Autocrine and exogenous transforming growth factor beta control cell cycle inhibition through pathways with different sensitivity

Targeting alternative splicing of fibronectin in human renal proximal tubule epithelial cells with antisense oligonucleotides to reduce EDA+ fibronectin production and block an autocrine loop that drives renal fibrosis

TGFβ1 is a powerful regulator of fibrosis; secreted in a latent form, it becomes active after release from the latent complex. During tissue fibrosis, the EDA + isoform of cellular fibronectin is overexpressed. In pulmonary fibrosis it has been proposed that the fibronectin splice variant including an EDA domain (FN EDA+) activates latent TGFβ. Our work investigates the potential of blocking the 'splicing in' of EDA with antisense oligonucleotides to inhibit TGFβ1-induced EDA + fibronectin and to prevent the cascade of events initiated by TGFβ1 in human renal proximal tubule cells (PTEC). Human primary PTEC were treated with TGFβ1 for 48 h, medium removed and the cells transfected with RNase H-independent antisense oligonucleotides (ASO) designed to block EDA exon inclusion (ASO5). The efficacy of ASO to block EDA exon inclusion was assessed by EDA + fibronectin RNA and protein expression; the expression of TGFβ, αSMA (α smooth muscle actin), MMP2 (matrix metalloproteinse-2), MMP9 (matrix metalloproteinse-9), Collagen I, K Cadherin and connexin 43 was analysed. Targeting antisense oligonucleotides designed to block EDA exon inclusion in fibronectin pre mRNA were effective in reducing the amount of TGFβ1 -induced cellular EDA + fibronectin RNA and secreted EDA + fibronectin protein (assessed by western immunoblotting and immunocytochemistry) in human proximal tubule cells in an in vitro cell culture model. The effect was selective for EDA + exon with no effect on EDB + fibronectin RNA and total fibronectin mRNA. Exogenous TGFβ1 induced endogenous TGFβ, αSMA, MMP2, MMP9 and Col I mRNA. TGFβ1 treatment for 48h reduced the expression of K-Cadherin and increased the expression of connexin-43. These TGFβ1-induced pro-fibrotic changes were attenuated by ASO5 treatment. 48 h after the removal of exogenous TGFβ, further increases in αSMA, MMP2, MMP9 was observed; ASO5 significantly inhibited this subsequent increase. ASO5 treatment also significantly inhibited ability of the cell culture medium harvested at the end of the experiment (96h) to stimulate SMAD3 reporter cells. The role of endogenous TGFβ1 was confirmed by the use of a TGFβ receptor inhibitor. Our results demonstrate a critical role of FN EDA+ in a cycle of TGFβ driven pro-fibrotic responses in human PTEC and blocking its production with ASO technology offers a potential therapy to interrupt this vicious circle and hence limit the progression of renal fibrosis.

Pirfenidone suppressed triple-negative breast cancer metastasis by inhibiting the activity of the TGF-β/SMAD pathway

Among breast cancer patients, metastases are the leading cause of death. Despite decades of effort, little progress has been made to improve the treatment of breast cancer metastases, especially triple-negative breast cancer (TNBC). The extracellular matrix plays an important role in tumour growth and metastasis by causing its deposition, remodelling, and signalling. As we know, the process of fibrosis results in excessive amounts of extracellular matrix being deposited within the cells. So, it will be interesting to study if the use of anti-fibrotic drugs in combination with conventional chemotherapy drugs can produce synergistic antitumor effects. In this study, we assessed the efficacy of Pirfenidone (PFD), an FDA-approved medication for the treatment of idiopathic pulmonary fibrosis, on TNBC cells as well as its anti-tumour effects in xenograft tumour model. PFD inhibited in a dose-dependent manner breast cancer cell proliferation, migration, and invasion, while promoted their apoptosis in vitro. PFD also suppressed TGF-β-induced activation of Smad signalling pathway and expression level of EMT-inducing transcription factors (e.g. SNAI2, TWIST1, ZEB1) as well as the mesenchymal genes such as VIMENTIN and N-Cadherin. On the contrary, the expression level of epithelial marker gene E-Cadherin was up-regulated in the presence of PFD. In vivo, PFD alone exerted a milder but significant anti-tumour effect than the chemotherapy drug nanoparticle albumin-bound paclitaxel (nab-PTX) did in the breast cancer xenograft mouse model. Interestingly, PFD synergistically boosted the cancer-killing effect of nab-PTX. Furthermore, Our data suggest that PFD suppressed breast cancer metastasis by inhibiting the activity of the TGFβ/SMAD pathway.

