Role of CK1 in GSK3beta-mediated phosphorylation and degradation of snail

Decidual stromal cells-derived exosomes incurred insufficient migration and invasion of trophoblast by disturbing of β-TrCP-mediated snail ubiquitination and degradation in unexplained recurrent spontaneous abortion

BACKGROUND

Exosomes released from decidual stromal cells (DSC-exos) play a crucial role in facilitating the epithelial-mesenchymal transition (EMT) of trophoblasts and insufficient trophoblasts EMT are associated with URSA (unexplained recurrent spontaneous abortion). However, the mechanisms underlying DSC-exos inducing EMT is not completely understood.

METHODS

DSC-exos of normal pregnant women (N-DSC-exos) and URSA patients (URSA-DSC-exos) were extracted and characterized. Characterization of the isolated DSC-exos was performed using with TEM (transmission electron microscopy), NTA (nanoparticle tracking analysis), and WB (western blot) techniques. Subsequently, these DSC-exos were co-cultured with trophoblasts cell lines (HTR-8/SVneo). The influence of both N-DSC-exos and URSA-DSC-exos on trophoblasts proliferation, invasion and migration, as well as on the expression of EMT-related proteins, was evaluated through a series of assays including CCK8 assays, wound healing assays, transwell assays, and western blot, respectively. Then rescue experiments were performed by β-TrCP knockdown or β-TrCP overexpressing trophoblasts with snail-siRNA transfection or β-TrCP overexpressing Lentivirus infection, respectively. Finally, animal experiments were employed to explore the effect of N-DSC-exos on embryo absorption in mice.

RESULTS

We found increased β-TrCP expression in the villus of URSA patients when compared to the normal pregnant women, alongside reduction in the levels of both snail and N-cadherin within URSA patients. N-DSC-exos can promote the EMT of the trophoblast by inhibiting β-TrCP-mediated ubiquitination and degradation of transcription factor snail. Moreover the capacity to promote EMT was found to be more potent in N-DSC-exos than URSA-DSC-exos. Down-regulation of snail or overexpression of β-TrCP can reverse the effects of N-DSC-exos on trophoblast. Finally, in vivo experiment suggested that N-DSC-exos significantly reduced the embryo resorption rate of spontaneous abortion mouse model.

CONCLUSIONS

Our findings indicate that URSA-DSC-exos caused insufficient migration and invasion of trophoblast because of disturbing of β-TrCP-mediated ubiquitination and degradation of EMT transcription factor snail. Elucidating the underlying mechanism of this dysregulation may shed light on the novel pathways through which DSC-exos influence trophoblast function, thereby contributing to our understanding of their role in URSA.

Targeting CSC-related transcription factors by E3 ubiquitin ligases for cancer therapy

Evidence has revealed that transcription factors play essential roles in regulation of multiple cellular processes, including cell proliferation, metastasis, EMT, cancer stem cells and chemoresistance. Dysregulated expression levels of transcription factors contribute to tumorigenesis and malignant progression. The expression of transcription factors is tightly governed by several signaling pathways, noncoding RNAs and E3 ubiquitin ligases. Cancer stem cells (CSCs) have been validated in regulation of tumor metastasis, reoccurrence and chemoresistance in human cancer. Transcription factors have been verified to participate in regulation of CSC formation, including Oct4, SOX2, KLF4, c-Myc, Nanog, GATA, SALL4, Bmi-1, OLIG2, POU3F2 and FOX proteins. In this review article, we will describe the critical role of CSC-related transcription factors. We will further discuss which E3 ligases regulate the degradation of these CSC-related transcription factors and their underlying mechanisms. We also mentioned the functions and mechanisms of EMT-associated transcription factors such as ZEB1, ZEB2, Snail, Slug, Twist1 and Twist2. Furthermore, we highlight the therapeutic potential via targeting E3 ubiquitin ligases for modulation of these transcription factors.

