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We have demonstrated a specific receptor for somatomedin-like growth polypeptides in human fibroblasts in culture using the closely related polypeptide, multiplication stimulating activity (MSA), as the radioligand. Polypeptides purified from human plasma, somatomedin A and acid soluble nonsuppressible insulin-like activity (NSILA-s), competed potently for 125I-MSA binding, as did unlabeled MSA. Although insulin and proinsulin also strongly inhibited MSA binding, the properties of the growth peptide receptor differed from those of the human fibroblasts insulin receptor. Somatomedin A, NSILA-s, MSA, insulin and proinsulin all stimulated the incorporation of 3Hthymidine into DNA in human fibroblasts. We propose that these polypeptides induce DNA synthesis through their interaction with the growth peptide receptor.
Rechler et al. (Sun,) studied this question.