Characterization of Nkx3.2 DNA binding specificity and its requirement for somitic chondrogenesis

J Biol Chem. 2003 Jul 25;278(30):27532-9. doi: 10.1074/jbc.M301461200. Epub 2003 May 13.

Abstract

We have previously shown that Nkx3.2, a member of the NK class of homeoproteins, functions as a transcriptional repressor to promote somitic chondrogenesis. However, it has not been addressed whether Nkx3.2 can bind to DNA in a sequence-specific manner and whether DNA binding by Nkx3.2 is required for its biological activity. In this work, we employed a DNA binding site selection assay, which identified TAAGTG as a high affinity Nkx3.2 binding sequence. Sequence-specific binding of Nkx3.2 to the TAAGTG motif in vitro was confirmed by electrophoretic mobility shift assays, and mutagenesis of this sequence revealed that HRAGTG (where H represents A, C, or T, and R represents A or G) comprises the consensus DNA binding site for Nkx3.2. Consistent with these findings, the expression of a reporter gene containing reiterated Nkx3.2 binding sites was repressed in vivo by Nkx3.2 co-expression. In addition, we have generated a DNA nonbinding point mutant of Nkx3.2 (Nkx3.2-N200Q), which contains an asparagine to glutamine missense mutation in the homeodomain. Interestingly, despite being defective in DNA binding, Nkx3.2-N200Q still retains its intrinsic transcriptional repressor function. Finally, we demonstrate that unlike wild-type Nkx3.2, Nkx3.2-N200Q is unable to activate the chondrocyte differentiation program in somitic mesoderm, indicating that DNA binding by Nkx3.2 is critical for this factor to induce somitic chondrogenesis.

Publication types

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

MeSH terms

  • 3T3 Cells
  • Amino Acid Motifs
  • Animals
  • Asparagine / chemistry
  • Base Sequence
  • Binding Sites
  • Chick Embryo
  • Chondrocytes / metabolism
  • Cloning, Molecular
  • DNA / metabolism*
  • Genes, Reporter
  • Glutamine / chemistry
  • Glutathione Transferase / metabolism
  • Homeodomain Proteins / chemistry*
  • Homeodomain Proteins / genetics
  • Homeodomain Proteins / metabolism
  • Mice
  • Molecular Sequence Data
  • Mutation, Missense
  • Plasmids / metabolism
  • Protein Binding
  • Protein Structure, Tertiary
  • Recombinant Fusion Proteins / metabolism
  • Recombinant Proteins / metabolism
  • Retroviridae / genetics
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sequence Homology, Nucleic Acid
  • Transcription Factors / chemistry*
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • Transcription, Genetic

Substances

  • Homeodomain Proteins
  • Nkx3-2 protein, mouse
  • Recombinant Fusion Proteins
  • Recombinant Proteins
  • Transcription Factors
  • Glutamine
  • Asparagine
  • DNA
  • Glutathione Transferase