The Interaction between Autophagy, Helicobacter pylori, and Gut Microbiota in Gastric Carcinogenesis

Abstract

Chronic infection with Helicobacter pylori is the primary risk factor for the development of gastric cancer. Hindering our ability to comprehend the precise role of autophagy during H. pylori infection is the complexity of context-dependent autophagy signaling pathways. Recent and ongoing progress in understanding H. pylori virulence allows new frontiers of research for the crosstalk between autophagy and H. pylori. Novel approaches toward discovering autophagy signaling networks have further revealed their critical influence on the structure of gut microbiota and metabolome. Here we intend to obtain a holistic view of the perplexing role of autophagy in H. pylori pathogenesis and carcinogenesis. We also discuss the intermediate role of autophagy in H. pylori-mediated modification of gut inflammatory responses and microbiota structure.

An Overview of Autophagy

Three primary types of autophagy (see Glossary) have been introduced based on different mechanisms underlying cargo sequestration. Direct lysosomal uptake and degradation of cytoplasmic components is referred to as microautophagy, while selective unfolding of individual cargo proteins that are subsequently translocated into lysosomes via the action of chaperone complexes is distinguished as chaperone-mediated autophagy. Finally, the main autophagic response maintaining eukaryotic cell homeostasis, macroautophagy (autophagy hereafter) extensively contributes to the sequestration of damaged or otherwise dispensable proteins, aggregates, droplets, and organelles [1]. Considering the involvement of several autophagic components in a variety of intracellular signaling networks and intercellular interactions, the detailed molecular mechanism of autophagy is illustrated in Figure 1. Following intracellular stress and/or nutrient or energy deprivation, the initiation of basal or adaptive autophagy is a keystone of preserving cellular homeostasis [2]. However, a disrupted autophagy response can cause the aggregation of impaired cellular components, which results in cellular senescence or autophagic cell death. Typically, autophagy shuts off apoptosis, and pro-apoptotic caspase activation interferes with the autophagy flux. In particular conditions, however, autophagy may excessively degrade the cytoplasm and facilitate apoptosis or necrosis, bringing about autophagic cell death [3]. The intricate interplay between autophagic cell death, apoptosis, and necrosis determines the pathological conditions of several diseases [4]. Among the wide spectrum of cellular functions regulated by autophagy, metabolic responses may critically contribute to the orchestration of autophagic cell death and apoptosis.

Figure 1.

The Molecular Mechanism of Autophagy Flux in The Host Cell. Upon suppression of MTORC1 or stimulation of AMP-activated protein kinase (AMPK), the autophagy process initiates following the activation of the ULK1 complex. Following ULK1 activation, membrane nucleation requires phosphatidylinositol-3-phosphate (PtdIns3P), which is produced by the lipid kinase function of the PtdIns3K-CI at the phagophore (the initial sequestering compartment). PtdIns3K-CI subunits include ATG14, PIK3C3, BECN1, PIK3R4/VPS15/p150 (phosphoinositide-3-kinase regulatory subunit 4), AMBRA1 (autophagy and beclin 1 regulator 1), and NRBF2 (nuclear receptor binding factor 2). Various membranous organelles such as the mitochondria, plasma membrane, and Golgi complex donate membrane precursor, contributing to phagophore expansion. Phagophore expansion proceeds as ATG12 conjugates to ATG5 and the non-covalent interaction of the ATG12–ATG5 complex with ATG16L1 forms the ATG12–ATG5-ATG16L1 ternary complex. The recruitment of WIPI2 (WD repeat domain, phosphoinositide interacting 2) and ZFYVE1/DFCP1 (zinc finger FYVE-type containing 1) by PtdIns3P promotes the conjugation of LC3 to PE (phosphatidylethanolamine). LC3 mediates selective autophagy by interacting with cargo and further facilitates phagophore expansion and sealing. ATG4 removes LC3 from the autophagosome outer membrane and then autophagosome-lysosome fusion is mediated by HOPS, small GTPase-family proteins such as RAB7, and soluble N-ethylmaleimide-sensitive fusion attachment protein receptors/SNAREs. The reformation of lysosomes from autolysosomes accelerates the next cycle of autolysosome formation.

Autophagy and Gut Homeostasis

Autophagy and the gut epithelial barrier

The integrity of the gut epithelium has a major influence on gut homeostasis and the host’s inflammatory response. Dysfunctional autophagy can impair tight junction proteins and damage epithelial barrier integrity (Box 1), which would be vulnerable to bleeding and perforation, leading to the development of primary gastrointestinal diseases [5]. Therefore, autophagy modulation can influence the integrity of the gut epithelium. As such, high concentrations of the pro-inflammatory cytokine TNF/TNF-α (tumor necrosis factor) stimulate CLDN2 (claudin 2) expression in colonic Caco-2 monolayers and induce intestinal permeability partly through autophagy inhibition [6]. Autophagy is negatively associated with non-essential amino acid deprivation, which can lower trans-epithelial resistance and downregulate the production of CLDN1 and TJP1/ZO-1 (tight junction protein 1) tight junction proteins in intestinal porcine epithelial cells [7]. As Helicobacter pylori (H. pylori) exotoxin-dependent mitochondrial perturbations interrupt cellular metabolism and alter cellular amino acid homeostasis [8], the effect of amino acid homeostasis disruption on the production of tight junction proteins could be investigated in H. pylori-infected gastric epithelial cells. Moreover, BECN1 (beclin 1) promotes OCLN (occludin) endocytosis in colonic Caco-2 cells, thereby reducing the extracellular presence of OCLN tight junctions in an autophagy-independent manner. However, an enhanced autophagy response suppresses the constitutive activity of BECN1 and ultimately preserves intestinal homeostasis [9]. Furthermore, autophagy signaling plays a major role in regulating the production of adherens junction proteins (CTNNB1/β-catenin and CDH1/E-cadherin) and the degradation of gap junctions [10]. While several studies have deepened our understanding of autophagy in intestinal stem cells, Paneth cells, and goblet cells, much more remains to be elucidated regarding other epithelial cell populations. Additionally, the underpinning mechanism of cytokine-oriented autophagy dysregulation and the ultimate epithelial cell apoptosis is yet to be fully explicated.

Box 1. Autophagy and gut immune homeostasis.

