Transcription factor E3, a major regulator of mast cell-mediated allergic response

TFE3-Rearranged Tumors of the Kidney: An Emerging Conundrum

Background: Identical translocations involving the TFE3 gene and various partners have been found in both renal and soft tissue tumors, like alveolar soft part sarcoma (ASPSCR1), ossifying fibromyxoid tumor (PHF1), epithelioid hemangioendothelioma, and the clear cell stromal tumor of the lung (YAP1). Methods: Herein, we review in detail the clinicopathologic and molecular data of TFE3-rearranged renal tumors and propose our perspective, which may shed light on this emerging conundrum. Results: Among the kidney tumors carrying TFE3 translocations, most are morphologically heterogeneous carcinomas labeling for the tubular marker PAX8. The others are mesenchymal neoplasms known as PEComas, characterized by epithelioid cells co-expressing smooth muscle actin, cathepsin-K, melanogenesis markers, and sometimes melanin pigment deposition. Over the past 30 years, numerous TFE3 fusion partners have been identified, with ASPL/ASPSCR1, PRCC, SFPQ/PSF, and NONO being the most frequent. Conclusions: It is not well understood why similar gene fusions can give rise to renal tumors with different morpho-immunophenotypes, which may contribute to the recent disagreement regarding their classification. However, as these two entities, respectively, epithelial and mesenchymal in nature, are widely recognized by the pathology community and their clinicopathologic features well established, we overall believe it is still better to retain the names TFE3-rearranged renal cell carcinoma and TFE3-rearranged PEComa.

IRF3 Activation in Mast Cells Promotes FcεRI-Mediated Allergic Inflammation

(1) Background: This study aims to elucidate a novel non-transcriptional action of IRF3 in addition to its role as a transcription factor in mast cell activation and associated allergic inflammation; (2) Methods: For in vitro experiments, mouse bone-marrow-derived mast cells (mBMMCs) and a rat basophilic leukemia cell line (RBL-2H3) were used for investigating the underlying mechanism of IRF3 in mast-cell-mediated allergic inflammation. For in vivo experiments, wild-type and Irf3 knockout mice were used for evaluating IgE-mediated local and systemic anaphylaxis; (3) Results: Passive cutaneous anaphylaxis (PCA)-induced tissues showed highly increased IRF3 activity. In addition, the activation of IRF3 was observed in DNP-HSA-treated mast cells. Phosphorylated IRF3 by DNP-HSA was spatially co-localized with tryptase according to the mast cell activation process, and FcεRI-mediated signaling pathways directly regulated that activity. The alteration of IRF3 affected the production of granule contents in the mast cells and the anaphylaxis responses, including PCA- and ovalbumin-induced active systemic anaphylaxis. Furthermore, IRF3 influenced the post-translational processing of histidine decarboxylase (HDC), which is required for granule maturation; and (4) Conclusion: Through this study, we demonstrated the novel function of IRF3 as an important factor inducing mast cell activation and as an upstream molecule for HDC activity.

Folliculin promotes substrate-selective mTORC1 activity by activating RagC to recruit TFE3

Mechanistic target of rapamycin complex I (mTORC1) is central to cellular metabolic regulation. mTORC1 phosphorylates a myriad of substrates, but how different substrate specificity is conferred on mTORC1 by different conditions remains poorly defined. Here, we show how loss of the mTORC1 regulator folliculin (FLCN) renders mTORC1 specifically incompetent to phosphorylate TFE3, a master regulator of lysosome biogenesis, without affecting phosphorylation of other canonical mTORC1 substrates, such as S6 kinase. FLCN is a GTPase-activating protein (GAP) for RagC, a component of the mTORC1 amino acid (AA) sensing pathway, and we show that active RagC is necessary and sufficient to recruit TFE3 onto the lysosomal surface, allowing subsequent phosphorylation of TFE3 by mTORC1. Active mutants of RagC, but not of RagA, rescue both phosphorylation and lysosomal recruitment of TFE3 in the absence of FLCN. These data thus advance the paradigm that mTORC1 substrate specificity is in part conferred by direct recruitment of substrates to the subcellular compartments where mTORC1 resides and identify potential targets for specific modulation of specific branches of the mTOR pathway.

