Chlamydia trachomatis seroassays used in epidemiologic research: a narrative review and practical considerations

Chlamydia trachomatis (CT) is a sexually transmitted infection that can lead to adverse reproductive health outcomes. CT prevalence estimates are primarily derived from screening using nucleic acid amplification tests (NAATs). However, screening guidelines in the United States only include particular subpopulations, and NAATs only detect current infections. In contrast, seroassays identify past CT infections which are important for understanding the public health impacts of CT, including pelvic inflammatory disease and tubal factor infertility. Older seroassays have been plagued by low sensitivity and specificity and have not been validated using a consistent reference measure, making it challenging to compare studies, define the epidemiology of CT and determine the effectiveness of control programs. Newer seroassays have better performance characteristics. This narrative review summarizes the "state of the science" for CT seroassays that have been applied in epidemiologic studies and provides practical considerations for interpreting the literature and employing seroassays in future research.

Antibodies from chlamydia-infected individuals facilitate phagocytosis via Fc receptors

Non-neutralizing functions of antibodies, including phagocytosis, may play a role in Chlamydia trachomatis (CT) infection, but these functions have not been studied and assays are lacking. We utilized a flow-cytometry-based assay to determine whether serum samples from a well-characterized cohort of CT-infected and naïve control individuals enhanced phagocytosis via Fc-receptor-expressing THP-1 cells, and whether this activity correlated with antibody titers. Fc-receptor-mediated phagocytosis was detected only in CT+ donors. Phagocytosis generally did not correlate well with antibody titer. In addition, we found that complement from both CT+ and negative individuals enhanced phagocytosis of CT into primary neutrophils. These results suggest that anti-CT antibodies can have functions that are not reflected by titer. This method could be used to quantitively measure Fc-receptor-mediated function of anti-CT antibodies or complement activity and could reveal new immune correlates of protection.

Crystal structure of an inorganic pyrophosphatase from Chlamydia trachomatis D/UW-3/Cx

Chlamydia trachomatis is the leading cause of bacterial sexually transmitted infections globally and is one of the most commonly reported infections in the United States. There is a need to develop new therapeutics due to drug resistance and the failure of current treatments to clear persistent infections. Structures of potential C. trachomatis rational drug-discovery targets, including C. trachomatis inorganic pyrophosphatase (CtPPase), have been determined by the Seattle Structural Genomics Center for Infectious Disease. Inorganic pyrophosphatase hydrolyzes inorganic pyrophosphate during metabolism. Furthermore, bacterial inorganic pyrophosphatases have shown promise for therapeutic discovery. Here, a 2.2 Å resolution X-ray structure of CtPPase is reported. The crystal structure of CtPPase reveals shared structural features that may facilitate the repurposing of inhibitors identified for bacterial inorganic pyrophosphatases as starting points for new therapeutics for C. trachomatis.

A broad-spectrum cloning vector that exists as both an integrated element and a free plasmid in Chlamydia trachomatis

Plasmid transformation of chlamydiae has created new opportunities to investigate host-microbe interactions during chlamydial infections; however, there are still limitations. Plasmid transformation requires a replicon derived from the native Chlamydia plasmid, and these transformations are species-specific. We explored the utility of a broad host-range plasmid, pBBR1MCS-4, to transform chlamydiae, with a goal of simplifying the transformation process. The plasmid was modified to contain chromosomal DNA from C. trachomatis to facilitate homologous recombination. Sequences flanking incA were cloned into the pBBR1MCS-4 vector along with the GFP:CAT cassette from the pSW2-GFP chlamydial shuttle vector. The final plasmid construct, pBVR2, was successfully transformed into C. trachomatis strain L2-434. Chlamydial transformants were analyzed by immunofluorescence microscopy and positive clones were sequentially purified using limiting dilution. PCR and PacBio-based whole genome sequencing were used to determine if the plasmid was maintained within the chromosome or as an episome. PacBio sequencing of the cloned transformants revealed allelic exchange events between the chromosome and plasmid pBVR2 that replaced chromosomal incA with the plasmid GFP:CAT cassette. The data also showed evidence of full integration of the plasmid into the bacterial chromosome. While some plasmids were fully integrated, some were maintained as episomes and could be purified and retransformed into E. coli. Thus, the plasmid can be successfully transformed into chlamydia without a chlamydial origin of replication and can exist in multiple states within a transformed population.