Autophagy-mediated modulation of the host immunity occurs through maintaining immune cell homeostasis and regulating cellular activity (Figure I). Cytosolic receptors for pathogen-associated molecular patterns (PAMPs) and DAMPs, NOD (nucleotide binding oligomerization domain containing)-like receptors (NLRs) include inflammasome subunits that contribute to autophagy, pyroptosis, and cytokine expression. Key members of the NLR family, NOD1 and NOD2, signal by the adaptor kinase RIPK2/RIP2 (receptor interacting serine/threonine kinase 2) to activate NFKB and MAPK (mitogen-activated protein kinase). Additionally, NOD1 and NOD2 accelerate MAP1LC3/LC3 recruitment to phagosomes and stimulate xenophagy [94]. H. pylori peptidoglycan (PG) can induce gastric inflammation through NOD1 activation [95]. Likewise, outer membrane vesicles (OMVs) of H. pylori can activate the NOD1-RIPK2 axis to induce autophagy and promote the production of IL8 (interleukin 8) and CXCL1 (C-X-C motif chemokine ligand 1). Both the inflammatory and autophagy responses require autophagosome formation as ATG5 and LC3 knockdown or knockout epithelial cells demonstrate lower response rates [64]. Conversely, autophagy can regulate NLR activation by eliminating endogenous NLR activators as well as NLR-forming components [96].

Whereas NLRs sense cytosolic components, cell surface TLR (toll like receptor) signals the extracellular presence of pathogen-associated molecular patterns through MYD88 (MYD88 innate immune signal transduction adaptor), TICAM1/TRIF (TIR domain containing adaptor molecule 1), MAPK/ERK, and/or MAPK/JNK. TLR2 promotes the host’s innate immunity by activating MAPK and inducing autophagy through MAPK/ERK and MAPK/JNK [97, 98]. Upon lipopolysaccharide (LPS) exposure, TLR4 interaction with TRAF6 accelerates lysine 63 (K63) ubiquitination of BECN1 to facilitate the formation of the PtdIns3K-CI complex [99]. TLR4 further takes part in xenophagy via K63 ubiquitination of TBK1 (TANK binding kinase 1) following TRIF and TRAF3 activation to increase LC3 recruitment of Gram-negative bacteria [100]. TLR7 stimulates mitophagy by engaging with BNIP3 (BCL2 interacting protein 3) and BECN1 and might elevate autophagic programmed cell death through MAPK/p38 or MAP2K/MEK-MAPK/ERK signaling pathways [101].

Autophagy regulatory proteins are involved in various critical aspects of innate and adaptive immunity. Autophagy is involved in mast cell degranulation [102], monocyte differentiation [103], eosinophil differentiation and infiltration [104], neutrophil proliferation and differentiation [105, 106], and natural killer (NK) cell development [107]. While in the context of the adaptive immune response, autophagy regulates dendritic cell presentation of endogenous antigens and cross-presentation of exogenous antigens [108], differentiation of T helper 1 (Th1), Th2, and Th9 cells [109, 110], memory T cell response [111], B cell maturation [112], and secondary immune responses in memory B cells [113].

Autophagy and immune response

Autophagy signaling can converge with the immune response to establish intricate signaling networks that orchestrate immune defense strategies (Box 1). Throughout all immune cell types and subsets, autophagy is critically involved in cellular maturation, activity, and homeostasis. Additionally, autophagy contributes to other strategies in host defense such as the engulfment and degradation of intracellular pathogens (known as xenophagy), antigen presentation/cross-presentation, and the modulation of inflammatory responses [11]. However, the reasons for the difference in the sensitivity of immune cells to the loss of autophagy remain unanswered. The extracellular presence of danger/damage-associated molecular patterns/DAMPs that include nucleic acid, ATP, and HMGB1 (high mobility group box 1) can potentially regulate autophagy flux and inflammatory response [12]. H. pylori-induced expression of HMGB1 triggers gastric inflammation through NFKB/NF-κB activation [13]. As the extracellular release of HMGB1 can be detected by AGER/RAGE (advanced glycation end-product specific receptor) and suppress the MTOR (mechanistic target of rapamycin kinase) complex, the primary negative regulator of autophagy, H. pylori infection may stimulate autophagy through the excessive accumulation of HMGB1 as well as the increased rate of cellular apoptosis and necrosis [14, 15]. Reactive oxygen species (ROS), a key mediator of H. pylori pathogenesis, promote the cytosolic translocation of HMGB1 wherein it prevents BECN1 suppression by BCL2 (BCL2 apoptosis regulator) and ultimately induces an autophagic response [16]. The inhibition of calpain-mediated cleavage of BECN1 and ATG5 (autophagy-related 5) represents another autophagy-inducing mechanism for cytosolic HMGB1 [17].

Given the particular significance of autophagy in the immune response, many conceptual and technical questions remain to be answered. How can we explain the mechanistic basis of the disparate impact of autophagy deletions on different immune cells or subsets? Particularly, what source of metabolites regulates the autophagic signaling pathways in each immune cell? One major obstacle hindering the resolution of these knowledge gaps is the complexity of detecting autophagosome contents during autophagy flux. Thus, the development of novel techniques that would be able to do so is of great importance in addressing several pending issues in the field.

Autophagy and Gut Microbiota

The overwhelming majority of the human microbiota reside within the gastrointestinal tract collectively referred to as the gut microbiota. These microorganisms are fundamentally important for various host physiological functions. Therefore, preserving the inherent composition of the gut microbiota is of great significance, and an aberrant profile of the gut microbiota (known as dysbiosis) may lead to various gastrointestinal and extra-gastrointestinal disorders [18]. Dysfunctional autophagy is associated with gut dysbiosis, which might also be the case for tumor microbiota and its influence on the immune landscape of the tumor microenvironment (TME).

ATG7 deficiency of intestinal epithelial cells in mouse models was demonstrated to cause intestinal dysbiosis characterized by increased abundance of Firmicutes Gram-positive bacteria and a reduced proportion of Pseudomonadota/Proteobacteria in mice stool samples [19]. Colonic epithelial cell-specific atg7 conditional knockout mice further exhibit higher fecal DNA loads, as well as enriched bacterial populations compared to the control group [20]. Similar outcomes are seen with an increased number of pro-inflammatory bacteria due to autophagy failure in the intestine of atg5 knockout mice [21] and in a mouse model for the ATG16L1^T300A polymorphism, which contributes to the development of inflammatory bowel disease [22].

Pathogenic bacteria are considered targets of xenophagy, through which autophagy prevents bacterial infection and directly influence gut dysbiosis. Intracellular restriction of bacterial replication is mainly executed by Atg8-family protein recognition of receptors that target bacterial components or ubiquitin on the bacterial surface, leading to sequestration by a phagophore [23]. Furthermore, Paneth cell secretion of lysozyme is a key antimicrobial defense occurring via secretory autophagy; therefore, autophagy deficiency can ultimately disrupt the defensive mechanism of Paneth cells and promote intestinal inflammation [24, 25]. In the context of autophagy-gut microbiota interaction, efforts have been made to develop autophagy-regulating therapeutics. Notably, some derivatives of dietary products such as vitamin D modulate autophagy and modify the gut microbial structure including H. pylori decolonization [26]. However, one issue concerns the huge intra-individual variation of the gut microbiota profile and how this affects H. pylori virulence. Accordingly, the development of individually tailored therapeutics appears mandatory.

