Smad3 mutant mice develop metastatic colorectal cancer

Ovarian follicle development and transgenic mouse models

Ovarian follicle development is a complex process that begins with the establishment of what is thought to be a finite pool of primordial follicles and culminates in either the atretic degradation of the follicle or the release of a mature oocyte for fertilization. This review highlights the many advances made in understanding these events using transgenic mouse models. Specifically, this review describes the ovarian phenotypes of mice with genetic mutations that affect ovarian differentiation, primordial follicle formation, follicular growth, atresia, ovulation and corpus luteum (CL) formation. In addition, this review describes the phenotypes of mice with mutations in a variety of genes, which affect the hormones that regulate folliculogenesis. Because studies using transgenic animals have revealed a variety of reproductive abnormalities that resemble many reproductive disorders in women, it is likely that studies using transgenic mouse models will impact our understanding of ovarian function and fertility in women.

Beta-catenin regulates wound size and mediates the effect of TGF-beta in cutaneous healing

After cutaneous injury, a variety of cell types are activated to reconstitute the epithelial and dermal components of the skin. beta-Catenin plays disparate roles in keratinocytes and fibroblasts, inhibiting keratinocyte migration and activating fibroblast proliferation, suggesting that beta-catenin could either inhibit or enhance the healing process. How beta-catenin functions in concert with other signaling pathways important in the healing process is unknown. Wound size was examined in mice expressing conditional null or conditional stabilized alleles of beta-catenin, regulated by an adenovirus expressing cre-recombinase. The size of the wounds in the mice correlated with the protein level of beta-catenin. Using mice expressing these conditional alleles, we found that the wound phenotype imparted by Smad3 deficiency and by the injection of TGFbeta before wounding is mediated in part by beta-catenin. TGFbeta was not able to regulate proliferation in beta-catenin null fibroblasts, whereas keratinocyte proliferation rate was independent of beta-catenin. When mice are treated with lithium, beta-catenin-mediated signaling was activated in cutaneous wounds, which healed with a larger size. These results demonstrate a crucial role for beta-catenin in regulating cutaneous wound size. Furthermore, these data implicate mesenchymal cells as playing a critical role regulating wound size.

Mouse models of gastrointestinal tumors

The laboratory mouse (Mus musculus) has become one of the best model animal species in biomedical research today because of its abundant genetic/genomic information, and easy mutagenesis using transgenic and gene knockout technology. Genetically engineered mice have become essential tools in both mechanistic studies and drug development. In this article I will review recent topics in gastrointestinal cancer model mice, with emphasis on the results obtained in our laboratory. They include: (i) mouse models for familial adenomatous polyposis (Apc mutant mice; modifier genes of Apc intestinal polyposis; stabilizing beta-catenin mutant mice); (ii) mouse models for colon cancer (mouse models for hereditary non-polyposis colon cancer; additional mutations in Apc mutant mice; models with mutations in other genes; models for colon cancer associated with inflammatory bowel diseases); and (iii) mouse models for gastric cancer.

TGF-beta inhibitors for the treatment of cancer

Advances in understanding the role of transforming growth factor (TGF)-beta in tumorigenesis have led to the development of TGF-beta inhibitors for cancer treatment. Three platforms of TGF-beta inhibitors have evolved: antisense oligonucleotides, monoclonal antibodies and small molecules. In this review, the current stage of development of each known TGF-beta inhibitor will be discussed. As part of the risk/benefit assessment of TGF-beta inhibitors, the known effects of TGF-beta deficiency in mice, non-clinical toxicology studies with TGF-beta inhibitors in rats, and the clinical studies with monoclonal antibodies against TGF-beta will be summarised.

Smad signalling in the ovary

It has now been a decade since the first discovery of the intracellular Smad proteins, the downstream signalling molecules of one of the most important growth factor families in the animal kingdom, the transforming growth factor beta (TGF-beta) superfamily. In the ovary, several TGF-beta superfamily members are expressed by the oocyte, granulosa and thecal cells at different stages of folliculogenesis, and they signal mainly through two different Smad pathways in an autocrine/paracrine manner. Defects in the upstream signalling cascade molecules, the ligands and receptors, are known to have adverse effects on ovarian organogenesis and folliculogenesis, but the role of the individual Smad proteins in the proper function of the ovary is just beginning to be understood for example through the use of Smad knockout models. Although most of the different Smad knockouts are embryonic lethal, it is known, however, that in Smad1 and Smad5 knockout mice primordial germ cell development is impaired and that Smad3 deficient mice harbouring a deletion in exon 8 exhibit impaired folliculogenesis and reduced fertility. In this minireview we discuss the role of Smad structure and function in the ovarian context.

B cell-specific deficiency for Smad2 in vivo leads to defects in TGF-beta-directed IgA switching and changes in B cell fate

Smad2 is a member of the intracellular mediators that transduce signals from TGF-beta receptors and activin receptors. Targeted inactivation of Smad2 in mice leads to early lethality before gastrulation. It was shown previously that TGF-betaRII deficiency in vivo leads to defects in B cell homeostasis, Ag responsiveness, and IgA class switch recombination of B cells. To investigate the importance of Smad2-mediated signaling in B lymphocytes, we generated a B cell-specific inactivation of Smad2 in mice (bSmad2(-/-)). bSmad2(-/-) mice had normal B cell numbers in the spleen but showed a reduced population of marginal zone B cells. In contrast, B cells in Peyer's patches and peritoneal B-1a cells of bSmad2(-/-) mice were increased in numbers. bSmad2(-/-) mice showed a reduced number of surface-IgA(+) B cells and of IgA-secreting cells in Peyer's patches, decreased levels of IgA in serum, and, after immunization with a T cell-dependent Ag, a reduced IgA response. Class switch recombination to IgA was impaired in Smad2-deficient B cells, when stimulated in vitro with LPS in the presence of TGF-beta. The growth-inhibitory effects of TGF-beta in LPS-stimulated B cells were not affected in Smad2-deficient B cells. In summary, our data indicate a crucial role of Smad2 in mediating signals for the TGF-beta-directed class switch to IgA and the induction of IgA responses in vivo. Other B cell functions like growth-inhibitory signaling, which are known to be regulated by signals via the TGF-betaR, are not affected in Smad2-deficient B cells.

Smad3 knock-out mice as a useful model to study intestinal fibrogenesis

AIM: To evaluate the possible differences in morphology and immunohistochemical expression of CD3, transforming growth factor β1(TGF-β1), Smad7, α-smooth muscle actin (α-Sma), and collagen types I-VII of small and large intestine in Smad3 null and wild-type mice.

METHODS: Ten null and ten wild-type adult mice were sacrificed at 4 mo of age and the organs (esophagus, small and large bowel, ureters) were collected for histology(hematoxylin and eosin, Masson thrichrome, silver staining), morphometry and immunohistochemistry analysis. TGF-β1 levels of intestinal tissue homogenates were assessed by ELISA.

RESULTS: No macroscopic intestinal lesions were detected both in null and wild-type mice. Histological and morphometric evaluation revealed a significant reduction in muscle layer thickness of small and large intestine in null mice as compared to wild-type mice. Immunohistochemistry evaluation showed a significant increase of CD3+T cell, TGF-β1 and Smad7 staining in the small and large intestine mucosa of Smad3 null mice as compared to wild-type mice. α-Sma and collagen I-VII staining of small and large intestine did not differ between the two groups of mice. TGF-β1 levels of colonic tissue homogenates were significantly higher in null mice than in wild-type mice. In preliminary experiments a significant reduction of TNBS-induced intestinal fibrosis was observed in null mice as compared to wild-type mice.

