Biological activity of the virulence factor cagA of Helicobacter pylori.
BACKGROUND
China is one of the countries with the highest incidence of H. pylori and more than 9090 isolates possessed the cagA gene. This study was to evaluate the biological activity of the H. pylori virulence factor cagA isolated from Chinese patients.


METHODS
cagA DNA fragments were amplified from the genomic DNA and subsequently cloned into the mammalian expression vector for cell transfection and DNA sequencing. cagA protein, phosphorylated-tyrosine cagA and the complex of cagA precipitated with SHP-2 were identified respectively by western blot in the crude cell lysate from conditionally immortalized gastric epithelial cells at 48 hours after transfection with cagA DNA. In addition, the ability of induction of scattering phenotype was examined after transient expression of cagA in AGS cells.


RESULTS
The C-terminal half of cagA contained only one repeated sequence and three tandem five-amino-acid motifs glutamic acid-proline-isoleucine-tyrosine-alanine (EPIYA). Moreover, the amino acid sequence of D2 region in repeated sequence was aspartic acid-phenylanaline-aspartic acid (D-F-D) which was significantly distinguished from the three repeated sequences and aspartic acid-aspartic adid-leucine (D-D-L) in the western standard strain NCTC11637. Western blot revealed that cagA became phosphorylated in tyrosine site and bound with SHP-2 after transient expression of cagA DNA in gastric epithelial cells. Transient expression of cagA in AGS cells showed that cagA was able to induce the elongation phenotype although to a lesser extent than western strains.


CONCLUSIONS
cagA perturbs cell signaling pathways by binding with SHP-2. However, significant difference exists in amino acid sequence and biological function of cagA in Chinese compared with those of western countries.
Zhu
Yong-liang
YL
Gastroenterological Department, Second Affiliated Hospital of Zhejiang University College of Medicine, Hangzhou 310009, China.
Zheng
Shu
S
Qian
Ke-da
KD
Fang
Ping-chu
PC
D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000737:chemistry / Q000502:physiology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000502:physiology*; D015153:Blotting, Western; D002478:Cells, Cultured; D005753:Gastric Mucosa; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D010641:Phenotype; D010766:Phosphorylation; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D015398:Signal Transduction
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D047908:Intracellular Signaling Peptides and Proteins; C080866:cagA protein, Helicobacter pylori; C516724:PTPN11 protein, human; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D017027:Protein Tyrosine Phosphatases