Non-Canonical NF-κB Activation and Abnormal B Cell Accumulation in Mice Expressing Ubiquitin Protein Ligase-Inactive c-IAP2

Loss of c-IAP2 ubiquitin ligase activity, which occurs in the lymphoma-causing c-IAP2/MALT1 fusion protein, activates non-canonical NF-κB signaling and results in B cell abnormalities characteristic of MALT lymphoma

Identification of Candida glabrata genes involved in pH modulation and modification of the phagosomal environment in macrophages

notes: PMCID: PMC4006850types: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov'tCandida glabrata currently ranks as the second most frequent cause of invasive candidiasis. Our previous work has shown that C. glabrata is adapted to intracellular survival in macrophages and replicates within non-acidified late endosomal-stage phagosomes. In contrast, heat killed yeasts are found in acidified matured phagosomes. In the present study, we aimed at elucidating the processes leading to inhibition of phagosome acidification and maturation. We show that phagosomes containing viable C. glabrata cells do not fuse with pre-labeled lysosomes and possess low phagosomal hydrolase activity. Inhibition of acidification occurs independent of macrophage type (human/murine), differentiation (M1-/M2-type) or activation status (vitamin D3 stimulation). We observed no differential activation of macrophage MAPK or NFκB signaling cascades downstream of pattern recognition receptors after internalization of viable compared to heat killed yeasts, but Syk activation decayed faster in macrophages containing viable yeasts. Thus, delivery of viable yeasts to non-matured phagosomes is likely not triggered by initial recognition events via MAPK or NFκB signaling, but Syk activation may be involved. Although V-ATPase is abundant in C. glabrata phagosomes, the influence of this proton pump on intracellular survival is low since blocking V-ATPase activity with bafilomycin A1 has no influence on fungal viability. Active pH modulation is one possible fungal strategy to change phagosome pH. In fact, C. glabrata is able to alkalinize its extracellular environment, when growing on amino acids as the sole carbon source in vitro. By screening a C. glabrata mutant library we identified genes important for environmental alkalinization that were further tested for their impact on phagosome pH. We found that the lack of fungal mannosyltransferases resulted in severely reduced alkalinization in vitro and in the delivery of C. glabrata to acidified phagosomes. Therefore, protein mannosylation may play a key role in alterations of phagosomal properties caused by C. glabrata.Deutsche ForschungsgemeinschaftNational Institutes for HealthWellcome TrustBBSR

Signal transduction controls heterogeneous NF-κB dynamics and target gene expression through cytokine-specific refractory states

Cells respond dynamically to pulsatile cytokine stimulation. Here we report that single, or well-spaced pulses of TNFα (>100 min apart) give a high probability of NF-κB activation. However, fewer cells respond to shorter pulse intervals (<100 min) suggesting a heterogeneous refractory state. This refractory state is established in the signal transduction network downstream of TNFR and upstream of IKK, and depends on the level of the NF-κB system negative feedback protein A20. If a second pulse within the refractory phase is IL-1β instead of TNFα, all of the cells respond. This suggests a mechanism by which two cytokines can synergistically activate an inflammatory response. Gene expression analyses show strong correlation between the cellular dynamic response and NF-κB-dependent target gene activation. These data suggest that refractory states in the NF-κB system constitute an inherent design motif of the inflammatory response and we suggest that this may avoid harmful homogenous cellular activation

QD-antibody conjugates via carbodiimide-mediated coupling: a detailed study of the variables involved and a possible new mechanism for the coupling reaction under basic aqueous conditions

