Mycobacterium tuberculosis modulators of the macrophage's cellular events

Characterization of spectinamide 1599 efficacy against different mycobacterial phenotypes

Spectinamides are a novel series of spectinomycin analogs being developed for the treatment of tuberculosis. The preclinical lead spectinamide 1599 is an antituberculosis drug that possesses robust in vivo efficacy, good pharmacokinetic properties, and excellent safety profiles in rodents. In individuals infected with Mycobacterium tuberculosis or Mycobacterium bovis, causative agents of tuberculosis, the host immune system is capable of restraining these mycobacteria within granulomatous lesions. The harsh microenvironmental conditions of these granuloma lead to phenotypic transformation of mycobacteria. Phenotypically transformed bacteria display suboptimal growth, or complete growth arrest and are frequently associated with drug tolerance. Here we quantified the effect of spectinamide 1599 on log-phase and phenotypically tolerant isoforms of Mycobacterium bovis BCG using various in vitro approaches as a first indicator of spectinamide 1599 activity against various mycobacterial isoforms. We also used the hollow fiber infection model to establish time-kill curves and deployed pharmacokinetic/pharmacodynamic modeling to characterize the activity differences of spectinamide 1599 towards the different phenotypic subpopulations. Our results indicate that spectinamide 1599 is more efficacious against log phase bacteria when compared to its activity against other phenotypically tolerant forms such as acid phase bacteria and hypoxic phase bacteria, a behavior similar to the established antituberculosis drug isoniazid.

Enhanced immunogenicity of the tuberculosis subunit Rv0572c vaccine delivered in DMT liposome adjuvant as a BCG-booster

COVID-19 has affected the progress made in the prevention and treatment of tuberculosis (TB); hence, the mortality of tuberculosis has risen. Different strategies-based novel TB vaccine candidates have been developed. This study identifies strategies to overcome the limitations of Bacille Calmette-Guérin (BCG) in preventing latent infection and reactivation of TB. The latency antigen Rv0572c was selected based on the mechanism of interaction between Mycobacterium tuberculosis and its host. The rRv0572c protein was used to stimulate whole blood samples derived from patients with clinically diagnosed active TB (ATBs) or latent TB infections (LTBIs) and healthy control (HCs) donors, confirming that this protein can be recognized by T cells in patients with TB, especially LTBIs. C57BL/6 mice were used to investigate the immunogenicity of the rRv0572c protein emulsified in the liposome adjuvant dimethyldioctadecylammonium [DDA], monophosphoryl lipid A [MPLA], trehalose-6, 6′-dibehenate [TDB] (DMT). The results demonstrated that rRv0572c/DMT could boost BCG-primed mice to induce antigen-specific CD4⁺ T cell production and generate functional T cells dominated by antigen-specific CD8⁺ T cells. The rRv0572c/DMT vaccine could also trigger limited Th2 humoral immune responses. These findings suggest that rRv0572c/DMT is a potential subunit vaccine candidate that can be used as a booster vaccine for BCG.

Host-Pathogen Dialogues in Autophagy, Apoptosis, and Necrosis during Mycobacterial Infection

Mycobacterium tuberculosis (Mtb) is an etiologic pathogen of human tuberculosis (TB), a serious infectious disease with high morbidity and mortality. In addition, the threat of drug resistance in anti-TB therapy is of global concern. Despite this, it remains urgent to research for understanding the molecular nature of dynamic interactions between host and pathogens during TB infection. While Mtb evasion from phagolysosomal acidification is a well-known virulence mechanism, the molecular events to promote intracellular parasitism remains elusive. To combat intracellular Mtb infection, several defensive processes, including autophagy and apoptosis, are activated. In addition, Mtb-ingested phagocytes trigger inflammation, and undergo necrotic cell death, potentially harmful responses in case of uncontrolled pathological condition. In this review, we focus on Mtb evasion from phagosomal acidification, and Mtb interaction with host autophagy, apoptosis, and necrosis. Elucidation of the molecular dialogue will shed light on Mtb pathogenesis, host defense, and development of new paradigms of therapeutics.

