Abstract P1143: Med12 “Mediates” Transcriptional Regulation In The Heart

Abstract

The Mediator complex serves as a bridge to link transcriptional machinery and transcription factors (TFs) to control transcription, but the molecular mechanisms of transcriptional regulation by Mediator are not well-understood. Mediator is a large multiprotein complex organized as submodules, known as the head, body, tail, and kinase submodule. The CDK8 kinase submodule is known to regulate Mediator - RNA Polymerase II interaction. MED12 is an essential Mediator component, and within the kinase submodule, is required for CDK8 kinase activity. MED12 protein levels are increased in human heart failure biopsies and in the mouse heart after transverse aortic constriction (TAC)-induced heart failure. To test the hypothesis that increased levels of MED12 contributes to development of heart failure we generated cardiac-specific Med12 transgenic mice (cTg) by driving increased MED12 expression in cardiomyocytes using the αMHC promoter. Med12 overexpression leads to decreased cardiac function, measured as fractional shortening by serial echocardiography. Decreased cardiac function was accompanied by increased cardiac chamber size and dilation, without cardiac fibrosis. RNA sequencing of cardiomyocytes from cTg and control mice revealed that increased levels of MED12 leads to dysregulated calcium handling gene expression. MED12 is a transcriptional regulator, but does not directly bind DNA. To determine how MED12 regulates gene expression we screened for TFs that interact with MED12. We performed immunoprecipitation of MED12 and by mass spectrometry and determined that MED12 interacts with the TFs MEF2, CREB, and SRF. In follow-up experiments we demonstrated that MED12 interacts with the transcription factor (TF) MEF2 to regulate calcium handling genes. Current studies are focused on determining how MED12 binding coordinates gene expression through multiple TFs in cardiomyocytes. Collectively, our data demonstrate that increased MED12 expression leads to the development of heart failure, in part by dysregulation of gene expression. Therefore, precise regulation of MED12 levels is important to maintain normal cardiac function.