Transforming growth factor-beta1 is a new form of tumor suppressor with true haploid insufficiency.

Components of the transforming growth factor-beta (TGF-beta) signal pathway function as classic tumor suppressors, but the role of the TGF-betas themselves is less clear. Here we show that mice heterozygous for deletion of the TGF-beta1 gene express only 10-30% of wild-type TGF-beta1 protein levels. Although grossly normal, these mice have a subtly altered proliferative phenotype, with increased cell turnover in the liver and lung. Treatment of these mice with chemical carcinogens resulted in enhanced tumorigenesis when compared with wild-type littermates. However, tumors in the heterozygous mice did not lose the remaining wild-type TGF-beta1 allele, indicating that the TGF-beta1 ligand is a new form of tumor suppressor that shows true haploid insufficiency in its ability to protect against tumorigenesis.

Early progression of thymocytes along the CD4/CD8 developmental pathway is regulated by a subset of thymic epithelial cells expressing transforming growth factor beta.

Precursor cells differentiate into mature CD4+ and CD8+ T cells in the inductive environment of the thymus by undergoing a series of distinct developmental steps marked by expression of the coreceptor molecules CD4 and CD8. Among the earliest cells to enter the CD4/CD8 developmental pathway are CD4-CD8lo precursors cells that differentiate into CD4+CD8+ thymocytes. Here we show that differentiation of precursor cells into CD4+CD8+ thymocytes requires at least one cell division and that their progression through a cell cycle is specifically retarded in the thymus by interaction with thymic epithelial cells that express transforming growth factor beta (TGF-beta) proteins. We also demonstrate that TGF-beta proteins, either in solution or bound to cell membranes, can regulate cell cycle progression and differentiation of CD4-CD8lo precursor cells into CD4+CD8+ thymocytes. The regulatory effect of TGF-beta is specific for CD4-CD8lo precursor cells as TGF-beta proteins do not regulate the earlier generation of CD4-CD8lo precursor cells from CD4-CD8- thymocytes. Finally, we demonstrate that TGF-beta proteins are expressed in vivo in the intact thymus on subcapsular and cortical thymic epithelium where they can contact developing CD4-CD8lo precursor cells. Thus, thymic epithelial cells expressing TGF-beta proteins can actively regulate the rate at which CD4+CD8+ thymocytes are generated from CD4-CD8lo precursor cells.

A role for endogenous transforming growth factor beta 1 in Langerhans cell biology: the skin of transforming growth factor beta 1 null mice is devoid of epidermal Langerhans cells.

Transforming growth factor beta 1 (TGF-beta 1) regulates leukocytes and epithelial cells. To determine whether the pleiotropic effects of TGF-beta 1, a cytokine that is produced by both keratinocytes and Langerhans cells (LC), extend to epidermal leukocytes, we characterized LC (the epidermal contingent of the dendritic cell [DC] lineage) and dendritic epidermal T cells (DETC) in TGF-beta 1 null (TGF-beta 1 -/-) mice. I-A+ LC were not detected in epidermal cell suspensions or epidermal sheets prepared from TGF-beta 1 -/- mice, and epidermal cell suspensions were devoid of allostimulatory activity. In contrast, TCR-gamma delta + DETC were normal in number and appearance in TGF-beta 1 -/- mice and, importantly, DETC represented the only leukocytes in the epidermis. Immunolocalization studies revealed CD11c+ DC in lymph nodes from TGF-beta 1 -/- mice, although gp40+ DC were absent. Treatment of TGF-beta 1 -/- mice with rapamycin abrogated the characteristic inflammatory wasting syndrome and prolonged survival indefinitely, but did not result in population of the epidermis with LC. Thus, the LC abnormality in TGF-beta 1 -/- mice is not a consequence of inflammation in skin or other organs, and LC development is not simply delayed in these animals. We conclude that endogenous TGF-beta 1 is essential for normal murine LC development or epidermal localization.

Spontaneously increased production of nitric oxide and aberrant expression of the inducible nitric oxide synthase in vivo in the transforming growth factor beta 1 null mouse.