"It Takes Two to Tango": Role of Neglected Macrophage Manipulators Coronin 1 and Protein Kinase G in Mycobacterial Pathogenesis

Macrophages being the connecting link between innate and adaptive immune system plays a crucial role in microbial antigen presentation and orchestrates the subsequent clearance of microorganisms. Microbial invasion of macrophages trigger a plethora of signaling cascades, which interact among them to generate a dynamically altered hostile environment, that ultimately leads to disruption of microbial pathogenesis. Paradoxically, Mycobacterium sp. exploits macrophage proteins such as Coronin 1, Calcineurin, LRG47, SOCS1, CISH, Gbp5 etc. and secretes virulence proteins such as PknG, PtpA, SapM, Eis etc. to hijack these intra-macrophage, signaling cascades and thereby develop its own niche. Coronin 1, being a cortical protein is transiently recruited to all mycobacteria containing phagosomes, but only pathogenic mycobacteria can retain it on the phagosome, to hinder its maturation. Additionally, mycobacterial infection linked secretion of virulence factor Protein Kinase G through its phosphorylation, manipulates several macrophage signaling pathways and thus promotes pathogenesis at various stages, form early infection to latency to granuloma formation. Here we discuss the present status of mycobacteria engaged Coronin 1-dependent signaling cascades and secreted PknG related sequence of events promoting mycobacterial pathogenesis. Current knowledge about these two proteins in context of macrophage signaling manipulation encompassing diverse mechanisms like calcium-calcineurin signaling, reduced proinflamtory cytokine secretion, cytoskeletal changes, and adaptation in acidic environment, which ultimately converge toward mycobacterial survival inside the macrophages has been discussed.

High-Content Screening of Eukaryotic Kinase Inhibitors Identify CHK2 Inhibitor Activity Against Mycobacterium tuberculosis

A screen of a eukaryotic kinase inhibitor library in an established intracellular infection model identified a set of drug candidates enabling intracellular killing of Mycobacterium tuberculosis (M.tb). Screen validity was confirmed internally by a Z′ = 0.5 and externally by detecting previously reported host-targeting anti-M.tb compounds. Inhibitors of the CHK kinase family, specifically checkpoint kinase 2 (CHK2), showed the highest inhibition and lowest toxicity of all kinase families. The screen identified and validated DDUG, a CHK2 inhibitor, as a novel bactericidal anti-M.tb compound. CHK2 inhibition by RNAi phenocopied the intracellular inhibitory effect of DDUG. DDUG was active intracellularly against M.tb, but not other mycobacteria. DDUG also had extracellular activity against 4 of 12 bacteria tested, including M.tb. Combined, these observations suggest DDUG acts in tandem against both host and pathogen. Importantly, DDUG’s validation highlights the screening and analysis methodology developed for this screen, which identified novel host-directed anti-M.tb compounds.

DMN-Tre Labeling for Detection and High-Content Screening of Compounds against Intracellular Mycobacteria

4-N,N-Dimethylamino-1,8-naphthalimide conjugate of trehalose (DMN-Tre) is a fluorogenic dye recently developed as a diagnostic tool for tuberculosis. DMN-Tre selectively labels the mycobacterial cell wall through the Ag85 enzymes. In this work, we disclose a protocol describing the total synthesis of DMN-Tre with more than 99% purity. We further developed a protocol for in vitro and intercellular labeling of various mycobacterial strains. DMN-Tre labeling was found to be a useful tool to study in vitro and intracellular Mycobacterium tuberculosis (Mtb) physiology and as an end-point readout system in high-content image-based screening (HCS) of drug molecules. Such uses of DMN-Tre labeling provide a simple, fast, and cheap alternative to the existing, time-consuming approach that requires Mtb strains to be genetically transformed with fluorescent reporter genes.

A Two-Way Proteome Microarray Strategy to Identify Novel Mycobacterium tuberculosis-Human Interactors

Tuberculosis (TB) is still a serious threat to human health which is caused by mycobacterium tuberculosis (Mtb). The main reason for failure to eliminate TB is lack of clearly understanding the molecular mechanism of Mtb pathogenesis. Determining human Mtb-interacting proteins enables us to characterize the mechanism and identify potential molecular targets for TB diagnosis and treatment. However, experimentally systematic Mtb interactors are not readily available. In this study, we performed an unbiased, comprehensive two-way proteome microarray based approach to systematically screen global human Mtb interactors and determine the binding partners of Mtb effectors. Our results, for the first time, screened 84 potential human Mtb interactors. Bioinformatic analysis further highlighted these protein candidates might engage in a wide range of cellular functions such as activation of DNA endogenous promoters, transcription of DNA/RNA and necrosis, as well as immune-related signaling pathways. Then, using Mtb proteome microarray followed His tagged pull-down assay and Co-IP, we identified one interacting partner (Rv0577) for the protein candidate NRF1 and three binding partners (Rv0577, Rv2117, Rv2423) for SMAD2, respectively. This study gives new insights into the profile of global Mtb interactors potentially involved in Mtb pathogenesis and demonstrates a powerful strategy in the discovery of Mtb effectors.

