Aspirin blocks formation of metastatic intravascular niches by inhibiting platelet-derived COX-1/thromboxane A2

Because metastasis is associated with the majority of cancer-related deaths, its prevention is a clinical aspiration. Prostanoids are a large family of bioactive lipids derived from the activity of cyclooxygenase-1 (COX-1) and COX-2. Aspirin impairs the biosynthesis of all prostanoids through the irreversible inhibition of both COX isoforms. Long-term administration of aspirin leads to reduced distant metastases in murine models and clinical trials, but the COX isoform, downstream prostanoid, and cell compartment responsible for this effect are yet to be determined. Here, we have shown that aspirin dramatically reduced lung metastasis through inhibition of COX-1 while the cancer cells remained intravascular and that inhibition of platelet COX-1 alone was sufficient to impair metastasis. Thromboxane A2 (TXA2) was the prostanoid product of COX-1 responsible for this antimetastatic effect. Inhibition of the COX-1/TXA2 pathway in platelets decreased aggregation of platelets on tumor cells, endothelial activation, tumor cell adhesion to the endothelium, and recruitment of metastasis-promoting monocytes/macrophages, and diminished the formation of a premetastatic niche. Thus, platelet-derived TXA2 orchestrates the generation of a favorable intravascular metastatic niche that promotes tumor cell seeding and identifies COX-1/TXA2 signaling as a target for the prevention of metastasis.

Blocking bacterial entry at the adhesion step reveals dynamic recruitment of membrane and cytosolic probes

BACKGROUND

Bacterial invasion covers two steps: adhesion and entry per se. The cell signalling response is triggered upon pathogen interaction at the cell surface. This response continues when the pathogen is internalised. It is likely that these two steps activate different molecular machineries. So far, it has not been possible to easily follow in physiological conditions these events separately. We thus developed an approach to uncouple adhesion from entry using atomic force microscopy (AFM)-driven force and fluorescence measurements.

RESULTS

We report nanometric-scale, high-resolution, functional dynamic measurements of bacterial interaction with the host cell surface using photonic and adhesion force analyses. We describe how to achieve a precise monitoring of iterative cell-bacterium interactions to analyse host cell signalling responses to infection. By applying this method to Yersinia pseudotuberculosis, we first unveil glycosylphosphatidylinositol-anchored protein domains recruitment to the bacterium cell surface binding site and concomitant cytoskeleton rearrangements using super-resolution fluorescence microscopy. Second, we demonstrate the feasibility of monitoring post-translationally modified proteins, for example, via ubiquitylation, during the first step of infection.

CONCLUSION

We provide an approach to discriminate between cellular signalling response activated at the plasma membrane during host-pathogen interaction and that is triggered during the internalisation of the pathogen within the cell.

SIGNIFICANCE

This approach adds to the technological arsenal to better understand and fight against pathogens and beyond the scope of microbiology to address conceptual issues of cell surface signalling.

Abstract 4196: Aspirin inhibits metastasis in the intravascular phase through the blockade of COX-1-TXA2 pathway in platelets

Evidence from experimental studies and clinical trials has shown that aspirin reduces the incidence of distant metastases. Aspirin inhibits cyclooxygenase (COX)-1 and COX-2, triggering anti-thrombotic and anti-inflammatory effects, respectively. However, the mechanisms underlying the anti-metastatic effect of aspirin are still largely unknown.

By employing mouse models of experimental and spontaneous metastasis, we have shown that aspirin and a selective COX-1 inhibitor dramatically reduced metastatic lung nodules, an effect that was not replicated by selective inhibition of COX-2. Metastasis was impaired in COX-1 deficient mice as well, suggesting a pivotal role of microenvironmental COX-1 in the metastatic process. In particular, COX-1 activity was essential during the intravascular phase of pulmonary metastasis. Using a model of platelet depletion and re-infusion we identified platelet-derived thromboxane A2 (TXA2) as the main product of COX-1 responsible for its permissive effect on metastasis. The inhibition of the COX-1-TXA2 pathway in platelets decreased the aggregation of platelets on tumor cells and was associated with a reduction in endothelial activation, in tumor cell adhesion to the endothelium, in recruitment of metastasis-promoting monocytes/macrophages and in transendothelial migration. Thus, platelet-derived TXA2 orchestrates the generation of a favorable intravascular metastatic niche that promotes tumor cell seeding and metastasis.

Taken together, our data suggest that COX-1 inhibition in platelets by aspirin is sufficient to exert an anti-metastatic effect and shed a new light on COX-1-TXA2 signalling in the context of tumor cell dissemination. From this perspective, TXA2 might present a more selective therapeutic target for the prevention of metastasis.

