Molecular cloning and structure of the human transforming growth factor-beta 2 gene promoter

The Research Progress in Transforming Growth Factor-β2

Transforming growth factor-beta 2 (TGF-β2), an important member of the TGF-β family, is a secreted protein that is involved in many biological processes, such as cell growth, proliferation, migration, and differentiation. TGF-β2 had been thought to be functionally identical to TGF-β1; however, an increasing number of recent studies uncovered the distinctive features of TGF-β2 in terms of its expression, activation, and biological functions. Mice deficient in TGF-β2 showed remarkable developmental abnormalities in multiple organs, especially the cardiovascular system. Dysregulation of TGF-β2 signalling was associated with tumorigenesis, eye diseases, cardiovascular diseases, immune disorders, as well as motor system diseases. Here, we provide a comprehensive review of the research progress in TGF-β2 to support further research on TGF-β2.

Roles of vitamins in stem cells

Stem cells can differentiate to diverse cell types in our body, and they hold great promises in both basic research and clinical therapies. For specific stem cell types, distinctive nutritional and signaling components are required to maintain the proliferation capacity and differentiation potential in cell culture. Various vitamins play essential roles in stem cell culture to modulate cell survival, proliferation and differentiation. Besides their common nutritional functions, specific vitamins are recently shown to modulate signal transduction and epigenetics. In this article, we will first review classical vitamin functions in both somatic and stem cell cultures. We will then focus on how stem cells could be modulated by vitamins beyond their nutritional roles. We believe that a better understanding of vitamin functions will significantly benefit stem cell research, and help realize their potentials in regenerative medicine.

Role of areca nut induced JNK/ATF2/Jun axis in the activation of TGF-β pathway in precancerous Oral Submucous Fibrosis

Oral submucous fibrosis (OSF) is potentially premalignant with progressive and irreversible extracellular matrix deposition accompanied by epithelial atrophy and like other fibrotic disorders, is primarily a TGF-β driven disease. OSF is caused by prolonged chewing of areca nut. Our previous studies reported a pivotal role for TGF-β activation and its effects contributing to OSF. However, the mechanism for activation of TGF-β signaling in OSF is still unknown. In this study we demonstrate activation of TGF-β signaling with sub-cytotoxic dose of areca nut in epithelial cells and discovered a key role for pJNK in this process. In good correlation; pJNK was detected in OSF tissues but not in normal tissues. Moreover, activation of JNK was found to be dependent on muscarinic acid receptor induced Ca²⁺/CAMKII as well as ROS. JNK dependent phosphorylation of ATF2/c-Jun transcription factors resulted in TGF-β transcription and its signaling. pATF2/p-c-Jun were enriched on TGF-β promoter and co-localized in nuclei of epithelial cells upon areca nut treatment. In corroboration, OSF tissue sections also had nuclear pATF2 and p-c-Jun. Our results provide comprehensive mechanistic details of TGF-β signaling induced by etiological agent areca nut in the manifestation of fibrosis which can lead to new therapeutic modalities for OSF.

Primary culture of avian embryonic heart forming region cells to study the regulation of vertebrate early heart morphogenesis by vitamin A

Background

Important knowledge about the role of vitamin A in vertebrate heart development has been obtained using the vitamin A-deficient avian in ovo model which enables the in vivo examination of very early stages of vertebrate heart morphogenesis. These studies have revealed the critical role of the vitamin A-active form, retinoic acid (RA) in the regulation of several developmental genes, including the important growth regulatory factor, transforming growth factor-beta2 (TGFβ2), involved in early events of heart morphogenesis. However, this in ovo model is not readily available for elucidating details of molecular mechanisms determining RA activity, thus limiting further examination of RA-regulated early heart morphogenesis. In order to obtain insights into RA-regulated gene expression during these early events, a reliable in vitro model is needed. Here we describe a cell culture that closely reproduces the in ovo observed regulatory effects of RA on TGFβ2 and on several developmental genes linked to TGFβ signaling during heart morphogenesis.

Results

We have developed an avian heart forming region (HFR) cell based in vitro model that displays the characteristics associated with vertebrate early heart morphogenesis, i.e. the expression of Nkx2.5 and GATA4, the cardiogenesis genes, of vascular endothelial growth factor (VEGF-A), the vasculogenesis gene and of fibronectin (FN1), an essential component in building the heart, and the expression of the multifunctional genes TGFβ2 and neogenin (NEO). Importantly, we established that the HFR cell culture is a valid model to study RA-regulated molecular events during heart morphogenesis and that the expression of TGFβ2 as well as the expression of several TGFβ2-linked developmental genes is regulated by RA.

Conclusions

Our findings reported here offer a biologically relevant experimental in vitro system for the elucidation of RA-regulated expression of TGFβ2 and other genes involved in vertebrate early cardiovascular morphogenesis.

Transforming growth factor beta2 is negatively regulated by endogenous retinoic acid during early heart morphogenesis

Vitamin A-deficient (VAD) quail embryos lack the vitamin A-active form, retinoic acid (RA) and are characterized by a phenotype that includes a grossly abnormal cardiovascular system that can be rescued by RA. Here we report that the transforming growth factor, TGFbeta2 is involved in RA-regulated cardiovascular development. In VAD embryos TGFbeta2 mRNA and protein expression are greatly elevated. The expression of TGFbeta receptor II is also elevated in VAD embryos but is normalized by treatment with TGFbeta2-specific antisense oligonucleotides (AS). Administration of this AS or an antibody specific for TGFbeta2 to VAD embryos normalizes posterior heart development and vascularization, while the administration of exogenous active TGFbeta2 protein to normal quail embryos mimics the excessive TGFbeta2 status of VAD embryos and induces VAD cardiovascular phenotype. In VAD embryos pSmad2/3 and pErk1 are not activated, while pErk2 and pcRaf are elevated and pSmad1/5/8 is diminished. We conclude that in the early avian embryo TGFbeta2 has a major role in the retinoic acid-regulated posterior heart morphogenesis for which it does not use Smad2/3 pathways, but may use other signaling pathways. Importantly, we conclude that retinoic acid is a critical negative physiological regulator of the magnitude of TGFbeta2 signals during vertebrate heart formation.

Microenvironment alters epigenetic and gene expression profiles in Swarm rat chondrosarcoma tumors

BACKGROUND

Chondrosarcomas are malignant cartilage tumors that do not respond to traditional chemotherapy or radiation. The 5-year survival rate of histologic grade III chondrosarcoma is less than 30%. An animal model of chondrosarcoma has been established--namely, the Swarm Rat Chondrosarcoma (SRC)--and shown to resemble the human disease. Previous studies with this model revealed that tumor microenvironment could significantly influence chondrosarcoma malignancy.

METHODS

To examine the effect of the microenvironment, SRC tumors were initiated at different transplantation sites. Pyrosequencing assays were utilized to assess the DNA methylation of the tumors, and SAGE libraries were constructed and sequenced to determine the gene expression profiles of the tumors. Based on the gene expression analysis, subsequent functional assays were designed to determine the relevancy of the specific genes in the development and progression of the SRC.

RESULTS

The site of transplantation had a significant impact on the epigenetic and gene expression profiles of SRC tumors. Our analyses revealed that SRC tumors were hypomethylated compared to control tissue, and that tumors at each transplantation site had a unique expression profile. Subsequent functional analysis of differentially expressed genes, albeit preliminary, provided some insight into the role that thymosin-β4, c-fos, and CTGF may play in chondrosarcoma development and progression.

CONCLUSION

This report describes the first global molecular characterization of the SRC model, and it demonstrates that the tumor microenvironment can induce epigenetic alterations and changes in gene expression in the SRC tumors. We documented changes in gene expression that accompany changes in tumor phenotype, and these gene expression changes provide insight into the pathways that may play a role in the development and progression of chondrosarcoma. Furthermore, specific functional analysis indicates that thymosin-β4 may have a role in chondrosarcoma metastasis.

Vitamin A-not for your eyes only: requirement for heart formation begins early in embryogenesis

Vitamin A insufficiency has profound adverse effects on embryonic development. Major advances in understanding the role of vitamin A in vertebrate heart formation have been made since the discovery that the vitamin A active form, all-trans-retinoic acid, regulates many genes, including developmental genes. Among the experimental models used, the vitamin A-deficient avian embryo has been an important tool to study the function of vitamin A during early heart formation. A cluster of retinoic acid-regulated developmental genes have been identified that participate in building the heart. In the absence of retinoic acid the embryonic heart develops abnormally leading to embryolethality.

