Inhibitors of the TGF-β Superfamily and their Clinical Applications

Chamaejasmenin B, a novel candidate, inhibits breast tumor metastasis by rebalancing TGF-beta paradox

Metastasis is the leading lethal factor severely restraining the effectiveness of clinical treatment. TGF-beta is the key regulator for metastasis and influences paradoxically on cancer progression. The known TGF-beta blockers exert little selectivity on its functions, indiscriminately causing the anti-metastatic and pro-growth effects. Under such circumstances, specifically rebalancing the oncological function of TGF-beta provides a crucial oncotarget against metastasis. In our study, we established the screening platform targeting cell motility and identified a potential flavonoid, Chamaejasmenin B (ICJ), extracted from Stellera chamaejasme L. It suppressed the migration and invasion in breast cancer cells in vitro. Moreover, by dynamical quantification of breast cancer progression in small-animal imaging system, ICJ was proved to be a potent inhibitor of metastasis with minimal toxic side effects. Mechanism study further revealed that ICJ efficiently blocked TGF-beta induced EMT, disrupted the interaction between β3 integrin-TβRII complex and, consequently, resulted in the selective inhibition of FAK:Src:p38 pathway. Meanwhile, specific blockage of this pathway largely attenuated the anti-metastatic function of ICJ. Importantly, in contrast with the antagonistic effects on TGF-beta induced metastasis, ICJ obviously sensitized its cytostatic activity, suggesting that it was not a pan-blocker but a rebalancer for the functional output of TGF-beta. Collectively, by targeting TGF-beta Paradox, we experimentally provided a promising candidate for metastatic intervention.

Quantitative single-molecule study of TGF-β/Smad signaling

TGF-β/Smad signaling pathway triggers diverse cellular responses among different cell types and environmental conditions. Quantitative analysis of protein-protein interactions involved in TGF-β/Smad signaling is demanded for understanding the molecular mechanism of this signaling pathway. Live-cell single-molecule microcopy with high spatiotemporal resolution is a new tool to monitor key molecular events in a real-time manner. In this review, we mainly presented the recent work on the quantitative characterization of TGF-β/Smad signaling proteins by single-molecule method, and showed how it enabled us to obtain new insights about this canonical signaling process.

Adeno-associated virus-mediated expression of myostatin propeptide improves the growth of skeletal muscle and attenuates hyperglycemia in db/db mice

Inhibition of myostatin, a negative growth modulator for muscle, can functionally enhance muscle mass and improve glucose and fat metabolism in myostatin propeptide (MPRO) transgenic mice. This study was to investigate whether myostatin inhibition by adeno-associated virus (AAV)-mediated gene delivery of MPRO could improve muscle mass and achieve therapeutic effects on glucose regulation and lipid metabolism in the db/db mice and the mechanisms involved in that process. Eight-week-old male db/db mice were administered saline, AAV-GFP and AAV-MPRO/Fc vectors and monitored random blood glucose levels and body weight for 36 weeks. Body weight gain was not different during follow-up among the groups, but AAV-MPRO/Fc vectors resulted high level of MPRO in the blood companied by an increase in skeletal muscle mass and muscle hypertrophy. In addition, AAV-MPRO/Fc-treated db/db mice showed significantly lower blood glucose and insulin levels and significantly increased glucose tolerance and insulin sensitivity compared with the control groups (P<0.05). Moreover, these mice exhibited lower triglyceride (TG) and free fatty acid (FFA) content in the skeletal muscle, although no difference was observed in fat pad weights and serum TG and FFA levels. Finally, AAV-MPRO/Fc-treated mice had enhanced insulin signaling in the skeletal muscle. These data suggest that AAV-mediated MPRO therapy may provide an important clue for potential clinical applications to prevent type II diabetes, and these studies confirm that MPRO is a therapeutic target for type II diabetes.

