Inhibition of T-cell proliferation by Helicobacter pylori gamma-glutamyl transpeptidase.
OBJECTIVE
Helicobacter pylori colonizes the human gastric mucosa of >50% of the world's population. Most of the patients have no overt clinical symptoms. However, the infection is invariably associated with the development of active chronic gastritis, leading in some cases to the development of peptic ulcer disease, distal gastric adenocarcinoma, and mucosa-associated lymphoid tissue lymphoma. In contrast to most other pathogens, infection with H pylori persists lifelong, but reasons for the persistence remain obscure. CD4-positive T cells are crucial for bacterial elimination but are inhibited by H pylori. We aimed to identify the factor responsible for suppression of T-cell response and characterize this inhibitory effect on a cellular and molecular level.


METHODS
Using size-exclusion chromatography, sodium dodecyl sulfate/polyacrylamide gel electrophoresis, and a spectrophotometric enzyme assay, we identified the secreted gamma-glutamyl transpeptidase of H pylori (HPGGT) as the factor responsible for inhibition of T-cell proliferation.


RESULTS
Mutagenesis of HPGGT in different H pylori strains completely abrogated this inhibitory effect. Recombinantly expressed HPGGT protein showed full antiproliferative activity. Site-directed mutagenesis and application of the GGT inhibitor acivicin revealed that inhibition of T cells depends on catalytic activity of HPGGT. Cell cycle analysis of human T cells indicated that HPGGT was necessary and sufficient to induce G(1) arrest. Reduced levels of c-Myc and phosphorylated c-Raf protein suggest the disruption of Ras-dependent signaling by HPGGT.


CONCLUSIONS
GGT is a novel immunosuppressive factor of H pylori inhibiting T-cell proliferation by induction of a cell cycle arrest in the G(1) phase.
Schmees
Christian
C
Department of Medicine II, Technical University of Munich, Munich, Germany.
Prinz
Christian
C
Treptau
Tilman
T
Rad
Roland
R
Hengst
Ludger
L
Voland
Petra
P
Bauer
Stefan
S
Brenner
Lena
L
Schmid
Roland M
RM
Gerhard
Markus
M
D017209:Apoptosis / Q000502:physiology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D016193:G1 Phase / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D016480:Helicobacter pylori / Q000201:enzymology*; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism; D007376:Interleukin-2 / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D011994:Recombinant Proteins; D015398:Signal Transduction / Q000502:physiology; D013601:T-Lymphocytes / Q000166:cytology* / Q000502:physiology; D005723:gamma-Glutamyltransferase / Q000235:genetics / Q000378:metabolism*
D007376:Interleukin-2; D011994:Recombinant Proteins; D007371:Interferon-gamma; D005723:gamma-Glutamyltransferase