title: NF-kappaB activates transcription of the RNA-binding factor HuR, via PI3K-AKT signaling, to promote gastric tumorigenesis.
abstract: OBJECTIVE
  HuR is a RNA-binding factor whose expression is commonly upregulated in some human tumor types. We explored the molecular mechanism underlying HuR elevation and its role in gastric cancer tumorigenesis.
  
  
  METHODS
  HuR expression and subcellular localization were determined by polymerase chain reaction, immunoblot, and immunohistochemical analyses. Its effect on tumor growth was characterized using flow cytometry, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling, and soft agar analyses. Luciferase reporter, chromatin immunoprecipitation, and electrophoretic mobility shift assays were used to measure transcriptional activation by nuclear factor kappaB (NF-kappaB) signaling.
  
  
  RESULTS
  Compared with normal gastric tissues, HuR was expressed at higher levels in gastric tumors, particularly in advanced versus early tumors; this increase was associated with enhanced cytoplasmic translocation of HuR. HuR overexpression increased proliferation of tumor cells, activating the G(1) to S transition of the cell cycle, DNA synthesis, and anchorage-independent growth. Small interfering RNA-mediated knockdown of HuR expression reduced tumor cell proliferation and response to apoptotic stimuli. No genetic or epigenetic alterations of HuR were observed in gastric tumor cell lines or primary tumors; overexpression depended on phosphatidylinositol 3-kinase/AKT signaling and NF-kappaB activity. AKT activation increased p65/RelA binding to a putative NF-kappaB binding site in the HuR promoter, the stability of HuR target transcripts, and the cytoplasmic import of HuR.
  
  
  CONCLUSIONS
  HuR is a direct transcription target of NF-kappaB; its activation in gastric cancer cell lines depends on phosphatidylinositol 3-kinase/AKT signaling. HuR activation by this pathway has proliferative and antiapoptotic effects on gastric cancer cells.
authors.affiliation: School of Life Sciences and Biotechnology, Korea University, Seoul, Korea.
authors.forename: Min-Ju
authors.initials: MJ
authors.lastname: Kang
authors.forename: Byung-Kyu
authors.initials: BK
authors.lastname: Ryu
authors.forename: Min-Goo
authors.initials: MG
authors.lastname: Lee
authors.forename: Jikhyon
authors.initials: J
authors.lastname: Han
authors.forename: Jin-Hee
authors.initials: JH
authors.lastname: Lee
authors.forename: Tae-Kyu
authors.initials: TK
authors.lastname: Ha
authors.forename: Do-Sun
authors.initials: DS
authors.lastname: Byun
authors.forename: Kwon-Seok
authors.initials: KS
authors.lastname: Chae
authors.forename: Bong-Hee
authors.initials: BH
authors.lastname: Lee
authors.forename: Hyang Sook
authors.initials: HS
authors.lastname: Chun
authors.forename: Kil Yeon
authors.initials: KY
authors.lastname: Lee
authors.forename: Hyo-Jong
authors.initials: HJ
authors.lastname: Kim
authors.forename: Sung-Gil
authors.initials: SG
authors.lastname: Chi
mesh_terms: D000954:Antigens, Surface / Q000235:genetics*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D016328:NF-kappa B / Q000235:genetics* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D012334:RNA, Neoplasm / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics*; D013274:Stomach Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D014158:Transcription, Genetic
chemical_list: D000954:Antigens, Surface; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; C098770:ELAVL1 protein, human; D016328:NF-kappa B; D012334:RNA, Neoplasm; D016601:RNA-Binding Proteins; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt