Association of protein-tyrosine kinase with phospholipase C-gamma 1 in bone marrow-derived mouse mast cells

Mast cell activation syndrome: a review

Mast cell activation syndrome (MCAS) is a condition with signs and symptoms involving the skin, gastrointestinal, cardiovascular, respiratory, and neurologic systems. It can be classified into primary, secondary, and idiopathic. Earlier proposed criteria for the diagnosis of MCAS included episodic symptoms consistent with mast cell mediator release affecting two or more organ systems with urticaria, angioedema, flushing, nausea, vomiting, diarrhea, abdominal cramping, hypotensive syncope or near syncope, tachycardia, wheezing, conjunctival injection, pruritus, and nasal stuffiness. Other criteria included a decrease in the frequency, severity, or resolution of symptoms with anti-mediator therapy including H(1) and H(2)histamine receptor antagonists, anti-leukotrienes, or mast cell stabilizers. Laboratory data that support the diagnosis include an increase of a validated urinary or serum marker of mast cell activation (MCA), namely the documentation of an increase of the marker above the patient's baseline value during symptomatic periods on more than two occasions, or baseline serum tryptase levels that are persistently above 15 ng/ml, or documentation of an increase of the tryptase level above baseline value on one occasion. Less specific assays are 24-h urine histamine metabolites, PGD(2) (Prostaglandin D(2)) or its metabolite, 11-β-prostaglandin F(2) alpha. A recent global definition, criteria, and classification include typical clinical symptoms, a substantial transient increase in serum total tryptase level or an increase in other mast cell derived mediators, such as histamine or PGD2 or their urinary metabolites, and a response of clinical symptoms to agents that attenuate the production or activities of mast cell mediators.

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.

Analysis of oligomeric proteins during unfolding by pH and temperature

During thermal transition and variation of pH, structural properties of 35 proteins and their complexes (bound with substrate and co-factor) were analyzed in detail. During pH alteration, these proteins were shown to have substantial differences in conformations. pH conformers were analyzed in detail. Free energy and other energy parameters were also estimated for these proteins at various pH and temperatures. Detailed structural analysis and binding interfaces of various substrates, inhibitors and cofactor of these proteins were also investigated using docking and molecular dynamic simulation.

Differential regulation of phospholipase Cgamma subtypes through FcepsilonRI, high affinity IgE receptor

The high affinity IgE receptor (FcepsilonRI) usually exists as a tetramer composed of alphabetagamma2 subunits. The COOH-tail of beta and gamma subunits contains consensus sequence termed 'immunoreceptor tyrosine-based activation motif' (ITAM). Tyrosine phosphorylated ITAM interacts with signaling proteins that contain the Src homology domain, forming a main amplifying and signaling route for FcepsilonRI. Unlike the COOH-tail, the functional role of NH(2)-tail of beta subunit in the signaling of FcepsilonRI is not clear because it lacks the ITAM sequences. To study the roles of NH(2)-tail of beta subunit, the cDNA library of RBL-2H3 cells was screened by yeast two-hybrid assay, and the NH(2)-tail of the beta subunit was found to interact with phospholipase Cgamma2 (PLCgamma2) but not with PLCgamma1. Since both PLCgamma1 and PLCgamma2 are expressed in RBL-2H3 cells and they possess identical cellular functions, the functional meaning of the protein-protein interaction between PLCgamma2 and NH(2)-tail of beta subunit was studied by comparing the regulatory pathways that control the FcepsilonRI-mediated tyrosine phosphorylation of the two enzymes. Our study shows that PI3-kinase and PMA-sensitive PKCs were required exclusively for the FcepsilonRI-mediated tyrosine phosphorylation of PLCgamma1. Also the FcepsilonRI-mediated tyrosine phosphorylation of PLCgamma1 was more sensitive to the inhibitors of Src and Syk kinases. These results therefore suggest that PLCgamma1 is involved in dynamic regulation of protein kinase C activity and inositol triphosphate levels in response to cellular needs. In contrast, PLCgamma2, through continuous interaction with the NH(2)-tail of beta subunit, co-localizes with FcepsilonRI in the same signaling domain, and maintains the basal cellular PLC activity.

