c-Ski inhibits the TGF-beta signaling pathway through stabilization of inactive Smad complexes on Smad-binding elements

Repression of SMAD3 by STAT3 and c-Ski induces conventional dendritic cell differentiation

A pleiotropic immunoregulatory cytokine, TGF-β, signals via the receptor-regulated SMADs: SMAD2 and SMAD3, which are constitutively expressed in normal cells. Here, we show that selective repression of SMAD3 induces cDC differentiation from the CD115+ common DC progenitor (CDP). SMAD3 was expressed in haematopoietic cells including the macrophage DC progenitor. However, SMAD3 was specifically down-regulated in CD115+ CDPs, SiglecH- pre-DCs, and cDCs, whereas SMAD2 remained constitutive. SMAD3-deficient mice showed a significant increase in cDCs, SiglecH- pre-DCs, and CD115+ CDPs compared with the littermate control. SMAD3 repressed the mRNA expression of FLT3 and the cDC-related genes: IRF4 and ID2. We found that one of the SMAD transcriptional corepressors, c-SKI, cooperated with phosphorylated STAT3 at Y705 and S727 to repress the transcription of SMAD3 to induce cDC differentiation. These data indicate that STAT3 and c-Ski induce cDC differentiation by repressing SMAD3: the repressor of the cDC-related genes during the developmental stage between the macrophage DC progenitor and CD115+ CDP.

Nucleotide substitutions at the p.Gly117 and p.Thr180 mutational hot-spots of SKI alter molecular dynamics and may affect cell cycle

Heterozygous deleterious variants in SKI cause Shprintzen-Goldberg Syndrome, which is mainly characterized by craniofacial features, neurodevelopmental disorder and thoracic aorta dilatations/aneurysms. The encoded protein is a member of the transforming growth factor beta signaling. Paucity of reported studies exploring the SGS molecular pathogenesis hampers disease recognition and clinical interpretation of private variants. Here, the unpublished c.349G>A, p.[Gly117Ser] and the recurrent c.539C>T, p.[Thr180Met] SKI variants were studied combining in silico and in vitro approach. 3D comparative modeling and calculation of the interaction energy predicted that both variants alter the SKI tertiary protein structure and its interactions. Computational data were functionally corroborated by the demonstration of an increase of MAPK phosphorylation levels and alteration of cell cycle in cells expressing the mutant SKI. Our findings confirmed the effects of SKI variants on MAPK and opened the path to study the role of perturbations of the cell cycle in SGS.

Honokiol inhibits epithelial-mesenchymal transition and hepatic fibrosis via activation of Ecadherin/GSK3β/JNK and inhibition of AKT/ERK/p38/β-catenin/TMPRSS4 signaling axis

Though Honokiol was known to have anti-inflammatory, antioxidant, anticancer, antithrombotic, anti-viral, metabolic, antithrombotic, and neurotrophic activities, the underlying mechanisms of Honokiol on epithelial-mesenchymal transition (EMT) mediated liver fibrosis still remain elusive so far. Anti-EMT and antifibrotic effects of Honokiol were explored in murine AML-12 hepatocyte cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, wound healing assay, Western blotting and also in CCl4-induced liver injury mouse model by immunohistochemistry. Honokiol significantly suppressed transforming growth factor β1 (TGF-β1)-induced EMT and migration of AML-12 cells along with decreased EMT phenotypes such as loss of cell adhesion and formation of fibroblast like mesenchymal cells in TGF-β1-treated AML-12 cells. Consistently, Honokiol suppressed the expression of Snail and transmembrane protease serine 4 (TMPRSS4), but not p-Smad3, and activated E-cadherin in TGF-β1-treated AML-12 cells. Additionally, Honokiol reduced the expression of β-catenin, p-AKT, p-ERK, p-p38 and increased phosphorylation of glycogen synthase kinase 3 beta (GSK3β) and JNK in TGF-β1-treated AML-12 cells via TGF-β1/nonSmad pathway. Conversely, GSK3β inhibitor SB216763 reversed the ability of Honokiol to reduce Snail, β-catenin and migration and activate E-cadherin in TGF-β1-treated AML-12 cells. Also, Honokiol suppressed hepatic steatosis and necrosis by reducing the expression of TGF-β1 and α-SMA in liver tissues of CCl4 treated mice. These findings provide scientific evidence that Honokiol suppresses EMT and hepatic fibrosis via activation of E-cadherin/GSK3β/JNK and inhibition of AKT/ERK/p38/β-catenin/TMPRSS4 signaling axis.

Apigenin inhibits isoproterenol‐induced myocardial fibrosis and Smad pathway in mice by regulating oxidative stress and miR‐122‐5p/155‐5p expressions

Apigenin, a flavonoid isolated from Apium graveolens, is an effective natural active ingredient that inhibits transforming growth factor-β1 (TGF-β1)-induced cardiac fibroblasts (CFs) differentiation and collagen synthesis. However, its effects on isoproterenol-induced myocardial fibrosis in mice remain unknown. This study aimed to examine the effect of apigenin in the prevention of myocardial fibrosis. A mouse model of myocardial fibrosis induced by isoproterenol was established, and the mice were given apigenin 75-300 mg/kg orally for 40 days. The results showed that the heart weight coefficient, myocardial hydroxyproline, collagen accumulation, and malondialdehyde levels in the apigenin-treated groups were significantly reduced. In contrast, the activity of myocardial superoxide dismutase and glutathione peroxidase were significantly enhanced. The results of real-time quantitative polymerase chain reaction and western blot assays showed that apigenin could significantly upregulate the expressions of myocardial microRNA-122-5p (miR-122-5p), c-Ski, and Smad7 and downregulate the expressions of myocardial miR-155-5p, α-smooth muscle actin, collagen I/III, NF-κB, TGF-β1, hypoxia-inducible factor-1α (HIF-1α), Smad2/3, and p-Smad2/3. In vitro, the differentiation and extracellular matrix production, as well as TGF-β1/Smads axis, were further reduced after treatment of miR-122-5p mimic or miR-155-5p inhibitor-transfected and TGF-β1-stimulated CFs with apigenin. These results suggested that apigenin increased the expression of miR-122-5p and decreased the expression of miR-155-5p, which subsequently downregulated and upregulated the target genes HIF-1α and c-Ski, respectively. Furthermore, apigenin administration downregulated TGF-β1-induced Smad2/3 and upregulated Smad7. In addition, it reduced the NF-κB/TGF-β1 signaling pathway axis by increasing antioxidant ability to exert the antifibrotic effects.

Ski regulates proliferation and migration of reactive astrocytes induced by lipopolysaccharide (LPS) through PI3K/Akt pathway

Spinal cord injury (SCI) is a leading cause of disability and death worldwide. Reactive astrogliosis, a typical feature of SCI, undergoes various molecular and morphological changes and contributes to glial scar formation, which impedes axonal regeneration. Ski is a novel molecule that regulates the biological characteristics of astrocytes after spinal cord injury, but its function and the exact mechanism of its overexpression in reactive astrocyte proliferation and migration after SCI remain unclear. The purpose of this study was to elucidate the effect and mechanism of Ski on the proliferation and migration of reactive astrocytes, and to regulate the spatiotemporal formation of glial scars after SCI. In an in vitro lipopolysaccharide (LPS)-induced astrocyte injury model, the expression of Ski was upregulated in a time-dependent manner in LPS-induced astrocytes, and the upregulation of Ski was accompanied by that of PCNA, CDK4, CyclinD1, and other proliferation-related proteins. Our findings suggest that Ski promotes the proliferation and migration of reactive astrocytes. Next, astrocytes were transfected with a specific lentivirus to cause the overexpression of Ski, which significantly enhanced the proliferation and migration of reactive astrocytes and LPS-induced activation of the PI3K/Akt pathway. The PI3K/Akt pathway inhibitor LY294002 significantly inhibited the proliferation and migration of LPS-induced reactive astrocytes after Ski overexpression. In conclusion, Ski regulates LPS-induced astrocyte proliferation and migration through the PI3K/Akt pathway, making Ski a promising target for strategies to combat glial scarring after SCI.

Jiangtang Tongmai Prescription Reduced Diabetic Lung Injury Through SnoN and TGF-β1/Smads Signaling Pathway

By establishing a rat diabetes model in rats with intervening treatment by Jiangtang Tongmai Prescription (JTTMP), this study explored the restorative pairing effect of JTTMP on diabetic lung injury. The model of type II diabetes model was used to establish the rat diabetes model, using a high-fat diet and streptozotocin (STZ) induction. Different doses of JTTMP and metformin were administered as a therapeutic to intervene, and blood was collected to assess the blood glucose level of each group of rats. HE (Hematoxylin and eosin (H&E) staining was performed to detect the morphological changes in rat lung tissue and enzyme-linked immunoassay ELISA was used to detect and quantify the expression of interleukin (IL)-6, TNF tumor necrosis factor-ɑa, and IL-1β in serum and the lung tissue of each group of rats. The level expression of TGF-β1 [transforming growth factor (TGF)-β1), SnoN (transcriptional co-repressor Ski-N terminal (SnoN)], Smad2, Smad3, Smad7, and other signaling pathway proteins were assessed by Western blot. In comparison with the normal control (NC) group, rats in the diabetes model (DM) group lost weight and showed significantly increased blood sugar levels. The levels of TGF-β1 and Smad2/3 were increased in the DM group but Smad7 decreased. After 8 weeks of JTTMP intervention, the level of TGF-β1 and Smad2/3 decreased but Smad7 increased, blood sugar decreased significantly and the expression of inflammatory factors in lung tissue decreased. Therefore, JTTMP may activate SnoN and the downstream TGF-β1/Smads signaling pathway to repair diabetic lung injury, which suggests its application has potential for future clinical treatment of diabetes with lung injury.

Intersecting single-cell transcriptomics and genome-wide association studies identifies crucial cell populations and candidate genes for atherosclerosis

Aims

Genome-wide association studies (GWASs) have discovered hundreds of common genetic variants for atherosclerotic disease and cardiovascular risk factors. The translation of susceptibility loci into biological mechanisms and targets for drug discovery remains challenging. Intersecting genetic and gene expression data has led to the identification of candidate genes. However, previously studied tissues are often non-diseased and heterogeneous in cell composition, hindering accurate candidate prioritization. Therefore, we analysed single-cell transcriptomics from atherosclerotic plaques for cell-type-specific expression to identify atherosclerosis-associated candidate gene–cell pairs.

Methods and results

We applied gene-based analyses using GWAS summary statistics from 46 atherosclerotic and cardiovascular disease, risk factors, and other traits. We then intersected these candidates with single-cell RNA sequencing (scRNA-seq) data to identify genes specific for individual cell (sub)populations in atherosclerotic plaques. The coronary artery disease (CAD) loci demonstrated a prominent signal in plaque smooth muscle cells (SMCs) (SKI, KANK2, and SORT1) P-adj. = 0.0012, and endothelial cells (ECs) (SLC44A1, ATP2B1) P-adj. = 0.0011. Finally, we used liver-derived scRNA-seq data and showed hepatocyte-specific enrichment of genes involved in serum lipid levels.

Conclusion

We discovered novel and known gene–cell pairs pointing to new biological mechanisms of atherosclerotic disease. We highlight that loci associated with CAD reveal prominent association levels in mainly plaque SMC and EC populations. We present an intuitive single-cell transcriptomics-driven workflow rooted in human large-scale genetic studies to identify putative candidate genes and affected cells associated with cardiovascular traits. Collectively, our workflow allows for the identification of cell-specific targets relevant for atherosclerosis and can be universally applied to other complex genetic diseases and traits.

MAB21L4 regulates the TGF-β-induced expression of target genes in epidermal keratinocytes

Smad proteins transduce signals downstream of transforming growth factor-β (TGF-β) and are one of the factors that regulate the expression of genes related to diseases affecting the skin. In the present study, we identified MAB21L4, also known as male abnormal 21 like 4 or C2orf54, as the most up-regulated targets of TGF-β and Smad3 in differentiated human progenitor epidermal keratinocytes using chromatin immunoprecipitation sequencing (ChIP-seq) and RNA sequencing (RNA-seq). We found that TGF-β induced expression of the barrier protein involucrin (encoded by the IVL gene). Transcriptional activity of the IVL promoter induced by TGF-β was inhibited by MAB21L4 siRNAs. Further analysis revealed that MAB21L4 siRNAs also down-regulated the expression of several target genes of TGF-β. MAB21L4 protein was located mainly in the cytosol, where it was physically bound to Smad3 and a transcriptional corepressor c-Ski. siRNAs for MAB21L4 did not inhibit the binding of Smad3 to their target genomic regions but down-regulated the acetylation of histone H3 lys 27 (H3K27ac), an active histone mark, near the Smad3 binding regions. These findings suggest that TGF-β-induced MAB21L4 up-regulates the gene expression induced by TGF-β, possibly through the inhibition of c-Ski via physical interaction in the cytosol.

miR-155 promotes T reg cell development by safeguarding medullary thymic epithelial cell maturation

During thymocyte development, medullary thymic epithelial cells (mTECs) provide appropriate instructive cues in the thymic microenvironment for not only negative selection but also the generation of regulatory T (T reg) cells. Here, we identify that miR-155, a microRNA whose expression in T reg cells has previously been shown to be crucial for their development and homeostasis, also contributes to thymic T reg (tT reg) cell differentiation by promoting mTEC maturation. Mechanistically, we show that RANKL stimulation induces expression of miR-155 to safeguard the thymic medulla through targeting multiple known and previously uncharacterized molecules within the TGFβ signaling pathway, which is recognized for its role in restricting the maturation and expansion of mTECs. Our work uncovers a miR-155–TGFβ axis in the thymic medulla to determine mTEC maturity and, consequently, the quantity of tT reg cells and suggests that miR-155 ensures proper tT reg cell development in both cell-intrinsic and -extrinsic manners.

Decreased phosphorylation facilitates the degradation of the endogenous protective molecule c-Ski in vascular smooth muscle cells

The dysfunction of vascular smooth muscle cells (VSMCs) is critical for atherosclerosis (AS) progression. Autophagy is indispensable during phenotypic switching and proliferation of VSMCs, contribute to AS development. Cellular Sloan-Kettering Institute (c-Ski), the repressor of TGF-β signaling, is involved in diverse physiological and pathological processes. We previously defined c-Ski also as an endogenous protective molecule against AS via inhibiting abnormal proliferation and autophagy of VSMCs. However, the endogenous level of c-Ski in VSMCs is markedly decreased during the progression of AS, so that the protective effect is drastically weakened. Elucidating the molecular mechanisms is key to the understanding of AS development and treatment. We determined that oxidized low-density lipoprotein (ox-LDL) and platelet-derived growth factor (PDGF) directly induced the degradation of c-Ski protein, closely associated with reducing its phosphorylation. Serine₃₈₃ (S383) was identified as the crucial phosphorylation site for stabilizing protein expression and nuclear location of c-Ski, which was responsible for its transcriptional suppression of autophagy-related genes. Decreased S383 phosphorylation facilitated nuclear export and degradation of c-Ski, thereby lessened its inhibitory effect on induction of autophagy genes. These findings provide a novel view of c-Ski modification and function modulation under some vascular injury factors, which point to a new potential therapeutic strategy by targeting c-Ski.