Transforming growth factor beta 1 null mice (TGF-beta 1-/-) suffer from multifocal inflammation and die by 3-4 wk of age. In these mice, levels of nitric oxide (NO) reaction products in serum are elevated approximately fourfold over levels in controls, peaking at 15-17 d of life. Shortterm treatment of TGF-beta 1-/- mice with NG-monomethyl-L-arginine suppressed this elevated production of NO. Expression of inducible NO synthase (iNOS) mRNA and protein is increased in the kidney and heart of TGF-beta 1-/- mice. These findings demonstrate that TGF-beta 1 negatively regulates iNOS expression in vivo, as had been inferred from mechanistic studies on the control of iNOS expression by TGF-beta 1 in vitro.

Pertussis toxin-sensitive pathway in the stimulation of c-myc expression and DNA synthesis by bombesin.

The bombesin-like peptides are potent mitogens for Swiss 3T3 fibroblasts, human bronchial epithelial cells, and cells isolated from small cell carcinoma of the lung. The mechanism of signal transduction in the proliferative response to bombesin was investigated by studying the effect of Bordetella pertussis toxin on bombesin-stimulated mitogenesis. At nanomolar concentrations, bombesin increased levels of c-myc messenger RNA and stimulated DNA synthesis in Swiss 3T3 cells. Treatment of the cells with pertussis toxin (5 nanograms per milliliter) completely blocked bombesin-enhanced c-myc expression and eliminated bombesin-stimulated DNA synthesis. This treatment had essentially no effect on the mitogenic responses to either platelet-derived growth factor or phorbol 12,13-dibutyrate. These results suggest that the mitogenic actions of bombesin-like growth factors are mediated through a pertussis toxin-sensitive guanine nucleotide-binding protein. Furthermore they indicate that bombesin-like growth factors act through pathways that are different from those activated by platelet-derived growth factor.

Maternal rescue of transforming growth factor-beta 1 null mice.

Maternal sources of transforming growth factor-beta 1 (TGF-beta 1) are shown here to contribute to the normal appearance and perinatal survival of TGF-beta 1 null newborn mice. Labeled TGF-beta 1 crossed the placenta and was recovered intact from various tissues after oral administration to mouse pups. TGF beta-1 protein was also detected in cells recovered from breast milk. In immunohistochemical analyses, TGF-beta 1 null embryos and null newborn pups born to TGF-beta 1 heterozygotes stained positive for TGF-beta 1, whereas those born to a null female were negative and had severe cardiac abnormalities. These results suggest an important role for maternal sources of TGF-beta 1 during development and, more generally, provide evidence for maternal rescue of targeted gene disruption in the fetus.

A role for TGFbeta1 in langerhans cell biology. Further characterization of the epidermal Langerhans cell defect in TGFbeta1 null mice.

Previous studies of TGFbeta1 null (-/-) mice indicated that the epidermis was devoid of Langerhans cells (LC) and that the LC deficiency was not secondary to the inflammation that is the dominant feature of the -/- phenotype (Borkowski, T.A., J.J. Letterio, A.G. Farr, and M.C. Udey. 1996. J. Exp. Med. 184:2417-2422). Herein, we demonstrate that dendritic cells could be expanded from the bone marrow of -/- mice and littermate controls. Bone marrow from -/- mice also gave rise to LC after transfer into lethally irradiated recipients. Thus, the LC defect in TGFbeta1 null mice does not result from an absolute deficiency in bone marrow precursors, and paracrine TGFbeta1 production is sufficient for LC development. Several approaches were used to assess the suitability of -/- skin for LC localization. A survey revealed that although a number of cytokine mRNAs were expressed de novo, mRNAs encoding proinflammatory cytokines known to mobilize LC from epidermis (IL-1 and TNFalpha) were not strikingly overrepresented in -/- skin. In addition, bone marrow-derived LC populated full-thickness TGFbeta1 null skin after engraftment onto BALB/c nu/nu recipients. Finally, the skin of transgenic mice expressing a truncated loricrin promoter-driven dominant-negative TGFbeta type II receptor contained normal numbers of LC. Because TGFbeta1 signaling in these mice is disrupted only in keratinocytes and the keratinocyte hyperproliferative component of the TGFbeta1 -/- phenotype is reproduced, these results strongly suggest that the LC defect in TGFbeta1 null mice is not due to an epidermal abnormality but reflects a requirement of murine LC (or their precursors) for TGFbeta1.

Autoimmunity associated with TGF-beta1-deficiency in mice is dependent on MHC class II antigen expression.

