Cellular Regulation of Protein Phosphatase 2A Following DNA Damage

Danielle Grams1,2, Jessica McDaniel2, Fanqi Bai2, Jeff Painter2 and PK Epling-Burnette2,3, 1The Honors College, University of South Florida, Tampa, FL, 2Immunology Program, H. Lee Moffitt Cancer Center, Tampa, FL, 3James A. Haley VA Hospital, Tampa, FL. Protein phosphatase 2A (PP2A), the most abundant serine/threonine phosphatase in the cell, is involved in multiple processes including cell cycle regulation, signal transduction, apoptosis and DNA repair. Post-translational modifications on the catalytic subunit of the trimeric holoenzyme, including phosphorylation of Tyr307, regulate its phosphatase activity. It is suspected that dephosphorylation of this regulatory site may be mediated through an autocatalytic event that would require acquisition of phospho-tyrosine substrate specificity. The goal of this study was to determine whether DNA damage alters the phosphorylation of Tyr307 and if the phosphorylation status of PP2A can be reversed in the presence of PP2Ac pharmacologic inhibitors. Human Embryonic Kidney (HEK) cells stably transfected with Hemagglutinin (HA)-tagged PP2A or control vector were treated with DNA damaging stimuli. Phosphorylation of subsequent HA-PP2A was determined via immunoprecipitation and Western Blot analysis. After exposure to DNA damaging agents (TNFα, UVB), the phosphorylation of PP2A is significantly reduced. Collectively, the results suggest that DNA damaging agents regulate PP2A phosphorylation in HEK cells. Further experiments, however, are needed to fully elucidate this mechanism. Understanding the precise pathway involved in PP2A regulation will allow us to target this important enzyme in cancer and Alzheimer\u27s disease where it is involved in the pathophysiology