Id2 and Id3 define the potency of cell proliferation and differentiation responses to transforming growth factor beta and bone morphogenetic protein

Autocrine BMP4 signalling regulates ID3 proto-oncogene expression in human ovarian cancer cells

Bone morphogenetic protein (BMP)-4 signalling leads to the direct upregulation of ID3 proto-oncogene expression in human ovarian cancer cells. An upstream BMP4-responsive enhancer element consisting of a palindromic BMP response element (BRE) site and CAGA box was identified ~3.0 kb upstream of the human ID3 gene, and a nearly-identical element exists in the second intron of the ID3 gene. BMP4 stimulation leads to the direct binding of Smads 1/5 and Smad4 to the upstream and intronic enhancers, and together both enhancers cooperate to yield heightened BMP4-mediated ID3 promoter activity. We further demonstrate that ID3 is overexpressed in human ovarian cancer cells when compared to normal ovarian surface epithelial cells, and treatment of ovarian cancer cells with the BMP4 antagonist Noggin abrogates endogenous ID3 gene expression. Our findings define the mechanism of BMP4-mediated ID3 gene expression, and support the notion that ovarian cancer cells possess autocrine BMP4 signalling required to sustain ID3 overexpression which may contribute to human ovarian cancer pathogenesis.

Conditional deletion of Smad1 and Smad5 in somatic cells of male and female gonads leads to metastatic tumor development in mice

The transforming growth factor beta (TGFbeta) family has critical roles in the regulation of fertility. In addition, the pathogenesis of some human cancers is attributed to misregulation of TGFbeta function and SMAD2 or SMAD4 mutations. There are limited mouse models for the BMP signaling SMADs (BR-SMADs) 1, 5, and 8 because of embryonic lethality and suspected genetic redundancy. Using tissue-specific ablation in mice, we deleted the BR-SMADs from somatic cells of ovaries and testes. Single conditional knockouts for Smad1 or Smad5 or mice homozygous null for Smad8 are viable and fertile. Female double Smad1 Smad5 and triple Smad1 Smad5 Smad8 conditional knockout mice become infertile and develop metastatic granulosa cell tumors. Male double Smad1 Smad5 conditional knockout mice are fertile but demonstrate metastatic testicular tumor development. Microarray analysis indicated significant alterations in expression of genes related to the TGFbeta pathway, as well as genes involved in infertility and extracellular matrix production. These data strongly implicate the BR-SMADs as part of a critical developmental pathway in ovaries and testis that, when disrupted, leads to malignant transformation.

Role of WISP-2/CCN5 in the maintenance of a differentiated and noninvasive phenotype in human breast cancer cells

WISP-2/CCN5 is an estrogen-regulated member of the "connective tissue growth factor/cysteine-rich 61/nephroblastoma overexpressed" (CCN) family of the cell growth and differentiation regulators. The WISP-2/CCN5 mRNA transcript is undetectable in normal human mammary cells, as well as in highly aggressive breast cancer cell lines, in contrast with its higher level in the breast cancer cell lines characterized by a more differentiated phenotype. We report here that knockdown of WISP-2/CCN5 by RNA interference in estrogen receptor alpha (ERalpha)-positive MCF-7 breast cancer cells induced an estradiol-independent growth linked to a loss of ERalpha expression and promoted epithelial-to-mesenchymal transdifferentiation. In contrast, forced expression of WISP-2/CCN5 directed MCF-7 cells toward a more differentiated phenotype. When introduced into the poorly differentiated, estrogen-independent, and invasive MDA-MB-231 breast cancer cells, WISP-2/CCN5 was able to reduce their proliferative and invasive phenotypes. In a series of ERalpha-positive tumor biopsies, we found a positive correlation between the expression of WISP-2/CCN5 and ID2, a transcriptional regulator of differentiation in normal and transformed breast cells. We propose that WISP-2/CCN5 is an important regulator involved in the maintenance of a differentiated phenotype in breast tumor epithelial cells and may play a role in tumor cell invasion and metastasis.

Inhibitory effects and target genes of bone morphogenetic protein 6 in Jurkat TAg cells

Bone morphogenetic proteins (BMP) are multifunctional cytokines that belong to the TGF-beta superfamily. BMP have been shown to regulate haematopoietic stem cells, B lymphopoiesis and early thymocyte differentiation. In the present study we explored the role of BMP-6 in Jurkat TAg cells. BMP-6 rapidly induced phosphorylation of Smad1/5/8, p38 and ERK1/2, followed by a potent up-regulation of ID1, ID2 and ID3. ID1 and ID3 were also induced at the protein level. Genome-wide expression profiling of cells treated with BMP-6 compared to medium confirmed that ID1-ID3 were target genes of BMP-6 together with Noggin and Smad6. Furthermore, several genes involved in transcriptional regulation were also identified, including NFKBIA, HEY1, DLX2, KLF10 and early growth response 1. Stimulation with BMP-6 exerted an antiproliferative effect that was counteracted by inhibitor of DNA binding (Id)1 siRNA, indicating that Id1 is an important downstream mediator in Jurkat TAg cells. A subset of CD4(+) T cells were found to express the BMP receptors Alk-2 and Alk-3 (type I), in addition to BMPRII (type II). BMP-6 also induced phosphorylation of Smad1/5/8, followed by transcriptional increase in ID1-ID3 mRNA expression. However, we did not observe significant changes in Id protein expression in CD4(+) T cells. Altogether, the data indicate a role for BMP-6 in human T lineage cells.

Overexpression of cyclin B1 in human esophageal squamous cell carcinoma cells induces tumor cell invasive growth and metastasis

Cyclin B1, a key component in the control of cell cycle progression from G(2) to M phase, has been implicated in tumorigenesis and the development of malignancy. However, the underlying mechanism by which cyclin B1 acts as an important oncogenic molecule remains largely unknown. Here we show that ectopic expression of cyclin B1 promotes cell proliferation, enhances cell motility and migration and results in increased ability of cells extravasating through the capillary endothelium. Interestingly, isogenic esophageal squamous cell carcinoma (ESCC) cells overexpressing cyclin B1 reveal strong invasive growth and high potential of metastasis to lung in xenograft mice. Suppression of cyclin B1 expression via small interfering RNA approach in high-metastatic esophagus carcinoma cells specifically inhibits their ability to metastasize from the primary ESCC to lung. Notably, altered expression of epithelial markers and mesenchymal markers were observed in the cells overexpressing cyclin B1, suggesting that cyclin B1 contributes to metastasis probably by promoting an epithelial-mesenchymal transition. These results establish a mechanistic link between cyclin B1 and ESCC metastasis and provide novel insight into understanding of cyclin B1 in the development of ESCC malignancy.

Genetic profiling of epithelial cells expressing E-cadherin repressors reveals a distinct role for Snail, Slug, and E47 factors in epithelial-mesenchymal transition

The transcription factors Snail, Slug, and bHLH E47 have been recently described as direct repressors of E-cadherin and inducers of epithelial-mesenchymal transition (EMT) and invasion when overexpressed in epithelial cells. Although a role of those factors in tumor progression and invasion has been proposed, whether the different repressors play distinct or redundant roles in the tumorigenic process has not been established. To further investigate this important issue, we have analyzed the gene expression profiling of Madin-Darby canine kidney (MDCK) epithelial cells expressing the different repressors (MDCK-Snail, MDCK-Slug, and MDCK-E47 cells) versus control MDCK cells by cDNA microarrays. A total of 243 clones (228 genes and 15 expressed sequence tags) were found to be differentially expressed between either of the three MDCK-derived cell lines and control MDCK cells. Twenty two of the candidate genes were validated by Northern blot, Western blot, immunofluorescence, and promoter analyses in cell lines and by immunohistochemistry in xenografted tumors. Gene clustering analysis indicated that about a third of the 243 candidate genes were common to MDCK cells expressing Snail, Slug, or E47 factors, whereas the rest of the genes were regulated in only one or two cell types. Differentially regulated genes include those related to EMT (45 genes), transcriptional regulation (18 genes), cell proliferation and signaling (54 genes), apoptosis (12 genes), and angiogenesis (9 genes). These results indicate that Snail, Slug, and E47 transcription factors induce common and specific genetic programs, supporting a differential role of the factors in tumor progression and invasion.

