Initiation of Antiviral B Cell Immunity Relies on Innate Signals from Spatially Positioned NKT Cells.

B cells constitute an essential line of defense from pathogenic infections through the generation of class-switched antibody-secreting cells (ASCs) in germinal centers. Although this process is known to be regulated by follicular helper T (TfH) cells, the mechanism by which B cells initially seed germinal center reactions remains elusive. We found that NKT cells, a population of innate-like T lymphocytes, are critical for the induction of B cell immunity upon viral infection. The positioning of NKT cells at the interfollicular areas of lymph nodes facilitates both their direct priming by resident macrophages and the localized delivery of innate signals to antigen-experienced B cells. Indeed, NKT cells secrete an early wave of IL-4 and constitute up to 70% of the total IL-4-producing cells during the initial stages of infection. Importantly, the requirement of this innate immunity arm appears to be evolutionarily conserved because early NKT and IL-4 gene signatures also positively correlate with the levels of neutralizing antibodies in Zika-virus-infected macaques. In conclusion, our data support a model wherein a pre-TfH wave of IL-4 secreted by interfollicular NKT cells triggers the seeding of germinal center cells and serves as an innate link between viral infection and B cell immunity.

The V-ATPase/ATG16L1 axis is controlled by the V1H subunit.

Defects in organellar acidification indicate compromised or infected compartments. Recruitment of the autophagy-related ATG16L1 complex to pathologically neutralized organelles targets ubiquitin-like ATG8 molecules to perturbed membranes. How this process is coupled to proton gradient disruption is unclear. Here, we reveal that the V1H subunit of the vacuolar ATPase (V-ATPase) proton pump binds directly to ATG16L1. The V1H/ATG16L1 interaction only occurs within fully assembled V-ATPases, allowing ATG16L1 recruitment to be coupled to increased V-ATPase assembly following organelle neutralization. Cells lacking V1H fail to target ATG8s during influenza infection or after activation of the immune receptor stimulator of interferon genes (STING). We identify a loop within V1H that mediates ATG16L1 binding. A neuronal V1H isoform lacks this loop and is associated with attenuated ATG8 targeting in response to ionophores in primary murine and human iPSC-derived neurons. Thus, V1H controls ATG16L1 recruitment following proton gradient dissipation, suggesting that the V-ATPase acts as a cell-intrinsic damage sensor.

The actin and tetraspanin networks organize receptor nanoclusters to regulate B cell receptor-mediated signaling.

A key role is emerging for the cytoskeleton in coordinating receptor signaling, although the underlying molecular requirements remain unclear. Here we show that cytoskeleton disruption triggered signaling requiring not only the B cell receptor (BCR), but also the coreceptor CD19 and tetraspanin CD81, thus providing a mechanism for signal amplification upon surface-bound antigen stimulation. By using superresolution microscopy, we demonstrated that endogenous IgM, IgD, and CD19 exhibited distinct nanoscale organization within the plasma membrane of primary B cells. Upon stimulation, we detect a local convergence of receptors, although their global organization was not dramatically altered. Thus, we postulate that cytoskeleton reorganization releases BCR nanoclusters, which can interact with CD19 held in place by the tetraspanin network. These results not only suggest that receptor compartmentalization regulates antigen-induced activation but also imply a potential role for CD19 in mediating ligand-independent "tonic" BCR signaling necessary for B cell survival.

The Small Rho GTPase TC10 Modulates B Cell Immune Responses.

Rho family GTPases regulate diverse cellular events, such as cell motility, polarity, and vesicle traffic. Although a wealth of data exists on the canonical Rho GTPases RhoA, Rac1, and Cdc42, several other family members remain poorly studied. In B cells, we recently demonstrated a critical role for Cdc42 in plasma cell differentiation. In this study, we focus on a close homolog of Cdc42, TC10 (also known as RhoQ), and investigate its physiological role in B cells. By generating a TC10-deficient mouse model, we show that despite reduced total B cell numbers, B cell development in these mice occurs normally through distinct developmental stages. Upon immunization, IgM levels were reduced and, upon viral infection, germinal center responses were defective in TC10-deficient mice. BCR signaling was mildly affected, whereas cell migration remained normal in TC10-deficient B cells. Furthermore, by generating a TC10/Cdc42 double knockout mouse model, we found that TC10 can compensate for the lack of Cdc42 in TLR-induced cell activation and proliferation, so the two proteins play partly redundant roles. Taken together, by combining in vivo and in vitro analysis using TC10-deficient mice, we define the poorly studied Rho GTPase TC10 as an immunomodulatory molecule playing a role in physiological B cell responses.

