Enterohaemorrhagic Escherichia coli serogroup O111 inhibits NF-(kappa)B-dependent innate responses in a manner independent of a type III secreted OspG orthologue

From bench to bedside: an interdisciplinary journey through the gut-lung axis with insights into lung cancer and immunotherapy

This comprehensive review undertakes a multidisciplinary exploration of the gut-lung axis, from the foundational aspects of anatomy, embryology, and histology, through the functional dynamics of pathophysiology, to implications for clinical science. The gut-lung axis, a bidirectional communication pathway, is central to understanding the interconnectedness of the gastrointestinal- and respiratory systems, both of which share embryological origins and engage in a continuous immunological crosstalk to maintain homeostasis and defend against external noxa. An essential component of this axis is the mucosa-associated lymphoid tissue system (MALT), which orchestrates immune responses across these distant sites. The review delves into the role of the gut microbiome in modulating these interactions, highlighting how microbial dysbiosis and increased gut permeability ("leaky gut") can precipitate systemic inflammation and exacerbate respiratory conditions. Moreover, we thoroughly present the implication of the axis in oncological practice, particularly in lung cancer development and response to cancer immunotherapies. Our work seeks not only to synthesize current knowledge across the spectrum of science related to the gut-lung axis but also to inspire future interdisciplinary research that bridges gaps between basic science and clinical application. Our ultimate goal was to underscore the importance of a holistic understanding of the gut-lung axis, advocating for an integrated approach to unravel its complexities in human health and disease.

NF-κB Regulation by Gut Microbiota Decides Homeostasis or Disease Outcome During Ageing

Human beings and their indigenous microbial communities have coexisted for centuries, which led to the development of co-evolutionary mechanisms of communication and cooperation. Such communication machineries are governed by sophisticated multi-step feedback loops, which typically begin with the recognition of microbes by pattern recognition receptors (PRRs), followed by a host transcriptional response leading to the release of effector molecules. Our gastrointestinal tract being the main platform for this interaction, a variety of host intestinal cells tightly regulate these loops to establish tolerance towards the microbial communities of the gut and maintain homeostasis. The transcription factor, nuclear factor kappa B (NF-κB) is an integral component of such a communication apparatus, which plays a critical role in determining the state of homeostasis or inflammation associated with dysbiosis in the host. Here we outline the crucial role of NF-κB in host response to microbial cues in the context of ageing and associated diseases.

Attaching and effacing pathogens: the effector ABC of immune subversion

The innate immune response resembles an essential barrier to bacterial infection. Many bacterial pathogens have, therefore, evolved mechanisms to evade from or subvert the host immune response in order to colonize, survive and multiply. The attaching and effacing pathogens enteropathogenic Escherichia coli, enterohaemorrhagic E. coli, Escherichia albertii and Citrobacter rodentium are Gram-negative extracellular gastrointestinal pathogens. They use a type III secretion system to inject effector proteins into the host cell to manipulate a variety of cellular processes. Over the last decade, considerable progress was made in identifying and characterizing the effector proteins of attaching and effacing pathogens that are involved in the inhibition of innate immune signaling pathways, in determining their host cell targets and elucidating the mechanisms they employ. Their functions will be reviewed here.

EspFu-Mediated Actin Assembly Enhances Enteropathogenic Escherichia coli Adherence and Activates Host Cell Inflammatory Signaling Pathways

EPEC is among the leading causes of diarrheal disease worldwide. The colonization of the gut mucosa by EPEC results in actin pedestal formation at the site of bacterial attachment. These pedestals are referred to as attaching and effacing (AE) lesions. Here, we exploit the different molecular mechanisms used by EPEC to induce AE lesions on epithelial cells, showing that the effector EspFu is associated with increased bacterial attachment and enhanced epithelial colonization compared to the Tir-Nck pathway. Moreover, we also showed that actin pedestal formation can counterbalance the anti-inflammatory activity induced by EPEC, especially when driven by EspFu. Collectively, our findings provide new insights into virulence mechanisms employed by EPEC to colonize epithelial cells, as well as the host response to this enteric pathogen.