H. pylori Infection

The infection-driven nature of most gastric cancers has encouraged researchers to seek for potential carcinogenic signaling networks affecting cancer development and progression [27]. The high pathogenicity of H. pylori along with its genetic diversity and the presence of various virulence factors have challenged our understanding of the definite mechanisms underpinning H. pylori-induced gastric carcinogenesis. Chronic inflammation, mucosal damage, genetic and epigenetic alteration, and modification in gene expression are the foremost characteristics of H. pylori infection resulting in gastric tumorigenesis [28]. H. pylori pathogenesis mainly relies on the detrimental effect of virulence factors VacA (vacuolating cytotoxin A) and CagA (cytotoxin-associated gene A). Intracellular VacA exerts several cellular effects including cell vacuolation to increase the longevity of infection, as well as mitochondrial stress and perturbation, and apoptosis [29]. The injection of CagA oncoprotein into the host cell by a type IV secretion system (T4SS), encoded by cag pathogenicity island/cagPAI, impairs cellular proliferation and the apoptotic process. However, a noteworthy characteristic of H. pylori infection lies in its capacity for immune escape. H. pylori-induced alteration in the expression of autophagy-related genes and manipulation of autophagy flux and apoptotic process are of great significance for its survival, replication, and pathogenesis. Autophagy flux is disrupted and utilized by H. pylori to flee from host immunity and antibiotic exposure [30]. Moreover, H. pylori modulation of autophagy and subsequent alteration of cellular apoptosis contributes to the etiology of gastritis, peptic ulcers, and neoplasia. The interplay between autophagy and apoptosis in the acute and chronic stages of H. pylori infection is yet to be elucidated. In the next section, we meticulously discuss the cross-talk between autophagy, H. pylori, and its virulence factors.

Autophagy and H. pylori Infection

H. pylori is attached to the plasma membrane during the early exposure of macrophages, dendritic cells, and gastric epithelial cells, whereas at 12 h of post-infection in vitro, H. pylori bacteria are mainly internalized into the cytoplasm residing within autophagosomes; this localization allows the bacteria to avoid acidic conditions, and resist bactericidal treatments, and impairs the cellular immune response [31, 32]. Thus, researchers have envisioned the development of novel drug delivery systems that target intracellular pathogens, using immune cell-derived exosomes and nanotechnology.

Acute H. pylori infection predominantly induces autophagosome formation while at the same time interfering with autophagy flux to establish intracellular niches for bacterial replication [33] (Figure 2). The nutrient requirement of H. pylori can further explain autophagy stimulation as this pathogen shifts certain metabolic pathways within the host cell. The upregulation of the tricarboxylic acid/TCA cycle and amino acid metabolism are reported as the in vitro characteristic of AGS cells 6 h post-infection, which can regulate the MTOR complex 1 (MTORC1) signaling pathway in the gastric epithelium and immune cells [34, 35].

Figure 2.

Autophagy and Acute Infection with H. pylori. H. pylori suppresses ILK to induce autophagy and apoptosis in the host cell. Urease-mediate accumulation of ammonia inhibits VacA degradation and augments VacA-induced apoptosis. The interaction of VacA with LRP1 stimulates ROS production, ER stress, apoptosis, and autophagy, which leads to CagA degradation. Similarly, CGT and OMV-derived PG induce autophagy, meanwhile, CGT prevents autophagosome-lysosome fusion. H. pylori-mediated mitochondrial perturbation, lysosomal damage, and MIR99B upregulation further trigger an autophagy response.

The H. pylori type 1 capJ (capsular polysaccharide biosynthesis protein J) gene encodes cholesterol-α-glucosyltransferase (CGT) that transforms cellular cholesterol into cholesteryl glucosides to stimulate autophagy, while interfering with lysosome-autophagosome fusion in macrophage cell line J774A.1 [36]. Cholesteryl 6′-O-acyl-α-D-glucoside augments the H. pylori-induced autophagy response by inhibiting autophagosome degradation and suppressing lysosome biogenesis [37]. Autophagy induction may facilitate H. pylori-induced gastric carcinogenesis. For example, excessive production of ROS contributes to the stimulation of the NFE2L2/Nrf2-HMOX1/HO-1 axis, which is considered a mechanism underlying H. pylori-associated gastric carcinogenesis via autophagy induction [38]. The progression of gastric cancer, however, mainly relies on the persistence of H. pylori infection, which is characterized by the suppression of the autophagy response [39] (Figure 3). Through the NOD1-RIPK2-MAPK/ERK-FOXO4 pathway, prolonged exposure of gastric epithelial cells with H. pylori lysate promotes cellular proliferation, inhibits autophagy and apoptosis, and suppresses the production of CCL20, CCL28, and CXCL2 [40]. Furthermore, the infection of gastric epithelial cell lines and gastric mucosal tissue of patients with H. pylori is accompanied by MIR30B (microRNA 30b) upregulation and consequent suppression of ATG12 and BECN1 [41]. MIR30D was further described in AGS and GES-1 cells as the regulator of core autophagy proteins ATG2B, ATG5, ATG12, BECN1, and BNIP3L (BCL2 interacting protein 3 like), through which H. pylori suppresses the autophagy pathway in the gastric epithelium [42]. However, MIR99B overexpression in H. pylori-infected gastric cancer tissues substantially induces autophagy and inhibits cellular proliferation via regulating the MTOR signaling pathway [43]. Likewise, H. pylori-induced overexpression of MIF (macrophage migration inhibitory factor) in the serum and gastric epithelium is associated with gastric cancer and intestinal metaplasia, respectively. Yet, MIF probably contributes to the H. pylori induction of autophagy as the MIF concentration is correlated with autophagy markers LC3A, LC3B, and ATG5 [44].

Figure 3.

Autophagy and Chronic Infection with H. pylori. Sustained exposure of the host cell to H. pylori mainly results in autophagy suppression. In the chronic stage of H. pylori infection, VacA and secretory protein HpGGT disrupt endolysosomal trafficking, leading to CagA accumulation and autophagy inhibition. H. pylori-mediated activation of NOD1 and expression of MIR30B and MIR30D further prevent autophagy flux. However, secretory protein Hp0175 and H. pylori-induced secretion of MIF from macrophages might induce the autophagy process in the host cell.

The convergence of bacteria with autophagy illustrates the double-edged nature of this process. That is, autophagy can be used to eliminate bacteria via xenophagy, but H. pylori promotes autophagy—while blocking complete autophagic flux—to establish a replicative niche. Later on, however, H. pylori may suppress autophagy which disrupts cellular homeostasis and promotes carcinogenesis. As clinical manifestations attributed to chronic H. pylori infection, gastric tissue samples predominantly present autophagy suppression, whereas in vitro experiments or the exposure of organoids to H. pylori within several hours mainly present autophagy induction. Owing to this type of complexity, H. pylori interaction with the autophagy response requires further elucidation. To simplify the multivariate structure of this interaction, several studies have evaluated the specific effect of H. pylori virulence factors on the autophagy flux as further described below (Table 1).

