Pharmacological targeting of the KIT growth factor receptor: a therapeutic consideration for mast cell disorders

Exosome regulation of immune response mechanism: Pros and cons in immunotherapy

Due to its multiple features, including the ability to orchestrate remote communication between different tissues, the exosomes are the extracellular vesicles arousing the highest interest in the scientific community. Their size, established as an average of 30-150 nm, allows them to be easily uptaken by most cells. According to the type of cells-derived exosomes, they may carry specific biomolecular cargoes used to reprogram the cells they are interacting with. In certain circumstances, exosomes stimulate the immune response by facilitating or amplifying the release of foreign antigens-killing cells, inflammatory factors, or antibodies (immune activation). Meanwhile, in other cases, they are efficiently used by malignant elements such as cancer cells to mislead the immune recognition mechanism, carrying and transferring their cancerous cargoes to distant healthy cells, thus contributing to antigenic invasion (immune suppression). Exosome dichotomic patterns upon immune system regulation present broad advantages in immunotherapy. Its perfect comprehension, from its early biogenesis to its specific interaction with recipient cells, will promote a significant enhancement of immunotherapy employing molecular biology, nanomedicine, and nanotechnology.

CREB Is Indispensable to KIT Function in Human Skin Mast Cells-A Positive Feedback Loop between CREB and KIT Orchestrates Skin Mast Cell Fate

Skin mast cells (MCs) are critical effector cells in acute allergic reactions, and they contribute to chronic dermatoses like urticaria and atopic and contact dermatitis. KIT represents the cells' crucial receptor tyrosine kinase, which orchestrates proliferation, survival, and functional programs throughout the lifespan. cAMP response element binding protein (CREB), an evolutionarily well-conserved transcription factor (TF), regulates multiple cellular programs, but its function in MCs is poorly understood. We recently reported that CREB is an effector of the SCF (Stem Cell Factor)/KIT axis. Here, we ask whether CREB may also act upstream of KIT to orchestrate its functioning. Primary human MCs were isolated from skin and cultured in SCF+IL-4 (Interleukin-4). Pharmacological inhibition (666-15) and RNA interference served to manipulate CREB function. We studied KIT expression using flow cytometry and RT-qPCR, KIT-mediated signaling using immunoblotting, and cell survival using scatterplot and caspase-3 activity. The proliferation and cycle phases were quantified following BrdU incorporation. Transient CREB perturbation resulted in reduced KIT expression. Conversely, microphthalmia transcription factor (MITF) was unnecessary for KIT maintenance. KIT attenuation secondary to CREB was associated with heavily impaired KIT functional outputs, like anti-apoptosis and cell cycle progression. Likewise, KIT-elicited phosphorylation of ERK1/2 (Extracellular Signal-Regulated Kinase 1/2), AKT, and STAT5 (Signal Transducer and Activator of Transcription) was substantially diminished upon CREB inhibition. Surprisingly, the longer-term interference of CREB led to complete cell elimination, in a way surpassing KIT inhibition. Collectively, we reveal CREB as non-redundant in MCs, with its absence being incompatible with skin MCs' existence. Since SCF/KIT regulates CREB activity and, vice versa, CREB is required for KIT function, a positive feedforward loop between these elements dictates skin MCs' fate.

Genome Variation Map of Domestic Qinghai-Tibet Plateau Yaks by SLAF-Seq Reveals Genetic Footprint during Artificial Selection

The yak (Bos grunniens) was domesticated in the high-altitude QTP. Research about their genetic diversity and population structure is limited. In this study, we resequenced the genome of 494 domestic yaks using Specific-Locus Amplified Fragment Sequencing (SLAF-seq). The survey was conducted on six populations sampled from isolated locations in China in order to analyze their structure and genetic diversity. These six domestic populations were clearly grouped into two independent clusters, with Jinchuan, Changtai, and Jiulong showing a tight genetic relationship with the wild yak. Nerve development pathways were enriched with GO enrichment analysis of 334 domesticated genes. Major genomic regions associated with the differentiation of domestic yaks were detected. These findings provide preliminary information on the yak genome variability, useful to understand the genomic characteristics of different populations in QTP.

CRISPR/Cas9-engineering of HMC-1.2 cells renders a human mast cell line with a single D816V-KIT mutation: An improved preclinical model for research on mastocytosis

The HMC-1.2 human mast cell (huMC) line is often employed in the study of attributes of neoplastic huMCs as found in patients with mastocytosis and their sensitivity to interventional drugs in vitro and in vivo. HMC-1.2 cells express constitutively active KIT, an essential growth factor receptor for huMC survival and function, due to the presence of two oncogenic mutations (D816V and V560G). However, systemic mastocytosis is commonly associated with a single D816V-KIT mutation. The functional consequences of the coexisting KIT mutations in HMC-1.2 cells are unknown. We used CRISPR/Cas9-engineering to reverse the V560G mutation in HMC-1.2 cells, resulting in a subline (HMC-1.3) with a single mono-allelic D816V-KIT variant. Transcriptome analyses predicted reduced activity in pathways involved in survival, cell-to-cell adhesion, and neoplasia in HMC-1.3 compared to HMC-1.2 cells, with differences in expression of molecular components and cell surface markers. Consistently, subcutaneous inoculation of HMC-1.3 into mice produced significantly smaller tumors than HMC-1.2 cells, and in colony assays, HMC-1.3 formed less numerous and smaller colonies than HMC-1.2 cells. However, in liquid culture conditions, the growth of HMC-1.2 and HMC-1.3 cells was comparable. Phosphorylation levels of ERK1/2, AKT and STAT5, representing pathways associated with constitutive oncogenic KIT signaling, were also similar between HMC-1.2 and HMC-1.3 cells. Despite these similarities in liquid culture, survival of HMC-1.3 cells was diminished in response to various pharmacological inhibitors, including tyrosine kinase inhibitors used clinically for treatment of advanced systemic mastocytosis, and JAK2 and BCL2 inhibitors, making HMC-1.3 more susceptible to these drugs than HMC-1.2 cells. Our study thus reveals that the additional V560G-KIT oncogenic variant in HMC-1.2 cells modifies transcriptional programs induced by D816V-KIT, confers a survival advantage, alters sensitivity to interventional drugs, and increases the tumorigenicity, suggesting that engineered huMCs with a single D816V-KIT variant may represent an improved preclinical model for mastocytosis.

Therapeutic application of PPE2 protein of Mycobacterium tuberculosis in inhibiting tissue inflammation

There is an increasing need to develop biological anti-inflammatory agents that are more targeted, effective, and with lesser side effects as compared to conventional chemical drugs. In the present study, we found that Mycobacterium tuberculosis protein PPE2 and a synthetic derivative peptide can suppress the mast cell population and inhibit several vasoactive and fibrogenic mediators and pro-inflammatory cytokines induced by mast cells in formalin-induced tissue injury. PPE2 was found to inhibit transcription from the promoter of stem cell factor, important for mast cell maintenance and migration. Thus, PPE2/peptide can be used as a potent nonsteroidal therapeutic agent for the treatment of inflammation and tissue injury.

