title: Longitudinal inhibition of PI3K/Akt/mTOR signaling by LY294002 and rapamycin induces growth arrest of adult T-cell leukemia cells.
abstract: This study found that phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling was activated in human T-cell lymphotropic virus type I (HTLV-1)-infected leukemia cells. Rapamycin (1-100 nM, 48h), the inhibitor of mTOR and its analog RAD001 (1-100 nM, 48 h)-induced growth inhibition and G0/G1 cell cycle arrest of these cells in association with de-phosphorylation of p70S6K and 4E-BP-1, although IC50 was not achieved. Paradoxically, rapamycin-stimulated phosphorylation of Akt at Ser473. Blockade of Akt signaling by the PI3K inhibitor LY294002 (1-20 microM, 48 h) also resulted in the growth inhibition and G0/G1 cell cycle arrest of HTLV-1-infected cells, with IC50 ranging from 5 to 20muM, and it caused de-phosphorylation of p70S6K and 4E-BP-1. Of note, when rapamycin was combined with LY294002, rapamycin-induced phosphorylation of Akt was blocked, and the ability of rapamycin to induce growth arrest of HTLV-1-infected T-cells and suppress the p-p70S6K and p-4E-BP-1 proteins was potentiated. Moreover, both LY294002 and rapamycin down-regulated the levels of c-Myc and cyclin D1 proteins in these cells, and their combination further decreased levels of these cell cycle-regulating proteins. Taken together, longitudinal inhibition of PI3K/Akt/mTOR signaling represents a promising treatment strategy for individuals with adult T-cell leukemia.
authors.affiliation: Department of Hematology and Respiratory Medicine, Kochi University, Nankoku, Kochi 783-8505, Japan. ikezoet@med.kochi-u.ac.jp
authors.forename: Takayuki
authors.initials: T
authors.lastname: Ikezoe
authors.forename: Chie
authors.initials: C
authors.lastname: Nishioka
authors.forename: Kentaro
authors.initials: K
authors.lastname: Bandobashi
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kuwayama
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Adachi
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Takeuchi
authors.forename: H Phillip
authors.initials: HP
authors.lastname: Koeffler
authors.forename: Hirokuni
authors.initials: H
authors.lastname: Taguchi
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins; D002867:Chromones / Q000494:pharmacology*; D056741:Cyclin D; D016213:Cyclins / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015368:Human T-lymphotropic virus 1; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000378:metabolism / Q000473:pathology*; D009025:Morpholines / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology*; D013601:T-Lymphocytes / Q000378:metabolism / Q000821:virology; D058570:TOR Serine-Threonine Kinases; D014407:Tumor Cells, Cultured
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D002867:Chromones; D056741:Cyclin D; D016213:Cyclins; D004791:Enzyme Inhibitors; D007166:Immunosuppressive Agents; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D016271:Proto-Oncogene Proteins c-myc; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C087000:EIF4EBP1 protein, human; C489427:MYC protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546842:MTOR protein, human