title: Rapamycin sensitizes glucocorticoid resistant acute lymphoblastic leukemia CEM-C1 cells to dexamethasone induced apoptosis through both mTOR suppression and up-regulation and activation of glucocorticoid receptor.
abstract: OBJECTIVE
  To explore the role of glucocorticoid (GC) receptor (GR) in rapamycin's reversion of GC resistance in human GC-resistant T-acute lymphoblastic leukemia (ALL) CEM-C1 cells.
  
  
  METHODS
  CEM-C1 cells were cultured in vitro and treated with rapamycin at different concentrations with or without 1 μmol/L dexamethasone (Dex). 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) test was performed to assess cell proliferation. The cell cycle and cell apoptosis were analyzed by flow cytometry. The expression of GRα mRNA was determined by real-time quantitative RT-PCR. The expression of GR, p-70S6K, Mcl-1, and Bim proteins was detected by Western blot.
  
  
  RESULTS
  When incubated with rapamycin at different concentrations, CEM-C1 cells showed significant growth inhibition in a time- and concentration-dependent manner. The growth inhibition was synergistically increased when CEM-C1 cells were treated with rapamycin plus 1 μmol/L Dex. CEM-C1 cells treated with rapamycin alone showed no apparent apoptosis, and were arrested at G0/G1 phase. After the treatment with Dex plus rapamycin, CEM-C1 cells demonstrated apparent apoptosis and increased the cell cycle arrested at G0/G1 phase. Rapamycin combined with Dex up-regulated GRα, phosphorylated GR(p-GR), and pro-apoptotic protein Bim-EL in CEM-C1 cells, but inhibited the expression of p-p70S6K, a downstream target protein of mTOR (mammalian target of rapamycin).
  
  
  CONCLUSIONS
  After the treatment with rapamycin plus Dex, Dex resistant CEM-C1 cells induce growth inhibition and apoptosis. The underlying mechanism may involve inhibition of the mTOR signaling pathway and also be associated with up-regulation of GR expression and activation of GC-GR signaling pathway.
authors.affiliation: Department of Pediatric Hematology/Oncology, West China Second University Hospital, Sichuan University, Chengdu, Sichuan 610041, China.
authors.forename: Xia
authors.initials: X
authors.lastname: Guo
authors.forename: Chen Yan
authors.initials: CY
authors.lastname: Zhou
authors.forename: Qiang
authors.initials: Q
authors.lastname: Li
authors.forename: Ju
authors.initials: J
authors.lastname: Gao
authors.forename: Yi Ping
authors.initials: YP
authors.lastname: Zhu
authors.forename: Ling
authors.initials: L
authors.lastname: Gu
authors.forename: Zhi Gui
authors.initials: ZG
authors.lastname: Ma
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D017931:DNA Primers; D003907:Dexamethasone / Q000494:pharmacology*; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000378:metabolism* / Q000473:pathology; D060888:Real-Time Polymerase Chain Reaction; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects*
chemical_list: D017931:DNA Primers; D005938:Glucocorticoids; D011965:Receptors, Glucocorticoid; D003907:Dexamethasone; D020123:Sirolimus
keywords: Acute lymphoblastic leukemia; Glucocorticoid receptor; Glucocorticoid resistance; Rapamycin; mTOR