title: Glycogen synthase kinase 3beta phosphorylates p21WAF1/CIP1 for proteasomal degradation after UV irradiation.
abstract: UV irradiation has been reported to induce p21(WAF1/CIP1) protein degradation through a ubiquitin-proteasome pathway, but the underlying biochemical mechanism remains to be elucidated. Here, we show that ser-114 phosphorylation of p21 protein by glycogen synthase kinase 3beta (GSK-3beta) is required for its degradation in response to UV irradiation and that GSK-3beta activation is a downstream event in the ATR signaling pathway triggered by UV. UV transiently increased GSK-3beta activity, and this increase could be blocked by caffeine or by ATR small interfering RNA, indicating ATR-dependent activation of GSK-3beta. ser-114, located within the putative GSK-3beta target sequence, was phosphorylated by GSK-3beta upon UV exposure. The nonphosphorylatable S114A mutant of p21 was protected from UV-induced destabilization. Degradation of p21 protein by UV irradiation was independent of p53 status and prevented by proteasome inhibitors. In contrast to the previous report, the proteasomal degradation of p21 appeared to be ubiquitination independent. These data show that GSK-3beta is activated by UV irradiation through the ATR signaling pathway and phosphorylates p21 at ser-114 for its degradation by the proteasome. To our knowledge, this is the first demonstration of GSK-3beta as the missing link between UV-induced ATR activation and p21 degradation.
authors.affiliation: Korea University College of Medicine, 126-1 Anam-Dong 5-Ga, Sungbuk-Gu, Seoul 136-705, South Korea. biojs@korea.ac.kr.
authors.forename: Ji Young
authors.initials: JY
authors.lastname: Lee
authors.forename: Su Jin
authors.initials: SJ
authors.lastname: Yu
authors.forename: Yun Gyu
authors.initials: YG
authors.lastname: Park
authors.forename: Joon
authors.initials: J
authors.lastname: Kim
authors.forename: Jeongwon
authors.initials: J
authors.lastname: Sohn
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D002384:Catalysis / Q000528:radiation effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D004789:Enzyme Activation / Q000528:radiation effects; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D050505:Mutant Proteins / Q000378:metabolism; D010766:Phosphorylation / Q000528:radiation effects; D010768:Phosphoserine / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000528:radiation effects*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000528:radiation effects; D025801:Ubiquitin / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050505:Mutant Proteins; D025801:Ubiquitin; D010768:Phosphoserine; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D017346:Protein Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3; D046988:Proteasome Endopeptidase Complex