Absence of TGF-beta receptors and growth inhibitory responses in retinoblastoma cells

The role of the TGF-β1 signaling pathway in the process of amelogenesis

Amelogenesis is a highly regulated process involving multiple signaling pathways, among which the transforming growth factor-β1 (TGF-β1) signaling pathway plays a pivotal role in enamel formation. This review firstly elucidates the critical functions of TGF-β1 in regulating ameloblast behavior and enamel development, encompassing ameloblast proliferation, differentiation, apoptosis, enamel matrix protein synthesis, and mineralization. Secondly, based on emerging evidence, we further discuss potential interactions between TGF-β signaling and circadian regulation in enamel formation, although this relationship requires further experimental validation. Finally, future research directions are proposed to further investigate the relationship between TGF-β1 and the circadian clock in the context of amelogenesis.

TGF-β Superfamily Signaling in the Eye: Implications for Ocular Pathologies

The TGF-β signaling pathway plays a crucial role in several key aspects of development and tissue homeostasis. TGF-β ligands and their mediators have been shown to be important regulators of ocular physiology and their dysregulation has been described in several eye pathologies. TGF-β signaling participates in regulating several key developmental processes in the eye, including angiogenesis and neurogenesis. Inadequate TGF-β signaling has been associated with defective angiogenesis, vascular barrier function, unfavorable inflammatory responses, and tissue fibrosis. In addition, experimental models of corneal neovascularization, diabetic retinopathy, proliferative vitreoretinopathy, glaucoma, or corneal injury suggest that aberrant TGF-β signaling may contribute to the pathological features of these conditions, showing the potential of modulating TGF-β signaling to treat eye diseases. This review highlights the key roles of TGF-β family members in ocular physiology and in eye diseases, and reviews approaches targeting the TGF-β signaling as potential treatment options.

Gene expression profiling of tumor stroma interactions in retinoblastoma

We aimed to identify the critical molecular pathways altered upon tumor stroma interactions in retinoblastoma (RB). In vitro 2 D cocultures of RB tumor cells (Weri-Rb-1 and NCC-RbC-51) with primary bone marrow stromal cells (BMSC) was established. Global gene expression patterns in coculture samples were assessed using Affymetrix Prime view human gene chip microarray and followed with bioinformatics analyses. Key upregulated genes from Weri-Rb-1 + BMSC and NCC-RbC-51 + BMSC coculture were validated using qRT-PCR to ascertain their role in RB progression. Whole genome microarray experiments identified significant (P ≤ 0.05, 1.1 log 2 FC) transcriptome level changes induced upon coculture of RB cells with BMSC. A total of 1155 genes were downregulated and 1083 upregulated in Weri-Rb-1 + BMSC coculture. Similarly, 1865 genes showed downregulation and 1644 genes were upregulation in NCC-RbC-51 + BMSC coculture. The upregulated genes were significantly associated with pathways of focal adhesion, PI3K-Akt signalling, ECM-receptor interaction, JAK-STAT, TGF-β signalling thus contributing to RB progression. Validation of key genes by qRT-PCR revealed significant overexpression of IL8, IL6, MYC and SMAD3 in the case of Weri-Rb-1 + BMSC coculture and IL6 in the case of NCC-RbC-51 + BMSC coculture. The microarray expression study on in vitro RB coculture models revealed the pathways that could be involved in the progression of RB. The gene signature obtained in a stimulated model when a growing tumor interacts with its microenvironment may provide new horizons for potential targeted therapy in RB.

Role of TGF-β in Alcohol-Induced Liver Disease

Over 90% of hepatocellular carcinoma (HCC) occurs against a background of chronic liver disease or cirrhosis induced from viral hepatitis to alcohol injury. One third of patients with cirrhosis will develop HCC during their lifetime, with a 3-5% annual incidence. However, little is known about the key mechanisms by which toxins mediate DNA damage in the liver. Recent studies support a central role for TGF-β signaling in conferring genomic stability yet the precise mechanism of action and the specific stages of tumor suppression remain unclear (Bornstein S, White R, Malkoski S, Oka M, Han G, Cleaver T, Reh D, Andersen P, Gross N, Olson S, Deng C, Lu SL, Wang XJ. J Clin Invest 119:3408-3419 (2009); Korc M. J Clin Invest 119:3208-3211 (2009); Glick A, Popescu N, Alexander V, Ueno H, Bottinger E, Yuspa SH. Proc Natl Acad Sci U S A 96:14949-14954 (1999)). Furthermore, it has recently been shown that β2SP^+/- and β2SP^+/-/Smad3^+/- mice phenocopy a hereditary human cancer syndrome, the Beckwith-Wiedemann syndrome (BWS), which has an 800 fold risk of cancers including HCC, hepatoblastoma, and a range of liver disorders. Identifying key biological pathways and mechanisms for suppressing alcohol-induced stem cell injury and HCC will be critical for enhancing patient care and the employment of new therapeutic approaches.

Regulated differentiation of WERI-Rb-1 cells into retinal neuron-like cells

The encouraging response and improved survival of acute promyelocytic leukemia patients following retinoic acid treatment has rendered differentiation therapy an attractive option in cancer treatment. Given that terminal differentiation represents a considerable barrier in retinoblastoma tumorigenesis and that retinoblastoma has a significantly higher spontaneous degeneration rate compared with other tumors (1,000-fold change), differentiation therapy represents a promising alternative in the treatment of retinoblastoma. However, the full differentiation potential of retinoblastoma still unknown. The present study was designed to investigate the extend differentiation of the classical retinoblastoma cell line WERI-Rb-1 (W-RBCs). Several critical cell signaling pathways and key genes related to cell proliferation and differentiation were comprehensively regulated to control the fate of W-RBCs. Various strategies were applied to optimize simple and time-saving methods to induce W-RBCs into different types of retinal neuron-like cells (RNLCs) in vitro. Further, the tumorigenesis of these differentiated W-RBCs was tested in nude mice in vivo. W-RBCs were found to inherently express both retinal progenitor cell- and embryonic stem cell-related genes or proteins. Moreover, the addition of antagonists of critical cell signals (Wnt, Nodal, BMP4 and Notch), even without atonal bHLH transcription factor 7 gene transfection, could directly induce W-RBCs into RNLCs, and especially into photoreceptor-like and retinal ganglion-like cells. Interestingly, the differentiated cells showed remarkably poorer tumorigenesis in vivo. These findings may offer new insights on the oriented differentiation of W-RBCs into RNLCs with low tumorigenicity and provide potential targets for retinoblastoma differentiation therapy.

Mathematical model of TGF-βsignalling: feedback coupling is consistent with signal switching

Background

Transforming growth factor β (TGF-β) signalling regulates the development of embryos and tissue homeostasis in adults. In conjunction with other oncogenic changes, long-term perturbation of TGF-β signalling is associated with cancer metastasis. Although TGF-β signalling can be complex, many of the signalling components are well defined, so it is possible to develop mathematical models of TGF-β signalling using reduction and scaling methods. The parameterization of our TGF-β signalling model is consistent with experimental data.