A Signaling Crosstalk Links SNAIL to the 37/67 kDa Laminin-1 Receptor Ribosomal Protein SA and Regulates the Acquisition of a Cancer Stem Cell Molecular Signature in U87 Glioblastoma Neurospheres

Background: Three-dimensional in vitro neurospheres cultures recapitulate stemness features associated with poor clinical outcome in glioblastoma patients. They are commonly used to address brain cancer stem cell (CSC) signal transducing biology that regulates spheroids formation and stemness phenotype, and to assess the in vitro pharmacological impact of chemotherapeutic drugs. Objective: Here, we addressed the role of a new signaling axis involved in the regulation of in vitro spheroids formation and assessed the chemopreventive ability of diet-derived epigallocatechin gallate (EGCG) to impact the processes that govern the acquisition of spheroids CSC stemness traits. Methods: Neurospheres were generated from adherent human U87 glioblastoma cancer cell cultures under conditions that recapitulate stemness features. Total RNA and protein lysates were isolated for gene expression by RT-qPCR and protein expression by immunoblot. Transcriptomic analysis was performed through RNA-Seq. Results: Compared to their parental adherent cells, tumorspheres expressed increased levels of the CSC markers NANOG, SOX2, PROM1 (CD133), as well as of the epithelial-to-mesenchymal transition (EMT) markers Fibronectin, SNAI1, and 37/67 kDa laminin-1 receptor ribosomal protein SA (RPSA). Increased PROM1, SOX2, Fibronectin, and RPSA transcripts level were also observed in clinical grade IV glioblastoma tissues compared to normal tissue. EGCG treatment reduced dose-dependently tumorspheres size and inhibited the transcriptional regulation of those genes. An apoptotic signature was also found in spheroids with increased signal transducing events involving GSK3α/β, RSK, and CREB. These were repressed upon RPSA gene silencing and partially by SNAI1 silencing. Conclusion: This work highlights a signaling axis linking RPSA upstream of SNAIL in neurospheres genesis and supports the chemopreventive impact that diet-derived EGCG may exert on the acquisition of CSC traits.

Targeting tumor-intrinsic PD-L1 suppresses the progression and aggressiveness of head and neck cancer by inhibiting GSK3β-dependent Snail degradation

PURPOSE

PD-L1 is an immune checkpoint protein that allows cells to evade T-cell-mediated immune responses. Herein, we uncover a tumor-intrinsic mechanism of PD-L1 that is responsible for the progression and aggressiveness of HNC and reveal that the extracts of a brown alga can target the tumor-intrinsic signaling pathway of PD-L1.

METHODS

The biological functions of PD-L1 in the proliferation and aggressiveness of HNC cells in vitro were examined by metabolic activity, clonogenic, tumorigenicity, wound healing, migration, and invasion assays. The clinical importance of PD-L1 in the prognosis of patients with HNC was analyzed by immunohistochemistry. The relationship between PD-L1 and EMT was confirmed via western blotting, qPCR, and immunocytochemistry.

RESULTS

Through our in silico approach, we found that PD-L1 was upregulated in HNC and was correlated with an unfavorable clinical outcome in patients with HNC. PD-L1 was crucial for promoting tumor growth, both in vitro and in vivo. High expression of PD-L1 was closely correlated with LN metastasis in OSCC. PD-L1 facilitated the cytoskeletal reorganization and aggressiveness of HNC cells. Moreover, PD-L1 enhanced the EMT of HNC cells by regulating the Snail/vimentin axis. Consistently, MEIO suppressed the PD-L1/Snail/vimentin axis, thereby inhibiting the aggressiveness of HNC cells. Inhibition of PD-L1 induced by PD-L1 silencing or MEIO treatment caused Snail degradation through a GSK3β-dependent mechanism. The tumor-intrinsic function of PD-L1 could be attributed to the regulation of the GSK3β/Snail/vimentin axis.

CONCLUSION

The discovery of MEIO targeting the tumor-intrinsic function of PD-L1 may prove particularly valuable for the development of novel and effective anticancer drug candidates for HNCs overexpressing PD-L1.

SIRT2 promotes the viability, invasion and metastasis of osteosarcoma cells by inhibiting the degradation of Snail

Osteosarcomas (OS) are highly metastatic and usually lead to poor outcomes. Epithelial-mesenchymal transition (EMT) is reported to be a critical event in metastasis. SIRT2 exerts dual functions in many different tumors. However, the underlying molecular mechanisms of SIRT2 in osteosarcoma cell metastasis and the question of whether SIRT2 regulates EMT have not been fully explored. In this study, we confirmed that SIRT2 was highly-expressed in human osteosarcoma MG63 and Saos-2 cell lines. The viability, migration and invasion of osteosarcoma cells were inhibited by knockdown of SIRT2 and were enhanced by overexpression of SIRT2. Moreover, SIRT2 positively regulated EMT and upregulated the protein levels of the mesenchymal markers N-cadherin and Vimentin and the levels of MMP2 and MMP9. A xenograft mouse model showed that SIRT2 knockdown in osteosarcoma cells led to reduced tumor growth, decreased expression of mesenchymal markers and impaired lung and liver metastasis in vivo. Furthermore, we showed that SIRT2 interacted with and upregulated the protein level of the EMT-associated transcription factor Snail. SIRT2 inhibited Snail degradation via its deacetylase activity. Knockdown of Snail abrogated the promoting effects of SIRT2 on migration and invasion of osteosarcoma cells. In conclusion, SIRT2 plays a crucial role in osteosarcoma metastasis by inhibiting Snail degradation and may serve as a novel therapeutic target to manage osteosarcoma.

