Transcriptional regulation of the transforming growth factor beta 1 promoter by v-src gene products is mediated through the AP-1 complex

Alterations in TGFβ signaling during prostate cancer progression

During prostate cancer progression, TGF-β acts as both a tumor suppressor and tumor promoter. TGF-β inhibits cell proliferation in normal and early-stage prostate cancer cells, but during later stages of the disease the cancer cells develop resistance to inhibitory effects on cell proliferation. In these cells, TGF-β promotes cancer progression due to its effects on epithelial to mesenchymal transition (EMT), cell migration and invasion, and immune suppression. The intracellular mechanisms involved in the development of resistance to TGF-β effects on cell proliferation are largely unknown. In this review, we summarized the roles of several intracellular proteins including PTEN, Id1 and JunD, which may play a role in this transition. The role of Ski/SnoN proteins in inhibition of Smad2/3 signaling is highlighted.

Transforming growth factor-beta1 and myeloid-derived suppressor cells: A cancerous partnership

Transforming growth factor-beta1 (TGF-β1) plays a crucial role in tumor progression. It can inhibit early cancer stages but promotes tumor growth and development at the late stages of tumorigenesis. TGF-β1 has a potent immunosuppressive function within the tumor microenvironment that largely contributes to tumor cells' immune escape and reduction in cancer immunotherapy responses. Likewise, myeloid-derived suppressor cells (MDSCs) have been postulated as leading tumor promoters and a hallmark of cancer immune evasion mechanisms. This review attempts to analyze the prominent roles of both TGF-β1 and MDSCs and their interplay in cancer immunity. Furthermore, therapies against either TGF-β1 or MDSCs, and their potential synergistic combination with immunotherapies are discussed. Simultaneous TGF-β1 and MDSCs inhibition suggest a potential improvement in immunotherapy or subverted tumor immune resistance.

Elucidating the cellular mechanism for E2-induced dermal fibrosis

BACKGROUND

Both TGFβ and estradiol (E2), a form of estrogen, are pro-fibrotic in the skin. In the connective tissue disease, systemic sclerosis (SSc), both TGFβ and E2 are likely pathogenic. Yet the regulation of TGFβ in E2-induced dermal fibrosis remains ill-defined. Elucidating those regulatory mechanisms will improve the understanding of fibrotic disease pathogenesis and set the stage for developing potential therapeutics. Using E2-stimulated primary human dermal fibroblasts in vitro and human skin tissue ex vivo, we identified the important regulatory proteins for TGFβ and investigated the extracellular matrix (ECM) components that are directly stimulated by E2-induced TGFβ signaling.

METHODS

We used primary human dermal fibroblasts in vitro and human skin tissue ex vivo stimulated with E2 or vehicle (ethanol) to measure TGFβ1 and TGFβ2 levels using quantitative PCR (qPCR). To identify the necessary cell signaling proteins in E2-induced TGFβ1 and TGFβ2 transcription, human dermal fibroblasts were pre-treated with an inhibitor of the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) pathway, U0126. Finally, human skin tissue ex vivo was pre-treated with SB-431542, a TGFβ receptor inhibitor, and ICI 182,780, an estrogen receptor α (ERα) inhibitor, to establish the effects of TGFβ and ERα signaling on E2-induced collagen 22A1 (Col22A1) transcription.

RESULTS

We found that expression of TGFβ1, TGFβ2, and Col22A1, a TGFβ-responsive gene, is induced in response to E2 stimulation. Mechanistically, Col22A1 induction was blocked by SB-431542 and ICI 182,780 despite E2 stimulation. Additionally, inhibiting E2-induced ERK/MAPK activation and early growth response 1 (EGR1) transcription prevents the E2-induced increase in TGFβ1 and TGFβ2 transcription and translation.

CONCLUSIONS

We conclude that E2-induced dermal fibrosis occurs in part through induction of TGFβ1, 2, and Col22A1, which is regulated through EGR1 and the MAPK pathway. Thus, blocking estrogen signaling and/or production may be a novel therapeutic option in pro-fibrotic diseases.

Transforming growth factor beta type 1 (TGF-β) and hypoxia-inducible factor 1 (HIF-1) transcription complex as master regulators of the immunosuppressive protein galectin-9 expression in human cancer and embryonic cells

Galectin-9 is one of the key proteins employed by a variety of human malignancies to suppress anti-cancer activities of cytotoxic lymphoid cells and thus escape immune surveillance. Human cancer cells in most cases express higher levels of galectin-9 compared to non-transformed cells. However, the biochemical mechanisms underlying this phenomenon remain unclear.

Here we report for the first time that in human cancer as well as embryonic cells, the transcription factors hypoxia-inducible factor 1 (HIF-1) and activator protein 1 (AP-1) are involved in upregulation of transforming growth factor beta 1 (TGF-β1) expression, leading to activation of the transcription factor Smad3 through autocrine action. This process triggers upregulation of galectin-9 expression in both malignant (mainly in breast and colorectal cancer as well as acute myeloid leukaemia (AML)) and embryonic cells. The effect, however, was not observed in mature non-transformed human cells. TGF-β1-activated Smad3 therefore displays differential behaviour in human cancer and embryonic vs non-malignant cells. This study uncovered a self-supporting biochemical mechanism underlying high levels of galectin-9 expression operated by the human cancer and embryonic cells employed in our investigations. Our results suggest the possibility of using the TGF-β1 signalling pathway as a potential highly efficient target for cancer immunotherapy.

Human immunodeficiency virus interaction with oral and genital mucosal epithelia may lead to epithelial-mesenchymal transition and sequestration of virions in the endosomal compartments

Oral and genital mucosal epithelia are multistratified epithelial barriers with well-developed tight and adherens junctions. These barriers serve as the first line of defense against many pathogens, including human immunodeficiency virus (HIV). HIV interaction with the surface of mucosal epithelial cells, however, may activate transforming growth factor-beta (TGF-β) and mitogen-activated protein kinase signaling pathways. When activated, these pathways may lead to the disruption of epithelial junctions and epithelial-mesenchymal transition (EMT). HIV-induced impairment of the mucosal barrier may facilitate the spread of pathogenic viral, bacterial, fungal, and other infectious agents. HIV-induced EMT promotes highly motile/migratory cells. In oral and genital mucosa, if EMT occurs within a human papillomavirus (HPV)-infected premalignant or malignant cell environment, the HPV-associated neoplastic process could be accelerated by promoting viral invasion of malignant cells. HIV also internalizes into oral and genital mucosal epithelial cells. The majority (90%) of internalized virions do not cross the epithelium, but are retained in endosomal compartments for several days. These sequestered virions are infectious. Upon interaction with activated peripheral blood mononuclear cells and CD4+ T lymphocytes, epithelial cells containing the virus can be transferred. The induction of HIV-1 release and the cell-to-cell spread of virus from epithelial cells to lymphocytes is mediated by interaction of lymphocyte receptor function-associated antigen-1 with the epithelial cell receptor intercellular adhesion molecule-1. Thus, mucosal epithelial cells may serve as a transient reservoir for HIV, which could play a critical role in viral transmission.

HIV-1 proteins gp120 and tat induce the epithelial-mesenchymal transition in oral and genital mucosal epithelial cells

The oral, cervical, and genital mucosa, covered by stratified squamous epithelia with polarized organization and strong tight and adherens junctions, play a critical role in preventing transmission of viral pathogens, including human immunodeficiency virus (HIV). HIV-1 interaction with mucosal epithelial cells may depolarize epithelia and disrupt their tight and adherens junctions; however, the molecular mechanism of HIV-induced epithelial disruption has not been completely understood. We showed that prolonged interaction of cell-free HIV-1 virions, and viral envelope and transactivator proteins gp120 and tat, respectively, with tonsil, cervical, and foreskin epithelial cells induces an epithelial-mesenchymal transition (EMT). EMT is an epigenetic process leading to the disruption of mucosal epithelia and allowing the paracellular spread of viral and other pathogens. Interaction of cell-free virions and gp120 and tat proteins with epithelial cells substantially reduced E-cadherin expression and activated vimentin and N-cadherin expression, which are well-known mesenchymal markers. HIV gp120- and tat-induced EMT was mediated by SMAD2 phosphorylation and activation of transcription factors Slug, Snail, Twist1 and ZEB1. Activation of TGF-β and MAPK signaling by gp120, tat, and cell-free HIV virions revealed the critical roles of these signaling pathways in EMT induction. gp120- and tat-induced EMT cells were highly migratory via collagen-coated membranes, which is one of the main features of mesenchymal cells. Inhibitors of TGF-β1 and MAPK signaling reduced HIV-induced EMT, suggesting that inactivation of these signaling pathways may restore the normal barrier function of mucosal epithelia.