Results

We developed our mathematical model for the TGF-β signalling pathway, i.e. the RF- model of TGF-β signalling, using the “rapid equilibrium assumption” to reduce the network of TGF-β signalling reactions based on the time scales of the individual reactions. By adding time-delayed positive feedback to the inherent time-delayed negative feedback for TGF-β signalling. We were able to simulate the sigmoidal, switch-like behaviour observed for the concentration dependence of long-term (> 3 hours) TGF-β stimulation. Computer simulations revealed the vital role of the coupling of the positive and negative feedback loops on the regulation of the TGF-β signalling system. The incorporation of time-delays for the negative feedback loop improved the accuracy, stability and robustness of the model. This model reproduces both the short-term and long-term switching responses for the intracellular signalling pathways at different TGF-β concentrations. We have tested the model against experimental data from MEF (mouse embryonic fibroblasts) WT, SV40-immortalized MEFs and Gp130 ^F/F MEFs. The predictions from the RF- model are consistent with the experimental data.

Conclusions

Signalling feedback loops are required to model TGF-β signal transduction and its effects on normal and cancer cells. We focus on the effects of time-delayed feedback loops and their coupling to ligand stimulation in this system. The model was simplified and reduced to its key components using standard methods and the rapid equilibrium assumption. We detected differences in short-term and long-term signal switching. The results from the RF- model compare well with experimental data and predict the dynamics of TGF-β signalling in cancer cells with different mutations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-017-0421-5) contains supplementary material, which is available to authorized users.

Clinical significance of high levels of survivin and transforming growth factor beta-1 proteins in aqueous humor and serum of retinoblastoma patients

PURPOSE

To evaluate the diagnostic and prognostic values of survivin and transforming growth factor beta-1 (TGF-B1) expression in aqueous humor and serum of retinoblastoma (RB) in comparison to the conventional RB marker lactate dehydrogenase (LDH) and to elucidate a possible correlation between them and the clinicopathological features of the disease.

METHODS

This prospective, comparative study included 88 newly diagnosed children with RB and 80 age-matched controls with ophthalmic conditions other than tumors prepared for intraocular surgeries. Concentrations of survivin, TGF-B1, and LDH were measured in serum and aqueous humor before and 6 months after completion of therapy.

RESULTS

High serum and aqueous humor concentrations of the three proteins were detected in RB patients before treatment compared to the control group (P < 0.01), with a significant reduction of serum concentrations after treatment (P < 0.01). For the highest sensitivity and specificity, the optimal cutoff values of serum and aqueous survivin were 12.9 pg/ml and 25.2 pg/mg, with a significant positive correlation between aqueous survivin and RB staging and presence of optic nerve infiltration (r = 0.43, P = 0.04); the best cutoff values of serum and aqueous TGF-B1, 370.7 pg/ml and 39.8 pg/mg, with a significant positive correlation between aqueous TGF-B1 and poor differentiation of the tumor (r = 0.69, P = 0.001).

CONCLUSIONS

The high sensitivity, specificity, and accuracy of serum and aqueous humor survivin and TGF-B1 proteins make them promising markers for early detection and follow-up of RB patients.

Evolution of Microbial Quorum Sensing to Human Global Quorum Sensing: An Insight into How Gap Junctional Intercellular Communication Might Be Linked to the Global Metabolic Disease Crisis

The first anaerobic organism extracted energy for survival and reproduction from its source of nutrients, with the genetic means to ensure protection of its individual genome but also its species survival. While it had a means to communicate with its community via simple secreted molecules (“quorum sensing”), the eventual shift to an aerobic environment led to multi-cellular metazoan organisms, with evolutionary-selected genes to form extracellular matrices, stem cells, stem cell niches, and a family of gap junction or “connexin” genes. These germinal and somatic stem cells responded to extracellular signals that triggered intra-cellular signaling to regulate specific genes out of the total genome. These extra-cellular induced intra-cellular signals also modulated gap junctional intercellular communication (GJIC) in order to regulate the new cellular functions of symmetrical and asymmetrical cell division, cell differentiation, modes of cell death, and senescence. Within the hierarchical and cybernetic concepts, differentiated by neurons organized in the brain of the Homo sapiens, the conscious mind led to language, abstract ideas, technology, myth-making, scientific reasoning, and moral decision–making, i.e., the creation of culture. Over thousands of years, this has created the current collision between biological and cultural evolution, leading to the global “metabolic disease” crisis.

TGF-β and the TGF-β Family: Context-Dependent Roles in Cell and Tissue Physiology

The transforming growth factor-β (TGF-β) is the prototype of the TGF-β family of growth and differentiation factors, which is encoded by 33 genes in mammals and comprises homo- and heterodimers. This review introduces the reader to the TGF-β family with its complexity of names and biological activities. It also introduces TGF-β as the best-studied factor among the TGF-β family proteins, with its diversity of roles in the control of cell proliferation and differentiation, wound healing and immune system, and its key roles in pathology, for example, skeletal diseases, fibrosis, and cancer.

Mechanisms of BMP-Receptor Interaction and Activation

Bone morphogenetic proteins (BMPs), together with the eponymous transforming growth factor (TGF) β and the Activins form the TGFβ superfamily of ligands. This protein family comprises more than 30 structurally highly related proteins, which determine formation, maintenance, and regeneration of tissues and organs. Their importance for the development of multicellular organisms is evident from their existence in all vertebrates as well as nonvertebrate animals. From their highly specific functions in vivo either a strict relation between a particular ligand and its cognate cellular receptor and/or a stringent regulation to define a distinct temperospatial expression pattern for the various ligands and receptor is expected. However, only a limited number of receptors are found to serve a large number of ligands thus implicating highly promiscuous ligand-receptor interactions instead. Since in tissues a multitude of ligands are often found, which signal via a highly overlapping set of receptors, this raises the question how such promiscuous interactions between different ligands and their receptors can generate concerted and highly specific cellular signals required during embryonic development and tissue homeostasis.

Hepatocellular carcinoma biology

Hepatocellular carcinoma (HCC) is the most common primary hepatic malignancy. Its incidence and prevalence is globally heterogeneous with the highest rates in Southeast Asia and Sub-Saharan Africa. In Western Industry nations, its incidence has significantly increased throughout the previous three decades. Its global heterogeneity is in part a reflection of the global distribution of its risk factors. Its prognosis is dismal with a 5-year survival of 11 %. The only potentially curative treatment is surgical with either resection or orthotopic liver transplantation. However, the majority of HCC patients are diagnosed at an advanced stage at which surgical therapies are not feasible. HCC is considered chemotherapy-resistant-a characteristic thought to be mediated in part through stem-like tumor initiating cells (STICs). Recent studies have provided significant insights in the hepatocarcinogenesis and the molecular signaling pathways of this malignancy resulting in the development of novel, molecular targeted therapies with modest therapeutic benefit. Our growing understanding of the biology of this malignancy will help in the development of novel, molecular-targeted therapies.

Hepatic stem cells and transforming growth factor β in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common and lethal cancers worldwide. It arises from modulation of multiple genes by mutations, epigenetic regulation, noncoding RNAs and translational modifications of encoded proteins. Although >40% of HCCs are clonal and thought to arise from cancer stem cells (CSCs), the precise identification and mechanisms of CSC formation remain poorly understood. A functional role of transforming growth factor (TGF)-β signalling in liver and intestinal stem cell niches has been demonstrated through mouse genetics. These studies demonstrate that loss of TGF-β signalling yields a phenotype similar to a human CSC disorder, Beckwith-Wiedemann syndrome. Insights into this powerful pathway will be vital for developing new therapeutics in cancer. Current clinical approaches are aimed at establishing novel cancer drugs that target activated pathways when the TGF-β tumour suppressor pathway is lost, and TGF-β itself could potentially be targeted in metastases. Studies delineating key functional pathways in HCC and CSC formation could be important in preventing this disease and could lead to simple treatment strategies; for example, use of vitamin D might be effective when the TGF-β pathway is lost or when wnt signalling is activated.

