Deletion of 343 amino acids from the carboxyl terminus of the beta-subunit of the insulin receptor inhibits insulin signaling.

Naturally occurring mutations in the insulin receptor gene that impair the receptor tyrosine kinase activity cause insulin resistance in vivo in a dominant fashion. Previously, two unrelated families have been described that express an insulin receptor with a truncation due to a premature chain termination at codon 1000 (delta 1000), thereby deleting 343 amino acids from the carboxyl terminus of the beta-subunit. While clinical findings suggest that the truncated receptor does not mediate insulin action in vivo, a recent study suggested that a similarly truncated receptor enhanced insulin sensitivity in transfected cells by augmenting the signaling by endogenous receptors [Sasaoka, T., Takata, Y., Kusari, J., Anderson, C. M., Langlois, W. J., & Olefsky, J. M. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 4379-4383]. To investigate these paradoxical data, we studied the structure and function of delta 1000 truncated insulin receptors when expressed in NIH-3T3 cells. We found that, despite the deletion of most of the tyrosine kinase domain and all of the C-terminal domain of the beta-subunit of the insulin receptor, the delta 1000 mutant receptors were processed normally and were transported to the plasma membrane where they bind insulin with high affinity. Following ligand addition, the truncated receptors are degraded with a normal half-life. However, they fail to undergo insulin-stimulated internalization, do not regulate the phosphorylation of insulin receptor substrate 1, and are unable to mediate an insulin-stimulated increase in DNA synthesis and c-jun and c-fos expression.(ABSTRACT TRUNCATED AT 250 WORDS)