Different roles of TGF-β in the multi-lineage differentiation of stem cells

Stem cells are a population of cells that has infinite or long-term self-renewal ability and can produce various kinds of descendent cells.Transforming growth factor β(TGF-β) family is a superfamily of growth factors,including TGF-β1,TGF-β2 and TGF-β3,bone morphogenetic proteins,activin/inhibin,and some other cytokines such as nodal,which plays very important roles in regulating a wide variety of biological processes,such as cell growth,differentiation,cell death.TGF-β,a pleiotropic cytokine,has been proved to be differentially involved in the regulation of multi-lineage differentiation of stem cells,through the Smad pathway,non-Smad pathways including mitogen-activated protein kinase pathways,phosphatidylinositol-3-kinase/AKT pathways and Rholike GTPase signaling pathways,and their cross-talks.For instance,it is generally known that TGF-β promotes the differentiation of stem cells into smooth muscle cells,immature cardiomyocytes,chondrocytes,neurocytes,hepatic stellate cells,Th17 cells,and dendritic cells.However,TGF-β inhibits the differentiation of stem cells into myotubes,adipocytes,endothelial cells,and natural killer cells.Additionally,TGF-β can provide competence for early stages of osteoblastic differentiation,but at late stages TGF-β acts as an inhibitor.The three mammalian isoforms(TGF-β1,2 and 3) have distinct but overlapping effects on hematopoiesis.Understanding the mechanisms underlying the regulatory effect of TGF-β in the stem cell multi-lineage differentiation is of importance in stem cell biology,and will facilitate both basic research and clinical applications of stem cells.In this article,we discuss the current status and progress in our understanding of different mechanisms by which TGF-β controls multi-lineage differentiation of stem cells.     

Reversion of malignancy in human gastric cancer MKN—45 cells through the transfection of transforming growth factor—β type Ⅱ receptor gene

Human gastric cancer MKN-45 cells which are resistant to TGF-β growth inhibition and possess TGF-β type I and type Ⅲ receptors,but not type Ⅱ receptors,have been used as a model system to reconstitute these cancer cells with TGF-β RII cDNA.The results of these experiments indicated that the reexpression of TGF-β RII gene in MKN-45 cells can restore their sensitivity to TGF-β growth inhibition,decrease their growth rate,reduce their cloning efficiency in soft agar and tumorigenicity in nude mice in stable transfectants,in comparison with their control MKN-45 cells.Among different RII transfectants,their difference in the changes of these parameters,as a result of the regain of autocrine negative growth control by TGF-β,is roughly proportional to their level of expression of transfected RII mRNA.From these data,it is concluded that the inactivation of TGF-β RII gene is related to the escape of growth control by TGF-β in MKN-45 cells.The importance of the study of the interplay of TGF-β and its receptor system in the negative growth control of gastric cancer,and possibly also of other cancers,is discussed.     

ALK-mediated Tyr95 phosphorylation of Smad4 impairs its transcription activity and the tumor suppressive activity of TGF-β

<正>Transforming growth factorβ(TGF-β) regulates various physiological processes such as cell proliferation, differentiation, morphogenesis, andt tissue homeostasis and regeneration. The deregulation of these processes leads to many types of human diseases such as cancer (Massagué,2008). TGF-βsignaling is initiated upon active TGF-βdimer     

Use of bone morphogenetic proteins in mesenchymal stem cell stimulation of cartilage and bone repair

The extracellular matrix-associated bone morphogenetic proteins(BMPs) govern a plethora of biological processes. The BMPs are members of the transforming growth factor-β protein superfamily, and they actively participate to kidney development, digit and limb formation, angiogenesis, tissue fibrosis and tumor development. Since their discovery, they have attracted attention for their fascinating perspectives in the regenerative medicine and tissue engineering fields. BMPs have been employed in many preclinical and clinical studies exploring their chondrogenic or osteoinductive potential in several animal model defects and in human diseases. During years of research in particular two BMPs, BMP2 and BMP7 have gained the podium for their use in the treatment of various cartilage and bone defects. In particular they have been recently approved for employment in non-union fractures as adjunct therapies. On the other hand, thanks to their potentialities in biomedical applications, there is a growing interest in studying the biology of mesenchymal stem cell(MSC), the rules underneath their differentiation abilities, and to test their true abilities in tissue engineering. In fact, the specific differentiation of MSCs into targeted celltype lineages for transplantation is a primary goal of the regenerative medicine. This review provides an overview on the current knowledge of BMP roles and signaling in MSC biology and differentiation capacities. In particular the article focuses on the potential clinical use of BMPs and MSCs concomitantly, in cartilage and bone tissue repair.     