The translocation of effectors into the host cell through type 3 secretion systems (T3SS) is a sophisticated strategy employed by pathogenic bacteria to subvert host responses and facilitate colonization. Enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic E. coli (EHEC) utilize the Tir and EspFu (also known as TccP) effectors to remodel the host cytoskeleton, culminating in the formation of attaching and effacing (AE) lesions on enterocytes. While some EPEC strains require tyrosine phosphorylation of Tir and recruitment of the host Nck to trigger actin polymerization, EHEC and certain EPEC strains, whose Tir is not phosphorylated, rely on the effector EspFu for efficient actin remodeling. Here, we investigated the role played by Tir-Nck and Tir-EspFu actin polymerization pathways during the infection of epithelial cells, as well as the host transcriptional response to the AE lesion formation induced by EPEC. We found that EspFu-mediated actin assembly promotes bacterial attachment and epithelial colonization more efficiently than Tir-Nck. Moreover, we showed that both actin polymerization mechanisms can activate inflammatory pathways and reverse the anti-inflammatory response induced by EPEC in epithelial cells. However, this activity is remarkably more evident in infections with EspFu-expressing EPEC strains. This study demonstrates the complex interactions between effector-mediated actin remodeling and inflammation. Different strains carry different combinations of these two effectors, highlighting the plasticity of pathogenic E. coli enteric infections.

Transcriptional regulation in model organisms: recent progress and clinical implications

In this review, we will summarize model organisms used by scientists in the laboratory, including Escherichia coli, yeast, Arabidopsis thaliana, nematodes, Drosophila, zebrafish, mice and other animals. We focus on the progress in research exploring different types of E. coli in the human body, and the specific molecular mechanisms by which they play a role in humans. First, we discuss the specific transcriptional regulation mechanism of E. coli in cell development, maturation, ageing and longevity, as well as tumorigenesis and development. Then, we discuss how the synthesis of some important substances in cells is regulated and how this affects biological behaviour. Understanding and applying these mechanisms, presumably, can greatly improve the quality of people's lives as well as increase their lifespan. For example, some E. coli can activate certain cells by secreting insulin-like growth factor-1, thus activating the inflammatory response of the body, while other E. coli can inactivate the immune response of the body by secreting toxic factors.

Clever Cooperation: Interactions Between EspF and Host Proteins

EspF is a central effector protein of enterohemorrhagic Escherichia coli (EHEC), enteropathogenic E. coli (EPEC), and Citrobacter rodentium (CR) that is secreted through the type III secretion system to host cells. The interaction between EspF and host proteins plays an important role in bacterial pathogenesis. EspF protein binds to host SNX9 and N-WASP proteins to promote the colonization of pathogenic bacteria in intestinal epithelial cells; combines with cytokeratin 18, actin, 14-3-3ζ, Arp2/3, profilin, and ZO-1 proteins to intervene in the redistribution of intermediate filaments, the rearrangement of actin, and the disruption of tight junctions; acts together with Abcf2 to boost host cell intrinsic apoptosis; and collaborates with Anxa6 protein to inhibit phagocytosis. The interaction between EspF and host proteins is key to the pathogenic mechanism of EHEC and EPEC. Here, we review how EspF protein functions through interactions with these 10 host proteins and contributes to the pathogenicity of EHEC/EPEC.

Role of virulence factors on host inflammatory response induced by diarrheagenic Escherichia coli pathotypes

ABSTRACT 

Pathogens are able to breach the intestinal barrier, and different bacterial species can display different abilities to colonize hosts and induce inflammation. Inflammatory response studies induced by enteropathogens as Escherichia coli are interesting since it has acquired diverse genetic mobile elements, leading to different E. coli pathotypes. Diarrheagenic E. coli secrete toxins, effectors and virulence factors that exploit the host cell functions to facilitate the bacterial colonization. Many bacterial proteins are delivered to the host cell for subverting the inflammatory response. Hereby, we have highlighted the specific processes used by E. coli pathotypes, by that subvert the inflammatory pathways. These mechanisms include an arrangement of pro- and anti-inflammatory responses to favor the appropriate environmental niche for the bacterial survival and growth.

Bacterial effectors and their functions in the ubiquitin-proteasome system: insight from the modes of substrate recognition

Protein ubiquitination plays indispensable roles in the regulation of cell homeostasis and pathogenesis of neoplastic, infectious, and neurodegenerative diseases. Given the importance of this modification, it is to be expected that several pathogenic bacteria have developed the ability to utilize the host ubiquitin system for their own benefit. Modulation of the host ubiquitin system by bacterial effector proteins inhibits innate immune responses and hijacks central signaling pathways. Bacterial effectors mimic enzymes of the host ubiquitin system, but may or may not be structurally similar to the mammalian enzymes. Other effectors bind and modify components of the host ubiquitin system, and some are themselves subject to ubiquitination. This review will describe recent findings, based on structural analyses, regarding how pathogens use post-translational modifications of proteins to establish an infection.