Rectal Chlamydia trachomatis Infection: A Narrative Review of the State of the Science and Research Priorities

ABSTRACT

Chlamydia trachomatis (CT) is the most commonly reported infection in the United States. Most chlamydial research to date has focused on urogenital infection, but a growing body of research has demonstrated that rectal chlamydia is a relatively common infection among clinic-attending men and women. We know that most rectal CT infections are asymptomatic, but the health implications of these infections, particularly for women, are unclear. In addition, there are key knowledge gaps related to the epidemiologic parameters of rectal chlamydia, the routes of acquisition, the duration of infection, and the clinical significance of a positive rectal CT test result. This lack of information has led to a blind spot in the potential role of rectal chlamydia in sustaining high levels of CT transmission in the United States. Furthermore, recent findings from animal models suggest that the immune response generated from gastrointestinal chlamydial infection can protect against urogenital infection; however, it remains to be determined whether rectal chlamydia similarly modulates anti-CT immunity in humans. This is a critical question in the context of ongoing efforts to develop a CT vaccine. In this narrative review, we summarize the state of the science for rectal chlamydia and discuss the key outstanding questions and research priorities in this neglected area of sexual health research.

Inter-species lateral gene transfer focused on the Chlamydia plasticity zone identifies loci associated with immediate cytotoxicity and inclusion stability

Chlamydia muridarum actively grows in murine mucosae and is a representative model of human chlamydial genital tract disease. In contrast, C. trachomatis infections in mice are limited and rarely cause disease. The factors that contribute to these differences in host adaptation and specificity remain elusive. Overall genomic similarity leads to challenges in the understanding of these significant differences in tropism. A region of major genetic divergence termed the plasticity zone (PZ) has been hypothesized to contribute to the host specificity. To evaluate this hypothesis, lateral gene transfer was used to generate multiple hetero-genomic strains that are predominately C. trachomatis but have replaced regions of the PZ with those from C. muridarum. In vitro analysis of these chimeras revealed C. trachomatis-like growth as well as poor mouse infection capabilities. Growth-independent cytotoxicity phenotypes have been ascribed to three large putative cytotoxins (LCT) encoded in the C. muridarum PZ. However, analysis of PZ chimeras supported that gene products other than the LCTs are responsible for cytopathic and cytotoxic phenotypes. Growth analysis of associated chimeras also led to the discovery of an inclusion protein, CTL0402 (CT147), and homolog TC0424, which was critical for the integrity of the inclusion and preventing apoptosis.

Wikidata as a knowledge graph for the life sciences

Wikidata is a community-maintained knowledge base that has been assembled from repositories in the fields of genomics, proteomics, genetic variants, pathways, chemical compounds, and diseases, and that adheres to the FAIR principles of findability, accessibility, interoperability and reusability. Here we describe the breadth and depth of the biomedical knowledge contained within Wikidata, and discuss the open-source tools we have built to add information to Wikidata and to synchronize it with source databases. We also demonstrate several use cases for Wikidata, including the crowdsourced curation of biomedical ontologies, phenotype-based diagnosis of disease, and drug repurposing.

Recurrent/Intermittent Vaginal and Rectal Chlamydial Infection Following Treatment: A Prospective Cohort Study Among Female Sexually Transmitted Disease Clinic Patients

BACKGROUND

Rectal Chlamydia trachomatis (CT) is common among clinic-attending women, but little is known about clearance and health implications of rectal CT.

METHODS

At the municipal sexually transmitted disease clinic in Seattle, Washington, in 2017-2018, we enrolled women at high risk for urogenital CT into an 8-week prospective study. Women received standard CT treatment at enrollment. Women self-collected daily rectal and vaginal specimens for nucleic acid amplification tests (NAATs) and completed weekly sexual exposure diaries. We performed CT culture on the enrollment rectal specimen.