How does the mTORC1 complex, which influences myriad cellular processes, achieve specificity? This study shows that substrate specificity is in part conferred by modulating the recruitment of substrates, in this case the transcription factor TFE3, to mTORC1.

The Critical Role Played by Mitochondrial MITF Serine 73 Phosphorylation in Immunologically Activated Mast Cells

In recent years, growing evidence has indicated the pivotal role of mitochondria in mast cell immunological activation. We have previously reported a decrease in degranulation and cytokine secretion following the inhibition of pyruvate dehydrogenase (PDH) either by CPI-613 (PDH inhibitor/anti-cancer drug) or through its interaction with mitochondrial microphthalmia-associated transcription factor (MITF). In the present study, we further explored the role played by mitochondrial MITF in mast cell exocytosis using rat basophil leukemia cells [RBL], as well as mouse bone marrow-derived mast cells (BMMCs). Here, we report that mast cell degranulation, cytokine secretion and oxidative phosphorylation (OXPHOS) activities were associated with phosphorylation of Serine 73 of mitochondrial MITF, controlled by extracellular signals regulated by protein kinase (ERK1/2) activity. Also, we report here that decreased OXPHOS activity following ERK1/2 inhibition (U0126 treatment) during IgE-Ag activation was mediated by the dephosphorylation of Serine 73 mitochondrial MITF, which inhibited its association with PDH. This led to a reduction in mast cell reactivity. In addition, a phosphorylation-mimicking mitochondrial MITF-S73D positively regulated the mitochondrial activity, thereby supporting mast cell degranulation. Thus, the present research findings highlight the prominence of mitochondrial MITF Serine 73 phosphorylation in immunologically activated mast cells.

The Role Played by Transcription Factor E3 in Modulating Cardiac Hypertrophy

Transcription factor E3 (TFE3), which is a key regulator of cellular adaptation, is expressed in most tissues, including the heart, and is reportedly overexpressed during cardiac hypertrophy. In this study, TFE3's role in cardiac hypertrophy was investigated. To understand TFE3's physiological importance in cardiac hypertrophy, pressure-overload cardiac hypertrophy was induced through transverse aortic constriction (TAC) in both wild-type (WT) and TFE3 knockout mice (TFE3-/-). Eleven weeks after TAC induction, cardiac hypertrophy was observed in both WT and TFE3-/- mice. However, significant reductions in ejection fraction and fractional shortening were observed in WT mice compared to TFE3-/- mice. To understand the mechanism, we found that myosin heavy chain (Myh7), which increases during hemodynamic overload, was lower in TFE3-/- TAC mice than in WT TAC mice, whereas extracellular signal-regulated protein kinases (ERK) phosphorylation, which confers cardioprotection, was lower in the left ventricles of WT mice than in TFE3-/- mice. We also found high expressions of TFE3, histone, and MYH7 and low expression of pERK in the normal human heart compared to the hypertensive heart. In the H9c2 cell line, we found that ERK inhibition caused TFE3 nuclear localization. In addition, we found that MYH7 was associated with TFE3, and during TFE3 knockdown, MYH7 and histone were downregulated. Therefore, we showed that TFE3 expression was increased in the mouse model of cardiac hypertrophy and tissues from human hypertensive hearts, whereas pERK was decreased reversibly, which suggested that TFE3 is involved in cardiac hypertrophy through TFE3-histone-MYH7-pERK signaling.

