Transcriptional regulation of plasminogen activator inhibitor-1 by transforming growth factor-β, activin A and microphthalmia-associated transcription factor

Follistatin and follistatin-like 3 in metabolic disorders

Follistatin (FST) is a glycoprotein which main role is antagonizing activity of transforming growth factor β superfamily members. Folistatin-related proteins such as follistatin-like 3 (FSTL3) also reveal these properties. The exact function of them has still not been established, but it can be bound to the pathogenesis of metabolic disorders. So far, there were performed a few studies about their role in type 2 diabetes, obesity or gestational diabetes and even less in type 1 diabetes. The outcomes are contradictory and do not allow to draw exact conclusions. In this article we summarize the available information about connections between follistatin, as well as follistatin-like 3, and metabolic disorders. We also emphasize the strong need of performing further research to explain their exact role, especially in the pathogenesis of diabetes and obesity.

Tranexamic acid inhibits melanogenesis partially via stimulation of TGF-β1 expression in human epidermal keratinocytes

Oral tranexamic acid (TA) has been an effective treatment for melasma with unclear mechanism. The present study aimed to demonstrate the effect of TA on melanogenesis via regulation of TGF-β1 expression in keratinocytes. We firstly determined the expression level of TGF-β1 in TA-treated keratinocyte-conditioned medium (KCM). Then, the mRNA and protein levels of microphthalmia-associated transcription factor (MITF), tyrosinase (TYR) and tyrosinase-related protein 1 (TRP-1) of human epidermal melanocytes (NHEMs) in the presence of TA-treated KCM were evaluated via RT-PCR and western blot analysis. Moreover, melanin content and tyrosinase activity were quantified. TGF-β1 gene was knocked down by small interfering RNA (siRNA) in keratinocytes. The mRNA and protein levels of TGF-β1 in keratinocytes were significantly increased after TA treatment. Melanin contents, tyrosinase activity, protein and mRNA levels of TYR, MITF and TRP-1 were downregulated in NHEMs in the presence of TA-treated KCM. Knockdown of TGF-β1 in keratinocytes could attenuate the inhibitory effect of TA-treated KCM on melanogenesis. TA could stimulate TGF-β1 expression in keratinocytes, which further inhibits melanogenesis through the paracrine signalling.

The underestimated role of the microphthalmia-associated transcription factor (MiTF) in normal and pathological haematopoiesis

Haematopoiesis, the process by which a restrained population of stem cells terminally differentiates into specific types of blood cells, depends on the tightly regulated temporospatial activity of several transcription factors (TFs). The deregulation of their activity or expression is a main cause of pathological haematopoiesis, leading to bone marrow failure (BMF), anaemia and leukaemia. TFs can be induced and/or activated by different stimuli, to which they respond by regulating the expression of genes and gene networks. Most TFs are highly pleiotropic; i.e., they are capable of influencing two or more apparently unrelated phenotypic traits, and the action of a single TF in a specific setting often depends on its interaction with other TFs and signalling pathway components. The microphthalmia-associated TF (MiTF) is a prototype TF in multiple situations. MiTF has been described extensively as a key regulator of melanocyte and melanoma development because it acts mainly as an oncogene. Mitf-mutated mice show a plethora of pleiotropic phenotypes, such as microphthalmia, deafness, abnormal pigmentation, retinal degeneration, reduced mast cell numbers and osteopetrosis, revealing a greater requirement for MiTF activity in cells and tissue. A growing amount of evidence has led to the delineation of key roles for MiTF in haematopoiesis and/or in cells of haematopoietic origin, including haematopoietic stem cells, mast cells, NK cells, basophiles, B cells and osteoclasts. This review summarizes several roles of MiTF in cells of the haematopoietic system and how MiTFs can impact BM development.

