Tim N. Mak

Proteomic identification of secreted proteins of Propionibacterium acnes

BackgroundThe anaerobic Gram-positive bacterium Propionibacterium acnes is a human skin commensal that resides preferentially within sebaceous follicles; however, it also exhibits many traits of an opportunistic pathogen, playing roles in a variety of inflammatory diseases such as acne vulgaris. To date, the underlying disease-causing mechanisms remain ill-defined and knowledge of P. acnes virulence factors remains scarce. Here, we identified proteins secreted during anaerobic cultivation of a range of skin and clinical P. acnes isolates, spanning the four known phylogenetic groups.ResultsCulture supernatant proteins of P. acnes were separated by two-dimensional electrophoresis (2-DE) and all Coomassie-stained spots were subsequently identified by MALDI mass spectrometry (MALDI-MS). A set of 20 proteins was secreted in the mid-exponential growth phase by the majority of strains tested. Functional annotation revealed that many of these common proteins possess degrading activities, including glycoside hydrolases with similarities to endoglycoceramidase, β-N-acetylglucosaminidase and muramidase; esterases such as lysophospholipase and triacylglycerol lipase; and several proteases. Other secreted factors included Christie-Atkins-Munch-Petersen (CAMP) factors, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and several hypothetical proteins, a few of which are unique to P. acnes. Strain-specific differences were apparent, mostly in the secretion of putative adhesins, whose genes exhibit variable phase variation-like sequence signatures.ConclusionsOur proteomic investigations have revealed that the P. acnes secretome harbors several proteins likely to play a role in host-tissue degradation and inflammation. Despite a large overlap between the secretomes of all four P. acnes phylotypes, distinct differences between predicted host-tissue interacting proteins were identified, providing potential insight into the differential virulence properties of P. acnes isolates. Thus, our data presents a rich resource for guiding much-needed investigations on P. acnes virulence factors and host interacting properties.

Prevalence of Propionibacterium acnes in diseased prostates and its inflammatory and transforming activity on prostate epithelial cells

Prostate cancer (PCa) is the second leading cause of male cancer deaths in the Western world. Mounting evidence has revealed that chronic inflammation can be an important initiating factor of PCa. Recent work has detected the anaerobic Gram-positive bacterium Propionibacterium acnes in cancerous prostates, but with wide-ranging detection rates. Here, using in situ immunofluorescence (ISIF), P. acnes was found in 58 out of 71 (81.7%) tested cancerous prostate tissue samples, but was absent from healthy prostate tissues (20 samples) and other cancerous tissue biopsies (59 mamma carcinoma samples). Live P. acnes bacteria were isolated from cancerous prostates and cocultured with the prostate epithelial cell line RWPE1. Microarray analysis showed that the host cell responded to P. acnes with a strong multifaceted inflammatory response. Active secretion of cytokines and chemokines, such as IL-6 and IL-8, from infected cells was confirmed. The host cell response was likely mediated by the transcriptional factors NF-κB and STAT3, which were both activated upon P. acnes infection. The P. acnes-induced host cell response also included the activation of the COX2-prostaglandin, and the plasminogen-matrix metalloproteinase pathways. Long-term exposure to P. acnes altered cell proliferation, and enabled anchorage-independent growth of infected epithelial cells, thus initiating cellular transformation. Our results suggest that P. acnes infection could be a contributing factor to the initiation or progression of PCa.

A mouse model of chronic prostatic inflammation using a human prostate cancer‐derived isolate of Propionibacterium acnes

Prostatic inflammation has been linked to a number of prostatic diseases such as benign prostatic hyperplasia (BPH), prostatitis syndromes, and prostate cancer. Major unanswered questions include what pathogenic mechanisms, such as bacterial infections, may drive the accumulation of inflammatory infiltrates in the human prostate, and how inflammation might contribute to disease. To study this potential link in an in vivo system, we developed a mouse model of long‐term bacteria‐induced chronic inflammation of the prostate using a human prostatectomy‐derived strain of Propionibacterium acnes.

