Fibrinogen is a major
plasma protein (350 kDa) that induces proliferative signals by serving as a scaffold to support the binding of
growth factors and to promote the cellular responses of adhesion, proliferation, and migration during wound healing, angiogenesis, and
tumor growth.
Fibrin(
ogen) degradation products generated during fibrinolysis are implicated in tissue injury. The
fibrinogen gamma chain has a COOH-terminal globular domain (gamma C, residues 151-411 of the gamma chain, 30 kDa) to which several
integrin cell adhesion receptors (e.g., platelet alpha(IIb)beta(3), endothelial alpha(v)beta(3), and leukocyte alpha(M)beta(2)) bind.
Integrins play a critical role in signal transduction from
fibrin(
ogen). We found that gamma C and its truncation mutant (designated gamma C399tr), with a deletion of the COOH-terminal 12 residues, induced apoptosis of endothelial cells and blocked tube formation of endothelial cells. DLD-1 human
colon cancer cells that secrete gamma C or gamma C399tr grew at similar levels in vitro but grew much slower in vivo than mock-transfected cells. The recombinant purified gamma C399tr fragment markedly suppressed
tumor growth, development of intratumoral vasculature, and
tumor metastasis in vivo in the highly metastatic Met-1
breast cancer model. The determinant responsible for binding to endothelial cells is cryptic in native
fibrinogen but is exposed in gamma C and gamma C399tr. These results suggest that
fibrinogen has a novel cryptic determinant, which can exert apoptosis-inducing activity on endothelial cells when exposed, and
polypeptides containing this determinant have therapeutic potential.