Expression of Smad4 and Smad7 in human thyroid follicular carcinoma cell lines

Osteopontin Expression in Thyroid Cancer: Deciphering EMT-Related Molecular Mechanisms

Thyroid cancer is the most common tumor arising from the endocrine system and generally presents good prognosis. However, its aggressive subtypes are related to therapeutic resistance and early metastasis. Epithelial–mesenchymal transition (EMT) and its reverse process, the mesenchymal–epithelial transition (MET), are key events mediating cancer progression, including in thyroid cancer. The matricellular protein osteopontin (OPN) has been reported as a master regulator of EMT in many tumor types. Although high OPN expression has been described and associated with important aspects of thyroid cancer progression, there is no clear evidence regarding OPN as a regulator of EMT in thyroid cancer. Thus, taking together the known roles of OPN in the modulation of EMT in cancer and the information reporting the expression of OPN in thyroid tumor progression, this review aims at summarizing and discussing data related to EMT in thyroid cancer and its putative relation to the roles of OPN in the development of thyroid cancer. These data provide new insights into the molecular mechanisms by which OPN could potentially modulate EMT in thyroid tumors, generating evidence for future studies that may contribute to new therapeutic, prognostic and/or diagnostic tools.

Clinical development of therapies targeting TGFβ: current knowledge and future perspectives

Transforming growth factor beta (TGFβ) is a pleiotropic cytokine that plays a key role in both physiologic and pathologic conditions, including cancer. Importantly, TGFβ can exhibit both tumor-suppressive and oncogenic functions. In normal epithelial cells TGFβ acts as an antiproliferative and differentiating factor, whereas in advanced tumors TGFβ can act as an oncogenic factor by creating an immune-suppressive tumor microenvironment, and inducing cancer cell proliferation, angiogenesis, invasion, tumor progression, and metastatic spread. A wealth of preclinical findings have demonstrated that targeting TGFβ is a promising means of exerting antitumor activity. Based on this rationale, several classes of TGFβ inhibitors have been developed and tested in clinical trials, namely, monoclonal, neutralizing, and bifunctional antibodies; antisense oligonucleotides; TGFβ-related vaccines; and receptor kinase inhibitors. It is now >15 years since the first clinical trial testing an anti-TGFβ agent was engaged. Despite the promising preclinical studies, translation of the basic understanding of the TGFβ oncogenic response into the clinical setting has been slow and challenging. Here, we review the conclusions and status of all the completed and ongoing clinical trials that test compounds that inhibit the TGFβ pathway, and discuss the challenges that have arisen during their clinical development. With none of the TGFβ inhibitors evaluated in clinical trials approved for cancer therapy, clinical development for TGFβ blockade therapy is primarily oriented toward TGFβ inhibitor combinations. Immune checkpoint inhibitors are considered candidates, albeit with efficacy anticipated to be restricted to specific populations. In this context, we describe current efforts in the search for biomarkers for selecting the appropriate cancer patients who are likely to benefit from anti-TGFβ therapies. The knowledge accumulated during the last 15 years of clinical research in the context of the TGFβ pathway is crucial to design better, innovative, and more successful trials.

Metastatic propagation of thyroid cancer; organ tropism and major modulators

Thyroid cancer, as the most prevalent endocrine malignancy, comprises nearly 1% of all cancers in the world. The metastatic propagation of thyroid cancer is under the control of a number of modulating processes and factors such as signaling pathways and their components, cell division regulators, metabolic reprogramming factors, extracellular matrix remodelers, epithelial to mesenchymal transition modulators, epigenetic mechanisms, hypoxia and cytokines. Identifying the exact molecular mechanisms of these dysregulated processes could help to discover the key targets for therapeutic purposes and utilizing them as diagnostic, prognostic and predictors of the clinical course of patients. In this review article, we describe different aspects of thyroid cancer metastasis by focusing on defective genes and pathways involved in its metastatic spread.

Epithelial-to-mesenchymal transition in thyroid cancer: a comprehensive review

The Metastatic progression of solid tumors, such as thyroid cancer is a complex process which involves various factors. Current understanding on the role of epithelial-mesenchymal transition (EMT) in thyroid carcinomas suggests that EMT is implicated in the progression from follicular thyroid cancer (FTC) and papillary thyroid cancer (PTC) to poorly differentiated thyroid carcinoma (PDTC) and anaplastic thyroid cancer (ATC). According to the literature, the initiation of the EMT program in thyroid epithelial cells elevates the number of stem cells, which contribute to recurrent and metastatic diseases. The EMT process is orchestrated by a complex network of transcription factors, growth factors, signaling cascades, epigenetic modulations, and the tumor milieu. These factors have been shown to be dysregulated in thyroid carcinomas. Therefore, molecular interferences restoring the expression of tumor suppressors, or thwarting overexpressed oncogenes is a hopeful therapeutic method to improve the treatment of progressive diseases. In this review, we summarize the recent findings on EMT in thyroid cancer focusing on the main role-players and regulators of this process in thyroid tumors.

SMAD7 is a novel independent predictor of survival in patients with cutaneous melanoma

Overexpression of SMAD7-a hallmark inhibitor of transforming growth factor β (TGFβ) signaling-has been documented and related with adverse prognosis in a number of epithelial malignancies, suggesting that it may be responsible for resistance to TGFβ-induced growth arrest of cancer cells. The involvement of SMAD7 in development and progression of malignant melanoma is unclear, and its expression has not been characterized so far at the protein level in clinical melanoma tissue samples. We evaluated SMAD7 expression in 205 skin melanoma primary tumors by immunohistochemistry and correlated the findings with clinicopathological profiles of patients. Melanocytic SMAD7 was evidenced in 204 cases, and the expression pattern was predominantly nuclear. High expression of SMAD7 was positively associated with several features of tumor aggressiveness, for example, presence of ulceration (P < 0.001), higher tumor thickness (P < 0.001), and mitotic rate (P < 0.001), but not presence of regional or distant metastases. Moreover, high SMAD7 expression independently predicted unfavorable outcome: melanoma-specific survival (hazard ratio = 3.16, P < 0.001) and recurrence-free survival (hazard ratio = 2.88, P < 0.001). Taken together, our results underline the importance of TGFβ signaling in cancer and define SMAD7 as a marker of aggressive tumor behavior and adverse clinical outcomes in melanoma patients.