The Epithelial-to-Mesenchymal Transition as a Possible Therapeutic Target in Fibrotic Disorders

Fibrosis is a chronic and progressive disorder characterized by excessive deposition of extracellular matrix, which leads to scarring and loss of function of the affected organ or tissue. Indeed, the fibrotic process affects a variety of organs and tissues, with specific molecular background. However, two common hallmarks are shared: the crucial role of the transforming growth factor-beta (TGF-β) and the involvement of the inflammation process, that is essential for initiating the fibrotic degeneration. TGF-β in particular but also other cytokines regulate the most common molecular mechanism at the basis of fibrosis, the Epithelial-to-Mesenchymal Transition (EMT). EMT has been extensively studied, but not yet fully explored as a possible therapeutic target for fibrosis. A deeper understanding of the crosstalk between fibrosis and EMT may represent an opportunity for the development of a broadly effective anti-fibrotic therapy. Here we report the evidences of the relationship between EMT and multi-organ fibrosis, and the possible therapeutic approaches that may be developed by exploiting this relationship.

Transforming Growth Factor-β and the Renin-Angiotensin System in Syndromic Thoracic Aortic Aneurysms: Implications for Treatment

Thoracic aortic aneurysms (TAAs) are permanent pathological dilatations of the thoracic aorta, which can lead to life-threatening complications, such as aortic dissection and rupture. TAAs frequently occur in a syndromic form in individuals with an underlying genetic predisposition, such as Marfan syndrome (MFS) and Loeys-Dietz syndrome (LDS). Increasing evidence supports an important role for transforming growth factor-β (TGF-β) and the renin-angiotensin system (RAS) in TAA pathology. Eventually, most patients with syndromic TAAs require surgical intervention, as the ability of present medical treatment to attenuate aneurysm growth is limited. Therefore, more effective medical treatment options are urgently needed. Numerous clinical trials investigated the therapeutic potential of angiotensin receptor blockers (ARBs) and β-blockers in patients suffering from syndromic TAAs. This review highlights the contribution of TGF-β signaling, RAS, and impaired mechanosensing abilities of aortic VSMCs in TAA formation. Furthermore, it critically discusses the most recent clinical evidence regarding the possible therapeutic benefit of ARBs and β-blockers in syndromic TAA patients and provides future research perspectives and therapeutic implications.

Ski: Double roles in cancers

The Ski (Sloan-Kettering Institute) is an evolutionarily conserved protein that plays a dual role as an oncoprotein and tumor suppressor gene in the development of human cancer. The Ski oncogene was first identified as a transforming protein of the avian Sloan-Kettering retrovirus in 1986. Since its discovery, Ski has been identified as a carcinogenic regulator in a variety of malignant tumors. Later, it was reported that Ski regulates the occurrence and development of some cancers by acting as an oncogene. Ski mediates the proliferation, differentiation, metastasis, and invasion of numerous cancer cells through various mechanisms. Several studies have shown that Ski expression is correlated with the clinical characteristics of cancer patients and is a promising biomarker and therapeutic target for cancer. In this review, we summarize the mechanisms and potential clinical implications of Ski in dimorphism, cancer occurrence, and progression in various types of cancer.

Histone deacetylase inhibitors promote epithelial-mesenchymal transition in Hepatocellular Carcinoma via AMPK-FOXO1-ULK1 signaling axis-mediated autophagy

Hepatocellular carcinoma (HCC) is the third most frequent cause of cancer-related deaths globally because of high metastasis and recurrence rates. Elucidating the molecular mechanisms of HCC recurrence and metastasis and developing effective targeted therapies are expected to improve patient survival. The promising anti-cancer agents for the treatment of hematological malignancies, histone deacetylase inhibitors (HDIs), have limited effects against epithelial cell-derived cancers, including HCC, the mechanisms involved have not been elucidated. Herein, we studied the molecular mechanisms underlying HDI-induced epithelial-mesenchymal transition (EMT) involving FOXO1-mediated autophagy. Methods: The biological functions of HDIs in combination with autophagy inhibitors were examined both in vitro and in vivo. Cell autophagy was assessed using the generation of mRFP-GFP-LC3-expressing cells and fluorescent LC3 puncta analysis, Western blotting, and electron microscopy. An orthotopic hepatoma model was established in mice for the in vivo experiments. Results: Our study provided novel mechanistic insights into HDI-induced EMT mediated by the autophagy AMPK-FOXO1-ULK1-Snail signaling axis. We demonstrated that autophagy served as a pro-metastasis mechanism in HDI-treated hepatoma cells. HDIs induced autophagy via a FOXO1-dependent pathway, and FOXO1 inhibition promoted HDI-mediated apoptosis in hepatoma cells. Thus, our findings provided novel insights into the molecular mechanisms underlying HDI-induced EMT involving FOXO1-mediated autophagy and demonstrated that a FOXO1 inhibitor exerted a synergistic effect with an HDI to inhibit cell growth and metastasis in vitro and in vivo. Conclusion: We demonstrated that HDIs triggers FOXO1-dependent autophagy, which ultimately promotes EMT, limiting the clinical outcome of HDI-based therapies. Our study suggests that the combination of an HDI and a FOXO1 inhibitor is an effective therapeutic strategy for the treatment of HCC.

Effect of c-Ski on atrial remodelling in a rapid atrial pacing canine model

Atrial fibrosis is an important factor in the initiation and maintenance of atrial fibrillation (AF); therefore, understanding the pathogenesis of atrial fibrosis may reveal promising therapeutic targets for AF. In this study, we successfully established a rapid atrial pacing canine model and found that the inducibility and duration of AF were significantly reduced by the overexpression of c‐Ski, suggesting that this approach may have therapeutic effects. c‐Ski was found to be down‐regulated in the atrial tissues of the rapid atrial pacing canine model. We artificially up‐regulated c‐Ski expression with a c‐Ski–overexpressing adenovirus. Haematoxylin and eosin, Masson's trichrome and picrosirius red staining showed that c‐Ski overexpression alleviated atrial fibrosis. Furthermore, we found that the expression levels of collagen III and α‐SMA were higher in the groups of dogs subjected to right‐atrial pacing, and this increase was attenuated by c‐Ski overexpression. In addition, c‐Ski overexpression decreased the phosphorylation of smad2, smad3 and p38 MAPK (p38α and p38β) as well as the expression of TGF‐β1 in atrial tissues, as shown by a comparison of the right‐atrial pacing + c‐Ski‐overexpression group to the control group with right‐atrial pacing only. These results suggest that c‐Ski overexpression improves atrial remodelling in a rapid atrial pacing canine model by suppressing TGF‐β1–Smad signalling and p38 MAPK activation.

Transformation of the Transcriptomic Profile of Mouse Periocular Mesenchyme During Formation of the Embryonic Cornea

Purpose

Defects in neural crest development are a major contributing factor in corneal dysgenesis, but little is known about the genetic landscape during corneal development. The purpose of this study was to provide a detailed transcriptome profile and evaluate changes in gene expression during mouse corneal development.

Methods

RNA sequencing was used to uncover the transcriptomic profile of periocular mesenchyme (pNC) isolated at embryonic day (E) 10.5 and corneas isolated at E14.5 and E16.5. The spatiotemporal expression of several differentially expressed genes was validated by in situ hybridization.

Results

Analysis of the whole-transcriptome profile between pNC and embryonic corneas identified 3815 unique differentially expressed genes. Pathway analysis revealed an enrichment of differentially expressed genes involved in signal transduction (retinoic acid, transforming growth factor-β, and Wnt pathways) and transcriptional regulation.

Conclusions

Our analyses, for the first time, identify a large number of differentially expressed genes during progressive stages of mouse corneal development. Our data provide a comprehensive transcriptomic profile of the developing cornea. Combined, these data serve as a valuable resource for the identification of novel regulatory networks crucial for the advancement of studies in congenital defects, stem cell therapy, bioengineering, and adult corneal diseases.

