Transcriptional Activation of the Insulin-Like Growth Factor I Receptor Gene by the Kruppel-Like Factor 6 (KLF6) Tumor Suppressor Protein: Potential Interactions between KLF6 and p53

• Published in: Endocrinology (Philadelphia) 2004-08, Vol.145 (8), p.3769-3777
• Main Authors: Rubinstein, Moran, Idelman, Gila, Plymate, Stephen R, Narla, Goutham, Friedman, Scott L, Werner, Haim
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cancer; CHO Cells; Colorectal carcinoma; Cricetinae; Fundamental and applied biological sciences. Psychology; Gene deletion; Gene expression; Gene regulation; Growth factors; Humans; Insulin-like growth factor I; Insulin-like growth factor I receptors; Insulin-like growth factor II; Insulin-like growth factors; Ir gene; Krueppel-like factor; Kruppel-Like Factor 6; Kruppel-Like Transcription Factors; Metastases; Metastasis; Nucleotides; p53 Protein; Phenotypes; Promoter Regions, Genetic; Prostate; Prostate cancer; Proto-Oncogene Proteins; Receptor, IGF Type 1 - genetics; Receptors; Trans-Activators - physiology; Transcription activation; Transcription factors; Transcriptional Activation; Tumor suppressor genes; Tumor Suppressor Protein p53 - physiology; Vertebrates: endocrinology; Zinc finger proteins
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2004-0173

The IGF system plays an important role in prostate cancer initiation and progression. Most of the biological actions of IGF-I and IGF-II are mediated by activation of the IGF-I receptor (IGF-IR). Evidence accumulated in recent years indicates that acquisition of the malignant phenotype is initially IGF-IR dependent, but progression toward metastatic stages is usually associated with a decrease in IGF-IR levels. The Kruppel-like factor 6 (KLF6) is a zinc finger-containing transcription factor that was shown to be mutated in a significant portion of prostate and other types of cancer. To examine the potential regulation of IGF-IR gene expression by KLF6, we measured KLF6 levels in prostate-derived cell lines displaying different levels of IGF-IR. The results of Western analysis showed that KLF6 levels were higher in nontumorigenic P69 cells expressing high IGF-IR levels than in metastatic M12 cells containing reduced IGF-IR levels. Transient coexpression of wild-type, but not mutated, KLF6 together with an IGF-IR promoter-luciferase reporter plasmid resulted in an approximately 3.4-fold stimulation of IGF-IR promoter activity. Furthermore, KLF6 expression induced a significant increment in endogenous IGF-IR levels. Deletion analysis of the IGF-IR promoter revealed that a cluster of four GC boxes located between nucleotides −399 and −331 mediates a significant portion of the transactivating effect of KLF6. KLF6, although unable to stimulate IGF-IR promoter activity in Sp1-null Drosophila-derived Schneider cells, significantly enhanced the effect of Sp1. To assess the potential interactions between KLF6 and p53 in the regulation of IGF-IR gene expression, transfections were performed in the colorectal cancer cell line HCT116+/+, which expresses p53, and its HCT116−/− derivative, which lacks p53. KLF6 exhibited an enhanced activity in p53-containing, compared with p53-null, cells. In addition, we were able to detect a physical interaction between KLF6 and p53. In summary, we have identified the IGF-IR gene as a novel downstream target for transcription factor KLF6. The regulation of IGF-IR gene expression by KLF6 may have significant implications in terms of cancer initiation and/or progression.