Immunohistochemical Expression of TGF-Β1, SMAD4, SMAD7, TGFβRII and CD68-Positive TAM Densities in Papillary Thyroid Cancer

BACKGROUND:

Papillary thyroid carcinoma (PTC) accounts for 80% of the thyroid malignancies that are characterised by slow growth and an excellent prognosis. Over-expression of SMAD4 protein restores TGF-β signalling, determines a strong increase in anti-proliferative effect and reduces invasive potential of tumour cells expressing it.

AIM:

The study aimed to analyse the immunohistochemical expression of TGF-β1 and its downstream phosphorylated SMAD4, element and of the inhibitory SMAD7 PTC variants and their association with the localisation of TAMs within the tumour microenvironment.

METHODS:

For this retrospective study we investigated 69 patients immunohistochemistry with antibodies against TGF-β, TGF – β-RII, SMAD4, SMAD7, CD68+ macrophages.

RESULTS:

Patients with low infiltration with CD68+ cells in tumour stroma has significantly shorter survival (median of 129.267 months) compared to those with high CD68+ cells infiltration (p = 0.034). From the analysis of CD68+ cells in tumour border and tumour stroma correlated with expression of TGF-β1 / SMAD proteins, we observed that the positive expression of TGF-β1 in tumour cytoplasm, significantly correlated with increased number of CD68+ cells in tumour border (X² = 5,945; p = 0.015).

CONCLUSION:

TGF-β enhances motility and stimulates recruitment of monocytes, macrophages and other immune cells while directly inhibiting their anti-tumour effector functions.

TGF-β Family Signaling in Tumor Suppression and Cancer Progression

Transforming growth factor-β (TGF-β) induces a pleiotropic pathway that is modulated by the cellular context and its integration with other signaling pathways. In cancer, the pleiotropic reaction to TGF-β leads to a diverse and varied set of gene responses that range from cytostatic and apoptotic tumor-suppressive ones in early stage tumors, to proliferative, invasive, angiogenic, and oncogenic ones in advanced cancer. Here, we review the knowledge accumulated about the molecular mechanisms involved in the dual response to TGF-β in cancer, and how tumor cells evolve to evade the tumor-suppressive responses of this signaling pathway and then hijack the signal, converting it into an oncogenic factor. Only through the detailed study of this complexity can the suitability of the TGF-β pathway as a therapeutic target against cancer be evaluated.

MicroRNAs in thyroid development, function and tumorigenesis

MicroRNAs (miRNAs) are important post-transcriptional regulators of gene expression that modulate the vast majority of cellular processes. During development, the correct timing and expression of miRNAs in the tissue differentiation is essential for organogenesis and functionality. In thyroid gland, DICER and miRNAs are necessary for accurately establishing thyroid follicles and hormone synthesis. Moreover, DICER1 mutations and miRNA deregulation observed in human goiter influence thyroid tumorigenesis. The thyroid malignant transformation by MAPK oncogenes is accompanied by global miRNA changes, with a marked reduction of "tumor-suppressor" miRNAs and activation of oncogenic miRNAs. Loss of thyroid cell differentiation/function, and consequently iodine trapping impairment, is an important clinical characteristic of radioiodine-refractory thyroid cancer. However, few studies have addressed the direct role of miRNAs in thyroid gland physiology. Here, we focus on what we have learned in the thyroid follicular cell differentiation and function as revealed by cell and animal models and miRNA modulation in thyroid tumorigenesis.

TGF-β signaling in liver and gastrointestinal cancers

Transforming Growth Factor-β (TGF-β) plays crucial and complex roles in liver and gastrointestinal cancers. These include a multitude of distinct functions, such as maintaining stem cell homeostasis, promoting fibrosis, immune modulating, as a tumor suppressor and paradoxically, as a tumor progressor. However, key mechanisms for the switches responsible for these distinct actions are poorly understood, and remain a challenge. The Cancer Genome Atlas (TCGA) analyses and genetically engineered mouse models now provide an integrated approach to dissect these multifaceted and context-dependent driving roles of the TGF-β pathway. In this review, we will discuss the molecular mechanisms of TGF-β signaling, focusing on colorectal, gastric, pancreatic, and liver cancers. Novel drugs targeting the TGF-β pathway have been developed over the last decade, and some have been proven effective in clinical trials. A better understanding of the TGF-β pathway may improve our ability to target it, thus providing more tools to the armamentarium against these deadly cancers.

SMAD4 gene promoter mutations in patients with thyroid tumors

As a key component of the transforming growth factor beta (TGFB) pathway, which regulates the expression of thyroid-specific genes, tumor suppressor SMAD4 is crucial for thyroid development and function. Aberrant expression of SMAD4 in thyroid tumor tissue was reported and mutations affecting the coding region have been detected, but a potential role of mutations in SMAD4 gene regulatory regions remains unexplored. The aim of this study was to analyze SMAD4 gene promoters in thyroid tumors. A total of 76 thyroidectomy specimens were studied, including 42 malignant and 34 benign tumors. The presence of mutations in four SMAD4 gene promoters was analyzed in thyroid tumor tissue and peripheral blood by PCR and DNA sequencing. The expression and intracellular localization of endogenous SMAD4 protein in selected tumor samples was studied by immunostaining and confocal microscopy. Of three novel variants detected, two were within promoter A (-204T/C and -5C/T) and one in promoter D (-180delA). Unlike somatic mutations previously detected in the nearby region, germline mutation -180delA in promoter D doesn't appear to affect SMAD4 expression in the thyroid tumor tissue. However, all newly detected SMAD4 promoter variants affect predicted binding sites of transcription factors involved in cell cycle regulation and should be further characterized functionally. Although not directly involved in carcinogenesis, detected variants may alter SMAD4 transcriptional regulation to some extent. Considering that dosage dependence is of great importance for the role of SMAD4 protein as a tumor suppressor, potential clinical significance of SMAD4 gene promoter mutations is worth further investigation.

miR-367 promotes epithelial-to-mesenchymal transition and invasion of pancreatic ductal adenocarcinoma cells by targeting the Smad7-TGF-β signalling pathway

BACKGROUND

Aberrant Smad7 expression contributes to the invasion and metastasis of pancreatic cancer cells. However, the potential mechanism underlying aberrant Smad7 expression in human pancreatic ductal adenocarcinoma (PDAC) remains largely unknown.

