Multiple forms of heparan sulfate proteoglycans in the Engelbreth-Holm-Swarm mouse tumor. The occurrence of high density forms bearing both heparan sulfate and chondroitin sulfate side chains

Abstract

Heparan sulfate proteoglycan from the Engelbreth-Holm-Swarm mouse tumor was previously separated into two forms: a high density form (Form HD) and low density form (Form LD). In this study, the two forms were radiolabeled either metabolically with [35S]sulfate or [3H]serine or chemically with 125I. Pulse-chase experiments with [35S]sulfate showed no clear precursor-product relationship between the two forms. Analyses of the labeled proteoglycan samples with heparitinase and chondroitinase ABC indicated that Form LD is a large proteoglycan containing heparan sulfate chains attached to a single core molecule (Mr = 450,000), whereas Form HD is a mixture of small proteoglycans with four different size core molecules (Mr = 34,000, 29,000, 27,000, and 21,000), most, if not all, of which bear both heparan sulfate (Mr = 60,000) and chondroitin sulfate (Mr = 17,000) chains. Glycosaminoglycan-enriched fragments obtained from Form HD by V8 protease digestion were also shown to contain both heparitinase-susceptible chains and chondroitinase ABC-susceptible chains. Tryptic peptide maps of 125I-labeled Form HD and the glycosaminoglycan-enriched fragments derived therefrom were quite different from the corresponding maps for Form LD.