Impact of Leishmania infection on host macrophage nuclear physiology and nucleopore complex integrity

The protease GP63 is an important virulence factor of Leishmania parasites. We previously showed that GP63 reaches the perinuclear area of host macrophages and that it directly modifies nuclear translocation of the transcription factors NF-κB and AP-1. Here we describe for the first time, using molecular biology and in-depth proteomic analyses, that GP63 alters the host macrophage nuclear envelope, and impacts on nuclear processes. Our results suggest that GP63 does not appear to use a classical nuclear localization signal common between Leishmania species for import, but degrades nucleoporins, and is responsible for nuclear transport alterations. In the nucleoplasm, GP63 activity accounts for the degradation and mislocalization of proteins involved amongst others in gene expression and in translation. Collectively, our data indicates that Leishmania infection strongly affects nuclear physiology, suggesting that targeting of nuclear physiology may be a strategy beneficial for virulent Leishmania parasites.

Unicellular parasites of the genus Leishmania are the causative agent of leishmaniasis, a disease affecting 12 million people worldwide, mainly in tropical and subtropical regions of the developing world. They have evolved strategies to circumvent cellular defense mechanisms favouring their survival. This includes the cleavage and activation of proteins and the subsequent block of signals within the host cells. In this study we discovered that a Leishmania virulence factor, GP63, is able to reach host cell nuclei and affect protein transport from and into the nucleus. Through the analysis of the protein content of nuclei after parasite infection we revealed that Leishmania, predominantly through the protein cleaving enzyme GP63, can alter several processes within the nucleus, amongst others mechanisms associated with gene expression and nucleic acid metabolism. Thus, we here introduce a novel strategy of how Leishmania parasites may overcome host cell defense and ensure their own survival.

Targeting of a chlamydial protease impedes intracellular bacterial growth

Chlamydiae are obligate intracellular bacteria that propagate in a cytosolic vacuole. Recent work has shown that growth of Chlamydia induces the fragmentation of the Golgi apparatus (GA) into ministacks, which facilitates the acquisition of host lipids into the growing inclusion. GA fragmentation results from infection-associated cleavage of the integral GA protein, golgin-84. Golgin-84-cleavage, GA fragmentation and growth of Chlamydia trachomatis can be blocked by the peptide inhibitor WEHD-fmk. Here we identify the bacterial protease chlamydial protease-like activity factor (CPAF) as the factor mediating cleavage of golgin-84 and as the target of WEHD-fmk-inhibition. WEHD-fmk blocked cleavage of golgin-84 as well as cleavage of known CPAF targets during infection with C. trachomatis and C. pneumoniae. The same effect was seen when active CPAF was expressed in non-infected cells and in a cell-free system. Ectopic expression of active CPAF in non-infected cells was sufficient for GA fragmentation. GA fragmentation required the small GTPases Rab6 and Rab11 downstream of CPAF-activity. These results define CPAF as the first protein that is essential for replication of Chlamydia. We suggest that this role makes CPAF a potential anti-infective therapeutic target.

Chlamydiae are bacteria that replicate only inside host (for instance human) cells and that are frequent agents of human disease, in particular sexually transmitted disease. Chlamydia lives in a vacuole inside the cell, surrounded by a lipid membrane, and must acquire nutrients and other factors from the host cell for its replication and for the growth of the vacuole. Recent results show that for this, Chlamydia relies on its ability to induce the loss of an individual protein of the Golgi apparatus (a cellular structure that sorts materials for transport in the cell) called golgin-84. In this work we find that Chlamydia does this using its protein-cleaving enzyme CPAF (which is made by Chlamydia and transported from the vacuole into the cell). CPAF cleaves golgin-84 and thereby induces changes in the Golgi apparatus that are linked to the acquisition of some cellular material by Chlamydia. We further show that a synthetic inhibitor, which was recently found to block chlamydial growth, does that by inhibiting CPAF. CPAF therefore seems necessary for chlamydial growth and blocking CPAF may be a therapeutic strategy against infections with Chlamydia.

Raman microspectroscopy reveals long-term extracellular activity of Chlamydiae

The phylum Chlamydiae consists exclusively of obligate intracellular bacteria. Some of them are formidable pathogens of humans, while others occur as symbionts of amoebae. These genetically intractable bacteria possess a developmental cycle consisting of replicative reticulate bodies and infectious elementary bodies, which are believed to be physiologically inactive. Confocal Raman microspectroscopy was applied to differentiate between reticulate bodies and elementary bodies of Protochlamydia amoebophila and to demonstrate in situ the labelling of this amoeba symbiont after addition of isotope-labelled phenylalanine. Unexpectedly, uptake of this amino acid was also observed for both developmental stages for up to 3 weeks, if incubated extracellularly with labelled phenylalanine, and P. amoebophila remained infective during this period. Furthermore, P. amoebophila energizes its membrane and performs protein synthesis outside of its host. Importantly, amino acid uptake and protein synthesis after extended extracellular incubation could also be demonstrated for the human pathogen Chlamydia trachomatis, which synthesizes stress-related proteins under these conditions as shown by 2-D gel electrophoresis and MALDI-TOF/TOF mass spectrometry. These findings change our perception of chlamydial biology and reveal that host-free analyses possess a previously not recognized potential for direct experimental access to these elusive microorganisms.

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.

Chlamydia trachomatis can protect host cells against apoptosis in the absence of cellular Inhibitor of Apoptosis Proteins and Mcl-1

Infection with Chlamydia protects mammalian host cells against apoptosis. Hypotheses have been proposed to explain this molecularly, including the up-regulation of host anti-apoptotic proteins such as cellular Inhibitor of Apoptosis Protein (IAP) 2 and the Bcl-2 protein Mcl-1. To test for the importance of these proteins, we used mouse embryonic fibroblasts from gene-targeted mice that were deficient in cIAP1, cIAP2, cIAP1/cIAP2, XIAP, or Mcl-1. Infection with Chlamydia trachomatis protected all cells equally well against apoptosis, which was induced either with tumour necrosis factor/cycloheximide (IAP-knock-out cells) or staurosporine (Mcl-1-knock-out). Therefore, these cellular anti-apoptotic proteins are not essential for apoptosis-protection by C. trachomatis.

Nitrous Oxide Produced by the Catalytic Oxidation of Organic Nitrogen Compounds

Nitrous oxide is produced by the catalytic oxidation of organic nitrogen compounds of several distinct structural types with Hopcalite catalyst at a space velocity of 21,000 hours(-1) and at temperatures near 300 degrees C.