Distinct Ras effector pathways are involved in Fc epsilon R1 regulation of the transcriptional activity of Elk-1 and NFAT in mast cells

CREB Is Activated by the SCF/KIT Axis in a Partially ERK-Dependent Manner and Orchestrates Survival and the Induction of Immediate Early Genes in Human Skin Mast Cells

cAMP response element binding protein (CREB) functions as a prototypical stimulus-inducible transcription factor (TF) that initiates multiple cellular changes in response to activation. Despite pronounced expression in mast cells (MCs), CREB function is surprisingly ill-defined in the lineage. Skin MCs (skMCs) are critical effector cells in acute allergic and pseudo-allergic settings, and they contribute to various chronic dermatoses such as urticaria, atopic dermatitis, allergic contact dermatitis, psoriasis, prurigo, rosacea and others. Using MCs of skin origin, we demonstrate herein that CREB is rapidly phosphorylated on serine-133 upon SCF-mediated KIT dimerization. Phosphorylation initiated by the SCF/KIT axis required intrinsic KIT kinase activity and partially depended on ERK1/2, but not on other kinases such as p38, JNK, PI3K or PKA. CREB was constitutively nuclear, where phosphorylation occurred. Interestingly, ERK did not translocate to the nucleus upon SCF activation of skMCs, but a fraction was present in the nucleus at baseline, and phosphorylation was prompted in the cytoplasm and nucleus in situ. CREB was required for SCF-facilitated survival, as demonstrated with the CREB-selective inhibitor 666-15. Knock-down of CREB by RNA interference duplicated CREB's anti-apoptotic function. On comparison with other modules (PI3K, p38 and MEK/ERK), CREB was equal or more potent at survival promotion. SCF efficiently induces immediate early genes (IEGs) in skMCs (FOS, JUNB and NR4A2). We now demonstrate that CREB is an essential partaker in this induction. Collectively, the ancient TF CREB is a crucial component of skMCs, where it operates as an effector of the SCF/KIT axis, orchestrating IEG induction and lifespan.

Targeting Mast Cells in Allergic Disease: Current Therapies and Drug Repurposing

The incidence of allergic disease has grown tremendously in the past three generations. While current treatments are effective for some, there is considerable unmet need. Mast cells are critical effectors of allergic inflammation. Their secreted mediators and the receptors for these mediators have long been the target of allergy therapy. Recent drugs have moved a step earlier in mast cell activation, blocking IgE, IL-4, and IL-13 interactions with their receptors. In this review, we summarize the latest therapies targeting mast cells as well as new drugs in clinical trials. In addition, we offer support for repurposing FDA-approved drugs to target mast cells in new ways. With a multitude of highly selective drugs available for cancer, autoimmunity, and metabolic disorders, drug repurposing offers optimism for the future of allergy therapy.

Inhibition of Calcineurin/NFAT Signaling Blocks Oncogenic H-Ras Induced Autophagy in Primary Human Keratinocytes

Mutations of H-Ras, a member of the RAS family, are preferentially found in cutaneous squamous cell carcinomas (SCCs). H-Ras has been reported to induce autophagy, which plays an essential role in tissue homeostasis in multiple types of cancer cells and in fibroblasts, however, the potential role of H-Ras in regulating autophagy in human keratinocytes has not been reported. In this study, we found that the stable expression of the G12V mutant of H-RAS (H-Ras ^G12V ) induced autophagy in human keratinocytes, and interestingly, the induction of autophagy was strongly blocked by inhibiting the calcineurin/nuclear factor of activated T cells (NFAT) pathway with either a calcineurin inhibitor (Cyclosporin A) or a NFAT inhibitor (VIVIT), or by the small interfering RNA (siRNA) mediated knockdown of calcineurin B1 or NFATc1 in vitro, as well as in vivo. To characterize the role of the calcineurin/NFAT pathway in H-Ras induced autophagy, we found that H-Ras ^G12V promoted the nuclear translocation of NFATc1, an indication of the activation of the calcineurin/NFAT pathway, in human keratinocytes. However, activation of NFATc1 either by the forced expression of NFATc1 or by treatment with phenformin, an AMPK activator, did not increase the formation of autophagy in human keratinocytes. Further study revealed that inhibiting the calcineurin/NFAT pathway actually suppressed H-Ras expression in H-Ras ^G12V overexpressing cells. Finally, chromatin immunoprecipitation (ChIP) assays showed that NFATc1 potentially binds the promoter region of H-Ras and the binding efficiency was significantly enhanced by the overexpression of H-Ras ^G12V , which was abolished by treatment with the calcineurin/NFAT pathway inhibitors cyclosporine A (CsA) or VIVIT. Taking these data together, the present study demonstrates that the calcineurin/NFAT signaling pathway controls H-Ras expression and interacts with the H-Ras pathway, involving the regulation of H-Ras induced autophagy in human keratinocytes.

SLAP Is a Negative Regulator of FcεRI Receptor-Mediated Signaling and Allergic Response

Binding of antigen to IgE-high affinity FcεRI complexes on mast cells and basophils results in the release of preformed mediators such as histamine and de novo synthesis of cytokines causing allergic reactions. Src-like adapter protein (SLAP) functions co-operatively with c-Cbl to negatively regulate signaling downstream of the T cell receptor, B cell receptor, and receptor tyrosine kinases (RTK). Here, we investigated the role of SLAP in FcεRI-mediated mast cell signaling, using bone marrow derived mast cells (BMMCs) from SLAP knock out (SLAP KO) mice. Mature SLAP-KO BMMCs displayed significantly enhanced antigen induced degranulation and synthesis of IL-6, TNFα, and MCP-1 compared to wild type (WT) BMMCs. In addition, SLAP KO mice displayed an enhanced passive cutaneous anaphylaxis response. In agreement with a negative regulatory role, SLAP KO BMMCs showed enhanced FcεRI-mediated signaling to downstream effector kinases, Syk, Erk, and Akt. Recombinant GST-SLAP protein binds to the FcεRIβ chain and to the Cbl-b in mast cell lysates, suggesting a role in FcεRI down regulation. In addition, the ubiquitination of FcεRIγ chain and antigen mediated down regulation of FcεRI is impaired in SLAP KO BMMCs compared to the wild type. In line with these findings, stimulation of peripheral blood human basophils with FcεRIα antibody, or a clinically relevant allergen, resulted in increased SLAP expression. Together, these results indicate that SLAP is a dynamic regulator of IgE-FcεRI signaling, limiting allergic responses.

Emodin Isolated from Polygoni cuspidati Radix Inhibits TNF-α and IL-6 Release by Blockading NF-κB and MAP Kinase Pathways in Mast Cells Stimulated with PMA Plus A23187

Emodin, a naturally occurring anthraquinone derivative isolated from Polygoni cuspidati radix, has several beneficial pharmacologic effects, which include anti-cancer, anti-diabetic, and anti-inflammatory activities. In this study, the authors examined the effect of emodin on the production of proinflammatory cytokines, such as, tumor necrosis factor (TNF)-α and interleukin (IL)-6, in mouse bone marrow-derived mast cells (BMMCs) stimulated with phorbol 12-myristate 13-acetate (PMA) plus the calcium ionophore A23187. To investigate the mechanism responsible for the regulation of pro-inflammatory cytokine production by emodin, the authors assessed its effects on the activations of transcriptional factor nuclear factor-κB (NF-κB) and mitogen-activated protein kinases (MAPKs). Emodin attenuated the nuclear translocation of (NF)-κB p65 and its DNA-binding activity by reducing the phosphorylation and degradation of IκBα and the phosphorylation of IκB kinase B (IKK). Furthermore, emodin dose-dependently attenuated the phosphorylations of MAPKs, such as, extracellular signal-regulated kinase 1/2 (ERK1/2), p38 MAP kinase, and the stress-activated protein kinases (SAPK)/c-Jun-N-terminal kinase (JNK). Taken together, the findings of this study suggest that the anti-inflammatory effects of emodin on PMA plus A23187-stimulated BMMCs are mediated via the inhibition of NF-κB activation and of the MAPK pathway.