Mycobacterium tuberculosis Rv3463 induces mycobactericidal activity in macrophages by enhancing phagolysosomal fusion and exhibits therapeutic potential

Macrophages are responsible for innate and adaptive immune response activation necessary for eliminating infections. Optimal activation of macrophages to phagocytize Mycobacterium tuberculosis is critical in anti-mycobacterial defense. Here, we identified a novel Rv3463 hypothetical protein that induces macrophage activation in Mtb culture filtrate. Recombinant Rv3463 activated mouse bone marrow-derived macrophages to induce the expression of surface molecules and secrete pro-inflammatory cytokines via the TLR2 and TLR4 pathways. Mitogen activated protein kinase, phospatidylinositol-4,5-bisphosphate 3-kinases, and the NF-κB signaling pathways are involved in Rv3463-mediated macrophage activation. Furthermore, Rv3463 induced bactericidal effects in Mtb-infected macrophages through phagosome maturation and phagolysosomal fusion enhanced by phospatidylinositol-4,5-bisphosphate 3-kinases and Ca²⁺ signaling pathways and exhibited therapeutic effects in a short-term Mtb-infection mouse model. Overexpression of Rv3463 in M. smegmatis caused rapid clearance of bacteria in macrophages and mice. Our study suggests that Rv3463 is a promising target for the development of post-exposure tuberculosis vaccines or adjunct immune-therapy.

The SecA2 pathway of Mycobacterium tuberculosis exports effectors that work in concert to arrest phagosome and autophagosome maturation

To subvert host defenses, Mycobacterium tuberculosis (Mtb) avoids being delivered to degradative phagolysosomes in macrophages by arresting 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. The SecA2 dependent protein export system is required for phagosome maturation arrest and consequently growth of Mtb in macrophages. To better understand the role of the SecA2 pathway in phagosome maturation arrest, we identified two effectors exported by SecA2 that contribute to this process: the phosphatase SapM and the kinase PknG. Then, utilizing the secA2 mutant of Mtb as a platform to study effector functions, we identified specific steps in phagosome maturation inhibited by SapM and/or PknG. By identifying a histidine residue that is essential for SapM phosphatase activity, we confirmed for the first time that the phosphatase activity of SapM is required for its effects on phagosome maturation in macrophages. We further demonstrated that SecA2 export of SapM and PknG contributes to the ability of Mtb to replicate in macrophages. Finally, we extended our understanding of the SecA2 pathway, SapM, and PknG by revealing that their contribution goes beyond preventing Mtb delivery to mature phagolysosomes and includes inhibiting Mtb delivery to autophagolysosomes. Together, our results revealed SapM and PknG to be two effectors exported by the SecA2 pathway of Mtb with distinct as well as cumulative effects on phagosome and autophagosome maturation. Our results further reveal that Mtb must have additional mechanisms of limiting acidification of the phagosome, beyond inhibiting recruitment of the V-ATPase proton pump to the phagosome, and they indicate differences between effects of Mtb on phagosome and autophagosome maturation.

Mycobacterium tuberculosis (Mtb) is the infectious agent of the disease tuberculosis. Inside the host, Mtb replicates primarily within the phagosome of macrophages. To replicate within macrophages, Mtb modifies the phagosome by inhibiting the normal host process of phagosomes maturing into acidified degradative phagolysosomes. In order to arrest this process of phagosome maturation, Mtb exports multiple effectors to the host-pathogen interface. Here we found that the specialized SecA2 protein export pathway of Mtb exports two such effectors: SapM and PknG. We discovered that SapM and PknG play non-redundant functions in phagosome maturation arrest by Mtb. We further demonstrated that SecA2 export of both SapM and PknG contributes to the ability of Mtb to replicate in macrophages. We also identified a role for the SecA2 pathway, SapM and PknG in arresting the host process of autophagosome maturation. Our research highlights how two effectors, SapM and PknG, work in concert but also have distinct roles in phagosome and autophagosome maturation arrest by Mtb.

