Regulation of the TGF-β pathway by deubiquitinases in cancer

Deubiquitinases in cancer

Ubiquitination is an essential regulator of most, if not all, signalling pathways, and defects in cellular signalling are central to cancer initiation, progression and, eventually, metastasis. The attachment of ubiquitin signals by E3 ubiquitin ligases is directly opposed by the action of approximately 100 deubiquitinating enzymes (DUBs) in humans. Together, DUBs and E3 ligases coordinate ubiquitin signalling by providing selectivity for different substrates and/or ubiquitin signals. The balance between ubiquitination and deubiquitination is exquisitely controlled to ensure properly coordinated proteostasis and response to cellular stimuli and stressors. Not surprisingly, then, DUBs have been associated with all hallmarks of cancer. These relationships are often complex and multifaceted, highlighted by the implication of multiple DUBs in certain hallmarks and by the impact of individual DUBs on multiple cancer-associated pathways, sometimes with contrasting cancer-promoting and cancer-inhibiting activities, depending on context and tumour type. Although it is still understudied, the ever-growing knowledge of DUB function in cancer physiology will eventually identify DUBs that warrant specific inhibition or activation, both of which are now feasible. An integrated appreciation of the physiological consequences of DUB modulation in relevant cancer models will eventually lead to the identification of patient populations that will most likely benefit from DUB-targeted therapies.

Hydronidone ameliorates liver fibrosis by inhibiting activation of hepatic stellate cells via Smad7-mediated degradation of TGFβRI

BACKGROUND AND PURPOSE

Liver fibrosis is a wound-healing reaction that eventually leads to cirrhosis. Hydronidone is a new pyridine derivative with the potential to treat liver fibrosis. In this study, we explored the antifibrotic effects of hydronidone and its potential mode of action.

METHODS

The anti-hepatic fibrosis effects of hydronidone were studied in carbon tetrachloride (CCl4 )- and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)- induced animal liver fibrosis. The antifibrotic mechanisms of hydronidone were investigated in hepatic stellate cells (HSCs). The antifibrotic effect of hydronidone was further tested after Smad7 knockdown in HSCs in mouse models of fibrosis.

RESULTS

In animal models, hydronidone attenuated liver damage and collagen accumulation, and reduced the expression of fibrosis-related genes. Hydronidone decreased the expression of fibrotic genes in HSCs. Impressively, hydronidone significantly upregulated Smad7 expression and promoted the degradation of transforming growth factor β receptor I (TGFβRI) in HSCs and thus inhibited the TGFβ-Smad signalling pathway. Specific knockdown of Smad7 in HSCs in vivo blocked the antifibrotic effect of hydronidone.

CONCLUSION

Hydronidone ameliorates liver fibrosis by inhibiting HSCs activation via Smad7-mediated TGFβRI degradation. Hydronidone is a potential drug candidate for the treatment of liver fibrosis.

Opposing USP19 splice variants in TGF-β signaling and TGF-β-induced epithelial-mesenchymal transition of breast cancer cells

Ubiquitin-specific protease (USP)19 is a deubiquitinating enzyme that regulates the stability and function of multiple proteins, thereby controlling various biological responses. The alternative splicing of USP19 results in the expression of two major encoded variants that are localized to the endoplasmic reticulum (ER) (USP19-ER) and cytoplasm (USP19-CY). The importance of alternative splicing for the function of USP19 remains unclear. Here, we demonstrated that USP19-CY promotes TGF-β signaling by directly interacting with TGF-β type I receptor (TβRI) and protecting it from degradation at the plasma membrane. In contrast, USP19-ER binds to and sequesters TβRI in the ER. By decreasing cell surface TβRI levels, USP19-ER inhibits TGF-β/SMAD signaling in a deubiquitination-independent manner. Moreover, USP19-ER inhibits TGF-β-induced epithelial-mesenchymal transition (EMT), whereas USP19-CY enhances EMT, as well as the migration and extravasation of breast cancer cells. Furthermore, USP19-CY expression is correlated with poor prognosis and is higher in breast cancer tissues than in adjacent normal tissues. Notably, the splicing modulator herboxidiene inhibits USP19-CY, increases USP19-ER expression and suppresses breast cancer cell migration. Targeting USP19 splicing or its deubiquitinating activity may have potential therapeutic effects on breast cancer.