Characterization of enterohemorrhagic Escherichia coli O111 and O157 strains isolated from outbreak patients in Japan

In April and May 2011, there was a serious food-poisoning outbreak in Japan caused by enterohemorrhagic Escherichia coli (EHEC) strains O111:H8 and O157:H7 from raw beef dishes at branches of a barbecue restaurant. This outbreak involved 181 infected patients, including 34 hemolytic-uremic syndrome (HUS) cases (19%). Among the 34 HUS patients, 21 developed acute encephalopathy (AE) and 5 died. Patient stool specimens yielded E. coli O111 and O157 strains. We also detected both EHEC O111 stx2 and stx-negative E. coli O111 strains in a stock of meat block from the restaurant. Pulsed-field gel electrophoresis (PFGE) and multilocus variable-number tandem-repeat analysis (MLVA) showed that the stx-negative E. coli O111 isolates were closely related to EHEC O111 stx2 isolates. Although the EHEC O157 strains had diverse stx gene profiles (stx1, stx2, and stx1 stx2), the PFGE and MLVA analyses indicated that these isolates originated from a single clone. Deletion of the Stx2-converting prophage from the EHEC O111 stx2 isolates was frequently observed during in vitro growth, suggesting that strain conversion from an EHEC O111 stx2 to an stx-negative strain may have occurred during infection.

E2~Ub conjugates regulate the kinase activity of Shigella effector OspG during pathogenesis

Pathogenic bacteria introduce effector proteins directly into the cytosol of eukaryotic cells to promote invasion and colonization. OspG, a Shigella spp. effector kinase, plays a role in this process by helping to suppress the host inflammatory response. OspG has been reported to bind host E2 ubiquitin-conjugating enzymes activated with ubiquitin (E2~Ub), a key enzyme complex in ubiquitin transfer pathways. A co-crystal structure of the OspG/UbcH5c~Ub complex reveals that complex formation has important ramifications for the activity of both OspG and the UbcH5c~Ub conjugate. OspG is a minimal kinase domain containing only essential elements required for catalysis. UbcH5c~Ub binding stabilizes an active conformation of the kinase, greatly enhancing OspG kinase activity. In contrast, interaction with OspG stabilizes an extended, less reactive form of UbcH5c~Ub. Recognizing conserved E2 features, OspG can interact with at least ten distinct human E2s~Ub. Mouse oral infection studies indicate that E2~Ub conjugates act as novel regulators of OspG effector kinase function in eukaryotic host cells.

Enterohaemorrhagic, but not enteropathogenic, Escherichia coli infection of epithelial cells disrupts signalling responses to tumour necrosis factor-alpha

Enterohaemorrhagic Escherichia coli (EHEC), serotype O157 : H7 is a non-invasive, pathogenic bacterium that employs a type III secretion system (T3SS) to inject effector proteins into infected cells. In this study, we demonstrate that EHEC blocks tumour necrosis factor-alpha (TNFα)-induced NF-κB signalling in infected epithelial cells. HEK293T and INT407 epithelial cells were challenged with EHEC prior to stimulation with TNFα. Using complementary techniques, stimulation with TNFα caused activation of NF-κB, as determined by luciferase reporter assay (increase in gene expression), Western blotting (phosphorylation of IκBα), immunofluorescence (p65 nuclear translocation) and immunoassay (CXCL-8 secretion), and each was blocked by EHEC O157 : H7 infection. In contrast, subversion of host cell signalling was not observed following exposure to either enteropathogenic E. coli, strain E2348/69 (O127 : H6) or the laboratory E. coli strain HB101. Heat-killed EHEC had no effect on NF-κB activation by TNFα. Inhibition was mediated, at least in part, by Shiga toxins and by the O157 plasmid, but not by the T3SS or flagellin, as demonstrated by using isogenic mutant strains. These findings indicate the potential for developing novel therapeutic targets to interrupt the infectious process.

Role of EscU auto-cleavage in promoting type III effector translocation into host cells by enteropathogenic Escherichia coli

Background

Type III secretion systems (T3SS) of bacterial pathogens coordinate effector protein injection into eukaryotic cells. The YscU/FlhB group of proteins comprises members associated with T3SS which undergo a specific auto-cleavage event at a conserved NPTH amino acid sequence. The crystal structure of the C-terminal portion of EscU from enteropathogenic Escherichia coli (EPEC) suggests this auto-cleaving protein provides an interface for substrate interactions involved in type III secretion events.

