TRAF6 stimulates the tumor-promoting effects of TGFβ type I receptor through polyubiquitination and activation of presenilin 1

TRAF6 enhances PD-L1 expression through YAP1-TFCP2 signaling in melanoma

Immunotherapy represented by programmed cell death protein 1 (PD-1)/programmed death ligand 1 (PD-L1) monoclonal antibodies has led tumor treatment into a new era. However, the low overall response rate and high incidence of drug resistance largely damage the clinical benefits of existing immune checkpoint therapies. Recent studies correlate the response to PD-1/PD-L1 blockade with PD-L1 expression levels in tumor cells. Hence, identifying molecular targets and pathways controlling PD-L1 protein expression and stability in tumor cells is a major priority. In this study, we performed a Stress and Proteostasis CRISPR interference screening to identify PD-L1 positive modulators. Here, we identified TRAF6 as a critical regulator of PD-L1 in melanoma cells. As a non-conventional E3 ubiquitin ligase, TRAF6 is inclined to catalyze the synthesis and linkage of lysine-63 (K63) ubiquitin which is related to the stabilization of substrate proteins. Our results showed that suppression of TRAF6 expression down-regulates PD-L1 expression on the membrane surface of melanoma cells. We then used in vitro and in vivo assays to investigate the biological function and mechanism of TRAF6 and its downstream YAP1/TFCP2 signaling in melanoma. TRAF6 stabilizes YAP1 by K63 poly-ubiquitination modification, subsequently promoting the formation of YAP1/TFCP2 transcriptional complex and PD-L1 transcription. Inhibition of TRAF6 by Bortezomib enhanced cytolytic activity of CD8+ T cells by reduction of endogenous PD-L1. Notably, Bortezomib enhances anti-tumor immunity to an extent comparable to anti-PD-1 therapies with no obvious toxicity. Our findings reveal the potential of inhibiting TRAF6 to stimulate internal anti-tumor immunological effect for TRAF6-PD-L1 overexpressing cancers.

Design, synthesis and evaluation of a pyrazolo[3,4-d]pyrimidine derivative as a novel and potent TGFβ1R1 inhibitor

The transforming growth factor β1 (TGFβ1)/SMAD signaling pathway regulates many vital physiological processes. The development of potent inhibitors targeting activin receptor-like kinase 5 (ALK5) would provide potential treatment reagents for various diseases. A significant number of ALK5 inhibitors have been discovered, and they are currently undergoing clinical evaluation at various stages. However, the clinical demands were far from being met. In this study, we utilized an alternative conformation-similarity-based virtual screening (CSVS) combined with a fragment-based drug designing (FBDD) strategy to efficiently discover a potent and active hit with a novel chemical scaffold. After structural optimization in the principle of group replacement, compound 57 was identified as the most promising ALK5 inhibitor. Compound 57 demonstrated significant inhibitory effects against the TGF-β1/SMAD signaling pathway. It could markedly attenuate the production of extracellular matrix (ECM) and deposition of collagen. Also, the lead compound showed adequate pharmacokinetic (PK) properties and good in vivo tolerance. Moreover, treatment with compound 57 in two different xerograph models showed significant inhibitory effects on the growth of pancreatic cancer cells. These results suggested that lead compound 57 refers as a promising ALK5 inhibitor both in vitro and in vivo, which merits further validation.

Targeting SMAD-Dependent Signaling: Considerations in Epithelial and Mesenchymal Solid Tumors

SMADs are the canonical intracellular effector proteins of the TGF-β (transforming growth factor-β). SMADs translocate from plasma membrane receptors to the nucleus regulated by many SMAD-interacting proteins through phosphorylation and other post-translational modifications that govern their nucleocytoplasmic shuttling and subsequent transcriptional activity. The signaling pathway of TGF-β/SMAD exhibits both tumor-suppressing and tumor-promoting phenotypes in epithelial-derived solid tumors. Collectively, the pleiotropic nature of TGF-β/SMAD signaling presents significant challenges for the development of effective cancer therapies. Here, we review preclinical studies that evaluate the efficacy of inhibitors targeting major SMAD-regulating and/or -interacting proteins, particularly enzymes that may play important roles in epithelial or mesenchymal compartments within solid tumors.

Ubiquitin Engineering for Interrogating the Ubiquitin-Proteasome System and Novel Therapeutic Strategies

Protein turnover, a highly regulated process governed by the ubiquitin-proteasome system (UPS), is essential for maintaining cellular homeostasis. Dysregulation of the UPS has been implicated in various diseases, including viral infections and cancer, making the proteins in the UPS attractive targets for therapeutic intervention. However, the functional and structural redundancies of UPS enzymes present challenges in identifying precise drug targets and achieving target selectivity. Consequently, only 26S proteasome inhibitors have successfully advanced to clinical use thus far. To overcome these obstacles, engineered peptides and proteins, particularly engineered ubiquitin, have emerged as promising alternatives. In this review, we examine the impact of engineered ubiquitin on UPS and non-UPS proteins, as well as on viral enzymes. Furthermore, we explore their potential to guide the development of small molecules targeting novel surfaces, thereby expanding the range of druggable targets.

TRAF6 Promotes PRMT5 Activity in a Ubiquitination-Dependent Manner

Protein arginine methyltransferase 5 (PRMT5) is the primary enzyme generating symmetric dimethylarginine (sDMA) on numerous substrates, through which it regulates many cellular processes, such as transcription and DNA repair. Aberrant expression and activation of PRMT5 is frequently observed in various human cancers and associated with poor prognosis and survival. However, the regulatory mechanisms of PRMT5 remain poorly understood. Here, we report that TRAF6 serves as an upstream E3 ubiquitin ligase to promote PRMT5 ubiquitination and activation. We find that TRAF6 catalyzes K63-linked ubiquitination of PRMT5 and interacts with PRMT5 in a TRAF6-binding-motif-dependent manner. Moreover, we identify six lysine residues located at the N-terminus as the primarily ubiquitinated sites. Disruption of TRAF6-mediated ubiquitination decreases PRMT5 methyltransferase activity towards H4R3 in part by impairing PRMT5 interaction with its co-factor MEP50. As a result, mutating the TRAF6-binding motifs or the six lysine residues significantly suppresses cell proliferation and tumor growth. Lastly, we show that TRAF6 inhibitor enhances cellular sensitivity to PRMT5 inhibitor. Therefore, our study reveals a critical regulatory mechanism of PRMT5 in cancers.

The Ubiquitin-Proteasome System in Tumor Metabolism

Metabolic reprogramming, which is considered a hallmark of cancer, can maintain the homeostasis of the tumor environment and promote the proliferation, survival, and metastasis of cancer cells. For instance, increased glucose uptake and high glucose consumption, known as the "Warburg effect," play an essential part in tumor metabolic reprogramming. In addition, fatty acids are harnessed to satisfy the increased requirement for the phospholipid components of biological membranes and energy. Moreover, the anabolism/catabolism of amino acids, such as glutamine, cystine, and serine, provides nitrogen donors for biosynthesis processes, development of the tumor inflammatory environment, and signal transduction. The ubiquitin-proteasome system (UPS) has been widely reported to be involved in various cellular biological activities. A potential role of UPS in the metabolic regulation of tumor cells has also been reported, but the specific regulatory mechanism has not been elucidated. Here, we review the role of ubiquitination and deubiquitination modification on major metabolic enzymes and important signaling pathways in tumor metabolism to inspire new strategies for the clinical treatment of cancer.