Systems biology of host-mycobiota interactions: dissecting Dectin-1 and Dectin-2 signalling in immune cells with DC-ATLAS

Modelling the networks sustaining the fruitful coexistence between fungi and their mammalian hosts is becoming increasingly important to control emerging fungal pathogens. The C-type lectins Dectin-1 and Dectin-2 are involved in host defense mechanisms against fungal infection driving inflammatory and adaptive immune responses and complement in containing fungal burdens. Recognizing carbohydrate structures in pathogens, their engagement induces maturation of dendritic cells (DCs) into potent immuno-stimulatory cells endowed with the capacity to efficiently prime T cells. Owing to these properties, Dectin-1 and Dectin-2 agonists are currently under investigation as promising adjuvants in vaccination procedures for the treatment of fungal infection. Thus, a detailed understanding of events' cascade specifically triggered in DCs upon engagement is of great interest in translational research. Here, we summarize the current knowledge on Dectin-1 and Dectin-2 signalling in DCs highlighting similarities and differences. Detailed maps are annotated, using the Biological Connection Markup Language (BCML) data model, and stored in DC-ATLAS, a versatile resource for the interpretation of high-throughput data generated perturbing the signalling network of DCs.

Citreorosein inhibits production of proinflammatory cytokines by blocking mitogen activated protein kinases, nuclear factor-κB and activator protein-1 activation in mouse bone marrow-derived mast cells

Citreorosein (CIT), an anthraquinone component of Polygoni cuspidati (P. cuspidati) radix, suppressed gene expression of proinflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1β in mouse bone marrow-derived mast cells (BMMCs) stimulated with phorbol 12-myristate 13-acetate (PMA) plus the calcium ionophore A23187. To investigate the molecular mechanisms underlying CIT inhibition of the pro-inflammatory cytokine production, its effects on the activation of both nuclear factor-κB (NF-κB) and mitogen-activated protein kinases (MAPKs) were assessed. CIT attenuated phosphorylation of the MAPKs including extracellular signal-regulated kinase 1/2 (ERK1/2), p38 MAP kinase and c-Jun NH(2)-terminal kinase (JNK). Furthermore, CIT strongly inhibited DNA binding activity of NF-κB through the inhibition of phosphorylation and degradation of inhibitor of kappaB (IκB) as well as activator protein-1 (AP)-1 through the reduction of phosphorylation of c-Jun. These results demonstrate that CIT inhibits proinflammatory cytokines production through the inhibition of both MAPKs and AKT-mediated IκB kinase (IKK) phosphorylation and subsequent inhibition of transcription factor NF-κB activation, thereby attenuating the production of proinflammatory cytokines.

p15(INK4b) plays a crucial role in murine lymphoid development and tumorigenesis

To investigate if the cooperation between the Rgr oncogene and the inactivation of INK4b (a CDK inhibitor), as described previously in a sarcoma model, would be operational in a lymphoid system in vivo, we generated a transgenic/knockout murine model. Transgenic mice expressing the Rgr oncogene under a CD4 promoter were crossed into a p15(INK4b)-deficient background. Unexpectedly, mice with a complete ablation of both p15(INK4b) alleles had a lower tumor incidence and higher survival rate when compared with CD4-Rgr progeny with homozygous or heterozygous expression of p15(INK4b). Also, a similar survival pattern was observed in a parallel model in which transgenic mice expressing a constitutively activated N-Ras mutant were crossed into a p15(INK4b)-deficient background. To analyze this paradoxical event, we investigated the hypothesis that the absence of both p15(INK4b) alleles in the presence of the Rgr oncogene could be deleterious for proper thymocyte development. When analyzed, thymocyte development was blocked at the double negative (DN) 3 and DN4 stages in mice missing one or both alleles of p15(INK4b), respectively. We found reduction in overall apoptotic levels in the thymocytes of mice expressing Rgr, compared with their wild-type mice, supporting thymocyte escape from programmed cell death and subsequently facilitating the onset of thymic lymphomas but less for those missing both p15 alleles. These findings provide evidence of the complex interplay between oncogenes and tumor suppressor genes in tumor development and indicate that in the lymphoid tissue the inactivation of both p15 alleles is unlikely to be the first event in tumor development.

Phospholipase Cγ2 (PLCγ2) is key component in Dectin-2 signaling pathway, mediating anti-fungal innate immune responses

C-type lectin receptors (CLRs) such as Dectin-2 function as pattern recognition receptors to sense fungal infection. However, the signaling pathways induced by these receptors remain largely unknown. Previous studies suggest that the CLR-induced signaling pathway may utilize similar signaling components as the B cell receptor-induced signaling pathway. Phospholipase Cγ2 (PLCγ2) is a key component in B cell receptor signaling, but its role in other signaling pathways has not been fully characterized. Here, we show that PLCγ2 functions downstream of Dectin-2 in response to the stimulation by the hyphal form of Candida albicans, an opportunistic pathogenic fungus. Using PLCγ2- and PLCγ1-deficient macrophages, we found that the lack of PLCγ2, but not PLCγ1, impairs cytokine production in response to infection with C. albicans. PLCγ2 deficiency results in the defective activation of NF-κB and MAPK and a significantly reduced production of reactive oxygen species following fungal challenge. In addition, PLCγ2-deficient mice are defective in clearing C. albicans infection in vivo. Together, these findings demonstrate that PLCγ2 plays a critical role in CLR-induced signaling pathways, governing antifungal innate immune responses.

Receptor signaling in immune cell development and function

Immune cell development and function must be tightly regulated through cell surface receptors to ensure proper responses to pathogen and tolerance to self. In T cells, the signal from the T-cell receptor is essential for T-cell maturation, homeostasis, and activation. In mast cells, the high-affinity receptor for IgE transduces signal that promotes mast cell survival and induces mast cell activation. In dendritic cells and macrophages, the toll-like receptors recognize microbial pathogens and play critical roles for both innate and adaptive immunity against pathogens. Our research explores how signaling from these receptors is transduced and regulated to better understand these immune cells. Our recent studies have revealed diacylglycerol kinases and TSC1/2-mTOR as critical signaling molecules/regulators in T cells, mast cells, dendritic cells, and macrophages.

Regulation of mast cell responses in health and disease

Mast cells are multifunctional cells that initiate not only IgE-dependent allergic diseases but also play a fundamental role in innate and adaptive immune responses to microbial infection. They are also thought to play a role in angiogenesis, tissue remodeling, wound healing, and tumor repression or growth. The broad scope of these physiologic and pathologic roles illustrates the flexible nature of mast cells, which is enabled in part by their phenotypic adaptability to different tissue microenvironments and their ability to generate and release a diverse array of bioactive mediators in response to multiple types of cell-surface and cytosolic receptors. There is increasing evidence from studies in cell cultures that release of these mediators can be selectively modulated depending on the types or groups of receptors activated. The intent of this review is to foster interest in the interplay among mast cell receptors to help understand the underlying mechanisms for each of the immunological and non-immunological functions attributed to mast cells. The second intent of this review is to assess the pathophysiologic roles of mast cells and their products in health and disease. Although mast cells have a sufficient repertoire of bioactive mediators to mount effective innate and adaptive defense mechanisms against invading microorganisms, these same mediators can adversely affect surrounding tissues in the host, resulting in autoimmune disease as well as allergic disorders.

A preliminary examination of the role of NFAT 3 in human skin, cultured keratocytes and dermal fibroblasts

BACKGROUND

Ciclosporin A (CsA) is widely utilized for the treatment of inflammatory skin diseases such as psoriasis.The therapeutic effects of CsA are thought to be mediated via its immunosuppressive action on infiltrating lymphocytes in skin lesions. CsA and tacrolimus block T cell activation by inhibiting the phosphatase calcineurin and preventing translocation from the cytoplasm to the nucleus of the transcription factor Nuclear Factor of Activated T cells (NFAT).