Results

We demonstrate EscU must be auto-cleaved for bacteria to efficiently deliver type III effectors into infected cells. A non-cleaving EscU(N262A) variant supported very low levels of in vitro effector secretion. These effector proteins were not able to support EPEC infection of cultured HeLa cells. In contrast, EscU(P263A) was demonstrated to be partially auto-cleaved and moderately restored effector translocation and functionality during EPEC infection, revealing an intermediate phenotype. EscU auto-cleavage was not required for inner membrane association of the T3SS ATPase EscN or the ring forming protein EscJ. In contrast, in the absence of EscU auto-cleavage, inner membrane association of the multicargo type III secretion chaperone CesT was altered suggesting that EscU auto-cleavage supports docking of chaperone-effector complexes at the inner membrane. In support of this interpretation, evidence of novel effector protein breakdown products in secretion assays were linked to the non-cleaved status of EscU(N262A).

Conclusions

These data provide new insight into the role of EscU auto-cleavage in EPEC. The experimental data suggests that EscU auto-cleavage results in a suitable binding interface at the inner membrane that accommodates protein complexes during type III secretion events. The results also demonstrate that altered EPEC genetic backgrounds that display intermediate levels of effector secretion and translocation can be isolated and studied. These genetic backgrounds should be valuable in deciphering sequential and temporal events involved in EPEC type III secretion.

Enteropathogenic and enterohaemorrhagic Escherichia coli: even more subversive elements

The human pathogens enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC) share a unique mechanism of colonization that results from the concerted action of effector proteins translocated into the host cell by a type III secretion system (T3SS). EPEC and EHEC not only induce characteristic attaching and effacing (A/E) lesions, but also subvert multiple host cell signalling pathways during infection. Our understanding of the mechanisms by which A/E pathogens hijack host cell signalling has advanced dramatically in recent months with the identification of novel activities for many effectors. In addition to further characterization of established effectors (Tir, EspH and Map), new effectors have emerged as important mediators of virulence through activities such as mimicry of Rho guanine nucleotide exchange factors (Map and EspM), inhibition of apoptosis (NleH and NleD), interference with inflammatory signalling pathways (NleB, NleC, NleE and NleH) and phagocytosis (EspF, EspH and EspJ). The findings have highlighted the multifunctional nature of the effectors and their ability to participate in redundant, synergistic or antagonistic relationships, acting in a co-ordinated spatial and temporal manner on different host organelles and cellular pathways during infection.

Modulation of NF-κB signalling by microbial pathogens

The nuclear factor-κB (NF-κB) family of transcription factors plays a central part in the host response to infection by microbial pathogens, by orchestrating the innate and acquired host immune responses. The NF-κB proteins are activated by diverse signalling pathways that originate from many different cellular receptors and sensors. Many successful pathogens have acquired sophisticated mechanisms to regulate the NF-κB signalling pathways by deploying subversive proteins or hijacking the host signalling molecules. Here, we describe the mechanisms by which viruses and bacteria micromanage the host NF-κB signalling circuitry to favour the continued survival of the pathogen.

Evolutionary analysis and distribution of type III effector genes in pathogenic Escherichia coli from human, animal and food sources

Molecular analysis of Shiga toxin-producing Escherichia coli (STEC) from different sources is considered as a major approach to assess their risk potential. However, only limited data are available about the correlation of evolutionary relationship, the presence of major virulence factor genes and the putative risk of an STEC strain for human infection. In this study, we analysed the evolutionary relationship of 136 pathogenic E. coli strains from human, animal and food sources by multi-locus sequence typing (MLST) and molecular subtyping of their Shiga toxin (stx) and intimin (eae) genes. Moreover, the distribution of three type III effector genes, encoded within the locus of enterocyte effacement (LEE), and 16 effector genes, which are encoded outside the LEE, was analysed. One hundred and five strains from different sources harboured 5-15 of the analysed non-LEE-encoded effector genes. In 101 of these strains, the LEE genes eae, map, espF and espG were present simultaneously. Thirty-one isolates deriving mainly from food and patients suffering from haemolytic uraemic syndrome (HUS) were eae-negative and did not carry any of the analysed effector genes. By combination of MLST and virulence gene data, we defined five genetic clusters. Within these clusters a clear-cut affiliation of particular sequence types and the occurrence of certain effector genes was observed. However, in contrast to other studies, a significant correlation between the amount and type of effector genes and the risk to cause HUS could not be demonstrated.