Phosphorylation of Tyr342 in the linker region of Syk is critical for Fc epsilon RI signaling in mast cells

The linker region of Syk and ZAP70 tyrosine kinases plays an important role in regulating their function. There are three conserved tyrosines in this linker region; Tyr317 of Syk and its equivalent residue in ZAP70 were previously shown to negatively regulate the function of Syk and ZAP70. Here we studied the roles of the other two tyrosines, Tyr342 and Tyr346 of Syk, in Fc epsilon RI-mediated signaling. Antigen stimulation resulted in Tyr342 phosphorylation in mast cells. Syk with Y342F mutation failed to reconstitute Fc epsilon RI-initiated histamine release. In the Syk Y342F-expressing cells there was dramatically impaired receptor-induced phosphorylation of multiple signaling molecules, including LAT, SLP-76, phospholipase C-gamma2, but not Vav. Compared to wild-type Syk, Y342F Syk had decreased binding to phosphorylated immunoreceptor tyrosine-based activation motifs and reduced kinase activity. Surprisingly, mutation of Tyr346 had much less effect on Fc epsilon RI-dependent mast cell degranulation. An anti-Syk-phospho-346 tyrosine antibody indicated that antigen stimulation induced only a very minor increase in the phosphorylation of this tyrosine. Therefore, Tyr342, but not Tyr346, is critical for regulating Syk in mast cells and the function of these tyrosines in immune receptor signaling appears to be different from what has been previously reported for the equivalent residues of ZAP70.

The adapter molecule Gab2 regulates Fc epsilon RI-mediated signal transduction in mast cells

The recently cloned scaffolding molecule Gab2 can assemble multiple molecules involved in signaling pathways. Bone marrow-derived mast cells isolated from Gab2(-/-) mice have defective signaling probably due to the lack of the activation of phosphatidylinositol-3 kinase (PI3-kinase). In this study, we investigated the role of Gab2 using the rat basophilic leukemia 2H3 cell line mast cells. Fc epsilon RI aggregation induced the tyrosine phosphorylation of Gab2 and translocation of a significant fraction of it from the cytosol to the plasma membrane. As in other cells, Gab2 was found to associate with several signaling molecules including Src homology 2-containing protein tyrosine phosphatase 2, Grb2, Lyn, and phospholipase C gamma (PLC gamma). The association of Gab2 with Lyn and PLC gamma were enhanced after receptor aggregation. Overexpression of Gab2 in rat basophilic leukemia 2H3 cell line cells inhibited the Fc epsilon RI-induced tyrosine phosphorylation of the subunits of the receptor, and the phosphorylation and/or activation of Syk and mitogen-activated protein kinase. Downstream events such as calcium mobilization, degranulation, and induction of TNF-alpha and IL-6 gene transcripts were decreased in Gab2 overexpressing cells, although Akt phosphorylation as a measure of PI3-kinase activation was unaffected. These results suggest that in addition to the positive effects mediated by PI3-kinase that are apparent in Gab2(-/-) mast cells, Gab2 by interacting with Lyn and PLC gamma may have negative regulatory effects on Fc epsilon RI-induced mast cell signaling and functions.