The Role of Deubiquitinating Enzyme in Head and Neck Squamous Cell Carcinoma

Ubiquitination and deubiquitination are two popular ways for the post-translational modification of proteins. These two modifications affect intracellular localization, stability, and function of target proteins. The process of deubiquitination is involved in histone modification, cell cycle regulation, cell differentiation, apoptosis, endocytosis, autophagy, and DNA repair after damage. Moreover, it is involved in the processes of carcinogenesis and cancer development. In this review, we discuss these issues in understanding deubiquitinating enzyme (DUB) function in head and neck squamous cell carcinoma (HNSCC), and their potential therapeutic strategies for HNSCC patients are also discussed.

To Ub or not to Ub: a regulatory question in TGF-β signaling

The transforming growth factor β (TGF-β) superfamily controls a wide spectrum of biological processes in metazoans, including cell proliferation, apoptosis, differentiation, cell-fate determination, and embryonic development. Deregulation of TGF-β-Smad signaling contributes to developmental anomalies and a variety of disorders and diseases such as tumorigenesis, fibrotic disorders, and immune diseases. In cancer, TGF-β has dual effects through its antiproliferative and prometastatic actions. At the cellular level, TGF-β functions mainly through the canonical Smad-dependent pathway in a cell type-specific and context-dependent manner. Accumulating evidence has demonstrated that ubiquitination plays a vital role in regulating TGF-β-Smad signaling. We summarize current progress on ubiquitination (Ub) and the ubiquitin ligases that regulate TGF-β-Smad signaling.

Comprehensive analysis of INHBA: A biomarker for anti-TGFβ treatment in head and neck cancer

Inhibin subunit βA (INHBA) is a protein-coding gene belonging to the transforming growth factor β (TGFβ) superfamily, which is associated with the development of a variety of cancers. However, the role of INHBA in head and neck squamous cell carcinoma (HNSC) remains unclear. The expression profile and prognostic significance of INHBA in HNSC were assessed using a variety of informatics methods. The level of INHBA expression was significantly higher in patients with HNSC, and it was correlated with sex, tumor-node-metastasis (TNM) stage, histological grade, and human papillomavirus (HPV) status. Kaplan-Meier (K-M) analysis indicated that poor overall survival (OS) and disease-free survival (DFS) were significantly associated with INHBA upregulation in HNSC. INHBA overexpression was validated as an independent poor prognostic factor by multivariate Cox regression, and including INHBA expression level in the prognostic model could increase prediction accuracy. In addition, copy number alterations (CNAs) of INHBA and miR-217-5p downregulation are potential mechanisms for elevated INHBA expression in HNSC. In conclusion, INHBA may represent a promising predictive biomarker and candidate target for anti-TGFβ therapy in HNSC.

Understanding the Renal Fibrotic Process in Leptospirosis

Leptospirosis is a neglected infectious disease caused by pathogenic species of the genus Leptospira. The acute disease is well-described, and, although it resembles other tropical diseases, it can be diagnosed through the use of serological and molecular methods. While the chronic renal disease, carrier state, and kidney fibrosis due to Leptospira infection in humans have been the subject of discussion by researchers, the mechanisms involved in these processes are still overlooked, and relatively little is known about the establishment and maintenance of the chronic status underlying this infectious disease. In this review, we highlight recent findings regarding the cellular communication pathways involved in the renal fibrotic process, as well as the relationship between renal fibrosis due to leptospirosis and CKD/CKDu.