A Critical Function for the Transcription Factors GLI1 and GLI2 in the Proliferation and Survival of Human Mast Cells

Mast cell hyperactivity and accumulation in tissues are associated with allergy and other mast cell-related disorders. However, the molecular pathways regulating mast cell survival in homeostasis and disease are not completely understood. As glioma-associated oncogene (GLI) proteins are involved in both tissue homeostasis and in the hematopoietic system by regulating cell fate decisions, we sought to investigate the role for GLI proteins in the control of proliferation and survival of human mast cells. GLI1 transcripts were present in primary human mast cells and mast cell lines harboring or not activating mutations in the tyrosine kinase receptor KIT (HMC-1.1 and HMC-1.2, and LAD2 cells, respectively), while GLI2 transcripts were only present in HMC-1.1 and HMC-1.2 cells, suggesting a role for oncogenic KIT signaling in the regulation of GLI2. Reduction in GLI activity by small molecule inhibitors, or by shRNA-mediated knockdown of GLI1 or GLI2, led to increases in apoptotic cell death in both cultured human and murine mast cells, and reduced the number of peritoneal mast cells in mice. Although GLI proteins are typically activated via the hedgehog pathway, steady-state activation of GLI in mast cells occurred primarily via non-canonical pathways. Apoptosis induced by GLI silencing was associated with a downregulation in the expression of KIT and of genes that influence p53 stability and function including USP48, which promotes p53 degradation; and iASPP, which inhibits p53-induced transcription, thus leading to the induction of p53-regulated apoptotic genes. Furthermore, we found that GLI silencing inhibited the proliferation of neoplastic mast cell lines, an effect that was more pronounced in rapidly growing cells. Our findings support the conclusion that GLI1/2 transcription factors are critical regulators of mast cell survival and that their inhibition leads to a significant reduction in the number of mast cells in vitro and in vivo, even in cells with constitutively active KIT variants. This knowledge can potentially be applicable to reducing mast cell burden in mast cell-related diseases.

Few, but Efficient: The Role of Mast Cells in Breast Cancer and Other Solid Tumors

Tumor outcome is determined not only by cancer cell-intrinsic features but also by the interaction between cancer cells and their microenvironment. There is great interest in tumor-infiltrating immune cells, yet mast cells have been less studied. Recent work has highlighted the impact of mast cells on the features and aggressiveness of cancer cells, but the eventual effect of mast cell infiltration is still controversial. Here, we review multifaceted findings regarding the role of mast cells in cancer, with a particular focus on breast cancer, which is further complicated because of its classification into subtypes characterized by different biological features, outcome, and therapeutic strategies.

Targeting KIT by frameshifting mRNA transcripts as a therapeutic strategy for aggressive mast cell neoplasms

Activating mutations in c-KIT are associated with the mast cell (MC) clonal disorders cutaneous mastocytosis and systemic mastocytosis and its variants, including aggressive systemic mastocytosis, MC leukemia, and MC sarcoma. Currently, therapies inhibiting KIT signaling are a leading strategy to treat MC proliferative disorders. However, these approaches may have off-target effects, and in some patients, complete remission or improved survival time cannot be achieved. These limitations led us to develop an approach using chemically stable exon skipping oligonucleotides (ESOs) that induce exon skipping of precursor (pre-)mRNA to alter gene splicing and introduce a frameshift into mature KIT mRNA transcripts. The result of this alternate approach results in marked downregulation of KIT expression, diminished KIT signaling, inhibition of MC proliferation, and rapid induction of apoptosis in neoplastic HMC-1.2 MCs. We demonstrate that in vivo administration of KIT targeting ESOs significantly inhibits tumor growth and systemic organ infiltration using both an allograft mastocytosis model and a humanized xenograft MC tumor model. We propose that our innovative approach, which employs well-tolerated, chemically stable oligonucleotides to target KIT expression through unconventional pathways, has potential as a KIT-targeted therapeutic alone, or in combination with agents that target KIT signaling, in the treatment of KIT-associated malignancies.

SLAM family member 8 is involved in oncogenic KIT-mediated signalling in human mastocytosis

The signalling lymphocytic activation molecule family member 8 (SLAMF8)/CD353 is a member of the CD2 family of proteins. Its ligand has not been identified. SLAMF8 is expressed by macrophages and suppresses cellular functions. No study has yet explored SLAMF8 expression or function in human mastocytosis, which features oncogenic KIT-mediated proliferation of human mast cells. SLAMF8 protein was expressed in human mastocytosis cells, immunohistochemically. SLAMF8 expression was also evident in the human mast cell lines, HMC1.2 (expressing oncogenic KIT) and LAD2 (expressing wild-type KIT) cells. SLAMF8 knock-down significantly reduced the KIT-mediated growth of HMC1.2 cells but not that of LAD2 cells. SLAMF8 knock-down HMC1.2 cells exhibited significant attenuation of SHP-2 activation and oncogenic KIT-mediated RAS-RAF-ERK signalling. An interaction between SLAMF8 and SHP-2 was confirmed in HMC1.2 cells and all pathological mastocytosis specimens examined (19 of 19 cases, 100%). Thus, SLAMF8 is involved in oncogenic KIT-mediated RAS-RAF-ERK signalling and the subsequent growth of human neoplastic mast cells mediated by SHP-2. SLAMF8 is a possible therapeutic target in human mastocytosis patients.

Divergent Evolutional Mode and Purifying Selection of the KIT Gene in European and Asian Domestic Pig Breeds

The recent geographic expansion of wild boars and the even more recent development of numerous domestic pigs have spurred exploration on pig domestic origins. The porcine KIT gene has been showed to affect pleiotropic effects, blood parameters, and coat colour phenotypes, especially the white colour phenotype formation in European commercial breeds. Here, we described the use of SNPs to identify different selection patterns on the porcine KIT gene and the phylogenetic relationships of the inferred haplotypes. The phylogenetic tree revealed four clades in European and Asian wild and domestic pigs: two major clades with European and Asian origins and one minor clade with Iberian origins as well as the other minor clade in Asia, consistent with the major introgression of domestic Asian pigs in Europe around 18th -19th century. The domestication history of pigs, which occurred in the domestication centers (Europe and Asia), has also been demonstrated by mtDNA analysis. Furthermore, both Asian and European domestic pigs evolved under purifying selection. This study indicated that domestic pigs in Europe and Asia have different lineage origins but the porcine KIT gene was undergoing a purifying selection during their evolutional histories.

