BLT1-mediated O-GlcNAcylation is required for NOX2-dependent migration, exocytotic degranulation and IL-8 release of human mast cell induced by Trichomonas vaginalis-secreted LTB4

O-GlcNAcylation and immune cell signaling: A review of known and a preview of unknown

The dynamic and reversible modification of nuclear and cytoplasmic proteins by O-GlcNAcylation significantly impacts the function and dysfunction of the immune system. O-GlcNAcylation plays crucial roles under both physiological and pathological conditions in the biochemical regulation of all immune cell functions. Three and a half decades of knowledge acquired in this field is merely sufficient to perceive that what we know is just the prelude. This review attempts to mark out the known regulatory roles of O-GlcNAcylation in key signal transduction pathways and specific protein functions in the immune system and adumbrate ensuing questions toward the unknown functions.

Candidalysin, a Virulence Factor of Candida albicans, Stimulates Mast Cells by Mediating Cross-Talk Between Signaling Pathways Activated by the Dectin-1 Receptor and MAPKs

PURPOSE

Although mast cells (MCs) modulate the activity of effector cells during Candida albicans infection, their role in the pathogenesis of candidiasis remains unclear. Candidalysin, a C. albicans-derived peptide toxin, is a crucial factor in fungal infections. We aimed to investigate the effect of candidalysin on MC activation and the underlying molecular mechanism.

METHODS

Serum from candidalysin-immunized mice was used to measure candidalysin expression in patients infected with C. albicans. MC degranulation and migration were evaluated by β-hexosaminidase release assay and chemotaxis assay, respectively. EIA and ELISA were used to evaluate the production of eicosanoids and cytokines/chemokines, respectively. The production of nitric oxide (NO) was measured with a DAF-FM diacetate kit, while reactive oxygen species (ROS) production was analyzed by flow cytometry. MAPK activation was evaluated by Western blotting.

RESULTS

We detected high candidalysin expression in the lesions of patients infected with C. albicans, and the MC number was increased in these lesions. LL-37 colocalized with MCs in the lesions of candidiasis patients. Candidalysin-enhanced MC accumulation in mice and treating LAD2 and HMC-1 cells with candidalysin induced their degranulation, migration, and production of pro- and anti-inflammatory cytokines/chemokines, eicosanoids, ROS, NO, and LL-37. Interestingly, C. albicans strains lacking candidalysin failed to induce MC activation. Moreover, candidalysin increased dectin-1 expression, and the inhibition of dectin-1 decreased MC activation. Downstream dectin-1 signaling involved the MAPK pathways.

CONCLUSION

The finding that candidalysin causes cutaneous MC activation may improve our understanding of the role of MCs in the pathology of cutaneous C. albicans infection.

Nutraceutical Aid for Allergies - Strategies for Down-Regulating Mast Cell Degranulation

Interactions of antigens with the mast cell FcεRI-IgE receptor complex induce degranulation and boost synthesis of pro-inflammatory lipid mediators and cytokines. Activation of spleen tyrosine kinase (Syk) functions as a central hub in this signaling. The tyrosine phosphatase SHP-1 opposes Syk activity; stimulation of NADPH oxidase by FcεRI activation results in the production of oxidants that reversibly inhibit SHP-1, up-regulating the signal from Syk. Activated AMPK can suppress Syk activation by the FcεRI receptor, possibly reflecting its ability to phosphorylate the FcεRI beta subunit. Cyclic GMP, via protein kinase G II, enhances the activity of SHP-1 by phosphorylating its C-terminal region; this may explain its inhibitory impact on mast cell activation. Hydrogen sulfide (H₂S) likewise opposes mast cell activation; H₂S can boost AMPK activity, up-regulate cGMP production, and trigger Nrf2-mediated induction of Phase 2 enzymes - including heme oxygenase-1, whose generation of bilirubin suppresses NADPH oxidase activity. Phycocyanobilin (PCB), a chemical relative of bilirubin, shares its inhibitory impact on NADPH oxidase, rationalizing reported anti-allergic effects of PCB-rich spirulina ingestion. Phase 2 inducer nutraceuticals can likewise oppose the up-regulatory impact of NADPH oxidase on FcεRI signaling. AMPK can be activated with the nutraceutical berberine. High-dose biotin can boost cGMP levels in mast cells via direct stimulation of soluble guanylate cyclase. Endogenous generation of H₂S in mast cells can be promoted by administering N-acetylcysteine and likely by taurine, which increases the expression of H₂S-producing enzymes in the vascular system. Mast cell stabilization by benifuuki green tea catechins may reflect the decreased surface expression of FcεRI.

