Effects of acetylation on the function of a transcriptional co-activator

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The transcriptional co-activator p300 contains an intrinsic histone acetyltransferase (HAT) activity and is required for an array of cellular processes. Tight control of p300 is critical to ensure precise histone acetylation and gene activation. We have established that p300 is dynamically regulated by post-translational modifications and cellular distributions. In addition, we are the first to show that p300 is regulated by the cytoplasmic proteasome system. Our studies have provided novel insight on how cellular trafficking and spatial redistributions control the protein stability and transcriptional activity of p300. Interestingly, p300 is a bona fide acetylation substrate in vivo, and we have mapped the acetylation sites to its C-terminal region. We also found that E1A viral protein, a repressor of p300, enhances p300 autoacetylation while repressing p300 HAT activity. Based on these observations, we hypothesize that reversible acetylation plays critical roles in the control of p300 activity, which in turn affects p300 function in important cellular processes. We will first study the effects of acetylation on p300 function and turnover. We will identify and characterize the specific acetylation sites in p300. We will also generate mutants that mimic the acetylation sites and produce antibodies against the specific acetylated-lysine to study the impact of acetylation on protein stability and transcriptional activity of p300. Our goal is to determine the molecular basis for acetylation-mediated p300 regulation and their consequences on the function of p300 as a HAT, a scaffold, or a bridge on chromatin with respect to transcriptional activation. Our long term goals are to determine how these regulatory mechanisms affect p300-dependent gene expression from intracellular trafficking, protein turnover to transcriptional activation, and to determine the molecular basis for p300 regulation in a network biology fashion.