Autocrine Transforming Growth Factor-beta Growth Pathway in Murine Osteosarcoma Cell Lines Associated with Inability to Affect Phosphorylation of Retinoblastoma Protein

Purpose. Production of active transforming growth factor-β (TGF-β ) by human osteosarcoma may contribute to malignant progression through mechanisms that include induction of angiogenesis, immune suppression and autocrine growth stimulation of tumor cell growth.To study events associated with induction of cell proliferation by TGF-β , we have evaluated the TGF-β pathway in two murine osteosarcoma cell lines, K7 and K12.

Results. Northern and immunohistochemical analyses show that each cell line expressesTGF-β1 and TGF-β3 mRNA and protein. Both cell lines secrete activeTGF-β 1 and display a 30–50% reduction in growth when cultured in the presence of a TGF-β blocking antibody. Expression of TGF-β receptors TβRI, TβRII and TβRIII is demonstrated by affinity labeling with ¹²⁵ -TGF-β 1, and the intermediates, Smads 2, 3 and 4, are uniformly expressed. Smads 2 and 3 are phosphorylated in response toTGF-β , while pRb phosphorylation in each osteosarcoma cell line is not affected by either exogenousTGF-β or TGF-β antibody.

Conclusions. The data implicate events downstream of Smad activation, including impaired regulation of pRb, in the lack of a growth inhibitory response toTGF-β , and indicate that this murine model of osteosarcoma is valid for investigating the roles of autocrineTGF-β in vivo.

Smad4 inactivation promotes malignancy and drug resistance of colon cancer

SMAD4 is localized to chromosome 18q21, a frequent site for loss of heterozygosity in advanced stage colon cancers. Although Smad4 is regarded as a signaling mediator of the TGFβ signaling pathway, its role as a major suppressor of colorectal cancer progression and the molecular events underlying this phenomenon remain elusive. Here, we describe the establishment and use of colon cancer cell line model systems to dissect the functional roles of TGFβ and Smad4 inactivation in the manifestation of a malignant phenotype. We found that loss of function of Smad4 and retention of intact TGFβ receptors could synergistically increase the levels of VEGF, a major proangiogenic factor. Pharmacologic inhibition studies suggest that overactivation of the TGFβ-induced MEK-Erk and p38-MAPK (mitogen-activated protein kinase) auxiliary pathways are involved in the induction of VEGF expression in SMAD4 null cells. Overall, SMAD4 deficiency was responsible for the enhanced migration of colon cancer cells with a corresponding increase in matrix metalloprotease 9 enhanced hypoxia-induced GLUT1 expression, increased aerobic glycolysis, and resistance to 5'-fluoruracil-mediated apoptosis. Interestingly, Smad4 specifically interacts with hypoxia-inducible factor (HIF) 1α under hypoxic conditions providing a molecular basis for the differential regulation of target genes to suppress a malignant phenotype. In summary, our results define a molecular mechanism that explains how loss of the tumor suppressor Smad4 promotes colorectal cancer progression. These findings are also consistent with targeting TGFβ-induced auxiliary pathways, such as MEK-ERK, and p38-MAPK and the glycolytic cascade, in SMAD4-deficient tumors as attractive strategies for therapeutic intervention.

Bone morphogenetic protein 4 (BMP4) signaling in retinoblastoma cells

Bone morphogenetic proteins (BMPs) - expressed in the developing retina - are known to be involved in the regulation of cell proliferation and apoptosis in several tumor entities. The objective of this study was to determine the role of the BMP4 pathway in retinoblastoma cells, which are absent in a functional retinoblastoma (RB1) gene. BMP receptors were detected in all retinoblastoma cell lines investigated. A correct transmission of BMP signaling via the Smad1/5/8 pathway could be demonstrated in WERI-Rb1 retinoblastoma cells and application of recombinant human BMP4 resulted in an increase in apoptosis, which to a large extend is caspase independent. Cell proliferation was not affected by BMP4 signaling, although the pRb-related proteins p107 and p130, contributing to the regulation of the same genes, are still expressed. WERI-Rb1 cells exhibit elevated endogenous levels of p21(CIP1) and p53, but we did not detect any increase in p53, p21(CIP1)or p27(KIP1) expression levels. Id proteins became, however, strongly up-regulated upon exogenous BMP4 treatment. Thus, RB1 loss in WERI-Rb1 cells is obviously not compensated for by pRb-independent (e.g. p53-dependent) cell cycle control mechanisms, preventing an anti-proliferative response to BMP4, which normally induces cell cycle arrest.

SMAD6 contributes to patient survival in non-small cell lung cancer and its knockdown reestablishes TGF-beta homeostasis in lung cancer cells

The malignant transformation in several types of cancer, including lung cancer, results in a loss of growth inhibition by transforming growth factor-beta (TGF-beta). Here, we show that SMAD6 expression is associated with a reduced survival in lung cancer patients. Short hairpin RNA (shRNA)-mediated knockdown of SMAD6 in lung cancer cell lines resulted in reduced cell viability and increased apoptosis as well as inhibition of cell cycle progression. However, these results were not seen in Beas2B, a normal bronchial epithelial cell line. To better understand the mechanism underlying the association of SMAD6 with poor patient survival, we used a lentivirus construct carrying shRNA for SMAD6 to knock down expression of the targeted gene. Through gene expression analysis, we observed that knockdown of SMAD6 led to the activation of TGF-beta signaling through up-regulation of plasminogen activator inhibitor-1 and phosphorylation of SMAD2/3. Furthermore, SMAD6 knockdown activated the c-Jun NH2-terminal kinase pathway and reduced phosphorylation of Rb-1, resulting in increased G0-G1 cell arrest and apoptosis in the lung cancer cell line H1299. These results jointly suggest that SMAD6 plays a critical role in supporting lung cancer cell growth and survival. Targeted inactivation of SMAD6 may provide a novel therapeutic strategy for lung cancers expressing this gene.

Hepatocellular cancer arises from loss of transforming growth factor beta signaling adaptor protein embryonic liver fodrin through abnormal angiogenesis

We have previously demonstrated that 40%-70% of elf(+/-) mice spontaneously develop hepatocellular cancer (HCC) within 15 months, revealing the importance of the transforming growth factor-beta (TGF-beta) signaling pathway in suppressing tumorigenesis in the liver. The current study was carried out to investigate mechanisms by which embryonic liver fodrin (ELF), a crucial Smad3/4 adaptor, suppresses liver tumor formation. Histological analysis of hyperplastic liver tissues from elf(+/-) mice revealed abundant newly formed vascular structures, suggesting aberrant angiogenesis with loss of ELF function. In addition, elf(+/-) mice displayed an expansion of endothelial progenitor cells. Ectopic ELF expression in fetal bovine heart endothelial (FBHE) cells resulted in cell cycle arrest and apoptosis. Further analysis of developing yolk sacs of elf(-/-) mice revealed a failure of normal vasculature and significantly decreased endothelial cell differentiation with embryonic lethality. Immunohistochemical analysis of hepatocellular cancer (HCC) from the elf(+/-) mice revealed an abnormal angiogenic profile, suggesting the role of ELF as an angiogenic regulator in suppressing HCC. Lastly, acute small interfering RNA (siRNA) inhibition of ELF raised retinoblastoma protein (pRb) levels nearly fourfold in HepG2 cells (a hepatocellular carcinoma cell line) as well as in cow pulmonary artery endothelial (CPAE) cells, respectively.