ROCK1 via LIM kinase regulates growth, maturation and actin based functions in mast cells

Understanding mast cell development is essential due to their critical role in regulating immunity and autoimmune diseases. Here, we show how Rho kinases (ROCK) regulate mast cell development and can function as therapeutic targets for treating allergic diseases. Rock1 deficiency results in delayed maturation of bone marrow derived mast cells (BMMCs) in response to IL-3 stimulation and reduced growth in response to stem cell factor (SCF) stimulation. Further, integrin-mediated adhesion and migration, and IgE-mediated degranulation are all impaired in Rock1-deficient BMMCs. To understand the mechanism behind altered mast cell development in Rock1-/- BMMCs, we analyzed the activation of ROCK and its downstream targets including LIM kinase (LIMK). We observed reduced activation of ROCK, LIMK, AKT and ERK1/2 in Rock1-deficient BMMCs in response to SCF stimulation. Further, loss of either Limk1 or Limk2 also demonstrated altered BMMC maturation and growth; combined deletion of both Limk1 and Limk2 resulted in further reduction in BMMC maturation and growth. In passive cutaneous anaphylaxis model, deficiency of Rock1 or treatment with ROCK inhibitor Fasudil protected mice against IgE-mediated challenge. Our results identify ROCK/LIMK pathway as a novel therapeutic target for treating allergic diseases involving mast cells.

Early molecular correlates of adverse events following yellow fever vaccination

The innate immune response shapes the development of adaptive immunity following infections and vaccination. However, it can also induce symptoms such as fever and myalgia, leading to the possibility that the molecular basis of immunogenicity and reactogenicity of vaccination are inseparably linked. To test this possibility, we used the yellow fever live-attenuated vaccine (YFLAV) as a model to study the molecular correlates of reactogenicity or adverse events (AEs). We analyzed the outcome of 68 adults who completed a YFLAV clinical trial, of which 43 (63.2%) reported systemic AEs. Through whole-genome profiling of blood collected before and after YFLAV dosing, we observed that activation of innate immune genes at day 1, but not day 3 after vaccination, was directly correlated with AEs. These findings contrast with the gene expression profile at day 3 that we and others have previously shown to be correlated with immunogenicity. We conclude that although the innate immune response is a double-edged sword, its expression that induces AEs is temporally distinct from that which engenders robust immunity. The use of genomic profiling thus provides molecular insights into the biology of AEs that potentially forms a basis for the development of safer vaccines.

Detection of initial angiogenesis from dorsal aorta into metanephroi and elucidation of its role in kidney development

Reconstruction of blood vessels is considered the most difficult part for the complicated organs, therefore, blood vessel construction is regarded as a key point for kidney regeneration in vitro. Vasculogenesis and angiogenesis are the two mechanisms to form blood vessels in embryonic organs, and most studies resided in vaculogenesis. Angiogenesis resided mostly in adult diseases such as wound healing, growth of tumors, and psoriasis diseases. However, renal angiogenesis is simply attributed to the sprouting of pre-existing blood vessel from dorsal aorta into metanephroi, and its occurrence is considered to be at a late stage of metanephric development. Since no techniques are available for delicate detection, the initial angiogenesis from dorsal aorta into metanephroi as well as its role in kidney development still remained unclear. In this study, we developed a method to detect the initial angiogenesis of dorsal aorta into metanephroi, and firstly clarified that dorsal aorta angiogenesis occurred at an early stage of metanephric development. We also elucidated the role of dorsal aorta angiogenesis in promoting the early blood vessel formation, tubule formation and glomeruli maturation. It is suggested that blood flow and dynamic circulation of various factors at the early developing stage may be prerequisite to a successful construction of blood vessels in the complicated organs either in vitro or in vivo. These findings contribute to a better understanding of dorsal aorta angiogenesis during kidney development and shed light on its significant value for the application of tissue engineering to complicated organs.

In vivo model for mastocytosis: A comparative review

Human mastocytosis are heterogeneous group of neoplastic diseases characterized by a different degree of uncontrolled mast cell (MC) proliferation and activation. Interestingly, human mastocytosis share several biological and clinical features with canine mast cell disorders, so called canine mast cell tumors (CMCTs). These CMCTs are the most common spontaneous cutaneous tumors found in dogs representing a valid model to study neoplastic mast cell disorders. It has been discovered that the pathological activation of c-Kit receptor (c-KitR), expressed by MCs, has been involved in the pathogenesis of neoplastic MC disorders. In this review we have focused on human mastocytosis in terms of: (i) epidemiology and classification; (ii) pathogenesis at molecular levels; (iii) clinical presentation. In addition, we have summarized animal models useful to study neoplastic MC disorders including CMCTs and murine transgenic models. Finally, we have revised therapeutic approaches mostly common in human and canine MCTs and novel tyrosine kinase inhibitors approved for CMCTs and recently translated in human clinical trials.

Mast cell exosomes promote lung adenocarcinoma cell proliferation - role of KIT-stem cell factor signaling

Background

Human cells release nano-sized vesicles called exosomes, containing mRNA, miRNA and specific proteins. Exosomes from one cell can be taken up by another cell, which is a recently discovered cell-to-cell communication mechanism. Also, exosomes can be taken up by different types of cancer cells, but the potential functional effects of mast cell exosomes on tumor cells remain unknown.

Methods and results

Exosomes were isolated from the human mast cell line, HMC-1, and uptake of PKH67-labelled exosomes by the lung epithelial cell line, A549, was examined using flow cytometry and fluorescence microscopy. The RNA cargo of the exosomes was analyzed with a Bioanalyzer and absence or presence of the c-KIT mRNA was determined by RT-PCR. The cell proliferation was determined in a BrdU incorporation assay, and proteins in the KIT-SCF signaling pathway were detected by Western blot. Our result demonstrates that exosomes from mast cells can be taken up by lung cancer cells. Furthermore, HMC-1 exosomes contain and transfer KIT protein, but not the c-KIT mRNA to A549 cells and subsequently activate KIT-SCF signal transduction, which increase cyclin D1 expression and accelerate the proliferation in the human lung adenocarcinoma cells.

Conclusions

Our results indicate that exosomes can transfer KIT as a protein to tumor cells, which can affect recipient cell signaling events through receptor-ligand interactions.

Functional deregulation of KIT: link to mast cell proliferative diseases and other neoplasms

In this review, the authors discuss common gain-of-function mutations in the stem cell factor receptor KIT found in mast cell proliferation disorders and summarize the current understanding of the molecular mechanisms by which these transforming mutations may affect KIT structure and function leading to altered downstream signaling and cellular transformation. Drugs targeting KIT have shown mixed success in the treatment of mastocytosis and other hyperproliferative diseases. A brief overview of the most common KIT inhibitors currently used, the reasons for the varied clinical results of such inhibitors and a discussion of potential new strategies are provided.

CD72 regulates the growth of KIT-mutated leukemia cell line Kasumi-1

Gain-of-function mutations in KIT, a member of the receptor type tyrosine kinases, are observed in certain neoplasms, including mast cell tumors (MCTs) and acute myelogenous leukemias (AMLs). A MCT line HMC1.2 harboring the KIT mutation was reported to express CD72, which could suppress the cell proliferation. Here, we examined the ability of CD72 to modify the growth of AMLs harboring gain-of-function KIT mutations. CD72 was expressed on the surface of the AML cell line, Kasumi-1. CD72 ligation by an agonistic antibody BU40 or by a natural ligand CD100, suppressed the proliferation of the Kasumi-1 cells and enhanced cell death, as monitored by caspase-3 cleavage. These responses were associated with the phosphorylation of CD72, the formation of the CD72 - SHP-1 complex and dephosphorylation of src family kinases and JNK. Thus, these results seemed to suggest that CD72 was the therapeutic potential for AML, as is the case of MCTs.