ALK4-SMAD3/4 mediates the effects of activin A on the upregulation of PAI-1 in human granulosa lutein cells

In the mammalian ovary, the proteolysis of the extracellular matrix is dynamically regulated by plasminogen activator and plasminogen activator inhibitor (PAI), and it is a critical event that influences various physiological and pathological processes. Activin A is a member of the transforming growth factor-β superfamily and is expressed at a high level in human luteal cells that play an essential role in the regulation of the luteal function. At present, it is not known whether activin A can regulate the expression and production of PAI in human granulosa lutein (hGL) cells. The present study aimed to examine the effects of activin A on the expression and production of intraovarian PAI-1 and the underlying molecular mechanisms. Using primary and immortalized hGL cells as the cell model, we demonstrated that activin A upregulated the expression of PAI-1 and increased the production of PAI-1 in an autocrine/paracrine manner. Additionally, using a dual inhibition approach (molecular inhibitors and siRNA-mediated knockdown), we showed that this biological function is mediated by the ALK4-mediated SMAD3-SMAD4-dependent signaling pathway. Our findings suggest that activin A may be involved in the regulation of luteal function via the induction of PAI-1 expression and an increase in PAI-1 production.

TGF-β Negatively Regulates Mitf-E Expression and Canine Osteoclastogenesis

With longevity, the prevalence of osteoporosis, which occurs when the activity of osteoclast surpasses that of osteoblasts, has increased in dogs. However, limited information is available on canine osteoclastogenesis. We herein described culture conditions to induce osteoclasts from canine bone marrow cells, and identified factors affecting canine osteoclastogenesis. Tartrate-resistant acid phosphatase-positive multinucleated cells were efficiently formed in a culture of bone marrow mononuclear cells with macrophage colony-stimulating factor (M-CSF 25 ng/mL) for 3 days and a subsequent culture in the presence of M-CSF (25 ng/mL) and soluble receptor activator of NF-κB ligand (RANKL 50 ng/mL) for 4 days. We previously reported in a murine cell system that gene induction of the E isoform of microphthalmia-associated transcription factor (Mitf-E) was required and sufficient for osteoclastogenesis, while transforming growth factor-β (TGF-β) enhanced RANKL-induced Mitf-E expression and osteoclastogenesis. Mitf-E expression also increased during RANKL-induced osteoclastogenesis in canine cells; however, TGF-β down-regulated Mitf-E expression and osteoclastogenesis, indicating a species-dependent response. The results of the present study show that, consistent with murine cells, M-CSF and soluble RANKL enable canine bone marrow cells to differentiate into osteoclasts, and Mitf-E expression is induced during osteoclastogenesis. However, the role of TGF-β in osteoclast formation is distinct between murine and canine cells, suggesting the necessity of analyses using canine cells to examine the factors affecting canine osteoclastogenesis.

Role of Activins in Hepcidin Regulation during Malaria

Epidemiological observations have linked increased host iron with malaria susceptibility, and perturbed iron handling has been hypothesized to contribute to the potentially life-threatening anemia that may accompany blood-stage malaria infection. To improve our understanding of these relationships, we examined the pathways involved in regulation of the master controller of iron metabolism, the hormone hepcidin, in malaria infection. We show that hepcidin upregulation in Plasmodium berghei murine malaria infection was accompanied by changes in expression of bone morphogenetic protein (BMP)/sons of mothers against decapentaplegic (SMAD) pathway target genes, a key pathway involved in hepcidin regulation. We therefore investigated known agonists of the BMP/SMAD pathway and found that Bmp gene expression was not increased in infection. In contrast, activin B, which can signal through the BMP/SMAD pathway and has been associated with increased hepcidin during inflammation, was upregulated in the livers of Plasmodium berghei-infected mice; hepatic activin B was also upregulated at peak parasitemia during infection with Plasmodium chabaudi Concentrations of the closely related protein activin A increased in parallel with hepcidin in serum from malaria-naive volunteers infected in controlled human malaria infection (CHMI) clinical trials. However, antibody-mediated neutralization of activin activity during murine malaria infection did not affect hepcidin expression, suggesting that these proteins do not stimulate hepcidin upregulation directly. In conclusion, we present evidence that the BMP/SMAD signaling pathway is perturbed in malaria infection but that activins, although raised in malaria infection, may not have a critical role in hepcidin upregulation in this setting.