METHODS

RT-PCR and Western Analysis were used to investigate the presence of NFAT-3 mRNA and protein in human keratocytes. Tissue culture of human keratocytes and immunostaining of cells on coverslips and confocal microscopy were used to assess the degree of nuclear localisation of NFAT-3 in cultured cells. Keratome biopsies were taken from patients with psoriasis (lesional and non-lesional skin) and normal skin and immunohistochemistry was used to assess the NFAT-3 localisation in these biopsies using a well characterized anti-NFAT-3 antibody.

RESULTS

The NFAT-3 mRNA and protein expression was demonstrated using RT-PCR and Western blotting. The expression of NFAT-3 in human keratocytes and response to different agonists provides perhaps a unique opportunity to examine the regulation, subcellular localization and kinetics of translocation of different NFATs in primary cultured human cells. As with NFAT 1, NFAT 2 and recently NFAT 5, differentiation-promoting agents that increase intracellular calcium concentration induced nuclear translocation of NFAT-3 in cultured keratocytes but with different kinetics.

CONCLUSION

These data provide the first evidence of that NFAT-3 is expressed in normal skin, psoriasis and that NFAT-3 functionally active in human keratocytes and that nuclear translocation of NFAT-3 in human skin cells has different kinetics than NFAT 1 suggesting that NFAT-3 may play an important role in regulation of keratocytes proliferation and differentiation at a different stage. Inhibition of this pathway in human epidermal keratocytes many account, in part for the therapeutic effects of CsA and tacrolimus in skin disorders such as psoriasis.

The protein tyrosine kinase Tec regulates mast cell function

Mast cells play crucial roles in a variety of normal and pathophysiological processes and their activation has to be tightly controlled. Here, we demonstrate that the protein tyrosine kinase Tec is a crucial regulator of murine mast cell function. Tec was activated upon Fc epsilon RI stimulation of BM-derived mast cells (BMMC). The release of histamine in the absence of Tec was normal in vitro and in vivo; however, leukotriene C(4) levels were reduced in Tec(-) (/) (-) BMMC. Furthermore, the production of IL-4 was severely impaired, and GM-CSF, TNF-alpha and IL-13 levels were also diminished. Finally, a comparison of WT, Tec(-) (/) (-), Btk(-) (/) (-) and Tec(-) (/) (-)Btk(-) (/) (-) BMMC revealed a negative role for Btk in the regulation of IL-4 production, while for the efficient production of TNF-alpha, IL-13 and GM-CSF, both Tec and Btk were required. Our results demonstrate a crucial role for Tec in mast cells, which is partially different to the function of the well-characterized family member Btk.

Expression, localisation and functional activation of NFAT-2 in normal human skin, psoriasis, and cultured keratocytes

Ciclosporin A (CsA) is widely utilized for the treatment of inflammatory skin diseases such as psoriasis. The therapeutic effects of CsA are thought to be mediated via its immunosuppressive action on infiltrating lymphocytes in skin lesions. CsA and tacrolimus block T cell activation by inhibiting the phosphatase calcineurin and preventing translocation from the cytoplasm to the nucleus of the transcription factor Nuclear Factor of Activated T cells (NFAT). As calcineurin and NFAT 1 have been shown to be functionally active in cultured human keratocytes, expression of other NFAT family members such as NFAT-2 and possible functional activation was investigated in human keratocytes. RT-PCR and Western Analysis were used to investigate the presence of NFAT-2 mRNA and protein in human keratocytes. Tissue culture of human keratocytes and immunostaining of cells on coverslips and confocal microscopy were used to assess the degree of nuclear localisation of NFAT-2 in cultured cells. Keratome biopsies were taken from patients with psoriasis (lesional and non-lesional skin) and normal skin and immunohistochemistry was used to assess the NFAT-2 localisation in these biopsies using a well characterized anti-NFAT-2 antibody. The NFAT-2 mRNA and protein expression was demonstrated using RT-PCR and Western blotting. Moreover, the expression of NFAT-2 in normal skin, non-lesional and lesional psoriasis showed a striking basal staining suggesting a role for NFAT-2 in keratocytes proliferation. A range of cell types in the skin express NFAT-2. The expression of NFAT-2 in human keratocytes and response to different agonists provides perhaps a unique opportunity to examine the regulation, subcellular localization and kinetics of translocation of different NFATs in primary cultured human cells. In these experiments the author assessed the expression, localization of NFAT-2 in cultured human keratocytes and measured the degree of nuclear localisaion of NFAT-2 using immunofluorescence and confocal microscopy and whether CsA and tacrolimus inhibit NFAT-2 nuclear translocation. As with NFAT 1, differentiation-promoting agents that increase intracellular calcium concentration induced nuclear translocation of NFAT-2 in cultured keratocytes but with different kinetics. These data provide the first evidence of that NFAT-2 is expressed in normal skin, psoriasis and that NFAT-2 functionally active in human keratocytes and that nuclear translocation of NFAT-2 in human skin cells has different kinetics than NFAT 1 suggesting that NFAT-2 may play an important role in regulation of keratocytes proliferation and differentiation at a different stage. Inhibition of this pathway in human epidermal keratocytes many account, in part for the therapeutic effects of CsA and tacrolimus in skin disorders such as psoriasis. Thus, supporting our previous work data that calcineurin/NFAT is functionally active not only in T cells, but in skin cells.

SWAP-70 regulates mast cell FcepsilonRI-mediated signaling and anaphylaxis

Mast cells, perhaps best known by their ability to trigger allergic reactions after stimulation through the FcepsilonRI, express the unusual phosphatidylinositol 3-kinase (PI3K)-dependent, Rac-binding protein SWAP-70. Here, we show that the IgE-mediated passive cutaneous and the systemic anaphylactic responses are strongly reduced in SWAP-70(-/-) mice. Cultured SWAP-70(-/-) immature bone marrow mast cells (BMMC) are also impaired in FcepsilonRI-mediated degranulation, which can be restored by expression of exogenous wild-type SWAP-70, but less so if a phosphatidylinositol trisphosphate (PIP(3)) binding mutant is expressed. SWAP-70 itself supports inositol-3-phosphate and PIP(3) production, the latter indicating a potential feedback from SWAP-70 towards PI3K. FcepsilonRI-stimulated transcription and release of cytokines is controlled by SWAP-70. Key FcepsilonRI signal transduction events like activation of LAT by phosphorylation, activation of Akt/PKB and of p38 MAP kinase are reduced in SWAP-70(-/-) BMMC, but ERK is strongly hyperactivated. Some requirements for SWAP-70 were apparent only under limited-strength signaling conditions. We suggest that SWAP-70 defines a new element of efficient mast cell activation upon FcepsilonRI signaling, important for the control of mast cell-dependent anaphylaxis.

Src family kinases and lipid mediators in control of allergic inflammation

The Src family kinases Fyn and Lyn are important modulators of the molecular events initiated by engagement of the high-affinity IgE receptor (Fc epsilon RI). These kinases control many of the early signaling events and initiate the production of several lipid metabolites that have an important role in regulating mast cell responses. The intracellular level of phosphatidylinositol (3,4,5)-trisphosphate (PIP(3)), which is produced by phosphatidylinositol 3-OH kinase, plays an important role in determining the extent of a mast cells response to a stimulus. Enhanced levels lead to a hyperdegranulating phenotype (as seen in SHIP-1(-/-) and Lyn(-/-) mast cells), whereas decreased levels cause hypodegranulation (as seen in Fyn(-/-) mast cells). Downregulation of mast cell phosphatase and tensin homologue deleted on chromosone 10 expression, a phosphatase that reduces cellular levels of PIP(3), caused constitutive cytokine production, demonstrating that this response is particularly sensitive to PIP(3) levels. Lyn and Fyn are also intimately linked to other lipid kinases, like sphingosine kinases (SphK). By producing sphingosine-1-phosphate (S1P), SphKs contribute to mast cell chemotaxis and degranulation. In vivo studies now reveal that circulating S1P as well as that found within the mast cell is important in determining mast cell responsiveness. These studies demonstrate the connection between Src protein tyrosine kinases and lipid second messengers that control mast cell function and allergic responses.

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.

