EVIDENCE THAT CARBOXYL-REDUCED HEPARIN FAILS TO POTENTIATE ACIDIC FIBROBLAST GROWTH-FACTOR ACTIVITY DUE TO AN INABILITY TO INTERACT WITH CELL-SURFACE HEPARIN RECEPTORS

Recently we reported that carboxyl-reduced heparin (CR-heparin), despi te binding acidic fibroblast growth factor (aFGF) as effectively as na tive heparin, was much less potent at augmenting aFGF-induced mitogene sis. This paper describes experiments which examined this phenomenon i n more detail in the hope that it would shed light on the mechanism by which heparin potentiates aFGF activity. Initial studies confirmed th at heparin, with 60% of its carboxyl groups reduced, although binding aFGF with the same affinity as native heparin (K-d 35 +/- 5 nM), was a poor potentiator of aFGF-induced mitogenic activity. Proteolysis prot ection experiments also revealed that CR-heparin was as effective as n ative heparin at protecting aFGF from proteolytic degradation. In cont rast, CR-heparin was considerably less effective than native heparin a t enhancing the binding of aFGF to the fibroblast growth factor recept or (FGFR) on 3T3 cells. Furthermore, CR-heparin only bound to a subset (approximately 1/3) of heparin receptors on 3T3 cells. Based on these data, it is proposed that CR-heparin is less efficient than heparin a t facilitating the formation of a quaternary complex among aFGF, the F GFR, and cell surface heparin receptors. (C) 1995 Academic Press, Inc.