Targeting TGF-β Mediated SMAD Signaling for the Prevention of Fibrosis

Fibrosis occurs when there is an imbalance in extracellular matrix (ECM) deposition and degradation. Excessive ECM deposition results in scarring and thickening of the affected tissue, and interferes with tissue and organ homeostasis – mimicking an exaggerated “wound healing” response. Many transforming growth factor-β (TGF-β) ligands are potent drivers of ECM deposition, and additionally, have a natural affinity for the ECM, creating a concentrated pool of pro-fibrotic factors at the site of injury. Consequently, TGF-β ligands are upregulated in many human fibrotic conditions and, as such, are attractive targets for fibrosis therapy. Here, we will discuss the contribution of TGF-β proteins in the pathogenesis of fibrosis, and promising anti-fibrotic approaches that target TGF-β ligands.

WITHDRAWN: Modulation of adipocyte function by the TGF-β family

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Enhancement of RANKL-induced MITF-E expression and osteoclastogenesis by TGF-β

Microphthalmia-associated transcription factor (MITF) is a transcription factor that is expressed in limited types of cells, including osteoclasts, but the expression and role of MITF during osteoclastogenesis have not been fully elucidated. The expression of the MITF-E isoform but not that of the MITF-A isoform was induced in response to differentiation stimulation towards osteoclasts by receptor activator of NF-κB ligand (RANKL) in both RAW264.7 cells and primary bone marrow cells. The RANKL-induced formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells was inhibited in RAW264.7 cells expressing siRNA for MITF-E. Transforming growth factor-β (TGF-β) enhanced RANKL-induced MITF-E expression and -TRAP positive multinucleated cell formation. In particular, TGF-β potentiated the formation of larger osteoclasts. The expression levels of NFATc1, TRAP and CtsK, genes related to osteoclast development and activity, were concurrently enhanced by TGF-β in the presence of RANKL. Furthermore, the expression of dendritic cell-specific transmembrane protein (DC-STAMP), Itgav, Itga2, Itga5, Itgb1, Itgb3 and Itgb5, genes related to cell adhesion and fusion, were up-regulated by co-treatment with TGF-β. In particular, the regulatory expression of Itgav and Itgb5 in response to RANKL with or without TGF-β resembled that of MITF-E. Because MITF is involved in cell fusion in some cell systems, these results imply a role for MITF-E as an enhancer of osteoclastogenesis and that RANKL-induced levels of both MITF-E mRNA and of MITF-dependent gene expression are enhanced by treatment with TGF-β.

The activins and their binding protein, follistatin-Diagnostic and therapeutic targets in inflammatory disease and fibrosis

The activins, as members of the transforming growth factor-β superfamily, are pleiotrophic regulators of cell development and function, including cells of the myeloid and lymphoid lineages. Clinical and animal studies have shown that activin levels increase in both acute and chronic inflammation, and are frequently indicators of disease severity. Moreover, inhibition of activin action can reduce inflammation, damage, fibrosis and morbidity/mortality in various disease models. Consequently, activin A and, more recently, activin B are emerging as important diagnostic tools and therapeutic targets in inflammatory and fibrotic diseases. Activin antagonists such as follistatin, an endogenous activin-binding protein, offer considerable promise as therapies in conditions as diverse as sepsis, liver fibrosis, acute lung injury, asthma, wound healing and ischaemia-reperfusion injury.

The roles of activin A and its binding protein, follistatin, in inflammation and tissue repair

Activin A, a member of the transforming growth factor-β superfamily of cytokines, is a critical controller of inflammation, immunity and fibrosis. It is rapidly released into the blood following a lipopolysaccharide challenge in experimental animals, through activation of the Toll-like receptor 4 signalling pathway. Blocking activin action by pre-treatment with its binding protein, follistatin, modifies the inflammatory cytokine cascade, and reduces the severity of the subsequent inflammatory response and mortality. Likewise, high serum levels of activin A are predictive of death in patients with septicaemia. However, activin A has complex immunomodulatory actions. It is produced by inflammatory macrophages, but can regulate either pro- or anti-inflammatory responses in these cells, depending on their prior activation status. Activin A is also produced by Th2 cells, and stimulates antibody production by B cells and the development of regulatory T cells. Production of activin A during inflammatory responses stimulates fibrosis and tissue remodelling, and follistatin inhibits these actions of activin A. The modulation of activin by follistatin may represent an important therapeutic target for the modulation and amelioration of inflammatory and fibrotic disorders.

