Hormonal control of protein synthesis in chick chondrocytes: a comparison of effects of insulin, somatomedin C and triiodothyronine

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Abstract
Somatomedin C (SM-C), insulin and triiodothyronine (T3) each result in a 2-fold stimulation of incorporation of [125I]leucine into protein by cultured chick sternal chondrocytes. Maximal stimulation occurred at concentrations of 12.5 .times. 10-9 M T3. Submaximal concentrations of SM-C and T3 were additive in their effect, and together stimulated [125I]leucine incorporated to a level greater than that achieved by either alone. Submaximal concentrations of SM-C and insulin were also additive in their stimulatory effect, but only to the level achieved by either alone. It was possible to demonstrate specific binding [14C]SM-C to chondrocytes, and bound SM-C could be displaced by either unlabeled SM-C or insulin at concentrations similar to concentrations that stimulated protein synthesis. Actinomycin D abolished stimulation by T3, but not by insulin or SM-C. SM-C and insulin apparently increase protein synthesis by stimulating the translational process after binding to the same receptor. T3 appears to act through a different mechanism, which requires stimulation of transcription.