The relation of protein synthesis to chondroitin sulphate biosynthesis in cultured bovine cartilage

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Abstract
The effect of cycloheximide on chondroitin sulfate biosynthesis was studied in bovine articular cartilage maintained in culture. Addition of 0.4 mM cycloheximide to the culture medium was followed, over the next 4 h, by a 1st order decrease in the rate of incorporation of [35S]sulfate into glycosaminoglycan (half-life, t1/2 = 32 min), which is consistent with the depletion of a pool of proteoglycan core protein. Addition of 1.0 mM benzyl .beta.-D-xyloside increased the rate of incorporation of [35S]sulfate and [3H]acetate into glycosaminoglycan, but this elevated rate was also diminished by cycloheximide. Cycloheximide exerted 2 effects on the tissue; not only did it inhibit the synthesis of the core protein, but it also lowered the tissue''s capacity for chondroitin sulfate chain synthesis. Similar results were obtained with chick condrocytes grown in high density cultures. Although the exact mechanism of this secondary effect of cycloheximide is not known, there was no detectable change in cellular ATP concentration or in the amount of 3 glycosyltransferases (galactosyltransferase I, N-acetylgalactosaminyltransferase and glucuronosyltransferase II) involved in chondroitin sulfate chain synthesis. The sizes of the glycosaminoglycan chains formed in the presence of cycloheximide were larger than those formed in control cutlures; those synthesized in the larger than those formed in control cultures; those synthesized in the presence of benzyl .beta.-D-xyloside were consistently smaller, irrespective of the presence of cycloheximide. .beta.-D-Xylosides must be used with caution to study chondroitin sulfate biosynthesis as an event entirely independent of proteoglycan core protein synthesis, and they also indicate a possible involvement of the core protein in the activation of the enzymes of chondroitin sulfate synthesis.