Glioma-derived macrophage migration inhibitory factor (MIF) promotes mast cell recruitment in a STAT5-dependent manner

Recently, glioma research has increased its focus on the diverse types of cells present in brain tumors. We observed previously that gliomas are associated with a profound accumulation of mast cells (MCs) and here we investigate the underlying mechanism. Gliomas express a plethora of chemoattractants. First, we demonstrated pronounced migration of human MCs toward conditioned medium from cultures of glioma cell lines. Subsequent cytokine array analyses of media from cells, cultured in either serum-containing or -free conditions, revealed a number of candidates which were secreted in high amounts in both cell lines. Among these, we then focused on macrophage migration inhibitory factor (MIF), which has been reported to be pro-inflammatory and -tumorigenic. Infiltration of MCs was attenuated by antibodies that neutralized MIF. Moreover, a positive correlation between the number of MCs and the level of MIF in a large cohort of human glioma tissue samples was observed. Further, both glioma-conditioned media and purified MIF promoted differential phosphorylation of a number of signaling molecules, including signal transducer and activator of transcription 5 (STAT5), in MCs. Inhibition of pSTAT5 signaling significantly attenuated the migration of MCs toward glioma cell-conditioned medium shown to contain MIF. In addition, analysis of tissue microarrays (TMAs) of high-grade gliomas revealed a direct correlation between the level of pSTAT5 in MCs and the level of MIF in the medium. In conclusion, these findings indicate the important influence of signaling cascades involving MIF and STAT5 on the recruitment of MCs to gliomas.

Role of mast cells in mucosal diseases: current concepts and strategies for treatment

Mast cells are well known for their role in type I hypersensitivity. However, their role in the immune system as well as their pathophysiological role in other diseases is underacknowledged. The role of mast cells in inflammatory bowel disease, allergic contact dermatitis and asthma is illustrated in this review. The contribution of mast cell activation in these diseases is controversial and two alternative means are proposed: activation via stress response pathways and immunoglobulin-free light chains. Activation of the mast cells leads to release of preformed mediators and to generation of other potent biological substances that have both physiological and pathophysiological effects. The role of these mediators in the aforementioned diseases is also outlined in this review. When the roles of mast cells are better understood, drugs specifically targeting mast cells may be developed to effectively treat a wide range of diseases.

KIT GNNK splice variants: expression in systemic mastocytosis and influence on the activating potential of the D816V mutation in mast cells

Stem cell factor-dependent KIT activation is an essential process for mast cell homeostasis. The two major splice variants of KIT differ by the presence or absence of four amino acids (GNNK) at the juxta-membrane region of the extracellular domain. We hypothesized that the expression pattern of these variants differs in systemic mastocytosis and that transcripts containing the KIT D816V mutation segregate preferentially to one GNNK variant. A quantitative real-time PCR assay to assess GNNK(-) and GNNK(+) transcripts from bone marrow mononuclear cells was developed. The GNNK(-)/GNNK(+) copy number ratio showed a trend toward a positive correlation with the percentage of neoplastic mast cell involvement, and KIT D816V containing transcripts displayed a significantly elevated GNNK(-)/GNNK(+) copy number ratio. Relative expression of only the GNNK(-) variant correlated with increasing percentage of neoplastic mast cell involvement. A mast cell transfection system revealed that the GNNK(-) isoform of wild type KIT was associated with increased granule formation, histamine content, and growth. When accompanying the KIT D816V mutation, the GNNK(-) isoform enhanced cytokine-free metabolism and moderately reduced sensitivity to the tyrosine kinase inhibitor, PKC412. These data suggest that neoplastic mast cells favor a GNNK(-) variant predominance, which in turn enhances the activating potential of the KIT D816V mutation and thus could influence therapeutic sensitivity in systemic mastocytosis.

PD-1 regulates the growth of human mastocytosis cells

BACKGROUND

Programmed death-1 (PD-1) is a marker for human neoplastic T cells. Here, we evaluated whether or not PD-1 was also a marker for human mastocytosis, and explored the role of PD-1 in human mastocytosis cells.

METHODS

Immunohistochemical analysis was used to evaluate the expression of PD-1 in clinical samples of human cutaneous mastocytosis. The expression of PD-1 in human mastocytosis cell lines was checked by RT-PCR, western blotting and flow cytometry. We stimulated human mastocytosis cell lines (LAD2 and HMC1.2) with recombinant ligand for PD-1, PD-L1 (rPD-L1), and tested the proliferative activity and the status of signal molecules by Cell Counting Kit-8 and ELISA, respectively.

RESULTS

Ten of 30 human cutaneous mastocytosis cases (33.3%) expressed PD-1 protein. We also found that a human mastocytosis line LAD2 cells expressed PD-1 protein on their surfaces. The administration with rPD-L1 suppressed the stem cell factor-dependent growth of the LAD2 cells. And, rPD-L1 activated SHP-1 and SHP-2 simultaneously, and decreased the phosphorylation of AKT, in LAD2 cells. In contrast, we could not detect the expression of PD-1, and the significant effect of rPD-L1 on the mutated KIT-driven growth of HMC1.2 cells.

CONCLUSIONS

PD-1 could be a marker for human cutaneous mastocytosis and regulate the growth of human PD-1-positive mastocytosis cells.

A novel KIT-deficient mouse mast cell model for the examination of human KIT-mediated activation responses

Activation of KIT, by its ligand, stem cell factor (SCF), results in the initiation of signal transduction pathways that influence mast cell survival and proliferation. Activating mutations in KIT have thus been linked to clonal MC proliferation associated with systemic mastocytosis. SCF also modulates MC function by inducing MC chemotaxis and by potentiating antigen (Ag)/IgE-mediated MC degranulation. Thus, mutations in KIT also have the potential to affect these processes in allergic and other mast cell-related diseases. Studies to determine how native and mutated KIT may modulate MC chemotaxis and activation have, however, been limited due to the lack of availability of a suitable functional MC line lacking native KIT which would allow transduction of KIT constructs. Here we describe a novel mouse MC line which allows the study of normal and mutated KIT constructs. These cells originated from a bone marrow-derived mouse MC culture out of which a rapidly dividing mast cell sub-population spontaneously arose. Over time, these cells lost KIT expression while continuing to express functional high affinity receptors for IgE (FcεRI). As a consequence, these cells degranulated in response to Ag/IgE but did not migrate nor show any evidence of potentiation of Ag/IgE degranulation in response to SCF. Retroviral transduction of the cells with a human (hu)KIT construct resulted in surface expression of huKIT which responded to huSCF by potentiation of Ag/IgE-induced degranulation and chemotaxis. This cell line thus presents a novel system to delineate how MC function is modulated by native and mutated KIT and for the identification of novel inhibitors of these processes.

