An unusual class of PITX2 mutations in Axenfeld-Rieger syndrome

Birth Defects Res A Clin Mol Teratol. 2006 Mar;76(3):175-81. doi: 10.1002/bdra.20226.

Abstract

Background: Mutations in the PITX2 homeobox gene are known to contribute to Axenfeld-Rieger syndrome (ARS), an autosomal-dominant developmental disorder. Although most mutations are in the homeodomain and result in a loss of function, there is a growing subset in the C-terminal domain that has not yet been characterized. These mutations are of particular interest because the C-terminus has both inhibitory and stimulatory activities.

Methods: In this study we used a combination of in vitro DNA binding and transfection reporter assays to investigate the fundamental issue of whether C-terminal mutations result in gain or loss of function at a cellular level.

Results: We report a new frameshift mutation in the PITX2 allele that predicts a truncated protein lacking most of the C-terminal domain (D122FS). This newly reported mutant and another ARS C-terminal mutant (W133Stop) both have greater binding than wild-type to the bicoid element. Of interest, the mutants yielded approximately 5-fold greater activation of the prolactin promoter in CHO cells, even though the truncated proteins were expressed at lower levels than the wild-type protein. The truncated proteins also had greater than wild-type activity in 2 other cell lines, including the LS8 oral epithelial line that expresses the endogenous Pitx2 gene.

Conclusions: The results indicate that the PITX2 C-terminal domain has inhibitory activity and support the notion that ARS may also be caused by gain-of-function mutations.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Abnormalities, Multiple / genetics*
  • Abnormalities, Multiple / metabolism
  • Animals
  • Anterior Eye Segment / abnormalities*
  • CHO Cells
  • Child, Preschool
  • Cricetinae
  • Cricetulus
  • DNA Mutational Analysis
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / metabolism
  • Dimerization
  • Female
  • Homeodomain Proteins / chemistry
  • Homeodomain Proteins / genetics*
  • Homeodomain Proteins / metabolism
  • Humans
  • Male
  • Mice
  • Mutation*
  • Syndrome
  • Tooth Abnormalities / genetics*
  • Tooth Abnormalities / metabolism
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism
  • Transcriptional Activation / physiology
  • Umbilical Cord / abnormalities*

Substances

  • DNA-Binding Proteins
  • Homeodomain Proteins
  • Transcription Factors
  • homeobox protein PITX2