Functional Properties of Helicobacter pylori VacA Toxin m1 and m2 Variants

Abstract

Helicobacter pylori colonizes the gastric mucosa and secretes a pore-forming toxin (VacA). Two main types of VacA, m1 and m2, can be distinguished by phylogenetic analysis. Type m1 forms of VacA have been extensively studied, but there has been relatively little study of m2 forms. In this study, we generated H. pylori strains producing chimeric proteins in which VacA m1 segments of a parental strain were replaced by corresponding m2 sequences. In comparison to the parental m1 VacA protein, a chimeric protein (designated m2/m1) containing m2 sequences in the N-terminal portion of the m region was less potent in causing vacuolation of HeLa cells, AGS gastric cells, and AZ-521 duodenal cells and had reduced capacity to cause membrane depolarization or death of AZ-521 cells. Consistent with the observed differences in activity, the chimeric m2/m1 VacA protein bound to cells at reduced levels compared to the binding levels of the parental m1 protein. The presence of two strain-specific insertions or deletions within or adjacent to the m region did not influence toxin activity. Experiments with human gastric organoids grown as monolayers indicated that m1 and m2/m1 forms of VacA had similar cell-vacuolating activities. Interestingly, both forms of VacA bound preferentially to the basolateral surface of organoid monolayers and caused increased cell vacuolation when interacting with the basolateral surface compared to the apical surface. These data provide insights into functional correlates of sequence variation in the VacA midregion (m region).

Genome of Helicobacter pylori and Serotype of HPV Detected in Oropharyngeal and Laryngeal Cancer and Chronic Inflammation Patients

“…The toxin has multiple effects in epithelial cells and immune cells such as T lymphocytes, B lymphocytes, macrophages, and dendritic cells [ 38 ]. The activity of this pore-forming cytotoxin in the immune system can be modified by the cytokine activity in the cells and/or can influence apoptotic activity, too [ 39 ].…”

There Are No Insurmountable Barriers: Passage of the Helicobacter pylori VacA Toxin from Bacterial Cytoplasm to Eukaryotic Cell Organelle

“…VacA was shown to bind to plasma membranes of different types of human/mammalian cells e.g., HeLa [ 90 , 108 , 109 ], AGS [ 90 ], G401 [ 110 , 111 ], AZ-521 [ 110 , 111 , 112 , 113 , 114 ], RK-13 [ 111 ], primary mouse glandular stomach epithelial cells [ 115 ], primary human T lymphocytes [ 116 ], and others. Most cellular alterations caused by VacA, like permeabilization, increased current, membrane depolarization, and ion conductivity, are attributed to membrane channel formation, either in the plasma membrane or in the membranes of endosomes, lysosomes, or mitochondria [ 2 , 101 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 ]. VacA is found in glycosylphosphatidyl inositol anchored protein (GPI-AP)-enriched early endosomal compartments (GEECs) within 10 min after internalization and within next 10ths of minutes in early endosomes (EEs), and then in late endosomes (LEs) [ 129 ].…”

“…The VacA-induced permeabilization of cells is attributed to the formation of VacA channels in the plasma membrane [ 118 , 119 , 120 ]. Channel formation is accompanied by several phenomena such as membrane depolarization [ 118 , 125 , 126 , 127 ], increased current detected in the cell plasma membranes [ 118 ] or lipid bilayers [ 117 , 119 , 120 , 185 ], and ion conductivity. The conductivity of the VacA channel is very low, and, depending on the experimental conditions, values between 10 and 30 pS were obtained [ 107 , 118 , 119 , 120 ].…”

Microbiota and the Immune System—Actors in the Gastric Cancer Story

“…It is also involved in the process of weakening gastric epithelial cells by increasing the permeability of the mitochondrial membrane, disrupting transport or inducing apoptosis. It also has the ability to modulate the immune response by inhibiting the proliferation of immune cells and stimulate the production of pro-inflammatory cytokines (TNF-α or IL-6) by mast cells, which contributes to the development of inflammation in the stomach [ 115 , 116 , 117 ]. The second protein, CagA, interacts with gastric epithelial cells, inducing inflammation, which is strongly associated with the development of the carcinogenesis process.…”