Genes involved in TGF beta1-driven epithelial-mesenchymal transition of renal epithelial cells are topologically related in the human interactome map

BACKGROUND

Understanding how mesenchymal cells arise from epithelial cells could have a strong impact in unveiling mechanisms of epithelial cell plasticity underlying kidney regeneration and repair. In primary human tubular epithelial cells (HUTEC) under different TGF beta 1 concentrations we had observed epithelial-to-mesenchymal transition (EMT) but not epithelial-myofibroblast transdifferentiation. We hypothesized that the process triggered by TGFbeta 1 could be a dedifferentiation event. The purpose of this study is to comprehensively delineate genetic programs associated with TGF beta 1-driven EMT in our in vitro model using gene expression profile on large-scale oligonucleotide microarrays.

RESULTS

In HUTEC under TGF beta 1 stimulus, 977 genes were found differentially expressed. Thirty genes were identified whose expression depended directly on TGF beta 1 concentration. By mapping the differentially expressed genes in the Human Interactome Map using Cytoscape software, we identified a single scale-free network consisting of 2630 interacting proteins and containing 449 differentially expressed proteins. We identified 27 hub proteins in the interactome with more than 29 edges incident on them and encoded by differentially expressed genes. The Gene Ontology analysis showed an excess of up-regulated proteins involved in biological processes, such as "morphogenesis", "cell fate determination" and "regulation of development", and the most up-regulated genes belonged to these categories. In addition, 267 genes were mapped to the KEGG pathways and 14 pathways with more than nine differentially expressed genes were identified. In our model, Smad signaling was not the TGF beta 1 action effector; instead, the engagement of RAS/MAPK signaling pathway seems mainly to regulate genes involved in the cell cycle and proliferation/apoptosis.

CONCLUSION

Our present findings support the hypothesis that context-dependent EMT generated in our model by TGF beta 1 might be the outcome of a dedifferentiation. In fact: 1) the principal biological categories involved in the process concern morphogenesis and development; 2) the most up-regulated genes belong to these categories; and, finally, 3) some intracellular pathways are involved, whose engagement during kidney development and nephrogenesis is well known. These long-term effects of TGF beta 1 in HUTEC involve genes that are highly interconnected, thereby generating a scale-free network that we named the "TGF beta 1 interactome", whose hubs represent proteins that may have a crucial role for HUTEC in response to TGF beta 1.

Signaling networks guiding epithelial-mesenchymal transitions during embryogenesis and cancer progression

Epithelial-mesenchymal transition (EMT) describes the differentiation switch between polarized epithelial cells and contractile and motile mesenchymal cells, and facilitates cell movements and generation of new tissue types during embryogenesis. Many secreted polypeptides are implicated in the EMT process and their corresponding intracellular transduction pathways form highly interconnected networks. Transforming growth factor-beta, Wnt, Notch and growth factors acting through tyrosine kinase receptors induce EMT and often act in a sequential manner. Such growth factors orchestrate the concerted regulation of an elaborate gene program and a complex protein network, needed for establishment of new mesenchymal phenotypes after disassembly of the main elements of epithelial architecture, such as desmosomes, as well as tight, adherens and gap junctions. EMT of tumor cells occurs during cancer progression and possibly generates cell types of the tumor stroma, such as cancer-associated myofibroblasts. EMT contributes to new tumor cell properties required for invasiveness and vascular intravasation during metastasis. Here we present some of the current mechanisms that mediate the process of EMT and discuss their relevance to cancer progression.

Smad signaling in the neural crest regulates cardiac outflow tract remodeling through cell autonomous and non-cell autonomous effects

Neural crest cells (NCCs) are indispensable for the development of the cardiac outflow tract (OFT). Here, we show that mice lacking Smad4 in NCCs have persistent truncus arteriosus (PTA), severe OFT cushion hypoplasia, defective OFT elongation, and mispositioning of the OFT. Cardiac NCCs lacking Smad4 have increased apoptosis, apparently due to decreased Msx1/2 expression. This contributes to the reduction of NCCs in the OFT. Unexpectedly, mutants have MF20-expressing cardiomyocytes in the splanchnic mesoderm within the second heart field (SHF). This may result from abnormal differentiation or defective recruitment of differentiating SHF cells into OFT. Alterations in Bmp4, Sema3C, and PlexinA2 signals in the mutant OFT, SHF, and NCCs, disrupt the communications among different cell populations. Such disruptions can further affect the recruitment of NCCs into the OFT mesenchyme, causing severe OFT cushion hypoplasia and OFT septation failure. Furthermore, these NCCs have drastically reduced levels of Ids and MT1-MMP, affecting the positioning and remodeling of the OFT. Thus, Smad-signaling in cardiac NCCs has cell autonomous effects on their survival and non-cell autonomous effects on coordinating the movement of multiple cell lineages in the positioning and the remodeling of the OFT.

Sustained TGF beta exposure suppresses Smad and non-Smad signalling in mammary epithelial cells, leading to EMT and inhibition of growth arrest and apoptosis

To better understand the dual, tumour-suppressive and tumour-promoting function of transforming growth factor-beta (TGFbeta), we analysed mammary epithelial NMuMG cells in response to short and long-term TGFbeta exposure. NMuMG cells became proliferation-arrested and apoptotic after exposure to TGFbeta for 2-5 days, whereas surviving cells underwent epithelial-mesenchymal transition (EMT). After chronic TGFbeta exposure (2-3 weeks), however, NMuMG cells became resistant to proliferation arrest and apoptosis, showing sustained EMT instead (TD cells). EMT was fully reversed by a pharmacologic TGFbeta-receptor-I kinase inhibitor or withdrawal of TGFbeta for 6-12 days. Interestingly, both cell cycle arresting/proapoptotic (Smads, p38 kinase) and antiapoptotic, proliferation and EMT-promoting signalling pathways (PI3K-PKB/Akt, ERK) were co-suppressed to low, but significant levels. Except for PI3K-Akt, TGFbeta-dependent downregulation of these signalling pathways in transdifferentiated (TD) cells was fully reversed upon TGFbeta withdrawal, together with partial re-induction of proliferation arrest and apoptosis. Co-injection of non-tumorigenic NMuMG cells with tumour-forming CHO cells oversecreting exogenous TGFbeta1 (CHO-TGFbeta1) allowed outgrowth of epithelioid cells in CHO-TGFbeta1 cell-induced tumours. These epithelial islands enhanced CHO-TGFbeta1 tumour cell proliferation, possibly due to chemokines (for example, JE/MCP-1) secreted by NMuMG/TD cells. We conclude that suppression of antiproliferative, proapoptotic TGFbeta signalling in TD cells may permit TGFbeta-dependent proliferation, survival and EMT-enhancing signalling pathways to act at low levels. Thus, TGFbeta may modulate its own signalling to facilitate switching from tumour suppression to tumour progression.

