Endocrinology, Vol 132, 1132-1138, Copyright © 1993 by Endocrine Society

ARTICLES

Ligand-binding properties of the two isoforms of the human insulin receptor

Y Yamaguchi, JS Flier, H Benecke, BJ Ransil and DE Moller
Charles A. Dana Research Institute, Harvard-Thorndike Laboratory, Beth Israel Hospital, Boston, Massachusetts 02215.

Tissue-specific alternative splicing of exon 11 of the insulin receptor gene results in 2 mRNAs that differ by 36 nucleotides within the coding region. The 2 transcripts encode 2 protein isoforms with (Ex11+) or without (Ex11-) 12 additional amino acids at the carboxy-terminus of the receptor alpha-subunit. Previous studies of the 2 isoforms of the human insulin receptor expressed in mammalian cell transfectants have revealed small functional differences at the levels of equilibrium insulin binding affinity and acute ligand-induced receptor internalization. In the present study, we determined the biochemical basis for differential insulin binding affinity. Further functional characterization of the 2 receptor isoforms was also performed. The results obtained were as follows. 1) Studies of ligand association demonstrated a faster (1.8-fold) "on rate" for Ex11- receptors than for Ex11+ receptors, as determined by the kinetics of [125I]insulin binding to transfected cells. In addition, dissociation of prebound [125I]insulin from Ex11- receptors was characterized by an accelerated "off rate" relative to that of Ex11+ receptors. 2) Using both intact Chinese hamster ovary (CHO) cells and partially purified solubilized insulin receptors, the ability of insulin-like growth factor-I to compete for [125I]insulin binding to either isoform differed markedly. The mean IC50 for Ex11- was 40 nM vs. 350 nM for Ex11+. 3) Both Ex11- and Ex11+ receptors were equally capable of hybrid formation with endogenous CHO cell insulin-like growth factor-I receptors. 4) The relative abilities of 2 inhibitory polyclonal antiinsulin receptor antisera to displace [125I]insulin binding did not differ between the two isoforms. 5) Studies of insulin-induced (300 nM) receptor down- regulation in CHO cell transfectants suggested preferential down- regulation of Ex11- receptors; however, no down-regulation difference was observed when Rat 1 cell transfectants expressing the two splice variants were studied. These findings further support the idea that the 2 isoforms of the insulin receptor are functionally distinct in important ways.

This article has been cited by other articles:

				A. Navarrete Santos, N. Ramin, S. Tonack, and B. Fischer Cell Lineage-Specific Signaling of Insulin and Insulin-Like Growth Factor I in Rabbit Blastocysts Endocrinology, February 1, 2008; 149(2): 515 - 524. [Abstract] [Full Text] [PDF]

				A. Navarrete Santos, S. Tonack, M. Kirstein, S. Kietz, and B. Fischer Two insulin-responsive glucose transporter isoforms and the insulin receptor are developmentally expressed in rabbit preimplantation embryos Reproduction, November 1, 2004; 128(5): 503 - 516. [Abstract] [Full Text] [PDF]

				J. Whittaker, H. Sorensen, V. L. Gadsboll, and J. Hinrichsen Comparison of the Functional Insulin Binding Epitopes of the A and B Isoforms of the Insulin Receptor J. Biol. Chem., November 27, 2002; 277(49): 47380 - 47384. [Abstract] [Full Text] [PDF]

				K. H. Surinya, L. Molina, M. A. Soos, J. Brandt, C. Kristensen, and K. Siddle Role of Insulin Receptor Dimerization Domains in Ligand Binding, Cooperativity, and Modulation by Anti-receptor Antibodies J. Biol. Chem., May 3, 2002; 277(19): 16718 - 16725. [Abstract] [Full Text] [PDF]

				J. Nakae, Y. Kido, and D. Accili Distinct and Overlapping Functions of Insulin and IGF-I Receptors Endocr. Rev., December 1, 2001; 22(6): 818 - 835. [Abstract] [Full Text] [PDF]

				F. Frasca, G. Pandini, P. Scalia, L. Sciacca, R. Mineo, A. Costantino, I. D. Goldfine, A. Belfiore, and R. Vigneri Insulin Receptor Isoform A, a Newly Recognized, High-Affinity Insulin-Like Growth Factor II Receptor in Fetal and Cancer Cells Mol. Cell. Biol., May 1, 1999; 19(5): 3278 - 3288. [Abstract] [Full Text] [PDF]

				C. Kristensen, F. C. Wiberg, L. Schaffer, and A. S. Andersen Expression and Characterization of a 70-kDa Fragment of the Insulin Receptor That Binds Insulin. MINIMIZING LIGAND BINDING DOMAIN OF THE INSULIN RECEPTOR J. Biol. Chem., July 10, 1998; 273(28): 17780 - 17786. [Abstract] [Full Text] [PDF]

				S. L. Calzi, C. V. Choice, and S. M. Najjar Differential effect of pp120 on insulin endocytosis by two variant insulin receptor isoforms Am J Physiol Endocrinol Metab, October 1, 1997; 273(4): E801 - E808. [Abstract] [Full Text] [PDF]

				P.-Y. Chang, L. J. Goodyear, H. Benecke, J. S. Markuns, and D. E. Moller Impaired Insulin Signaling in Skeletal Muscles from Transgenic Mice Expressing Kinase-deficient Insulin Receptors J. Biol. Chem., May 26, 1995; 270(21): 12593 - 12600. [Abstract] [Full Text] [PDF]