Activation of renal profibrotic TGFβ controlled signaling cascades by calcineurin and mTOR inhibitors

The calcineurin inhibitors (CNI) cyclosporine A (CsA) and tacrolimus represent potent immunosuppressive agents frequently used for solid organ transplantation and treatment of autoimmune disorders. Despite of their immense therapeutic benefits, residual fibrosis mainly in the kidney represents a common side effect of long-term therapy with CNI. Regardless of the immunosuppressive action, an increasing body of evidence implicates that a drug-induced increase in TGFβ and subsequent activation of TGFβ-initiated signaling pathways is closely associated with the development and progression of CNI-induced nephropathy. Mechanistically, an increase in reactive oxygen species (ROS) generation due to drug-induced changes in the intracellular redox homeostasis functions as an important trigger of the profibrotic signaling cascades activated under therapy with CNI. Although, inhibitors of the mechanistic target of rapamycin (mTOR) kinase have firmly been established as alternative compounds with a lower nephrotoxic potential, an activation of fibrogenic signaling cascades has been reported for these drugs as well. This review will comprehensively summarize recent advances in the understanding of profibrotic signaling events modulated by these widely used compounds with a specific focus put on mechanisms occurring independent of their respective immunosuppressive action. Herein, the impact of redox modulation, the activation of canonical TGFβ and non-Smad pathways and modulation of autophagy by both classes of immunosuppressive drugs will be highlighted and discussed in a broader perspective. The comprehensive knowledge of profibrotic signaling events specifically accompanying the immunomodulatory activity of these widely used drugs is needed for a reliable benefit-risk assessment under therapeutic regimens.

Butyrate produced by gut commensal bacteria activates TGF-beta1 expression through the transcription factor SP1 in human intestinal epithelial cells

The intestinal microbiota contributes to the global wellbeing of their host by their fundamental role in the induction and maintenance of a healthy immune system. Commensal bacteria shape the mucosal immune system by influencing the proportion and the activation state of anti-inflammatory regulatory T cells (Treg) by metabolites that are still only partially unravelled. Microbiota members such as Clostridiales provide a transforming growth factor β (TGFβ)-rich environment that promotes the accumulation of Treg cells in the gut. The intestinal epithelial cells (IECs) take a central part in this process, as they are a major source of TGFβ1 upon bacterial colonisation. In this study, we investigated which gut commensal bacteria were able to regulate the TGFB1 human promoter in IECs using supernatants from cultured bacteria. We reported that Firmicutes and Fusobacteria supernatants were the most potent TGFB1 modulators in HT-29 cells. Furthermore, we demonstrated that butyrate was the main metabolite in bacterial supernatants accounting for TGFβ1 increase. This butyrate-driven effect was independent of the G-protein coupled receptors GPR41, GPR43 and GPR109a, the transporter MCT1 as well as the transcription factors NF-κB and AP-1 present on TGFB1 promoter. Interestingly, HDAC inhibitors were inducing a similar TGFB1 increase suggesting that butyrate acted through its HDAC inhibitor properties. Finally, our results showed that SP1 was the main transcription factor mediating the HDAC inhibitor effect of butyrate on TGFB1 expression. This is, to our knowledge, the first characterisation of the mechanisms underlying TGFB1 regulation in IEC by commensal bacteria derived butyrate.

Blockade of Eosinophil-Induced Bronchial Epithelial-Mesenchymal Transition with a Geranyl Acetophenone in a Coculture Model

Epithelial-mesenchymal transition (EMT) is currently recognized as the main cellular event that contributes to airway remodeling. Eosinophils can induce EMT in airway epithelial cells via increased transforming growth factor (TGF)-β production. We assessed the effect of synthetic 2,4,6-trihydroxy-3-geranyl acetophenone (tHGA) upon eosinophil-induced EMT in a cellular model. The human eosinophil cell line EoL-1 was used to induce EMT in BEAS-2B human bronchial epithelial cells. The induction of EMT was dose-dependently suppressed following tHGA treatment in which the epithelial morphology and E-cadherin expression were not altered. Protein and mRNA expression of vimentin, collagen I and fibronectin in eosinophil-induced epithelial cells were also significantly suppressed by tHGA treatment. Following pathway analysis, we showed that tHGA suppressed eosinophil-induced activator protein-1-mediated TGF-β production by targeting c-Jun N-terminal kinase and phosphoinositide 3-kinase signaling pathways. These findings corroborated previous findings on the ability of tHGA to inhibit experimental murine airway remodeling.

LIM-Only Protein FHL2 Is a Negative Regulator of Transforming Growth Factor β1 Expression

Transforming growth factor β1 (TGF-β1) is a master cytokine in many biological processes, including tissue homeostasis, epithelial-to-mesenchymal transition, and wound repair. Here, we report that four and a half LIM-only protein 2 (FHL2) is a critical regulator of TGF-β1 expression. Devoid of a DNA-binding domain, FHL2 is a transcriptional cofactor that plays the role of coactivator or corepressor, depending on the cell and promoter contexts. We detected association of FHL2 with the TGF-β1 promoter, which showed higher activity in Fhl2^-/- cells than in wild-type (WT) cells in a reporter assay. Overexpression of FHL2 abrogates the activation of the TGF-β1 promoter, whereas the upregulation of TGF-β1 gene transcription correlates with reduced occupancy of FHL2 on the promoter. Moreover, ablation of FHL2 facilitates recruitment of RNA polymerase II on the TGF-β1 promoter, suggesting that FHL2 may be involved in chromatin remodeling in the control of TGF-β1 gene transcription. Enhanced expression of TGF-β1 mRNA and cytokine was evidenced in the livers of Fhl2^-/- mice. We tested the in vivo impact of Fhl2 loss on hepatic fibrogenesis that involves TGF-β1 activation. Fhl2^-/- mice developed more severe fibrosis than their WT counterparts. These results demonstrate the repressive function of FHL2 on TGF-β1 expression and contribute to the understanding of the TGF-β-mediated fibrogenic response.

Dysregulation of TGFβ1 Activity in Cancer and Its Influence on the Quality of Anti-Tumor Immunity

TGFβ1 is a pleiotropic cytokine that exhibits a variety of physiologic and immune regulatory functions. Although its influence on multiple cell types is critical for the regulation of numerous biologic processes in the host, dysregulation of both TGFβ1 expression and activity is frequently observed in cancer and contributes to various aspects of cancer progression. This review focuses on TGFβ1’s contribution to tumor immune suppression and escape, with emphasis on the influence of this regulatory cytokine on the differentiation and function of dendritic cells and T cells. Clinical trials targeting TGFβ1 in cancer patients are also reviewed, and strategies for future therapeutic interventions that build on our current understanding of immune regulation by TGFβ1 are discussed.

IL-10 is required for polarization of macrophages to M2-like phenotype by mycobacterial DnaK (heat shock protein 70)

Macrophages are key cells in the innate immune system. They phagocytose pathogens and cellular debris, promote inflammation, and have important roles in tumor immunity. Depending on the microenvironment, macrophages can polarize to M1 (inflammatory) or M2 (anti-inflammatory) phenotypes. Extracellular DnaK (the bacterial ortholog of the mammalian Hsp70) from Mycobacterium tuberculosis (Mtb) was described to exert immune modulatory roles in an IL-10 dependent manner. We have previously observed that endotoxin-free DnaK can polarize macrophages to an M2-like phenotype. However, the mechanisms that underlie this polarization need to be further investigated. IL-10 has been described to promote macrophage polarization, so we investigated the involvement of this cytokine in macrophages stimulated with extracellular DnaK. IL-10 was required to induce the expression of M2 markers - Ym1 and Fizz, when macrophages were treated with DnaK. Blockade of IL-10R also impaired DnaK induced polarization, demonstrating the requirement of the IL-10/IL-10R signaling pathway in this polarization. DnaK was able to induce TGF-β mRNA in treated macrophages in an IL-10 dependent manner. However, protein TGF-β could not be detected in culture supernatants. Finally, using an in vivo allogeneic melanoma model, we observed that DnaK-treated macrophages can promote tumor growth in an IL-10-dependent manner. Our results indicate that the IL-10/IL-10R axis is required for DnaK-induced M2-like polarization in murine macrophages.