Targeting the KIT activating switch control pocket: a novel mechanism to inhibit neoplastic mast cell proliferation and mast cell activation

Activating mutations in the receptor tyrosine kinase KIT, most notably KIT D816V, are commonly observed in patients with systemic mastocytosis. Thus, inhibition of KIT has been a major focus for treatment of this disorder. Here we investigated a novel approach to such inhibition. Utilizing rational drug design, we targeted the switch pocket (SP) of KIT which regulates its catalytic conformation. Two SP inhibitors thus identified, DP-2976 and DP-4851, were examined for effects on neoplastic mast cell proliferation and mast cell activation. Autophosphorylation of both wild type (WT) and, where also examined, KIT D816V was blocked by these compounds in transfected 293T cells, HMC 1.1 and 1.2 human mast cell lines; and in CD34⁺-derived human mast cells activated by stem cell factor (SCF). Both inhibitors induced apoptosis in the neoplastic mast cell lines and reduced survival of primary bone marrow mast cells from patients with mastocytosis. Moreover, the SP inhibitors more selectively blocked SCF potentiation of FcεRI-mediated degranulation. Overall, SP inhibitors represent an innovative mechanism of KIT inhibition whose dual suppression of KIT D816V neoplastic mast cell proliferation and SCF enhanced mast cell activation may provide significant therapeutic benefits.

Targeting c-kit in the therapy of mast cell disorders: current update

Classically, mast cells have been widely associated with allergic reactions and parasite infections, but recent studies have elucidated the important role of these cells in innate and acquired immunity, wound healing, fibrosis, and chronic inflammatory diseases. Mast cells release an impressive array of proinflammatory and immunoregulatory mediators after activation induced by either immunoglobulin-E (IgE)-dependent or IgE-independent mechanisms. Proliferation, differentiation, survival and activation of mast cells are regulated by stem cell factor (SCF), the ligand for the c-kit tyrosine kinase receptor which is expressed on the mast cell surface. Inappropriate c-kit activation causes accumulation of mast cells in tissues resulting in mastocytosis. A number of activating mutations in c-kit have recently been identified and these mutations results in aberrant mast cell growth. Thus, c-kit inhibitors may have potential application in multiple conditions associated with mast cell disorders including systemic mastocytosis, anaphylaxis, and asthma. The present perspective aims to summarize recent findings in mast cell biology and the role of c-kit tyrosine kinase inhibitors in the treatment of different mast cell associated disorders.

Systemic Mastocytosis With Associated Clonal Hematologic Nonmast Cell Lineage Disease: A Clinicopathologic Review

Systemic mastocytosis (SM) is a heterogeneous disease with 6 subtypes, including systemic mastocytosis with associated clonal hematologic nonmast cell lineage disease (SM-AHNMD). Bone marrow biopsy specimens show multifocal aggregates of mast cells with predominantly spindle-shaped morphology associated with a myeloid or, less frequently, a lymphoproliferative neoplasm defined by World Health Organization criteria. Neoplastic mast cells abnormally express CD2 and/or CD25, which may be detected by flow cytometry or immunohistochemistry. The pathogenesis of SM-AHNMD is not well understood; however, combined KIT tyrosine kinase receptor mutations and additional genetic events in myeloid stem cells may have a pathogenic role. Reactive mast cell hyperplasia, monocytic/histiocytic proliferations, SM without sufficient criteria for a diagnosis of AHNMD, atypical mast cells associated with PDGFRA rearrangements, and other tryptase-positive myeloid proliferations should be excluded. Overall, the prognosis is poor and largely related to the AHNMD. Cytoreductive therapies, splenectomy, allogeneic bone marrow transplant, and tyrosine kinase inhibitors, excluding imatinib, may have potential efficacy in the treatment of these diseases.

p85β regulatory subunit of class IA PI3 kinase negatively regulates mast cell growth, maturation, and leukemogenesis

We show that loss of p85α inhibits the growth and maturation of mast cells, whereas loss of p85β enhances this process. Whereas restoring the expression of p85α in P85α(-/-) cells restores these functions, overexpression of p85β has the opposite effect. Consistently, overexpression of p85β in WT mast cells represses KIT-induced proliferation and IL-3-mediated maturation by inhibiting the expression of Microphthalmia transcription factor. Because p85α and p85β differ in their N-terminal sequences, chimeric proteins consisting of amino or carboxy-terminal of p85α and/or p85β do not rescue the growth defects of p85α(-/-) cells, suggesting cooperation between these domains for normal mast cell function. Loss of p85β impaired ligand induced KIT receptor internalization and its overexpression enhanced this process, partly because of increased binding of c-Cbl to p85β relative to p85α. In vivo, loss of p85β resulted in increased mast cells, and bone marrow transplantation of cells overexpressing p85β resulted in significant reduction in some tissue mast cells. Overexpression of p85β suppressed the growth of oncogenic KIT-expressing cells in vitro and prolonged the survival of leukemic mice in vivo. Thus, p85α and p85β differentially regulate SCF and oncogenic KIT-induced signals in myeloid lineage-derived mast cells.

Immunohistochemical evaluation of AKT protein activation in canine mast cell tumours

The pathogenesis of canine mast cell tumour (MCT) remains unknown. Moreover, therapeutic options are limited and resistance to targeted drugs and recurrences are common, necessitating the identification of additional cellular targets for therapy. In this study we investigated the expression of phosphorylated AKT protein in 25 archival canine MCT samples by immunohistochemistry and examined the correlation between the immunohistochemical scores and histopathological tumour grades. AKT protein was detected in all of the samples and 24 of the 25 samples expressed the phosphorylated form of the protein, albeit with variable intensity. However, when the immunohistochemical scores of weak, intermediate and strong labelling were compared with the histopathological grades I to III, there was no strong correlation. This study suggests that canine MCT cells have activated AKT and indicates the need for further research on the role of the AKT protein and the possibility of targeting the AKT signalling pathway in MCTs.

Tyrosine kinase inhibitor sunitinib relieves systemic and oral antigen-induced anaphylaxes in mice

BACKGROUND

  Systemic and oral antigen-induced anaphylaxes are mediated by immunoglobulin (Ig) E and mast cells, but there is no satisfactory treatment for the life-threatening allergic reaction. We investigated the potential of the multitargeted receptor tyrosine kinase inhibitor sunitinib to relieve anaphylactic reactions in food allergy and systemic anaphylaxis.

METHODS

  Efficacy of oral sunitinib on oral and parenteral antigen-induced anaphylaxes in Balb/c mice was evaluated. IgE-dependent degranulation and growth of rat basophilic leukemia RBL2H3 and bone marrow-derived mast cells (BMMCs) in response to sunitinib were investigated.

RESULTS

  Daily administration of sunitinib throughout antigen challenges prevented oral antigen-induced anaphylaxis including diarrhea, anaphylactic symptoms, and hypothermia. The mouse mast cell protease (MMCP)-1 concentration in serum and mast cell number in intestinal tissue after challenge were also decreased by the treatment. Spleen cells from sunitinib-treated mice contained smaller numbers of antigen-specific IgG-producing cells and secreted lower amounts of both Th1 and Th2 cytokines than those of the control mice, whereas the levels of antigen-specific antibodies in serum were not decreased. The reactions and MMCP-1 release in oral antigen-induced anaphylaxis and passive systemic anaphylaxis were attenuated even by a single predose of sunitinib. Degranulation and growth of RBL2H3 cells and BMMCs were greatly reduced by sunitinib.