The role of erythrocytes and erythroid progenitor cells in tumors

In the current research context of precision treatment of malignant tumors, the advantages of immunotherapy are unmatched by conventional antitumor therapy, which can prolong progression-free survival and overall survival. The search for new targets and novel combination therapies can improve the efficacy of immunotherapy and reduce adverse effects. Since current research targets for immunotherapy mainly focus on lymphocytes, little research has been done on erythrocytes. Nucleated erythroid precursor stem cells have been discovered to play an essential role in tumor progression. Researchers are exploring new targets and therapeutic approaches for immunotherapy from the perspective of erythroid progenitor cells (EPCs). Recent studies have shown that different subtypes of EPCs have specific surface markers and distinct biological roles in tumor immunity. CD45⁺ EPCs are potent myeloid-derived suppressor cell-like immunosuppressants that reduce the patient's antitumor immune response. CD45^- EPCs promote tumor invasion and metastasis by secreting artemin. A specific type of EPC also promotes angiogenesis and provides radiation protection. Therefore, EPCs may be involved in tumor growth, infiltration, and metastasis. It may also be an important cause of anti-angiogenesis and immunotherapy resistance. This review summarizes recent research advances in erythropoiesis, EPC features, and their impacts and processes on tumors.

TGFβ1 Secreted by Cancer-Associated Fibroblasts as an Inductor of Resistance to Photodynamic Therapy in Squamous Cell Carcinoma Cells

Simple Summary

Photodynamic therapy (PDT) is used for the treatment of in situ cutaneous squamous cell carcinoma (cSCC), the second most common form of skin cancer, as well as for its precancerous form, actinic keratosis. However, relapses after the treatment can occur. Transforming growth factor β1 (TGFβ1) produced by cancer-associated fibroblasts (CAFs) in the tumor microenvironment has been pointed as a key player in the development of cSCC resistance to other therapies, such as chemotherapy. Here, we demonstrate that TGFβ1 produced by CAFs isolated from patients with cSCC can drive resistance to PDT in SCC cells. This finding opens up novel possibilities for strategy optimization in the field of cSCC resistance to PDT and highlights CAF-derived TGFβ1 as a potential target to improve the efficacy of PDT.

Abstract

As an important component of tumor microenvironment, cancer-associated fibroblasts (CAFs) have lately gained prominence owing to their crucial role in the resistance to therapies. Photodynamic therapy (PDT) stands out as a successful therapeutic strategy to treat cutaneous squamous cell carcinoma. In this study, we demonstrate that the transforming growth factor β1 (TGFβ1) cytokine secreted by CAFs isolated from patients with SCC can drive resistance to PDT in epithelial SCC cells. To this end, CAFs obtained from patients with in situ cSCC were firstly characterized based on the expression levels of paramount markers as well as the levels of TGFβ1 secreted to the extracellular environment. On a step forward, two established human cSCC cell lines (A431 and SCC13) were pre-treated with conditioned medium obtained from the selected CAF cultures. The CAF-derived conditioned medium effectively induced resistance to PDT in A431 cells through a reduction in the cell proliferation rate. This resistance effect was recapitulated by treating with recombinant TGFβ1 and abolished by using the SB525334 TGFβ1 receptor inhibitor, providing robust evidence of the role of TGFβ1 secreted by CAFs in the development of resistance to PDT in this cell line. Conversely, higher levels of recombinant TGFβ1 were needed to reduce cell proliferation in SCC13 cells, and no induction of resistance to PDT was observed in this cell line in response to CAF-derived conditioned medium. Interestingly, we probed that the comparatively higher intrinsic resistance to PDT of SCC13 cells was mediated by the elevated levels of TGFβ1 secreted by this cell line. Our results point at this feature as a promising biomarker to predict both the suitability of PDT and the chances to optimize the treatment by targeting CAF-derived TGFβ1 in the road to a more personalized treatment of particular cSCC tumors.