CONCLUSION

Taken together these results, ELF, a TGF-beta adaptor and signaling molecule, functions as a critical adaptor protein in TGF-beta modulation of angiogenesis as well as cell cycle progression. Loss of ELF in the liver leads the cancer formation by deregulated hepatocyte proliferation and stimulation of angiogenesis in early cancers. Our studies propose that ELF is potentially a powerful target for mimetics enhancing the TGF-beta pathway tumor suppression of HCC.

Transforming growth factor-beta signaling and ubiquitinators in cancer

Transforming growth factor-beta (TGF-beta) represents a large family of growth and differentiation factors that mobilize complex signaling networks to regulate cellular differentiation, proliferation, motility, adhesion, and apoptosis. TGF-beta signaling is tightly regulated by multiple complex mechanisms, and its deregulation plays a key role in the progression of many forms of cancer. Upon ligand binding, TGF-beta signals are transduced by Smad proteins, which in turn are tightly dependent on modulation by adaptor proteins such as embryonic liver fodrin, Smad anchor for receptor activation, filamin, and crkl. A further layer of regulation is imposed by ubiquitin-mediated targeting and proteasomal degradation of specific components of the TGF-beta signaling pathway. This review focuses on the ubiquitinators that regulate TGF-beta signaling and the association of these ubiquitin ligases with various forms of cancer. Delineating the role of ubiquitinators in the TGF-beta signaling pathway could yield powerful novel therapeutic targets for designing new cancer treatments.

The soluble transforming growth factor-beta receptor: advantages and applications

Transforming growth factor-beta (TGF-beta) is a cytokine that plays a pivotal role in growth, differentiation, development, immune response and wound healing. TGF-beta is upregulated following wound infliction and inflammation, and plays an important role in the production of extracellular matrix proteins that contribute to tissue repair. However, in some diseases, TGF-beta dysregulation can lead to tumor formation, organ fibrosis and the disruption of organ function. A number of molecules have been designed to counteract the effects of TGF-beta, including anti-TGF-beta monoclonal antibodies and various small molecules. Here we discuss the design, use and advantages of the highly specific TGF-beta binding molecule, the soluble human TGF-beta receptor (sTbetaR.Fc) as a TGF-beta sequestering agent.

Mechanisms in TGF-beta action

The various isoforms of TGF-beta are multifunctional. We are exploring pathways of cellular regulation by TGF-beta that lead to suppression of cell proliferation, modulation of cell adhesion and control of cell differentiation. These cellular responses appear to be activated by binding of TGF-beta to a similar set of receptor glycoproteins in all cell types. TGF-beta receptor types I and II are specifically lost in cell mutants that are resistant to TGF-beta. The concomitant loss of these two receptors in certain mutants suggests that they are components of the TGF-beta signal-transducing receptor complex. Inhibition of epithelial cell proliferation by TGF-beta is linked to retention of the retinoblastoma growth suppressor gene product in an underphosphorylated state that is presumed to have growth suppressive activity. Inhibition of myogenic differentiation by TGF-beta involves a block in the expression of the master myogenic differentiation genes, such as myogenin, but appears also to involve up-regulation of extracellular matrix production. Expression of components of the cell adhesion apparatus--cell adhesion receptors and extracellular matrix proteins--is controlled by TGF-beta in an array of cell types. This response could have a great impact on the ability of cells to migrate, home to specific tissue locations and differentiate during development, invasion and metastasis.

In vivo and in vitro effects of TGF-beta 1 on normal and neoplastic haemopoiesis

TGF-beta 1 and TGF-beta 2 are equipotent selective inhibitors of murine and human haemopoiesis in vitro. Primitive haemopoietic cells such as the high proliferative potential progenitor cell and the colony-forming unit (CFU)-GEMM are directly inhibited by TGF-beta whereas the more differentiated CFU-G, CFU-M and CFU-E are not. Recombinant TGF-beta 1 administered intraperitoneally or intravenously to mice selectively inhibits haemopoietic colony formation in a time- and dose-dependent manner to the same extent as seen in vitro. The progenitors are reversibly prevented from entering the cell cycle. This inhibitory action of TGF-beta functions on at least two levels: (1) down-modulation of the cell surface expression of receptors for growth stimulatory molecules and (2) interference with the intracellular signalling pathways of these molecules. In addition, expression of TGF-beta receptors is regulated during cytokine stimulation of haemopoiesis. Neoplastic B lymphocytes can proliferate by escaping from a TGF-beta-mediated autocrine inhibitory loop. Activation signals (e.g. phorbol esters) inhibit tumour cell growth by stimulating active TGF-beta production and inducing cell surface expression of TGF-beta receptors. These results indicate that TGF-beta may be useful as a bone marrow protective and/or an antitumour agent.

Transforming growth factor-[beta]1 -509T reduces risk of colorectal cancer, but not adenoma in Koreans

The proliferation of colorectal epithelial cells is regulated by various stimuli including cytokines and growth factors, thus the variants of those genes can modify the colorectal cancer risk. TGF-[beta]1 can act as both a tumor suppressor and a stimulator of tumor progression. TGF-[beta]1 C-509T polymorphism in the promoter sequence has been associated with increased levels of plasma TGF-[beta]1 in individuals with T allele. To evaluate the potential influences of this polymorphism on colorectal adenoma and cancer risk, a case-control study was conducted in Korea. A total of 646 subjects were prospectively enrolled in Seoul National University Hospital. Risk of colorectal neoplasms was evaluated separately for 244 patients with colorectal adenoma, 152 patients with colorectal cancer relative to 250 healthy controls. Genotypes were determined by the PCR-RFLP method. ORs and 95% CIs were calculated by a multivariate logistic regression analysis. The TGF-[beta]1 -509T allele containing genotypes posed a reduced risk of colorectal cancer (adjusted OR = 0.59, 95% CI = 0.28-0.92). But there was no association between this polymorphism and colorectal adenoma. Our results suggest that the TGF-[beta]1 -509T allele may have a protective role in the development of colorectal cancer, possibly consistent with its role as an inhibitor of epithelial malignant transformation.

Inactivation of TGF-β signaling in lung cancer results in increased CDK4 activity that can be rescued by ELF

Escape from TGF-beta inhibition of proliferation is a hallmark of multiple cancers including lung cancer. We explored the role of ELF, crucial TGF-beta adaptor protein identified from endodermal progenitor cells, in lung carcinogenesis and cell-cycle regulation. Interestingly, elf-/- mice develop multiple defects that include lung, liver, and cardiac abnormalities. Four out of 6 lung cancer and mesothelioma cell lines displayed deficiency of ELF expression with increased CDK4 expression. Immunohistochemistry and Western blot analysis of primary human lung cancers also showed decreased ELF expression and overexpression of CDK4. Moreover, rescue of ELF in ELF-deficient cell lines decreased the expression of CDK4 and resulted in accumulation of G1/S checkpoint arrested cells. These results suggest that disruption in TGF-beta signaling mediated by loss of ELF in lung cancer leads to cell-cycle deregulation by modulating CDK4 and ELF highlights a key role of TGF-beta adaptor protein in suppressing early lung cancer.