Subtractive CRISPR screen identifies the ATG16L1/vacuolar ATPase axis as required for non-canonical LC3 lipidation.

Although commonly associated with autophagosomes, LC3 can also be recruited to membranes by covalent lipidation in a variety of non-canonical contexts. These include responses to ionophores such as the M2 proton channel of influenza A virus. We report a subtractive CRISPR screen that identifies factors required for non-canonical LC3 lipidation. As well as the enzyme complexes directly responsible for LC3 lipidation in all contexts, we show the RALGAP complex is important for M2-induced, but not ionophore drug-induced, LC3 lipidation. In contrast, ATG4D is responsible for LC3 recycling in M2-induced and basal LC3 lipidation. Identification of a vacuolar ATPase subunit in the screen suggests a common mechanism for non-canonical LC3 recruitment. Influenza-induced and ionophore drug-induced LC3 lipidation lead to association of the vacuolar ATPase and ATG16L1 and can be antagonized by Salmonella SopF. LC3 recruitment to erroneously neutral compartments may therefore represent a response to damage caused by diverse invasive pathogens.

Novel DNA lesions generated by the interaction between therapeutic thiopurines and UVA light.

The therapeutic effect of the thiopurines, 6-thioguanine (6-TG), 6-mercaptopurine, and its prodrug azathioprine, depends on the incorporation of 6-TG into cellular DNA. Unlike normal DNA bases, 6-TG absorbs UVA radiation, and UVA-mediated photochemical damage of DNA 6-TG has potentially harmful side effects. When free 6-TG is UVA irradiated in solution in the presence of molecular oxygen, reactive oxygen species are generated and 6-TG is oxidized to guanine-6-sulfonate (G(SO3)) and guanine-6-thioguanine in reactions involving singlet oxygen. This conversion is prevented by antioxidants, including the dietary vitamin ascorbate. DNA G(SO3) is also the major photoproduct of 6-TG in DNA and it can be selectively introduced into DNA or oligonucleotides in vitro by mild chemical oxidation. Thermal stability measurements indicate that G(SO3) does not form stable base pairs with any of the normal DNA bases in duplex oligonucleotides and is a powerful block for elongation by Klenow DNA polymerase in primer extension experiments. In cultured human cells, DNA damage produced by 6-TG and UVA treatment is associated with replication inhibition and provokes a p53-dependent DNA damage response.

Dynamic reorganisation of intermediate filaments coordinates early B-cell activation.

During B-cell activation, the dynamic reorganisation of the cytoskeleton is crucial for multiple cellular responses, such as receptor signalling, cell spreading, antigen internalisation, intracellular trafficking, and antigen presentation. However, the role of intermediate filaments (IFs), which represent a major component of the mammalian cytoskeleton, is not well defined. Here, by using multiple super-resolution microscopy techniques, including direct stochastic optical reconstruction microscopy, we show that IFs in B cells undergo drastic reorganisation immediately upon antigen stimulation and that this reorganisation requires actin and microtubules. Although the loss of vimentin in B cells did not impair B-cell development, receptor signalling, and differentiation, vimentin-deficient B cells exhibit altered positioning of antigen-containing and lysosomal associated membrane protein 1 (LAMP1+) compartments, implying that vimentin may play a role in the fine-tuning of intracellular trafficking. Indeed, vimentin-deficient B cells exhibit impaired antigen presentation and delayed antibody responses in vivo. Thus, our study presents a new perspective on the role of IFs in B-cell activation.

Increased Vascular Permeability in the Bone Marrow Microenvironment Contributes to Disease Progression and Drug Response in Acute Myeloid Leukemia.