Roles of mitogen-activated protein kinase pathways for mediator release from human cultured mast cells

Human cultured mast cells (HCMC) secrete histamine, sulfidoleukotrienes (LTs), and prostaglandin D(2) (PGD(2)), and produce a variety of cytokines after aggregation of high-affinity receptors for IgE (FcepsilonRI). With respect to the mitogen-activated protein kinase (MAPK) family, extracellular signal-regulated kinases (ERKs), c-Jun NH(2)-terminal kinases (JNKs), and p38 mitogen-activated protein kinase (p38 MAPK) are known. To investigate the roles of these kinase pathways for mediator release from human mast cells, we examined the participation of the activation of these kinases in mediator release, using 1,4-diamino-2, 3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126), an ERK pathway inhibitor, and 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imid azo le (SB203580), a p38 MAPK pathway inhibitor. U0126 inhibited ERK activation, LT and PGD(2) release, and granulocyte macrophage-colony stimulating factor (GM-CSF) production after stimulation of HCMC. SB203580, on the other hand, potentiated JNK activation and GM-CSF production. The findings of the present study demonstrated that: (i) the release of arachidonic acid metabolites is mediated by the ERK pathway; (ii) GM-CSF production may be driven by both the ERK and JNK pathways; and (iii) the p38 MAPK pathway negatively regulates the JNK pathway. This suggests that MAPK pathways play important roles in mediator release from human mast cells.

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.

Ca2+ and protein kinase C signaling for histamine and sulfidoleukotrienes released from human cultured mast cells

Human cultured mast cells (HCMC) release histamine and sulfidoleukotrienes (LTs) upon IgE-FcepsilonRI-mediated mast cell activation. We analyzed the Ca2+ and PKC signaling in HCMC and compared it to that in rodent mast cells. In HCMC, after IgE-mediated stimulation, an elevation of [Ca2+]i and PKC translocation to the membrane fraction was observed. As concerns Ca2+ signaling, 1) IgE-mediated histamine and LTs release was abolished after Ca2+ depletion, and the reconstitution of Ca2+ recovered the release of histamine and LTs. As regards PKC signaling, 1) staurosporine inhibited IgE-mediated mediator release. 2) PKC-downregulated mast cells did not release histamine and LTs. A23187 and PMA synergistically potentiated the activation of extracellular-regulated kinase and synergistically induced histamine and LTs release. These results demonstrated that HCMC might be useful for analysis of the signal transduction pathway for mediator release, such as histamine and LTs.

Phosphatidylinositol 3-kinase and Ca2+ influx dependence for ligand-stimulated internalization of the c-Kit receptor

We have evaluated the role of phosphatidylinositol 3-kinase (PI3-kinase) and Ca2+ influx in ligand-stimulated internalization of the c-Kit receptor. The wild type (wt) c-Kit receptor and YF719, a mutant receptor in which the SH2-mediated binding site for the p85 subunit of PI3-kinase is disrupted, were expressed in DA-1 cells. YF719 internalized with similar kinetics as wt c-Kit although the receptor remained localized close to the plasma membrane. However, in the absence of extracellular Ca2+, or in the presence of the competitive Ca2+ influx blocker Ni2+, the YF719 mutant failed to internalize. Failure to internalize in the absence of Ca2+ was also observed for the wt c-Kit receptor in cells that were pretreated with the PI3-kinase inhibitor, wortmannin. Following stimulation with ligand, clathrin heavy chains were found to co-immunoprecipitate with c-Kit. However, under conditions in which PI3-kinase activity is inhibited and Ca2+ influx is blocked, clathrin failed to co-immunoprecipitate with c-Kit. Our results demonstrate that both Ca2+ influx and PI3-kinase activity influence c-Kit endocytosis, and inhibition of these two signals disrupts the earliest stages of ligand-mediated internalization.