TGF-β as Predictive Marker and Pharmacological Target in Lung Cancer Approach

Lung cancer (LC) represents the leading cause of cancer incidence and mortality worldwide. LC onset is strongly related to genetic mutations and environmental interactions, such as tobacco smoking, or pathological conditions, such as chronic inflammation. Despite advancement in knowledge of the molecular mechanisms involved in LC, this tumor is still characterized by an unfavorable prognosis, and the current therapeutic options are unsatisfactory. TGF-β is a cytokine that regulates different biological processes, particularly at the pulmonary level, and its alteration has been demonstrated to be associated with LC progression. Moreover, TGF-β is involved in promoting invasiveness and metastasis, via epithelial to mesenchymal transition (EMT) induction, where TGF-β is the major driver. Thus, a TGF-β-EMT signature may be considered a potential predictive marker in LC prognosis, and TGF-β-EMT inhibition has been demonstrated to prevent metastasis in various animal models. Concerning a LC therapeutic approach, some TGF-β and TGF-β-EMT inhibitors could be used in combination with chemo- and immunotherapy without major side effects, thereby improving cancer therapy. Overall, targeting TGF-β may be a valid possibility to fight LC, both in improving LC prognosis and cancer therapy, via a novel approach that could open up new effective strategies against this aggressive cancer.

A spotlight on the interplay of signaling pathways and the role of miRNAs in osteosarcoma pathogenesis and therapeutic resistance

Osteosarcoma (OS) is one of the most common bone cancers that constantly affects children, teenagers, and young adults. Numerous epigenetic elements, such as miRNAs, have been shown to influence OS features like progression, initiation, angiogenesis, and treatment resistance. The expression of numerous genes implicated in OS pathogenesis might be regulated by miRNAs. This effect is ascribed to miRNAs' roles in the invasion, angiogenesis, metastasis, proliferation, cell cycle, and apoptosis. Important OS-related mechanistic networks like the WNT/b-catenin signaling, PTEN/AKT/mTOR axis, and KRAS mutations are also affected by miRNAs. In addition to pathophysiology, miRNAs may influence how the OS reacts to therapies like radiotherapy and chemotherapy. With a focus on how miRNAs affect OS signaling pathways, this review seeks to show how miRNAs and OS are related.

Significance of miRNAs on the thyroid cancer progression and resistance to treatment with special attention to the role of cross-talk between signaling pathways

Thyroid cancer (TC) is the most prevalent endocrine malignant tumor. It has many types, the Papillary thyroid cancer (PTC)(most common and follicular thyroid carcinoma (FTC). Several risk factors have been associated with TC radiation exposure, autoimmunity, and genetics. Microribonucleic acids (miRNAs) are the most important genetic determinants of TC. They are small chains of nucleic acids that are able to inhibit the expression of several target genes. They could target several genes involved in TC proliferation, angiogenesis, apoptosis, development, and even resistance to therapy. Besides, they could influence the stemness of TC. Moreover, they could regulate several signaling pathways such as WNT/β-catenin, PI3K/AKT/mTOR axis, JAK/STAT, TGF- β, EGFR, and P53. Besides signaling pathways, miRNAs are also involved in the resistance of TC to major treatments such as surgery, thyroid hormone-inhibiting therapy, radioactive iodine, and adjuvant radiation. The stability and sensitivity of several miRNAs might be exploited as an approach for the usage of miRNAs as diagnostic and/or prognostic tools in TC.

Roles of TGF-β in cancer hallmarks and emerging onco-therapeutic design

Transforming growth factor-beta (TGF-β) is a double-edged sword in cancer treatment because of its pivotal yet complex and roles played during cancer initiation/development. Current anti-cancer strategies involving TGF-β largely view TGF-β as an onco-therapeutic target that not only substantially hinders its full utilisation for cancer control, but also considerably restricts innovations in this field. Thereby, how to take advantages of therapeutically favourable properties of TGF-β for cancer management represents an interesting and less investigated problem. Here, by categorising cancer hallmarks into four critical transition events and one enabling characteristic controlling cancer initiation and progression, and delineating TGF-β complexities according to these cancer traits, we identify the suppressive role of TGF-β in tumour initiation and early-stage progression and its promotive functionalities in cancer metastasis as well as other cancer hallmarks. We also propose the feasibility and possible scenarios of combining cold atmospheric plasma (CAP) with onco-therapeutics utilising TGF-β for cancer control given the intrinsic properties of CAP against cancer hallmarks.

The ubiquitin-ligase TRAF6 and TGFβ type I receptor form a complex with Aurora kinase B contributing to mitotic progression and cytokinesis in cancer cells

Background

Transforming growth factor β (TGFβ) is overexpressed in several advanced cancer types and promotes tumor progression. We have reported that the intracellular domain (ICD) of TGFβ receptor (TβR) I is cleaved by proteolytic enzymes in cancer cells, and then translocated to the nucleus in a manner dependent on the endosomal adaptor proteins APPL1/2, driving an invasiveness program. How cancer cells evade TGFβ-induced growth inhibition is unclear.

Methods

We performed microarray analysis to search for genes regulated by APPL1/2 proteins in castration-resistant prostate cancer (CRPC) cells. We investigated the role of TβRI and TRAF6 in mitosis in cancer cell lines cultured in 10% FBS in the absence of exogenous TGFβ. The molecular mechanism of the ubiquitination of AURKB by TRAF6 in mitosis and the formation of AURKB–TβRI complex in cancer cell lines and tissue microarrays was also studied.

Findings

During mitosis and cytokinesis, AURKB–TβRI complexes formed in midbodies in CRPC and KELLY neuroblastoma cells. TRAF6 induced polyubiquitination of AURKB on K85 and K87, protruding on the surface of AURKB to facilitate its activation. AURKB–TβRI complexes in patient's tumor tissue sections correlated with the malignancy of prostate cancer.

Interpretation

The AURKB–TβRI complex may become a prognostic biomarker for patients with risk of developing aggressive PC.

Funding

Swedish Medical Research Council (2019-01598, ML; 2015-02757 and 2020-01291, CHH), the Swedish Cancer Society (20 0964, ML), a regional agreement between Umeå University and Region Västerbotten (ALF; RV-939377, -967041, -970057, ML). The European Research Council (787472, CHH). KAW 2019.0345, and the Kempe Foundation SMK-1866; ML. National Microscopy Infrastructure (NMI VR-RFI 2016-00968).

MicroRNAs as the critical regulators of cell migration and invasion in thyroid cancer

Thyroid cancer (TC) is one of the most frequent endocrine malignancies that is more common among females. Tumor recurrence is one of the most important clinical manifestations in differentiated TC which is associated with different factors including age, tumor size, and histological features. Various molecular processes such as genetic or epigenetic modifications and non-coding RNAs are also involved in TC progression and metastasis. The epithelial-to-mesenchymal transition (EMT) is an important biological process during tumor invasion and migration that affects the initiation and transformation of early-stage tumors into invasive malignancies. A combination of transcription factors, growth factors, signaling pathways, and epigenetic regulations affect the thyroid cell migration and EMT process. MicroRNAs (miRNAs) are important molecular factors involved in tumor metastasis by regulation of EMT-activating signaling pathways. Various miRNAs are involved in the signaling pathways associated with TC metastasis which can be used as diagnostic and therapeutic biomarkers. Since, the miRNAs are sensitive, specific, and non-invasive, they can be suggested as efficient and optimal biomarkers of tumor invasion and metastasis. In the present review, we have summarized all of the miRNAs which have been significantly involved in thyroid tumor cells migration and invasion. We also categorized all of the reported miRNAs based on their cellular processes to clarify the molecular role of miRNAs during thyroid tumor cell migration and invasion. This review paves the way of introducing a non-invasive diagnostic and prognostic panel of miRNAs in aggressive and metastatic TC patients.

