Determinants and consequences of different levels of CagA phosphorylation for clinical isolates of Helicobacter pylori.
OBJECTIVE
The Helicobacter pylori cag pathogenicity island encodes a secretory system that translocates CagA into epithelial cells, where it becomes tyrosine phosphorylated and induces cytoskeletal rearrangements. Strains with more CagA tyrosine phosphorylation motifs are most closely associated with gastric cancer. Here we assess whether clinical strains can deliver CagA, whether strains with different numbers of CagA phosphorylation motifs have CagA phosphorylated to different degrees, and whether this induces different amounts of epithelial cytoskeletal change.


METHODS
Forty-four H. pylori strains from South African patients, all cagA gene positive, were cocultured with the gastric adenocarcinoma cell line AGS. CagA expression and phosphorylation were determined by Western blot and interleukin-8 secretion by enzyme-linked immunosorbent assay. The cagA 3' variable regions of 22 strains were sequenced and shown to possess 3-6 phosphorylation motifs. These strains were used to quantify CagA phosphorylation and cytoskeletal rearrangements.


RESULTS
cagA genotype and typing of cag pathogenicity island genes were poorly predictive of phenotype. Thirty-four of 44 strains expressed CagA protein that could be delivered to and phosphorylated within AGS cells. Only these 34 strains induced interleukin-8 secretion from AGS cells. Among those strains, the number of CagA tyrosine phosphorylation motifs determined the degree of CagA phosphorylation and the level of biologic activity in terms of degree and extent of AGS cell elongation.


CONCLUSIONS
H. pylori strains that deliver CagA with more phosphorylation motifs induce higher levels of CagA phosphorylation in epithelial cells, induce more cytoskeletal changes, and are more likely to be associated with gastric cancer.
Institute of Infection, Immunity and Inflammation, and the Wolfson Digestive Diseases Centre, University of Nottingham, Queen's Medical Centre, England. richard.argent@nottingham.ac.uk
Richard H
RH
Argent
Mark
M
Kidd
Robert J
RJ
Owen
Rachael J
RJ
Thomas
Marie C
MC
Limb
John C
JC
Atherton
D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism / Q000382:microbiology; D015870:Gene Expression; D016481:Helicobacter Infections / Q000378:metabolism*; D016480:Helicobacter pylori / Q000472:pathogenicity*; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D014443:Tyrosine / Q000378:metabolism; D014774:Virulence
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D016209:Interleukin-8; D010446:Peptide Fragments; C080866:cagA protein, Helicobacter pylori; D014443:Tyrosine