Table 1.

H. pylori-mediated mechanisms of autophagy regulation

Modulatory agent	H. pylori strain/isolate	Experimental model	Mediators	Molecular mechanism	Outcome	Reference
H. pylori (104 CFU/ml) and recombinant CGT (10 μg/ml)	ATCC 700392	J774A.1 macrophage cells	↑BECN1, LC3-II, SQSTM1, EEA1, ATG12 ↓LAMP1	Cholesterol modulation	↑Autophagy, bacterial survival, lipid raft formation ↓Lysosome formation, autophagosome-lysosome fusion	[36]
H. pylori (104−6 CFU/ml) and CAG (20 μM)	ATCC 700392	AGS gastric cancer cells, C57BL/6 male mice	↑LC3-II	-	↑Autophagy, H. pylori intercellular survival ↓Lysosome formation, autophagosome degradation	[37]
H. pylori (200 and 400 MOI)	ATCC 700392, NCTC 11637	AGS gastric cancer cells	↑LC3-II, CALCOCO2/NDP52	Lysosomal damage, O-glycan and LGALS8 accumulation	↑Autophagy	[114]
H. pylori (100 MOI)	ATCC 700392	GES-1 gastric epithelial cells, clinical specimens, SPF grade Babl/c male mice	↑LC3-II, PAK1, ROCK1, ROCK2, LIMK1 ↓RAC1, RHOA, CFL (cofilin)	ILK suppression, F-actin depolymerization	↑Autophagy	[115]
H. pylori (100 MOI)	ATCC 43504	AGS gastric cancer cells	↑LC3-II	STAT3 phosphorylation on Ser727	↑Autophagy, mitochondrial damage	[116]
H. pylori (100 MOI)	ATCC 43504, SS1	AGS gastric cancer cells, female C57BL/6J mice	↑LC3-II, NFE2L2/Nrf2, HMOX1/HO-1	ROS production	↑Autophagy ↓Apoptosis	[38]
H. pylori (6×106 CFU/ml) or H. pylori lysate (1.5−2 μg/ml)	ATCC 43504	MKN-45 gastric cancer cells, GES-1 gastric epithelial cells, Mongolian gerbils	↑SQSTM1 ↓LC3-II, CASP3 (caspase 3), SLPI	Targeting NOD1-RIPK2-MAPK/ERK-FOXO4 pathway, CCL20, CCL28, and CXCL2 decreased in GES-1 cells but increased in MKN-45 cells	↑Proliferation ↓Autophagy, apoptosis, GES-1 cell migration	[40]
H. pylori (100 MOI)	ATCC 700392	AGS and HGC-27 gastric cancer cells, chronic gastritis clinical specimens	↑SQSTM1 ↓LC3-II	MIR30B upregulation, ATG12 and BECN1 suppression	↑H. pylori intercellular survival ↓Autophagy	[41]
H. pylori	ATCC 700392	AGS gastric cancer cells, GES-1 gastric epithelial cells	↓LC3-II, ATG2B, ATG5, ATG12, BECN1, BNIP3L	MIR30D upregulation	↑H. pylori intercellular survival ↓Autophagy	[42]
H. pylori (100 MOI)	ATCC 700392	BGC-823 gastric cancer cells	↑LC3-II	MIR99B upregulation, MTOR suppression	↑Autophagy ↓Proliferation, H. pylori intercellular survival	[43]
H. pylori	-	Gastric dysplasia and cancer clinical specimens	↑LC3A, LC3B, ATG5	MIF upregulation	↑Autophagy, risk of cancer development	[44]
H. pylori (100 MOI), VacA (35−250 nM)	ATCC 49503, ATCC 700392	HEK293T, AGS, NCI-N87 and AZ-521 cell lines, C57BL/6J mice	↑LC3-II ↓p-RPS6KB/S6K	MTORC1 suppression, ULK1 activation	↑Autophagy,mitochondrialdamage ↓Cell energy and nutrients	[8]
H. pylori (100 MOI), H. pylori supernatant (1:25)	ATCC 43629	SGC-7901 gastric cancer cells	↑LC3-II, BECN1, ATG7, PIK3C3 ↓SQSTM1	ROS production	↑Autophagy	[45]
VacA (10 μM)	-	MCF10A human breast epithelial cells	↑LC3-II	V-ATPase-dependency of LC3 lipidation	↑Autophagy	[47]
H. pylori (50 MOI)	ATCC 49503, J166, SS1	AGS gastric cancer cells, gastric organoid, C57/Bl6 mice	↑LC3-II ↓CTSD	MCOLN1 inhibition, lysosomal calcium dysregulation	↑H. pylori intercellular survival ↓Endolysosomal trafficking	[48]
H. pylori	ATCC 49503	AGS gastric cancer cells, murine primary gastric cells	↑SQSTM1, LC3-II ↓CTSD	ROS production	↑Autophagy ↓Endolysosomal trafficking, H. pylori intercellular survival	[49]
H. pylori (100 MOI), purified VacA (100 ng/ml)	cagA-/vacA s1m1 and cagA-/vacA s1m2 H. pylori clinical isolates	AGS and AZ-521 gastric cancer cells, C57BL/6 mice	↑LC3-II, EIF2S1	ER stress, EIF2S1 phosphorylation, DDIT3 and TRIB3 upregulation	↑Autophagy, autophagic cell death	[117]
Purified VacA (100 nM)	ATCC 49503	AGS and AZ-521 gastric cancer cells	↑LC3-II, CASP7	LRP1 stimulation, PARP activation	↑Autophagy, apoptosis	[118]
Wild-type or heatinactivated VacA (120 nM)	ATCC 49503	AZ-521 gastric cancer cells, clinical specimens	↑LC3-II, CASP9 ↓GSH	GJA1/Cx43 accumulation in autophagic vesicles, RAC1-GTP formation, MAPK/ERK activation	↑Autophagy, apoptosis	[50]
H. pylori (50 MOI)	ATCC 700392 (s1m1VacA)	AGS gastric cancer cells	↑LC3-II ↓GSH, SQSTM1	LRP1 stimulation, ROS production, MDM2 activation, AKT activation	↑Autophagy, CagA degradation	[54]
Purified VacA (35 nM)	ATCC 49503	AGS gastric cancer cells	↑SQSTM1 ↓LC3-II	Suppression of CagA proteasome degradation	↑CagA accumulation ↓Autophagy	[55]
H. pylori	ATCC 43504	GES-1 gastric epithelial cells, C57BL/6 mice, Mongolian gerbils	↑SQSTMl, γH2AX, TP53 ↓RAD51	S-phase arrest, CagA-dependent DNA damage	↑DNA damage, DNA damage response ↓Autophagy	[56]
H. pylori (100 MOI)	B128, 7.13	AGS and SNU-1 gastric cancer cells, clinical specimens	↑TRIP12 ↓LC3-II, BECN1, ARF	CDKN2A/p14ARF ubiquitination and degradation	↑ CagA-dependent TRIP12 induction ↓Autophagy	[57]
H. pylori (50 MOI/109 CFU/ml)	ATCC 700392	AGS gastric cancer cells, Mongolian gerbils, gastric adenocarcinoma clinical specimens	↑CAPZA1 ↓LAMPl	LRP1 stimulation, LRP1-ICD nuclear translocation, CAPZA1 linkage to LRP1-ICD	↑CagA accumulation ↓Autolysosomeformation	[119]
H. pylori (10, 50, 100, 200 MOI)	ATCC 43504, cagA-/vacAs1m2 and cagA+/vacAs1m2 clinical isolates	AGS gastric cancer cells, dyspeptic clinical specimens	↑SQSTM1 ↓LC3-II, LAMP1	MET/c-Met-AKT activation	CagA suppression of autophagosome formation and starvation-induced autophagy	[82]
H. pylori (100 MOI/108 CFU)	ATCC 700392, ATCC 49503, ATCC 51932	SNU1, AGS, MGC-803, and MKN1 gastric cancer cells, C57BL/6 mice, gastric cancer clinical specimens	↑SQSTMl, CDH2/N-cadherin, SNAI/Snail ↓LC3-II	CagA-dependent MIR543 upregulation, SIRT1 suppression	↑EMT, cellproliferation, metastasis,invasion ↓Autophagy	[58]
H. pylori (100 MOI)	ATCC 700392, ATCC 43504	AGS, BGC-823, SGC-7901 and GES-1 cell lines, superficial gastritis, atrophic gastritis and dysplasia clinical specimens	↑SQSTMl, LC3-II ↓RUNX3	SIRT1 suppression	↑Autophagosome formation ↓Autophagy	[120]
H. pylori (100 MOI)	ATCC 43504	AGS, GES‐1, and HGC‐27 cell lines, C57BL/6 mice, clinical specimens	↑p-MTOR, p-AKT, p-RPS6KB/S6K, DEPTOR	CagA-dependent MTORC1 activation	↑lnflammation ↓Bacterial colonization burden	[59]
H. pylori (50, 100 MOI), HP0175 (1 μg/ml)	ATCC 700392	AGS gastric cancer cells	↑LC3-II, ULK1, ATG5, BECN1, EIF2AK3/PERK, ATF4, DDIT3/CHOP ↓CASP3	UPR activation	↑Autophagy ↓Apoptosis	[60]
H. pylori (100 MOI), H. pylori supernatant (1:25)	ATCC 700392	AGS gastric cancer cells, GES-1 gastric epithelial cells	↓CTSD	Lysosomal damage	↑H. pylori intercellular survival ↓Autophagy	[61]
Purified OMV (50 mg/ml)	251	HeLa and AGS cell lines, primary epithelial cells	↑LC3-II, ATG5	NOD1 stimulation, RIPK2 activation	↑Autophagy	[64]
H. pylori (10 MOI)	B128, 7.13	AGS and HEK 293 cell lines, Mongolian gerbils	↑LC3-II	pgdA-mediated peptidoglycan deacetylation	↑Autophagy	[65]