B cell lymphoma 10 is essential for FcepsilonR-mediated degranulation and IL-6 production in mast cells

The adaptor protein B cell lymphoma 10 (Bcl10) plays an essential role in the functions of the AgRs in T and B cells. In this study, we report that Bcl10 also plays an important role in mast cells. Bcl10 is expressed in mast cells. Although Bcl10-deficient mast cells undergo normal development, we demonstrate that Bcl10 is essential for specific functions of FcepsilonR. Although Bcl10-deficient mast cells have normal de novo synthesis and release of the lipid mediator arachidonic acid, the mutant cells possess impaired FcepsilonR-mediated degranulation, indicated by decreased serotonin release, and impaired cytokine production, measured by release of IL-6. In addition, Bcl10-deficient mice display impaired IgE-mediated passive cutaneous anaphylaxis. Moreover, although Bcl10-deficient mast cells have normal FcepsilonR-mediated Ca(2+) flux, activation of PI3K, and activation of the three types of MAPKs (ERKs, JNK, and p38), the mutant cells have markedly diminished FcepsilonR-mediated activation of NF-kappaB and decreased activation of AP-1. Thus, Bcl10 is essential for FcepsilonR-induced activation of AP-1, NF-kappaB, degranulation, and cytokine production in mast cells.

Impaired degranulation but enhanced cytokine production after Fc epsilonRI stimulation of diacylglycerol kinase zeta-deficient mast cells

Calcium and diacylglycerol are critical second messengers that together effect mast cell degranulation after allergen cross-linking of immunoglobulin (Ig)E-bound FcepsilonRI. Diacylglycerol kinase (DGK)zeta is a negative regulator of diacylglycerol-dependent signaling that acts by converting diacylglycerol to phosphatidic acid. We reported previously that DGKzeta-/- mice have enhanced in vivo T cell function. Here, we demonstrate that these mice have diminished in vivo mast cell function, as revealed by impaired local anaphylactic responses. Concordantly, DGKzeta-/- bone marrow-derived mast cells (BMMCs) demonstrate impaired degranulation after Fc epsilonRI cross-linking, associated with diminished phospholipase Cgamma activity, calcium flux, and protein kinase C-betaII membrane recruitment. In contrast, Ras-Erk signals and interleukin-6 production are enhanced, both during IgE sensitization and after antigen cross-linking of Fc epsilonRI. Our data demonstrate dissociation between cytokine production and degranulation in mast cells and reveal the importance of DGK activity during IgE sensitization for proper attenuation of Fc epsilonRI signals.

Negative Signaling in Fc Receptor Complexes

Cell activation results from the transient displacement of an active balance between positive and negative signaling. This displacement depends in part on the engagement of cell surface receptors by extracellular ligands. Among these are receptors for the Fc portion of immunoglobulins (FcRs). FcRs are widely expressed by cells of hematopoietic origin. When binding antibodies, FcRs provide these cells with immunoreceptors capable of triggering numerous biological responses in response to a specific antigen. FcR-dependent cell activation is regulated by negative signals which are generated together with positive signals within signalosomes that form upon FcR engagement. Many molecules involved in positive signaling, including the FcRbeta subunit, the src kinase lyn, the cytosolic adapter Grb2, and the transmembrane adapters LAT and NTAL, are indeed also involved in negative signaling. A major player in negative regulation of FcR signaling is the inositol 5-phosphatase SHIP1. Several layers of negative regulation operate sequentially as FcRs are engaged by extracellular ligands with an increasing valency. A background protein tyrosine phosphatase-dependent negative regulation maintains cells in a "resting" state. SHIP1-dependent negative regulation can be detected as soon as high-affinity FcRs are occupied by antibodies in the absence of antigen. It increases when activating FcRs are engaged by multivalent ligands and, further, when FcR aggregation increases, accounting for the bell-shaped dose-response curve observed in excess of ligand. Finally, F-actin skeleton-associated high-molecular weight SHIP1, recruited to phosphorylated ITIMs, concentrates in signaling complexes when activating FcRs are coengaged with inhibitory FcRs by immune complexes. Based on these data, activating and inhibitory FcRs could be used for new therapeutic approaches to immune disorders.

Live Cell Imaging to Study Signaling Molecules in Allergic Reactions

Mast cells are widely distributed throughout the body, predominantly near blood vessels and nerves, and express effector functions in allergic reactions, inflammatory diseases, and host defense. The activation of mast cells results in secretion of the preformed chemical mediators in their granules by a regulated process of exocytosis and leads to synthesis and secretion of lipid mediators and cytokines. Their soluble factors contribute to allergic inflammation. Mast cells are associated with hypersensitivity reactions, not only in the classical immunoglobulin E (IgE)-dependent mechanism but also in an IgE-independent manner. In particular, investigations of potential anatomical and functional interactions between mast cells and the nervous system have recently attracted great interest. To understand these molecular mechanisms in mast cell activation, the ability to visualize, track, and quantify molecules and events in living mast cells is an essential and powerful tool. Recent dramatic advances in imaging technology and labeling techniques have enabled us to carry out these tasks with high spatiotemporal resolution using confocal laser scanning microscopes, green fluorescent protein and its derivatives, and image analysis systems. Here we review our investigations of the dynamic processes of intracellular signaling molecules, cellular structure, and interactions with neurons in mast cells to provide basic and valuable information for allergy and clinical immunology using these new imaging methods.

C3a enhances nerve growth factor-induced NFAT activation and chemokine production in a human mast cell line, HMC-1

Activation of cell surface G protein-coupled receptors leads to transphosphorylation and activation of a number of receptor tyrosine kinases. Human mast cells express G protein-coupled receptors for the complement component C3a (C3aR) and high affinity nerve growth factor (NGF) receptor tyrosine kinase, TrkA. To determine whether C3a cross-regulates TrkA signaling and biological responses, we used a human mast cell-line, HMC-1, that natively expresses both receptors. We found that NGF caused tyrosine phosphorylation of TrkA, resulting in a sustained Ca(2+) mobilization, NFAT activation, extracellular-signal regulated kinase (ERK) phosphorylation, and chemokine, macrophage inflammatory protein-1beta (MIP-1beta) production. In contrast, C3a induced a transient Ca(2+) mobilization and ERK phosphorylation but failed to stimulate TrkA phosphorylation, NFAT activation, or MIP-1beta production. Surprisingly, C3a significantly enhanced NGF-induced NFAT activation, ERK phosphorylation, and MIP-1beta production. Pertussis toxin, a G(i/o) inhibitor, selectively blocked priming by C3a but had no effect on NGF-induced responses. Mitogen-activated protein/ERK kinase inhibitor U0126 caused approximately 30% inhibition of NGF-induced MIP-1beta production but had no effect on priming by C3a. However, cyclosporin A, an inhibitor of calcineurin-mediated NFAT activation, caused substantial inhibition of NGF-induced MIP-1beta production both in the absence and presence of C3a. These data demonstrate that NGF caused tyrosine phosphorylation of TrkA to induce chemokine production in HMC-1 cells via a pathway that mainly depends on sustained Ca(2+) mobilization and NFAT activation. Furthermore, C3a enhances NGF-induced transcription factor activation and chemokine production via a G protein-mediated pathway that does not involve TrkA phosphorylation.

