Mountain cedar pollen induces IgE-independent mast cell degranulation, IL-4 production, and intracellular reactive oxygen species generation

Cedar pollens cause severe allergic disease throughout the world. We have previously characterized allergenic pollen glycoproteins from mountain cedar (Juniperus ashei) that bind to allergen-specific immunoglobulin E (IgE). In the present report, we investigated an alternative pathway of mast cell activation by mountain cedar pollen extract through IgE-independent mechanisms. We show that mountain cedar pollen directly induces mast cell serotonin and IL-4 release and enhances release induced by IgE cross-linking. Concomitant with mediator release, high levels of intracellular reactive oxygen species (ROS) were generated, and both ROS and serotonin release were inhibited by anti-oxidants. These findings suggest that alternative mechanisms exist whereby pollen exposure enhances allergic inflammatory mediator release through mechanisms that involve ROS. These mechanisms have the potential for enhancing the allergenic potency of pollens.     

NEU1 Sialidase Regulates the Sialylation State of CD31 and Disrupts CD31-driven Capillary-like Tube Formation in Human Lung Microvascular Endothelia

The highly sialylated vascular endothelial surface undergoes changes in sialylation upon adopting the migratory/angiogenic phenotype. We recently established endothelial cell (EC) expression of NEU1 sialidase (Cross, A. S., Hyun, S. W., Miranda-Ribera, A., Feng, C., Liu, A., Nguyen, C., Zhang, L., Luzina, I. G., Atamas, S. P., Twaddell, W. S., Guang, W., Lillehoj, E. P., Puché, A. C., Huang, W., Wang, L. X., Passaniti, A., and Goldblum, S. E. (2012) NEU1 and NEU3 sialidase activity expressed in human lung microvascular endothelia. NEU1 restrains endothelial cell migration whereas NEU3 does not. J. Biol. Chem. 287, 15966–15980). We asked whether NEU1 might regulate EC capillary-like tube formation on a Matrigel substrate. In human pulmonary microvascular ECs (HPMECs), prior silencing of NEU1 did not alter tube formation. Infection of HPMECs with increasing multiplicities of infection of an adenovirus encoding for catalytically active WT NEU1 dose-dependently impaired tube formation, whereas overexpression of either a catalytically dead NEU1 mutant, NEU1-G68V, or another human sialidase, NEU3, did not. NEU1 overexpression also diminished EC adhesion to the Matrigel substrate and restrained EC migration in a wounding assay. In HPMECs, the adhesion molecule, CD31, also known as platelet endothelial cell adhesion molecule-1, was sialylated via α2,6-linkages, as shown by Sambucus nigra agglutinin lectin blotting. NEU1 overexpression increased CD31 binding to Arachis hypogaea or peanut agglutinin lectin, indicating CD31 desialylation. In the postconfluent state, when CD31 ectodomains are homophilically engaged, NEU1 was recruited to and desialylated CD31. In postconfluent ECs, CD31 was desialylated compared with subconfluent cells, and prior NEU1 silencing completely protected against CD31 desialylation. Prior CD31 silencing and the use of CD31-null ECs each abrogated the NEU1 inhibitory effect on EC tube formation. Sialyltransferase 6 GAL-I overexpression increased α2,6-linked CD31 sialylation and dose-dependently counteracted NEU1-mediated inhibition of EC tube formation. These combined data indicate that catalytically active NEU1 inhibits in vitro angiogenesis through desialylation of its substrate, CD31.     

Cytotoxic T lymphocyte lysis of HTLV-1 infected cells is limited by weak HBZ protein expression,but non-specifically enhanced on induction of Tax expression

Background

Immunogenetic evidence indicates that cytotoxic T lymphocytes (CTLs) specific for the weak CTL antigen HBZ limit HTLV-1 proviral load in vivo, whereas there is no clear relationship between the proviral load and the frequency of CTLs specific for the immunodominant antigen Tax. In vivo, circulating HTLV-1-infected cells express HBZ mRNA in contrast, Tax expression is typically low or undetectable. To elucidate the virus-suppressing potential of CTLs targeting HBZ, we compared the ability of HBZ- and Tax-specific CTLs to lyse naturally-infected cells, by co-incubating HBZ- and Tax-specific CTL clones with primary CD4⁺ T cells from HLA-matched HTLV-1-infected donors. We quantified lysis of infected cells, and tested whether specific virus-induced host cell surface molecules determine the susceptibility of infected cells to CTL-mediated lysis.

Results

Primary infected cells upregulated HLA-A*02, ICAM-1, Fas and TRAIL-R1/2 in concert with Tax expression, forming efficient targets for both HTLV-1-specific CTLs and CTLs specific for an unrelated virus. We detected expression of HBZ mRNA (spliced isoform) in both Tax-expressing and non-expressing infected cells, and the HBZ_26–34 epitope was processed and presented by cells transfected with an HBZ expression plasmid. However, when coincubated with primary cells, a high-avidity HBZ-specific CTL clone killed significantly fewer infected cells than were killed by a Tax-specific CTL clone. Finally, incubation with Tax- or HBZ-specific CTLs resulted in a significant decrease in the frequency of cells expressing high levels of HLA-A*02.