Autocrine TGFβ1 Opposes Exogenous TGFβ1-Induced Cell Migration and Growth Arrest through Sustainment of a Feed-Forward Loop Involving MEK-ERK Signaling

Simple Summary

Transforming growth factor (TGF) β signaling is intimately involved in nearly all aspects of tumor development and is known for its role as both a tumor suppressor in benign tissues and a tumor promoter in advanced cancers. This dual role is also reflected by cancer cell-produced TGFβ that eventually acts on the same cell(s) in an autocrine fashion. Recently, we observed that endogenous TGFB1 can inhibit rather than stimulate cell motility in cell lines with high autocrine TGFβ production. The unexpected anti-migratory role prompted us to evaluate how autocrine TGFβ1 impacts the cells’ migratory and proliferative responses to exogenous (recombinant human) TGFβ. Surprisingly, endogenous TGFB1 opposed the migratory and growth-inhibitory responses induced by exogenous TGFβ1 by driving a self-perpetuating feedforward loop involving MEK-ERK signaling. Our observation has implications for the use of TGFβ signaling inhibitors in cancer therapy.

Abstract

Autocrine transforming growth factor β (aTGFβ) has been implicated in the regulation of cell invasion and growth of several malignant cancers such as pancreatic ductal adenocarcinoma (PDAC) or triple-negative breast cancer (TNBC). Recently, we observed that endogenous TGFB1 can inhibit rather than stimulate cell motility in cell lines with high aTGFβ production and mutant KRAS, i.e., Panc1 (PDAC) and MDA-MB-231 (TNBC). The unexpected anti-migratory role prompted us to evaluate if aTGFβ1 may be able to antagonize the action of exogenous (recombinant human) TGFβ (rhTGFβ), a well-known promoter of cell motility and growth arrest in these cells. Surprisingly, RNA interference-mediated knockdown of the endogenous TGFB1 sensitized genes involved in EMT and cell motility (i.e., SNAI1) to up-regulation by rhTGFβ1, which was associated with a more pronounced migratory response following rhTGFβ1 treatment. Ectopic expression of TGFB1 decreased both basal and rhTGFβ1-induced migratory activities in MDA-MB-231 cells but had the opposite effect in Panc1 cells. Moreover, silencing TGFB1 reduced basal proliferation and enhanced growth inhibition by rhTGFβ1 and induction of cyclin-dependent kinase inhibitor, p21^WAF1. Finally, we show that aTGFβ1 promotes MEK-ERK signaling and vice versa to form a self-perpetuating feedforward loop that is sensitive to SB431542, an inhibitor of the TGFβ type I receptor, ALK5. Together, these data suggest that in transformed cells an ALK5-MEK-ERK-aTGFβ1 pathway opposes the promigratory and growth-arresting function of rhTGFβ1. This observation has profound translational implications for TGFβ signaling in cancer.

Autocrine TGF-β in Cancer: Review of the Literature and Caveats in Experimental Analysis

Autocrine signaling is defined as the production and secretion of an extracellular mediator by a cell followed by the binding of that mediator to receptors on the same cell to initiate signaling. Autocrine stimulation often operates in autocrine loops, a type of interaction, in which a cell produces a mediator, for which it has receptors, that upon activation promotes expression of the same mediator, allowing the cell to repeatedly autostimulate itself (positive feedback) or balance its expression via regulation of a second factor that provides negative feedback. Autocrine signaling loops with positive or negative feedback are an important feature in cancer, where they enable context-dependent cell signaling in the regulation of growth, survival, and cell motility. A growth factor that is intimately involved in tumor development and progression and often produced by the cancer cells in an autocrine manner is transforming growth factor-β (TGF-β). This review surveys the many observations of autocrine TGF-β signaling in tumor biology, including data from cell culture and animal models as well as from patients. We also provide the reader with a critical discussion on the various experimental approaches employed to identify and prove the involvement of autocrine TGF-β in a given cellular response.

Pien Tze Huang inhibits liver metastasis by targeting TGF-β signaling in an orthotopic model of colorectal cancer

