TGF-beta Family Members Research Articles

The complex pattern of SMAD signaling in the cardiovascular system☆

The SMAD (small mother against decapentaplegic) family comprises transcription factors that function as signal transducers of TGFbeta (transforming growth factor) superfamily members. The number of studies showing expression, activation or involvement of both SMAD and TGFbeta family members in cardiovascular diseases is constantly rising. In this context, the position of SMADs in the diseased heart is particularly interesting because, besides their well-known fibrotic effects, increasing evidence demonstrates direct action of SMADs on cardiomyocytes as well as on the vascular system. In these systems, SMAD proteins are described to have effects on heart development, cell proliferation, cell growth, and apoptosis. As will be discussed in this review, these different consequences of SMAD activation are dependent on different SMAD isoforms, interaction of SMAD with other transcription factors in the particular situation, and modulation of SMAD activity by various kinases. As a result of all these influences, it turns out that activation of SMAD by members of the BMP (bone morphogenetic protein) family, which is a subfamily of the TGFbeta superfamily, is necessary for correct heart development. On the other hand, activation of SMADs by TGFbeta family members results in fibrotic, apoptotic, and anti-hypertrophic processes that are related to a detrimental cardiac remodeling and progression to heart failure.

Identification of 40LoVe, a Xenopus hnRNP D Family Protein Involved in Localizing a TGF-β-Related mRNA during Oogenesis

Asymmetric distribution of cellular components underlies many biological processes, and the localization of mRNAs within domains of the cytoplasm is one important mechanism of establishing and maintaining cellular asymmetry. mRNA localization often involves assembly of large ribonucleoproteins (RNPs) in the cytoplasm. Using an RNA affinity chromatography approach, we investigated localization RNP formation on the vegetal localization element (VLE) of the mRNA encoding Vg1, a Xenopus TGF-beta family member. We identified 40LoVe, an hnRNP D family protein, as a specific VLE binding protein from Xenopus oocytes. Interaction of 40LoVe with the VLE strictly correlates with the ability of the RNA to localize, and antibodies against 40LoVe inhibit vegetal localization in vivo in oocytes. Our results associate an hnRNP D protein with mRNA localization and have implications for several functions mediated by this important protein family.

Effects of Lactobacillus GG on genes expression pattern in small bowel mucosa

Background and aims. Probiotics have been used for cure and prevention of several clinical conditions. However, further insights into the mechanism of action are needed to understand the rationale of their use. The aim of this study was to investigate the influence of Lactobacillus GG on the genetic expression patterns in the small bowel mucosa. Methods. Six male patients (38 ± 5 years) with endoscopically proven oesophagitis were enrolled. All patients were treated for 1 month with esomeprazole and randomised to receive Lactobacillus GG or placebo. After 1 month of treatment, upper endoscopy was repeated. Biopsies of the duodenal mucosa were taken prior to and after the treatment, and the genes expression patterns were assessed using GeneChip Human U133A array. Genes with significant expression changes were selected and analysed to identify specific cellular pathways modified by Lactobacillus GG. To support the array data, 10 target genes were studied using Syber-Green PCR. Results. Microarray analysis showed that Lactobacillus GG administration determined the up- and down-regulation of 334 and 92 genes, respectively. Real-time PCR confirmed the reliability of the analysis. Lactobacillus GG mainly affected the expression of genes involved in immune response and inflammation (TGF-beta and TNF family members, cytokines, nitric oxide synthase 1, defensin alpha 1), apoptosis, cell growth and cell differentiation (cyclins and caspases, oncogenes), cell–cell signalling (ICAMs and integrins), cell adhesion (cadherins), signal transcription and transduction. Conclusions. These data indicate that administration of Lactobacillus GG is associated with a complex genetic response of the duodenal mucosa, reflected by the up- and down-regulation of several genes involved in specific cellular pathways.

