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

IgA monoclonal gammopathies are accompanied by higher total TGF-β1 levels than IgG or IgM monoclonal gammopathies

The progression of monoclonal gammopathies is affected by a range of factors, including the microenvironment surrounding plasma cells. It is recognized that TGF-β1 plays a distinct role in stimulating IgA production. Hence, this study aims to investigate whether individuals with serum IgA monoclonal immunoglobulins (paraproteins) exhibit elevated total TGF-β1 levels compared to those with IgG or IgM paraproteins. To achieve this goal, individuals with a positive laboratory finding of monoclonal gammopathy were segregated according to the paraprotein class as well as according to the type of the light chain. Total TGF-β1 levels were assessed in blood serum samples containing IgG (n = 50), IgA (n = 46), and IgM (n = 31) paraproteins. Elevated level of TGF-β1 was confirmed in sera with IgA paraproteins (median 25.8 ng/mL; interquartile range IQR: 19.0-33.7) compared to those having IgG (median: 18.2 ng/mL; IQR: 14.3-22.1; p < 0.001) or IgM paraproteins (21.5 ng/mL; IQR: 15.0-27.4; p = 0.043). Also, a higher TGF-β1 level was detected in sera with IgMλ than those with IgMκ paraproteins (p = 0.043). This research affirms the role of TGF-β1 in the pathophysiology of IgA monoclonal gammopathies and the potential switch towards the IgA isotype, known for a less favourable prognosis.

Extracellular matrix and its therapeutic potential for cancer treatment

The extracellular matrix (ECM) is one of the major components of tumors that plays multiple crucial roles, including mechanical support, modulation of the microenvironment, and a source of signaling molecules. The quantity and cross-linking status of ECM components are major factors determining tissue stiffness. During tumorigenesis, the interplay between cancer cells and the tumor microenvironment (TME) often results in the stiffness of the ECM, leading to aberrant mechanotransduction and further malignant transformation. Therefore, a comprehensive understanding of ECM dysregulation in the TME would contribute to the discovery of promising therapeutic targets for cancer treatment. Herein, we summarized the knowledge concerning the following: (1) major ECM constituents and their functions in both normal and malignant conditions; (2) the interplay between cancer cells and the ECM in the TME; (3) key receptors for mechanotransduction and their alteration during carcinogenesis; and (4) the current therapeutic strategies targeting aberrant ECM for cancer treatment.

p190-B RhoGAP and intracellular cytokine signals balance hematopoietic stem and progenitor cell self-renewal and differentiation

The mechanisms regulating hematopoietic stem and progenitor cell (HSPC) fate choices remain ill-defined. Here, we show that a signalling network of p190-B RhoGAP-ROS-TGF-β-p38^MAPK balances HSPC self-renewal and differentiation. Upon transplantation, HSPCs express high amounts of bioactive TGF-β1 protein, which is associated with high levels of p38^MAPK activity and loss of HSC self-renewal in vivo. Elevated levels of bioactive TGF-β1 are associated with asymmetric fate choice in vitro in single HSPCs via p38MAPK activity and this is correlated with the asymmetric distribution of activated p38MAPK. In contrast, loss of p190-B, a RhoGTPase inhibitor, normalizes TGF-β levels and p38MAPK activity in HSPCs and is correlated with increased HSC self-renewal in vivo. Loss of p190-B also promotes symmetric retention of multi-lineage capacity in single HSPC myeloid cell cultures, further suggesting a link between p190-B-RhoGAP and non-canonical TGF-β signalling in HSPC differentiation. Thus, intracellular cytokine signalling may serve as ‘fate determinants' used by HSPCs to modulate their activity.

The success of hematopoietic stem cell (HSC) transplantation relies on understanding what regulates the fate decision to self-renew. Here, the authors show using both in vitro assays and in vivo transplantation that loss of the RhoGAP p190-B enhances self-renewal by inhibiting TGFβ/p38 signalling.