Autophagy in Xp11 translocation renal cell carcinoma: from bench to bedside

Xp11 translocation renal cell carcinoma (tRCC) characterized by the rearrangement of the TFE3 is recently identified as a unique subtype of RCC that urgently requires effective prevention and treatment strategies. Therefore, determining suitable therapeutic targets and fully understanding the biological significance of tRCC is essential. The importance of autophagy is increasingly acknowledged because it shows carcinogenic activity or suppressor effect. Autophagy is a physiological cellular process critical to maintaining cell homeostasis, which is involved in the lysosomal degradation of cytoplasmic organelles and macromolecules via the lysosomal pathway, suggesting that targeting autophagy is a potential therapeutic approach for cancer therapies. However, the underlying mechanism of autophagy in tRCC is still ambiguous. In this review, we summarize the autophagy-related signaling pathways associated with tRCC. Moreover, we examine the roles of autophagy and the immune response in tumorigenesis and investigate how these factors interact to facilitate or prevent tumorigenesis. Besides, we review the findings regarding the treatment of tRCC via induction or inhibition of autophagy. Hopefully, this study will shed some light on the functions and implications of autophagy and emphasize its role as a potential molecular target for therapeutic intervention in tRCC.

MiT Family Transcriptional Factors in Immune Cell Functions

The microphthalmia-associated transcription factor family (MiT family) proteins are evolutionarily conserved transcription factors that perform many essential biological functions. In mammals, the MiT family consists of MITF (microphthalmia-associated transcription factor or melanocyte-inducing transcription factor), TFEB (transcription factor EB), TFE3 (transcription factor E3), and TFEC (transcription factor EC). These transcriptional factors belong to the basic helix-loop-helix-leucine zipper (bHLH-LZ) transcription factor family and bind the E-box DNA motifs in the promoter regions of target genes to enhance transcription. The best studied functions of MiT proteins include lysosome biogenesis and autophagy induction. In addition, they modulate cellular metabolism, mitochondria dynamics, and various stress responses. The control of nuclear localization via phosphorylation and dephosphorylation serves as the primary regulatory mechanism for MiT family proteins, and several kinases and phosphatases have been identified to directly determine the transcriptional activities of MiT proteins. In different immune cell types, each MiT family member is shown to play distinct or redundant roles and we expect that there is far more to learn about their functions and regulatory mechanisms in host defense and inflammatory responses.

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.

Modulation of lactate-lysosome axis in dendritic cells by clotrimazole potentiates antitumor immunity

BACKGROUND

Dendritic cells (DCs) play a critical role in antitumor immunity, but the therapeutic efficacy of DC-mediated cancer vaccine remains low, partly due to unsustainable DC function in tumor antigen presentation. Thus, identifying drugs that could enhance DC-based antitumor immunity and uncovering the underlying mechanism may provide new therapeutic options for cancer immunotherapy.

METHODS

In vitro antigen presentation assay was used for DC-modulating drug screening. The function of DC and T cells was measured by flow cytometry, ELISA, or qPCR. B16, MC38, CT26 tumor models and C57BL/6, Balb/c, nude, and Batf3-/- mice were used to analyze the in vivo therapy efficacy and impact on tumor immune microenvironment by clotrimazole treatment.

RESULTS

By screening a group of small molecule inhibitors and the US Food and Drug Administration (FDA)-approved drugs, we identified that clotrimazole, an antifungal drug, could promote DC-mediated antigen presentation and enhance T cell response. Mechanistically, clotrimazole acted on hexokinase 2 to regulate lactate metabolic production and enhanced the lysosome pathway and Chop expression in DCs subsequently induced DC maturation and T cell activation. Importantly, in vivo clotrimazole administration induced intratumor immune infiltration and inhibited tumor growth depending on both DCs and CD8+ T cells and potentiated the antitumor efficacy of anti-PD1 antibody.

CONCLUSIONS

Our findings showed that clotrimazole could trigger DC activation via the lactate-lysosome axis to promote antigen cross-presentation and could be used as a potential combination therapy approach to improving the therapeutic efficacy of anti-PD1 immunotherapy.