Metastasis is the leading cause of cancer-related mortality in almost all types of cancers, including colorectal cancer (CRC). Epithelial-mesenchymal transition (EMT) is a critical process during the metastatic cascade. This process may be a potential target for the diagnosis and treatment of CRC. Pien Tze Huang (PZH), a well-known traditional Chinese formula, has been demonstrated to be clinically effective in treating various types of human malignancies, including CRC. Our published data suggest that PZH can induce apoptosis, as well as inhibit cell proliferation and tumor angiogenesis, thus suppressing CRC growth in vitro and in vivo. We evaluated the therapeutic efficacy of PZH against CRC metastasis using a CRC liver metastasis mouse model to further explore the mechanisms underlying the antitumor action of PZH. MTT, migration, and Matrigel invasion assays were used to assess the effect of PZH on cell viability, migration and invasion. We then established an orthotopic liver metastasis model of colon cancer using microsurgical techniques. Mice were intragastrically administered 234 mg/kg/day dose of either PZH or saline for 14 days. The body and tumor weights of the mice were measured after they were sacrificed. Moreover, we examined the effect of PZH inhibition on liver metastasis. Finally, EMT-related proteins and the TGF-β signaling pathway were assessed using immunohistochemical staining (IHS). The present data revealed that PZH significantly inhibited the migration and invasion of CT-26 cells in a dose-dependent manner, which affirmed the inhibitory effect of PZH on CRC cell metastasis. No significant change was observed between the in vivo primary tumor growth and body weight. However, the control group had five cases of liver metastasis (5/6), whereas one case was found in the PZH group (1/6). Thus, PZH exhibited therapeutic efficacy against CRC metastasis without apparent toxicity. The inhibitory effect of PZH on EMT resulted in an increase in E-cadherin expression, as well as a decrease in N-cadherin expression. In addition, PZH significantly inhibited TGF-β, as well as the phosphorylation of Smad2/3 and Smad4 in the tumor tissues, indicating its suppressive action on TGF-β signaling. These molecular effects ultimately resulted in the inhibition of cancer cell EMT and tumor metastasis.

Enteric glial cells and their role in the intestinal epithelial barrier

The intestinal epithelium constitutes a physical and functional barrier between the external environment and the host organism. It is formed by a continuous monolayer of intestinal epithelial cells maintained together by intercellular junctional complex, limiting access of pathogens, toxins and xenobiotics to host tissues. Once this barrier integrity is disrupted, inflammatory disorders and tissue injury are initiated and perpetuated. Beneath the intestinal epithelial cells lies a population of astrocyte-like cells that are known as enteric glia. The morphological characteristics and expression markers of these enteric glia cells were identical to the astrocytes of the central nervous system. In the past few years, enteric glia have been demonstrated to have a trophic and supporting relationship with intestinal epithelial cells. Enteric glia lesions and/or functional defects can be involved in the barrier dysfunction. Besides, factors secreted by enteric glia are important for the regulation of gut barrier function. Moreover, enteric glia have an important impact on epithelial cell transcriptome and induce a shift in epithelial cell phenotype towards increased cell adhesion and cell differentiation. Enteric glia can also preserve epithelial barrier against intestinal bacteria insult. In this review, we will describe the current body of evidence supporting functional roles of enteric glia on intestinal barrier.

TGF-Beta suppresses VEGFA-mediated angiogenesis in colon cancer metastasis

The FET cell line, derived from an early stage colon carcinoma, is non-tumorigenic in athymic nude mice. Engineered FET cells that express TGF-α (FETα) display constitutively active EGFR/ErbB signaling. These cells readily formed xenograft tumors in athymic nude mice. Importantly, FETα cells retained their response to TGF-beta-mediated growth inhibition, and, like the parental FET cells, expression of a dominant negative TGF-beta type II receptor (DNRII) in FETα cells (FETα/DNRII) abrogated responsiveness to TGF-beta-induced growth inhibition and apoptosis under stress conditions in vitro and increased metastatic potential in an orthotopic model in vivo, which indicates metastasis suppressor activity of TGF-beta signaling in this model. Cancer angiogenesis is widely regarded as a key attribute for tumor formation and progression. Here we show that TGF-beta signaling inhibits expression of vascular endothelial growth factor A (VEGFA) and that loss of autocrine TGF-beta in FETα/DNRII cells resulted in increased expression of VEGFA. Regulation of VEGFA expression by TGF-beta is not at the transcriptional level but at the post-transcriptional level. Our results indicate that TGF-beta decreases VEGFA protein stability through ubiquitination and degradation in a PKA- and Smad3-dependent and Smad2-independent pathway. Immunohistochemical (IHC) analyses of orthotopic tumors showed significantly reduced TGF-beta signaling, increased CD31 and VEGFA staining in tumors of FETα/DNRII cells as compared to those of vector control cells. These results indicate that inhibition of TGF-beta signaling increases VEGFA expression and angiogenesis, which could potentially contribute to enhanced metastasis of those cells in vivo. IHC studies performed on human colon adenocarcinoma specimens showed that TGF-beta signaling is inversely correlated with VEGFA expression, indicating that TGF-beta-mediated suppression of VEGFA expression exists in colon cancer patients.

