title: Up-regulation of P21 inhibits TRAIL-mediated extrinsic apoptosis, contributing resistance to SAHA in acute myeloid leukemia cells.
abstract: OBJECTIVE
  P21, a multifunctional cell cycle-regulatory molecule, regulates apoptotic cell death. In this study we examined the effect of altered p21 expression on the sensitivity of acute myeloid leukemia cells in response to HDAC inhibitor SAHA treatment and investigated the underlying mechanism.
  
  
  METHODS
  Stably transfected HL60 cell lines were established in RPMI-1640 with supplementation of G-418. Cell viability was measured by MTT assay. Western blot was applied to assess the protein expression levels of target genes. Cell apoptosis was monitored by AnnexinV-PE/7AAD assay.
  
  
  RESULTS
  We showed HL60 cells that that didn't up-regulate p21 expression were more sensitive to SAHA-mediated apoptosis than NB4 and U937 cells that had increased p21 level. Enforced expression of p21 in HL60 cells reduced sensitivity to SAHA and blocked TRAIL-mediated apoptosis. Conversely, p21 silencing in NB4 cells enhanced SAHA-mediated apoptosis and lethality. Finally, we found that combined treatment with SAHA and rapamycin down-regulated p21 and enhanced apoptosis in AML cells.
  
  
  CONCLUSIONS
  We conclude that up-regulated p21 expression mediates resistance to SAHA via inhibition of TRAIL apoptotic pathway. P21 may serve as a candidate biomarker to predict responsiveness or resistance to SAHA-based therapy in AML patients. In addition, rapamycin may be an effective agent to override p21-mediated resistance to SAHA in AML patients.
authors.affiliation: Department of Hematology, the Third Affiliated Hospital, Sun Yat-sen University, Guangzhou; Institute of Cancer Stem Cell, Dalian Medical University, Dalian, China.
authors.forename: Xing
authors.initials: X
authors.lastname: Wu
authors.forename: Na
authors.initials: N
authors.lastname: Yang
authors.forename: Wei-hua
authors.initials: WH
authors.lastname: Zhou
authors.forename: Jie
authors.initials: J
authors.lastname: Xu
authors.forename: Jia-jie
authors.initials: JJ
authors.lastname: Chen
authors.forename: Fei-meng
authors.initials: FM
authors.lastname: Zheng
authors.forename: Zi-jie
authors.initials: ZJ
authors.lastname: Long
authors.forename: Cai-feng
authors.initials: CF
authors.lastname: Yue
authors.forename: Ke-xin
authors.initials: KX
authors.lastname: Ai
authors.forename: Ling-ling
authors.initials: LL
authors.lastname: Liu
authors.forename: Xian-yao
authors.initials: XY
authors.lastname: Wan
authors.forename: Quentin
authors.initials: Q
authors.lastname: Liu
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D001483:Base Sequence; D015153:Blotting, Western; D053181:Caspase 8 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D018922:HL-60 Cells; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology*; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000378:metabolism / Q000473:pathology*; D034622:RNA Interference; D020123:Sirolimus / Q000494:pharmacology; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000502:physiology*; D015854:Up-Regulation
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; D056572:Histone Deacetylase Inhibitors; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D053181:Caspase 8; D020123:Sirolimus