Glucocorticoids Enhance Muscle Proteolysis through a Myostatin-Dependent Pathway at the Early Stage

Myostatin, a member of the TGF-β superfamily of secreted proteins, is expressed primarily in skeletal muscle. It negatively regulates muscle mass and is associated with glucocorticoid-induced muscle atrophy. However, it remains unclear whether myostatin is involved in glucocorticoid-induced muscle protein turnover. The aim of the present study was to investigate the role of myostatin in protein metabolism during dexamethasone (DEX) treatment. Protein synthesis rates and the expression of the genes for myostatin, ubiquitin-proteasome atrogin-1, MuRF1, FoxO1/3a and mTOR/p70S6K were determined. The results show that DEX decreased (P<0.05) protein synthesis rates while increasing the abundance of myostatin. DEX increased (P<0.05) the level of phospho-FoxO1/3a (Thr 24/32) and the expression of MuRF1. In contrast, DEX treatment had no detectable effect on atrogin-1 protein levels (P>0.05). The phosphorylation levels of mTOR and p70S6K were decreased by DEX treatment (P<0.05). Follistatin treatment inhibited the DEX-induced increase in myostatin (P<0.05) and the activation of phosphor-FoxO1/3a (Thr 24/32) (P< 0.05) and MuRF1 (P<0.05). Follistatin treatment had no influence on the protein synthesis rate or on the phosphorylation levels of mTOR (Ser 2448) and p70S6K (Thr 389) (P> 0.05). In conclusion, the present study suggests that the myostatin signalling pathway is associated with glucocorticoid-induced muscle protein catabolism at the beginning of exposure. Myostatin is not a main pathway associated with the suppression of muscle protein synthesis by glucocorticoids.

Promising molecular targets and biomarkers for male BPH and LUTS

Benign prostatic hyperplasia (BPH) is a major health concern for aging men. BPH is associated with urinary voiding dysfunction and lower urinary tract symptoms (LUTS), which negatively affects quality of life. Surgical resection and medical approaches have proven effective for improving urinary flow and relieving LUTS but are not effective for all men and can produce adverse effects that require termination of the therapeutic regimen. Thus, there is a need to explore other therapeutic targets to treat BPH/LUTS. Complicating the treatment of BPH/LUTS is the lack of biomarkers to effectively identify pathobiologies contributing to BPH/LUTS or to gauge successful response to therapy. This review will briefly discuss current knowledge and will highlight new studies that illuminate the pathobiologies contributing to BPH/LUTS, potential new therapeutic strategies for successfully treating BPH/LUTS, and new approaches for better defining these pathobiologies and response to therapeutics through the development of biomarkers and phenotyping strategies.

Saponins from the roots of Platycodon grandiflorum suppresses TGFβ1-induced epithelial-mesenchymal transition via repression of PI3K/Akt, ERK1/2 and Smad2/3 pathway in human lung carcinoma A549 cells

Transforming growth factor β (TGFβ) is a multifunctional cytokine that induces growth arrest, tissue fibrosis, and epithelial-mesenchymal transition (EMT) through activation of Smad and non-Smad signaling pathways. EMT is the differentiation switch by which polarized epithelial cells differentiate into contractile and motile mesenchymal cells. Our previous studies have shown that saponins from the roots of Platycodon grandiflorum (CKS) have antiinflammatory, antioxidant, antimetastatic, and hepatoprotective effects. In this study, we investigated the inhibitory effect of CKS on TGFβ1-induced alterations characteristic of EMT in human lung carcinoma A549 cells. We found that CKS-treated cells displayed inhibited TGFβ1-mediated E-cadherin downregulation and Vimentin upregulation and also retained epithelial morphology. Furthermore, TGFβ1-increased Snail expression, a repressor of E-cadherin and an inducer of the EMT, was reduced by CKS. CKS inhibited TGFβ1-induced phosphorylation of Akt, ERK1/2, and glycogen synthase kinase-3β (GSK-3β). Inhibition of PI3K/Akt and ERK1/2 also blocked TGFβ1-induced GSK-3β phosphorylation and Snail activation. Furthermore, TGFβ1-increased Snail expression was reduced by selective inhibitors of Akt and ERK1/2. Moreover, CKS treatment attenuated TGFβ1-induced Smad2/3 phosphorylation and upregulated Smad7 expression. These results indicate that pretreatment with the CKS inhibits the TGFβ1-induced EMT through PI3K/Akt, ERK1/2, GSK-3β and Smad2/3 in human lung carcinoma cells.