Inhibitor of differentiation 1 promotes endothelial survival in a bleomycin model of lung injury in mice

The Id family of genes encodes negative regulators of basic helix-loop-helix transcription factors and has been implicated in diverse cellular processes such as proliferation, apoptosis, differentiation, and migration. However, the specific role of Id1 in lung injury has not been investigated. Bleomycin has been widely used to generate animal models of acute lung injury and fibrogenesis. In this study we found that, on bleomycin challenge, Id1 expression was significantly up-regulated in the lungs, predominantly in endothelial cells, as revealed by double immunolabeling and quantitative flow cytometric analysis. Mice with Id1 loss-of-function (Id1(-/-)) displayed increased vascular permeability and endothelial apoptosis in the lungs after bleomycin-induced injury. Cultured Id1(-/-) lung microvascular endothelial cells also showed decreased survival when exposed to bleomycin. We detected a decrease in the level of Bcl-2, a primary anti-apoptotic protein, in Id1(-/-) endothelial cells, suggesting that down-regulated Bcl-2 may promote endothelial apoptosis in the lung. Therefore, we propose that Id1 plays a crucial role in promoting endothelial survival in the adult lung on injury. In addition, bleomycin-exposed Id1(-/-) mice showed increased lung collagen accumulation and fibrogenesis, suggesting that Id1 up-regulation in the lung may play a critical role in lung homeostasis.

Importance of inhibitor of DNA binding/differentiation 2 in hepatic stellate cell differentiation and proliferation

BACKGROUND/AIM

In liver fibrosis, activated hepatic stellate cells (HSC) are transformed into myofibroblasts. Helix-loop-helix (HLH) transcriptional factors such as MyoD regulate the differentiation of myocytes, and the inhibitor of DNA binding/differentiation (Id) family comprises dominant negative HLH transcriptional regulators that inhibit differentiation and promote cell proliferation. In the present study, we investigated how the Id family proteins regulate HSC.

METHODS

In primary rat HSC, inhibitor of DNA binding/differentiation (Id)2 and alpha-smooth muscle actin (alpha-SMA) mRNA expression increased 4 days after isolation. Next we established Id2 expressing HSC (HSC-T6-Id2-green fluorescent protein (GFP)) using HSC-T6 cells with retrovirus that expressed GFP-tagged Id2.

RESULTS

HSC-T6-Id2-GFP increased cell proliferation with cyclin D1 expression. In contrast, alpha-SMA expression wassuppressed. Real-time reverse transcription-polymerase chain reaction analysis showed Id2 induction significantly suppressed alpha-SMA, collagen-1, matrix metalloproteinase (MMP)-2, and MMP-9 mRNA (P < 0.05) but had no effect on tissue inhibitor of metalloproteinase or transforming growth factor-beta1 levels.

CONCLUSION

These findings suggest Id2, an HLH transcriptional regulator, plays an important regulatory role in the proliferation and differentiation of HSC.

Smad4-independent TGF-beta signaling in tumor cell migration

Transforming growth factor-beta (TGF-beta) belongs to a family of multifunctional growth factors that participates in the regulation of a variety of cellular activities. Beside induction of growth inhibition and differentiation of epithelial cells, TGF-beta has been shown to promote epithelial-mesenchymal transition in most epithelial tumors. While inhibition of epithelial cell proliferation in response to TGF-beta is mainly mediated by the well-characterized Smad pathway and subsequent inhibition of gene transcription, the molecular mechanism leading to TGF-beta-induced invasiveness and metastasis of epithelial tumors is less clear. Recent results from several groups suggest that the induction of tumorigenic activity by TGF-beta includes not only signaling by Smads, but also by Rho-GTPases and mitogen-activated protein kinases (MAP kinases). Activation of the MAP kinases extracellular signal-regulated kinases (ERK) 1 and 2 as well as c-jun N-terminal kinase (JNK) has been identified as important steps in TGF-beta-induced, Smad4-independent signal transduction in epithelial cells. Recent results identify a role of activated ERK and JNK and their association with focal complexes in TGF-beta-induced, Smad4-independent cell migration of breast carcinoma cells, and are reviewed here.

Complexity in interpretation of embryonic epithelial-mesenchymal transition in response to transforming growth factor-beta signaling

Epithelial-mesenchymal transition (EMT) is a highly conserved and fundamental process that governs morphogenesis in development and may also contribute to cancer metastasis. Transforming growth factor (TGF-beta) is a potent inducer of EMT in various developmental and tumor systems. The analysis of TGF-beta signal transduction pathways is now considered a critically important area of biology, since many defects occur in these pathways in embryonic development. The complexity of TGF-beta signal transduction networks is overwhelming due to the large numbers of interacting constituents, complicated feedforward, feedback and crosstalk circuitry mechanisms that they involve in addition to the cellular kinetics and enzymatics that contribute to cell signaling. As a result of this complexity, apparently simple but highly important questions remain unanswered, that is, how do epithelial cells respond to such TGF-beta signals? System biology and cellular kinetics play a crucial role in cellular function; omissions of such a critical contributor may lead to inaccurate understanding of embryonic EMT. In this review, we identify and explain why certain conditions need to be considered for a true representation of TGF-beta signaling in vivo to better understand the controlled, yet delicate mechanism of embryonic EMT.

TGF-beta-induced EMT: mechanisms and implications for fibrotic lung disease

Epithelial-mesenchymal transition (EMT), a process whereby fully differentiated epithelial cells undergo transition to a mesenchymal phenotype giving rise to fibroblasts and myofibroblasts, is increasingly recognized as playing an important role in repair and scar formation following epithelial injury. The extent to which this process contributes to fibrosis following injury in the lung is a subject of active investigation. Recently, it was demonstrated that transforming growth factor (TGF)-beta induces EMT in alveolar epithelial cells (AEC) in vitro and in vivo, and epithelial and mesenchymal markers have been colocalized to hyperplastic type II (AT2) cells in lung tissue from patients with idiopathic pulmonary fibrosis (IPF), suggesting that AEC may exhibit extreme plasticity and serve as a source of fibroblasts and/or myofibroblasts in lung fibrosis. In this review, we describe the characteristic features of EMT and its mechanistic underpinnings. We further describe the contribution of EMT to fibrosis in adult tissues following injury, focusing especially on the critical role of TGF-beta and its downstream mediators in this process. Finally, we highlight recent descriptions of EMT in the lung and the potential implications of this process for the treatment of fibrotic lung disease. Treatment for fibrosis of the lung in diseases such as IPF has heretofore focused largely on amelioration of potential inciting processes such as inflammation. It is hoped that this review will stimulate further consideration of the cellular mechanisms of fibrogenesis in the lung and especially the role of the epithelium in this process, potentially leading to innovative avenues of investigation and treatment.

Differential regulation of epithelial and mesenchymal markers by deltaEF1 proteins in epithelial mesenchymal transition induced by TGF-beta

Epithelial-mesenchymal transition (EMT), a crucial event in cancer progression and embryonic development, is induced by transforming growth factor (TGF)-beta in mouse mammary NMuMG epithelial cells. Id proteins have previously been reported to inhibit major features of TGF-beta-induced EMT. In this study, we show that expression of the deltaEF1 family proteins, deltaEF1 (ZEB1) and SIP1, is gradually increased by TGF-beta with expression profiles reciprocal to that of E-cadherin. SIP1 and deltaEF1 each dramatically down-regulated the transcription of E-cadherin in NMuMG cells through direct binding to the E-cadherin promoter. Silencing of the expression of both SIP1 and deltaEF1, but not either alone, completely abolished TGF-beta-induced E-cadherin repression. However, expression of mesenchymal markers, including fibronectin, N-cadherin, and vimentin, was not affected by knockdown of SIP1 and deltaEF1. TGF-beta-induced the expression of Ets1, which in turn activated deltaEF1 promoter activity. Moreover, up-regulation of SIP1 and deltaEF1 expression by TGF-beta was suppressed by knockdown of Ets1 expression. In addition, Id2 suppressed the TGF-beta- and Ets1-induced up-regulation of deltaEF1. Taken together, these findings suggest that the deltaEF1 family proteins, SIP1 and deltaEF1, are necessary, but not sufficient, for TGF-beta-induced EMT and that Ets1 induced by TGF-beta may function as an upstream transcriptional regulator of SIP1 and deltaEF1.

Genes and molecular pathways related to radioresistance of oral squamous cell carcinoma cells

To identify genes associated with radioresistant oral squamous cell carcinoma (OSCC), we compared gene expression signatures between OSCC cell lines exhibiting radioresistance and cells with radiosensitivity after X-ray irradiation in a dose-dependent manner using Affymetrix GeneChip analysis with Human Genome-U133 plus 2.0 GeneChip. The microarray data identified 167 genes that were significantly overexpressed in radioresistant cells after X-ray irradiation. Among the genes identified, 40 were mapped to 3 highly significant genetic networks identified by the Ingenuity Pathway Analysis tool. Gene ontology analysis showed that cancer-related function had the highest significance. The 40 genes included 25 cancer-related genes that formed 1 network and were categorized by function into growth and proliferation, apoptosis, and adhesion. Furthermore, real-time quantitative reverse transcriptase-polymerase chain reaction showed that the mRNA expression levels of the 25 genes were higher in radioresistant cells than in radiosensitive cells in a dose-dependent manner and in a time-dependent manner. Our results suggest that the identified genes help to elucidate the molecular mechanisms of the radioresistance of OSCC and could be radiotherapeutic molecular markers for choosing the appropriate radiotherapy for this disease.

Adenovirus-mediated expression of BMP-7 suppresses the development of liver fibrosis in rats

BACKGROUND

Liver cirrhosis, which is caused by the accumulation of extracellular matrix materials, is a serious clinical problem that can progress to hepatic failure. Transforming growth factor-beta (TGFbeta) plays a pivotal role in extracellular matrix production, but bone morphogenetic protein (BMP)-7, a member of the TGFbeta superfamily, can antagonise the fibrogenic activity of TGFbeta.

AIM

In this study, we examined whether adenovirus-mediated overexpression of BMP-7 (Ad-BMP-7) antagonised the effect of TGFbeta in vitro and in vivo.

METHODS AND RESULTS

In primary cultured rat stellate cells and the LX-2 human stellate cell line, induction of BMP-7 by Ad-BMP-7 infection decreased the expression of collagen 1A2 mRNA and smooth muscle alpha-actin in the presence or absence of TGFbeta, via Smad 1/5/8 phosphorylation. BMP-7 triggered the mRNA expression of inhibitors of differentiation 2 (Id2) in LX-2. Although endogenous expression of BMP-7 was hardly detectable, Smad1 and Id2 overexpression increased BMP-7 expression in LX-2. A liver fibrosis model was induced by the repetitive intraperitoneal injection of thioacetamide (200 mg/kg body weight) twice per week for up to 7 weeks. In rats administered Ad-BMP-7 via the tail vein, hydroxyproline content and the areas stained by Sirius red dye in the liver were significantly reduced compared to controls. Ad-Id2 also reduced fibrosis.

CONCLUSION

These data demonstrate that BMP-7, Smad 1/5/8 and Ids interact to antagonise hepatic fibrogenesis.

Id3 is a novel regulator of p27kip1 mRNA in early G1 phase and is required for cell-cycle progression

P27kip is a key inhibitory protein of the cell-cycle progression, which is rapidly downregulated in early G1 phase by a post-translational mechanism involving the proteosomal degradation. In this study, using a wounding model that induces cell-cycle entry of human dermal fibroblasts, we demonstrate that p27mRNA is downregulated when cells progress into the G1 phase, and then it returns to its basal level when cells approach the S phase. By using a quantitative polymerase chain reaction screening we identified inhibitors of differentiation (Id3), a bHLH transcriptional repressor, as a candidate mediator accounting for p27 mRNA decrease. Id3 silencing, using an small interfering RNA approach, reversed the injury mediated p27 downregulation demonstrating that Id3 is involved in the transcriptional repression of p27. Reporter gene experiments and a chromatin immunoprecipitation assay showed that Id3 likely exerts its repressive action through ELK1 inhibition. By inhibiting early p27 downregulation, Id3 depletion blocked (i) the G1-phase progression as assessed by the inhibition of pRb phosphorylation and p130 degradation and (ii) the G1/S transition as observed by the inhibition of cyclin A induction, demonstrating that p27 mRNA decrease is required for cell proliferation. Apart from its effect on the early p27 diminution, Id3 appears also involved in the control of the steady-state level of p27 at the G1/S boundary. In conclusion, this study identifies a novel mechanism of p27 regulation which besides p27 protein degradation also implicates a transcriptional mechanism mediated by Id3.

Smad4 regulates claudin-1 expression in a transforming growth factor-beta-independent manner in colon cancer cells

We have recently reported that the expression of a tight junction protein, claudin-1, is increased during colon carcinogenesis and particularly metastatic colorectal cancer. Manipulation of claudin-1 levels in colon cancer cells showed a positive correlation between claudin-1 expression and tumor growth and metastasis. However, the mechanisms underlying the increased claudin-1 expression in colorectal cancer remains unknown. The tumor suppressor Smad4 is a central intracellular signal transduction component of the transforming growth factor-beta (TGF-beta) family of cytokines. Loss of Smad4 protein expression is correlated with poor prognosis and is frequently observed in invasive and metastatic colorectal carcinoma. In the present study, we report an inverse relationship between Smad4 and claudin-1 expression in human colorectal carcinoma tumor samples and in human colon cancer cell lines. We found that the expression of Smad4 in Smad4-deficient but claudin-1-positive SW480 or HT29 colon cancer cell lines down-regulates claudin-1 expression through transcriptional repression by modulating beta-catenin/T-cell factor/lymphocyte enhancer factor activity. Furthermore, this Smad4-dependent inhibition of claudin-1 expression is independent of TGF-beta signaling because Smad4 expression alone is insufficient to restore TGF-beta signaling in the SW480 cells, and the selective TGF-beta receptor kinase inhibitor LY364947 did not prevent the Smad4 suppression of claudin-1 protein expression in either SW480 or HT29 cells. Taken together, these findings suggest a novel mechanism underlying Smad4 tumor-suppressive function through regulation of a potential metastatic modulator, claudin-1, in a TGF-beta-independent manner.

Functional role of Meox2 during the epithelial cytostatic response to TGF-beta

Transforming growth factor beta (TGF-beta) suppresses epithelial cell growth. We have identified a new target gene of the TGF-beta/Smad pathway, Meox2, encoding the homeodomain transcription factor that is known to regulate endothelial cell proliferation and muscle development. Knockdown of endogenous Meox2 by RNA interference prevented the TGF-beta1-induced cytostatic response. Moreover, ectopic Meox2 suppressed epithelial cell proliferation in cooperation with TGF-beta1, and mediated induction of the cell cycle inhibitor gene p21. Transcriptional induction of p21 by Meox2 required a distal region of the p21 promoter that spans the p53-binding site. We show that Meox2 can form protein complexes with Smads leading to cooperative regulation of p21 gene expression. Finally, we found that in cell models that undergo both cell cycle arrest and epithelial-mesenchymal transition (EMT), ectopic Meox2 failed to induce EMT and inhibited the proper EMT response to TGF-beta. Thus, Meox2 is primarily involved in the TGF-beta tumor suppressor pathway.

BMP4 induces EMT and Rho GTPase activation in human ovarian cancer cells

We identified previously an autocrine bone morphogenetic protein-4 (BMP4) signalling pathway in primary human normal ovarian surface epithelial (OSE) and epithelial ovarian cancer (OvCa) cells. Herein we show that treatment of OvCa cells with BMP4 produced morphological alterations and increased cellular adhesion, motility and invasion. The BMP4 inhibitor noggin blocked the BMP4-induced phenotype, and decreased autocrine BMP4-mediated OvCa cell motility and adherence. In response to exogenous BMP4, the epithelial-mesenchymal transition (EMT) markers Snail and Slug mRNA and protein were up-regulated, E-cadherin mRNA and protein were down-regulated and the network of alpha smooth muscle actin changed to resemble a mesenchymal cell. We also observed changes in the level of activated Rho GTPases in OvCa cells treated with BMP4, strongly suggesting that the changes in morphology, adhesion, motility and invasion are probably mediated through the activation of these molecules. Strikingly, treatment of normal OSE cells with BMP4 or noggin failed to alter cell motility, providing evidence that OSE and OvCa cells possess a distinct capability to respond to BMP4. Overall, our studies suggest a link between autocrine BMP signalling mediated through the Rho GTPase family and Snail- and Slug-induced EMT that may collectively contribute to aggressive OvCa behaviour.

Inhibition of growth and metastasis of mouse mammary carcinoma by selective inhibitor of transforming growth factor-beta type I receptor kinase in vivo

PURPOSE

Transforming growth factor-beta (TGF-beta) suppresses tumor development by inhibiting cellular proliferation, inducing differentiation and apoptosis, and maintaining genomic integrity. However, once tumor cells escape from the tumor-suppressive effects of TGF-beta, they often constitutively overexpress and activate TGF-beta, which may promote tumor progression by enhancing invasion, metastasis, and angiogenesis and by suppressing antitumor immunity. The purpose of this study was to test this hypothesis using TGF-beta pathway antagonists.

EXPERIMENTAL DESIGN

We examined the effects of selective TGF-beta type I receptor kinase inhibitors, SD-093 and SD-208, on two murine mammary carcinoma cell lines (R3T and 4T1) in vitro and in vivo.

RESULTS

Both agents blocked TGF-beta-induced phosphorylation of the receptor-associated Smads, Smad2 and Smad3, in a dose-dependent manner, with IC50 between 20 and 80 nmol/L. TGF-beta failed to inhibit growth of these cell lines but stimulated epithelial-to-mesenchymal transdifferentiation, migration, and invasiveness into Matrigel in vitro. These effects were inhibited by SD-093, indicating that these processes are partly driven by TGF-beta. Treatment of syngeneic R3T or 4T1 tumor-bearing mice with orally given SD-208 inhibited primary tumor growth as well as the number and size of metastases. In contrast, SD-208 failed to inhibit R3T tumor growth or metastasis in athymic nude mice. Moreover, in vitro anti-4T1 cell cytotoxic T-cell responses of splenocytes from drug-treated animals were enhanced compared with cells from control animals. In addition, SD-208 treatment resulted in a decrease in tumor angiogenesis.

CONCLUSION

TGF-beta type I receptor kinase inhibitors hold promise as novel therapeutic agents for metastatic breast cancer.

Inhibition of histone deacetylase activity suppresses epithelial-to-mesenchymal transition induced by TGF-beta1 in human renal epithelial cells

Histone acetylation plays an important role in regulating gene expressions by modulating chromatin structure. Histone deacetylase (HDAC) inhibitors have been reported to have an antifibrogenic effect in some organs, such as the liver, skin, and lung, but the underlying mechanisms remain to be clarified. In the kidney, bone morphologic protein 7 (BMP-7) and hepatocyte growth factor are reported to antagonize TGF-beta1-induced tubular epithelial-to-mesenchymal transition (EMT), but nothing is known concerning the effect of HDAC inhibitors on EMT. It was shown that trichostatin A (TSA), an HDAC inhibitor, prevented TGF-beta1-induced EMT in cultured human renal proximal tubular epithelial cells. Treatment with TGF-beta1 induced morphologic changes such as EMT in human renal proximal tubular epithelial cells. However, co-treatment with TSA completely prevented TGF-beta1-induced morphologic changes and significantly prevented TGF-beta1-induced downregulation of E-cadherin and upregulation of collagen type I. Treatment with TSA did not alter TGF-beta1-induced phosphorylation of Smad2 and Smad3 but induced several inhibitory factors of TGF-beta1 signals, such as inhibitors of DNA binding/differentiation 2 (Id2) and BMP-7. Chromatin immunoprecipitation assay confirmed that histone acetylation was involved in the downregulation of E-cadherin and upregulation of Id2 and BMP-7. These results suggest that TSA and other HDAC inhibitors could be new therapeutic agents for tubular EMT.

BMPs regulate multiple aspects of growth-plate chondrogenesis through opposing actions on FGF pathways

Bone morphogenetic protein (BMP) signaling pathways are essential regulators of chondrogenesis. However, the roles of these pathways in vivo are not well understood. Limb-culture studies have provided a number of essential insights, including the demonstration that BMP pathways are required for chondrocyte proliferation and differentiation. However, limb-culture studies have yielded contradictory results; some studies indicate that BMPs exert stimulatory effects on differentiation, whereas others support inhibitory effects. Therefore, we characterized the skeletal phenotypes of mice lacking Bmpr1a in chondrocytes (Bmpr1a(CKO)) and Bmpr1a(CKO);Bmpr1b+/- (Bmpr1a(CKO);1b+/-) in order to test the roles of BMP pathways in the growth plate in vivo. These mice reveal requirements for BMP signaling in multiple aspects of chondrogenesis. They also demonstrate that the balance between signaling outputs from BMP and fibroblast growth factor (FGF) pathways plays a crucial role in the growth plate. These studies indicate that BMP signaling is required to promote Ihh expression, and to inhibit activation of STAT and ERK1/2 MAPK, key effectors of FGF signaling. BMP pathways inhibit FGF signaling, at least in part, by inhibiting the expression of FGFR1. These results provide a genetic in vivo demonstration that the progression of chondrocytes through the growth plate is controlled by antagonistic BMP and FGF signaling pathways.

STAT1-independent inhibition of cyclooxygenase-2 expression by IFNgamma; a common pathway of IFNgamma-mediated gene repression but not gene activation

Cyclooxygenase-2 (COX-2), the rate-limiting enzyme in the synthesis of prostaglandins, promotes the development of colorectal cancer, and is a key molecular target of non-steroidal anti-inflammatory drugs, compounds that reduce the relative risk of developing colon cancer. In this study, we showed that interferon gamma (IFNgamma) inhibits the expression of COX-2 protein in intestinal epithelial cells (IECs) through a pathway that requires Janus-activated kinase (JAK) activity. In contrast, we demonstrated that transcriptional inhibition of COX-2 by IFNbeta or IFNgamma occurs in cells with silenced signal transducer and activator of transcription 1 (STAT1) expression and that IFNs retained the ability to inhibit COX-2 transcription in cells with activated RasV12, in which IFNgamma failed to induce STAT1. Thus, unlike the activity of JAK, STAT1 is not required for the inhibition of COX-2 expression by IFNgamma. In contrast to COX-2, the activation of genes in response to IFNgamma, such as interferon regulatory factor-1, was severely impaired by both STAT1 silencing and by constitutive Ras signaling. To determine whether there is a general differential requirement for STAT1 in gene activation and gene repression in response to IFNgamma in intestinal cells, we performed genome-wide analysis of IFNgamma target genes in an IEC line in which STAT1 expression was silenced by small interfering RNA. The results confirmed that the activation of the majority of genes by IFNgamma required STAT1. In contrast, the repression of several genes, as we showed for COX-2 specifically, was largely unaffected in cells with silenced STAT1. Our results therefore demonstrate that in general gene activation by IFNgamma is more sensitive to STAT1 deficiency than gene repression, and suggest that IFNgamma activates and represses gene expression via distinct pathways that can be distinguished, at least in part, by their requirement for STAT1.

