Cellular regulation of heparan sulfate structure and function

Sammanfattning: Heparan sulfate (HS) is a sulfated glycosaminoglycan found on cell surfaces and in the extracellular matrix as HS proteoglycans. HS is synthesized as a polymer of alternating glucuronic acid and N-acetylglucosamine units. Parts of the polymer are subsequently modified by N-deacetylation/N-sulfation of the glucosamine units, C-5 epimerization of glucuronic acid to iduronic acid and O-sulfation at various positions.We studied whether the HS biosynthesis is affected by malignant transformation and cell differentiation using established cell culture models for the two processes. Structural analysis of HS indicated that transformation anddifferentiation were accompanied by structural alterations in HS, particularly with regard to 6-O-sulfation. Reduced 6-O-sulfation resulted in decreased binding of HS to the platelet derived growth factor.The biosynthesis of the sulfate donor 3'-phosphoadenosine 5'-phosphosulfate (PAPS) can be inhibited by treatment of cells with sodium chlorate. We studied the effects of decreased PAPS availability on HS biosynthesis. The sulfation reactions were affected in the order of 6-O-sulfation>2-O-sulfation>>N-sulfation, suggesting that the various sulfotransferase species have different affinities to PAPS. Moreover, we found that 6-O-sulfation of HS was affected in a domain selective fashion. We also studied the influence of the length of N-sulfated HS domains on their further polymer modification. The domain length had distinct effects on the various polymer modifications reactions. The efficiency of 2-O-sulfation was increased along with increasing domain length, whereas 6-O-sulfation was not affected by the domain length. N-sulfated domains from different HS species displayed marked structural diversity, perhaps due to the specialized functions of HS in different tissues.