Stress‐induced proteins in chondrocytes from patients with osteoarthritis

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Abstract
Recent studies have shown that a specific set of proteins is produced by a variety of cells after the application of some forms of stress, including heat shock. Human chondrocytes isolated from cartilage with moderate to severe osteoarthritis synthesize at least 1 of these stress proteins (Mr 70, 000) at physiologic temperature (37°C), whereas chondrocytes isolated from non‐pathologic cartilage synthesize this protein only in response to incubation at temperatures above 39°C. The active synthesis of this protein (SP‐70) at 37°C is positively correlated with the severity of osteoarthritis and can be a characteristic indicator of this degenerative disease. We identified the active synthesis of stress proteins after incubating the cartilage tissue in medium containing 35S‐methionine and separating the cell‐associated proteins by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. The radioactive proteins were visualized by autoradiography. Analysis of the longevity of cell‐associated proteins was determined by pulsing the tissue with 35S‐methionine, and after different periods of chase in medium, the proteins were separated by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Specific protein bands were then excised, and the radioactivity was determined by liquid scintillation counting.