Stat4 suppresses the proliferation of connective tissue-type mast cells

The miR-141/200c-STAT4 Axis Contributes to Leukemogenesis by Enhancing Cell Proliferation in T-PLL

T-prolymphocytic leukemia (T-PLL) is a rare and mature T-cell malignancy with characteristic chemotherapy-refractory behavior and a poor prognosis. Molecular concepts of disease development have been restricted to protein-coding genes. Recent global microRNA (miR) expression profiles revealed miR-141-3p and miR-200c-3p (miR-141/200c) as two of the highest differentially expressed miRs in T-PLL cells versus healthy donor-derived T cells. Furthermore, miR-141/200c expression separates T-PLL cases into two subgroups with high and low expression, respectively. Evaluating the potential pro-oncogenic function of miR-141/200c deregulation, we discovered accelerated proliferation and reduced stress-induced cell death induction upon stable miR-141/200c overexpression in mature T-cell leukemia/lymphoma lines. We further characterized a miR-141/200c-specific transcriptome involving the altered expression of genes associated with enhanced cell cycle transition, impaired DNA damage responses, and augmented survival signaling pathways. Among those genes, we identified STAT4 as a potential miR-141/200c target. Low STAT4 expression (in the absence of miR-141/200c upregulation) was associated with an immature phenotype of primary T-PLL cells as well as with a shortened overall survival of T-PLL patients. Overall, we demonstrate an aberrant miR-141/200c-STAT4 axis, showing for the first time the potential pathogenetic implications of a miR cluster, as well as of STAT4, in the leukemogenesis of this orphan disease.

Anaphylaxis: Focus on Transcription Factor Activity

Anaphylaxis is a severe allergic reaction, rapid in onset, and can lead to fatal consequences if not promptly treated. The incidence of anaphylaxis has risen at an alarming rate in past decades and continues to rise. Therefore, there is a general interest in understanding the molecular mechanism that leads to an exacerbated response. The main effector cells are mast cells, commonly triggered by stimuli that involve the IgE-dependent or IgE-independent pathway. These signaling pathways converge in the release of proinflammatory mediators, such as histamine, tryptases, prostaglandins, etc., in minutes. The action and cell targets of these proinflammatory mediators are linked to the pathophysiologic consequences observed in this severe allergic reaction. While many molecules are involved in cellular regulation, the expression and regulation of transcription factors involved in the synthesis of proinflammatory mediators and secretory granule homeostasis are of special interest, due to their ability to control gene expression and change phenotype, and they may be key in the severity of the entire reaction. In this review, we will describe our current understanding of the pathophysiology of human anaphylaxis, focusing on the transcription factors' contributions to this systemic hypersensitivity reaction. Host mutation in transcription factor expression, or deregulation of their activity in an anaphylaxis context, will be updated. So far, the risk of anaphylaxis is unpredictable thus, increasing our knowledge of the molecular mechanism that leads and regulates mast cell activity will enable us to improve our understanding of how anaphylaxis can be prevented or treated.

Small-molecule inhibition of STAT3 in radioresistant head and neck squamous cell carcinoma

While STAT3 has been validated as a target for treatment of many cancers, including head and neck squamous cell carcinoma (HNSCC), a STAT3 inhibitor is yet to enter the clinic. We used the scaffold of C188, a small-molecule STAT3 inhibitor previously identified by us, in a hit-to-lead program to identify C188-9. C188-9 binds to STAT3 with high affinity and represents a substantial improvement over C188 in its ability to inhibit STAT3 binding to its pY-peptide ligand, to inhibit cytokine-stimulated pSTAT3, to reduce constitutive pSTAT3 activity in multiple HNSCC cell lines, and to inhibit anchorage dependent and independent growth of these cells. In addition, treatment of nude mice bearing xenografts of UM-SCC-17B, a radioresistant HNSCC line, with C188-9, but not C188, prevented tumor xenograft growth. C188-9 treatment modulated many STAT3-regulated genes involved in oncogenesis and radioresistance, as well as radioresistance genes regulated by STAT1, due to its potent activity against STAT1, in addition to STAT3. C188-9 was well tolerated in mice, showed good oral bioavailability, and was concentrated in tumors. Thus, C188-9, either alone or in combination with radiotherapy, has potential for use in treating HNSCC tumors that demonstrate increased STAT3 and/or STAT1 activation.

STAT4 expression and activation is increased during mitosis in vitro and in vivo in skin- and mucosa-derived cell types: implications in neoplastic and inflammatory skin diseases

BACKGROUND

The signal transducer and activator of transcription-4 (STAT4/Stat4) is a transcription factor known to convey signals from interleukin-12, interleukin-23, and interferon-alpha/beta to the nucleus, resulting in activation of dendritic cells, T-helper cell differentiation and production of interferon-gamma.

OBJECTIVE

To demonstrate a novel role for STAT4 in cell mitosis.

RESULTS

Phosphoserine STAT4 (pSerSTAT4) is increased in cells undergoing mitosis and is distributed throughout the cytoplasm during this stage of the cell cycle, whilst phosphotyrosine STAT4 (pTyrSTAT4) is confined to the chromosomal compartment. This distinct pattern of pSerSTAT4 during mitosis is seen in vitro in human keratinocytes and in other cell types. This is also present in vivo in cells undergoing mitosis in normal skin, psoriasis and squamous cell carcinoma. Inhibition of STAT4 phosphorylation by lisofylline and depletion of STAT4 by RNA interference results in a delay in progression of mitosis and leads to a reduction in cells completing cytokinesis.

CONCLUSION

Our data demonstrate that STAT4 plays a role in enabling the normal and timely division of cells undergoing mitosis.

