A Novel Secreted Metalloprotease (CD2830) from Clostridium difficile Cleaves Specific Proline Sequences in LPXTG Cell Surface Proteins

Bacterial secreted proteins constitute a biologically important subset of proteins involved in key processes related to infection such as adhesion, colonization, and dissemination. Bacterial extracellular proteases, in particular, have attracted considerable attention, as they have been shown to be indispensable for bacterial virulence.Here, we analyzed the extracellular subproteome of Clostridium difficile and identified a hypothetical protein, CD2830, as a novel secreted metalloprotease. Following the identification of a CD2830 cleavage site in human HSP90β, a series of synthetic peptide substrates was used to identify the favorable CD2830 cleavage motif. This motif was characterized by a high prevalence of proline residues. Intriguingly, CD2830 has a preference for cleaving Pro–Pro bonds, unique among all hitherto described proteases. Strikingly, within the C. difficile proteome two putative adhesion molecules, CD2831 and CD3246, were identified that contain multiple CD2830 cleavage sites (13 in total). We subsequently found that CD2830 efficiently cleaves CD2831 between two prolines at all predicted cleavage sites. Moreover, native CD2830, secreted by live cells, cleaves endogenous CD2831 and CD3246.These findings highlight CD2830 as a highly specific endoproteinase with a preference for proline residues surrounding the scissile bond. Moreover, the efficient cleavage of two putative surface adhesion proteins points to a possible role of CD2830 in the regulation of C. difficile adhesion.Clostridium difficile is an anaerobic, Gram-positive, spore-forming bacterium. Human intake of spores occurs through the fecal-oral route. Upon leaving the stomach and becoming exposed to bile acids in the small intestine, the C. difficile spores germinate. Once germinated, the vegetative cells in the colon encounter an unreceptive environment (1). Competition with the normal flora, immune responses, gastric fluids (2), and specialized antimicrobial peptides all act against a developing infection. Moreover, the physical barrier formed by a layer of glycoproteins (mucins) covering the underlying epithelial cells forms a major hurdle for firm adhesion.Many enteric pathogens express factors that reduce competition, allow evasion of host immune responses, and promote adhesion and/or invasion of tissues. These virulence factors are located in the cell membrane or wall (controlling adhesion and protection) or are secreted (modifying the surrounding environment). The best studied virulence factors in C. difficile are the toxins TcdA and TcdB (3, 4), which cause destruction of the intestinal barrier by disrupting the epithelial actin cytoskeleton. It is speculated that the subsequent increased permeability of the intestinal epithelium leads to increased exudation of fluids, including nutritional substances. Damage to the intestinal mucosa causes the main symptoms of C. difficile infection, including pseudomembranous colitis (1).Data illustrating how C. difficile circumvents host defense mechanisms are limited. As an example, in response to attack by antimicrobial peptides, C. difficile expresses a set of genes that change the surface charge, thereby diminishing the interaction of cationic antimicrobial peptides on the bacterial surface (5). C. difficile cell membrane and cell wall proteins are obvious candidate molecules for direct interaction with the host and are most likely involved in processes such as adhesion and colonization. Footholds on the host cell surface proteins include the extracellular matrix components fibronectin, laminin, collagen, and fibrinogen, which all have been implicated in C. difficile adhesion (6–9). In addition, C. difficile secretory proteins are released into the surrounding environment, where they can exert their function. However, besides the toxins, little is known about extracellular factors that contribute to C. difficile infection (8, 10).In this study we analyzed the secreted proteins of C. difficile and characterized a very specific, highly active secreted metalloprotease, CD2830. We demonstrate that it has a unique preference for hydrolyzing Pro–Pro bonds in an overall proline-rich cleavage motif. The identification of two C. difficile LPXTG surface proteins as highly efficient substrates for CD2830 indicates a role for this enzyme in bacterial motility.     

The Relevance of External Quality Assessment for Molecular Testing for ALK Positive Non-Small Cell Lung Cancer: Results from Two Pilot Rounds Show Room for Optimization

Background and Purpose

Molecular profiling should be performed on all advanced non-small cell lung cancer with non-squamous histology to allow treatment selection. Currently, this should include EGFR mutation testing and testing for ALK rearrangements. ROS1 is another emerging target. ALK rearrangement status is a critical biomarker to predict response to tyrosine kinase inhibitors such as crizotinib. To promote high quality testing in non-small cell lung cancer, the European Society of Pathology has introduced an external quality assessment scheme. This article summarizes the results of the first two pilot rounds organized in 2012–2013.