Palladin mediates stiffness-induced fibroblast activation in the tumor microenvironment

Mechanical properties of the tumor microenvironment have emerged as key factors in tumor progression. It has been proposed that increased tissue stiffness can transform stromal fibroblasts into carcinoma-associated fibroblasts. However, it is unclear whether the three to five times increase in stiffness seen in tumor-adjacent stroma is sufficient for fibroblast activation. In this study we developed a three-dimensional (3D) hydrogel model with precisely tunable stiffness and show that a physiologically relevant increase in stiffness is sufficient to lead to fibroblast activation. We found that soluble factors including CC-motif chemokine ligand (CCL) chemokines and fibronectin are necessary for this activation, and the combination of C-C chemokine receptor type 4 (CCR4) chemokine receptors and β1 and β3 integrins are necessary to transduce these chemomechanical signals. We then show that these chemomechanical signals lead to the gene expression changes associated with fibroblast activation via a network of intracellular signaling pathways that include focal adhesion kinase (FAK) and phosphoinositide 3-kinase (PI3K). Finally, we identify the actin-associated protein palladin as a key node in these signaling pathways that result in fibroblast activation.

Macrophage Akt1 Kinase-Mediated Mitophagy Modulates Apoptosis Resistance and Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a devastating lung disorder with increasing incidence. Mitochondrial oxidative stress in alveolar macrophages is directly linked to pulmonary fibrosis. Mitophagy, the selective engulfment of dysfunctional mitochondria by autophagasomes, is important for cellular homeostasis and can be induced by mitochondrial oxidative stress. Here, we show Akt1 induced macrophage mitochondrial reactive oxygen species (ROS) and mitophagy. Mice harboring a conditional deletion of Akt1 in macrophages (Akt1(-/-)Lyz2-cre) and Park2(-/-) mice had impaired mitophagy and reduced active transforming growth factor-β1 (TGF-β1). Although Akt1 increased TGF-β1 expression, mitophagy inhibition in Akt1-overexpressing macrophages abrogated TGF-β1 expression and fibroblast differentiation. Importantly, conditional Akt1(-/-)Lyz2-cre mice and Park2(-/-) mice had increased macrophage apoptosis and were protected from pulmonary fibrosis. Moreover, IPF alveolar macrophages had evidence of increased mitophagy and displayed apoptosis resistance. These observations suggest that Akt1-mediated mitophagy contributes to alveolar macrophage apoptosis resistance and is required for pulmonary fibrosis development.

Smad2 and Smad3 Inversely Regulate TGF-β Autoinduction in Clostridium butyricum-Activated Dendritic Cells

Colonization with a mixture of Clostridium species has been shown to induce accumulation of induced regulatory T (iTreg) cells in the colon. Transforming growth factor-β (TGF-β) is an essential factor for iTreg cell induction; however, the relationship between Clostridium species and TGF-β remains to be clarified. Here we demonstrated that a gram-positive probiotic bacterial strain, Clostridium butyricum (C. butyricum), promoted iTreg cell generation in the intestine through induction of TGF-β1 from lamina propria dendritic cells (LPDCs). C. butyricum-mediated TGF-β1 induction was mainly Toll-like receptor 2 (TLR2) dependent, and the ERK-AP-1 kinase pathway played an important role. In addition, the autocrine TGF-β-Smad3 transcription factor signal was necessary for robust TGF-β expression in DCs, whereas Smad2 negatively regulated TGF-β expression. Smad2-deficient DCs expressed higher concentrations of TGF-β and were tolerogenic for colitis models. This study reveals a novel mechanism of TGF-β induction by Clostridia through a cooperation between TLR2-AP-1 and TGF-β-Smad signaling pathways.

Computational identification of potential transcriptional regulators of TGF-ß1 in human atherosclerotic arteries

TGF-ß is protective in atherosclerosis but deleterious in metastatic cancers. Our aim was to determine whether TGF-ß transcriptional regulation is tissue-specific in early atherosclerosis. The computational methods included 5 steps: (i) from microarray data of human atherosclerotic carotid tissue, to identify the 10 best co-expressed genes with TGFB1 (TGFB1 gene cluster), (ii) to choose the 11 proximal promoters, (iii) to predict the TFBS shared by the promoters, (iv) to identify the common TFs co-expressed with the TGFB1 gene cluster, and (v) to compare the common TFs in the early lesions to those identified in advanced atherosclerotic lesions and in various cancers. Our results show that EGR1, SP1 and KLF6 could be responsible for TGFB1 basal expression, KLF6 appearing specific to atherosclerotic lesions. Among the TFs co-expressed with the gene cluster, transcriptional activators (SLC2A4RG, MAZ) and repressors (ZBTB7A, PATZ1, ZNF263) could be involved in the fine-tuning of TGFB1 expression in atherosclerosis.

The expression of HIV-1 Vpu in monocytes causes increased secretion of TGF-β that activates profibrogenic genes in hepatic stellate cells

There is faster progression to fibrosis in persons with liver injury who are also infected with HIV. Other reports have suggested that HIV can directly infect and activate stellate cells, and the viral Tat and gp160 proteins also induce profibrogenic factors from peripheral blood mononuclear cells (PBMCs). We tested the role of HIV-1 Vpu accessory protein in promoting profibrogenic activation of hepatic stellate cells. Human stellate LX2 cells were cocultured with human monocytic U937 cells stably expressing the Vpu protein or latently infected U1 cells knocked down for Vpu expression, LX2 cells were also cultured with the supernatants from these cells. The expression of profibrogenic markers was evaluated in LX2 cells usingquantitative reverse transcription polymerase chain reaction (qRT-PCR),western blotting, immunofluorescence,flow cytometry and ELISA were used to confirm and quantitate protein expression. Monocytic cells expressing Vpu increased the expression of profibrogenic markers in LX2 cells. The culture supernatants of these cells contained increased levels of transforming growth factor beta (TGF-β), which correlated with increased activity of the AP-1 transcription factor. Antibodies against TGF-β or a TGF-β receptor inhibitor (SB431452) reversed Vpu-mediated profibrogenic activation of LX2 cells, suggesting that TGF-β mediated these effects. The cytokine macrophage migration inhibitory factor (MIF) attenuated Vpu-mediated TGF-β secretion and profibrogenic effects on LX2 cells. Besides its other roles in pathogenesis, Vpu is likely to contribute to hepatic fibrosis through this hitherto unknown mechanism.

Transforming growth factor-Beta and urokinase-type plasminogen activator: dangerous partners in tumorigenesis-implications in skin cancer

Transforming growth factor-beta (TGF-β) is a pleiotropic factor, with several different roles in health and disease. TGF-β has been postulated as a dual factor in tumor progression, since it represses epithelial tumor development in early stages, whereas it stimulates tumor progression in advanced stages. During tumorigenesis, cancer cells acquire the capacity to migrate and invade surrounding tissues and to metastasize different organs. The urokinase-type plasminogen activator (uPA) system, comprising uPA, the uPA cell surface receptor, and plasminogen-plasmin, is involved in the proteolytic degradation of the extracellular matrix and regulates key cellular events by activating intracellular signal pathways, which together allow cancer cells to survive, thus, enhancing cell malignance during tumor progression. Due to their importance, uPA and its receptor are tightly transcriptionally regulated in normal development, but are deregulated in cancer, when their activity and expression are related to further development of cancer. TGF-β regulates uPA expression in cancer cells, while uPA, by plasminogen activation, may activate the secreted latent TGF-β, thus, producing a pernicious cycle which contributes to the enhancement of tumor progression. Here we review the specific roles and the interplay between TGF-β and uPA system in cancer cells and their implication in skin cancer.

