title: Triggering senescence programs suppresses Chk1 kinase and sensitizes cells to genotoxic stresses.
abstract: Depletion of the major heat shock protein Hsp72 leads to activation of the senescence program in a variety of tumor cell lines via both p53-dependent and p53-independent pathways. Here, we found that the Hsp72-depleted cells show defect in phosphorylation and activation of the protein kinase Chk1 by genotoxic stresses, such as UVC irradiation or camptothecin. Under these conditions, phosphorylation of Rad17 was also suppressed, whereas phosphorylation of p53 at Ser(15) was not affected, indicating a specific defect in phosphorylation of a subset of the ATR kinase substrates. Similarly, suppression of Chk1 activation was seen when senescence signaling was triggered by direct stimulation of p53, depletion of Cdc2, or overexpression of the cell cycle inhibitors p21 or p16. Thus, defect in Chk1 activation was not a consequence of the chaperone imbalance, but rather a downstream effect of activation of the senescence signaling. Inhibition of Chk1 was associated with inefficient inter-S phase checkpoint, as Hsp72 depleted cells failed to halt cell cycle progression upon UVC irradiation. Accordingly, sensitivity of cells to genotoxic stimuli after Hsp72 depletion was significantly enhanced. Thus, activation of the senescence signaling causes a defect in the DNA damage response manifested in increased sensitivity to genotoxic stresses.
authors.affiliation: Department of Biochemistry, Boston University Medical School, Boston, MA 02118, USA.
authors.forename: Vladimir L
authors.initials: VL
authors.lastname: Gabai
authors.forename: Cornelia
authors.initials: C
authors.lastname: O'Callaghan-Sunol
authors.forename: Le
authors.initials: L
authors.lastname: Meng
authors.forename: Michael Y
authors.initials: MY
authors.lastname: Sherman
authors.forename: Julia
authors.initials: J
authors.lastname: Yaglom
mesh_terms: D000782:Aneuploidy; D002166:Camptothecin / Q000494:pharmacology; D002453:Cell Cycle / Q000502:physiology; D045744:Cell Line, Tumor; D016922:Cellular Senescence / Q000502:physiology; D000071877:Checkpoint Kinase 1; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004249:DNA Damage / Q000502:physiology*; D004260:DNA Repair; D015536:Down-Regulation; D004789:Enzyme Activation; D045325:HCT116 Cells; D050884:HSP72 Heat-Shock Proteins / Q000172:deficiency / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009369:Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D011494:Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050884:HSP72 Heat-Shock Proteins; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D002166:Camptothecin