title: Persistent DNA damage caused by low levels of mitomycin C induces irreversible cell senescence.
abstract: Mutations of oncogenes and tumor suppressor genes which activate mTOR through several downstream signaling pathways are common to cancer. Activation of mTOR when combined with inhibition of cell cycle progression or DNA replication stress has previously been shown to promote cell senescence. In the present study, we examined the conditions under which human non-small cell lung carcinoma A549 cells can undergo senescence when treated with the DNA alkylating agent mitomycin C (MMC). While exposure of A549 cells to 0.1 or 0.5 µg/ml of MMC led to their arrest in S phase of the cell cycle and subsequent apoptosis, exposure to 0.01 or 0.02 µg/ml for 6 d resulted in induction of cell senescence and near total (0.01 µg/ml) or total (0.02 µg/ml) elimination of their reproductive potential. During exposure to these low concentrations of MMC, the cells demonstrated evidence of DNA replication stress manifested by expression of γH2AX, p21 (WAF1)  and a very low level of EdU incorporation into DNA. The data are consistent with the notion that enduring DNA replication stress in cells known to have activated oncogenes leads to their senescence. It is reasonable to expect that tumors having constitutive activation of oncogenes triggering mTOR signaling may be particularly predisposed to undergoing senescence following prolonged treatment with low doses of DNA damaging drugs.
authors.affiliation: Brander Cancer Research Institute, Department of Pathology, New York Medical College, Valhalla, NY, USA.
authors.forename: Elise
authors.initials: E
authors.lastname: McKenna
authors.forename: Frank
authors.initials: F
authors.lastname: Traganos
authors.forename: Hong
authors.initials: H
authors.lastname: Zhao
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Darzynkiewicz
mesh_terms: D017209:Apoptosis; D002289:Carcinoma, Non-Small-Cell Lung / Q000378:metabolism; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D016922:Cellular Senescence; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage; D004261:DNA Replication; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D016685:Mitomycin / Q000009:adverse effects*; D011003:Ploidies; D059807:S Phase Cell Cycle Checkpoints; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; C468783:H2AX protein, human; D006657:Histones; D016685:Mitomycin; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; C505407:CASP3 protein, human; D053148:Caspase 3