Differential mast cell phenotypes in benign versus cancer tissues and prostate cancer oncologic outcomes

We reported previously that high numbers of mast cells in benign (extra-tumoral) regions of the prostate are associated with worse outcomes after radical prostatectomy including biochemical recurrence and the development of metastases. Herein, with a cohort of 384 men, we performed mast cell subtyping and report that higher minimum number of the tryptase-only (MC_T ) subset of extra-tumoral mast cells is associated with increased risk of biochemical recurrence (comparing highest to lowest tertiles: HR 2.32, 95% CI 1.37-3.93; P-trend = 0.002), metastases (HR 3.62, 95% CI 1.75-7.47; P-trend 0.001), and death from prostate cancer (HR 2.87, 95% CI 1.19-6.95; P-trend = 0.02). Preliminary RNA sequencing and comparison of benign versus cancer tissue mast cells revealed differential expression of additional site-specific genes. We further demonstrate that the genes CXCR4 and TFE3 are more highly expressed in tumor-infiltrating mast cells as well as other tumor-infiltrating immune cells and in tumor cells, respectively, and represent an altered tumor microenvironment. KIT variants were also differentially expressed in benign versus cancer tissue mast cells, with KIT variant 1 (GNNK⁺ ) mast cells identified as more prevalent in extra-tumoral regions of the prostate. Finally, using an established mouse model, we found that mast cells do not infiltrate Hi-Myc tumors, providing a model to specifically examine the role of extra-tumoral mast cells in tumorigenesis. Hi-Myc mice crossed to mast cell knockout (Wsh) mice and aged to 1 year revealed a higher degree of pre-invasive lesions and invasive cancer in wild-type mice versus heterozygous and knockout mice. This suggests a dosage effect where higher numbers of extra-tumoral mast cells resulted in higher cancer invasion. Overall, our studies provide further evidence for a role of extra-tumoral mast cells in driving adverse prostate cancer outcomes. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Dual role of G-quadruplex in translocation renal cell carcinoma: Exploring plausible Cancer therapeutic innovation

BACKGROUND

Renal Cell Carcinoma (RCC) is the ninth leading cause of death among kidney cancer. Xp11.2 translocation harboring TFE3 fusion proteins, act as an oncogene in translocation cancers that constitute the hallmark of translocation renal cell carcinoma (tRCC). G-quadruplex (G4), an alternative nucleic acid structure is an emerging and promising factor in cancer. The presence of G4 within the genome plays a pioneering role in cancer as it contributes to genomic aberration as well as inhibition in cell proliferation.

SCOPE OF REVIEW

Here we discuss the link between G4 and tRCC. We compile the available information of G-quadruplex & propose their dual role in tRCC, suggesting both stabilization and destabilization of G-quadruplex could be considered targets for tRCC.

MAJOR CONCLUSIONS

Our in Silico analysis of TFE3 and their three fusions partner's PRCC, SFPQ, and ASPSCR1 discloses a few putative G4 forming sequences (PQS) in their corresponding fusion gene or fusion transcript. Stabilization of G4 structure within fusion gene/transcript can be of great use towards potential therapeutics targeting fusion protein derived oncogenesis, as G4 is a serious menace for DNA polymerization, transcription & translation. G-quadruplex at intron-2 of the TFE3 has been reported to mediate its translocation also. Both stabilization and destabilization of the G4 structure would be a promising approach in the suppression of cancerous cell proliferation.

GENERAL SIGNIFICANCE

Pioneering studies discovered the relevance of G4 in cancer therapy and explore our approaches towards therapeutic innovation against oncogenic fusion protein and tRCC. Selectively targeting G4 in oncogenic fusion transcript will emerge as potential druggable structures.

