Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 280, Issue 26, Pages 24412-24419Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M501129200
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- NHLBI NIH HHS [HL16037, HL 70631] Funding Source: Medline
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The insulin-like growth factor-1 receptor ( IGF-1R) plays important roles in physiological growth and aging as well as promoting several crucial functions in cancer cells. However, the molecular mechanisms involved in expression and down- regulation of IGF-1R are still poorly understood. Here we provide evidence that beta-arrestin, otherwise known to be involved in the regulation of G protein- coupled receptors, serves as an adaptor to bring the oncoprotein E3 ubiquitin ligase MDM2 to the IGF-1R. In this way, beta-arrestin acts as a crucial component in the ubiquitination and down-regulation of the receptor. Both MDM2 and beta-arrestin co-immunoprecipitated with the IGF-1R. The beta-arrestin isoform 1 appeared to be more strongly associated with the receptor than isoform 2, and in a molecular context it was 4-fold more efficient in inducing polyubiquitination of IGF-1R, a reaction that required the presence of beta-arrestin and MDM2. Ligand stimulation accelerated IGF-1R ubiquitination. In mouse P6 cells (overexpressing human IGF-1R) absence of beta-arrestin 1, but not of beta-arrestin 2, blocked ubiquitination of IGF-1R. Conversely, in the two studied human melanoma cell lines both beta-arrestin isoforms seemed to be involved in IGF-1R ubiquitination. However, because depletion of beta-arrestin 1 almost completely eliminated degradation, and IGF-1 induced down-regulation of the receptor in these cells, whereas beta-arrestin 2 only had a partial effect, beta-arrestin 1 seems to the more important isoform in affecting the expression of IGF-1R. To our knowledge this is the first study demonstrating a defined molecular role of beta-arrestin with direct relevance to cell growth and cancer.
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