Chlamydia trachomatis infection induces cleavage of the mitotic cyclin B1

In Search of a Mechanistic Link between Chlamydia trachomatis-Induced Cellular Pathophysiology and Oncogenesis

Centrosome duplication and cell cycle progression are essential cellular processes that must be tightly controlled to ensure cellular integrity. Despite their complex regulatory mechanisms, microbial pathogens have evolved sophisticated strategies to co-opt these processes to promote infection. While misregulation of these processes can greatly benefit the pathogen, the consequences to the host cell can be devastating. During infection, the obligate intracellular pathogen Chlamydia trachomatis induces gross cellular abnormalities, including supernumerary centrosomes, multipolar spindles, and defects in cytokinesis. While these observations were made over 15 years ago, identification of the bacterial factors responsible has been elusive due to the genetic intractability of Chlamydia. Recent advances in techniques of genetic manipulation now allows for the direct linking of bacterial virulence factors to manipulation of centrosome duplication and cell cycle progression. In this review, we discuss the impact, both immediate and downstream, of C. trachomatis infection on the host cell cycle regulatory apparatus and centrosome replication. We highlight links between C. trachomatis infection and cervical and ovarian cancers and speculate whether perturbations of the cell cycle and centrosome are sufficient to initiate cellular transformation. We also explore the biological mechanisms employed by Inc proteins and other secreted effector proteins implicated in the perturbation of these host cell pathways. Future work is needed to better understand the nuances of each effector's mechanism and their collective impact on Chlamydia's ability to induce host cellular abnormalities.

Deregulation of the cyclin-dependent kinase inhibitor p27 as a putative candidate for transformation in Chlamydia trachomatis infected mesenchymal stem cells

Purpose

Several pathological conditions might cause the degradation of the cyclin-dependent kinase inhibitor (CKI) p27 and cell cycle arrest at the G1 phase, including cancers and infections. Chlamydia trachomatis (Ctr), as an obligatory intracellular pathogen, has been found to alter the fate of the cell from different aspects. In this study, we aimed to investigate the effect of Ctr infection on the expression of the important cell cycle regularity protein p27 in mesenchymal stem cells (MSCs).

Methods

Isolation of MSCs from healthy human fallopian tube was confirmed by detection of the stemness markers Sox2, Nanog and Oct4 and the surface markers CD44, CD73 and CD90 by Western blotting and fluorescence-activated cell sorting analysis. The expression of p27 was downregulated at the protein level upon Ctr D infection measured by Real-Time Quantitative Reverse Transcription PCR (qRT-PCR), IF and Western blotting. Recovery of p27 in Ctr D-infected MSCs was achieved by treatment with difluoromethylornithine (DFMO). Ctr D infected MSCs were able to produce colonies in anchorage-independent soft agar assay.

Conclusion

Ctr D infection was able to downregulate the expression of the important cell cycle regulator protein p27, which will be considered a putative candidate for transformation in Ctr D infected MSCs.

Aberrant gene expression of superoxide dismutases in Chlamydia trachomatis-infected recurrent spontaneous aborters

Study aimed to characterize the expression of antioxidant genes SOD1 and SOD2 in Chlamydia trachomatis-induced recurrent spontaneous aborters and further determine their role by in silico analysis. First void urine was collected from 130 non-pregnant women with history of recurrent spontaneous abortion (RSA) (Group I) and 130 non-pregnant women (Group II; control) attending Obstetrics and Gynecology Department, SJH, New Delhi, India. C. trachomatis detection was performed by conventional PCR in urine. Gene expression of SOD1 and SOD2 was performed by quantitative real-time PCR. Further, its interacting partners were studied by in silico analysis. 22 patients were positive for C. trachomatis in Group I. Significant upregulation was observed for SOD2 gene in C. trachomatis-infected RSA patients while SOD1 was found to be downregulated. Increased concentration of oxidative stress biomarkers 8-hydroxyguanosine and 8-isoprostane was found in C. trachomatis-infected RSA patients. Protein–protein interaction (PPI) of SOD proteins and its interacting partners viz.; CCS, GPX1, GPX2, GPX3, GPX4, GPX5, GPX7, GPX8, CAT, PRDX1, TXN, SIRT3, FOXO3, and AKT1 were found to be involved in MAPK, p53 and foxo signaling pathways. Molecular pathways involved in association with SODs indicate reactive oxygen species (ROS) detoxification, apoptotic pathways and cell cycle regulation. Overall data revealed alleviated levels of SOD2 gene and decreased expression of SOD1 gene in response to C. trachomatis-infection leading to production of oxidative stress and RSA.