Targeting the Transforming Growth Factor-β Signaling in Cancer Therapy

TGF-β pathway is being extensively evaluated as a potential therapeutic target. The transforming growth factor-β (TGF-β) signaling pathway has the dual role in both tumor suppression and tumor promotion. To design cancer therapeutics successfully, it is important to understand TGF-β related functional contexts. This review discusses the molecular mechanism of the TGF-β pathway and describes the different ways of tumor suppression and promotion by TGF-β. In the last part of the review, the data on targeting TGF-β pathway for cancer treatment is assessed. The TGF-β inhibitors in pre-clinical studies, and Phase I and II clinical trials are updated.

The role of bone morphogenetic proteins in myeloma cell survival

Multiple myeloma is characterized by slowly growing clones of malignant plasma cells in the bone marrow. The malignant state is frequently accompanied by osteolytic bone disease due to a disturbed balance between osteoblasts and osteoclasts. Bone morphogenetic proteins (BMPs) are present in the bone marrow and are important for several aspects of myeloma pathogenesis including growth and survival of tumor cells, bone homeostasis, and anemia. Among cancer cells, myeloma cells are particularly sensitive to growth inhibition and apoptosis induced by BMPs and therefore represent good models to study BMP receptor usage and signaling. Our review highlights and discusses the current knowledge on BMP signaling in myeloma.

Fibroblast growth factor receptor 3 interacts with and activates TGFβ-activated kinase 1 tyrosine phosphorylation and NFκB signaling in multiple myeloma and bladder cancer

Cancer is a major public health problem worldwide. In the United States alone, 1 in 4 deaths is due to cancer and for 2013 a total of 1,660,290 new cancer cases and 580,350 cancer-related deaths are projected. Comprehensive profiling of multiple cancer genomes has revealed a highly complex genetic landscape in which a large number of altered genes, varying from tumor to tumor, impact core biological pathways and processes. This has implications for therapeutic targeting of signaling networks in the development of treatments for specific cancers. The NFκB transcription factor is constitutively active in a number of hematologic and solid tumors, and many signaling pathways implicated in cancer are likely connected to NFκB activation. A critical mediator of NFκB activity is TGFβ-activated kinase 1 (TAK1). Here, we identify TAK1 as a novel interacting protein and target of fibroblast growth factor receptor 3 (FGFR3) tyrosine kinase activity. We further demonstrate that activating mutations in FGFR3 associated with both multiple myeloma and bladder cancer can modulate expression of genes that regulate NFκB signaling, and promote both NFκB transcriptional activity and cell adhesion in a manner dependent on TAK1 expression in both cancer cell types. Our findings suggest TAK1 as a potential therapeutic target for FGFR3-associated cancers, and other malignancies in which TAK1 contributes to constitutive NFκB activation.

Targeting TGF-β signaling in cancer

INTRODUCTION

The transforming growth factor-β (TGF-β) signaling pathway has a pivotal role in tumor suppression and yet, paradoxically, in tumor promotion. Functional context dependent insights into the TGF-β pathway are crucial in developing TGF-β-based therapeutics for cancer.

AREAS COVERED

This review discusses the molecular mechanism of the TGF-β pathway and describes the different ways of tumor suppression by TGF-β. It is then explained how tumors can evade these effects and how TGF-β contributes to further growing and spreading of some of the tumors. In the last part of the review, the data on targeting TGF-β pathway for cancer treatment is assessed. This review focuses on anti-TGF-β based treatment and other options targeting activated pathways in tumors where the TGF-β tumor suppressor pathway is lost. Pre-clinical as well up to date results of the most recent clinical trials are given.

EXPERT OPINION

Targeting the TGF-β pathway can be a promising direction in cancer treatment. However, several challenges still exist, the most important are differentiating between the carcinogenic effects of TGF-β and its other physiological roles, and delineating the tumor suppressive versus the tumor promoting roles of TGF-β in each specific tumor. Future studies are needed in order to find safer and more effective TGF-β-based drugs.