The progressive inflammatory process found in transforming growth factor beta1 (TGF-beta1)-deficient mice is associated with several manifestations of autoimmunity, including circulating antibodies to nuclear antigens, immune complex deposition, and increased expression of both class I and class II major histocompatibility complex (MHC) antigens. The contribution of MHC class II antigens to the genesis of this phenotype has been determined by crossing the TGF-beta1-null [TGF-beta1(-/-)] genotype into the MHC class II-deficient [MHC-II(-/-)] background. Mice homozygous for both the TGF-beta1 null allele and the class II null allele [TGF-beta1(-/-);MHC-II(-/-)] are without evidence of inflammatory infiltrates, circulating autoantibodies, or glomerular immune complex deposits. Instead, these animals exhibit extensive extramedullary hematopoiesis with progressive splenomegaly and adenopathy, surviving only slightly longer than TGF-beta1(-/-);MHC-II(+/+) mice. The role of CD4+ T cells, which are also absent in MHC class II-deficient mice, is directly demonstrated through the administration of anti-CD4 monoclonal antibodies in class II-positive, TGF-beta1(-/-) mice. The observed reduction in inflammation and improved survival emphasize the significance of CD4+ cells in the pathogenesis of the autoimmune process and suggest that the additional absence of class II antigens in TGF-beta1(-/-);MHC-II(-/-) mice may contribute to their extreme myeloid metaplasia. Thus, MHC class II antigens are essential for the expression of autoimmunity in TGF-beta1-deficient mice, and normally may cooperate with TGF-beta1 to regulate hematopoiesis.

Hereditary and acquired p53 gene mutations in childhood acute lymphoblastic leukemia.

The p53 gene was examined in primary lymphoblasts of 25 pediatric patients with acute lymphoblastic leukemia by the RNase protection assay and by single strand conformation polymorphism analysis in 23 of 25 cases. p53 mutations were found to occur, but at a low frequency (4 of 25). While all four mutations were identified by single strand conformation polymorphism, the comparative sensitivity of RNase protection was 50% (2 of 4). Heterozygosity was retained at mutated codons in 3 of 4 cases. One pedigree was consistent with the Li-Fraumeni syndrome, and bone marrow from both diagnosis and remission indicated a germline G to T transversion at codon 272 (valine to leucine). Although members of another family were affected with leukemia, a 2-bp deletion in exon 6 was nonhereditary. The other two nonhereditary p53 mutations included a T to G transversion at codon 270 (phenylalanine to cysteine) and a G to C transversion at codon 248 (arginine to proline). These data support the role of both hereditary and acquired p53 mutations in the pathogenesis and/or progression of some cases of childhood acute lymphoblastic leukemia.

Murine models define the role of TGF-beta as a master regulator of immune cell function.

Many members of transforming growth factor-beta (TGF-beta) superfamily, including not only TGF-beta, but also the activins, and bone morphogenetic proteins (BMPs), have been demonstrated to affect the development and function of immune cells. From the proliferation and differentiation of pluripotent stem cells, to the activation and migration of mature lymphoid and myeloid lineages, the TGF-betas have been recognized for their ability to modulate the manner in which such cells respond to stimuli in their environment. Recent studies involving disruption of this pathway in genetically engineered mice now emphasize the importance of this activity and validate functional models predicted by in vitro studies. Phenotypic differences between mice harboring mutations in the TGF-beta1 ligand and the TGF-beta receptor-activated signaling intermediate Smad3 are presented and serve to highlight the valuable role of these in vivo genetic tests of function.

Induction of transforming growth factor beta 1 and its receptors during all-trans-retinoic acid (RA) treatment of RA-responsive human neuroblastoma cell lines.