Early Transcriptional Landscapes of Chlamydia trachomatis-Infected Epithelial Cells at Single Cell Resolution

Chlamydia are Gram-negative obligate intracellular bacterial pathogens responsible for a variety of disease in humans and animals worldwide. Chlamydia trachomatis causes trachoma in disadvantaged populations, and is the most common bacterial sexually transmitted infection in humans, causing reproductive tract disease. Antibiotic therapy successfully treats diagnosed chlamydial infections, however asymptomatic infections are common. High-throughput transcriptomic approaches have explored chlamydial gene expression and infected host cell gene expression. However, these were performed on large cell populations, averaging gene expression profiles across all cells sampled and potentially obscuring biologically relevant subsets of cells. We generated a pilot dataset, applying single cell RNA-Seq (scRNA-Seq) to C. trachomatis infected and mock-infected epithelial cells to assess the utility, pitfalls and challenges of single cell approaches applied to chlamydial biology, and to potentially identify early host cell biomarkers of chlamydial infection. Two hundred sixty-four time-matched C. trachomatis-infected and mock-infected HEp-2 cells were collected and subjected to scRNA-Seq. After quality control, 200 cells were retained for analysis. Two distinct clusters distinguished 3-h cells from 6- and 12-h. Pseudotime analysis identified a possible infection-specific cellular trajectory for Chlamydia-infected cells, while differential expression analyses found temporal expression of metallothioneins and genes involved with cell cycle regulation, innate immune responses, cytoskeletal components, lipid biosynthesis and cellular stress. We find that changes to the host cell transcriptome at early times of C. trachomatis infection are readily discernible by scRNA-Seq, supporting the utility of single cell approaches to identify host cell biomarkers of chlamydial infection, and to further deconvolute the complex host response to infection.

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.

Chlamydia trachomatis Inclusion Disrupts Host Cell Cytokinesis to Enhance Its Growth in Multinuclear Cells

Chlamydia trachomatis, the leading cause of bacterial sexually transmitted infections, disrupts cytokinesis and causes significant multinucleation in host cells. Here, we demonstrate that multinuclear cells that result from unsuccessful cell division contain significantly higher Golgi content, an important source of lipids for chlamydiae. Using immunofluorescence and fluorescent live cell imaging, we show that C. trachomatis in multinuclear cells indeed intercept Golgi-derived lipid faster than in mononuclear cells. Moreover, multinuclear cells enhance C. trachomatis inclusion growth and infectious particle formation. Together, these results indicate that C. trachomatis robustly position inclusions to the cell equator to disrupt host cell division in order to acquire host Golgi-derived lipids more quickly in multinucleated progeny cells.

Conjunctival fibrosis and the innate barriers to Chlamydia trachomatis intracellular infection: a genome wide association study

Chlamydia trachomatis causes both trachoma and sexually transmitted infections. These diseases have similar pathology and potentially similar genetic predisposing factors. We aimed to identify polymorphisms and pathways associated with pathological sequelae of ocular Chlamydia trachomatis infections in The Gambia. We report a discovery phase genome-wide association study (GWAS) of scarring trachoma (1090 cases, 1531 controls) that identified 27 SNPs with strong, but not genome-wide significant, association with disease (5 × 10⁻⁶ > P > 5 × 10⁻⁸). The most strongly associated SNP (rs111513399, P = 5.38 × 10⁻⁷) fell within a gene (PREX2) with homology to factors known to facilitate chlamydial entry to the host cell. Pathway analysis of GWAS data was significantly enriched for mitotic cell cycle processes (P = 0.001), the immune response (P = 0.00001) and for multiple cell surface receptor signalling pathways. New analyses of published transcriptome data sets from Gambia, Tanzania and Ethiopia also revealed that the same cell cycle and immune response pathways were enriched at the transcriptional level in various disease states. Although unconfirmed, the data suggest that genetic associations with chlamydial scarring disease may be focussed on processes relating to the immune response, the host cell cycle and cell surface receptor signalling.