Actions of TGF-beta as tumor suppressor and pro-metastatic factor in human cancer

Transforming growth factor-beta (TGF-beta) is a secreted polypeptide that signals via receptor serine/threonine kinases and intracellular Smad effectors. TGF-beta inhibits proliferation and induces apoptosis in various cell types, and accumulation of loss-of-function mutations in the TGF-beta receptor or Smad genes classify the pathway as a tumor suppressor in humans. In addition, various oncogenic pathways directly inactivate the TGF-beta receptor-Smad pathway, thus favoring tumor growth. On the other hand, all human tumors overproduce TGF-beta whose autocrine and paracrine actions promote tumor cell invasiveness and metastasis. Accordingly, TGF-beta induces epithelial-mesenchymal transition, a differentiation switch that is required for transitory invasiveness of carcinoma cells. Tumor-derived TGF-beta acting on stromal fibroblasts remodels the tumor matrix and induces expression of mitogenic signals towards the carcinoma cells, and upon acting on endothelial cells and pericytes, TGF-beta regulates angiogenesis. Finally, TGF-beta suppresses proliferation and differentiation of lymphocytes including cytolytic T cells, natural killer cells and macrophages, thus preventing immune surveillance of the developing tumor. Current clinical approaches aim at establishing novel cancer drugs whose mechanisms target the TGF-beta pathway. In conclusion, TGF-beta signaling is intimately implicated in tumor development and contributes to all cardinal features of tumor cell biology.

Inactivation of ELF/TGF-beta signaling in human gastrointestinal cancer

TGF-beta/Smads regulate a wide variety of biological responses through transcriptional regulation of target genes. ELF, a beta-spectrin, plays a key role in the transmission of TGF-beta-mediated transcriptional response through Smads. ELF was originally identified as a key protein involved in endodermal stem/progenitor cells committed to foregut lineage. Also, as a major dynamic adaptor and scaffolding protein, ELF is important for the generation of functionally distinct membranes, protein sorting and the development of polarized differentiated epithelial cells. Disruption of elf results in the loss of Smad3/Smad4 activation and, therefore, a disruption of the TGF-beta pathway. These observations led us to pursue the function of ELF in gastrointestinal (GI) epithelial cell-cell adhesion and tumor suppression. Here, we show a significant loss of ELF and reduced Smad4 expression in human gastric cancer tissue samples. Also, of the six human gastric cancer cell lines examined, three show deficient ELF expression. Furthermore, we demonstrate the rescue of E-cadherin-dependent homophilic cell-cell adhesion by ectopic expression of full-length elf. Our results suggest that ELF has an essential role in tumor suppression in GI cancers.

Restoration of TGF-beta signalling reduces tumorigenicity in human lung cancer cells

Members of the transforming growth factor-beta (TGF-beta) family regulate a wide range of biological processes including cell proliferation, migration, differentiation, apoptosis, and extracellular matrix deposition. Resistance to TGF-beta-mediated tumour suppressor function in human lung cancer may occur through the loss of type II receptor (TbetaRII) expression. In this study, we investigated the expression pattern of TbetaRII in human lung cancer tissues by RT-PCR and Western blot analyses. We observed downregulation of TbetaRII in 30 out of 46 NSCLC samples (65%) by semiquantitative RT-PCR. Western blot analyses with tumour lysates showed reduced expression of TbetaRII in 77% cases. We also determined the effect of TbetaRII expression in lung adenocarcinoma cell line (VMRC-LCD) that is not responsive to TGF-beta due to lack of TbetaRII expression. Stable expression of TbetaRII in these cells restored TGF-beta-mediated effects including Smad2/3 and Smad4 complex formation, TGF-beta-responsive reporter gene activation, inhibition of cell proliferation and increased apoptosis. Clones expressing TbetaRII showed reduced colony formation in soft-agarose assay and significantly reduced tumorigenicity in athymic nude mice. Therefore, these results suggest that reestablishment of TGF-beta signalling in TbetaRII null cells by stable expression of TbetaRII can reverse malignant behaviour of cells and loss of TbetaRII expression may be involved in lung tumour progression.

Transforming growth factor-beta pathway serves as a primary tumor suppressor in CD8+ T cell tumorigenesis

Tumorigenesis in rodents, as well as in humans, has been shown to be a multistep process, with each step reflecting an altered gene product or gene regulatory process leading to autonomy of cell growth. Initial genetic mutations are often associated with dysfunctional growth regulation, as is demonstrated in several transgenic mouse models. These changes are often followed by alterations in tumor suppressor gene function, allowing unchecked cell cycle progression and, by genomic instability, additional genetic mutations responsible for tumor metastasis. Here we show that reduced transforming growth factor-beta signaling in T lymphocytes leads to a rapid expansion of a CD8+ memory T-cell population and a subsequent transformation to leukemia/lymphoma as shown by multiple criteria, including peripheral blood cell counts histology, T-cell receptor monoclonality, and host transferability. Furthermore, spectral karyotype analysis of the tumors shows that the tumors have various chromosomal aberrations. These results suggest that reduced transforming growth factor-beta signaling acts as a primary carcinogenic event, allowing uncontrolled proliferation with consequent accumulation of genetic defects and leukemic transformation.

What is transforming growth factor-beta (TGF-β)?

The TGF-beta superfamily of proteins produces a wide range of frequently opposing effects in different cells and tissues in the body. However, its activation and mode of action are only partially understood because of its complexity in structure and functions and the variability in its downstream targets. Current work on these cytokines focuses on their receptors and the intercellular signalling pathways, comparing bioactivities between cell types and tracking their physiological and immunological effects in vivo. Future research will yield important therapeutic applications and the ability to manipulate these proteins in vivo.

Nerve growth factor mediates activation of the Smad pathway in PC12 cells

Ligand-induced oligomerization of receptors is a key step in initiating growth factor signaling. Nevertheless, complex biological responses often require additional trans-signaling mechanisms involving two or more signaling cascades. For cells of neuronal origin, it was shown that neurotrophic effects evoked by nerve growth factor or other neurotrophins depend highly on the cooperativity with cytokines that belong to the transforming growth factor beta (TGF-beta) superfamily. We found that rat pheochromocytoma cells, which represent a model system for neuronal differentiation, are unresponsive to TGF-beta1 due to limiting levels of its receptor, TbetaRII. However, stimulation with nerve growth factor leads to activation of the Smad pathway independent of TGF-beta. In contrast to TGF-beta signaling, activation of Smad3 by nerve growth factor does not occur via phosphorylation of the C-terminal SSXS-motif, but leads to heteromeric complex formation with Smad4, nuclear translocation of Smad3 and transcriptional activation of Smad-dependent reporter genes. This response is direct and does not require de novo protein synthesis, as shown by cycloheximide treatment. This initiation of transcription is dependent on functional tyrosine kinase receptors and can be blocked by Smad7. These data provide further evidence that the Smad proteins are not exclusively activated by the classical TGF-beta triggered mechanism. The potential of NGF to activate the Smad pathway independent of TGF-beta represents an important regulatory mechanism with special relevance for the development and function of neuronal cells or of other NGF-sensitive cells, in particular those that are TGF-beta-resistant.

