Calcium-regulated expression of activin A in RBL-2H3 mast cells

In vivo induction of activin A-producing alveolar macrophages supports the progression of lung cell carcinoma

Alveolar macrophages (AMs) are crucial for maintaining normal lung function. They are abundant in lung cancer tissues, but their pathophysiological significance remains unknown. Here we show, using an orthotopic murine lung cancer model and human carcinoma samples, that AMs support cancer cell proliferation and thus contribute to unfavourable outcome. Inhibin beta A (INHBA) expression is upregulated in AMs under tumor-bearing conditions, leading to the secretion of activin A, a homodimer of INHBA. Accordingly, follistatin, an antagonist of activin A is able to inhibit lung cancer cell proliferation. Single-cell RNA sequence analysis identifies a characteristic subset of AMs specifically induced in the tumor environment that are abundant in INHBA, and distinct from INHBA-expressing AMs in normal lungs. Moreover, postnatal deletion of INHBA/activin A could limit tumor growth in experimental models. Collectively, our findings demonstrate the critical pathological role of activin A-producing AMs in tumorigenesis, and provides means to clearly distinguish them from their healthy counterparts.

Activin A is a prominent autocrine regulator of hepatocyte growth arrest

Activin A, a multifunctional cytokine, plays an important role in hepatocyte growth suppression and is involved in liver size control. The present study was aimed to determine the cell location of activin A in the normal rat liver microenvironment and the contribution of activin A signaling to the hepatocyte phenotype to obtain insight into molecular mechanisms. Immunohistochemical and in situ hybridization analyses identified hepatocytes as the major activin A‐positive cell population in normal liver and identified mast cells as an additional activin A source. To investigate paracrine and autocrine activin A‐stimulated effects, hepatocytes were cocultured with engineered activin A‐secreting cell lines (RF1, TL8) or transduced with an adeno‐associated virus vector encoding activin βA, which led to strikingly altered expression of cell cycle‐related genes (Ki‐67, E2F transcription factor 1 [E2F1], minichromosome maintenance complex component 2 [Mcm2], forkhead box M1 [FoxM1]) and senescence‐related genes (cyclin‐dependent kinase inhibitor 2B [p15^INK4b/CDKN2B], differentiated embryo‐chondrocyte expressed gene 1 [DEC1]) and reduced proliferation and induction of senescence. Microarray analyses identified 453 differentially expressed genes, many of which were not yet recognized as activin A downstream targets (e.g., ADAM metallopeptidase domain 12 [Adam12], semaphorin 7A [Sema7a], LIM and cysteine‐rich domains‐1 [Lmcd1], DAB2, clathrin adaptor protein [Dab2]). Among the main activin A‐mediated molecular/cellular functions are cellular growth/proliferation and movement, molecular transport, and metabolic processes containing highly down‐regulated genes, such as cytochrome P450, subfamily 2, polypeptide 11 (Cyp2C11), sulfotransferase family 1A, member 1 (Sult1a1), glycine‐N‐acyltransferase (Glyat), and bile acid‐CoA:amino acid N‐acyltransferase (Baat). Moreover, Ingenuity Pathway Analyses identified particular gene networks regulated by hepatocyte nuclear factor (HNF)‐4α and peroxisome proliferator‐activated receptor gamma (PPARγ) as key targets of activin A signaling. Conclusion: Our in vitro models demonstrated that activin A‐stimulated growth inhibition and cellular senescence is mediated through p15^INK4b/CDKN2B and is associated with up‐ and down‐regulation of numerous target genes involved in multiple biological processes performed by hepatocytes, suggesting that activin A fulfills a critical role in normal liver function. (Hepatology Communications 2017;1:852‐870)

Activin A and follistatin in patients with asthma. Does severity make the difference?

BACKGROUND AND OBJECTIVE

Activin A is a pleiotropic cytokine holding a fundamental role in inflammation and tissue remodelling. Follistatin can modulate the bioactivity of activin. We aimed to measure activin A and follistatin in sputum supernatants and bronchoalveolar lavage (BAL) of asthmatic patients and to determine the possible associations with severity as well as with inflammatory and remodelling indices.

METHODS

A total of 58 asthmatic patients (33 with severe refractory asthma (SRA)) and 10 healthy controls underwent sputum induction for % cells, activin A, follistatin, eosinophilic cationic protein (ECP), transforming growth factor beta 1 (TGF-β1), IL-13 and IL-8 measurements. In 22 asthmatic patients, BAL and bronchial biopsies were also performed for the assessment of the above-mentioned variables, measurement of remodelling indices and immunostaining for different activin A receptors.

