Activation of Abl by Helicobacter pylori: a novel kinase for CagA and crucial mediator of host cell scattering.
OBJECTIVE
The pathogenesis of Helicobacter pylori (Hp)-associated diseases depends on a specialized type IV secretion system. This type IV secretion system injects the cytotoxin-associated gene A (CagA) effector protein into target cells where CagA becomes phosphorylated on tyrosine residues by Src. Src then is inactivated rapidly, suggesting the presence of another host tyrosine kinase to ensure constant CagA phosphorylation in sustained Hp infections. We aimed to identify this kinase.


METHODS
By using the AGS gastric epithelial cell model, we performed a detailed functional characterization of Abl tyrosine kinase in signaling during Hp infections.


RESULTS
We showed that Abl kinase is activated and a novel crucial mediator of Hp infections. First, Abl-specific inhibitors SKI-DV2-43 or STI571 (Gleevec, Novartis) and knockdown of c-Abl/Abl-related gene Arg by small hairpin and interfering RNAs efficiently inhibit CagA phosphorylation and cell scattering. Second, during infection, Abl is activated rapidly by autophosphorylation at Y-412. Third, both Abl and Src phosphorylated Y-899, Y-918, and Y-972 of CagA. Fourth, we found that the Abl substrate CrkII is phosphorylated at Y-221 in vivo. Fifth, overexpression of kinase-dead Abl (K290M) blocked Hp-induced actin cytoskeletal rearrangements. We further showed that sustained activity of Abl is required to maintain CagA in a phosphorylated state. Moreover, phosphorylated CagA forms a physical complex with Abl and activated CrkII in vivo.


CONCLUSIONS
We propose a model in which Hp has evolved a mechanism to use at least 2 tyrosine kinases, Abl and Src, for CagA phosphorylation and subsequent actin-cytoskeletal rearrangements leading to cell scattering and elongation.
Tammer
Ina
I
Department of Medical Microbiology, Otto von Guericke University, Magdeburg, Germany.
Brandt
Sabine
S
Hartig
Roland
R
König
Wolfgang
W
Backert
Steffen
S
D000942:Antigens, Bacterial / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001549:Benzamides; D002460:Cell Line; D004848:Epithelium / Q000378:metabolism / Q000382:microbiology / Q000473:pathology; D005753:Gastric Mucosa / Q000378:metabolism* / Q000382:microbiology / Q000473:pathology; D005786:Gene Expression Regulation; D016481:Helicobacter Infections / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D016480:Helicobacter pylori / Q000378:metabolism*; D006801:Humans; D000068877:Imatinib Mesylate; D015151:Immunoblotting; D047468:Immunoprecipitation; D034982:Integration Host Factors / Q000235:genetics; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D012329:RNA, Bacterial / Q000235:genetics*; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D001549:Benzamides; D034982:Integration Host Factors; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D012329:RNA, Bacterial; C080866:cagA protein, Helicobacter pylori; D000068877:Imatinib Mesylate; C426236:ARG tyrosine kinase; D011505:Protein-Tyrosine Kinases; D019061:src-Family Kinases