Chlamydia trachomatis-induced alterations in the host cell proteome are required for intracellular growth

Intracellular pathogens directly alter host cells in order to replicate and survive. While infection-induced changes in host transcription can be readily assessed, posttranscriptional alterations are more difficult to catalog. We applied the global protein stability (GPS) platform, which assesses protein stability based on relative changes in an adjoining fluorescent tag, to identify changes in the host proteome following infection with the obligate intracellular bacteria Chlamydia trachomatis. Our results indicate that C. trachomatis profoundly remodels the host proteome independently of changes in transcription. Additionally, C. trachomatis replication depends on a subset of altered proteins, such as Pin1 and Men1, that regulate the host transcription factor AP-1 controlling host inflammation, stress, and cell survival. Furthermore, AP-1-dependent transcription is activated during infection and required for efficient Chlamydia growth. In summary, this experimental approach revealed that C. trachomatis broadly alters host proteins and can be applied to examine host-pathogen interactions and develop host-based therapeutics.

CPAF: a Chlamydial protease in search of an authentic substrate

Bacteria in the genus Chlamydia are major human pathogens that cause an intracellular infection. A chlamydial protease, CPAF, has been proposed as an important virulence factor that cleaves or degrades at least 16 host proteins, thereby altering multiple cellular processes. We examined 11 published CPAF substrates and found that there was no detectable proteolysis when CPAF activity was inhibited during cell processing. We show that the reported proteolysis of these putative CPAF substrates was due to enzymatic activity in cell lysates rather than in intact cells. Nevertheless, Chlamydia-infected cells displayed Chlamydia-host interactions, such as Golgi reorganization, apoptosis resistance, and host cytoskeletal remodeling, that have been attributed to CPAF-dependent proteolysis of host proteins. Our findings suggest that other mechanisms may be responsible for these Chlamydia-host interactions, and raise concerns about all published CPAF substrates and the proposed roles of CPAF in chlamydial pathogenesis.

Chlamydia are bacteria that invade eukaryotic host cells and live within a membrane-bound compartment called the chlamydial inclusion. Growth and survival of these important human and animal pathogens depends on extensive interactions with the host cell, which allow chlamydiae to acquire critical nutrients and to avoid host anti-microbial defenses. Chlamydiae are proposed to cause many of these host-pathogen interactions through the cleavage or degradation of host proteins by the chlamydial protease CPAF, which is secreted into the host cytoplasm. Here, we raise questions about the proposed roles of this virulence factor during infection, as well as its published substrates. We found that there was no detectable cleavage or degradation of 11 previously reported CPAF substrates in Chlamydia-infected cells and that CPAF-mediated proteolysis of these host proteins occurs during cell harvest and lysis. However, we still observed host-pathogen interactions previously attributed to CPAF proteolysis of these proteins, suggesting that Chlamydia is likely to cause these effects on the host cell through other mechanisms. Our findings call for a re-evaluation of all published CPAF substrates as well as the proposed roles of this protease in chlamydial pathogenesis.

Chlamydial infection induces host cytokinesis failure at abscission

Chlamydia trachomatis is an obligate intracellular bacteria and the infectious agent responsible for the sexually transmitted disease Chlamydia. Infection with Chlamydia can lead to serious health sequelae such as pelvic inflammatory disease and reproductive tract scarring contributing to infertility and ectopic pregnancies. Additionally, chlamydial infections have been epidemiologically linked to cervical cancer in patients with a prior human papilomavirus (HPV) infection. Chlamydial infection of cultured cells causes multinucleation, a potential pathway for chromosomal instability. Two mechanisms that are known to initiate multinucleation are cell fusion and cytokinesis failure. This study demonstrates that multinucleation of the host cell by Chlamydia is entirely due to cytokinesis failure. Moreover, cytokinesis failure is due in part to the chlamydial effector CPAF acting as an anaphase promoting complex mimic causing cells to exit mitosis with unaligned and unattached chromosomes. These lagging and missegregated chromosomes inhibit cytokinesis by blocking abscission, the final stage of cytokinesis.