METHODS

Bioinformatic prediction programmes and luciferase reporter assay were used to identify microRNAs regulating Smad7. The association between miR-367 expression and the overall survival of PDAC patients was evaluated by Kaplan-Meier analysis. The effects of miR-367 and Smad7 on the invasion and metastasis of pancreatic cancer cells were investigated both in vitro and in vivo.

RESULTS

We found that miR-367 downregulated Smad7 expression by directly targeting its 3'-UTR in human pancreatic cancer cells. High level of miR-367 expression correlated with poor prognosis of PDAC patients. Functional studies showed that miR-367 promoted pancreatic cancer invasion in vitro and metastasis in vivo through downregulating Smad7. In addition, we showed that miR-367 promoted epithelial-to-mesenchymal transition by increasing transforming growth factor-β (TGF-β)-induced transcriptional activity.

CONCLUSIONS

The present study identified and characterised a signalling pathway, the miR-367/Smad7-TGF-β pathway, which is involved in the invasion and metastasis of pancreatic cancer cells. Our results suggest that miR-367 may be a promising therapeutic target for the treatment of human pancreatic cancer.

MTA1-mediated transcriptional repression of SMAD7 in breast cancer cell lines

Metastasis is a complex process facilitated by the action of several genes. Metastasis associated 1 (MTA1) gene is one such gene which assists the process of metastasis by regulating several molecular targets. MTA1 acts as part of a nucleosome remodelling and histone deacetylation complex, which is involved in transcriptional regulation. Expression of MTA1 has been shown to be closely correlated with aggressiveness in several types of cancers, including breast cancer. In the present study we show that MTA1 regulates SMAD7, a component of Transforming growth factor beta (TGFbeta) signalling. TGFbeta signals are transduced to the nucleus by the Smad family of proteins, which includes Smad7, an inhibitory SMAD, which acts as a negative regulator of TGFbeta. On knockdown of MTA1, SMAD7 expression increases. Treating cells with a histone deacetylase inhibitor also increases SMAD7 expression. MTA1 is recruited to SMAD7 promoter region. SMAD7 inhibits activation of SMAD2 and SMAD3 and we show that the levels of these active SMAD proteins are decreased in cells expressing shRNA against MTA1. We further show that on MTA1 knockdown, the expression of downstream targets of SMAD7 is decreased. MTA1 thus appears to regulate a key inhibitor of TGFbeta signalling, SMAD7. By regulating molecules like SMAD7 MTA1 might assist the process of tumourigenesis and metastasis.

The Dual Role of TGFβ in Human Cancer: From Tumor Suppression to Cancer Metastasis

The transforming growth factor-beta (TGFβ) superfamily encompasses widespread and evolutionarily conserved polypeptide growth factors that regulate and orchestrate growth and differentiation in all cell types and tissues. While they regulate asymmetric cell division and cell fate determination during early development and embryogenesis, TGFβ family members play a major regulatory role in hormonal and immune responses, cell growth, cell death and cell immortalization, bone formation, tissue remodeling and repair, and erythropoiesis throughout adult life. The biological and physiological functions of TGFβ, the founding member of this family, and its receptors are of central importance to human diseases, particularly cancer. By regulating cell growth, death, and immortalization, TGFβ signaling pathways exert tumor suppressor effects in normal cells and early carcinomas. Thus, it is not surprising that a high number of human tumors arise due to mutations or deletions in the genes coding for the various TGFβ signaling components. As tumors develop and progress, these protective and cytostatic effects of TGFβ are often lost. TGFβ signaling then switches to promote cancer progression, invasion, and tumor metastasis. The molecular mechanisms underlying this dual role of TGFβ in human cancer will be discussed in depth in this paper, and it will highlight the challenge and importance of developing novel therapeutic strategies specifically aimed at blocking the prometastatic arm of the TGFβ signaling pathway without affecting its tumor suppressive effects.

Alterations in the Smad pathway in human cancers

Members of the TGF-beta superfamily exhibit various biological activities, and perturbations of their signaling are linked to certain clinical disorders including cancer. The role of TGF-beta signaling as a tumor suppressor pathway is best illustrated by the presence of inactivating mutations in genes encoding TGF-beta receptors and Smads in human carcinomas. This perspective is further supported by studies of tumor development in mouse models after modulation of receptors and Smads. TGF-beta also controls processes such as cell invasion, immune regulation, and microenvironment alterations that cancer cells may exploit to their advantage for their progression. Consequently, the output of a TGF-beta response is highly situation dependent, across different tissues, and also in cancer in general. Understanding the mechanisms of TGF-beta superfamily signaling is thus important for the development of new ways to treat various types of cancer. This review focuses on recent advances in understanding the Smad dependent TGF-beta pathway as it relates to human carcinogenesis.

