title: Let-7b is involved in the inflammation and immune responses associated with Helicobacter pylori infection by targeting Toll-like receptor 4.
abstract: OBJECTIVE
  Toll-like receptors (TLRs) are important initiators in native immune responses to microbial infections. TLR4 is up-regulated in response to H.pylori infection in gastric epithelial cells. However, the regulatory mechanisms for the expression of TLR4 in H.pylori infection have not been clearly defined. The aims of this study are to present the evidence that microRNA let-7b directly regulates TLR4 expression in human gastric epithelial cells, and subsequently influences the activation of NF-κB and the expression of the downstream genes in H.pylori infection.
  
  
  METHODS
  The expression of let-7b was determined in gastric mucosa specimens and in two gastric epithelial cell lines using quantitative RT-PCR. The expression of TLR4 was determined by immunohistochemistry staining and RT-PCR. The potential target of let-7b was identified by luciferase reporter assay and Western blot. Let-7b mimics and inhibitors were used to examine the effects of let-7b on NF-κB activity. The expression of the downstream genes of NF-κB was also determined in cells infected with H.pylori 26695.
  
  
  RESULTS
  Let-7b was significantly decreased in gastric mucosa specimens and in gastric epithelial cell lines (AGS, GES-1) infected with H.pylori 26695 (cagA+). Let-7b was complementary to the 3'-UTR of TLR4 mRNA and regulated TLR4 expression via post-transcriptional suppression in gastric epithelium. Infection of H.pylori induced the expression of TLR4 and activated NF-κB in AGS and GES-1 cells. Overexpression of let-7b by mimics downregulated TLR4, and subsequently attenuated NF-κB, MyD88, NF-κB1/p50, RelA/p65. The expression of IL-8, COX-2 and CyclinD1 was inhibited in H.pylori infected cells with let-7b overexpression. Both TAK-242 (TLR4 inhibitor) and SN50 (NF-κB inhibitor) significantly inhibited the H.pylori induced downregulation of let-7b.
  
  
  CONCLUSIONS
  Let-7b targets at TLR4 mRNA, and regulates the activation of NF-κB and the expression of the downstream genes related to the inflammation and immune responses in H.pylori infection.
authors: Department of Gastroenterology, Peking University First Hospital, Beijing, China.
authors: Gui-gen
authors: GG
authors: Teng
authors: Wei-hong
authors: WH
authors: Wang
authors: Yun
authors: Y
authors: Dai
authors: Shu-jun
authors: SJ
authors: Wang
authors: Yun-xiang
authors: YX
authors: Chu
authors: Jiang
authors: J
authors: Li
mesh_terms: D015536:Down-Regulation; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005753:Gastric Mucosa / Q000378:metabolism; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D016481:Helicobacter Infections / Q000235:genetics* / Q000382:microbiology; D016480:Helicobacter pylori / Q000235:genetics* / Q000472:pathogenicity; D006801:Humans; D007113:Immunity, Innate / Q000235:genetics; D007249:Inflammation / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010455:Peptides / Q000008:administration & dosage; D013449:Sulfonamides / Q000008:administration & dosage; D051197:Toll-Like Receptor 4 / Q000235:genetics* / Q000378:metabolism
chemical_list: D035683:MicroRNAs; D016328:NF-kappa B; D010455:Peptides; C118258:SN50 peptide; D013449:Sulfonamides; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; C507035:ethyl 6-(N-(2-chloro-4-fluorophenyl)sulfamoyl)cyclohex-1-ene-1-carboxylate; C487931:mirnlet7 microRNA, human