Characterization and binding activity of the chondroitin/dermatan sulfate chain from Endocan, a soluble endothelial proteoglycan

Abstract

Endocan is a recently identified soluble chondroitin/dermatan sulfate (CS/DS) proteoglycan. Synthesized by endothelial cells, it has been found to be over-expressed in the vasculature surrounding a number of tumors, and by promoting growth factor mitogenic activities, hepatocyte growth factor/scatter factor (HGF/SF) in particular, it supports cellular proliferation. In this work, we characterized the glycosaminoglycan (GAG) chain of Endocan, purified either from the naturally producing human umbilical vein endothelial cells (HUVEC) or from a recombinant over-expression system in human embryonic kidney cells (HEK). Compositional analysis using different chondroitinases as well as nuclear magnetic resonance studies revealed that the GAG chains from both sources share many characteristics, with the exception of size (15 and 40 kDa, respectively, for HUVEC and HEK-293 cells). The DS-specific, IdoA-containing disaccharides contribute 30% of the chain (15% of which are 2-O-sulfated) and are mostly clustered in tetra- (35%), hexa- (12%), and octa- (5%) saccharide domains. Highly sulfated D, E, and B disaccharide units (HexA2S-GalNAc6S, HexA-GalNAc4S6S, and HexA2S-GalNAc4S) were also detected in significant amounts in both chains and may account for the HGF/SF-binding activity of the CS/DS. This work establishes that HEK-293 cells can be engineered to provide a valuable source of Endocan with authentic CS/DS chains, enabling the purification of sufficient amounts for structural and/or binding analysis and providing a possible model of Endocan CS/DS chain organization.