Conditional radioresistance of Tet-inducible manganese superoxide dismutase bone marrow stromal cell lines

Mitochondrial targeted manganese superoxide dismutase is a major antioxidant enzyme, the levels of which modulate the response of cells, tissues and organs to ionizing irradiation. We developed a Tet-regulated MnSOD mouse (MnSOD(tet)) to examine the detailed relationship between cellular MnSOD concentration and radioresistance and carried out in vitro studies using bone marrow culture derived stromal cell lines (mesenchymal stem cells). Homozygous MnSOD(tet/tet) cells had low levels of MnSOD, reduced viability and proliferation, increased radiosensitivity, elevated overall antioxidant stores, and defects in cell proliferation and DNA strand-break repair. Doxycycline (doxy) treatment of MnSOD(tet/tet) cells increased MnSOD levels and radioresistance from ñ of 2.79 ± 1.04 to 8.69 ± 1.09 (P = 0.0060) and normalized other biologic parameters. In contrast, MnSOD(tet/tet) cells showed minimal difference in baseline and radiation induced mRNA and protein levels of TGF-β, Nrf2 and NF-κB and radiation induced cell cycle arrest was not dependent upon MnSOD level. These novel MnSOD(tet/tet) mouse derived cells should be valuable for elucidating several parameters of the oxidative stress response to ionizing radiation.

Pathological in situ reprogramming of somatic cells by the unfolded protein response

In response to tissue injuries, terminally differentiated cells are reprogrammed to undergo dedifferentiation to gain mitogenic and metabolic properties. The dedifferentiated cells acquire an immature phenotype, proliferate actively, produce abundant extracellular matrix, and recruit circulating leukocytes via secretion of chemokines, contributing to tissue repair and/or fibrosis. However, this remodeling process is self-limiting, and in the later phase, the activated, dedifferentiated cells are reprogrammed to redifferentiate into a mature, quiescent phenotype. Currently, molecular mechanisms underlying this bidirectional pathological reprogramming remain elusive. It is known that the unfolded protein response (UPR) is induced at local tissues under pathological situations and affects cellular fate-survival or death. It is also known that the UPR is involved in cell differentiation and organogenesis during embryonic development. In this review, we describe a hypothesis for regulatory roles of the UPR in the pathological reprogramming of somatic cells (ie, cellular dedifferentiation and redifferentiation at the sites of injury).

Activation of TGF-β1 promoter by hepatitis C virus-induced AP-1 and Sp1: role of TGF-β1 in hepatic stellate cell activation and invasion

Our previous studies have shown the induction and maturation of transforming growth factor-beta 1 (TGF-β1) in HCV-infected human hepatoma cells. In this study, we have investigated the molecular mechanism of TGF-β1 gene expression in response to HCV infection. We demonstrate that HCV-induced transcription factors AP-1, Sp1, NF-κB and STAT-3 are involved in TGF-β1 gene expression. Using chromatin immunoprecipitation (ChIP) assay, we further show that AP-1 and Sp1 interact with TGF-b1 promoter in vivo in HCV-infected cells. In addition, we demonstrate that HCV-induced TGF-β1 gene expression is mediated by the activation of cellular kinases such as p38 MAPK, Src, JNK, and MEK1/2. Next, we determined the role of secreted bioactive TGF-β1 in human hepatic stellate cells (HSCs) activation and invasion. Using siRNA approach, we show that HCV-induced bioactive TGF-β1 is critical for the induction of alpha smooth muscle actin (α-SMA) and type 1 collagen, the markers of HSCs activation and proliferation. We further demonstrate the potential role of HCV-induced bioactive TGF-β1 in HSCs invasion/cell migration using a transwell Boyden chamber. Our results also suggest the role of HCV-induced TGF-β1 in HCV replication and release. Collectively, these observations provide insight into the mechanism of TGF-β1 promoter activation, as well as HSCs activation and invasion, which likely manifests in liver fibrosis associated with HCV infection.

Inhibitory effects of enalaprilat on rat cardiac fibroblast proliferation via ROS/P38MAPK/TGF-β1 signaling pathway

Enalaprilat (Ena.), an angiotensin II (Ang II) converting enzyme inhibitor (ACEI), can produce some therapeutic effects on hypertension, ventricular hypertrophy and myocardial remodeling in clinic, but its precise mechanism, especially its signaling pathways remain elusive. In this study, cardiac fibroblasts (CFb) was isolated by the trypsin digestion method; a BrdU proliferation assay was adopted to determine cell proliferation; an immunofluorescence assay was used to measure intracellular reactive oxygen species (ROS); immunocytochemistry staining and Western blotting assay were used to detect phosphorylated p38 mitogen activated protein kinase (p-p38MAPK) and transforming growth factor-β₁ (TGF-β₁) protein expression, respectively. The results showed that Ang II (10^–7 M) stimulated the cardiac fibroblast proliferation which was inhibited by NAC (an antioxidant), SB203580 (a p38MAPK inhibitor) or enalaprilat; Ang II caused an burst of intracellular ROS level within thirty minutes, an increase in p-p38MAPK (3.6-fold of that in the control group), as well as an elevation of TGF-β₁ meantime; NAC, an antioxidant, and enalaprilat treatment attenuated cardiac fibroblast proliferation induced by Ang II and decreased ROS and p-p38MAPK protein levels in rat cardiac fibroblast; SB203580 lowered TGF-β₁ protein expression in rats’ CFb in a dose-dependent manner. It could be concluded that enalaprilat can inhibit the cardiac fibroblast proliferation induced by Ang II via blocking ROS/P38MAPK/TGF-β₁ signaling pathways and the study provides a theoretical proof for the application of ACEIs in treating myocardial fibrosis and discovering the primary mechanism through which ACEIs inhibit CFb proliferation.

Stretch augments TGF-beta1 expression through RhoA/ROCK1/2, PTK, and PI3K in airway smooth muscle cells

Transforming growth factor-beta1 (TGF-beta1) expression in smooth muscle cells may play an important role in the pathogenesis of asthma. However, mechanisms that are involved in the regulation of TGF-beta1 gene expression in human airway smooth muscle cells (HASMCs) remain elusive. Here, we show that mechanical stretch of HASMCs augmented TGF-beta1 expression through a de novo RNA synthesis mechanism. Luciferase reporter assays revealed that stretch-induced TGF-beta1 expression was mediated through the enhanced activation of TGF-beta1 promoter. Interestingly, selective inhibitors of PTK, PI3K, or MEK1/2 attenuated TGF-beta1 expression through blocking ERK1/2 phosphorylation and TGF-beta1 promoter activity in response to stretch. In addition, stretch rapidly and transiently augmented GTP-bound RhoA and Rac1 but not Cdc42 GTPase. Either blockade of RhoA GTPase using C3 transferase, ROCK1/2 using Y27632, or knockdown of endogenous RhoA using RhoA siRNA attenuated stretch-induced TGF-beta1 expression through the inhibition of ERK1/2 phosphorylation. Moreover, stretch augmented DNA binding activity of AP-1 in a time-dependent manner. Either treatment of HASMCs with the inhibitors of RhoA, ROCK1/2, PTK, PI3K, MEK1/2, or AP-1 or transfection of HASMCs with AP-1 decoy oligonucleotide attenuated stretch-induced TGF-beta1 expression through repressing the DNA binding activity of AP-1. Site-directed mutagenesis demonstrated that two AP-1 binding sites in the TGF-beta1 promoter region are responsible for stretch-induced TGF-beta1 expression. Overall, in HASMCs, mechanical stretch plays an important role in TGF-beta1 gene upregulation through a stretch-induced signaling pathway, which could be a potential therapeutic intervention for TGF-beta1-induced pathogenesis in asthma.

Herb medicine Gan-fu-kang attenuates liver injury in a rat fibrotic model

AIM OF THE STUDY

To verify therapeutic effects of Gan-fu-kang (GFK), a traditional Chinese medicine compound, in a rat model and to investigate the underlying mechanisms.

MATERIALS AND METHODS

Liver fibrosis was established by 12 weeks of carbon tetrachloride (CCl(4)) treatment (0.5mg/kg, twice per week) followed by 8 weeks of "recovery" in rats. Rats randomly received GFK (31.25, 312.5 and 3125 mg/kg/day, p.o.) or vehicle from weeks 9 to 20, and were sacrificed at the end of week 20 for histological, biochemical, and molecular biological examinations. In a separate set of experiments, rats received 12 weeks of CCl(4) treatment, concomitant with GFK (312.5mg/kg/day, p.o.) during the same period in some subjects, but were then sacrificed immediately. An additional group of rats receiving no CCl(4) treatment served as normal controls.