The Chlamydia effector chlamydial outer protein N (CopN) sequesters tubulin and prevents microtubule assembly

Chlamydia species are obligate intracellular pathogens that utilize a type three secretion system to manipulate host cell processes. Genetic manipulations are currently not possible in Chlamydia, necessitating study of effector proteins in heterologous expression systems and severely complicating efforts to relate molecular strategies used by Chlamydia to the biochemical activities of effector proteins. CopN is a chlamydial type three secretion effector that is essential for virulence. Heterologous expression of CopN in cells results in loss of microtubule spindles and metaphase plate formation and causes mitotic arrest. CopN is a multidomain protein with similarity to type three secretion system "plug" proteins from other organisms but has functionally diverged such that it also functions as an effector protein. We show that CopN binds directly to αβ-tubulin but not to microtubules (MTs). Furthermore, CopN inhibits tubulin polymerization by sequestering free αβ-tubulin, similar to one of the mechanisms utilized by stathmin. Although CopN and stathmin share no detectable sequence identity, both influence MT formation by sequestration of αβ-tubulin. CopN displaces stathmin from preformed stathmin-tubulin complexes, indicating that the proteins bind overlapping sites on tubulin. CopN is the first bacterial effector shown to disrupt MT formation directly. This recognition affords a mechanistic understanding of a strategy Chlamydia species use to manipulate the host cell cycle.

Chlamydia trachomatis infection causes mitotic spindle pole defects independently from its effects on centrosome amplification

Chlamydiae are Gram negative, obligate intracellular bacteria, and Chlamydia trachomatis is the etiologic agent of the most commonly reported sexually transmitted disease in the United States. Chlamydiae undergo a biphasic life cycle that takes place inside a parasitophorous vacuole termed an inclusion. Chlamydial infections have been epidemiologically linked to cervical cancer in patients previously infected by human papillomavirus (HPV). The inclusion associates very closely with host cell centrosomes, and this association is dependent upon the host motor protein dynein. We have previously reported that this interaction induces supernumerary centrosomes in infected cells, leading to multipolar mitotic spindles and inhibiting accurate chromosome segregation. Our findings demonstrate that chlamydial infection causes mitotic spindle defects independently of its effects on centrosome amplification. We show that chlamydial infection increases centrosome spread and inhibits the spindle assembly checkpoint delay to disrupt centrosome clustering. These data suggest that chlamydial infection exacerbates the consequences of centrosome amplification by inhibiting the cells' ability to suppress the effects of these defects on mitotic spindle organization. We hypothesize that these combined effects on mitotic spindle architecture identifies a possible mechanism for Chlamydia as a cofactor in cervical cancer formation.

Chlamydia trachomatis secretion of proteases for manipulating host signaling pathways

The human pathogen Chlamydia trachomatis secretes numerous effectors into host cells in order to successfully establish and complete the intracellular growth cycle. Three C. trachomatis proteases [chlamydial proteasome/protease-like activity factor (CPAF), tail-specific protease (Tsp), and chlamydial high temperature requirement protein A (cHtrA)] have been localized in the cytosol of the infected cells either by direct immunofluorescence visualization or functional implication. Both CPAF and Tsp have been found to play important roles in C. trachomatis interactions with host cells although the cellular targets of cHtrA have not been identified. All three proteases contain a putative N-terminal signal sequence, suggesting that they may be secreted via a sec-dependent pathway. However, these proteases are also found in chlamydial organism-free vesicles in the lumen of the chlamydial inclusions before they are secreted into host cell cytosol, suggesting that these proteases may first be translocated into the periplasmic region via a sec-dependent pathway and then exported outside of the organisms via an outer membrane vesicles (OMVs) budding mechanism. The vesiculized proteases in the inclusion lumen can finally enter host cell cytosol via vesicle fusing with or passing through the inclusion membrane. Continuing identification and characterization of the C. trachomatis-secreted proteins (CtSPs) will not only promote our understanding of C. trachomatis pathogenic mechanisms but also allow us to gain novel insights into the OMV pathway, a well-known mechanism used by bacteria to export virulence factors although its mechanism remains elusive.