Trichomonas vaginalis-secreted cysteinyl leukotrienes promote migration, degranulation and MCP-1 production in mast cells

Trichomonas vaginalis, a flagellated extracellular protozoan parasite that infects the human genitourinary tract, is usually transmitted by sexual contact. Our previous study showed that the leukotriene B₄ (LTB₄ ), a T vaginalis-secreted lipid mediator, induces interleukin (IL)-8 production and promotes mast cell degranulation and migration via BLT1 in human. In this study, we investigated whether T vaginalis produces another leukotrienes and whether it causes increased MCP-1 production, mast cell migration and degranulation by activating mast cells. We found that cysteinyl leukotrienes (CysLTs) were contained in T vaginalis-derived secretory product (TvSP) by ELISA. The TvSP-stimulated human mast cell line (HMC-1) exhibited significantly increased monocyte chemoattractant protein-1 (MCP-1) secretion compared to the unstimulated cells. Inhibition of NOX2 activation of cells by treatment of NOX inhibitor or NOX2 siRNA reduced TvSP-stimulated MCP-1 production in HMC-1 cells. It was also confirmed that the receptor for CysLTs is expressed in mast cells. The CysLT receptor (CysLTR) antagonist inhibited TvSP-stimulated MCP-1 production of mast cells, as well as ROS production, migration and degranulation of mast cells, and reduced phospho-NF-kB expression. These results suggest that T vaginalis-secreted CysLTs promote migration, degranulation and MCP-1 production in human mast cells through CysLT receptor-mediated NOX2 activation.

The role of O-GlcNAcylation in immunity against infections

Mounting an effective immune response is crucial for the host to protect itself against invading pathogens. It is now well appreciated that reprogramming of core metabolic pathways in immune cells is a key requirement for their activation and function during infections. The role of several ancillary metabolic pathways in shaping immune cell function is less well understood. One such pathway, for which interest has recently been growing, is the hexosamine biosynthesis pathway (HBP) that generates uridine diphosphate N‐acetylglucosamine (UDP‐GlcNAc), the donor substrate for a specific form of glycosylation termed O‐GlcNAcylation. O‐GlcNAc is an intracellular post‐translational modification that alters the functional properties of the modified proteins, in particular transcription factors and epigenetic regulators. An increasing number of studies suggest a central role for the HBP and O‐GlcNAcylation in dictating immune cell function, including the response to different pathogens. We here discuss the most recent insights regarding O‐GlcNAcylation and immunity, and explore whether targeting of O‐GlcNAcylation could hold promise as a therapeutic approach to modulate immune responses to infections.

The Emerging Role of Galectins and O-GlcNAc Homeostasis in Processes of Cellular Differentiation

Galectins are a family of soluble β-galactoside-binding proteins with diverse glycan-dependent and glycan-independent functions outside and inside the cell. Human cells express twelve out of sixteen recognized mammalian galectin genes and their expression profiles are very different between cell types and tissues. In this review, we summarize the current knowledge on the changes in the expression of individual galectins at mRNA and protein levels in different types of differentiating cells and the effects of recombinant galectins on cellular differentiation. A new model of galectin regulation is proposed considering the change in O-GlcNAc homeostasis between progenitor/stem cells and mature differentiated cells. The recognition of galectins as regulatory factors controlling cell differentiation and self-renewal is essential for developmental and cancer biology to develop innovative strategies for prevention and targeted treatment of proliferative diseases, tissue regeneration, and stem-cell therapy.

Redundant and Cooperative Roles for Yersinia pestis Yop Effectors in the Inhibition of Human Neutrophil Exocytic Responses Revealed by Gain-of-Function Approach

Yersinia pestis causes a rapid, lethal disease referred to as plague. Y. pestis actively inhibits the innate immune system to generate a noninflammatory environment during early stages of infection to promote colonization. The ability of Y. pestis to create this early noninflammatory environment is in part due to the action of seven Yop effector proteins that are directly injected into host cells via a type 3 secretion system (T3SS). While each Yop effector interacts with specific host proteins to inhibit their function, several Yop effectors either target the same host protein or inhibit converging signaling pathways, leading to functional redundancy. Previous work established that Y. pestis uses the T3SS to inhibit neutrophil respiratory burst, phagocytosis, and release of inflammatory cytokines. Here, we show that Y. pestis also inhibits release of granules in a T3SS-dependent manner. Moreover, using a gain-of-function approach, we discovered previously hidden contributions of YpkA and YopJ to inhibition and that cooperative actions by multiple Yop effectors are required to effectively inhibit degranulation. Independent from degranulation, we also show that multiple Yop effectors can inhibit synthesis of leukotriene B₄ (LTB₄), a potent lipid mediator released by neutrophils early during infection to promote inflammation. Together, inhibition of these two arms of the neutrophil response likely contributes to the noninflammatory environment needed for Y. pestis colonization and proliferation.