RESULTS

We enrolled 50 women; 13 (26%) tested positive for vaginal (n = 11) and/or rectal (n = 11) CT. Sixty percent of women with rectal CT per NAAT were also culture positive. Median time to CT clearance after azithromycin treatment was 8.0 days for vaginal CT and 7.0 days for rectal CT. Eight women with rectal CT at enrollment had at least 1 rectal CT-positive NAAT after clearance of the initial infection; none reported anal sex.

CONCLUSIONS

Most NAAT-positive rectal infections were culture positive, suggesting active infection. Time to NAAT clearance of rectal and genital tract CT was similar, and intermittent rectal CT positivity was common in the absence of anal sexual exposure. The cause of recurrent/intermittent rectal CT and the clinical implications of these infections require further study.

Structures of glyceraldehyde 3-phosphate dehydrogenase in Neisseria gonorrhoeae and Chlamydia trachomatis

Neisseria gonorrhoeae (Ng) and Chlamydia trachomatis (Ct) are the most commonly reported sexually transmitted bacteria worldwide and usually present as co-infections. Increasing resistance of Ng to currently recommended dual therapy of azithromycin and ceftriaxone presents therapeutic challenges for syndromic management of Ng-Ct co-infections. Development of a safe, effective, and inexpensive dual therapy for Ng-Ct co-infections is an effective strategy for the global control and prevention of these two most prevalent bacterial sexually transmitted infections. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a validated drug target with two approved drugs for indications other than antibacterials. Nonetheless, any new drugs targeting GAPDH in Ng and Ct must be specific inhibitors of bacterial GAPDH that do not inhibit human GAPDH, and structural information of Ng and Ct GAPDH will aid in finding such selective inhibitors. Here, we report the X-ray crystal structures of Ng and Ct GAPDH. Analysis of the structures demonstrates significant differences in amino acid residues in the active sites of human GAPDH from those of the two bacterial enzymes suggesting design of compounds to selectively inhibit Ng and Ct is possible. We also describe an efficient in vitro assay of recombinant GAPDH enzyme activity amenable to high-throughput drug screening to aid in identifying inhibitory compounds and begin to address selectivity.

The Chlamydia trachomatis Extrusion Exit Mechanism Is Regulated by Host Abscission Proteins

The cellular exit strategies of intracellular pathogens have a direct impact on microbial dissemination, transmission, and engagement of immune responses of the host. Chlamydia exit their host via a budding mechanism called extrusion, which offers protective benefits to Chlamydia as they navigate their extracellular environment. Many intracellular pathogens co-opt cellular abscission machinery to facilitate cell exit, which is utilized to perform scission of two newly formed daughter cells following mitosis. Similar to viral budding exit strategies, we hypothesize that an abscission-like mechanism is required to physically sever the chlamydial extrusion from the host cell, co-opting the membrane fission activities of the endosomal sorting complex required for transport (ESCRT) family of proteins that are necessary for cellular scission events, including abscission. To test this, C. trachomatis L2-infected HeLa cells were depleted of key abscission machinery proteins charged multivesicle body protein 4b (CHMP4B), ALIX, centrosome protein 55 (CEP55), or vacuolar protein sorting-associated protein 4A (VPS4A), using RNA interference (RNAi). Over 50% reduction in extrusion formation was achieved by depletion of CHMP4B, VPS4A, and ALIX, but no effect on extrusion was observed with CEP55 depletion. These results demonstrate a role for abscission machinery in C. trachomatis extrusion from the host cell, with ALIX, VPS4A and CHMP4B playing key functional roles in optimal extrusion release.