Strain-dependent perinatal lethality of Ovol1-deficient mice and identification of Ovol2 as a downstream target of Ovol1 in skin epidermis

Ovol1 encodes a zinc finger transcriptional repressor that is downstream of the LEF1/beta-catenin complex, nuclear effectors of canonical Wnt signaling. Previous gene knockout studies performed in a 129SvxC57BL/6 mixed genetic background revealed that Ovol1-deficient mice survive to adulthood but display multiple tissue defects. In this study, we describe a C57BL/6 strain-specific reduction in perinatal survival of Ovol1 mutant mice. The perinatal lethality is accompanied by kidney epithelial cysts of embryonic onset and delayed skin barrier acquisition. Genetic analysis suggests a partial functional compensation by Ovol2 for the loss of Ovol1. The expression of Ovol2 was up-regulated in Ovol1-deficient epidermis, and Ovol1 represses the activity of Ovol2 promoter in a DNA binding-dependent manner. Collectively, these studies uncover novel functions of Ovol1 in mouse development and identify Ovol2 as a downstream target of Ovol1.

A Critical Look at Growth Factors and Epithelial-to-Mesenchymal Transition in the Adult Kidney

In the adult kidney, the cellular phenotypes are maintained by a strict balance of growth factors. Epithelial-to-mesenchymal transition (EMT) is a program whereby injured epithelial cells that function as ion and fluid transporters become matrix remodelling mesenchymal cells. This process requires either transcriptional repression of genes that maintain the epithelial phenotype and transcriptional activation, or relieved repression of genes needed for functional myofibroblasts. The transcriptional regulators are controlled by several integrated signalling pathways which are triggered by growth factors. Emerging evidence indicates that the growth factors TGFbeta/CTGF and BMP-7/HGF are the main determinants that maintain the two cellular phenotypes. Both TGFbeta and BMP-7 counteract the activity of each other by cross-inducing their respective inhibitory Smads. Both growth factors may also induce the expression of other factors that can change the cellular environment and enhance their function. Chronic kidney diseases (regardless of the aetiology of the disease) are associated with increased TGFbeta and CTGF expression levels which, in turn, have an inverse effect on the activity level of BMP-7 and HGF, leading to an EMT of injured tubular epithelial cells and a progression of the disease. A detailed understanding of the complex interrelationship between these growth factors may lead to the development of novel drugs.

Transforming growth factor-beta employs HMGA2 to elicit epithelial-mesenchymal transition

Epithelial–mesenchymal transition (EMT) occurs during embryogenesis, carcinoma invasiveness, and metastasis and can be elicited by transforming growth factor-β (TGF-β) signaling via intracellular Smad transducers. The molecular mechanisms that control the onset of EMT remain largely unexplored. Transcriptomic analysis revealed that the high mobility group A2 (HMGA2) gene is induced by the Smad pathway during EMT. Endogenous HMGA2 mediates EMT by TGF-β, whereas ectopic HMGA2 causes irreversible EMT characterized by severe E-cadherin suppression. HMGA2 provides transcriptional input for the expression control of four known regulators of EMT, the zinc-finger proteins Snail and Slug, the basic helix-loop-helix protein Twist, and inhibitor of differentiation 2. We delineate a pathway that links TGF-β signaling to the control of epithelial differentiation via HMGA2 and a cohort of major regulators of tumor invasiveness and metastasis. This network of signaling/transcription factors that work sequentially to establish EMT suggests that combinatorial detection of these proteins could serve as a new tool for EMT analysis in cancer patients.

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.

Functional gene expression analysis uncovers phenotypic switch in aggressive uveal melanomas

Microarray gene expression profiling is a powerful tool for generating molecular cancer classifications. However, elucidating biological insights from these large data sets has been challenging. Previously, we identified a gene expression-based classification of primary uveal melanomas that accurately predicts metastatic death. Class 1 tumors have a low risk and class 2 tumors a high risk for metastatic death. Here, we used genes that discriminate these tumor classes to identify biological correlates of the aggressive class 2 signature. A search for Gene Ontology categories enriched in our class-discriminating gene list revealed a global down-regulation of neural crest and melanocyte-specific genes and an up-regulation of epithelial genes in class 2 tumors. Correspondingly, class 2 tumors exhibited epithelial features, such as polygonal cell morphology, up-regulation of the epithelial adhesion molecule E-cadherin, colocalization of E-cadherin and beta-catenin to the plasma membrane, and formation of cell-cell adhesions and acinar structures. One of our top class-discriminating genes was the helix-loop-helix inhibitor ID2, which was strongly down-regulated in class 2 tumors. The class 2 phenotype could be recapitulated by eliminating Id2 in cultured class 1 human uveal melanoma cells and in a mouse ocular melanoma model. Id2 seemed to suppress the epithelial-like class 2 phenotype by inhibiting an activator of the E-cadherin promoter. Consequently, Id2 loss triggered up-regulation of E-cadherin, which in turn promoted anchorage-independent cell growth, a likely antecedent to metastasis. These findings reveal new roles for Id2 and E-cadherin in uveal melanoma progression, and they identify potential targets for therapeutic intervention.

Degradation of Id2 by the anaphase-promoting complex couples cell cycle exit and axonal growth

In the developing nervous system, Id2 (inhibitor of DNA binding 2, also known as inhibitor of differentiation 2) enhances cell proliferation, promotes tumour progression and inhibits the activity of neurogenic basic helix-loop-helix (bHLH) transcription factors. The anaphase promoting complex/cyclosome and its activator Cdh1 (APC/C(Cdh1)) restrains axonal growth but the targets of APC/C(Cdh1) in neurons are unknown. Id2 and other members of the Id family are very unstable proteins that are eliminated as cells enter the quiescent state, but how they are targeted for degradation has remained elusive. Here we show that Id2 interacts with the core subunits of APC/C and Cdh1 in primary neurons. APC/C(Cdh1) targets Id2 for degradation through a destruction box motif (D box) that is conserved in Id1 and Id4. Depletion of Cdh1 stabilizes Id proteins in neurons, whereas Id2 D-box mutants are impaired for Cdh1 binding and remain stable in cells that exit from the cell cycle and contain active APC/C(Cdh1). Mutants of the Id2 D box enhance axonal growth in cerebellar granule neurons in vitro and in the context of the cerebellar cortex, and overcome the myelin inhibitory signals for growth. Conversely, activation of bHLH transcription factors induces a cluster of genes with potent axonal inhibitory functions including the gene coding for the Nogo receptor, a key transducer of myelin inhibition. Degradation of Id2 in neurons permits the accumulation of the Nogo receptor, thereby linking APC/C(Cdh1) activity with bHLH target genes for the inhibition of axonal growth. These findings indicate that deregulated Id activity might be useful to reprogramme quiescent neurons into the axonal growth mode.

Id proteins: novel targets of activin action, which regulate epidermal homeostasis

Activin is a member of the transforming growth factor beta (TGF-beta) family, which plays a crucial role in skin morphogenesis and wound healing. To gain insight into the underlying mechanisms of action, we searched for activin-regulated genes in cultured keratinocytes. One of the identified target genes encodes Id1, a negative regulator of helix-loop-helix transcription factors. We show that Id1, Id2, and Id3 are strongly downregulated by activin in keratinocytes in vitro and in vivo. To determine the role of Id1 in keratinocyte biology, we generated stable HaCaT keratinocyte cell lines overexpressing this protein. Our results revealed that enhanced levels of Id1 do not affect proliferation of keratinocytes in monoculture under exponential culture conditions or in response to activin or TGF-beta1. However, in three-dimensional organotypic cultures, Id1-overexpressing HaCaT cells formed a hyperthickened and disorganized epithelium that was characterized by enhanced keratinocyte proliferation, abnormal differentiation, and an increased rate of apoptosis. These results identify an important function of Id1 in the regulation of epidermal homeostasis.