Functional interaction between type III-secreted protein IncA of Chlamydophila psittaci and human G3BP1

Chlamydophila (Cp.) psittaci, the causative agent of psittacosis in birds and humans, is the most important zoonotic pathogen of the family Chlamydiaceae. These obligate intracellular bacteria are distinguished by a unique biphasic developmental cycle, which includes proliferation in a membrane-bound compartment termed inclusion. All Chlamydiaceae spp. possess a coding capacity for core components of a Type III secretion apparatus, which mediates specific delivery of anti-host effector proteins either into the chlamydial inclusion membrane or into the cytoplasm of target eukaryotic cells. Here we describe the interaction between Type III-secreted protein IncA of Cp. psittaci and host protein G3BP1 in a yeast two-hybrid system. In GST-pull down and co-immunoprecipitation experiments both in vitro and in vivo interaction between full-length IncA and G3BP1 were shown. Using fluorescence microscopy, the localization of G3BP1 near the inclusion membrane of Cp. psittaci-infected Hep-2 cells was demonstrated. Notably, infection of Hep-2 cells with Cp. psittaci and overexpression of IncA in HEK293 cells led to a decrease in c-Myc protein concentration. This effect could be ascribed to the interaction between IncA and G3BP1 since overexpression of an IncA mutant construct disabled to interact with G3BP1 failed to reduce c-Myc concentration. We hypothesize that lowering the host cell c-Myc protein concentration may be part of a strategy employed by Cp. psittaci to avoid apoptosis and scale down host cell proliferation.

Killing me softly: chlamydial use of proteolysis for evading host defenses

Chlamydial infections in humans cause severe health problems, including blinding trachoma and sexually transmitted diseases. Although the involved pathogenic mechanisms remain unclear, the ability to replicate and maintain long-term residence in the infected cells seems to significantly contribute to chlamydial pathogenicity. These obligate intracellular parasites maintain a delicate balance between exploiting and protecting their host: they occupy intracellular space and acquire nutrients from the infected cells, but at the same time they have to maintain the integrity of the host cells for the completion of their intracellular growth. For this purpose, chlamydiae hijack certain signaling pathways that prevent the host cells from undergoing apoptosis induced by intracellular stress and protect the infected cells from recognition and attack by host defenses. Interestingly, one of the strategies that chlamydiae use for these purposes is the induction of limited proteolysis of host proteins, which is the main focus of this article.

Cytokinesis is blocked in mammalian cells transfected with Chlamydia trachomatis gene CT223

Background

The chlamydiae alter many aspects of host cell biology, including the division process, but the molecular biology of these alterations remains poorly characterized. Chlamydial inclusion membrane proteins (Incs) are likely candidates for direct interactions with host cell cytosolic proteins, as they are secreted to the inclusion membrane and exposed to the cytosol. The inc gene CT223 is one of a sequential set of orfs that encode or are predicted to encode Inc proteins. CT223p is localized to the inclusion membrane in all tested C. trachomatis serovars.

Results

A plasmid transfection approach was used to examine the function of the product of CT223 and other Inc proteins within uninfected mammalian cells. Fluorescence microscopy was used to demonstrate that CT223, and, to a lesser extent, adjacent inc genes, are capable of blocking host cell cytokinesis and facilitating centromere supranumeracy defects seen by others in chlamydiae-infected cells. Both phenotypes were associated with transfection of plasmids encoding the carboxy-terminal tail of CT223p, a region of the protein that is likely exposed to the cytosol in infected cells.

Conclusion

These studies suggest that certain Inc proteins block cytokinesis in C. trachomatis-infected cells. These results are consistent with the work of others showing chlamydial inhibition of host cell cytokinesis.