VacA

To provide the nutrients required for H. pylori colonization and render intracellular niches for H. pylori replication, VacA inhibits MTORC1 and induces autophagy through mitochondria perturbation and subsequent depletion of cellular amino acids [8]. The exposure of the SGC7901 human gastric cancer cell line to VacA leads to increased production levels of ROS, BECN1, ATG7, and PIK3C3/VPS34 (phosphatidylinositol 3-kinase catalytic subunit type 3) [45]. VacA is sufficient for autophagy formation and its channel-forming activity significantly influences autophagy initiation [46]. Disruption of cellular osmotic properties and stimulation of V-ATPase activity describes the potential mechanism through which VacA induces endolysosomal LC3 lipidation and noncanonical autophagy in MCF10A human breast epithelial cells [47], which should also be investigated in gastric epithelial cells. VacA further prevents endolysosomal trafficking by targeting the lysosomal calcium channel MCOLN1/TRPML1 and disrupting CTSD (cathepsin D) delivery to lysosomes in the gastric epithelium of mouse models [48]. Sustained exposure of AGS and mouse gastric cells to VacA triggers the formation of autophagosomes deficient in CTSD and consequently results in the accumulation of ROS and the SQSTM1 autophagy receptor [49]. VacA is normally degraded in the acidified lysosome; importantly, accumulation of VacA can lead to apoptosis presented in different gastric epithelial cell lines [50].

CagA

CagA injection into the epithelial cells by the T4SS leads to genomic instability, tumor-promoting inflammation, and sustained proliferation of tumor cells [51]. Furthermore, T4SS-dependent translocation of H. pylori DNA into epithelial cells activates STING1 (stimulator of interferon response cGAMP interactor 1). Recruitment of autophagy-inducing effectors following the detection of cytosolic DNA fragments is an innate immune response by STING1 complexes. However, it has been recently demonstrated that H. pylori suppresses STING1 signaling while the H. pylori-induced autophagic response remains intact [52].

As an innate immune mechanism, autophagy can degrade the CagA protein preventing its pro-inflammatory and pre-cancerous activity. The autophagy mediator LRP1 prevents CagA accumulation in patients with non-invasive differentiated-type gastric cancer; consequently, LRP1 mutation significantly contributes to the progression of gastric cancer through CagA-mediated signaling pathways [53]. Notably, the VacA m1 allelic type can activate autophagy in gastric epithelial cells, resulting in consequent CagA degradation [54]. However, upon sustained exposure, as noted above, VacA perturbs endolysosomal trafficking, which leads to the formation of autophagosomes deficient in CTSD. Thus, in addition to promoting the intracellular replication of H. pylori, VacA facilitates CagA accumulation during chronic infection with H. pylori [55].

CagA can contribute to carcinogenesis in several other ways: (1) Gradual suppression of autophagy by CagA in the chronic stage of H. pylori infection leads to the accumulation of SQSTM1, which reduces RAD51 expression. This can cause the aggravation of the DNA damage response owing to the induction of double-strand breaks and dysfunctional DNA repair, which can ultimately induce intestinal metaplasia and gastric cancer [56]. (2) CagA promotes the production of the TRIP12 protein that induces the ubiquitination and degradation of the tumor suppressor CDKN2A/p14ARF. The deficiency of CDKN2A can compromise the oncogenic stress response and further inhibit autophagy in a TP53-independent manner [57]. (3) CagA promotes MIR543 expression to target SIRT1 (sirtuin 1) and thereafter inhibit autophagy flux [58]. (4) In a CagA-dependent manner, H. pylori promotes MTORC1 activation, which inhibits autophagy and upregulates the expression of pro-inflammatory cytokines IL1B, IL6, TNF, CCL7, and CXCL16, as well as antimicrobial peptide CAMP/LL37 to reduce the gastric bacterial burden [59].

