Regulation of FcepsilonRI-mediated signaling by an adaptor protein STAP-2/BSK in rat basophilic leukemia RBL-2H3 cells

Potential of targeting signal-transducing adaptor protein-2 in cancer therapeutic applications

Adaptor proteins play essential roles in various intracellular signaling pathways. Signal-transducing adaptor protein-2 (STAP-2) is an adaptor protein that possesses pleckstrin homology (PH) and Src homology 2 (SH2) domains, as well as a YXXQ signal transducer and activator of transcription 3 (STAT3)-binding motif in its C-terminal region. STAP-2 is also a substrate of breast tumor kinase (BRK). STAP-2/BRK expression is deregulated in breast cancers and enhances STAT3-dependent cell proliferation. In prostate cancer cells, STAP-2 interacts with and stabilizes epidermal growth factor receptor (EGFR) after stimulation, resulting in the upregulation of EGFR signaling, which contributes to cancer-cell proliferation and tumor progression. Therefore, inhibition of the interaction between STAP-2 and BRK/EGFR may be a possible therapeutic strategy for these cancers. For this purpose, peptides that interfere with STAP-2/BRK/EGFR binding may have great potential. Indeed, the identified peptide inhibitor successfully suppressed the STAP-2/EGFR protein interaction, EGFR stabilization, and cancer-cell growth. Furthermore, the peptide inhibitor suppressed tumor formation in human prostate- and lung-cancer cell lines in a murine xenograft model. This review focuses on the inhibitory peptide as a promising candidate for the treatment of prostate and lung cancers.

STAP-2-Derived Peptide Suppresses TCR-Mediated Signals to Initiate Immune Responses

Signal-transducing adaptor protein-2 (STAP-2) is an adaptor protein that contains pleckstrin and Src homology 2-like domains, as well as a proline-rich region in its C-terminal region. Our previous study demonstrated that STAP-2 positively regulates TCR signaling by associating with TCR-proximal CD3ζ ITAMs and the lymphocyte-specific protein tyrosine kinase. In this study, we identify the STAP-2 interacting regions of CD3ζ ITAMs and show that the STAP-2-derived synthetic peptide (iSP2) directly interacts with the ITAM sequence and blocks the interactions between STAP-2 and CD3ζ ITAMs. Cell-penetrating iSP2 was delivered into human and murine T cells. iSP2 suppressed cell proliferation and TCR-induced IL-2 production. Importantly, iSP2 treatment suppressed TCR-mediated activation of naive CD4+ T cells and decreased immune responses in CD4+ T cell-mediated experimental autoimmune encephalomyelitis. It is likely that iSP2 is a novel immunomodulatory tool that modulates STAP-2-mediated activation of TCR signaling and represses the progression of autoimmune diseases.

A peptide derived from adaptor protein STAP-2 inhibits tumor progression by downregulating epidermal growth factor receptor signaling

Signal-transducing adaptor family member-2 (STAP-2) is an adaptor protein that regulates various intracellular signals. We previously demonstrated that STAP-2 binds to epidermal growth factor receptor (EGFR) and facilitates its stability and activation of EGFR signaling in prostate cancer cells. Inhibition of this interaction may be a promising direction for cancer treatment. Here, we found that 2D5 peptide, a STAP-2-derived peptide, blocked STAP-2-EGFR interactions and suppressed EGFR-mediated proliferation in several cancer cell lines. 2D5 peptide inhibited tumor growth of human prostate cancer cell line DU145 and human lung cancer cell line A549 in murine xenograft models. Additionally, we determined that EGFR signaling and its stability were decreased by 2D5 peptide treatment during EGF stimulation. In conclusion, our study shows that 2D5 peptide is a novel anticancer peptide that inhibits STAP-2-mediated activation of EGFR signaling and suppresses prostate and lung cancer progression.

