Expression of CEACAM1 or CEACAM5 in AZ-521 cells restores the type IV secretion deficiency for translocation of CagA by<i>Helicobacter pylori</i>

Abstract

Helicobacter pylori represents an important pathogen involved in diseases ranging from gastritis, peptic ulceration, to gastric malignancies. Prominent virulence factors comprise the vacuolating cytotoxin VacA and the cytotoxin-associated genes pathogenicity island (cagPAI)-encoded type IV secretion system (T4SS). The T4SS effector protein CagA can be translocated into AGS and other gastric epithelial cells followed by phosphorylation through c-Src and c-Abl tyrosin kinases to hijack signalling networks. The duodenal cell line AZ-521 has been recently introduced as novel model system to investigate CagA delivery and phosphorylation in a VacA-dependent fashion. In contrast, we discovered that AZ-521 cells display a T4SS incompetence phenotype for CagA injection, which represents the first reported gastrointestinal cell line with a remarkable T4SS defect. We proposed that this deficiency may be due to an imbalanced coexpression of T4SS receptor integrin-β1 or carcinoembryonic antigen-related cell adhesion molecules (CEACAMs), which were described recently as novel H. pylori receptors. We demonstrate that AZ-521 cells readily express integrin-β1, but overexpression of integrin-β1 constructs did not restore the T4SS defect. We further show that AZ-521 cells lack the expression of CEACAMs. We demonstrate that genetic introduction of either CEACAM1 or CEACAM5, but not CEACAM6, in AZ-521 cells is sufficient to permit injection and phosphorylation of CagA by H. pylori to degrees observed in the AGS cell model. Expression of CEACAM1 or CEACAM5 in infected AZ-521 cells was also accompanied by tyrosine dephosphorylation of the cytoskeletal proteins vinculin and cortactin, a hallmark of H. pylori-infected AGS cells. Our results suggest the existence of an integrin-β1- and CEACAM1- or CEACAM5-dependent T4SS delivery pathway for CagA, which is clearly independent of VacA. The presence of two essential host protein receptors during infection with H. pylori represents a unique feature in the bacterial T4SS world. Further detailed investigation of these T4SS functions will help to better understand infection strategies by bacterial pathogens.