Hepatitis C virus core protein triggers hepatic angiogenesis by a mechanism including multiple pathways

Chronic hepatitis C virus (HCV) infection is associated with the production of serum cytokines, including transforming growth factor (TGF)-beta2. Despite the occurrence of hepatic angiogenesis in liver conditions, the role of HCV proteins in this context is currently unknown. We demonstrated that the development of hepatic neoangiogenesis in patients infected with HCV is associated with the expression of TGF-beta2 and vascular endothelial growth factor (VEGF) and with activation of endothelial cells, as evidenced by CD34 expression. The analysis of liver biopsies of HCV-positive and HCV-negative patients using immunostaining showed significant elevation of TGF-beta2, VEGF, and CD34 expression in patients who were HCV-positive. Using an HCV established culture system, we confirmed further the production of both TGF-beta2 and VEGF proteins, in the hepatoma cell lines HepG2 and Huh7 by transfection with full-length HCV RNA (JFH1) or by the regulated expression of core. In addition, regulated expression of core protein in HepG2 or Huh7 cells was found to induce expression and activation of the transcription factor E2F1 and apoptosis signal-regulating kinase 1 (ASK1), activation of c-jun-N-terminal kinase (JNK) and p38, and extracellular-regulated kinase (ERK), and transcription factors activator protein 1 (AP-1), activating transcription factor 2 (ATF-2), cyclic adenosine monophosphate response element binding (CREB), E2F1, hypoxia inducing factor 1 alpha (HIF-1alpha), and specificity protein 1. Furthermore, data obtained from inhibitor experiments revealed the importance of E2F1 and ASK1 in the modulation of core-induced activation of JNK and p38 pathways and suggested an essential role for JNK, p38, and ERK pathways in the regulation of core-induced production of TGF-beta2 and VEGF proteins. Thus, our data provide insight into the molecular mechanisms whereby core protein mediates the development of hepatic angiogenesis in patients with chronic HCV infection.

Interferon-gamma differentially regulates TGF-beta1 and TGF-beta2 expression in human retinal pigment epithelial cells through JAK-STAT pathway

Retinal pigment epithelium (RPE) and transforming growth factor-beta (TGF-beta) have been shown to be involved in various retinal diseases. We have studied the role of inflammatory cytokines on the expression and secretion of TGF-beta in human RPE cells (HRPE). Confluent cultures of HRPE derived from donor eyes were used. RT-PCR analyses showed that TNF-alpha and IL-1beta increased the mRNA levels of both TGF-beta1 and TGF-beta2. IFN-gamma enhanced constitutively expressed, as well as, TNF-alpha-and IL-1beta-induced TGF-beta1 mRNA levels but decreased TGF-beta2 mRNA. The effects of these cytokines on TGF-beta1 and TGF-beta2 secretion correlated with the mRNA levels. TGF-beta1 was always produced as the latent form while 21-31% of TGF-beta2 was in the active form. IFN-gamma reduced the production of active form of TGF-beta2 to 4-9%. TGF-beta3 secretion was not detectable under any of the conditions. The Real-Time PCR analysis of TGF-beta mRNAs confirmed the observed results. The TGF-beta1 and TGF-beta2 secretion was induced by TGF-beta2 and TGF-beta1, respectively. Under these conditions, the contrasting effects of IFN-gamma on TGF-beta1 and TGF-beta2 secretion were also observed. JAK inhibitor selectively inhibited IFN-gamma induced TGF-beta1 secretion and mRNA levels while reversing the inhibitory effects of IFN-gamma on TGF-beta2. Analyses of transcription factor activity strongly indicated the role of STAT-1 but not NFkappaB, C-Myc, C-Jun, SP-1, MEF-2. Our data demonstrate that IFN-gamma differentially regulates constitutively expressed, as well as, cytokine-induced TGF-beta1 and TGF-beta2 mRNA levels and secretion of TGF-betas by HRPE.

A novel functional polymorphism in the transforming growth factor-beta2 gene promoter and tumor progression in breast cancer

Transforming growth factor-beta (TGF-beta), a multifunctional growth factor, plays an important role in breast cancer. There is increasing evidence that enhanced expression of TGF-beta promotes breast cancer progression contributing to metastasis and invasiveness of the tumor. We identified a functional polymorphism in the TGFB2 promoter, a 4-bp insertion at position -246 relative to the transcriptional start site (-246ins). Transient transfection experiments showed that the -246ins polymorphism significantly increased TGFB2 promoter activity in breast cancer cells. Electrophoretic mobility shift assays revealed binding of the transcription factor Sp1 to the -246ins allele. Overexpression of Sp1 enhanced promoter activity of the -246ins allele, demonstrating that Sp1 mediates transcriptional activation. Furthermore, the -246ins allele was associated with enhanced TGF-beta(2) expression in breast cancer tissue (P = 0.0005). To evaluate the role of the polymorphism in breast cancer, frequency of the -246ins allele was determined in breast cancer patients (n = 78) and healthy female controls (n = 143). No significant differences were found. However, the presence of the -246ins allele was associated with lymph node metastasis (P = 0.003). The -246ins allele was a significant predictor for lymph node metastasis independent of estrogen and progesterone receptor status in a multivariate logistic regression analysis (P = 0.0118, odds ratio, 5.18; 95% confidence interval, 1.44-18.62). We provide evidence that the TGFB2 -246ins polymorphism leads to enhanced TGF-beta(2) expression levels in vivo and might thereby contribute to tumor progression and development of metastases.

Keratocan expression of murine keratocytes is maintained on amniotic membrane by down-regulating transforming growth factor-beta signaling

Keratocytes in the corneal stroma express keratan sulfate-containing proteoglycans including cornea-specific keratocan. On plastic dishes, human, bovine, and rabbit keratocytes lose their characteristic dendritic morphology and keratocan expression when cultured in serum-containing media. Herein, we demonstrated that murine keratocytes also acquired a fibroblastic shape and lost keratocan expression after first passage when cultured on plastic in the presence of serum. In contrast, cells expanded on human amniotic membrane (AM) stromal matrix maintained a three-dimensional dendritic morphology and expressed keratocan mRNA and protein for at least 8 passages before senescence. When keratocytes were cultured on AM, the promoter activity of transforming growth factor (TGF)-beta2 and TGF-beta receptor II was down-regulated as compared with that on plastic. Furthermore, cells on AM continuously retained Smad 2 and Smad 4 in the cytoplasm and did not express alpha-smooth muscle actin, even when 10 ng/ml TGF-beta1 was added in a serum-free medium for up to 5 days. In parallel to such down-regulation of TGF-beta signaling, keratocan promoter-driven ECFP expression was observed in cells cultured either on AM in the presence of serum or on plastic containing serum treated with a neutralizing antibody to TGF-beta. Collectively, these results indicate that down-regulation of Smad-mediated TGF-beta signaling is an important mechanism for cultured keratocytes to maintain a normal phenotype while continuously expanded in a serum-containing medium. This strategy of suppressing TGF-beta signaling, achieved by AM stromal matrix in part via suppression of TGF-beta gene transcription, can be used to expand keratocytes in culture without the use of AM in the future.

Effect of hypoxia and reoxygenation on gene expression and response to interleukin-1 in cultured articular chondrocytes

OBJECTIVE

To determine the effects of hypoxia and reoxygenation on the metabolism of chondrocytes and their response to interleukin-1beta (IL-1beta). The study included activation of hypoxia-inducible factor 1 (HIF-1), NF-kappaB, and activator protein 1 (AP-1) transcription factors, expression of matrix components and metalloproteases and transforming growth factor beta (TGFbeta) and TGFbeta receptors, and production of nitric oxide (NO) and prostaglandin E(2) (PGE(2)).

METHODS

Bovine articular chondrocytes (BACs) were cultured to confluency in either 5% O(2) (hypoxia) or 21% O(2) (normoxia) in media supplemented with 10% fetal calf serum (FCS). BACs were preincubated for 18 hours in media with 1% FCS only and then incubated for 24 hours in the presence of IL-1beta. For reoxygenation experiments, cells were treated in the same way in 5% O(2), except that cultures were transferred to normal atmospheric conditions and used after 4 hours for RNA extraction or after 30 minutes for cytoplasmic or nuclear protein extraction.