CONCLUSION: Smad3 null mice are a useful model to investigate the in vivo role of the TGF-β/Smad signalling pathway in intestinal inflammation and fibrosis.

Helicobacter infection is required for inflammation and colon cancer in SMAD3-deficient mice

Accumulating evidence suggests that intestinal microbial organisms may play an important role in triggering and sustaining inflammation in individuals afflicted with inflammatory bowel disease (IBD). Moreover, individuals with IBD are at increased risk for developing colorectal cancer, suggesting that chronic inflammation may initiate genetic or epigenetic changes associated with cancer development. We tested the hypothesis that bacteria may contribute to the development of colon cancer by synergizing with defective transforming growth factor-beta (TGF-beta) signaling, a pathway commonly mutated in human colon cancer. Although others have reported that mice deficient in the TGF-beta signaling molecule SMAD3 develop colon cancer, we found that SMAD3-deficient mice maintained free of the Gram-negative enterohepatic bacteria Helicobacter spp. for up to 9 months do not develop colon cancer. Furthermore, infection of SMAD3(-/-) mice with Helicobacter triggers colon cancer in 50% to 66% of the animals. Using real-time PCR, we found that Helicobacter organisms concentrate in the cecum, the preferred site of tumor development. Mucinous adenocarcinomas develop 5 to 30 weeks after infection and are preceded by an early inflammatory phase, consisting of increased proliferation of epithelial cells; increased numbers of cyclooxygenase-2-positive cells, CD4(+) T cells, macrophages; and increased MHC class II expression. Colonic tissue revealed increased transcripts for the oncogene c-myc and the proinflammatory cytokines interleukin-1alpha (IL-1alpha), IL-1beta, IL-6, IFN-gamma, and tumor necrosis factor-alpha, some of which have been implicated in colon cancer. These results suggest that bacteria may be important in triggering colorectal cancer, notably in the context of gene mutations in the TGF-beta signaling pathway, one of the most commonly affected cellular pathways in colorectal cancer in humans.

KLF4, p21 and context-dependent opposing forces in cancer

Krüppel-like factors are transcriptional regulators that influence several cellular functions, including proliferation. Recent studies have shown that one family member, KLF4, can function both as a tumour suppressor and an oncogene. The ability of KLF4 to affect the levels of expression of the cell-cycle regulator p21 seems to be involved, in that this protein might function as a switch that determines the outcome of KLF4 signalling. Is this role of p21 restricted to KLF4, or does p21 represent a nodal point for signals from multiple other factors with opposing functions in cancer?

Smad3-null mice lack interstitial cells of Cajal in the colonic wall

BACKGROUND

Transforming growth factor-beta (TGF-beta)/Smad's signalling pathway plays a pivotal role in organogenesis, oncogenesis, inflammation, repair and fibrosis. The aim of this study was to evaluate the morphology of muscle layers and the density and distribution of interstitial cells of Cajal (ICC) in the colon of Smad3 knockout mice.

MATERIALS AND METHODS

Eighteen Smad3 wild-type mice and 12 null mice were sacrificed at age 4 months and the colons were collected for histology (Haematoxilin-Eosin, Masson thrichrome and Gomori silver staining), morphometry and immunohistochemistry (IHC) analysis. For IHC we used the c-Kit, alpha-smooth muscle actine (alpha-SMA), vimentin, desmin and neuronal cocktail (S-100, NSE, neurofilament 200) antibodies.

RESULTS

When sacrificed, 40% of the null mice showed different degrees of colon dilatation when compared with the wild-type. Histological and morphometric evaluation revealed a significant reduction in muscle layer thickness of the colon in all the null mice when compared with the wild-type. Immunohistochemistry evaluation showed a marked reduction, or even absence, of c-Kit immunoreactivity, which identifies ICC, in the colon of all the null mice, compared with the wild-type.

CONCLUSIONS

Smad3 null mice showed a marked reduction, or even absence, of ICC in the colon together with a concomitant reduction of intestinal smooth muscle layer thickness. This data could account for the colonic dilation observed in approximately 40% of the Smad3 null mice. Alteration of intestinal smooth muscle layers and ICC could also be involved in the resistance of the Smad3 null mice to develop colonic fibrosis.

Pro-metastasis function of TGFβ mediated by the smad pathway

The transforming growth factor beta (TGFbeta) signaling pathway plays a vital role in the development and homeostasis of normal tissues. Abnormal function of this pathway contributes to the initiation and progression of cancer. Smad proteins are key signal transducers of the TGFbeta pathway and are essential for the growth suppression function of TGFbeta. Smads are bona fide tumor suppressors whose mutation, deletion, and silencing are associated with many types of human cancer. However, the involvement and functional mechanism of Smad proteins in cancer metastasis are poorly defined. Recent studies using genetically modified cancer cells and mouse tumor models have provided concrete evidence for a Smad-dependent mechanism for metastasis promotion by TGFbeta. Understanding the dual roles of Smad proteins in tumor initiation and progression has important implications for cancer therapeutics.

TGF-beta regulates the mechanical properties and composition of bone matrix

The characteristic toughness and strength of bone result from the nature of bone matrix, the mineralized extracellular matrix produced by osteoblasts. The mechanical properties and composition of bone matrix, along with bone mass and architecture, are critical determinants of a bone's ability to resist fracture. Several regulators of bone mass and architecture have been identified, but factors that regulate the mechanical properties and composition of bone matrix are largely unknown. We used a combination of high-resolution approaches, including atomic-force microscopy, x-ray tomography, and Raman microspectroscopy, to assess the properties of bone matrix independently of bone mass and architecture. Properties were evaluated in genetically modified mice with differing levels of TGF-beta signaling. Bone matrix properties correlated with the level of TGF-beta signaling. Smad3+/- mice had increased bone mass and matrix properties, suggesting that the osteopenic Smad3-/- phenotype may be, in part, secondary to systemic effects of Smad3 deletion. Thus, a reduction in TGF-beta signaling, through its effector Smad3, enhanced the mechanical properties and mineral concentration of the bone matrix, as well as the bone mass, enabling the bone to better resist fracture. Our results provide evidence that bone matrix properties are controlled by growth factor signaling.

Inactivation of NF1 in CNS causes increased glial progenitor proliferation and optic glioma formation

The gene responsible for neurofibromatosis type 1 (NF1) encodes a tumor suppressor that functions as a negative regulator of the Ras proto-oncogene. Individuals with germline mutations in NF1 are predisposed to the development of benign and malignant tumors of the peripheral and central nervous system (CNS). Children with this disease suffer a high incidence of optic gliomas, a benign but potentially debilitating tumor of the optic nerve; and an increased incidence of malignant astrocytoma, reactive astrogliosis and intellectual deficits. In the present study, we have sought insight into the molecular and cellular basis of NF1-associated CNS pathologies. We show that mice genetically engineered to lack NF1 in CNS exhibit a variety of defects in glial cells. Primary among these is a developmental defect resulting in global reactive astrogliosis in the adult brain and increased proliferation of glial progenitor cells leading to enlarged optic nerves. As a consequence, all of the mutant optic nerves develop hyperplastic lesions, some of which progress to optic pathway gliomas. These data point to hyperproliferative glial progenitors as the source of the optic tumors and provide a genetic model for NF1-associated astrogliosis and optic glioma.