RESULTS AND CONCLUSIONS

(1) CCl(4) treatment resulted in severe liver damage and fibrosis. (2) In the main block of the 20-week study, GFK attenuated liver damage and fibrosis. (3) In the 12-week study, GFK produced prevention effect against hepatic injury. (4) GFK suppressed the expression of tissue inhibitor of metalloproteinase-1 (TIMP-1), type I collagen, platelet-derived growth factor-BB (PDGF-BB)/PDGF receptor-beta chains (PDGFRbeta) and mitogen-activated protein kinases (MAPKs)/active protein-1 (AP-1) signal pathways. Taken together, these results indicated that GFK could attenuate liver injuries in both settings. Our findings also suggest that the AP-1 pathway is the likely molecular substrate for the observed GFK effects.

Osteopontin: regulation in tumor metastasis

Osteopontin is a secreted phosphoprotein that has been implicated as an important mediator of tumor metastasis and has been investigated for use as a biomarker for advanced disease and as a potential therapeutic target in the regulation of cancer metastasis. The OPN DNA sequence is highly conserved and the protein contains several important functional domains including alpha(v)beta integrin and CD44 binding sites. High levels of OPN expression correlate with tumor invasion, progression or metastasis in multiple cancer. Studies demonstrate that osteopontin mediates the molecular mechanisms which determine metastatic spread, such as prevention of apoptosis, extracellular matrix proteolysis and remodeling, cell migration, evasion of host-immune cells and neovascularization. Transcriptional regulation of OPN is complex and involves multiple pathways, including AP-1, Myc, v-Src, Runx/CBF, TGF-B/BMPs/Smad/Hox, and Wnt/ss-catenin/APC/GSK-3ss/Tcf-4. The current state of knowledge of OPN biology suggests that it is an attractive target for therapeutic modulation of metastatic disease.

v-Src-mediated Down-regulation of SSeCKS Metastasis Suppressor Gene Promoter by the Recruitment of HDAC1 into a USF1-Sp1-Sp3 Complex

SSeCKS (Src-suppressed C kinase substrate), also called gravin/AKAP12, is a large scaffolding protein with metastasis suppressor activity. Two major isoforms of SSeCKS are expressed in most cell and tissue types under the control of two independent promoters, designated alpha and beta, separated by 68 kb. SSeCKS transcript and protein levels are severely decreased in Src- and Ras-transformed fibroblasts and in many epithelial tumors. By dissecting its promoters with progressive deletion analysis, we identified the sequence between -106 and -49 in the alpha proximal promoter as the minimal v-Src-responsive element, which contains E- and GC-boxes bound by USF1 and Sp1/Sp3, respectively. Both E- and GC-boxes are crucial for v-Src-responsive and basal promoter activities. v-Src does not alter USF1 binding levels at the E-box, but it increases Sp1/Sp3 binding to the GC-box despite no change in their cellular protein abundance. SSeCKS alpha and beta transcript levels in v-Src/3T3 cells can be restored by treatment with the histone deacetylase inhibitor, trichostatin A, but not with the DNA demethylation agent, 5-azacytidine. Chromatin changes are found only on the alpha promoter even though the beta proximal promoter contains a similar E- and GC-box arrangement. Recruitment of HDAC1 is necessary and sufficient to cause repression of alpha proximal promoter activity, and the addition of Sp1 and/or Sp3 potentiates the repression. Our data suggest that suppression of the beta promoter is facilitated by Src-induced changes in the alpha promoter chromatinization mediated by a USF1-Sp1-Sp3 complex.

Role of activator protein-1 on the effect of arginine-glycine-aspartic acid containing peptides on transforming growth factor-β1 promoter activity

While arginine-glycine-aspartic acid-based peptidomimetics have been employed for the treatment of cardiovascular disorders and cancer, their use in other contexts remains to be explored. Arginine-glycine-aspartic acid-serine induces Transforming growth factor-beta1 transcription in human mesangial cells, but the molecular mechanisms involved have not been studied extensively. We explored whether this effect could be due to Activator protein-1 activation and studied the potential pathways involved. Addition of arginine-glycine-aspartic acid-serine promoted Activator protein-1 binding to its cognate sequence within the Transforming growth factor-beta1 promoter as well as c-jun and c-fos protein abundance. Moreover, this effect was suppressed by curcumin, a c-Jun N terminal kinase inhibitor, and was absent when the Activator protein-1 cis-regulatory element was deleted. Activator protein-1 binding was dependent on the activity of integrin linked kinase, as transfection with a dominant negative mutant suppressed both Activator protein-1 binding and c-jun and c-fos protein increment. Integrin linked kinase was, in turn, dependent on Phosphoinositol-3 kinase activity. Arginine-glycine-aspartic acid-serine stimulated Phosphoinositol-3 kinase activity, and Transforming growth factor-beta1 promoter activation was abrogated by the use of Phosphoinositol-3 kinase specific inhibitors. In summary, we propose that arginine-glycine-aspartic acid-serine activates Integrin linked kinase via the Phosphoinositol-3 kinase pathway and this leads to activation of c-jun and c-fos and increased Activator protein-1 binding and Transforming growth factor-beta1 promoter activity. These data may contribute to understand the molecular mechanisms involved in the cellular actions of arginine-glycine-aspartic acid-related peptides and enhance their relevance as these products evolve into clinical therapeutic use.

Induction of transforming growth factor-β1 by basic fibroblast growth factor in rat C6 glioma cells and astrocytes is mediated by MEK/ERK signaling and AP-1 activation

Basic fibroblast growth factor (bFGF) and transforming growth factor-beta1 (TGF-beta1) play an important role in proliferation, differentiation, and survival of malignant gliomas and in normal glial cell biology. Because of these critical roles, potential interactions between these key growth factors were investigated. We previously demonstrated that bFGF potently stimulates TGF-beta1 release from rat glioma cells. The purpose of the present study was to elucidate the mechanism(s) of this regulatory effect, establish its functional importance, and examine whether it extends to nontransformed rat hypothalamic astrocytes (RHA). The results revealed that RHA express the high-affinity FGF(1-4) receptors, and similarly to glioma cells, bFGF stimulated TGF-beta1 release in an isoform-specific manner. A mediatory role for ERK signaling in bFGF-induced TGF-beta release was suggested by the fact that MEK1 inhibition prevented this effect. Additionally, bFGF enhanced MEK1/2 phosphorylation and ERK activation/nuclear translocation, which culminated in increased activity of AP-1-mediated gene transcription. bFGF markedly induced TGF-beta1 mRNA levels in an isoform-specific manner, an effect that was dependent on MEK/ERK/AP-1 signaling. Functionally, bFGF-induced proliferation of glioma cells was attenuated by MEK/ERK inhibition or immunoneutralization of TGF-beta1, suggesting that this pathway may have important implications for brain tumor progression.

The role of Osteopontin in tumor metastasis

Osteopontin (OPN) is a glyco-phosphoprotein that is expressed and secreted by numerous human cancers. OPN functions in cell adhesion, chemotaxis, macrophage-directed interleukin-10 (IL-10) suppression, stress-dependent angiogenesis, prevention of apoptosis, and anchorage-independent growth of tumor cells by regulating cell-matrix interactions and cellular signaling through binding with integrin and CD44 receptors. While constitutive expression of OPN exists in several cell types, induced expression has been detected in T-lymphocytes, epidermal cells, bone cells, macrophages, and tumor cells in remodeling processes such as inflammation, ischemia-reperfusion, bone resorption, and tumor progression. Recently, substantial evidence has linked OPN with the regulation of metastatic spread by tumor cells. However, the molecular mechanisms that define the role of OPN in tumor metastasis are incompletely understood. Transcriptional regulators that contribute to the induction of OPN expression have received significant attention as potential modulators of the OPN-mediated metastatic phenotype. The following review will discuss the molecular structure of OPN, the evidence for its functional role in tumor cell metastasis, the downstream signals that activate invasive mechanisms, and the recent reports concerning regulation of OPN transcription.