The Synergistic Cooperation between TGF-β and Hypoxia in Cancer and Fibrosis

Transforming growth factor β (TGF-β) is a multifunctional cytokine regulating homeostasis and immune responses in adult animals and humans. Aberrant and overactive TGF-β signaling promotes cancer initiation and fibrosis through epithelial–mesenchymal transition (EMT), as well as the invasion and metastatic growth of cancer cells. TGF-β is a key factor that is active during hypoxic conditions in cancer and is thereby capable of contributing to angiogenesis in various types of cancer. Another potent role of TGF-β is suppressing immune responses in cancer patients. The strong tumor-promoting effects of TGF-β and its profibrotic effects make it a focus for the development of novel therapeutic strategies against cancer and fibrosis as well as an attractive drug target in combination with immune regulatory checkpoint inhibitors. TGF-β belongs to a family of cytokines that exert their function through signaling via serine/threonine kinase transmembrane receptors to intracellular Smad proteins via the canonical pathway and in combination with co-regulators such as the adaptor protein and E3 ubiquitin ligases TRAF4 and TRAF6 to promote non-canonical pathways. Finally, the outcome of gene transcription initiated by TGF-β is context-dependent and controlled by signals exerted by other growth factors such as EGF and Wnt. Here, we discuss the synergistic cooperation between TGF-β and hypoxia in development, fibrosis and cancer.

Multiple variants of soluble CD146 are involved in Systemic Sclerosis: identification of a novel pro-fibrotic factor

OBJECTIVE

Systemic sclerosis (SSc) is an autoimmune disorder characterized by excessive fibrosis, immune dysfunction and vascular damages, in which expression of many growth factors is deregulated. CD146 was recently described as a major actor in SSc. As CD146 also exists as a circulating soluble form (sCD146) acting as a growth factor in numerous angiogenic- and inflammatory-related pathologies, we sought to identify the mechanisms underlying the generation of sCD146 and characterized the regulation and functions of the different identified variants in SSc.

METHODS

To this end, we performed in vitro experiments, including RNA-seq and antibody arrays, and in vivo experiments using animal models of SSc induced by bleomycin and of hindlimb ischemia.

RESULTS

Multiple forms of sCD146, generated by both shedding and alternative splicing of the primary transcript, were discovered. The shed form of sCD146 was generated from the cleavage of both long and short membrane isoforms of membrane CD146 through Adam10 and Tace metalloproteinases, respectively. In addition, two novel sCD146 splice variants, I5-13-sCD146 and I10-sCD146 were identified. Of interest, I5-13-sCD146 was significantly increased in sera of SSc patients, in particular in patients with pulmonary fibrosis, whereas I10-sCD146 was decreased. Further experiments revealed that shed sCD146 and I10-sCD146 displayed pro-angiogenic activity through FAK and PKCε signalling pathways, respectively, whereas I5-13-sCD146 displayed pro-fibrotic effects through wint1/β-catenin/wisp1 pathway.

CONCLUSION

Variants of sCD146, and in particular the novel I5-13-sCD146 splice variant, could thus constitute novel biomarkers and/or molecular targets for the diagnosis and treatment of SSc, but also of other angiogenesis- or fibrosis-related pathologies.

A narrative review of the relationship between TGF-β signaling and gynecological malignant tumor

Objective

This paper reviews the association between transforming growth factor-β (TGF-β) and its receptor and tumor, focusing on gynecological malignant tumors. we hope to provide more methods to help increase the potential of TGF-β signaling targeted treatment of specific cancers.

Background

The occurrence of a malignant tumor is a complex process of multi-step, multi-gene regulation, and its progression is affected by various components of the tumor cells and/or tumor microenvironment. The occurrence of gynecological diseases not only affect women's health, but also bring some troubles to their normal life. Especially when gynecological malignant tumors occur, the situation is more serious, which will endanger the lives of patients. Due to differences in environmental and economic conditions, not all women have access to assistance and treatment specifically meeting their needs. TGF-β is a multi-potent growth factor that maintains homeostasis in mammals by inhibiting cell growth and promoting apoptosis in vivo. TGF-β signaling is fundamental to inflammatory disease and favors the emergence of tumors, and it also plays an important role in immunosuppression in the tumor microenvironment. In the early stages of the tumor, TGF-β acts as a tumor inhibitor, whereas in advanced tumors, mutations or deletion of the TGF-β signaling core component initiate neogenesis.

Methods

Literatures about TGF-β and gynecological malignant tumor were extensively reviewed to analyze and discuss.

Conclusions

We discussed the role of TGF-β signaling in different types of gynecological tumor cells, thus demonstrating that targeted TGF-β signaling may be an effective tumor treatment strategy.

MicroRNA-146b-5p suppresses cholangiocarcinoma cells by targeting TRAF6 and modulating p53 translocation

BACKGROUND

In view of the poor prognosis and high mortality of cholangiocarcinoma, there is a need for new therapeutic strategies. This study aims to reveal the biological function of miR-146b-5p in cholangiocarcinoma cell and its possible mechanism.

METHODS

The expression level and prognostic information on miR-146b-5p in cholangiocarcinoma were obtained in TCGA database. The biological function of miR-146b-5p on proliferation and vitality of cholangiocarcinoma cell HUCCT-1 was examined by EdU and MTT assay, and the apoptosis of HUCCT-1 cells transfected with miR-146b-5p mimic, mimic control, inhibitor, inhibitor control was detected by flow cytometry analysis. The western blot was done to evaluate the effect of miR-146b-5p targeting substrate and the expression of p53 in whole-cell protein and mitochondria fractions.

RESULTS

Our finding revealed that miR-146b-5p expression in patients with CHOL was lower than the normal group(p＜0.001). MiR-146b-5p expression was down-regulated in human cholangiocarcinoma HUCCT-1 and RBE cells compared to normal control HIBEC and other cancer cells. The miR-146b-5p mimic could inhibit HUCCT-1 cell proliferation (p＜0.05) and promote HUCCT-1 cell apoptosis significantly (p＜0.05). The results of western blot showed that miR-146b-5p mimic could directly target TRAF6 3'UTR region and up-regulate the expression of p53 in mitochondria and miR-146b-5p inhibitor could down-regulated the level of p53 in mitochondria.

CONCLUSION

MiR-146b-5p is a cholangiocarcinoma suppressor by inhibiting cell proliferation and promoting cell apoptosis with targeting TRAF6, possibly via modulating p53 translocation to mitochondria.

