4-(Benzyloxy)phenol-induced p53 exhibits antimycobacterial response triggering phagosome-lysosome fusion through ROS-dependent intracellular Ca2+ pathway in THP-1 cells.

Drug-resistant tuberculosis (TB) outbreak has emerged as a global public health crisis. Therefore, new and innovative therapeutic options like host-directed therapies (HDTs) through novel modulators are urgently required to overcome the challenges associated with TB. In the present study, we have investigated the anti-mycobacterial effect of 4-(Benzyloxy)phenol. Cell-viability assay asserted that 50 µM of 4-(Benzyloxy)phenol was not cytotoxic to phorbol 12-myristate 13-acetate (PMA) differentiated THP-1 (dTHP-1) cells. It was observed that 4-(Benzyloxy)phenol activates p53 expression by hindering its association with KDM1A. Increased ROS, intracellular Ca2+ and phagosome-lysosome fusion, were also observed upon 4-(Benzyloxy)phenol treatment. 4-(Benzyloxy)phenol mediated killing of intracellular mycobacteria was abrogated in the presence of specific inhibitors of ROS, Ca2+ and phagosome-lysosome fusion like NAC, BAPTA-AM, and W7, respectively. We further demonstrate that 4-(Benzyloxy)phenol mediated enhanced ROS production is mediated by acetylation of p53. Blocking of p53 acetylation by Pifithrin-α (PFT- α) enhanced intracellular mycobacterial growth by blocking the mycobactericidal effect of 4-(Benzyloxy)phenol. Altogether, the results showed that 4-(Benzyloxy)phenol executed its anti-mycobacterial effect by modulating p53-mediated ROS production to regulate phagosome-lysosome fusion through Ca2+ production.

Mycobacterium tuberculosis hijacks host macrophages-derived interleukin 16 to block phagolysosome maturation for enhancing intracellular growth.

The discovery of promising cytokines and clarification of their immunological mechanisms in controlling the intracellular fate of Mycobacterium tuberculosis (Mtb) are necessary to identify effective diagnostic biomarkers and therapeutic targets. To escape immune clearance, Mtb can manipulate and inhibit the normal host process of phagosome maturation. Phagosome maturation arrest by Mtb involves multiple effectors and much remains unknown about this important aspect of Mtb pathogenesis. In this study, we found that interleukin 16 (IL-16) is elevated in the serum samples of Tuberculosis (TB) patients and can serve as a specific target for treatment TB. There was a significant difference in IL-16 levels among active TB, latent TB infection (LTBI), and non-TB patients. This study first revealed that macrophages are the major source of IL-16 production in response to Mtb infection, and elucidated that IL-16 can promote Mtb intracellular survival by inhibiting phagosome maturation and suppressing the expression of Rev-erbα which can inhibit IL-10 secretion. The experiments using zebrafish larvae infected with M. marinum and mice challenged with H37Rv demonstrated that reducing IL-16 levels resulted in less severe pathology and improved survival, respectively. In conclusion, this study provided direct evidence that Mtb hijacks the host macrophages-derived interleukin 16 to enhance intracellular growth. It is suggesting the immunosuppressive role of IL-16 during Mtb infection, supporting IL-16 as a promising therapeutic target.

Pathogenicity and virulence of Francisella tularensis.

Tularaemia is a zoonotic disease caused by the Gram-negative bacterium, Francisella tularensis. Depending on its entry route into the organism, F. tularensis causes different diseases, ranging from life-threatening pneumonia to less severe ulceroglandular tularaemia. Various strains with different geographical distributions exhibit different levels of virulence. F. tularensis is an intracellular bacterium that replicates primarily in the cytosol of the phagocytes. The main virulence attribute of F. tularensis is the type 6 secretion system (T6SS) and its effectors that promote escape from the phagosome. In addition, F. tularensis has evolved a peculiar envelope that allows it to escape detection by the immune system. In this review, we cover tularaemia, different Francisella strains, and their pathogenicity. We particularly emphasize the intracellular life cycle, associated virulence factors, and metabolic adaptations. Finally, we present how F. tularensis largely escapes immune detection to be one of the most infectious and lethal bacterial pathogens.

Host-directed therapy for bacterial infections -Modulation of the phagolysosome pathway.