Proximity-dependent proteomics of the Chlamydia trachomatis inclusion membrane reveals functional interactions with endoplasmic reticulum exit sites

Chlamydia trachomatis is the most common cause of bacterial sexually transmitted infection, responsible for millions of infections each year. Despite this high prevalence, the elucidation of the molecular mechanisms of Chlamydia pathogenesis has been difficult due to limitations in genetic tools and its intracellular developmental cycle. Within a host epithelial cell, chlamydiae replicate within a vacuole called the inclusion. Many Chlamydia-host interactions are thought to be mediated by the Inc family of type III secreted proteins that are anchored in the inclusion membrane, but their array of host targets are largely unknown. To investigate how the inclusion membrane proteome changes over the course of an infected cell, we have adapted the APEX2 system of proximity-dependent biotinylation. APEX2 is capable of specifically labeling proteins within a 20 nm radius in living cells. We transformed C. trachomatis to express the enzyme APEX2 fused to known inclusion membrane proteins, allowing biotinylation and purification of inclusion-associated proteins. Using quantitative mass spectrometry against APEX2 labeled samples, we identified over 400 proteins associated with the inclusion membrane at early, middle, and late stages of epithelial cell infection. This system was sensitive enough to detect inclusion interacting proteins early in the developmental cycle, at 8 hours post infection, a previously intractable time point. Mass spectrometry analysis revealed a novel, early association between C. trachomatis inclusions and endoplasmic reticulum exit sites (ERES), functional regions of the ER where COPII-coated vesicles originate. Pharmacological and genetic disruption of ERES function severely restricted early chlamydial growth and the development of infectious progeny. APEX2 is therefore a powerful in situ approach for identifying critical protein interactions on the membranes of pathogen-containing vacuoles. Furthermore, the data derived from proteomic mapping of Chlamydia inclusions has illuminated an important functional role for ERES in promoting chlamydial developmental growth.

ChlamBase: a curated model organism database for the Chlamydia research community

The accelerating growth of genomic and proteomic information for Chlamydia species, coupled with unique biological aspects of these pathogens, necessitates bioinformatic tools and features that are not provided by major public databases. To meet these growing needs, we developed ChlamBase, a model organism database for Chlamydia that is built upon the WikiGenomes application framework, and Wikidata, a community-curated database. ChlamBase was designed to serve as a central access point for genomic and proteomic information for the Chlamydia research community. ChlamBase integrates information from numerous external databases, as well as important data extracted from the literature that are otherwise not available in structured formats that are easy to use. In addition, a key feature of ChlamBase is that it empowers users in the field to contribute new annotations and data as the field advances with continued discoveries. ChlamBase is freely and publicly available at chlambase.org.

Direct visualization of the expression and localization of chlamydial effector proteins within infected host cells

Chlamydia secrete into host cells a diverse array of effector proteins, but progress in characterizing the spatiotemporal localization of these proteins has been hindered by a paucity of genetic approaches in Chlamydia and also by the challenge of studying these proteins within the live cellular environment. We adapted a split-green fluorescent protein (GFP) system for use in Chlamydia to label chlamydial effector proteins and track their localization in host cells under native environment. The efficacy of this system was demonstrated by detecting several known Chlamydia proteins including IncA, CT005 and CT694. We further used this approach to detect two chlamydial deubiquitinases (CT867 and CT868) within live cells during the infection. CT868 localized only to the inclusion membrane at early and late developmental stages. CT867 localized to the chlamydial inclusion membrane at an early developmental stage and was concomitantly localized to the host plasma membrane at a late stage during the infection. These data suggest that chlamydial deubiquitinase play important roles for chlamydial pathogenesis by targeting proteins at both the plasma membrane and the chlamydial inclusion membrane. The split-GFP technology was demonstrated to be a robust and efficient approach to identify the secretion and cellular localization of important chlamydial virulence factors.

Orchestration of the mammalian host cell glucose transporter proteins-1 and 3 by Chlamydia contributes to intracellular growth and infectivity