Materials and Methods

Tissue microarray slides consisting of cell-lines and resection specimens were distributed with the request for routine ALK testing using IHC or FISH. Participation in ALK FISH testing included the interpretation of four digital FISH images.

Results

Data from 173 different laboratories was obtained. Results demonstrate decreased error rates in the second round for both ALK FISH and ALK IHC, although the error rates were still high and the need for external quality assessment in laboratories performing ALK testing is evident. Error rates obtained by FISH were lower than by IHC. The lowest error rates were observed for the interpretation of digital FISH images.

Conclusion

There was a large variety in FISH enumeration practices. Based on the results from this study, recommendations for the methodology, analysis, interpretation and result reporting were issued. External quality assessment is a crucial element to improve the quality of molecular testing.     

Measuring the Chemical and Cytotoxic Variability of Commercially Available Kava (Piper methysticum G. Forster)

Formerly used world-wide as a popular botanical medicine to reduce anxiety, reports of hepatotoxicity linked to consuming kava extracts in the late 1990s have resulted in global restrictions on kava use and have hindered kava-related research. Despite its presence on the United States Food and Drug Administration consumer advisory list for the past decade, export data from kava producing countries implies that US kava imports, which are not publicly reported, are both increasing and of a fairly high volume. We have measured the variability in extract chemical composition and cytotoxicity towards human lung adenocarcinoma A549 cancer cells of 25 commercially available kava products. Results reveal a high level of variation in chemical content and cytotoxicity of currently available kava products. As public interest and use of kava products continues to increase in the United States, efforts to characterize products and expedite research of this potentially useful botanical medicine are necessary.     

Attitudes of People in the UK with HIV Who Are Antiretroviral (ART) Na?ve to Starting ART at High CD4 Counts for Potential Health Benefit or to Prevent HIV Transmission

Objective

To assess if a strategy of early ART to prevent HIV transmission is acceptable to ART naïve people with HIV with high CD4 counts.

Design

ASTRA is a UK multicentre, cross sectional study of 3258 HIV outpatients in 2011/12. A self-completed questionnaire collected sociodemographic, behavioral and health data, and attitudes to ART; CD4 count was recorded from clinical records.

Methods

ART naïve participants with CD4 ≥350 cells/µL (n = 281) were asked to agree/disagree/undecided with the statements (i) I would want to start treatment now if this would slightly reduce my risk of getting a serious illness, and (ii) I would want to start treatment now if this would make me less infectious to a sexual partner, even if there was no benefit to my own health.

Results

Participants were 85% MSM, 76% white, 11% women. Of 281 participants, 49.5% and 45.2% agreed they would start ART for reasons (i) and (ii) respectively; 62.6% agreed with either (i) or (ii); 12.5% agreed with neither; 24.9% were uncertain. Factors independently associated (p<0.1) with agreement to (i) were: lower CD4, more recent HIV diagnosis, physical symptoms, not being depressed, greater financial hardship, and with agreement to (ii) were: being heterosexual, more recent HIV diagnosis, being sexually active.

Conclusions

A strategy of starting ART at high CD4 counts is likely to be acceptable to the majority of HIV-diagnosed individuals. Almost half with CD4 >350 would start ART to reduce infectiousness, even if treatment did not benefit their own health. However a significant minority would not like to start ART either for modest health benefit or to reduce infectivity. Any change in approach to ART initiation must take account of individual preferences. Transmission models of potential benefit of early ART should consider that ART uptake may be lower than that seen with low CD4 counts.     

Cytoplasmic ACK1 Interaction with Multiple Receptor Tyrosine Kinases Is Mediated by Grb2: AN ANALYSIS OF ACK1 EFFECTS ON Axl SIGNALING*

ACK1 (activated Cdc42-associated kinase 1), a cytoplsmic tyrosine kinase, is implicated in metastatic behavior, cell spreading and migration, and epidermal growth factor receptor (EGFR) signaling. The function of ACK1 in the regulation of receptor tyrosine kinases requires a C-terminal region that demonstrates a significant homology to the EGFR binding domain of MIG6. In this study, we have identified additional receptor tyrosine kinases, including Axl, leukocyte tyrosine kinase, and anaplastic lymphoma kinase, that can bind to the ACK1/MIG6 homology region. Unlike the interaction between MIG6 and EGFR, our data suggest that these receptor tyrosine kinases require the adaptor protein Grb2 for efficient binding, which interacts with highly conserved proline-rich regions that are conserved between ACK1 and MIG6. We have focused on Axl and compared how ACK1/Axl differs from the ACK1/EGFR axis by investigating effects of knockdown of endogenous ACK1. Although EGFR activation promotes ACK1 turnover, Axl activation by GAS6 does not; interestingly, the reciprocal down-regulation of GAS6-stimulated Axl is blocked by removing ACK1. Thus, ACK1 functions in part to control Axl receptor levels. Silencing of ACK1 also leads to diminished ruffling and migration in DU145 and COS7 cells upon GAS6-Axl signaling. The ability of ACK1 to modulate Axl and perhaps anaplastic lymphoma kinase (altered in anaplastic large cell lymphomas) might explain why ACK1 can promote metastatic and transformed behavior in a number of cancers.     