Ras activation in Jurkat T cells following low-grade stimulation of the T-cell receptor is specific to N-Ras and occurs only on the Golgi apparatus

Ras activation is critical for T-cell development and function, but the specific roles of the different Ras isoforms in T-lymphocyte function are poorly understood. We recently reported T-cell receptor (TCR) activation of ectopically expressed H-Ras on the the Golgi apparatus of T cells. Here we studied the isoform and subcellular compartment specificity of Ras signaling in Jurkat T cells. H-Ras was expressed at much lower levels than the other Ras isoforms in Jurkat and several other T-cell lines. Glutathione S-transferase-Ras-binding domain (RBD) pulldown assays revealed that, although high-grade TCR stimulation and phorbol ester activated both N-Ras and K-Ras, low-grade stimulation of the TCR resulted in specific activation of N-Ras. Surprisingly, whereas ectopically expressed H-Ras cocapped with the TCRs in lipid microdomains of the Jurkat plasma membrane, N-Ras did not. Live-cell imaging of Jurkat cells expressing green fluorescent protein-RBD, a fluorescent reporter of GTP-bound Ras, revealed that N-Ras activation occurs exclusively on the Golgi apparatus in a phospholipase Cgamma- and RasGRP1-dependent fashion. The specificity of N-Ras signaling downstream of low-grade TCR stimulation was dependent on the monoacylation of the hypervariable membrane targeting sequence. Our data show that, in contrast to fibroblasts stimulated with growth factors in which all three Ras isoforms become activated and signaling occurs at both the plasma membrane and Golgi apparatus, Golgi-associated N-Ras is the critical Ras isoform and intracellular pool for low-grade TCR signaling in Jurkat T cells.

Blockade of airway inflammation and hyperresponsiveness by HIV-TAT-dominant negative Ras

We have reported previously that HIV-TAT-dominant negative (dn) Ras inhibits eosinophil adhesion to ICAM-1 after activation by IL-5 and eotaxin. In this study, we evaluated the role of Ras in Ag-induced airway inflammation and hyperresponsiveness by i.p. administration into mice of dnRas, which was fused to an HIV-TAT protein transduction domain (TAT-dnRas). Uptake of TAT-dnRas (t(1/2) = 12 h) was demonstrated in leukocytes after i.p. administration. OVA-sensitization significantly increased eosinophil and lymphocyte numbers in bronchoalveolar lavage fluid 24 h after final challenge. Treatment of animals with 3-10 mg/kg TAT-dnRas blocked the migration of eosinophils from 464 +/- 91 x 10(3)/ml to 288 +/- 79 x 10(3)/ml with 3 mg/kg of TAT-dnRas (p < 0.05), and further decreased to 116 +/- 63 x 10(3)/ml after 10 mg/kg TAT-dnRas (p < 0.01). Histological examination demonstrated that inflammatory cell infiltration (largely eosinophils and mononuclear cells) and mucin production around the airways caused by OVA were blocked by TAT-dnRas. OVA challenge also caused airway hyperresponsiveness to methacholine, which was dose dependently blocked by treatment with TAT-dnRas. TAT-dnRas also blocked Ag-induced IL-4 and IL-5, but not IFN-gamma, production in lung tissue. Intranasal administration of IL-5 caused eosinophil migration into the airway lumen, which was attenuated by pretreatment with TAT-dnRas. By contrast, TAT-green fluorescent protein or dnRas lacking the TAT protein transduction domain did not block airway inflammation, cytokine production, or airway hyperresponsiveness. We conclude that Ras mediates Th2 cytokine production, airway inflammation, and airway hyperresponsiveness in immune-sensitized mice.

Polyphenolic antioxidants inhibit peptide presentation by antigen-presenting cells

Antigen-presenting cells (APC) provide two essential signals, e.g., antigenic peptides as well as costimulatory molecules for T-cell activation. Small molecules of smoke tobacco extracts (SM-STE) inhibited antigen presentation of A20 to OVAp-specific T-cell hybridomas. Pretreatment of A20 but not T hybridomas abrogates the APC function. Viability of APC and levels of MHCII, CD40 and B7 of APC were not affected by this treatment. The active principle, inhibiting APC was reproduced with pure tobacco polyphenols, quercetin and its glycoside, rutin. Antioxidant activity of rutin is relevant since rutin downregulated levels of reactive oxygen species (ROS) in phorbol ester-stimulated A20; moreover, another antioxidant, N-acetyl cysteine (NAC) also inhibited antigen presentation, albeit at a higher concentration. Other types of APC, such as bone marrow-derived mast cells (BMMC), MHCII-transfected fibroblast, and splenocytes are affected by tobacco polyphenols. We propose that polyphenols may affect redox-sensitive signal transduction pathway since APC function of PD 98059, MEK inhibitor-pretreated A20 were similarly abrogated. Taken together, we propose that maintaining appropriate intracellular redox of APC is crucial for its antigen-presenting function.

Phospholipase C gamma 2 is essential for specific functions of Fc epsilon R and Fc gamma R

Phospholipase Cgamma2 (PLCgamma2) plays a critical role in the functions of the B cell receptor in B cells and of the FcRgamma chain-containing collagen receptor in platelets. Here we report that PLCgamma2 is also expressed in mast cells and monocytes/macrophages and is activated by cross-linking of Fc(epsilon)R and Fc(gamma)R. Although PLCgamma2-deficient mice have normal development and numbers of mast cells and monocytes/macrophages, we demonstrate that PLCgamma2 is essential for specific functions of Fc(epsilon)R and Fc(gamma)R. While PLCgamma2-deficient mast cells have normal mitogen-activated protein kinase activation and cytokine production at mRNA levels, the mutant cells have impaired Fc(epsilon)R-mediated Ca(2+) flux and inositol 1,4,5-trisphosphate production, degranulation, and cytokine secretion. As a physiological consequence of the effect of PLCgamma2 deficiency, the mutant mice are resistant to IgE-mediated cutaneous inflammatory skin reaction. Macrophages from PLCgamma2-deficient mice have no detectable Fc(gamma)R-mediated Ca(2+) flux; however, the mutant cells have normal Fc(gamma)R-mediated phagocytosis. Moreover, PLCgamma2 plays a nonredundant role in Fc(gamma)R-mediated inflammatory skin reaction.

Granulocyte/macrophage-colony-stimulating factor (GM-CSF) regulates lung innate immunity to lipopolysaccharide through Akt/Erk activation of NFkappa B and AP-1 in vivo

The lung innate immune response to lipopolysaccharide (LPS) coordinates cellular inflammation, mediator, and protease release essential for host defense but deleterious in asthma, chronic obstructive pulmonary disease, and cystic fibrosis. In vitro, LPS signals to the transcription factors NFkappaB via TLR4, MyD88, and IL-1R-associated kinase (IRAK), to AP-1 by mitogen-activated protein (MAP) kinases, and via an alternate route in IRAK-deficient mice, but the in vivo lung signaling pathway(s) are not understood. We investigated the role of Akt and Erk1/2 as LPS intensely stimulates granulocyte/macrophage-colony-stimulating factor (GM-CSF) release, and neutralizing GM-CSF profoundly suppressed LPS-induced inflammation, suppressed expression and activity of lung proteases, significantly reduced GM-CSF and tumor necrosis factor alpha (TNFalpha) mRNA expression, and dampened nuclear localization of both NFkappaB (p50/65) and AP-1. LPS markedly activated Akt and Erk1/2, but not p38, in a GM-CSF-dependent manner in direct temporal association with NFkappaB and AP-1 activation. Pharmacological inhibition of Akt or Erk activation in LPS-treated tracheal explants ex vivo inhibited the release of GM-CSF. These data implicate GM-CSF-dependent activation of Akt in the amplification of this response and demonstrate the role of Erks rather than p38 in lung LPS inflammatory responses. Inhibition of GM-CSF may be of therapeutic benefit in inflammatory diseases in which LPS contributes to lung damage.

Ras and relatives--job sharing and networking keep an old family together

Many members of the Ras superfamily of GTPases have been implicated in the regulation of hematopoietic cells, with roles in growth, survival, differentiation, cytokine production, chemotaxis, vesicle-trafficking, and phagocytosis. The well-known p21 Ras proteins H-Ras, N-Ras, K-Ras 4A, and K-Ras 4B are also frequently mutated in human cancer and leukemia. Besides the four p21 Ras proteins, the Ras subfamily of the Ras superfamily includes R-Ras, TC21 (R-Ras2), M-Ras (R-Ras3), Rap1A, Rap1B, Rap2A, Rap2B, RalA, and RalB. They exhibit remarkable overall amino acid identities, especially in the regions interacting with the guanine nucleotide exchange factors that catalyze their activation. In addition, there is considerable sharing of various downstream effectors through which they transmit signals and of GTPase activating proteins that downregulate their activity, resulting in overlap in their regulation and effector function. Relatively little is known about the physiological functions of individual Ras family members, although the presence of well-conserved orthologs in Caenorhabditis elegans suggests that their individual roles are both specific and vital. The structural and functional similarities have meant that commonly used research tools fail to discriminate between the different family members, and functions previously attributed to one family member may be shared with other members of the Ras family. Here we discuss similarities and differences in activation, effector usage, and functions of different members of the Ras subfamily. We also review the possibility that the differential localization of Ras proteins in different parts of the cell membrane may govern their responses to activation of cell surface receptors.

