Abstract 350: High-Mobility Group Protein B2 is Essential in Maintaining Normal Cardiac Gene Expression

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Heart hypertrophy is a complex disease that involves differential expression of hundreds of genes and requires highly coordinated chromatin remodeling events that must facilitate such genome-wide changes in gene expression. We examine the genome-wide distribution of a chromatin structural protein, High-Mobility Group Protein B2 (HMGB2) in isolated cardiac myocytes with or without adrenergic receptor agonist. We report a comprehensive map of HMGB2 binding in both normal and hypertrophic cardiac myocytes, and find that HMGB2 preferentially localizes to promoters, CpG islands, enhancers and transcription factor binding sites. Moreover, we find that upon hypertrophic stimulation, HMGB2 peaks move from regulatory elements to intergenic regions. Because both HMGB2 knock-down and PHE treatment can induce hypertrophic growth, we compare gene expression dynamics between HMGB2 knock-down and PHE treatment, and find hypertrophy-related gene expression pattern upon HMGB2 knock-down is different from the one after PHE treatment. This also indicates the existence of multiple pathways that lead to hypertrophic growth. Further study reveals that HMGB2 co-localizes with many other functional elements including p300 and CTCF. Interestingly, we find that HMGB2 binding profiles are different at the binding sites of four cardiac transcription factors, MEF2A, NKX2.5, GATA4 and SRF. More specifically, HMGB2 localization is higher at MEF2A binding sites, indicating that HMGB2 may be involved in facilitating the functioning of MEF2A. Finally, we calculate the DNA bendability score based on the primary sequence of genome and correlate it with HMGB2 binding intensity. Consistent with the understanding that HMGB2 bends DNA toward DNA major groove, we find a positive correlation between HMGB2 binding and DNA bending propensity. Surprisingly, PHE treatment in NRVMs induced the relocation of HMGB2 to less bendable intergenic regions. Taken together, our data conclude that HMGB2 is required for maintaining the normal cardiac gene expression pattern, and its binding to cardiac chromatin is dynamically altered during hypertrophic growth.

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