Presentation description

Heart disease is the leading cause of death in the United States. It can be caused by changes in gene expression in the cardiomyocyte that lead to cellular and structural alterations of the heart. Thus, understanding the cellular mechanisms that lead to these changes could have future therapeutic applications for heart disease. Changes in gene expression are often a result of post-translational modifications (PTM) to chromatin, such as methylation. SMYD1 is a cardiomyocyte-specific methyltransferase (MT) enzyme that has been shown to regulate gene expression and play a role in preventing ischemic injury. Its characteristic PTM is the tri-methylation of histone H3 at K4. Its activity has also been shown to vary depending on the source of the histone H3 substrate. Our recent ChIP-MS experiments found that SMYD1a preferentially binds to nucleosomes containing the histone H3.3 variant. We hypothesize that variability in SMYD1's enzymatic activity stems from its substrate preference for histone variant H3.3. To investigate this, I utilized in-vitro histone MT assays and western blotting to quantify SMYD1's ability to methylate histone variants H3.1 and H3.3, the most abundant in human cardiomyocytes. My results suggest that SMYD1 methylates H3.3 at a two-fold higher rate in the presence of HSP90, a molecular chaperone shown to enhance SMYD1's enzymatic activity. This suggests that SMYD1 does preferentially methylate histone variant H3.3 over H3.1. Of over 300 known MT enzymes, only ATRX5 has been reported to show a substrate preference for different H3 variants. My results are the first report of a muscle-specific MT demonstrating preferential methylation of a specific histone H3 variant. These results provide insight on how SMYD1 regulates gene expression to influence the structure and function of the heart. Further research must investigate the interaction between H3 and HSP90 and the mechanism by which it influences SMYD1's preferential methylation of H3.3. This can advance our understanding of MT activity and the cellular mechanisms that influence heart disease.