title: Activation of mammalian target of rapamycin signaling promotes cell cycle progression and protects cells from apoptosis in mantle cell lymphoma.
abstract: Mantle cell lymphoma (MCL) is characterized by the t(11;14) and cyclin D1 overexpression. However, additional molecular events are most likely required for oncogenesis, possibly through cell cycle and apoptosis deregulation. We hypothesized that mammalian target of rapamycin (mTOR) is activated in MCL and contributes to tumor proliferation and survival. In MCL cell lines, pharmacological inhibition of the phosphoinositide 3-kinase/AKT pathway was associated with decreased phosphorylation (activation) of mTOR and its downstream targets phosphorylated (p)-4E-BP1, p-p70S6 kinase, and p-ribosomal protein S6, resulting in apoptosis and cell cycle arrest. These changes were associated with down-regulation of cyclin D1 and the anti-apoptotic proteins cFLIP, BCL-XL, and MCL-1. Furthermore, silencing of mTOR expression using mTOR-specific short interfering RNA decreased phosphorylation of mTOR signaling proteins and induced cell cycle arrest and apoptosis. Silencing of eukaryotic initiation factor (eIF4E), a downstream effector of mTOR, recapitulated these results. We also assessed mTOR signaling in MCL tumors using immunohistochemical methods and a tissue microarray: 10 of 30 (33%) expressed Ser473p-AKT, 13 of 21 (62%) Ser2448p-mTOR, 22 of 22 (100%) p-p70S6K, and 5 of 20 (25%) p-ribosomal protein S6. Total eIF4E binding protein 1 and eukaryotic initiation factor 4E were expressed in 13 of 14 (93%) and 16 of 29 (55%) MCL tumors, respectively. These findings suggest that the mTOR signaling pathway is activated and may contribute to cell cycle progression and tumor cell survival in MCL.
authors.affiliation: Department of Hematopathology, Unit 72, The University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA.
authors.forename: Evangelia
authors.initials: E
authors.lastname: Peponi
authors.forename: Elias
authors.initials: E
authors.lastname: Drakos
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Reyes
authors.forename: Vasiliki
authors.initials: V
authors.lastname: Leventaki
authors.forename: George Z
authors.initials: GZ
authors.lastname: Rassidakis
authors.forename: L Jeffrey
authors.initials: LJ
authors.lastname: Medeiros
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D017209:Apoptosis; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D015536:Down-Regulation; D039561:Eukaryotic Initiation Factor-4E / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D020522:Lymphoma, Mantle-Cell / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D039561:Eukaryotic Initiation Factor-4E; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D058570:TOR Serine-Threonine Kinases; C087000:EIF4EBP1 protein, human; C546842:MTOR protein, human