Optimal development of Chlamydophila psittaci in L929 fibroblast and BGM epithelial cells requires the participation of microfilaments and microtubule-motor proteins

Chlamydia psittaci: update on an underestimated zoonotic agent

Chlamydia (C.) psittaci is an economically relevant pathogen in poultry and pet birds, where it causes psittacosis/ornithosis, and also a human pathogen causing atypical pneumonia after zoonotic transmission. Despite its well-documented prevalence, the agent has received less attention by researchers than other Chlamydia spp. in the last decades. In the present paper, we review recently published data on C. psittaci infection and attempt to single out characteristic features distinguishing it from related chlamydial agents. It is remarkable that C. psittaci is particularly efficient in disseminating in the host organism causing systemic disease, which occasionally can take a fulminant course. At the cellular level, the pathogen's broad host cell spectrum (from epithelial cells to macrophages), its rapid entry and fast replication, proficient use of intracellular transport routes to mitochondria and the Golgi apparatus, the pronounced physical association of chlamydial inclusions with energy-providing cell compartments, as well as the subversive regulation of host cell survival during productive and persistent states facilitate the characteristic efficient growth and successful host-to-host spread of C. psittaci. At the molecular level, the pathogen was shown to upregulate essential chlamydial genes when facing the host immune response. We hypothesize that this capacity, in concert with expression of specific effectors of the type III secretion system and efficient suppression of selected host defense signals, contributes to successful establishment of the infection in the host. Concerning the immunology of host-pathogen interactions, C. psittaci has been shown to distinguish itself by coping more efficiently than other chlamydiae with pro-inflammatory mediators during early host response, which can, to some extent, explain the effective evasion and adaptation strategies of this bacterium. We conclude that thorough analysis of the large number of whole-genome sequences already available will be essential to identify genetic markers of the species-specific features and trigger more in-depth studies in cellular and animal models to address such vital topics as treatment and vaccination.

Chlamydia psittaci inclusion membrane protein IncB associates with host protein Snapin

Chlamydia (C.) psittaci, the causative agent of psittacosis in birds and humans, is the most important zoonotic pathogen of the family Chlamydiaceae. During a unique developmental cycle of this obligate intracellular pathogen, the infectious elementary body gains access to the susceptible host cell, where it transforms into the replicative reticulate body. C. psittaci uses dynein motor proteins for optimal early development. Chlamydial proteins that mediate this process are unknown. Two-hybrid screening with the C. psittaci inclusion protein IncB as bait against a HeLa Yeast Two-hybrid (YTH) library revealed that the host protein Snapin interacts with IncB. Snapin is a cytoplasmic protein that plays a multivalent role in intracellular trafficking. Confocal fluorescence microscopy using an IncB-specific antibody demonstrated that IncB, Snapin, and dynein were co-localized near the inclusion of C. psittaci-infected HEp-2 cells. This co-localization was lost when Snapin was depleted by RNAi. The interaction of Snapin with both IncB and dynein has been shown in vitro and in vivo. We propose that Snapin connects chlamydial inclusions with the microtubule network by interacting with both IncB and dynein.

Cytoskeleton and motor proteins are required for the transcytosis of Neisseria gonorrhoeae through polarized epithelial cells

Neisseria gonorrhoeae interact with polarized T84 epithelial cells by engaging carcinoembryonic antigen-related cellular adhesion molecule (CEACAM) receptors. Adherent bacteria that are taken up by the cells are able to traverse the epithelial layer from the apical to the basal side. Herein, we demonstrate that the actin cytoskeleton of the cells is not required for the initial adherence of the bacteria, however, it is essential for invasion into and traversal through T84 cells. Furthermore, microtubule inhibitors blocked the traversal, but not the adherence and invasion of the bacteria. Inhibition of the motor activity of myosins reduced invasion and traversal, but not bacterial adherence. Immunofluorescence confocal laser scanning microscopy revealed the colocalization of the microtubule-based kinesin and dynein motors, and the actin-based motor myosin with adherent and intracellular gonococci. Transcytosis was reduced by blocking kinesin and myosin with specific antibodies. This underlines the importance of these motor proteins for the transcytosis of epithelial monolayers by N. gonorrhoeae.

Chlamydia trachomatis Causes Centrosomal Defects Resulting in Chromosomal Segregation Abnormalities

Chlamydiae traffic along microtubules to the microtubule organizing center (MTOC) to establish an intracellular niche within the host cell. Trafficking to the MTOC is dynein dependent although the activating and cargo-linking function of the dynactin complex is supplanted by unknown chlamydial protein(s). We demonstrate that once localized to the MTOC, the chlamydial inclusion maintains a tight association with cellular centrosomes. This association is sustained through mitosis and leads to a significant increase in supernumerary centrosomes, abnormal spindle poles, and chromosomal segregation defects. Chlamydial infection thus can lead to chromosome instability in cells that recover from infection.

Chlamydia trachomatis uses host cell dynein to traffic to the microtubule-organizing center in a p50 dynamitin-independent process

Chlamydiae are pathogenic obligate intracellular bacteria with a biphasic developmental cycle that involves cell types adapted for extracellular survival (elementary bodies, EBs) and intracellular multiplication (reticulate bodies, RBs). The intracellular development of chlamydiae occurs entirely within a membrane-bound vacuole termed an inclusion. Within 2 hours after entry into host cells, Chlamydia trachomatis EBs are trafficked to the perinuclear region of the host cell and remain in close proximity to the Golgi apparatus, where they begin to fuse with a subset of host vesicles containing sphingomyelin. Here, we provide evidence that chlamydial migration from the cell periphery to the peri-Golgi region resembles host cell vesicular trafficking. Chlamydiae move towards the minus end of microtubules and aggregate at the microtubule-organizing center (MTOC). In mammalian cells the most important minus-end-directed microtubule motor is cytoplasmic dynein. Microinjection of antibodies to a subunit of cytoplasmic dynein inhibited movement of chlamydiae to the MTOC, whereas microinjection of antibodies to the plus-directed microtubule motor, kinesin, had no effect. Surprisingly, overexpression of the protein p50 dynamitin, a subunit of the dynactin complex that links vesicular cargo to the dynein motor in minus directed vesicle trafficking, did not abrogate chlamydial migration even though host vesicle transport was inhibited. Nascent chlamydial inclusions did, however, colocalize with the p150(Glued) dynactin subunit, which suggests that p150(Glued) may be required for dynein activation or processivity but that the cargo-binding activity of dynactin, supplied by p50 dynamitin subunits and possibly other subunits, is not. Because chlamydial transcription and translation were required for this intracellular trafficking, chlamydial proteins modifying the cytoplasmic face of the inclusion membrane are probable candidates for proteins fulfilling this function.

Kinesin motors and disease

Kinesins are motor proteins that move cargoes such as vesicles, organelles and chromosomes along microtubules. They are best known for their role in axonal transport and in mitosis. There is a diverse family of kinesins, members of which differ in composition and functions. Roles of kinesins in diseases typically involve defective transport of cell components, transport of pathogens, or cell division.