Citation Format: Serena Lucotti, Camilla Cerutti, Magali Soyer, Ana M. Gil-Bernabé, Ana L. Gomes, Philip D. Allen, Sean Smart, Bostjan Markelc, Karla Watson, Paul C. Armstrong, Jane A. Mitchell, Timothy D. Warner, Anne J. Ridley, Ruth J. Muschel. Aspirin inhibits metastasis in the intravascular phase through the blockade of COX-1-TXA2 pathway in platelets [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4196.

RhoC and ROCKs regulate cancer cell interactions with endothelial cells

RhoC is a member of the Rho GTPase family that is implicated in cancer progression by stimulating cancer cell invasiveness. Here we report that RhoC regulates the interaction of cancer cells with vascular endothelial cells (ECs), a crucial step in the metastatic process. RhoC depletion by RNAi reduces PC3 prostate cancer cell adhesion to ECs, intercalation between ECs as well as transendothelial migration in vitro. Depletion of the kinases ROCK1 and ROCK2, two known RhoC downstream effectors, similarly decreases cancer interaction with ECs. RhoC also regulates the extension of protrusions made by cancer cells on vascular ECs in vivo. Transient RhoC depletion is sufficient to reduce both early PC3 cell retention in the lungs and experimental metastasis formation in vivo. Our results indicate RhoC plays a central role in cancer cell interaction with vascular ECs, which is a critical event for cancer progression.

Introducing shear stress in the study of bacterial adhesion

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the initial and determining step of the pathogenesis. Although experimentally adhesion is mostly studied in static conditions adhesion actually takes place in the presence of flowing liquid. First encounters between bacteria and their host often occur at the mucosal level, mouth, lung, gut, eye, etc. where mucus flows along the surface of epithelial cells. Later in infection, pathogens occasionally access the blood circulation causing life-threatening illnesses such as septicemia, sepsis and meningitis. A defining feature of these infections is the ability of these pathogens to interact with endothelial cells in presence of circulating blood. The presence of flowing liquid, mucus or blood for instance, determines adhesion because it generates a mechanical force on the pathogen. To characterize the effect of flowing liquid one usually refers to the notion of shear stress, which is the tangential force exerted per unit area by a fluid moving near a stationary wall, expressed in dynes/cm(2). Intensities of shear stress vary widely according to the different vessels type, size, organ, location etc. (0-100 dynes/cm(2)). Circulation in capillaries can reach very low shear stress values and even temporarily stop during periods ranging between a few seconds to several minutes (1). On the other end of the spectrum shear stress in arterioles can reach 100 dynes/cm(2)(2). The impact of shear stress on different biological processes has been clearly demonstrated as for instance during the interaction of leukocytes with the endothelium (3). To take into account this mechanical parameter in the process of bacterial adhesion we took advantage of an experimental procedure based on the use of a disposable flow chamber (4). Host cells are grown in the flow chamber and fluorescent bacteria are introduced in the flow controlled by a syringe pump. We initially focused our investigations on the bacterial pathogen Neisseria meningitidis, a Gram-negative bacterium responsible for septicemia and meningitis. The procedure described here allowed us to study the impact of shear stress on the ability of the bacteria to: adhere to cells (1), to proliferate on the cell surface (5)and to detach to colonize new sites (6) (Figure 1). Complementary technical information can be found in reference 7. Shear stress values presented here were chosen based on our previous experience(1) and to represent values found in the literature. The protocol should be applicable to a wide range of pathogens with specific adjustments depending on the objectives of the study.

Posttranslational modification of pili upon cell contact triggers N. meningitidis dissemination

The Gram-negative bacterium Neisseria meningitidis asymptomatically colonizes the throat of 10 to 30% of the human population, but throat colonization can also act as the port of entry to the blood (septicemia) and then the brain (meningitis). Colonization is mediated by filamentous organelles referred to as type IV pili, which allow the formation of bacterial aggregates associated with host cells. We found that proliferation of N. meningitidis in contact with host cells increased the transcription of a bacterial gene encoding a transferase that adds phosphoglycerol onto type IV pili. This unusual posttranslational modification specifically released type IV pili-dependent contacts between bacteria. In turn, this regulated detachment process allowed propagation of the bacterium to new colonization sites and also migration across the epithelium, a prerequisite for dissemination and invasive disease.