The biological and clinical behaviors of hematological malignancies can be influenced by the active crosstalk with an altered bone marrow (BM) microenvironment. In the present study, we provide a detailed picture of the BM vasculature in acute myeloid leukemia using intravital two-photon microscopy. We found several abnormalities in the vascular architecture and function in patient-derived xenografts (PDX), such as vascular leakiness and increased hypoxia. Transcriptomic analysis in endothelial cells identified nitric oxide (NO) as major mediator of this phenotype in PDX and in patient-derived biopsies. Moreover, induction chemotherapy failing to restore normal vasculature was associated with a poor prognosis. Inhibition of NO production reduced vascular permeability, preserved normal hematopoietic stem cell function, and improved treatment response in PDX.

A switch from canonical to noncanonical autophagy shapes B cell responses.

Autophagy is important in a variety of cellular and pathophysiological situations; however, its role in immune responses remains elusive. Here, we show that among B cells, germinal center (GC) cells exhibited the highest rate of autophagy during viral infection. In contrast to mechanistic target of rapamycin complex 1-dependent canonical autophagy, GC B cell autophagy occurred predominantly through a noncanonical pathway. B cell stimulation was sufficient to down-regulate canonical autophagy transiently while triggering noncanonical autophagy. Genetic ablation of WD repeat domain, phosphoinositide-interacting protein 2 in B cells alone enhanced this noncanonical autophagy, resulting in changes of mitochondrial homeostasis and alterations in GC and antibody-secreting cells. Thus, B cell activation prompts a temporal switch from canonical to noncanonical autophagy that is important in controlling B cell differentiation and fate.

Cell cycle arrest and proapoptotic effects of the anticancer cyclodepsipeptide serratamolide (AT514) are independent of p53 status in breast cancer cells.

In a search for new anticancer agents, we have identified serratamolide (AT514), a cyclodepsipeptide from Serratia marcescens 2170 that induces cell cycle arrest and apoptosis in various cancer cell lines. A cell viability assay showed that the concentrations that cause 50% inhibition (IC50) in human cancer cell lines range from 5.6 to 11.5 microM depending on the cell line. Flow cytometry analysis revealed that AT514 caused cell cycle arrest in G0/G1 or cell death, depending on the cell type and the length of time for which the cells were exposed to the drug. Subsequent studies revealed that AT514-induced cell death is caused by apoptosis, as indicated by caspases activation (8, 9, 2 and 3) and cleavage of poly (ADP-ribose) polymerase (PARP), release of cytochrome c and apoptosis inducing factor (AIF) from mitochondria, and the appearance of apoptotic bodies and DNA laddering. Alterations in protein levels of Bcl-2 family members might be involved in the mitochondrial disruption observed. AT514 induced p53 accumulation in wild-type p53 cells but cell death was observed in both deficient and wild-type p53 cells. Our results indicate that AT514 induces cell cycle arrest and apoptosis in breast cancer cells irrespectively of p53 status, suggesting that it might represent a potential new chemotherapeutic agent.

DNA interaction and dual topoisomerase I and II inhibition properties of the anti-tumor drug prodigiosin.

Prodigiosin is a red pigment produced by Serratia marcescens with apoptotic activity. We examined the mechanism of action of this tripyrrole alkaloid, focusing on its interaction with DNA and its ability to inhibit both topoisomerase I and topoisomerase II. We also evaluated the DNA damage induced in cancer cell lines. Prodigiosin-DNA intercalation was analyzed using a competition dialysis assay with different DNA base sequences. Topoisomerase I and II inhibition was studied in vitro by a cleavage assay, and in cultured cells, by analysis of its ability to form covalent complexes. Furthermore, we analyzed DNA damage by pulse-field gel electrophoresis and by immunocytochemistry. Apoptosis inducing factor (AIF)/phospho-H2AX (p-H2AX) double labeling by confocal microscopy was performed to determine the possible implication of AIF in the prodigiosin-DNA damage. Finally, we studied the ability of this drug to induce copper-mediated DNA damage at different pH by a DNA cleavage assay. Our results demonstrate prodigiosin-DNA interaction in vitro and in cultured cells. It involves prodigiosin-DNA intercalation, with some preference for the alternating base pairs but with no discrimination between AT or CG sequences, dual abolition of topoisomerase I and II activity and, as consequence, DNA cleavage. Prodigiosin-DNA damage is independent of AIF. Furthermore, we found that copper-mediated cleavage activity is associated with pH (occurring at pH 6.8 rather than pH 7.4) and with the Cu(2+) ion concentration. These results indicate DNA a therapeutic target for prodigiosin and could explain the apoptosis mechanism of action induced by this antineoplastic drug.