Human stem cells as targets for the aging and diseases of aging processes

While many theories have been proposed for the aging process, and many debates on the matter of aging and the diseases of aging being either the result of the same or independent processes, most have not considered humans as a hierarchical system made up of cybernetically interacting levels of organization. To understand the aging process and the diseases of aging, one must view the human as the result of the total genomic DNA in the single fertilized egg that proliferates, differentiates and develops into an individual of about 100 trillion cells, organized by different cell types (pluri-potent stem cells, progenitor stem cells, terminally differentiated cells) into multiple tissue, organ and organ systems which interact with each other via endogenous factors and with exogenous factors. Our hypothesis is that both aging and diseases of aging are dependent of the normal functioning of the pluri-potent stem cell pool. Specifically, the concept involves the cybernetic feedback between the 'quantity' of the stem cell pool in each tissue niche with the 'quality' of the stem cells in the pool. The process of gap junctional inter-cellular communication (GJIC), which has been implicated in the evolution from the single cell organism to the multi-cellular organisms, requiring growth control, differentiation, apoptosis, adaptive response capability of differentiated cells and senescence, is speculated to be a shared mechanism in stem cell biology and in many chronic disease processes (teratogenesis; carcinogenesis, atherogenesis, diabetigenesis, etc.). Specifically, stem cells are assumed to be 'immortal' until induced to express their connexin genes and have functional GJIC, at which time they can differentiate and become 'mortal'. As long as the stem cells are communicating with their differentiated daughters via some extra-cellular soluble negative growth factor, the homeostatic control of their growth and differentiation is maintained for the organism. However, if the stem cell pool is depleted by any process, replacement of tissue due to wear and tear is diminished. The dependence of this tissue/organ to maintain homeostatic control of other organ systems then diminishes, leading to 'systems failure'. In addition, if the stem cells in the pool have been exposed to agents that prevent the normal terminal differentiation of that cell, but whereby these 'initiated' stem cells can be expanded in any tissue, clones of partially differentiated and non-functional appear in the tissue. This diminishes the efficacy of that tissue to function properly and, thereby, also contributes to 'system failure' by contributing to the breakdown of homeostatic organ system control. One clear example, that of carcinogenesis, illustrates this point.

Rap1 reverses transcriptional repression of TGF-beta type II receptor by a mechanism involving AP-1 in the human pancreatic cancer cell line, UK Pan-1

The TGF-beta signaling pathway has potent anti-mitogenic effects in epithelial cells and loss of negative growth regulation is often associated with increased tumorigenicity. The human pancreatic ductal adenocarcinoma cell line, UK Pan-1, which expresses DPC4, is not highly responsive to TGF-beta due to transcriptional repression of TGF-beta type II receptor (RII). Here, we show that UK Pan-1 cells transfected with a plasmid to overexpress rap1 protein (UK/rap1) causes an increase in RII transcription and restores sensitivity to TGF-beta growth inhibition. The overexpression of rap1 was associated with diminished ras signaling as measured by ras binding domain (RBD)-binding assays. Electrophoretic mobility shift assays (EMSA) analysis revealed increased binding of nuclear proteins to a previously identified positive regulatory element (PRE1) of the RII promoter in rap1 transfected cells. Competition with an oligo containing the AP-1 consensus site was able to inhibit this binding of nuclear proteins to the PRE1 region. Further EMSA analysis using antibodies to various AP-1 components revealed that junB antibodies partially depleted the increase in binding to the PRE1 seen in UK/rap1 cells while antibodies to other AP-1 constituents such as c-jun, c-fos, and ATF-1 had no effect on binding. Consistent with this data, transient transfection of UK Pan-1 cells with junB resulted in greater RII transcription (twofold) as measured by RII-luciferase assay. Mutation of the AP-1 site inhibited junB-mediated or rap1-mediated increases in RII promoter activity. These data suggest that rap1 signaling may mediate an increase in RII transcription via increased binding of nuclear factors including junB to the PRE1 region of the RII promoter.

Role of TGF-beta 1 and TGF-beta type II receptor in gastric cancer

BACKGROUND

TGF-beta is known as a cell growth inhibitory factor to suppress almost all cells, including the epithelial cell. Unlike normal cells, cancer cells are not affected by TGF-beta growth inhibitory action and the lack of TGF-beta receptor expression or mutation is being reported as its mechanism, which is rarely studied in Korea. Therefore, we investigated this study to clarify the role of TGF-beta I and TGF-beta II receptors in gastric cancer.

METHODS

23 cases that underwent operations for gastric cancer provided RNA collected from their carcinoma tissues and adjacent normal tissues. We investigated the level of TGF-beta 1 and T beta R-II mRNA expression with semi-quantitatively reverse transcription PCR and analyzed the correlation with prognostic factors, such as tumor size, depth of invasion, tumor differentiation and lymph-node metastasis.

RESULTS

(1) TGF-beta 1 and T beta R-II mRNA were expressed in all carcinoma tissues and adjacent normal tissues of the 23 cases without statistical difference in the level of the expression. (2) The level of TGF-beta 1 mRNA expression was higher in patients with gastric cancer invaded only at the mucosa and submucosa than in patients with gastric cancer invaded over muscular propria, and also higher in the patients without lymph-node metastasis or perineural invasion than in the patients with lymph-node metastasis or perineural invasion. There was no significant correlation between the level of T beta R-II mRNA expression and several parameters, such as age, gender, tumor size, location, differentiation, Lauren's classification and vascular invasion. (3) There was a significant correlation between the level of TGF-beta 1 and T beta R-II mRNA expression in carcinoma tissues.

CONCLUSION

It indicated that TGF-beta 1 mRNA expression in gastric cancer might concern the early stage of gastric carcinogenesis and, unlike the earlier reports, it was higher in patients with early gastric cancer, negative lymph-nodes or negative perineural invasion. Further studies are required to clarify the role of TGF-beta 1 in gastric carcinogenesis with more patients.

Ectopic expression of eIF-4E in human colon cancer cells promotes the stimulation of adhesion molecules by transforming growth factorbeta

Transforming growth factor beta1 (TGFbeta) inhibits cellular proliferation, promotes differentiation, and stimulates the expression and secretion of the extracellular matrix adhesion molecules fibronectin and laminin and the colon-associated intercellular adhesion molecule carcinoembryonic antigen. This is collectively called the TGFbeta-mediated adhesion response and occurs in the human colon cancer cell line Moser while the cell line KM12SM is relatively unresponsive to TGFbeta. We have previously shown that TGFbeta rapidly stimulates protein kinase C (PKC) phosphotransferase activity in the Moser cells and that the induction of the adhesion response (but not antiproliferation) by TGFbeta is dependent on PKC. Because resistance to growth factors may be due to translational suppression and the translation initiation factor eIF-4E may alleviate translational suppression, we determined the effect of eIF-4E expression on the responses of Moser and KM12SM cells to TGFbeta. Ectopic expression of eIF-4E in the TGFbeta-responsive Moser cells enhanced the activation of PKC by TGFbeta and the induction of the adhesion response, especially the secretion of adhesion molecules, but not the antiproliferative response. Ectopic expression of eIF-4E in the TGFbeta-resistant KM12SM cells increased TGFbeta stimulation of PKC and the TGFbeta-mediated adhesion response (but not antiproliferation). The secretion of adhesion molecules was significantly increased by TGFbeta. These results showed in these cells that eIF-4E promotes TGFbeta-regulated adhesion but not antiproliferation in a PKC-dependent manner.

