Nuclear translocation of insulin receptor substrate‐1 by the insulin receptor in mouse embryo fibroblasts

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Abstract
Translocation of the insulin receptor substrate‐1 (IRS‐1) to the nuclei has been reported to occur in cells stimulated by insulin‐like growth factor‐1 (IGF‐I) or expressing certain viral and cellular oncogenes. We show here that insulin can also induce nuclear translocation of IRS‐1 in mouse embryo fibroblasts (MEF), that do not express the type 1 insulin‐like growth factor receptor (IGF‐IR). Only the A isoform of the insulin receptor (IR) can induce IRS‐1 nuclear translocation, which is significant when the receptor is over‐expressed. At physiological receptor levels, translocation occurs only in a fraction of cells, and only at high concentrations of ligand.