Simultaneous delivery of doxorubicin and curcumin encapsulated in liposomes of pegylated RGDK-lipopeptide to tumor vasculature

Curcumin, because of its distinguishing ability to inhibit activation of transcription factor linked to chemoresistance and drug transporters, is now being co-administered with various potent anti-cancer drugs. In the present study, we report on such potentiating capabilities of curcumin in anti-angiogenic cancer therapy. With a view to simultaneously deliver curcumin and doxorubicin to tumor vasculature in anti-angiogenic cancer therapy, herein we report on the design & synthesis of a tumor vasculature targeting pegylated RGDK-lipopeptide. We show that curcumin & doxorubicin co-encapsulated within the liposomes of the presently described pegylated RGDK-lipopeptide exhibit synergism in inhibiting proliferation, invasion and migration of both tumor and endothelial cells presumably by inhibiting proliferation and metastasis related genes both at mRNA & protein levels. Pronounced tumor growth inhibition was observed in mice treated with formulations containing both the drugs. Tumor growth inhibition was found to be 2-3 folds less in mice treated with formulations containing only curcumin or only doxorubicin. The presently described liposomal system is expected to find future use for simultaneously delivering potentially any combinations of hydrophilic and hydrophobic potent small molecule cancer therapeutics to tumor vasculature in anti-angiogenic cancer therapy.

TGFβ1 Polymorphisms Predict Distant Metastasis-Free Survival in Patients with Inoperable Non-Small-Cell Lung Cancer after Definitive Radiotherapy

Purpose

Transforming growth factor (TGF) -β1 signaling is involved in cancer-cell metastasis. We investigated whether single nucleotide polymorphisms (SNPs) at TGFβ1 were associated with overall survival (OS) and distant metastasis-free survival (DMFS) in patients with non-small cell lung cancer (NSCLC) treated with definitive radiotherapy, with or without chemotherapy.

Methods

We genotyped TGFβ1 SNPs at rs1800469 (C–509T), rs1800471 (G915C), and rs1982073 (T+29C) by polymerase chain reaction-restriction fragment length polymorphism in blood samples from 205 NSCLC patients who had had definitive radiotherapy at one institution in November 1998–January 2005. We also tested whether the TGF-β1 rs1982073 (T+29C) SNP affected the migration and invasion of A549 and PC9 lung cancer cells.

Results

Median follow-up time for all patients was 17 months (range, 1–97 months; 39 months for patients alive at the time of analysis). Multivariate analysis showed that the TGFβ1 rs1800469 CT/CC genotype was associated with poor OS (hazard ratio [HR] = 1.463 [95% confidence interval {CI} = 1.012–2.114], P = 0.043) and shorter DMFS (HR = 1.601 [95% CI = 1.042–2.459], P = 0.032) and that the TGFβ1 rs1982073 CT/CC genotype predicted poor DMFS (HR = 1.589 [95% CI = 1.009–2.502], P = 0.046) and poor brain MFS (HR = 2.567 [95% CI = 1.155–5.702], P = 0.021) after adjustment for age, sex, race, performance status, smoking status, tumor histology and volume, stage, receipt of concurrent radiochemotherapy, number of chemotherapy cycles, and radiation dose. Transfection with TGFβ1+29C (vs. +29T) stimulated the migration and invasion of A549 and PC9 cells, suggesting that TGFβ1+29C may be linked with increased metastatic potential.

Conclusions

TGFβ1 genotypes at rs1800469 and rs1982073 could be useful for predicting DMFS among patients with NSCLC treated with definitive radiation therapy. These findings require validation in larger prospective trials and thorough mechanistic studies.