TGF-β signaling: A recap of SMAD-independent and SMAD-dependent pathways

Transforming growth factor-β (TGF-β) is a proinflammatory cytokine known to control a diverse array of pathological and physiological conditions during normal development and tumorigenesis. TGF-β-mediated physiological effects are heterogeneous and vary among different types of cells and environmental conditions. TGF-β serves as an antiproliferative agent and inhibits tumor development during primary stages of tumor progression; however, during the later stages, it encourages tumor development and mediates metastatic progression and chemoresistance. The fundamental elements of TGF-β signaling have been divulged more than a decade ago; however, the process by which the signals are relayed from cell surface to nucleus is very complex with additional layers added in tumor cell niches. Although the intricate understanding of TGF-β-mediated signaling pathways and their regulation are still evolving, we tried to make an attempt to summarize the TGF-β-mediated SMAD-dependent andSMAD-independent pathways. This manuscript emphasizes the functions of TGF-β as a metastatic promoter and tumor suppressor during the later and initial phases of tumor progression respectively.

Post-Translational Modifications That Drive Prostate Cancer Progression

While a protein primary structure is determined by genetic code, its specific functional form is mostly achieved in a dynamic interplay that includes actions of many enzymes involved in post-translational modifications. This versatile repertoire is widely used by cells to direct their response to external stimuli, regulate transcription and protein localization and to keep proteostasis. Herein, post-translational modifications with evident potency to drive prostate cancer are explored. A comprehensive list of proteome-wide and single protein post-translational modifications and their involvement in phenotypic outcomes is presented. Specifically, the data on phosphorylation, glycosylation, ubiquitination, SUMOylation, acetylation, and lipidation in prostate cancer and the enzymes involved are collected. This type of knowledge is especially valuable in cases when cancer cells do not differ in the expression or mutational status of a protein, but its differential activity is regulated on the level of post-translational modifications. Since their driving roles in prostate cancer, post-translational modifications are widely studied in attempts to advance prostate cancer treatment. Current strategies that exploit the potential of post-translational modifications in prostate cancer therapy are presented.

TGFβ Signaling in the Tumor Microenvironment

Transforming growth factor beta (TGFβ) is a pleiotropic growth factor. Under normal physiological conditions, TGFβ maintains homeostasis in mammalian tissues by restraining the growth of cells and stimulating apoptosis. However, the role of TGFβ signaling in the carcinogenesis is complex. TGFβ acts as a tumor suppressor in the early stages of disease and as a tumor promoter in its later stages where cancer cells have been relieved from TGFβ growth controls. Overproduction of TGFβ by cancer cells lead to a local fibrotic and immune-suppressive microenvironment that fosters tumor growth and correlates with invasive and metastatic behavior of the cancer cells. Here, we present an overview of the complex biology of the TGFβ family, and we discuss the roles of TGFβ signaling in carcinogenesis and how this knowledge is being leveraged to develop TGFβ inhibition therapies against the tumor.

The dichotomous role of TGF-β in controlling liver cancer cell survival and proliferation

Hepatocellular carcinoma (HCC) is the major form of primary liver cancer and one of the most prevalent and life-threatening malignancies globally. One of the hallmarks in HCC is the sustained cell survival and proliferative signals, which are determined by the balance between oncogenes and tumor suppressors. Transforming growth factor beta (TGF-β) is an effective growth inhibitor of epithelial cells including hepatocytes, through induction of cell cycle arrest, apoptosis, cellular senescence, or autophagy. The antitumorigenic effects of TGF-β are bypassed during liver tumorigenesis via multiple mechanisms. Furthermore, along with malignant progression, TGF-β switches to promote cancer cell survival and proliferation. This dichotomous nature of TGF-β is one of the barriers to therapeutic targeting in liver cancer. Thereafter, understanding the underlying molecular mechanisms is a prerequisite for discovering novel antitumor drugs that may specifically disable the growth-promoting branch of TGF-β signaling or restore its tumor-suppressive arm. This review summarizes how TGF-β inhibits or promotes liver cancer cell survival and proliferation, highlighting the functional switch mechanisms during the process.

Smad7 Enhances TGF-β-Induced Transcription of c-Jun and HDAC6 Promoting Invasion of Prostate Cancer Cells

Transforming growth factor β (TGF-β) enhances migration and invasion of cancer cells, causing life-threatening metastasis. Smad7 expression is induced by TGF-β to control TGF-β signaling in a negative feedback manner. Here we report an additional function of Smad7, i.e., to enhance TGF-β induction of c-Jun and HDAC6 via binding to their regulatory regions, promoting migration and invasion of prostate cancer cells. Lysine 102 in Smad7 is crucial for binding to specific consensus sites in c-Jun and HDAC6, even when endogenous Smad2, 3, and 4 were silenced by siRNA. A correlation between the mRNA expression of Smad7 and HDAC6, Smad7 and c-Jun, and c-Jun and HDAC6 was found in public databases from analyses of prostate cancer tissues. High expression of Smad7, HDAC6, and c-Jun correlated with poor prognosis for patients with prostate cancer. The knowledge that Smad7 can activate transcription of proinvasive genes leading to prostate cancer progression provides clinically relevant information.

TAK1: a potent tumour necrosis factor inhibitor for the treatment of inflammatory diseases

Aberrant tumour necrosis factor (TNF) signalling is a hallmark of many inflammatory diseases including rheumatoid arthritis (RA), irritable bowel disease and lupus. Maladaptive TNF signalling can lead to hyper active downstream nuclear factor (NF)-κβ signalling in turn amplifying a cell's inflammatory response and exacerbating disease. Within the TNF intracellular inflammatory signalling cascade, transforming growth factor-β-activated kinase 1 (TAK1) has been shown to play a critical role in mediating signal transduction and downstream NF-κβ activation. Owing to its role in TNF inflammatory signalling, TAK1 has become a potential therapeutic target for the treatment of inflammatory diseases such as RA. This review highlights the current development of targeting the TNF-TAK1 signalling axis as a novel therapeutic strategy for the treatment of inflammatory diseases.

By targeting TRAF6, miR-140-3p inhibits TGF-β1-induced human osteosarcoma epithelial-to-mesenchymal transition, migration, and invasion

OBJECTIVES

We evaluated the effects of miR-140-3p on EMT, cellular migration, and invasion in TGF-β1 treated human OS cells. Human fresh OS tissue and normal bone tissue specimens were gathered from 42 patients (29 male and 13 female, 11 to 24 years of age with a mean age of 17.5 ± 2.3 years) diagnosed with OS by pathology. By targeting TRAF6, miR-140-3p inhibits TGF-β1-induced human osteosarcoma epithelial-to-mesenchymal transition, migration, and invasion.

RESULTS

In this study, we found microRNA (miR)-140-3p to be down-regulated and tumor necrosis factor receptor-associated factor 6 (TRAF6) to be up-regulated in patient OS samples. Lower levels of miR-140-3p and higher levels of TRAF6 were found in the advanced Enneking stage of OS. Furthermore, both mRNA and protein levels of TRAF6 were negatively associated with miR-140-3p mRNA expression in human OS tissue. TRAF6 was verified as a direct target of miR-140-3p in TGF-β1-treated human U2OS cells. Further, a miR-140-3p mimic dramatically inhibited while a miR-140-3p inhibitor enhanced TGF-β1-induced epithelial-to-mesenchymal transition, migration, and invasion of U2OS cells. Small interfering RNA was found to silence TRAF6 and to partly reverse the effects of the miR-140-3p inhibitor on TGF-β1-treated U2OS cells in vitro.

CONCLUSION

These results demonstrate miR-140-3p to function as a tumor inhibitor of human OS cells by decreasing TRAF6 expression. miR-140-3p and TRAF6 may be valuable and novel biomarkers for diagnosis and treatment of OS.