Elimination of Myostatin Does Not Combat Muscular Dystrophy in dy Mice but Increases Postnatal Lethality

Myostatin is a TGF-beta family member and a negative regulator of skeletal muscle growth. It has been proposed that reduction or elimination of myostatin could be a treatment for degenerative muscle diseases such as muscular dystrophy. Laminin-deficient congenital muscular dystrophy is one of the most severe forms of muscular dystrophy. To test the possibility of ameliorating the dystrophic phenotype in laminin deficiency by eliminating myostatin, we crossed dy(W) laminin alpha2-deficient and myostatin null mice. The resulting double-deficient dy(W)/dy(W);Mstn(-/-) mice had a severe clinical phenotype similar to that of dy(W)/dy(W) mice, even though muscle regeneration was increased. Degeneration and inflammation of muscle were not alleviated. The pre-weaning mortality of dy(W)/dy(W);Mstn(-/-) mice was increased compared to dy(W)/dy(W), most likely due to significantly less brown and white fat in the absence of myostatin, and postweaning mortality was not significantly improved. These results show that eliminating myostatin in laminin-deficiency promotes muscle formation, but at the expense of fat formation, and does not reduce muscle pathology. Any future therapy based on myostatin may have undesirable side effects.

Visualizing Long-Range Movement of the Morphogen Xnr2 in the Xenopus Embryo

One way in which cells acquire positional information during embryonic development is by measuring the local concentration of a signaling factor, or morphogen, that is secreted by an organizing center . The ways in which morphogen gradients are established, particularly in vertebrates, remain obscure, although various suggestions have been made for the mechanisms by which signaling molecules traverse fields of cells. These include simple diffusion, "cytonemes", filopodia, "argosomes", and "transcytosis". In this study, we use a functional EGFP-tagged ligand to visualize long-range signaling in the Xenopus embryo in real time. Our results show that the TGF-beta family member Xnr2 is secreted efficiently from embryonic cells, and a new method of tissue recombination allows us to investigate the way in which the morphogen traverses multiple cell diameters. This reveals that Xnr2 exerts long-range effects by diffusing rapidly through the extracellular milieu of nonexpressing cells. No evidence has been obtained for long-range signaling through cytonemes, filopodia, argosomes, or transcytosis. In demonstrating that long-range signaling in the early Xenopus embryo occurs by diffusion rather than by these alternative routes, our results suggest that different morphogens in different developmental contexts use different means of transport.

Transforming growth factor-beta as a therapeutic target

Transforming growth factor-beta (TGF-beta) family members include TGF-beta, activins, and bone morphogenetic proteins (BMP). These proteins are structurally related cytokines secreted in diverse Metazoans. TGF-beta family members regulate cellular functions such as proliferation, apoptosis, differentiation, and migration, and play an important role in organism development. Deregulated TGF-beta family signaling participates in various human pathologies including autoimmune diseases, vascular disorders, fibrotic disease, and cancer. Ligand-induced activation of TGF-beta family receptors with intrinsic serine/threonine kinase activity, triggers phosphorylation of the intracellular effectors of TGF-beta signaling, the Smads proteins. Once these proteins are activated they translocate into the nucleus, where they induce transcription of target genes and regulate cellular processes and functions. Novel therapeutic strategies are currently being developed to correct alterations in pathologies that involve TGF-beta as the main mediator. The English version of this paper is available at: http://www.insp.mx/salud/index.html.

Genetic susceptibility to keloid disease: transforming growth factor beta receptor gene polymorphisms are not associated with keloid disease.

Keloid disease (KD) is an abnormal form of scarring with a familial predisposition. Genetic studies have yet to identify the genes involved in KD. Transforming growth factor beta (TGF-beta) has multiple cellular activities including cellular proliferation, differentiation and extracellular matrix production. TGF-beta family members such as TGF-beta(1) and TGF-beta(2) are known to be involved in KD formation. However, we previously demonstrated a lack of association between common TGF-beta(1) and TGF-beta(2) polymorphisms and KD. Other studies have implicated TGF-beta receptors in KD pathogenesis. TGF-beta receptors were therefore selected as candidate-susceptibility genes for this condition. Single-nucleotide polymorphisms (SNPs) in TGF-beta receptors I, II and III (TGF-betaRI, TGF-betaRII and TGF-betaRIII) were identified and investigated for association with the risk of developing KD. A polymerase chain reaction-restriction fragment length polymorphism method was used for genotyping novel and known TGF-beta receptor polymorphisms. DNA samples from 92 KD cases and 181 controls were examined. There were no statistically significant differences in genotype or allele frequency distributions between cases and controls for the TGF-beta receptor SNPs. Therefore, these TGF-beta receptor polymorphisms are unlikely to be associated with keloid scarring. It is possible that other SNPs in other TGF-beta family members are associated with KD. To our knowledge, this is the first report of a case-control association study with KD and TGF-beta receptor gene polymorphisms.