Activin-A in diabetes-induced cardiac malformations in embryos

BACKGROUND

Heart defects are the most common abnormalities in infants of diabetic mothers. Cardiac malformation is associated with altered expression of the genes in the transforming growth factor β system, including inhibin βA, which forms activin-A as a homodimer and functions through its effectors, Smad2 and Smad3. This study aimed to investigate the role of activin-A in diabetes-induced cardiac malformations.

METHODS

Diabetes mellitus in female mice (C57BL/6J) was induced via intravenous injection of streptozotocin. The expression of inhibin βA protein and phosphorylation of Smad2 and Smad3 in the embryonic hearts were examined using immunohistochemical, in situ proximity ligation, and immunoblot assays. Embryos and endocardial cushions of nondiabetic mice were cultured in a high concentration of glucose and treated with activin-A. Mitosis was examined using BrdU incorporation assay and immunohistochemistry of phosphorylated histone H3. Migration of the endocardial cells was assessed using a collagen-based cell migration assay.

RESULTS

The levels of inhibin βA expression and Smad2 and Smad3 activation were significantly reduced by maternal diabetes. Treatment with activin-A significantly increased cell proliferation in the myocardium and migration of endocardial cells, compared with those in vehicle-treated high glucose group, to the level in the euglycemic control group.

CONCLUSIONS

Maternal diabetes suppresses the expression of inhibin βA protein, as well as the activation of Smad2 and Smad3. Activin-A rescues cell proliferation in the myocardium and migration of the endocardial cells suppressed by hyperglycemia. The activin-Smad2/3 signaling system appears to play a role in cardiac malformation in diabetic embryopathy.

Development of a small-molecule screening method for inhibitors of cellular response to myostatin and activin A

Myostatin, a member of the transforming growth factor (TGF)-β family of secreted ligands, is a strong negative regulator of muscle growth. As such, therapeutic inhibitors of myostatin are actively being investigated for their potential in the treatment of muscle-wasting diseases such as muscular dystrophy and sarcopenia. Here, we sought to develop a high-throughput screening (HTS) method for small-molecule inhibitors that target myostatin. We created a HEK293 stable cell line that expresses the (CAGA)12-luciferase reporter construct and robustly responds to signaling of certain classes of TGF-β family ligands. After optimization and miniaturization of the assay to a 384-well format, we successfully screened a library of compounds for inhibition of myostatin and the closely related activin A. Selection of some of the tested compounds was directed by in silico screening against myostatin, which led to an enrichment of target hits as compared with random selection. Altogether, we present an HTS method that will be useful for screening potential inhibitors of not only myostatin but also many other ligands of the TGF-β family.

Insulin resistance and the polycystic ovary syndrome revisited: an update on mechanisms and implications

Polycystic ovary syndrome (PCOS) is now recognized as an important metabolic as well as reproductive disorder conferring substantially increased risk for type 2 diabetes. Affected women have marked insulin resistance, independent of obesity. This article summarizes the state of the science since we last reviewed the field in the Endocrine Reviews in 1997. There is general agreement that obese women with PCOS are insulin resistant, but some groups of lean affected women may have normal insulin sensitivity. There is a post-binding defect in receptor signaling likely due to increased receptor and insulin receptor substrate-1 serine phosphorylation that selectively affects metabolic but not mitogenic pathways in classic insulin target tissues and in the ovary. Constitutive activation of serine kinases in the MAPK-ERK pathway may contribute to resistance to insulin's metabolic actions in skeletal muscle. Insulin functions as a co-gonadotropin through its cognate receptor to modulate ovarian steroidogenesis. Genetic disruption of insulin signaling in the brain has indicated that this pathway is important for ovulation and body weight regulation. These insights have been directly translated into a novel therapy for PCOS with insulin-sensitizing drugs. Furthermore, androgens contribute to insulin resistance in PCOS. PCOS may also have developmental origins due to androgen exposure at critical periods or to intrauterine growth restriction. PCOS is a complex genetic disease, and first-degree relatives have reproductive and metabolic phenotypes. Several PCOS genetic susceptibility loci have been mapped and replicated. Some of the same susceptibility genes contribute to disease risk in Chinese and European PCOS populations, suggesting that PCOS is an ancient trait.