Cloning and expression analysis of the transforming growth factor-beta receptors type 1 and 2 in the rainbow trout Oncorhynchus mykiss

Transforming growth factor-β (TGF-β) binding to the TGF-β type I (TGFBR1) and type II (TGFBR2) receptors delivers a plethora of cell-type specific effects. Moreover, the responses to TGF-β are tuned by regulatory mechanisms at the receptor level itself. To further elucidate TGF-β family signal transduction in teleosts, we therefore cloned the first complete set of a putative TGF-β receptor complex in salmonids. Rainbow trout TGFBR1 and TGFBR2 are transmembrane proteins with a serine/threonine kinase domain and are highly conserved within vertebrates. High expression levels in muscle and brain indicate regulation of the TGF-β system in muscular and nervous systems. Lipopolysaccharide (LPS) induced expression of both receptor chains in RTgill cells while bacterial and viral mimics modulated the two receptors inversely in head kidney (HK) macrophages. In addition, T cell mitogens lowered receptor levels in HK leukocytes. These data provide the first insights into TGF-β type I and II receptor modulation during immune responses in teleost fish.

Histone deacetylase inhibitor belinostat represses survivin expression through reactivation of transforming growth factor beta (TGFbeta) receptor II leading to cancer cell death

Survivin is a cancer-associated gene that functions to promote cell survival, cell division, and angiogenesis and is a marker of poor prognosis. Histone deacetylase inhibitors induce apoptosis and re-expression of epigenetically silenced tumor suppressor genes in cancer cells. In association with increased expression of the tumor suppressor gene transforming growth factor β receptor II (TGFβRII) induced by the histone deacetylase inhibitor belinostat, we observed repressed survivin expression. We investigated the molecular mechanisms involved in survivin down-regulation by belinostat downstream of reactivation of TGFβ signaling. We identified two mechanisms. At early time points, survivin protein half-life was decreased with its proteasomal degradation. We observed that belinostat activated protein kinase A at early time points in a TGFβ signaling-dependent mechanism. After longer times (48 h), survivin mRNA was also decreased by belinostat. We made the novel observation that belinostat mediated cell death through the TGFβ/protein kinase A signaling pathway. Induction of TGFβRII with concomitant survivin repression may represent a significant mechanism in the anticancer effects of this drug. Therefore, patient populations exhibiting high survivin expression with epigenetically silenced TGFβRII might potentially benefit from the use of this histone deacetylase inhibitor.

Differential roles of Smad2 and Smad3 in the regulation of TGF-β1-mediated growth inhibition and cell migration in pancreatic ductal adenocarcinoma cells: control by Rac1

BACKGROUND

Progression of pancreatic ductal adenocarcinoma (PDAC) is largely the result of genetic and/or epigenetic alterations in the transforming growth factor-beta (TGF-β)/Smad signalling pathway, eventually resulting in loss of TGF-β-mediated growth arrest and an increase in cellular migration, invasion, and metastasis. These cellular responses to TGF-β are mediated solely or partially through the canonical Smad signalling pathway which commences with activation of receptor-regulated Smads (R-Smads) Smad2 and Smad3 by the TGF-β type I receptor. However, little is known on the relative contribution of each R-Smad, the possible existence of functional antagonism, or the crosstalk with other signalling pathways in the control of TGF-β1-induced growth inhibition and cell migration. Using genetic and pharmacologic approaches we have inhibited in PDAC cells endogenous Smad2 and Smad3, as well as a potential regulator, the small GTPase Rac1, and have analysed the consequences for TGF-β1-mediated growth inhibition and cell migration (chemokinesis).

RESULTS

SiRNA-mediated silencing of Smad3 in the TGF-β responsive PDAC cell line PANC-1 reduced TGF-β1-induced growth inhibition but increased the migratory response, while silencing of Smad2 enhanced growth inhibition but decreased chemokinesis. Interestingly, siRNA-mediated silencing of the small GTPase Rac1, or ectopic expression of a dominant-negative Rac1 mutant largely mimicked the effect of Smad2 silencing on both TGF-β1-induced growth inhibition, via upregulation of the cdk inhibitor p21WAF1, and cell migration. Inhibition of Rac1 activation reduced both TGF-β1-induction of a Smad2-specific transcriptional reporter and Smad2 C-terminal phosphorylation in PDAC cells while Smad3-specific transcriptional activity and Smad3 C-terminal phosphorylation appeared increased. Disruption of autocrine TGF-β signalling in PANC-1 cells rendered cells less susceptible to the growth-suppressive effect of Rac1 inhibition, suggesting that the decrease in "basal" proliferation upon Rac1 inhibition was caused by potentiation of autocrine TGF-β growth inhibition.

