Heat‐killed Helicobacter pylori upregulates NKG2D ligands expression on gastric adenocarcinoma cells via Toll‐like receptor 4

Abstract

Background: Natural killer (NK) cells are paramount for immunity against infectious agents and tumors. Their cytokine and cytolytic responses can be mediated by natural killer group 2, member D (NKG2D), an activating receptor whose ligands (NKG2DL) expression is induced in conditions of cell stress and malignant transformation. Since sustained expression of NKG2DL MICA is related to lower survival rates in gastric adenocarcinoma patients, and Helicobacter pylori infection contributes to tumorigenesis; we asked whether H. pylori stimulus could promote NKG2DL expression on human gastric adenocarcinoma cells.Methods: Heat-killed H. pylori (HKHP) was used to stimulate MKN45 cells before analysis of NKG2DL and Toll-like receptor 4 (TLR4) protein levels by flow cytometry and transcripts by real-time PCR. LPS from Rhodobacter sphaeroides and inhibitory peptide Pepinh MYD were used to inhibit TLR4/MyD88 signaling pathway to assess its participation on NKG2DL expression. NK cell-mediated cytotoxicity was measured by lactate dehydrogenase (LDH) and CD107a mobilization assays.Results: Stimulation of MKN45 cells with HKHP increased MICA, ULBP4 (another NKG2DL), and TLR4 at the protein and transcriptional levels. MICA, but not ULBP4 expression, was upregulated in a TLR4/MyD88-dependent manner. Furthermore, the presence of NKG2DL on the surface of HKHP-stimulated MKN45 cells enabled NK cell cytotoxic activation. Conclusions:Our data indicate that induction of NKG2DL expression on gastric adenocarcinoma cells by H. pylori promotes an immune response that may ultimately contribute to either gastric tissue damage, as a consequence of persistent activation of immunity, or tumor immune evasion due to chronic NKG2DL expression.

Immune evasion by proteolytic shedding of natural killer group 2, member D ligands in Helicobacter pylori infection

“…Thus, induction of NKG2D-L gene expression is likely associated with specific H. pylori strains leading to varying disease outcomes ( 1 ). So far only a single report describes the effect of H. pylori on the NKG2D axis ( 73 ). Heat-killed H. pylori induced MICA gene expression but not MICB , driven by H. pylori -LPS stimulating TLR4 in gastric epithelial cell lines activating also the cytotoxicity of peripheral blood lymphocytes.…”

Regulation of NKG2D Stress Ligands and Its Relevance in Cancer Progression

“…Since the NKG2D ligands are stress responsive, a process such as tumorigenesis can have an overlap of stimuli that regulate NKG2D ligand expression. For example, infection with the bacteria Helicobacter pylori (H. pylori) is an established risk factor associated with the onset of gastric adenocarcinoma [97]. A recent study by Hernandez et al demonstrated that exposure to H. pylori induced MICA and ULBP4 in gastric adenocarcinoma cell lines, which promoted NK cell cytotoxic activation [97].…”

“…For example, infection with the bacteria Helicobacter pylori (H. pylori) is an established risk factor associated with the onset of gastric adenocarcinoma [97]. A recent study by Hernandez et al demonstrated that exposure to H. pylori induced MICA and ULBP4 in gastric adenocarcinoma cell lines, which promoted NK cell cytotoxic activation [97]. In addition, stress to the endoplasmic reticulum induced MULT-1 expression in human endothelial cells is also linked to tumorigenesis [98].…”

Enhancing anti-gastrointestinal cancer activities of CLDN18.2 CAR-T armored with novel synthetic NKG2D receptors Containing DAP10 and DAP12 signaling domains

“…Under physiological conditions, NKG2D ligands were usually overexpressed on viral infected or DNA damaged cells but not expressed in healthy tissues 20,21 . However, human cancers including gastric adenocarcinoma can upregulate NKG2D ligand expression [22][23][24] .…”