An overview of apoptosis and the prevention of colorectal cancer

Colorectal cancer arises as a result of the accumulation of genetic errors many of which affect the control of apoptosis. Effective chemoprevention strategies for colorectal cancer must rectify these genetic defects. Mutation of apc is often the initiating genetic lesion in colorectal cancers that develop along the chromosomal instability pathway. Depending on the cellular context, loss of apc activates the Wnt signalling pathway causing immediate widespread apoptosis of colorectal epithelial cells and defects in differentiation and cell migration. Only cells that are inherently resistant to apoptosis survive this initial wave of apoptosis. These surviving cells constitute the epithelial population that develop into adenomas. Two gene targets of the Wnt signalling pathway are of particular relevance to apoptosis. Although controversial, survivin may function to inhibit apoptosis. MYC has two outputs in normal cells, the induction of apoptosis and proliferation. These opposing functions work so that MYC can only induce cell proliferation in cells if apoptosis is disabled. p53 couples apoptosis to mitogenic signals and survival pathways. Under some circumstances, NF-kappaB can act as an inhibitor of apoptosis possibly through increased expression of bcl-x(L). Tumours that evolve by the microsatellite instability pathway often have mutations in the proapoptotic gene bax. Colonic adenomas express cyclo-oxygenase-2 (COX-2) and may be targets of chemoprevention before the development of malignancy. However, the recent discovery that coxibs increase the risk of serious cardiovascular events limits their use as chemopreventive agents. Nevertheless, aspirin remains a drug of great interest as it is already known to reduce the risk of colorectal cancer by up to 50%. The balance of evidence shows that high vegetable fibre diets can prevent colorectal cancer, probably via the fermentation of butyrate enhancing the apoptotic response to DNA damage.

Smad proteins are targets of transforming growth factor beta1 in immortalised gonadotrophin-releasing hormone releasing neurones

Transforming growth factor beta (TGFbeta) is one of the growth factors involved in the neuroendocrine control of the gonadotrophin-releasing hormone (GnRH) neurones. It is produced and released by the astrocytes surrounding GnRH neurones and directly controls their secretory activity. TGFbeta signalling is based on a complex of two receptors that transduces the signal through peculiar intracellular substrates, the Smad proteins, which, upon activation, move into the nucleus, and modify the transcription of TGFbeta responsive genes. The present study aimed to verify whether TGFbeta1 is able to regulate the Smad pathway in GT1-1 cells (i.e. an immortalised neuronal cell line releasing GnRH). We show that: (i) GT1-1 cells express Smad 2, 3, 4, and 7; (ii) TGFbeta1 enhances the phosphorylation of Smad 2 and 3 at short times of exposure (15-30 min); (iii) TGFbeta1 induces the synthesis of the inhibitory Smad 7 at longer times (60-120-240 min); (iv) the conditioned medium of type 1 astrocytes enhances the phosphorylation of Smad 2 and 3 in GT1-1 cells and a TGFbeta1 neutralising antibody counteracts this effect. The results indicate that Smads are targets of TGFbeta1 and that astrocytes are able to modulate Smads proteins in GT1-1 cells through the release of TGFbeta1. Taken together, the data provide new evidence that glial cells are important regulators of the GnRH neuronal activity.

Transforming growth factor-beta1 to the bone

TGF-beta1 is a ubiquitous growth factor that is implicated in the control of proliferation, migration, differentiation, and survival of many different cell types. It influences such diverse processes as embryogenesis, angiogenesis, inflammation, and wound healing. In skeletal tissue, TGF-beta1 plays a major role in development and maintenance, affecting both cartilage and bone metabolism, the latter being the subject of this review. Because it affects both cells of the osteoblast and osteoclast lineage, TGF-beta1 is one of the most important factors in the bone environment, helping to retain the balance between the dynamic processes of bone resorption and bone formation. Many seemingly contradictory reports have been published on the exact functioning of TGF-beta1 in the bone milieu. This review provides an overall picture of the bone-specific actions of TGF-beta1 and reconciles experimental discrepancies that have been reported for this multifunctional cytokine.

The endogenous ratio of Smad2 and Smad3 influences the cytostatic function of Smad3

Although Smad2 and Smad3, critical transcriptional mediators of transforming growth factor-beta (TGF-beta) signaling, are supposed to play a role in the TGF-beta cytostatic program, it remains unclear whether TGF-beta delivers cytostatic signals through both Smads equally or through either differentially. Here, we report that TGF-beta cytostatic signals rely on a Smad3-, but not a Smad2-, dependent pathway and that the intensity of TGF-beta cytostatic signals can be modulated by changing the endogenous ratio of Smad3 to Smad2. Depleting endogenous Smad3 by RNA interference sufficiently interfered with TGF-beta cytostatic actions in various TGF-beta-sensitive cell lines, whereas raising the relative endogenous ratio of Smad3 to Smad2, by depleting Smad2, markedly enhanced TGF-beta cytostatic response. Consistently, Smad3 activation and its transcriptional activity upon TGF-beta stimulation were facilitated in Smad2-depleted cells relative to controls. Most significantly, a single event of increasing this ratio by Smad2 depletion was sufficient to restore TGF-beta cytostatic action in cells resistant to TGF-beta. These findings suggest a new important determinant of sensitivity to TGF-beta cytostatic signaling.

TGF-beta signaling in T cells: roles in lymphoid and epithelial neoplasia

Transforming growth factor-beta (TGF-beta) plays an essential role in regulating the homeostasis of cells in the lymphoid lineage. TGF-beta signaling is not required for normal thymopoiesis, but is essential for regulating the expansion, activation, and effector function of the mature CD4+ and CD8+ T cells in the peripheral lymphoid organs and target tissues. Recent studies in both mice and humans have elucidated an important and complex role for TGF-beta in regulatory T-cell biology. Disruption of TGF-beta signaling in T cells impairs the maintenance of regulatory T cells, results in the expansion of activated effector T cells, and is associated with the production of cytokines that have major effects on cells in their environment. While autoimmunity and inflammation are the principal phenotypes associated with the abrogation of TGF-beta signaling in T cells in mice, emerging evidence now also directly links Smad-dependent TGF-beta signaling in T cells to the suppression of epithelial neoplasia. The TGF-beta receptor-activated Smad3 plays a critical role in mediating many of the inhibitory effects of TGF-beta signaling in T cells, and has now been established as an important suppressor of leukemogenesis. These studies are increasing our awareness of the many complex mechanisms through which TGF-beta signaling controls the pathogenesis of cancer.