TGF-β - an excellent servant but a bad master

The transforming growth factor (TGF-β) family of growth factors controls an immense number of cellular responses and figures prominently in development and homeostasis of most human tissues. Work over the past decades has revealed significant insight into the TGF-β signal transduction network, such as activation of serine/threonine receptors through ligand binding, activation of SMAD proteins through phosphorylation, regulation of target genes expression in association with DNA-binding partners and regulation of SMAD activity and degradation. Disruption of the TGF-β pathway has been implicated in many human diseases, including solid and hematopoietic tumors. As a potent inhibitor of cell proliferation, TGF-β acts as a tumor suppressor; however in tumor cells, TGF-β looses anti-proliferative response and become an oncogenic factor. This article reviews current understanding of TGF-β signaling and different mechanisms that lead to its impairment in various solid tumors and hematological malignancies.

The type III transforming growth factor-β receptor inhibits proliferation, migration, and adhesion in human myeloma cells

Transforming growth factor-β (TGF-β) plays an important role in regulating hematopoiesis, inhibiting proliferation while stimulating differentiation when appropriate. We previously demonstrated that the type III TGF-β receptor (TβRIII, or betaglycan) serves as a novel suppressor of cancer progression in epithelial tumors; however, its role in hematologic malignancies is unknown. Here we demonstrate that TβRIII protein expression is decreased or lost in the majority of human multiple myeloma specimens. Functionally, restoring TβRIII expression in myeloma cells significantly inhibited cell growth, proliferation, and motility, largely independent of its ligand presentation role. In a reciprocal fashion, shRNA-mediated silencing of endogenous TβRIII expression enhanced cell growth, proliferation, and motility. Although apoptosis was not affected, TβRIII inhibited proliferation through induction of the cyclin-dependent kinase inhibitors p21 and p27. TβRIII further regulated myeloma cell adhesion, increasing homotypic myeloma cell adhesion while decreasing myeloma heterotropic adhesion to bone marrow stromal cells. Mechanistically, live cell imaging of myeloma and stroma cell cocultures revealed that TβRIII-mediated inhibition of heterotropic adhesion was associated with decreased duration of myeloma/bone marrow stromal cell interaction. These results suggest that loss of TβRIII expression during multiple myeloma progression contributes to disease progression through its functional effects on increased cell growth, proliferation, motility, and adhesion.

Transient inhibition of transforming growth factor-beta1 in human diabetic CD34+ cells enhances vascular reparative functions

OBJECTIVE

Peripheral blood CD34(+) cells from diabetic patients demonstrate reduced vascular reparative function due to decreased proliferation and diminished migratory prowess, largely resulting from decreased nitric oxide (NO) bioavailability. The level of TGF-beta, a key factor that modulates stem cell quiescence, is increased in the serum of type 2 diabetic patients. We asked whether transient TGF-beta1 inhibition in CD34(+) cells would improve their reparative ability.

RESEARCH DESIGN AND METHODS

To inhibit TGF-beta1 protein expression, CD34(+) cells were treated ex vivo with antisense phosphorodiamidate morpholino oligomers (TGF-beta1-PMOs) and analyzed for cell surface CXCR4 expression, cell survival in the absence of added growth factors, SDF-1-induced migration, NO release, and in vivo retinal vascular reparative ability.

RESULTS

TGF-beta1-PMO treatment of diabetic CD34(+) cells resulted in increased expression of CXCR4, enhanced survival in the absence of growth factors, and increased migration and NO release as compared with cells treated with control PMO. Using a retinal ischemia reperfusion injury model in mice, we observed that recruitment of diabetic CD34(+) cells to injured acellular retinal capillaries was greater after TGF-beta1-PMO treatment compared with control PMO-treated cells.

CONCLUSIONS

Transient inhibition of TGF-beta1 may represent a promising therapeutic strategy for restoring the reparative capacity of dysfunctional diabetic CD34(+) cells.

