title: Pharmacological inhibition of DNA repair enzymes differentially modulates telomerase activity and apoptosis in two human leukaemia cell lines.
abstract: OBJECTIVE
  To investigate the effect of wortmannin and 3-aminobenzamide (3-AB) on telomerase activity and apoptosis in two human leukaemia cells.
  
  
  METHODS
  MOLT-4 (p53-wild type) and KG1a (p53-null) cells were irradiated with gamma-rays (3 Gy at 1.57 Gy min(-1)) and the effects of wortmannin and 3-AB were evaluated. Telomerase activity was measured by polymerase chain reaction and the expression of human telomerase reverse transcriptase, human telomerase RNA and telomerase-associated protein 1 was assessed by reverse transcriptase-polymerase chain reaction. Apoptosis was evaluated by fluorescence microscopy and flow cytometry.
  
  
  RESULTS
  A radiation-induced up-regulation of telomerase activity was observed from 4 h post-irradiation in both cell lines. This up-regulation was abrogated by wortmannin and 3-AB. Telomerase activity was maximal 24 h post-irradiation, coinciding with an accumulation of human telomerase reverse transcriptase mRNA. Apoptosis and G2/M arrest were evident from 4 h post-irradiation in MOLT-4 cells. KG1a cells exhibited a G2/M block at 24 h post-irradiation and apoptosis increased between 24 and 48 h post-irradiation. 3-AB abolished G2/M blockage and enhanced radiation-induced apoptosis in both cell lines, while wortmannin increased apoptosis only in MOLT-4 cells.
  
  
  CONCLUSIONS
  3-AB inhibits the radiation-associated telomerase activity increase and enhances apoptosis in MOLT-4 and KG1a cells. Wortmannin, which also inhibits the radiation-associated telomerase activity increase in both cell lines, does not modify radiation-induced apoptosis in KG1a cells. DNA repair enzymes might be selective targets for enhancing radiosensitivity in certain tumour cells.
authors.affiliation: Autoridad Regulatoria Nuclear, Gerencia de Apoyo Científico Laboratorio de Radiopatología, Avenida del Libertador 8250 (C1429BNP) Buenos Aires, Argentina. ddubner@cae.arn.gov.ar
authors.forename: D
authors.initials: D
authors.lastname: Dubner
authors.forename: M
authors.initials: M
authors.lastname: del Rosario Pérez
authors.forename: S
authors.initials: S
authors.lastname: Michelin
authors.forename: M
authors.initials: M
authors.lastname: Bourguignon
authors.forename: P
authors.initials: P
authors.lastname: Moreau
authors.forename: E D
authors.initials: ED
authors.lastname: Carosella
authors.forename: P
authors.initials: P
authors.lastname: Gisone
mesh_terms: D000730:Androstadienes / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D004260:DNA Repair / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D000081082:Phosphoinositide-3 Kinase Inhibitors; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D019098:Telomerase / Q000037:antagonists & inhibitors*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D001549:Benzamides; D004791:Enzyme Inhibitors; D000081082:Phosphoinositide-3 Kinase Inhibitors; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C025160:3-aminobenzamide; D019098:Telomerase; D000077191:Wortmannin