A detailed study into the optimization of carbodiimide-mediated coupling of antibodies (Ab) and quantum dots (QD) for use in cellular imaging has been undertaken. This involved the grafting of commercially available carboxyl-modified QDs (Evident Technologies “Lake Placid Blue” Evitag and eBioscience’s eflour nanocrystals) with anti-Cdc8 Abs to produce conjugates with specific affinity for fission yeast tropomyosin Cdc8 protein. The water-soluble carbodiimide 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) was used to activate the QDs prior to their incubation with antibody, and a range of QD-carboxyl/EDC/Ab mole ratios were used in the experiments in attempts to optimize fluorescence and bioaffinity of the conjugate products (EDC to QD-carboxyl-600 nmol/15pmol to 0.12 nmol/15 pmol and QD to Ab 120 pmol/24 pmol to 120 pmol/1.2 pmol). It was observed that a specific “optimum” ratio of the three reactants was required to produce the most fluorescent and biologically active product and that it was generated at alkaline pH 10.8. Increasing the ratio of Ab to QD produced conjugate which was less fluorescent while reducing the ratio of EDC to QD in the activation step led to increased fluorescence of product. Conjugates were tested for their possession of antibody by measurement of their absorption at OD280 nm and for their fluorescence by assay λmaxem at 495 nm. A quantitative assay of the bioactivity of the conjugates was developed whereby a standardized amount of Cdc8 antigen was spotted onto nylon membranes and reacted with products from conjugation reactions in a sandwich-type colormetric assay The “best” conjugate was used in intracellular imaging of yeast Cdc8 protein and produced brighter, higher definition images of fixed yeast cell actin structure than a fluorescein–Ab conjugate routinely produced in our laboratory. The QD–Ab conjugate was also significantly more resistant to photobleaching than the fluorescein–Ab conjugate. Results from other experiments involving EDC, the water-soluble carbodiimide 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide metho-p-toluenesulphonate (CMC), and EDC.HCl have suggested a new reaction mechanism for EDC coupling under basic aqueous conditions. In summary, a robust understanding of commercial QD-COOH surface chemistry and the variables involved in the materials’ efficient conjugation with a bioligand using carbidiimide has been obtained along with an optimized approach for Ab–QD conjugate production. A novel assay has been developed for bioassay of QD–Ab conjugates and a new mechanism for EDC coupling under basic aqueous conditions is proposed

Observing Single Cell NF-κB Dynamics under Stimulant Concentration Gradient

Study of cell signaling often requires examination of the cellular dynamics under variation in the stimulant concentration. Such variation has typically been conducted by dispensing cell populations in a number of chambers or wells containing discrete concentrations. Such practice adds to the complexity associated with experimental or device design and requires substantial labor for implementation. Furthermore, there is also potential risk of missing important results due to the often arbitrary selection of discrete concentration values for testing. In this letter, we study NF-κB activation and translocation at the single cell level using a microfluidic device that generates continuously varying concentration gradient. We use only three device settings to cover stimulant (interleukin-1β) concentrations of four orders of magnitude (0.001-10 ng/ml). Such device allows us to study temporal dynamics of NF-κB in single cells under different stimulant concentrations by real-time imaging. Interestingly, our results reveal that while the percent of cells with NF-κB translocation decreases with lower stimulant concentration in the range of 0.1-0.001 ng/ml, the response time of such translocation remains constant, reflected by the single cell data

The protease activity of the paracaspase MALT1 is controlled by monoubiquitination.

The protease activity of the paracaspase MALT1 is central to lymphocyte activation and lymphomagenesis, but how this activity is controlled remains unknown. Here we identify a monoubiquitination of MALT1 on Lys644 that activated the protease function of MALT1. Monoubiquitinated MALT1 had enhanced protease activity, whereas a ubiquitination-deficient MALT1 mutant with replacement of that lysine with arginine (MALT1(K644R)) had less protease activity, which correlated with impaired induction of interleukin 2 (IL-2) via the T cell antigen receptor in activated T cells. Expression of MALT1(K644R) diminished the survival of cells derived from diffuse large B cell lymphoma of the activated B cell-like subtype (ABC DLBCL), which require constitutive protease activity of MALT1 for survival. Thus, monoubiquitination of MALT1 is essential for its catalytic activation and is therefore a potential target for the treatment of ABC-DLBCL and for immunomodulation