Mouse models expressing human carcinoembryonic antigen (CEA) as a transgene: evaluation of CEA-based cancer vaccines

In recent years, investigators have carried out several studies designed to evaluate whether human tumor-associated antigens might be exploited as targets for active specific immunotherapy, specifically human cancer vaccines. Not too long ago such an approach would have been met with considerable skepticism because the immune system was believed to be a rigid discriminator between self and non-self which, in turn, protected the host from a variety of pathogens. That viewpoint has been challenged in recent years by a series of studies indicating that antigenic determinants of self have not induced absolute host immune tolerance. Moreover, under specific conditions that evoke danger signals, peptides from self-antigen can be processed by the antigen-presenting cellular machinery, loaded onto the major histocompatibility antigen groove to serve as targets for immune intervention. Those findings provide the rationale to investigate a wide range of tumor-associated antigens, including differentiation antigens, oncogenes, and tumor suppressor genes as possible immune-based targets. One of those tumor-associated antigens is the carcinoembryonic antigen (CEA). Described almost 40 years ago, CEA is a M(r) 180-200,000 oncofetal antigen that is one of the more widely studied human tumor-associated antigens. This review will provide: (i) a brief overview of the CEA gene family, (ii) a summary of early preclinical findings on overcoming immune tolerance to CEA, and (iii) the rationale to develop mouse models which spontaneously develop gastrointestinal tumors and express the CEA transgene. Those models have been used extensively in the study of overcoming host immune tolerance to CEA, a self, tumor-associated antigen, and the experimental findings have served as the rationale for the design of early clinical trials to evaluate CEA-based cancer vaccines.

The role of TGF-beta and Wnt signaling in gastrointestinal stem cells and cancer

The past three decades have seen an unremitting quest to identify and understand gastrointestinal stem cells, their plasticity in differentiating across cell types, as well as their role in normal, regenerative, and cancer cells. A fascinating hallmark of stem cells is their ability to undergo assymetric cell division, which entails replication of the DNA followed by division of the nucleus and partitioning of the cytoplasm to yield two different daughter cells: a stem cell as well as a committed progenitor cell, the latter proliferating into differentiated progeny. We are only just beginning to understand how normally quiescent, tissue-specific stem cells interpret a vast array of signals to develop into the gastrointestinal system. These signaling pathways include the transforming growth factor-beta (TGF-beta) superfamily, Wnt, FGFs, Hedgehog, Hox proteins that originate from surrounding mesodermal/stromal tissue as well as endodermal/epithelial tissue. TGF-beta and wnt proteins are key morphogens that ultimately influence cell division and cell fate, so that gut endodermal stem cells enter the cell cycle, and undergo cell division that ultimately leads to differentiated cells such as functional hepatocytes, gastric parietal cells, or gut epithelial cells. Disruptions and errors in this process usually lead to tissue-specific gastrointestinal cancers such as hepatocellular cancers, gastric adenocarcinomas, and colonic adenocarcinomas. An increasingly complex and coherent view of stem/progenitor cell signaling networks, which coordinate cell growth, proliferation, stress management, and survival, is helping to define the fragile areas where malignancies are likely to develop and shows promise for the development of better cancer therapies.

Gene deregulation in gastric cancer

Despite its decreasing frequency in the Western world during recent decades, gastric cancer is still one of the leading causes of cancer-related deaths worldwide. Due to the oligosymptomatic course of early gastric cancer, most cases are diagnosed in the advanced stages of the disease. The curative potential of current standard treatment continues to be unsatisfactory, despite multimodal approaches involving surgery, chemotherapy and radiotherapy. Novel therapeutics including small molecules and monoclonal antibodies are being developed and have been partially introduced into clinical use in connection with neoplastic diseases such as chronic myeloid leukemia, non-Hodgkin's lymphoma and colorectal cancer. Thorough understanding of the changes in gene expression occurring during gastric carcinogenesis may help to develop targeted therapies and improve the treatment of this disease. Novel molecular biology techniques have generated a wealth of data on up- and down-regulation, activation and inhibition of specific pathways in gastric cancer. Here, we provide an overview of the different aspects of aberrant gene expression patterns in gastric cancer.

The role of Smad signaling in hematopoiesis

The TGF-beta family of ligands, including TGF-beta, bone morphogenetic protein (BMP) and activin, signal through Smad pathways to regulate the fate of hematopoietic progenitor and stem cells during development and postnatally. BMP regulates hematopoietic stem cell (HSC) specification during development, while TGF-beta1, 2 and 3 are not essential for the generation of HSCs. BMP4 can increase proliferation of human hematopoietic progenitors, while TGF-beta acts as a negative regulator of hematopoietic progenitor and stem cells in vitro. In contrast, TGF-beta signaling deficiency in vivo does not affect proliferation of HSCs and does not affect lineage choice either. Therefore, the outcome of Smad signaling is very context dependent in hematopoiesis and regulation of hematopoietic stem and progenitor cells is more complicated in the bone marrow microenvironment in vivo than is seen in liquid cultures ex vivo. Smad signaling regulates hematopoiesis by crosstalk with other regulatory signals and future research will define in more detail how the various pathways interact and how the knowledge obtained can be used to develop advanced cell therapies.

Disruption of the TGF-beta pathway and modeling human cancer in mice

There is considerable complexity underlying the mechanisms through which the TGF-beta signaling pathway regulates the initiation and progression of cancer. Analysis of this pathway and the role that it plays in human malignancy continues to elucidate novel mechanisms through which various genetic and epigenetic events subvert the controls that TGF-beta exerts over cell growth, differentiation, and malignant transformation. Modeling these events in the mouse represents an important goal, as the relevant preclinical models are essential not only for improving our understanding of the role of the TGF-beta pathway in the molecular pathogenesis of cancer, but also as tools for evaluating the impact of novel therapeutics on TGF-beta signaling and the role they may play in the prevention and treatment of malignancies. Here, we consider highlights from a number of in vivo murine model systems and relate a few of the significant observations to what we know about TGF-beta signaling in human cancer.

Early inactivation of p53 tumor suppressor gene cooperating with NF1 loss induces malignant astrocytoma

Malignant astrocytoma, the most prevalent primary brain tumor, is resistant to all known therapies and frequently harbors mutations that inactivate p53 and activate Ras signaling. We have generated mouse strains that lack p53 and harbor a conditional allele of the NF1 tumor suppressor that negatively regulates Ras signaling. The mice develop malignant astrocytomas with complete penetrance. The majority of tumors display characteristics of glioblastoma multiforme with concomitant alteration of signaling pathways previously described in the human counterparts of this neoplasm. We find that the sequence of tumor suppressor inactivation influences tumorigenicity and that earliest evidence of tumor formation localizes to regions of the brain that contain a multipotent stem cell population capable of in vivo differentiation into neurons and glia.

Hyperactivation of Stat3 in gp130 mutant mice promotes gastric hyperproliferation and desensitizes TGF-beta signaling

The latent transcription factor Stat3 is activated by gp130, the common receptor for the interleukin (IL)-6 cytokine family and other growth factor and cytokine receptors. Ligand-induced dimerization of gp130 leads to activation of the Stat1, Stat3 and Shp2-Ras-Erk signaling pathways. Here we assess genetically the contribution of exaggerated Stat3 activation to the phenotype of gp130 (Y757F/Y757F) mice, in which a knock-in mutation disrupts the negative feedback mechanism on gp130-dependent Stat signaling. Compared to gp130 (Y757F/Y757F) mice, reduced Stat3 activation in gp130 (Y757F/Y757F) Stat3(+/-) mice increased their lifespan, prevented splenomegaly, normalized exaggerated hepatic acute-phase response and lymphocyte trafficking, and suppressed the growth of spontaneously arising gastric adenomas in young mice. These lesions share histological features of gastric polyps in aging mice with monoallelic null mutations in Smad4, which encodes the common transducer for transforming growth factor (TGF)-beta signaling. Indeed, hyperactivation of Stat3 desensitizes gp130 (Y757F/Y757F) cells to the cytostatic effect of TGF-beta through transcriptional induction of inhibitory Smad7, thereby providing a novel link for cross-talk between Stat and Smad signaling in gastric homeostasis.