Participation of the SMAD2/3 signalling pathway in the down regulation of megalin/LRP2 by transforming growth factor beta (TGF-ß1)

Megalin/LRP2 is a receptor that plays important roles in the physiology of several organs, such as kidney, lung, intestine, and gallbladder and also in the physiology of the nervous system. Megalin expression is reduced in diseases associated with fibrosis, including diabetic nephropathy, hepatic fibrosis and cholelithiasis, as well as in some breast and prostate cancers. One of the hallmarks of these conditions is the presence of the cytokine transforming growth factor beta (TGF-ß). Although TGF-ß has been implicated in the reduction of megalin levels, the molecular mechanism underlying this regulation is not well understood. Here, we show that treatment of two epithelial cell lines (from kidney and gallbladder) with TGF-ß1 is associated with decreased megalin mRNA and protein levels, and that these effects are reversed by inhibiting the TGF-ß1 type I receptor (TGF-ßRI). Based on in silico analyses, the two SMAD-binding elements (SBEs) in the megalin promoter are located at positions -57 and -605. Site-directed mutagenesis of the SBEs and chromatin immunoprecipitation (ChIP) experiments revealed that SMAD2/3 transcription factors interact with SBEs. Both the presence of SMAD2/3 and intact SBEs were associated with repression of the megalin promoter, in the absence as well in the presence of TGF-ß1. Also, reduced megalin expression and promoter activation triggered by high concentration of albumin are dependent on the expression of SMAD2/3. Interestingly, the histone deacetylase inhibitor Trichostatin A (TSA), which induces megalin expression, reduced the effects of TGF-ß1 on megalin mRNA levels. These data show the significance of TGF-ß and the SMAD2/3 signalling pathway in the regulation of megalin and explain the decreased megalin levels observed under conditions in which TGF-ß is upregulated, including fibrosis-associated diseases and cancer.

Endothelial to Mesenchymal Transition in Cardiovascular Disease: JACC State-of-the-Art Review

Endothelial to mesenchymal transition (EndMT) is a process whereby an endothelial cell undergoes a series of molecular events that lead to a change in phenotype toward a mesenchymal cell (e.g., myofibroblast, smooth muscle cell). EndMT plays a fundamental role during development, and mounting evidence indicates that EndMT is involved in adult cardiovascular diseases (CVDs), including atherosclerosis, pulmonary hypertension, valvular disease, and fibroelastosis. Therefore, the targeting of EndMT may hold therapeutic promise for treating CVD. However, the field faces a number of challenges, including the lack of a precise functional and molecular definition, a lack of understanding of the causative pathological role of EndMT in CVDs (versus being a "bystander-phenomenon"), and a lack of robust human data corroborating the extent and causality of EndMT in adult CVDs. Here, we review this emerging but exciting field, and propose a framework for its systematic advancement at the molecular and translational levels.

Sorafenib and fluvastatin synergistically alleviate hepatic fibrosis via inhibiting the TGFβ1/Smad3 pathway

BACKGROUND

Effective strategies for the treatment of hepatic fibrosis are urgently in need.

AIMS

To investigate the effect of the co-treatment of sorafenib and fluvastatin on hepatic fibrosis and the underlying mechanisms.

METHODS

A diethylnitrosamine-induced hepatic fibrosis rat model was used to evaluate the anti-fibrosis effect. Epithelial mesenchymal transition (EMT) of hepatocytes and hepatic stellate cells (HSCs) in response to sorafenib and fluvastatin was explored. A co-treatment effect on TGFβ1 expression was explored in the Kupffer cells of rats. The effect of co-treatment on the regulation of the TGFβ1/Smad3 pathway was investigated in both L02 cells and LX-2 cells.

RESULTS

Sorafenib and fluvastatin synergistically reduced collagen content, α-SMA expression, lamin level, and hyaluronic acid level in the rat hepatic model. Combination treatment significantly inhibited the expression of mesenchymal markers and promoted the expression of epithelial markers in hepatocytes. Co-treatment statistically suppressed the production of TGFβ1 in Kupffer cells. Suppression of EMT in parallel with alleviated up-regulation of fibronectin and α-SMA expression was observed in TGFβ1-activated LX-2 cells. Mechanistically, sorafenib plus fluvastatin blocked the TGFβ1/Smad3 signaling pathway via inhibiting phosphorylation of TβR II in hepatocytes and HSCs.

CONCLUSIONS

Sorafenib and fluvastatin synergistically alleviated diethylnitrosamine-induced hepatic fibrosis in rats. Sorafenib plus fluvastatin may be a potential combination treatment for hepatic fibrotic diseases.

Silencing of c-Ski augments TGF-b1-induced epithelial-mesenchymal transition in cardiomyocyte H9C2 cells

BACKGROUND

The shRNA lentiviral vector was constructed to silence c-Ski expression in cardiac mus- cle cells, with the aim of exploring the role of c-Ski in transforming growth factor b1 (TGF-b1)-induced epithelial-mesenchymal transitions (EMT) in H9C2 cells.

METHODS

Real-time polymerase chain reaction (RT-PCR) and western blot were used to detect c-Ski ex- pression at protein and messenger ribonucleic acid (mRNA) levels in 5 different cell lines. Then, lentiviral vector was constructed to silence or overexpress c-Ski in H9C2 cells. MTT and/or soft agar assay and tran- swell assay were used to detect cell proliferation and migration, respectively. The expression levels of c-Ski under different concentrations of TGF-b1 stimulation were detected by RT-qPCR and immunocytochemi- cal analysis. In the presence or absence of TGF-b1 stimulation, the proteins' expression levels of a-SMA, FN and E-cadherin, which are closely correlated with the process of EMT, were measured by western blot after c-Ski silencing or overexpression. Meanwhile, the effect of c-Ski on Samd3 phosphorylation with TGF-b1 stimulation was investigated.

RESULTS

There is a high expression of c-Ski at protein and mRNA levels in H9C2 cell line, which first demonstrated the presence of c-Ski expression in H9C2 cells. Overexpression of c-Ski significantly increased H9C2 cell proliferation. The ability of c-Ski gene silencing to suppress cell proliferation was gradually enhanced, and inhibition efficiency was the highest after 6 to 7 d of transfection. Moreover, H9C2 cells with c-Ski knockdown gained significantly aggressive invasive potential when compared with the control group. TGF-b1 stimulation could dose-independently reduce c-Ski expression in H9C2 cells and lead to obvious down-regulated expression of E-cadherin. Interestingly, c-Ski could restore E-cadherin expression while suppressing a-SMA and/or FN expression stimulated by TGF-b1. How- ever, shRNA-induced c-Ski knockdown aggravated only the TGF-b1-induced EMT. Moreover, c-Ski- -shRNA also promoted the phosphorylation of Samd3 induced by TGF-b1.

CONCLUSIONS

c-Ski expression in cardiac muscle cells could be down-regulated by TGF-b1. Silencing of c-Ski gene was accompanied by down-regulation of E-cadherin, up-regulation of a-SMA and/or FN and Smad3 phosphorylation induced by TGF-b1, promoting EMT process. Therefore, c-Ski may be closely associated with TGF-b1-induced EMT and play an important role in cardiac fibrosis develop- ment and progression.

miR-27a inhibits cervical adenocarcinoma progression by downregulating the TGF-βRI signaling pathway

High-risk human papillomavirus infection is essential for the malignant transformation of cervical cancer and can inhibit host miR-27a expression. We investigated the role and mechanism of miR-27a in cervical cancer progression. miR-27a is decreased in cervical cancer cell lines and miR-27a-agomir inhibited the cell proliferation, migration, and invasion properties of HeLa (adenocarcinoma) cells, but not in SiHa cells (squamous cell carcinoma). Luciferase assays revealed that miR-27a directly targets the 3′-UTR of transforming growth factor beta receptor I (TGF-βRI) and downregulates TGF-β signaling. The co-transfection of a TGF-βRI expression vector largely restored the inhibition of TGF-β signaling, cell proliferation, migration, and invasion mediated by miR-27a-agomir. Also, miR-27a-agomir slows down the growth of subcutaneous HeLa xenografts and downregulates the TGF-βRI expression and TGF-β signaling in tumor in vivo. Tissue microarray analysis revealed a low miR-27a level in adenocarcinoma cells, but not in squamous cell carcinoma cells, which was negatively associated with TGF-βRI expression. High TGF-βRI correlated with deep stromal invasion and lymph node metastasis. These results suggest that miR-27a acts as a tumor suppressor in cervical cancer, especially in adenocarcinoma, by inhibiting TGF-βRI signaling pathway. Thus, enhancing miR-27a expression and function may be a novel treatment strategy for cervical adenocarcinoma.

