title: Mdm2-dependent ubiquitination and degradation of the insulin-like growth factor 1 receptor.
abstract: Recently, p53 was demonstrated to affect the expression of the insulin-like growth factor 1 receptor (IGF-1R), a receptor tyrosine kinase that plays a crucial role in growth and survival of cancer cells. However, the underlying mechanisms for interaction between p53 and IGF-1R are still not fully understood. One of the challenging questions remaining to be answered is why the wild-type p53, which per se represses the transcription of the IGF-1R gene, in overexpressed form is necessary for a high IGF-1R expression. In this study, we show that inhibition of p53 causes ubiquitination and down-regulation, through increased degradation, of the IGF-1R in human malignant melanoma cells. This effect, which was independent of the p53 status (i.e., wild type or mutated), was prevented if Mdm2 was coinhibited. Similar results were obtained in UV-irradiated human melanocytes (harboring wild-type p53), in which level of the IGF-1R increased after up-regulation of p53. Interestingly, the basal ubiquitination of the IGF-1R in untreated cells also depended on Mdm2. We could prove that Mdm2 physically associates with IGF-1R and that Mdm2 causes IGF-1R ubiquitination in an in vitro assay. Taken together our data provide evidence that Mdm2 serves as a ligase in ubiquitination of the IGF-1R and thereby causes its degradation by the proteasome system. Consequently, by sequestering Mdm2 in the cell nuclei, the level of p53 may indirectly influence the expression of IGF-1R. This role of Mdm2 and p53 represents an unexpected mechanism for the regulation of IGF-1R and cell growth.
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: Ada
authors.initials: A
authors.lastname: Girnita
authors.forename: Olle
authors.initials: O
authors.lastname: Larsson
mesh_terms: D016475:3T3 Cells / Q000378:metabolism; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology / Q000528:radiation effects; D016158:Genes, p53; D006801:Humans; D008545:Melanoma / Q000378:metabolism / Q000473:pathology; D051379:Mice; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D009687:Nuclear Proteins; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D025941:Protein Interaction Mapping; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000528:radiation effects; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D025801:Ubiquitin; D014466:Ultraviolet Rays
chemical_list: D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D020319:Oligodeoxyribonucleotides, Antisense; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D016159:Tumor Suppressor Protein p53; D025801:Ubiquitin; C497206:MDM2 protein, human; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; D017526:Receptor, IGF Type 1; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease