Chlamydial infection induces pathobiotype-specific protein tyrosine phosphorylation in epithelial cells

Regeneration of Pulmonary Tissue in a Calf Model of Fibrinonecrotic Bronchopneumonia Induced by Experimental Infection with Chlamydia Psittaci

Pneumonia is a cause of high morbidity and mortality in humans. Animal models are indispensable to investigate the complex cellular interactions during lung injury and repair in vivo. The time sequence of lesion development and regeneration is described after endobronchial inoculation of calves with Chlamydia psittaci. Calves were necropsied 2-37 days after inoculation (dpi). Lesions and presence of Chlamydia psittaci were investigated using histology and immunohistochemistry. Calves developed bronchopneumonia at the sites of inoculation. Initially, Chlamydia psittaci replicated in type 1 alveolar epithelial cells followed by an influx of neutrophils, vascular leakage, fibrinous exudation, thrombosis and lobular pulmonary necrosis. Lesions were most extensive at 4 dpi. Beginning at 7 dpi, the number of chlamydial inclusions declined and proliferation of cuboidal alveolar epithelial cells and sprouting of capillaries were seen at the periphery of necrotic tissue. At 14 dpi, most of the necrosis had been replaced with alveoli lined with cuboidal epithelial cells resembling type 2 alveolar epithelial cells and mild fibrosis, and hyperplasia of organized lymphoid tissue were observed. At 37 dpi, regeneration of pulmonary tissue was nearly complete and only small foci of remodeling remained. The well-defined time course of development and regeneration of necrotizing pneumonia allows correlation of morphological findings with clinical data or treatment regimen.

iTRAQ-Based Quantitative Proteomics Analysis of HeLa Cells Infected With Chlamydia muridarum TC0668 Mutant and Wild-Type Strains

Chlamydia muridarum, an obligate intracellular pathogen, was used to establish a murine model of female upper genital tract infection by Chlamydia trachomatis. TC0668 in C. muridarum is a hypothetical chromosomal virulence protein that is involved in upper genital tract pathogenesis. The infection of mice with the C. muridarum TC0668-mutant (G216*) strain results in less pathological damage in the upper genital tract. In this study, an isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomics analysis was performed to identify differentially expressed proteins between TC0668 wild-type (TC0668^wt) and TC0668 mutant (TC0668^mut) strains at 6, 12, 18, and 24 h post-infection (p.i.). Of the 550 proteins differentially expressed at 18 h p.i., 222 and 328 were up-regulated and down-regulated, respectively, inTC0668^mut-infected cells. The expression of seven up-regulated proteins (encoded by SRPRB, JAK1, PMM1, HLA-DQB1, THBS1, ITPR1, and BCAP31) and three down-regulated proteins (encoded by MAPKAPK2, TRAFD1, and IFI16) from the iTRAQ analysis were validated using quantitative real-time (qRT)-PCR. The qRT-PCR results were consistent with those of iTRAQ. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that the differentially expressed proteins primarily participated in inflammatory responses, fibrosis, metabolic processes, and complement coagulation cascades, and were mainly enriched in the phosphatidylinositol 3′-kinase (PI3K)/Akt, nuclear factor kappa-B (NF-κB), and other signaling pathways. Using western-blotting and immunofluorescence detection, significant differences in activation of the PI3K/Akt and NF-κB signaling pathways were observed between the TC0668^wt- and TC0668^mut-infected cells. Differentially expressed proteins linked with inflammation and fibrosis were used in a protein-protein interaction network analysis. The results suggest that TC0668 may play a pivotal role in C. muridarum-induced genital pathology by inducing inflammatory responses and fibrosis, which may involve the activation of the PI3K/Akt and NF-κB signaling pathways.

Higher titers of anti-Chlamydia pneumoniae IgG in diabetic retinopathy: a cross-sectional study

BACKGROUND

Chronic inflammation has a role in the pathogenesis of diabetic retinopathy. Infection with intracellular organisms may incite chronic inflammation. This study was conducted to investigate the association between previous infection with Chlamydia pneumoniae (an intracellular microorganism) and diabetic retinopathy.

METHODS

Patients with type 2 diabetes mellitus (30-60 years old) and age-matched normal controls were recruited. Patients with history of cardiovascular or cerebrovascular disease, recent pulmonary infection and the presence of age-related macular degeneration were excluded from the study. Complete ophthalmic examinations were performed. Fasting blood sugar and haemoglobin levels were measured in diabetic patients and controls, and HgbA1c , blood urea nitrogen, creatinine and 24-h urine protein were measured in diabetic patients. Anti-C. pneumoniae IgG (enzyme-linked immunosorbent assay) was measured in the sera of all participants.

RESULTS

A total of 215 type 2 diabetic patients and 243 normal healthy controls were included. Anti-C. pneumoniae IgG titers were higher in patients affected by diabetic retinopathy than participants without retinopathy (74.78 ± 33.38 vs 66.18 ± 31.40, p = 0.028). Diabetic patients with diabetic retinopathy also had higher titers than diabetic patients without diabetic retinopathy (74.78 ± 33.38 vs 66.11 ± 33.41, p = 0.042). Of different variables including age, body mass index, haemoglobin level, glycated haemoglobin level, fasting blood sugar, mean arterial pressure and blood urea nitrogen, only age (r = 0.17; p = 0.001) and body mass index (r = 0.15; p = 0.003) were correlated with anti-C. pneumoniae IgG levels. In regression analysis, the presence of diabetic retinopathy was still a determinant of the antibody level (p = 0.03).

CONCLUSION

Anti-C. pneumoniae IgG titers were higher in patients with diabetic retinopathy, which may indicate a role of this infection in the pathogenesis of diabetic retinopathy.

Nitropropenyl benzodioxole, an anti-infective agent with action as a protein tyrosine phosphatase inhibitor

We report on the activities of a broad spectrum antimicrobial compound,nitropropenyl benzodioxole (NPBD) which are of relevance to its potential as an anti-infective drug. These investigations support the proposal that a major mechanism of NPBD is action as a tyrosine mimetic, competitively inhibiting bacterial and fungal protein tyrosine phosphatases (PTP). NPBD did not affect major anti-bacterial drug targets, namely, ATP production, cell wall or cell membrane integrity, or transcription and translation of RNA. NPBD inhibited bacterial YopH and human PTP1B and not human CD45 in enzyme assays. NPBD inhibited PTP-associated bacterial virulence factors, namely, endospore formation in Bacillus cereus, prodigiosin secretion in Serratia marcescens , motility in Proteus spp., and adherence and invasion of mammalian cells by Yersinia enterocolitica . NPBD acts intracellularly to inhibit the early development stages of the Chlamydia trachomatis infection cycle in mammalian cells known to involve sequestration of host cell PTPs. NPBD thus both kills pathogens and inhibits virulence factors relevant to early infection, making it a suitable candidate for development as an anti-infective agent, particularly for pathogens that enter through, or cause infections at, mucosal surfaces. Though much is yet to be understood about bacterial PTPs, they are proposed as suitable anti-infective targets and have been linked to agents similar to NPBD. The structural and functional diversity and heterogeneous distribution of PTPs across microbial species make them suitably selective targets for the development of both broadly active and pathogen-specific drugs.

Abl family of tyrosine kinases and microbial pathogenesis

Abl nonreceptor tyrosine kinases are activated by multiple stimuli and regulate cytoskeletal reorganization, cell proliferation, survival, and stress responses. Several downstream pathways have direct impact on physiological processes, including development and maintenance of the nervous and immune systems and epithelial morphogenesis. Recent studies also indicated that numerous viral and bacterial pathogens highjack Abl signaling for different purposes. Abl kinases are activated to reorganize the host actin cytoskeleton and promote the direct tyrosine phosphorylation of viral surface proteins and injected bacterial type-III and type-IV effector molecules. However, Abl kinases also play other roles in infectious processes of bacteria, viruses, and prions. These activities have crucial impact on microbial invasion and release from host cells, actin-based motility, pedestal formation, as well as cell-cell dissociation involved in epithelial barrier disruption and other responses. Thus, Abl kinases exhibit important functions in pathological signaling during microbial infections. Here, we discuss the different signaling pathways activated by pathogens and highlight possible therapeutic intervention strategies.

Transcriptome analysis indicates an enhanced activation of adaptive and innate immunity by chlamydia-infected murine epithelial cells treated with interferon γ

BACKGROUND

Interferon γ (IFN‐γ) is the major cytokine involved in the elimination of Chlamydia infection. Despite its importance, the combined effect of Chlamydia infection and IFN‐γ on the gene expression of murine epithelial cells has only partially been described.

METHODS

The DNA chip method was used to evaluate the impact of IFN‐γ and both the human strain Chlamydia trachomatis L2 infection and the murine strain Chlamydia muridarum infection on the transcriptome of murine epithelial cells.

RESULTS

The gene expression analysis revealed that IFN‐γ had an enhancing effect on both the up‐regulation and down‐regulation of the epithelial gene expression. The influenced gene functional classes included cytokine and chemokine expression, antigen presentation, apoptosis, and genes involved in basic metabolic processes such as fatty acid oxidation. We also detected the up‐regulation of various genes that could be directly antichlamydial, such as members of the p47 GTPase family, inducible nitric oxide synthase, and monokine induced by IFN‐γ (MIG). As a functional validation of DNA chip data, we measured the antichlamydial effect of MIG on the extracellular form of Chlamydia.

CONCLUSIONS

Our results show that IFN‐γ is a key cytokine that primes epithelial cells to activate adaptive and innate immunity and to express antichlamydial effector genes both intracellularly and extracellularly.

The Chlamydial Type III Secretion Mechanism: Revealing Cracks in a Tough Nut

Present-day members of the Chlamydiaceae contain parasitic bacteria that have been co-evolving with their eukaryotic hosts over hundreds of millions of years. Likewise, a type III secretion system encoded within all genomes has been refined to complement the unique obligate intracellular niche colonized so successfully by Chlamydia spp. All this adaptation has occurred in the apparent absence of the horizontal gene transfer responsible for creating the wide range of diversity in other Gram-negative, type III-expressing bacteria. The result is a system that is, in many ways, uniquely chlamydial. A critical mass of information has been amassed that sheds significant light on how the chlamydial secretion system functions and contributes to an obligate intracellular lifestyle. Although the overall mechanism is certainly similar to homologous systems, an image has emerged where the chlamydial secretion system is essential for both survival and virulence. Numerous apparent differences, some subtle and some profound, differentiate chlamydial type III secretion from others. Herein, we provide a comprehensive review of the current state of knowledge regarding the Chlamydia type III secretion mechanism. We focus on the aspects that are distinctly chlamydial and comment on how this important system influences chlamydial pathogenesis. Gaining a grasp on this fascinating system has been challenging in the absence of a tractable genetic system. However, the surface of this tough nut has been scored and the future promises to be fruitful and revealing.

A systemic network for Chlamydia pneumoniae entry into human cells

Bacterial entry is a multistep process triggering a complex network, yet the molecular complexity of this network remains largely unsolved. By employing a systems biology approach, we reveal a systemic bacterial-entry network initiated by Chlamydia pneumoniae, a widespread opportunistic pathogen. The network consists of nine functional modules (i.e., groups of proteins) associated with various cellular functions, including receptor systems, cell adhesion, transcription, and endocytosis. The peak levels of gene expression for these modules change rapidly during C. pneumoniae entry, with cell adhesion occurring at 5 min postinfection, receptor and actin activity at 25 min, and endocytosis at 2 h. A total of six membrane proteins (chemokine C-X-C motif receptor 7 [CXCR7], integrin beta 2 [ITGB2], platelet-derived growth factor beta polypeptide [PDGFB], vascular endothelial growth factor [VEGF], vascular cell adhesion molecule 1 [VCAM1], and GTP binding protein overexpressed in skeletal muscle [GEM]) play a key role during C. pneumoniae entry, but none alone is essential to prevent entry. The combination knockdown of three genes (coding for CXCR7, ITGB2, and PDGFB) significantly inhibits C. pneumoniae entry, but the entire network is resistant to the six-gene depletion, indicating a resilient network. Our results reveal a complex network for C. pneumoniae entry involving at least six key proteins.

Evidence that CT694 is a novel Chlamydia trachomatis T3S substrate capable of functioning during invasion or early cycle development

Chlamydia trachomatis is an obligate intracellular parasite, occupies a membrane-bound vacuole throughout development and is capable of manipulating the eukaryotic host by translocating effector molecules via a type III secretion system (T3SS). The infectious chlamydial elementary body (EB) is metabolically inactive yet possesses a functional T3S apparatus capable of translocating effector proteins into the host cell to facilitate invasion and other early cycle events. We present evidence here that the C. trachomatis protein CT694 represents an early cycle-associated effector protein. CT694 is secreted by the Yersinia T3SS and immunodetection studies of infected HeLa cultures indicate that CT694-specific signal accumulates directly adjacent to, but not completely overlapping with EBs during invasion. Yeast two-hybrid analyses revealed an interaction of CT694 with the repeat region and C-terminus of human AHNAK. Immunolocalization studies of CT694 ectopically expressed in HeLa cells were consistent with an interaction with endogenous AHNAK. Additionally, expression of CT694 in HeLa cells resulted in alterations in the detection of stress fibres that correlated with the ability of CT694 to interact with AHNAK. These data indicate that CT694 is a novel T3S-dependent substrate unique to C. trachomatis, and that its interaction with host proteins such as AHNAK may be important for aspects of invasion or development particular to this species.