The immunophilin FKBP12: a molecular guardian of the TGF-beta family type I receptors.

FKBP12 as an immunophilin that binds to two well-known immunosuppressive macrolides, FK506 and rapamycin, has attracted immense attention and its role in mediating the immunosuppressive functions of these macrolides has been extensively studied. Since FKBP12 is a well-conserved protein among many species and is also highly expressed in almost all cells, it must play important roles in cellular function in the absence of macrolides. In one such a role, FKBP12 interacts with and regulates the functional state of the ryanodine Ca2+ channel receptor by altering protein conformation and coordinating multi-protein complex formation. This review summarizes another physiological role of FKBP12 as an interactor and a regulator of the type I serine/threonine kinase receptors of TGF-beta superfamily. Current data, derived from detailed biochemical studies as well as from functional studies in various systems, suggest that FKBP12 functions as a "guardian" for the type I receptors to prevent them from leaky signaling under sub-optimal ligand concentrations, thereby providing a molecular "gradient reader" for TGF-beta family morphogens. This aspect of FKBP12 function may be critical for cellular responsiveness to morphogenetic gradients of the TGF-beta family members during early development, serving to assure the translation of different ligand concentrations into different signaling readouts.

Mutations of the anti-mullerian hormone gene in patients with persistent mullerian duct syndrome: biosynthesis, secretion, and processing of the abnormal proteins and analysis using a three-dimensional model.

Anti-Müllerian hormone (AMH), a TGF-beta family member, determines whether an individual develops a uterus and Fallopian tubes. Mutations in the AMH gene lead to persistent Müllerian duct syndrome in males. The wild-type human AMH protein is synthesized as a disulfide-linked dimer of two identical 70-kDa polypeptides, which undergoes proteolytic processing to generate a 110-kDa N-terminal dimer and a bioactive 25-kDa TGF-beta-like C-terminal dimer. We have studied the biosynthesis and secretion of wild-type AMH and of seven persistent Müllerian duct syndrome proteins, containing mutations in either the N- or C-terminal domain. Mutant proteins lacking the C-terminal domain are secreted more rapidly than full-length AMH, whereas single amino acid changes in both domains can have profound effects on protein stability and folding. The addition of a cysteine in an N-terminal domain mutant, R194C, prevents proper folding, whereas the elimination of the cysteine involved in forming the interchain disulfide bond, in a C-terminal domain mutant, C525Y, leads to a truncation at the C terminus. A molecular model of the AMH C-terminal domain provides insights into how some mutations could affect biosynthesis and function.

Alk8 is required for neural crest cell formation and development of pharyngeal arch cartilages.

The type I TGFbeta family member receptor alk8 acts in bone morphogenetic protein (BMP) signaling pathways to establish dorsoventral patterning in the early zebrafish embryo. Here, we present evidence that alk8 is required for neural crest cell (NCC) formation and that alk8 signaling gradients direct the proper patterning of premigratory NCCs. We extend our previous functional studies of alk8 to demonstrate that ectopic expression of constitutively active and dominant negative Alk8, consistently results in more medially or laterally positioned premigratory NCCs, respectively. We also demonstrate that patterning defects in premigratory NCCs, induced by alk8 misexpression, correlate with subsequent defects in NCC-derived pharyngeal arch cartilages. Furthermore, an anteroposterior effect is revealed, where overexpression of Alk8 more severely affects anterior arch cartilages and decreased Alk8 activity more severely affects posterior arch cartilage formation. Ectopic expression studies of alk8 are supported by analyses of zygotic and maternal-zygotic laf/alk8 mutants and of several BMP pathway mutants. Pharyngeal mesodermal and endodermal defects in laf/alk8 mutants suggest additional roles for alk8 in patterning of these tissues. Our results provide insight into alk8-mediated BMP signaling gradients and the establishment of premigratory NCC mediolateral positioning, and extend the model for BMP patterning of the neural crest to include that of NCC-derived pharyngeal arch cartilages.