Targeting the transforming growth factor-beta signalling pathway in metastatic cancer

Transforming growth factor (TGF)-beta signalling plays a dichotomous role in tumour progression, acting as a tumour suppressor early and as a pro-metastatic pathway in late-stages. There is accumulating evidence that advanced-stage tumours produce excessive levels of TGF-beta, which acts to promote tumour growth, invasion and colonisation of secondary organs. In light of the pro-metastasis function, many strategies are currently being explored to antagonise the TGF-beta pathway as a treatment for metastatic cancers. Strategies such as using large molecule ligand traps, reducing the translational efficiency of TGF-beta ligands using antisense technology, and antagonising TGF-beta receptor I/II kinase function using small molecule inhibitors are the most prominent methods being explored today. Administration of anti-TGF-beta therapies alone, or in combination with immunosuppressive or cytotoxic therapies, has yielded promising results in the preclinical and clinical settings. Despite these successes, the temporal- and context-dependent roles of TGF-beta signalling in cancer has made it challenging to define patient subgroups that are most likely to respond, and the therapeutic regimens that will be most effective in the clinic. Novel mouse models and diagnostic tools are being developed today to circumvent these issues, which may potentially expedite anti-TGF-beta drug development and clinical application.

Activation of TGF-beta within cultured hepatocytes and in liver injury leads to intracrine signaling with expression of connective tissue growth factor

Recently, synthesis and secretion of connective tissue growth factor (CTGF)/CYR61/CTGF/NOV-family member 2 (CCN2) in cultures of hepatocytes were shown, which are sensitively up-regulated by exogenous TGF-beta. In this study TGF-beta-dependent CTGF/CCN2 expression in hepatocytes cultured under completely TGF-beta-free conditions was analysed by Western-blots, metabolic labelling, and CTGF-reporter gene assays. In alkaline phosphatase monoclonal anti-alkaline phosphatase complex (APAAP)-staining of cultured hepatocytes it was demonstrated that latent TGF-beta within the hepatocytes becomes rapidly detectable during culture indicating an intracellular demasking of the mature TGF-beta antigen. Subsequent signaling to theCTGF/CCN2 promoter occurs via p-Smad2, whereas p-Smad3 does not seem to be involved. Cycloheximide did not abolish the rapid immunocytochemical appearance of mature TGF-beta, but calpain inhibitors partially suppressed intracellular TGF-beta activation and subsequently CTGF up-regulation. Calpain treatment had the reverse effect. None of the inhibitors of extracellular TGF-beta signalling was effective in the reduction of spontaneous CTGF synthesis, but intracellularly acting Alk 4-/Alk 5-specific inhibitor SB-431542 was able to diminish CTGF expression. The assumption that latent intracellular TGF-beta is activated by calpains during culture-induced stress or injurious conditions in the liver in vivo was further validated by a direct effect of calpains on the activation of recombinant latent TGF-beta. In conclusion, these data are the first to suggest the possibility of intracrine TGF-beta signalling due to calpain-dependent intracellular proteolytic activation leading to transcriptional activation of CTGF/CCN2 as a TGF-beta-sensitive reporter gene. This mechanism might be deleterious for keeping long-term hepatocyte cultures due to TGF-beta-induced apoptosis and, further, might be of relevance for induction of apoptosis or epithelial-mesenchymal transition of hepatocytes in injured liver.

Transforming Growth Factor-βSignaling in Normal and Malignant Hematopoiesis

Transforming growth factor-beta (TGF-beta) is an important physiologic regulator of cell growth and differentiation. TGF-beta has been shown to inhibit the proliferation of quiescent hematopoietic stem cells and stimulate the differentiation of late progenitors to erythroid and myeloid cells. Insensitivity to TGF-beta is implicated in the pathogenesis of many myeloid and lymphoid neoplasms. Loss of extracellular TGF receptors and disruption of intracellular TGF-beta signaling by oncogenes is seen in a variety of malignant and premalignant states. TGF-beta can also affect tumor growth and survival by influencing the secretion of other growth factors and manipulation of the tumor microenvironment. Recent development of small molecule inhibitors of TGF-beta receptors and other signaling intermediaries may allow us to modulate TGF signaling for future therapeutic interventions in cancer.