Reinforcing the Functionality of Mononuclear Phagocyte System to Control Tuberculosis

The mononuclear phagocyte system (MPS) constitutes dendritic cells, monocytes, and macrophages. This system contributes to various functions that are essential for maintaining homeostasis, activation of innate immunity, and bridging it with the adaptive immunity. Consequently, MPS is highly important in bolstering immunity against the pathogens. However, MPS is the frontline cells in destroying Mycobacterium tuberculosis (Mtb), yet the bacterium prefers to reside in the hostile environment of macrophages. Therefore, it may be very interesting to study the struggle between Mtb and MPS to understand the outcome of the disease. In an event when MPS predominates Mtb, the host remains protected. By contrast, the situation becomes devastating when the pathogen tames and tunes the host MPS, which ultimately culminates into tuberculosis (TB). Hence, it becomes extremely crucial to reinvigorate MPS functionality to overwhelm Mtb and eliminate it. In this article, we discuss the strategies to bolster the function of MPS by exploiting the molecules associated with the innate immunity and highlight the mechanisms involved to overcome the Mtb-induced suppression of host immunity. In future, such approaches may provide an insight to develop immunotherapeutics to treat TB.

Protein tyrosine kinase, PtkA, is required for Mycobacterium tuberculosis growth in macrophages

Protein phosphorylation plays a key role in Mycobacterium tuberculosis (Mtb) physiology and pathogenesis. We have previously shown that a secreted protein tyrosine phosphatase, PtpA, is essential for Mtb inhibition of host macrophage acidification and maturation, and is a substrate of the protein tyrosine kinase, PtkA, encoded in the same operon. In this study, we constructed a ∆ptkA deletion mutant in Mtb and found that the mutant exhibited impaired intracellular survival in the THP-1 macrophage infection model, correlated with the strain's inability to inhibit macrophage phagosome acidification. By contrast, the mutant displayed increased resistance to oxidative stress in vitro. Proteomic and transcriptional analyses revealed upregulation of ptpA, and increased secretion of TrxB2, in the ΔptkA mutant. Kinase and protein-protein interaction studies demonstrated that TrxB2 is a substrate of PtkA phosphorylation. Taken together these studies establish a central role for the ptkA-ptpA operon in Mtb pathogenesis.

Genome Sequences of the Mycobacterium tuberculosis H37Rv-ptkA Deletion Mutant and Its Parental Strain

Mycobacterium tuberculosis, the etiological agent of tuberculosis, is one of the most devastating infectious agents in the world. Here, we report the draft genome sequences of the M. tuberculosis protein tyrosine kinase (ptkA) deletion mutant and its parental strain H37Rv, which are used in genetic studies and for drug discovery.

A Water-Bridged Cysteine-Cysteine Redox Regulation Mechanism in Bacterial Protein Tyrosine Phosphatases

The emergence of multidrug-resistant Mycobacterium tuberculosis (Mtb) strains highlights the need to develop more efficacious and potent drugs. However, this goal is dependent on a comprehensive understanding of Mtb virulence protein effectors at the molecular level. Here, we used a post-expression cysteine (Cys)-to-dehydrolanine (Dha) chemical editing strategy to identify a water-mediated motif that modulates accessibility of the protein tyrosine phosphatase A (PtpA) catalytic pocket. Importantly, this water-mediated Cys-Cys non-covalent motif is also present in the phosphatase SptpA from Staphylococcus aureus, which suggests a potentially preserved structural feature among bacterial tyrosine phosphatases. The identification of this structural water provides insight into the known resistance of Mtb PtpA to the oxidative conditions that prevail within an infected host macrophage. This strategy could be applied to extend the understanding of the dynamics and function(s) of proteins in their native state and ultimately aid in the design of small-molecule modulators.