CONCLUSIONS

In malignant cells with a functional TGF-β signalling pathway Rac1 antagonizes the TGF-β1 growth inhibitory response and enhances cell migration by antagonistically regulating Smad2 and Smad3 activation. This study reveals that Rac1 is prooncogenic in that it can alter TGF-β signalling at the R-Smad level from a tumour-suppressive towards a tumour-promoting outcome. Hence, Rac1 might represent a viable target for therapeutic intervention to inhibit PDAC progression.

Suppression of latent transforming growth factor (TGF)-beta1 restores growth inhibitory TGF-beta signaling through microRNAs

Cancer cells secreting excess latent TGF-β are often resistant to TGF-β induced growth inhibition. We observed that RNAi against TGF-β1 led to apoptotic death in such cell lines with features that were, paradoxically, reminiscent of TGF-β signaling activity and that included transiently enhanced SMAD2 and AKT phosphorylation. A comprehensive search in Hela cells for potential microRNA drivers of this mechanism revealed that RNAi against TGF-β1 led to induction of pro-apoptotic miR-34a and to a globally decreased oncomir expression. The reduced levels of the oncomirs miR-18a and miR-24 accounted for the observed derepression of two TGF-β1 processing factors, thrombospondin-1, and furin, respectively. Our data suggest a novel mechanism in which latent TGF-β1, thrombospondin 1, and furin form a microRNA-mediated regulatory feedback loop. For cells with high levels of latent TGF-β, this provides a potentially widespread mechanism of escape from TGF-β-mediated growth arrest at the earliest point in the signaling pathway, TGF-β processing.

TGF-beta receptor levels regulate the specificity of signaling pathway activation and biological effects of TGF-beta

TGF-beta is a pluripotent cytokine that mediates its effects through a receptor composed of TGF-beta receptor type II (TGFBR2) and type I (TGFBR1). The TGF-beta receptor can regulate Smad and nonSmad signaling pathways, which then ultimately dictate TGF-beta's biological effects. We postulated that control of the level of TGFBR2 is a mechanism for regulating the specificity of TGF-beta signaling pathway activation and TGF-beta's biological effects. We used a precisely regulatable TGFBR2 expression system to assess the effects of TGFBR2 expression levels on signaling and TGF-beta mediated apoptosis. We found Smad signaling and MAPK-ERK signaling activation levels correlate directly with TGFBR2 expression levels. Furthermore, p21 levels and TGF-beta induced apoptosis appear to depend on relatively high TGFBR2 expression and on the activation of the MAPK-ERK and Smad pathways. Thus, control of TGFBR2 expression and the differential activation of TGF-beta signaling pathways appears to be a mechanism for regulating the specificity of the biological effects of TGF-beta.

Transforming growth factor beta1 signaling via interaction with cell surface Hyal-2 and recruitment of WWOX/WOX1

Transforming growth factor beta (TGF-beta) initiates multiple signal pathways and activates many downstream kinases. Here, we determined that TGF-beta1 bound cell surface hyaluronidase Hyal-2 on microvilli in type II TGF-beta receptor-deficient HCT116 cells, as determined by immunoelectron microscopy. This binding resulted in recruitment of proapoptotic WOX1 (also named WWOX or FOR) and formation of Hyal-2.WOX1 complexes for relocation to the nuclei. TGF-beta1 strengthened the binding of the catalytic domain of Hyal-2 with the N-terminal Tyr-33-phosphorylated WW domain of WOX1, as determined by time lapse fluorescence resonance energy transfer analysis in live cells, co-immunoprecipitation, and yeast two-hybrid domain/domain mapping. In promoter activation assay, ectopic WOX1 or Hyal-2 alone increased the promoter activity driven by Smad. In combination, WOX1 and Hyal-2 dramatically enhanced the promoter activation (8-9-fold increases), which subsequently led to cell death (>95% of promoter-activated cells). TGF-beta1 supports L929 fibroblast growth. In contrast, transiently overexpressed WOX1 and Hyal-2 sensitized L929 to TGF-beta1-induced apoptosis. Together, TGF-beta1 invokes a novel signaling by engaging cell surface Hyal-2 and recruiting WOX1 for regulating the activation of Smad-driven promoter, thereby controlling cell growth and death.