Helicobacter pylori-induced modification of the histone H3 phosphorylation status in gastric epithelial cells reflects its impact on cell cycle regulation

Post-translational modifications of core histones are important components of the epigenetic landscape. Recent investigations of bacterial or toxin-induced effects on histone phosphorylation and acetylation in host cells have linked the changes to transcriptional alterations of key cellular response pathways. However, these changes may have other reasons and functional consequences. Here, we show that infection of gastric epithelial cell lines with the carcinogenic bacterium Helicobacter pylori leads to changes in histone H3 phosphorylation: type IV secretion system (T4SS)-dependent decreases of H3 phosphorylation levels at serine 10 (pH3Ser10) and threonine 3 (pH3Thr3) were observed. Immunofluorescence experiments with pH3Ser10 and cyclin B1 revealed that a H. pylori-induced transient pre-mitotic arrest was responsible for the observed reduction. This causal link was substantiated further by showing that H. pylori causes a strong decrease of the cell division cycle 25 (CDC25C) phosphatase. As a consequence, mitotic histone H3 kinases such as vaccinia-related kinase 1 (VRK1) and Aurora B were not fully activated in infected cells. We show that VRK1 activity, measured using a kinase activity assay, was reduced after H. pylori infection by approximately 40%. Moreover, over–expression of VRK1, but not Aurora B, compensated for the H. pylori-induced decrease of pH3Ser10. Rephosphorylation of H3Ser10 was IκB kinase α (IKKα)-dependent and occurred at later time points of infection. Taken together, our work highlights the impact of bacterial pathogens on host cell chromatin; this modulation reflects the subversion of key cellular processes such as cell cycle progression.

Multilocus sequence typing (MLST) analysis of Propionibacterium acnes isolates from radical prostatectomy specimens.

Inflammation is commonly observed in radical prostatectomy specimens, and evidence suggests that inflammation may contribute to prostate carcinogenesis. Multiple microorganisms have been implicated in serving as a stimulus for prostatic inflammation. The pro‐inflammatory anaerobe, Propionibacterium acnes, is ubiquitously found on human skin and is associated with the skin disease acne vulgaris. Recent studies have shown that P. acnes can be detected in prostatectomy specimens by bacterial culture or by culture‐independent molecular techniques.

Propionibacterium acnes host cell tropism contributes to vimentin-mediated invasion and induction of inflammation

The contribution of the human microbiota to health and disease is poorly understood. Propionibacterium acnes is a prominent member of the skin microbiota, but is also associated with acne vulgaris. This bacterium has gained recent attention as a potential opportunistic pathogen at non‐skin infection sites due to its association with chronic pathologies and its isolation from diseased prostates. We performed comparative global‐transcriptional analyses for P. acnes infection of keratinocytes and prostate cells. P. acnes induced an acute, transient transcriptional inflammatory response in keratinocytes, whereas this response was delayed and sustained in prostate cells. We found that P. acnes invaded prostate epithelial cells, but not keratinocytes, and was detectable intracellularly 7 days post infection. Further characterization of the host cell response to infection revealed that vimentin was a key determinant for P. acnes invasion in prostate cells. siRNA‐mediated knock‐down of vimentin in prostate cellsattenuated bacterial invasion and the inflammatory response to infection. We conclude that host cell tropism, which may depend on the host protein vimentin, is relevant for P. acnes invasion and in part determines its sustained inflammatory capacity and persistence of infection.

Mutagenesis of Propionibacterium acnes and analysis of two CAMP factor knock-out mutants

P. acnes is a skin commensal that is frequently associated with inflammatory diseases such as acne vulgaris. Despite the availability of the genome sequence functional studies on P. acnes are scarce due to a lack of methods for genetic manipulation of this bacterium. Here we present an insertional mutagenesis approach for the inactivation of specific P. acnes genes. The gene of interest can be disrupted and replaced with an erythromycin-resistance cassette by employing homologous recombination. We used this method to generate knock-out mutants of camp2 (PPA0687) and camp4 (PPA1231), encoding CAMP factor homologs with predicted co-hemolytic activities. The successful inactivation of the two genes was confirmed by PCR and Western blotting experiments using specific anti-CAMP2/CAMP4 sera. The Δcamp2 but not the Δcamp4 mutant exhibited reduced hemolytic activity in the CAMP reaction with sheep erythrocytes, indicating that CAMP2 is the major active co-hemolytic factor of P. acnes. The biological relevance of the CAMP factors remains unclear as disruption of camp2 or camp4 did not significantly alter the transcriptome response of HaCaT cells to P. acnes. The here presented insertional mutagenesis approach will facilitate future studies on P. acnes.