RESULTS

In hypoxic and reoxygenated chondrocytes, we observed strong DNA binding of HIF-1. IL-1beta-induced DNA binding of NF-kappaB and AP-1 was significantly higher in hypoxic and reoxygenated cultures than in normoxia. Greater activation of the MAPKs was also observed with IL-1beta treatment in hypoxia compared with normoxia. Steady-state levels of type II collagen and aggrecan core protein messenger RNA (mRNA) were decreased by IL-1beta in all instances. Matrix metalloprotease 1 (MMP-1) and MMP-3 mRNA were increased by IL-1beta in normoxia and hypoxia, whereas only MMP-3 mRNA was enhanced in reoxygenated cultures. The MMP-2 mRNA level was not significantly affected by IL-1beta in normoxia or hypoxia, whereas it was enhanced in reoxygenated cultures. MMP-9 mRNA was dramatically decreased by IL-1beta only in low oxygen tension. Tissue inhibitor of metalloproteinases 1 (TIMP-1) message was significantly enhanced by the cytokine in most instances, whereas TIMP-2 message was markedly decreased by IL-1beta in reoxygenated cultures. Stimulation of TGFbeta1 expression by IL-1beta was observed only in normal atmospheric conditions. One of the more striking findings of the study was the greater stimulating effect of IL-1beta on NO production observed in hypoxia, which was much higher than in normoxia, whereas the reverse was observed for IL-1beta-induced PGE(2) production.

CONCLUSION

Oxygen level and reoxygenation stress significantly modulate gene expression and the response of articular chondrocytes to cytokines such as IL-1beta. In hypoxic conditions, which mimic the in vivo condition of cartilage, the effects of IL-1beta on both synthesis and degradative processes are significantly different from those in normoxia, conditions that are unlikely encountered by chondrocytes in a normal state. In low oxygen tension, high IL-1beta-induced NO production is associated with a significant decrease in PGE(2) synthesis. These data should influence our concept of the role of oxygen in the pathophysiology of joint disease and may help define the best conditions in which to develop bioartificial cartilage.

Glucocorticoid regulation of human BMP-6 transcription

Addition of dexamethasone (Dex) to human mesenchymal stem cells (hMSCs) resulted in a 16-fold increase in human bone morphogenetic protein-6 (hBMP-6) mRNA levels 24 h after treatment. Evaluation of luciferase expression after transfection of HeLa cells with hBMP-6 promoter/luciferase reporter constructs indicated that the hBMP-6 promoter activity was contained in a 268-bp region (-1051 to -784 where +1 is the translation start site) over 600 bases 5' to that previously published. It further showed that the promoter activity is regulated by glucocorticoid treatment. Analysis of RNA from hMSCs and HeLa cells by primer extension, RNase protection, and 5' RACE further narrowed the location of the transcription start site to an 84-bp region (-940 to -857). To determine whether this start site was regulated in hMSCs, hBMP-6 mRNA levels in control and Dex-treated cells were quantitated by RT-PCR using one primer set in the translated region of the gene and one located just 3' of the 84-bp region. Both primer sets showed hBMP-6 mRNA levels approximately 16- to 22-fold higher in the Dex-treated cells, demonstrating that hBMP-6 transcription is being regulated by glucocorticoids in the pluripotent hMSCs at the upstream transcription start site.

eIF-4E expression and its role in malignancies and metastases

The contribution of the mRNA cap-binding protein, eIF-4E, to malignant transformation and progression has been illuminated over the past decade. eIF-4E overexpression has been demonstrated in human tumors of the breast, head and neck, colon, prostate, bladder, cervix and lung, and has been related to disease progression. Overexpression of eIF-4E in experimental models dramatically alters cellular morphology, enhances proliferation and induces cellular transformation, tumorigenesis and metastasis. Conversely, blocking eIF-4E function by expression of antisense RNA, or overexpression of the inhibitory eIF-4E binding proteins (4E-BPs), suppresses cellular transformation, tumor growth, tumor invasiveness and metastasis. Although eIF-4E regulates the recruitment of mRNA to ribosomes, and thereby globally regulates cap-dependent protein synthesis, eIF-4E contributes to malignancy by selectively enabling the translation of a limited pool of mRNAs--those that generally encode key proteins involved in cellular growth, angiogenesis, survival and malignancy (e.g. cyclin D1, c-myc, vascular endothelial growth factor, matrix metalloprotease 9). A deeper understanding of the role of eIF-4E in regulating the translation of the diverse gene products involved in all aspects of malignancy will improve the capacity to exploit eIF-4E as a therapeutic target and as a marker for human cancer progression.

Comparative functional analysis of rat TGF-beta1 and Xenopus laevis TGF-beta5 promoters suggest differential regulations

We have carried out a comparative functional analysis of the rat TGF-beta1 and Xenopus laevis TGF-beta5 promoters across several mammalian and amphibian cell lines. Progressive deletion constructs of both the promoters have been made using a PCR based approach and the basal promoter activities studied in Xenopus tadpole cell line (XTC), Xenopus adult kidney fibroblast cell line (A6), human hepatoma cell line (HepG2), normal rat kidney cell line (NRK), and Chinese hamster ovary cell line (CHO). Data suggests that the basal promoter activity of TGF-beta1 is low as compared to TGF-beta5 promoter in XTC cells but comparable in A6 cells, while TGF-beta5 promoter shows nearly negligible activity as compared to TGF-beta5 promoter in all the tested mammalian cell lines. Moreover, TGF-beta5 promoter is found to be repressed in XTC cells on treatment with TGF-beta5 protein. Thus, the regulation of TGF-beta1 and TGF-beta5 promoters is distinct in amphibian and mammalian species. We therefore suggest that contrary to the suggested functional equivalence of TGF-beta1 and TGF-beta5 proteins, TGF-beta1 and TGF-beta5 genes have distinct functions in their respective species.

Mediation of interleukin-1beta-induced transforming growth factor beta1 expression by activator protein 4 transcription factor in primary cultures of bovine articular chondrocytes: possible cooperation with activator protein 1

OBJECTIVE

Interleukin-1 (IL-1) and transforming growth factor beta1 (TGFbeta1) play major roles in osteoarticular diseases, exerting opposite effects on both the catabolism and anabolism of cartilage matrix. Previous findings suggest that IL-1 and TGFbeta1 could function in a feedback interaction. However, the effect exerted by IL-1 on expression of TGFbeta by articular chondrocytes is, so far, poorly understood. The present study was carried out to determine the influence of IL-1beta on the expression of TGFbeta1 by bovine articular chondrocytes (BACs) in primary culture.

METHODS

BAC primary cultures were treated with IL-1beta, and TGFbeta1 messenger RNA (mRNA) steady-state levels and protein expression were measured by real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Transient transfection of TGFbeta1 gene promoter constructs was performed to delineate the DNA sequences that mediate the IL-1beta effect. Electrophoretic mobility shift assays (EMSAs) and supershift analysis were used to characterize the transcription factors binding to these sequences.

RESULTS

Cultured BACs responded to IL-1beta exposure by exhibiting an increase of TGFbeta1 expression at both the mRNA and protein levels. The effect was found to be mediated by a major 80-bp sequence located between -732 and -652 upstream of the transcription initiation site. EMSA and supershift analysis revealed that the transcription factors activator protein 4 (AP-4) and AP-1 specifically bound to the -720/-696 part of this sequence under IL-1beta treatment. Overexpression of AP-4 in the BAC cultures resulted in stimulation of the transcriptional activity of the -732/+11 TGFbeta1 promoter construct through the same IL-1beta-responsive element.

CONCLUSION

IL-1beta induces an increase of TGFbeta1 in articular chondrocytes through activation of AP-4 and AP-1 binding to the TGFbeta1 gene promoter. These findings may help us understand the role of IL-1beta in the disease process. Notwithstanding its deleterious effect on cartilage, IL-1 could initiate the repair response displayed by injured cartilage in the early stages of osteoarthritis through its ability to enhance TGFbeta1 expression by local chondrocytes.