Extracellular bacterial pathogen induces host cell surface reorganization to resist shear stress

Bacterial infections targeting the bloodstream lead to a wide array of devastating diseases such as septic shock and meningitis. To study this crucial type of infection, its specific environment needs to be taken into account, in particular the mechanical forces generated by the blood flow. In a previous study using Neisseria meningitidis as a model, we observed that bacterial microcolonies forming on the endothelial cell surface in the vessel lumen are remarkably resistant to mechanical stress. The present study aims to identify the molecular basis of this resistance. N. meningitidis forms aggregates independently of host cells, yet we demonstrate here that cohesive forces involved in these bacterial aggregates are not sufficient to explain the stability of colonies on cell surfaces. Results imply that host cell attributes enhance microcolony cohesion. Microcolonies on the cell surface induce a cellular response consisting of numerous cellular protrusions similar to filopodia that come in close contact with all the bacteria in the microcolony. Consistent with a role of this cellular response, host cell lipid microdomain disruption simultaneously inhibited this response and rendered microcolonies sensitive to blood flow–generated drag forces. We then identified, by a genetic approach, the type IV pili component PilV as a triggering factor of plasma membrane reorganization, and consistently found that microcolonies formed by a pilV mutant are highly sensitive to shear stress. Our study shows that bacteria manipulate host cell functions to reorganize the host cell surface to form filopodia-like structures that enhance the cohesion of the microcolonies and therefore blood vessel colonization under the harsh conditions of the bloodstream.

Certain infectious agents reach the bloodstream and succeed in surviving and multiplying at this site. This stage of the infection is associated with a life-threatening condition. The Gram-negative bacterium meningococcus, responsible for septicemia and meningitis, stands out as a paradigm of such a pathogen. Despite the characteristic flow-generated hydrodynamic forces of the bloodstream, meningococci have the striking ability to bind to the endothelium and to multiply in bacterial aggregates called microcolonies. Meningococci form aggregates in absence of eukaryotic cells, but we show that such aggregates are sensitive to mechanical stress, indicating that the presence of host cells enhances microcolony cohesion. Consistently, analysis of meningococcal microcolonies growing on the host cellular surface reveals that these structures are dense with cellular material in the form of cellular protrusions. Blocking this bacteria-induced cellular response renders microcolonies sensitive to blood flow. We then identify a bacterial component located on the outside of the bacteria and in direct contact with host cells as a key factor in the induction of this cellular response. This bacteria-induced cellular response is therefore a striking example of how pathogens exploit cellular functions as a survival strategy, in this case in the particular context of the bloodstream.

The bicarbonate transporter is essential for Bacillus anthracis lethality

In the pathogenic bacterium Bacillus anthracis, virulence requires induced expression of the anthrax toxin and capsule genes. Elevated CO2/bicarbonate levels, an indicator of the host environment, provide a signal ex vivo to increase expression of virulence factors, but the mechanism underlying induction and its relevance in vivo are unknown. We identified a previously uncharacterized ABC transporter (BAS2714-12) similar to bicarbonate transporters in photosynthetic cyanobacteria, which is essential to the bicarbonate induction of virulence gene expression. Deletion of the genes for the transporter abolished induction of toxin gene expression and strongly decreased the rate of bicarbonate uptake ex vivo, demonstrating that the BAS2714-12 locus encodes a bicarbonate ABC transporter. The bicarbonate transporter deletion strain was avirulent in the A/J mouse model of infection. Carbonic anhydrase inhibitors, which prevent the interconversion of CO2 and bicarbonate, significantly affected toxin expression only in the absence of bicarbonate or the bicarbonate transporter, suggesting that carbonic anhydrase activity is not essential to virulence factor induction and that bicarbonate, and not CO2, is the signal essential for virulence induction. The identification of this novel bicarbonate transporter essential to virulence of B. anthracis may be of relevance to other pathogens, such as Streptococcus pyogenes, Escherichia coli, Borrelia burgdorferi, and Vibrio cholera that regulate virulence factor expression in response to CO2/bicarbonate, and suggests it may be a target for antibacterial intervention.

Reduction of acoustic annoyance in school dining halls

The sound levels in dbA and the reverberation times in sec were measured in 18 school dining areas in and around Rennes. Of these, 12 had had acoustic treatment, 6 had not. The range of levels in all schools exceeded those recommended in the literature for the avoidance of noise-induced fatigue, while the reverberation times were acceptable (less than 0.8 sec) only in those spaces acoustically treated. There was a clear relation between sound level and reverberation times, but it was not directly proportional, as other parameters influenced sound level. Suggestions for acoustic treatment of surfaces were made, together with suggestions for treatment and placement of furniture and for compartmenting the interior space. An example was given of a large dining area (2,280 m3) in which the beneficial effects of acoustic treatment of ceiling and of walls separately was demonstrated, the sound level being reduced by 4-8 dbA. It was recommended that persons at all levels, from administrators to the children themselves become aware of the necessity to lower noise levels to facilitate relaxation and communication at meal time and to control noise to innocuous levels.