Regulation of chondroitin sulfate synthesis. Effect of beta-xylosides on synthesis of chondroitin sulfate proteoglycan, chondroitin sulfate chains, and core protein.
Monolayer cultures of embryonic chick chondrocytes were incubated with 35SO42- in the presence and absence of 1.0 mM p-nitrophenyl-beta-d-xyloside for 2 days. The relative amounts of chondroitin sulfate proteoglycan and free polysaccharide chains were measured following gel filtration on Sephadex G-200. Synthesis of beta-xyloside-initiated polysaccharide chains was accompanied by an apparent decrease in chondroitin sulfate proteoglycan production by the treated cultures. When levels of cartilage-specific core protein were determined by a radioimmunoassay, similar amounts of core protein were found in both beta-xyloside and control cultures, indicating that decreased synthesis of core protein is not responsible for the observed decrease in chondroitin sulfate proteoglycan production. Activity levels of the chain-initiating glycosyltransferases (UDP-D-xylose: core protein xylosyltransferase and UDP-D-galactose:D-xylose galactosyltransferase) as well as the extent of xylosylation of core protein were found to be similar in cell extracts from both culture types. Furthermore, beta-xylosides did not inhibit the xylosyltransferase reaction in cell-free studies. In contrast, the beta-xylosides effectively competed with several galactose acceptors, including an enzymatically synthesized xylosylated core protein acceptor, in the first galactosyltransferase reaction.
D000818:Animals; D002356:Cartilage / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D002807:Chondroitin / Q000031:analogs & derivatives*; D002809:Chondroitin Sulfates / Q000096:biosynthesis*; D005700:Galactosyltransferases / Q000378:metabolism; D006027:Glycosides / Q000494:pharmacology; D010430:Pentosyltransferases / Q000378:metabolism; D014176:Protein Biosynthesis; D011509:Proteoglycans / Q000096:biosynthesis*; D014994:Xylose / Q000494:pharmacology*
D006027:Glycosides; D011509:Proteoglycans; D002807:Chondroitin; D002809:Chondroitin Sulfates; D014994:Xylose; D005700:Galactosyltransferases; D010430:Pentosyltransferases