Systematic Identification of Mycobacterium tuberculosis Effectors Reveals that BfrB Suppresses Innate Immunity

Mycobacterium tuberculosis (Mtb) has evolved multiple strategies to counter the human immune system. The effectors of Mtb play important roles in the interactions with the host. However, because of the lack of highly efficient strategies, there are only a handful of known Mtb effectors, thus hampering our understanding of Mtb pathogenesis. In this study, we probed Mtb proteome microarray with biotinylated whole-cell lysates of human macrophages, identifying 26 Mtb membrane proteins and secreted proteins that bind to macrophage proteins. Combining GST pull-down with mass spectroscopy then enabled the specific identification of all binders. We refer to this proteome microarray-based strategy as SOPHIE (Systematic unlOcking of Pathogen and Host Interacting Effectors). Detailed investigation of a novel effector identified here, the iron storage protein BfrB (Rv3841), revealed that BfrB inhibits NF-κB-dependent transcription through binding and reducing the nuclear abundance of the ribosomal protein S3 (RPS3), which is a functional subunit of NF- κB. The importance of this interaction was evidenced by the promotion of survival in macrophages of the mycobacteria, Mycobacterium smegmatis, by overexpression of BfrB. Thus, beyond demonstrating the power of SOPHIE in the discovery of novel effectors of human pathogens, we expect that the set of Mtb effectors identified in this work will greatly facilitate the understanding of the pathogenesis of Mtb, possibly leading to additional potential molecular targets in the battle against tuberculosis.

Identification potential biomarkers in pulmonary tuberculosis and latent infection based on bioinformatics analysis

Background

The study aimed to identify the potential biomarkers in pulmonary tuberculosis (TB) and TB latent infection based on bioinformatics analysis.

Methods

The microarray data of GSE57736 were downloaded from Gene Expression Omnibus database. A total of 7 pulmonary TB and 8 latent infection samples were used to identify the differentially expressed genes (DEGs). The protein-protein interaction (PPI) network was constructed by Cytoscape software. Then network-based neighborhood scoring analysis was performed to identify the important genes. Furthermore, the functional enrichment analysis, correlation analysis and logistic regression analysis for the identified important genes were performed.

Results

A total of 1084 DEGs were identified, including 565 down- and 519 up-regulated genes. The PPI network was constructed with 446 nodes and 768 edges. Down-regulated genes RIC8 guanine nucleotide exchange factor A (RIC8A), basic leucine zipper transcription factor, ATF-like (BATF) and microtubule associated monooxygenase, calponin LIM domain containing 1 (MICAL1) and up-regulated genes ATPase, Na+/K+ transporting, alpha 4 polypeptide (ATP1A4), histone cluster 1, H3c (HIST1H3C), histone cluster 2, H3d (HIST2H3D), histone cluster 1, H3e (HIST1H3E) and tyrosine kinase 2 (TYK2) were selected as important genes in network-based neighborhood scoring analysis. The functional enrichment analysis results showed that these important DEGs were mainly enriched in regulation of osteoblast differentiation and nucleoside triphosphate biosynthetic process. The gene pairs RIC8A-ATP1A4, HIST1H3C-HIST2H3D, HIST1H3E-BATF and MICAL1-TYK2 were identified with high positive correlations. Besides, these genes were selected as significant feature genes in logistic regression analysis.

Conclusions

The genes such as RIC8A, ATP1A4, HIST1H3C, HIST2H3D, HIST1H3E, BATF, MICAL1 and TYK2 may be potential biomarkers in pulmonary TB or TB latent infection.

Insufficient Generation of Mycobactericidal Mediators and Inadequate Level of Phagosomal Maturation Are Related with Susceptibility to Virulent Mycobacterium tuberculosis Infection in Mouse Macrophages