Aggregation of the high-affinity IgE receptor Fc(epsilon)RI on human monocytes and dendritic cells induces NF-kappaB activation

In contrast to mast cells and basophils, the high-affinity IgE receptor (Fc(epsilon)RI) on monocytes and dendritic cells (DC), including epidermal Langerhans cells, is not constitutively expressed and lacks the beta-chain. Fc(epsilon)RI is upregulated on Langerhans cells of atopic individuals, particularly in atopic dermatitis skin. Although Fc(epsilon)RI provides IgE-mediated antigen focusing on monocytes and DC/Langerhans cells, its relevance for cell activation remains elusive, and the transcription factors regulating Fc(epsilon)RI-induced genes are unknown. We show that NF-kappaB, known to regulate genes essential for inflammatory responses and DC differentiation and function, is activated upon Fc(epsilon)RI ligation in primary human monocytes and DC. In Langerhans cells isolated from epidermis, NF-kappaB activation is restricted to donors expressing high Fc(epsilon)RI amounts. Fc(epsilon)RI-induced NF-kappaB complexes in monocytes and DC contain p50 and p65, but no other NF-kappaB subunits despite increased RelB expression during differentiation. NF-kappaB activation is preceded by serine phosphorylation and degradation of its inhibitory protein IkappaB-alpha without involving other IkappaB proteins. Finally, we show that Fc(epsilon)RI ligation on monocytes and DC leads to synthesis and release of tumor necrosis factor-alpha and monocyte chemoattractant protein-1, which is decreased by two mechanistically distinct inhibitors of NF-kappaB activation. Thus NF-kappaB activation represents a novel mechanism by which Fc(epsilon)RI on monocytes and DC potentially controls inflammatory reactions.

The Ras-pathway inhibitor, S-trans-trans-farnesylthiosalicylic acid, suppresses experimental allergic encephalomyelitis

AIM

To evaluate the effects of the synthetic Ras-pathway inhibitor, S-trans-trans-farnesylthiosalicylic acid (FTS) on acute and chronic experimental autoimmune encephalomyelitis (EAE and CR-EAE).

BACKGROUND

Treatment of EAE and MS is based on immunosuppression aiming at downregulation of the proliferating myelin-reactive lymphocytes. One of the pathways of lymphocyte activation involves the GTP-binding protein Ras. FTS destabilizes the attachment of Ras to the cell membrane, resulting in an inhibition of the Ras-mediated signal transduction pathways.

MATERIALS AND METHODS

EAE was induced in SJL/J mice by immunization with spinal cord homogenate (MSCH) in adjuvant and two i.v. boosts of pertussis antigen and CR-EAE with passive transfer of proteolipid protein (PLP)-activated lymphocytes. Animals were treated daily starting either from the day of EAE-induction (or cell transfer) or at a later stage, with i.p. injections of FTS (5 mg/kg/day). The clinical severity of the disease was evaluated daily and scored using a 0-6 scale.

RESULTS

In six separate experiments, 27 of the 38 (71.7%) vehicle-treated animals developed clinical signs of EAE compared to 17/38 (44.7%) of the FTS-treated mice (p=0.02, t-test). The maximal average score in the control group was 2.94+/-2.2, whereas in the FTS group it was significantly lower (1.63+/-2.2, p=0.01). Mortality was 26.3% and 10.5% in the two groups, respectively (p=0.03). When treatment was initiated at a later stage, just before the onset of the clinical signs, the protective effect was even more pronounced. A significant suppression of clinical signs was also observed in the CR-EAE model (p=0.02). Lymphocyte proliferation assays demonstrated a more than twofold decrease in the reactivity to myelin antigens (MBP and PLP) and downregulation of the activated lymphocytes (expressing the CD62L, and IA-k-MHC Class I markers and the Vb17 T-cell receptor) in the FTS-treated group; in vitro FTS suppressed the Ras activity of lymphocytes and inhibited the proliferative ability of the lymphocytes in a dose-dependent manner.

CONCLUSIONS

FTS suppresses EAE by downregulation of myelin-reactive activated T-lymphocytes. Since FTS did not induce generalized immunosuppressive effects, it may offer significant advantages over the broad immunosuppressive modalities and may be a candidate treatment for autoimmune diseases, such as MS.

Fc epsilon ri-mediated activation of transcription factors in antigen-presenting cells

Professional antigen-presenting cells (APC) such as monocytes and dendritic cells (DC) bearing high-affinity IgE receptors (Fc epsilon RI) efficiently present IgE-bound antigens to T cells. Fc epsilon RI expression is upregulated on APC from atopic donors, especially in inflamed tissues. These data suggest a pathophysiological concept of an IgE-mediated delayed-type hypersensitivity reaction in atopic diseases. However, Fc epsilon RI ligation also leads to the synthesis of proinflammatory cytokines and other molecules involved in inflammatory reactions. The investigation of transcription factors mediating these effects has only recently commenced. In general, members of the NF-kappa B family are known to regulate APC function and differentiation, with the RelB subunit being especially important in DC generation. In addition, Ikaros and PU.1 have also been shown to be essential factors for DC differentiation, whereas Oct-2 is upregulated by differentiation towards macrophages. Recently, Fc epsilon RI has been demonstrated to induce NF-kappa B activation via I kappa B-alpha serine phosphorylation and degradation in monocytes and DC. Inhibitors of NF-kappa B activation such as N-acetylcysteine or N-tosyl-L-phenylalanine chloromethyl ketone can suppress Fc epsilon RI-induced TNF-alpha and MCP-1 release. Interestingly, in human epidermal Langerhans' cells (LC), NF-kappa B activation can only be observed when large amounts of Fc epsilon RI are present. In addition, the composition of NF-kappa B complexes differs between monocytes, monocyte-derived DC and LC, suggesting a cell type-specific regulation. Moreover, the transcription factor NFAT is induced upon Fc epsilon RI ligation in human APC. The elucidation of further transcription factors involved in Fc epsilon RI signaling in APC should contribute to the employment of new inhibition strategies for the treatment of atopic and other inflammatory diseases.

T cell activation signals upregulate CBP-dependent transcriptional activity

The transcriptional coactivator CREB-binding protein (CBP) is known to play an important role in coupling signal transduction pathways to changes in gene expression. In many cases, this is achieved by the stimulus-specific recruitment of CBP to promoter-bound transcription factors. However, a number of recent studies have suggested that signal transduction pathways can also directly influence CBP-mediated transcriptional activity. Here we show that in Jurkat cells the activity of the CBP C-terminal transactivation domain is strongly upregulated in response to either T cell receptor stimulation or the combination of ionomycin and phorbol ester. We further show that maximal stimulation of CBP-mediated transcription requires the synergistic activation of both the calcineurin and Ras-MAPK signaling pathways. These results indicate that CBP can function as a T cell activation-inducible transcriptional coactivator and is therefore likely to play an important role in T cell activation-induced gene expression.