Mutational inactivation of TGFBR2 in microsatellite unstable colon cancer arises from the cooperation of genomic instability and the clonal outgrowth of transforming growth factor beta resistant cells

The mutational inactivation of transforming growth factor beta receptor type II (TGFBR2) occurs in approximately 30% of colon cancers and promotes the formation of colon cancer by inhibiting the tumor suppressor activity of the TGFB signaling pathway. TGFBR2 mutations occur in >90% of microsatellite unstable (MSI) colon cancers and affect a polyadenine tract in exon 3 of TGFBR2, called BAT-RII, which is vulnerable to mutation in the setting of DNA mismatch repair (MMR) system deficiency. In light of the vulnerable nature of the BAT-RII tract in the setting of MMR inactivation and the favorable effects of TGFBR2 inactivation in colon cancer, analysis of TGFBR2 inactivation provides an opportunity to assess the roles of genomic instability vs. clonal selection in cells acquiring TGFBR2 BAT-RII tract mutations in MSI colon cancer formation. The contribution of genomic instability and/or clonal evolution to the mutational inactivation of TGBFR2 in MSI colon cancers has not been studied in a systematic way that would allow a determination of the relative contribution of these two mechanisms in the formation of MSI colon cancer. It has not been demonstrated whether the BAT-RII tract mutations are strictly a consequence of the BAT-RII region being hypermutable in the setting of MMR deficiency or if the mutations are rather a consequence of clonal selection pressure against the TGFB receptor. Through the use of defined cell line systems, we show that both genomic instability and clonal selection of TGFB resistant cells contribute to the high frequency of TGFBR2 mutations in MSI colon cancer.

Transforming growth factor beta induces apoptosis through repressing the phosphoinositide 3-kinase/AKT/survivin pathway in colon cancer cells

FET cells, derived from an early-stage colon carcinoma, are nontumorigenic in athymic mice. Stable transfection of a dominant-negative transforming growth factor beta (TGFbeta) type II receptor (DNRII) into FET cells that express autocrine TGFbeta shows loss of TGFbeta signaling and increased tumorigenicity in vivo indicating tumor suppressor activity of TGFbeta signaling in this model. The ability of tumorigenic cells to withstand growth factor and nutrient deprivation stress (GFDS) is widely regarded as a key attribute for tumor formation and progression. We hypothesized that increased tumorigenicity of FET/DNRII cells was due to loss of participation of autocrine TGFbeta in a "fail-safe" mechanism to generate cell death in response to this stress. Here, we document that loss of autocrine TGFbeta in FET/DNRII cells resulted in greater endogenous cell survival in response to GFDS due to activation of the phosphoinositide 3-kinase (PI3K)/Akt/survivin pathway. Treatment of FET DNRII cells with a PI3K inhibitor (LY294002) inhibited Akt phosphorylation and reduced survivin expression resulting in increased apoptosis in FET/DNRII cells. We also show that exogenous TGFbeta increased apoptosis in FET cells through repression of the PI3K/Akt/survivin pathway during GFDS. These results indicate that the PI3K/Akt/survivin pathway is blocked by TGFbeta signaling and that loss of autocrine TGFbeta leads to increased cell survival during GFDS through the novel linkage of TGFbeta-mediated repression of survivin expression. Inhibition of survivin function by dominant-negative approaches showed that this inhibitor of apoptosis family member is critical to cell survival in the FET/DNRII cells, thus indicating the importance of this target for TGFbeta-mediated apoptosis.

Microsatellite unstable colorectal cancer cell lines with truncating TGFβRII mutations remain sensitive to endogenous TGFβ

Disruptions to the TGFbeta signalling pathway have been implicated in most human adenocarcinomas. As cancers progress, many acquire resistance to the growth-suppressing properties of TGFbeta while retaining sensitivity to its tumour-promoting effects. Microsatellite unstable colorectal cancers (MSI-H CRCs) possess truncating mutations in the type II TGFbeta receptor (TGFbetaRII) gene that have been assumed to render these tumours insensitive to TGFbeta. However, numerous reports of TGFbetaRII bypass exist and this study was thus undertaken in order to clarify the true extent of TGFbeta sensitivity in MSI-H CRCs. Using stimulation with exogenous TGFbeta, we demonstrated that, while MSI-H CRCs are capable of binding soluble TGFbeta, two out of three cell lines examined remain refractory to its signalling effects. In contrast, use of a specific inhibitor of the type I TGFbeta receptor (TGFbetaRI) revealed that all remain sensitive to signalling by endogenously produced TGFbeta. Specifically, autocrine signalling via TGFbetaRI mediates constitutive activation of Smad2 as well as repression of Erk signalling. Real-time PCR confirmed that these effects are sufficient to affect the expression level of various TGFbeta-modulated genes. An invasion assay revealed that autocrine TGFbetaRI signalling also promotes the invasion capacity of MSI-H CRCs to an extent similar to that seen in their non-MSI-H counterparts. Independent TGFbetaRI signalling, however, has no effect on the rate of proliferation of MSI-H CRC cells. Together, these results demonstrate that MSI-H CRC cell lines are not completely refractory to TGFbeta, despite lacking functional TGFbetaRII. In addition to clarifying the true consequences of natural TGFbetaRII loss and the independent function of TGFbetaRI, our results highlight the selective nature of TGFbeta resistance developed by cancers.

