A Transgenic Drosophila Model Demonstrates That the Helicobacter pylori CagA Protein Functions as a Eukaryotic Gab Adaptor

Abstract

Infection with the human gastric pathogen Helicobacter pylori is associated with a spectrum of diseases including gastritis, peptic ulcers, gastric adenocarcinoma, and gastric mucosa–associated lymphoid tissue lymphoma. The cytotoxin-associated gene A (CagA) protein of H. pylori, which is translocated into host cells via a type IV secretion system, is a major risk factor for disease development. Experiments in gastric tissue culture cells have shown that once translocated, CagA activates the phosphatase SHP-2, which is a component of receptor tyrosine kinase (RTK) pathways whose over-activation is associated with cancer formation. Based on CagA's ability to activate SHP-2, it has been proposed that CagA functions as a prokaryotic mimic of the eukaryotic Grb2-associated binder (Gab) adaptor protein, which normally activates SHP-2. We have developed a transgenic Drosophila model to test this hypothesis by investigating whether CagA can function in a well-characterized Gab-dependent process: the specification of photoreceptors cells in the Drosophila eye. We demonstrate that CagA expression is sufficient to rescue photoreceptor development in the absence of the Drosophila Gab homologue, Daughter of Sevenless (DOS). Furthermore, CagA's ability to promote photoreceptor development requires the SHP-2 phosphatase Corkscrew (CSW). These results provide the first demonstration that CagA functions as a Gab protein within the tissue of an organism and provide insight into CagA's oncogenic potential. Since many translocated bacterial proteins target highly conserved eukaryotic cellular processes, such as the RTK signaling pathway, the transgenic Drosophila model should be of general use for testing the in vivo function of bacterial effector proteins and for identifying the host genes through which they function.

c-Src and c-Abl kinases control hierarchic phosphorylation and function of the CagA effector protein in Western and East Asian Helicobacter pylori strains

“…Grab2-associated binder (Gab), another docking protein family member, is phosphorylated on 2 tyrosine residues by the c-Met receptor tyrosine kinase (54), creating Gab1 binding motifs for SHP-2, stimulating SHP-2 phosphatase, and activating MAP kinase cascades (55). Genetic studies have suggested that CagA may show Gab-like adapter protein activity in Drosophila (56). Thus, CagA PY has striking functional similarities to p130-Cas and Gab adapter proteins, in terms of both tyrosine phosphorylation and recruitment of SH2 factors that induce downstream signaling cascades.…”

Helicobacter pylori cytotoxin-associated gene A (CagA) subverts the apoptosis-stimulating protein of p53 (ASPP2) tumor suppressor pathway of the host

“…For example, destabilization of the E-Cadherin/β-catenin complex by CagA induces abnormal activation of the wingless/int (WNT)/ β-catenin pathway (17,18). However, the effects of CagA on tumor suppressor pathways have remained obscure.…”

J-Western Forms of Helicobacter pylori cagA Constitute a Distinct Phylogenetic Group with a Widespread Geographic Distribution

“…CagA is translocated into gastric epithelial cells through a type IV secretion system, and upon entry into cells, it causes a complex set of alterations in signal transduction (2,8,11,27,33,42,49,54,56). Many of the alterations caused by CagA are associated with malignant transformation of cells (2, 8, 11, 27-29, 33, 49, 54, 56).…”