CagA Effector Protein in Helicobacter pylori-Infected Human Gastric Epithelium in Vivo: From Bacterial Core and Adhesion/Injection Clusters to Host Cell Proteasome-Rich Cytosol.

Vittorio Necchi,Vittorio Ricci,Enrico Solcia,Patrizia Sommi

doi:10.3390/toxins11110618

Abstract

A key role in the carcinogenic action of Helicobacter pylori is played by the effector protein CagA, the first identified oncoprotein of the bacterial world. However, the present knowledge in regard to the bacterial injection of CagA into epithelial cells (through a type IV secretion system) and its intracellular fate is based primarily on experimental studies in vitro. Our study was aimed to investigate, in H. pylori-infected human gastric epithelium, CagA delivery and intracellular distribution in order to identify any in vivo counterpart of the cell injection mechanism described in vitro and any intracellular cytoplasmic site of preferential CagA distribution, thus shedding light on the natural history of CagA in vivo. By transmission electron microscopy and ultrastructural immunocytochemistry (which combine precise molecule localization with detailed analysis of bacterial-host cell interaction and epithelial cell ultrastructure), we investigated endoscopic biopsies of gastric antrum from H. pylori-infected dyspeptic patients. Our findings provide support for CagA direct injection into gastric epithelial cells at bacterial adhesion sites located on the lateral plasma membrane and for its cytosolic intracellular distribution with selective concentration inside peculiar proteasome-rich areas, which might be site not only of CagA degradation but also of CagA-promoted crucial events in gastric carcinogenesis.

Highlights

The Gram-negative bacterium Helicobacter pylori infects about half of the world’s population and plays a key role in human carcinogenesis
Ultrastructural investigation of gastric antral biopsies from patients known from previous studies to be colonized by H. pylori at the level of the gastric luminal surface [16,17] allowed us to detect bacteria infiltrating lateral intercellular spaces of the epithelium, often with patterns of bacterial-to-epithelial cell adhesion (Figure 1A,B)
T4SS injection mechanism identified in co-culture experiments in vitro and by scanning electron microscopy [7,18,19]

Summary

Introduction

The Gram-negative bacterium Helicobacter pylori infects about half of the world’s population and plays a key role in human carcinogenesis. Classified by the World Health Organization as a class-I carcinogen [1], H. pylori infection is the strongest known risk factor for gastric neoplasms [2,3]. Among several different virulence factors produced by the bacterium, a key role in the carcinogenic action of H. pylori is played by the effector protein CagA [4,5,6]. Toxins 2019, 11, 618 cells, CagA is the first identified bacterial oncoprotein, i.e., a protein playing a well-established role in human carcinogenesis. H. pylori interaction with the basolaterally-located integrin-β1 membrane receptor promotes the cellular injection of CagA through the bacterial

Methods

Results

Conclusion