Smad3 deficiency in mast cells provides efficient host protection against acute septic peritonitis

Mast cells play an important role in innate immunity as well as in allergic reaction. However, regulatory mechanisms underlying mast cell-mediated innate immune responses remain largely unknown. Here we determined whether Smad3, a major signal transducer of TGF-beta, regulates innate immune response by mast cells against Gram-negative bacteria. Bone marrow-derived mast cells (BMMC) obtained from Smad3 null mutant mice showed augmented capacity to produce proinflammatory cytokines upon stimulation with a Gram-negative bacteria-associated product, LPS. In acute septic peritonitis model induced by cecal ligation and puncture, mast cell-deficient W/W(v) mice reconstituted with Smad3 null BMMC had significantly higher survival rate than W/W(v) mice reconstituted with wild-type BMMC, which was associated with higher production of proinflammatory cytokines in the peritoneal cavity. These in vitro and in vivo results suggest that Smad3 in mast cells functions as inhibitory for mast cell-mediated innate immune response against Gram-negative bacteria. Suppression of Smad3 expression in mast cells may thus have therapeutic potential for Gram-negative bacterial infection such as acute septic peritonitis by augmenting innate immune responses of mast cells.

Wnt signaling in the intestinal epithelium: from endoderm to cancer

The Wnt pathway controls cell fate during embryonic development. It also persists as a key regulator of homeostasis in adult self-renewing tissues. In these tissues, mutational deregulation of the Wnt cascade is closely associated with malignant transformation. The intestinal epithelium represents the best-understood example for the closely linked roles of Wnt signaling in homeostatic self-renewal and malignant transformation. In this review, we outline current understanding of the physiological role of Wnt signaling in intestinal biology. From this perspective, we then describe how mutational subversion of the Wnt cascade leads to colorectal cancer.

BMP signaling and early embryonic patterning

Bone morphogenetic proteins (BMPs) play pleiotropic roles during embryonic development as well as throughout life. Recent genetic approaches especially using the mouse gene knockout system revealed that BMP signaling is greatly involved in early embryonic patterning, which is a dynamic event to establish three-dimensional polarities. The purpose of this review is to describe the diverse function of BMPs through different receptor signaling systems during embryonic patterning including gastrulation and establishment of the left-right asymmetry.

Transforming growth factor beta facilitates beta-TrCP-mediated degradation of Cdc25A in a Smad3-dependent manner

Ubiquitin-dependent degradation of Cdc25A is a major mechanism for damage-induced S-phase checkpoint. Two ubiquitin ligases, the Skp1-cullin-beta-TrCP (SCFbeta-TrCP) complex and the anaphase-promoting complex (APCCdh1), are involved in Cdc25A degradation. Here we demonstrate that the transforming growth factor beta (TGF-beta)-Smad3 pathway promotes SCF(beta-TrCP)-mediated Cdc25A ubiquitination. Cells treated with TGF-beta, as well as cells transfected with Smad3 or a constitutively active type I TGF-beta receptor, exhibit increased ubiquitination and markedly shortened half-lives of Cdc25A. Furthermore, Cdc25A is stabilized in cells transfected with Smad3 small interfering RNA (siRNA) and cells from Smad3-null mice. TGF-beta-induced ubiquitination is associated with Cdc25A phosphorylation at the beta-TrCP docking site (DS82G motif) and physical association of Cdc25A with Smad3 and beta-TrCP. Cdc25A mutant proteins deficient in DS82G phosphorylation are resistant to TGF-beta-Smad3-induced degradation, whereas a Cdc25A mutant protein defective in APCCdh1 recognition undergoes efficient degradation. Smad3 siRNA inhibits beta-TrCP-Cdc25A interaction and Cdc25A degradation in response to TGF-beta. beta-TrCP2 siRNA also inhibits Smad3-induced Cdc25A degradation. In contrast, Cdh1 siRNA had no effect on Cdc25A down-regulation by Smad3. These data suggest that Smad3 plays a key role in the regulation of Cdc25A ubiquitination by SCFbeta-TrCP and that Cdc25A stabilization observed in various cancers could be associated with defects in the TGF-beta-Smad3 pathway.

Activin A suppresses neuroblastoma xenograft tumor growth via antimitotic and antiangiogenic mechanisms

The tumor suppressor function of activin A, together with our findings that activin A is an inhibitor of angiogenesis, which is down-regulated by the N-MYC oncogene, prompted us to investigate in more detail its role in the malignant transformation process of neuroblastomas. Indeed, neuroblastoma cells with restored activin A expression exhibited a diminished proliferation rate and formed smaller xenograft tumors with reduced vascularity, whereas lung metastasis rate remained unchanged. In agreement with the decreased vascularity of the xenograft tumors, activin A inhibited several crucial angiogenic responses of cultured endothelial cells, such as proteolytic activity, migration, and proliferation. Endothelial cell proliferation, activin A, or its constitutively active activin receptor-like kinase 4 receptor (ALK4T206D), increased the expression of CDKN1A (p21), CDKN2B (p15), and CDKN1B (p27) CDK inhibitors and down-regulated the expression of vascular endothelial growth factor receptor-2, the receptor of a key angiogenic factor in cancer. The constitutively active forms of SMAD2 and SMAD3 were both capable of inhibiting endothelial cell proliferation, whereas the dominant-negative forms of SMAD3 and SMAD4 released the inhibitory effect of activin A on endothelial cell proliferation by only 20%. Thus, the effects of activin A on endothelial cell proliferation seem to be conveyed via the ALK4/SMAD2-SMAD3 pathways, however, non-SMAD cascades may also contribute. These results provide novel information regarding the role of activin A in the malignant transformation process of neuroblastomas and the molecular mechanisms involved in regulating angiogenesis thereof.

TGFbeta1/Smad3 counteracts BRCA1-dependent repair of DNA damage

Inactivation of the BRCA1 gene has been found to confer susceptibility to early-onset familial breast and ovarian cancers. BRCA1 regulates DNA repair, chromatin remodeling and affects gene transcription. Transforming growth factor-beta (TGFbeta) is a potent regulator of growth, apoptosis and invasiveness of tumor cells, including breast cancer cells. Here we show that Smad3 which is a component of the TGFbeta signaling pathway, forms a complex with BRCA1 in vitro and in vivo. The interaction is mediated by the MH1 domain of Smad3 and the C-terminal part of BRCA1. We observed a co-localization of Smad3 and BRCA1 in nuclear complexes. We also found that TGFbeta1/Smad3 counteracted BRCA1-dependent repair of DNA double-strand breaks in human breast epithelial cells, as evaluated by BRCA1 nuclear foci formation, single-cell gel electrophoresis and cell survival assays. Thus, TGFbeta1/Smad3 suppresses BRCA1-dependent DNA repair in response to a DNA damaging agent.