Bacterial infections still impose a significant burden on humanity, even though antimicrobial agents have long since been developed. In addition to individual severe infections, the f fatality rate of sepsis remains high, and the threat of antimicrobial-resistant bacteria grows with time, putting us at inferiority. Although tremendous resources have been devoted to the development of antimicrobial agents, we have yet to recover from the lost ground we have been driven into. Looking back at the evolution of treatment for cancer, which, like infectious diseases, has the similarity that host immunity eliminates the lesion, the development of drugs to eliminate the tumor itself has shifted from a single-minded focus on drug development to the establishment of a treatment strategy in which the de-suppression of host immunity is another pillar of treatment. In infectious diseases, on the other hand, the development of therapies that strengthen and support the immune system has only just begun. Among innate immunity, the first line of defense that bacteria encounter after invading the host, the molecular mechanisms of the phagolysosome pathway, which begins with phagocytosis to fusion with lysosome, have been elucidated in detail. Bacteria have a large number of strategies to escape and survive the pathway. Although the full picture is still unfathomable, the molecular mechanisms have been elucidated for some of them, providing sufficient clues for intervention. In this article, we review the host defense mechanisms and bacterial evasion mechanisms and discuss the possibility of host-directed therapy for bacterial infection by intervening in the phagolysosome pathway.

Subversion strategies of lysosomal killing by intracellular pathogens.

Many pathogenic organisms need to reach either an intracellular compartment or the cytoplasm of a target cell for their survival, replication or immune system evasion. Intracellular pathogens frequently penetrate into the cell through the endocytic and phagocytic pathways (clathrin-mediated endocytosis, phagocytosis and macropinocytosis) that culminates in fusion with lysosomes. However, several mechanisms are triggered by pathogenic microorganisms - protozoan, bacteria, virus and fungus - to avoid destruction by lysosome fusion, such as rupture of the phagosome and thereby release into the cytoplasm, avoidance of autophagy, delaying in both phagolysosome biogenesis and phagosomal maturation and survival/replication inside the phagolysosome. Here we reviewed the main data dealing with phagosome maturation and evasion from lysosomal killing by different bacteria, protozoa, fungi and virus.

Activation of inflammasomes and mechanisms for intracellular recognition of Listeria monocytogenes.

The high mortality rate associated with Listeria monocytogenes can be attributed to its ability to invade the body systemically and to activate inflammasomes. Both of these processes are facilitated by expressing a major virulence factor known as listeriolysin O, a 56 kDa pore-forming protein encoded by the hly gene. Listeriolysin O plays a crucial role in the pathogenesis of the bacterium by facilitating the escape of the pathogen from the phagosome into the cytosol. This process is essential for the successful establishment of infection. In addition, listeriolysin O is known as an immunomodulator that activates host signal transduction. In addition to listeriolysin O, Listeria expresses a variety of bacterial ligands, such as lipoteichoic acid, nucleotide, and flagellin, that are recognized by host intracellular pattern-recognition receptors including Nod-like receptors, AIM2-like receptors, and RIG-I-like receptors. This review introduces intracellular recognition of Listeria monocytogenes since recent studies have revealed that the activation of inflammasome exacerbates Gram-positive bacteria infection.

The nucleotide receptor STING translocates to the phagosomes to negatively regulate anti-fungal immunity.

STING (stimulator of interferon genes) exerts protective cellular responses to viral infection via induction of interferon production and autophagy. Here, we report the role of STING in modulating the immune responses toward fungal infection. Upon Candida albicans stimulation, STING transited alongside the endoplasmic reticulum (ER) to the phagosomes. In phagosomes, STING directly bound with Src via the N-terminal 18 amino acids of STING, and this binding prevented Src from recruiting and phosphorylating Syk. Consistently, Syk-associated signaling and production of pro-inflammatory cytokines and chemokines were increased in mouse BMDCs (bone-marrow-derived dendritic cells) lacking STING with fungal treatment. STING deficiency improved anti-fungal immunity in systemic C. albicans infection. Importantly, administration of the N-terminal 18-aa (amino acid) peptide of STING improved host outcomes in disseminated fungal infection. Overall, our study identifies a previously unrecognized function of STING in negatively regulating anti-fungal immune responses and offers a potential therapeutic strategy for controlling C. albicans infection.

The dynamics of Mycobacterium tuberculosis phagosome and the fate of infection.

