Abstract
The actions of IGF-I and IGF-II are thought to be largely due to their activation of the IGF-I receptor. However, IGF-II can also bind with high affinity to, and effectively activate, an isoform of the insulin receptor (IR-A) that lacks a sequence at the carboxyl-terminal end of the extracellular α subunit due to the alternative splicing of exon 11. This isoform is poorly activated by IGF-I. Here, we show that IGF-II, but not IGF-I, induces potent autophosphorylation of residues Y1158, Y1162, and Y1163 in the activation loop of the kinase domain and tyrosine 960 in the juxtamembrane region of both IR-A and IR-B (exon 11+) isoforms. We have also found, by using IGF chimeras, that the C domain of IGF-II completely accounts for the ability of IGF-II to stimulate IR autophosphorylation compared with IGF-I. We further show that the C domains are responsible for the differential abilities of IGF-II and IGF-I to activate phosphorylation of insulin receptor substrate-1 and Akt, as well as their ability to induce migration and cell survival via the IR-A. Finally, we show for the first time that IGF signaling through the IR-A can protect cells from butyrate-induced apoptosis. In summary, our studies define the structural determinants that allow potent IGF-II signaling and regulation of cellular functions through the IR-A and provide novel insights into IGF signaling via the IR.
Original language | English (US) |
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Pages (from-to) | 1029-1036 |
Number of pages | 8 |
Journal | Endocrinology |
Volume | 147 |
Issue number | 2 |
DOIs | |
State | Published - Feb 2006 |
ASJC Scopus subject areas
- Endocrinology