Structural characterization of Alpiniae oxyphyllae fructus polysaccharide 2 and its activation effects on RAW264.7 macrophages

Polysaccharides are important components of Alpiniae oxyphyllae fructus that have been shown to exhibit significant immunomodulatory activity in our previous study. However, whether and how A. oxyphyllae fructus polysaccharides (AOFP) affect macrophages has not been determined. To further study the immunomodulatory activity of AOFP, the effect of AOFP on RAW264.7 cell activation was investigated in the present work. The results showed that AOFP2 significantly increased the phagocytic activity of RAW264.7 macrophages. AOFP2 promoted the secretion of TNF-α, IL-6, IL-10, TGF-β, NO and iNOS and enhanced the Th2-type immune response via its activation effect on macrophages. Additionally, the structure of AOFP2 was characterized in the present study, as the structural features of polysaccharides determine their biological activities. AOFP2 was only composed of glucose, exhibiting an average molecular weight of 44.3 kDa. Furthermore, the infrared spectroscopy, methylation and nuclear magnetic resonance results indicated that AOFP2 consisted of → 4)-α-D-Glcp-(1→, →4,6)-α-D-Glcp-(1 → and T-α-Glcp.

Targeting TGFβ signal transduction for cancer therapy

Transforming growth factor-β (TGFβ) family members are structurally and functionally related cytokines that have diverse effects on the regulation of cell fate during embryonic development and in the maintenance of adult tissue homeostasis. Dysregulation of TGFβ family signaling can lead to a plethora of developmental disorders and diseases, including cancer, immune dysfunction, and fibrosis. In this review, we focus on TGFβ, a well-characterized family member that has a dichotomous role in cancer progression, acting in early stages as a tumor suppressor and in late stages as a tumor promoter. The functions of TGFβ are not limited to the regulation of proliferation, differentiation, apoptosis, epithelial-mesenchymal transition, and metastasis of cancer cells. Recent reports have related TGFβ to effects on cells that are present in the tumor microenvironment through the stimulation of extracellular matrix deposition, promotion of angiogenesis, and suppression of the anti-tumor immune reaction. The pro-oncogenic roles of TGFβ have attracted considerable attention because their intervention provides a therapeutic approach for cancer patients. However, the critical function of TGFβ in maintaining tissue homeostasis makes targeting TGFβ a challenge. Here, we review the pleiotropic functions of TGFβ in cancer initiation and progression, summarize the recent clinical advancements regarding TGFβ signaling interventions for cancer treatment, and discuss the remaining challenges and opportunities related to targeting this pathway. We provide a perspective on synergistic therapies that combine anti-TGFβ therapy with cytotoxic chemotherapy, targeted therapy, radiotherapy, or immunotherapy.

E3 Ubiquitin Ligases: Key Regulators of TGFβ Signaling in Cancer Progression

Transforming growth factor β (TGFβ) is a secreted growth and differentiation factor that influences vital cellular processes like proliferation, adhesion, motility, and apoptosis. Regulation of the TGFβ signaling pathway is of key importance to maintain tissue homeostasis. Perturbation of this signaling pathway has been implicated in a plethora of diseases, including cancer. The effect of TGFβ is dependent on cellular context, and TGFβ can perform both anti- and pro-oncogenic roles. TGFβ acts by binding to specific cell surface TGFβ type I and type II transmembrane receptors that are endowed with serine/threonine kinase activity. Upon ligand-induced receptor phosphorylation, SMAD proteins and other intracellular effectors become activated and mediate biological responses. The levels, localization, and function of TGFβ signaling mediators, regulators, and effectors are highly dynamic and regulated by a myriad of post-translational modifications. One such crucial modification is ubiquitination. The ubiquitin modification is also a mechanism by which crosstalk with other signaling pathways is achieved. Crucial effector components of the ubiquitination cascade include the very diverse family of E3 ubiquitin ligases. This review summarizes the diverse roles of E3 ligases that act on TGFβ receptor and intracellular signaling components. E3 ligases regulate TGFβ signaling both positively and negatively by regulating degradation of receptors and various signaling intermediates. We also highlight the function of E3 ligases in connection with TGFβ's dual role during tumorigenesis. We conclude with a perspective on the emerging possibility of defining E3 ligases as drug targets and how they may be used to selectively target TGFβ-induced pro-oncogenic responses.