Phagosomes are vesicles produced by phagocytosis of phagocytes, which are crucial in immunity against Mycobacterium tuberculosis (Mtb) infection. After the phagocyte ingests the pathogen, it activates the phagosomes to recruit a series of components and process proteins, to phagocytose, degrade and kill Mtb. Meanwhile, Mtb can resist acid and oxidative stress, block phagosome maturation, and manipulate host immune response. The interaction between Mtb and phagocytes leads to the outcome of infection. The dynamic of this process can affect the cell fate. This article mainly reviews the development and maturation of phagosomes, as well as the dynamics and modifications of Mtb effectors and phagosomes components, and new diagnostic and therapeutic markers involved in phagosomes.

Histoplasma capsulatum Relies on Tryptophan Biosynthesis To Proliferate within the Macrophage Phagosome.

Histoplasma capsulatum yeasts reside and proliferate within the macrophage phagosome during infection. This nutrient-depleted phagosomal environment imposes challenges to Histoplasma yeasts for nutrition acquisition. Histoplasma yeasts require all 20 amino acids, which can be formed by de novo biosynthesis and/or acquired directly from the phagosomal environment. We investigated how Histoplasma obtains aromatic amino acids (i.e., phenylalanine, tyrosine, and tryptophan) within the phagosome during infection of macrophages. Depletion of key enzymes of the phenylalanine or tyrosine biosynthetic pathway neither impaired Histoplasma's ability to proliferate within macrophages nor resulted in attenuated virulence in vivo. However, loss of tryptophan biosynthesis resulted in reduced growth within macrophages and severely attenuated virulence in vivo. Together, these results indicate that phenylalanine and tyrosine, but not tryptophan, are available to Histoplasma within the macrophage phagosome. The herbicide glyphosate, which targets 5-enolpyruvylshikimate-3-phosphate synthase of the aromatic amino acid biosynthetic pathway, inhibited Histoplasma yeast growth, and this growth inhibition was partially reversed by aromatic amino acid supplementation or overexpression of ARO1. These results suggest that the aromatic amino acid biosynthetic pathway is a candidate drug target to develop novel antifungal therapeutics.

Inside the phagosome: A bacterial perspective.

The neutrophil phagosome is one of the most hostile environments that bacteria must face and overcome if they are to succeed as pathogens. Targeting bacterial defense mechanisms should lead to new therapies that assist neutrophils to kill pathogens, but this has not yet come to fruition. One of the limiting factors in this effort has been our incomplete knowledge of the complex biochemistry that occurs within the rapidly changing environment of the phagosome. The same compartmentalization that protects host tissue also limits our ability to measure events within the phagosome. In this review, we highlight the limitations in our knowledge, and how the contribution of bacteria to the phagosomal environment is often ignored. There appears to be significant heterogeneity among phagosomes, and it is important to determine whether survivors have more efficient defenses or whether they are ingested into less threatening environments than other bacteria. As part of these efforts, we discuss how monitoring or recovering bacteria from phagosomes can provide insight into the conditions they have faced. We also encourage the use of unbiased screening approaches to identify bacterial genes that are essential for survival inside neutrophil phagosomes.

Zooming in on common immune evasion mechanisms of pathogens in phagolysosomes: potential broad-spectrum therapeutic targets against infectious diseases.

The intracellular viral, bacterial, or parasitic pathogens evade the host immune challenges to propagate and cause fatal diseases. The microbes overpower host immunity at various levels including during entry into host cells, phagosome formation, phagosome maturation, phagosome-lysosome fusion forming phagolysosomes, acidification of phagolysosomes, and at times after escape into the cytosol. Phagolysosome is the final organelle in the phagocyte with sophisticated mechanisms to degrade the pathogens. The immune evasion strategies by the pathogens include the arrest of host cell apoptosis, decrease in reactive oxygen species, the elevation of Th2 anti-inflammatory response, avoidance of autophagy and antigen cross-presentation pathways, and escape from phagolysosomal killing. Since the phagolysosome organelle in relation to infection/cure is seldom discussed in the literature, we summarize here the common host as well as pathogen targets manipulated or utilized by the pathogens established in phagosomes and phagolysosomes, to hijack the host immune system for their benefit. These common molecules or pathways can be broad-spectrum therapeutic targets for drug development for intervention against infectious diseases caused by different intracellular pathogens.

High content quantitative imaging of Mycobacterium tuberculosis responses to acidic microenvironments within human macrophages.