The prodigiosins: a new family of anticancer drugs.

Apoptosis is involved in the action of several (and perhaps all) cancer-chemotherapeutic agents. Prodigiosins, a family of natural red pigments characterized by a common pyrrolylpyrromethene skeleton, are produced by various bacteria. Three members of the prodigiosin family, viz. prodigiosin (PG), undecylprodigiosin (UP) and cycloprodigiosin hydrochloride (cPrG.HCl), have immunosuppressive properties and apoptotic effects on cancer cells in vitro and in vivo. Their cytotoxic effect is attributed to the presence of the C-6 methoxy substituent. The A-pyrrole ring plays a key role in both the copper nuclease activity and the cytotoxicity of prodigiosins. Here, we have reviewed the pharmacological activity of PG and related compounds, including novel synthetic PG-derivatives with lower toxicity. The mechanism of action for these molecules is a current topic in biomedicine. The molecular targets of prodigiosins are also discussed.

Host response. Inflammation-induced disruption of SCS macrophages impairs B cell responses to secondary infection.

The layer of macrophages at the subcapsular sinus (SCS) captures pathogens entering the lymph node, preventing their global dissemination and triggering an immune response. However, how infection affects SCS macrophages remains largely unexplored. Here we show that infection and inflammation disrupt the organization of SCS macrophages in a manner that involves the migration of mature dendritic cells to the lymph node. This disrupted organization reduces the capacity of SCS macrophages to retain and present antigen in a subsequent secondary infection, resulting in diminished B cell responses. Thus, the SCS macrophage layer may act as a sensor or valve during infection to temporarily shut down the lymph node to further antigenic challenge. This shutdown may increase an organism's susceptibility to secondary infections.

The prodigiosins, proapoptotic drugs with anticancer properties.

The family of natural red pigments, called prodigiosins (PGs), characterised by a common pyrrolylpyrromethene skeleton, are produced by various bacteria. Some members have immunosuppressive properties and apoptotic effects in vitro and they have also displayed antitumour activity in vivo. Understanding the mechanism of action of PGs is essential for drug development and will require the identification and characterisation of their still unidentified cell target. Four possible mechanisms of action have been suggested for these molecules: (i) PGs as pH modulators; (ii) PGs as cell cycle inhibitors; (iii) PGs as DNA cleavage agents; (iv) PGs as mitogen-activated protein kinase regulators. Here, we review the pharmacological activity of PG and related compounds, including novel synthetic PG derivatives with lower toxicity and discuss the mechanisms of action and the molecular targets of those molecules. The results reported in this review suggest that PGs are a new class of anticancer drugs, which hold out considerable promise for the Pharmacological Industry.

Mitochondria-mediated apoptosis operating irrespective of multidrug resistance in breast cancer cells by the anticancer agent prodigiosin.

Prodigiosin (PG) is a red pigment produced by Serratia marcescens with pro-apoptotic activity in haematopoietic and gastrointestinal cancer cell lines, but no marked toxicity in non-malignant cells. Breast cancer is the most frequent malignancy among women in the European Union and better therapies are needed, especially for metastatic tumors. Moreover, multidrug resistance is a common phenomenon that appears during chemotherapy, necessitating more aggressive treatment as prognosis worsens. In this work, we extend our experiments on PG-induced apoptosis to breast cancer cells. PG was potently cytotoxic in both estrogen receptor positive (MCF-7) and negative (MDA-MB-231) breast cancer cell lines. Cytochrome c release, activation of caspases-9, -8 and -7 and cleavage of poly (ADP-ribose) polymerase protein typified the apoptotic event and caspase inhibition revealed that PG acts via the mitochondrial pathway. In a multidrug-resistant subline of MCF-7 cells that over-expresses the breast cancer resistance protein, the cytotoxic activity of PG was slightly reduced. However, flow-cytometry analysis of PG accumulation and efflux in MCF-7 sublines showed that PG is not a substrate for this resistance protein. These results suggest that PG is an interesting and potent new pro-apoptotic agent for the treatment of breast cancer even when multidrug resistance transporter molecules are present.