Ras regulates NFAT3 activity in cardiac myocytes

Multiple distinct signal transduction pathways have been implicated in the development of cardiac myocyte hypertrophy. These hypertrophic pathways include those regulated by the Ras superfamily of small GTPases and a separate calcineurin-regulated pathway that culminates in the activation of the transcription factor NFAT3. In this report, we demonstrate a functional interaction between Ras-regulated and calcineurin-regulated pathways. In particular, expression in neonatal myocytes of a constitutively active form of Ras (V12ras), but not activating mutants of Rac1, RhoA, or Cdc42, results in an increase in NFAT activity. Similarly, expression of an activated Ras, but not other small GTPases, results in the nuclear translocation of an NFAT3 fusion protein. Expression of a dominant negative ras gene product blocks phenylephrine-stimulated NFAT transcriptional activity and the ligand-stimulated NFAT3 nuclear localization. Ras proteins appear to function upstream of calcineurin, because cyclosporin A blocks the ability of V12ras to stimulate NFAT-dependent transcription and nuclear localization. Similarly, expression of a dominant negative ras gene inhibits phenylephrine-stimulated calcineurin activity. Pharmacological inhibition of MEK1 or expression of a dominant negative form of c-Raf or ERK2 inhibits phenylephrine-stimulated NFAT3 activation. Conversely, NFAT activity was stimulated by expression of constitutively active forms of c-Raf or MEK1. Taken together, these results imply that, in cardiac myocytes, a Ras-regulated pathway involving stimulation of mitogen-activated protein kinase regulates NFAT3 activity.

Human alpha (1,3)-fucosyltransferase IV (FUTIV) gene expression is regulated by elk-1 in the U937 cell line

The alpha1,3-fucosyltransferase IV (FucTIV) encoded by its gene (FUTIV) is responsible for synthesis of Le(x) (Galbeta4[Fucalpha3]GlcNAcbeta3Galbeta1,R), which causes compaction in the morula stage of the preimplantation mouse embryo, as well as alpha1,3-fucosylation at multiple internal GlcNAc of unbranched poly-N-acetyllactosamine, termed "myeloglycan," the physiological epitope of E-selectin. Since myeloglycan-type structure is also expressed in various types of human cancer and may mediate E-selectin-dependent metastasis, expression of FUTIV is oncodevelopmentally regulated. The mechanisms controlling FUTIV expression remain to be clarified. In this report, we further characterize FUTIV gene structure and define a non-TATA box-dependent transcriptional start region just upstream from the translational start. FUTIV promoter/reporter fusion constructs defined a "full-length" promoter and highly active fragments in the macrophage-derived U937 and myeloid HL60 cell lines. One highly active fragment contains a consensus binding site for the Ets-1 transcription factor (Withers, D. A., and Hakomori, S. (1997) Glycoconj. J. 14, 764). Gel shift analysis shows specific binding to this site in nuclear extracts from U937 cells. Mutation of the Ets consensus site significantly reduces FUTIV promoter activity in both cell lines. Gel supershift and dominant negative cotransfection experiments identified the Ets family member Elk-1 as one component binding and regulating the FUTIV promoter in U937 cells. The significance of FUTIV regulation by Elk-1 is discussed.

Chemokine production by G protein-coupled receptor activation in a human mast cell line: roles of extracellular signal-regulated kinase and NFAT

Chemoattractants are thought to be the first mediators generated at sites of bacterial infection. We hypothesized that signaling through G protein-coupled chemoattractant receptors may stimulate cytokine production. To test this hypothesis, a human mast cell line (HMC-1) that normally expresses receptors for complement components C3a and C5a at low levels was stably transfected to express physiologic levels of fMLP receptors. We found that fMLP, but not C3a or C5a, induced macrophage inflammatory protein (MIP)-1ss (CCL4) and monocyte chemoattractant protein-1 (CCL2) mRNA and protein. Although fMLP stimulated both sustained Ca(2+) mobilization and phosphorylation of extracellular signal-regulated kinase (ERK), these responses to C3a or C5a were transient. However, transient expression of C3a receptors in HMC-1 cells rendered the cells responsive to C3a for sustained Ca(2+) mobilization and MIP-1ss production. The fMLP-induced chemokine production was blocked by pertussis toxin, PD98059, and cyclosporin A, which respectively inhibit G(i)alpha activation, mitgen-activated protein kinase kinase-mediated ERK phosphorylation, and calcineurin-mediated activation of NFAT. Furthermore, fMLP, but not C5a, stimulated NFAT activation in HMC-1 cells. These data indicate that chemoattractant receptors induce chemokine production in HMC-1 cells with a selectivity that depends on the level of receptor expression, the length of their signaling time, and the synergistic interaction of multiple signaling pathways, including extracellular signal-regulated kinase phosphorylation, sustained Ca(2+) mobilization and NFAT activation.

Protein kinase D. A selective target for antigen receptors and a downstream target for protein kinase C in lymphocytes

Protein kinase Cs (PKCs) are activated by antigen receptors in lymphocytes, but little is known about proximal targets for PKCs in antigen receptor-mediated responses. In this report, we define a role for diacylglycerol-regulated PKC isoforms in controlling the activity of the serine/threonine kinase protein kinase D (PKD; also known as PKC mu) in T cells, B cells, and mast cells. Antigen receptor activation of PKD is a rapid and sustained response that can be seen in T cells activated via the T cell antigen receptor, B cells activated via the B cell antigen receptor, and in mast cells triggered via the high-affinity receptor for IgE (FcepsilonR1). Herein, we show that antigen receptor activation of PKD requires the activity of classical/novel PKCs. Moreover, PKC activity is sufficient to bypass the requirement for antigen receptor signals in the induction of PKD activity. These biochemical and genetic studies establish a role for antigen receptor-regulated PKC enzymes in the control of PKD activity. Regulation of PKD activity through upstream PKCs reveals a signaling network that exists between different members of the PKC superfamily of kinases that can operate to amplify and disseminate antigen receptor signals generated at the plasma membrane.

Spatial and temporal regulation of protein kinase D (PKD)

Protein kinase D (PKD; also known as PKCmicro) is a serine/threonine kinase activated by diacylglycerol signalling pathways in a variety of cells. PKD has been described previously as Golgi-localized, but herein we show that it is present within the cytosol of quiescent B cells and mast cells and moves rapidly to the plasma membrane after antigen receptor triggering. The membrane redistribution of PKD requires the diacylglycerol-binding domain of the enzyme, but is independent of its catalytic activity and does not require the integrity of the pleckstrin homology domain. Antigen receptor signalling initiates in glycosphingolipid-enriched microdomains, but membrane-associated PKD does not co-localize with these specialized structures. Membrane targeting of PKD is transient, the enzyme returns to the cytosol within 10 min of antigen receptor engagement. Strikingly, the membrane-recycled PKD remains active in the cytosol for several hours. The present work thus characterizes a sustained antigen receptor-induced signal transduction pathway and establishes PKD as a serine kinase that temporally and spatially disseminates antigen receptor signals away from the plasma membrane into the cytosol.

Ras regulation and function in lymphocytes

The GTPase, Ras, is rapidly activated in antigen receptor stimulated T. cells, B cells and mast cells. Ras can bind to diverse effector molecules when activated and thereby switch on multiple downstream effector pathways. In lymphocytes Ras plays an important role in the signalling pathways that activate transcription factors involved in cytokine gene induction. Ras is also a key component of the complex regulatory networks that control T and B cell development.

Transcriptional regulation of the cyclooxygenase-2 gene in activated mast cells

Activation of mast cells by aggregation of their IgE receptors induces rapid and transient synthesis of cyclooxygenase-2 (COX-2). In this study we investigated (i) the cis-acting response elements and transcription factors active at the COX-2 promoter and (ii) the signal transduction pathways mediating COX-2 induction following aggregation of mast cell IgE receptors. Transient transfection assays with COX-2 promoter/luciferase constructs suggest that a consensus cyclic AMP response element is essential for induced COX-2 expression. Cotransfection studies with plasmids expressing c-Jun, dominant negative Ras, dominant negative c-Jun NH(2)-terminal kinase, and dominant negative MEKK1 demonstrate that activation of the Ras/MEKK1/c-Jun NH(2)-terminal kinase/c-Jun pathway is required for COX-2 promoter-mediated luciferase expression. Attenuation of COX-2 promoter activity by dominant negative constructs for Raf-1, ERK1, and ERK2 suggests that the Ras/Raf-1/extracellular signal-regulated kinase pathway is also necessary for COX-2 induction. Although mutating the two NF-IL6 sites individually did not affect COX-2 promoter activity, mutating both NF-IL6 sites substantially inhibits COX-2 promoter activity. Moreover, overexpression of wild type CCAAT/enhancer-binding protein-beta (C/EBPbeta) augments COX-2 promoter activity in activated mast cells and cotransfection of a dominant negative C/EBPbeta construct completely blocks COX-2 promoter/luciferase expression. Our data suggest that in activated mast cells, a Ras/MEKK1/c-Jun NH(2)-terminal kinase signal transduction pathway activating c-Jun, a Ras/Raf-1/extracellular signal-regulated kinase pathway, and activated C/EBPbeta facilitate COX-2 induction via the cyclic AMP response element and NF-IL6 sites of the COX-2 promoter.