STAP-2 Is a Novel Positive Regulator of TCR-Proximal Signals

TCR ligation with an Ag presented on MHC molecules promotes T cell activation, leading to the selection, differentiation, and proliferation of T cells and cytokine production. These immunological events are optimally arranged to provide appropriate responses against a variety of pathogens. We here propose signal-transducing adaptor protein-2 (STAP-2) as a new positive regulator of TCR signaling. STAP-2-deficient T cells showed reduced, whereas STAP-2-overexpressing T cells showed enhanced, TCR-mediated signaling and downstream IL-2 production. For the mechanisms, STAP-2 associated with TCR-proximal CD3ζ immunoreceptor tyrosine activation motifs and phosphorylated LCK, resulting in enhancement of their binding after TCR stimulation. In parallel, STAP-2 expression is required for full activation of downstream TCR signaling. Importantly, STAP-2-deficient mice exhibited slight phenotypes of CD4⁺ T-cell-mediated inflammatory diseases, such as experimental autoimmune encephalomyelitis, whereas STAP-2-overexpressing transgenic mice showed severe phenotypes of these diseases. Together, STAP-2 is an adaptor protein to enhance TCR signaling; therefore, manipulating STAP-2 will have an ability to improve the treatment of patients with autoimmune diseases as well as the chimeric Ag receptor T cell therapy.

STAP-2 Adaptor Protein Regulates Multiple Steps of Immune and Inflammatory Responses

Signal-transducing adaptor protein (STAP)-2 is an adaptor molecule involved in regulation of several intracellular signaling events in immune cells. STAP-2 contains a pleckstrin homology domain at the N-terminus, an src homology domain in the central portion and a proline-rich region at the C-terminus. STAP-2 also has a YXXQ motif, which is a potential signal transducer and activator of transcription (STAT)3-binding site. STAP-2 influences the STAT3 and STAT5 activity, integrin-mediated T cell adhesion, chemokine-induced T cell migration, Fas-mediated T cell apoptosis, Toll-like receptor-mediated macrophage functions, macrophage colony-stimulating factor-induced macrophage activation, and the high-affinity immunoglobulin E receptor-mediated mast cell activation. This article reviews the current understanding of roles of the STAP-2 during immune and/or inflammatory responses, and discusses possible therapeutic applications of targeting STAP-2 proteins in immune-related disorders.

α-Linolenic acid attenuates pseudo-allergic reactions by inhibiting Lyn kinase activity

BACKGROUND

Pseudo-allergic reactions are potentially fatal hypersensitivity responses caused by mast cell activation. α-linolenic acid (ALA) is known for its anti-allergic properties. However, its potential anti-pseudo-allergic effects were not much investigated.

PURPOSE

To investigate the inhibitory effects of ALA on IgE-independent allergy in vitro, and in vivo, as well as the mechanism underlying its effects.

METHODS/STUDY DESIGNS

The anti-anaphylactoid activity of ALA was evaluated in passive cutaneous anaphylaxis reaction (PCA) and systemic anaphylaxis models. Calcium imaging was used to assess intracellular Ca2+ mobilization. The release of cytokines and chemokines was measured using enzyme immunoassay kits. Western blot analysis was conducted to investigate the molecules of Lyn-PLCγ-IP3R-Ca2+ and Lyn-p38/NF-κB signaling pathway.

RESULTS

ALA (0, 1.0, 2.0, and 4.0 mg/kg) dose-dependently reduced serum histamine, chemokine release, vasodilation, eosinophil infiltration, and the percentage of degranulated mast cells in C57BL/6 mice. In addition, ALA (0, 50, 100, and 200 μM) reduced Compound 48/80 (C48/80) (30 μg/ml)-or Substance P (SP) (4 μg/ml)-induced calcium influx, mast cell degranulation and cytokines and chemokine release in Laboratory of Allergic Disease 2 (LAD2) cells via Lyn-PLCγ-IP3R-Ca2+ and Lyn-p38/NF-κB signaling pathway. Moreover, ALA (0, 50, 100, and 200 μM) inhibited C48/80 (30 μg/ml)- and SP (4 μg/ml)-induced calcium influx in Mas-related G-protein coupled receptor member X2 (MrgX2)-HEK293 cells and in vitro kinase assays confirmed that ALA inhibited the activity of Lyn kinase. In response to 200 μM of ALA, the activity of Lyn kinase by (7.296 ± 0.03751) × 10-5 units/μl and decreased compared with C48/80 (30 μg/ml) by (8.572 ± 0.1365) ×10-5 units/μl.

CONCLUSION

Our results demonstrate that ALA might be a potential Lyn kinase inhibitor, which could be used to treat pseudo-allergic reaction-related diseases such as urticaria.

