Helicobacter pylori CagA protein activates serum response element-driven transcription independently of tyrosine phosphorylation.
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.
Hirata
Yoshihiro
Y
Department of Gastroenterology, University of Tokyo, Japan. HIRATAY-INT@h.u-tokyo.ac.jp
Maeda
Shin
S
Mitsuno
Yuzo
Y
Tateishi
Keisuke
K
Yanai
Ayako
A
Akanuma
Masao
M
Yoshida
Haruhiko
H
Kawabe
Takao
T
Shiratori
Yasushi
Y
Omata
Masao
M
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
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