Association of Abl interactor 2, ABI2, with platelet/lymphocyte ratio in patients with renal cell carcinoma: A pilot study

There are many unknown aspects of the pathogenesis of renal cell carcinoma (RCC). The aim of the current study was to define new RCC-related genes and measure their associations with RCC and clinical parameters, especially platelet/lymphocyte ratio which may be an independent predictor of prognosis in patients with RCC and other forms of cancer. Via in silico analysis upon RCC-specific deleted genes in chromosome 3, four possible ceRNAs (ATXN3, ABI2, GOLGB1 and SMAD2) were identified. Then, the expression levels of these genes in tumour and adjacent healthy kidney tissues of 19 RCC patients were determined by real-time PCR. ATXN3 and GOLGB1 gene expression levels increased but ABI2 gene expression level decreased in tumour kidney tissues when compared to normal ones. ATXN3, ABI2 and GOLGB1 gene expression levels were significantly higher in Fuhrman grade 4 than other grades (P < .001). ABI2 gene expression levels were significantly associated with higher platelet/lymphocyte ratio of the patients with RCC (P < .05). ATXN3, ABI2 and GOLGB1 may predict higher RCC grades. Also, ABI2 may regulate platelet/lymphocyte ratio which may be an independent predictor of RCC and other forms of cancer.

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.

The role of proteases in epithelial-to-mesenchymal cell transitions in cancer

Changing the characteristics of cells from epithelial states to mesenchymal properties is a key process involved in developmental and physiological processes as well as in many diseases with cancer as the most prominent example. Nowadays, a great deal of work and literature concerns the understanding of the process of epithelial-to-mesenchymal transition (EMT) in terms of its molecular regulation and its implications for cancer. Similar statements can certainly be made regarding the investigation of the more than 500 proteases typically encoded by a mammalian genome. Specifically, the impact of proteases on tumor biology has been a long-standing topic of interest. However, although EMT actively regulates expression of many proteases and proteolytic enzymes are clearly involved in survival, division, differentiation, and movements of cells, information on the diverse roles of proteases in EMT has been rarely compiled. Here we aim to conceptually connect the scientific areas of "EMT" and "protease" research by describing how several important classes of proteolytic enzymes are regulated by EMT and how they are involved in initiation and execution of the EMT program. To do so, we briefly introduce the evolving key features of EMT and its regulation followed by discussion of protease involvement in this process.

The Clinical Significance of PPEF1 as a Promising Biomarker and Its Potential Mechanism in Breast Cancer

Background

Breast cancer (BC) is the leading cause of malignancy death in females worldwide. While intense efforts have been made to elucidate the pathogeny, the molecular mechanism of BC remains elusive. Thus, this study aimed to investigate the role of PPEF1 in the progression of BC and further explore the better clinical significance.

Methods

The diagnostic and prognostic values of elevated PPEF1 expression in BC were unveiled via public databases analysis. In addition, Gene Ontology (GO), Gene Set Enrichment Analysis (GSEA) and Protein–protein interaction (PPI) analysis were performed to explore the potential functions and molecular mechanisms of PPEF1 in BC progression. Experimentally, transwell and CCK-8 assays were carried out to estimate the effects of PPEF1 on the BC metastasis. Meanwhile, the differential expressions of PPEF1 in paraffin-embedded tissues and serum samples were, respectively, analyzed by Immunohistochemical (IHC) analysis and enzyme-linked immunosorbent assay (ELISA) kit.

Results

The transcriptional levels of PPEF1 were higher in BC than in normal breast tissues or adjacent normal tissues. Moreover, survival analysis revealed that higher PPEF1 expression was negatively associated with overall survival (OS), all events-free (AE-free) and metastatic recurrence-free (MR-free) survival, and further was an independent risk factor of unfavorable prognosis in BC patients. Additionally, the present study provided the first evidence that PPEF1 participated in multiple biological processes and underly signaling pathways involving in tumorigenesis and development of BC. Furthermore, PPEF1 promotes the BC progression and can be used as a noninvasive diagnostic marker. Noteworthy, the combined determination of serum PPEF1 and traditional tumor markers can enhance diagnostic accuracy thus is of vital importance in the early diagnosis of BC.

Conclusion

PPEF1 exerted a tumorigenic role and involved in molecular mechanism of tumorigenesis in BC which served as a promising biomarker for prognosis and diagnosis.

Deubiquitinase Activity Profiling Identifies UCHL1 as a Candidate Oncoprotein That Promotes TGFβ-Induced Breast Cancer Metastasis

PURPOSE

Therapies directed to specific molecular targets are still unmet for patients with triple-negative breast cancer (TNBC). Deubiquitinases (DUB) are emerging drug targets. The identification of highly active DUBs in TNBC may lead to novel therapies.

EXPERIMENTAL DESIGN

Using DUB activity probes, we profiled global DUB activities in 52 breast cancer cell lines and 52 patients' tumor tissues. To validate our findings in vivo, we employed both zebrafish and murine breast cancer xenograft models. Cellular and molecular mechanisms were elucidated using in vivo and in vitro biochemical methods. A specific inhibitor was synthesized, and its biochemical and biological functions were assessed in a range of assays. Finally, we used patient sera samples to investigate clinical correlations.

RESULTS

Two DUB activity profiling approaches identified UCHL1 as being highly active in TNBC cell lines and aggressive tumors. Functionally, UCHL1 promoted metastasis in zebrafish and murine breast cancer xenograft models. Mechanistically, UCHL1 facilitates TGFβ signaling-induced metastasis by protecting TGFβ type I receptor and SMAD2 from ubiquitination. We found that these responses are potently suppressed by the specific UCHL1 inhibitor, 6RK73. Furthermore, UCHL1 levels were significantly increased in sera of patients with TNBC, and highly enriched in sera exosomes as well as TNBC cell-conditioned media. UCHL1-enriched exosomes stimulated breast cancer migration and extravasation, suggesting that UCHL1 may act in a paracrine manner to promote tumor progression.

CONCLUSIONS

Our DUB activity profiling identified UCHL1 as a candidate oncoprotein that promotes TGFβ-induced breast cancer metastasis and may provide a potential target for TNBC treatment.

A Perspective on the Development of TGF-β Inhibitors for Cancer Treatment

Transforming growth factor (TGF)-β is a secreted multifunctional cytokine that signals via plasma membrane TGF-β type I and type II receptors and intercellular SMAD transcriptional effectors. Aberrant inter- and intracellular TGF-β signaling can contribute to cancer progression. In normal cells and early stages of cancer, TGF-β can stimulate epithelial growth arrest and elicit a tumor suppressor function. However, in late stages of cancer, when the cytostatic effects of TGF-β in cancer cells are blocked, TGF-β signaling can act as tumor promoter by its ability to stimulate epithelial-to-mesenchymal transition of cancer cells, by stimulating angiogenesis, and by promoting evasion of immune responses. In this review, we will discuss the rationale and challenges of targeting TGF-β signaling in cancer and summarize the clinical status of TGF-β signaling inhibitors that interfere with TGFβ bioavailability, TGF-βreceptor interaction, or TGF-β receptor kinase function. Moreover, we will discuss targeting of TGF-β signaling modulators and downstream effectors as well as alternative approaches by using promising technologies that may lead to entirely new classes of drugs.