Transforming growth factor-beta 2 is a transcriptional target for Akt/protein kinase B via forkhead transcription factor

Tumors evade cell death by constitutively activating cell survival pathways and suppressing intrinsic death machinery. Activation of cell survival pathways leads to transcriptional repression of genes associated with cell death and activation of ones promoting anti-apoptosis. Akt/protein kinase B phosphorylates forkhead transcription factors and prevents their nuclear localization, leading to repression of genes involved in apoptosis, such as Fas ligand (FasL). Using bioinformatic approaches, we have identified three consensus sequences for forkhead transcription factor binding in transforming growth factor beta2 (TGF-beta2) promoter. TGF-beta inhibits cell proliferation and induces apoptosis in many cell types, and acquisition of TGF-beta resistance is linked to tumorigenesis. In this study, we show that activated Akt down-regulates TGF-beta2 promoter, and sequences within the promoter that are related to consensus forkhead binding sites are necessary for repression. Forkhead factor FKHRL1 binds in vitro to the three consensus sequences and can activate TGF-beta2 promoter in normal and Akt-transformed cell lines. In human breast and pancreatic tumors, activated Akt expression correlated with down-regulation of TGF-beta 2 mRNA levels. A number of tumor cells expressing activated Akt were responsive to TGF-beta addition, indicating the presence of an intact TGF-beta-signaling pathway. These results suggest that repression of TGF-beta 2 promoter activity in cells expressing activated Akt may play a role in promoting tumorigenesis and escape from the growth-inhibitory and/or apoptotic effects of TGF-beta.

Genetic susceptibility to keloid disease and transforming growth factor beta 2 polymorphisms

Keloid disease (KD) is a benign fibroproliferative scarring condition of unknown aetiopathogenesis. There is a familial predisposition to keloid scarring. The genes involved in the pathogenesis of abnormal dermal scarring have yet to be identified. Transforming growth factor beta (TGF beta) is a family of multifunctional cytokines, which play a central role in wound healing and fibrosis. The TGF beta 2 isoform is a member of this cytokine family and has previously been implicated in KD pathogenesis. We tested for an association between KD and two novel polymorphisms within the TGF beta 2 gene: an insertion polymorphism within the 59-untranslated region, 109 base pairs away from the initiation codon, and a single nucleotide polymorphism in exon one. We examined DNA samples from 101 patients with KD and 187 ethnically matched controls. No statistically significant differences in TGF beta 2 genotype or allele frequency distribution were observed between the patients and the controls. We believe this to be the first report of a case-control association study in KD and TGF beta 2 polymorphisms.

Expression of TGF-betas and their receptors is differentially modulated by reactive oxygen species and nitric oxide in human articular chondrocytes

OBJECTIVES

To study the effects exerted by two antioxidants, N-monomethyl-L-arginine (L-NMMA), as an inhibitor of nitric oxide (NO) synthesis, and N-acetylcysteine (NAC), a reactive oxygen species (ROS) scavenger, on the expression of the major growth factor involved in cartilage repair, TGF-beta, under the three isoforms beta1, beta2 and beta3, and the receptors I and II of this factor, using lipopolysaccharide (LPS)-treated human chondrocytes in culture.

METHODS

Suspension cultures of human chondrocytes derived from the knee of osteoarthritic patients were treated for 48 h with lipopolysaccharide (LPS) (10 microg/ml), L-NMMA (0.5 mM) or NAC (1 mM). Nitrite levels were assayed on the culture media using the Griess spectrophotometric method. After total RNA extraction, the expression of inducible NO synthase (iNOS), TGF-beta1, TGF-beta2, TGF-beta3, TGF-beta receptors I and II, was determined by semi-quantitative polymerase chain-reaction (RT-PCR).

RESULTS

LPS induced a dramatic increase of both NO production and iNOS mRNA level. The addition of L-NMMA (0.5 mM) abolished NO production without affecting iNOS mRNA levels. In contrast NAC (1 mM) strongly synergized with LPS to stimulate NO synthesis. LPS treatment did not significantly alter TGF-beta1 expression whereas L-NMMA inhibited its production. TGF-beta2 mRNA level was decreased by LPS and was not changed in the presence of L-NMMA. On the other hand, NAC was capable of counteracting the LPS-induced inhibition of TGF-beta2 expression. TGFbeta3 mRNA level was markedly reduced by LPS alone, or with both L-NMMA and NAC. Finally, the expression of TGF-betaRI was slightly increased in the presence of combined LPS and L-NMMA or NAC whereas that of TGFbeta-RII was reduced in the same conditions.

CONCLUSIONS

The modulation of TGF-beta system was found to be differentially controlled by NO and ROS productions. Indeed, the control exerted on TGF-beta expression varied according to the isoform: TGF-beta1 mRNA level depends on NO whereas that of TGF-beta2 is regulated by ROS and TGF-beta3 seems to be unaffected by both of them. The expression of TGF-beta receptors appeared to be modulated by NO and ROS levels. The relevance of the present findings to osteoarthritis (OA) physiopathology and the potential use of antioxidant therapy to treat this disease are discussed.

The retinoic acid receptor antagonist, BMS453, inhibits normal breast cell growth by inducing active TGFbeta and causing cell cycle arrest

We have previously shown that a retinoic acid receptor (RAR) antagonist BMS453, which does not activate RAR-dependent gene transcription in breast cells, inhibits normal breast cell growth. In this study we have investigated the mechanisms by which this retinoid receptor antagonist inhibits cell growth. Both all trans retinoic acid (atRA) and BMS453 inhibited the proliferation of normal breast cell growth without significantly inducing apoptosis. Both retinoids caused a G1 block in the cell cycle with an increase in the proportion of cells in G0/G1 and a decrease in the proportion of cells in S phase. We then investigated the effects of the retinoids on molecules that regulate the G1 to S transition. These studies demonstrated that both atRA and BMS453 induce Rb hypophosphorylation and decrease CDK2 kinase activity. We then studied the effect of the retinoids on the expression of CDK inhibitors. atRA and BMS453 increased total p21 protein levels and CDK2-bound p21 protein, but did not change CDK4-bound p21. These results suggest that atRA and BMS453 increase p21, decrease CDK2 kinase activity, which in turn leads to hypophosphorylation of Rb and G1 arrest. Because transforming growth factor beta (TGFbeta) has been proposed as a mediator of retinoid-induced growth inhibition, we next investigated whether TGFbeta mediates the anti-proliferative effect of atRA and BMS453 in normal breast cells. These studies showed that atRA and BMS453 increased total TGFbeta activity by 3-5-fold. However, BMS453 increased active TGFbeta activity by 33-fold while atRA increased active TGFbeta activity by only threefold. These results suggest that BMS453 treatment induces conversion of latent TGFbeta to active TGFbeta. To investigate whether this increase in active TGFbeta mediates the anti-proliferative effects of these retinoids, a TGFbeta-blocking antibody was used in an attempt to prevent retinoid-induced growth inhibition. Results from these experiments showed that the anti-TGFbeta antibody prevented the inhibition of cell proliferation induced by BMS453, but did not prevent the inhibition of cell proliferation induced by atRA. These results demonstrate that BMS453 inhibits breast cell growth predominantly through the induction of active TGFbeta, while atRA inhibits growth through other mechanisms. These results suggest that retinoid analogs that increase active TGFbeta may be promising agents for the prevention of breast cancer.

Translational regulation of renal proximal tubular epithelial cell transforming growth factor-beta1 generation by insulin

We have previously demonstrated that the proximal tubular cell may contribute to the pathogenesis of renal interstitial fibrosis in diabetes. Transforming growth factor (TGF)-beta1 is one of a group of pro-fibrotic cytokines and growth factors, which have been associated with the development of interstitial fibrosis. The aim of the current study was to examine the effect of insulin on the generation of TGF-beta1 by proximal tubular cells. HK-2 cells were grown to confluence in the absence of insulin, and serum deprived for 48 hours before all experimental manipulations. Addition of insulin (5 microg/ml) to the culture medium led to a time-dependent increase in TGF-beta1 concentration in the cell culture supernatant, and increased incorporation of radiolabeled amino acids into TGF-beta1 suggestive of de novo TGF-beta1 protein synthesis. Addition of insulin did not alter TGF-beta1 mRNA expression as assessed by reverse transcriptase-polymerase chain reaction or Northern analysis. Insulin-induced increase in TGF-beta1 concentration was not abrogated by actinomycin D, however, stimulation by insulin, in the presence of cycloheximide led to a dose-dependent decrease in TGF-beta1 production. Addition of insulin had no effect on TGF-beta1 mRNA stability as assessed by actinomycin D chase, but led to increased binding of a cytoplasmic protein to a putative stem loop structure in the 5'-UTR of TGF-beta1 mRNA, previously implicated in the posttranscriptional control of TGF-beta1 synthesis. To address the functional significance of insulin-induced alteration in TGF-beta1 synthesis, we examined its effect on matrix turnover. Insulin stimulated type IV collagen gene expression and an increase in the concentrations of the type IV collagen laid down in the extracellular matrix. This increase in type IV collagen was abrogated when cells were stimulated by insulin in the presence of an anti-TGF-beta1-blocking antibody. In conclusion the data demonstrate that insulin may directly alter the production of TGF-beta1 by renal proximal tubular cells by a posttranscriptional mechanism, and that this may have implications for the increase in extracellular matrix that accompanies diabetic nephropathy.

