beta-D-xyloside-mediated alteration in the synthesis of basement membrane proteoglycan

The effect of nitrophenyl-beta-D-xyloside (xyloside), a synthetic initiator of glycosaminoglycan synthesis, on proteoglycan and glycosaminoglycan synthesis by a basement membrane producing tumor was studied. While xyloside markedly stimulated the formation of chondroitin sulfate chains, it depressed the formation of a basement membrane heparan sulfate proteoglycan and caused only little formation of free heparan sulfate chains. However, when the synthesis of the core protein of the proteoglycan was inhibited by cycloheximide, heparan sulfate chains were produced by xyloside treatment. These heparan sulfate chains had a sulfate content higher than that of heparan sulfate found on the proteoglycan. The data indicate that xyloside can substitute for the heparan sulfate initiation site on the core protein of the proteoglycan and that this initiation is enhanced in the absence of core protein. This suggests that under normal conditions the formation of heparan sulfate chains may be tightly linked to the production of the core protein.