Murine and human mast cell progenitors

The development of mature mast cells (MCs) from hematopoietic progenitor cells as well as the identification and characterization of committed progenitor cells are a current focus of mast cell research. Most published reports in this area are on the origin and differentiation of MCs in mice. Evidence for the human system, i.e. derived from primary human MCs, is widely lacking. Based on the published data, MCs develop either from a committed progenitor or from a common basophil/mast cell precursor. This review summarizes the current knowledge on MC development and MC differentiation.

Therapeutic potential of STAT4 in autoimmunity

INTRODUCTION

STAT4, which acts as the major signaling transducing STATs in response to IL-12, is a central mediator in generating inflammation during protective immune responses and immune-mediated diseases.

AREAS COVERED

This review summarizes that STAT4 is essential for the differentiation and function of a wide variety of immune cells, including natural killer cells, mast cells, dendritic cells and T helper cells. In addition, STAT4-mediated signaling promoted the production of autoimmune-associated components, which are implicated in the pathogenesis of autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis and psoriasis.

EXPERT OPINION

Due to its crucial roles in inflammation and autoimmunity, STAT4 may have promise as an effective therapeutic target for autoimmune diseases. Understanding the molecular mechanisms driving STAT4, together with knowledge on the ability of current immunosuppressive treatment to target this process, may open an avenue to novel therapeutic options.

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.

The role of SHIP in the development and activation of mouse mucosal and connective tissue mast cells

Although SHIP is a well-established suppressor of IgE plus Ag-induced degranulation and cytokine production in bone marrow-derived mast cells (BMMCs), little is known about its role in connective tissue (CTMCs) or mucosal (MMCs) mast cells. In this study, we compared SHIP's role in the development as well as the IgE plus Ag and TLR-induced activation of CTMCs, MMCs, and BMMCs and found that SHIP delays the maturation of all three mast cell subsets and, surprisingly, that it is a positive regulator of IgE-induced BMMC survival. We also found that SHIP represses IgE plus Ag-induced degranulation of all three mast cell subsets and that TLR agonists do not trigger their degranulation, whether SHIP is present or not, nor do they enhance IgE plus Ag-induced degranulation. In terms of cytokine production, we found that in MMCs and BMMCs, which are poor producers of TLR-induced cytokines, SHIP is a potent negative regulator of IgE plus Ag-induced IL-6 and TNF-α production. Surprisingly, however, in splenic or peritoneal derived CTMCs, which are poor producers of IgE plus Ag-induced cytokines, SHIP is a potent positive regulator of TLR-induced cytokine production. Lastly, cell signaling and cytokine production studies with and without LY294002, wortmannin, and PI3Kα inhibitor-2, as well as with PI3K p85α(-/-) BMMCs and CTMCs, are consistent with SHIP positively regulating TLR-induced cytokine production via an adaptor-mediated pathway while negatively regulating IgE plus Ag-induced cytokine production by repressing the PI3K pathway.

Effects of parathyroid hormone-related protein and macrophage inflammatory protein-1α in Jurkat T-cells on tumor formation in vivo and expression of apoptosis regulatory genes in vitro

Parathyroid hormone-related protein (PTHrP) and macrophage inflammatory protein-1α (MIP-1α) have been implicated in the pathogenesis of adult T-cell leukemia/lymphoma, but their effects on T-cells have not been well studied. Here we analyzed the functions of PTHrP and MIP-1α on T-cell growth and death both in vitro and in vivo by overexpressing either factor in human Jurkat T-cells. PTHrP or MIP-1α did not affect Jurkat cell growth in vitro, but PTHrP increased their sensitivity to apoptosis. Importantly, PTHrP and MIP-1α decreased both tumor incidence and growth in vivo. To investigate possible mechanisms, polymerase chain reaction (PCR) arrays and real-time reverse transcription (RT)-PCR assays were performed. Both PTHrP and MIP-1α increased the expression of several factors including signal transducer and activator of transcription 4, tumor necrosis factor α, receptor activator of nuclear factor κB ligand and death-associated protein kinase 1, and decreased the expression of inhibitor of DNA binding 1, interferon γ and CD40 ligand in Jurkat cells. In addition, MIP-1α also increased the expression of transcription factor AP-2α and PTHrP increased expression of the vitamin D3 receptor. These data demonstrate that PTHrP and MIP-1α exert a profound antitumor effect presumably by increasing the sensitivity to apoptotic signals through modulation of transcription and apoptosis factors in T-cells.

Targeting CD44 in mast cell regulation

IMPORTANCE OF THE FIELD

Accumulating evidence suggests that mast cells are involved in a wide variety of immune responses including chronic inflammation, immune tolerance and tumor immunity. Mast cells originate from hematopoietic stem cells and undergo terminal differentiation in the tissues, in which they are ultimately resident. Heterogeneity of tissue mast cells is, therefore, one of the key concepts for a better understanding of various immune responses.

AREAS COVERED IN THIS REVIEW

This review describes the candidate genes involved in regulation of cutaneous mast cell differentiation, with a particular attention to CD44, which is the primary receptor for hyaluronan.

WHAT THE READER WILL GAIN

CD44 is involved in various aspects of cutaneous inflammation. Regarding mast cells, CD44 is upregulated upon differentiation and maturation of mast cells, and plays a critical role in regulation of cutaneous mast cell number. Since both degradation and decrease of hyaluronan are often observed upon chronic inflammation, CD44 might be involved in modulation of local immune responses through regulation of cutaneous mast cell functions.

TAKE HOME MESSAGE

Understanding of cutaneous immune responses should require clarification of local mast cell functions, a part of which is regulated by extracellular matrix components and their membrane receptors.

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.