Two novel polymorphisms in the human transforming growth factor beta 2 gene

We have identified two novel polymorphisms in the transforming growth factor beta 2 (TGFbeta2) gene; an insertion in the 5'-untranslated region (5'UTR) and a single nucleotide polymorphism (SNP) in exon 1. A 895-bp fragment was analysed covering part of the 5'UTR and exon 1. Single-strand conformation polymorphism (SSCP) analysis of polymerase chain reaction (PCR) products was performed to detect sequence variations. This was followed by the sequencing of samples demonstrating distinct banding patterns. A 4-bp insertion (ACAA) in the 5'UTR and a SNP (G > A) within exon 1 was identified. The 5'UTR polymorphism was found to be common in three Caucasian populations from Spain, Turkey and the UK. Exon 1 polymorphism is rare and results in an R to H amino acid substitution in codon 91. Both polymorphisms may prove useful for investigating possible associations of TGFbeta2 with disease.

Characterization of human bone morphogenetic protein (BMP)-4 and -7 gene promoters: activation of BMP promoters by Gli, a sonic hedgehog mediator

Among the bone morphogenetic protein (BMP) family, which plays a crucial role not only in bone formation but also in development, BMP-2, -4, and -7 participate predominantly in various aspects. To undertake complex tasks, their expression is strictly controlled. In this study we isolated and analyzed the 5'-flanking regions of the human BMP-4 and -7 genes to elucidate the mechanism of their temporally and spatially specific expression. As for BMP-4 expression, a reverse transcription-polymerase chain reaction (RT-PCR) assay with specially designed sets of primers demonstrated that osteoblastic SaOS-2 and Hos cells expressed two types of transcripts comprising one of the 5'-untranslated first exons, whereas MG63 cells displayed only the transcript with the BMP-4 proximal first exon. Likewise, RT-PCR revealed that Hos and MG63 cells expressed BMP-7. Subsequent 5'-RACE confirmed an alternative usage of the BMP-4 first exons with clustered multiple transcription start sites in the distal exon and the sole start site in the proximal exon. The transcription start site of the BMP-7 gene was found to be far upstream (764 bp) of the initiation ATG codon. We constructed a series of deletion mutants of fusions between these BMP promoters and the luciferase gene and examined their activity by transient transfection into osteoblastic Hos and renal COS-7 cells. The degree of distal and proximal BMP-4 promoter activity was in accordance with the expression level of the corresponding transcripts. Both distal and proximal BMP-4 promoters possessed suppressor elements that are operative only in Hos cells. The positive and negative elements identified in the BMP-7 promoter were more remarkably effective in Hos cells. The activities of the respective BMP-4 promoters and BMP-7 promoter were all stimulated upon the cotransfection of a potential sonic hedgehog (SHH) mediator, Gli1 or Gli3 into COS-7 cells, providing direct evidence that the Gli proteins are capable of inducing the BMP expression. Our systems are helpful for assessment of the complicated interactions of molecules involved in the skeletogenesis and developmental processes.

Isolation and characterization of the murine transforming growth factor-beta2 promoter

This report describes the isolation and characterization of the 5' flanking region of the murine transforming growth factor beta-2 (TGF-beta2) gene. A genomic clone containing the promoter region of the gene was isolated after screening a bacteriophage P1 genomic library. The resulting clone was sequenced and compared to promoters for the human and chicken TGF-beta2 genes. The sequence located near the transcription start site is highly conserved. It includes a TATA box, an E-box, and a largely conserved CRE/ATF site. A series of murine TGF-beta2 promoter/reporter constructs was generated to identify regulatory regions of the gene. As in the case of the human TGF-beta2 gene, sequences just upstream of the TATA box, including the CRE/ATF site, actively stimulate the murine TGF-beta2 promoter. However, unlike the human TGF-beta2 gene, the 5' flanking region of the murine TGF-beta2 gene contains a long alternating purine/pyrimidine repeat that unexpectedly exerts a strong positive effect on its promoter. This is of particular interest since alternating purine/pyrimidine repeats in other promoters have been observed to be inhibitory.

Transforming growth factor-beta signaling in cancer

Transforming growth factor (TGF-beta) is a multifunctional polypeptide implicated in the regulation of a variety of cellular processes including growth, differentiation, apoptosis, adhesion, and motility. Abnormal activation or inhibition of these TGF-beta regulated processes is implicated in many diseases, including cancer. Cancers can develop through selective exploitation of defects in TGF-beta signaling that occur at several different levels in the pathway. The TGF-beta signal transduction cascade is initiated when TGF-beta binds to transmembrane receptors. The TGF-beta receptors then phosphorylate and activate Smad proteins, which transduce the signal from the cytoplasm to the nucleus. In the nucleus, Smads can bind directly to DNA and cooperate with other transcription factors to induce transcription of TGF-beta target genes. Mutations in target genes, Smads, or the TGF-beta receptor are associated with certain human cancers.

Smad2, Smad3 and Smad4 cooperate with Sp1 to induce p15(Ink4B) transcription in response to TGF-beta

Transforming growth factor-beta (TGF-beta) arrests growth of epithelial cells by inducing the transcription of p15(Ink4B), a cyclin-dependent kinase inhibitor. In this study, we demonstrate that p15(Ink4B) induction was mediated by a TGF-beta-induced complex of Smad2, Smad3, Smad4 and Sp1. Mutations in the Sp1- or Smad-binding sequences decreased or abolished the TGF-beta responsiveness of the p15(Ink4B) promoter. Interference with, or deficiency in, Smad2, Smad3 or Smad4 functions also reduced or abolished the TGF-beta-dependent p15(Ink4B) induction, whereas the absence of Sp1 reduced the basal and TGF-beta-induced p15(Ink4B) transcription. In the nucleoprotein complex, Smad2 interacted through its C-domain with Sp1 and enhanced the DNA binding and transcriptional activity of Sp1. Smad3 interacted indirectly with Sp1 through its association with Smad2 and/or Smad4, and bound directly to the p15(Ink4B) promoter. Finally, Smad4 interacted through its N-domain with Sp1. Our data demonstrate the physical interactions and functional cooperativity of Sp1 with a complex of Smad2, Smad3 and Smad4 in the induction of the p15(Ink4B) gene. These findings explain the tumor suppressor roles of Smad2 and Smad4 in growth arrest signaling by TGF-beta.

Transforming growth factor-beta2 mediates mesenchymal-epithelial interactions of testicular somatic cells

Transforming growth factor-beta2 (TGFbeta2) is an important mediator of growth and differentiation. We here describe for the first time the complete sequence of the TGFbeta2 complementary DNA derived from peritubular myoid cells of the rat testis. The size of the rat TGFbeta2 complementary DNA was 1245 bp, and the deduced protein sequence contained 414 amino acids. Sequence comparison with the human and mouse amino acid sequences demonstrated 96.4% and 97.9% sequence identities, respectively. To elucidate the functional role of TGFbeta2 in testicular somatic cells, we studied its secretion in vitro in monocultures and cocultures of mesenchymal peritubular and epithelial Sertoli cells. The highest amounts of TGFbeta2 protein were secreted in the cocultures and by peritubular cells, whereas Sertoli cells secreted only minor amounts. Stimulation experiments with FSH revealed a reduced secretion of TGFbeta2 in cocultures, probably mediated by a paracrine interaction of the FSH-responsive Sertoli cells. In contrast, TGFbeta2 secretion by peritubular cells was increased after stimulation with glucocorticoids and after addition of recombinant TGFbeta2, indicating an autoregulation of TGFbeta2. Furthermore, application of recombinant TGFbeta2 to cocultures resulted in an enhanced aggregation and cell clustering of Sertoli cells, pointing to an important role of TGFbeta2 in the paracrine interaction of peritubular and Sertoli cells of the developing rat testis.