Intracellular pathogens such as Mycobacterium tuberculosis (Mtb) have evolved diverse strategies to counteract macrophage defence mechanisms including phagolysosomal biogenesis. Within macrophages, Mtb initially resides inside membrane-bound phagosomes that interact with lysosomes and become acidified. The ability of Mtb to control and subvert the fusion between phagosomes and lysosomes plays a key role in the pathogenesis of tuberculosis. Therefore, understanding how pathogens interact with the endolysosomal network and cope with intracellular acidification is important to better understand the disease. Here, we describe in detail the use of fluorescence microscopy-based approaches to investigate Mtb responses to acidic environments in cellulo. We report high-content imaging modalities to probe Mtb sensing of external pH or visualise in real-time Mtb intrabacterial pH within infected human macrophages. We discuss various methodologies with step-by-step analyses that enable robust image-based quantifications. Finally, we highlight the advantages and limitations of these different approaches and discuss potential alternatives that can be applied to further investigate Mtb-host cell interactions. These methods can be adapted to study host-pathogen interactions in different biological systems and experimental settings. Altogether, these approaches represent a valuable tool to further broaden our understanding of the cellular and molecular mechanisms underlying intracellular pathogen survival.

Persistence of Mycobacterium tuberculosis in response to infection burden and host-induced stressors.

Introduction: As infection with Mycobacterium tuberculosis progresses, the bacilli experience various degrees of host stressors in the macrophage phagosome such as low pH, nutrient deprivation, or exposure to toxic agents, which promotes cell-to-cell phenotypic variation. This includes a physiologically viable but non- or slowly replicating persister subpopulation, which is characterised by a loss of growth on solid media, while remaining metabolically active. Persisters additionally evade the host immune response and macrophage antimicrobial processes by adapting their metabolic pathways to maintain survival and persistence in the host. Methods: A flow cytometry-based dual-fluorescent replication reporter assay, termed fluorescence dilution, provided a culture-independent method to characterize the single-cell replication dynamics of M. tuberculosis persisters following macrophage infection. Fluorescence dilution in combination with reference counting beads and a metabolic esterase reactive probe, calcein violet AM, provided an effective approach to enumerate and characterize the phenotypic heterogeneity within M. tuberculosis following macrophage infection. Results: Persister formation appeared dependent on the initial infection burden and intracellular bacterial burden. However, inhibition of phagocytosis by cytochalasin D treatment resulted in a significantly higher median percentage of persisters compared to inhibition of phagosome acidification by bafilomycin A1 treatment. Discussion: Our results suggest that different host factors differentially impact the intracellular bacterial burden, adaptive mechanisms and entry into persistence in macrophages.

Real-time visualization of phagosomal pH manipulation by Cryptococcus neoformans in an immune signal-dependent way.

Understanding of how intracellular pathogens survive in their host cells is important to improve management of their diseases. This has been fruitful for intracellular bacteria, but it is an understudied area in fungal pathogens. Here we start elucidating and characterizing the strategies used by one of the commonest fungal pathogens, Cryptococcus neoformans, to survive intracellularly. The ability of the fungus to survive inside host cells is one of the main drivers of disease progression, yet it is unclear whether C. neoformans resides in a fully acidified, partially acidic, or neutral phagosome. Using a dye that only fluoresce under acidic conditions to stain C. neoformans, a hypha-defective Candida albicans mutant, and the nonpathogenic Saccharomyces cerevisiae, we characterized the fungal behaviors in infected macrophages by live microscopy. The main behavior in the C. albicans mutant strain and S. cerevisiae-phagosomes was rapid acidification after internalization, which remained for the duration of the imaging. In contrast, a significant number of C. neoformans-phagosomes exhibited alternative behaviors distinct from the normal phagosomal maturation: some phagosomes acidified with subsequent loss of acidification, and other phagosomes never acidified. Moreover, the frequency of these behaviors was affected by the immune status of the host cell. We applied the same technique to a flow cytometry analysis and found that a substantial percentage of C. neoformans-phagosomes showed impaired acidification, whereas almost 100% of the S. cerevisiae-phagosomes acidify. Lastly, using a membrane-damage reporter, we show phagosome permeabilization correlates with acidification alterations, but it is not the only strategy that C. neoformans uses to manipulate phagosomal acidification. The different behaviors described here provide an explanation to the confounding literature regarding cryptococcal-phagosome acidification and the methods can be applied to study other intracellular fungal pathogens.

