title: Down-regulation of AP-4 inhibits proliferation, induces cell cycle arrest and promotes apoptosis in human gastric cancer cells.
abstract: BACKGROUND
  AP-4 belongs to the basic helix-loop-helix leucine-zipper subgroup; it controls target gene expression, regulates growth, development and cell apoptosis and has been implicated in tumorigenesis. Our previous studies indicated that AP-4 was frequently overexpressed in gastric cancers and may be associated with the poor prognosis. The purpose of this study is to examine whether silencing of AP-4 can alter biological characteristics of gastric cancer cells.
  
  
  METHODS
  Two specific siRNAs targeting AP-4 were designed, synthesized, and transfected into gastric cancer cell lines and human normal mucosa cells. AP-4 expression was measured with real-time quantitative PCR and Western blot. Cell proliferation and chemo-sensitivity were detected by CCK-8 assay. Cell cycle assay and apoptosis assay were performed by flow cytometer, and relative expression of cell cycle regulators were detected by real-time quantitative PCR and Western blot, expression of the factors involved in the apoptosis pathway were examined in mRNA and protein level.
  
  
  RESULTS
  The expression of AP-4 was silenced by the siRNAs transfection and the effects of AP-4 knockdown lasted 24 to 96 hrs. The siRNA-mediated silencing of AP-4 suppressed the cellular proliferation, induced apoptosis and sensitized cancer cells to anticancer drugs. In addition, the expression level of p21, p53 and Caspase-9 were increased when AP-4 was knockdown, but the expression of cyclin D1, Bcl-2 and Bcl-x(L) was inhibited. It didn't induce cell cycle arrest when AP-4 was knockdown in p53 defect gastric cancer cell line Kato-III.
  
  
  CONCLUSIONS
  These results illustrated that gene silencing of AP-4 can efficiently inhibited cell proliferation, triggered apoptosis and sensitized cancer cells to anticancer drugs in vitro, suggesting that AP-4 siRNAs mediated silencing has a potential value in the treatment of human gastric cancer.
authors.affiliation: Department of General Surgery, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
authors.forename: Xinghua
authors.initials: X
authors.lastname: Liu
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.forename: Yan
authors.initials: Y
authors.lastname: Guo
authors.forename: Qi
authors.initials: Q
authors.lastname: Liang
authors.forename: Changyao
authors.initials: C
authors.lastname: Wu
authors.forename: Lei
authors.initials: L
authors.lastname: Wu
authors.forename: Kaixiong
authors.initials: K
authors.lastname: Tao
authors.forename: Guobin
authors.initials: G
authors.lastname: Wang
authors.forename: Jianying
authors.initials: J
authors.lastname: Chen
mesh_terms: D033964:Adaptor Protein Complex 4 / Q000235:genetics* / Q000378:metabolism; D017209:Apoptosis / Q000235:genetics*; D053453:Caspase 9 / Q000235:genetics / Q000378:metabolism; D059447:Cell Cycle Checkpoints / Q000235:genetics*; D048708:Cell Growth Processes / Q000235:genetics; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D013274:Stomach Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D033964:Adaptor Protein Complex 4; C530104:CCND1 protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D051020:bcl-X Protein; D019938:Cyclin D1; D053453:Caspase 9