Wdr. Ji et al., Characterization of kringle domains of angiostatin as antagonists of endothelial cell migration, an important process in angiogenesis, FASEB J, 12(15), 1998, pp. 1731-1738
Angiogenesis is a complex process that involves endothelial cell proliferat
ion, migration, basement membrane degradation, and neovessel organization.
Angiostatin, consisting of four homologous triple-disulfide bridged kringle
domains, has previously been shown to exhibit profound inhibition of endot
helial cell proliferation in vitro and angiogenesis in vivo. It was also de
monstrated that angiostatin could suppress the growth of a variety of tumor
s via the blocking of angiogenesis. The primary aim of our study was to cha
racterize the kringle domains of angiostatin for their inhibitory activitie
s of endothelial cell migration in order to elucidate their contributions t
o the anti-angiogenic function of angiostatin. In this report, we demonstra
te for the first time that the kringles of angiostatin play different roles
in inhibiting endothelial cell migration, a crucial process in angiogenesi
s. Kringle 4, which has only marginal anti-proliferative activity, is among
the most potent fragments in inhibiting endothelial cell. migration (IC50
Of approximately 500 nM). In contrast, kringle 1-3, which is equivalent to
angiostatin in inhibiting endothelial cell proliferation, manifests only a
modest anti-migratory effect. The combination of kringle 1-3 and kringle 4
results in an anti-migratory activity comparable to that of angiostatin. Wh
en kringle 1 is removed from kringle 1-3, the resulting kringle 2-3 becomes
more potent than kringle 1-3. This implies that kringle 1, although virtua
lly ineffective in inhibiting endothelial cell migration, may influence the
conformation of kringle 1-3 to alter its anti-migratory activity. We also
show that disruption of the kringle structure by reducing/alkylating agents
markedly attenuates the anti-migratory activity of angiostatin, demonstrat
ing the significance of kringle conformation in maintaining the anti-angiog
enic activity of angiostatin. Our data suggest that different kringle domai
ns may contribute to the overall anti-angiogenic function of angiostatin by
their distinct anti-migratory activities.