RESULTS

Sputum activin A (pg/mL) was higher in patients with SRA (median (interquartile ranges): 76 (33-185)) compared to mild-to-moderate asthma (44 (18-84); P = 0.005), whereas follistatin did not differ between the two groups. BAL activin A (pg/mL) was higher in patients with SRA compared to those with mild-to-moderate disease. A significant association was observed between activin A and TGF-β1, eosinophils in sputum and/or in BAL, while reticular basement membrane (RBM) thickness was significantly associated with BAL activin levels only. No difference in immunostaining for activin receptor type IB was observed between patients with SRA and those with mild-to-moderate asthma.

CONCLUSION

Sputum and BAL levels of activin A are higher in SRA. The association of activin A with TGF-β1, eosinophils and RBM thickness may indicate a role of this cytokine in the inflammatory and remodelling process in SRA.

Follistatin: a novel therapeutic for the improvement of muscle regeneration

Follistatin (FST) is a member of the tissue growth factor β family and is a secreted glycoprotein that antagonizes many members of the family, including activin A, growth differentiation factor 11, and myostatin. The objective of this study was to explore the use of an engineered follistatin therapeutic created by fusing FST315 lacking heparin binding activity to the N terminus of a murine IgG1 Fc (FST315-ΔHBS-Fc) as a systemic therapeutic agent in models of muscle injury. Systemic administration of this molecule was found to increase body weight and lean muscle mass after weekly administration in normal mice. Subsequently, we tested this agent in several models of muscle injury, which were chosen based on their severity of damage and their ability to reflect clinical settings. FST315-ΔHBS-Fc treatment proved to be a potent inducer of muscle remodeling and regeneration. FST315-ΔHBS-Fc induced improvements in muscle repair after injury/atrophy by modulating the early inflammatory phase allowing for increased macrophage density, and Pax7-positive cells leading to an accelerated restoration of myofibers and muscle function. Collectively, these data demonstrate the benefits of a therapeutically viable form of FST that can be leveraged as an alternate means of ameliorating muscle regeneration.

Eicosapentaenoic acid and docosahexaenoic acid suppress Th2 cytokine expression in RBL-2H3 basophilic leukemia cells

It is known that the intake of omega-3 fatty acids, such as eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), is beneficial for preventing and/or treating allergic diseases. The pathogenesis of allergic diseases is associated with overactivation of Th2-skewed immunity. Basophils generate large amounts of Th2 cytokines such as interleukin (IL)-4 and IL-13, which are critically involved in allergic inflammation. We investigated how EPA and DHA affect Th2 cytokine expression in phorbol 12-myristate 13-acetate- and ionomycin (PI)-activated RBL-2H3 basophilic leukemia cells. EPA and DHA induced a dramatic decrease in the production of IL-4 and IL-13 and their transcription in a dose-dependent manner. Luciferase assays of RBL-2H3 cells stably expressing Il4 and Il13 promoter-reporter plasmids demonstrated a significant suppression of PI-induced promoter activation. Analysis of certain transcription factors revealed that nuclear expression of c-Fos and the mRNA expression were suppressed by EPA and DHA. Furthermore, they significantly inhibited the nuclear expression and translocation of nuclear factor of activated T cells (NF-AT)1. In contrast, the expression levels of nuclear factor kappa-B (NF-κB), GATA-binding proteins (GATAs), and CCAAT/enhancer binding protein alpha (C/EBPα) were not significantly affected by EPA and DHA. Phosphorylation of extracellular signal-related kinase was inhibited by EPA and DHA, and phosphorylation of p38 mitogen-activated protein kinase was decreased by DHA, but not by EPA. Taken together, our data suggest that EPA and DHA may suppress Th2-skewed allergic immune responses by inhibiting the expression of basophilic IL-4 and IL-13.

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.

Activin, neutrophils, and inflammation: just coincidence?

