title: Dissecting the Relation between a nuclear receptor and GATA: binding affinity studies of thyroid hormone receptor and GATA2 on TSHβ promoter.
abstract: BACKGROUND
  Much is known about how genes regulated by nuclear receptors (NRs) are switched on in the presence of a ligand. However, the molecular mechanism for gene down-regulation by liganded NRs remains a conundrum. The interaction between two zinc-finger transcription factors, Nuclear Receptor and GATA, was described almost a decade ago as a strategy adopted by the cell to up- or down-regulate gene expression. More recently, cell-based assays have shown that the Zn-finger region of GATA2 (GATA2-Zf) has an important role in down-regulation of the thyrotropin gene (TSHβ) by liganded thyroid hormone receptor (TR).
  
  
  RESULTS
  In an effort to better understand the mechanism that drives TSHβ down-regulation by a liganded TR and GATA2, we have carried out equilibrium binding assays using fluorescence anisotropy to study the interaction of recombinant TR and GATA2-Zf with regulatory elements present in the TSHβ promoter. Surprisingly, we observed that ligand (T3) weakens TR binding to a negative regulatory element (NRE) present in the TSHβ promoter. We also show that TR may interact with GATA2-Zf in the absence of ligand, but T3 is crucial for increasing the affinity of this complex for different GATA response elements (GATA-REs). Importantly, these results indicate that TR complex formation enhances DNA binding of the TR-GATA2 in a ligand-dependent manner.
  
  
  CONCLUSIONS
  Our findings extend previous results obtained in vivo, further improving our understanding of how liganded nuclear receptors down-regulate gene transcription, with the cooperative binding of transcription factors to DNA forming the core of this process.
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, São Paulo, Brazil.
authors.forename: Ana Carolina Migliorini
authors.initials: AC
authors.lastname: Figueira
authors.forename: Igor
authors.initials: I
authors.lastname: Polikarpov
authors.forename: Dmitry
authors.initials: D
authors.lastname: Veprintsev
authors.forename: Guilherme Martins
authors.initials: GM
authors.lastname: Santos
mesh_terms: D001483:Base Sequence; D015536:Down-Regulation; D050989:GATA2 Transcription Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020218:Response Elements; D037042:Thyroid Hormone Receptors beta / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D037322:Thyrotropin, beta Subunit / Q000235:genetics* / Q000378:metabolism; D014284:Triiodothyronine / Q000378:metabolism
chemical_list: D050989:GATA2 Transcription Factor; D037042:Thyroid Hormone Receptors beta; D037322:Thyrotropin, beta Subunit; D014284:Triiodothyronine