Structural determinants for high-affinity binding of insulin-like growth factor II to insulin receptor (IR)-A, the exon 11 minus isoform of the IR

Mol Endocrinol. 2004 Oct;18(10):2502-12. doi: 10.1210/me.2004-0183. Epub 2004 Jun 17.


The insulin receptor (IR) lacking the alternatively spliced exon 11 (IR-A) is preferentially expressed in fetal and cancer cells. The IR-A has been identified as a high-affinity receptor for insulin and IGF-II but not IGF-I, which it binds with substantially lower affinity. Several cancer cell types that express the IR-A also overexpress IGF-II, suggesting a possible autocrine proliferative loop. To determine the regions of IGF-I and IGF-II responsible for this differential affinity, chimeras were made where the C and D domains were exchanged between IGF-I and IGF-II either singly or together. The abilities of these chimeras to bind to, and activate, the IR-A were investigated. We also investigated the ability of these chimeras to bind and activate the IR exon 11+ isoform (IR-B) and as a positive control, the IGF-I receptor (IGF-1R). We show that the C domain and, to a lesser extent, the D domains represent the principal determinants of the binding differences between IGF-I and IGF-II to IR-A. The C and D domains of IGF-II promote higher affinity binding to the IR-A than the equivalent domains of IGF-I, resulting in an affinity close to that of insulin for the IR-A. The C and D domains also regulate the IR-B binding specificity of the IGFs in a similar manner, although the level of binding for all IGF ligands to IR-B is lower than to IR-A. In contrast, the C and D domains of IGF-I allow higher affinity binding to the IGF-1R than the analogous domains of IGF-II. Activation of IGF-1R by the chimeras reflected their binding affinities whereas the phosphorylation of the two IR isoforms was more complex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Alternative Splicing
  • Amino Acid Sequence
  • Animals
  • Exons / genetics*
  • Humans
  • Insulin / chemistry
  • Insulin / genetics
  • Insulin-Like Growth Factor I / genetics
  • Insulin-Like Growth Factor I / metabolism
  • Insulin-Like Growth Factor II / chemistry
  • Insulin-Like Growth Factor II / genetics
  • Insulin-Like Growth Factor II / metabolism*
  • Mice
  • Mice, Inbred BALB C
  • Molecular Sequence Data
  • Protein Isoforms / chemistry
  • Protein Isoforms / genetics
  • Receptor, Insulin / genetics*
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Restriction Mapping
  • Sequence Deletion


  • Insulin
  • Protein Isoforms
  • Recombinant Fusion Proteins
  • Insulin-Like Growth Factor I
  • Insulin-Like Growth Factor II
  • Receptor, Insulin