title: Helicobacter pylori CagA protein activates serum response element-driven transcription independently of tyrosine phosphorylation.
abstract: OBJECTIVE
  Infection with Helicobacter pylori possessing the cag pathogenicity island (PAI) is associated with severe gastritis and gastric cancer. CagA protein, one of the products of cag PAI, is translocated into epithelial cells, where cytoskeletal rearrangements occur as a result of CagA tyrosine (Tyr) phosphorylation. Here we identify a new role for CagA protein as an activator of host cell signaling.
  
  
  METHODS
  We transfected CagA into epithelial cells and analyzed its effect on transcription by reporter assays. The mechanism of reporter activation was assessed by electrophoretic mobility shift assays (EMSA) and immunoblots. Responsible regions of CagA for reporter activation were determined by truncation and mutagenesis of cagA gene.
  
  
  RESULTS
  In HeLa cells, expression of CagA increased serum response element (SRE)-driven and serum response factor (SRF)-driven transcription by 40-fold and 3.3-fold, respectively, but did not affect nuclear factor kappaB- or AP-1-driven transcription. CagA-mediated SRE activation was also observed in gastric cell lines. Immunoblotting and EMSA revealed that transfection of CagA enhanced phosphorylation of and DNA binding by Elk1. Furthermore, involvement of Ras and MEK in CagA-mediated Elk1 phosphorylation was observed. SRE activation was dependent on several regions within the C-terminal portion of CagA (CagA(873-1002)), and independent of Tyr phosphorylation.
  
  
  CONCLUSIONS
  The C-terminal portion of CagA enhances SRE-driven transcription by activating an upstream signaling cascade without requiring CagA Tyr phosphorylation. This result suggests that translocated CagA regulates 2 distinct cellular responses: phosphorylation-dependent cytoskeletal rearrangement and phosphorylation-independent transcriptional activation.
authors.affiliation: Department of Gastroenterology, University of Tokyo, Japan. HIRATAY-INT@h.u-tokyo.ac.jp
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Hirata
authors.forename: Shin
authors.initials: S
authors.lastname: Maeda
authors.forename: Yuzo
authors.initials: Y
authors.lastname: Mitsuno
authors.forename: Keisuke
authors.initials: K
authors.lastname: Tateishi
authors.forename: Ayako
authors.initials: A
authors.lastname: Yanai
authors.forename: Masao
authors.initials: M
authors.lastname: Akanuma
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Yoshida
authors.forename: Takao
authors.initials: T
authors.lastname: Kawabe
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Shiratori
authors.forename: Masao
authors.initials: M
authors.lastname: Omata
mesh_terms: D000595:Amino Acid Sequence / Q000502:physiology; D000942:Antigens, Bacterial; D001426:Bacterial Proteins / Q000502:physiology*; D001667:Binding, Competitive; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins; D004847:Epithelial Cells / Q000502:physiology; D006367:HeLa Cells; D016480:Helicobacter pylori / Q000378:metabolism*; D006801:Humans; D020929:Mitogen-Activated Protein Kinase Kinases / Q000502:physiology; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D027602:Serum Response Element / Q000502:physiology*; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism; D050807:ets-Domain Protein Elk-1; D018631:ras Proteins / Q000502:physiology
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C494112:ELK1 protein, human; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; C080866:cagA protein, Helicobacter pylori; D050807:ets-Domain Protein Elk-1; D014443:Tyrosine; D004247:DNA; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins