Abstract 12567: Cardiomyocyte Hypertrophy is Regulated by P300 Binding Protein 1, a Novel Binding Protein

Abstract

Background: Hypertrophic stimuli such as hemodynamic overload activate the cardiac signaling pathway that terminates in cardiomyocyte nuclei, thus changing the pattern of gene expression associated with cardiomyocyte hypertrophy. This hypertrophy eventually leads to systolic dysfunction and decompensated heart failure. Nuclear acetylation is a critical event in the activation of this hypertrophic gene expression and is mediated in part by intrinsic histone acetyltransferases (HAT) such as coactivator p300. p300-HAT activity is a potential pharmacological target for the prevention of heart failure. However, the regulation mechanism of p300-HAT activity is still unclear. In this study, we identified novel p300 binding partners by proteomic analysis and investigated the role of one of these proteins, p300 binding protein 1 (p300BP1), in the hypertrophic responses of cardiomyocytes. Methods and Results: To identify novel p300 binding proteins, cardiac-specific FLAG-p300 overexpressing mice were generated. Protein fractions from heart tissues of these mice and wild-type mice were purified with anti-FLAG-M2 agarose. Mass spectrometry analysis identified 553 novel p300 binding proteins, including kinases, phosphatases, methyltransferases, and transcriptional regulators. p300BP1 was selected for analysis. Binding was found to occur between baculovirus-expressed the recombinant genes FLAG-p300 full length and HA-p300BP1. The aa762-aa1098 fragment of p300 was required for this binding. In cultured cardiomyocytes, knockdown of p300BP1 prevented phenylephrine-induced increases in cardiomyocyte surface area and hypertrophic gene transcription factors such as ANF and BNP. Conversely, the overexpression of p300BP1 increased the surface area of cardiomyocytes and hypertrophic gene transcriptions. Furthermore, overexpression of p300BP1 significantly increased H3K9 acetylation in cultured cardiomyocytes. A reporter gene assay showed that p300BP1 enhanced p300/GATA4-mediated ANF and BNP promoter activation in HEK293T cells. Conclusions: We have identified multiple novel p300 binding proteins using a proteomics approach. p300BP1 may play an important role in p300/GATA4-dependent hypertrophic responses in cardiomyocytes.