Abstract 12693: SNF5/INI1 Inhibits Hypertrophic Responses by Suppressing p300/GATA4-Dependent Pathways in Cardiomyocytes
Introduction: Nuclear acetylation is recognized as a critical event during myocardial cell hypertrophy. An intrinsic histone acetyltransferase (HAT), p300, is required for acetylation and the transcriptional activity of GATA4 as well as for pathological cardiomyocyte hypertrophy and the development of heart failure in vivo. Employing mass spectrometric analyses, we recently identified SNF5/INI1, a component of the human SWI/SNF chromatin remodeling complex, as a novel GATA4-binding partner. However, the precise roles of SNF5/INI1 during cardiomyocyte hypertrophy are unknown.
Methods and Results: Using glutathione S-transferase pull-down assays, we showed that SNF5/INI1 directly bound not only to GATA4 but also to p300. A series of assays using multiple mutants of SNF5/INI1 and GATA4 revealed that the SNF5/INI1 Repeat I domain bound to the GATA4 C-terminal zinc finger domain, and that the SNF5/INI1 Repeat II domain bound to the p300 C/H-3 domain. In HEK293 cells, immunoprecipitation followed by Western-blot analysis demonstrated that SNF5/INI1 bound to both GATA4 and p300. The overexpression of SNF5/INI1 inhibited a p300-induced increase in the acetylation of GATA4 and p300/GATA4-induced activities of hypertrophy-responsive atrial natriuretic factor (ANF) and endothelin-1 (ET-1) promoters. Based on the chromatin immunoprecipitation assays, the overexpression of SNF5/INI1 suppressed the p300-induced increase in the DNA-binding activity of GATA4 onto GATA elements within the ANF promoter in HEK293 cells. Conversely, knockdown of SNF5/INI1 by siRNA increased p300/GATA4-induced hypertrophy-responsive gene transcription in these cells. Moreover, the overexpression of SNF5/INI1 significantly repressed phenylephrine-induced hypertrophic responses such as the myofibrillar organization, increase in cell size and activation of the ANF and ET-1 promoters in cardiomyocytes.
Conclusions: SNF5/INI1 forms a functional complex with p300/GATA4 on hypertrophic response gene promoters in cardiomyocytes. SNF5/INI1 plays an inhibitory role in cardiomyocyte hypertrophy by suppressing p300/GATA4-dependent transcription.
- © 2011 by American Heart Association, Inc.