Th3 Cells in Peripheral Tolerance. I. Induction of Foxp3-Positive Regulatory T Cells by Th3 Cells Derived from TGF-β T Cell-Transgenic Mice

TGF-beta has been shown to be critical in the generation of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs). Because Th3 cells produce large amounts of TGF-beta, we asked whether induction of Th3 cells in the periphery was a mechanism by which CD4(+)CD25(+) Tregs were induced in the peripheral immune compartment. To address this issue, we generated a TGF-beta1-transgenic (Tg) mouse in which TGF-beta is linked to the IL-2 promoter and T cells transiently overexpress TGF-beta upon TCR stimulation but produce little or no IL-2, IL-4, IL-10, IL-13, or IFN-gamma. Naive TGF-beta-Tg mice are phenotypically normal with comparable numbers of lymphocytes and thymic-derived Tregs. We found that repeated antigenic stimulation of pathogenic myelin oligodendrocyte glycoprotein (MOG)-specific CD4(+)CD25(-) T cells from TGF-beta Tg mice crossed to MOG TCR-Tg mice induced Foxp3 expression in both CD25(+) and CD25(-) populations. Both CD25 subsets were anergic and had potent suppressive properties in vitro and in vivo. Furthermore, adoptive transfer of these induced regulatory CD25(+/-) T cells suppressed experimental autoimmune encephalomyelitis when administrated before disease induction or during ongoing experimental autoimmune encephalomyelitis. The suppressive effect of TGF-beta on T cell responses was due to the induction of Tregs and not to the direct inhibition of cell proliferation. The differentiation of Th3 cells in vitro was TGF-beta dependent as anti-TGF-beta abrogated their development. Thus, Ag-specific TGF-beta-producing Th3 cells play a crucial role in inducing and maintaining peripheral tolerance by driving the differentiation of Ag-specific Foxp3(+) regulatory cells in the periphery.

Proliferation and Cdk4 expression in microsatellite unstable colon cancers with TGFBR2 mutations

Approximately 15% of human colon cancers have microsatellite instability (MSI) and carry frameshift mutations in a polyadenine tract (BAT-RII) in the type II transforming growth factor beta (TGF-beta) receptor (TGFBR2), a required component of the TGF-beta receptor. The BAT-RII mutations in MSI colon cancers make the tumors resistant to the effects of TGF-beta. In cultured epithelial cells, TGF-beta can inhibit cell proliferation and induce apoptosis, and in vitro it can regulate the expression of a variety of cyclins, cyclin-dependent kinases (cdks) and cdk inhibitors. These effects are context- and tissue type-dependent, raising questions about which of these in vitro effects of TGF-beta signaling inactivation contribute to the formation of primary colon cancer. Thus, this study sought to determine the pathogenetically relevant effects of TGFBR2 inactivation in primary MSI colon cancers with mutant BAT-RII. Colon cancers with mutant BAT-RII were found to have increased proliferation compared to cancers with wild-type BAT-RII. Assessment of cdk4, cyclin D1 and p27(kip1) expression revealed that only cdk4 expression was increased in the cancers with mutant BAT-RII. In order to determine if TGFBR2 inactivation was the cause of these changes, TGFBR2 was reconstituted in an MSI colon cancer cell line, resulting in decreased proliferation and decreased cdk4 expression and kinase activity. These results suggest that TGFBR2 mutations in primary colon cancers may be responsible for the increased proliferation and cdk4 expression in these tumors and provide evidence that deregulation of cdk4 is a pathogenic in vivo consequence of TGFBR2 inactivation in primary colon cancer.