Ng MDSCs [1]. In addition, the lack of effect of NOXon MDSC

Ng MDSCs [1]. In addition, the lack of effect of NOXon MDSC accumulation and function does not rule out an effect of other sources of ROIs. There are NOX2-independent sources of ROI generation, including xanthine oxidase [50] and mitochondrial ROIs [51] that have antimicrobial host defense capacity and, conceivably, could contribute to MDSC generation and/or function in the absence of NOX2. These NOX2-independent pathways could potentially react with nitrogen intermediates to generate Title Loaded From File peroxynitrite, which is required for nitration of TCR/CD8 and induction of T cell tolerance [4]. As a precedent for this concept, the Title Loaded From File interaction of xanthine oxidase and reactive nitrogen intermediates overcame the requirement for NOX2 as a mediator of ROImediated acute lung injury [52]. We speculate that NOX2 and other ROI-generating enzymes represent alternative pathways for ROI generation that can prime the development of MDSCs. Further 16574785 work using small molecule inhibitors and genetically engineered mice with deficiencies in specific ROI-generating pathways will be required to test this concept.Author ContributionsConceived and designed the experiments: HEG ANHK RRV MJG KLS NK SIA KO BHS. Performed the experiments: HEG ANHK RRV MJG KLS NK KJS AP. Analyzed the data: HEG ANHK RRV MJG KLS NK KJS AP SIA KO BHS. Wrote the paper: HEG ANHK BHS.Myeloid-Derived Suppressor Cells and NADPH Oxidase
Persistent H. pylori infection is one major cause of gastric cancer. The H. pylori-dependent activation of diverse signaling cascades induces the upregulation of proinflammatory chemokines and induces morphological rearrangements of epithelial cells, resulting in chronic gastritis, which progresses from atrophy, to intestinal and spasmolytic metaplasia, dysplasia, and finally to cancer. This diverse clinical outcome may be associated with the expression of bacterial virulence factors. Two major virulence factors have been studied extensively, the cytotoxin-associated antigen A (CagA) and the vacuolating cytotoxin A (VacA) [1]. Proteolysis is instrumental for extracellular matrix (ECM) degradation during tumor invasion and metastasis. However, the proteases involved are not solely produced by cancer cells. The activated tumor microenvironment, including inflammatory immune cells, such as macrophages, supplies many active proteases already during premalignant stages of tumorigenesis [2,3]. H. pylori has been described in conjunction with increased expression of certain matrix metalloproteinases (MMPs), such as MMP-1, MMP-7, or MMP-9 [4,5,6,7,8,9]. In contrast, among the cysteine proteases, only one cathepsin was found to be upregulated in H. pylori-infected gastric mucosa, cathepsin X/Z (Ctsz) [10]. Itsexpression is mostly restricted to cells of the immune system, however the increase of Ctsz in gastric cancer was attributed to epithelial expression [11]. H. pylori-induced cytokine expression stimulates overexpression of Ctsz via ERK1/2 and JNK/p38 pathways in macrophages and epithelial cells, respectively [12]. Due to its unique carboxypeptidase specificity, Ctsz is unable to participate in bulk ECM degradation, thus questioning its direct contribution to the invasive processes of tumor cells [13]. The question of physiological or pathological functions for Ctsz is not yet fully clarified. Although reduced invasive capacity of tumor cells after Ctsz inhibition in Boyden chamber assays has been reported, the explanations for potential mechanisms are still questionable. Ctsz.Ng MDSCs [1]. In addition, the lack of effect of NOXon MDSC accumulation and function does not rule out an effect of other sources of ROIs. There are NOX2-independent sources of ROI generation, including xanthine oxidase [50] and mitochondrial ROIs [51] that have antimicrobial host defense capacity and, conceivably, could contribute to MDSC generation and/or function in the absence of NOX2. These NOX2-independent pathways could potentially react with nitrogen intermediates to generate peroxynitrite, which is required for nitration of TCR/CD8 and induction of T cell tolerance [4]. As a precedent for this concept, the interaction of xanthine oxidase and reactive nitrogen intermediates overcame the requirement for NOX2 as a mediator of ROImediated acute lung injury [52]. We speculate that NOX2 and other ROI-generating enzymes represent alternative pathways for ROI generation that can prime the development of MDSCs. Further 16574785 work using small molecule inhibitors and genetically engineered mice with deficiencies in specific ROI-generating pathways will be required to test this concept.Author ContributionsConceived and designed the experiments: HEG ANHK RRV MJG KLS NK SIA KO BHS. Performed the experiments: HEG ANHK RRV MJG KLS NK KJS AP. Analyzed the data: HEG ANHK RRV MJG KLS NK KJS AP SIA KO BHS. Wrote the paper: HEG ANHK BHS.Myeloid-Derived Suppressor Cells and NADPH Oxidase
Persistent H. pylori infection is one major cause of gastric cancer. The H. pylori-dependent activation of diverse signaling cascades induces the upregulation of proinflammatory chemokines and induces morphological rearrangements of epithelial cells, resulting in chronic gastritis, which progresses from atrophy, to intestinal and spasmolytic metaplasia, dysplasia, and finally to cancer. This diverse clinical outcome may be associated with the expression of bacterial virulence factors. Two major virulence factors have been studied extensively, the cytotoxin-associated antigen A (CagA) and the vacuolating cytotoxin A (VacA) [1]. Proteolysis is instrumental for extracellular matrix (ECM) degradation during tumor invasion and metastasis. However, the proteases involved are not solely produced by cancer cells. The activated tumor microenvironment, including inflammatory immune cells, such as macrophages, supplies many active proteases already during premalignant stages of tumorigenesis [2,3]. H. pylori has been described in conjunction with increased expression of certain matrix metalloproteinases (MMPs), such as MMP-1, MMP-7, or MMP-9 [4,5,6,7,8,9]. In contrast, among the cysteine proteases, only one cathepsin was found to be upregulated in H. pylori-infected gastric mucosa, cathepsin X/Z (Ctsz) [10]. Itsexpression is mostly restricted to cells of the immune system, however the increase of Ctsz in gastric cancer was attributed to epithelial expression [11]. H. pylori-induced cytokine expression stimulates overexpression of Ctsz via ERK1/2 and JNK/p38 pathways in macrophages and epithelial cells, respectively [12]. Due to its unique carboxypeptidase specificity, Ctsz is unable to participate in bulk ECM degradation, thus questioning its direct contribution to the invasive processes of tumor cells [13]. The question of physiological or pathological functions for Ctsz is not yet fully clarified. Although reduced invasive capacity of tumor cells after Ctsz inhibition in Boyden chamber assays has been reported, the explanations for potential mechanisms are still questionable. Ctsz.