Parathyroid hormone regulates transforming growth factor beta1 and beta2 synthesis in osteoblasts via divergent signaling pathways

Parathyroid hormone 1-34 [PTH(1-34)] was shown to increase transforming growth factor beta1 (TGF-beta1) and TGF-beta2 concentrations in supernatants of cultured human osteoblasts and to increase TGF-beta1 and TGF-beta2 messenger RNA (mRNA) concentrations and gene transcription in these cells. Because PTH(1-34) activates both protein kinase C (PKC) and protein kinase A (PKA) pathways in osteoblasts, we investigated the role of each kinase pathway in activation of TGF-beta isoforms. PTH(29-32), which activates the PKC pathway in rat osteoblasts, increased TGF-beta1 but not TGF-beta2 concentrations in supernatants of osteoblasts. Phorbol myristate acetate (PMA), a PKC agonist, increased TGF-beta1 but not TGF-beta2 concentrations. Specific PKC antagonists safingol and Gö6976 attenuated PTH(1-34)-mediated increases in TGF-beta1 but not TGF-beta2 synthesis. PTH(1-31), which increases PKA activity in several cell culture systems, increased TGF-beta2 but not TGF-beta1 concentrations in human osteoblast supernatants. Forskolin, a PKA agonist, increased TGF-beta2 but not TGF-beta1 concentrations in supernatants of human osteoblasts. The PKA antagonist H-89 blunted PTH(1-34)-mediated increases in TGF-beta2 but not TGF-beta1 synthesis. Our results are consistent with the concept that PTH increases TGF-beta1 expression and secretion by pathways that involve the PKC pathway, whereas it increases TGF-beta2 expression and secretion via the PKA pathway.

Transcriptional regulation of the transforming growth factor-beta2 promoter by cAMP-responsive element-binding protein (CREB) and activating transcription factor-1 (ATF-1) is modulated by protein kinases and the coactivators p300 and CREB-binding protein

Transcription of the transforming growth factor-beta2 (TGF-beta2) gene is dependent on a cAMP-response element/activating transcription factor (CRE/ATF) site that is bound by CREB and ATF-1 as well as an E-box motif that is bound by upstream stimulatory factors 1 and 2 (USF1 and USF2). To identify additional factors involved in the expression of the TGF-beta2 gene, we employed F9 embryonal carcinoma (EC) cells, which express TGF-beta2 only after the cells differentiate. We show that overexpression of the transcription factors, CREB, ATF-1, USF1, and USF2 dramatically increases TGF-beta2 promoter activity in F9-differentiated cells. We further show that the coactivators p300 and CBP up-regulate the TGF-beta2 promoter when CREB and ATF-1 are expressed in conjunction with protein kinases that phosphorylate CREB on serine 133 and ATF-1 on serine 63. Importantly, we identify the presence of serine 133-phosphorylated CREB in the nucleus of F9-differentiated cells but not in the nucleus of F9 EC cells. This phosphorylated form is present in whole cell extracts of both the parental and differentiated cells, suggesting that nuclear accumulation of serine 133-phosphorylated CREB is regulated during differentiation of F9 EC cells and is likely to play an important role in the activation of the TGF-beta2 gene.

Lack of association of transforming growth factor (TGF)-beta 1 and beta 2 gene polymorphisms with multiple sclerosis (MS) in Northern Ireland

OBJECTIVE

To examine the influence of TGF-beta genes on MS susceptibility.

BACKGROUND

TGF-beta, of which three homologous isoforms exist (1, 2 and 3), is a strongly immunosuppressive cytokine-inhibiting expression of pro-inflammatory cytokines and blocking cytokine induction of adhesion molecules. TGF-beta delays onset of EAE and TGF-beta 1 gene knockout mice develop fatal multifocal inflammatory disease. High TGF-beta levels exist during MS remission whilst E-selectin, whose expression is inhibited by TGF-beta, is found at higher levels in primary progressive disease (PPMS) and it is postulated that the unremitting course of PPMS may be due to low levels of TGF-beta.

METHODS

Gene association studies using separate polymorphic microsatellite markers for TGF-beta 1 and TGF-beta 2 were performed, incorporating 151 relapsing-remitting or secondary progressive MS (RR/SPMS) patients, 104 PPMS patients and 159 normal controls (Nor). Forward primers were 5' end-labelled with 6-Fam, PCR products were analysed on an Applied Biosystems 373A fluorescent fragment analyser and Genescan 672 software was used for allele sizing.

RESULTS

No significant differences existed in allele frequencies between either MS group and controls regarding the TGF-beta 1 marker: RR/SPMS vs Nor (P = 0.48, df = 8); PPMS vs Nor (P = 0.34, df = 8). Similarly there were no associations demonstrated with the TGF-beta 2 marker: RR/SPMS vs Nor (P = 0.24, df = 2); PPMS vs Nor (P = 0.53, df = 2).

CONCLUSION

These data indicate that TGF-beta 1 and beta 2 genes are not loci influencing MS susceptibility, either RR/SPMS or PPMS, in this population.

eIF4E expression in tumors: its possible role in progression of malignancies

A central issue in the study of neoplastic transformation is to understand how proto-oncogene products deregulate normal processes of cell growth and differentiation: an intrinsic aspect of this is to probe the sequence of events leading to altered expression of proto-oncogenes. In the past few years, studies aimed at understanding the regulation and function of protein synthesis initiation factors, eIF4E initially, culminated in the unexpected finding that a moderate overexpression of this factor results in dramatic phenotypic changes, including rapid proliferation and malignant transformation. Conversely, the tumorigenic properties of cancer cells can be strongly inhibited by antisense-RNA against eIF4E, or overexpression of the inhibitory proteins: 4E-BPs. Furthermore, eIF4E is elevated in carcinomas of the breast, head and neck (HNSCC) and prostate, but not in typical benign lesions. This is a strong indication that elevated eIF4E expression may mark a critical transition in cancer progression. Establishing a greater protein synthesis output may be a necessary step for cancer cells in order to sustain their rapid proliferation. However, analysis of cells transformed by eIF4E revealed that the synthesis of only a few proteins was greatly enhanced, while synthesis of most was minimally increased. One possible explanation is that eIF4E causes these effects by specifically increasing the translational efficiency of several oncogene transcripts, leading to overexpression of their products. The feasibility of this hypothesis was confirmed experimentally with the identification of several important products that are specifically upregulated in eIF4E-overexpressing cells. These include: c-Myc, cyclin DI and ODC, which control cycle progression and tumorigenesis; basic fibroblast growth factor (FGF-2) and vascular endothelial growth factor (VEGF), which are powerful promoters of cell growth and angiogenesis. A deeper understanding of the mRNAs that are strongly dependent on excess eIF4E/F for efficient translation will eventually result in fuller understanding of the fundamental role of translational control in different pathophysiological conditions, including malignancy.

Beta transforming growth factors (TGFss) at the porcine conceptus-maternal interface. Part I: expression of TGFbeta1, TGFbeta2, and TGFbeta3 messenger ribonucleic acids

Spatial and temporal mRNA expression of beta transforming growth factors (TGFbeta1, TGFbeta2, and TGFbeta3) in porcine uterus and conceptuses was determined during the peri-implantation period (Days 10-14 of gestation). Northern blotting identified a major 3. 5-kilobase (kb) and a minor 2.5-kb transcript for TGFbeta1 mRNA. TGFbeta2 transcripts were 6.2 kb, 5.4 kb, and 2.7 kb, and a single 3. 5-kb transcript was detected for TGFbeta3. With semiquantitative in situ hybridization analysis, progressive increases were detected in TGFbetas 1, 2, and 3 mRNA expression in uterine luminal epithelium (ULE), uterine glands (UGs), and underlying stroma (stroma spongiosum, SS) from Days 10 through 14 of gestation (p < 0.05). In myometrium, TGFbeta mRNA expression did not differ between Days 10 through 14 of gestation. In porcine conceptuses, TGFbetas 1, 2, and 3 mRNA expression was detected in trophectoderm, endoderm, embryonic ectoderm, and mesoderm. For the three TGFbeta isoforms examined, mRNA expression increased 2- to 4-fold in trophectoderm and endoderm between Days 10 and 14 of gestation. TGFbeta1 mRNA levels increase significantly in embryonic ectoderm, but not mesoderm, between Days 12 and 14 of gestation; during that same time, TGFbeta2 mRNA levels increased, but no change was detected in TGFbeta3 mRNA levels, in embryonic ectoderm and mesoderm. Progressive increases in TGFbeta mRNA expression in conceptus trophectoderm, endoderm, ULE, UGs, and SS suggest important roles for these growth factors in porcine conceptus development during the peri-implantation period.