Melanoma: from mutations to medicine

Melanoma is often considered one of the most aggressive and treatment-resistant human cancers. It is a disease that, due to the presence of melanin pigment, was accurately diagnosed earlier than most other malignancies and that has been subjected to countless therapeutic strategies. Aside from early surgical resection, no therapeutic modality has been found to afford a high likelihood of curative outcome. However, discoveries reported in recent years have revealed a near avalanche of breakthroughs in the melanoma field-breakthroughs that span fundamental understanding of the molecular basis of the disease all the way to new therapeutic strategies that produce unquestionable clinical benefit. These discoveries have been born from the successful fruits of numerous researchers working in many-sometimes-related, although also distinct-biomedical disciplines. Discoveries of frequent mutations involving BRAF(V600E), developmental and oncogenic roles for the microphthalmia-associated transcription factor (MITF) pathway, clinical efficacy of BRAF-targeted small molecules, and emerging mechanisms underlying resistance to targeted therapeutics represent just a sample of the findings that have created a striking inflection in the quest for clinically meaningful progress in the melanoma field.

PAI-1 in tissue fibrosis

Fibrosis is defined as a fibroproliferative or abnormal fibroblast activation-related disease. Deregulation of wound healing leads to hyperactivation of fibroblasts and excessive accumulation of extracellular matrix (ECM) proteins in the wound area, the pathological manifestation of fibrosis. The accumulation of excessive levels of collagen in the ECM depends on two factors: an increased rate of collagen synthesis and or decreased rate of collagen degradation by cellular proteolytic activities. The urokinase/tissue type plasminogen activator (uPA/tPA) and plasmin play significant roles in the cellular proteolytic degradation of ECM proteins and the maintenance of tissue homeostasis. The activities of uPA/tPA/plasmin and plasmin-dependent MMPs rely mostly on the activity of a potent inhibitor of uPA/tPA, plasminogen activator inhibitor-1 (PAI-1). Under normal physiologic conditions, PAI-1 controls the activities of uPA/tPA/plasmin/MMP proteolytic activities and thus maintains the tissue homeostasis. During wound healing, elevated levels of PAI-1 inhibit uPA/tPA/plasmin and plasmin-dependent MMP activities, and, thus, help expedite wound healing. In contrast to this scenario, under pathologic conditions, excessive PAI-1 contributes to excessive accumulation of collagen and other ECM protein in the wound area, and thus preserves scarring. While the level of PAI-1 is significantly elevated in fibrotic tissues, lack of PAI-1 protects different organs from fibrosis in response to injury-related profibrotic signals. Thus, PAI-1 is implicated in the pathology of fibrosis in different organs including the heart, lung, kidney, liver, and skin. Paradoxically, PAI-1 deficiency promotes spontaneous cardiac-selective fibrosis. In this review, we discuss the significance of PAI-1 in the pathogenesis of fibrosis in multiple organs.

Activins and cell migration

Activins are the members of transforming growth factor β superfamily and act as secreted proteins; they were originally identified with a reproductive function, acting as endocrine-derived regulators of pituitary follicular stimulating hormone. In recent years, additional functions of activins have been discovered, including a regulatory role during crucial phases of growth, differentiation, and development such as wound healing, tissue repair, and regulation of branching morphogenesis. The functions of activins through activin receptors are pleiotrophic, while involving in the etiology and pathogenesis of a variety of diseases and being cell type-specific, they have been identified as important players in cancer metastasis, immune responses, inflammation, and are most likely involved in cell migration. In this chapter, we highlight the current knowledge of activin signaling and discuss the potential physiological and pathological roles of activins acting on the migration of various cell types.

