Inhibition of cartilage proteoglycan synthesis by interleukin I

We have investigated the mechanism of inhibition of cartilage proteoglycan by interleukin 1. Proteoglycan synthesis was inhibited using lower doses of interleukin 1 than those required to cause cartilage resorption. There was no significant effect on DNA or total protein synthesis. Gel electrophoresis showed a direct inhibitory effect on core protein synthesis while pulse-chase experiments using radiolabelled sulphate showed no alteration in the rate of intracellular transport and secretion of completed proteoglycan. Chondrocytes incubated with cycloheximide showed a first-order decrease in rate of uptake of radiolabelled sulphate (t1/2 = 25 mins) but interleukin 1 induced inhibition showed a delay of at least 1 hr, consistent with a requirement to deplete intracellular pools of protein before effects on post-translational events could be observed. Foetal and neonatal cartilage responded to the cytokine in a similar way to adult cartilage.