Characterization of CagA variable region of Helicobacter pylori isolates from Chinese patients

Abstract

Aim: To characterize the CagA variable region of Helicobacter pylori isolates from Chinese patients.

Methods: DNA fragments in CagA variable region were amplified and sequenced respectively from genomic DNA of 19 isolates from patients with gastric cancer and 20 isolates from patients with chronic gastritis. The tendency of phosphorylation in tyrosine(s) of CagA proteins was evaluated subsequently by phosphorylation assay in vivo and in vitro respectively.

Results: About 97.44% (38/39) H pylori isolates possessed CagA gene. CagA(+) strains contained 2-4 tandem five-amino-acid motifs EPIYA but only one EPIYA had repeated sequence in CagA variable region in different isolates. There was no significant difference between the number of EPIYA motifs in H pylori from patients with different diseases. However, only tyrosine site in EPIYA within repeated sequence could be phosphorylated by AGS cells in vivo although all tyrosine sites in EPIYA could be phosphorylated in vitro.

Conclusion: CagA in Chinese has no functional difference in perturbing cellular signal pathway among different H pylori isolates.

Figure 1

Amino acid sequence characteristics of CagA variable region. CZU-1,2,3: Isolates from Chinese patients stand for the three types of CagA variable region respectively; CZU-1: CagA with 2 EPIYAs; CZU-2: CagA with 3 EPIYAs and CZU-3: CagA with 4 EPIYAs. The red letters stand for the deletion of amino acids in CZU-1 and the letters underline the mean extra amino acids in CZU-3 when compared to CZU-2. NCTC11637 was a Western standard strain.

Figure 2

Tyrosine phosphorylation sites in EPIYA in vitro and in vivo. A-F: tyrosine phosphorylation in vitro. Lane A: CagA with 4 EPIYAs; lane B: CagA with 3 EPIYAs; lane C: CagA with 2 EPIYAs; lane D: EPIFA with 1 EPIYA; lane E: EPIFA with 2 EPIYAs; lane F: EPIFA with 3 EPIYAs. lane G-L: tyrosine phosphorylation in vivo. G: CagA with 4 EPIYAs; H: CagA with 3 EPIYAs; I: CagA with 2 EPIYAs; lane J: EPIFA with 3 EPIYAs; lane K: EPIFA with 2 EPIYAs; lane L: EPIFA with 1 EPIYA.