The regulation and functions of activin and follistatin in inflammation and immunity

The activins are members of the transforming growth factor β superfamily with broad and complex effects on cell growth and differentiation. Activin A has long been known to be a critical regulator of inflammation and immunity, and similar roles are now emerging for activin B, with which it shares 65% sequence homology. These molecules and their binding protein, follistatin, are widely expressed, and their production is increased in many acute and chronic inflammatory conditions. Synthesis and release of the activins are stimulated by inflammatory cytokines, Toll-like receptor ligands, and oxidative stress. The activins interact with heterodimeric serine/threonine kinase receptor complexes to activate SMAD transcription factors and the MAP kinase signaling pathways, which mediate inflammation, stress, and immunity. Follistatin binds to the activins with high affinity, thereby obstructing the activin receptor binding site, and targets them to cell surface proteoglycans and lysosomal degradation. Studies on transgenic mice and those with gene knockouts, together with blocking studies using exogenous follistatin, have established that activin A plays critical roles in the onset of cachexia, acute and chronic inflammatory responses such as septicemia, colitis and asthma, and fibrosis. However, activin A also directs the development of monocyte/macrophages, myeloid dendritic cells, and T cell subsets to promote type 2 and regulatory immune responses. The ability of both endogenous and exogenous follistatin to block the proinflammatory and profibrotic actions of activin A has led to interest in this binding protein as a potential therapeutic for limiting the severity of disease and to improve subsequent damage associated with inflammation and fibrosis. However, the ability of activin A to sculpt the subsequent immune response as well means that the full range of effects that might arise from blocking activin bioactivity will need to be considered in any therapeutic applications.

Plasminogen activator inhibitor-1 and asthma: role in the pathogenesis and molecular regulation

Plasminogen activator inhibitor (PAI)-1 is a major inhibitor of the fibrinolytic system. PAI-1 levels are markedly increased in asthmatic airways, and mast cells (MCs), a pivotal cell type in the pathogenesis of asthma, are one of the main sources of PAI-1 production. Recent studies suggest that PAI-1 may promote the development of asthma by regulating airway remodelling, airway hyperresponsiveness (AHR), and allergic inflammation. The single guanosine nucleotide deletion/insertion polymorphism (4G/5G) at -675 bp of the PAI-1 gene is the major genetic determinant of PAI-1 expression. Plasma PAI-1 level is higher in people with the 4G/4G genotype than in those with the 5G/5G genotype. A strong association between the 4G/5G polymorphism and the risk and the severity of asthma has been suggested. Levels of plasma IgE and PAI-1 and severity of AHR are greater in asthmatic patients with the 4G/4G genotype than in those with the 5G/5G genotype. The PAI-1 promoter with the 4G allele renders higher transcription activity than the PAI-1 promoter with the 5G allele in stimulated MCs. The molecular mechanism for the 4G allele-mediated higher PAI-1 expression is associated with greater binding of upstream stimulatory factor-1 to the E-box adjacent to the 4G site (E-4G) than to the E-5G. In summary, PAI-1 may play an important role in the pathogenesis of asthma. Further studies evaluating the mechanisms of PAI-1 action and regulation may lead to the development of a novel prognostic factor and therapeutic target for the treatment and prevention of asthma and other PAI-1-associated diseases.

Regulatory expression of genes related to metastasis by TGF-beta and activin A in B16 murine melanoma cells