Secretory proteins

H. pylori Hp0175 (peptidyl-prolyl cis-trans isomerase) contributes to H. pylori stimulation of autophagy through upregulating the production of ULK1 (unc-51 like autophagy activating kinase 1), ATG5, BECN1, and MAP1LC3B independent of VacA vacuolating activity. The exposure of AGS cells to Hp0175 results in high expression levels of ATF4 (activating transcription factor 4) and DDIT3/CHOP (DNA damage inducible transcript 3); as transcription factors, ATF4 regulates MAP1LC3B, DDIT3, ULK1, and ATG5, whereas DDIT3 regulates ATG5 expression. In gastric epithelial cells, Hp0175 can also induce the conversion of LC3-I to LC3-II through the unfolded protein response/UPR activation of EIF2AK3/PERK [60].

H. pylori HpGGT (γ-glutamyl transpeptidase) is involved in the pathogenesis of almost all H. pylori strains and is required for H. pylori internalization into AGS and GES-1 gastric epithelial cells. In AGS cells but not in GES-1 cells, HpGGT inhibits the late stages of autophagy influx by reducing the activity of CTSB (cathepsin B) in the lysosome and inducing lysosomal permeabilization; however, lysosome acidification remains intact [61]. Therefore, HpGGT inhibition of autophagy and induction of oxidative stress and genome instability renders a favorable environment for the development of gastric adenocarcinoma.

Outer membrane vesicles

The bilayered lipid membrane nanostructures of outer membrane vesicles contain a wide spectrum of the bacterial biological contents including PG, LPS, outer membrane proteins, periplasmic proteins, enzymes, DNA, and toxins [62]. The introduction of H. pylori PG fragments to gastric epithelial cells through OMV or the T4SS can induce a pro-inflammatory response through NOD1 receptor stimulation and NFKB signaling activation [63]. Using LC3 or ATG5 siRNA-transfected AGS cells, an in vitro study elucidated the significant involvement of autophagic components in the H. pylori OMV-induced inflammatory response through NOD1. NOD1 migration following the detection of PG-containing OMV is independent of NFKB activation, yet intracellular migration of NOD1 is regulated by RIPK2. Thus, OMV-delivered PG can signal through the NOD1-RIPK2 axis to induce autophagosome formation and stimulate a pro-inflammatory response [64]. Mutation in the H. pylori PG deacetylase PgdA reduces H. pylori intracellular survival, attenuates the autophagy response through the PG-NOD1 axis, and increases lysosome formation independent of autophagy pathways [65].

Taken together, many molecular mechanisms in the interaction of H. pylori and its virulence factors with autophagy core proteins remain to be elucidated. For instance, several aspects of the interplay between the MTOR signaling network, VacA, and host cells’ energy metabolism require further in-depth investigation. Furthermore, the fate of CagA translocation by OMV into the host cell during acute H. pylori infection remains to be addressed. However, the main issue is the discrimination of acute and chronic stages of H. pylori infection. Despite the resolution of key autophagy signaling pathways during H. pylori infection, the precise role of autophagy in gastric cancer differentiation and metastasis is contentious. The conceptual fog around the functional influence of autophagy on H. pylori carcinogenesis is retained by a lack of adequate mechanism-oriented clinical studies.

Autophagy and Gastric Carcinogenesis

From the acute to chronic stages of infection, H. pylori can contribute in different ways to promote the risk of cancer progression (Figure 4). Acute infection with H. pylori is mainly accompanied by autophagy stimulation and the co-expression of the gastric cancer stem cell marker CD44, which is associated with the mesenchymal phenotype and metastatic properties of epithelial-mesenchymal transition (EMT) [66]. However, autophagy inhibition in the chronic stages of H. pylori infection may establish the major signaling network contributing to gastric carcinogenesis. For example, the accumulation of SQSTM1 in gastric epithelial cells following autophagy disruption can alter NFKB regulation [49], and, as noted in the section on CagA above, reduce RAD51 expression, induce double-strand breaks, and prevent DNA repair [56]. H. pylori can further induce genomic instability by oxidative stress and ROS aggregation as a consequence of autophagy impairment [67]. Aggravation of the DNA damage response and genomic instability can stimulate EMT unequivocally. Conversely, H. pylori suppression of MIR1298–5p and autophagy promotes gastric cancer cell proliferation and motility through targeting the MAP2K6-MAPK/p38 axis in human and mouse gastric tissues [68]. Methylation silencing of MAP1LC3A variant 1/MAP1LC3Av1 by H. pylori impairs the autophagy response and induces the survival, migration, and invasion of the normal gastric epithelium in rats [69]. More precisely, CagA-induced expression of MIR543 in human gastric cancer tissue was shown by in vitro experiments to suppress SIRT1 and autophagy, leading to EMT, cell migration, and invasion [58]. Moreover, ATG16L1^T300A polymorphism is considered a risk factor for the development of gastric cancer [70]. Regulation of H. pylori-induced ER stress and pro-inflammatory responses may explain the underlying mechanisms associating the genetic polymorphism with the development of premalignant lesions of gastric cancer [71]. Notwithstanding the suppressing role of autophagy in gastric carcinogenesis, autophagy is required for tumor angiogenesis in human gastric cancer SGC7901 cells [72].

Figure 4.

H. pylori-Induced Gastric Cancer Through Autophagy Modulation. (A) EMT progression from chronic gastritis to dysplasia and carcinoma. (B) Acute H. pylori infection induces autophagy that can promote angiogenesis and the expression of the CD44 tumor marker. (C) Chronic H. pylori infection mainly suppresses autophagy, resulting in DNA damage, inflammation, and EMT progression.

As noted above, a major complexity concerns the context-dependent dual role of autophagy in gastric carcinogenesis—autophagy can inhibit and promote tumor formation depending on the stage of development and specific conditions. Autophagy is essential for angiogenesis and tumor cells’ energy metabolism, for which autophagy inhibitors (e.g., chloroquine) are being developed as anti-tumor therapeutics [73]. Yet, H. pylori suppresses autophagy in the last stages of infection, which promotes gastric carcinogenesis. The mechanistic role of H. pylori-induced autophagy in EMT and the development of cancer stem cell features should be considered for anti-cancer therapeutics.

