Insulin resistance by uncleaved insulin proreceptor. Emergence of binding site by trypsin.

Two sisters presented with severe insulin resistance and markedly decreased insulin binding to erythrocytes, cultured fibroblasts, and transformed lymphocytes. The dose-response curve of insulin-stimulated amino acid uptake in the fibroblasts was shifted to the right. The molecular weight of the insulin receptor on the transformed lymphocytes from the patients was 210,000 and could not be dissociated to alpha- and beta-subunits by dithiothreitol treatment. However, the proreceptor was cleaved by trypsin, and this led to production of a 135,000-Mr alpha-subunit. Insulin binding to the trypsin-treated cells increased to the normal level, and insulin action was normalized. These results suggest that the failure of proreceptor cleavage produces hormone-resistant states and that a proreceptor syndrome may be a unique disease entity for hormone resistance.