Chlamydia are gram-negative obligate intracellular bacteria that replicate within a discrete cellular vacuole, called an inclusion. Although it is known that Chlamydia require essential nutrients from host cells to support their intracellular growth, the molecular mechanisms for acquiring these macromolecules remain uncharacterized. In the present study, it was found that the expression of mammalian cell glucose transporter proteins 1 (GLUT1) and glucose transporter proteins 3 (GLUT3) were up-regulated during chlamydial infection. Up-regulation was dependent on bacterial protein synthesis and Chlamydia-induced MAPK kinase activation. GLUT1, but not GLUT3, was observed in close proximity to the inclusion membrane throughout the chlamydial developmental cycle. The proximity of GLUT1 to the inclusion was dependent on a brefeldin A-sensitive pathway. Knockdown of GLUT1 and GLUT3 with specific siRNA significantly impaired chlamydial development and infectivity. It was discovered that the GLUT1 protein was stabilized during infection by inhibition of host-dependent ubiquitination of GLUT1, and this effect was associated with the chlamydial deubiquitinase effector protein CT868. This report demonstrates that Chlamydia exploits host-derived transporter proteins altering their expression, turnover and localization. Consequently, host cell transporter proteins are manipulated during infection as a transport system to fulfill the carbon source requirements for Chlamydia.

Extrusions are phagocytosed and promote Chlamydia survival within macrophages

The precise strategies that intracellular pathogens use to exit host cells have a direct impact on their ability to disseminate within a host, transmit to new hosts, and engage or avoid immune responses. The obligate intracellular bacterium Chlamydia trachomatis exits the host cell by two distinct exit strategies, lysis and extrusion. The defining characteristics of extrusions, and advantages gained by Chlamydia within this unique double-membrane structure, are not well understood. Here, we define extrusions as being largely devoid of host organelles, comprised mostly of Chlamydia elementary bodies, and containing phosphatidylserine on the outer surface of the extrusion membrane. Extrusions also served as transient, intracellular-like niches for enhanced Chlamydia survival outside the host cell. In addition to enhanced extracellular survival, we report the key discovery that chlamydial extrusions are phagocytosed by primary bone marrow-derived macrophages, after which they provide a protective microenvironment for Chlamydia. Extrusion-derived Chlamydia staved off macrophage-based killing and culminated in the release of infectious elementary bodies from the macrophage. Based on these findings, we propose a model in which C. trachomatis extrusions serve as "trojan horses" for bacteria, by exploiting macrophages as vehicles for dissemination, immune evasion, and potentially transmission.

Conservation of extrusion as an exit mechanism for Chlamydia

Chlamydiae exit via membrane-encased extrusion or through lysis of the host cell. Extrusions are novel, pathogen-containing structures that confer infectious advantages to Chlamydia, and are hypothesized to promote cell-to-cell spread, dissemination to distant tissues and facilitate immune evasion. The extrusion phenomenon has been characterized for several Chlamydia trachomatis serovars, but a thorough investigation of extrusion for additional clinically relevant C. trachomatis strains and Chlamydia species has yet to be performed. The key parameters investigated in this study were: (i) the conservation of extrusion across the Chlamydia genus, (ii) the functional requirement for candidate Chlamydia genes in extrusion formation i.e. IncA and CT228 and (iii) extrusion-mediated uptake, and consequent survival of Chlamydia inside macrophages. Inclusion morphology was characterized by live fluorescence microscopy, using an inverted GFP strategy, at early and mid-stages of infection. Enriched extrusions were used to infect bone marrow-derived macrophages, and bacterial viability was measured following macrophage engulfment. Our results demonstrate that extrusion is highly conserved across chlamydiae, including ocular, STD and LGV biovars and divergent Chlamydia species. Consequently, this exit mechanism for Chlamydia may fulfill common advantages important for pathogenesis.

Using Fluorescent Proteins to Visualize and Quantitate Chlamydia Vacuole Growth Dynamics in Living Cells

The obligate intracellular bacterium Chlamydia elicits a great burden on global public health. C. trachomatis is the leading bacterial cause of sexually transmitted infection and also the primary cause of preventable blindness in the world. An essential determinant for successful infection of host cells by Chlamydia is the bacterium's ability to manipulate host cell signaling from within a novel, vacuolar compartment called the inclusion. From within the inclusion, Chlamydia acquire nutrients required for their 2-3 day developmental growth, and they additionally secrete a panel of effector proteins onto the cytosolic face of the vacuole membrane and into the host cytosol. Gaps in our understanding of Chlamydia biology, however, present significant challenges for visualizing and analyzing this intracellular compartment. Recently, a reverse-imaging strategy for visualizing the inclusion using GFP expressing host cells was described. This approach rationally exploits the intrinsic impermeability of the inclusion membrane to large molecules such as GFP. In this work, we describe how GFP- or mCherry-expressing host cells are generated for subsequent visualization of chlamydial inclusions. Furthermore, this method is shown to effectively substitute for costly antibody-based enumeration methods, can be used in tandem with other fluorescent labels, such as GFP-expressing Chlamydia, and can be exploited to derive key quantitative data about inclusion membrane growth from a range of Chlamydia species and strains.

