Insulin Resistance by Uncleaved Insulin Proreceptor: Emergence of Binding Site by Trypsin

Abstract

Two sisters presented with severe insulin resistance and markedly decreased insulin binding to erythrocytes, cultured fibroblasts, and transformed lymphocytes. The dose-response curve of insulinstimulated 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 a-and p-subunits by dithiothreitol treatment. However, the proreceptor was cleaved by trypsin, and this led to production of a 135,000-M r a-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. Diabetes 37:653-56, 1988

A nonsense mutation causing decreased levels of insulin receptor mRNA: detection by a simplified technique for direct sequencing of genomic DNA amplified by the polymerase chain reaction.

“…In addition, mutational analysis has provided insights into the functional roles of specific structural domains in the receptors. In some patients, mutations have been described that impair posttranslational processing and transport of receptors to the plasma membrane (4)(5)(6)(7) or alter the affinity with which the receptor binds its ligand (6)(7)(8)(9). Furthermore, mutations have been described that interfere with other functions of the receptor such as receptor-mediated endocytosis and delivery of low density lipoprotein for utilization within the cell (10) or transmembrane signaling by inactivating the insulin receptor tyrosine kinase activity (11)(12)(13)(14).…”

The Paired Basic Amino Acid-cleaving Enzyme 4 (PACE4) Is Involved in the Maturation of Insulin Receptor Isoform B

“…The ␣ and ␤ subunits are synthesized as a single precursor polypeptide (proIR) that is cleaved after being transported to the Golgi compartments (2) on the carboxyl side of the tetrabasic amino acid sequence (Arg-LysArg-Arg 735 ) located at the junction between the two subunits (3,4). The physiological importance of proteolytic proIR maturation was demonstrated in patients who were suffering major insulin-resistant diabetes because of an Arg 735 3 Ser substitution at the proIR processing site (5,6). Moreover, a processing defect in the proIR was observed in the livers of a particular animal model for diabetes (7).…”

“…The mature insulin receptor (IR) 5 is a heterotetrameric transmembrane protein composed of two disulfide-linked dimmers, each of which has an amino-terminal ligand-binding ␣ subunit and a carboxyl-terminal tyrosine kinase active ␤ subunit (for review, see Ref. 1).…”

Binding specificity and intramolecular signal transmission of uncleaved insulin proreceptor in transformed lymphocytes from a patient with extreme insulin resistance

“…Thus, a primary defect in insulin receptors leads to extreme insulin resistance as demonstrated in type A insulin resistance [3][4][5][6][7][8][9][10][11][12][13][14], leprechaunism [4,6,7,11,[14][15][16][17][18][19][20][21][22][23][24], and Rabson-Mendenhall syndrome [14,[25][26][27]. Recently, we [28,29] and Kakehi et al [30] reported a patient with type A extreme insulin resistance due to abnormal processing of the insulin proreceptor. Subsequently, DNA sequencing of the interconnecting region between alpha-and beta-subunits revealed G-+T point mutation which changed -Arg-Lys-Arg-Argto -Arg-Lys-Arg-Ser- [31,32].…”

“…The Arg---+Ser structural change appeared to be the cause for abnormal processing of the insulin proreceptor. However, attention has been focused on the mechanism of abnormal processing of the proreceptor in the previous studies [28][29][30][31][32], and functional properties of the unprocessed insulin proreceptor itself have not been investigated in detail. Since insulin binding was markedly decreased, hormone binding specificity and intramolecular signal transmission may also undergo a change by structural alteration due to abnormal processing of the insulin proreceptor.…”