Myostatin signals through a transforming growth factor beta-like signaling pathway to block adipogenesis.

Myostatin, a transforming growth factor beta (TGF-beta) family member, is a potent negative regulator of skeletal muscle growth. In this study we characterized the myostatin signal transduction pathway and examined its effect on bone morphogenetic protein (BMP)-induced adipogenesis. While both BMP7 and BMP2 activated transcription from the BMP-responsive I-BRE-Lux reporter and induced adipogenic differentiation, myostatin inhibited BMP7- but not BMP2-mediated responses. To dissect the molecular mechanism of this antagonism, we characterized the myostatin signal transduction pathway. We showed that myostatin binds the type II Ser/Thr kinase receptor. ActRIIB, and then partners with a type I receptor, either activin receptor-like kinase 4 (ALK4 or ActRIB) or ALK5 (TbetaRI), to induce phosphorylation of Smad2/Smad3 and activate a TGF-beta-like signaling pathway. We demonstrated that myostatin prevents BMP7 but not BMP2 binding to its receptors and that BMP7-induced heteromeric receptor complex formation is blocked by competition for the common type II receptor, ActRIIB. Thus, our results reveal a strikingly specific antagonism of BMP7-mediated processes by myostatin and suggest that myostatin is an important regulator of adipogenesis.

Growth differentiation factor-9 induces Smad2 activation and inhibin B production in cultured human granulosa-luteal cells.

The TGF beta family member growth differentiation factor-9 (GDF-9) is an oocyte-derived factor that is essential for mammalian ovarian folliculogenesis. GDF-9 mRNAs have been shown to be expressed in the human ovarian follicle from the primary follicle stage onward, and recombinant GDF-9 has been shown to promote human ovarian follicle growth in vitro. In this study with primary cultures of human granulosa-luteal (hGL) cells, we investigated whether recombinant GDF-9 activates components of the Smad signaling pathways known to be differentially activated by TGF beta and the bone morphogenetic proteins (BMPs). As with TGF beta, GDF-9 treatment caused the phosphorylation of endogenous 53-kDa proteins detected in Western blots with antiphospho-Smad2 antibodies (alpha PS2). However, unlike BMP-2, GDF-9 did not activate the phosphorylation of antiphospho-Smad1 antibody (alphaPS1)-immunoreactive proteins in hGL cells. Infection of hGL cells with an adenovirus expressing Smad2 (Ad-Smad2) confirmed that GDF-9 activates specifically phosphorylation of the Smad2 protein. Infection of hGL cells with Ad-Smad7, which expresses the inhibitory Smad7 protein, suppressed the levels of both GDF-9-induced endogenous and adenoviral alpha PS2-reactive proteins. Furthermore, GDF-9 increased the steady state levels of inhibin beta(B)-subunit mRNAs in hGL cells and strongly stimulated the secretion of dimeric inhibin B. Again, Ad-Smad7 blocked GDF-9-stimulated inhibin B production in a concentration-dependent manner. We identify here for the first time distinct molecular components of the GDF-9 signaling pathway in the human ovary. Our data suggest that GDF-9 mediates its effect through the pathway commonly activated by TGF beta and activin, but not that activated by many BMPs. The results are also consistent with the suggestion that in addition to endocrine control of inhibin production by gonadotropins, a local paracrine control of inhibin production is likely to occur via oocyte-derived factors in the human ovary.

Receptor-regulated Smads in TGF-beta signaling.

