HEPARAN-SULFATE OLIGOSACCHARIDES REQUIRE 6-O-SULFATION FOR PROMOTION OF BASIC FIBROBLAST-GROWTH-FACTOR MITOGENIC ACTIVITY

The interaction of heparan sulfate (HS) with basic fibroblast growth f actor (bFGF) is influential in enabling the growth factor to bind to i ts cell surface tyrosine kinase receptor. In this study, we have inves tigated further the structural properties of HS required to mediate th e activity of bFGF in a mitogenic assay. We have prepared a library of heparinase m-generated HS oligosaccharides fractionated by both their size (dp6-dp12) and sulfate content. The ability of these oligosaccha rides to activate bFGF in a mitogenic assay was then correlated with t heir length and disaccharide composition. All octa- and hexasaccharide fractions tested were unable to activate bFGF. Dodeca- and decasaccha ride fractions were found to contain both activating and nonactivating oligosaccharides, and showed a clear correlation between total sulfat e content and the level of activatory activity. Disaccharide analysis of a range of dodeca- and decasaccharide fractions showed that both ac tivating and non-activating oligosaccharides were composed mainly of N -sulfated and IdoA(2S)-containing disaccharides. The only significant difference between activating and non-activating oligosaccharides was the content of 6-O-sulfated disaccharides, in particular the disacchar ide IdoA(2S)alpha 1,4GlcNSO(3)(6S). These results show that there is a requirement for B-O-sulfation of N-sulfated glucosamine residues, in addition to the 2-0-sulfation of IdoA, for the promotion of bFGF mitog enic activity by naturally occurring HS oligosaccharides. Analysis of the structure-activity relationships in the dodecasaccharide fractions in particular, suggests that a minimum bFGF activation sequence exist s which is dependent on the positioning of at least one 6-O-sulfate gr oup.