title: Temozolomide induced c-Myc-mediated apoptosis via Akt signalling in MGMT expressing glioblastoma cells.
abstract: OBJECTIVE
  We investigated the molecular mechanisms underlying the cytotoxic effect of Temozolomide (TMZ) in both O(6)-methylguanine-DNA methyl transferase (MGMT) depleted as well as undepleted glioblastoma cell lines. Since TMZ is used in clinics in combination with radiotherapy, we also studied the effects of TMZ in combination with ionising radiation (IR).
  
  
  METHODS
  Cell colony-forming ability was measured using a clonogenic assay. Cell cycle analysis and apoptosis were evaluated by Flow Cytometry (FCM). Proteins involved in cell cycle control were detected by Western blot and co-immunoprecipitation assays.
  
  
  RESULTS
  Our data showed that TMZ, independent of MGMT expression, inhibited glioblastoma cell growth via an irreversible G(2) block in MGMT depleted cells or the induction of apoptosis in MGMT normal expressing cells. When TMZ was administered in combination with IR, apoptosis was greater than observed with either agent separately. This TMZ-induced apoptosis in the MGMT expressing cells occurred through Akt/Glycogen-Synthase-Kinase-3ß (GSK3ß) signalling and was mediated by Myelocytomatosis (c-Myc) oncoprotein. Indeed, TMZ phosphorylated/activated Akt led to phosphorylation/inactivation of GSK3ß which resulted in the stabilisation of c-Myc protein and subsequent modulation of the c-Myc target genes involved in the apoptotic processes.
  
  
  CONCLUSIONS
  C-Myc expression could be considered a good indicator of TMZ effectiveness.
authors.affiliation: Centro Ricerca S. Pietro, Fatebenefratelli Hospital, Via Cassia 600, Rome, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: De Salvo
authors.forename: Giovanna
authors.initials: G
authors.lastname: Maresca
authors.forename: Igea
authors.initials: I
authors.lastname: D'agnano
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Marchese
authors.forename: Antonio
authors.initials: A
authors.lastname: Stigliano
authors.forename: Raffaella
authors.initials: R
authors.lastname: Gagliassi
authors.forename: Ercole
authors.initials: E
authors.lastname: Brunetti
authors.forename: Giorgio H
authors.initials: GH
authors.lastname: Raza
authors.forename: Ugo
authors.initials: U
authors.lastname: De Paula
authors.forename: Barbara
authors.initials: B
authors.lastname: Bucci
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology; D017209:Apoptosis; D001932:Brain Neoplasms / Q000378:metabolism*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D015254:DNA Modification Methylases / Q000096:biosynthesis*; D045643:DNA Repair Enzymes / Q000096:biosynthesis*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D005434:Flow Cytometry / Q000379:methods; D005909:Glioblastoma / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D011839:Radiation, Ionizing; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis*
chemical_list: D018906:Antineoplastic Agents, Alkylating; D016271:Proto-Oncogene Proteins c-myc; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D045643:DNA Repair Enzymes; D000077204:Temozolomide