Ovol1 regulates the growth arrest of embryonic epidermal progenitor cells and represses c-myc transcription

Transcriptional control plays a key role in regulating epidermal proliferation and differentiation. Although ample information has been obtained on how epidermal homeostasis is controlled in adult skin, less is known about the control of proliferation/differentiation of epidermal stem/progenitor cells in the developing embryo. Ovol1, encoding a zinc finger protein homologous to Drosophila melanogaster Ovo, is expressed in embryonic epidermal progenitor cells that are transiting from proliferation to terminal differentiation. In this study, we demonstrate a function for Ovol1 in interfollicular epidermal development. In its absence, developing epidermis fails to properly restrict the proliferative potential of progenitor cells, and cultured keratinocytes fail to efficiently undergo growth arrest in response to extrinsic growth-inhibitory signals. We present molecular evidence that c-myc expression is up-regulated in Ovol1-deficient suprabasal cells and that Ovol1 represses c-myc transcription by directly binding to its promoter. Collectively, our findings indicate that Ovol1 is required for proliferation exit of committed epidermal progenitor cells and identify c-myc as an Ovol1 target.

Patterns of gene expression in pituitary carcinomas and adenomas analyzed by high-density oligonucleotide arrays, reverse transcriptase-quantitative PCR, and protein expression

Very few of the genes that are important in pituitary tumor initiation, progression, and metastasis have been identified to date. To identify potential genes that may be important in pituitary tumor progression and carcinoma development, we used Affymetrix GeneChip HGU-133A-oligonucleotide arrays, which contain more than 15,000 characterized genes from the human genome to study gene expression in an ACTH pituitary carcinoma metastatic to the liver and four pituitary adenomas. Reverse-transcriptase real-time quantitative- PCR (RT-qPCR) was then used to analyze 4 nonneoplastic pituitaries, 19 adenomas, and the ACTH carcinoma. A larger series of pituitary adenomas and carcinomas were also analyzed for protein expression using tissue microarrays (TMA) (n = 233) and by Western blotting (n = 18). There were 4298 genes that were differentially expressed among the adenomas compared to the carcinoma, with 2057 genes overexpressed and 2241 genes underexpressed in the adenomas. The beta-galactoside binding protein galactin-3 was underexpressed in some adenomas compared to the carcinomas. Prolactin (PRL) and ACTH tumors had the highest levels of expression of galectin-3. The human achaetescute homolog-1 ASCL1 (hASH-1) gene was also underexpressed in some adenomas compared to the carcinoma. Prolactin and ACTH tumors had the highest levels of expression of hASH-1. ID2, which has an important role in cell development and tumorigenesis, was underexpressed in some adenomas compared to the carcinomas. Transducin-like enhancer of split four/ Groucho (TLE-4) was over-expressed in adenomas compared to the ACTH carcinoma. The differential expression of these genes was validated by RT-qPCR, by immunohistochemistry using TMA and by Western blotting. These results indicate that the LGALS3, hASH1, ID2, and TLE-4 genes may have important roles in the development of pituitary carcinomas.

Genetic variants of Tgfb1 act as context-dependent modifiers of mouse skin tumor susceptibility

The human TGFB1 gene is polymorphic, and genetic variants are associated with altered cancer risk. However, human genetic association studies have had variable outcomes because TGFbeta1 action is context-dependent. We used the murine skin model of chemical carcinogenesis in genetic linkage analysis of three independent Mus musculus NIH/Ola x (Mus spretus x M. musculus NIH/Ola)F1 backcrosses, to identify a skin tumor susceptibility locus, Skts14, on proximal chromosome 7. Tgfb1 maps at the peak of linkage. The mouse Tgfb1 gene is polymorphic, resulting in cis-regulated differential allelic mRNA expression between M. spretus and M. musculus in F1 mouse skin. This phenomenon is reflected in differential phospho-SMAD2 levels, downstream of TGFbeta signaling, between these two mouse species. In normal F1 mouse skin, the Tgfb1SPR allele is expressed at higher levels than the Tgfb1NIH allele, and this differential is accentuated by phorbol 12-myristate 13-acetate treatment. In benign F1 papillomas, this imbalance is reversed, possibly by selection against expression of a hyperactive Tgfb1SPR allele in TGFbeta growth-responsive tumors. We demonstrate that skin tumor susceptibility is altered by Tgfb1 gene dosage, but that manifestation of Tgfb1-linked skin tumor susceptibility in M. musculus NIH/Ola x (M. spretus x M. musculus NIH/Ola)F1 backcross mice depends on interactions with another unlinked tumor modifying locus, Skts15, that overlaps Tgfbm3 on chromosome 12. These findings illustrate the power of complex genetic interactions in determining disease outcome and have major implications to the assessment of disease risk in individuals harboring variant TGFB1 alleles.

Id1 is a critical mediator in TGF-beta-induced transdifferentiation of rat hepatic stellate cells

Transforming growth factor (TGF)-beta is critically involved in the activation of hepatic stellate cells (HSCs) that occurs during the process of liver damage, for example, by alcohol, hepatotoxic viruses, or aflatoxins. Overexpression of the TGF-beta antagonist Smad7 inhibits transdifferentiation and arrests HSCs in a quiescent stage. Additionally, bile duct ligation (BDL)-induced fibrosis is ameliorated by introducing adenoviruses expressing Smad7 with down-regulated collagen and alpha-smooth muscle actin (alpha-SMA) expression. The aim of this study was to further characterize the molecular details of TGF-beta pathways that control the transdifferentiation process. In an attempt to elucidate TGF-beta target genes responsible for fibrogenesis, an analysis of Smad7-dependent mRNA expression profiles in HSCs was performed, resulting in the identification of the inhibitor of differentiation 1 (Id1) gene. Ectopic Smad7 expression in HSCs strongly reduced Id1 mRNA and protein expression. Conversely, Id1 overexpression in HSCs enhanced cell activation and circumvented Smad7-dependent inhibition of transdifferentiation. Moreover, knock-down of Id1 in HSCs interfered with alpha-SMA fiber formation, indicating a pivotal role of Id1 for fibrogenesis. Treatment of HSCs with TGF-beta1 led to increased Id1 protein expression, which was not directly mediated by the ALK5/Smad2/3, but the ALK1/Smad1 pathway. In vivo, Id1 expression and Smad1 phosphorylation were co-induced during fibrogenesis. In conclusion, Id1 is identified as TGF-beta/ALK1/Smad1 target gene in HSCs and represents a critical mediator of transdifferentiation that might be involved in hepatic fibrogenesis. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

CITED1 homozygous null mice display aberrant pubertal mammary ductal morphogenesis

Expression microarray analysis identified CITED1 among a group of genes specifically upregulated in the pubertal mouse mammary gland. At puberty, CITED1 localizes to the luminal epithelial cell population of the mammary ducts and the body cells of the terminal end buds. Generation of CITED1 gene knockout mice showed that homozygous null mutants exhibit retarded mammary ductal growth at puberty and, in addition, dilated ductal structures with a lack of spatial restriction of the subtending branches. Analysis of CITED1 homozygous null and heterozygous null mammary gland gene expression using microarrays suggested that the mammary-specific phenotype seen in the homozygous null females is due to a disturbance in the transcription of a number of key mediators of pubertal ductal morphogenesis. These include estrogen and TGFbeta responsive genes, such as the EGFR/ErbB2 ligand, amphiregulin, whose transcription we suggest is directly or indirectly regulated by CITED1.

BMP receptor signaling: transcriptional targets, regulation of signals, and signaling cross-talk

Bone morphogenetic proteins (BMPs), members of the transforming growth factor-beta (TGF-beta) superfamily, bind to two different serine/threonine kinase receptors, and mediate their signals through Smad-dependent and Smad-independent pathways. Receptor regulated-Smad (R-Smad) proteins specific for the BMP pathways interact with various proteins, including transcription factor Runx, and transmit specific signals in target cells. The recent development of DNA microarray techniques has allowed us to identify many BMP target genes. BMP signaling is modulated by various molecules, including inhibitory Smads (I-Smads). Moreover, recent findings have revealed that BMP pathways interact with other signaling pathways, and such signaling cross-talk plays pivotal roles in growth and differentiation of target cells.

