Insulin induces heterologous desensitization of G-protein-coupled receptor and insulin-like growth factor I signaling by downregulating beta-arrestin-1.
beta-Arrestin-1 mediates agonist-dependent desensitization and internalization of G protein- coupled receptors (GPCRs) and is also essential for GPCR mitogenic signaling. In addition, insulin-like growth factor I receptor (IGF-IR) endocytosis is facilitated by beta-arrestin-1, and internalization is necessary for IGF-I-stimulated mitogen-activated protein (MAP) kinase activation. Here, we report that treatment of cells for 12 h with insulin (100 ng/ml) induces an approximately 50% decrease in cellular beta-arrestin-1 content due to ubiquitination of beta-arrestin-1 and proteosome-mediated degradation. This insulin-induced decrease in beta-arrestin-1 content was blocked by inhibition of phosphatidylinositol-3 kinase (PI-3 kinase) and MEK with wortmannin and PD98059, respectively. We also found a marked decrease in the association of beta-arrestin-1 with the IGF-IR and a 55% inhibition of IGF-I-stimulated MAP kinase phosphorylation. In insulin-treated, beta-arrestin-1-downregulated cells, there was complete inhibition of lysophosphatidic acid (LPA) or isoproterenol (ISO)-stimulated MAP kinase phosphorylation. This was associated with a decrease in beta-arrestin-1 association with the beta2-AR as well as a decrease in beta-arrestin-1-Src and Src-beta2-AR association. Ectopic expression of wild-type beta-arrestin-1 in insulin-treated cells in which endogenous beta-arrestin-1 had been downregulated rescued IGF-I- and LPA-stimulated MAP kinase phosphorylation. In conclusion, we found the following. (i) Chronic insulin treatment leads to enhanced beta-arrestin-1 degradation. (ii) This downregulation of endogenous beta-arrestin-1 is associated with decreased IGF-I-, LPA-, and ISO-mediated MAP kinase signaling, which can be rescued by ectopic expression of wild-type beta-arrestin-1. (iii) Finally, these results describe a novel mechanism for heterologous desensitization, whereby insulin treatment can impair GPCR signaling, and highlight the importance of beta-arrestin-1 as a target molecule for this desensitization mechanism.[1]References
- Insulin induces heterologous desensitization of G-protein-coupled receptor and insulin-like growth factor I signaling by downregulating beta-arrestin-1. Dalle, S., Imamura, T., Rose, D.W., Worrall, D.S., Ugi, S., Hupfeld, C.J., Olefsky, J.M. Mol. Cell. Biol. (2002) [Pubmed]
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