title: Cisplatin-induced caspase activation mediates PTEN cleavage in ovarian cancer cells: a potential mechanism of chemoresistance.
abstract: BACKGROUND
  The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) tumor suppressor protein is a central negative regulator of the PI3K/AKT signaling cascade and suppresses cell survival as well as cell proliferation. PTEN is found to be either inactivated or mutated in various human malignancies. In the present study, we have investigated the regulation of PTEN during cisplatin induced apoptosis in A2780, A270-CP (cisplatin resistant), OVCAR-3 and SKOV3 ovarian cancer cell lines.
  
  
  METHODS
  Cells were treated with 10μM of cisplatin for 24h. Transcript and protein levels were analysed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and western blotting, respectively. Immunofluorescence microscopy was used to assess the intracellular localization of PTEN. Proteasome inhibitor and various caspases inhibitors were used to find the mechanism of PTEN degradation.
  
  
  RESULTS
  PTEN protein levels were found to be decreased significantly in A2780 cells; however, there was no change in PTEN protein levels in A2780-CP, OVCAR-3 and SKOV3 cells with cisplatin treatment. The decrease in PTEN protein was accompanied with an increase in the levels of AKT phosphorylation (pAKT) in A2780 cells and a decrease of BCL-2. Cisplatin treatment induced the activation/cleavage of caspase-3, -6, -7, -8, -9 in all cell lines tested in this study except the resistant variant A2780-CP cells. In A2780 cells, restoration of PTEN levels was achieved upon pre-treatment with Z-DEVD-FMK (broad range caspases inhibitor) and not with MG132 (proteasome inhibitor) and by overexpression of BCL-2, suggesting that caspases and BCL-2 are involved in the decrease of PTEN protein levels in A2780 cells.
  
  
  CONCLUSIONS
  The decrease in pro-apoptotic PTEN protein levels and increase in survival factor pAKT in A2780 ovarian cancer cells suggest that cisplatin treatment could further exacerbate drug resistance in A2780 ovarian cancer cells.
authors.affiliation: Department of Medical Biology, Research group in Molecular Oncology and Endocrinology, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada.
authors.forename: Mohan
authors.initials: M
authors.lastname: Singh
authors.forename: Parvesh
authors.initials: P
authors.lastname: Chaudhry
authors.forename: Francois
authors.initials: F
authors.lastname: Fabi
authors.forename: Eric
authors.initials: E
authors.lastname: Asselin
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D061945:Caspase Inhibitors / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation / Q000187:drug effects*; D005260:Female; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D010051:Ovarian Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D061988:Proteasome Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D061945:Caspase Inhibitors; D007976:Leupeptins; D009842:Oligopeptides; D061988:Proteasome Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; C110772:benzoylcarbonyl-aspartyl-glutamyl-valyl-aspartyl-fluoromethyl ketone; D051057:Proto-Oncogene Proteins c-akt; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; D020169:Caspases; D002945:Cisplatin; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde