title: Enforced expression of the tumor suppressor p53 renders human leukemia cells (U937) more sensitive to 1-[beta-D-arabinofuranosyl]cytosine (ara-C)-induced apoptosis.
abstract: The effects of enforced expression of p53 on the sensitivity of p53(-/-) human monocytic leukemia cells (U937) to apoptosis following exposure to the S-phase-specific antimetabolite 1-[beta-D-arabinofuranosyl]cytosine (ara-C) were examined. Cells were stably transfected with a plasmid containing a chimeric DNA construct encoding a temperature-sensitive p53 variant (135(ala-->val)), which transactivates at 32 degrees but is non-functional at 37 degrees. A significant reduction in the S-phase population was observed in ptsp53 mutants incubated at 32 degrees. Nevertheless, while vector controls did not exhibit differential sensitivity to ara-C at 32 degrees versus 37 degrees, temperature-sensitive p53 mutants displayed a significant increase in apoptosis at the permissive temperature. This was not accompanied by increased ara-CTP formation, DNA incorporation of [3H]ara-C, or altered expression of Bcl-2 or Bax. Enhanced sensitivity was associated with increased mitochondrial injury (e.g. cytochrome c release), caspase activation, and loss of clonogenic survival. Significantly, ptsp53 cells synchronized in S phase were markedly more sensitive to ara-C-mediated mitochondrial injury and apoptosis at 32 degrees, indicating that wild-type p53 specifically enhances the susceptibility of this subpopulation to ara-C lethality. Consistent with these results, transient transfection of human wild-type p53 cDNA rendered parental U937 cells more sensitive to ara-C-mediated cell death. Collectively, these findings indicate that p53 expression renders S-phase U937 cells more susceptible to ara-C-mediated mitochondrial dysfunction, cytochrome c release, apoptosis, and loss of clonogenic survival without enhancing ara-C metabolism. Such findings raise the possibility that loss of functional p53 activity allows leukemia cells to circumvent ara-C lethality.
authors.affiliation: Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298, USA.
authors.forename: Roy H
authors.initials: RH
authors.lastname: Decker
authors.forename: Jay
authors.initials: J
authors.lastname: Levin
authors.forename: Lora B
authors.initials: LB
authors.lastname: Kramer
authors.forename: Yun
authors.initials: Y
authors.lastname: Dai
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis; D001085:Arabinofuranosylcytosine Triphosphate / Q000378:metabolism; D003561:Cytarabine / Q000378:metabolism / Q000494:pharmacology*; D016147:Genes, Tumor Suppressor / Q000502:physiology*; D016158:Genes, p53 / Q000502:physiology*; D006801:Humans; D007938:Leukemia / Q000473:pathology; D020298:U937 Cells
chemical_list: D000964:Antimetabolites, Antineoplastic; D003561:Cytarabine; D001085:Arabinofuranosylcytosine Triphosphate