During the 26 years that have elapsed since its discovery, activin-A, a member of the transforming growth factor β super-family originally discovered from its capacity to stimulate follicle-stimulating hormone production by cultured pituitary gonadotropes, has been established as a key regulator of various fundamental biological processes, such as development, homeostasis, inflammation, and tissue remodeling. Deregulated expression of activin-A has been observed in several human diseases characterized by an immuno-inflammatory and/or tissue remodeling component in their pathophysiology. Various cell types have been recognized as sources of activin-A, and plentiful, occasionally contradicting, functions have been described mainly by in vitro studies. Not surprisingly, both harmful and protective roles have been postulated for activin-A in the context of several disorders. Recent findings have further expanded the functional repertoire of this molecule demonstrating that its ectopic overexpression in mouse airways can cause pathology that simulates faithfully human acute respiratory distress syndrome, a disorder characterized by strong involvement of neutrophils. This finding when considered together with the recent discovery that neutrophils constitute an important source of activin-A in vivo and earlier observations of upregulated activin-A expression in diseases characterized by strong activation of neutrophils may collectively imply a more intimate link between activin-A expression and neutrophil reactivity. In this review, we provide an outline of the functional repertoire of activin-A and suggest that this growth factor functions as a guardian of homeostasis, a modulator of immunity and an orchestrator of tissue repair activities. In this context, a relationship between activin-A and neutrophils may be anything but coincidental.

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.

Activin A promotes multiple myeloma-induced osteolysis and is a promising target for myeloma bone disease

Understanding the pathogenesis of cancer-related bone disease is crucial to the discovery of new therapies. Here we identify activin A, a TGF-beta family member, as a therapeutically amenable target exploited by multiple myeloma (MM) to alter its microenvironmental niche favoring osteolysis. Increased bone marrow plasma activin A levels were found in MM patients with osteolytic disease. MM cell engagement of marrow stromal cells enhanced activin A secretion via adhesion-mediated JNK activation. Activin A, in turn, inhibited osteoblast differentiation via SMAD2-dependent distal-less homeobox-5 down-regulation. Targeting activin A by a soluble decoy receptor reversed osteoblast inhibition, ameliorated MM bone disease, and inhibited tumor growth in an in vivo humanized MM model, setting the stage for testing in human clinical trials.

Differential responses to oxidative stress and calcium influx on expression of the transforming growth factor-beta family in myoblasts and myotubes

Changes in gene expression of TGF-beta family members and their receptors in response to treatment with H(2)O(2) and a calcium ionophore, A23187, were examined in C2C12 myoblasts and myotubes. The expression of Myf5, an initial regulator of myogenesis, was increased by A23187, and H(2)O(2) inhibited the up-regulation of Myf5. Treatment with H(2)O(2) decreased the expression of MHC IIb, a protein component of the myofibrils, irrespective of the presence of A23187, suggesting an inhibitory role of oxidative stress for myogenesis. Expression of ligands and receptors for the TGF-beta family was modulated in response to H(2)O(2) and A23187. Treatment with H(2)O(2) decreased expression of TGF-beta3, BMP-4, ALK4, ALK5, and ActRIIB, and increased expression of inhibin alpha and inhibin betaA in either the myoblast stage or the myotube stage, or both. A23187 potentiated down-regulation of BMP-4 and ALK4 expression, and up-regulation of TGF-beta1, TGF-beta2, inhibin alpha, inhibin betaA, ALK2, and ALK3 expression. These results indicate that oxidative stress and Ca(2+) influx affect expression of the TGF-beta family in C2C12 myoblasts and myotubes.

Elevating calcium in Th2 cells activates multiple pathways to induce IL-4 transcription and mRNA stabilization

PMA and ionomycin cause T cell cytokine production. We report that ionomycin alone induces IL-4 and IFN-gamma, but not IL-2, from in vivo- and in vitro-generated murine Th2 and Th1 cells. Ionomycin-induced cytokine production requires NFAT, p38, and calmodulin-dependent kinase IV (CaMKIV). Ionomycin induces p38 phosphorylation through a calcium-dependent, cyclosporine A-inhibitable pathway. Knocking down ASK1 inhibits ionomycin-induced p38 phosphorylation and IL-4 production. Ionomycin also activates CaMKIV, which, together with p38, induces AP-1. Cooperation between AP-1 and NFAT leads to Il4 gene transcription. p38 also regulates IL-4 production by mRNA stabilization. TCR stimulation also phosphorylates p38, partially through the calcium-dependent pathway; activated p38 is required for optimal IL-4 and IFN-gamma.

