title: {beta}-Arrestin is crucial for ubiquitination and down-regulation of the insulin-like growth factor-1 receptor by acting as adaptor for the MDM2 E3 ligase.
abstract: 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.
authors.affiliation: Department of Oncology and Pathology, Division of Cellular and Molecular Tumor Pathology, Cancer Center Karolinska, R8:04, Karolinska Hospital, SE-171 76 Stockholm, Sweden.
authors.forename: Leonard
authors.initials: L
authors.lastname: Girnita
authors.forename: Sudha K
authors.initials: SK
authors.lastname: Shenoy
authors.forename: Bita
authors.initials: B
authors.lastname: Sehat
authors.forename: Radu
authors.initials: R
authors.lastname: Vasilcanu
authors.forename: Ada
authors.initials: A
authors.lastname: Girnita
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Lefkowitz
authors.forename: Olle
authors.initials: O
authors.lastname: Larsson
mesh_terms: D000818:Animals; D019390:Arrestins / Q000378:metabolism / Q000502:physiology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D047468:Immunoprecipitation; D008024:Ligands; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry; D011485:Protein Binding; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2; D034741:RNA, Small Interfering / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D025801:Ubiquitin / Q000737:chemistry* / Q000378:metabolism; D000071559:beta-Arrestin 1; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins
chemical_list: C000605253:ARRB1 protein, human; C000605254:ARRB2 protein, human; C000605255:Arrb1 protein, mouse; C000605258:Arrb2 protein, mouse; D019390:Arrestins; D008024:Ligands; D009687:Nuclear Proteins; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D043562:Receptors, G-Protein-Coupled; D025801:Ubiquitin; D000071559:beta-Arrestin 1; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins; C497206:MDM2 protein, human; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; D017526:Receptor, IGF Type 1; D046988:Proteasome Endopeptidase Complex