TGF-β Signaling

Transforming growth factor-β (TGF-β) represents an evolutionarily conserved family of secreted polypeptide factors that regulate many aspects of physiological embryogenesis and adult tissue homeostasis. The TGF-β family members are also involved in pathophysiological mechanisms that underlie many diseases. Although the family comprises many factors, which exhibit cell type-specific and developmental stage-dependent biological actions, they all signal via conserved signaling pathways. The signaling mechanisms of the TGF-β family are controlled at the extracellular level, where ligand secretion, deposition to the extracellular matrix and activation prior to signaling play important roles. At the plasma membrane level, TGF-βs associate with receptor kinases that mediate phosphorylation-dependent signaling to downstream mediators, mainly the SMAD proteins, and mediate oligomerization-dependent signaling to ubiquitin ligases and intracellular protein kinases. The interplay between SMADs and other signaling proteins mediate regulatory signals that control expression of target genes, RNA processing at multiple levels, mRNA translation and nuclear or cytoplasmic protein regulation. This article emphasizes signaling mechanisms and the importance of biochemical control in executing biological functions by the prototype member of the family, TGF-β.

Resveratrol induces depletion of TRAF6 and suppresses prostate cancer cell proliferation and migration

Although the early diagnosis of prostate cancer (PCa) enhances life expectancy with a 5-year survival rate of 100 %, metastasized-PCa is the fundamental reason for death by PCa, hence requires an advanced and target-directed treatment strategy. Metastasis is considered to be initiated with the epithelial-mesenchymal transition (EMT) event in which tumor cells change their epithelial characteristics into mesenchymal form and exacerbates the cancer progression. Herein, we investigated the effect and mechanism of resveratrol function in PCa cell proliferation and migration and reported that TNF-receptor associated factor 6 (TRAF6), an unconventional E3 ligase, is a key mediator of resveratrol function to inhibit PCa cell growth and proliferation and targeted for lysosomal degradation by resveratrol. MTT and cell counting demonstrated that resveratrol inhibited the viability and proliferation in DU145 and PC3 cells. Resveratrol (50 μM) mediated the degradation of TRAF6 which in turn facilitated repression of the NF-κB pathway. Also, wound healing and transwell migration assays and level of EMT-related proteins showed that resveratrol used TRAF6, at least in part to inhibit cell migration. Overexpression of TRAF6 augmented EMT in PCa by upregulating the expression of transcription factor SLUG. Moreover, TRAF6 overexpression was closely associated with EMT process through the NF-κB pathway. Our exploration exhibited that resveratrol may inhibit EMT through the TRAF6/NF-κB/SLUG axis. Altogether, this study represents that TRAF6 acts as an intermediary of resveratrol action to suppress PCa cell proliferation and migration, and concerns future attention to obtain as a therapeutic target for the treatment of PCa.

Interactions between TGF-β type I receptor and hypoxia-inducible factor-α mediates a synergistic crosstalk leading to poor prognosis for patients with clear cell renal cell carcinoma

To investigate the significance of expression of HIF-1α, HIF-2α, and SNAIL1 proteins; and TGF-β signaling pathway proteins in ccRCC, their relation with clinicopathological parameters and patient's survival were examined. We also investigated potential crosstalk between HIF-α and TGF-β signaling pathway, including the TGF-β type 1 receptor (ALK5-FL) and the intracellular domain of ALK5 (ALK5-ICD). Tissue samples from 154 ccRCC patients and comparable adjacent kidney cortex samples from 38 patients were analyzed for HIF-1α/2α, TGF-β signaling components, and SNAIL1 proteins by immunoblot. Protein expression of HIF-1α and HIF-2α were significantly higher, while SNAIL1 had similar expression levels in ccRCC compared with the kidney cortex. HIF-2α associated with poor cancer-specific survival, while HIF-1α and SNAIL1 did not associate with survival. Moreover, HIF-2α positively correlated with ALK5-ICD, pSMAD2/3, and PAI-1; HIF-1α positively correlated with pSMAD2/3; SNAIL1 positively correlated with ALK5-FL, ALK5-ICD, pSMAD2/3, PAI-1, and HIF-2α. Intriguingly, in vitro experiments performed under normoxic conditions revealed that ALK5 interacts with HIF-1α and HIF-2α, and promotes their expression and the expression of their target genes GLUT1 and CA9, in a VHL dependent manner. We found that ALK5 induces expression of HIF-1α and HIF-2α, through its kinase activity. Under hypoxic conditions, HIF-α proteins correlated with the activated TGF-β signaling pathway. In conclusion, we reveal that ALK5 plays a pivotal role in synergistic crosstalk between TGF-β signaling and hypoxia pathway, and that the interaction between ALK5 and HIF-α contributes to tumor progression.

TRAF6 function as a novel co-regulator of Wnt3a target genes in prostate cancer

Background

Tumour necrosis factor receptor associated factor 6 (TRAF6) promotes inflammation in response to various cytokines. Aberrant Wnt3a signals promotes cancer progression through accumulation of β-Catenin. Here we investigated a potential role for TRAF6 in Wnt signaling.

Methods

TRAF6 expression was silenced by siRNA in human prostate cancer (PC3U) and human colorectal SW480 cells and by CRISPR/Cas9 in zebrafish. Several biochemical methods and analyses of mutant phenotype in zebrafish were used to analyse the function of TRAF6 in Wnt signaling.

Findings

Wnt3a-treatment promoted binding of TRAF6 to the Wnt co-receptors LRP5/LRP6 in PC3U and LNCaP cells in vitro. TRAF6 positively regulated mRNA expression of β-Catenin and subsequent activation of Wnt target genes in PC3U cells. Wnt3a-induced invasion of PC3U and SW480 cells were significantly reduced when TRAF6 was silenced by siRNA. Database analysis revealed a correlation between TRAF6 mRNA and Wnt target genes in patients with prostate cancer, and high expression of LRP5, TRAF6 and c-Myc correlated with poor prognosis. By using CRISPR/Cas9 to silence TRAF6 in zebrafish, we confirm TRAF6 as a key molecule in Wnt3a signaling for expression of Wnt target genes.

Interpretation

We identify TRAF6 as an important component in Wnt3a signaling to promote activation of Wnt target genes, a finding important for understanding mechanisms driving prostate cancer progression.

Fund

KAW 2012.0090, CAN 2017/544, Swedish Medical Research Council (2016-02513), Prostatacancerförbundet, Konung Gustaf V:s Frimurarestiftelse and Cancerforskningsfonden Norrland. The funders did not play a role in manuscript design, data collection, data analysis, interpretation nor writing of the manuscript.

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TRAF6 positively regulated mRNA expression of b-Catenin and subsequent activation of Wnt target genes in prostate cancer cells in vitro.

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High expression of LRP5, TRAF6 and c-Myc correlated with poor prognosis for patients with prostate cancer.

Hypomethylation-mediated activation of cancer/testis antigen KK-LC-1 facilitates hepatocellular carcinoma progression through activating the Notch1/Hes1 signalling

Objectives

Kita‐Kyushu lung cancer antigen‐1 (KK‐LC‐1) is a cancer/testis antigen reactivated in several human malignancies. So far, the major focus of studies on KK‐LC‐1 has been on its potential as diagnostic biomarker and immunotherapy target. However, its biological functions and molecular mechanisms in cancer progression remain unknown.