Downstream signaling molecules bind to different phosphorylated immunoreceptor tyrosine-based activation motif (ITAM) peptides of the high affinity IgE receptor

The cytoplasmic tails of both the beta and gamma subunits of the high affinity IgE receptor (FcepsilonRI) contain a consensus sequence termed the immunoreceptor tyrosine-based activation motif (ITAM). This motif plays a critical role in receptor-mediated signal transduction. Synthetic peptides based on the ITAM sequences of the beta and gamma subunits of FcepsilonRI were used to investigate which proteins associate with these motifs. Tyrosine-phosphorylated beta and gamma ITAM peptides immobilized on beads precipitated Syk, Lyn, Shc, Grb2, and phospholipase C-gamma1 from lysates of rat basophilic leukemia RBL-2H3 cells. Syk was precipitated predominantly by the tyrosine-diphosphorylated gamma ITAM peptide, but much less by the diphosphorylated beta ITAM peptide or by the monophosphorylated peptides. Phospholipase C-gamma1, Shc, and Grb2 were precipitated only by the diphosphorylated beta ITAM peptide. Non-phosphorylated ITAM peptides did not precipitate these proteins. In membrane binding assays, fusion proteins containing the Src homology 2 domains of phospholipase C-gamma1, Shc, Syk, and Lyn directly bound the tyrosine-phosphorylated ITAM peptides. Although the ITAM sequences of the beta and gamma subunits of FcepsilonRI are similar, once they are tyrosine-phosphorylated they preferentially bind different downstream signaling molecules. Tyrosine phosphorylation of the ITAM of the gamma subunit recruits and activates Syk, whereas the beta subunit may be important for the Ras signaling pathway.

Transfection of Syk protein tyrosine kinase reconstitutes high affinity IgE receptor-mediated degranulation in a Syk-negative variant of rat basophilic leukemia RBL-2H3 cells

Aggregation of the high affinity receptor for immunoglobulin E (Fc epsilon RI) on mast cells results in rapid tyrosine phosphorylation and activation of Syk, a cytoplasmic protein tyrosine kinase. To examine the role of Syk in the Fc epsilon RI signaling pathway, we identified a variant of RBL-2H3 cells that has no detectable Syk by immunoblotting and by in vitro kinase reactions. In these Syk-deficient TB1A2 cells, aggregation of Fc epsilon RI induced no histamine release and no detectable increase in total cellular protein tyrosine phosphorylation. However, stimulation of these cells with the calcium ionophore did induce degranulation. Fc epsilon RI aggregation induced tyrosine phosphorylation of the beta and gamma subunits of the receptor, but no increase in the tyrosine phosphorylation of phospholipase C-gamma 1 and phospholipase C-gamma 2 and no detectable increase in intracellular free Ca2+ concentration. By transfection, cloned lines were established with stable expression of Syk. In these reconstituted cells, Fc epsilon RI aggregation induced tyrosine phosphorylation of phospholipase C-gamma 1 and phospholipase C-gamma 2, an increase in intracellular free Ca2+ and histamine release. These results demonstrate that Syk plays a critical role in the early Fc epsilon RI-mediated signaling events. It further demonstrates that Syk activation occurs downstream of receptor phosphorylation, but upstream of most of the Fc epsilon RI-mediated protein tyrosine phosphorylations.

Mast cell activation involves plasma membrane potential- and thapsigargin-sensitive intracellular calcium pools

The regulation and role of the intracellular Ca2+ pools were studied in rat peritoneal mast cells. Cytosolic free calcium concentration ([Ca2+]i) was monitored in fura-2 loaded mast cells. In the presence of Ca2+ and K+, compound 48/80 induced a biphasic increase in [Ca2+]i composed of a fast transient phase and an apparent sustained phase. The sustained phase was partially inhibited by the addition of Mn2+. DTPA, a cell-impermeant chelator of Mn2+, reversed this inhibition, suggesting that a quenching of fura-2 fluorescence occurs in the extracellular medium. In the absence of extracellular Ca2+, the transient phase, but not the sustained one, could be preserved, provided that mast cells were depolarized. The transient phase was completely abolished by thapsigargin, a microsomal Ca(2+)-ATPase inhibitor. Maximum histamine release induced by either compound 48/80 or antigen was obtained in the absence of added Ca2+ only when mast cells were depolarized. These histamine releases were inhibited by low doses (< 30 nM) of thapsigargin. Thapsigargin at higher doses induced histamine release which was unaffected by changing the plasma membrane potential, but was completely dependent on extracellular Ca2+, showing that a Ca2+ influx is required for thapsigargin-induced exocytosis. Together, these results suggest that the mobilization of Ca2+ from thapsigargin sensitive-intracellular pools induced by compound 48/80 or antigen is sufficient to trigger histamine release. The modulation of these pools by the plasma membrane potential suggest their localization is close to the plasma membrane.