Inhibition of TGF-β2 with AP 12009 in Recurrent Malignant Gliomas: From Preclinical to Phase I/II Studies

Transforming growth factor-beta2 (TGF-beta2) is known to suppress the immune response to cancer cells and plays a pivotal role in tumor progression by regulating key mechanisms including proliferation, metastasis, and angiogenesis. For targeted protein suppression the TGF-beta2-specific antisense oligodeoxynucleotide AP 12009 was developed. In vitro experiments have been performed to prove specificity and efficacy of the TGF-beta2 inhibitor AP 12009 employing patient-derived malignant glioma cells as well as peripheral blood mononuclear cells (PBMCs) from patients. Clinically, the antisense compound AP 12009 was assessed in three Phase I/II-studies for the treatment of patients with recurrent or refractory malignant (high-grade) glioma WHO grade III or IV. Although the study was not primarily designed as an efficacy evaluation, prolonged survival compared to literature data and response data were observed, which are very rarely seen in this tumor indication. Two patients experienced long-lasting complete tumor remissions. These results implicate targeted TGF-beta2-suppression using AP 12009 as a promising novel approach for malignant gliomas and other highly aggressive, TGF-beta-2-overexpressing tumors.

The synthetic triterpenoid CDDO-Imidazolide suppresses STAT phosphorylation and induces apoptosis in myeloma and lung cancer cells

PURPOSE

Excessive activity of the transcription factors known as signal transducers and activators of transcription (STAT) contributes to the development and progression of malignancy in many organs. It is, therefore, important to develop new drugs to control the STATs, particularly their phosphorylation state, which is required for their transcriptional activity.

EXPERIMENTAL DESIGN

Myeloma and lung cancer cells were treated with the new synthetic triterpenoid CDDO-Imidazolide, and STAT phosphorylation and apoptosis were evaluated by immunoblotting and fluorescence-activated cell sorting analysis.

RESULTS

We now report that CDDO-Imidazolide, previously shown to be a potent agent for control of inflammation, cell proliferation, and apoptosis, rapidly (within 30-60 minutes) and potently (at nanomolar levels) suppresses either constitutive or interleukin-6-induced STAT3 and STAT5 phosphorylation in human myeloma and lung cancer cells. Furthermore, in these cells, CDDO-Imidazolide also up-regulates critical inhibitors of STATs, such as suppressor of cytokine signaling-1 and SH2-containing phosphatase-1 (a tyrosine phosphatase). Moreover, gene array studies reported here show that CDDO-Imidazolide potently regulates the transcription of important genes that are targets of the STATs.

CONCLUSIONS

Our new data thus show that CDDO-Imidazolide is a potent suppressor of STAT signaling and provide a further mechanistic basis for future clinical use of this agent to control inflammation or cell proliferation.

Role of transforming growth factor-beta in hematologic malignancies

The transforming growth factor-beta (TGF-beta) signaling pathway is an essential regulator of cellular processes, including proliferation, differentiation, migration, and cell survival. During hematopoiesis, the TGF-beta signaling pathway is a potent negative regulator of proliferation while stimulating differentiation and apoptosis when appropriate. In hematologic malignancies, including leukemias, myeloproliferative disorders, lymphomas, and multiple myeloma, resistance to these homeostatic effects of TGF-beta develops. Mechanisms for this resistance include mutation or deletion of members of the TGF-beta signaling pathway and disruption of the pathway by oncoproteins. These alterations define a tumor suppressor role for the TGF-beta pathway in human hematologic malignancies. On the other hand, elevated levels of TGF-beta can promote myelofibrosis and the pathogenesis of some hematologic malignancies through their effects on the stroma and immune system. Advances in the TGF-beta signaling field should enable targeting of the TGF-beta signaling pathway for the treatment of hematologic malignancies.

Death receptor-mediated apoptosis in human malignant glioma cells: modulation by the CD40/CD40L system

CD40, a TNF-R-related cell surface receptor, is shown here to be expressed by glioma cells in vitro and in vivo. Glioma cell lines expressing low levels of CD40 at the cell surface resist cytotoxic effects of CD40L. CD40 gene transfer sensitizes glioma cells to CD40L. Inhibition of protein synthesis potentiates cell death which involves CD40 clustering and caspases 8 and 3 processing. CD40-transfected LN-18 cells acquire resistance to CD95L. In contrast, subtoxic concentrations of CD40L strongly sensitize these cells for TNF-alpha-induced apoptosis. Bispecific CD40xCD95 antibodies specifically kill glioma cells, disclosing the property of endogenous CD40 to facilitate death signalling.

