Specific repression of beta-globin promoter activity by nuclear ferritin

Proc Natl Acad Sci U S A. 2001 Jul 31;98(16):9145-50. doi: 10.1073/pnas.151147098.

Abstract

Developmental hemoglobin switching involves sequential globin gene activations and repressions that are incompletely understood. Earlier observations, described herein, led us to hypothesize that nuclear ferritin is a repressor of the adult beta-globin gene in embryonic erythroid cells. Our data show that a ferritin-family protein in K562 cell nuclear extracts binds specifically to a highly conserved CAGTGC motif in the beta-globin promoter at -153 to -148 bp from the cap site, and mutation of the CAGTGC motif reduces binding 20-fold in competition gel-shift assays. Purified human ferritin that is enriched in ferritin-H chains also binds the CAGTGC promoter segment. Expression clones of ferritin-H markedly repress beta-globin promoter-driven reporter gene expression in cotransfected CV-1 cells in which the beta-promoter has been stimulated with the transcription activator erythroid Krüppel-like factor (EKLF). We have constructed chloramphenicol acetyltransferase reporter plasmids containing either a wild-type or mutant beta-globin promoter for the -150 CAGTGC motif and have compared the constructs for susceptibility to repression by ferritin-H in cotransfection assays. We find that stimulation by cotransfected EKLF is retained with the mutant promoter, whereas repression by ferritin-H is lost. Thus, mutation of the -150 CAGTGC motif not only markedly reduces in vitro binding of nuclear ferritin but also abrogates the ability of expressed ferritin-H to repress this promoter in our cell transfection assay, providing a strong link between DNA binding and function, and strong support for our proposal that nuclear ferritin-H is a repressor of the human beta-globin gene. Such a repressor could be helpful in treating sickle cell and other genetic diseases.

MeSH terms

  • Animals
  • Base Sequence
  • Cell Line
  • DNA / metabolism
  • DNA-Binding Proteins / metabolism
  • Ferritins / metabolism
  • Ferritins / physiology*
  • Globins / genetics*
  • Humans
  • Kruppel-Like Transcription Factors
  • Nuclear Proteins / metabolism
  • Nuclear Proteins / physiology*
  • Promoter Regions, Genetic*
  • Protein Binding
  • Sequence Homology, Nucleic Acid
  • Transcription Factors / metabolism
  • Transfection

Substances

  • DNA-Binding Proteins
  • Kruppel-Like Transcription Factors
  • Nuclear Proteins
  • Transcription Factors
  • erythroid Kruppel-like factor
  • Globins
  • DNA
  • Ferritins