Actin recruitment to the Chlamydia inclusion is spatiotemporally regulated by a mechanism that requires host and bacterial factors

The ability to exit host cells at the end of their developmental growth is a critical step for the intracellular bacterium Chlamydia. One exit strategy, extrusion, is mediated by host signaling pathways involved with actin polymerization. Here, we show that actin is recruited to the chlamydial inclusion as a late event, occurring after 20 hours post-infection (hpi) and only within a subpopulation of cells. This event increases significantly in prevalence and extent from 20 to 68 hpi, and actin coats strongly correlated with extrusions. In contrast to what has been reported for other intracellular pathogens, actin nucleation on Chlamydia inclusions did not 'flash', but rather exhibited moderate depolymerization dynamics. By using small molecule agents to selectively disrupt host signaling pathways involved with actin nucleation, modulate actin polymerization dynamics and also to disable the synthesis and secretion of chlamydial proteins, we further show that host and bacterial proteins are required for actin coat formation. Transient disruption of either host or bacterial signaling pathways resulted in rapid loss of coats in all infected cells and a reduction in extrusion formation. Inhibition of Chlamydia type III secretion also resulted in rapid loss of actin association on inclusions, thus implicating chlamydial effector proteins(s) as being central factors for engaging with host actin nucleating factors, such as formins. In conclusion, our data illuminate the host and bacterial driven process by which a dense actin matrix is dynamically nucleated and maintained on the Chlamydia inclusion. This late stage event is not ubiquitous for all infected cells in a population, and escalates in prevalence and extent throughout the developmental cycle of Chlamydia, culminating with their exit from the host cell by extrusion. The initiation of actin recruitment by Chlamydia appears to be novel, and may serve as an upstream determinant of the extrusion mechanism.

Effects of cystic fibrosis transmembrane conductance regulator and DeltaF508CFTR on inflammatory response, ER stress, and Ca2+ of airway epithelia

We tested whether cystic fibrosis (CF) airway epithelia have larger innate immune responses than non-CF or cystic fibrosis transmembrane conductance regulator (CFTR)-corrected cells, perhaps resulting from ER stress due to retention of DeltaF508CFTR in the endoplasmic reticulum (ER) and activation of cytosolic Ca(2+) (Ca(i)) and nuclear factor (NF)-kappaB signaling. Adenovirus infections of a human CF (DeltaF508/DeltaF508) nasal cell line (CF15) provided isogenic comparisons of wild-type (wt) CFTR and DeltaF508CFTR. In the absence of bacteria, there were no or only small differences among CF15, CF15-lacZ (beta-galactosidase-expressing), CF15-wtCFTR (wtCFTR-corrected), and CF15-DeltaF508CFTR (to test ER retention of DeltaF508CFTR) cells in NF-kappaB activity, interleukin (IL)-8 secretion, Ca(i) responses, and ER stress. Non-CF and CF primary cultures of human bronchial epithelial cells (HBE) secreted IL-8 equivalently. Upon infection with Pseudomonas aeruginosa (PA) or flagellin (key activator for airway epithelia), CF15, CF15-lacZ, CF15-wtCFTR, and CF15DeltaF508CFTR cells exhibited equal PA binding, NF-kappaB activity, and IL-8 secretion; cells also responded similarly to flagellin when both CFTR (forskolin) and Ca(i) signaling (ATP) were activated. CF and non-CF HBE responded similarly to flagellin + ATP. Thapsigargin (Tg, releases ER Ca(2+)) increased flagellin-stimulated NF-kappaB and ER stress similarly in all cells. We conclude that ER stress, Ca(i), and NF-kappaB signaling and IL-8 secretion were unaffected by wt- or DeltaF508CFTR in control and during exposure to PA, flagellin, flagellin + ATP, or flagellin + ATP + forskolin. Tg, but not wt- or DeltaF508CFTR, triggered ER stress. Previous measurements showing hyperinflammatory responses in CF airway epithelia may have resulted from cell-specific, rather than CFTR- or DeltaF508CFTR-specific effects.