Materials and Methods

Expression of KK‐LC‐1 in HCC was analysed using RT‐qPCR, Western blot and immunohistochemistry. The roles of KK‐LC‐1 on HCC progression were examined by loss‐of‐function and gain‐of‐function approaches. Pathway inhibitor DAPT was employed to confirm the regulatory effect of KK‐LC‐1 on the downstream Notch signalling. The interaction of KK‐LC‐1 with presenilin‐1 was determined by co‐immunoprecipitation. The association of CpG island methylation status with KK‐LC‐1 reactivation was evaluated by methylation‐specific PCR, bisulphite sequencing PCR and 5‐Aza‐dC treatment.

Results

We identified that HCC tissues exhibited increased levels of KK‐LC‐1. High KK‐LC‐1 level independently predicted poor survival outcome. KK‐LC‐1 promoted cell growth, migration, invasion and epithelial‐mesenchymal transition in vitro and in vivo. KK‐LC‐1 modulated the Notch1/Hes1 pathway to exacerbate HCC progression through physically interacting with presenilin‐1. Upregulation of KK‐LC‐1 in HCC was attributed to hypomethylated CpG islands.

Conclusions

This study identified that hypomethylation‐induced KK‐LC‐1 overexpression played an important role in HCC progression and independently predicted poor survival. We defined the KK‐LC‐1/presenilin‐1/Notch1/Hes1 as a novel signalling pathway that was involved in the growth and metastasis of HCC.

Specificity, versatility, and control of TGF-β family signaling

Encoded in mammalian cells by 33 genes, the transforming growth factor-β (TGF-β) family of secreted, homodimeric and heterodimeric proteins controls the differentiation of most, if not all, cell lineages and many aspects of cell and tissue physiology in multicellular eukaryotes. Deregulation of TGF-β family signaling leads to developmental anomalies and disease, whereas enhanced TGF-β signaling contributes to cancer and fibrosis. Here, we review the fundamentals of the signaling mechanisms that are initiated upon TGF-β ligand binding to its cell surface receptors and the dependence of the signaling responses on input from and cooperation with other signaling pathways. We discuss how cells exquisitely control the functional presentation and activation of heteromeric receptor complexes of transmembrane, dual-specificity kinases and, thus, define their context-dependent responsiveness to ligands. We also introduce the mechanisms through which proteins called Smads act as intracellular effectors of ligand-induced gene expression responses and show that the specificity and impressive versatility of Smad signaling depend on cross-talk from other pathways. Last, we discuss how non-Smad signaling mechanisms, initiated by distinct ligand-activated receptor complexes, complement Smad signaling and thus contribute to cellular responses.

Revisiting Bacterial Ubiquitin Ligase Effectors: Weapons for Host Exploitation

Protein ubiquitylation plays a central role in eukaryotic cell physiology. It is involved in several regulatory processes, ranging from protein folding or degradation, subcellular localization of proteins, vesicular trafficking and endocytosis to DNA repair, cell cycle, innate immunity, autophagy, and apoptosis. As such, it is reasonable that pathogens have developed a way to exploit such a crucial system to enhance their virulence against the host. Hence, bacteria have evolved a wide range of effectors capable of mimicking the main players of the eukaryotic ubiquitin system, in particular ubiquitin ligases, by interfering with host physiology. Here, we give an overview of this topic and, in particular, we detail and discuss the mechanisms developed by pathogenic bacteria to hijack the host ubiquitination system for their own benefit.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

TGF-β receptors: In and beyond TGF-β signaling

Transforming growth factor β (TGF-β) plays an important role in normal development and homeostasis. Dysregulation of TGF-β responsiveness and its downstream signaling pathways contribute to many diseases, including cancer initiation, progression, and metastasis. TGF-β ligands bind to three isoforms of the TGF-β receptor (TGFBR) with different affinities. TGFBR1 and 2 are both serine/threonine and tyrosine kinases, but TGFBR3 does not have any kinase activity. They are necessary for activating canonical or noncanonical signaling pathways, as well as for regulating the activation of other signaling pathways. Another prominent feature of TGF-β signaling is its context-dependent effects, temporally and spatially. The diverse effects and context dependency are either achieved by fine-tuning the downstream components or by regulating the expressions and activities of the ligands or receptors. Focusing on the receptors in events in and beyond TGF-β signaling, we review the membrane trafficking of TGFBRs, the kinase activity of TGFBR1 and 2, the direct interactions between TGFBR2 and other receptors, and the novel roles of TGFBR3.

Targeting TGF-β Signaling in Kidney Fibrosis

Renal fibrosis is the final common pathway of numerous progressive kidney diseases, and transforming growth factor-β (TGF-β) has an important role in tissue fibrosis by up-regulating matrix protein synthesis, inhibiting matrix degradation, and altering cell-cell interaction. Many strategies targeting TGF-β, including inhibition of production, activation, binding to the receptor, and intracellular signaling, have been developed. Some of them were examined in clinical studies against kidney fibrosis, and some are applied to other fibrotic diseases or cancer. Here, I review the approaches targeting TGF-β signaling in kidney fibrosis.

Intracellular and extracellular TGF-β signaling in cancer: some recent topics

Transforming growth factor (TGF)-β regulates a wide variety of cellular responses, including cell growth arrest, apoptosis, cell differentiation, motility, invasion, extracellular matrix production, tissue fibrosis, angiogenesis, and immune function. Although tumor-suppressive roles of TGF-β have been extensively studied and well-characterized in many cancers, especially at early stages, accumulating evidence has revealed the critical roles of TGF-β as a pro-tumorigenic factor in various types of cancer. This review will focus on recent findings regarding epithelial-mesenchymal transition (EMT) induced by TGF-β, in relation to crosstalk with some other signaling pathways, and the roles of TGF-β in lung and pancreatic cancers, in which TGF-β has been shown to be involved in cancer progression. Recent findings also strongly suggested that targeting TGF-β signaling using specific inhibitors may be useful for the treatment of some cancers. TGF-β plays a pivotal role in the differentiation and function of regulatory T cells (Tregs). TGF-β is produced as latent high molecular weight complexes, and the latent TGF-β complex expressed on the surface of Tregs contains glycoprotein A repetitions predominant (GARP, also known as leucine-rich repeat containing 32 or LRRC32). Inhibition of the TGF-β activities through regulation of the latent TGF-β complex activation will be discussed.