Temporal expression of activin in acute burn wounds—From inflammatory cells to fibroblasts

Activin A is a member of the transforming growth factor-beta (TGF-beta) family of cytokines and growth factors and upregulation of this protein has been linked with a number of disease processes associated with chronic inflammation and fibrosis. Its potential involvement in burns has not yet been investigated. We therefore studied the localization of activin in tissue sections from excised mid- and deep dermal and full thickness cutaneous burn by immunohistochemistry. There was cell-specific temporal expression in tissues with prominent expression from day 4 onwards in lymphocytes and histiocytes and expression from day 8 onwards in reactive fibroblasts and endothelial cells. Immunopositivity over the first 18 days persisted in reactive fibroblasts and lymphocytes although the latter were in most circumstances decreasing in number. These data are consistent with activin A being central to the inflammatory and repair phases occurring in burnt skin and early scar formation. Modulation of activin expression and actions may, therefore, be a target for the management of burns.

Activin A functions as a Th2 cytokine in the promotion of the alternative activation of macrophages

Activin A, a member of the TGF-beta superfamily, is a pluripotent growth and differentiation factor. In this study, we report that murine Th cells produce activin A upon activation. Activin activity in the cultured CD4+ T cells was induced by anti-CD3 cross-linking. Activin betaA mRNA level was increased in response to activation, indicating that activin production in CD4+ T cells is regulated at the mRNA level. Activin production was detected exclusively in CD4+CD25- T cells, but not in CD4+CD25+ regulatory T cells. When CD4+ T cells were differentiated into Th cell subsets, higher activin secretion was detected when cultured under Th2-skewing conditions. The mRNA level of activin betaA was abundant in Th2, but not in Th1 cells. Furthermore, secretion of activin was significantly higher in activated Th2 clones than in Th1 clones. The activin betaA-proximal promoter contains a binding site for c-Maf, a Th2-specific transcriptional factor, at close proximity with an NF-AT binding site. c-Maf was able to synergize with NF-AT to transactivate activin betaA gene, and both factors are implicated in activin betaA transcription in Th2 cells. Activin A induced macrophages to express arginase-1 (M-2 phenotype), whereas it inhibited inducible NO synthase expression (M-1 phenotype) induced by IFN-gamma. Taken together, these observations suggest that activin A is a novel Th2 cytokine that promotes differentiation of macrophages toward the M-2 phenotype.

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.

Molecular responses to acidosis of central chemosensitive neurons in brain

Significant advances have been made in understanding how neurons sense and respond to acidosis at the cellular level. Decrease in pH of the cerebrospinal fluid followed by hypercapnia (increased arterial CO2) is monitored by the chemosensory neurons of the medulla oblongata. Then the intracellular signalling pathways are activated to regulate specific gene expression, which leads to a hyperventilatory response. However, little is known about molecular details of such cellular responses. Recent studies have identified several transcription factors such as c-Jun, Fos and small Maf proteins that may play critical roles in the brain adaptation to hypercapnia. Hypercapnic stimulation also activates c-Jun NH2-terminal kinase (JNK) cascade via influx of extracellular Ca2+ through voltage-gated Ca2+ channels. In addition, several transmembrane proteins including Rhombex-29 (rhombencephalic expression protein-29 kDa) and Past-A (proton-associated sugar transporter-A) have been implicated in regulation of H+ sensitivity and brain acidosis-mediated energy metabolism, respectively. This review discusses current knowledge on the signalling mechanisms and molecular basis of neuronal adaptation during acidosis.

Phosphorylation of JNK is involved in regulation of H(+)-induced c-Jun expression

Cells respond to physical and chemical stimulations mediated by pH, osmolarity, and oxidative and mechanical stresses. Various signal transduction pathways cooperate and participate in these responses. Here we describe the role of c-Jun NH2-terminal kinase (JNK) in regulation of gene transcription after an increase in extracellular H+. When cells were incubated in low pH medium, the promotion of JNK phosphorylation and c-Jun expression was clearly observed in cells in an extracellular pH- and time-dependent manner. Activation of p38 and extracellular signal-regulated kinase 1/2 (ERK1/2) was extremely weak compared with that of JNK. An increase in extracellular H+ led to enhanced nuclear translocation of phosphorylated JNK leading to augmentation of the transcriptional activity of c-Jun. Nimodipine, a blocker of voltage-gated Ca2+ ion channels, prevented the phosphorylation of JNK and expression of c-Jun in a dose-dependent manner. These results suggest a novel intracellular signalling pathway for H+-induced c-Jun expression: an increase of extracellular H+ induces JNK phosphorylation and c-Jun expression via partly extracellular Ca2+ influx through voltage-gated Ca2+ channels.