Tuberculosis is caused by Mycobacterium tuberculosis infection, and it remains major life-threatening infectious diseases worldwide. Although, M. tuberculosis has infected one-third of the present human population, only 5–10% of immunocompetent individuals are genetically susceptible to tuberculosis. All inbred strains of mice are susceptible to tuberculosis; however, some mouse strains are much more susceptible than others. In a previous report, we showed that Th1-mediated immunity was not responsible for the differential susceptibility between mouse models. To examine whether these susceptibility differences between inbred mouse strains are due to the insufficient production of effector molecules in the early stage of innate immunity, we investigated mycobacteriostatic function of bone marrow-derived macrophages (BMDMs) in resistant (BALB/c and C57BL/6) and susceptible strains (DBA/2) that were infected with virulent M. tuberculosis (H37Rv) or attenuated M. tuberculosis (H37Ra). The growth rate of virulent M. tuberculosis in infected cells was significantly higher in DBA/2 BMDMs, whereas the growth of the attenuated strain was similar in the three inbred mouse BMDM strains. In addition, the death rate of M. tuberculosis-infected cells increased with the infectious dose when DBA/2 BMDMs were infected with H37Rv. The intracellular reactive oxygen species level was lower in DBA/2 BMDMs that were infected with virulent M. tuberculosis at an early post-infection time point. The expression levels of phagosomal maturation markers, including early endosomal antigen-1 (EEA1) and lysosome-associated membrane protein-1 (LAMP-1), were significantly decreased in DBA/2 BMDM that were infected with virulent M. tuberculosis, whereas IFNγ-treatment restored the phagosomal maturation activity. The nitric oxide (NO) production levels were also significantly lower in DBA/2 BMDMs that were infected with virulent H37Rv at late post-infection points; however, this was not observed with the attenuated H37Ra strain. Furthermore, IFNγ-treatment rescued the low NO production level and insufficient M. tuberculosis growth control of DBA/2 BMDMs to the same level as of both resistant strains. The secreted TNF-α and IL-10 level were not significantly different between strains. Therefore, our findings suggest that DBA/2 BMDMs may have defects in the phagosomal maturation process and in inflammatory mediator production, as they showed innate immune defects when infected with the virulent, but not attenuated M. tuberculosis strain.

Mycobacterium tuberculosis AtsG (Rv0296c), GlmU (Rv1018c) and SahH (Rv3248c) Proteins Function as the Human IL-8-Binding Effectors and Contribute to Pathogen Entry into Human Neutrophils

Mycobacterium tuberculosis is an extremely successful intracellular pathogen that has evolved a broad spectrum of pathogenic mechanisms that enable its manipulation of host defense elements and its survival in the hostile environment inside phagocytes. Cellular influx into the site of mycobacterial entry is mediated by a variety of chemokines, including interleukin-8 (IL-8), and the innate cytokine network is critical for the development of an adaptive immune response and infection control. Using affinity chromatography, liquid chromatography electrospray ionization tandem mass spectrometry and surface plasmon resonance techniques, we identified M. tuberculosis AtsG arylsulphatase, bifunctional glucosamine-1-phosphate acetyltransferase and N-acetylglucosamine-1-phosphate uridyl transferase (GlmU) and S-adenosyl-L-homocysteine hydrolase (SahH) as the pathogen proteins that bind to human IL-8. The interactions of all of the identified proteins (AtsG, GlmU and SahH) with IL-8 were characterized by high binding affinity with K_D values of 6.83x10^-6 M, 5.24x10^-6 M and 7.14x10^-10 M, respectively. Furthermore, the construction of Mtb mutant strains overproducing AtsG, GlmU or SahH allowed determination of the contribution of these proteins to mycobacterial entry into human neutrophils. The significantly increased number of intracellularly located bacilli of the overproducing M. tuberculosis mutant strains compared with those of “wild-type” M. tuberculosis and the binding interaction of AtsG, GlmU and SahH proteins with human IL-8 may indicate that these proteins participate in the modulation of the early events of infection with tubercle bacilli and could affect pathogen attachment to target cells.

Phosphorylation of Mycobacterium tuberculosis protein tyrosine kinase A PtkA by Ser/Thr protein kinases

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), has inflicted about one third of mankind and claims millions of deaths worldwide annually. Signalling plays an important role in Mtb pathogenesis and persistence, and thus represents attractive resource for drug target candidates. Here, we show that protein tyrosine kinase A (PtkA) can be phosphorylated by Mtb endogenous eukaryotic-like Ser/Thr protein kinases (eSTPKs). Kinase assays showed that PknA, PknD, PknF, and PknK can phosphorylate PtkA in dose- and time-dependent manner. Enzyme kinetics suggests that PknA has the highest affinity and enzymatic efficiency towards PtkA. Furthermore, protein-protein interaction assay in surrogate host showed that PtkA interacts with multi-eSTPKs in vivo, including PknA. Lastly, we show that PtkA phosphorylation by eSTPKs occurs on threonine residues and may effect tyrosine phosphorylation levels and thus PtkA activity in vitro. These results demonstrate that PtkA can serve as a substrate to many eSTPKs and suggests that's its activity can be regulated.