Histone deacetylase inhibitors upregulate Snail via Smad2/3 phosphorylation and stabilization of Snail to promote metastasis of hepatoma cells

Hepatocellular carcinoma (HCC) remains the third most common cause of cancer-related mortality. Resection and transplantation are the only curative treatments available, but are greatly hampered by high recurrence rates. Histone deacetylase inhibitors (HDACIs) are considered to be promising anticancer agents in drug development. Currently, four HDACIs have been granted Food and Drug Administration (FDA) approval for cancer. HDACIs have shown significant efficacy in hematological malignancies. However, they have limited effects in epithelial cell-derived cancers, including HCC, and the mechanisms of these are not elucidated. In this study, our results demonstrated that HDACIs were able to induce epithelial-mesenchymal transitions (EMT) in hepatoma cells which are believed to trigger tumor cell invasion and metastasis. We found that HDACIs promoted the expression of Snail and Snail-induced EMT was critical for HDACI-initiated invasion and metastasis. We indicated that HDACIs upregulated Snail in two ways. Firstly, HDACIs upregulated Snail at the transcriptional level by promoting Smad2/3 phosphorylation and nuclear translocation, then combined with the promoter to activate the transcription of Snail. Secondly, we showed that HDACIs regulated the stabilization of Snail via upregulating the expression of COP9 signalosome 2 (CSN2), which combined with Snail and exposed its acetylation site, then promoted acetylation of Snail, thereby inhibiting its phosphorylation and ubiquitination to repress the degradation of Snail. All these results highlighted that HDACIs have limited effects in HCC, and the use of HDACIs combined with other targeted strategies to inhibit EMT, which explored in this study is a promising treatment method for treating HCC.

Regulation of c-MYC transcriptional activity by transforming growth factor-beta 1-stimulated clone 22

c‐MYC stimulates cell proliferation through the suppression of cyclin‐dependent kinase (CDK) inhibitors including P15 (CDKN2B) and P21 (CDKN1A). It also activates E‐box‐mediated transcription of various target genes including telomerase reverse transcriptase (TERT) that is involved in cellular immortality and tumorigenesis. Transforming growth factor‐beta 1 (TGF‐β1)‐stimulated clone 22 (TSC‐22/TSC22D1) encodes a highly conserved leucine zipper protein that is induced by various stimuli, including TGF‐β. TSC‐22 inhibits cell growth in mammalian cells and in Xenopus embryos. However, underlying mechanisms of growth inhibition by TSC‐22 remain unclear. Here, we show that TSC‐22 physically interacts with c‐MYC to inhibit the recruitment of c‐MYC on the P15 (CDKN2B) and P21 (CDKN1A) promoters, effectively inhibiting c‐MYC‐mediated suppression of P15 (CDKN2B) and also P21 (CDKN1A) promoter activities. In contrast, TSC‐22 enhances c‐MYC‐mediated activation of the TERT promoter. Additionally, the expression of TSC‐22 in embryonic stem cells inhibits cell growth without affecting its pluripotency‐related gene expression. These results indicate that TSC‐22 differentially regulates c‐MYC‐mediated transcriptional activity to regulate cell proliferation.

Smad3-STAT3 crosstalk in pathophysiological contexts

Smad3 and STAT3 are intracellular molecules that transmit signals from plasma membrane receptors to the nucleus. Smad3 operates downstream of growth/differentiation factors that utilize activin receptor-like kinase (ALK)-4, 5, or 7, such as transforming growth factor-β (TGF-β), activin, and myostatin. STAT3 principally functions downstream of cytokines that exert their effects via gp130 and Janus family kinases, including interleukin-6 (IL-6), leukemia inhibitory factor (LIF), and oncostatin M. Accumulating evidence indicates that Smad3 and STAT3 engage in crosstalk in a highly context-dependent fashion, cooperating in some conditions while acting antagonistically each other in others. Here, we review the crosstalk between Smad3 and STAT3 in various biological contexts, including early tumorigenesis, epithelial-mesenchymal transition, fibrosis, and T cell differentiation.

Changes in DNA methylation induced by multi-walled carbon nanotube exposure in the workplace

This study was designed to assess the epigenetic alterations in blood cells, induced by occupational exposure to multi-wall carbon nanotubes (MWCNT). The study population comprised of MWCNT-exposed workers (n=24) and unexposed controls (n=43) from the same workplace. We measured global DNA methylation/hydroxymethylation levels on the 5th cytosine residues using a validated liquid chromatography tandem-mass spectrometry (LC-MS/MS) method. Sequence-specific methylation of LINE1 retrotransposable element 1 (L1RE1) elements, and promoter regions of functionally important genes associated with epigenetic regulation [DNA methyltransferase-1 (DNMT1) and histone deacetylase 4 (HDAC4)], DNA damage/repair and cell cycle pathways [nuclear protein, coactivator of histone transcription/ATM serine/threonine kinase (NPAT/ATM)], and a potential transforming growth factor beta (TGF-β) repressor [SKI proto-oncogene (SKI)] were studied using bisulfite pyrosequencing. Analysis of global DNA methylation levels and hydroxymethylation did not reveal significant difference between the MWCNT-exposed and control groups. No significant changes in Cytosine-phosphate-Guanine (CpG) site methylation were observed for the LINE1 (L1RE1) elements. Further analysis of gene-specific DNA methylation showed a significant change in methylation for DNMT1, ATM, SKI, and HDAC4 promoter CpGs in MWCNT-exposed workers. Since DNA methylation plays an important role in silencing/regulation of the genes, and many of these genes have been associated with occupational and smoking-induced diseases and cancer (risk), aberrant methylation of these genes might have a potential effect in MWCNT-exposed workers.

Curcumin downregulates the expression of Snail via suppressing Smad2 pathway to inhibit TGF-β1-induced epithelial-mesenchymal transitions in hepatoma cells

Hepatocellular carcinoma (HCC) remains the third cause of cancer-related mortality. Resection and transplantation are the only curative treatments available but are greatly hampered by high recurrence rates and development of metastasis, the initiation of cancer metastasis requires migration and invasion of cells, which is enabled by epithelial-mesenchymal transitions (EMT). TGF-β1 is a secreted protein that performs many cellular functions, including the control of cell growth, cell proliferation, cell differentiation and apoptosis. TGF-β1 is known as a major inducer of EMT, and it was reported that TGF-β1 induced EMT via Smad-dependent and Smad-independent pathways. However, the extrinsic signals of TGF-β1 regulated the EMT in hepatoma cells remains to be elucidated, and searching drugs to inhibit TGF-β1 induced EMT may be considered to be a potentially effective therapeutic strategy in HCC. Fortunately, in this study, we found that curcumin inhibited TGF-β1-induced EMT in hepatoma cells. Furthermore, we demonstrated that curcumin inhibited TGF-β1-induced EMT via inhibiting Smad2 phosphorylation and nuclear translocation, then suppressing Smad2 combined with the promoter of Snail which inhibited the transcriptional expression of Snail. These findings suggesting curcumin could be a useful agent for antitumor therapy and also a promising drug combined with other strategies to preventing and treating HCC.