Gene of the month: TFE 3

Transcription factor enhancer 3 (TFE3), on the short arm of chromosome Xp11.23 and its protein, belongs to the microphthalmia transcription family (MiTF) of transcription factors. It shares close homology with another member of the family, MiTF which is involved in melanocyte development. When a cell is stressed and/or starved, TFE3 protein translocates into the nucleus. TFE3 gene fusions with multiple different partner genes occur in several tumours with resultant nuclear expression of TFE3 protein. The main tumours associated with TFE3 gene fusions are: renal cell carcinoma, alveolar soft part sarcoma, a subset of epithelioid haemangioendotheliomas (EHE), some perivascular epithelioid cell tumours and rare examples of ossifying fibromyxoid tumour and malignant chondroid syringoma. TFE3 immunohistochemistry is of use in routine diagnostic practice with the aforementioned tumours harbouring TFE3 fusions leading to nuclear staining. In addition, there are tumours lacking TFE3 fusions but also display TFE3 nuclear immunolabeling, and these include: granular cell tumour, solid pseudopapillary neoplasm of the pancreas and ovarian sclerosing stromal tumour.

Emerging roles and regulation of MiT/TFE transcriptional factors

The MiT/TFE transcription factors play a pivotal role in the regulation of autophagy and lysosomal biogenesis. The subcellular localization and activity of MiT/TFE proteins are primarily regulated through phosphorylation. And the phosphorylated protein is retained in the cytoplasm and subsequently translocates to the nucleus upon dephosphorylation, where it stimulates the expression of hundreds of genes, leading to lysosomal biogenesis and autophagy induction. The transcription factor-mediated lysosome-to-nucleus signaling can be directly controlled by several signaling molecules involved in the mTORC1, PKC, and AKT pathways. MiT/TFE family members have attracted much attention owing to their intracellular clearance of pathogenic factors in numerous diseases. Recently, multiple studies have also revealed the MiT/TFE proteins as master regulators of cellular metabolic reprogramming, converging on autophagic and lysosomal function and playing a critical role in cancer, suggesting that novel therapeutic strategies could be based on the modulation of MiT/TFE family member activity. Here, we present an overview of the latest research on MiT/TFE transcriptional factors and their potential mechanisms in cancer.

Characterisation of a murine model of the late asthmatic response

BACKGROUND

The incidence of asthma is increasing at an alarming rate. While the current available therapies are effective, there are associated side effects and they fail to adequately control symptoms in all patient subsets. In the search to understand disease pathogenesis and find effective therapies hypotheses are often tested in animal models before progressing into clinical studies. However, current dogma is that animal model data is often not predictive of clinical outcome. One possible reason for this is the end points measured such as antigen-challenge induced late asthmatic response (LAR) is often used in early clinical development, but seldom in animal model systems. As the mouse is typically selected as preferred species for pre-clinical models, we wanted to characterise and probe the validity of a murine model exhibiting an allergen induced LAR.

METHODS

C57BL/6 mice were sensitised with antigen and subsequently topically challenged with the same antigen. The role of AlumTM adjuvant, glucocorticoid, long acting muscarinic receptor antagonist (LAMA), TRPA1, CD4+ and CD8+ T cells, B cells, Mast cells and IgE were determined in the LAR using genetically modified mice and a range of pharmacological tools.

RESULTS

Our data showed that unlike other features of asthma (e.g. cellular inflammation, elevated IgE levels and airway hyper-reactivity (AHR) the LAR required AlumTMadjuvant. Furthermore, the LAR appeared to be sensitive to glucocorticoid and required CD4+ T cells. Unlike in other species studied, the LAR was not sensitive to LAMA treatment nor required the TRPA1 ion channel, suggesting that airway sensory nerves are not involved in the LAR in this species. Furthermore, the data suggested that CD8+ T cells and the mast cell-B-cell - IgE axis appear to be protective in this murine model.

CONCLUSION

Together we can conclude that this model does feature steroid sensitive, CD4+ T cell dependent, allergen induced LAR. However, collectively our data questions the validity of using the murine pre-clinical model of LAR in the assessment of future asthma therapies.

