STAP-2 positively regulates FcεRI-mediated basophil activation and basophil-dependent allergic inflammatory reactions

STAP-2 negatively regulates BCR-mediated B cell activation by recruiting tyrosine-protein kinase CSK to LYN

Although signal-transducing adaptor protein-2 (STAP-2) acts in certain immune responses, its role in B cell receptor (BCR)-mediated signals remains unknown. In this study, we have revealed that BCR-mediated signals, cytokine production and antibody production were increased in STAP-2 knockout (KO) mice compared with wild-type (WT) mice. Phosphorylation of tyrosine-protein kinase LYN Y508 was reduced in STAP-2 KO B cells after BCR stimulation. Mechanistic analysis revealed that STAP-2 directly binds to LYN, dependently of STAP-2 Y250 phosphorylation by LYN. Furthermore, phosphorylation of STAP-2 enhanced interactions between LYN and tyrosine-protein kinase CSK, resulting in enhanced CSK-mediated LYN Y508 phosphorylation. These results suggest that STAP-2 is crucial for controlling BCR-mediated signals and antibody production by enhanced CSK-mediated feedback regulation of LYN.

Signal-transducing adaptor protein-1 and protein-2 in hematopoiesis and diseases

Inflammatory and immune signals are involved in stressed hematopoiesis under myeloablation, infection, chronic inflammation, and aging. These signals also affect malignant pathogenesis, and the dysregulated immune environment which causes the resistance to treatment. On activation, various types of protein tyrosine kinases in the cytoplasm mediate the cascade, leading to the transcription of target genes in the nucleus. Adaptor molecules are commonly defined as proteins that lack enzymatic activity, DNA-binding or receptor functions and possess protein-protein or protein-lipid interaction domains. By binding to specific domains of signaling molecules, adaptor proteins adjust the signaling responses after the ligation of receptors of soluble factors, including cytokines, chemokines, and growth factors, as well as pattern recognition receptors such as toll-like receptors. The signal-transducing adaptor protein (STAP) family regulates various intracellular signaling pathways. These proteins have a pleckstrin homology domain in the N-terminal region and an SRC-homology 2-like domain in the central region, representing typical binding structures as adapter proteins. Following the elucidation of the effects of STAPs on terminally differentiated immune cells, such as macrophages, T cells, mast cells, and basophils, recent findings have indicated the critical roles of STAP-2 in B-cell progenitor cells in marrow under hematopoietic stress and STAP-1 and -2 in BCR-ABL-transduced leukemogenesis. In this review, we focus on the role of STAPs in the bone marrow.

Signal-transducing adaptor protein-2 has a nonredundant role for IL-33-triggered mast cell activation

Signal-transducing adaptor protein (STAP)-2 is one of the STAP family adaptor proteins and ubiquitously expressed in a variety types of cells. Although STAP-2 is required for modification of FcεRI signal transduction in mast cells, other involvement of STAP-2 in mast cell functions is unknown, yet. In the present study, we mainly investigated functional roles of STAP-2 in IL-33-induced mast cell activation. In STAP-2-deficient, but not STAP-1-deficient, mast cells, IL-33-induced IL-6 and TNF-α production was significantly decreased compared with that of wild-type mast cells. In addition, STAP-2-deficiency greatly reduced TLR4-mediated mast cell activation and cytokine production. For the mechanisms, STAP-2 directly binds to IKKα after IL-33 stimulation, leading to elevated NF-κB activity. In conclusion, STAP-2, but not STAP-1, participates in IL-33-induced mast cells activation.

Propolis suppresses cytokine production in activated basophils and basophil-mediated skin and intestinal allergic inflammation in mice

BACKGROUND

Propolis is a resinous mixture produced by honey bees that contains cinnamic acid derivatives and flavonoids. Although propolis has been reported to inhibit mast cell functions and mast cell-dependent allergic responses, the effect of propolis on basophil biology remains unknown. This study aimed to investigate the inhibitory effect of propolis on FcεRI-mediated basophil activation.

METHODS

To determine the inhibitory effect of propolis on basophil activation in vitro, cytokine production and FcεRI signal transduction were analyzed by ELISA and western blotting, respectively. To investigate the inhibitory effect of propolis in vivo, IgE-CAI and a food allergy mouse model were employed.

RESULTS

Propolis treatment resulted in the suppression of IgE/antigen-induced production of IL-4, IL-6 and IL-13 in basophils. Phosphorylation of FcεRI signaling molecules Lyn, Akt and ERK was inhibited in basophils treated with propolis. While propolis did not affect the basophil population in the treated mice, propolis did inhibit IgE-CAI. Finally, ovalbumin-induced intestinal anaphylaxis, which involves basophils and basophil-derived IL-4, was attenuated in mice prophylactically treated with propolis.

CONCLUSIONS

Taken together, these results demonstrate the ability of propolis to suppress IgE-dependent basophil activation and basophil-dependent allergic inflammation. Therefore, prophylactic treatment with propolis may be useful for protection against food allergic reactions in sensitive individuals.