Activation of the high-affinity immunoglobulin E receptor Fc epsilon RI in RBL-2H3 cells is inhibited by Syk SH2 domains

Antigen-mediated aggregation of the high-affinity receptor for immunoglobulin E, Fc epsilon RI, results in the activation of multiple signaling pathways, leading to the release of mediators of the allergic response. One of the earliest responses to receptor stimulation is the tyrosine phosphorylation of the beta and gamma subunits of Fc epsilon RI and the association of the tyrosine kinase Syk with the phosphorylated receptor. This association is mediated by the SH2 domains of Syk and is believed to be critical for activating signaling pathways resulting in mediator release. To examine the importance of the interaction of Syk with Fc epsilon RI in signaling events following receptor activation, we introduced a protein containing the SH2 domains of Syk into streptolysin O-permeabilized RBL-2H3 cells. The Syk SH2 domains completely inhibited degranulation and leukotriene production following receptor aggregation, and they blocked the increase in protein tyrosine phosphorylation observed after receptor activation. Inhibition was specific for Fc epsilon RI-mediated signaling, since degranulation of cells activated by alternative stimuli was not blocked by the Syk SH2 domains. A protein containing a point mutation in the carboxy-terminal SH2 domain which abolishes phosphotyrosine binding was not inhibitory. In addition, inhibition of degranulation was reversed by pretreatment of the SH2 domains with a tyrosine phosphorylated peptide corresponding to the tyrosine-based activation motif found in the gamma subunit of Fc epsilon RI, the nonphosphorylated peptide had no effect. The association of Syk with the tyrosine-phosphorylated gamma subunit of the activated receptor was blocked by the Syk SH2 domains, and deregulation in cells activated by clustering of Syk directly without Fc epsilon RI aggregation was not affected by the Syk SH2 domains. These results demonstrate that the association of Syk with the activated Fc epsilon RI is critical for both early and late events following receptor activation and confirm the key role Syk plays in signaling through the high-affinity IgE receptor.

Clustering of Syk is sufficient to induce tyrosine phosphorylation and release of allergic mediators from rat basophilic leukemia cells

In mast cells, antigen-mediated aggregation of the high-affinity receptor for immunoglobulin E, Fc epsilon RI, stimulates tyrosine phosphorylation and activation of multiple signaling pathways leading to the release of several classes of mediators of the allergic response. Early events induced upon cross-linking of Fc epsilon RI include tyrosine phosphorylation of Fc epsilon RI subunits and activation of the tyrosine kinase p72syk (Syk), which binds to tyrosine-phosphorylated Fc epsilon RI. Clustering of Syk, as a result of its interaction with aggregated Fc epsilon RI, may play a role in activating one or more of the signaling pathways leading to mediator release. To test this possibility, Syk was introduced into a model mast cell line (rat basophilic leukemia cells) as part of a chimeric transmembrane protein containing the extracellular and transmembrane domains of CD16 and CD7, respectively. Clustering of the Syk chimera, using antibodies against CD16, was found to be sufficient to stimulate early and late events normally induced by clustering of Fc epsilon RI. Specifically, aggregation of Syk induced degranulation, leukotriene synthesis, and expression of cytokine genes. Induction of mediator release was dependent on the kinase activity of Syk. Consistent with this finding, clustering of Syk also induced the tyrosine phosphorylation of a profile of proteins, including phospholipase C-gamma 1 and mitogen-activated protein kinase, similar to that induced upon clustering of Fc epsilon RI. These results strongly suggest that Syk is an early and critical mediator of multiple signaling pathways that emanate from the Fc epsilon RI receptor and give rise to the allergic response.