Mycobacterium tuberculosis RecA is indispensable for inhibition of the mitogen-activated protein kinase-dependent bactericidal activity of THP-1-derived macrophages in vitro

Our knowledge about the mechanisms utilized by Mycobacterium tuberculosis to survive inside macrophages is still incomplete. One of the mechanism that protects M. tuberculosis from the host's microbicidal products and allows bacteria to survive involves DNA repair systems such as the homologous recombination (HR) and nonhomologous end-joining (NHEJ) pathways. It is accepted that any pathway that contributes to genome maintenance should be considered as potentially important virulence factor. In these studies, we investigated reactive oxygen species, nitric oxide and tumor necrosis factor-α production by macrophages infected with wild-type M. tuberculosis, with an HR-defective mutant (∆recA), with an NHEJ-defective mutant [∆(ku,ligD)], with a mutant defective for both HR and NHEJ [∆(ku,ligD,recA)], or with appropriate complemented strains. We also assessed the involvement of extracellular signal-regulated kinases (ERKs) 1 and 2 in the response of macrophages to infection with the above-mentioned strains, and ERK1/2 phosphorylation in M. tuberculosis-infected macrophages. We found that mutants lacking RecA induced a greater bactericidal response by macrophages than did the wild-type strain or an NHEJ-defective mutant, and activated ERK1/2 was involved only in the response of macrophages to recA deletion mutants [∆(ku,ligD,recA) and ∆recA]. We also demonstrated that only the triple mutant induced ERK1/2 phosphorylation in phorbol-12-myristate-13-acetate-stimulated macrophages. Moreover, HR-defective mutants induced lower amounts of tumor necrosis factor-α secretion than did the wild-type or ∆(ku,ligD). Our results indicate that RecA contributes to M. tuberculosis virulence, and also suggest that diminished ERK1/2 activation in macrophages infected with M. tuberculosis possessing recA may be an important mechanism by which wild-type mycobacteria escape intracellular killing.

Phosphorylation control of protein tyrosine phosphatase A activity in Mycobacterium tuberculosis

Protein tyrosine phosphatase A (PtpA) has been shown to play a key role in human macrophage infection by Mycobacterium tuberculosis (Mtb). Protein tyrosine kinase A (PtkA) was the first protein tyrosine kinase shown to phosphorylate PtpA. Here, we found that PtkA-mediated phosphorylation of PtPA on Tyr-128 and Tyr-129 enhances the PtPA phosphatase activity. Moreover, ex-vivo protein-protein interaction assays showed that PtpA can be phosphorylated by several eukaryotic-like Ser/Thr protein kinases, such as protein kinase A (PknA). PknA was found to regulate PtpA phosphatase activity through Thr-45 phosphorylation. These results indicate that members of two independent families of protein kinases tune PtpA activity in Mtb.

Mycobacterium tuberculosis promotes anti-apoptotic activity of the macrophage by PtpA protein-dependent dephosphorylation of host GSK3α

Mycobacterium tuberculosis tyrosine phosphatase PtpA inhibits two key cellular events in macrophages required for the elimination of invading organisms, phagosome acidification, and maturation. Kinome analysis revealed multiple PtpA-dependent changes to the phosphorylation status of macrophage proteins upon M. tuberculosis infection. Among those proteins we show that PtpA dephosphorylates GSK3α on amino acid Tyr(279), which leads to modulation of GSK3α anti-apoptotic activity, promoting pathogen survival early during infection.

microRNA-124 negatively regulates TLR signaling in alveolar macrophages in response to mycobacterial infection