Mechanisms of host cell exit by the intracellular bacterium Chlamydia

The mechanisms that mediate the release of intracellular bacteria from cells are poorly understood, particularly for those that live within a cellular vacuole. The release pathway of the obligate intracellular bacterium Chlamydia from cells is unknown. Using a GFP-based approach to visualize chlamydial inclusions within cells by live fluorescence videomicroscopy, we identified that Chlamydia release occurred by two mutually exclusive pathways. The first, lysis, consisted of an ordered sequence of membrane permeabilizations: inclusion, nucleus and plasma membrane rupture. Treatment with protease inhibitors abolished inclusion lysis. Intracellular calcium signaling was shown to be important for plasma membrane breakdown. The second release pathway was a packaged release mechanism, called extrusion. This slow process resulted in a pinching of the inclusion, protrusion out of the cell within a cell membrane compartment, and ultimately detachment from the cell. Treatment of Chlamydia-infected cells with specific pharmacological inhibitors of cellular factors demonstrated that extrusion required actin polymerization, neuronal Wiskott-Aldrich syndrome protein, myosin II and Rho GTPase. The participation of Rho was unique in that it functioned late in extrusion. The dual nature of release characterized for Chlamydia has not been observed as a strategy for intracellular bacteria.

Mechanisms of Chlamydia trachomatis entry into nonphagocytic cells

The mechanisms of entry for the obligate intracellular bacterium C. trachomatis were examined by functional disruption of proteins essential for various modes of entry. RNA interference was used to disrupt proteins with established roles in clathrin-mediated endocytosis (clathrin heavy chain, dynamin-2, heat shock 70-kDa protein 8, Arp2, cortactin, and calmodulin), caveola-mediated endocytosis (caveolin-1, dynamin-2, Arp2, NSF, and annexin II), phagocytosis (RhoA, dynamin-2, Rac1, and Arp2), and macropinocytosis (Pak1, Rac1, and Arp2). Comparative quantitative PCR analysis was performed on small interfering RNA-transfected HeLa cells to accurately determine the extent of C. trachomatis entry after these treatments. Key structural and regulatory factors associated with clathrin-mediated endocytosis were found to be involved in Chlamydia entry, whereas those for caveola-mediated endocytosis, phagocytosis, and macropinocytosis were not. Thus, clathrin and its coordinate accessory factors were required for entry of C. trachomatis, although additional, uncharacterized mechanisms are also utilized.

Cystic fibrosis airway epithelial cell polarity and bacterial flagellin determine host response toPseudomonas aeruginosa

The role of epithelial polarity and bacterial factors in the control of the innate immune response of airway epithelial cells to Pseudomonas aeruginosa PAK was investigated using a human, nasal cystic fibrosis (DeltaF508/DeltaF508) epithelial cell line CF15 grown as confluent layers on permeable supports. Addition of PAK to the basal surface of CF15 layers caused significant expression changes in 1525 different genes (out of 12 625 examined), including the cytokines IL-6, IL-8, IL-1beta and TNF-alpha, as well as genes associated with leucocyte adhesion, antibacterial factors, and NF-kappaB signalling. Confocal microscopy showed that nuclear migration of NF-kappaB in all CF15 cells was preceded by PAK binding to the basal and lateral surfaces of some cells. Addition of PAK to the apical surface of CF15 monolayers elicited changes in expression of only 602 genes, including 256 not affected during basolateral PAK exposure. Over time, cytokine expression during apical PAK was similar to that exhibited by basal PAK, but the magnitudes during apical treatment were much smaller with little/no nuclear migration of NF-kappaB in CF15 cells. Furthermore, these responses depended on the presence of flagellin, but not pili on the bacteria. Thus, P. aeruginosa triggered a strong innate immune response that depended on the apical versus basolateral polarity of CF15 cells and the presence of flagellin on the bacteria.

