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

Endocrinology. 2004 Aug;145(8):3769-77. doi: 10.1210/en.2004-0173. Epub 2004 May 6.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • CHO Cells
  • Cricetinae
  • Humans
  • Kruppel-Like Factor 6
  • Kruppel-Like Transcription Factors
  • Promoter Regions, Genetic
  • Proto-Oncogene Proteins*
  • Receptor, IGF Type 1 / genetics*
  • Trans-Activators / physiology*
  • Transcriptional Activation*
  • Tumor Suppressor Protein p53 / physiology*


  • KLF6 protein, human
  • Kruppel-Like Factor 6
  • Kruppel-Like Transcription Factors
  • Proto-Oncogene Proteins
  • Trans-Activators
  • Tumor Suppressor Protein p53
  • Receptor, IGF Type 1