Mycobacterium tuberculosis Utilizes Host Histamine Receptor H1 to Modulate Reactive Oxygen Species Production and Phagosome Maturation via the p38MAPK-NOX2 Axis.

Tuberculosis (TB), which is caused by the single pathogenic bacterium, Mycobacterium tuberculosis, is among the top 10 lethal diseases worldwide. This situation has been exacerbated by the increasing number of cases of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB). Histamine is an organic nitrogenous compound that mediates a plethora of cell processes via different receptors. The expression of histamine receptor H1 (HRH1), one of the four histamine receptors identified to date was previously reported to be augmented by M. tuberculosis infection, although the underlying mechanism is unclear. In the present study, we applied confocal microscopy, flow cytometry, and Western blotting to show that HRH1 expression was enhanced in macrophages following mycobacterial infection. Furthermore, by combining techniques of gene knockdown, immunoprecipitation, intracellular bacterial burden analysis, fluorescence labeling, and imaging, we found that M. tuberculosis targeted the host HRH1 to suppress NOX2-mediated cROS production and inhibit phagosome maturation and acidification via the GRK2-p38MAPK signaling pathway. Our findings clarified the underlying mechanism of the M. tuberculosis and host HRH1 interaction and may provide useful information for the development of novel antituberculosis treatments. IMPORTANCE Once engulfed in macrophage phagosomes, M. tuberculosis adopts various strategies to take advantage of the host environment for its intracellular survival. Histamine is an organic nitrogen-containing compound that mediates a plethora of cellular processes via different receptors, but the crosstalk mechanism between M. tuberculosis and HRH1 in macrophages is not clear. Our results revealed that M. tuberculosis infection enhanced HRH1 expression, which in turn restrained macrophage bactericidal activity by modulating the GRK2-p38MAPK signaling pathway, inhibiting NOX2-mediated cROS production and phagosome maturation. Clarification of the underlying mechanism by which M. tuberculosis utilizes host HRH1 to favor its intracellular survival may provide useful information for the development of novel antituberculosis treatments.

Mycobacterial response to an acidic environment: protective mechanisms.

Given the emergence and spread of multidrug-resistant and extensively drug-resistant strains of Mycobacterium tuberculosis (Mtb), the world faces the urgency of finding new drugs to combat tuberculosis. Understanding the biochemical/physiological processes enabling Mtb to survive the stressful environment within macrophages and acquire tolerance, resistance and persistence against the stresses are the key to developing new approaches to tackle this health problem. As Mtb gains entry into the respiratory tract and is engulfed by macrophages, lowering pH acts as a primary defence of phagosomes within macrophages and also in the centres of caseating granulomas. It becomes essential for the pathogen to maintain pH homeostasis for survival in these conditions. Acid resistance mechanisms are well known and extensively studied in other bacteria such as Escherichia coli, Lactobacillus spp., Brucella spp., Helicobacter pylori and Listeria monocytogenes. However, in the case of Mtb, acid tolerance and resistance mechanisms still need to be explored in detail. This review aims to describe the current understanding of underlying mechanisms involved in countering low pH faced by Mtb as the acid resistance/tolerance mechanisms contribute to the pathogenesis of the disease.

Francisella tularensis Exploits AMPK Activation to Harvest Host-Derived Nutrients Liberated from Host Lipolysis.

Francisella tularensis is a zoonotic, facultative intracellular bacterial pathogen that replicates in a variety of cell types during infection. Following entry into the cell and phagosome escape, the bacterium replicates rapidly in the cytoplasm. F. tularensis intracellular growth depends on the availability of metabolizable essential nutrients to support replication. However, the mechanism by which metabolizable nutrients become available to the bacterium in the intracellular environment is not fully understood. We found that F. tularensis-infected cells had significantly smaller and fewer lipid droplets than uninfected cells. Inhibition of triacylglycerol degradation significantly reduced bacterial growth, whereas inhibition of triacylglycerol formation did not reduce bacterial growth, suggesting that triacylglycerols sequestered within lipid droplets are important nutrient sources for F. tularensis. We found that F. tularensis-infected cells had increased activation of lipolysis and the upstream regulatory protein AMP protein kinase (AMPK). These data suggest that F. tularensis exploits AMPK activation and lipid metabolism to use host-derived nutrients. Finally, we found that AMPK activation is correlated with an increased bacterial burden, which suggests that it is a host-mediated response to nutrient starvation that results from increased bacterial replication. Altogether, we conclude that F. tularensis exploits AMPK activation to access nutrients sequestered in lipid droplets, specifically glycerol and fatty acids, to undergo efficient bacterial replication and cause successful infection.