The mechanism of TGF-β/miR-155/c-Ski regulates endothelial-mesenchymal transition in human coronary artery endothelial cells

Human coronary artery endothelial cells (HCAECs) have the potential to undergo fibrogenic endothelial–mesenchymal transition (EndMT), which results in matrix-producing fibroblasts and thereby contributes to the pathogenesis of cardiac fibrosis. Recently, the profibrotic cytokine transforming growth factor-β (TGF-β) is shown to be the crucial pathogenic driver which has been verified to induce EndMT. C-Ski is an important regulator of TGF-β signaling. However, the detailed role of c-Ski and the molecular mechanisms by which c-Ski affects TGF-β-induced EndMT in HCAECs are not largely elucidated. In the present study, we treated HCAECs with TGF-β of different concentrations to induce EndMT. We found that overexpression of c-Ski in HCAECs either blocked EndMT via hindering Vimentin, Snail, Slug, and Twist expression while enhancing CD31 expression, with or without TGF-β treatment. In contrast, suppression of c-Ski further enhanced EndMT. Currently, miRNA expression disorder has been frequently reported associating with cardiac fibrosis. By using online tools, we regarded miR-155 as a candidate miRNA that could target c-Ski, which was verified using luciferase assays. C-Ski expression was negatively regulated by miR-155. TGF-β-induced EndMT was inhibited by miR-155 silence; the effect of TGF-β on Vimentin, CD31, Snail, Slug, and Twist could be partially restored by miR-155. Altogether, these findings will shed light on the role and mechanism by which miR-155 regulates TGF-β-induced HCAECs EndMT via c-Ski to affect cardiac fibrosis, and miR-155/c-Ski may represent novel biomarkers and therapeutic targets in the treatment of cardiac fibrosis.

USP4 inhibits SMAD4 monoubiquitination and promotes activin and BMP signaling

SMAD4 is a common intracellular effector for TGF-β family cytokines, but the mechanism by which its activity is dynamically regulated is unclear. We demonstrated that ubiquitin-specific protease (USP) 4 strongly induces activin/BMP signaling by removing the inhibitory monoubiquitination from SMAD4. This modification was triggered by the recruitment of the E3 ligase, SMURF2, to SMAD4 following ligand-induced regulatory (R)-SMAD-SMAD4 complex formation. Whereas the interaction of the negative regulator c-SKI inhibits SMAD4 monoubiquitination, the ligand stimulates the recruitment of SMURF2 to the c-SKI-SMAD2 complex and triggers c-SKI ubiquitination and degradation. Thus, SMURF2 has a role in termination and initiation of TGF-β family signaling. An increase in monoubiquitinated SMAD4 in USP4-depleted mouse embryonic stem cells (mESCs) decreased both the BMP- and activin-induced changes in the embryonic stem cell fate. USP4 sustained SMAD4 activity during activin- and BMP-mediated morphogenic events in early zebrafish embryos. Moreover, zebrafish depleted of USP4 exhibited defective cell migration and slower coordinated cell movement known as epiboly, both of which could be rescued by SMAD4. Therefore, USP4 is a critical determinant of SMAD4 activity.

SETBP1 dysregulation in congenital disorders and myeloid neoplasms

Myeloid malignancies are characterized by an extreme molecular heterogeneity, and many efforts have been made in the past decades to clarify the mechanisms underlying their pathogenesis.

In this scenario SET binding protein 1 (SETBP1) has attracted a lot of interest as a new oncogene and potential marker, in addition to its involvement in the Schinzel-Giedon syndrome (SGS). Our review starts with the analysis of the structural characteristics of SETBP1, and extends to its corresponding physiological and pathological functions. Next, we describe the prevalence of SETBP1 mutations in congenital diseases and in hematologic malignancies, exploring how its alterations might contribute to tumor development and provoke clinical effects. Finally, we consider to understand how SETBP1 activation could be exploited in molecular medicine to enhance the cure rate.

The Role of c-SKI in Regulation of TGFβ-Induced Human Cardiac Fibroblast Proliferation and ECM Protein Expression

Cardiac fibrosis is characterized by over-deposition of extracellular matrix (ECM) proteins and over-proliferation of cardiac fibroblast, and contributes to both systolic and diastolic dysfunction in many cardiac pathophysiologic conditions. Transforming growth factor β 1 (TGFβ1) is as an essential inducing factor of cardiac fibrosis. C-Ski protein has been identified as an inhibitory regulator of TGFβ signaling. In the present study, we revealed the repressive effect of c-Ski on TGFβ1-induced human cardiac fibroblast (HCFB) proliferation and ECM protein increase (Collagen I and α-SMA). Moreover, miR-155 and miR-17 could inhibit SKI mRNA expression by direct binding to the 3'UTR of SKI, so as to reduce c-Ski protein level. Either miR-155 inhibition or miR-17 inhibition could reverse TGFβ1-induced HCFB proliferation and ECM protein increase. Taken together, we provided a potential therapy to treat cardiac fibrosis by inhibiting miR-155/miR-17 so as to restore the repressive effect of c-Ski on TGFβ1 signaling. J. Cell. Biochem. 118: 1911-1920, 2017. © 2017 Wiley Periodicals, Inc.

Repression of Smad3 by Stat3 and c-Ski/SnoN induces gefitinib resistance in lung adenocarcinoma

Cancer-associated inflammation develops resistance to the epidermal growth-factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) in non-small cell lung cancers (NSCLCs) harboring oncogenic EGFR mutations. Stat3-mediated interleukin (IL)-6 signaling and Smad-mediated transforming growth factor-β (TGF-β) signaling pathways play crucial regulatory roles in cancer-associated inflammation. However, mechanisms how these pathways regulate sensitivity and resistance to EGFR-TKI in NSCLCs remain largely undetermined. Here we show that signal transducer and activator of transcription (Stat)3 represses Smad3 in synergy with the potent negative regulators of TGF-β signaling, c-Ski and SnoN, whereby renders gefitinib-sensitive HCC827 cells resistant. We found that IL-6 signaling via phosphorylated Stat3 induced gefitinib resistance as repressing transcription of Smad3, whereas TGF-β enhanced gefitinib sensitivity as activating transcription of Smad3 in HCC827 cells with gefitinib-sensitizing EGFR mutation. Promoter analyses showed that Stat3 synergized with c-Ski/SnoN to repress Smad2/3/4-induced transcription of the Smad3 gene. Smad3 was found to be an apoptosis inducer, which upregulated pro-apoptotic genes such as caspase-3 and downregulated anti-apoptotic genes such as Bcl-2. Our results suggest that derepression of Smad3 can be a therapeutic strategy to prevent gefitinib-resistance in NSCLCs with gefitinib-sensitizing EGFR mutation.

Biglycan Intensifies ALK5-Smad2/3 Signaling by TGF-β1 and Downregulates Syndecan-4 in Cultured Vascular Endothelial Cells

Proteoglycans are macromolecules that consist of a core protein and one or more glycosaminoglycan side chains. A small leucine‐rich dermatan sulfate proteoglycan, biglycan, is one of the predominant types of proteoglycans synthesized by vascular endothelial cells; however, the physiological functions of biglycan are not completely understood. In the present study, bovine aortic endothelial cells in culture were transfected with small interfering RNAs for biglycan, and the expression of other proteoglycans was examined. Transforming growth factor‐β₁ signaling was also investigated, because the interaction of biglycan with cytokines has been reported. Biglycan was found to form a complex with either transforming growth factor‐β₁ or the transforming growth factor‐β₁ type I receptor, ALK5, and to intensify the phosphorylation of Smad2/3, resulting in a lower expression of the transmembrane heparan sulfate proteoglycan, syndecan‐4. This is the first report to clarify the function of biglycan as a regulatory molecule of the ALK5–Smad2/3 TGF‐β₁ signaling pathway that mediates the suppression of syndecan‐4 expression in vascular endothelial cells. J. Cell. Biochem. 118: 1087–1096, 2017. © 2016 Wiley Periodicals, Inc.