Autophagy as the Mediator of H. pylori-Gut Microbiota Interaction

The clinical implications of H. pylori infection include the alteration of gastric, intestinal, and fecal microbial composition. Modification of mucosal immunity, alteration of host cell signaling, disruption of the gastric epithelial cell architecture, and modulation of gastric acidity are considered the predominant mechanisms shifting the structure of the gut microbiota [74]. Below, we discuss the potential role of autophagy signaling in coordinating H. pylori-gut microbiota interaction.

Gut metabolic homeostasis

The gut microbiota modulates host physiology and pathophysiology through the production of a diverse array of metabolites and byproducts. The absorption of these metabolites contributes to host metabolic reactions as signaling molecules [75]. Short-chain fatty acids (SCFAs), key bacterial metabolites, not only contribute to the promotion of local immune responses but also to the modification of intracellular signaling pathways. In colon cancer cells, propionate and butyrate stimulate autophagy to modulate apoptosis through the suppression of MTOR signaling [76]. Butyrate is further suggested to trigger autophagy by inducing ER stress in HCT-116 and HT-29 colorectal cancer cells [77]. Through the induction of MTOR-dependent autophagy and ROS-mediated apoptosis, butyrate prevents bladder cancer cell metastasis [78].

Controversially, the utilization of butyrate as the primary energy source in colonocytes prevents the development of starvation conditions and dampens the autophagy flux [79]. Notwithstanding the mechanisms underlying the potential effect of SCFAs on the autophagy response of gastric epithelial cells, alteration in the composition of gastric microbiota, particularly SCFA-producing bacteria, may affect cellular autophagy flux and H. pylori-induced pathogenesis and carcinogenesis. Shifts in the concentration of other microbial metabolites and byproducts that regulate energy metabolism such as branched-chain amino acids might influence the host cell autophagy and consequently H. pylori carcinogenesis [34]. Microbiome-based therapeutics, from dietary changes to the administration of defined microbial consortia, are developing exciting opportunities to more precisely modify the gut microbial and metabolic profile. Recent and ongoing advances in the knowledge about host-microbiota interactions are unveiling novel frontiers of research for modulating the host immune response and fighting against pathophysiological conditions [80].

Host inflammatory response

H. pylori infection can induce local inflammation, which may develop into systemic inflammation and establish low-grade and chronic inflammation. An inflammatory environment within the gut is conducive to compositional and functional alterations of the microbial community often by blooms of opportunistic pathogens and depletion of commensal bacteria [81]. In vivo ATG5 knockdown and in vitro LC3 or ATG5 siRNA-transfection confirm that H. pylori-induced activation of NFKB through the NOD1 receptor and subsequent production of inflammatory cytokines, particularly CXCL2 and IL8, depends on autophagic pathways [64]. CagA-dependent activation of MTORC1 and inhibition of autophagy increase the expression and secretion of pro-inflammatory cytokines IL1B, IL6, TNF, CCL7, and CXCL16. Furthermore, the overexpression of antimicrobial peptide CAMP/LL37 reduces the colonization burden of gastric niches [59]. Transfection of AGS cells with siRNAs for ATG5 or ATG12 stimulates pro-inflammatory cytokine production through NFKB activation in a CagA-dependent manner [82]. A cytokine storm can further disrupt the integrity of epithelial tight junctions, perturb epithelial barriers, and aggravate gut dysbiosis during inflammation [83]. Thus, as a key mediator, autophagy contributes to H. pylori-induced cytokine production, inflammation, and subsequent gastric dysbiosis.

H. pylori inhibition of autophagy impairs the trafficking of major histocompatibility complex class-II (MHC-II) components from the cytoplasm to the plasma membrane and prevents the surface expression of CD80 and CD86 in murine bone marrow-derived dendritic cells/BMDCs [32]. The intact activity of dendritic cells is required by the immune system to establish tolerance against commensal microbiota and to develop an adaptive immune response against pathogenic microorganisms [84]. Dysregulation in the cross-presentation of exogenous antigens to CD4⁺ T cells and disruption of indigenous immune tolerance might be considered other mechanisms through which H. pylori modifies the composition of gastric microbiota utilizing autophagy flux.

A defective autophagy response following ER stress in intestinal epithelial cells is characterized by an elevated abundance of IgA-producing plasma cells [85]. IgA mainly blocks the translocation of bacteria from the lamina propria to the bloodstream, prevents conjugative plasmid transfer, restricts pathogen overgrowth, and accelerates the survival of commensal microorganisms. IgA binding to gut-colonizing bacteria can vastly modify the composition of the gut microbiota [86]. Thus H. pylori modification of autophagy may influence the host microbiota structure via adjusting the concentration of IgA antibody in the gastric environment. To our knowledge the intermediate role of autophagy in H. pylori-gut microbiota crosstalk has not been previously discussed; this paves the way for novel study design considerations. In this regard, we propose multi-omics approaches to further explore the dynamics and interactions of the gut microbiota with autophagy core proteins and regulatory factors during H. pylori infection. Subsequently, we suggest utilizing artificial intelligence-based technologies and techniques to describe the infrastructure of the intriguing triangle between H. pylori, autophagy, and gut microbiota.

Knowledge Gaps and Golden Opportunities

Over the past decades, progress in biotechnology, development of myriad therapeutics, and improvement in clinical infrastructure have provided us with heightened efficacy in preventing and treating gastric malignancies. However, due to the high risk of developing metastatic gastric adenocarcinoma from localized gastric cancer, therapeutic choices in the clinic are still quite limited. The complex systemic nature of gastric carcinogenesis hinders the understanding of some basic notions regarding the progression of H. pylori-induced gastric cancer [87].

One major bottleneck in the study of gastric carcinogenesis is the lack of a competent biological model to thoroughly mimic the carcinogenic cascades. The emergence of cancer organoids has provided a comprehensive tool for studying cancer development, progression, and the TME. Moreover, the potential of organ-on-a-chip technology holds great promise in facilitating cancer organoid sustained co-culture with the gut microbiota to better anticipate human clinical responses [88]. The extended co-culture of cancer tissues with living microbiota not only can predict the human drug pharmacokinetics but also measure the potential capacity of microbiome-based therapeutics in modulating gastric malignancies. However, this technology is in its infancy and primarily requires the standardization of different platforms for reproducibility and robustness in distinct conditions [89].

Recent studies not only focus on modifying the gut microbiota structure but also seek to modulate the tumor microbiota to barricade tumor growth and metastasis while improving tumor cell sensitivity to cancer therapy and immunotherapy [90]. In patients with cancer, gut microbiota signatures can predict the toxicity and efficacy of immunotherapy, such as the immune checkpoint blockade-promoting effect of microbiome-derived inosine [91]. A recent study demonstrated the translocation of particular gut bacteria into secondary lymphoid organs and subcutaneous melanoma tumors upon immune checkpoint blockade therapy [92]. This, in principle, presents a fundamental mechanism through which gut microbiota can modify the TME. However, to establish a predictive signature, sophisticated metagenomics approaches should be developed and integrated with microbiome multi-omics data.