Virulence-Associated Secretion in Mycobacterium abscessus.

Non-tuberculous mycobacteria (NTM) are a heterogeneous group of originally environmental organi3sms, increasingly recognized as pathogens with rising prevalence worldwide. Knowledge of NTM's mechanisms of virulence is lacking, as molecular research of these bacteria is challenging, sometimes more than that of M. tuberculosis (Mtb), and far less resources are allocated to their investigation. While some of the virulence mechanisms are common to several mycobacteria including Mtb, others NTM species-specific. Among NTMs, Mycobacterium abscessus (Mabs) causes some of the most severe and difficult to treat infections, especially chronic pulmonary infections. Mabs survives and proliferates intracellularly by circumventing host defenses, using multiple mechanisms, many of which remain poorly characterized. Some of these immune-evasion mechanisms are also found in Mtb, including phagosome pore formation, inhibition of phagosome maturation, cytokine response interference and apoptosis delay. While much is known of the role of Mtb-secreted effector molecules in mediating the manipulation of the host response, far less is known of the secreted effector molecules in Mabs. In this review, we briefly summarize the knowledge of secreted effectors in Mtb (such as ESX secretion, SecA2, TAT and others), and draw the parallel pathways in Mabs. We also describe pathways that are unique to Mabs, differentiating it from Mtb. This review will assist researchers interested in virulence-associated secretion in Mabs by providing the knowledge base and framework for their studies.

Bet-hedging antimicrobial strategies in macrophage phagosome acidification drive the dynamics of Cryptococcus neoformans intracellular escape mechanisms.

The fungus Cryptococcus neoformans is a major human pathogen with a remarkable intracellular survival strategy that includes exiting macrophages through non-lytic exocytosis (Vomocytosis) and transferring between macrophages (Dragotcytosis) by a mechanism that involves sequential events of non-lytic exocytosis and phagocytosis. Vomocytosis and Dragotcytosis are fungal driven processes, but their triggers are not understood. We hypothesized that the dynamics of Dragotcytosis could inherit the stochasticity of phagolysosome acidification and that Dragotcytosis was triggered by fungal cell stress. Consistent with this view, fungal cells involved in Dragotcytosis reside in phagolysosomes characterized by low pH and/or high oxidative stress. Using fluorescent microscopy, qPCR, live cell video microscopy, and fungal growth assays we found that the that mitigating pH or oxidative stress reduced Dragotcytosis frequency, whereas ROS susceptible mutants of C. neoformans underwent Dragotcytosis more frequently. Dragotcytosis initiation was linked to phagolysosomal pH, oxidative stresses, and macrophage polarization state. Dragotcytosis manifested stochastic dynamics thus paralleling the dynamics of phagosomal acidification, which correlated with the inhospitality of phagolysosomes in differently polarized macrophages. Hence, randomness in phagosomal acidification randomly created a population of inhospitable phagosomes where fungal cell stress triggered stochastic C. neoformans non-lytic exocytosis dynamics to escape a non-permissive intracellular macrophage environment.

Label-free quantitative proteomics reveals the Steap3-Gm2a axis inhibiting the phagosomal escape of Listeria monocytogenes.

As a pathogenic microorganism, Listeria monocytogenes is widely used in the research of bacterial pathogenesis and host defense. The phagosomal escape of L. monocytogenes is essential for its replication in the cytoplasm of the host. Here, we reported that the protein abundance of the Six-transmembrane epithelial antigen of the prostate 3 (Steap3) was decreased upon L. monocytogenes infection compared to uninfected cells in macrophages. However, the decreased Steap3 abundance was not regulated by the host but was caused by LLO secreted by L. monocytogenes. Functional experiments showed that deletion of Steap3 facilitated entry of L. monocytogenes from the phagosome into the cytoplasm. Then, the comprehensive proteomic analysis revealed that the deletion of Steap3 could affect the proteins abundance of the lysosomal signaling pathway in macrophages. Among these proteins affected by Steap3, we discovered that only the Ganglioside GM2 activator (Gm2a) inhibited the phagosomal escape of L. monocytogenes as Steap3. In summary, we found that the Steap3-Gm2a axis could restrict the phagosomal escape of L. monocytogenes and serve the potential molecular drug targets for antibacterial treatment.