title: p53 regulates insulin-like growth factor-I (IGF-I) receptor expression and IGF-I-induced tyrosine phosphorylation in an osteosarcoma cell line: interaction between p53 and Sp1.
abstract: The insulin-like growth factor-I receptor (IGF-IR) is involved in tumorigenesis. The aim of the present study was to investigate whether the IGF-IR is a physiological target for p53 in osteosarcoma cells. The p53-induced regulation of IGF-IR levels was studied in a tetracycline-regulated expression system. When expressed in Saos-2, osteosarcoma cells that lack p53, wild-type p53 decreased, whereas mutated p53 increased IGF-IR expression, and IGF-I-induced tyrosine phosphorylation of the IGF-IR. Similarly, wild-type p53 decreased IGF-I-induced tyrosine phosphorylation of IRS-1. A functional and physical interaction between p53 and Sp1, in the regulation of the IGF-R, was studied in osteosarcoma cells. Expression of p53 decreased IGF-IR promoter activity, whereas no effect on promoter activity was seen by Sp1 expressed alone. However, Sp1 counteracted the inhibitory effect of p53 on IGF-IR promoter activity in a dose-dependent manner. Furthermore, wild-type and mutated p53 were coimmunoprecipitated with Sp1, indicating a physical interaction between p53 and Sp1. In conclusion, p53 regulates IGF-IR expression, as reflected by a reduction in IGF-IR protein and a parallel reduction in IGF-I-induced tyrosine phosphorylation of the IGF-IR and IRS-1 in an osteosarcoma cell line. These data indicate that the IGF-I receptor is a physiological target for p53 in osteosarcoma cells. Furthermore, data supporting an interaction between p53 and Sp1 in the regulation of the promoter activity of IGF-IR are presented.
authors.affiliation: Diabetes Branch, National Institute of Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-1770, USA. claes@ss.gu.se
authors.forename: C
authors.initials: C
authors.lastname: Ohlsson
authors.forename: N
authors.initials: N
authors.lastname: Kley
authors.forename: H
authors.initials: H
authors.lastname: Werner
authors.forename: D
authors.initials: D
authors.lastname: LeRoith
mesh_terms: D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009154:Mutation; D012516:Osteosarcoma / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D017526:Receptor, IGF Type 1 / Q000032:analysis* / Q000235:genetics; D016329:Sp1 Transcription Factor / Q000502:physiology*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000502:physiology; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D016329:Sp1 Transcription Factor; D016159:Tumor Suppressor Protein p53; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1