Transforming growth factor beta (TGF-beta) and related polypeptides, including activins and bone morphogenetic proteins (BMPs), constitute the largest cytokine family, possessing fascinating features. TGF-beta and related peptides are multifunctional growth factors and they regulate many aspects of cellular processes such as proliferation, differentiation, adhesion and apoptosis. These evolutionarily conserved cytokines play an essential role in the development and homeostasis of virtually every tissue in organisms ranging from fruit flies to humans. Accordingly, inactivating mutations in several components of the TGF-beta signaling pathways have been found to cause a number of human disorders. The TGF-beta family members signal through cell surface serine/threonine kinase receptors. A family of proteins, designated as Smads (mammalian homologues of Drosophila Mad and C. elegans Sma), transduces the TGF-beta signal from cell surface to the nucleus. Upon activation, the TGF-beta type I receptor phosphorylates Smad2 and Smad3, which then form complexes with Smad4 and accumulate in the nucleus to regulate transcription of a variety of genes that encode crucial determinants of cell fate, such as cell cycle components, differentiation factors and cell adhesion molecules. Although Smad2 and Smad3 are highly homologous and share some overlapping activities, they have distinct functions and are regulated differentially. This review is primarily focused on our understanding of the similar as well as distinct function and regulation of Smad2 and Smad3 in TGF-beta signaling, their physiological roles revealed by knockout studies and their tumor suppressive functions.

Microarray analysis of bone morphogenetic protein, transforming growth factor beta, and activin early response genes during osteoblastic cell differentiation.

Bone morphogenetic protein (BMP) 2, a member of the transforming growth factor (TGF) beta family, is a potent regulator of osteoblast differentiation. In addition, both TGF-beta and activin A can either induce bone formation or inhibit bone formation depending on cell type and differentiation status. Although much is known about the receptors and intracellular second messengers involved in the action of TGF-beta family members, little is known about how selectivity in the biological response of individual family members is controlled. In this study, we have investigated selective gene induction by BMP-2, TGF-beta1 and activin A in relation to their ability to control differentiation of mouse mesenchymal precursor cells C2C12 into osteoblastic cells. TGF-beta1 can inhibit BMP-2-induced differentiation of these cells, whereas activin A was found to be without morphogenetic effect. Using a gene expression microarray approach covering 8636 sequences, we have identified a total of 57 established genes and expressed sequence tags (ESTs) that were either up-regulated or down-regulated 2 h after treatment with at least one of these three stimuli. With respect to the established genes, 15 new target genes for TGF-beta family members thus were identified. Furthermore, a set of transcripts was identified, which was oppositely regulated by TGF-beta1 and BMP-2. Based on the inverse biological effects of TGF-beta1 and BMP-2 on C2C12 cells, these genes are important candidates for controlling the process of growth factor-induced osteoblast differentiation.

Transcriptional activation of endoglin and transforming growth factor-β signaling components by cooperative interaction between Sp1 and KLF6: their potential role in the response to vascular injury

Endoglin is an endothelial membrane glycoprotein involved in cardiovascular morphogenesis and vascular remodeling. It associates with transforming growth factor-beta (TGF-beta) signaling receptors to bind TGF-beta family members, forming a functional receptor complex. Arterial injury leads to up-regulation of endoglin, but the underlying regulatory events are unknown. The transcription factor KLF6, an immediate-early response gene induced in endothelial cells during vascular injury, transactivates TGF-beta, TGF-beta signaling receptors, and TGF-beta-stimulated genes. KLF6 and, subsequently, endoglin were colocalized to vascular endothelium (ie, expressed in the same cell type) following carotid balloon injury in rats. After endothelial denudation, KLF6 was induced and translocated to the nucleus; this was followed 6 hours later by increased endoglin expression. Transient overexpression of KLF6, but not Egr-1, stimulated endogenous endoglin mRNA and transactivated the endoglin promoter. This transactivation was dependent on a GC-rich tract required for basal activity of the endoglin promoter driven by the related GC box binding protein, Sp1. In cells lacking Sp1 and KLF6, transfected KLF6 and Sp1 cooperatively transactivated the endoglin promoter and those of collagen alpha1(I), urokinase-type plasminogen activator, TGF-beta1, and TGF-beta receptor type 1. Direct physical interaction between Sp1 and KLF6 was documented by coimmunoprecipitation, pull-down experiments, and the GAL4 one-hybrid system, mapping the KLF6 interaction to the C-terminal domain of Sp1. These data provide evidence that injury-induced KLF6 and preexisting Sp1 may cooperate in regulating the expression of endoglin and related members of the TGF-beta signaling complex in vascular repair.