Gene expression profile of human thyroid cancer in relation to its mutational status

This review describes the gene expression profile changes associated with the presence of different mutations that contribute to thyroid cell carcinogenesis. The results are discussed in the context of thyroid cancer biology and of the implications for disease prognosis, while the diagnostic aspect has been omitted. For papillary thyroid cancer (PTC), the most characteristic gene expression profile is associated with the presence of BRAF mutation. BRAF-associated PTC differ profoundly from RET/PTC or RAS-associated cancers. Simultaneously, they retain many characteristic gene expression features common for all PTCs, induced by the alternative mutations activating MAPK pathway. Although the difference between papillary and follicular thyroid cancer (FTC) is significant at the gene expression profile level, surprisingly, the RAS-related signature of FTC is not well specified. PAX8/peroxisome proliferator-activated receptor γ (PPARγ) rearrangements, which occur in FTC as an alternative to the RAS mutation, are associated with specific changes in gene expression. Furthermore, the difference between well-differentiated thyroid cancers and poorly differentiated and anaplastic thyroid cancers is mainly a reflection of tumor degree of differentiation and may not be attributed to the presence of characteristic mutations.

TGF-β promotes proliferation of thyroid epithelial cells in IFN-γ(-/-) mice by down-regulation of p21 and p27 via AKT pathway

IFN-γ(-/-) NOD.H-2h4 mice develop an autoimmune disease characterized by hyperplasia and proliferation of thyroid epithelial cells (TEC H/P). Proliferating TECs produce TGF-β, and IFN-γ inhibits TEC H/P. In the present study, cultured TECs were used to directly determine the mechanisms by which these cytokines act on TECs to result in proliferation or inhibition of proliferation. With TECs from IFN-γ(-/-) NOD.H-2h4 mice or mice expressing the dominant negative TGF-β type II receptor on TECs, TGF-β was shown to promote TEC proliferation and IFN-γ was shown to inhibit TEC proliferation in vitro. TGF-β may promote TEC proliferation by down-regulating antiproliferative molecules p21 and p27, whereas IFN-γ may inhibit proliferation by up-regulating antiproliferative molecules p18 and p21 and down-regulating the pro-proliferative molecule cyclin D. Inhibition of AKT abolished the effect of TGF-β on p21 and p27, resulting in similar proliferation of TGF-β-treated and control TECs. Increased expression of proliferating cell nuclear antigen (PCNA), TGF-β, and p-AKT and decreased expression of p21 and p27 by proliferating TECs correlated with the proliferative state of TEC H/P. Taken together, the results suggest that TGF-β promotes TEC proliferation by down-regulating p21 and p27 via the AKT pathway in IFN-γ(-/-) NOD.H-2h4 mice, which may have significant implications for development of effective therapeutic strategies targeting the TGF-β and AKT pathways for treatment of hyperplasia and/or neoplasia.

MicroRNA miR-146b-5p regulates signal transduction of TGF-β by repressing SMAD4 in thyroid cancer

MicroRNAs (miRNA) are small non-coding RNAs involved in post-transcriptional gene regulation that have crucial roles in several types of tumors, including papillary thyroid carcinoma (PTC). miR-146b-5p is overexpressed in PTCs and is regarded as a relevant diagnostic marker for this type of cancer. A computational search revealed that miR-146b-5p putatively binds to the 3' untranslated region (UTR) of SMAD4, an important member of the transforming growth factor β (TGF-β) signaling pathway. The TGF-β pathway is a negative regulator of thyroid follicular cell growth, and the mechanism by which thyroid cancer cells evade its inhibitory signal remains unclear. We questioned whether the modulation of the TGF-β pathway by miR-146b-5p can contribute to thyroid tumorigenesis. Luciferase reporter assay confirmed the direct binding of miR-146b-5p on the SMAD4 3'UTR. Specific inhibition of miR-146b-5p with a locked nucleic acid-modified anti-miR-146b oligonucleotide significantly increased SMAD4 levels in the human papillary carcinoma cell lines, TPC-1 and BCPAP. Moreover, suppression of miR-146b-5p increased the cellular response to the TGF-β anti-proliferative signal, significantly decreasing the proliferation rate. The overexpression of miR-146b-5p in normal rat follicular PCCL3 cells decreased SMAD4 levels and disrupted TGF-β signal transduction. MiR-146b-5p overexpression in PCCL3 cells also significantly increased cell proliferation in the absence of thyroid-stimulating hormone and conferred resistance to TGF-β-mediated cell-cycle arrest. Additionally, the activation of thyroid most common oncogenes RET/PTC3 and BRAF in PCCL3 cells upregulated miR-146b-5p expression. Our results confirm the oncogenic role of miR-146b-5p in thyroid follicular cells and contribute to knowledge regarding the modulation of TGF-β signal transduction by miRNAs in PTCs.

EGF and TGF-β1 Effects on Thyroid Function

Normal epithelial thyroid cells in culture are inhibited by TGF-β1. Instead, transformed thyroid cell lines are frequently resistant to its growth inhibitory effect. Loss of TGF-β responsiveness could be due to a reduced expression of TGF-β receptors, as shown in transformed rat thyroid cell lines and in human thyroid tumors, or to alterations of other genes controlling TGF-β signal transduction pathway. However, in thyroid neoplasia, a complex pattern of alterations occurring during transformation and progression has been identified. Functionally, TGF-β1 acts as a tumor suppressor in the early stage of transformation or as a tumor promoter in advanced cancer. This peculiar pleiotropic behaviour of TGF-β may result from cross-talk with signalling pathways mediated by other growth factors, among which EGF-like ligands play an important role. This paper reports evidences on TGF-β1 and EGF systems in thyroid tumors and on the cross-talk between these growth factors in thyroid cancer.

Smad7: not only a regulator, but also a cross-talk mediator of TGF-β signalling

TGF-β (transforming growth factor-β) is a pleiotropic cytokine regulating diverse cellular processes. It signals through membrane-bound receptors, downstream Smad proteins and/or other signalling mediators. Smad7 has been well established to be a key negative regulator of TGF-β signalling. It antagonizes TGF-β signalling through multiple mechanisms in the cytoplasm and in the nucleus. Smad7 can be transcriptionally induced by TGF-β and other growth factors and serves as an important cross-talk mediator of the TGF-β signalling pathway with other signalling pathways. Accordingly, it plays pivotal roles in embryonic development and adult homoeostasis, and altered expression of Smad7 is often associated with human diseases, such as cancer, tissue fibrosis and inflammatory diseases.