Unique and redundant roles of Smad3 in TGF-beta-mediated regulation of long bone development in organ culture

The most well-characterized intracellular signaling molecules for transforming growth factor-beta (TGF-beta) are the Smads. R-Smads interact with and are phosphorylated directly by the TGF-beta type I receptor. Phosphorylated R-Smads can then associate with Smad4, translocate to the nucleus and regulate transcription. Specific R-Smads transduce distinct signals for members of the TGF-beta superfamily. Smad2 and -3 mediate signaling by TGF-beta/activin, whereas Smad1, -5, and -8 mediate bone morphogenetic protein signaling. TGF-beta inhibits proliferation and hypertrophic differentiation in metatarsal organ cultures by a perichondrium-dependent mechanism. To determine the mechanism of TGF-beta signaling in the perichondrium, we tested the hypothesis that TGF-beta-restricted Smad2 and Smad3 regulate chondrocyte proliferation and differentiation in embryonic metatarsal organ cultures. Perichondrium was infected with adenoviruses containing dominant-negative forms of Smad2 (Ad-Smad2-3SA) and Smad3 (Ad-Smad3 Delta C). Proliferation and differentiation were measured in response to treatment with TGF-beta 1. Results were compared with control bones infected with a beta-galactosidase reporter virus (Ad-beta-gal). Infection with Ad-Smad2-3SA completely blocked the effects of TGF-beta 1 on metatarsal development while Ad-Smad3 Delta C only partially blocked TGF-beta 1 effects. To further characterize the role of Smad3 in long bone development, TGF-beta 1 responsiveness in cultures from Smad3(+/+) and Smad3(ex8/ex8) mice were compared. Loss of Smad3 only partially blocked the effects of TGF-beta1 on differentiation. In contrast, the effects of TGF-beta 1 on chondrocyte proliferation were blocked completely. We conclude that Smad2 signaling in the perichondrium can compensate for the loss of Smad3 to regulate inhibition of hypertrophic differentiation; however, Smad3 is required for TGF-beta 1-mediated effects on proliferation.

Abnormal mouse lung alveolarization caused by Smad3 deficiency is a developmental antecedent of centrilobular emphysema

Transforming growth factor-β (TGF-β) signaling plays an important regulatory role during lung development and remodeling. Smad3 is a major downstream signal transducer in the TGF-β pathway from the cell membrane to the nucleus. In Smad3 null mutant mice, we have observed retarded lung alveolarization from postnatal day 7 to day 28, and subsequently centrilobular emphysema starting from day 28, as determined by morphometric analysis. In addition to the morphological changes, peripheral lung cell proliferation in Smad3 knockout mice was reduced compared with the wild-type control between postnatal days 7 and 28. Expression of tropoelastin at the mRNA level was also dramatically decreased in Smad3 knockout lungs from postnatal day 28 through adulthood. Furthermore, increased matrix metalloproteinase-9 protein expression and activity were detected in the Smad3 knockout mouse lung tissue and the bronchoalveolar lavage fluid at postnatal day 28 when the centrilobular emphysema pathology was just beginning to appear. Therefore, these results indicate that Smad3 not only has a positive regulatory impact on neonatal lung alveolarization but also potentially plays a protective role against the occurrence of centrilobular emphysema later on in life.

The promise of genetically engineered mice for cancer prevention studies

Sophisticated genetic technologies have led to the development of mouse models of human cancers that recapitulate important features of human oncogenesis. Many of these genetically engineered mouse models promise to be very relevant and relatively rapid systems for determining the efficacy of chemopreventive agents and their mechanisms of action. The validation of such models for chemoprevention will help the selection of appropriate agents for large-scale clinical trials and allow the testing of combination therapies.

Mice exclusively expressing the short isoform of Smad2 develop normally and are viable and fertile

Smad2 and Smad3 are closely related effectors of TGFbeta/Nodal/Activin-related signaling. Smad3 mutant mice develop normally, whereas Smad2 plays an essential role in patterning the embryonic axis and specification of definitive endoderm. Alternative splicing of Smad2 exon 3 gives rise to two distinct protein isoforms. The short Smad2(Deltaexon3) isoform, unlike full-length Smad2, Smad2(FL), retains DNA-binding activity. Here, we show that Smad2(FL) and Smad2(Deltaexon3) are coexpressed throughout mouse development. Directed expression of either Smad2(Deltaexon3) or Smad3, but not Smad2(FL), restores the ability of Smad2-deficient embryonic stem (ES) cells to contribute descendants to the definitive endoderm in wild-type host embryos. Mice engineered to exclusively express Smad2(Deltaexon3) correctly specify the anterior-posterior axis and definitive endoderm, and are viable and fertile. Moreover, introducing a human Smad3 cDNA into the mouse Smad2 locus similarly rescues anterior-posterior patterning and definitive endoderm formation and results in adult viability. Collectively, these results demonstrate that the short Smad2(Deltaexon3) isoform or Smad3, but not full-length Smad2, activates all essential target genes downstream of TGFbeta-related ligands, including those regulated by Nodal.

Signaling pathways in intestinal development and cancer

The study of the epithelium of the adult mammalian intestine touches upon many modern aspects of biology. The epithelium is in a constant dialogue with the underlying mesenchyme to control stem cell activity, proliferation in transit-amplifying compartments, lineage commitment, terminal differentiation and, ultimately, cell death. There are spatially distinct compartments dedicated to each of these events. The Wnt, TGF-beta, BMP, Notch, and Par polarity pathways are the major players in homeostatic control of the adult epithelium. Several hereditary cancer syndromes deregulate these same signaling cascades through mutational (in)activation. Moreover, these mutations often also occur in sporadic tumors. Thus symmetry exists between the roles that these signaling pathways play in physiology and in cancer of the intestine. This is particularly evident for the Wnt/APC pathway, for which the mammalian intestine has become one of the most-studied paradigms. Here, we integrate recent knowledge of the molecular inner workings of the prototype signaling cascades with their specific roles in intestinal epithelial homeostasis and in neoplastic transformation of the epithelium.

Conditional overexpression of active transforming growth factor beta1 in vivo accelerates metastases of transgenic mammary tumors

To address the role of transforming growth factor (TGF) beta in the progression of established tumors while avoiding the confounding inhibitory effects of TGF-beta on early transformation, we generated doxycycline (DOX)-inducible triple transgenic mice in which active TGF-beta1 expression could be conditionally regulated in mouse mammary tumor cells transformed by the polyomavirus middle T antigen. DOX-mediated induction of TGF-beta1 for as little as 2 weeks increased lung metastases >10-fold without a detectable effect on primary tumor cell proliferation or tumor size. DOX-induced active TGF-beta1 protein and nuclear Smad2 were restricted to cancer cells, suggesting a causal association between autocrine TGF-beta and increased metastases. Antisense-mediated inhibition of TGF-beta1 in polyomavirus middle T antigen-expressing tumor cells also reduced basal cell motility, survival, anchorage-independent growth, tumorigenicity, and metastases. Therefore, induction and/or activation of TGF-beta in hosts with established TGF-beta-responsive cancers can rapidly accelerate metastatic progression.