Inhibitory effect of the branches of Hovenia dulcis Thunb. and its constituent pinosylvin on the activities of IgE-mediated mast cells and passive cutaneous anaphylaxis in mice

Hovenia dulcis Thunb. (Rhamnaceae) is a hardy tree native to Europe, the Middle East, and North Africa, and it is also grown in parts of Asia and has been used in traditional medicine to treat liver toxicity, stomach disorders, and inflammation. This study investigated the anti-allergy potential of an extract of the branches of H. dulcis (HDB) using the antigen-stimulated mast cell-like cell line rat basophilic leukemia (RBL)-2H3 and a passive cutaneous anaphylaxis (PCA) mouse model. Degranulation assay, reverse transcription PCR, enzyme-lined immunosorbent assays, western blot analyses, and PCA were performed to measure allergic responses and proinflammatory mediators in antigen-stimulated rat basophilic leukemia (RBL)-2H3 mast cells and the PCA mouse model. In antigen-stimulated RBL-2H3 cells, HDB inhibited the secretion of β-hexosaminidase (indicating the inhibition of degranulation) and histamine release; decreased expression and production of the inflammatory mediators, cyclooxygenase-2 and prostaglandin E2, and cytokines interleukin-4 and tumor necrosis factor-α; and suppressed activation of nuclear factor κB, a transcription factor involved in the response to cytokines. HDB attenuated phosphorylation of the mast cell downstream effectors Lyn, Syk, phospholipase Cγ, protein kinase Cμ, extracellular signal-regulated kinase and p38. In IgE-sensitized mice, HDB inhibited mast cell-dependent PCA. Furthermore, HDB contained pinosylvin and possessed significant anti-allergic activities. These results suggest that HDB would be of value in the prevention and treatment of allergic diseases.

STAP-2 Protein Expression in B16F10 Melanoma Cells Positively Regulates Protein Levels of Tyrosinase, Which Determines Organs to Infiltrate in the Body

Melanoma is the most serious type of skin cancer, with a highly metastatic phenotype. In this report, we show that signal transducing adaptor protein 2 (STAP-2) is involved in cell migration, proliferation, and melanogenesis as well as chemokine receptor expression and tumorigenesis in B16F10 melanoma cells. This was evident in mice injected with STAP-2 shRNA (shSTAP-2)-expressing B16F10 cells, which infiltrated organs in a completely different pattern from the original cells, showing massive colonization in the liver, kidney, and neck but not in the lung. The most important finding was that STAP-2 expression determined tyrosinase protein content. STAP-2 colocalized with tyrosinase in lysosomes and protected tyrosinase from protein degradation. It is noteworthy that B16F10 cells with knocked down tyrosinase showed similar cell characteristics as shSTAP-2 cells. These results indicated that tyrosinase contributed to some cellular events beyond melanogenesis. Taken together, one possibility is that STAP-2 positively regulates the protein levels of tyrosinase, which determines tumor invasion via controlling chemokine receptor expression.

Signal-transducing adaptor protein-2 controls the IgE-mediated, mast cell-mediated anaphylactic responses

Signal-transducing adaptor protein-2 (STAP-2) is a recently identified adaptor protein that regulates immune and inflammatory responses through interactions with a variety of signaling and transcriptional molecules. In the current study, we clarified the physiological role of STAP-2 in mast cell function, a key mediator of IgE-associated allergic responses. STAP-2 is constitutively expressed in mast cells. STAP-2 deficiency in mast cells greatly enhances FcεRI-mediated signals, resulting in the increased tyrosine phosphorylation of the phospholipase C-γ isoform, calcium mobilization, and degranulation. Of importance, STAP-2-deficient mice challenged with DNP-BSA after passive sensitization with anti-DNP IgE show more severe rectal temperature decrease than do wild-type mice. STAP-2-deficient mice also show increased vascular permeability and more severe cutaneous anaphylaxis after DNP-BSA injection. These regulatory functions performed by STAP-2 indicate that there is an interaction between STAP-2 and FcεRI. In addition, our previous data indicate that STAP-2 binds to the phospholipase C-γ isoform and IκB kinase-β. Therefore, our data described in this article strongly suggest that manipulation of STAP-2 expression in mast cells may control the pathogenesis of allergic diseases and have the potential for treating patients with allergy.