Concluding Remarks and Future Perspectives

There is an urgent need for the investigation of more specific mechanisms underlying gastric carcinogenesis. H. pylori modulation of autophagy signaling may directly contribute to gastric dysbiosis, inflammation, tumorigenesis, and metastasis. While the biphasic activity of autophagy determines the turnover of cytoplasmic organelles, apoptosis profoundly influences the entire cell. The complex ambiguous interconnection between autophagy and apoptosis is one factor that determines the fate of gastric tumor cells [93]. Further studies are required to explain the discrepancies in the protective and suppressive role of autophagy in H. pylori-induced gastric cancer progression, probably based on its dichotomous function in different stages of cancer development (see Outstanding questions). Broad clinical trials should focus on how to preserve the delicate equilibrium between the dual roles of autophagy. Moreover, mechanism-oriented in vitro and in vivo studies should clarify the shifts in autophagy signaling as H. pylori diminishes toward advanced stages of gastric cancer.

Outstanding Questions Box.

Given the changes in the gut microbiota composition during gastric cancer development, could these structural or functional alterations drive suppression rather than promotion of autophagy flux?

What are the impacts of autophagy-mediated regulation of host cell nutrient and energy status on the gut microbial profile during H. pylori infection?

Can H. pylori infection of gastric epithelial cells interfere with secretory autophagy? Will the aberrant secretory autophagy compromise the innate gastric antimicrobial defense against H. pylori?

What are the effects of OMV-mediated translocation of CagA on the host cell autophagy signaling during H. pylori infection?

How does the complex interconnection between autophagy and apoptosis affect the turnover of H. pylori-infected cells and the development of cancer stem cells?

What other polymorphisms in autophagy-related genes contribute to H. pylori pathogenesis and carcinogenesis? Do germline genetic variants influencing autophagy flux also modulate H. pylori-induced carcinogenic pathways?

Can we develop a microbiome-based therapeutic strategy to manipulate autophagy and trigger autophagic cell death in gastric cancer cells by modifying the composition of tumor microbiota?

Figure I.

Autophagy and Gut Immune Homeostasis. The gut microbiota, particularly probiotic strains, can induce autophagy, whereas pathogenic bacteria mainly suppress autophagy flux. Autophagy activation preserves the integrity of the epithelial barrier by stimulating the production of tight junctions while suppressing gap junctions. Autophagy-mediated secretion of CAMP and inhibition of ROS production and NLRP3 inflammasome activation reduce the risk of inflammation. Conversely, phosphoinositide 3-kinase/PI3K and the MTOR-HIF1A/HIF-1α (hypoxia inducible factor 1 subunit alpha) axis engage with ROS production by neutrophils. ATG7 contributes to the degranulation of mast cells. The MTOR complex is involved in eosinophil differentiation and infiltration. MTOR also activates bioenergetic metabolism via IL15 signaling in NK cells, whereas ATG3 is required for memory NK cell formation. The activation of AMPK, ULK1, ATG5, and ATG7 directs monocytes away from apoptosis and toward differentiation. ATG3, ATG16L1, and MAP1LC3-II regulate DC maturation, whereas ATG5, ATG7, ATG16L1, and BECN1 coordinate antigen presentation and cross-presentation. Furthermore, LPS-mediated stimulation of TLR4 in macrophages can trigger different autophagy signaling pathways.

Highlights.

Autophagy orchestrates cell homeostasis and cellular stress signaling, and implements a dichotomous function in different stages of cancer development.

The stress signals in the tumor microenvironment differentially regulate the autophagy pathway, subsequently modulating tumor immunity, progression, and metastasis.

Autophagy manipulation represents a prominent strategy for intracellular Helicobacter pylori replication and timely release of oncoproteins.

Autophagy signaling network widely contributes to gut homeostasis persistence, gut ecology architecture, and anti-microbial protection.

H. pylori-induced dysbiosis of gut microbiota and metabolic profiles can provide an infrastructure for gastric cancer development and progression.

Although not confirmed, evidence suggests the potential for H. pylori to modify the gut microbiota through autophagy modulation.

Abbreviations:

AMPK

AMP-activated protein kinase

EMT

epithelial-mesenchymal transition

LPS

lipopolysaccharide

MTORC1

mechanistic target of rapamycin kinase complex 1

NK

natural killer

PG

peptidoglycan

PtdIns3K-CI

class III phosphatidylinositol 3-kinase complex I

PtdIns3P

phosphatidylinositol-3-phosphate

ROS

reactive oxygen species

SCFAs

short-chain fatty acids

T4SS

type IV secretion system

TME

tumor microenvironment

Glossary

Apoptosis

a type of regulated cell death that involves the action of caspases

Autophagic cell death

autophagy-mediated induction of apoptosis or the activation of a distinct autophagy-dependent mechanism that leads to cell death

Autophagy

processes involved in the lysosomal degradation and recycling of cytoplasmic components

Autophagy-related genes

these genes encode the components of the macroautophagy machinery. The acronym “ATG” indicates an autophagy-related gene, but some components such as BECN1 are also considered to be part of this group

BECN1 (beclin 1)

a component of the class III PtdIns3K that generates phosphatidylinositol-3-phosphate; this lipid is required for autophagy

cag pathogenicity island/cagPAI

a 40-kb genomic DNA segment that encodes the T4SS; these genes are the most well-recognized virulence determinants for H. pylori

Cytokine

a small protein secreted by different types of cells including immune and endothelial cells that interact with cell surface receptors to trigger various responses within the target cells

Dysbiosis

aberrant compositional and functional modification of the microbiota that disturbs the indigenous microbial ecosystem

Inflammasome

a cytoplasmic multiprotein complex that detects pathogenic microorganisms and danger signals in the host cells

Mitophagy

a type of selective autophagy that degrades dysfunctional or damaged mitochondria

MTOR (mechanistic target of rapamycin kinase)

MTOR regulates cell growth and is the primary negative regulator of macroautophagy

Phagophore

the initial sequestering compartment of macroautophagy; the phagophore surrounds cargo and matures into a double-membrane autophagosome

Pyroptosis

a lytic type of cell death triggered by inflammasome stimulation and consequent inflammatory caspase activation

Reactive oxygen species (ROS)

chemical byproducts derived from oxygen including peroxides, superoxide and hydroxy radical; these highly reactive species can damage cellular components

Tumor microenvironment (TME)

the dynamic surrounding microenvironment of tumor cells that is spatially and temporally modified in response to environmental factors and anti-tumor therapeutics

Type IV secretion system (T4SS)

a bacterial protein complex located in the plasma membrane that transports protein and DNA into the extracellular space

Xenophagy

a selective form of macroautophagy involving the elimination of intracellular microbes