Pivotal Role of Signal-Transducing Adaptor Protein-2 in Pathogenesis of Autoimmune Hepatitis

Signal-transducing adaptor protein-2 (STAP-2) is an adaptor protein involved in inflammatory and immune responses, such as inflammatory bowel disease and allergic responses. In this study, we investigated the role of STAP-2 in the pathogenesis of autoimmune hepatitis. After intravenous injection of concanavalin A (ConA), STAP-2 knock out (KO) mice showed more severe liver necrosis along with substantial lymphocyte infiltration compared to wild type (WT) mice. Serum alanine aminotransferase levels were significantly higher in ConA-injected STAP-2 KO mice than in WT mice. Levels of interferon-γ (IFN-γ), an important factor for liver necrosis, were also significantly increased in sera of STAP-2 KO mice compared to WT mice after ConA injection. Statistically significant upregulation of Fas ligand (FasL) expression was observed in the livers of ConA-injected STAP-2 KO mice compared to WT mice. In accordance with these results, apoptotic signals were facilitated in STAP-2 KO mice compared to WT mice after ConA injection. Correctively, these results suggest that STAP-2 is involved in the pathogenesis of autoimmune hepatitis by regulating the expression of FasL and the production of IFN-γ.

Mechanisms of Allergen Immunotherapy in Allergic Rhinitis

PURPOSE OF REVIEW

Allergic rhinitis (AR) is a chronic inflammatory immunoglobulin (Ig) E-mediated disease of the nasal mucosa that can be triggered by the inhalation of seasonal or perennial allergens. Typical symptoms include sneezing, rhinorrhea, nasal itching, nasal congestion and symptoms of allergic conjunctivitis. AR affects a quarter of the population in the United States of America and Europe.

RECENT FINDINGS

AR has been shown to reduce work productivity in 36-59% of the patients with 20% reporting deteriorated job attendance. Moreover, 42% of children with AR report reduced at-school productivity and lower grades. Most importantly, AR impacts the patient's quality of life, due to sleep deprivation. However, a proportion of patients fails to respond to conventional medication and opts for the allergen immunotherapy (AIT), which currently is the only disease-modifying therapeutic option. AIT can be administered by either subcutaneous (SCIT) or sublingual (SLIT) route. Both routes of administration are safe, effective, and can lead to tolerance lasting years after treatment cessation. Both innate and adaptive immune responses that contribute to allergic inflammation are suppressed by AIT. Innate responses are ameliorated by reducing local mast cell, basophil, eosinophil, and circulating group 2 innate lymphoid cell frequencies which is accompanied by decreased basophil sensitivity. Induction of allergen-specific blocking antibodies, immunosuppressive cytokines, and regulatory T and B cell phenotypes are key pro-tolerogenic adaptive immune responses.

CONCLUSION

A comprehensive understanding of these mechanisms is necessary for optimal selection of AIT-responsive patients and monitoring treatment efficacy. Moreover, it could inspire novel and more efficient AIT approaches.

Expression of signal-transducing adaptor protein-1 attenuates experimental autoimmune hepatitis via down-regulating activation and homeostasis of invariant natural killer T cells

Objective

Signal-transducing adaptor protein (STAP) family members function as adaptor molecules and are involved in several events during immune responses. Notably however, the biological functions of STAP-1 in other cells are not known. We aimed to investigate the functions of STAP-1 in invariant natural killer T (iNKT) cells and iNKT cell-dependent hepatitis.

Methods

We employed concanavalin A (Con A)-induced hepatitis and α-galactosylceramide (α-GalCer)-induced hepatitis mouse models, both are models of iNKT cell-dependent autoimmune hepatitis, and STAP-1 overexpressing 2E10 cells to investigate the role of STAP-1 in iNKT cell activation in vivo an in vitro, respectively.

Results

After Con A- or α-GalCer-injection, hepatocyte necrotic areas and plasma alanine aminotransferase elevation were more severe in STAP-1 knockout (S1KO) mice and milder in lymphocyte-specific STAP-1 transgenic (S1Tg) mice, as compared to wild-type (WT) mice. Two events that may be related to Con A-induced and/or α-GalCer-induced hepatitis were influenced by STAP-1 manipulation. One is that iNKT cell populations in the livers and spleens were increased in S1KO mice and were decreased in S1Tg mice. The other is that Con A-induced interleukin-4 and interferon-γ production was attenuated by STAP-1 overexpression. These effects of STAP-1 were confirmed using 2E10 cells overexpressing STAP-1 that showed impairment of interleukin-4 and interferon-γ production as well as phosphorylation of Akt and mitogen-activated protein kinases in response to Con A stimulation.

Conclusions

These results conclude that STAP-1 regulates iNKT cell maintenance/activation, and is involved in the pathogenesis of autoimmune hepatitis.