The type III effectors NleE and NleB from enteropathogenic E. coli and OspZ from Shigella block nuclear translocation of NF-kappaB p65

Many bacterial pathogens utilize a type III secretion system to deliver multiple effector proteins into host cells. Here we found that the type III effectors, NleE from enteropathogenic E. coli (EPEC) and OspZ from Shigella, blocked translocation of the p65 subunit of the transcription factor, NF-kappaB, to the host cell nucleus. NF-kappaB inhibition by NleE was associated with decreased IL-8 expression in EPEC-infected intestinal epithelial cells. Ectopically expressed NleE also blocked nuclear translocation of p65 and c-Rel, but not p50 or STAT1/2. NleE homologues from other attaching and effacing pathogens as well OspZ from Shigella flexneri 6 and Shigella boydii, also inhibited NF-kappaB activation and p65 nuclear import; however, a truncated form of OspZ from S. flexneri 2a that carries a 36 amino acid deletion at the C-terminus had no inhibitory activity. We determined that the C-termini of NleE and full length OspZ were functionally interchangeable and identified a six amino acid motif, IDSY(M/I)K, that was important for both NleE- and OspZ-mediated inhibition of NF-kappaB activity. We also established that NleB, encoded directly upstream from NleE, suppressed NF-kappaB activation. Whereas NleE inhibited both TNFalpha and IL-1beta stimulated p65 nuclear translocation and IkappaB degradation, NleB inhibited the TNFalpha pathway only. Neither NleE nor NleB inhibited AP-1 activation, suggesting that the modulatory activity of the effectors was specific for NF-kappaB signaling. Overall our data show that EPEC and Shigella have evolved similar T3SS-dependent means to manipulate host inflammatory pathways by interfering with the activation of selected host transcriptional regulators.

Bacterial effector binding to ribosomal protein s3 subverts NF-kappaB function

Enteric bacterial pathogens cause food borne disease, which constitutes an enormous economic and health burden. Enterohemorrhagic Escherichia coli (EHEC) causes a severe bloody diarrhea following transmission to humans through various means, including contaminated beef and vegetable products, water, or through contact with animals. EHEC also causes a potentially fatal kidney disease (hemolytic uremic syndrome) for which there is no effective treatment or prophylaxis. EHEC and other enteric pathogens (e.g., enteropathogenic E. coli (EPEC), Salmonella, Shigella, Yersinia) utilize a type III secretion system (T3SS) to inject virulence proteins (effectors) into host cells. While it is known that T3SS effectors subvert host cell function to promote diarrheal disease and bacterial transmission, in many cases, the mechanisms by which these effectors bind to host proteins and disrupt the normal function of intestinal epithelial cells have not been completely characterized. In this study, we present evidence that the E. coli O157:H7 nleH1 and nleH2 genes encode T3SS effectors that bind to the human ribosomal protein S3 (RPS3), a subunit of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappaB) transcriptional complexes. NleH1 and NleH2 co-localized with RPS3 in the cytoplasm, but not in cell nuclei. The N-terminal region of both NleH1 and NleH2 was required for binding to the N-terminus of RPS3. NleH1 and NleH2 are autophosphorylated Ser/Thr protein kinases, but their binding to RPS3 is independent of kinase activity. NleH1, but not NleH2, reduced the nuclear abundance of RPS3 without altering the p50 or p65 NF-kappaB subunits or affecting the phosphorylation state or abundance of the inhibitory NF-kappaB chaperone IkappaBalpha NleH1 repressed the transcription of a RPS3/NF-kappaB-dependent reporter plasmid, but did not inhibit the transcription of RPS3-independent reporters. In contrast, NleH2 stimulated RPS3-dependent transcription, as well as an AP-1-dependent reporter. We identified a region of NleH1 (N40-K45) that is at least partially responsible for the inhibitory activity of NleH1 toward RPS3. Deleting nleH1 from E. coli O157:H7 produced a hypervirulent phenotype in a gnotobiotic piglet model of Shiga toxin-producing E. coli infection. We suggest that NleH may disrupt host innate immune responses by binding to a cofactor of host transcriptional complexes.