A genetic screen to identify latent transforming growth factor beta activators

The mechanisms by which latent transforming growth factor beta (TGFbeta) is converted to the active cytokine are largely unknown. Here we present a genetic screen that combines retroviral mutagenesis and cDNA expression cloning to reveal proteins involved in the extracellular regulation of latent TGFbeta activation. The screen employs a cell line engineered to express green fluorescent protein (GFP) in response to TGFbeta. The cells produce their own latent TGFbeta. Therefore, after transduction with a retroviral cDNA library that contains an insert for an activator of latent TGFbeta, cells expressing the activator are GFP-bright. These cells are enriched by fluorescence-activated cell sorting and grown as individual clones. The isolated clones are cocultured with a second TGFbeta reporter cell line that produces luciferase in response to TGFbeta. Cells that have acquired the ability to activate latent TGFbeta induce luciferase expression in the absence but not in the presence of neutralizing antibodies to TGFbeta. The activator expressed by the positive clones can be identified by retrieval of the retrovirus cDNA insert.

Immature B cell malignancies synthesize VEGF, VEGFR-1 (Flt-1) and VEGFR-2 (KDR)

Expression of VEGF and VEGFR support a role for angiogenic pathways in the pathogenesis of some hematological malignances. Our goal was to determine if expression of these angiogenic molecules also extend to childhood precursor B cell acute lymphoblastic leukemia (pre-B ALL). We now show that transcripts of VEGF, and its receptors VEGFR-1 and VEGFR-2 are concomitantly expressed in both ALL cell lines and primary pre-B ALL. Western blot and ELISA consistently detected VEGF protein in the supernatants of the cell lines. Similarly, VEGFR-1 and VEGFR-2 proteins are also detectable by FACS analysis. Interestingly, the expression of the receptors in immature B cells is limited to the intra-cytoplasmic compartment and may suggest either internalization of the receptors or a block in trafficking of the receptor to the surface.

Expression of TGF-beta type II receptor antisense RNA impairs TGF-beta signaling in vitro and promotes mammary gland differentiation in vivo

In order to clarify the role of TGF-beta in mammary development and tumorigenesis, we investigated the efficacy of full- or partial-length TbetaRII antisense RNA specifically to reduce TbetaRII levels in both in vitro and in vivo model systems. Here we show that the expression of TbetaRII antisense RNA in vitro reduced TbetaRII cell surface expression and inhibited the antiproliferative and transcriptional responses to exogenous TGF-beta. Expression of full-length TbetaRII antisense RNA in a transgenic mouse model under control of the mouse mammary tumor virus promotor resulted in precocious lobuloalveolar development of the mammary gland, a phenotype that resembles that of early pregnancy. These data demonstrate that TbetaRII plays a critical role in maintaining the nondifferentiated character of virgin mammary gland epithelium.

Neoplastic development in plasma cells

An increasing number of model systems of plasma cell tumor (PCT) formation have been and are being developed. Discussed here are six models in mice and multiple myeloma (MM) in humans. Each model illustrates a unique set of biological factors. There are two general types of model systems: those that depend upon naturally arising mutagenic changes (pristane-induced PCTs, 5TMM, and MM) and those that are associated with oncogenes (Emu-v-abl), growth factors [interleukin-6 (IL-6)], and anti-apoptotic factors (Bcl-xL/Bcl-2). PCTs develop in several special tissue microenvironments that provide essential cytokines (IL-6) and cell-cell interactions. In mice, the activation and deregulation of c-myc by chromosomal translocations is a major feature in many of the models. This mechanism is much less a factor in MM and the 5T model in mice. Genetically determined susceptibility is involved in many of the mouse models, but only a few genes have been implicated thus far.