Two-phase increment of Ca2+ uptake, intracellular Ca2+ concentration, and histamine release following antigen stimulation in mouse bone marrow-derived mast cells (BMMC)

The relationship between the influx of Ca2+ into cells or cytosolic Ca2+ concentration ([Ca2+]i) and the histamine release following antigen stimulation in mouse bone marrow-derived mast cells (BMMC) was examined, and the results were compared with those from human lung mast cells (HLMC) and rat peritoneal mast cells (RPMC) in some experiments. Anaphylactic histamine release from BMMC as well as HLMC, but not that from RPMC, was dependent on the extracellular Ca2+. When BMMC were challenged by antigen following radioactive 45Ca2+ addition, two phases of 45Ca2+ influx into the cells were observed. The first phase, which was initiated and completed within 30 sec and 2 min, respectively, after antigen treatment, appeared to be related to anaphylactic histamine release. The second influx began 30 sec subsequent to the first one and lasted for at least 2 min, and this occurred after the completion of the histamine release; So far, it is not known how this second influx participates in the intracellular event(s). On the other hand, only one sustained elevation of [Ca2+]i occurred that reached its maximum within 2 min after antigen stimulation. Following stimulation of BMMC with antigen in the absence of Ca2+, Ca2+ addition 1 to 5 min later time-dependently enhanced the histamine release, although the release was deteriorated by further extension of Ca2+ addition. In contrast, the releasability of HLMC was rapidly decreased. These results indicate that extracellular Ca2+ not only is prerequisite for anaphylactic histamine release from BMMC, but also may modulate the release and participate in some intracellular event(s) which has yet to be focused upon.

The pleckstrin homology domain of Bruton tyrosine kinase interacts with protein kinase C

Bruton tyrosine kinase (EC 2.7.1.112) [Btk, encoded by Btk in mice and BTK in humans (formerly known as atk, BPK, or emb)], which is variously mutated in chromosome X-linked agammaglobulinemia patients and X-linked immunodeficient (xid) mice, has the pleckstrin homology (PH) domain at its amino terminus. The PH domain of Btk expressed as a bacterial fusion protein directly interacts with protein kinase C in mast cell lysates. Evidence was obtained that Btk is physically associated with protein kinase C in intact murine mast cells as well. Both Ca(2+)-dependent (alpha, beta I, and beta II) and Ca(2+)-independent protein kinase C isoforms (epsilon and zeta) in mast cells interact with the PH domain of Btk in vitro, and protein kinase C beta I is associated with Btk in vivo. Btk served as a substrate of protein kinase C, and its enzymatic activity was down-regulated by protein kinase C-mediated phosphorylation. Furthermore, depletion or inhibition of protein kinase C with pharmacological agents resulted in an enhancement of the tyrosine phosphorylation of Btk induced by mast cell activation.

Tyrosine phosphorylation and activation of Bruton tyrosine kinase upon Fc epsilon RI cross-linking

Tyrosine phosphorylation of several cellular proteins is one of the earliest signaling events induced by cross-linking of the high-affinity receptor for immunoglobulin E (Fc epsilon RI) on mast cells or basophils. Tyrosine kinases activated during this process include the Src family kinases, Lyn, c-Yes, and c-Src, and members of another subfamily, Syk and PTK72 (identical or highly related to Syk). Recently, some of us described two novel tyrosine kinases, Emb and Emt, whose expression was limited to subsets of hematopoietic cells, including mast cells. Emb turned out to be identical to Btk, a gene product defective in human X-linked agammaglobulinemia and in X-linked immunodeficient (xid) mice. Here we report that Fc epsilon RI cross-linking induced rapid phosphorylation on tyrosine, serine, and threonine residues and activation of Btk in mouse bone marrow-derived mast cells. A small fraction of Btk translocated from the cytosol to the membrane compartment following receptor cross-linking. Tyrosine phosphorylation of Btk was not induced by either a Ca2+ ionophore (A23187), phorbol 12-myristate 13-acetate, or a combination of the two reagents. Co-immunoprecipitation between Btk and receptor subunit beta or gamma was not detected. The data collectively suggest that Btk is not associated with Fc epsilon but that its activation takes place prior to protein kinase C activation and plays a novel role in the Fc epsilon RI signaling pathway.

