title: The redox state of cytochrome c modulates resistance to methotrexate in human MCF7 breast cancer cells.
abstract: BACKGROUND
  Methotrexate is a chemotherapeutic agent used to treat a variety of cancers. However, the occurrence of resistance limits its effectiveness. Cytochrome c in its reduced state is less capable of triggering the apoptotic cascade. Thus, we set up to study the relationship among redox state of cytochrome c, apoptosis and the development of resistance to methotrexate in MCF7 human breast cancer cells.
  
  
  RESULTS
  Cell incubation with cytochrome c-reducing agents, such as tetramethylphenylenediamine, ascorbate or reduced glutathione, decreased the mortality and apoptosis triggered by methotrexate. Conversely, depletion of glutathione increased the apoptotic action of methotrexate, showing an involvement of cytochrome c redox state in methotrexate-induced apoptosis. Methotrexate-resistant MCF7 cells showed increased levels of endogenous reduced glutathione and a higher capability to reduce exogenous cytochrome c. Using functional genomics we detected the overexpression of GSTM1 and GSTM4 in methotrexate-resistant MCF7 breast cancer cells, and determined that methotrexate was susceptible of glutathionylation by GSTs. The inhibition of these GSTM isoforms caused an increase in methotrexate cytotoxicity in sensitive and resistant cells.
  
  
  CONCLUSIONS
  We conclude that overexpression of specific GSTMs, GSTM1 and GSTM4, together with increased endogenous reduced glutathione levels help to maintain a more reduced state of cytochrome c which, in turn, would decrease apoptosis, thus contributing to methotrexate resistance in human MCF7 breast cancer cells.
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Pharmacy, University of Barcelona, Barcelona, Spain.
authors.forename: Susana
authors.initials: S
authors.lastname: Barros
authors.forename: Núria
authors.initials: N
authors.lastname: Mencia
authors.forename: Laura
authors.initials: L
authors.lastname: Rodríguez
authors.forename: Carlota
authors.initials: C
authors.lastname: Oleaga
authors.forename: Conceição
authors.initials: C
authors.lastname: Santos
authors.forename: Verónique
authors.initials: V
authors.lastname: Noé
authors.forename: Carlos J
authors.initials: CJ
authors.lastname: Ciudad
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001205:Ascorbic Acid / Q000494:pharmacology; D045304:Cytochromes c / Q000235:genetics* / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D005978:Glutathione / Q000494:pharmacology; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D061986:MCF-7 Cells; D008727:Methotrexate / Q000494:pharmacology*; D010084:Oxidation-Reduction / Q000187:drug effects; D019163:Reducing Agents / Q000494:pharmacology; D015398:Signal Transduction; D013772:Tetramethylphenylenediamine / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D001205:Ascorbic Acid; D045304:Cytochromes c; D005978:Glutathione; D005982:Glutathione Transferase; D008727:Methotrexate; D019163:Reducing Agents; D013772:Tetramethylphenylenediamine; C514654:GSTM4 protein, human