Comparative genomics reveals distinct host-interacting traits of three major human-associated propionibacteria

BackgroundPropionibacteria are part of the human microbiota. Many studies have addressed the predominant colonizer of sebaceous follicles of the skin, Propionibacterium acnes, and investigated its association with the skin disorder acne vulgaris, and lately with prostate cancer. Much less is known about two other propionibacterial species frequently found on human tissue sites, Propionibacterium granulosum and Propionibacterium avidum. Here we analyzed two and three genomes of P. granulosum and P. avidum, respectively, and compared them to two genomes of P. acnes; we further highlight differences among the three cutaneous species with proteomic and microscopy approaches.ResultsElectron and atomic force microscopy revealed an exopolysaccharide (EPS)-like structure surrounding P. avidum cells, that is absent in P. acnes and P. granulosum. In contrast, P. granulosum possesses pili-like appendices, which was confirmed by surface proteome analysis. The corresponding genes were identified; they are clustered with genes encoding sortases. Both, P. granulosum and P. avidum lack surface or secreted proteins for predicted host-interacting factors of P. acnes, including several CAMP factors, sialidases, dermatan-sulphate adhesins, hyaluronidase and a SH3 domain-containing lipoprotein; accordingly, only P. acnes exhibits neuraminidase and hyaluronidase activities. These functions are encoded on previously unrecognized island-like regions in the genome of P. acnes.ConclusionsDespite their omnipresence on human skin little is known about the role of cutaneous propionibacteria. All three species are associated with a variety of diseases, including postoperative and device-related abscesses and infections. We showed that the three organisms have evolved distinct features to interact with their human host. Whereas P. avidum and P. granulosum produce an EPS-like surface structure and pili-like appendices, respectively, P. acnes possesses a number of unique surface-exposed proteins with host-interacting properties. The different surface properties of the three cutaneous propionibacteria are likely to determine their colonizing ability and pathogenic potential on the skin and at non-skin sites.

Deciphering the Intracellular Fate of Propionibacterium acnes in Macrophages

Propionibacterium acnes is a Gram-positive bacterium that colonizes various niches of the human body, particularly the sebaceous follicles of the skin. Over the last years a role of this common skin bacterium as an opportunistic pathogen has been explored. Persistence of P. acnes in host tissue has been associated with chronic inflammation and disease development, for example, in prostate pathologies. This study investigated the intracellular fate of P. acnes in macrophages after phagocytosis. In a mouse model of P. acnes-induced chronic prostatic inflammation, the bacterium could be detected in prostate-infiltrating macrophages at 2 weeks postinfection. Further studies performed in the human macrophage cell line THP-1 revealed intracellular survival and persistence of P. acnes but no intracellular replication or escape from the host cell. Confocal analyses of phagosome acidification and maturation were performed. Acidification of P. acnes-containing phagosomes was observed at 6 h postinfection but then lost again, indicative of cytosolic escape of P. acnes or intraphagosomal pH neutralization. No colocalization with the lysosomal markers LAMP1 and cathepsin D was observed, implying that the P. acnes-containing phagosome does not fuse with lysosomes. Our findings give first insights into the intracellular fate of P. acnes; its persistency is likely to be important for the development of P. acnes-associated inflammatory diseases.

Vimentin in Bacterial Infections

Despite well-studied bacterial strategies to target actin to subvert the host cell cytoskeleton, thus promoting bacterial survival, replication, and dissemination, relatively little is known about the bacterial interaction with other components of the host cell cytoskeleton, including intermediate filaments (IFs). IFs have not only roles in maintaining the structural integrity of the cell, but they are also involved in many cellular processes including cell adhesion, immune signaling, and autophagy, processes that are important in the context of bacterial infections. Here, we summarize the knowledge about the role of IFs in bacterial infections, focusing on the type III IF protein vimentin. Recent studies have revealed the involvement of vimentin in host cell defenses, acting as ligand for several pattern recognition receptors of the innate immune system. Two main aspects of bacteria-vimentin interactions are presented in this review: the role of vimentin in pathogen-binding on the cell surface and subsequent bacterial invasion and the interaction of cytosolic vimentin and intracellular pathogens with regards to innate immune signaling. Mechanistic insight is presented involving distinct bacterial virulence factors that target vimentin to subvert its function in order to change the host cell fate in the course of a bacterial infection.