Recent work on a variety of normal and malignant cell lines has shown that induction and secretion of biologically active TGF-beta may occur after exposure to all-trans-retinoic acid (RA), coincident with decreased growth rate and/or differentiation. This study evaluates the expression and regulation of transforming growth factor beta (TGF-beta) and its receptors during RA-induced cell growth arrest and induction of differentiation in the RA-sensitive human neuroblastoma cell line SMS-KCNR and the RA-resistant neuroblastoma cell line SK-N-AS. RA treatment of SMS-KCNR cells results in a 40-fold increase in TGF-beta 1 mRNA after 4 days of RA, a dose-dependent increase in TGF-beta 1 secretion, an increase in types I (TBRI) and III (TBRIII) TGF-beta receptor proteins, and an increase in type II TGF-beta receptor (TBRII) mRNA coincident with RA-responsiveness of the cells. However, in the RA-resistant line SK-N-AS, TGF-beta 1 is constitutively secreted at levels that are unchanged after RA treatment, and although TBRI and TBRIII mRNA is expressed in untreated SK-N-AS cells, levels of TBRI and TBRIII protein and TBRII mRNA decrease after RA treatment. Thus, in RA-sensitive neuroblastoma cells, RA treatment may result in the induction of a negative autocrine TGF-beta 1 growth regulatory loop. These results suggest the hypothesis that: (a) induction of a TGF-beta 1 negative autocrine growth loop may be a necessary component for RA-responsiveness of neuroblastoma cells in vivo; and (b) the inability to induce or maintain this TGF-beta 1 negative autocrine growth loop may be a mechanism of RA resistance in neuroblastoma.

1 alpha,25-Dihydroxy-16-ene-23-yne-26,27-hexafluorocholecalciferol (Ro24-5531), a new deltanoid (vitamin D analogue) for prevention of breast cancer in the rat.

We have used the vitamin D analogue, 1 alpha,25-dihydroxy-16-ene-23-yne-26,27-hexafluorocholecalcifero l (Ro24-5531), for inhibition of mammary carcinogenesis induced by N-nitroso-N-methylurea (NMU) in Sprague-Dawley rats. Rats were first treated with a single dose of either 15 or 50 mg/kg body weight NMU and then fed Ro24-5531 (2.5 or 1.25 nmol/kg of diet) for 5-7 months. Ro24-5531 significantly extended tumor latency and lessened tumor incidence as well as tumor number in rats treated with the lower dose of NMU. In rats treated with the higher dose of NMU, Ro24-5531 was fed in combination with tamoxifen; in these experiments, Ro24-5531 significantly enhanced the ability of tamoxifen to reduce total tumor burden, as well as to increase the probability that an animal would be tumor free at the end of the experiment. In vitro, Ro24-5531 was 10-100 times more potent than 1,25-dihydroxyvitamin D3 for inhibition of proliferation of human breast cancer cell lines as well as primary cultures of cells from 2 patients with acute myelogenous leukemia. When fed chronically, Ro24-5531 did not elevate serum calcium in the present studies. We propose the new term, "deltanoids," for the set of molecules composed of vitamin D and its synthetic analogues, in a manner similar to the naming of "retinoids" for the corresponding set of molecules related to vitamin A.

A novel synthetic oleanane triterpenoid, 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid, with potent differentiating, antiproliferative, and anti-inflammatory activity.

The new synthetic oleanane triterpenoid 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO) is a potent, multifunctional molecule. It induces monocytic differentiation of human myeloid leukemia cells and adipogenic differentiation of mouse 3T3-L1 fibroblasts and enhances the neuronal differentiation of rat PC12 pheochromocytoma cells caused by nerve growth factor. CDDO inhibits proliferation of many human tumor cell lines, including those derived from estrogen receptor-positive and -negative breast carcinomas, myeloid leukemias, and several carcinomas bearing a Smad4 mutation. Furthermore, it suppresses the abilities of various inflammatory cytokines, such as IFN-gamma, interleukin-1, and tumor necrosis factor-alpha, to induce de novo formation of the enzymes inducible nitric oxide synthase (iNos) and inducible cyclooxygenase (COX-2) in mouse peritoneal macrophages, rat brain microglia, and human colon fibroblasts. CDDO will also protect rat brain hippocampal neurons from cell death induced by beta-amyloid. The above activities have been found at concentrations ranging from 10(-6) to 10(-9) M in cell culture, and these results suggest that CDDO needs further study in vivo, for either chemoprevention or chemotherapy of malignancy as well as for neuroprotection.

Transforming growth factor-beta1 circulates in normal human plasma and is unchanged in advanced metastatic breast cancer.

