2 FUNCTIONALLY DISTINCT POOLS OF VITRONECTIN (VN) IN THE BLOOD-CIRCULATION - IDENTIFICATION OF A HEPARIN-BINDING COMPETENT POPULATION OF VNWITHIN PLATELET ALPHA-GRANULES
D. Seiffert et Rr. Schleef, 2 FUNCTIONALLY DISTINCT POOLS OF VITRONECTIN (VN) IN THE BLOOD-CIRCULATION - IDENTIFICATION OF A HEPARIN-BINDING COMPETENT POPULATION OF VNWITHIN PLATELET ALPHA-GRANULES, Blood, 88(2), 1996, pp. 552-560
The biological functions of vitronectin (Vn) are dependent on its conf
ormation. Whereas plasma Vn is present in a conformation that does not
bind to heparin, platelet Vn has been recognized to be in a multimeri
c, conformationally altered form. To further understand the characteri
stics of platelet Vn, the molecules present in plasma and total and si
ze-fractionated platelet releasates were compared (1) immunologically
using three conformationally sensitive epitope-defined monoclonal anti
bodies, (2) functionally for their ability to interact with heparin, a
nd (3) structurally using denaturing and nondenaturing polyacrylamide
gel electrophoresis (PAGE). Our data indicate that Vn is present in pl
atelet releasates in two molecular weight (M(r)) forms. The high M(r)
fractions contain conformationally and structurally altered Vn capable
of interacting with heparin, and this form is distinct from plasma Vn
and purified denatured Vn. In contrast, the lower M(r) forms of Vn ar
e similar to plasma Vn. To determine if the presence of multimeric Vn
requires platelet activation, platelets were disintegrated by sonicati
on and fractionated by density gradients. Combined sodium dodecyl sulf
ate-PAGE (SDS-PAGE) and immunoblotting analysis showed a codistributio
n of multimeric Vn and type 1 plasminogen activator inhibitor in alpha
-granule-rich fractions. Thus, platelet Vn is stored in a structurally
and functionally distinct form from the molecule in plasma, raising t
he possibility that platelet-derived heparin-binding competent Vn will
accumulate in areas of vascular injury. (C) 1996 by The American Soci
ety of Hematology.