ABI3 ectopic expression reduces in vitro and in vivo cell growth properties while inducing senescence

BACKGROUND

Mounting evidence has indicated that ABI3 (ABI family member 3) function as a tumor suppressor gene, although the molecular mechanism by which ABI3 acts remains largely unknown.

METHODS

The present study investigated ABI3 expression in a large panel of benign and malignant thyroid tumors and explored a correlation between the expression of ABI3 and its potential partner ABI3-binding protein (ABI3BP). We next explored the biological effects of ABI3 ectopic expression in thyroid and colon carcinoma cell lines, in which its expression was reduced or absent.

RESULTS

We not only observed that ABI3 expression is reduced or lost in most carcinomas but also that there is a positive correlation between ABI3 and ABI3BP expression. Ectopic expression of ABI3 was sufficient to lead to a lower transforming activity, reduced tumor in vitro growth properties, suppressed in vitro anchorage-independent growth and in vivo tumor formation while, cellular senescence increased. These responses were accompanied by the up-regulation of the cell cycle inhibitor p21 WAF1 and reduced ERK phosphorylation and E2F1 expression.

CONCLUSIONS

Our result links ABI3 to the pathogenesis and progression of some cancers and suggests that ABI3 or its pathway might have interest as therapeutic target. These results also suggest that the pathways through which ABI3 works should be further characterized.

The dynamic roles of TGF-β in cancer

The transforming growth factor-β (TGF-β) signalling pathway plays a critical and dual role in the progression of human cancer. During the early phase of tumour progression, TGF-β acts as a tumour suppressor, exemplified by deletions or mutations in the core components of the TGF-β signalling pathway. On the contrary, TGF-β also promotes processes that support tumour progression such as tumour cell invasion, dissemination, and immune evasion. Consequently, the functional outcome of the TGF-β response is strongly context-dependent including cell, tissue, and cancer type. In this review, we describe the molecular signalling pathways employed by TGF-β in cancer and how these, when perturbed, may lead to the development of cancer. Concomitantly with our increased appreciation of the molecular mechanisms that govern TGF-β signalling, the potential to therapeutically target specific oncogenic sub-arms of the TGF-β pathway increases. Indeed, clinical trials with systemic TGF-β signalling inhibitors for treatment of cancer patients have been initiated. However, considering the important role of TGF-β in cardiovascular and many other tissues, careful screening of patients is warranted to minimize unwanted on-target side effects.

Tgf-beta signaling alterations and colon cancer

Colorectal cancer is the second most common cause of cancer-related death in the United States. Twin studies suggest that 35% of all colorectal cancer cases are inherited. High-penetrance tumor susceptibility genes account for at most 3-6% of all colorectal cancer cases and the remainder of the unexplained risk is likely due to a combination of low to moderate penetrance genes. Recent genome-wide association studies have identified several SNPs near genes belonging to the transforming growth factor beta (TGF-beta) superfamily such as GREM1 and SMAD7. Together with the recent discovery that constitutively decreased TGFBR1 expression is a potent modifier of colorectal cancer risk, these findings strongly suggest that germline variants of the TGF-beta superfamily may account for a sizeable proportion of colorectal cancer cases. The TGF-beta superfamily signaling pathways mediate many different biological processes during embryonic development, and in adult organisms they play a role in tissue homeostasis. TGF-beta has a central role in inhibiting cell proliferation and also modulates processes such as cell invasion, immune regulation, and microenvironment modification. Mutations in the TGF-beta type II receptor (TGFBR2) are estimated to occur in approximately 30% of colorectal carcinomas. Mutations in SMAD4 and BMPR1A are found in patients with familial juvenile polyposis, an autosomal dominant condition associated with an increased risk of colorectal cancer. This chapter provides an overview of the genetic basis of colorectal cancer and discusses recent discoveries related to alterations in the TGF-beta pathways and their role in the development of colorectal cancer.

Regulation of TGF-beta signaling by Smad7

Transforming growth factor (TGF)-β is a pleiotropic cytokine regulating a variety of cellular processes such as cell growth, differentiation, apoptosis, migration, cell adhesion, and immune response. In the well-understood classical TGF-β signaling pathway, TGF-β activates Smad signalling via its two cell surface receptors such as TβRII and ALK5/TβRI, leading to Smad-mediated transcriptional regulation. In addition, TGF-β may also activate other signaling pathways like mitogen-activated protein kinase, PI3K, etc. The signaling of TGF-β is finely regulated at different levels. Inhibitory Smads, including Smad6 and Smad7, are key regulators of TGF-β/bone morphogenetic protein (BMP) signaling by negative feedback loops. They can form stable complexes with activated type I receptors and thereby blocking the phosphorylation of R-Smads, or recruit ubiquitin E3 ligases, such as Smurf1/2, resulting in the ubiquitination and degradation of the activated type I receptors. Besides, these inhibitory Smad proteins also inhibit TGF-β/BMP signaling in the nucleus by interacting with transcriptional repressors, such as histone deacetylases, Hoxc-8, and CtBP, or disrupting the formation of the TGF-β-induced functional Smad-DNA complexes. Smad7 is in turn regulated by different stimuli, including TGF-β, IFN-γ, TNF-α as well as ultraviolet and TPA, and mediates the crosstalk between TGF-β and other signaling pathways. Deregulation of Smad7 expression has been associated with various human diseases, such as tissue fibrosis, inflammatory disease as well as carcinogenesis. Overexpression of Smad7 has been shown to antagonize TGF-β-mediated fibrosis, carcinogenesis, and inflammation, suggesting a therapeutic potential of Smad7 to treat these diseases.