TGF-beta induces epithelial-mesenchymal transition, which occurs during tumor cell invasiveness in pathological state, in limited cells. As a first step to understand the role of TGF-beta and the structurally related activin during melanoma metastasis, expression of metastasis-related genes was examined in murine melanoma cells. Treatment with TGF-beta1 or activin A down-regulated E-cadherin in B16 cells in a dose-dependent manner. In epithelial cells, TGF-beta-induced high mobility group A2 (HMGA2) gene product is suggested to down-regulate E-cadherin through up-regulation of zinc-finger transcription factors Slug and Snail, and basic helix-loop-helix transcription factor Twist. Unlike the regulation in epithelial cells, TGF-beta1 treatment rather decreased mRNA expression of HMGA2, indicating a distinct mechanism on TGF-beta/activin-induced down-regulation. Transfection of double-stranded interfering RNA (dsRNAi) for activin receptor-like kinase (ALK) type I receptors revealed that ALK5, a prototype of TGF-beta receptor, mainly transmits TGF-beta signals on the E-cadherin down-regulation at the mRNA level, and that a prototype receptor ALK4 elicited the activin effect. TGF-beta/activin potentiated down-regulation of E-cadherin and HMGA2 also in B16 sublines that are susceptible to metastasis. However, the extent of down-regulation tended to be smaller, and less Smad2, a signal mediator for TGF-beta/activin, was phosphorylated in response to the ligand, resulting from less expression of type I receptors in the B16 sublines. These results suggest that the receptor expression level determines strength of the signals for TGF-beta/activin through phosphorylation of Smad2, which explains pluripotency of the ligand family partly.

Novel MITF targets identified using a two-step DNA microarray strategy

Malignant melanoma is a chemotherapy-resistant cancer with high mortality. Recent advances in our understanding of the disease at the molecular level have indicated that it shares many characteristics with developmental precursors to melanocytes, the mature pigment-producing cells of the skin and hair follicles. The development of melanocytes absolutely depends on the action of the microphthalmia-associated transcription factor (MITF). MITF has been shown to regulate a broad variety of genes, whose functions range from pigment production to cell-cycle regulation, migration and survival. However, the existing list of targets is not sufficient to explain the role of MITF in melanocyte development and melanoma progression. DNA microarray analysis of gene expression offers a straightforward approach to identify new target genes, but standard analytical procedures are susceptible to the generation of false positives and require additional experimental steps for validation. Here, we introduce a new strategy where two DNA microarray-based approaches for identifying transcription factor targets are combined in a cross-validation protocol designed to help control false-positive generation. We use this two-step approach to successfully re-identify thirteen previously recorded targets of MITF-mediated upregulation, as well as 71 novel targets. Many of these new targets have known relevance to pigmentation and melanoma biology, and further emphasize the critical role of MITF in these processes.

Regulation of melanin synthesis by the TGF-beta family in B16 melanoma cells

Effects of representative members of the transforming growth factor-beta (TGF-beta) family, TGF-beta1, activin A and BMP-2, on melanin content and expression of pigment-producing enzymes were examined in B16 melanoma cells. Treatment with TGF-beta1 or activin A but not with BMP-2 significantly decreased melanin content and expression of Tyrosinase and Tyrp-1, suggesting an inhibitory effect of TGF-beta1 and activin A on melanin synthesis. TGF-beta1 completely inhibited melanin synthesis induced by alpha-melanin stimulating hormone (alpha-MSH), whereas activin A only slightly did. As compared with parental B16 cells, the inhibitory effects of TGF-beta1 and activin A on melanin content were relative smaller in B16 F10 cells, a subline of B16 cells that contain more pigment. The present study indicates that in addition to TGF-beta, activin negatively regulates melanogenesis in the absence of alpha-MSH, but that the activity in the presence of alpha-MSH was slightly different between TGF-beta and activin.

Expression and transcriptional activity of alternative splice variants of Mitf exon 6

