Following pilus-mediated adhesion to human brain endothelial cells, meningococcus (N. meningitidis), the bacterium causing cerebrospinal meningitis, initiates signaling cascades, which eventually result in the opening of intercellular junctions, allowing meningeal colonization. The signaling receptor activated by the pathogen remained unknown. We report that N. meningitidis specifically stimulates a biased β2-adrenoceptor/β-arrestin signaling pathway in endothelial cells, which ultimately traps β-arrestin-interacting partners, such as the Src tyrosine kinase and junctional proteins, under bacterial colonies. Cytoskeletal reorganization mediated by β-arrestin-activated Src stabilizes bacterial adhesion to endothelial cells, whereas β-arrestin-dependent delocalization of junctional proteins results in anatomical gaps used by bacteria to penetrate into tissues. Activation of β-adrenoceptor endocytosis with specific agonists prevents signaling events downstream of N. meningitidis adhesion and inhibits bacterial crossing of the endothelial barrier. The identification of the mechanism used for hijacking host cell signaling machineries opens perspectives for treatment and prevention of meningococcal infection.

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.

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.

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 A 2 (TXA 2 ) was the prostanoid product of COX-1 responsible for this antimetastatic effect. Inhibition of the COX-1/TXA 2 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 TXA 2 orchestrates the generation of a favorable intravascular metastatic niche that promotes tumor cell seeding and identifies COX-1/TXA 2 signaling as a target for the prevention of metastasis.

Despite their initial efficient response to induction chemotherapy, relapse remains frequent in patients with T-cell acute lymphoblastic leukemia (T-ALL), an aggressive malignancy of immature T-cell progenitors. We previously reported sustained calcineurin (Cn) activation in human lymphoid malignancies, and showed that Cn inhibitors have antileukemic effects in mouse models of T-ALL. It was unclear, however, from these studies whether these effects resulted from Cn inhibition in leukemic cells themselves or were an indirect consequence of impaired Cn function in the supportive tumor microenvironment. We thus generated a Notch (intracellular Notch 1, ICN1)-induced T-ALL mouse model, in which conditional Cn genetic deletion is restricted to leukemic cells. Ex vivo, Cn deletion altered the adhesive interactions between leukemic cells and their supportive stroma, leukemic cell survival, proliferation, migration and clonogenic potential. In vivo, Cn activation was found to be critical for leukemia initiating/propagating cell activity as demonstrated by the failure of Cn-deficient leukemic cells to transplant the disease to syngeneic recipient mice. Importantly, combination of vincristine treatment with Cre-mediated Cn ablation cooperated to induce long-term remission of ICN1-induced T-ALL. These findings indicate that Cn is a promising target in T-ALL relapse prevention, and call for clinical trials incorporating Cn inhibitors during consolidation therapy.