Multiple roles of mothers against decapentaplegic homolog 4 in tumorigenesis,stem cells,drug resistance,and cancer therapy

The transforming growth factor(TGF)-βsignaling pathway controls many cellular processes,including proliferation,differentiation,and apoptosis.Abnormalities in the TGF-βsignaling pathway and its components are closely related to the occurrence of many human diseases,including cancer.Mothers against decapentaplegic homolog 4(Smad4),also known as deleted in pancreatic cancer locus 4,is a typical tumor suppressor candidate gene locating at q21.1 of human chromosome 18 and the common mediator of the TGF-β/Smad and bone morphogenetic protein/Smad signaling pathways.It is believed that Smad4 inactivation correlates with the development of tumors and stem cell fate decisions.Smad4 also interacts with cytokines,miRNAs,and other signaling pathways,jointly regulating cell behavior.However,the regulatory function of Smad4 in tumorigenesis,stem cells,and drug resistance is currently controversial.In addition,Smad4 represents an attractive therapeutic target for cancer.Elucidating the specific role of Smad4 is important for understanding the mechanism of tumorigenesis and cancer treatment.Here,we review the identification and characterization of Smad4,the canonical TGF-β/Smad pathway,as well as the multiple roles of Smad4 in tumorigenesis,stem cells,and drug resistance.Furthermore,we provide novel insights into the prospects of Smad4-targeted cancer therapy and the challenges that it will face in the future.     

Emerging roles of transforming growth factor β signaling in wet age-related macular degeneration

Age-related macular degeneration (AMD) is one of the major causes of irreversible blindness among aging populations in developed countries and can be classified as dry or wet according to its progression.Wet AMD,which is characterized by angiogenesis on the choroidal membrane,is uncommonly seen but more severe.Controlling or completely inhibiting the factors that contribute to the progression of events that lead to angiogenesis may be an effective strategy for treating wet AMD.Emerging evidence has shown that transforming growth factor-β(TGF-β) signaling plays a significant role in the progression of wet AMD.In this review,we described the roles of and changes in TGF-β signaling in the development of AMD and discussed the mechanisms of the TGF-β superfamily in choroidal neovascularization (CNV) and wet AMD,including the modulation of angiogenesis-related factors,inflammation,vascular fibrosis,and immune responses,as well as cross-talk with other signaling pathways.These remarkable findings indicate that TGF-β signaling is a potential target for wet AMD treatment.     

Role of glycosylation in TGF-β signaling and epithelial-to-mesenchymal transition in cancer

Glycosylation is a common posttranslational modification on membrane-associated and secreted proteins that is of pivotal importance for regulating cell functions.Aberrant glycosylation can lead to uncontrolled cell proliferation,cell-matrix interactions,migration and differentiation,and has been shown to be involved in cancer and other diseases.The epithelial-to-mesenchymal transition is a key step in the metastatic process by which cancer cells gain the ability to invade tissues and extravasate into the bloodstream.This cellular transformation process,which is associated by morphological change,loss of epithelial traits and gain of mesenchymal markers,is triggered by the secreted cytokine transforming growth factor-β(TGF-β).TGF-βbioactivity is carefully regulated,and its effects on cells are mediated by its receptors on the cell surface.In this review,we first provide a brief overview of major types of glycans,namely,N-glycans,O-glycans,glycosphingolipids and glycosaminoglycans that are involved in cancer progression.Thereafter,we summarize studies on how the glycosylation of TGF-βsignaling components regulates TGF-βsecretion,bioavailability and TGF-βreceptor function.Then,we review glycosylation changes associated with TGF-β-induced epithelial-to-mesenchymal transition in cancer.Identifying and understanding the mechanisms by which glycosylation affects TGF-βsignaling and downstream biological responses will facilitate the identification of glycans as biomarkers and enable novel therapeutic approaches.     

A mesenchymal-like subpopulation in non-neuroendocrine SCLC contributes to metastasis