Disruption of transforming growth factor beta signaling by a novel ligand-dependent mechanism

Transforming growth factor (TGF)-beta is the prototype in a family of secreted proteins that act in autocrine and paracrine pathways to regulate cell development and function. Normal cells typically coexpress TGF-beta receptors and one or more isoforms of TGF-beta, thus the synthesis and secretion of TGF-beta as an inactive latent complex is considered an essential step in regula-ting the activity of this pathway. To determine whether intracellular activation of TGF-beta results in TGF-beta ligand-receptor interactions within the cell, we studied pristane-induced plasma cell tumors (PCTs). We now demonstrate that active TGF-beta1 in the PCT binds to intracellular TGF-beta type II receptor (TbetaRII). Disruption of the expression of TGF-beta1 by antisense TGF-beta1 mRNA restores localization of TbetaRII at the PCT cell surface, indicating a ligand-induced impediment in receptor trafficking. We also show that retroviral expression of a truncated, dominant-negative TbetaRII (dnTbetaRII) effectively competes for intracellular binding of active ligand in the PCT and restores cell surface expression of the endogenous TbetaRII. Analysis of TGF-beta receptor-activated Smad2 suggests the intracellular ligand-receptor complex is not capable of signaling. These data are the first to demonstrate the formation of an intracellular TGF-beta-receptor complex, and define a novel mechanism for modulating the TGF-beta signaling pathway.

Transforming growth factor beta 1 dysregulation in a human oral carcinoma tumour progression model

A human oral tumour progression model was established that consists of normal epithelial cells and three cell lines representing stages from dysplastic to metastatic cells. To investigate the impact of exogenous transforming growth factor-beta 1 on this model system, we analysed the responsiveness of those cells to transforming growth factor-beta 1 and explored the potential mechanism underlying the transforming growth factor-beta 1 activity. We found that the growth of all cell types, regardless of their stage of tumour progression, is inhibited by transforming growth factor-beta 1, although to different degrees. Transforming growth factor-beta 1 induced the expression of cyclin-dependent kinase inhibitors p15(INK4B), p21WAF1/(CIP1) and p27(KIP1). In contrast, transforming growth factor-beta 1 was found to stimulate the invasive potential of one cell type that represents the most advanced stage of tumour phenotype, suggesting that the impact of transforming growth factor-beta 1 on functional features of tumour cells other than cellular proliferation may play a significant role in the process of oral tumour progression.

Transforming growth factor-beta regulation of estradiol-induced prolactinomas

Prolactin-secreting adenomas (prolactinomas) are the most prevalent form of pituitary tumors in humans, and increased tumor growth under estrogenic influence in female patients is often of clinical concern. Extensive experimental work has uncovered the roles of estrogen receptors and various growth-regulatory peptides in estradiol action on lactotropes. However, it is only recently that we are beginning to gain insight into how these growth factors interact to regulate estradiol action on lactotrope cell proliferation. Recent studies have identified the regulatory role of TGF-beta-related peptides in estradiol action on lactotropes. Additionally, these studies determined that TGF-beta and FGF interact to facilitate the communication between lactotropes and folliculostellate cells that is necessary for the mitogenic action of estradiol. This review addresses the role of estradiol in prolactinoma formation and summarizes data that support a novel concept: Alterations in the expression and action of TGF-beta isoforms are crucial steps in estradiol-induced tumorigenesis.

Expression and action of transforming growth factor beta (TGFbeta1, TGFbeta2, TGFbeta3) in normal bovine ovarian surface epithelium and implications for human ovarian cancer

The majority of ovarian tumors are derived from the single layer of epithelial cells on the surface of the ovary termed the ovarian surface epithelium (OSE). Stromal cell-OSE interactions are postulated to be an important aspect of normal OSE biology and the biology of ovarian cancer. Transforming growth factor beta (TGFbeta) has been shown to often be a mesenchymal cell-derived growth factor that mediates stromal cell-epithelial cell interactions in a variety of different tissues. The current study investigates the expression and action of TGFbeta isoforms (TGFbeta1, TGFbeta2, and TGFbeta3) in OSE and the underlying stroma in both normal bovine and human tumor tissues. Normal bovine ovaries are similar to human ovaries and are used as a model system to investigate normal OSE and stromal cell functions. All three TGFbeta isoforms and their receptor, transforming growth factor beta receptor type II (TGFbetaRII), proteins were found to be detected in the OSE from normal bovine ovaries using immunohistochemistry. Ovarian stromal tissue also contained positive immunostaining for TGFbeta isoforms and TGFbetaRII. RNA was collected from normal bovine OSE and ovarian stromal cells to examine TGFbeta gene expression. TGFbeta1, TGFbeta2, and TGFbeta3 transcripts were detected in both freshly isolated and cultured bovine OSE and stromal cells by a sensitive quantitative polymerase chain reaction assay. TGFbeta1 and TGFbeta2 mRNA levels were found to be present at similar levels in freshly isolated OSE and stroma. Interestingly, TGFbeta3 mRNA levels were significantly higher in freshly isolated OSE than stromal cells. All but TGFbeta3 mRNA in OSE increased when the cells were cultured. Observations indicate that normal bovine OSE and stroma cells express the three TGFbeta isoforms in vivo and in vitro. Human ovarian tumors from stage II, stage III and stage IV cases were found to express TGFbeta1, TGFbeta2, TGFbeta3 and TGFbetaRII protein primarily in the epithelial cell component by immunohistochemistry analysis. The stromal cell component of the human ovarian tumors contained little or no TGFbeta or TGFbetaRII immunostaining. TGFbeta actions on bovine OSE and stromal cells were also investigated. TGFbeta was found to inhibit the growth of OSE, but not stromal cells. To further examine the actions of TGFbeta on OSE, the expression of two growth factors previously shown to be expressed by OSE were analyzed. TGFbeta1 was found to stimulate the expression of both keratinocyte growth factor (KGF) and kit ligand/stem cell factor (KL) by bovine OSE. Therefore, TGFbeta actions on OSE will likely promote a cascade of cell-cell interactions and cellular responses involving multiple growth factors. The effects of regulatory agents on TGFbeta expression by the bovine OSE were examined. Transforming growth factor alpha (TGFalpha) stimulated TGFbeta1 expression, TGFbeta1 stimulated TGFbeta2 expression, and follicle stimulating hormone (FSH) stimulated TGFbeta3 expression. These results demonstrate that TGFbeta isoforms are regulated differently by the regulatory agents tested. In summary, all the TGFbeta isoforms are differentially expressed by the OSE and TGFbeta appears to have an important role in regulating OSE and possibly stromal-OSE interactions. A complex network of endocrine and paracrine interactions appears to influence the expression and actions of TGFbeta on OSE. Abnormal expression and/or action of TGFbeta is postulated to in part be involved in the onset and progression of ovarian cancer.