Pyruvate dehydrogenase has a major role in mast cell function, and its activity is regulated by mitochondrial microphthalmia transcription factor

BACKGROUND

We have recently observed that oxidative phosphorylation-mediated ATP production is essential for mast cell function. Pyruvate dehydrogenase (PDH) is the main regulator of the Krebs cycle and is located upstream of the electron transport chain. However, the role of PDH in mast cell function has not been described. Microphthalmia transcription factor (MITF) regulates the development, number, and function of mast cells. Localization of MITF to the mitochondria and its interaction with mitochondrial proteins has not been explored.

OBJECTIVE

We sought to explore the role played by PDH in mast cell exocytosis and to determine whether MITF is localized in the mitochondria and involved in regulation of PDH activity.

METHODS

Experiments were performed in vitro by using human and mouse mast cells, as well as rat basophil leukemia cells, and in vivo in mice. The effect of PDH inhibition on mast cell function was examined. PDH interaction with MITF was measured before and after immunologic activation. Furthermore, mitochondrial localization of MITF and its effect on PDH activity were determined.

RESULTS

PDH is essential for immunologically mediated degranulation of mast cells. After activation, PDH is serine dephosphorylated. In addition, for the first time, we show that MITF is partially located in the mitochondria and interacts with PDH. This interaction is dependent on the phosphorylation state of PDH. Furthermore, mitochondrial MITF regulates PDH activity.

CONCLUSION

The association of mitochondrial MITF with PDH emerges as an important regulator of mast cell function. Our findings indicate that PDH could arise as a new target for the manipulation of allergic diseases.

Role of the ion channel, transient receptor potential cation channel subfamily V member 1 (TRPV1), in allergic asthma

BACKGROUND

Asthma prevalence has increased world-wide especially in children; thus there is a need to develop new therapies that are safe and effective especially for patients with severe/refractory asthma. CD4(+) T cells are thought to play a central role in disease pathogenesis and associated symptoms. Recently, TRPV1 has been demonstrated to regulate the activation and inflammatory properties of CD4(+) cells. The aim of these experiments was to demonstrate the importance of CD4(+) T cells and the role of TRPV1 in an asthma model using a clinically ready TRPV1 inhibitor (XEN-D0501) and genetically modified (GM) animals.

METHODS

Mice (wild type, CD4 (-/-) or TRPV1 (-/-)) and rats were sensitised with antigen (HDM or OVA) and subsequently topically challenged with the same antigen. Key features associated with an allergic asthma type phenotype were measured: lung function (airway hyperreactivity [AHR] and late asthmatic response [LAR]), allergic status (IgE levels) and airway inflammation.

RESULTS

CD4(+) T cells play a central role in both disease model systems with all the asthma-like features attenuated. Targeting TRPV1 using either GM mice or a pharmacological inhibitor tended to decrease IgE levels, airway inflammation and lung function changes.

CONCLUSION

Our data suggests the involvement of TRPV1 in allergic asthma and thus we feel this target merits further investigation.

TFEB at a glance

The transcription factor EB (TFEB) plays a pivotal role in the regulation of basic cellular processes, such as lysosomal biogenesis and autophagy. The subcellular localization and activity of TFEB are regulated by mechanistic target of rapamycin (mTOR)-mediated phosphorylation, which occurs at the lysosomal surface. Phosphorylated TFEB is retained in the cytoplasm, whereas dephosphorylated TFEB translocates to the nucleus to induce the transcription of target genes. Thus, a lysosome-to-nucleus signaling pathway regulates cellular energy metabolism through TFEB. Recently, in vivo studies have revealed that TFEB is also involved in physiological processes, such as lipid catabolism. TFEB has attracted a lot of attention owing to its ability to induce the intracellular clearance of pathogenic factors in a variety of murine models of disease, such as Parkinson's and Alzheimer's, suggesting that novel therapeutic strategies could be based on the modulation of TFEB activity. In this Cell Science at a Glance article and accompanying poster, we present an overview of the latest research on TFEB function and its implication in human diseases.