VHL status regulates transforming growth factor-β signaling pathways in renal cell carcinoma

To evaluate the role of pVHL in the regulation of TGF-β signaling pathways in clear cell renal cell carcinoma (ccRCC) as well as in non-ccRCC; the expression of pVHL, and the TGF-β pathway components and their association with clinicopathological parameters and patient’s survival were explored. Tissue samples from 143 ccRCC and 58 non-ccRCC patients were examined by immunoblot. ccRCC cell lines were utilized for mechanistic in-vitro studies. Expression levels of pVHL were significantly lower in ccRCC compared with non-ccRCC. Non-ccRCC and ccRCC pVHL-High expressed similar levels of pVHL. Expression of the TGF-β type I receptor (ALK5) and intra-cellular domain were significantly higher in ccRCC compared with non-ccRCC. In non-ccRCC, expressions of ALK5-FL, ALK5-ICD, pSMAD2/3, and PAI-1 had no association with clinicopathological parameters and survival. In ccRCC pVHL-Low, ALK5-FL, ALK5-ICD, pSMAD2/3, and PAI-1 were significantly related with tumor stage, size, and survival. In ccRCC pVHL-High, the expression of PAI-1 was associated with stage and survival. In-vitro studies revealed that pVHL interacted with ALK5 to downregulate its expression through K48-linked poly-ubiquitination and proteasomal degradation, thus negatively controlling TGF-β induced cancer cell invasiveness. The pVHL status controls the ALK5 and can thereby regulate the TGF-β pathway, aggressiveness of tumors, and survival of the ccRCC and non-ccRCC patients.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

Transforming growth factor-β promotes aggressiveness and invasion of clear cell renal cell carcinoma

The molecular mechanisms whereby transforming growth factor-β (TGF-β) promotes clear cell renal cell carcinoma (ccRCC) progression is elusive. The cell membrane bound TGF-β type I receptor (ALK5), was recently found to undergo proteolytic cleavage in aggressive prostate cancer cells, resulting in liberation and subsequent nuclear translocation of its intracellular domain (ICD), suggesting that ALK5-ICD might be a useful cancer biomarker. Herein, the possible correlation between ALK5 full length (ALK5-FL) and ALK5-ICD protein, phosphorylated Smad2/3 (pSmad2/3), and expression of TGF-β target gene PAI-1, was investigated in a clinical ccRCC material, in relation to tumor grade, stage, size and cancer specific survival. Expression of ALK5-FL, ALK5-ICD, pSmad2/3 and PAI-1 protein levels were significantly higher in higher stage and associated with adverse survival. ALK5-ICD, pSmad2/3 and PAI-1 correlated with higher grade, and ALK5-FL, pSmad2/3 and PAI-1 protein levels were significantly correlated with larger tumor size. Moreover, the functional role of the TGF-β - ALK5-ICD pathway were investigated in two ccRCC cell lines by treatment with ADAM/MMP2 inhibitor TAPI-2, which prevented TGF-β-induced ALK5-ICD generation, nuclear translocation, as well as cell invasion. The present study demonstrated that canonical TGF-β Smad2/3 pathway and generation of ALK5-ICD correlates with poor survival and invasion of ccRCC in vitro.

Regulated intramembrane proteolysis: emergent role in cell signalling pathways

Receptor signalling events including those initiated following activation of cytokine and growth factor receptors and the well-characterised death receptors (tumour necrosis factor receptor, type 1, FasR and TRAIL-R1/2) are initiated at the cell surface through the recruitment and formation of intracellular multiprotein signalling complexes that activate divergent signalling pathways. Over the past decade, research studies reveal that many of these receptor-initiated signalling events involve the sequential proteolysis of specific receptors by membrane-bound proteases and the γ-secretase protease complexes. Proteolysis enables the liberation of soluble receptor ectodomains and the generation of intracellular receptor cytoplasmic domain fragments. The combined and sequential enzymatic activity has been defined as regulated intramembrane proteolysis and is now a fundamental signal transduction process involved in the termination or propagation of receptor signalling events. In this review, we discuss emerging evidence for a role of the γ-secretase protease complexes and regulated intramembrane proteolysis in cell- and immune-signalling pathways.

Targeting TGF-β Signaling for Therapeutic Gain

Transforming growth factor βs (TGF-βs) are closely related ligands that have pleiotropic activity on most cell types of the body. They act through common heterotetrameric TGF-β type II and type I transmembrane dual specificity kinase receptor complexes, and the outcome of signaling is context-dependent. In normal tissue, they serve a role in maintaining homeostasis. In many diseased states, particularly fibrosis and cancer, TGF-β ligands are overexpressed and the outcome of signaling is diverted toward disease progression. There has therefore been a concerted effort to develop drugs that block TGF-β signaling for therapeutic benefit. This review will cover the basics of TGF-β signaling and its biological activities relevant to oncology, present a summary of pharmacological TGF-β blockade strategies, and give an update on preclinical and clinical trials for TGF-β blockade in a variety of solid tumor types.

Pro-invasive properties of Snail1 are regulated by sumoylation in response to TGFβ stimulation in cancer

Transforming growth factor β (TGFβ) is a key regulator of epithelial-to-mesenchymal transition (EMT) during embryogenesis and in tumors. The effect of TGFβ, on ΕΜΤ, is conveyed by induction of the pro-invasive transcription factor Snail1. In this study, we report that TGFβ stimulates Snail1 sumoylation in aggressive prostate, breast and lung cancer cells. Sumoylation of Snail1 lysine residue 234 confers its transcriptional activity, inducing the expression of classical EMT genes, as well as TGFβ receptor I (TβRI) and the transcriptional repressor Hes1. Mutation of Snail1 lysine residue 234 to arginine (K234R) abolished sumoylation of Snail1, as well as its migratory and invasive properties in human prostate cancer cells. An increased immunohistochemical expression of Snail1, Sumo1, TβRI, Hes1, and c-Jun was observed in aggressive prostate cancer tissues, consistent with their functional roles in tumorigenesis.

C. elegans SMA-10 regulates BMP receptor trafficking

Signal transduction of the conserved transforming growth factor-β (TGFβ) family signaling pathway functions through two distinct serine/threonine transmembrane receptors, the type I and type II receptors. Endocytosis orchestrates the assembly of signaling complexes by coordinating the entry of receptors with their downstream signaling mediators. Recently, we showed that the C. elegans type I bone morphogenetic protein (BMP) receptor SMA-6, part of the TGFβ family, is recycled through the retromer complex while the type II receptor, DAF-4 is recycled in a retromer-independent, ARF-6 dependent manner. From genetic screens in C. elegans aimed at identifying new modifiers of BMP signaling, we reported on SMA-10, a conserved LRIG (leucine-rich and immunoglobulin-like domains) transmembrane protein. It is a positive regulator of BMP signaling that binds to the SMA-6 receptor. Here we show that the loss of sma-10 leads to aberrant endocytic trafficking of SMA-6, resulting in its accumulation in distinct intracellular endosomes including the early endosome, multivesicular bodies (MVB), and the late endosome with a reduction in signaling strength. Our studies show that trafficking defects caused by the loss of sma-10 are not universal, but affect only a limited set of receptors. Likewise, in Drosophila, we find that the fly homolog of sma-10, lambik (lbk), reduces signaling strength of the BMP pathway, consistent with its function in C. elegans and suggesting evolutionary conservation of function. Loss of sma-10 results in reduced ubiquitination of the type I receptor SMA-6, suggesting a possible mechanism for its regulation of BMP signaling.

Transforming Growth Factor-β Receptors and Smads: Regulatory Complexity and Functional Versatility

Transforming growth factor (TGF)-β family proteins control cell physiology, proliferation, and growth, and direct cell differentiation, thus playing key roles in normal development and disease. The mechanisms of how TGF-β family ligands interact with heteromeric complexes of cell surface receptors to then activate Smad signaling that directs changes in gene expression are often seen as established. Even though TGF-β-induced Smad signaling may be seen as a linear signaling pathway with predictable outcomes, this pathway provides cells with a versatile means to induce different cellular responses. Fundamental questions remain as to how, at the molecular level, TGF-β and TGF-β family proteins activate the receptor complexes and induce a context-dependent diversity of cell responses. Among the areas of progress, we summarize new insights into how cells control TGF-β responsiveness by controlling the TGF-β receptors, and into the key roles and versatility of Smads in directing cell differentiation and cell fate selection.

