title: Autophagy-dependent senescence in response to DNA damage and chronic apoptotic stress.
abstract: Autophagy regulates cell survival and cell death upon various cellular stresses, yet the molecular signaling events involved are not well defined. Here, we established the function of a proteolytic Cyclin E fragment (p18-CycE) in DNA damage-induced autophagy, apoptosis, and senescence. p18-CycE was identified in hematopoietic cells undergoing DNA damage-induced apoptosis. In epithelial cells exposed to DNA damage, chronic but not transient expression of p18-CycE leads to higher turnover of LC3 I/II and increased emergence of autophagosomes and autolysosomes. Levels of p18-CycE, which was generated by proteolytic cleavage of endogenous Cyclin E, were greatly increased by chloroquine and correlated with LC 3II conversion. Preventing p18-CycE genesis blocked conversion of LC3 I to LC3 II. Upon DNA damage, cytoplasmic ataxia-telangiectasia-mutated (ATM) was phosphorylated in p18-CycE-expressing cells resulting in sustained activation of the adenosine-mono-phosphate-dependent kinase (AMPK). These lead to sustained activation of mammalian autophagy-initiating kinase ULK1, which was abrogated upon inhibiting ATM and AMPK phosphorylation. Moreover, p18-CycE was degraded via autophagy followed by induction of senescence. Both autophagy and senescence were prevented by inhibiting autophagy, which leads to increased apoptosis in p18-CycE-expressing cells by stabilizing p18-CycE expression. Senescence was further associated with cytoplasmic co-localization and degradation of p18-CycE and Ku70. In brief, chronic p18-CycE expression-induced autophagy leads to clearance of p18-CycE following DNA damage and induction of senescence. Autophagy inhibition stabilized the cytoplasmic p18-CycE-Ku70 complex leading to apoptosis. Thus, our findings define how chronic apoptotic stress and DNA damage initiate autophagy and regulate cell survival through senescence and/or apoptosis.
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Kamini
authors.initials: K
authors.lastname: Singh
authors.forename: Shigemi
authors.initials: S
authors.lastname: Matsuyama
authors.forename: Judith A
authors.initials: JA
authors.lastname: Drazba
authors.forename: Alexandru
authors.initials: A
authors.lastname: Almasan
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism; D000818:Animals; D034961:Antigens, Nuclear / Q000378:metabolism; D017209:Apoptosis; D001343:Autophagy; D002460:Cell Line; D016922:Cellular Senescence; D019927:Cyclin E / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D000072200:Ku Autoantigen; D008855:Microscopy, Electron, Scanning; D010446:Peptide Fragments / Q000378:metabolism; D059748:Proteolysis; D013312:Stress, Physiological
chemical_list: D034961:Antigens, Nuclear; D019927:Cyclin E; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D000263:Adenylate Kinase; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen