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Molecular and Cellular Biology, January 2001, p. 26-38, Vol. 21, No. 1
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.1.26-38.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Insulin Receptor Substrate 3 (IRS-3) and IRS-4 Impair IRS-1- and IRS-2-Mediated Signaling

Kaku Tsuruzoe, Renee Emkey, Kristina M. Kriauciunas, Kohjiro Ueki, and C. Ronald Kahn*

Research Division, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215

Received 24 March 2000/Returned for modification 23 May 2000/Accepted 5 October 2000

To investigate the roles of insulin receptor substrate 3 (IRS-3) and IRS-4 in the insulin-like growth factor 1 (IGF-1) signaling cascade, we introduced these proteins into 3T3 embryonic fibroblast cell lines prepared from wild-type (WT) and IRS-1 knockout (KO) mice by using a retroviral system. Following transduction of IRS-3 or IRS-4, the cells showed a significant decrease in IRS-2 mRNA and protein levels without any change in the IRS-1 protein level. In these cell lines, IGF-1 caused the rapid tyrosine phosphorylation of all four IRS proteins. However, IRS-3- or IRS-4-expressing cells also showed a marked decrease in IRS-1 and IRS-2 phosphorylation compared to the host cells. This decrease was accounted for in part by a decrease in the level of IRS-2 protein but occurred with no significant change in the IRS-1 protein level. IRS-3- or IRS-4-overexpressing cells showed an increase in basal phosphatidylinositol 3-kinase activity and basal Akt phosphorylation, while the IGF-1-stimulated levels correlated well with total tyrosine phosphorylation level of all IRS proteins in each cell line. IRS-3 expression in WT cells also caused an increase in IGF-1-induced mitogen-activated protein kinase phosphorylation and egr-1 expression (~1.8- and ~2.4-fold with respect to WT). In the IRS-1 KO cells, the impaired mitogenic response to IGF-1 was reconstituted with IRS-1 to supranormal levels and was returned to almost normal by IRS-2 or IRS-3 but was not improved by overexpression of IRS-4. These data suggest that IRS-3 and IRS-4 may act as negative regulators of the IGF-1 signaling pathway by suppressing the function of other IRS proteins at several steps.

* Corresponding author. Mailing address: Joslin Diabetes Center, One Joslin Place, Boston, MA 02215. Phone: (617) 732-2635. Fax: (617) 732-2593. E-mail: c.ronald.kahn{at}joslin.harvard.edu.

Molecular and Cellular Biology, January 2001, p. 26-38, Vol. 21, No. 1
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.1.26-38.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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