Reliability of RT-PCR methods for measuring relative gene expression in mast cells

Three methods to quantify gene transcript levels in mast cells, real-time RT-PCR, competitive RT-PCR and conventional RT-PCR analyses, were compared. Linear regression analysis on five gene transcripts revealed that the mRNA levels measured by real-time RT-PCR analysis were minimally correlated with those by conventional RT-PCR analysis. In addition, differences in the mRNA level between samples measured by conventional RT-PCR analysis were smaller than those by real-time RT-PCR analysis, suggesting that conventional RT-PCR analysis is less sensitive at measuring mRNA levels. Results from competitive RT-PCR analysis correlated closely with those from real-time RT-PCR analysis. When the differences in mRNA level between samples are relatively smaller, however, the correlation tended to be weaker. Real-time RT-PCR analysis has higher reliability, but is expensive. In contrast, competitive RT-PCR analysis is inexpensive, but is weaker at detecting smaller differences in gene transcript level between samples. Therefore, the most appropriate analytical method to measure mRNA levels should be chosen, depending on the experimental conditions.

Transcriptional activation of mouse mast cell Protease-7 by activin and transforming growth factor-beta is inhibited by microphthalmia-associated transcription factor

Previous studies have revealed that activin A and transforming growth factor-beta1 (TGF-beta1) induced migration and morphological changes toward differentiation in bone marrow-derived cultured mast cell progenitors (BMCMCs). Here we show up-regulation of mouse mast cell protease-7 (mMCP-7), which is expressed in differentiated mast cells, by activin A and TGF-beta1 in BMCMCs, and the molecular mechanism of the gene induction of mmcp-7. Smad3, a signal mediator of the activin/TGF-beta pathway, transcriptionally activated mmcp-7. Microphthalmia-associated transcription factor (MITF), a tissue-specific transcription factor predominantly expressed in mast cells, melanocytes, and heart and skeletal muscle, inhibited Smad3-mediated mmcp-7 transcription. MITF associated with Smad3, and the C terminus of MITF and the MH1 and linker region of Smad3 were required for this association. Complex formation between Smad3 and MITF was neither necessary nor sufficient for the inhibition of Smad3 signaling by MITF. MITF inhibited the transcriptional activation induced by the MH2 domain of Smad3. In addition, MITF-truncated N-terminal amino acids could associate with Smad3 but did not inhibit Smad3-mediated transcription. The level of Smad3 was decreased by co-expression of MITF but not of dominant-negative MITF, which resulted from proteasomal protein degradation. The changes in the level of Smad3 protein were paralleled by those in Smad3-mediated signaling activity. These findings suggest that MITF negatively regulates Smad-dependent activin/TGF-beta signaling in a tissue-specific manner.

Role of activin A in murine mast cells: modulation of cell growth, differentiation, and migration

Activins, members of the transforming growth factor-beta (TGF-beta) superfamily, are potent growth and differentiation factors. Our previous studies revealed that activin A, a homodimer of inhibin/activin beta(A), was induced in mast cells and peritoneal macrophages in response to their activation. In the present study, we examined the roles of activin A in murine bone marrow-derived, cultured mast cell progenitors (BMCMCs), which expressed gene transcripts for molecules involved in activin signaling, suggesting that BMCMCs could be target cells of activin A. Treatment of activin A inhibited 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide uptake into BMCMCs in a dose-dependent manner. The IC(50) concentration was 2.1 nM, which was less potent than 185 pM TGF-beta(1). Activin A treatment caused morphological changes toward the differentiated cells at 2 nM and up-regulated mRNA of mouse mast cell protease-1 (mMCP-1), a marker enzyme of mature mucosal mast cells, at 1 nM. Activin A also showed activity in inducing migration of BMCMCs; the optimal concentration for maximal migration was 10 pM, which was much lower than the concentrations to inhibit cell growth and to activate the mMCP-1 gene. Taking the present results together with our previous results, it is suggested that activin A secreted from activated immune cells recruits mast cell progenitors to sites of inflammation and that with increasing activin A concentration, the progenitors differentiate into mature mast cells. Thus, activin A may positively regulate the functions of mast cells as effector cells of the immune system.