Chlamydia trachomatis species-specific induction of ezrin tyrosine phosphorylation functions in pathogen entry

Chlamydia trachomatis is an obligate intracellular pathogen of humans that exhibits species-specific biological characteristics in its early interactions with host cells that are likely important to pathogenesis. One such characteristic is the tyrosine phosphorylation (Tyr-P) of an approximately 70-kDa polypeptide that occurs only after infection of mammalian cells by human strains. We sought to identify this protein because of its potential significance to the pathogenesis of human chlamydial infections. Using an immunoproteomic approach we identified the host protein ezrin, a member of the ezrin-radixin-moesin (ERM) protein family that serves as a physical link between host cell receptors and the actin cytoskeleton. Confocal microscopy studies showed colocalization of ezrin and actin at the tips and crypts of microvilli, the site of chlamydial attachment and entry, respectively. To demonstrate a functional role for ezrin we infected cells with a dominant-negative (DN) ezrin phenotype or treated cells with ezrin-specific small interfering RNA (siRNA). We found that both DN and siRNA-treated cells were significantly less susceptible to infection by human chlamydial strains. Moreover, we demonstrated that inhibition of infection in ezrin DN cells occurred at the stage of chlamydial entry. We hypothesize that the C. trachomatis-specific Tyr-P of ezrin might relate to an undefined species-specific mechanism of pathogen entry that involves chlamydial specific ligand(s) and host cell coreceptor usage.

Chlamydophila pneumoniae PknD exhibits dual amino acid specificity and phosphorylates Cpn0712, a putative type III secretion YscD homolog

Chlamydophila pneumoniae is an obligate intracellular bacterium that causes bronchitis, pharyngitis, and pneumonia and may be involved in atherogenesis and Alzheimer's disease. Genome sequencing has identified three eukaryote-type serine/threonine protein kinases, Pkn1, Pkn5, and PknD, that may be important signaling molecules in Chlamydia. Full-length PknD was cloned and expressed as a histidine-tagged protein in Escherichia coli. Differential centrifugation followed by sodium carbonate treatment of E. coli membranes demonstrated that His-PknD is an integral membrane protein. Fusions of overlapping PknD fragments to alkaline phosphatase revealed that PknD contains a single transmembrane domain and that the kinase domain is in the cytoplasm. To facilitate solubility, the kinase domain was cloned and expressed as a glutathione S-transferase (GST) fusion protein in E. coli. Purified GST-PknD kinase domain autophosphorylated, and catalytic mutants (K33G, D156G, and K33G-D156G mutants) and activation loop mutants (T185A and T193A) were inactive. PknD phosphorylated recombinant Cpn0712, a type III secretion YscD homolog that has two forkhead-associated domains. Thin-layer chromatography revealed that the PknD kinase domain autophosphorylated on threonine and tyrosine and phosphorylated the FHA-2 domain of Cpn0712 on serine and tyrosine. To our knowledge, this is the first demonstration of a bacterial protein kinase with amino acid specificity for both serine/threonine and tyrosine residues and this is the first study to show phosphorylation of a predicted type III secretion structural protein.

Recent insights into the mechanisms of Chlamydia entry

Chlamydia are widespread bacteria that grow in human and animal cells. They enter their host cell, establish an intracellular environment favourable for their multiplication and finally exit the host cell. A combination of host cell factors and of bacterial proteins contribute to pathogen entry. Recent advances have shed new light on the entry mechanism, following attachment. Here we review recent data concerning endocytosis, host cell signalling, proteins secreted by the bacteria, the actin cytoskeleton in entry and the involvement of small GTPases.

Tyrosine-phosphorylated bacterial effector proteins: the enemies within

The tyrosine phosphorylation of proteins has a central role during signal transduction in eukaryotes. Recent progress shows that tyrosine phosphorylation is also a common feature of several effector proteins translocated by bacterial type III and type IV secretion systems. The involvement of these secretion systems in disease development is exemplified by a variety of pathogenic processes: pedestal formation (Tir of EPEC and Citrobacter), cell scattering (CagA of Helicobacter), invasion (Tarp of Chlamydia) and possibly proinflammatory responses and cell proliferation (BepD-F of Bartonella). The discovery that different bacterial pathogens use this common strategy to subvert host-cell function suggests that more examples will soon emerge.