A Perspective on the Development of TGF-β Inhibitors for Cancer Treatment

Transforming growth factor (TGF)-β is a secreted multifunctional cytokine that signals via plasma membrane TGF-β type I and type II receptors and intercellular SMAD transcriptional effectors. Aberrant inter- and intracellular TGF-β signaling can contribute to cancer progression. In normal cells and early stages of cancer, TGF-β can stimulate epithelial growth arrest and elicit a tumor suppressor function. However, in late stages of cancer, when the cytostatic effects of TGF-β in cancer cells are blocked, TGF-β signaling can act as tumor promoter by its ability to stimulate epithelial-to-mesenchymal transition of cancer cells, by stimulating angiogenesis, and by promoting evasion of immune responses. In this review, we will discuss the rationale and challenges of targeting TGF-β signaling in cancer and summarize the clinical status of TGF-β signaling inhibitors that interfere with TGF−β bioavailability, TGF-β/receptor interaction, or TGF-β receptor kinase function. Moreover, we will discuss targeting of TGF-β signaling modulators and downstream effectors as well as alternative approaches by using promising technologies that may lead to entirely new classes of drugs.

The deubiquitinating enzyme PSMD14 facilitates tumor growth and chemoresistance through stabilizing the ALK2 receptor in the initiation of BMP6 signaling pathway

BACKGROUND

Although bone morphogenetic protein 6 (BMP6) signaling pathway has been implicated in many types of cancer, its role of tumorigenesis seems to be controversial and its ubiquitin-modifying mechanisms have not been fully addressed. Our study was designed to investigate how BMP6 signaling pathway is regulated by ubiquitin-modifying systems and to address molecular and clinical significance in colorectal cancers.

METHODS

Human deubiquitnase (DUB) siRNA library was used to screen the specific DUB, named PSMD14, involved in BMP6 signaling pathway. Immunoblot, immunoprecipitation and ubiquitination assays were used to analyze targets of the PSMD14. A role of PSMD14-mediated BMP6 signaling pathway for malignant cancer progression was investigated using in vitro and in vivo model of colorectal cancers as well as clinical samples of colorectal cancer patients.

FINDINGS

The deubiquitinase PSMD14 acts as a positive regulator for the initiation of the BMP6 signaling pathway through deubiquitinating K48-linked ALK2 type I receptor ubiquitination mediated by Smurf1 E3 ligase, resulting in increased stability of the ALK2. This role of PSMD14 is independent of its intrinsic role in the 26S proteasome system. Furthermore, either PSMD14 or ALK2 depletion significantly decreases tumorigenesis of HCT116 colorectal cancer cells in a xenograft model as well as cancer stemness/chemoresistance, and expression of the PSMD14 and ALK2 gene are correlated with malignant progression and the survival of colorectal cancer patients.

INTERPRETATION

These findings suggest that the PSMD14-ALK2 axis plays an essential role in initiation of the BMP6 signaling pathway and contributes to tumorigenesis and chemoresistance of colorectal cancers.

Skeletal muscle atrogenes: From rodent models to human pathologies

Skeletal muscle atrophy is a common side effect of most human diseases. Muscle loss is not only detrimental for the quality of life but it also dramatically impairs physiological processes of the organism and decreases the efficiency of medical treatments. While hypothesized for years, the existence of an atrophying programme common to all pathologies is still incompletely solved despite the discovery of several actors and key regulators of muscle atrophy. More than a decade ago, the discovery of a set of genes, whose expression at the mRNA levels were similarly altered in different catabolic situations, opened the way of a new concept: the presence of atrogenes, i.e. atrophy-related genes. Importantly, the atrogenes are referred as such on the basis of their mRNA content in atrophying muscles, the regulation at the protein level being sometimes more complicate to elucidate. It should be noticed that the atrogenes are markers of atrophy and that their implication as active inducers of atrophy is still an open question for most of them. While the atrogene family has grown over the years, it has mostly been incremented based on data coming from rodent models. Whether the rodent atrogenes are valid for humans still remain to be established. An "atrogene" was originally defined as a gene systematically up- or down-regulated in several catabolic situations. Even if recent works often restrict this notion to the up-regulation of a limited number of proteolytic enzymes, it is important to keep in mind the big picture view. In this review, we provide an update of the validated and potential rodent atrogenes and the metabolic pathways they belong, and based on recent work, their relevance in human physio-pathological situations. We also propose a more precise definition of the atrogenes that integrates rapid recovery when catabolic stimuli are stopped or replaced by anabolic ones.