TFEB and TFE3: Linking Lysosomes to Cellular Adaptation to Stress

In recent years, our vision of lysosomes has drastically changed. Formerly considered to be mere degradative compartments, they are now recognized as key players in many cellular processes. The ability of lysosomes to respond to different stimuli revealed a complex and coordinated regulation of lysosomal gene expression. This review discusses the participation of the transcription factors TFEB and TFE3 in the regulation of lysosomal function and biogenesis, as well as the role of the lysosomal pathway in cellular adaptation to a variety of stress conditions, including nutrient deprivation, mitochondrial dysfunction, protein misfolding, and pathogen infection. We also describe how cancer cells make use of TFEB and TFE3 to promote their own survival and highlight the potential of these transcription factors as therapeutic targets for the treatment of neurological and lysosomal diseases.

TFEB and TFE3 cooperate in the regulation of the innate immune response in activated macrophages

The activation of transcription factors is critical to ensure an effective defense against pathogens. In this study we identify a critical and complementary role of the transcription factors TFEB and TFE3 in innate immune response. By using a combination of chromatin immunoprecipitation, CRISPR-Cas9-mediated genome-editing technology, and in vivo models, we determined that TFEB and TFE3 collaborate with each other in activated macrophages and microglia to promote efficient autophagy induction, increased lysosomal biogenesis, and transcriptional upregulation of numerous proinflammatory cytokines. Furthermore, secretion of key mediators of the inflammatory response (CSF2, IL1B, IL2, and IL27), macrophage differentiation (CSF1), and macrophage infiltration and migration to sites of inflammation (CCL2) was significantly reduced in TFEB and TFE3 deficient cells. These new insights provide us with a deeper understanding of the transcriptional regulation of the innate immune response.

Molecular genetics and cellular features of TFE3 and TFEB fusion kidney cancers

Despite nearly two decades passing since the discovery of gene fusions involving TFE3 or TFEB in sporadic renal cell carcinoma (RCC), the molecular mechanisms underlying the renal-specific tumorigenesis of these genes remain largely unclear. The recently published findings of The Cancer Genome Atlas Network reported that five of the 416 surveyed clear cell RCC tumours (1.2%) harboured SFPQ-TFE3 fusions, providing further evidence for the importance of gene fusions. A total of five TFE3 gene fusions (PRCC-TFE3, ASPSCR1-TFE3, SFPQ-TFE3, NONO-TFE3, and CLTC-TFE3) and one TFEB gene fusion (MALAT1-TFEB) have been identified in RCC tumours and characterized at the mRNA transcript level. A multitude of molecular pathways well-described in carcinogenesis are regulated in part by TFE3 or TFEB proteins, including activation of TGFβ and ETS transcription factors, E-cadherin expression, CD40L-dependent lymphocyte activation, mTORC1 signalling, insulin-dependent metabolism regulation, folliculin signalling, and retinoblastoma-dependent cell cycle arrest. Determining which pathways are most important to RCC oncogenesis will be critical in discovering the most promising therapeutic targets for this disease.

Mitochondrial STAT3 plays a major role in IgE-antigen-mediated mast cell exocytosis

BACKGROUND

The involvement of mitochondrial oxidative phosphorylation (OXPHOS) in mast cell exocytosis was recently suggested by the finding that mitochondria translocate to exocytosis sites upon mast cell activation. In parallel, mitochondrial signal transducer and activator of transcription 3 (STAT3) was found to be involved in ATP production. However, the regulation of mitochondrial STAT3 function and its connection to mast cell exocytosis is unknown.

OBJECTIVE

We sought to explore the role played by mitochondrial STAT3 in mast cell exocytosis.

METHODS

Experiments were performed in vitro with human and mouse mast cells and rat basophilic leukemia (RBL) cells and in vivo in mice. OXPHOS activity was measured after immunologic activation. The expression of STAT3, extracellular signal-regulated kinase 1/2, and protein inhibitor of activated STAT3 in the mitochondria during mast cell activation was determined, as was the effect of STAT3 inhibition on OXPHOS activity and mast cell function.