Dual Role of Transforming Growth Factor β in Mammary Tumorigenesis and Metastatic Progression

It is generally accepted that transforming growth factor β (TGFβ) is both a tumor suppressor and tumor promoter. Whereas loss or attenuation of TGFβ signal transduction is permissive for transformation, introduction of dominant-negative TGFβ receptors into metastatic breast cancer cells has been shown to inhibit epithelial-to-mesenchymal transition, motility, invasiveness, survival, and metastases. In addition, there is evidence that excess production and/or activation of TGFβ by cancer cells can contribute to tumor progression by paracrine mechanisms involving neoangiogenesis, production of stroma and proteases, and subversion of immune surveillance mechanisms in tumor hosts. These data provide a rationale in favor of blockade of autocrine/paracrine TGFβ signaling in human mammary tumors with therapeutic intent. Several treatment approaches are currently in early clinical development and have been the focus of our laboratory. These include (1) ligand antibodies or receptor-containing fusion proteins aimed at blocking ligand binding to cognate receptors and (2) small-molecule inhibitors of the type I TGFβ receptor serine/threonine kinase. Many questions remain about the viability of anti-TGFβ treatment strategies, the best molecular approach (or combinations) for inhibition of TGFβ function in vivo, the biochemical surrogate markers of tumor response, the molecular profiles in tumors for selection into clinical trials, and potential toxicities, among others.

Suppression of matrix metalloproteinase-9 transcription by transforming growth factor-beta is mediated by a nuclear factor-kappaB site

TGF-beta (transforming growth factor-beta) plays a critical role in modulating the inflammatory response and other biological processes through its regulation of the production of MMPs (matrix metalloproteinases). In both Mono-Mac-6 and RAW264.7 monocyte/macrophage cells, TGF-beta abrogated lipopolysaccharide-induced increases in the enzymic activity and mRNA level of MMP-9. A fragment of the human MMP-9 promoter was used to characterize its regulation by TGF-beta signalling. In RAW264.7 cells, TGF-beta or its downstream signalling protein, Smad3 (Sma- and Mad-related protein 3), inhibited lipopolysaccharide-stimulated promoter activity. The suppressive activity of TGF-beta on the MMP-9 promoter was abrogated by an inhibitory Smad, Smad7. The MMP-9 promoter contains a putative TIE (TGF-beta inhibitory element). However, neither mutation nor deletion of the TIE had any effect on the inhibitory activity of TGF-beta on MMP-9 transcription, indicating that the consensus TIE is not required for this effect of TGF-beta. Analysis using a series of deletion mutants of the MMP-9 promoter revealed that a region containing a consensus NF-kappaB (nuclear factor-kappaB) site is required for the basal activity and TGF-beta-mediated suppression of the promoter. Mutation of the putative NF-kappaB site not only markedly reduced the basal transcriptional activity of the promoter, but also abrogated the responsiveness of the promoter to TGF-beta. In addition, a minimal promoter containing one copy of the NF-kappaB sequence was responsive to TGF-beta treatment. Furthermore, an electrophoretic mobility shift assay was performed with the nuclear extracts from RAW264.7 cells, and it was found that TGF-beta treatment did not disrupt the binding of NF-kappaB p50 and p65 proteins to the NF-kappaB sequence. Taken together, these studies indicate that the NF-kappaB site is indispensable for the suppressive activity of TGF-beta in the regulation of MMP-9 transcription.

Colorectal cancers in a new mouse model of familial adenomatous polyposis: influence of genetic and environmental modifiers

Murine models of familial adenomatous polyposis harbor a germinal heterozygous mutation on Apc tumor suppressor gene. They are valuable tools for studying intestinal carcinogenesis, as most human sporadic cancers contain inactivating mutations of APC. However, Apc(+/-) mice, such as the well-characterized Apc(Min/+) model, develop cancers principally in the small intestine, while humans develop mainly colorectal cancers. We used a Cre-loxP strategy to achieve a new model of germline Apc invalidation in which exon 14 is deleted. We compared the phenotype of these Apc(Delta14/+) mice to that of the classical Apc(Min/+). The main phenotypic difference is the shift of the tumors in the distal colon and rectum, often associated with a rectal prolapse. Thus, the severity of the colorectal phenotype is partly due to the particular mutation Delta14, but also to environmental parameters, as mice raised in conventional conditions developed more colon cancers than those raised in pathogen-free conditions. All lesions, including early lesions, revealed Apc LOH and loss of Apc gene expression. They accumulated beta-catenin, overexpressed the beta-catenin target genes cyclin D1 and c-Myc, and the distribution pattern of glutamine synthetase, a beta-catenin target gene recently identified in the liver, was mosaic in intestinal adenomas. The Apc(Delta14/+) model is thus a useful new tool for studies on the molecular mechanisms of colorectal tumorigenesis.

Activin type II receptor restoration in ACVR2-deficient colon cancer cells induces transforming growth factor-beta response pathway genes

The activin type II receptor (ACVR2) gene is a putative tumor suppressor gene that is frequently mutated in microsatellite-unstable colon cancers (MSI-H colon cancers). ACVR2 is a member of the transforming growth factor (TGF)-beta type II receptor (TGFBR2) family and controls cell growth and differentiation. SMAD proteins are major intracellular effectors shared by ACVR2 and TGFBR2 signaling; however, additional shared effector mechanisms remain to be explored. To discover novel mechanisms transmitting the ACVR2 signal, we restored ACVR2 function by transfecting wild-type ACVR2 (wt-ACVR2) into a MSI-H colon cancer cell line carrying an ACVR2 frameshift mutation. The effect of ACVR2 restoration on cell growth, SMAD phosphorylation, and global molecular phenotype was then evaluated. Decreased cell growth was observed in wt-ACVR2 transfectants relative to ACVR2-deficient vector-transfected controls. Western blotting revealed higher expression of phosphorylated SMAD2 in wt-ACVR2 transfectants versus controls, suggesting cells deficient in ACVR2 had impaired SMAD signaling. Microarray-based differential expression analysis revealed substantial ACVR2-induced overexpression of genes implicated in the control of cell growth and tumorigenesis, including the activator protein (AP)-1 complex genes JUND, JUN, and FOSB, as well as the small GTPase signal transduction family members, RHOB, ARHE, and ARHGDIA. Overexpression of these genes is shared with TGFBR2 activation. This observed similarity between the activin and TGF-beta signaling systems suggests that activin may serve as an alternative activator of TGF-beta effectors, including SMADs, and that frameshift mutation of ACVR2 may contribute to MSI-H colon tumorigenesis via disruption of alternate TGF-beta effector pathways.

Transforming Growth Factor β–SMAD2 Signaling Regulates Aortic Arch Innervation and Development

Aortic arch interruptions in humans and animal models are mainly caused by aberrant development of the fourth pharyngeal arch artery. Little is known about the maturation of this vessel during normal and abnormal development, which is the subject of this study. Tgfbeta2 knockout mice that present with fourth artery defects have been associated with defective neural crest cell migration. In this study, we concentrated on pharyngeal arch artery development during developmental days 12.5 to 18.5, focusing on neural crest cell migration using a Wnt1-Cre by R26R neural crest cell reporter mouse. Fourth arch artery maturation was studied with antibodies directed against smooth muscle alpha-actin and neural NCAM-1 and RMO-270. For diminished transforming growth factor beta (TGF-beta) signaling, SMAD2 and fibronectin have been analyzed. Neural crest migration and differentiation into smooth muscle cells is unaltered in mutants, regardless of the cardiovascular defect found; however, innervation of the fourth arch artery is affected. Absent staining for nuclear SMAD2, NCAM-1, and RMO-270 in the fourth artery in mutant coincides with severe defects of this segment. Likewise, fibronectin expression is diminished in these cases. From these data we conclude the following: (1) neural crest cell migration is not a common denominator in cardiovascular defects of Tgfbeta2-/- mice; (2) fourth arch artery maturation is a complex process involving innervation; and (3) TGF-beta2 depletion diminishes SMAD2-signaling in the fourth arch artery and coincides with reduced vascular NCAM-1 expression and neural innervation of this artery. We hypothesize that disturbed maturation of the fourth pharyngeal arch artery, and especially abrogated vascular innervation, will result in fourth arch interruptions.