CONCLUSION

  These results suggested that sunitinib relieves systemic and oral antigen-induced anaphylaxes by the prevention of mast cell activation and hyperplasia in intestinal tissue directly and indirectly through an immunosuppressive effect. Sunitinib and its related kinase inhibitors might be potential drugs for the treatment of food allergy and systemic anaphylaxis.

Glycogen synthase kinase-3β is a prosurvival signal for the maintenance of human mast cell homeostasis

Homeostasis of mature tissue-resident mast cells is dependent on the relative activation of pro- and antiapoptotic regulators. In this study, we investigated the role of glycogen synthase kinase 3β (GSK3β) in the survival of neoplastic and nonneoplastic human mast cells. GSK3β was observed to be phosphorylated at the Y(216) activating residue under resting conditions in both the neoplastic HMC1.2 cell line and in peripheral blood-derived primary human mast cells (HuMCs), suggesting constitutive activation of GSK3β in these cells. Lentiviral-transduced short hairpin RNA knockdown of GSK3β in both the HMC1.2 cells and HuMCs resulted in a significant reduction in cell survival as determined with the MTT assay. The decrease in stem cell factor (SCF)-mediated survival in the GSK3β knockdown HuMCs was reflected by enhancement of SCF withdrawal-induced apoptosis, as determined by Annexin V staining and caspase cleavage, and this was associated with a pronounced reduction in SCF-mediated phosphorylation of Src homology 2 domain-containing phosphatase 2 and ERK1/2 and reduced expression of the antiapoptotic proteins Bcl-xl and Bcl-2. These data show that GSK3β is an essential antiapoptotic factor in both neopastic and nontransformed primary human mast cells through the regulation of SCF-mediated Src homology 2 domain-containing phosphatase 2 and ERK activation. Our data suggest that targeting of GSK3β with small m.w. inhibitors such as CHIR 99021 may thus provide a mechanism for limiting mast cell survival and subsequently decreasing the intensity of the allergic inflammatory response.

Pathophysiology of allergic inflammation

Allergic inflammation is due to a complex interplay between several inflammatory cells, including mast cells, basophils, lymphocytes, dendritic cells, eosinophils, and sometimes neutrophils. These cells produce multiple inflammatory mediators, including lipids, purines, cytokines, chemokines, and reactive oxygen species. Allergic inflammation affects target cells, such as epithelial cells, fibroblasts, vascular cells, and airway smooth muscle cells, which become an important source of inflammatory mediators. Sensory nerves are sensitized and activated during allergic inflammation and produce symptoms. Allergic inflammatory responses are orchestrated by several transcription factors, particularly NF-κB and GATA3. Inflammatory genes are also regulated by epigenetic mechanisms, including DNA methylation and histone modifications. There are several endogenous anti-inflammatory mechanisms, including anti-inflammatory lipids and cytokines, which may be defective in allergic disease, thus amplifying and perpetuating the inflammation. Better understanding of the pathophysiology of allergic inflammation has identified new therapeutic targets but developing effective novel therapies has been challenging. Corticosteroids are highly effective with a broad spectrum of anti-inflammatory effects, including epigenetic modulation of the inflammatory response and suppression of GATA3.

Involvement of mast cells in monocrotaline-induced pulmonary hypertension in rats

BACKGROUND

Mast cells (MCs) are implicated in inflammation and tissue remodeling. Accumulation of lung MCs is described in pulmonary hypertension (PH); however, whether MC degranulation and c-kit, a tyrosine kinase receptor critically involved in MC biology, contribute to the pathogenesis and progression of PH has not been fully explored.

METHODS

Pulmonary MCs of idiopathic pulmonary arterial hypertension (IPAH) patients and monocrotaline-injected rats (MCT-rats) were examined by histochemistry and morphometry. Effects of the specific c-kit inhibitor PLX and MC stabilizer cromolyn sodium salt (CSS) were investigated in MCT-rats both by the preventive and therapeutic approaches. Hemodynamic and right ventricular hypertrophy measurements, pulmonary vascular morphometry and analysis of pulmonary MC localization/counts/activation were performed in animal model studies.

RESULTS

There was a prevalence of pulmonary MCs in IPAH patients and MCT-rats as compared to the donors and healthy rats, respectively. Notably, the perivascular MCs were increased and a majority of them were degranulated in lungs of IPAH patients and MCT-rats (p < 0.05 versus donor and control, respectively). In MCT-rats, the pharmacological inhibitions of MC degranulation and c-kit with CSS and PLX, respectively by a preventive approach (treatment from day 1 to 21 of MCT-injection) significantly attenuated right ventricular systolic pressure (RVSP) and right ventricular hypertrophy (RVH). Moreover, vascular remodeling, as evident from the significantly decreased muscularization and medial wall thickness of distal pulmonary vessels, was improved. However, treatments with CSS and PLX by a therapeutic approach (from day 21 to 35 of MCT-injection) neither improved hemodynamics and RVH nor vascular remodeling.

CONCLUSIONS

The accumulation and activation of perivascular MCs in the lungs are the histopathological features present in clinical (IPAH patients) and experimental (MCT-rats) PH. Moreover, the accumulation and activation of MCs in the lungs contribute to the development of PH in MCT-rats. Our findings reveal an important pathophysiological insight into the role of MCs in the pathogenesis of PH in MCT-rats.

KIT signaling regulates MITF expression through miRNAs in normal and malignant mast cell proliferation

Activating mutations in codon D816 of the tyrosine kinase receptor, KIT, are found in the majority of patients with systemic mastocytosis. We found that the transcription factor, microphthalmia-associated transcription factor (MITF), is highly expressed in bone marrow biopsies from 9 of 10 patients with systemic mastocytosis and activating c-KIT mutations. In primary and transformed mast cells, we show that KIT signaling markedly up-regulates MITF protein. We demonstrate that MITF is required for the proliferative phenotype by inhibiting colony-forming units with sh-RNA knockdown of MITF. Furthermore, constitutively active KIT does not restore growth of primary MITF-deficient mast cells. MITF mRNA levels do not change significantly with KIT signaling, suggesting posttranscriptional regulation. An array screen from mast cells identified candidate miRNAs regulated by KIT signaling. We found that miR-539 and miR-381 are down-regulated by KIT signaling and they repressed MITF expression through conserved miRNA binding sites in the MITF 3'-untranslated region. Forced expression of these miRNAs suppressed MITF protein and inhibited colony-forming capacity of mastocytosis cell lines. This work demonstrates a novel regulatory pathway between 2 critical mast cell factors, KIT and MITF, mediated by miRNAs; dysregulation of this pathway may contribute to abnormal mast cell proliferation and malignant mast cell diseases.

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.