Two structurally distinct domains of the nucleoporin Nup170 cooperate to tether a subset of nucleoporins to nuclear pores

How individual nucleoporins (Nups) perform their role in nuclear pore structure and function is largely unknown. In this study, we examined the structure of purified Nup170 to obtain clues about its function. We show that Nup170 adopts a crescent moon shape with two structurally distinct and separable domains, a β-propeller N terminus and an α-solenoid C terminus. To address the individual roles of each domain, we expressed these domains separately in yeast. Notably, overexpression of the Nup170 C domain was toxic in nup170Δ cells and caused accumulation of several Nups in cytoplasmic foci. Further experiments indicated that the C-terminal domain anchors Nup170 to nuclear pores, whereas the N-terminal domain functions to recruit or retain a subset of Nups, including Nup159, Nup188, and Pom34, at nuclear pores. We conclude that Nup170 performs its role as a structural adapter between cytoplasmically oriented Nups and the nuclear pore membrane.     

DHPR activation underlies SR Ca2+ release induced by osmotic stress in isolated rat skeletal muscle fibers

Changes in skeletal muscle volume induce localized sarcoplasmic reticulum (SR) Ca²⁺ release (LCR) events, which are sustained for many minutes, suggesting a possible signaling role in plasticity or pathology. However, the mechanism by which cell volume influences SR Ca²⁺ release is uncertain. In the present study, rat flexor digitorum brevis fibers were superfused with isoosmotic Tyrode''s solution before exposure to either hyperosmotic (404 mOsm) or hypoosmotic (254 mOsm) solutions, and the effects on cell volume, membrane potential (E_m), and intracellular Ca²⁺ ([Ca²⁺]_i) were determined. To allow comparison with previous studies, solutions were made hyperosmotic by the addition of sugars or divalent cations, or they were made hypoosmotic by reducing [NaCl]_o. All hyperosmotic solutions induced a sustained decrease in cell volume, which was accompanied by membrane depolarization (by 14–18 mV; n = 40) and SR Ca²⁺ release. However, sugar solutions caused a global increase in [Ca²⁺]_i, whereas solutions made hyperosmotic by the addition of divalent cations only induced LCR. Decreasing osmolarity induced an increase in cell volume and a negative shift in E_m (by 15.04 ± 1.85 mV; n = 8), whereas [Ca²⁺]_i was unaffected. However, on return to the isoosmotic solution, restoration of cell volume and E_m was associated with LCR. Both global and localized SR Ca²⁺ release were abolished by the dihydropyridine receptor inhibitor nifedipine by sustained depolarization of the sarcolemmal or by the addition of the ryanodine receptor 1 inhibitor tetracaine. Inhibitors of the Na-K-2Cl (NKCC) cotransporter markedly inhibited the depolarization associated with hyperosmotic shrinkage and the associated SR Ca²⁺ release. These findings suggest (1) that the depolarization that accompanies a decrease in cell volume is the primary event leading to SR Ca²⁺ release, and (2) that volume-dependent regulation of the NKCC cotransporter contributes to the observed changes in E_m. The differing effects of the osmotic agents can be explained by the screening of fixed charges by divalent ions.     

Expression, purification, and characterization of an enzymatically active truncated human rho-kinase I (ROCK I) domain expressed in Sf-9 insect cells

Rho Kinase I (ROCK I) is a serine/threonine kinase that is involved in diverse cellular signaling. To further understand the physiological role of ROCK I and to identify and develop potent and selective inhibitors of ROCK I, we have overexpressed and purified a constitutively active dimeric human ROCK I (3-543) kinase domain using the Sf9-baculovirus expression system. In addition, using a limited proteolysis technique, we have identified a minimal functional subdomain of ROCK I that can be used in crystallization studies. The availability of multimilligram amounts of purified and well characterized functional human ROCK I kinase domains will be useful in screening and structural studies.