INTEGRIN-BINDING AND CELL-ADHESION STUDIES OF FIBULINS REVEAL A PARTICULAR AFFINITY FOR ALPHA-IIB-BETA-3

The extracellular matrix proteins fibulin-1 (variants C and D) and fib ulin-2 occur in basement membranes and in vessel walls and are thus po tential candidates for cellular interactions. Recombinant forms of the se proteins were obtained from stably transfected kidney cell clones a nd examined for cell-adhesion activity and binding to five different p urified integrins. The two variants of mouse fibulin-1 were inactive i n all these assays. Mouse fibulin-2, however, bound to alpha IIb beta 3 integrin almost as strongly as fibrinogen, while a lower activity wa s found for alpha V beta 3 and almost none for alpha 5 beta 1 integrin . Synthetic SVPRGDLDG peptide, corresponding to the single RGD site of mouse fibulin-2, was a strong antagonist of alpha IIb beta 3 integrin binding. Its affinity for alpha V beta 3 and alpha 5 beta 1 integrins was, however, 10- to 50-fold lower compared to GRGDS. Mouse fibulin-2 also promoted adhesion of thrombin-stimulated platelets and of some e stablished cell lines which could be inhibited by RGD peptides. Human fibulin-2, in which the RGD sequence is changed to RSS, bound less str ongly to alpha IIb beta 3 integrin and showed no cell-adhesion activit y. Together these data suggest a potential role in hemostatic control for mouse fibulin-2 and possibly also for human fibulin-2. (C) 1995 Ac ademic Press, Inc.