RESULTS

Here we show that mitochondrial STAT3 is essential for immunologically mediated degranulation of human and mouse mast cells and RBL cells. Additionally, in IgE-antigen-activated RBL cells, mitochondrial STAT3 was phosphorylated on serine 727 in an extracellular signal-regulated kinase 1/2-dependent manner, which was followed by induction of OXPHOS activity. Furthermore, the endogenous inhibitor of STAT3, protein inhibitor of activated STAT3, was found to inhibit OXPHOS activity in the mitochondria, resulting in inhibition of mast cell degranulation. Moreover, mice injected with Stattic, a STAT3 inhibitor, had a significant decrease in histamine secretion.

CONCLUSION

These results provide the first evidence of a regulatory role for mitochondrial STAT3 in mast cell functions, and therefore mitochondrial STAT3 could serve as a new target for the manipulation of allergic diseases.

Novel roles for the MiTF/TFE family of transcription factors in organelle biogenesis, nutrient sensing, and energy homeostasis

The MiTF/TFE family of basic helix-loop-helix leucine zipper transcription factors includes MITF, TFEB, TFE3, and TFEC. The involvement of some family members in the development and proliferation of specific cell types, such as mast cells, osteoclasts, and melanocytes, is well established. Notably, recent evidence suggests that the MiTF/TFE family plays a critical role in organelle biogenesis, nutrient sensing, and energy metabolism. The MiTF/TFE family is also implicated in human disease. Mutations or aberrant expression of most MiTF/TFE family members has been linked to different types of cancer. At the same time, they have recently emerged as novel and very promising targets for the treatment of neurological and lysosomal diseases. The characterization of this fascinating family of transcription factors is greatly expanding our understanding of how cells synchronize environmental signals, such as nutrient availability, with gene expression, energy production, and cellular homeostasis.

The nutrient-responsive transcription factor TFE3 promotes autophagy, lysosomal biogenesis, and clearance of cellular debris

The discovery of a gene network regulating lysosomal biogenesis and its transcriptional regulator transcription factor EB (TFEB) revealed that cells monitor lysosomal function and respond to degradation requirements and environmental cues. We report the identification of transcription factor E3 (TFE3) as another regulator of lysosomal homeostasis that induced expression of genes encoding proteins involved in autophagy and lysosomal biogenesis in ARPE-19 cells in response to starvation and lysosomal stress. We found that in nutrient-replete cells, TFE3 was recruited to lysosomes through interaction with active Rag guanosine triphosphatases (GTPases) and exhibited mammalian (or mechanistic) target of rapamycin complex 1 (mTORC1)-dependent phosphorylation. Phosphorylated TFE3 was retained in the cytosol through its interaction with the cytosolic chaperone 14-3-3. After starvation, TFE3 rapidly translocated to the nucleus and bound to the CLEAR elements present in the promoter region of many lysosomal genes, thereby inducing lysosomal biogenesis. Depletion of endogenous TFE3 entirely abolished the response of ARPE-19 cells to starvation, suggesting that TFE3 plays a critical role in nutrient sensing and regulation of energy metabolism. Furthermore, overexpression of TFE3 triggered lysosomal exocytosis and resulted in efficient cellular clearance in a cellular model of a lysosomal storage disorder, Pompe disease, thus identifying TFE3 as a potential therapeutic target for the treatment of lysosomal disorders.

Advances in mechanisms of allergy and clinical immunology in 2012

Manuscripts published in the "Mechanisms of allergy and clinical immunology" section of the Journal of Allergy and Clinical Immunology during 2012 enhanced our knowledge of the involvement of cytokines and other mediators in allergic disorders and described novel approaches for understanding mechanisms of allergic and immunologic diseases. Also published were articles focused on mechanisms of allergen-specific immunotherapy and the development of novel antiallergic treatments, as well as strategies to achieve tolerance to allergens. The highlights of these studies and their potential clinical implications are summarized in this review.