Prodigiosin induces caspase-9 and caspase-8 activation and cytochrome C release in Jurkat T cells.

Prodigiosin (PG) is an active component of bacterial origin, with reported apoptotic effects. We examined the activation of caspases-9, -8, and -3 in PG-treated Jurkat cells in a dose-response study. These caspases were activated in apoptotic cells, as judged by the appearance of cleavage products from procaspases, and cytochrome c (cyt c) was released to the cytosol. In addition, PG induced the cleavage of poly (ADP-ribose) polymerase (PARP). This study demonstrates that the activation of caspases-9, -8, and -3 mediates PG-induced apoptosis.

Prodigiosin induces apoptosis by acting on mitochondria in human lung cancer cells.

Prodigiosin (PG) is a secondary metabolite, isolated from a culture of Serratia marcescens, which has shown potent cytotoxicity against various human cancer cell lines as well as immunosuppressive activity. The purpose of this study was to evaluate the role of mitochondria in PG-induced apoptosis. Therefore, we evaluated the apoptotic action of PG in GLC4 small cell lung cancer cell line by Hoechst 33342 staining. In these cells, we examined mitochondrial apoptosis-inducing factor (AIF) and cytochrome c (cyt c) release to the cytosol in PG time-response studies. These findings suggest that PG induces apoptosis in both caspase-dependent and caspase-independent pathways.

The cytotoxic prodigiosin induces phosphorylation of p38-MAPK but not of SAPK/JNK.

Prodigiosin (PG) is a red pigment produced by Serratia marcescens, with cytotoxic and immunosuppressive activity. It induces apoptosis in several cancer cell lines, including Jurkat-T cells. Here we examine the role of two stress-stimulated kinase cascades in this induction. Time course experiments using polyclonal antibodies showed that p38-MAPK phosphorylation began at 15 min and lasted for 3 h, whereas JNK was not phosphorylated, although both proteins were present. SB203580, a selective inhibitor of p38-MAPK, blocked its phosphorylation in PG-treated cells. Taken together, these data suggest that the PG induces phosphorylation of p38-MAPK but not of SAPK/JNK and that it increases the expression of both c-jun and c-fos oncoproteins.

Asymmetric segregation of polarized antigen on B cell division shapes presentation capacity.

During the activation of humoral immune responses, B cells acquire antigen for subsequent presentation to cognate T cells. Here we show that after mouse B cells accumulate antigen, it is maintained in a polarized distribution for extended periods in vivo. Using high-throughput imaging flow cytometry, we observed that this polarization is preserved during B cell division, promoting asymmetric antigen segregation among progeny. Antigen inheritance correlates with the ability of progeny to activate T cells: Daughter cells receiving larger antigen stores exhibit a prolonged capacity to present antigen, which renders them more effective in competing for T cell help. The generation of progeny with differential capacities for antigen presentation may have implications for somatic hypermutation and class switching during affinity maturation and as B cells commit to effector cell fates.

Proteomic analysis of prodigiosin-induced apoptosis in a breast cancer mitoxantrone-resistant (MCF-7 MR) cell line.

Prodigiosin (PG) is a bacterial, red-pigmented antibiotic with immunosuppressive and apoptotic activities. To better understand its mechanisms of action, we tried to identify proteins associated with apoptosis induced by PG. For this purpose, the variation of protein expression on exposure to apoptotic concentrations of PG was examined, by high-resolution two-dimensional gel electrophoresis (2D-E), in the MCF-7 cancer cell line resistant to mitoxantrone (MCF-7-MR). Six PG apoptosis-associated protein spots were further characterized by complementary peptide mass fingerprinting and tandem mass spectrometry data obtained on a matrix-assisted laser desorption ionization-time-of-flight/time-of-flight (MALDI-TOF/TOF) mass spectrometer. The proteins identified were involved in various cellular functions, including cell defence, DNA repair and cellular organization. Our data provide novel information on cell response to PG, a new apoptotic drug with interesting anticancer activity.