Antiallergic activity of novel isoflavone methyl-glycosides from Cordyceps militaris grown on germinated soybeans in antigen-stimulated mast cells

Isoflavones are known to possess immunomodulating and antiallergic activities. Previously we identified novel isoflavone methyl-glycosides (daidzein 7-O-β-d-glucoside 4″-O-methylate (CDGM), glycitein 7-O-β-D-glucoside 4″-O-methylate (CGLM), genistein 7-O-β-D-glucoside 4″-O-methylate (CGNMI) and genistein 4'-O-β-D-glucoside 4″-O-methylate (CGNMII)) from Cordyceps militaris grown on germinated soybeans (GSC). The biological activity of novel isoflavone methyl-glycosides, however, remains unknown. In this study, CGNMII showed the strongest inhibition of degranulation. Additionally, the release of interleukin (IL)-4 and tumor necrosis factor (TNF)-α was decreased by CGNMII in antigen-stimulated RBL-2H3 cells. To elucidate the antiallergic mechanism of CGNMII, we examined whether it affected levels of signaling molecules responsible for degranulation. The levels of activated Lyn, Syk, PLCγ1 and LAT proteins were reduced in CGNMII treated RBL-2H3 cells. CGNMII also inhibited the activation of AKT and ERK1/2 proteins. These results suggest that CGNMII might be used as a therapeutic agent for allergic diseases.

Involvement of STAP-2 in Brk-mediated phosphorylation and activation of STAT5 in breast cancer cells

Signal-transducing adaptor protein (STAP)-2 is a recently identified adaptor protein that contains Pleckstrin homology and Src homology 2-like domains, and is also known to be a substrate of breast tumor kinase (Brk). In a previous study, we found that STAP-2 upregulated Brk-mediated activation of signal transducer and activator of transcription (STAT) 3 in breast cancer cells. Here, we examined the involvement of STAP-2 in Brk-mediated STAT5 activation in breast cancer cells. Ectopic expression of STAP-2 induced Brk-mediated transcriptional activity of STAT5. Furthermore, STAP-2-knockdown in T47D breast cancer cells induced a marked decrease in proliferation that was as strong as that after Brk- or STAT5b-knockdown. Regarding the mechanism, the Pleckstrin homology domain of STAP-2 is likely to participate in the process by which Brk phosphorylates and activates STAT5. Taken together, our findings provide insights toward the development of novel therapeutic strategies as well as novel prognostic values in breast carcinomas.

[Novel adaptor protein, STAP-2 functions as a signal modulator in immune system]

Signal-transducing adaptor protein-2 (STAP-2) was recently identified as a novel adaptor protein and is a family of STAP adaptor protein and has a variety of functions in cellular signal transductions. Especially STAP-2 has a crucial role in immune systems by controlling cytokine signal transduction. STAP-2 functionally interacts with STAT3 through its YXXQ motif and enhances STAT3 transcriptional activation. In contrast, STAP-2 interacts with STAT5 through its PH and SH2-like domains and decreases STAT5 activity. Importantly, STAP-2 also binds to MyD88 and IKK-alpha/beta and regulates LPS/TLR4 signaling. Moreover, STAP-2 interacts with Epstein-Barr virus-derived LMP1 and modulates LMP1-mediated NF-kappaB signaling. More importantly, experiments using STAP-2 deficient mice showed that STAP-2 modulated several T-cell functions. T-cells from STAP-2 deficient mice showed enhanced integrin-mediated cell adhesion to fibronectin. Furthermore STAP-2-deficient T-cells show reduced chemotaxis toward SDF-1alpha. These accumulated evidences indicate that novel adaptor protein STAP-2 plays an important modulator role in both of innate and adaptive immune systems.

Signal-transducing adaptor protein-2 regulates stromal cell-derived factor-1 alpha-induced chemotaxis in T cells

Signal-transducing adaptor protein-2 (STAP-2) is a recently identified adaptor protein that contains pleckstrin and Src homology 2-like domains, as well as a YXXQ motif in its C-terminal region. Our previous studies revealed that STAP-2 regulates integrin-mediated T cell adhesion. In the present study, we find that STAP-2 expression affects Jurkat T cell migration after stromal cell-derived factor-1alpha (SDF-1alpha)-treatment. Furthermore, STAP-2-deficient T cells exhibit reduced cell migration after SDF-1alpha-treatment. Importantly, overexpression of STAP-2 in Jurkat T cells induces activation of small guanine triphosphatases, such as Rac1 and Cdc42. Regarding the mechanism for this effect, we found that STAP-2 associates with Vav1, the guanine-nucleotide exchanging factor for Rac1, and enhances downstream Vav1/Rac1 signaling. These results reveal a novel STAP-2-mediated mechanism for the regulation of SDF-1alpha-induced chemotaxis of T cells via activation of Vav1/Rac1 signaling.