Inhibition of breast cancer metastases by a novel inhibitor of TGFβ receptor 1

BACKGROUND

Transforming growth factor beta (TGFβ), which is implicated in metastasis to various organs in breast cancer, is a potential target for new antitumor metastasis drugs.

METHODS

To identify specific inhibitors of TGFβ receptor 1 (TGFβR1) in breast cancer metastasis, a virtual library of more than 400000 different compounds was screened by molecular docking modeling and confirmed with Smad-binding element luciferase and TGFβR1 kinase assays. Affymetrix GeneChip expression analysis of mRNA levels and real-time polymerase chain reaction were performed to determine expression changes of TGFβ-mediated, metastasis-associated genes in breast cancer cells after treatment with the small-molecule inhibitor YR-290. YR-290 was also examined for its effects on breast cancer migration, invasion, and metastasis using transwell and epithelial-to-mesenchymal transition (EMT) assays in vitro and three different mouse (BALB/c and NU/NU nude) models (n = 10 per group). Kaplan-Meier analyses were used to assess survival. All statistical tests were two-sided.

RESULTS

YR-290 interacted with the kinase domain of TGFβR1, abrogated kinase activity (half maximal inhibitory concentration = 137nM, 95% confidence interval = 126.4 to 147.6nM) and inhibited the TGFβ-mediated downstream signaling pathway and metastasis-associated genes in breast cancer cells. YR-290 inhibited TGFβ-modulated breast cancer cell migration and invasion. In tumor metastasis mouse models, YR-290 almost completely blocked cancer metastasis. Numbers of lung tumor nodules of mice treated with 1mg/kg and 5mg/kg YR-290 were reduced by 74.93% (95% confidence interval = 61.45% to 88.41%) and 94.93% (95% confidence interval = 82.13% to 100%), respectively, compared with control mice. Treatment with YR-290 also statistically significantly prolonged the survival of tumor-bearing mice.

CONCLUSIONS

YR-290 is a novel inhibitor of tumor metastasis that works by blocking TGFβ signaling pathways.

Activins in adipogenesis and obesity

Activins are secreted proteins members of the transforming growth factor-β family. They are involved in many biological responses including regulation of apoptosis, proliferation and differentiation of different cell types. Activins A, B and AB are highly expressed in adipose tissue, and in this review we will illustrate that activins have a role in several steps of physiological and pathological development of adipose tissue. Activin A has been shown to be a critical regulator of human adipocyte progenitor proliferation and a potent inhibitor of their differentiation. Activin A could also be a mediator of fibrosis observed in obese adipose tissue. Activin B/AB is proposed as a new adipokine having a role in energy balance and insulin insensitivity associated with obesity. Therefore, activin pathway could represent a potential therapeutic target both for controlling the size and the phenotype of the adipose precursor pool and for obesity-associated metabolic complications.

Endoplasmic reticulum stress in maternal diabetes-induced cardiac malformations during critical cardiogenesis period

BACKGROUND

Cardiac abnormalities, including atrioventricular (AV) septal defects (AVSDs), are the most common birth defects in diabetic embryopathy. The AV septum is derived from the endocardial cushions, which undergo development and remodeling during septation. The impact of maternal diabetes on these processes needs to be identified. Maternal diabetes disturbs the function of the endoplasmic reticulum (ER). The role of ER stress in cardiac malformation remains to be delineated to gain information for developing therapy.

METHODS

Female mice were induced diabetic via intravenous injection of streptozotocin. Pregnant mice were made hyperglycemic at desired embryonic (E) days. AVSDs were examined histologically at E15.5. ER stress-associated factors were examined and quantified using immunohistochemical and immunoblot assays at E10.5. The role of ER stress in endocardial cell migration was investigated by treating endocardial cushion explants that were cultured in high glucose with an organic chaperone molecule, sodium 4-phenylbutyrate.