Small cell lung cancer (SCLC) is the most aggressive lung cancer with high heterogeneity.Mouse SCLC cells derived from the Rb1~(L/L)/Trp53~(L/L)(RP) autochthonous mouse model grew as adhesion or suspension in cell culture,and the adhesion cells are defined as non-neuroendocrine (non-NE) SCLC cells.Here,we uncover the heterogenous subpopulations within the non-NE cells and referred to them as mesenchymallike (Mes) and epithelial-like (Epi) SCLC cells.The Mes cells have increased capability to form colonies in soft agar and harbored stronger metastatic capability in vivo when compared with the Epi cells.Gene Set Enrichment Analysis reveals that the transforming growth factor (TGF)-β signaling is enriched in the Mes cells.Importantly,inhibition of the TGF-β signaling through ectopic expression of dominant-negative Tgfbr2(Tgfbr2-DN) or treatment with Tgfbr1 inhibitor SD-208 consistently abrogates tumor metastasis in nude mouse allograft assays.Moreover,genetic deletion of Tgfbr2 or Smad4,the key components of the TGF-β signaling pathway,dramatically attenuates SCLC metastasis in the RP autochthonous mouse model.Collectively,our results uncover the high heterogeneity in non-NE SCLC cells and highlight an important role of TGF-β signaling in promoting SCLC metastasis.     

The role of Smad signaling in vascular and hematopoietic development revealed by studies using genetic mouse models

Smads are intracellular mediators of transforming growth factor β (TGF-β) superfamily signaling. In this review, we focus on the genetic mouse models for Smad pathways, which have provided functional evidence regarding the complex circuitry in angiogenesis and hematopoiesis during development. In the early stages of vascular development, TGF-β signaling is a contri buting factor in angiogenesis and vascular maturation. Whereas in the later embryogenesis, selected molecules of Smad pathways, such as TGF-β type II receptor (TbRII), ALK5, and Smad5, seem to be dispensable for vessel morphogenesis and integrity. TGF-β signaling is not required in the induction of hematopoietic precursors from mesoderm, but inhibits the subsequent expansion of committed hematopoietic precursors. By contrast, bone morphogenetic protein 4 (BMP4) has long been acknowledged pivotal in mesoderm induction and hematopoietic commitment during development. However, recent genetic evidence shows the BMP4-ALK3 axis is not crucial for the formation of hematopoietic cells from FLK1+ mesoderm. Because of the highly redundant mechanisms within the Smad pathways, the precise role of the Smad signaling involved in vascular and hematopoietic development remains nebulous. The generation of novel cell lineage restricted Cre transgenes would shed new light on the future relevant investigations.     

Enhancement of Metastatic and Invasive Capacity of Gastric Cancer Cells by Transforming Growth Factor-β1

Transforming growth factor-β (TGF-β),a multifunctional cytokine,exerts contradictory rolesin different kinds of cells.A number of studies have revealed its involvement in the progression of many typesof tumors.To investigate the effect of TGF-β on gastric carcinoma,SGC7901,BGC823 and MKN28 (aTGF-β-resistant cell line) adenocarcinoma clones were used.After pretreatment in serum-free medium withor without 10 ng/ml TGF-β1,their experimental metastatic potential,chemotaxis,and invasive and adhesiveability were measured.Furthermore,zymography for gelatinase was processed.Liver colonies were alsomeasured 4 weeks after inoculation of SGC7901,BGC823 and MKN28 in Balb/c nude mice,and an increasein the number of surface liver metastases was seen in SGC7901 (from 11.0±3.0 to 53.3±3.3) and BGC823(from 9.3±2.5 to 60.0±2.8) groups,whereas there was no difference between MKN28 groups (from 35.2±3.8 to 38.5±2.7).In vitro experiments showed that TGF-β1 increased the adhesion capacity of SGC7901and BGC823 cells to immobilized reconstituted basement membrane/fibronectin matrices and promoted theirpenetration through reconstituted basement membrane barriers.Zymography demonstrated that enhancedinvasive potential was partly due to the increased type Ⅳ collagenolytic (gelatinolytic) activity,but there wasno difference in type Ⅳ collagenolytic activity and other biological behaviors between MKN28 groups.Theseresults suggested that TGF-β1 might modulate the metastatic potential of gastric cancer cells by promotingtheir ability to break down and penetrate basement membrane barriers and their adhesive and motile activities.We speculated that TGF-β1 might act as a progression-enhancing factor in gastric cancer.Therefore blockageof TGF-β or TGF-β signaling might prevent gastric cancer cells from invading and metastasizing.     