Microphthalmia-associated transcription factor (Mitf) is a tissue-specific transcription factor. At least nine distinct mouse isoform mRNAs are encoded by alternative splicing of the first exon of Mitf (Mitf-A, -B, -C, -D, -E, -H, -J, -M, and -mc), while exons 2-9 of all Mitf isoforms examined to date are identical. In addition, alternative splice variants of exon 6a encoding 6 amino acid proximal to the basic region of the protein are known in Mitf-A, -H, and -M. In this study, we identified alternative splice variants of exon 6a in other Mitf isoforms (Mitf-E, -J, and -mc) in melanocytes, mast cells, macrophages, and heart. We also compared the transcriptional activity of Mitf variants containing exon 6a to that of Mitf variants that did not contain exon 6a. PCR-RFLP analysis revealed that expression of Mitf with exon 6a was comparable with that of Mitf without exon 6a, irrespective of the specificity of the first exon, or cell type, although Mitf isoforms with different first exons were expressed in a cell type-dependent manner. Luciferase-based reporter assays revealed that transcription of Tyrosinase, which is known Mitf-regulated gene, was elicited more efficiently by expression of Mitf isoforms containing exon 6a, compared to isoforms that did not contain exon 6a. However, when transcription of Tyrp-1, Mmcp-6, and PAI-1 was examined, no significant differences were detected between Mitf isoforms with exon 6a and those without exon 6a, except for Tyrp-1 transcription by Mitf-D/E isoform. These results reveal a diverse pattern of gene expression and different transcriptional activities of Mitf isoforms, suggesting discrete regulation of gene transcription in specific tissues by Mitf.

Gene expression fingerprinting for human hereditary hemorrhagic telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) or Osler-Weber-Rendu syndrome is an autosomal dominant vascular disorder characterized by telangiectases and internal arteriovenous malformations. It is caused by mutations in elements of the transforming growth factor-beta (TGF-beta) receptor complex: endoglin, a co-receptor, responsible for HHT1, or ALK1 (activin receptor-like kinase 1), a type I receptor leading to HHT2. Recently, we have established cultures of HHT endothelial cells, primary targets of the disease. These cells showed deficient TGF-beta signaling and angiogenesis, representing a useful human model to study the molecular mechanism of this disease. To understand the pathogenic mechanism underlying HHT, we have used total RNA probes to compare HHT versus non-HHT cells by expression microarrays. This work represents a systematic study to identify target genes affected in HHT cells. Given the similarity of symptoms in HHT1 and HHT2, special interest has been put on the identification of common targets for both HHT types. As a result, 277 downregulated and 63 upregulated genes were identified in HHT versus control cells. These genes are involved in biological processes relevant to the HHT pathology, such as angiogenesis, cytoskeleton, cell migration, proliferation and NO synthesis. The type of misregulated genes found in HHT endothelial cells lead us to propose a model of HHT pathogenesis, opening new perspectives to understand this disorder. Moreover, as the disease is originated by mutations in proteins of the TGF-beta receptor complex, these results may be useful to find out targets of the TGF-beta pathway in endothelium.

Malignant melanoma: genetics and therapeutics in the genomic era

Cell for cell, probably no human cancer is as aggressive as melanoma. It is among a handful of cancers whose dimensions are reported in millimeters. Tumor thickness approaching 4 mm presents a high risk of metastasis, and a diagnosis of metastatic melanoma carries with it an abysmal median survival of 6-9 mo. What features of this malignancy account for such aggressive behavior? Is it the migratory history of its cell of origin or the programmed adaptation of its differentiated progeny to environmental stress, particularly ultraviolet radiation? While the answers to these questions are far from complete, major strides have been made in our understanding of the cellular, molecular, and genetic underpinnings of melanoma. More importantly, these discoveries carry profound implications for the development of therapies focused directly at the molecular engines driving melanoma, suggesting that we may have reached the brink of an unprecedented opportunity to translate basic science into clinical advances. In this review, we attempt to summarize our current understanding of the genetics and biology of this disease, drawing from expanding genomic information and lessons from development and genetically engineered mouse models. In addition, we look forward toward how these new insights will impact on therapeutic options for metastatic melanoma in the near future.