Conclusions

HTLV-1 gene expression in primary CD4⁺ T cells non-specifically increases susceptibility to CTL lysis. Despite the presence of HBZ spliced-isoform mRNA, HBZ epitope presentation by primary cells is significantly less efficient than that of Tax.

     

A model for the structure of the C-terminal domain of dragline spider silk and the role of its conserved cysteine

Dragline spider silk fibers have extraordinary attributes as biomaterials of superior strength and toughness. Previously we have shown that the conserved C-terminal domain of a dragline spider silk protein is necessary for directing oriented microfiber formation. Here we present for the first time a state-of-the-art model of the three-dimensional structure of this domain, and, by comparing several dragline proteins, identify its key evolutionarily conserved features. Further, using the baculovirus expression system, we produced recombinant proteins that are mutated in the unique cysteine residue present in the domain. While a conservative mutation to serine allows fiber formation, thus demonstrating that there is no need for disulfide bond formation in this system, a mutation to arginine significantly alters the local surface properties, preventing fiber formation. These experimental results are in agreement with our model, wherein the cysteine is localized in a highly conserved hydrophobic loop that we predict to be important for the protein-protein interactions of this domain and hence also for fiber formation.     

NEU1 sialidase expressed in human airway epithelia regulates epidermal growth factor receptor (EGFR) and MUC1 protein signaling

Epithelial cells (ECs) lining the airways provide a protective barrier between the external environment and the internal host milieu. These same airway epithelia express receptors that respond to danger signals and initiate repair programs. Because the sialylation state of a receptor can influence its function and is dictated in part by sialidase activity, we asked whether airway epithelia express catalytically active sialidase(s). Human primary small airway and A549 ECs expressed NEU1 sialidase at the mRNA and protein levels, and NEU1 accounted for >70% of EC sialidase activity. Blotting with Maackia amurensis and peanut agglutinin lectins established epidermal growth factor receptor (EGFR) and MUC1 as in vivo substrates for NEU1. NEU1 associated with EGFR and MUC1, and NEU1-EGFR association was regulated by EGF stimulation. NEU1 overexpression diminished EGF-stimulated EGFR Tyr-1068 autophosphorylation by up to 44% but enhanced MUC1-dependent Pseudomonas aeruginosa adhesion by 1.6-1.7-fold and flagellin-stimulated ERK1/2 activation by 1.7-1.9-fold. In contrast, NEU1 depletion increased EGFR activation (1.5-fold) and diminished MUC1-mediated bacterial adhesion (38-56%) and signaling (73%). These data indicate for the first time that human airway epithelia express catalytically active NEU1 sialidase that regulates EGFR- and MUC1-dependent signaling and bacterial adhesion. NEU1 catalytic activity may offer an additional level of regulation over the airway epithelial response to ligands, pathogens, and injurious stimuli.     

TRAF6 protein couples Toll-like receptor 4 signaling to Src family kinase activation and opening of paracellular pathway in human lung microvascular endothelia

Gram-negative bacteria release lipopolysaccharide (LPS) into the bloodstream. Here, it engages Toll-like receptor (TLR) 4 expressed in human lung microvascular endothelia (HMVEC-Ls) to open the paracellular pathway through Src family kinase (SFK) activation. The signaling molecules that couple TLR4 to the SFK-driven barrier disruption are unknown. In HMVEC-Ls, siRNA-induced silencing of TIRAP/Mal and overexpression of dominant-negative TIRAP/Mal each blocked LPS-induced SFK activation and increases in transendothelial [(14)C]albumin flux, implicating the MyD88-dependent pathway. LPS increased TRAF6 autoubiquitination and binding to IRAK1. Silencing of TRAF6, TRAF6-dominant-negative overexpression, or preincubation of HMVEC-Ls with a cell-permeable TRAF6 decoy peptide decreased both LPS-induced SFK activation and barrier disruption. LPS increased binding of both c-Src and Fyn to GST-TRAF6 but not to a GST-TRAF6 mutant in which the three prolines in the putative Src homology 3 domain-binding motif (amino acids 461-469) were substituted with alanines. A cell-permeable decoy peptide corresponding to the same proline-rich motif reduced SFK binding to WT GST-TRAF6 compared with the Pro → Ala-substituted peptide. Finally, LPS increased binding of activated Tyr(P)(416)-SFK to GST-TRAF6, and preincubation of HMVEC-Ls with SFK-selective tyrosine kinase inhibitors, PP2 and SU6656, diminished TRAF6 binding to c-Src and Fyn. During the TRAF6-SFK association, TRAF6 catalyzed Lys(63)-linked ubiquitination of c-Src and Fyn, whereas SFK activation increased tyrosine phosphorylation of TRAF6. The TRAF6 decoy peptide blocked both LPS-induced SFK ubiquitination and TRAF6 phosphorylation. Together, these data indicate that the proline-rich Src homology 3 domain-binding motif in TRAF6 interacts directly with activated SFKs to couple LPS engagement of TLR4 to SFK activation and loss of barrier integrity in HMVEC-Ls.