Thyroid transcription factor 1 rescues PAX8/p300 synergism impaired by a natural PAX8 paired domain mutation with dominant negative activity

Mol Endocrinol. 2005 Jul;19(7):1779-91. doi: 10.1210/me.2004-0426. Epub 2005 Feb 17.


Mutations in the paired domain transcription factor PAX8 are a rare cause of congenital hypothyroidism due to thyroid dysgenesis. We identified a novel and unique PAX8 mutation segregating in seven affected members of a three-generations family. The mutation replaces an invariant serine residue within helix 2 of the paired DNA-binding domain for phenylalanine. The mutant protein (PAX8-S48F) does not induce the thyroglobulin promoter in nonthyroid cells, but displays almost half of wild-type PAX8 activity in thyroid cells. PAX8-S48F shows no defect in expression, nuclear targeting, or DNA binding and retains the ability to synergize with thyroid transcription factor 1 (TTF-1, NKX2.1). However, we found that in nonthyroid cells, the acetylation-independent synergism with the general transcriptional adaptor p300 is completely abrogated, suggesting that PAX8-S48F may be unable to efficiently recruit p300. Reconstitution experiments in nonthyroid cells reveal that TTF-1 can partially rescue PAX8-S48F/p300 synergism and thus reproduce the situation in thyroid cells. These functional characteristics result in a dominant negative effect of PAX8-S48F on coexpressed wild-type PAX8 activity, which is not observed in paired domain mutations with DNA binding defect. Our results describe the first dominant negative missense mutation in a paired domain and provide evidence for a crucial role of the p300 coactivator in mediating the functional synergism between PAX8 and TTF-1 in thyroid-specific gene expression.

Publication types

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

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Cell Nucleus / chemistry
  • Cell Nucleus / metabolism
  • Child
  • DNA-Binding Proteins / analysis
  • DNA-Binding Proteins / genetics*
  • DNA-Binding Proteins / metabolism*
  • Female
  • Humans
  • Hypothyroidism / genetics*
  • Male
  • Middle Aged
  • Mutation, Missense
  • Nuclear Proteins / analysis
  • Nuclear Proteins / genetics*
  • Nuclear Proteins / metabolism*
  • PAX8 Transcription Factor
  • Paired Box Transcription Factors
  • Promoter Regions, Genetic / genetics
  • Protein Structure, Tertiary
  • Serine / genetics
  • Thyroglobulin / genetics
  • Thyroid Gland / cytology
  • Thyroid Gland / metabolism
  • Thyroid Nuclear Factor 1
  • Trans-Activators / analysis
  • Trans-Activators / genetics*
  • Trans-Activators / metabolism*
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcriptional Activation / genetics


  • DNA-Binding Proteins
  • NKX2-1 protein, human
  • Nuclear Proteins
  • PAX8 Transcription Factor
  • PAX8 protein, human
  • Paired Box Transcription Factors
  • Thyroid Nuclear Factor 1
  • Trans-Activators
  • Transcription Factors
  • Serine
  • Thyroglobulin