RESULTS

The rate of AVSDs in the embryos that were exposed to maternal hyperglycemia during the period of endocardial cushion development was significantly higher than that in those during endocardial cushion remodeling. ER stress was increased in the hearts. Amelioration of ER stress restored endocardial cell migration under hyperglycemic conditions.

CONCLUSIONS

The development, rather than remodeling, of the endocardial cushions is the cardiomorphogenic process that is susceptible to the insult of maternal hyperglycemia in the formation of AVSDs. Maternal diabetes increases ER stress in the developing heart. ER stress plays an essential role in mediating the effect of hyperglycemia on endocardial cell migration.

Increase in tumour permeability following TGF-beta type I receptor-inhibitor treatment observed by dynamic contrast-enhanced MRI

Background:

To enhance the success rate of nanocarrier-mediated chemotherapy combined with an anti-angiogenic agent, it is crucial to identify parameters for tumour vasculature that can predict a response to the treatment of the anti-angiogenic agent.

Methods:

To apply transforming growth factor (TGF)-β type I receptor (TβR-I) inhibitor, A-83-01, to combined therapy, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was carried out in mice bearing colon 26 cells using gadolinium (Gd)-DTPA and for its liposomal formulation to evaluate changes in tumour microvasculature following A-83-01. Tumour vascular parameters from DCE-MRI were compared with histological assessment and apparent diffusion coefficient of water in tumour generated by diffusion-weighted MRI.

Results:

Contrary to evaluations reported for anti-angiogenic agents, A-83-01 treatment increased the initial area under the Gd concentration–time curve (IAUGC₆₀), volume transfer constant (K^trans) and fractional plasma volume (v_p) significantly within 24 h, that was positively related to α-smooth muscle actin-positive pericyte coverage and tumour cell proliferation, and was correlated inversely with the apparent diffusion coefficient. The vascular function of the tumour improved by A-83-01 treatment was well assessed on post-liposomal Gd-DTPA-enhanced MR images, which predicted delivery of a liposomal drug to the tumour.

Conclusion:

These findings suggest that DCE-MRI and, in particular, K^trans and v_p quantitation, provide important additional information about tumour vasculature by A-83-01 treatment.

Imatinib mesylate ameliorates the dystrophic phenotype in exercised mdx mice

Myofiber degeneration, inflammation, and fibrosis are remarkable features of Duchenne muscular dystrophy. We hypothesized that the administration of imatinib mesylate, an inhibitor of tyrosine kinase and TGF-beta pro-fibrogenic activity, could improve the muscular conditions in mdx mice. Four-week old mdx mice were treated and exercised for 6 weeks. Gastrocnemius and diaphragm histopathology, strength, creatine kinase, and cytokine levels were evaluated. The treated group presented increased muscular strength and decreased CK levels, injured myofibers, and inflammatory infiltrates. Pro-inflammatory cytokines and TGF-beta were also reduced, while IL-10 was increased, suggesting an immunomodulatory effect of imatinib, which can ameliorate the dystrophic phenotype in mdx mice.

Doxorubicin inhibits TGF-beta signaling in human lung carcinoma A549 cells

Doxorubicin is a DNA-damaging drug, commonly used for treatment of cancer patients. Doxorubicin causes not only cytotoxic and cytostatic effects, but also inhibits metastasis formation, while TGFbeta1 (Transforming Growth Factor-beta1) is a cytokine that is often up-regulated in human cancers and can promote metastasis formation. We have studied the influence of Doxorubicin on TGFbeta signaling in tumor cells. Here we have demonstrated that Doxorubicin inhibited TGFbeta-signaling in human lung adenocarcinoma A549 cells, namely, it blocked TGFbeta1-induced activation of Smad3-responsive CAGA(12)-Luc reporter, but did not affect c-myc-Luc reporter. That effect was observed as early as after 1-3 h of treating these cells with Doxorubicin, while the other drugs cisplatin or methotrexate did not alter activation of CAGA(12)-Luc reporter under the same conditions. Besides, after 1 h action, Doxorubicin abrogated TGFbeta-induced translocation of Smad3-protein from the cytoplasm to the nucleus. Down-regulation of expression of Smad2, Smad3, and Smad4 proteins, and up-regulation of inhibitory Smad7 protein upon Doxorubicin treatment, were found after 12-24 h of Doxorubicin treatment. Phosphorylation of Smad2/3 proteins was also affected by Doxorubicin. Summarizing, we have found that human tumor cells treatment with Doxorubicin resulted in the inhibition of TGFbeta-signaling at both early (1 h) and later (12 h) stages of the drug action. Such inhibition can be a new potential mechanism for Doxorubicin action towards tumor cells.