Cytopathicity of Chlamydia is largely reproduced by expression of a single chlamydial protease

Chlamydiae replicate in a vacuole within epithelial cells and commonly induce cell damage and a deleterious inflammatory response of unknown molecular pathogenesis. The chlamydial protease-like activity factor (CPAF) translocates from the vacuole to the cytosol, where it cleaves several cellular proteins. CPAF is synthesized as an inactive precursor that is processed and activated during infection. Here, we show that CPAF can be activated in uninfected cells by experimentally induced oligomerization, reminiscent of the activation mode of initiator caspases. CPAF activity induces proteolysis of cellular substrates including two novel targets, cyclin B1 and PARP, and indirectly results in the processing of pro-apoptotic BH3-only proteins. CPAF activation induces striking morphological changes in the cell and, later, cell death. Biochemical and ultrastructural analysis of the cell death pathway identify the mechanism of cell death as nonapoptotic. Active CPAF in uninfected human cells thus mimics many features of chlamydial infection, implicating CPAF as a major factor of chlamydial pathogenicity, Chlamydia-associated cell damage, and inflammation.

The host adherens junction molecule nectin-1 is downregulated in Chlamydia trachomatis-infected genital epithelial cells

Nectin-1, a member of the immunoglobulin superfamily, is a Ca(2+)-independent cell adhesion protein implicated in the organization of E-cadherin-based adherens junctions (AJs) and claudin-based tight junctions (TJs) in epithelial cells. Nectin-1 also regulates cell-cell adhesion and cell polarization in a Cdc42- and Rac-dependent manner. Western blot analyses demonstrated that accumulation of host nectin-1 is decreased by 85 % at 48 hours post-infection (h.p.i.) in Chlamydia trachomatis serovar E-infected HeLa cells. Time-course experiments demonstrated that this decrease was sustained to 60 h.p.i. Nectin-1 downregulation in C. trachomatis-infected cells was prevented by both chloramphenicol exposure and prior inactivation of the chlamydiae with UV light, demonstrating that active C. trachomatis replication was required. Penicillin G-exposure studies demonstrated that nectin-1 accumulation was also altered during persistent infection. Finally, RT-PCR analyses indicated that chlamydial infection did not alter accumulation of any nectin-1 transcripts, demonstrating that nectin-1 accumulation is reduced at a post-transcriptional level. Intesrestingly, N-cadherin-dependent cell-cell junctions can be disrupted by C. trachomatis infection, as reported by Prozialeck et al. (2002). Because interaction of nectin molecules on adjacent cells is essential for AJ formation, these data suggest that C. trachomatis may disrupt AJs, at least in part, by diminishing nectin-1 accumulation. Notably, release of chlamydiae-infected epithelial cells has been observed both in vitro from polarized monolayers and in vivo from tissues, suggesting that chlamydia-modulated downregulation of adhesion molecules and the subsequent disruption of host cell adherence may be involved in chlamydial dissemination or pathogenesis.

Human GCIP interacts with CT847, a novel Chlamydia trachomatis type III secretion substrate, and is degraded in a tissue-culture infection model

The obligate intracellular bacterium Chlamydia trachomatis occupies a parasitophorous vacuole and employs a type III secretion mechanism to translocate host-interactive proteins. These proteins most likely contribute to pathogenesis through modulation of host cell mechanisms crucial for the establishment and maintenance of a permissive intracellular environment. Using a surrogate Yersinia type III secretion system (T3SS), we have identified the conserved gene product CT847 as a chlamydial T3SS substrate. Yeast two-hybrid studies using CT847 as bait to screen a HeLa cell cDNA library identified an interaction with mammalian Grap2 cyclin D-interacting protein (GCIP). Immunoblot analyses of C. trachomatis-infected HeLa cells showed that GCIP levels begin to decrease (as compared with mock-infected HeLa cells) between 8 h and 12 h post infection. GCIP was virtually undetectable in 24 h time point material. This decrease was inhibited by proteasome inhibitors lactacystin and MG-132, and the T3SS inhibitor Compound 1. CT847 was detectible in purified reticulate body but not elementary body lysates, and reverse transcription polymerase chain reaction (RT-PCR) expression analyses indicate a mid-cycle expression pattern. Both of these findings are consistent with CT847 contributing to the observed effect on GCIP. Given the established roles of GCIP, we believe that we have discovered a novel C. trachomatis antihost protein whose activity is relevant to chlamydial pathogenesis.