Smad4/Smad7 balance: a role of tumorigenesis in gastric cancer

Smad signaling pathway plays an important role in tumorigenesis and progression in cancer (Halder, S.K., Rachakonda, G., Deane, N.G., Datta, P.K., 2008. Smad7 induces hepatic metastasis in colorectal cancer. Br. J. Cancer 99, 957-965). The protein level of Smad is associated with growth, inhibition, and metastasis in different cancers. It is unclear if the differentiation, metastasis and apoptosis are reduced by Smad expression pattern in gastric cancer. To determine the effect of Smad on gastric cancer cells, we investigated the relationship of Smad4/Smad7 expression, and differentiation, metastasis, and apoptosis in different gastric cancer. The results show that Smad4 expression in the gastric cancer tissue was dramatically lower than that in the peritumoral tissue. A lower expression of Samd4 was significantly lower in the poorly differentiated tissue than that in the well and middle differentiated tissues (P<0.01). In contrast, Smad7 expression in gastric cancer tissues was significantly higher than that in the peritumoral tissue. Smad7 was overexpressed in poorly differentiated tissue, also higher than those in the middle, and well differentiated tissues (P<0.05). The Smad4 or Smad7 expression obviously related with the lymphatic metastasis in gastric cancer. There were 45 cases with lymphatic metastasis in all 78 patients. Smad4 expression in the cases with lymphatic metastasis was lower than the cases without metastasis (P<0.01), whereas Smad7 expression in the cases with lymphatic metastasis was much higher than the case without metastasis (P<0.01). To better understand the mechanisms involved in tumorigenesis of gastric cancer, we established SGC7901 gastric cancer cell lines transduced with Smad4 or Smad7 plasmid DNA. Apoptosis and survival of cancer cells was induced after Smad4 and Smad7 transduction. This effect is concentration and time dependent. Thus, this study provides a mechanism by which a balance between Smad4 and Smad7 in human gastric cancer is critical for differentiation, metastasis, and apoptosis of tumor cells.

Down-regulation of NR4A1 in follicular thyroid carcinomas is restored following lithium treatment

INTRODUCTION

The identification of follicular thyroid adenoma-associated transcripts will lead to a better understanding of the events involved in pathogenesis and progression of follicular tumours. Using Serial Analysis of Gene Expression, we identified five genes that are absent in a malignant follicular thyroid carcinoma (FTC) library, but expressed in follicular adenoma (FTA) and normal thyroid libraries.

METHODS

NR4A1, one of the five genes, was validated in a set of 27 normal thyroid tissues, 10 FTAs and 14 FTCs and three thyroid carcinoma cell lines by real time PCR. NR4A1 can be transiently increased by a variety of stimuli, including lithium, which is used as adjuvant therapy of thyroid carcinoma with (131)I. We tested if lithium could restore NR4A1 expression. The expression of other genes potentially involved in the same signalling pathway was tested. To this end, lithium was used at different concentration (10 mm or 20 mm) and time (2 h and 24 h) and the level of expression was tested by quantitative PCR. We next tested if Lithium could affect cell growth and apoptosis.

RESULTS

We observed that NR4A1 expression was under-expressed in most of the FTCs investigated, compared with expression in normal thyroid tissues and FTAs. We also found a positive correlation between NR4A1 and FOSB gene expression. Lithium induced NR4A1 and FOSB expression, reduced CCDN1 expression, inhibited cell growth and triggered apoptosis in a FTC cell line.

CONCLUSIONS

NR4A1 is under-expressed in most of FTCs. The loss of expression of both NR4A1 and the Wnt pathway gene FOSB was correlated with malignancy. This is consistent with the hypothesis that its loss of expression is part of the transformation process of FTCs, either as a direct or indirect consequence of Wnt pathway alterations. Lithium restores NR4A1 expression, induces apoptosis and reduces cell growth. These findings may explain a possible molecular mechanism of lithium's therapeutic action.

Low-level expression of Smad7 correlates with lymph node metastasis and poor prognosis in patients with pancreatic cancer

BACKGROUND

Whether Smad7 acts as a tumor proliferation promoting factor or as a metastatic suppressor in human pancreatic cancer remains unclear. This study aims to determine the prognostic value of Smad7 in patients with pancreatic adenocarcinoma.

METHODS

Surgical specimens obtained from 71 patients with pancreatic adenocarcinoma were immunohistochemically assessed for Smad7, Ki-67, MMP2, CD34, and Smad4 expression. The relationship between Smad7 expression and the clinicopathological characteristics of patients with pancreatic adenocarcinoma were also evaluated.

RESULTS

Fifty-one of 71 specimens (71.8%) were Smad7 positive and 20 specimens were Smad7 negative. Negative expression of Smad7 correlated with lymph node metastasis, liver metastasis after surgery, and a poor survival rate (P = 0.0004, 0.0044, and 0.0003, respectively). We also found an inverse correlation between the expression of Smad7 and MMP2 (P = 0.0189). Multivariate analysis revealed that Smad7 expression was an independent prognostic factor [hazard ratio (HR) 0.3902; 95% confidence interval (CI) 0.1839-0.8277; P = 0.0142]. Furthermore, in both Smad4-negative and Smad4-positive groups, survival of patients with Smad7-positive tumors was significantly better than those with Smad7-negative tumors (both P < 0.0001).

CONCLUSIONS

We conclude that low-level expression of Smad7 in pancreatic cancer is significantly associated with lymph node metastasis, high MMP2 expression, and poor prognosis.

TGFbeta in Cancer

The transforming growth factor beta (TGFbeta) signaling pathway is a key player in metazoan biology, and its misregulation can result in tumor development. The regulatory cytokine TGFbeta exerts tumor-suppressive effects that cancer cells must elude for malignant evolution. Yet, paradoxically, TGFbeta also modulates processes such as cell invasion, immune regulation, and microenvironment modification that cancer cells may exploit to their advantage. Consequently, the output of a TGFbeta response is highly contextual throughout development, across different tissues, and also in cancer. The mechanistic basis and clinical relevance of TGFbeta's role in cancer is becoming increasingly clear, paving the way for a better understanding of the complexity and therapeutic potential of this pathway.