The emerging roles of microRNAs (miRNAs) in regulating immune responses have attracted increasing attention in recent years; and the alveolar macrophages (AMs) are the main targets of mycobacterial infection, which play a pivotal role in the pathogenesis of Mycobacterium tuberculosis infection. However, the immunoregulatory role of miRNAs in AMs has not been fully demonstrated. In this study, we find that miR-124 is up-regulated in the peripheral leukocytes of patients with pulmonary tuberculosis; furthermore, the expression miR-124 can be induced upon Mycobacterium bovis Bacillus Calmette-Guerin (BCG) infection in both RAW264.7 AM cells in vitro and murine AMs in vivo. Mechanistically, miR-124 is able to modulate toll-like receptor (TLR) signaling activity in RAW264.7 cells in response to BCG infection. In this regard, multiple components of TLR signaling cascade, including the TLR6, myeloid differentiation factor 88 (MyD88), TNFR-associated factor 6 and tumor necrosis factor-α are directly targeted by miR-124. In addition, both overexpression of TLR signaling adaptor MyD88 and BCG infection are able to augment miR-124 transcription, while MyD88 expression silenced by small interfering RNA dramatically suppresses miR-124 expression in AMs in vitro. Moreover, the abundance of miR-124 transcript in murine AMs of MyD88 deficient mice is significantly less than that of their wild-type or heterozygous littermates; and the BCG infection fails to induce miR-124 expression in the lung of MyD88 deficient mouse. These results indicate a negative regulatory role of miR-124 in fine-tuning inflammatory response in AMs upon mycobacterial infection, in part through a mechanism by directly targeting TLR signaling.

An outer membrane channel protein of Mycobacterium tuberculosis with exotoxin activity

The ability to control the timing and mode of host cell death plays a pivotal role in microbial infections. Many bacteria use toxins to kill host cells and evade immune responses. Such toxins are unknown in Mycobacterium tuberculosis. Virulent M. tuberculosis strains induce necrotic cell death in macrophages by an obscure molecular mechanism. Here we show that the M. tuberculosis protein Rv3903c (channel protein with necrosis-inducing toxin, CpnT) consists of an N-terminal channel domain that is used for uptake of nutrients across the outer membrane and a secreted toxic C-terminal domain. Infection experiments revealed that CpnT is required for survival and cytotoxicity of M. tuberculosis in macrophages. Furthermore, we demonstrate that the C-terminal domain of CpnT causes necrotic cell death in eukaryotic cells. Thus, CpnT has a dual function in uptake of nutrients and induction of host cell death by M. tuberculosis.

Mycobacterium bovis BCG triggered MyD88 induces miR-124 feedback negatively regulates immune response in alveolar epithelial cells

The emerging roles of microRNAs (miRNAs) and pulmonary epithelial cells in regulating the immune response against microbial invasion has attracted increasing attention in recent years, however, the immunoregulatory roles of miRNAs in the pulmonary epithelial cells in response to mycobacterial infection has not been fully demonstrated. In this study, we show that miR-124 expression is induced upon Mycobacterium bovis Bacillus Calmette-Guerin (BCG) infection in A549 alveolar epithelial cells and murine lungs. miR-124 is able to modulate Toll-like receptor (TLR) signaling in A459 cells. In this regard, multiple components, including TLR6, myeloid differentiation factor 88 (MyD88), TNFR-associated factor 6 and tumor necrosis factor-α of the TLR signaling cascade are directly regulated by miR-124 in response to BCG stimulation. In addition, miR-124 expression was induced upon MyD88 overexpression and/or BCG stimulation, while silencing MyD88 expression by small interfering RNA dramatically down-regulated miR-124 transcription in A549 cells. These results indicate an underlying negative feedback mechanism between miR-124 and MyD88 in alveolar epithelial cells to prevent an excessive inflammatory response during mycobacterial infection. These observations suggest that miR-124 is a potential target for preventive and therapeutic intervention against the pulmonary tuberculosis, an infectious disease caused by Mycobacterium tuberculosis infection.

Mycobacterium tuberculosis EspB binds phospholipids and mediates EsxA-independent virulence

The type-VII ESX-1 secretion apparatus, encoded by the esx-1 genetic locus, is essential for the export of EsxA and EsxB, two major virulence factors of Mycobacterium tuberculosis. ESX-1 also requires the products of the unlinked espACD operon for optimal function and these proteins are considered integral parts of the secretion apparatus. Here we show that the espACD operon is not necessary for the secretion of EspB, another ESX-1 substrate, and this unimpeded secretion of EspB is associated with significant residual virulence. Upon further investigation, we found that purified EspB can facilitate M. tb virulence even in the absence of EsxA and EsxB, and may do so by binding the bioactive phospholipids phosphatidic acid and phosphatidylserine, both of which are potent bioactive molecules with prominent roles in eukaryotic cell signalling. Our findings provide new insights into the impact of the espACD operon on the ESX-1 apparatus and reveal a distinct virulence function for EspB with novel implications in M. tb-host interactions.