Endoglin in liver fibrogenesis: Bridging basic science and clinical practice

Endoglin, also known as cluster of differentiation CD105, was originally identified 25 years ago as a novel marker of endothelial cells. Later it was shown that endoglin is also expressed in pro-fibrogenic cells including mesangial cells, cardiac and scleroderma fibroblasts, and hepatic stellate cells. It is an integral membranebound disulfide-linked 180 kDa homodimeric receptor that acts as a transforming growth factor-β(TGF-β) auxiliary co-receptor. In humans, several hundreds of mutations of the endoglin gene are known that give rise to an autosomal dominant bleeding disorder that is characterized by localized angiodysplasia and arteriovenous malformation. This disease is termed hereditary hemorrhagic telangiectasia type Ⅰ and induces various vascular lesions, mainly on the face, lips, hands and gastrointestinal mucosa. Two variants of endoglin(i.e., S- and L-endoglin) are formed by alternative splicing that distinguishes from each other in the length of their cytoplasmic tails. Moreover, a soluble form of endoglin, i.e.,sol-Eng, is shedded by the matrix metalloprotease-14 that cleaves within the extracellular juxtamembrane region. Endoglin interacts with the TGF-β signaling receptors and influences Smad-dependent and-independent effects. Recent work has demonstrated that endoglin is a crucial mediator during liver fibrogenesis that critically controls the activity of the different Smad branches. In the present review, we summarize the present knowledge of endoglin expression and function, its involvement in fibrogenic Smad signaling, current models to investigate endoglin function, and the diagnostic value of endoglin in liver disease.     

Hydrogen sulfide suppresses transforming growth factor-β1-induced differentiation of human cardiac fibroblasts into myofibroblasts

In heart disease, transforming growth factor-β1(TGF-β1) converts fibroblasts into myofibroblasts, which synthesize and secrete fibrillar type I and III collagens. The purpose of the present study was to investigate how hydrogen sulfide(H2S) suppresses TGF-β1-induced differentiation of human cardiac fibroblasts to myofibroblasts. Human cardiac fibroblasts were serum-starved in fibroblast medium for 16 h before exposure to TGF-β1(10 ng m L-1) for 24 h with or without sodium hydrosulfide(Na HS, 100 μmol L-1, 30 min pretreatment) treatment. Na HS, an exogenous H2 S donor, potently inhibited the proliferation and migration of TGF-β1-induced human cardiac fibroblasts and regulated their cell cycle progression. Furthermore, Na HS treatment led to suppression of fibroblast differentiation into myofibroblasts, and reduced the levels of collagen, TGF-β1, and activated Smad3 in TGF-β1-induced human cardiac fibroblasts in vitro. We therefore conclude that H2 S suppresses TGF-β1-stimulated conversion of fibroblasts to myofibroblasts by inhibiting the TGF-β1/Smad3 signaling pathway, as well as by inhibiting the proliferation, migration, and cell cycle progression of human cardiac myofibroblasts. These effects of H2 S may play significant roles in cardiac remodeling associated with heart failure.     

New findings showing how DNA methylation influences diseases

In 1975, Holliday and Pugh as well as Riggs independently hypothesized that DNA methylation in eukaryotes could act as a hereditary regulation mechanism that influences gene expression and cell differentiation. Interest in the study of epigenetic processes has been inspired by their reversibility as well as their potentially preventable or treatable consequences. Recently, we have begun to understand that the features of DNA methylation are not the same for all cells.Major differences have been found between differentiated cells and stem cells.Methylation influences various pathologies, and it is very important to improve the understanding of the pathogenic mechanisms. Epigenetic modifications may take place throughout life and have been related to cancer, brain aging, memory disturbances, changes in synaptic plasticity, and neurodegenerative diseases,such as Parkinson's disease and Huntington's disease. DNA methylation also has a very important role in tumor biology. Many oncogenes are activated by mutations in carcinogenesis. However, many genes with tumor-suppressor functions are "silenced" by the methylation of CpG sites in some of their regions.Moreover, the role of epigenetic alterations has been demonstrated in neurological diseases. In neuronal precursors, many genes associated with development and differentiation are silenced by CpG methylation. In addition,recent studies show that DNA methylation can also influence diseases that do not appear to be related to the environment, such as IgA nephropathy, thus affecting,the expression of some genes involved in the T-cell receptor signaling. In conclusion, DNA methylation provides a whole series of fundamental information for the cell to regulate gene expression, including how and when the genes are read, and it does not depend on the DNA sequence.     

Ubiquitination in Abscisic Acid-Related Pathway

Ubiquitination is emerging as a tight regulatory mechanism that is necessary for all aspects of development and survival of all eukaryotes. Recent genomic and genetic analysis in Arabidopsis suggests that ubiquitination may also play important roles in plant response to the phytohormone abscisic acid （ABA）. Many components of the ubiquitination pathway, such as ubiquitin-conjugating enzyme E2, ubiquitin ligase E3 and components of the proteasome, have been identified or predicted to be essential in ABA biosynthesis, catabolism and signaling. In addition, the ubiquitination-related pathway, sumoylation, is also involved in ABA signaling. We summarize in this report recent developments to elucidate their roles in the ABA-related pathway.