Transcription Programming in Cardiac Growth

描述（由申请人提供）：转录辅激活因子和组蛋白乙酰转移酶p300最初被确定为腺病毒E1A的细胞靶标，并且涉及许多基本细胞功能，包括增殖，分化和组织特异性基因表达。其他人和我们已经证明心肌生长，发育和基因表达对p300水平非常敏感。心肌肥大与p300水平显著升高有关。为了研究这种增加的意义，我们培育了6株心肌过表达p300（是内源性水平的1.5 - 5倍）的转基因小鼠。所有6个毒株均发展为严重的心脏肥厚，并以与p300水平和心脏负荷成正比的方式发展为心力衰竭。p300单倍不全的小鼠对压力过载的肥厚反应明显降低，并且不会发生心力衰竭。这些发现表明p300在诱导肥厚和向心力衰竭过渡中起关键作用。本提案的目的是确定p300在肥厚中作用的分子机制。一个被广泛接受的p300功能模型预测转录因子竞争有限的p300供应。例如，Jun （AP-1）和MyoD1根据p300的可用性参与竞争性转录激活。目前的建议将验证p300供应的增加对心肌肥厚生长是充分和必要的假设，通过缓解生长促进和肌肉特异性转录程序之间的竞争性相互作用。一个推论是，p300依赖性生长途径的持续激活导致心肌生长和凋亡紊乱。肥大对p300的需求将在表达可诱导的、心脏受限的野生型和特定区域缺失的p300转基因的互补小鼠品系中进行测试。我们将通过协同使用全基因组转录分析、染色质免疫沉淀测定和定量RNA分析，在p300功能获得和功能丧失的小鼠中表征p300靶向心肌基因的功能和调控基序。最后，我们将研究p300的可用性对心肌细胞增殖和凋亡敏感性的功能影响。这些实验将确定心脏肥厚和衰竭的关键机制，并阐明p300在细胞肥厚生长中的作用。

DESCRIPTION (provided by applicant): The transcriptional coactivator and histone acetyltransferase p300 was originally identified as a cellular target of adenovirus E1A, and has been implicated in many basic cell functions including proliferation, differentiation and tissue-specific gene expression. Others and we have shown that myocardial growth, development, and gene expression are extremely sensitive to p300 levels. Myocardial hypertrophy is associated with marked increases in p300 levels. To investigate the significance of this increase, we have generated 6 strains of transgenic mice with myocardial overexpression of p300 (1.5 to 5-fold of endogenous levels). All 6 strains develop severe cardiac hypertrophy, and progress to heart failure in a manner that is proportionate to their p300 levels and cardiac workload. Mice with haploinsufficiency of p300 have a markedly reduced hypertrophic response to pressure overload, and do not develop heart failure. These findings indicate that p300 plays a critical role in the induction of hypertrophy and the transition to heart failure. The objective of this proposal is to identify the molecular mechanisms underlying the role of p300 in hypertrophy. A widely accepted model for p300 function predicts that transcription factors compete for a limiting supply of p300. For example, Jun (AP-1) and MyoD1 engage in competitive transcription activation depending on the availability of p300. The current proposal will test the hypothesis that an increase in p300 supply is both sufficient and necessary for hypertrophic growth of the myocardium, through relief of a competitive interaction between growth-promoting and muscle-specific transcription programs. A corollary is that sustained activation of p3OO-dependent growth pathways leads to disordered myocardial growth and apoptosis. The requirement for p300 in hypertrophy will be tested in complementary mouse strains expressing inducible, cardiac-restricted wild type and specific domain-deleted p300 transgenes. We will characterize the functions and regulatory motifs of myocardial genes targeted by p300 in vivo, by the concerted use of genome-wide transcription profiling, chromatin immunoprecipitation assays, and quantitative RNA analysis, in mice with p300 gain- and loss-of-function. Finally, we will examine the functional effects of p300 availability on cardiomyocyte proliferation and apoptosis susceptibility. These experiments will identify critical mechanisms underlying cardiac hypertrophy and failure, and illuminate the role of p300 in hypertrophic growth of the cell.