Regulation of MAPK Activation, AP-1 Transcription Factor Expression and Keratinocyte Differentiation in Wounded Fetal Skin

Fetal epithelium retains the ability to re-epithelialize a wound in organotypic culture in a manner not dependent on the presence of underlying dermal substrata. This capacity is lost late in the third trimester of gestation or after embryonic day 17 (E(17)) in the rat such that embryonic day 19 (E(19)) wounds do not re-epithelialize. Moreover, wounds created in E(17) fetuses in utero heal in a regenerative, scar-free fashion. To investigate the molecular events regulating re-epithelialization in fetal skin, the wound-induced expression profile and tissue localization of activator protein 1 (AP-1) transcription factors c-Fos and c-Jun was characterised in E(17) and E(19) skin using organotypic fetal cultures. The involvement of mitogen-activated protein kinase (MAPK) signaling in mediating wound-induced transcription factor expression and wound re-epithelialization was assessed, with the effect of wounding on the expression of keratinocyte differentiation markers determined. Our results show that expression of AP-1 transcription factors was induced immediately by wounding and localized predominantly to the epidermis in E(17) and E(19) skin. c-fos and c-jun induction was transient in E(17) skin with MAPK-dependent c-fos expression necessary for the re-epithelialization of an excisional wound in organotypic culture. In E(19) skin, AP-1 expression persisted beyond 12 h post-wounding, and marked upregulation of the keratinocyte differentiation markers keratin 10 and loricrin was observed. No such changes in the expression of keratin 10 or loricrin occurred in E(17) skin. These findings indicate that re-epithelialization in fetal skin is regulated by wound-induced AP-1 transcription factor expression via MAPK and the differentiation status of keratinocytes.

Genealogy, expression, and cellular function of transforming growth factor-beta

The transforming growth factor-beta (TGF-beta) gene superfamily expresses a large set of structurally and functionally related polypeptides. Three TGF-beta isoforms are regulated by specific genes and have been identified in mammals (TGF-beta1, -beta2, and -beta3). All three-protein isoforms are observed abundantly during development and display overlapping and distinct spatial and temporal patterns of expressions. Each isoform plays a distinct role, the nature of which depends on the cell type, its state of differentiation, and growth conditions, and on the other growth factors present. TGF-beta regulates many of the processes common to both tissue repair and disease, including angiogenesis, chemotoxins, fibroblast proliferation and the controlled synthesis, and degradation of matrix proteins, such as collagen and fibronectin. This review will examine the genealogy and mode of actions of TGF-beta on the cell types involved in inflammation and repair, as well as in carcinoma.

Leptin receptor-mediated signaling regulates hepatic fibrogenesis and remodeling of extracellular matrix in the rat

BACKGROUND & AIMS

In this study, we investigated the role of leptin and its receptors (Ob-R) in profibrogenic responses in the liver using Zucker (fa/fa) rats, a natural occurring Ob-R-deficient animal.

METHODS

Male Zucker (fa/fa) rats and their lean (+/?) littermates were given intraperitoneal injections of thioacetamide (TAA) (200 mg/kg body wt, 3 times/wk) for 4-8 weeks, and progression of hepatic fibrosis was evaluated. In vitro transactivation of hepatic stellate cells (HSCs) isolated from Zucker rats was evaluated by Western blotting and immunocytochemistry for alpha-smooth muscle actin and type I collagen. Further, a long-form Ob-R (Ob-Rb) in sinusoidal endothelial cells (SECs) and Kupffer cells was identified by reverse-transcription polymerase chain reaction. Moreover, transforming growth factor (TGF)-beta1 messenger RNA in LSE cells, a human SEC-derived cell line, was measured by Northern blotting.

RESULTS

Although the normal liver does not produce leptin, activated HSCs produced leptin in vivo during fibrogenesis caused by TAA. In Zucker rats, TAA-induced hepatic fibrosis was prevented almost completely, whereas induction of TGF-beta1 and activation of HSCs were abolished. It is less likely, however, that leptin plays an essential role in the activation of HSCs as a strong autocrine regulator, because HSCs isolated from Zucker rats undergo normal transactivation process in vitro. In contrast, SECs and Kupffer cells contain Ob-Rb, through which leptin up-regulates the expression of matrix remodeling genes including TGF-beta1.

CONCLUSIONS

Collectively, these findings indicated that leptin and its functional receptors (Ob-Rb) play a pivotal role in profibrogenic responses in the liver.

Administration of a decoy against the activator protein-1 binding site suppresses neointimal thickening in rabbit balloon-injured arteries

BACKGROUND

Transcription factor activator protein-1 (AP-1) is activated and upregulated in injured arterial smooth muscle cells in vivo, yet the exact role of the AP-1--related pathway in vascular disease in vivo has remained unclear. We examined the role of the transfer of synthetic double-stranded cis-element decoy oligodeoxynucleotides (ODNs) in balloon-injured rabbit carotid arteries and the effects of these ODNs on neointimal thickening.

METHODS AND RESULTS

Transfection of fluorescein isothiocyanate--labeled ODNs using the hemagglutinating virus of Japan liposome method resulted in widespread distribution of fluorescent nuclear signals over the entire medial layer in injured arteries. Gel mobility shift assay revealed that AP-1 DNA binding was activated and that the AP-1 decoy reduced AP-1 DNA binding activity as a result of specific binding affinity to AP-1 in vivo. In morphometric analyses, AP-1 decoy led to a significant reduction in the neointimal area and a significant reduction in cell number and transforming growth factor-beta(1) production of human aortic smooth muscle cells under conditions of platelet-derived growth factor stimulation.

CONCLUSIONS

Because AP-1 decoy transfection in vivo dramatically prevented neointimal thickening in balloon-injured arteries, AP-1 may be a useful molecular target for gene therapy to reduce restenosis.

Transcription factor activation in response to cutaneous injury: role of AP-1 in reepithelialization

Reepithelialization is the process responsible for restoring an intact epidermis following cutaneous injury. A change in the activity of keratinocytes is required for reepithelialization to occur, and this is likely to be regulated by the altered expression of effector genes, mediated by transcription factors. The injury itself provides a stimulus for transcription factor activation either directly due to mechanical stress, or via paracrine mechanisms such as the release of growth factors from damaged cells. Members of the activator protein-1 family, in particular c-fos and c-jun, have been the most widely studied wound-induced transcription factors. The signal transduction pathways linking cellular injury to activator protein-1 stimulation appear to involve an increase in intracellular Ca2+ and activation of mitogen-activated protein kinases. Given that a number of genes involved in the reepithelialization of wounds are regulated by activator protein-1, a distinct role for this transcription factor in reepithelialization is beginning to emerge. This article reviews the evidence for activator protein-1 involvement in reepithelialization, with particular focus on the activation of this transcription factor in response to wounding, the second messenger/kinase pathways involved, and the modulation of downstream genes that have the capacity to regulate keratinocyte function.

Stimulation of osteoprotegerin (OPG) gene expression by transforming growth factor-beta (TGF-beta). Mapping of the OPG promoter region that mediates TGF-beta effects

Transforming growth factor-beta (TGF-beta) regulates osteoclastogenesis and osteoclast survival, in part through the induction of osteoprotegerin (OPG), a protein known to inhibit osteoclast formation and function. To explore the molecular basis of TGF-beta regulation of OPG expression, we evaluated the effects of TGF-beta on osteoclast formation, OPG protein secretion, mRNA expression, and gene transcription. The marked inhibitory effect of TGF-beta on osteoclast differentiation was confirmed in a co-culture model utilizing murine stromal/osteoblastic BALC cells and bone marrow hematopoietic precursors. This inhibition in osteoclast differentiation was preceded by a decrease in RANKL mRNA expression (5-fold) and a reciprocal increase in OPG mRNA (6.1-fold) and protein (7.1-fold) expression in BALC cells. At the promoter/transcriptional level, TGF-beta treatment resulted in a 3-10-fold increase in reporter gene activity directed by a 5.9-kilobase fragment of the human OPG promoter in transfection assays performed in UMR106 cells. The effect of TGF-beta was mimicked by TGF-beta2 and -beta3 but not by BMP-4, suggesting a TGF-beta signal-specific effect. Deletion analysis revealed that a 183-base pair region (-372 to -190) in the promoter was required for TGF-beta responsiveness, and this region was sufficient to confer TGF-beta inducibility to a heterologous (osteocalcin) minimal promoter. Substitution mutations that disrupted the Cbfa1- and/or Smad-binding elements present in the 183-base pair region resulted in a decrease in base-line expression and in the responsiveness to TGF-beta and Cbfa1. Collectively, these studies indicate the involvement and possible interaction of Cbfa1 and Smad proteins in mediating the effects of TGF-beta on OPG transcription.