Epithelial–Mesenchymal Transition by Synergy between Transforming Growth Factor-β and Growth Factors in Cancer Progression

Epithelial–mesenchymal transition (EMT) plays a crucial role in appropriate embryonic development, as well as wound healing, organ fibrosis, and cancer progression. During cancer progression, EMT is associated with the invasion, metastasis, and generation of circulating tumor cells and cancer stem cells, as well as resistance to chemo- and radiation therapy. EMT is induced by several transcription factors, known as EMT transcription factors (EMT-TFs). In nearly all cases, EMT-TFs appear to be regulated by growth factors or cytokines and extracellular matrix components. Among these factors, transforming growth factor (TGF)-β acts as the key mediator for EMT during physiological and pathological processes. TGF-β can initiate and maintain EMT by activating intracellular/intercellular signaling pathways and transcriptional factors. Recent studies have provided new insights into the molecular mechanisms underlying sustained EMT in aggressive cancer cells, EMT induced by TGF-β, and crosstalk between TGF-β and growth factors.

Regulation of Autophagy by the Glycogen Synthase Kinase-3 (GSK-3) Signaling Pathway

Autophagy is a vital cellular mechanism that benefits cellular maintenance and survival during cell stress. It can eliminate damaged or long-lived organelles and improperly folded proteins to maintain cellular homeostasis, development, and differentiation. Impaired autophagy is associated with several diseases such as cancer, neurodegenerative diseases, and age-related macular degeneration (AMD). Several signaling pathways are associated with the regulation of the autophagy pathway. The glycogen synthase kinase-3 signaling pathway was reported to regulate the autophagy pathway. In this review, we will discuss the mechanisms by which the GSK-3 signaling pathway regulates autophagy. Autophagy and lysosomal function are regulated by transcription factor EB (TFEB). GSK-3 was shown to be involved in the regulation of TFEB nuclear expression in an mTORC1-dependent manner. In addition to mTORC1, GSK-3β also regulates TFEB via the protein kinase C (PKC) and the eukaryotic translation initiation factor 4A-3 (eIF4A3) signaling pathways. In addition to TFEB, we will also discuss the mechanisms by which the GSK-3 signaling pathway regulates autophagy by modulating other signaling molecules and autophagy inducers including, mTORC1, AKT and ULK1. In summary, this review provides a comprehensive understanding of the role of the GSK-3 signaling pathway in the regulation of autophagy.

Insights into the post-translational modification and its emerging role in shaping the tumor microenvironment

More and more in-depth studies have revealed that the occurrence and development of tumors depend on gene mutation and tumor heterogeneity. The most important manifestation of tumor heterogeneity is the dynamic change of tumor microenvironment (TME) heterogeneity. This depends not only on the tumor cells themselves in the microenvironment where the infiltrating immune cells and matrix together forming an antitumor and/or pro-tumor network. TME has resulted in novel therapeutic interventions as a place beyond tumor beds. The malignant cancer cells, tumor infiltrate immune cells, angiogenic vascular cells, lymphatic endothelial cells, cancer-associated fibroblastic cells, and the released factors including intracellular metabolites, hormonal signals and inflammatory mediators all contribute actively to cancer progression. Protein post-translational modification (PTM) is often regarded as a degradative mechanism in protein destruction or turnover to maintain physiological homeostasis. Advances in quantitative transcriptomics, proteomics, and nuclease-based gene editing are now paving the global ways for exploring PTMs. In this review, we focus on recent developments in the PTM area and speculate on their importance as a critical functional readout for the regulation of TME. A wealth of information has been emerging to prove useful in the search for conventional therapies and the development of global therapeutic strategies.

