title: Insulin-like growth factor-i regulates Kruppel-like factor-6 gene expression in a p53-dependent manner.
abstract: High-circulating IGF-I concentrations are associated with an increased risk for breast, prostate, and colorectal cancer. Krüppel-like factor-6 (KLF6) is a zinc finger tumor suppressor inactivated in prostate and other types of cancer. We have previously demonstrated that KLF6 is a potent transactivator of the IGF-I receptor promoter. The aim of the present study was to examine the potential regulation of KLF6 gene expression by IGF-I. The human colon cancer cell lines HCT116 +/+ and -/- (with normal and disrupted p53, respectively) were treated with IGF-I. Western blots, quantitative RT-PCR, and transfection assays were used to evaluate the effect of IGF-I on KLF-6 production. Signaling pathway inhibitors were used to identify the mechanisms responsible for regulation of KLF6 expression. Small interfering RNA against p53 and KLF6 was used to assess the role of p53 in regulation of KLF6 expression by IGF-I and to evaluate KLF6 involvement in cell cycle control. Results obtained showed that IGF-I stimulated KLF-6 transcription in cells with normal, but not disrupted, p53, suggesting that KLF6 is a downstream target for IGF-I action. Stimulation of KLF6 expression by IGF-I in a p53-dependent manner may constitute a novel mechanism of action of IGF-I, with implications in normal cell cycle progression and cancer biology.
authors.affiliation: Department of Human Molecular Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Itay
authors.initials: I
authors.lastname: Bentov
authors.forename: Goutham
authors.initials: G
authors.lastname: Narla
authors.forename: Hagit
authors.initials: H
authors.lastname: Schayek
authors.forename: Kuhihara
authors.initials: K
authors.lastname: Akita
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Plymate
authors.forename: Derek
authors.initials: D
authors.lastname: LeRoith
authors.forename: Scott L
authors.initials: SL
authors.lastname: Friedman
authors.forename: Haim
authors.initials: H
authors.lastname: Werner
mesh_terms: D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D045325:HCT116 Cells; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D000075723:Kruppel-Like Factor 6; D051741:Kruppel-Like Transcription Factors / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D034741:RNA, Small Interfering / Q000494:pharmacology; D017526:Receptor, IGF Type 1 / Q000502:physiology; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*
chemical_list: C105465:KLF6 protein, human; D000075723:Kruppel-Like Factor 6; D051741:Kruppel-Like Transcription Factors; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1