Structural Basis of Intracellular TGF-β Signaling: Receptors and Smads

Stimulation of the transforming growth factor β (TGF-β) family receptors activates an intracellular phosphorylation-dependent signaling cascade that culminates in Smad transcriptional activation and turnover. Structural studies have identified a number of allosteric mechanisms that control the localization, conformation, and oligomeric state of the receptors and Smads. Such mechanisms dictate the ordered binding of substrate and adaptor proteins that determine the directionality of the signaling process. Activation of the pathway has been illustrated by the various structures of the receptor-activated Smads (R-Smads) with SARA, Smad4, and YAP, respectively, whereas mechanisms of down-regulation have been elucidated by the structural complexes of FKBP12, Ski, and Smurf1. Interesting parallels have emerged between the R-Smads and the Forkhead-associated (FHA) and interferon regulatory factor (IRF)-associated domains, as well as the Hippo pathway. However, important questions remain as to the mechanism of Smad-independent signaling.

RETRACTED: Effects of geniposide on hepatocytes undergoing epithelial-mesenchymal transition in hepatic fibrosis by targeting TGFβ/Smad and ERK-MAPK signaling pathways

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief. The corresponding author, Dr Byoungduck Park, requested publication of a corrigendum to correct figure 2B which reused control data from a different publication (doi: 10.1016/j.intimp.2015.02.014). Upon further inspection, the Biochimie editorial team noticed that: Comparison of Fig 2B with Fig 4C of a previous publication in International Immunopharmacology by two co-authors (doi: 10.1016/j.intimp.2015.02.014) reveals that western blot β-actin control data from the earlier paper were re-used in a different experiment shown in Figure 2B of the article in Biochimie, after adjustment of the brightness/contrast. Furthermore, the same bands, after more image manipulation were presented as Smad3 data in Figure 4C of the Biochimie article. Here the image manipulation involved notably the rotation of the set of bands by 180° and some adjustment of the height/width ratio. The authors apologise for any confusion that may have arisen from their article.

Actin-cytoskeleton polymerization differentially controls the stability of Ski and SnoN co-repressors in normal but not in transformed hepatocytes

BACKGROUND

Ski and SnoN proteins function as transcriptional co-repressors in the TGF-β pathway. They regulate cell proliferation and differentiation, and their aberrant expression results in altered TGF-β signalling, malignant transformation, and alterations in cell proliferation.

METHODS

We carried out a comparative characterization of the endogenous Ski and SnoN protein regulation by TGF-β, cell adhesion disruption and actin-cytoskeleton rearrangements between normal and transformed hepatocytes; we also analyzed Ski and SnoN protein stability, subcellular localization, and how their protein levels impact the TGF-β/Smad-driven gene transcription.

RESULTS

Ski and SnoN protein levels are lower in normal hepatocytes than in hepatoma cells. They exhibit a very short half-life and a nuclear/cytoplasmic distribution in normal hepatocytes opposed to a high stability and restricted nuclear localization in hepatoma cells. Interestingly, while normal cells exhibit a transient TGF-β-induced gene expression, the hepatoma cells are characterized by a strong and sustained TGF-β-induced gene expression. A novel finding is that Ski and SnoN stability is differentially regulated by cell adhesion and cytoskeleton rearrangements in the normal hepatocytes. The inhibition of protein turnover down-regulated both Ski and SnoN co-repressors impacting the kinetic of expression of TGF-β-target genes.

CONCLUSION

Normal regulatory mechanisms controlling Ski and SnoN stability, subcellular localization and expression are altered in hepatocarcinoma cells.

GENERAL SIGNIFICANCE

This work provides evidence that Ski and SnoN protein regulation is far more complex in normal than in transformed cells, since many of the normal regulatory mechanisms are lost in transformed cells.

MiR-497∼195 cluster microRNAs regulate osteoblast differentiation by targeting BMP signaling

MicroRNAs play important roles during cell reprogramming and differentiation. In this study, we identified the miR-497∼195 cluster, a member of the miR-15 family, as strongly upregulated with age of postnatal bone development in vivo and late differentiation stages of primary osteoblasts cultured in vitro. Early expression of miR-195-5p inhibits differentiation and mineralization. Microarray analyses along with quantitative PCR demonstrate that miR-195-5p alters the gene regulatory network of osteoblast differentiation and impairs the induction of bone morphogenetic protein (BMP) responsive genes. Applying reporter gene and Western blot assays, we show that miR-195-5p interferes with the BMP/Smad-pathway in a dose-dependent manner. Systematically comparing the changes in mRNA levels in response to miR-195-5p overexpression with the changes observed in the natural course of osteoblast differentiation, we demonstrate that microRNAs of the miR-15 family affect several target genes involved in BMP signaling. Predicted targets including Furin, a protease that cleaves pro-forms, genes encoding receptors such as Acvr2a, Bmp1a, Dies1, and Tgfbr3, molecules within the cascade like Smad5, transcriptional regulators like Ski and Zfp423 as well as Mapk3 and Smurf1 were validated by quantitative PCR. Taken together, our data strongly suggest that miR-497∼195 cluster microRNAs act as intracellular antagonists of BMP signaling in bone cells.

Effect of oxymatrine on expression of molecules of Smad signal pathway in pancreatic stellate cells stimulated with TGF-β1

AIM: To investigate the effect of oxymatrine (OM) on the expression of molecules of the Smad signal pathway in pancreatic stellate cell line (LTC-14 cells) stimulated with transforming growth factor-β1 (TGF-β1).

METHODS: LTC-14 cells were divided into a normal control group, a TGF-β1 stimulated group and a TGF-β1 + OM (1 mg/mL) group. The mRNA and protein were extracted from LTC-14 cells 12 h after treatment. The mRNA and protein expression of Smad2/3/4/7 was detected by real-time PCR and Western blot, respectively.

RESULTS: Compared with the TGF-β1 stimulated group, the mRNA and protein expression of Smad2/3/4 was dramatically reduced in the OM treated group (P < 0.05). Compared with the TGF-β1 stimulated group, the mRNA expression of Smad7 was significantly decreased in the OM treated group (P < 0.05), whereas the Smad7 protein expression was increased.

CONCLUSION: OM might exert a therapeutic effect against pancreatic fibrosis in pancreatic stellate cells stimulated with TGF-β1 by interfering with the mRNA and protein expression of molecules of the TGF-β1/Smad pathway.

Ski diminishes TGF-β1-induced myofibroblast phenotype via up-regulating Meox2 expression

OBJECTIVE

The aim of the present work was to investigate the mechanism of transforming growth factor (TGF)-β1 and Sloan-Kettering Institute (Ski) in the pathogenesis of hypertrophic scars (HS).

BACKGROUND

Wound healing is an inherent process, but the aberrant wound healing of skin injury may lead to HS. There has been growing evidence suggesting a role for TGF-β1 and Ski in the pathogenesis of fibrosis.

MATERIAL AND METHODS

The MTT assay was used to detect the cell proliferation induced by TGF-β1. The Ski gene was transduced into cells with an adenovirus, and then the function of Ski in cell proliferation and differentiation was observed. Ski mRNA levels were measured by RT-PCR. Western blotting was used to detect the protein expression of α-SMA, E-cadherin, Meox1, Meox2, Zeb1 and Zeb2.

RESULTS

TGF-β1 can promote human skin fibroblast (HSF) cell proliferation in a time-dependent manner, but the promoting effect could be suppressed by Ski. TGF-β1 also induces the formation of the myofibroblast phenotype and the effect of TGF-β1 could be diminished by Ski. Also, Ski modulates the cardiac myofibroblast phenotype and function through suppression of Zeb2 by up-regulating the expression of Meox2.