Signal-Transducing Adaptor Protein-2 Regulates Integrin-Mediated T Cell Adhesion through Protein Degradation of Focal Adhesion Kinase

Signal-transducing adaptor protein-2 (STAP-2) is a recently identified adaptor protein that contains pleckstrin homology- and Src homology 2-like domains as well as a YXXQ motif in its C-terminal region. Our previous studies demonstrated that STAP-2 binds to STAT3 and STAT5, and regulates their signaling pathways. In the present study, we find that STAP-2-deficient splenocytes or T cells exhibit enhanced cell adhesion to fibronectin after PMA treatment, and that STAP-2-deficient T cells contain the increased protein contents of focal adhesion kinase (FAK). Furthermore, overexpression of STAP-2 induces a dramatic decrease in the protein contents of FAK and integrin-mediated T cell adhesion to fibronectin in Jurkat T cells via the degradation of FAK. Regarding the mechanism for this effect, we found that STAP-2 associates with FAK and enhances its degradation, proteasome inhibitors block FAK degradation, and STAP-2 recruits an endogenous E3 ubiquitin ligase, Cbl, to FAK. These results reveal a novel regulation mechanism for integrin-mediated signaling in T cells via STAP-2, which directly interacts with and degrades FAK.

Regulation of the mast cell response to the type 1 Fc epsilon receptor

The type I Fc epsilon receptor (Fc epsilon RI) is one of the better understood members of its class and is central to the immunological activation of mast cells and basophils, the key players in immunoglobulin E (IgE)-dependent immediate hypersensitivity. This review provides background information on several distinct regulatory mechanisms controlling this receptor's stimulus-response coupling network. First, we review the current understanding of this network's operation, and then we focus on the inhibitory regulatory mechanisms. In particular, we discuss the different known cytosolic molecules (e.g. kinases, phosphatases, and adapters) as well as cell membrane proteins involved in negatively regulating the Fc epsilon RI-induced secretory responses. Knowledge of this field is developing at a fast rate, as new proteins endowed with regulatory functions are still being discovered. Our understanding of the complex networks by which these proteins exert regulation is limited. Although the scope of this review does not include addressing several important biochemical and biophysical aspects of the regulatory mechanisms, it does provide general insights into a central field in immunology.

STAP-2 regulates c-Fms/M-CSF receptor signaling in murine macrophage Raw 264.7 cells

Signal-transducing adaptor protein-2 (STAP-2) is a recently identified adaptor protein as a c-Fms/M-CSF receptor-interacting protein and constitutively expressed in macrophages. Our previous studies also revealed that STAP-2 binds to MyD88 and IKK-alpha/beta, and modulates NF-kappaB signaling in macrophages. In the present study, we examined physiological roles of the interaction between STAP-2 and c-Fms in Raw 264.7 macrophage cells. Our immunoprecipitation has revealed that c-Fms directly interacts with the PH domain of STAP-2 independently on M-CSF-stimulation. Ectopic expression of STAP-2 markedly suppressed M-CSF-induced tyrosine phosphorylation of c-Fms as well as activation of Akt and extracellular signal regulated kinase. In addition, Raw 264.7 cells over-expressing STAP-2 showed impaired migration in response to M-CSF and wound-healing process. Taken together, our findings demonstrate that STAP-2 directly binds to c-Fms and interferes with the PI3K signaling, which leads to macrophage motility, in Raw 264.7 cells.