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

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

Smad3 deficiency attenuates renal fibrosis, inflammation,and apoptosis after unilateral ureteral obstruction

BACKGROUND

Transforming growth factor-beta (TGF-beta) has been implicated in the development of renal fibrosis induced by unilateral ureteral obstruction (UUO). However, there is little information on signaling pathways mediating TGF-beta activity involved in molecular and cellular events leading to renal fibrosis induced by UUO. In this study, we sought to determine whether Smad3, a major signaling component of TGF-beta, mediated renal fibrosis induced by UUO.

METHODS

Renal fibrosis, inflammation, and apoptosis induced by UUO were macroscopically and histologically compared between wild-type mice and Smad3 null mice.

RESULTS

Gross appearance of the kidney after UUO showed relatively intact kidney in Smad3 null mice [Smad3(-/-) mice] when compared with that of wild-type mice [Smad3(+/+) mice]. Renal interstitial fibrosis based on the interstitial area stained with Aniline-blue or Sirius red solution was significantly attenuated in the obstructed kidney of Smad3(-/-) mice when compared with that of Smad3(+/+) mice. Deposition of type I and type III collagens were also significantly reduced in the obstructed kidney of Smad3(-/-) mice. In addition, the numbers of myofibroblasts, macrophages, and CD4/CD8 T cells infiltrated into the kidney after UUO were significantly attenuated in the obstructed kidney of Smad3(-/-) mice when compared with that of Smad3(+/+) mice. Furthermore, terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) staining after UUO showed significantly reduced number of tubular apoptotic cells in the obstructed kidney of Smad3(-/-) mice when compared with that of Smad3(+/+) mice. Endogenous Smad pathway was activated in the obstructed kidney after UUO in wild-type mice as judged by the increase of phosphorylated Smad2 or phosphorylated Smad2/3-positive cells in renal interstitial area.

CONCLUSION

Smad3 deficiency attenuated renal fibrosis, inflammation, and apoptosis after UUO, suggesting that Smad3 was a key molecule mediating TGF-beta activity leading to real fibrosis after UUO.

Transforming growth factor-beta (TGF-beta) activates cytosolic phospholipase A2alpha (cPLA2alpha)-mediated prostaglandin E2 (PGE)2/EP1 and peroxisome proliferator-activated receptor-gamma (PPAR-gamma)/Smad signaling pathways in human liver cancer cells. A novel mechanism for subversion of TGF-beta-induced mitoinhibition

Transforming growth factor-beta (TGF-beta) potently inhibits the growth of human epithelial cells. However, neoplastic epithelial cells become resistant to TGF-beta-mediated mitoinhibition, and the mechanisms for this alteration during tumorigenesis are not fully understood. This study was designed to determine whether there is an association between the cytosolic phospholipase A2alpha (cPLA2alpha)-controlled eicosanoid metabolism and the growth response to TGF-beta in human liver cancer cells. TGF-beta treatment induced simultaneous Smad-mediated gene transcription and phosphorylation of cPLA2alpha. Whereas Smad activation inhibited tumor cell growth, phosphorylation of cPLA2 alpha promoted growth and counteracted Smad-mediated mitoinhibition. TGF-beta1 failed to prevent the growth of cells with high basal expression of cPLA2alpha, but inhibition of cPLA2 alpha, cyclooxygenase-2 (COX-2), or EP1 receptor restored mitoinhibition by TGF-beta1 in these cells. These results suggest that resistance of tumor cells to TGF-beta-mediated mitoinhibition involves activation of cPLA2alpha/COX-2/EP1 signaling. Furthermore, the TGF-beta1-induced Smad transcriptional activity and mitoinhibition were blocked by overexpression of cPLA2alpha or peroxisome proliferator-activated receptor-gamma (PPAR-gamma) but enhanced by depletion of cPLA2alpha or PPAR-gamma. These findings, along with the observations that cPLA2alpha activates PPAR-gamma and that PPAR-gamma binds Smad3, illustrate novel cPLA2alpha/COX-2/EP1 and cPLA2alpha/PPAR-gamma/Smad signaling pathways that counteract the mitoinhibition by TGF-beta in human cancer cells.

Genetic models for transforming growth factor beta superfamily signaling in ovarian follicle development

The transforming growth factor beta (TGFbeta) superfamily has wide-ranging and profound effects on many aspects of cellular growth and development. Many TGFbeta-related ligands, receptors, and intracellular signaling proteins are expressed in the ovary and are critical for normal follicle development. Our laboratory and others have analyzed the in vivo function of the TGFbeta superfamily signal transduction pathways by using gene knockout and knockin approaches. Two TGFbeta superfamily ligands, growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), are expressed in developing oocytes. Based on in vivo data using knockout models, GDF9 is critical at both the primary and preovulatory stages of follicle development, and physiologically interacts with BMP15 during the latter stages of folliculogenesis. A knockin model of activin betaB expressed from the activin betaA locus, revealed that activin betaB can act as a hypomorphic protein and rescue some but not all of activin betaAs functions. Questions of functional redundancy of signaling components and multiple receptor utilization by different ligands still need to be addressed for these pathways. Answers will likely come from using existing single null mouse models to generate combinatorial ligand and receptor null mice. These new models may reveal the in vivo genetic interactions of TGFbeta superfamily ligands, receptors, binding proteins, and downstream signaling pathways.

Transforming growth factor beta receptor type II inactivation promotes the establishment and progression of colon cancer

Deregulation of members of the transforming growth factor (TGF)-beta signaling pathway occurs often in colon cancers and is believed to affect the formation of primary colon cancer. Mutational inactivation of TGFBR2 is the most common genetic event affecting the TGF-beta signaling pathway and occurs in approximately 20-30% of all colon cancers. By mating Fabpl(4xat-132) Cre mice with Tgfbr2(flx/flx) mice, we have generated a mouse model that is null for Tgfbr2 in the colonic epithelium, and in this model system, we have assessed the effect of loss of TGF-beta signaling in vivo on colon cancer formation induced by azoxymethane (AOM). We have observed a significant increase in the number of AOM-induced adenomas and adenocarcinomas in the Fabpl(4xat-132) Cre Tgfbr2(flx/flx) mice compared with Tgfbr2(flx/flx) mice, which have intact TGF-beta receptor type II (TGFBR2) in the colon epithelium, and we have found increased proliferation in the neoplasms occurring in the Fabpl(4xat-132) Cre Tgfbr2(flx/flx) mice. These results implicate the loss of TGF-beta-mediated growth inhibition as one of the in vivo mechanisms through which TGFBR2 inactivation contributes to colon cancer formation. Thus, we have demonstrated that loss of TGFBR2 in colon epithelial cells promotes the establishment and progression of AOM-induced colon neoplasms, providing evidence from an in vivo model system that TGFBR2 is a tumor suppressor gene in the colon.