Differential expression and biological activity of retinoic acid-induced TGFbeta isoforms in embryonic palate mesenchymal cells

The effect of retinoic acid (RA) on TGF-beta mRNA expression and protein production in murine embryonic palate mesenchymal (MEPM) cells was examined by Northern blotting and TGF-beta bioassay in association with TGF-beta isoform-specific neutralizing antibodies. Heat or acid activation was used to distinguish between latent and active TGF-beta protein released into the culture medium. RA had little or no effect on TGF-beta1 mRNA expression and protein production. In contrast, RA increased TGF-beta2 and beta3 protein released into the culture medium, the protein being mostly in an inactive or latent form. The amount of active TGF-beta released was increased relative to the total increase in TGF-beta released, suggesting that RA treatment stimulated activation of latent TGF-beta. RA also increased TGF-beta2 mRNA expression; we have previously shown that RA upregulates TGF-beta3 mRNA in these cells. RA and TGF-beta individually inhibited 3H-thymidine incorporation into MEPM cell DNA, while, when administered simultaneously, they inhibited proliferative activity to a greater extent. Heat- or acid-activated conditioned medium (CM) from MEPM cells treated with RA was able to inhibit 3H-thymidine incorporation into MEPM cell DNA to an extent greater than seen with RA treatment alone. Coincubation of heat-activated CM from RA-treated MEPM cells with pan-specific or TGF-beta2 or beta3-specific neutralizing antibodies partially relieved the inhibitory effect on 3H-thymidine incorporation, suggesting that this proliferative response was due to RA-induced TGF-beta. Simultaneous treatment with RA and TGF-beta also stimulated gycosaminoglycan (GAG) synthesis to an extent greater than that seen with TGF-beta treatment alone, this despite the ability of RA to inhibit GAG synthesis. These data demonstrate a role for RA and RA-induced TGF-beta in the regulation of palate cell proliferation and GAG synthesis and suggest a role for TGF-beta in retinoid-induced cleft palate.

Extracellular matrix-associated transforming growth factor-beta: role in cancer cell growth and invasion

Growth factors of the transforming growth factor-beta (TGF-beta) family inhibit the proliferation of epithelial, endothelial, and hematopoietic cells, and stimulate the synthesis of extracellular matrix components. TGF-beta s are secreted from cells in high-molecular-mass protein complexes that are composed of three proteins, the mature TGF-beta-dimer, the TGF-beta propeptide dimer, or latency-associated protein (LAP), and the latent TGF-beta binding protein (LTBP). Mature TGF-beta is cleaved from its propeptide during secretion, but the proteins remain associated by noncovalent interactions. LTBP is required for efficient secretion and processing of latent TGF-beta and it binds to LAP via disulfide bond(s). LTBP is a component of extracellular matrix microfibrils, and it targets the latent TGF-beta complex to the extracellular matrix. TGF-beta signaling is initiated by proteolytic cleavage of LTBP that results in the release of the latent TGF-beta complex from the extracellular matrix. TGF-beta is activated by dissociation of LAP from the mature TGF-beta. Subsequent signaling involves binding of active TGF-beta to its type II cell surface receptors, which phosphorylate and activate type I TGF-beta receptors. Type I receptors, in turn, phosphorylate cytoplasmic transcriptional activator proteins Smad2 and Smad3, inducing their translocation to the nucleus. Recent evidence suggests that acquisition of resistance to TGF-beta growth inhibition plays a major role in the progression of epithelial and hematopoietic cell malignancies. The role of secretion of TGF-beta in tumorigenesis is more complex. The secretion of TGF-beta s by tumor cells may contribute to autocrine growth inhibition, but on the other hand, it may also promote invasion, metastasis, angiogenesis, and even immunosuppression. Tumor cells may also fail to deposit LTBP:TGF-beta complexes to the extracellular matrix. The elucidation of the mechanisms of the release of TGF-beta from the matrix and its subsequent activation aids the understanding of the pathophysiologic roles of TGF-beta in malignant growth, and allows the development of therapeutic agents that regulate the activity of TGF-beta.

Characterization of the 5' flanking region of the Xenopus laevis transforming growth factor-beta 5 (TGF-beta 5) gene

Transforming growth factors-beta are potent regulators of cellular proliferation, differentiation and morphogenesis. 2.41 kb of the 5' flanking region of the transforming growth factor-beta 5 (TGF-beta 5) gene has been isolated from a Xenopus laevis genomic library and sequenced. The transcription start site of this gene was determined by 5' RACE method. Promoter activity was demonstrated by transient transfection experiments using luciferase reporter gene constructs in XTC cells. A number of putative recognition sites for transcription factors were found in the 5' flanking region of the TGF-beta 5 gene.

Translational control elements in the major human transforming growth factor-beta 1 mRNA

Polysome analysis indicates that the major 2.4 kb transforming growth factor-beta 1 (TGF-beta 1) transcript is poorly translated, both in cultured cells, and in vivo in mouse liver. In contrast, the TGF-beta 2 transcripts are efficiently translated. The contribution of the 5'- and 3'-untranslated regions (UTRs) to the translational inhibition of the full-length TGF-beta 1 transcript was studied by deletion analysis. Despite their high G + C content, both UTRs stimulated translation in vitro. However, polysome analysis of synthetic TGF-beta 1 mRNAs transfected into MCF-7 cells suggests that the cell contains a limited pool of trans-acting factors that interact with the 5'UTR to make it inhibitory in vivo. Further deletion analysis in vitro revealed multiple stimulatory and inhibitory regions in the 5'UTR. This has important implications for the translatability of the naturally occurring shorter TGF-beta 1 transcripts and provides a framework for higher resolution mapping studies. Overall, the poor translational efficiency of the major TGF-beta 1 mRNA in vivo appears to be due to a combination of poor initiation sequence context, and inhibitory interactions of limiting transacting factors with cis-inhibitory elements embedded in an otherwise stimulatory 5'UTR.

Expression of Indian hedgehog in osteoblasts and its posttranscriptional regulation by transforming growth factor-beta

Indian hedgehog (Ihh) was recently reported to be expressed in chondrocytes and to regulate chondrocyte differentiation. This report examined the expression of Ihh in osteoblastic cells and its regulation by calcitropic cytokines. We found that Ihh messenger RNA (mRNA) was expressed as a single 2.5-kilobase band at a modest level in rat osteoblastic osteosarcoma ROS17/2.8 cells. In sharp contrast to the previous observation of dpp regulation of hedgehog expression in Drosophila embryos, bone morphogenetic protein-2 did not affect Ihh expression in these cells. On the other hand, treatment with 2 ng/ml transforming growth factor-beta1 (TGFbeta1) increased the steady state level of Ihh mRNA 2- to 4-fold. Western blot analysis of the cell lysates using antisera also showed enhancement of the Ihh protein level by TGFbeta1 treatment. The effect of TGFbeta1 on Ihh mRNA abundance started within 3 h, peaked at 24 h and lasted at least 48 h after the initiation of the treatment. The effect of TGFbeta1 on the increase in Ihh mRNA was dose dependent, starting at 0.2 ng/ml and saturating at 2 ng/ml. Neither actinomycin D nor cycloheximide blocked this effect. Experiments using 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole showed an enhancement of Ihh mRNA stability by TGFbeta1, indicating the presence of posttranscriptional regulation. We then examined the effects of TGFbeta1 on Ihh mRNA in osteoblast-enriched cells isolated from neonatal rat calvariae. TGFbeta1 also enhanced Ihh mRNA expression in these cells. Our data indicate for the first time that Ihh is one of the members of the cytokines produced by osteoblastic cells and that the expression of Ihh is regulated posttranscriptionally by TGFbeta.