Transforming growth factor-β (TGF-β)-induced up-regulation of TGF-β receptors at the cell surface amplifies the TGF-β response

Functional activation of the transforming growth factor-β (TGF-β) receptors (TGFBRs) is carefully regulated through integration of post-translational modifications, spatial regulation at the cellular level, and TGFBR availability at the cell surface. Although the bulk of TGFBRs resides inside the cells, AKT Ser/Thr kinase (AKT) activation in response to insulin or other growth factors rapidly induces transport of TGFBRs to the cell surface, thereby increasing the cell's responsiveness to TGF-β. We now demonstrate that TGF-β itself induces a rapid translocation of its own receptors to the cell surface and thus amplifies its own response. This mechanism of response amplification, which hitherto has not been reported for other cell-surface receptors, depended on AKT activation and TGF-β type I receptor kinase. In addition to an increase in cell-surface TGFBR levels, TGF-β treatment promoted TGFBR internalization, suggesting an overall amplification of TGFBR cycling. The TGF-β-induced increase in receptor presentation at the cell surface amplified TGF-β-induced SMAD family member (SMAD) activation and gene expression. Furthermore, bone morphogenetic protein 4 (BMP-4), which also induces AKT activation, increased TGFBR levels at the cell surface, leading to enhanced autocrine activation of TGF-β-responsive SMADs and gene expression, providing context for the activation of TGF-β signaling in response to BMP during development. In summary, our results indicate that TGF-β- and BMP-induced activation of low levels of cell surface-associated TGFBRs rapidly mobilizes additional TGFBRs from intracellular stores to the cell surface, increasing the abundance of cell-surface TGFBRs and cells' responsiveness to TGF-β signaling.

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.

POH1 contributes to hyperactivation of TGF-β signaling and facilitates hepatocellular carcinoma metastasis through deubiquitinating TGF-β receptors and caveolin-1

Background

Hyper-activation of TGF-β signaling is critically involved in progression of hepatocellular carcinoma (HCC). However, the events that contribute to the dysregulation of TGF-β pathway in HCC, especially at the post-translational level, are not well understood.

Methods

Associations of deubiquitinase POH1 with TGF-β signaling activity and the outcomes of HCC patients were examined by data mining of online HCC datasets, immunohistochemistry analyses using human HCC specimens, spearman correlation and survival analyses. The effects of POH1 on the ubiquitination and stability of the TGF-β receptors (TGFBR1 and TGFBR2) and the activation of downstream effectors were tested by western blotting. Primary mouse liver tissues from polyinosinic:polycytidylic acid (poly I:C)- treated Mx-Cre+, poh1^f/f mice and control mice were used to detect the TGF-β receptors. The metastatic-related capabilities of HCC cells were studied in vitro and in mice.

Findings

Here we show that POH1 is a critical regulator of TGF-β signaling and promotes tumor metastasis. Integrative analyses of HCC subgroups classified with unsupervised transcriptome clustering of the TGF-β response, metastatic potential and outcomes, reveal that POH1 expression positively correlates with activities of TGF-β signaling in tumors and with malignant disease progression. Functionally, POH1 intensifies TGF-β signaling delivery and, as a consequence, promotes HCC cell metastatic properties both in vitro and in vivo. The expression of the TGF-β receptors was severely downregulated in POH1-deficient mouse hepatocytes. Mechanistically, POH1 deubiquitinates the TGF-β receptors and CAV1, therefore negatively regulates lysosome pathway-mediated turnover of TGF-β receptors.

Conclusion

Our study highlights the pathological significance of aberrantly expressed POH1 in TGF-β signaling hyperactivation and aggressive progression in HCC.