The HECT family of E3 ubiquitin ligases: multiple players in cancer development

The involvement of the homologous to E6-AP carboxyl terminus (HECT)-type E3s in crucial signaling pathways implicated in tumorigenesis is presently an area of intense research and extensive scientific interest. This review highlights recent discoveries on the ubiquitin-mediated degradation of crucial tumor suppressor molecules catalyzed by the HECT-type E3s. By providing a portrait of their protein targets, we intend to link the substrate specificity of HECT-type E3s with their contribution to tumorigenesis. Moreover, we discuss the relevance of targeting the HECT E3s, through the development of small-molecule inhibitors, as an anticancer therapeutic strategy.

TGFbeta, activina e sinalização SMAD em câncer de tiróide

TGFbeta e activina são membros da superfamília TGFbeta e desempenham um amplo papel no desenvolvimento, proliferação e apoptose. Estes fatores de crescimento exercem seus efeitos biológicos ligando-se a receptores de membrana do tipo I e do tipo II que transduzem a sinalização até o núcleo através da fosforilação das proteínas R-SMADs (SMAD 2/3) e co-SMADs (SMAD4). O controle apropriado da via de TGFbeta/activina ainda depende da regulação negativa exercida pelo SMAD inibitório (SMAD7) e pelas enzimas E3 de ubiquitinação (Smurfs). Fisiologicamente, TGFbeta e activina atuam como potentes inibidores da proliferação na célula folicular tiroidiana. Desta forma, alterações de receptores e componentes da via de sinalização SMAD estão associadas a diferentes tipos de tumores. Desde que TGFbeta e activina geram sua sinalização intracelular utilizando os mesmos componentes da via SMAD, o desequilíbrio desta via prejudica dois processos anti-mitogênicos da célula. Nesta revisão, enfocamos aspectos que indicam o mecanismo de resistência ao efeito inibitório de TGFbeta e activina ocasionado pelo desequilíbrio da via de sinalização SMAD nas neoplasias da tiróide.

Participation of an abnormality in the transforming growth factor-beta signaling pathway in resistance of malignant glioma cells to growth inhibition induced by that factor

OBJECT

Malignant glioma cells secrete and activate transforming growth factor-beta (TGFbeta) and are resistant to growth inhibition by that factor. Nevertheless, the mechanism underlying this effect remains poorly understood. In this study, the mechanism of the resistance to growth inhibition induced by TGFbeta was investigated.

METHODS

The authors examined the expression of downstream components of the TGFbeta receptor, including Smad2, Smad3, Smad4, and Smad7, and the effect of TGFbeta1 treatment on the phosphorylation of Smad2 and the nuclear translocation of Smad2 and Smad3 by using 10 glioma cell lines and the A549 cell line, which is sensitive to TGFbeta-mediated growth inhibition. The expression of two transcriptional corepressor proteins, SnoN and Ski, and the effect of TGFbeta1 treatment on the expression of the SnoN protein and the cell cycle regulators p21, p15, cyclin-dependent kinase-4 (CDK4), and cyclin D1 were also examined. Expression of the Smad2 and Smad3 proteins was lower in the glioma cell lines than in the A549 cell line and in normal astrocytes. In particular, Smad3 expression was low or very low in nine of the 10 malignant glioma cell lines. Expression of Smad4 was low in four glioma cell lines, and expression of the Smad7 protein was similar when compared with protein expression in the A549 cell line and in normal astrocytes. The levels of Smad2 phosphorylation after TGFbeta1 treatment were lower in glioma cell lines than in the A549 cell line, except for one glioma cell line. Seven of the 10 glioma cell lines exhibited lower levels of nuclear translocation of Smad2 and Smad3, and two cell lines that expressed very low levels of Smad3 protein showed no nuclear translocation. All glioma cell lines expressed the SnoN protein and its expression was unaltered by treatment with TGFbeta1. Three glioma cell lines expressed high levels of the Ski protein. The expression of the p21(cip1), p15(INK4B), CDK4, and cyclin D1 proteins was not altered by TGFbeta1, treatment, except in one cell line that displayed a slight increase in p21 protein. Overall, the expression of the Smad2 and Smad3 proteins was low in the glioma cell lines, the phosphorylation and nuclear translocation of Smad2 and Smad3 were impaired, and the TGFbeta receptor signal did not affect the expression of the SnoN, p21, p15, cyclin D1, and CDK4 proteins.

CONCLUSIONS

These results suggest that the ability to resist TGFbeta-mediated growth inhibition in malignant glioma cells is due to abnormalities in the TGFbeta signaling pathway.

Tissue fibrosis and carcinogenesis: divergent or successive pathways dictate multiple molecular therapeutic targets for oligo decoy therapies

The extracellular matrix (ECM) is composed of several families of macromolecular components: fibrous proteins such as collagens, type I collagen (COL1), type III collagen (COL3), fibronectin, elastin, and glycoconjugates such as proteoglycans and matrix glycoproteins. Their receptors on the cell membrane, most of which in the case of the ECM belong to the integrins, which are heterodimeric proteins composed of alpha and beta chains. COL1 is the major fibrous collagen of bone, tendon, and skin; while COL3 is the more pliable collagen of organs like liver. Focus will not only be given to the regulation of synthesis of several fibrogenic parameters but also modulation of their degradation during growth factor-induced tissue fibrosis and cancer development. Evidence will be provided that certain tissues, which undergo fibrosis, also become cancerous. Why does there exist a divergency between tissues, which undergo frank fibrosis as an endpoint, and those tissues that undergo fibrosis and subsequently are susceptible to carcinogenicity; resulting from the etiological factor(s) causing the initial injury? For example, why does a polyvinyl alcohol (PVA) sponge implant become encapsulated and filled with fibrous tissue then fibrosis tissue growth stops? Why does the subcutaneous injection of a fibrogenic growth factor cause a benign growth and incisional wounding results in fibrosis and ultimately scarring? There are many examples of tissues, which undergo fibrosis as a prerequisite to carcinogenesis. Is there a cause-effect relationship? If you block tissue fibrosis in these precancerous tissues, would you block cancer formation? What are the molecular targets for blocking fibrosis and ultimately carcinogenesis? How can oligo decoys may be used to attenuate carcinogenesis and which oligo decoys specifically attenuate fibrogenesis as a prelude to carcinogenesis? What are other molecular targets for oligo decoy therapy in carcinogenesis?

