title: PP2A regulates ionizing radiation-induced apoptosis through Ser46 phosphorylation of p53.
abstract: In response to ionizing radiation, p53 plays a critical role in regulating DNA repair and apoptosis. Among multiple phosphorylation sites, evidence suggests that Ser46 promotes apoptotic cell death through mitochondrial outer membrane permeabilization (MOMP) and subsequent activation of the caspase 7-PARP pathway. Therefore, we investigated which phosphatase regulates Ser46 after ionizing radiation, reasoning that the responsible phosphatase should be a target for radiosensitization. We determined that both inhibition of PP2A by the cell-permeable inhibitor calyculin A and knockdown of PP2A by RNAi (a) enhanced Ser46 phosphorylation in p53 and (b) induced coincident caspase 7 and PARP cleavage in response to ionizing radiation. Furthermore, mutation of p53 Ser46 to Ala attenuated ionizing radiation-induced apoptotic signaling. Consequently, we concluded that PP2A regulates ionizing radiation-induced apoptotic signaling through dephosphorylation of p53 Ser46.
authors.affiliation: Department of Radiation Oncology, Center for Cell Signaling, University of Virginia Health System, Box 800383 Charlottesville, VA, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Mi
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Bolesta
authors.forename: David L
authors.initials: DL
authors.lastname: Brautigan
authors.forename: James M
authors.initials: JM
authors.lastname: Larner
mesh_terms: D017209:Apoptosis / Q000528:radiation effects*; D002460:Cell Line; D055785:Gene Knockdown Techniques; D006801:Humans; D010768:Phosphoserine / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D011839:Radiation, Ionizing; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D010768:Phosphoserine; D054648:Protein Phosphatase 2