Ubiquitin-specific protease USP34 controls osteogenic differentiation and bone formation by regulating BMP2 signaling

The osteogenic differentiation of mesenchymal stem cells (MSCs) is governed by multiple mechanisms. Growing evidence indicates that ubiquitin-dependent protein degradation is critical for the differentiation of MSCs and bone formation; however, the function of ubiquitin-specific proteases, the largest subfamily of deubiquitylases, remains unclear. Here, we identify USP34 as a previously unknown regulator of osteogenesis. The expression of USP34 in human MSCs increases after osteogenic induction while depletion of USP34 inhibits osteogenic differentiation. Conditional knockout of Usp34 from MSCs or pre-osteoblasts leads to low bone mass in mice. Deletion of Usp34 also blunts BMP2-induced responses and impairs bone regeneration. Mechanically, we demonstrate that USP34 stabilizes both Smad1 and RUNX2 and that depletion of Smurf1 restores the osteogenic potential of Usp34-deficient MSCs in vitro Taken together, our data indicate that USP34 is required for osteogenic differentiation and bone formation.

Epithelial-mesenchymal-transition-inducing transcription factors: new targets for tackling chemoresistance in cancer?

Chemoresistance remains a major complication of cancer treatments. Recent data provide strong evidence that chemoresistance is linked to epithelial-mesenchymal transition (EMT), a latent developmental process, which is re-activated during cancer progression. EMT involves transcriptional reprogramming and is driven by specific EMT transcription factors (EMT-TFs). In this review, we provide support for the idea that EMT-TFs contribute to the development of resistance against cancer therapy and discuss how EMT-TFs might be targeted to advance novel therapeutic approaches to the treatment of cancer.

HINT2 downregulation promotes colorectal carcinoma migration and metastasis

Histidine triad nucleotide-binding 2 (HINT2), a member of the histidine triad proteins family, sensitizes cells to apoptosis in hepatocellular carcinoma. Here, we showed that HINT2 expression is lower in primary colorectal cancer (CRC) and metastasis tissues than in normal colorectal tissues, and that HINT2 abundance is inversely correlated with CRC tumor stage. Treating CRC cells with 5-aza-2′-deoxycytidine, a demethylating agent, upregulated HINT2, suggesting HINT2 downregulation is caused by methylation of the gene promoter. HINT2 downregulation increased tumor migration and invasion in vitro, promoted CRC cell metastasis in vivo, and increased expression of epithelial-to-mesenchymal transition (EMT) markers. Furthermore, HINT2 downregulation depended on hypoxia inducible factor (HIF)-2α-mediated transcriptional activation of zinc finger E-box-binding homeobox 1 (ZEB1). These results suggest that HINT2 downregulation promotes HIF-2α expression, which induces EMT and enhances CRC cell migration and invasion. HINT2 may thus a useful clinical indicator of CRC progression and metastasis risk.

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.

Hidden targets of ubiquitin proteasome system: To prevent diabetic nephropathy

Diabetic nephropathy (DN) is the major cause of end stage renal failure. Although, several therapeutic targets have emerged to prevent the progression of DN, the number of people with DN still continues to rise worldwide, suggesting an urgent need of novel targets to prevent DN completely. Currently, the role of ubiquitin proteasome system (UPS) has been highlighted in the pathogenesis and progression of various diseases like obesity, insulin resistance, atherosclerosis, cancers, neurodegerative disorders and including secondary complications of diabetes. UPS mainly involves in protein homeostatis through ubiquitination (post translational modification) and proteasomal degradation of various proteins. Ubiquitination, not only involves in proteasomal degradation, but also directs the substrate proteins to participate in multitude of cell signalling pathways. However, very little is known about ubiquitination and UPS in the progression of DN. This review mainly focuses on UPS and its components including E2 conjugating enzymes, E3 ligases and deubiquitinases (DUBs) in the development of DN and thus may help us to find novel therapeutic targets with in UPS to prevent DN completely in future.