Tyrosine phosphorylation and activation of Bruton tyrosine kinase upon Fc epsilon RI cross-linking

Tyrosine phosphorylation of several cellular proteins is one of the earliest signaling events induced by cross-linking of the high-affinity receptor for immunoglobulin E (Fc epsilon RI) on mast cells or basophils. Tyrosine kinases activated during this process include the Src family kinases, Lyn, c-Yes, and c-Src, and members of another subfamily, Syk and PTK72 (identical or highly related to Syk). Recently, some of us described two novel tyrosine kinases, Emb and Emt, whose expression was limited to subsets of hematopoietic cells, including mast cells. Emb turned out to be identical to Btk, a gene product defective in human X-linked agammaglobulinemia and in X-linked immunodeficient (xid) mice. Here we report that Fc epsilon RI cross-linking induced rapid phosphorylation on tyrosine, serine, and threonine residues and activation of Btk in mouse bone marrow-derived mast cells. A small fraction of Btk translocated from the cytosol to the membrane compartment following receptor cross-linking. Tyrosine phosphorylation of Btk was not induced by either a Ca2+ ionophore (A23187), phorbol 12-myristate 13-acetate, or a combination of the two reagents. Co-immunoprecipitation between Btk and receptor subunit beta or gamma was not detected. The data collectively suggest that Btk is not associated with Fc epsilon but that its activation takes place prior to protein kinase C activation and plays a novel role in the Fc epsilon RI signaling pathway.

Ciclopirox olamine lotion 1%: bioequivalence to ciclopirox olamine cream 1% and clinical efficacy in tinea pedis

Studies were conducted to assess the bioequivalence of a new antimycotic formulation, ciclopirox olamine lotion 1%, to an established compound, ciclopirox olamine cream 1%. Results of in vitro studies, using skin samples from human cadavers and domestic pigs, demonstrated that the two formulations equally penetrate all layers of the stratum corneum and inhibit the growth of Trichophyton mentagrophytes and Candida albicans. In vivo studies in guinea pigs and in human volunteers demonstrated the comparable therapeutic efficacy of the lotion and the cream in experimental trichophytosis. In addition, a multicenter, double-blind clinical trial was undertaken to compare ciclopirox olamine lotion 1% with the vehicle alone in the treatment of patients with tinea pedis. Patients with plantar, interdigital, or vesicular tinea pedis were enrolled in the studies. Patients were treated for 28 days. Clinical and mycological responses were determined during treatment and two weeks posttreatment. Ciclopirox olamine lotion 1% was found to be significantly more effective than its vehicle in the treatment of patients with common tinea pedis. Minor localized side effects (pruritus, burning sensation) were reported in 2% of 89 patients treated with ciclopirox olamine lotion 1%. The results demonstrate the bioequivalence of ciclopirox olamine lotion 1% and ciclopirox olamine cream 1% and confirm the clinical effectiveness and safety of the lotion in the treatment of tinea pedis, a generally recalcitrant fungal infection. It is concluded that ciclopirox olamine lotion 1% can be used as an alternative to ciclopirox olamine cream 1% for treatment of tinea pedis, tinea versicolor, tinea cruris, tinea corporis, and cutaneous candidiasis when the convenience and/or cosmetic elegance of a lotion is desired.