Signal transduction pathway through activin receptors as a therapeutic target of musculoskeletal diseases and cancer

Activin, myostatin and other members of the TGF-beta superfamily signal through a combination of type II and type I receptors, both of which are transmembrane serine/threonine kinases. Activin type II receptors, ActRIIA and ActRIIB, are primary ligand binding receptors for activins, nodal, myostatin and GDF11. ActRIIs also bind a subset of bone morphogenetic proteins (BMPs). Type I receptors that form complexes with ActRIIs are dependent on ligands. In the case of activins and nodal, activin receptor-like kinases 4 and 7 (ALK4 and ALK7) are the authentic type I receptors. Myostatin and GDF11 utilize ALK5, although ALK4 could also be activated by these growth factors. ALK4, 5 and 7 are structurally and functionally similar and activate receptor-regulated Smads for TGF-beta, Smad2 and 3. BMPs signal through a combination of three type II receptors, BMPRII, ActRIIA, and ActRIIB and four type I receptors, ALK1, 2, 3, and 6. BMPs activate BMP-specific Smads, Smad1, 5 and 8. Smad proteins undergo multimerization with co-mediator Smad, Smad4, and translocated into the nucleus to regulate the transcription of target genes in cooperation with nuclear cofactors. The signal transduction pathway through activin type II receptors, ActRIIA and ActRIIB, with type I receptors is involved in various human diseases. In this review, we discuss the role of signaling through activin receptors as therapeutic targets of intractable neuromuscular diseases, endocrine disorders and cancers.

Pathobiology of transforming growth factor beta in cancer, fibrosis and immunologic disease, and therapeutic considerations

Transforming growth factor beta (TGF-beta) is a highly pleiotropic cytokine that plays an important role in wound healing, angiogenesis, immunoregulation and cancer. The cells of the immune system produce the TGF-beta1 isoform, which exerts powerful anti-inflammatory functions, and is a master regulator of the immune response. However, this is context dependent, because TGF-beta can contribute to the differentiation of both regulatory (suppressive) T cells (Tr cells) and inflammatory Th17 cells. While TGF-beta might be underproduced in some autoimmune diseases, it is overproduced in many pathological conditions. This includes pulmonary fibrosis, glomerulosclerosis, renal interstitial fibrosis, cirrhosis, Crohn's disease, cardiomyopathy, scleroderma and chronic graft-vs-host disease. In neoplastic disease, TGF-beta suppresses the progression of early lesions, but later this effect is lost and cancer cells produce TGF-beta, which then promotes metastasis. This cytokine also contributes to the formation of the tumor stroma, angiogenesis and immunosuppression. In view of this, several approaches are being studied to inhibit TGF-beta activity, including neutralizing antibodies, soluble receptors, receptor kinase antagonist drugs, antisense reagents and a number of less specific drugs such as angiotensin II antagonists and tranilast. It might be assumed that TGF-beta blockade would result in severe inflammatory disease, but this has not been the case, presumably because the neutralization is only partial. In contrast, the systemic administration of TGF-beta for therapeutic purposes is limited by toxicity and safety concerns, but local administration appears feasible, especially to promote wound healing. Immunotherapy or vaccination stimulating TGF-beta production and/or Tr differentiation might be applied to the treatment of autoimmune diseases. The benefits of new therapies targeting TGF-beta are under intense investigation.