Actions of TGF-beta as tumor suppressor and pro-metastatic factor in human cancer

Transforming growth factor-beta (TGF-beta) is a secreted polypeptide that signals via receptor serine/threonine kinases and intracellular Smad effectors. TGF-beta inhibits proliferation and induces apoptosis in various cell types, and accumulation of loss-of-function mutations in the TGF-beta receptor or Smad genes classify the pathway as a tumor suppressor in humans. In addition, various oncogenic pathways directly inactivate the TGF-beta receptor-Smad pathway, thus favoring tumor growth. On the other hand, all human tumors overproduce TGF-beta whose autocrine and paracrine actions promote tumor cell invasiveness and metastasis. Accordingly, TGF-beta induces epithelial-mesenchymal transition, a differentiation switch that is required for transitory invasiveness of carcinoma cells. Tumor-derived TGF-beta acting on stromal fibroblasts remodels the tumor matrix and induces expression of mitogenic signals towards the carcinoma cells, and upon acting on endothelial cells and pericytes, TGF-beta regulates angiogenesis. Finally, TGF-beta suppresses proliferation and differentiation of lymphocytes including cytolytic T cells, natural killer cells and macrophages, thus preventing immune surveillance of the developing tumor. Current clinical approaches aim at establishing novel cancer drugs whose mechanisms target the TGF-beta pathway. In conclusion, TGF-beta signaling is intimately implicated in tumor development and contributes to all cardinal features of tumor cell biology.

Smad4 protein expression correlates with grade, stage, and DNA ploidy in prostatic adenocarcinomas

The tumor suppressor gene Smad4 (DPC4) has been localized to chromosome 18q21.1 and is a member of the Smad family that mediates the transforming growth factor beta signaling pathway suppressing epithelial cell growth. However, variable expression of this protein has been reported, with a loss in some cancers and increased expression in others. Given both the variability and lack of consensus reported regarding Smad4 expression in prostate cancer, we assessed Smad4 immunoreactivity in prostatic adenocarcinomas (PACs). Formalin-fixed, paraffin-embedded tissue sections from 133 PACs were immunostained by a manual method using indirect biotin streptavidin horseradish peroxidase and diaminobenzidine detection using a monoclonal mouse antihuman Smad4 antibody (sc-7966; Santa Cruz Biotechnology Inc, Santa Cruz, Calif). Nuclear immunoreactivity and cytoplasmic immunoreactivity were each semiquantitatively scored based on intensity and percentage of positive cells. Deoxyribonucelic acid ploidy was determined on Feulgen-stained tissue sections by static image analysis. Results were correlated with morphological and prognostic variables. Variable nuclear and cytoplasmic Smad4 positivity was noted in the adjacent benign glands in all cases. Of 133 PACs, 64 (48%) featured increased nuclear and 68 (51%) featured increased cytoplasmic protein expression. Nuclear Smad4 overexpression correlated with tumor grade (P = .02), stage (P = .04), and DNA ploidy (P = .04). Cytoplasmic overexpression correlated with tumor grade (P = .04) and DNA ploidy (P = .04) while showing a trend for correlation with tumor stage (P = .08). Neither nuclear nor cytoplasmic Smad4 overexpression correlated with postsurgical biochemical disease recurrence. Smad4 protein expression persists in PACs compared with benign glands, with both nuclear and cytoplasmic overexpression correlating with prognostic variables indicative of aggressive tumor behavior. Given the significant reported variability of Smad4 in several different cancers, further studies in prostate and other tumors are warranted to elucidate its role in tumorigenesis.

Bone morphogenetic proteins in melanoma: Angel or devil?

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta (TGF-beta) superfamily serving multiple functions in many cell and tissue types including proliferation, apoptosis, differentiation, chemotaxis, angiogenesis, and matrix production during embryogenic development as well as in adult life. Despite the tremendous progress in delineating functional derangements of BMP pathways in carcinogenesis during the last decade, the biological significance of BMPs in human melanoma has received very little attention. It is now clear that biological responses to BMPs are cell type-specific and divergent effects, i.e., both oncogenic and tumor suppressor activities, have been described. Thus, knowledge generated in one system may not translate directly to another. In this review, we summarize the current understanding of BMP signaling in various human cancers and discuss original data pertaining to cutaneous melanoma obtained in our laboratory.

Marcadores biológicos de tumores tiroidianos

Um marcador biológico ideal deve ser específico e sensível para identificar o tipo tumoral e caracterizar o estágio da progressão neoplásica. Os tumores de tiróide originam-se de dois tipos celulares: 1) carcinoma medular originário de células parafoliculares; e 2) as neoplasias de células epiteliais foliculares, que incluem bócio, adenomas, carcinomas diferenciados (carcinoma papilífero e carcinoma folicular) e carcinoma indiferenciado (carcinoma anaplásico). O comportamento biológico distinto faz com que cada tipo tumoral necessite de uma conduta terapêutica específica. O conhecimento acumulado ao longo destes anos, utilizando métodos de biologia molecular e, mais recentemente, a genômica, identificou mutações específicas de câncer de tiróide e, atualmente, entendemos muito das alterações que ocorrem na expressão de fatores de crescimento, seus receptores e proteínas sinalizadoras intracelular nas neoplasias tiroidianas. Contudo, apesar desses, até o momento não dispomos de um marcador eficiente que auxilie no diagnóstico e prognóstico e, conseqüentemente, para indicação de uma terapêutica mais adequada. Nesta revisão, discutiremos os principais aspectos relacionados à tumorigênese tiroidiana, avaliando o potencial destes fatores como marcador em neoplasia folicular de tiróide.