Concurrent reduction in the sulfation of heparan sulfate and basement membrane assembly in a cell model system

Basement membranes (BMs) are specialized extracellular matrices that have important roles in cell attachment, migration, growth and differentiation. The murine teratocarcinoma cell line, M1536-B3, has been shown to produce a model BM composed of laminin, entactin and heparan sulfate proteoglycans but lacking collagen. Therefore, M1536-B3 cells are an excellent model system in which to study the role of non-collagenous components in BM assembly. We have used these cells to test for a requirement of mature heparan sulfate (HS) chains in BM assembly. Growth of M1536-B3 cells in the presence of chlorate, an inhibitor of activated sulfate synthesis, resulted in a dose-dependent decrease in the sulfation of glycosaminoglycans and reduction in the charge density of the isolated HS. The undersulfated HS from chlorate-treated cells had a decreased binding capacity for laminin when compared with control HS. Concurrent with these changes in sulfation, chlorate treatment of M1536-B3 cells resulted in the failure of BM assembly, which was restored upon removal of the chlorate from the growth medium. These results were not due to major alterations in cell attachment, spreading, growth, protein synthesis, or to an inability of the cells to synthesize and secrete laminin. These data suggest that the sulfation of HS and its subsequent ability to interact with other BM components play major roles in the assembly and structure of BMs.