Non-Smad Signaling Pathways of the TGF-β Family

Transforming growth factor β (TGF-β) and structurally related factors use several intracellular signaling pathways in addition to Smad signaling to regulate a wide array of cellular functions. These non-Smad signaling pathways are activated directly by ligand-occupied receptors to reinforce, attenuate, or otherwise modulate downstream cellular responses. This review summarizes the current knowledge of the mechanisms by which non-Smad signaling pathways are directly activated in response to ligand binding, how activation of these pathways impinges on Smads and non-Smad targets, and how final cellular responses are affected in response to these noncanonical signaling modes.

Two Paralogous Tetraspanins TSP-12 and TSP-14 Function with the ADAM10 Metalloprotease SUP-17 to Promote BMP Signaling in Caenorhabditis elegans

The highly conserved bone morphogenetic protein (BMP) signaling pathway regulates many developmental and homeostatic processes. While the core components of the BMP pathway have been well studied, much research is needed for understanding the mechanisms involved in the precise spatiotemporal control of BMP signaling in vivo. Here, we provide evidence that two paralogous and evolutionarily conserved tetraspanins, TSP-12 and TSP-14, function redundantly to promote BMP signaling in C. elegans. We further show that the ADAM10 (adisintegrin and metalloprotease 10) ortholog SUP-17 also functions to promote BMP signaling, and that TSP-12 can bind to and promote the cell surface localization of SUP-17. SUP-17/ADAM10 is known to be involved in the ligand-induced proteolytic processing of the Notch receptor. We have evidence that the function of SUP-17, and of TSP-12/TSP-14 in BMP signaling is independent of their roles in Notch signaling. Furthermore, presenilins, core components of the γ-secretase complex involved in processing Notch, do not appear to play a role in BMP signaling. These studies established a new role of the TSP-12/TSP-14/SUP-17 axis in regulating BMP signaling, in addition to their known function in the Notch signaling pathway. We also provide genetic evidence showing that a known BMP signaling modulator, UNC-40/neogenin/DCC, is one of the substrates of SUP-17/ADAM10 in the BMP signaling pathway.

Bone morphogenetic protein (BMP) signaling regulates multiple developmental and homeostatic processes. Misregulation of this pathway can cause various diseases, including cancers. Thus, it is essential to understand how BMP signaling is tightly regulated spatiotemporally in vivo. We have identified a highly conserved ADAM (a disintegrin and metalloprotease) protein, SUP-17/ADAM10, as an important factor in modulating BMP signaling in C. elegans. We showed that the proper localization and function of this ADAM protease require two conserved tetraspanin proteins, TSP-12 and TSP-14. We provided genetic evidence showing that one of the substrates of SUP-17/ADAM10 in the BMP signaling pathway is a known BMP signaling modulator, UNC-40/neogenin/DCC. Our studies established a new role of the TSP-12-TSP-14-SUP-17 axis in regulating BMP signaling, in addition to and independent of their known function in the Notch signaling pathway.

Signaling Cross Talk between TGF-β/Smad and Other Signaling Pathways

Cytokines of the transforming growth factor β (TGF-β) family, including TGF-βs, bone morphogenic proteins (BMPs), activins, and Nodal, play crucial roles in embryonic development and adult tissue homeostasis by regulating cell proliferation, survival, and differentiation, as well as stem-cell self-renewal and lineage-specific differentiation. Smad proteins are critical downstream mediators of these signaling activities. In addition to regulating the transcription of direct target genes of TGF-β, BMP, activin, or Nodal, Smad proteins also participate in extensive cross talk with other signaling pathways, often in a cell-type- or developmental stage-specific manner. These combinatorial signals often produce context-, time-, and location-dependent biological outcomes that are critical for development. This review discusses recent progress in our understanding of the cross talk between Smad proteins and signaling pathways of Wnt, Notch, Hippo, Hedgehog (Hh), mitogen-activated protein (MAP), kinase, phosphoinositide 3-kinase (PI3K)-Akt, nuclear factor κB (NF-κB), and Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways.

Signaling Cross Talk between TGF-β/Smad and Other Signaling Pathways

Cytokines of the transforming growth factor β (TGF-β) family, including TGF-βs, bone morphogenic proteins (BMPs), activins, and Nodal, play crucial roles in embryonic development and adult tissue homeostasis by regulating cell proliferation, survival, and differentiation, as well as stem-cell self-renewal and lineage-specific differentiation. Smad proteins are critical downstream mediators of these signaling activities. In addition to regulating the transcription of direct target genes of TGF-β, BMP, activin, or Nodal, Smad proteins also participate in extensive cross talk with other signaling pathways, often in a cell-type- or developmental stage-specific manner. These combinatorial signals often produce context-, time-, and location-dependent biological outcomes that are critical for development. This review discusses recent progress in our understanding of the cross talk between Smad proteins and signaling pathways of Wnt, Notch, Hippo, Hedgehog (Hh), mitogen-activated protein (MAP), kinase, phosphoinositide 3-kinase (PI3K)-Akt, nuclear factor κB (NF-κB), and Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways.

APPL proteins promote TGFβ-induced nuclear transport of the TGFβ type I receptor intracellular domain

The multifunctional cytokine transforming growth factor-β (TGFβ) is produced by several types of cancers, including prostate cancer, and promote tumour progression in autocrine and paracrine manners. In response to ligand binding, the TGFβ type I receptor (TβRI) activates Smad and non-Smad signalling pathways. The ubiquitin-ligase tumour necrosis factor receptor-associated factor 6 (TRAF6) was recently linked to regulate intramembrane proteolytic cleavage of the TβRI in cancer cells. Subsequently, the intracellular domain (ICD) of TβRI enters in an unknown manner into the nucleus, where it promotes the transcription of pro-invasive genes, such as MMP2 and MMP9. Here we show that the endocytic adaptor molecules APPL1 and APPL2 are required for TGFβ-induced nuclear translocation of TβRI-ICD and for cancer cell invasiveness of human prostate and breast cancer cell lines. Moreover, APPL proteins were found to be expressed at high levels in aggressive prostate cancer tissues, and to be associated with TβRI in a TRAF6-dependent manner. Our results suggest that the APPL–TβRI complex promotes prostate tumour progression, and may serve as a prognostic marker.

TGF-β Signaling from Receptors to Smads

Transforming growth factor β (TGF-β) and related growth factors are secreted pleiotropic factors that play critical roles in embryogenesis and adult tissue homeostasis by regulating cell proliferation, differentiation, death, and migration. The TGF-β family members signal via heteromeric complexes of type I and type II receptors, which activate members of the Smad family of signal transducers. The main attribute of the TGF-β signaling pathway is context-dependence. Depending on the concentration and type of ligand, target tissue, and developmental stage, TGF-β family members transmit distinct signals. Deregulation of TGF-β signaling contributes to developmental defects and human diseases. More than a decade of studies have revealed the framework by which TGF-βs encode a context-dependent signal, which includes various positive and negative modifiers of the principal elements of the signaling pathway, the receptors, and the Smad proteins. In this review, we first introduce some basic components of the TGF-β signaling pathways and their actions, and then discuss posttranslational modifications and modulatory partners that modify the outcome of the signaling and contribute to its context-dependence, including small noncoding RNAs.