Mast-cell responses in the development of asthma

Many cells participate in the pathogenesis of asthmatic inflammation. The mast cell is localized at the interface of the internal and external environment within the lung where it may respond to allergens and other exogenous stimuli. The activation of mast cells leads to the release of mediators that contribute to the early phase of asthmatic inflammation. Mast-cell-derived products may also contribute to the late-phase asthmatic response. This review summarizes the developmental biologic features of the mast cell, its receptor-mediated activation, and its range of preformed, newly synthesized, and induced mediators that contribute to asthmatic inflammation.

Molecular consequences of human mast cell activation following immunoglobulin E-high-affinity immunoglobulin E receptor (IgE-FcepsilonRI) interaction

The cross-linking by immunoglobulin E of its high-affinity receptor, FcepsilonRI, on mast cells initiates a complex series of biochemical events leading to degranulation and the synthesis and secretion of eicosanoids and cytokines through the action of transcription factors, such as nuclear factor-kappaB. The initial activation involves the phosphorylation of FcepsilonRI beta- and gamma-subunits through the actions of the tyrosine kinases lyn and syk. For the purposes of description, the subsequent events may be grouped in three cascades characterized by the key proteins involved. First, the phospholipase C-inositol phosphate cascade activates protein kinase C and is largely responsible for calcium mobilization and influx. Second, activation of Ras and Raf via mitogen-activated protein kinase causes the production of arachidonic acid metabolites. Third, the generation of sphingosine and sphingosine-1-phosphate occurs through activation of sphingomyelinase. While the early signaling events tend to be specific for the cited cascades, there is an increasing overlap of activated proteins with the downstream propagation of the signal. It is the balanced interaction between these proteins that culminates in degranulation, synthesis, and release of eicosanoids and cytokines.

Signalling through the high-affinity IgE receptor Fc epsilonRI

The Fc epsilonRI complex forms a high-affinity cell-surface receptor for the Fc region of antigen-specific immunoglobulin E (IgE) molecules. Fc epsilonRI is multimeric and is a member of a family of related antigen/Fc receptors which have conserved structural features and similar roles in initiating intracellular signalling cascades. In humans, Fc epsilonRI controls the activation of mast cells and basophils, and participates in IgE-mediated antigen presentation. Multivalent antigens bind and crosslink IgE molecules held at the cell surface by Fc epsilonRI. Receptor aggregation induces multiple signalling pathways that control diverse effector responses. These include the secretion of allergic mediators and induction of cytokine gene transcription, resulting in secretion of molecules such as interleukin-4, interleukin-6, tumour-necrosis factor-alpha and granulocyte-macrophage colony-stimulating factor. Fc epsilonRI is therefore central to the induction and maintenance of an allergic response and may confer physiological protection in parasitic infections.

Dynamic re-distribution of protein kinase D (PKD) as revealed by a GFP-PKD fusion protein: dissociation from PKD activation

Protein kinase D (PKD)/protein kinase Cmicro (PKCmicro, a serine/threonine protein kinase with distinct structural and enzymological properties, is rapidly activated in intact cells via PKC. The amino-terminal region of PKD contains a cysteine-rich domain (CRD) that directly binds phorbol esters with a high affinity. Here, we show that treatment of transfected RBL 2H3 cells with phorbol 12,13-dibutyrate (PDB) induces a striking CRD-dependent translocation of PKD from the cytosol to the plasma membrane, as shown by real time visualization of a functional green fluorescent protein (GFP)-PKD fusion protein. A single amino acid substitution in the second cysteine-rich motif of PKD (P287G) prevented PDB-induced membrane translocation but did not affect PKD activation. Our results indicate that PKD translocation and activation are distinct processes that operate in parallel to regulate the activity and localization of this enzyme in intact cells.

Involvement of farnesyl protein transferase (FPTase) in FcarepsilonRI-induced activation of RBL-2H3 mast cells

Changes in farnesyl protein transferase (FPTase) activity and FPTase beta-subunit protein levels were determined in IgE-sensitized RBL-2H3 mast cells in response to polyvalent antigen administration. Ten minutes after the addition of DNP modified BSA to mast cells, whose high affinity receptor for IgE (FcvarepsilonRI) contained bound anti-DNP IgE, FPTase specific activity increased by 54 +/- 28%. Time course studies showed FPTase specific activity doubled during a 20- to 30-min period after antigen-induced cell aggregation. Also, an increase in FPTase beta-subunit protein during this time ( approximately 30%) was observed; this protein increase was not accompanied by a similar increase in FPTase beta-subunit m-RNA levels. The FcvarepsilonRI aggregation had no significant effect on the activities of other enzymes involved with farnesyl diphosphate (FPP) metabolism: FPP synthase, isopentenyl diphosphate isomerase, geranylgeranyl protein transferase, and squalene synthase. Specific inhibition of FPTase activity by manumycin was studied to determine what role FPTase plays in mast cell activation. Manumycin profoundly inhibited hexosaminidase release in activated cells, indicating FPTase is required for signal transduction involved with protein exocytosis from RBL-2H3 mast cells.

Small GTPases in lymphocyte biology: Rho proteins take center stage

Almost a decade ago, the small GTPase Ras was shown to be activated in response to antigen receptor triggering in T cells. Since then, Ras has been further characterized as a central molecule for the regulation of signal transduction pathways in lymphocytes. However, over the last couple of years, its exclusive role in lymphocyte biology has been challenged by the emergence of its relatives of the Rho family. Today it is well established that Rho GTPases act as unique molecular switches at several critical checkpoints in lymphocyte development and function. Additionally, a new and critical concept in GTPase signaling has taken shape over the last couple of years in that small GTPases are able to regulate quite diverse cellular processes in the immune response by linking to multiple biochemical effector pathways.

Effector pathways regulating T cell activation

Activation of T lymphocytes is a key event for an efficient response of the immune system. It requires the involvement of the T cell receptor antigen as well as costimulatory molecules such as CD28. Engagement of these receptors through the interaction with a foreign antigen associated with major histocompatibility complex molecules and CD28 counter-receptors B7.1/B7.2, respectively, results in a series of signaling cascades acting in synergy and which culminate in activation of interleukin-2 gene transcription and eventually cell proliferation. Many studies aimed at characterizing these specific effector pathways have been published; however, the actual signaling molecules that transduce activation signals from the cell membrane to the nucleus and that directly regulate interleukin-2 gene transcription are not yet completely defined and remain a matter of debate. In this commentary, we have attempted to analyze the results, which are sometimes diverging if not totally contradictory, characterizing effector pathways that possibly are triggered during T cell activation.

The transcription factor NFAT4 is involved in the generation and survival of T cells

Nuclear factor of activated T cells (NFAT) is a family of four related transcription factors implicated in cytokine and early response gene expression in activated lymphocytes. Here we report that NFAT4, in contrast to NFATp and NFATc, is preferentially expressed in DP thymocytes. Mice lacking NFAT4 have impaired development of CD4 and CD8 SP thymocytes and peripheral T cells as well as hyperactivation of peripheral T cells. The thymic defect is characterized by increased apoptosis of DP thymocytes. The increased apoptosis and hyperactivation may reflect heightened sensitivity to TcR-mediated signaling. Further, mice lacking NFAT4 have impaired production of Bcl-2 mRNA and protein. NFAT4 thus plays an important role in the successful generation and survival of T cells.