Hepatocellular expression of a dominant-negative mutant TGF-beta type II receptor accelerates chemically induced hepatocarcinogenesis

The potent growth-inhibitory activity of cytokines of the transforming growth factor-beta (TGF-beta) superfamily and their widespread expression in epithelia suggest that they may play an important role in the maintenance of epithelial homeostasis. To analyse TGF-beta mediated tumor suppressor activity in the liver, we generated transgenic mice overexpressing a dominant negative type II TGF-beta receptor in hepatocytes under control of the regulatory elements of the human C-reactive protein gene promoter. Transgenic animals exhibited constitutive and liver-specific transgene expression. The functional inactivation of the TGF-beta signaling pathway in transgenic hepatocytes was shown by reduced TGF-beta induced inhibition of DNA synthesis in primary hepatocyte cultures. Liver morphology and spontaneous tumorigenesis were unchanged in transgenic mice suggesting that interruption of the signaling of all three isoforms of TGF-beta in hepatocytes does not disturb tissue homeostasis in the liver under physiological conditions. However, following initiation with the carcinogen diethylnitrosamine and tumor-promotion with phenobarbital transgenic mice exhibited a moderate albeit significant increase in the incidence, size and multiplicity of both preneoplastic tissue lesions in the liver and of hepatocellular carcinomas. These results give in vivo evidence for a tumor suppressor activity of the endogenous TGF-beta system in the liver during chemical hepatocarcinogenesis.

TGF-beta and colorectal carcinogenesis

There is substantial evidence to support the contention that the Smad portion of the TGF-beta signal transduction pathway provides an important tumor-suppressor function. Mutational loss of function of Smad pathway members have been associated with the development of human cancers and appear to be causative in selected rodent carcinogenesis models. TGF-beta also has multiple other actions that appear to be independent of the growth-inhibitory/tumor suppressor effects. The predominant effect of TGF-beta appears to be dependent on the context of the responding cell. Once transformation has occurred, TGF-beta effects may be detrimental and may actually promote tumor cell survival, invasion, and metastasis. Recent work suggests that these effects may involve TGF-beta regulation of COX-2 and other pathways that may contribute to tumor cell aggressiveness. In gaining a better understanding of the mechanisms by which TGF-beta may promote tumor progression, it is likely that new therapeutic strategies may be developed that preserve tumor-suppressor function of TGF-beta while inhibiting the tumor-promoting effects.

Responsiveness to transforming growth factor-beta (TGF-beta)-mediated growth inhibition is a function of membrane-bound TGF-beta type II receptor in human breast cancer cells

Transforming growth factor-beta (TGF-beta) is a potent inhibitor of growth and proliferation of breast epithelial cells, and loss of sensitivity to its effects has been associated with malignant transformation and tumorigenesis. The biological effects of TGF-beta are mediated by the TGF-beta receptor complex, a multimer composed of TGF-beta receptor type I (TbetaR-I) and TGF-beta receptor type II (TbetaR-II) subunits. Evidence suggests that loss of expression of Tbeta3R-II is implicated in the loss of sensitivity of tumorigenic breast cell lines to TGF-beta-mediated growth inhibition. A panel of human breast cell lines, including the immortalized MCF-10F and tumorigenic MCF-7, ZR75-1, BT474, T47-D, MDA-MB231, BT20, and SKBR-3 cell lines, was characterized for responsiveness to TGF-beta-induced G1 growth arrest. Only the nontumorigenic MCF-10F and the tumorigenic MDA-MB231 cell lines demonstrated a significant inhibitory response to TGF-beta1 and a significant binding of 125I-labeled TGF-beta ligand. While expression of TbetaR-I mRNA was similar across the panel of cell lines, TbetaR-II mRNA expression was decreased significantly in all seven tumorigenic cell lines in comparison with the nontumorigenic MCF- 10F cell line. When total cellular protein was fractionated by centrifugation, TbetaR-I protein was observed in both the cytosolic and membrane fractions at similar levels in all cell lines; however, TbetaR-II protein was present in the cytosolic fraction in all cell lines, but was observed in the membrane fraction of only the TGF-beta-responsive MCF-10F and MDA-MB231 cells. Thus, lack of membrane-bound TbetaR-II protein appears to be an important determinant of resistance to TGF-beta-mediated growth inhibition in this group of breast cell lines.

Disruption of TGF-beta growth inhibition by oncogenic ras is linked to p27Kip1 mislocalization

Expression of oncogenic Ras in epithelial tumor cells is linked to the loss of transforming growth factor-beta (TGF-beta) anti-proliferative activity, and was proposed to involve inhibition of Smad2/3 nuclear translocation. Here we studied several epithelial cell lines expressing oncogenic N-RasK61 and show that TGF-beta-induced nuclear translocation of and transcriptional activation by Smad2/3 were unaffected. In contrast, oncogenic Ras mediated nuclearto-cytoplasmic mislocalization of p27KiP1 (p27) and of the cyclin-dependent kinase (CDK) CDK6, but not CDK2. Concomitantly, oncogenic Ras abrogated the ability of TGF-beta to release p27 from CDK6, to enhance its binding to CDK2 and to inhibit CDK2 activity. Inactivation of Ras by a specific antagonist restored the growth inhibitory response to TGF-beta with concurrent normalization of p27 and CDK6 localization. Therefore, the disruption of TGF-beta-mediated growth inhibition by oncogenic Ras appears to be due to lack of inhibition of CDK2, caused by the sequestration of p27 and CDK2 in different subcellular compartments and by the loss of TGF-beta-induced partner switching of p27 from CDK6 to CDK2.

Vascular endothelial cell growth factors promote the in vitro development of rat photoreceptor cells

We have identified and characterized a novel trophic effect of vascular endothelial cell growth factor (VEGF) on photoreceptor cells. Treatment of retinal cultures, derived from postnatal day 1 (P1) rats, with VEGF-2 resulted in a dose- and time-dependent increase in the level of rhodopsin protein, as determined by ELISA assay. After 7-9 d of treatment the VEGF-1 or VEGF-2, at a concentration of 10 ng/ml, induced a 200-300% increase in rhodopsin protein and a 220% increase in the number of rhodopsin-immunopositive cells. Treatment with VEGF-2 induced a 250% increase in the number of syntaxin-immunopositive cells and a 67% increase in high-affinity GABA uptake, both markers for amacrine cells. In contrast, there was no increase in the non-neuronal cell populations. VEGF-2 induced an approximately 300% increase in the number of bromodeoxyuridine-labeled (BrdU) retinal cells within 48 hr of treatment. After 3 d in culture both the basal and stimulated levels of BrdU incorporation were reduced, suggesting that the proliferative effect of VEGF was restricted developmentally. Furthermore, there was a developmentally dependent increase in the mitogenic response to VEGF-2, with retinal cultures derived from E15, E20, or P1 animals demonstrating a 50, 100, and 300% increase in thymidine incorporation, respectively. However, VEGF treatment resulted in an increase in the number of rhodopsin-immunopositive cells only when the cultures were derived from P1 animals. Therefore, retinal progenitor cells appear to be targets for VEGF, and thus VEGF may be involved in the regulation of the early developmental program of retinal neurogenesis.

The physical parameters and molecular events associated with radiation-induced lung toxicity

Radiation therapy (RT) is frequently used to treat patients with tumors in and around the thorax. Clinical radiation pneumonitis is a common side effect, occurring in 5% to 20% of patients. Efforts to identify patients at risk for pneumonitis have focused on physical factors, such as dose and volume. Recently, the underlying molecular biological mechanisms behind RT-induced lung injury have come under study. Improved knowledge of the molecular events associated with RT-induced lung injury may translate into a better ability to individualized therapy. This review discusses our current understanding of the physical and molecular factors contributing to RT-induced pulmonary injury.