Efeito da proteína citosólica ligante de triiodotironina (p38CTBP) na regulação da transcrição mediada por T3 e suas interações com proteínas nucleares

AUTOR(ES)

Ranieri Rodrigues de Oliveira

DATA DE PUBLICAÇÃO

2008

RESUMO

Background: The importance of the cytoplasmatic proteins in the uptake, storage and nuclear translocation of thyroid hormone is poorly understood. Moreover, the relation of cytosolic thyroid binding protein 38kDa (p38CTBP or simply CTBP) with nuclear transport of T3 and T3-mediated gene transcription is still controversial. The aim of this work was to investigate the role of CTBP in the T3-mediated thyroid receptor (TR) activation. Methods: T3 dose response curves were performed in CHO cells cotransfected with plasmids expressing TRb1, CTBP, and thyroid responsive elements driving the luciferase gene (TREs DR4, F2, PAL and TRH promoter). Whole cell and nuclear [125I]T3 transport assays were performed in CHO cells transfected or not with CTBP. Since CTBP could be localizated in the nucleus, we also measured the interactions of CTBP with TR and coregulator proteins such as SMRT, SRC1 through GST-pull down assays. Results: Overexpression of CTBP increased [125I]T3 uptake from 61.69.4 cpm/mg protein in control cells to 151.623.7 cpm/mg protein (p<0.05). In reporter gene assays, CTBP cotransfection increased TR maximum activation on TRE-PAL by 42%. Additionally CTBP overexpression in CHO cells increased T3 EC50 on TRE-DR4 by 5.5 fold. On the other hand, on the TRE-F2 and TRH promoter, a T3 negatively regulated gene, the co-transfection of CTPB did not change T3 activation and repression, respectively. Interesting, GST pull-down assays showed that CTBP directly interacted in vitro with GST-TRb1 and GST-SMRT, but not GST-SRC1. Conclusion: We demonstrated that CTBP increases intracellular T3 concentration and modulates T3-mediated gene transcription and this effect is TRE specific. Furthermore, CTBP directly interacted with TRb1 and the corepressor SMRT, but not with coactivator GRIP1. Taken together, these results suggest that CTBP may affect T3 action not only by changing T3 intracellular levels, but also interacting with proteins involved in T3 response.

ASSUNTO(S)

t3 ativação gênica receptor do hormônio tireóideano ciencias da saude proteína citosólica lizante de triodolironina

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