Activin/TGF-beta induce apoptosis through Smad-dependent expression of the lipid phosphatase SHIP.

Members of the transforming growth factor beta (TGF-beta) family regulate fundamental physiological processes, such as cell growth, differentiation and apoptosis, in almost all cell types. As a result, defects in TGF-beta signalling pathways have been linked to uncontrolled cellular proliferation and carcinogenesis. Here, we explored the signal transduction mechanisms downstream of the activin/TGF-beta receptors that result in cell growth arrest and apoptosis. We show that in haematopoietic cells, TGF-beta family members regulate apoptosis through expression of the inositol phosphatase SHIP (Src homology 2 (SH2) domain-containing 5' inositol phosphatase), a central regulator of phospholipid metabolism. We also demonstrated that the Smad pathway is required in the transcriptional regulation of the SHIP gene. Activin/TGF-beta-induced expression of SHIP results in intracellular changes in the pool of phospholipids, as well as in inhibition of both Akt/PKB (protein kinase B) phosphorylation and cell survival. Our results link phospholipid metabolism to activin/TGF-beta-mediated apoptosis and define TGF-beta family members as potent inducers of SHIP expression.

Requirement of Bmpr1a for Müllerian duct regression during male sexual development.

Elimination of the developing female reproductive tract in male fetuses is an essential step in mammalian sexual differentiation. In males, the fetal testis produces the transforming growth factor beta (TGF-beta) family member anti-Müllerian hormone (Amh, also known as Müllerian-inhibiting substance (Mis)), which causes regression of the Müllerian ducts, the primordia of the oviducts, uterus and upper vagina. Amh induces regression by binding to a specific type II receptor (Amhr2) expressed in the mesenchyme surrounding the ductal epithelium. Mutations in AMH or AMHR2 in humans and mice disrupt signaling, producing male pseudohermaphrodites that possess oviducts and uteri. The type I receptor and Smad proteins that are required in vivo for Müllerian duct regression have not yet been identified. Here we show that targeted disruption of the widely expressed type I bone morphogenetic protein (BMP) receptor Bmpr1a (also known as Alk3) in the mesenchymal cells of the Müllerian ducts leads to retention of oviducts and uteri in males. These results identify Bmpr1a as a type I receptor for Amh-induced regression of Müllerian ducts. Because Bmpr1a is evolutionarily conserved, these findings indicate that a component of the BMP signaling pathway has been co-opted during evolution for male sexual development in amniotes.

Novel single nucleotide polymorphisms in the 3'-UTR of the TGFbetaRI and TGFbetaRIII genes.

Transforming growth factor beta (TGFbeta) family members are multifunctional cytokines that play a key role in cellular growth, proliferation and differentiation. Transmembrane signalling by TGFbeta occurs via a complex of the serine/threonine kinases TGFbeta type 1 (TGFbetaRI), type 2 (TGFbetaRII), and type 3 (TGFbetaRIII) receptors. Previous studies have implicated TGFbeta receptors (TGFbetaR) in a variety of important hereditary clinical disorders. Mutations of the TGFbetaR genes have been observed in several human cancers. The aim of this study was to identify and confirm novel single nucleotide polymorphisms (SNPs) in TGFbetaRI and RIII and to determine the relative allele and genotype frequencies of these SNPs. SNPs were identified from the examination of sequence alignments held in databases and were confirmed by DNA sequencing. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was devised for genotyping TGFbeta receptor polymorphisms. DNA samples from 91 controls were examined. The observed heterozygosities of TGFbetaRI and TGFbetaRIII gene polymorphisms in the control population were 43 and 33%, respectively, suggesting these SNPs could be useful markers in disease association studies.