CONCLUSIONS

Ski diminishes the myofibroblast phenotype induced by TGF-β1 through the suppression of Zeb2 by up-regulating the expression of Meox2.

Apamin inhibits hepatic fibrosis through suppression of transforming growth factor β1-induced hepatocyte epithelial-mesenchymal transition

Apamin is an integral part of bee venom, as a peptide component. It has long been known as a highly selective block Ca(2+)-activated K(+) (SK) channels. However, the cellular mechanism and anti-fibrotic effect of apamin in TGF-β1-induced hepatocytes have not been explored. In the present study, we investigated the anti-fibrosis or anti-EMT mechanism by examining the effect of apamin on TGF-β1-induced hepatocytes. AML12 cells were seeded at ∼60% confluence in complete growth medium. Twenty-four hours later, the cells were changed to serum free medium containing the indicated concentrations of apamin. After 30 min, the cells were treated with 2 ng/ml of TGF-β1 and co-cultured for 48 h. Also, we investigated the effects of apamin on the CCl4-induced liver fibrosis animal model. Treatment of AML12 cells with 2 ng/ml of TGF-β1 resulted in loss of E-cadherin protein at the cell-cell junctions and concomitant increased expression of vimentin. In addition, phosphorylation levels of ERK1/2, Akt, Smad2/3 and Smad4 were increased by TGF-β1 stimulation. However, cells treated concurrently with TGF-β1 and apamin retained high levels of localized expression of E-cadherin and showed no increase in vimentin. Specifically, treatment with 2 μg/ml of apamin almost completely blocked the phosphorylation of ERK1/2, Akt, Smad2/3 and Smad4 in AML12 cells. In addition, apamin exhibited prevention of pathological changes in the CCl4-injected animal models. These results demonstrate the potential of apamin for the prevention of EMT progression induced by TGF-β1 in vitro and CCl4-injected in vivo.

Transcriptional regulation of seprase in invasive melanoma cells by transforming growth factor-β signaling

The tumor invasive phenotype driven by seprase expression/activity has been widely examined in an array of malignant tumor cell types; however, very little is known about the transcriptional regulation of this critical protease. Seprase (also named fibroblast activation protein-α, antiplasmin-cleaving enzyme, and dipeptidyl prolyl peptidase 5) is expressed at high levels by stromal fibroblast, endothelial, and tumor cells in a variety of invasive tumors but is undetectable in the majority of normal adult tissues. To examine the transcriptional regulation of the gene, we cloned the human seprase promoter and demonstrated that endogenous seprase expression and exogenous seprase promoter activity are high in invasive melanoma cells but not in non-invasive melanoma cells/primary melanocytes. In addition, we identified a crucial TGF-β-responsive cis-regulatory element in the proximal seprase promoter region that enabled robust transcriptional activation of the gene. Treatment of metastatic but not normal/non-invasive cells with TGF-β1 caused a rapid and profound up-regulation of endogenous seprase mRNA, which coincided with an abolishment of the negative regulator c-Ski, and an increase in binding of Smad3/4 to the seprase promoter in vivo. Blocking TGF-β signaling in invasive melanoma cells through overexpression of c-Ski, chemically using SB-431542, or with a neutralizing antibody against TGF-β significantly reduced seprase mRNA levels. Strikingly, RNAi of seprase in invasive cells greatly diminished their invasive potential in vitro as did blocking TGF-β signaling using SB-431542. Altogether, we found that seprase is transcriptionally up-regulated in invasive melanoma cells via the canonical TGF-β signaling pathway, supporting the roles of both TGF-β and seprase in tumor invasion and metastasis.

Regulation of estrogen receptor signaling in breast carcinogenesis and breast cancer therapy

Estrogen and estrogen receptors (ERs) are critical regulators of breast epithelial cell proliferation, differentiation, and apoptosis. Compromised signaling vis-à-vis the estrogen receptor is believed to be a major contributing factor in the malignancy of breast cells. Targeting the ER signaling pathway has been a focal point in the development of breast cancer therapy. Although approximately 75 % of breast cancer patients are classified as luminal type (ER(+)), which predicts for response to endocrine-based therapy; however, innate or acquired resistance to endocrine-based drugs remains a serious challenge. The complexity of regulation for estrogen signaling coupled with the crosstalk of other oncogenic signaling pathways is a reason for endocrine therapy resistance. Alternative strategies that target novel molecular mechanisms are necessary to overcome this current and urgent gap in therapy. A thorough analysis of estrogen-signaling regulation is critical. In this review article, we will summarize current insights into the regulation of estrogen signaling as related to breast carcinogenesis and breast cancer therapy.

The SKI proto-oncogene enhances the in vivo repopulation of hematopoietic stem cells and causes myeloproliferative disease

The proto-oncogene SKI is highly expressed in human myeloid leukemia and also in murine hematopoietic stem cells. However, its operative relevance in these cells remains elusive. We have over-expressed SKI to define its intrinsic role in hematopoiesis and myeloid neoplasms, which resulted in a robust competitive advantage upon transplantation, a complete dominance of the stem and progenitor compartments, and a marked enhancement of myeloid differentiation at the expense of other lineages. Accordingly, enforced expression of SKI induced a gene signature associated with hematopoietic stem cells and myeloid differentiation, as well as hepatocyte growth factor signaling. Here we demonstrate that, in contrast to what has generally been assumed, the significant impact of SKI on hematopoiesis is independent of its ability to inhibit TGF-beta signaling. Instead, myeloid progenitors expressing SKI are partially dependent on functional hepatocyte growth factor signaling. Collectively our results demonstrate that SKI is an important regulator of hematopoietic stem cell activity and its overexpression leads to myeloproliferative disease.

The Ski-Zeb2-Meox2 pathway provides a novel mechanism for regulation of the cardiac myofibroblast phenotype

Cardiac fibrosis is linked to fibroblast-to-myofibroblast phenoconversion and proliferation but the mechanisms underlying this are poorly understood. Ski is a negative regulator of TGF-β-Smad signaling in myofibroblasts, and might redirect the myofibroblast phenotype back to fibroblasts. Meox2 could alter TGF-β-mediated cellular processes and is repressed by Zeb2. Here, we investigated whether Ski diminishes the myofibroblast phenotype by de-repressing Meox2 expression and function through repression of Zeb2 expression. We show that expression of Meox1 and Meox2 mRNA and Meox2 protein is reduced during phenoconversion of fibroblasts to myofibroblasts. Overexpression of Meox2 shifts the myofibroblasts into fibroblasts, whereas the Meox2 DNA-binding mutant has no effect on myofibroblast phenotype. Overexpression of Ski partially restores Meox2 mRNA expression levels to those in cardiac fibroblasts. Expression of Zeb2 increased during phenoconversion and Ski overexpression reduces Zeb2 expression in first-passage myofibroblasts. Furthermore, expression of Meox2 is decreased in scar following myocardial infarction, whereas Zeb2 protein expression increases in the infarct scar. Thus Ski modulates the cardiac myofibroblast phenotype and function through suppression of Zeb2 by upregulating the expression of Meox2. This cascade might regulate cardiac myofibroblast phenotype and presents therapeutic options for treatment of cardiac fibrosis.

TGF-β signaling in C. elegans

Transforming Growth Factor-β (TGF-β) superfamily ligands regulate many aspects of cell identity, function, and survival in multicellular animals. Genes encoding five TGF-β family members are present in the genome of C. elegans. Two of the ligands, DBL-1 and DAF-7, signal through a canonical receptor-Smad signaling pathway; while a third ligand, UNC-129, interacts with a noncanonical signaling pathway. No function has yet been associated with the remaining two ligands. Here we summarize these signaling pathways and their biological functions.