Intracellular distribution and functional importance of vesicle-associated membrane protein 2 in gastric parietal cells

BACKGROUND & AIMS

Acid secretion by parietal cells involves secretagogue-dependent recycling of the H+-K+-ATPase. Proteins called soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) have been implicated as participants in membrane trafficking, docking, and fusing processes. Here we studied the intracellular distribution and functional importance of one SNARE protein, vesicle associated membrane protein-2 (VAMP-2), in gastric parietal cells.

METHODS

Using an adenoviral recombinant expression system encoding VAMP-2 (synaptobrevin-2) fused to the green fluorescent protein (GFP), we expressed the GFP-VAMP-2 protein in primary cultures of rabbit parietal cells, which enables us to visualize the dynamics of GFP-VAMP-2 in a variety of functional states by fluorescence microscopy. To ascertain the function of VAMP-2 in parietal cell activation, streptolysin-O permeabilized gastric glands were treated with tetanus toxin, a potent and preferential protease for VAMP-2, and acid secretion was measured.

RESULTS

In resting parietal cells GFP was detected throughout the cytoplasm in a pattern of distribution that was very similar to that of H+-K+-ATPase. After stimulation, we observed that the GFP-VAMP-2 translocated to the apical plasma membrane along with the H+-K+-ATPase. A relatively high degree of co-localization was detected between GFP-VAMP-2 and H+-K+-ATPase. Tetanus toxin inhibited cAMP/ATP-stimulated acid secretion by about 45% in permeabilized gastric glands with a concomitant reduction in the level of immunoreactive VAMP-2.

CONCLUSIONS

Adenovirus-based GFP reporter fusion proteins can be used to efficiently study the functional dynamics of SNAREs. VAMP-2 is associated with tubulovesicle membranes in the parietal cell and plays a role in stimulation-associated membrane recruitment and acid secretion.

ENaC- and CFTR-dependent ion and fluid transport in mammary epithelia

Mammary epithelial 31EG4 cells (MEC) were grown as monolayers on filters to analyze the apical membrane mechanisms that help mediate ion and fluid transport across the epithelium. RT-PCR showed the presence of cystic fibrosis transmembrane conductance regulator (CFTR) and epithelial Na(+) channel (ENaC) message, and immunomicroscopy showed apical membrane staining for both proteins. CFTR was also localized to the apical membrane of native human mammary duct epithelium. In control conditions, mean values of transepithelial potential (apical-side negative) and resistance (R(T)) are -5.9 mV and 829 Omega x cm(2), respectively. The apical membrane potential (V(A)) is -40.7 mV, and the mean ratio of apical to basolateral membrane resistance (R(A)/R(B)) is 2.8. Apical amiloride hyperpolarized V(A) by 19.7 mV and tripled R(A)/R(B). A cAMP-elevating cocktail depolarized V(A) by 17.6 mV, decreased R(A)/R(B) by 60%, increased short-circuit current by 6 microA/cm(2), decreased R(T) by 155 Omega x cm(2), and largely eliminated responses to amiloride. Whole cell patch-clamp measurements demonstrated amiloride-inhibited Na(+) currents [linear current-voltage (I-V) relation] and forskolin-stimulated Cl(-) currents (linear I-V relation). A capacitance probe method showed that in the control state, MEC monolayers either absorbed or secreted fluid (2--4 microl x cm(-2) x h(-1)). Fluid secretion was stimulated either by activating CFTR (cAMP) or blocking ENaC (amiloride). These data plus equivalent circuit analysis showed that 1) fluid absorption across MEC is mediated by Na(+) transport via apical membrane ENaC, and fluid secretion is mediated, in part, by Cl(-) transport via apical CFTR; 2) in both cases, appropriate counterions move through tight junctions to maintain electroneutrality; and 3) interactions among CFTR, ENaC, and tight junctions allow MEC to either absorb or secrete fluid and, in situ, may help control luminal [Na(+)] and [Cl(-)].