Silencing IKBKE inhibits the migration and invasion of glioblastoma by promoting Snail1 degradation

PURPOSE

Glioblastoma multiforme (GBM) is one of the most common malignant brain tumors in adults and has high mortality and relapse rates. Over the past few years, great advances have been made in the diagnosis and treatment of GBM, but unfortunately, the five-year overall survival rate of GBM patients is approximately 5.1%. Inhibitor of nuclear factor kappa-B kinase subunit epsilon (IKBKE) is a major oncogenic protein in tumors and can promote evil development of GBM. Snail1, a key inducer of the epithelial-mesenchymal transition (EMT) transcription factor, is subjected to ubiquitination and degradation, but the mechanism by which Snail1 is stabilized in tumors remains unclear. Our study aimed to investigate the mechanism of IKBKE regulating Snail1 in GBM.

METHODS

First, we analyzed the correlation between the expression of IKBKE and the tumor grade and prognosis through public databases and laboratory specimen libraries. Second, immunohistochemistry (IHC) and western blot were used to detect the correlation between IKBKE and Snail expression in glioma samples and cell lines. Western blot and immunofluorescence (IF) experiments were used to detect the quality and distribution of IKBKE and Snail1 proteins. Third, In situ animal model of intracranial glioma to detect the regulatory effect of IKBKE on intracranial tumors.

RESULTS

In this study, Our study reveals a new connection between IKBKE and Snail1, where IKBKE can directly bind to Snail1, translocate Snail1 into the nucleus from the cytoplasm. Downregulation of IKBKE results in Snail1 destabilization and impairs the tumor cell migration and invasion capabilities.

CONCLUSION

Our studies suggest that the IKBKE-Snail1 axis may serve as a potential therapeutic target for GBM treatment.

Cyclical phosphorylation of LRAP35a and CLASP2 by GSK3β and CK1δ regulates EB1-dependent MT dynamics in cell migration

Mammalian cell cytoskeletal reorganization for efficient directional movement requires tight coordination of actomyosin and microtubule networks. In this study, we show that LRAP35a potentiates microtubule stabilization by promoting CLASP2/EB1 interaction besides its complex formation with MRCK/MYO18A for retrograde actin flow. The alternate regulation of these two networks by LRAP35a is tightly regulated by a series of phosphorylation events that dictated its specificity. Sequential phosphorylation of LRAP35a by Protein Kinase A (PKA) and Glycogen Synthase Kinase-3β (GSK3β) initiates the association of LRAP35a with CLASP2, while subsequent binding and further phosphorylation by Casein Kinase 1δ (CK1δ) induce their dissociation, which facilitates LRAP35a/MRCK association in driving lamellar actomyosin flow. Importantly, microtubule dynamics is directly moderated by CK1δ activity on CLASP2 to regulate GSK3β phosphorylation of the SxIP motifs that blocks EB1 binding, an event countered by LRAP35a interaction and its competition for CK1δ activity. Overall this study reveals an essential role for LRAP35a in coordinating lamellar contractility and microtubule polarization in cell migration.

Stress-activated kinases as therapeutic targets in pancreatic cancer

Pancreatic cancer is a dismal disease with high incidence and poor survival rates. With the aim to improve overall survival of pancreatic cancer patients, new therapeutic approaches are urgently needed. Protein kinases are key regulatory players in basically all stages of development, maintaining physiologic functions but also being involved in pathogenic processes. c-Jun N-terminal kinases (JNK) and p38 kinases, representatives of the mitogen-activated protein kinases, as well as the casein kinase 1 (CK1) family of protein kinases are important mediators of adequate response to cellular stress following inflammatory and metabolic stressors, DNA damage, and others. In their physiologic roles, they are responsible for the regulation of cell cycle progression, cell proliferation and differentiation, and apoptosis. Dysregulation of the underlying pathways consequently has been identified in various cancer types, including pancreatic cancer. Pharmacological targeting of those pathways has been the field of interest for several years. While success in earlier studies was limited due to lacking specificity and off-target effects, more recent improvements in small molecule inhibitor design against stress-activated protein kinases and their use in combination therapies have shown promising in vitro results. Consequently, targeting of JNK, p38, and CK1 protein kinase family members may actually be of particular interest in the field of precision medicine in patients with highly deregulated kinase pathways related to these kinases. However, further studies are warranted, especially involving in vivo investigation and clinical trials, in order to advance inhibition of stress-activated kinases to the field of translational medicine.

The Post-Translational Regulation of Epithelial-Mesenchymal Transition-Inducing Transcription Factors in Cancer Metastasis

Epithelial-mesenchymal transition (EMT) is generally observed in normal embryogenesis and wound healing. However, this process can occur in cancer cells and lead to metastasis. The contribution of EMT in both development and pathology has been studied widely. This transition requires the up- and down-regulation of specific proteins, both of which are regulated by EMT-inducing transcription factors (EMT-TFs), mainly represented by the families of Snail, Twist, and ZEB proteins. This review highlights the roles of key EMT-TFs and their post-translational regulation in cancer metastasis.

