Dissecting the Relation between a nuclear receptor and GATA: binding affinity studies of thyroid hormone receptor and GATA2 on TSHβ promoter.
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.
Figueira
Ana Carolina Migliorini
AC
Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, São Paulo, Brazil.
Polikarpov
Igor
I
Veprintsev
Dmitry
D
Santos
Guilherme Martins
GM
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
D050989:GATA2 Transcription Factor; D037042:Thyroid Hormone Receptors beta; D037322:Thyrotropin, beta Subunit; D014284:Triiodothyronine