Dissecting a post-translational modification code in cardiac reprogramming

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During development and evolution, cell fate changes are guided by cell’s ability to change its transcriptional program with posttranslational modifications (PTMs) on both proteins and chromatin. PTMs of histones have been extensively studied as a coding system to guide alterations in cell plasticity and cell fate, such as differentiation/programming and de-differentiation/reprogramming. The histone PTM coding system includes phosphorylation, acetylation, methylation, and ATP-dependent chromatin remodeling. In parallel, PTMs of free proteins, such as phosphorylation and acetylation of transcription factors, are also essential for organ development and cell differentiation. These PTMs in both histones and free proteins are often catalyzed by the same set of epigenetic enzymes, strongly suggesting a dynamic interplay of PTM coding between histones and epigenetic and transcription factors. However, few systematic studies have been pursued to define the functional output of PTMs as a coding system. Furthermore, the potential synergistic effect of PTMs on both histones and free factors in cell fate changes are poorly explored. Therefore, a deep understanding of the PTM code on both free proteins (ie. key cardiac transcription factors and epigenetic factors) and histones and how they work together will lead to novel insights into cell fate determination and cardiac reprogramming. Our investigation of cardiac reprogramming uncovered a unique phosphorylation code in 14-3-3 binding motifs (PC14-3-3). We hypothesize that activation of a phosphorylation code in 14-3-3 binding motifs triggers a re-arrangement of protein-protein interactome among PC14-3-3 containing reprogramming factors, epigenetic factors, and chromatin, which work synergistically in stimulating cardiac reprogramming. Specific aims: Aim 1: Identify the key factors containing PC14-3-3 essential for cardiac reprogramming. We will test the hypothesis that PC14-3-3 in key reprogramming, epigenetic and histone proteins plays a critical role in reprogramming. These studies will build a knowledge foundation of PC14-3-3 in cardiac reprogramming. Aim 2: Determine PC14-3-3 guided molecular mechanism in stimulating cardiac reprogramming. We will test the hypothesis that PC14-3-3 activation triggers a protein-protein dynamic interplay among PC14-3-3 code containing reprogramming factors (Mef2c and Gata4), epigenetic factors (Hdac4 and Brg1), and histones H3 (H3S10 and H3S28). These studies will establish PC14-3-3 directed epigenetic and chromatin landscape changes in driving cardiac reprogramming. Aim 3: Examine PC14-3-3-guided cardiac reprogramming toward therapeutic applications. We will test the hypothesis that PC14-3-3 stimulates cardiac reprogramming in human cells and clinically relevant animal models. These studies will establish the pre-clinical application of PC14-3-3 code in cardiac reprogramming and build a novel and efficient platform for reprogramming-mediated heart repair.