The Synergistic Activation Of Histone Acetylation P300on The Expression Of Marker Gene Of Myocardial Hypertrophy Induced By MRTFs

Cardiac hypertrophy is one of common pathological changes in heart diseases, and heartfailure and/or arrhythmia caused by further development of cardiac hypertrophy is still the maincauses of death. Cardiac hypertrophy closely related to the enhanced expression of cardiacembryonic genes, such as atrial natriuretic factor (ANF), cardiac-α-actin (α-actin), myosin heavychain (MHC). However, pathogenesis of cardiac hypertrophy, the molecular mechanism inparticular, has not yet been explained.Serum response factor (SRF) is a ubiquitous regulatory factor which, in particular, is closelyrelated to the development of muscle cells. Combined by cis-acting elements CarG box, it actson target genes to regulate expression of downstream genes. SRF can bind many commontranscription factors to form transcription complexes, which is the reason why it plays differentroles in the process of cell differentiation. It has been found so far that myocardin may be themost powerful transcription factor of SRF that is specifically expressed in cardiac and smoothmuscle cells. Through protein-protein interactions with SRF to form complexes and thenbind to CarG box on the target gene, the myocardin can activate the expression of cardiachypertrophy marker gene (including ANF, the α-actin, etc.) to regulate cell differentiation andproliferation and affect the development of heart and smooth muscle cell, growth, differentiationand apoptosis. The family members of myocardin include MRTF-A and MRTF-B, unlikemyocardin, their distribution is systemic. Our laboratory’s previous studies have confirmed thatmyocardin and MRTF-A can induce cardiac hypertrophy. However, the regulatory mechanismsof MRTFs in regulating cardiac hypertrophy remain to be elucidatied.Histone acetyltransferase (HATs) acetylates the end of the histone amino acids changing thenucleosome of compact type to dispersed structure, which allows the transcription activationfactor to approach the DNA inducing the gene expression. Studies have demonstrated that theexcessive acetylation of HATs and histone trigger cardiac hypertrophy, but how proteintranscription factors and/or synergistic transcription factors combine with HATs to affectcardiac hypertrophy needs further studies. The previous studies have shown that in smoothmuscle cells, histone deacetylase P300interacts with myocardin/MRTF-A-of SRF complexes tosynergistically induce the expression of relevant differentiation marker gene. However, how theyinteract in the myocardial cells and cardiac hypertrophy and its mechanism remain unclear.This study aimed to explore the interaction between p300and Myocardin/MRTF-A inmyocardial cells and the relationship of cardiac hypertrophy in animal models revealing theeffects of histone acetylation/deacetylation inducing myocardin cardiac hypertrophy and itspossible molecular mechanisms, which provides an important fundamental research forpathogenesis of cardiac hypertrophy, and preliminary studies for the development of new drugson prevention and treatment of pathological mechanisms.In this study, reporter gene assay was used to study p300and Myocardin/MRTF-Asynergistically enhancing the transcriptional activity of the downstream gene promoter in cos7 cells and myocardial cells. The result showed that p300in-Myocardin and p300in-MRTF-A canenhance the activity of ANF, α-actin and MHC promoter, especially ANF. However, thetranscription activation of p300is not obvious, which means that myocardin and MRTF-Atranscription are activated by interaction of p300and SRF binding to cis-acting elements CArGbox, thereby regulating the expression of cardiac hypertrophy marker genes ANF participating inthe regulation of cardiac hypertrophy in the pathological process. By comparison, we found thatMyocardin and p300-Myocardin was stronger than that of MRTF-A and p300in-MRTF-A,which was also consistent with the previous reports. Deacetylase HDAC5has significantinhibition on Myocardin, MRTF-A, p300in-Myocardin and p300in-MRTF-A, which showedthat the synergistic activation effect of p300on Myocardin/MRTF-A was accomplished throughacetylated histone.Inducing effect of p300with myocardin and MRTF-A on cardiac hypertrophy was studiedthrough the transcription in myocardial cells by myocardin and MRTF-A synergized by p300plus morphological observation, Western blotting and RT-PCR.The results showed that the histone acetyltransferase p300with myocardin can synergisticallyincrease the expression of differentiation marker genes ANF, α-actin and MHC, inducingcardiomyocyte hypertrophy.After establishment of animal models of cardiac hypertrophy by abdominal aortic ligation,the pathological changes of morphology in control group and model group were analyzed;Immunohistochemistry, RT-PCR and Western blot techniques were used to detectendogenous myocardin, MRTF-A, p300, HDAC5, the expression difference of mRNA andprotein level of differentiation and proliferation marker gene. The results showed that in thehypertrophy model, the differentiation marker gene expression was significantly enhanced whileproliferation marker gene expression were reduced accordingly; Meanwhile, MRTF-A and p300expression in the model group increased despite that there were no significant changes inmyocardin expression, which indicated that as the p300expression levels rised, the combinationof myocardin/MRTF-A and p300started the differentiation marker gene expression, whichled to cardiac hypertrophy. Of course, this needs to be confirmed by further studies.