Transcriptional regulation of the TGF-beta 2 gene in choriocarcinoma cells and breast carcinoma cells: differential utilization of Cis-regulatory elements

Previous studies have shown that the transcription of the TGF-beta 2 gene is controlled by at least one negative and two positive regulatory regions in differentiated cells derived from both embryonal carcinoma cells and embryonic stem cells. The use of TGF-beta 2 promoter/reporter gene constructs has also identified a CRE/ATF motif near the TATA box that appears to heavily influence the transcription of the TGF-beta 2 gene. In this study, two choriocarcinoma cell lines, JAR and JEG-3, and the breast cancer cell line, MCF-7, were used to determine whether differences exist in the transcriptional regulation of the TGF-beta 2 gene. We demonstrated that both similarities and differences exist in the transcriptional regulation of this gene. Common to all cells examined to date, the positive regulatory region just upstream of the TATA box contains an essential CRE/ATF motif that binds at least one transcription factor, ATF-1, in gel mobility shift assays. However, we did not detect ATF-2 binding to this site with any of the nuclear extracts used. We also determined that the effect of the region between -187 and -78 (relative to the transcription start site) is cell type dependent. Previous studies have shown that this region acts to reduce the activity of the TGF-beta 2 promoter in differentiated cells derived from embryonal carcinoma cells and embryonic stem cells. In direct contrast, this region acts as a strong positive regulatory region in JAR, JEC-3, and MCF-7 cells. The mechanisms responsible for these differing effects remain to be established. Interestingly, this region does not appear to contain sequence motifs that bind known transcription factors. Thus, this region is likely to bind one or more novel transcription factors or contain novel recognition sites for known transcription factors.

Effects of transforming growth factor-beta 1 and phorbol ester on PAI-1 and PA genes in human lung cells

Transforming growth factor-beta (TGF-beta) mediates the production of extracellular matrix proteins, proteases and protease inhibitors in epithelial cells. Both TGF-beta and phorbol-12-myristate-13-acetate (PMA) exert both positive and negative effects on mitogenesis in these as well as other cell types. Phorbol esters act through stimulation of protein kinase C (PKC) and are among the most potent tumor promoters known. The present study was conducted to determine whether the effect of TGF-beta in human non-small cell lung cancer (NSCLC) and normal human bronchial epithelial (NHBE) cells parallels that of the phorbol esters and whether this effect of TGF-beta involves PKC. TGF-beta 1 and PMA increased expression of TGF-beta 1 mRNA 24 hr after their addition to both NSCLC and NHBE cells. The effects of these agents on expression of the mRNAs for TGF-beta 2 and TGF-beta 3 were more complex; while TGF-beta 2 and TGF-beta 3 mRNAs increased transiently in response to TGF-beta 1 in NHBE cells and TGF-beta 3 mRNA increased transiently in some NSCLC cells, expression of these mRNAs decreased in most of these cells in response to PMA with the exception of the carcinoid NCI-H727 where TGF-beta 2 mRNA increased dramatically, TGF-beta 1 and PMA both caused a persistent increase in expression of the mRNAs for both plasminogen activator inhibitor-1 (PAI-1) and plasminogen activator (PA) up to 24 hr in most NSCLC cells, with the increase in PAI-1 mRNA beginning several hours before that of PA mRNA. In contrast, while TGF-beta 1 also increased expression of PAI-1 mRNA in NHBE cells, the expression of PA mRNA decreased simultaneously. The effect of PMA on PAI-1 and PA mRNAs was opposite of TGF-beta 1 in these cells, with expression of PAI-1 mRNA decreasing and PA mRNA increasing after addition of PMA. These data show that there is parallel regulation of the genes for TGF-beta 1, PAI-1 and PA by TGF-beta 1 and PMA in NSCLC, but differential regulation of the genes for PAI-1 and PA by these agents in NHBE cells. The responses of the mRNAs and proteins of TGF-beta 1, PAI-1 and PA to TGF-beta 1 and PMA were inhibited by the serine/ threonine kinase inhibitor H7 in NSCLC cells. Treatment of NSCLC cells with TGF-beta 1 and PMA resulted in a persistent increase in the expression of fibronectin mRNA and protein. This response was blocked by the addition of H7. Inhibition of these effects by H7 in NSCLC cells suggests that H7 blocks TGF-beta responses by inhibiting a protein serine/threonine kinase(s). Because the effects of TGF-beta and PMA on the different TGF-beta isoforms, PA, PAI and fibronectin in NHBE and NSCLC cells are complex, our data suggest that there are distinct mechanisms for controlling the different TGF-beta isoforms, PA, PAI and extracellular matrix proteins in normal lung and lung cancer cells.

Transcription of the transforming growth factor-beta2 gene is dependent on an E-box located between an essential cAMP response element/activating transcription factor motif and the TATA box of the gene

Transforming growth factor-beta2 (TGF-beta2) is an important regulator of cell proliferation and differentiation; however, its transcriptional regulation is not well understood. Here we report characterization of an essential E-box motif, positioned at -50/-45 between a previously described functional cAMP response element/activating transcription factor site and the TATA box of the human TGF-beta2 promoter. By site-directed mutagenesis, we demonstrate that this E-box motif is necessary for the promoter activity, not only in differentiated cells derived from embryonal carcinoma cells, but also in choriocarcinoma cells and in MCF-7 breast carcinoma cells. We also demonstrate that the transcription factors USF1 and USF2 bind to this E-box motif in vitro when nuclear extracts from each of these cell lines are examined by gel retardation assays. Moreover, using a dominant-negative USF2 protein, we show that USF proteins are critical for TGF-beta2 promoter activity in vivo. The importance of the E-box motif described in this study is supported by the presence of an E-box motif in the same position in the chicken TGF-beta2 gene promoter.

Differential regulation of TGF-beta 2 by hormones in rat uterus and mammary gland

Previous work from this laboratory has shown that transforming growth factor beta 2 (TGF-beta 2) mRNA is abundant in the pregnant uterus. In the present study, we examined the synthesis and secretion of TGF-beta 1,2 and 3 in the rat uterus and mammary gland and show differential secretion and expression of TGF-beta 2 in a tissue specific manner. Elevated levels of TGF-beta 2 were detected in late pregnant maternal plasmas (> 100 pM), and in the milk (> 500 pM) during early lactation. High concentrations of TGF-beta 2 (> 200 pM) were also detected in uterine fluids collected from ovariectomized adult rats after high dose estrogen treatment. TGF-beta 2 mRNA levels were elevated in lobuloalveolar epithelial cells isolated from pregnant mammary gland. Three major transcripts of 3.5, 4.0, and 4.7 kb were seen, of which the 4.7 kb, dominates. Mammary glands of estrogen treated ovariectomized rats showed a similar pattern of TGF-beta 2 transcripts. In contrast, four major TGF-beta 2 mRNA transcripts of 5.7, 4.7, 4.0, and 3.5 kb, with the dominant species of 4.0 and 5.7 kb, were observed in uteri from the estrogen treated animals up to 48 h after the last estrogen injection. This suggests that TGF-beta 2 is regulated in a tissue specific manner. We conclude that the secretion of TGF-beta 2 is tightly regulated by hormones and that estrogen and prolactin are critical factors in the tissue-specific regulation of the local production of TGF-beta 2 in the mammary gland and female reproductive tract.

Soluble factors secreted by activated T-lymphocytes modulate the transcription of the immunosuppressive cytokine TGF-beta 2 in glial cells

Coordination of the immune response to injury or disease in the brain is postulated to involve bi-directional discourse between the immune system and the central nervous system. This cross communication involves soluble mediators, including various growth factors, cytokines, and neuropeptides. In this report, we demonstrate that the supernatant from activated T-lymphocytes is able to induce the transcription of a potent cytokine, TGF-beta 2 in glial cells. The activating stimulus invokes signaling mechanisms distinct from known kinase or protease pathways. Activation of TGF-beta 2 transcription correlates with the loss of binding activity for an 80 kDA glial labile repressor protein, GLRP, to a responsive region within the TFG-beta 2 promoter. Although GLRP shares some characteristics with the inducible transcription factor AP-1, it appears to be distinct from known AP-1 family members. These data along with previous observations demonstrating the potent immunosuppressive activity of TGF-beta 2, support a model for a feedback mechanism between the activated T-lymphocytes and astrocytes via TGF-beta 2 to regulate the immune response.