BMP4 regulates pancreatic progenitor cell expansion through Id2

Inhibitor of DNA binding (Id) proteins bind to and inhibit the function of basic helix-loop-helix (bHLH) transcription factors including those that regulate pancreatic development. Moreover, bone morphogenetic proteins (BMPs) regulate the expression of Ids. We hypothesized that BMP4 and Id proteins play a role in the expansion and differentiation of epithelial progenitor cells. We demonstrate that BMP4 induces the expression of Id2 along with the expansion of AR42J pancreatic epithelial cells. Furthermore, neutralization of BMP4 significantly reduced duct epithelial cell expansion in a mouse model of islet regeneration. BMP4 stimulation promotes Id2 binding to the bHLH transcription factor NeuroD, which is required for the differentiation of pancreatic islet cells. Therefore, our results indicate that BMP4 stimulation blocks the differentiation of endocrine progenitor cells and instead promotes their expansion thereby revealing a novel paradigm of signaling explaining the balance between expansion and differentiation of pancreatic duct epithelial progenitors. Understanding the mechanisms of BMP and Id function elucidates a key step during pancreas embryogenesis, which is important knowledge for expanding pancreatic progenitors in vitro.

The mouse Ovol2 gene is required for cranial neural tube development

The Ovo gene family encodes a group of evolutionarily conserved transcription factors and includes members that reside downstream of key developmental signaling pathways such as Wg/Wnt and BMP/TGF-beta. In the current study, we explore the function of Ovol2, one of three Ovo paralogues in mice. We report that Ovol2 is expressed during early-mid embryogenesis, particularly in the inner cell mass at E3.5, in epiblast at E6.5, and at later stages in ectodermally derived tissues such as the rostral surface (epidermal) ectoderm. Embryos in which Ovol2 is ablated exhibit lethality by E10.5, prior to which they display severe defects including an open cranial neural tube. The neural defects are associated with improper Shh expression in the underlying rostral axial mesoderm and localized changes of neural marker expression along the dorsoventral axis, as well as with expanded cranial neural tissue and reduced cranial surface ectoderm culminating in a lateral shift of the neuroectoderm/surface ectoderm border. We propose that these defects reflect the involvement of Ovol2 in independent processes such as regionalized gene expression and neural/non-neural ectodermal patterning. Additionally, we present evidence that Ovol2 is required for efficient migration and survival of neural crest cells that arise at the neuroectoderm/surface ectoderm border, but not for their initial formation. Collectively, our studies indicate that Ovol2 is a key regulator of neural development and reveal a previously unexplored role for Ovo genes in mammalian embryogenesis.

A bone-derived mixture of TGFβ-superfamily members forms a more mature vascular network than bFGF or TGF-β2 in vivo

Clinical trials of therapeutic angiogenesis for the treatment of cardiovascular ischemia have failed to meet the expectations with the use of single growth factors, namely VEGF and bFGF. We show here that a bovine bone-derived growth factor mixture (GFM) of TGFbetas, BMPs, and no more than 0.1% aFGF can initiate a dose-dependent angiogenic response in subcutaneously implanted Growth Factor Reduced Matrigel plugs that includes abundant smooth muscle actin positive (SMA+) tubes and functional CD31+, red blood cell filled, capillaries. Tube forming activity of the single factors, recombinant bFGF and bone-derived TGF-beta2, were comparable to GFM, but only the bone-derived factors were able to create a larger fraction of SMA+ tubes than Matrigel alone at an equal dose. Basic FGF formed a greater number of RBC-filled capillaries within the plugs than GFM or TGF-beta2 at the highest doses, although GFM created RBC-filled capillaries that penetrated deeper into the plugs than bFGF. However, bFGF showed the greatest number of non-cell-lined, RBC-filled pools, suggestive of vessel rupture, and the largest number of plugs showing signs of fluid accumulation in the form of large, cell-lined clefts in the implants. TGF-beta2 showed less RBC-filled pools, but a significant number of implants with signs of fluid accumulation. At high doses of GFM penetration by blood vessels and mesenchymal cells was obstructed by cartilage development within the plugs accompanied by a prominent band of SMA+ granulation tissue with abundant RBC-filled capillaries encapsulating the implants. Thus, GFM is also capable of dramatically remodeling the vascular system in the interstitial space surrounding the plug. These results show that GFM is capable of inducing the formation of a more mature vascular system than that formed by the single factors bFGF and TGFbeta-2. Natural mixtures of TGFbetas, BMPs, and FGFs may have superior clinical utility in therapeutic angiogenesis applications.

Adenoviral gene transfer of BMP-7, Id2, or Id3 suppresses injury-induced epithelial-to-mesenchymal transition of lens epithelium in mice

We have examined the effect of adenovirus-mediated expression of bone morphogenic protein-7 (BMP-7) and inhibitors of differentiation 2 and 3 (Id2 and Id3) on injury-induced epithelial-to-mesenchymal transition (EMT) of lens epithelium in mice. Id2 and Id3 are known to be upregulated by BMP-7 and to antagonize Smad2/3 signaling. The Cre-LoxP system adenoviral gene transfer was used. Three microliters of adenoviral solution (2 × 107PFU/μl) were injected into the right lens of adult male C57BL/6 mice ( n = 144) at the time of capsular injury induced using a hypodermic needle under both general and topical anesthesia. A mixture of Cre-adenovirus (Cre-Ad) and vector encoding mBMP-7, mId2, or mId3 was administered in a test group. Control lenses were treated with Cre-Ad alone. After healing intervals of 5 or 10 days, the animals were killed and then we performed histological processes or RNA extraction from the lens. RT-PCR, real-time RT-PCR, and immunohistochemistry showed expression of each introduced gene in the lens. Exogenous BMP-7 upregulated expression of Id2 and Id3 in injured lenses, and gene introduction of Id2 or Id3 also upregulated BMP-7 expression. Gene transfer of BMP-7, Id2, or Id3 delayed injury-induced EMT of the lens epithelial cells as evaluated by histology and expression patterns of α-smooth muscle actin and collagens in association with reduction of Smad2 COOH-terminal phosphorylation. Gene transfer of BMP-7, Id2, or Id3 delayed injury-induced EMT of lens epithelial cells and subsequent sealing of the capsular break with fibrous tissue in mice.

Expression profiling correlates with treatment response in women with advanced serous epithelial ovarian cancer

The majority of epithelial ovarian carcinomas are of serous subtype, with most women presenting at an advanced stage. Approximately 70% respond to initial chemotherapy but eventually relapse. We aimed to find markers of treatment response that might be suitable for routine use, using the gene expression profile of tumor tissue. Thirty one women with histologically-confirmed late-stage serous ovarian cancer were classified into 3 groups based on response to treatment (nonresponders, responders with relapse less than 12 months and responders with no relapse within 12 months). Gene expression profiles of these specimens were analyzed with respect to treatment response and survival (minimum 36 months follow-up). Patients' clinical features did not correlate with prognosis, or with specific gene expression patterns of their tumors. However women who did not respond to treatment could be distinguished from those who responded with no relapse within 12 months based on 34 gene transcripts (p < 0.02). Poor prognosis was associated with high expression of inhibitor of differentiation-2 (ID2) (p = 0.001). High expression of decorin (DCN) and ID2 together was strongly associated with reduced survival (p = 0.003), with an estimated 7-fold increased risk of dying (95% CI 1.9-29.6; 14 months survival) compared with low expression (44 months). Immunohistochemical analysis revealed both nuclear and cytoplasmic distribution of ID2 in ovarian tumors. High percentage of nuclear staining was associated with poor survival, although not statistically significantly. In conclusion, elevated expression of ID2 and DCN was significantly associated with poor prognosis in a homogeneous group of ovarian cancer patients for whom survival could not be predicted from clinical factors.