Mast cell biology: introduction and overview

In recent years, the field of mast cell biology has expanded well beyond the boundaries of atopic disorders and anaphy laxis, on which it has been historically focused. The biochemical and signaling events responsible for the development and regulation of mast cells has been increasingly studied, aided in large part by novel breakthroughs in laboratory techniques used to study these cells. The result of these studies has been a more comprehensive definition of mast cells that includes added insights to their overall biology as well as the various disease states that can now be traced to defects in mast cells. This introductory chapter outlines and highlights the various topics of mast cell biology that will be discussed in further detail in subsequent chapters.

Masitinib for the treatment of systemic and cutaneous mastocytosis with handicap: a phase 2a study

Treatment options for patients suffering from indolent forms of mastocytosis remain inadequate with the hyperactivation of mast cells responsible for many of the disease's systemic manifestations. Masitinib is a potent and highly selective oral tyrosine kinase inhibitor. A combined inhibition of c-Kit and Lyn make it particularly efficient in controlling the activity of mast cells and therefore, of potential therapeutic benefit in mastocytosis. Masitinib was administered to 25 patients diagnosed as having systemic or cutaneous mastocytosis with related handicap (i.e., disabilities associated with flushes, depression, pruritus and quality-of-life) at the initial dose levels of 3 or 6 mg/kg/day over 12 weeks. In accordance with the AFIRMM study, response was based upon change of clinical symptoms associated with patient handicap at week 12 relative to baseline, regardless of disease subtype. Improvement was observed in all primary endpoints at week 12 including a reduction of flushes, Hamilton rating, and pruritus as compared with baseline by 64% (P = 0.0005), 43% (P = 0.0049), and 36% (P = 0.0077), respectively. An overall clinical response was observed in 14/25 patients (56%; [95%CI = 37%-75%]), with sustainable improvement observed throughout an extension phase (>60 weeks). Common adverse events were edema (44%), nausea (44%), muscle spasms (28%), and rash (28%), the majority of which were of mild or moderate severity with a significant decline in frequency observed after 12 weeks of treatment. One patient experienced a serious adverse event of reversible agranulocytosis. Masitinib is a promising treatment for indolent forms of mastocytosis with handicap and indicates acceptable tolerability for long-term treatment regimens.

CD72 negatively regulates KIT-mediated responses in human mast cells

KIT activation, through binding of its ligand, stem cell factor, is crucial for normal mast cell growth, differentiation, and survival. Furthermore, KIT may also contribute to mast cell homing and cytokine generation. Activating mutations in KIT lead to the dysregulated mast cell growth associated with the myeloproliferative disorder, mastocytosis. We investigated the potential of downregulating such responses through mast cell inhibitory receptor activation. In this study, we report that the B cell-associated ITIM-containing inhibitory receptor, CD72, is expressed in human mast cells. Ligation of CD72 with the agonistic Ab, BU40, or with recombinant human CD100 (rCD100), its natural ligand, induced the phosphorylation of CD72 with a resulting increase in its association with the tyrosine phosphatase SH2 domain-containing phosphatase-1. This, in turn, resulted in an inhibition of KIT-induced phosphorylation of Src family kinases and extracellular-regulated kinases (ERK1/2). As a consequence of these effects, KIT-mediated mast cell proliferation, chemotaxis, and chemokine production were significantly reduced by BU40 and rCD100. Furthermore, BU40 and rCD100 also downregulated the growth of the HMC1.2 human mast cell line. Thus, targeting CD72 may provide a novel approach to the suppression of mast cell disease such as mastocytosis.

The antitumor activity of homoharringtonine against human mast cells harboring the KIT D816V mutation

Gain-of-function mutations of the receptor tyrosine kinase KIT play a critical role in the pathogenesis of systemic mastocytosis (SM) and gastrointestinal stromal tumors. The various juxtamembrane type of KIT mutations, including V560G, are found in 60% to 70% of patients with gastrointestinal stromal tumors; loop mutant D816V, which exists in approximately 80% of SM patients, is completely resistant to imatinib. In the present study, we hypothesized that homoharringtonine (HHT), a protein synthesis inhibitor, would decrease the level of KIT protein by inhibiting translation, resulting in a decreased level of phospho-KIT and abrogating its constitutive downstream signaling. Imatinib-sensitive HMC-1.1 cells harboring the mutation V560G in the juxtamembrane domain of KIT, imatinib-resistant HMC-1.2 cells harboring both V560G and D816V mutations, and murine P815 cells were treated with HHT and analyzed in terms of growth, apoptosis, and signal transduction. The in vivo antitumor activity was evaluated by using the murine mast cell leukemia model. Our results indicated that HHT effectively inhibited the growth and induced apoptosis in cells bearing both V560G and D816V or D814Y KIT. Additionally, HHT inhibited the KIT-dependent phosphorylation of downstream signaling molecules Akt, signal transducer and activator of transcription 3 and 5, and extracellular signal-regulated kinase 1/2. Furthermore, HHT significantly prolonged the survival duration of mice with aggressive SM or mast cell leukemia by inhibiting the expansion and infiltration of imatinib-resistant mast tumor cells harboring imatinib-resistant D814Y KIT. Collectively, we show that HHT circumvents D816V KIT-elicited imatinib resistance. Our findings warrant a clinical trial of HHT in patients with SM harboring D816V or D814Y KIT.

Recent advances in mast cell clonality and anaphylaxis

Clonal expansion of mast cells carrying the D816V c-kit mutation results in mastocytosis. Recent studies identified the presence of clonal mast cells carrying this mutation in patients with anaphylaxis without classic diagnostic findings of systemic mastocytosis.

Glycogen synthase kinase 3beta activation is a prerequisite signal for cytokine production and chemotaxis in human mast cells

In addition to regulating mast cell homeostasis, the activation of KIT following ligation by stem cell factor promotes a diversity of mast cell responses, including cytokine production and chemotaxis. Although we have previously defined a role for the mammalian target of rapamycin complex 1 in these responses, it is clear that other signals are also required for maximal KIT-dependent cytokine production and chemotaxis. In this study, we provide evidence to support a role for glycogen synthase kinase 3beta (GSK3beta) in such regulation in human mast cells (HuMCs). GSK3beta was observed to be constitutively activated in HuMCs. This activity was inhibited by knockdown of GSK3beta protein following transduction of these cells with GSK3beta-targeted shRNA. This resulted in a marked attenuation in the ability of KIT to promote chemotaxis and, in synergy with FcepsilonRI-mediated signaling, cytokine production. GSK3beta regulated KIT-dependent mast cell responses independently of mammalian target of rapamycin. However, evidence from the knockdown studies suggested that GSK3beta was required for activation of the MAPKs, p38, and JNK and downstream phosphorylation of the transcription factors, Jun and activating transcription factor 2, in addition to activation of the transcription factor NF-kappaB. These studies provide evidence for a novel prerequisite priming mechanism for KIT-dependent responses regulated by GSK3beta in HuMCs.

