliferation, indep
endent of plasmin. Methods and Results: Using cultured canine ECs, tPA
(7.25 mu g/ml, similar to 107 nM) increased proliferation as much as
50 and 170% in the absence and presence of growth factors, respectivel
y. tPA-induced increases in EC proliferation occurred independent of p
lasmin generation, as the plasmin inhibitor, aprotinin (10 mu g/ml) di
d not inhibit tPA-induced proliferation. However, tPA-induced prolifer
ation was inhibited dose-dependently to a maximum of 78% using a monoc
lonal antibody against the tPA EGF-finger domain. This antibody, known
to inhibit tPA binding to its receptor, did not inhibit tPA-induced p
lasmin generation. To investigate the role of potential signal transdu
ction pathways, ECs were exposed to lavendustin A, a tyrosine kinase i
nhibitor, at 33.5 mu M (IC50 for basic fibroblast growth factor). Lave
ndustin A did not inhibit tPA-induced EC proliferation. However, Rp-cA
MP, an inhibitor of cAMP-dependent kinases, specifically inhibited tPA
-induced EC proliferation in a dose-dependent manner (IC50 = 50.5 mu m
). Pertussis toxin at maximal concentrations for this system (0.5 ng/m
l) did not inhibit tPA-induced EC proliferation. Conclusion: These res
ults lend support to the hypothesis that tPA may have a direct recepto
r-mediated effect on EC proliferation and that this effect occurs inde
pendent of plasmin and may be dependent upon protein kinase A activity
. (C) 1996 Academic Press, Inc.