Minimal effects on immune parameters following chronic anti-TGF-beta monoclonal antibody administration to normal mice

Mice genetically deficient in TGF-beta1 or TGF-beta signaling capacity in T or B cells demonstrate profound immune dysregulation, as evidenced by increased lymph node size, expression of markers of memory/activation on T cells, inflammation in a variety of tissues and development of autoantibodies. However, this constant and complete lack of TGF-beta1 or TGF-betaR signaling may not reflect effects of TGF-beta neutralization using antibodies in mature animals. Thus, the present studies were designed to determine if administration of an anti-TGF-beta monoclonal antibody (neutralizes TGF-beta1, 2 and 3) to mature, normal mice results in evidence of immune dysregulation or immune-mediated pathology. An initial study examined daily administration of 0.25, 0.75 and 2.5 mg/kg of anti-TGF-beta to mice for three weeks, achieving blood levels of as high as 9 mg/ml. Comprehensive hematological and histopathological evaluation showed no evidence of pathology. A second study was designed to extend the antibody treatment period and further examine the functional status of the immune system. Mice were injected with 1 mg/mouse (approximately 50 mg/kg) of anti-TGF-beta (1D11) three times per week achieving circulating blood levels of 1-2 mg/ml. Many parameters of immune status were assessed, including natural killer (NK) cell activity, lymphocyte proliferative responses, phagocytic activity, phenotypic assessment of leukocyte subsets, and serum measurements of proinflammatory cytokines, autoantibodies and immunoglobulin isotypes. In addition, histopathological assessment of heart, lungs, liver, kidney, salivary glands, skin, spleen and lymph nodes was also performed. Very few of the multiple immune parameters examined showed detectable changes in anti-TGF-beta-treated mice. Changes that were observed were primarily restricted to the spleen and included increased spleen cell recoveries, increased percentages of macrophages, decreased percentages of NK cells, decreased phagocytic activity, decreased proliferative responses to mitogens and slight increases in T and B cells displaying an activated phenotype. Many of these same parameters examined in the lymph nodes were not altered by the anti-TGF-beta treatment. The thymus was decreased in size, but altered only slightly in one population of developing T cells. Most of the changes observed were modest and returned to control levels after discontinuation of treatments. The only serological finding was an increase in IgA levels in anti-TGF-beta-treated mice, but not in any other isotype. Finally, there was no evidence of increased inflammation in any of the peripheral tissues examined in the anti-TGF-beta-treated mice. In conclusion, although there were changes in some of the immunological parameters examined in these studies, they were few and typically reversed following discontinuation of treatment. The modest nature of the changes observed in these studies is particularly evident when compared to published data of those same parameters examined in mice genetically deficient in TGF-beta1 or mice having TGF-beta unresponsive T or B cells. Thus, there does not appear to be any significant immune dysregulation detectable after long-term antibody-mediated neutralization of TGF-beta in normal mice.

Transforming growth factor-beta 1 mutations in Camurati-Engelmann disease lead to increased signaling by altering either activation or secretion of the mutant protein

Transforming growth factor-beta1 (TGF-beta1) is secreted as a latent precursor, consisting of a homodimer of the latency-associated peptide and the mature peptide. TGFbeta-1 can only exert its many functions after going from this latent to an active state, in which the binding site of the mature peptide for its receptor is no longer shielded by the latency-associated peptide. We and others reported that mutations in TGFB1 cause Camurati-Engelmann disease, a rare bone disorder. Until now, seven mutations have been published. In this study, we investigate the effect of the LLL12-13ins, Y81H, R218C, H222D, and C225R mutations on the functioning of TGF-beta1 in vitro. A luciferase reporter assay specific for TGF-beta-induced transcriptional response with wild type and mutant TGF-beta1 constructs showed a positive effect of all mutations on TGF-beta1 activity. By way of enzyme-linked immunosorbent assay, we found that in the R218C, H222D, and C225R mutant constructs, this effect is caused by an increase in active TGF-beta1 in the medium of transfected cells. The LLL12-13ins and Y81H mutations on the contrary have a profound effect on secretion; a decreased amount of TGF-beta1 is secreted, but the increased luciferase activity shows that the intracellular accumulation of (aberrant) TGF-beta1 can initiate an enhanced transcriptional response, suggesting the existence of an alternative signaling pathway. Our data indicate that the mutations in the signal peptide and latency-associated peptide facilitate TGF-beta1 signaling, thus causing Camurati-Engelmann disease.