Cultivation and characterization of canine skin-derived mast cells

It is essential to develop a technique to culture purified skin-derived mast cells (SMCs) to facilitate immunological research on allergic diseases in dogs. This study was performed to develop an efficient culture system for canine SMCs and to characterize the cells in comparison to canine bone marrow-derived mast cells (BMMCs). Enzymatically digested skin biopsy samples were cultivated in serum-free AIM-V medium supplemented with recombinant canine stem cell factor. Three to five weeks after the initiation of culture, mast cells were collected by a magnetic activated cell separation system using anti-c-Kit antibody. The collected cells were composed of a uniform population showing morphological characteristics of mast cells with a round or oval nucleus and abundant toluidine blue-positive metachromatic granules in the cytoplasm. The results of flow cytometric analysis for the presence of cell membrane c-Kit and Fc epsilon receptor I (FcepsilonRI) indicated that approximately 90% of the cells were mast cells. The cytoplasmic granules were positive for both tryptase and chymase. Apparent dose-dependent degranulation was induced by antibody-mediated cross-linking of immunoglobulin E (IgE) bound to the cells. These cytological and immunological characteristics observed in SMCs were mostly similar to those observed in BMMCs; however, IgE-mediated degranulation was significantly lower in SMCs than BMMCs. The culture system for canine SMCs developed in this study would be useful in understanding the pathophysiology and developing anti-allergic therapeutics in canine allergic dermatitis.

Amplification mechanisms for the enhancement of antigen-mediated mast cell activation

Activation of mast cells in the allergic inflammatory response occurs via the high affinity receptor for IgE (FcepsilonRI) following receptor aggregation induced by antigen-mediated cross-linking of IgE-occupied FcepsilonRI. Recent observations suggest this response is profoundly influenced by other factors that reduce the threshold for, and increase the extent of, mast cell activation. For example, under experimental conditions, cell surface receptors such as KIT and specific G protein-coupled receptors synergistically enhance FcepsilonRI-mediated mast cell degranulation and cytokine production. Activating mutations in critical signaling molecules may also contribute to such responses. In this review, we describe our research exploring the mechanisms regulating these synergistic interactions and, furthermore, discuss the relevance of our observations in the context of clinical considerations.

Growth-inhibitory effects of four tyrosine kinase inhibitors on neoplastic feline mast cells exhibiting a Kit exon 8 ITD mutation

Systemic mastocytosis (SM) in felines is a rare neoplasm defined by increased growth and accumulation of immature mast cells (MC) in various organs including the spleen. Although in many cases splenectomy is an effective approach, relapses may occur. In these patients, treatment options are limited. Recent data suggest that various Kit tyrosine kinase inhibitors (TKI) interfere with growth of neoplastic MC in humans. In the current study, we examined the effects of four TKI, imatinib, midostaurin, nilotinib, and dasatinib, on growth of spleen-derived feline neoplastic MC in three SM patients. Expression of Kit in neoplastic MC was confirmed by flow cytometry and/or Western blotting. In all three cases, a 12-bp internal tandem duplication in exon 8, resulting in a four amino acid-insertion between residues Thr418 and His419 in Kit, was detectable. As assessed by (3)H-thymidine incorporation experiments, all four TKI were found to inhibit the growth of feline neoplastic MC in a dose-dependent manner. The growth-inhibitory TKI effects were found to be associated with morphologic signs of apoptosis in MC. In conclusion, various Kit-targeting TKI can inhibit the in vitro growth and survival of feline neoplastic MC in SM.

Genome-wide association and meta-analysis of bipolar disorder in individuals of European ancestry

Bipolar disorder (BP) is a disabling and often life-threatening disorder that affects approximately 1% of the population worldwide. To identify genetic variants that increase the risk of BP, we genotyped on the Illumina HumanHap550 Beadchip 2,076 bipolar cases and 1,676 controls of European ancestry from the National Institute of Mental Health Human Genetics Initiative Repository, and the Prechter Repository and samples collected in London, Toronto, and Dundee. We imputed SNP genotypes and tested for SNP-BP association in each sample and then performed meta-analysis across samples. The strongest association P value for this 2-study meta-analysis was 2.4 x 10(-6). We next imputed SNP genotypes and tested for SNP-BP association based on the publicly available Affymetrix 500K genotype data from the Wellcome Trust Case Control Consortium for 1,868 BP cases and a reference set of 12,831 individuals. A 3-study meta-analysis of 3,683 nonoverlapping cases and 14,507 extended controls on >2.3 M genotyped and imputed SNPs resulted in 3 chromosomal regions with association P approximately 10(-7): 1p31.1 (no known genes), 3p21 (>25 known genes), and 5q15 (MCTP1). The most strongly associated nonsynonymous SNP rs1042779 (OR = 1.19, P = 1.8 x 10(-7)) is in the ITIH1 gene on chromosome 3, with other strongly associated nonsynonymous SNPs in GNL3, NEK4, and ITIH3. Thus, these chromosomal regions harbor genes implicated in cell cycle, neurogenesis, neuroplasticity, and neurosignaling. In addition, we replicated the reported ANK3 association results for SNP rs10994336 in the nonoverlapping GSK sample (OR = 1.37, P = 0.042). Although these results are promising, analysis of additional samples will be required to confirm that variant(s) in these regions influence BP risk.

The tyrosine kinase network regulating mast cell activation

Mast cell mediator release represents a pivotal event in the initiation of inflammatory reactions associated with allergic disorders. These responses follow antigen-mediated aggregation of immunoglobulin E (IgE)-occupied high-affinity receptors for IgE (Fc epsilon RI) on the mast cell surface, a response which can be further enhanced following stem cell factor-induced ligation of the mast cell growth factor receptor KIT (CD117). Activation of tyrosine kinases is central to the ability of both Fc epsilon RI and KIT to transmit downstream signaling events required for the regulation of mast cell activation. Whereas KIT possesses inherent tyrosine kinase activity, Fc epsilon RI requires the recruitment of Src family tyrosine kinases and Syk to control the early receptor-proximal signaling events. The signaling pathways propagated by these tyrosine kinases can be further upregulated by the Tec kinase Bruton's tyrosine kinase and downregulated by the actions of the tyrosine Src homology 2 domain-containing phosphatase 1 (SHP-1) and SHP-2. In this review, we discuss the regulation and role of specific members of this tyrosine kinase network in KIT and Fc epsilon RI-mediated mast cell activation.

The multiple roles of phosphoinositide 3-kinase in mast cell biology

Mast cells play a central role in the initiation of inflammatory responses associated with asthma and other allergic disorders. Receptor-mediated mast cell growth, differentiation, homing to their target tissues, survival and activation are all controlled, to varying degrees, by phosphoinositide-3-kinase (PI3K)-driven pathways. It is not fully understood how such diverse responses can be differentially regulated by PI3K. However, recent studies have provided greater insight into the mechanisms that control, and those that are controlled by, different PI3K subunit isoforms in mast cells. In this review, we discuss how PI3K influences the mast cell processes described above. Furthermore, we describe how different mast cell receptors use alternative isoforms of PI3K for these functions and discuss potential downstream targets of these isoforms.