A method has been developed to determine true plasma transforming growth factor beta (TGF-beta) levels by using the platelet alpha granule-specific marker, platelet factor 4, to correct for the TGF-beta contributed by platelets degranulated ex vivo. TGF-beta levels were measured on acid-ethanol extracts of human plasma using isoform-specific sandwich enzyme-linked immunosorbent assays. Normal human subjects had 4.1 +/- 2.0 ng/ml TGF-beta1 (range, 2.0-12.0; n = 42), <0.2 ng/ml TGF-beta2, and <0.1 ng/ml TGF-beta3 in their plasma. There were no significant changes with age or with hormonal status, but any given individual showed fluctuations of up to 3-fold in measured plasma TGF-beta levels due to unknown factors. Of 28 patients with advanced metastatic breast cancer, 2 had greatly elevated TGF-beta1 levels, while the rest were in the normal range. The presence of physiologically significant levels of TGF-beta1 in the plasmas of normal human subjects may indicate previously unsuspected endocrine roles for this peptide, while TGF-beta2 and TGF-beta3 appear to act only in a local autocrine/paracrine fashion.

Transforming growth factor-beta1-deficient mice: identification of isoform-specific activities in vivo.

A remarkable range of activities has been ascribed to the family of proteins known as transforming growth factor-beta (TGF-beta). Each plays an important role in development and homeostasis, influencing mesenchymal-epithelial interactions, regulating cellular differentiation, and maintaining control of cell proliferation. Although in vitro comparisons of activity demonstrate a high degree of functional similarity, recent studies of mice with a targeted deletion of the TGF-beta1 gene reveal that true isoform-specific activities do exist in vivo and that the three mammalian isoforms are not functionally redundant. This approach has defined a unique role for TGF-beta1 in the establishment and maintenance of normal immune function, shed new light on the relevance of endogenous TGF-beta1 to the normal wound healing process, and expanded the list of known mechanisms of TGF-beta1 activity to include endocrine functions. Thus, the TGF-beta1-deficient mouse allows the definition of isoform-specific activities, providing an invaluable window through which to view the principal functions of TGF-beta1 in vivo.

Control of nitric oxide production by endogenous TGF-beta1 and systemic nitric oxide in retinal pigment epithelial cells and peritoneal macrophages.

Both in vivo and in vitro experiments demonstrate that transforming growth factor-beta1 (TGF-beta1) suppresses expression of the inducible form of nitric oxide synthase (iNOS). In this study, we examined the effects of exogenous and endogenous TGF-beta1 on retinal pigment epithelial (RPE) cells and resident peritoneal macrophages ex vivo using cells from TGF-beta1 null (TGF-beta1-/-) mice or age-matched wild-type (TGF-beta1+/+) or heterozygous (TGF-beta1+/-) littermates. RPE cells from both TGF-beta1-/- mice and TGF-beta1+/+ littermates produced NO and were immunocytochemically positive for iNOS protein only following treatment with interferon-gamma (IFN-gamma) and bacterial lipopolysaccharide (LPS); however, RPE cells from TGF-beta1-/- mice produced 40% more NO than cells from TGF-beta1+/+ mice. In contrast, resident peritoneal macrophages from both TGF-beta1+/+ and TGF-beta1-/- mice expressed iNOS protein without stimulation and in the absence of detectable production of NO. The expression of iNOS was increased by treatment with IFN-gamma, resulting in detectable levels of NO. Macrophages from TGF-beta1+/+ mice appeared to produce NO in a manner inversely proportional to the serum content of NO2- and NO3- of the mice from which the cells were obtained; no such correlation existed in TGF-beta1+/- or TGF-beta1-/- mice. Treatment of RPE cells or macrophages from both TGF-beta1+/+ and TGF-beta1-/- mice with exogenous TGF-beta1 decreased both iNOS protein and NO production. These findings demonstrate a novel role of endogenous TGF-beta1 in coupling systemic NO production to the production of NO by macrophages, and demonstrate that endogenous and exogenous TGF-beta1 can act differently to suppress NO production.

TGF-beta1 null mutation leads to CD154 upregulated expression in affected tissues.

The TGF-beta1(-/-) mouse is a murine model for systemic autoimmune disease. The aim of this study is to elucidate the immunological mechanism that leads to multifocal tissue inflammation and autoantibody production in TGF-beta1(-/-) mice. Heart, lung, liver, and salivary gland from TGF-beta1(-/-) were assessed for CD154 expression by RT-PCR and immunohistochemistry. Compared to wild-type littermates, CD154 expression was elevated in all tissues studied. Furthermore, IL-12 mRNA was expressed in the salivary gland and heart of TGF-beta1(-/-) mice and not in wild-type littermates. This suggests that the CD154 pathway is activated in these tissues. This shows that TGF-beta1 regulates CD154 expression leading to spontaneous IL-12 production and autoimmunity.