Transforming growth factor-beta signal transduction in epithelial cells

Transforming growth factor (TGF)-beta is a natural and potent growth inhibitor of a variety of cell types, including epithelial, endothelial, and hematopoietic cells. The ability of TGF-beta to potently inhibit the growth of many solid tumors of epithelial origin, including breast and colon carcinomas, is of particular interest. However, many solid tumor cells become refractory to the growth inhibitory effects of TGF-beta due to defects in TGF-beta signaling pathways. In addition, TGF-beta may stimulate the invasiveness of tumor cells via the paracrine effects of TGF-beta. Accordingly, in order to develop more effective anticancer therapeutics, it is necessary to determine the TGF-beta signal transduction pathways underlying the growth inhibitory effects and other cellular effects of TGF-beta in normal epithelial cells. Thus far, two primary signaling cascades downstream of the TGF-beta receptors have been elucidated, the Sma and mothers against decapentaplegic homologues and the Ras/mitogen-activated protein kinase pathways. The major objective of this review is to summarize TGF-beta signaling in epithelial cells, focusing on recent advances involving the Sma and mothers against decapentaplegic homologues and Ras/mitogen-activated protein kinase pathways. This review is particularly timely in that it provides a comprehensive summary of both signal transduction mechanisms and the cell cycle effects of TGF-beta.

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.

Angiogenesis in breast cancer: the role of transforming growth factor beta and CD105

The progression of breast cancer depends on the establishment of a neovasculature, by a process called angiogenesis. Angiogenesis is an invasive cellular event that requires the co-ordination of numerous molecules including growth factors and their receptors, extracellular proteins, adhesion molecules, and proteolytic enzymes. TGFbeta has emerged to be a major modulator of angiogenesis by regulating endothelial cell proliferation, migration, extracellular matrix (ECM) metabolism, and the expression of adhesion molecules. It is a potent growth inhibitor of normal mammary epithelial cells and a number of breast cancer cell lines. It seems that TGFbeta exerts pleiotropic effects in the oncogenesis of breast cancers in a contextual manner, i.e., it suppresses tumourigenesis at an early stage by direct inhibition of angiogenesis and tumour cell growth. However, over-production of TGFbeta by an advanced tumour may accelerate disease progression through indirect stimulation of angiogenesis and immune suppression. The cell membrane antigen CD105 (endoglin) binds TGFbeta1 and TGFbeta3 and is preferentially expressed in angiogenic vascular endothelial cells. The reduction of CD105 levels in HUVEC leads to in vitro angiogenesis inhibition and massive cell mortality in the presence of TGFbeta1. CD105 null mice die in utero with impaired vasculature, indicating the pivotal role of CD105 in vascular development. The administration of an immunotoxin-conjugate, mab to CD105, induces long-term and complete regression of breast cancer growth in SCID mice. Therefore, CD105 is a promising vascular target for antiangiogenic therapy.

Chimeric constructs containing the SH4/Unique domains of cYes can restrict the ability of Src(527F) to upregulate heme oxygenase-1 expression efficiently

cSrc and cYes are the two most homologous members of the Src-family of nonreceptor tyrosine kinases. These kinases perform redundant signalling functions in cells; however, there is also evidence to support specificity in signalling. In this report, specificity in signalling between activated forms of the cSrc and cYes oncoproteins was examined at the level of downstream gene expression. Here, pp60c-src(527F) (Src(527F)) and chimeric constructs of Src(527F) containing combinations of the SH4/Unique/SH3/SH2 domains of cYes were generated to determine whether the individual modular domains of cSrc or cYes could direct distinct cellular signals leading to differential gene expression. A biased, differential display analysis approach was used to analyse changes in gene expression. The data indicate that Src(527F) is capable of upregulating heme oxygenase-1 (HO-1) in CEF cells at the level of transcription and protein expression. Chimeric constructs containing the SH4/Unique domains of cYes were less efficient in upregulating HO-1 expression. Activation of cSrc and expression of the HO-1 gene product are each induced under conditions of hypoxia. We hypothesize that activated cSrc can direct upregulation of HO-1 while activated cYes may be less efficient in stimulating signal transduction pathways that direct expression of HO-1.

The transcription factor EGR-1 directly transactivates the fibronectin gene and enhances attachment of human glioblastoma cell line U251

EGR-1, a transcription factor with important functions in the regulation of growth and differentiation, is highly expressed in brain. Previous studies have shown that EGR-1 suppresses the transformed phenotype. However, the expression and role of EGR-1 in human glioblastoma cells are not yet determined. In this study, we found that the basal expression of the EGR-1 protein is undetectable, but is inducible in four human glioblastoma cell lines. To determine EGR-1 functions, we re-expressed EGR-1 in human glioblastoma U251 cells and found that the secretion of transforming growth factor-beta1 (TGF-beta1), plasminogen activator inhibitor-1 (PAI-1), and fibronectin (FN) was greatly enhanced. Addition of anti-TGF-beta antibodies completely inhibited the secretion of PAI-1, but had little effect on secretion of FN, indicating that PAI-1 is under the control of EGR-1-induced TGF-beta1. An examination of the promoter of the FN gene revealed two EGR-1-binding sites between positions -75 and -52 and positions -4 and +14 that specifically bound EGR-1 in gel mobility shift experiments. Utilizing wild-type and mutant FN promoter/luciferase reporter genes, we demonstrated that EGR-1 positively regulated the activity of the FN gene. In addition, cell adhesion and migration were greatly increased in the EGR-1-expressing cells, and adhesion was reversed by addition of RGD-containing peptides. These results suggest that EGR-1 may regulate cell interaction with the extracellular matrix by coordinated induction of TGF-beta1, FN, and PAI-1 in human glioblastoma cells.

Activation of human CAII gene promoter by v-Src: existence of Ras-dependent and -independent pathways

Carbonic anhydrase II (CAII) catalyzes the reversible hydration of carbon dioxide and plays key roles in acid base homeostasis in mammals. We found that human CAII gene promoter could be activated in human cells such as HeLa and T47D cells when the CAII promoter-luciferase gene was transfected with v-Src and assayed as a reporter of the promoter activity. Kinase negative mutants of Src, in contrast, showed little activation. The activation was completely suppressed with the introduction of a dominant-negative Ras in T47D cells, while no suppression was observed in HeLa cells. Introduction of various kinds of deletions into the CAII promoter revealed two essential regions responsible for this activation. No activation, however, was observed in activated Fyn-transfected human cells or in v-Src-transfected rodent cells. These findings suggest that Src can modulate the human CAII promoter by exerting its tyrosine kinase activity in certain human cells, and that two types of Src signaling pathways, Ras-dependent and -independent, exist in a cell type dependent manner.

Transforming growth factor-beta1 enhances Ha-ras-induced expression of cyclooxygenase-2 in intestinal epithelial cells via stabilization of mRNA

Oncogenic ras induces the expression of cyclooxygenase-2 (COX-2) in a variety of cells. Here we investigated the role of transforming growth factor-beta (TGF-beta) in the Ras-mediated induction of COX-2 in intestinal epithelial cells (RIE-1). RIE-1 cells were transfected with an inducible Ha-Ras(Val12) cDNA and are referred as RIE-iRas cells. the addition of 5 mM isopropyl-1-thio-beta-D-galactopyranoside (IPTG) induced the expression of Ha-Ras(Val12), closely followed by an increase in the expression of COX-2. Neutralizing anti-TGF-beta antibody partially blocked the Ras-induced increase in COX-2. Combined treatment with IPTG and TGF-beta1 resulted in a 20-50-fold increase in the levels of COX-2 mRNA. The t1/2 of COX-2 mRNA was increased from 13 to 24 min by Ha-Ras induction alone. The addition of TGF-beta1 further stabilized the COX-2 mRNA (t1/2 > 50 min). Stable transfection of a luciferase reporter construct containing the COX-2 3'-untranslated region (3'-UTR) revealed that TGF-beta1 treatment and Ras induction each stabilized the COX-2 3'-UTR. Combined treatment with IPTG and TGF-beta1 synergistically increased the luciferase activity. Furthermore, a conserved AU-rich region located in the proximal COX-2 3'-UTR is required for maximal stabilization of COX-2 3'-UTR by Ras or TGF-beta1 and is necessary for the synergistic stabilization of COX-2 3'-UTR by oncogenic Ras and TGF-beta1.