Stem cell differentiation requires a paracrine pathway in the heart.

Members of the transforming growth factor beta1 (TGF-beta) superfamily--namely, TGF-beta and BMP2--applied to undifferentiated murine embryonic stem cells up-regulated mRNA of mesodermal (Brachyury) and cardiac specific transcription factors (Nkx2.5, MEF2C). Embryoid bodies generated from stem cells primed with these growth factors demonstrated an increased potential for cardiac differentiation with a significant increase in beating areas and enhanced myofibrillogenesis. In an environment of postmitotic cardiomyocytes, stem cells engineered to express a fluorescent protein under the control of a cardiac promoter differentiated into fluorescent ventricular myocytes beating in synchrony with host cells, a process significantly enhanced by TGF-beta or BMP2. In vitro, disruption of the TGF-beta/BMP signaling pathways by latency-associated peptide and/or noggin prevented differentiation of stem cells. In fact, only host cells that secrete a TGF-beta family member induced a cardiac phenotype in stem cells. In vivo, transplantation of stem cells into heart also resulted in cardiac differentiation provided that TGF-beta/BMP2 signaling was intact. In infarcted myocardium, grafted stem cells differentiated into functional cardiomyocytes integrated with surrounding tissue, improving contractile performance. Thus, embryonic stem cells are directed to differentiate into cardiomyocytes by signaling mediated through TGF-beta/BMP2, a cardiac paracrine pathway required for therapeutic benefit of stem cell transplantation in diseased heart.

Differential gene expression of TGF-beta family members and osteopontin in breast tumor tissue: analysis by real-time quantitative PCR.

Several cytokines including members of the transforming growth factor-beta (TGF-beta) and tumor necrosis factor (TNF) families have been implicated in the homing mechanism of breast cancer metastasis. We hypothesize that primary breast tumor tissues differentially express modulators of bone cell function and that this expression pattern contributes to their aggressive and metastatic potential and to their capacity to establish and grow in bone. We, therefore, examined the gene expression pattern of the TGF-beta family members (inhibin/activin betaA subunit (activin betaA), inhibin alpha subunit, and bone morphogenetic protein-2 (BMP-2)), the TNF family members (receptor activator of NF-KB ligand (RANKL) and osteoprotegerin (OPG)), and osteopontin (OPN) in normal, non-invasive, invasive, and metastatic human breast cancer specimens. The mRNA transcript levels of these genes were quantified by reverse transcription (RT) and fluorescent-based kinetic PCR in 18 normal breast tissues, five ductal carcinoma in situ (DCIS). 24 primary breast tumor tissue, and five distant metastases. The mRNA transcript level of each gene was normalized to the amount of beta-actin present in the samples. We observed differential gene expression of the selected TGF-beta family members as well as OPN in breast cancer progression. The average gene expression of the putative tumor suppressor, inhibin alpha, did not significantly change in any of the tumor tissues examined compared to normal breast tissue. The mRNA level of BMP-2, a protein with anti-proliferative effects in breast cancer cell lines and involved in bone formation, significantly decreased in non-invasive, invasive, and liver metastatic breast tumor tissue compared to normal breast tissue. The gene expression of activin betaA, a protein involved in cell proliferation and osteoclast induction, increased in invasive and bone metastatic tumor tissue compared to normal breast tissue. The mRNA level of OPN, a bone matrix protein associated with enhanced malignancy, increased in non-invasive, invasive, and liver and bone metastatic breast tumor tissue compared to normal breast tissue. In contrast, the average gene expressions of the TNF family members, RANKL and OPG, proteins involved in the regulation of osteoclastogenesis, were only slightly if at all changed in the different stage breast tumor tissues. These results suggest that differential gene expression of bone-related proteins, especially OPN, activin betaA, and BMP-2, by primary breast tumor tissues may play a significant role in the invasiveness and metastatic potential of breast cancer.