Leukemia inhibitory factor-induced phosphorylation of STAP-2 on tyrosine-250 is involved in its STAT3-enhancing activity

Signal transducing adaptor protein-2 (STAP-2) is a recently identified adaptor protein that contains Pleckstrin and Src homology 2 (SH2)-like domains as well as a YXXQ motif in its C-terminal region. Our previous studies revealed that STAP-2 binds to signal transducer and activator of transcription 3 (STAT3) and STAT5, and regulates their signaling pathways. In the present study, we identified tyrosine-250 (Tyr250) in STAP-2 as a major site of phosphorylation by v-src and Jak2, using a phospho-specific antibody against STAP-2 phosphorylated at Tyr250. Mutational analyses revealed that Tyr250 was involved in the STAT3-enhancing activity of STAP-2. We further found that leukemia inhibitory factor (LIF) stimulated STAP-2 Tyr250 phosphorylation in 293T and Hep3B cells. Moreover, endogenous STAP-2 was phosphorylated at Tyr250 following LIF stimulation of murine M1 cell line. Taken together, our findings demonstrate that endogenous STAP-2 is phosphorylated at Tyr250 and that this phosphorylation is involved in its function.

Stat5 in the mammary gland: controlling normal development and cancer

The signal transducer and activator of transcription (Stat5) funnels extracellular signals of cytokines, hormones, and growth factors into transcriptional activity in the mammary gland. Postnatal development and functionality of this tissue is synchronized with the reproductive cycle. Consequently, Stat5 involvement in lobuloalveolar development, milk-protein synthesis, or tissue remodeling is dictated by the particular reproductive stage. Latent deregulation of Stat5 activity during the reproductive cycle predisposes the tissue to tumorigenesis at a later stage, when the female is no longer fertile. Accumulating data from studies with mouse models and breast-cancer specimens demonstrate a dual role for Stat5 in this context. It causes tumorigenesis, but delays metastasis progression. Consequently, Stat5 activity in breast-cancer specimens marks a better prognosis for survival.

Modulation of TLR4 signaling by a novel adaptor protein signal-transducing adaptor protein-2 in macrophages

Signal-transducing adaptor protein-2 (STAP-2) is a recently identified adaptor protein that contains pleckstrin and Src homology 2-like domains as well as a YXXQ motif in its C-terminal region. Our previous studies have demonstrated that STAP-2 binds to STAT3 and STAT5, and regulates their signaling pathways. In the present study, STAP-2 was found to positively regulate LPS/TLR4-mediated signals in macrophages. Disruption of STAP-2 resulted in impaired LPS/TLR4-induced cytokine production and NF-kappaB activation. Conversely, overexpression of STAP-2 enhanced these LPS/TLR4-induced biological activities. STAP-2, particularly its Src homology 2-like domain, bound to both MyD88 and IkappaB kinase (IKK)-alphabeta, but not TNFR-associated factor 6 or IL-1R-associated kinase 1, and formed a functional complex composed of MyD88-STAP-2-IKK-alphabeta. These interactions augmented MyD88- and/or IKK-alphabeta-dependent signals, leading to enhancement of the NF-kappaB activity. These results demonstrate that STAP-2 may constitute an alternative LPS/TLR4 pathway for NF-kappaB activation instead of the TNFR-associated factor 6-IL-1R-associated kinase 1 pathway.

Physical and Functional Interactions between STAP-2/BKS and STAT5

Signal-transducing adaptor protein family of proteins (STAPs), which currently contains two members, are proposed to be adaptor molecules because of their pleckstrin homology (PH) and Src-homology 2 (SH2)-like domains. STAP-1 has been shown to interact with STAT5 and the tyrosine kinase Tec. With regard to STAP-2/BKS functions, immunoprecipitation experiments and intracellular stainings revealed STAP-2/BKS binds STAT5 in several types of cells. Mutational studies revealed that the PH- and SH2-like domains of STAP-2/BKS interacted with the C-terminal region of STAT5. STAP-2/BKS and STAT5 were found to constitutively co-localize in the cytoplasm of resting cells, but STAP-2/BKS was found to dissociate upon STAT5 phosphorylation, suggesting a role in regulating signaling of STAT5. The physiological role of these interactions is not fully understood, but in studies of overexpression of STAP-2/BKS, cytokine-induced tyrosine phosphorylation and transcriptional activation of STAT5 was diminished. In addition, thymocytes from STAP-2/BKS-deficient mice showed the enhanced interleukin-2-dependent cell growth. Taken together, STAP-2/BKS is an additional modulator of STAT5-mediated signaling.