Identification of tocopherol-associated protein as an activin/TGF-beta-inducible gene in mast cells

Previous studies have demonstrated that treatment with activin A and TGF-beta(1), members of the TGF-beta family, stimulated maturation of mouse bone marrow-derived cultured mast cells (BMMC), which was characterized by morphology and gene expression of mouse mast cell proteases (mmcps). In order to gain a better understanding of activin A- and TGF-beta(1)-induced maturation in mast cells, we investigated the genes that were up-regulated in response to treatment with these two members of the TGF-beta family. The cDNA microarray analyses indicated that in BMMC, five genes were induced by treatment with 4 nM activin A for 2 h. Tocopherol-associated protein (Tap) was one of the induced genes, and the Tap induction in response to activin A treatment was confirmed by real-time RT-PCR analyses. Treatment with TGF-beta(1) at 200 pM but not BMP-2 at 4 nM also increased Tap gene transcript in BMMC. Activin A-induced Tap expression was detected in BMMC but not in RAW264 macrophage-like cells, B16 melanoma cells or P19 embryonic carcinoma cells. Treatment with >1 muM SB431542, an inhibitor of activin and TGF-beta type I receptors ALK4/5, reduced responsiveness of Tap expression to TGF-beta(1), whereas <0.5 microM SB431542 effectively reduced TGF-beta(1)-induced expression of mmcp-1 and mmcp-7. These results suggest that inhibitory effects of SB431542 are different between TGF-beta-induced genes. Reporter assays indicated that Tap expression enhances transcription mediated by the activin/TGF-beta pathway. Thus, the present results suggest that Tap induction in response to activin/TGF-beta occurs predominantly in mast cells and serves as a positive regulator in activin/TGF-beta signaling.

Transforming growth factor-beta receptor inhibition enhances adenoviral infectability of carcinoma cells via up-regulation of Coxsackie and Adenovirus Receptor in conjunction with reversal of epithelial-mesenchymal transition

Expression of the Coxsackie and Adenovirus Receptor (CAR) is frequently reduced in carcinomas, resulting in decreased susceptibility of such tumors to infection with therapeutic adenoviruses. Because CAR participates physiologically in the formation of tight-junction protein complexes, we examined whether molecular mechanisms known to down-regulate cell-cell adhesions cause loss of CAR expression. Transforming growth factor-beta (TGF-beta)-mediated epithelial-mesenchymal transition (EMT) is a phenomenon associated with tumor progression that is characterized by loss of epithelial-type cell-cell adhesion molecules (including E-cadherin and the tight junction protein ZO-1), gain of mesenchymal biochemical markers, such as fibronectin, and acquisition of a spindle cell phenotype. CAR expression is reduced in tumor cells that have undergone EMT in response to TGF-beta. This down-regulation results from repression of CAR gene transcription, whereas altered RNA stability and increased proteasomal protein degradation play no role. Loss of CAR expression in response to TGF-beta is accompanied by reduced susceptibility to adenovirus infection. Indeed, treatment of carcinoma cells with LY2109761, a specific pharmacologic inhibitor of TGF-beta receptor types I and II kinases, resulted in increased CAR RNA and protein levels as well as improved infectability with adenovirus. This was observed in cells induced to undergo EMT by addition of exogenous TGF-beta and in those that were transformed by endogenous autocrine/paracrine TGF-beta. These findings show down-regulation of CAR in the context of EMT and suggest that combination of therapeutic adenoviruses and TGF-beta receptor inhibitors could be an efficient anticancer strategy.

Responses during cell preparation for functional analyses in mouse bone marrow-derived cultured mast cells

Murine bone marrow-derived cultured mast cells (BMMCs) are most widely used in in vitro experiments for evaluation of mast cell functions. The present study has shown that cell preparation procedure, i.e., cell collection by centrifugation and the subsequent adjustment and culture of cell density at the desired concentrations, transiently induced gene expression of plasminogen activator inhibitor-1 (PAI-1) and the AP-1 components (c-fos, c-jun, and junB). The level of PAI-1 gene transcript was closely related to the cell density and the gene expression was enhanced by pretreatment with okadaic acid, an inhibitor of protein phosphatases 1 (PP1) and 2A (PP2A). The cell preparation procedure also caused dephosphorylation of MAP kinases, i.e., ERK, p38, and JNK, resulting from PP1/PP2A activation. In view of the cell responses to the cell preparation procedure itself, care is needed in the interpretation of in vitro data using BMMCs.