Abstract 16877: Transducin Beta-Like Protein 1 Suppresses Hypertrophy-Responsive Gene Transcription in Cardiomyocytes by Inhibiting P300-Induced Acetylation of Gata4
Introduction: During the development of heart failure, cardiomyocytes undergo maladaptive hypertrophy by changing gene expression. GATA4 is one of the transcription factors involved in the regulation of cardiac hypertrophy. In response to hypertrophic stimuli, GATA4 forms a large complex with functional proteins including an intrinsic histone acetyltransferase, p300. p300 serves as a coactivator of GATA4 and is required for its acetylation and DNA binding. We analyzed GATA4-binding proteins using a proteomic approach and identified transducin beta-like protein 1 (TBL1) as a novel GATA4-binding partner. TBL1 is a component of nuclear receptor corepressor /histone deacetylase 3 (HDAC3) complex, which regulates various gene transcriptions. However, functional relationships between p300/GATA4 and TBL1/NCoR/HDAC3 remain unknown.
Hypothesis: We assessed the hypothesis that TBL1 regulates p300/GATA4-dependent transcriptional pathway and hypertrophy-responsive gene transcription in cardiomyocytes.
Methods and Results: GST pull-down assay and immunoprecipitation followed by western blotting demonstrated that TBL1 interacted with GATA4. Overexpression of TBL1 significantly repressed p300/GATA4-induced activations of atrial natriuretic factor (ANF) and endothelin-1 (ET-1) promoters in HEK293T cells. TBL1 repressed p300-induced acetylation of GATA4 and enhanced the binding between HDAC3 and GATA4. In contrast, a mutant of TBL1, lacking the activity of binding to HDAC3, was unable to suppress p300/GATA4-induced promoter activities. Furthermore, overexpression of TBL1 significantly inhibited phenylephrine (PE)-induced hypertrophic responses such as myofibrillar organization, an increase in the cell size, and the transcriptional activation of ANF and ET-1 promoters in primary cultured cardiomyocyte. Conversely, knockdown of TBL1 by RNAi enhanced mRNA level of ANF. Finally, the interaction of TBL1 with HDAC3 decreased by treatment with PE in cardiomyocytes.
Conclusion: TBL1 forms a functional protein complex with GATA4, and suppresses GATA4 acetylation and hypertrophic gene transcriptions in cardiomyocytes. These suppressive effects by TBL1 may be mediated, in part, through recruiting HDAC3 onto GATA4.
- © 2013 by American Heart Association, Inc.