Chronic activation of glomerular mitogen-activated protein kinases in Dahl salt-sensitive rats

The in vivo role of mitogen-activated protein kinases (MAPK) in the development of glomerular injury is poorly understood. In the present study, glomerular MAPK activities, including extracellular signal-regulated kinases (ERK), c-Jun NH2-terminal kinases (JNK), and transcriptional factor, activator protein-1 (AP-1) were examined in glomerular injury of salt-induced hypertensive rats. Six-week-old Dahl salt-sensitive (Dahl-S) and salt-resistant (Dahl-R) rats were maintained on a high-salt (8.0% NaCl) diet for 1, 5, and 10 wk. In Dahl-S rats, as shown by in-gel kinase assay, an increase in BP by a high-salt diet was followed by chronic activation of glomerular ERK and JNK, which continued until 10 wk after a high-salt diet. Western blot analysis demonstrated a significant increase in the protein expression of glomerular ERK and JNK in Dahl-S rats fed a high-salt diet. As determined by gel-mobility shift assay, ERK and JNK activations were associated with an increase in glomerular AP-1 DNA binding activity. On the other hand, in Dahl-R rats fed a high-salt diet, BP remained normal throughout the experiments. However, glomerular ERK and JNK activities and AP-1 DNA binding activity in Dahl-R rats were not affected by 1 or 5 wk of a high-salt diet, but significantly increased by 10 wk of treatment with a high-salt diet, indicating that chronic sodium overload itself stimulated glomerular ERK and JNK and AP-1 activities. These kinase activations in both Dahl-S and Dahl-R rats were accompanied by an increase in urinary protein excretion and renal growth. These observations provide the first evidence that salt-sensitive hypertension causes chronic activation of glomerular ERK and JNK, probably leading to the activation of AP-1. Thus, glomerular MAPK may be responsible for the development of salt-induced glomerular injury.

Down-regulation of TGF-beta receptors in human colorectal cancer: implications for cancer development

Many colorectal cancer cells are resistant to the anti-proliferative effects of transforming growth factor-beta (TGF-beta). TGF-beta also acts as paracrine factor from cancer cells on their mesenchymal cells. The aim of this study was to examine the expression of TGF-beta and its receptors in human colorectal cancer tissue and determine any relationship with cancer growth. In situ hybridization and Northern blot hybridization detection of TGF-beta1, type I and type II receptor mRNA and immunohistochemical staining of TGF-beta1 were performed using 11 human colorectal adenomas, 22 colorectal cancers and ten normal colorectal mucosas as control. TGF-beta receptor mRNAs were expressed mainly by normal colorectal epithelial cells and adenoma. However, mRNAs for TGF-beta receptors were only faintly, if at all, expressed in eight of 22 human colorectal cancers. In addition, intense signals of TGF-beta1 mRNA and the protein were detected in all colorectal cancers. TGF-beta receptor mRNAs and TGF-beta1 protein were also distributed in fibroblasts and endothelial cells in the interstitium. Moreover, Smad 4 protein was translocated to nucleus in primarily cultured adenoma cells, but not in cancer cells after TGF-beta stimulation. The escape of human colon cancer from TGF-beta-mediated growth inhibition by down-regulation of TGF-beta receptors as well as the effects of TGF-beta on stroma formation and angiogenesis indicate a possible role for TGF-beta in the progression of colon cancer in an intact host.

pp60(v-src) induction of cyclin D1 requires collaborative interactions between the extracellular signal-regulated kinase, p38, and Jun kinase pathways. A role for cAMP response element-binding protein and activating transcription factor-2 in pp60(v-src) signaling in breast cancer cells

The cyclin D1 gene is overexpressed in breast tumors and encodes a regulatory subunit of cyclin-dependent kinases that phosphorylate the retinoblastoma protein. pp60(c-src) activity is frequently increased in breast tumors; however, the mechanisms governing pp60(c-src) regulation of the cell cycle in breast epithelium are poorly understood. In these studies, pp60(v-src) induced cyclin D1 protein levels and promoter activity (48-fold) in MCF7 cells. Cyclin D1-associated kinase activity and protein levels were increased in mammary tumors from murine mammary tumor virus-pp60(c-src527F) transgenic mice. Optimal induction of cyclin D1 by pp60(v-src) involved the extracellular signal-regulated kinase, p38, and c-Jun N-terminal kinase members of the mitogen-activated protein kinase family. Cyclin D1 promoter activation by pp60(v-src) involved a cAMP response element-binding protein (CREB)/activating transcription factor 2 (ATF-2) binding site. Dominant negative mutants of CREB and ATF-2 but not c-Jun inhibited pp60(v-src) induction of cyclin D1. pp60(v-src) induction of CREB was blocked by the p38 inhibitor SB203580 or by mutation of CREB at Ser133. pp60(v-src) induction of ATF-2 was abolished by the c-Jun N-terminal kinase inhibitor JNK-interacting protein-1 or by mutation of ATF-2 at Thr69 and Thr71. CREB and ATF-2, which bind to a common pp60(v-src) response element, are transcriptionally activated by distinct mitogen-activated protein kinases. Induction of cyclin D1 activity by pp60(v-src) may contribute to breast tumorigenesis through phosphorylation and inactivation of the retinoblastoma protein.

Transformation of intestinal epithelial cells by chronic TGF-beta1 treatment results in downregulation of the type II TGF-beta receptor and induction of cyclooxygenase-2

The precise role of TGF-beta in colorectal carcinogenesis is not clear. The purpose of this study was to determine the phenotypic alterations caused by chronic exposure to TGF-beta in non-transformed intestinal epithelial (RIE-1) cells. Growth of RIE-1 cells was inhibited by >75% following TGF-beta1 treatment for 7 days, after which the cells resumed a normal growth despite the presence of TGF-beta1. These 'TGF-beta-resistant' cells (RIE-Tr) were continuously exposed to TGF-beta for >50 days. Unlike the parental RIE cells, RIE-Tr cells lost contact inhibition, formed foci in culture, grew in soft agarose. RIE-Tr cells demonstrated TGF-beta-dependent invasive potential in an in vitro assay and were resistant to Matrigel and Na-butyrate-induced apoptosis. The RIE-Tr cells were also tumorigenic in nude mice. The transformed phenotype of RIE-Tr cells was associated with a 95% decrease in the level of the type II TGF-beta receptor (TbetaRII) protein, a 40-fold increase in cyclooxygenase-2 (COX-2) protein, and 5.9-fold increase in the production of prostacyclin. Most RIE-Tr subclones that expressed low levels of TbetaRII and high levels of COX-2 were tumorigenic. Those subclones that express abundant TbetaRII and low levels of COX-2 were not tumorigenic in nude mice. A selective COX-2 inhibitor inhibited RIE-Tr cell growth in culture and tumor growth in nude mice. The reduced expression of TbetaRII, increased expression of COX-2, and the ability to form colonies in Matrigel were all reversible upon withdrawal of exogenous TGF-beta1 for the RIE-Tr cells.

In situ non-radioactive detection of nuclear factors in paraffin sections by Southwestern histochemistry

BACKGROUND

Transcriptional activities of genes require intermediary regulators (nuclear factors) that bind to specific segments of nuclear DNA. A method to localize in situ the distribution of these factors using nonradioactive oligonucleotides in paraffin wax-embedded tissues is described. The distribution of two nuclear factors, activated protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB), was studied in two experimental models of immune complex glomerulonephritis in rats and atherosclerosis in rabbits.

METHODS

Sections were fixed with 0.2% paraformaldehyde and were digested with pepsin A. Oligonucleotides containing the consensus sequence of NF-kappaB and AP-1 were 3'-labeled with digoxigenin. The preparations were incubated with the labeled probes (4 degreesC, overnight). After washing, the sections were incubated with an antidigoxigenin antibody conjugated with alkaline phosphatase, and the color reaction was developed. In addition, this method was combined with standard immunohistochemistry to identify the cell-type-specific localization of these DNA-binding factors.

RESULTS

Kidney sections from rats with immune complex nephritis showed positive nuclear staining for AP-1 in the nuclei of several glomerular and tubulointerstitial cells. Arteries from rabbits with focal atherosclerosis presented nuclear staining for NF-kappaB in the neointima and media. The nuclear staining was highly specific, as assessed by several negative controls. In addition, Southwestern histochemistry in rabbits, followed by immunohistochemistry, demonstrated that the NF-kappaB activity was present in the area occupied by macrophages and smooth muscle cells.

CONCLUSION

These results show a novel method of in situ transcription factors detection using nonradioactive probes in paraffin wax-embedded tissues, which allows a simultaneous visualization of the cell-type-specific localization of these nuclear factors.