Casein Kinase 1α as a Regulator of Wnt-Driven Cancer

Wnt signaling regulates numerous cellular processes during embryonic development and adult tissue homeostasis. Underscoring this physiological importance, deregulation of the Wnt signaling pathway is associated with many disease states, including cancer. Here, we review pivotal regulatory events in the Wnt signaling pathway that drive cancer growth. We then discuss the roles of the established negative Wnt regulator, casein kinase 1α (CK1α), in Wnt signaling. Although the study of CK1α has been ongoing for several decades, the bulk of such research has focused on how it phosphorylates and regulates its various substrates. We focus here on what is known about the mechanisms controlling CK1α, including its putative regulatory proteins and alternative splicing variants. Finally, we describe the discovery and validation of a family of pharmacological CK1α activators capable of inhibiting Wnt pathway activity. One of the important advantages of CK1α activators, relative to other classes of Wnt inhibitors, is their reduced on-target toxicity, overcoming one of the major impediments to developing a clinically relevant Wnt inhibitor. Therefore, we also discuss mechanisms that regulate CK1α steady-state homeostasis, which may contribute to the deregulation of Wnt pathway activity in cancer and underlie the enhanced therapeutic index of CK1α activators.

β-TrCP suppresses the migration and invasion of trophoblast cells in preeclampsia by down-regulating Snail

Insufficient trophoblast invasion has been shown to contribute to the occurrence and progression of preeclampsia (PE). Recently, beta-transducin repeat containing E3 ubiquitin protein (β-TrCP) was shown to function as a ubiquitination regulator in regulating the proliferation and invasion of various cell types. In this study, we employed an in vitro model of trophoblasts to investigate the role played by β-TrCP in the pathogenesis of PE. The levels of β-TrCP in newly delivered placentas from 15 pregnant women with PE and 15 healthy pregnant women were detected by quantitative real-time PCR and western blot assays. The effects of β-TrCP on cell migration, invasion, and epithelial-mesenchymal transition (EMT) in two trophoblast cell lines (HTR-8/SVneo and TEV-1) were examined using wound healing assays, Transwell assays, and western blot assays, respectively. Rescue experiments were performed by treating β-TrCP knockdown or β-TrCP expressing trophoblasts with si-Snail transfection or a proteasome inhibitor (MG132). β-TrCP mRNA and protein expression levels were significantly increased in the PE placentas when compared to the normal control placentas. β-TrCP overexpression significantly inhibited cell migration and invasion, while silencing of β-TrCP promoted cell migration and invasion of the two trophoblast cell lines. Furthermore, we demonstrated that β-TrCP-mediated ubiquitination might inhibit the EMT process of trophoblasts by down-regulating Snail expression. Our results suggest that both β-TrCP mRNA and protein expression were up-regulated in the PE placentas. β-TrCP impeded the migration and invasion of trophoblasts by suppressing Snail expression. This implicates the ubiquitin-proteasome pathway in the pathogenesis of PE, and suggests β-TrCP as a potential target for treating PE.

Se-methylselenocysteine stimulates migration and antioxidant response in HaCaT keratinocytes: Implications for wound healing

BACKGROUND

Se-methylselenocysteine (MSC), a natural organic selenium compound, is known for its anticancer effects. In the present study, we investigated the effects of MSC on cell migration, which is the most limiting step in the reepithelialization process of wound healing and the antioxidant response in HaCaT keratinocytes.

METHODS

HaCaT cells were treated with various concentrations of MSC. Cell migration and proliferation, the expression of proteins that are involved in the epidermal-mesenchymal transition (EMT) process, the extent of oxidative stress and the antioxidant response, and the associated signaling pathways were analyzed.

RESULTS

MSC (100-500 μM) increased HaCaT cell migration. MSC stimulated EMT, which was evidenced by a decrease in E-cadherin in the cells at the wound edge and increases in Snail, Twist, and matrix metalloproteinases. MSC increased the phosphorylation of Akt and glycogen synthase kinase 3β, which led to the stabilization and nuclear accumulation of β-catenin, a transcriptional coactivator involved in EMT. MSC caused a transient increase and then an eventual decrease in cellular reactive oxygen species, which appeared to be associated with the increase in nuclear factor erythroid 2-related factor 2, a key transcription factor for the antioxidant response.

CONCLUSION

Our results suggest that MSC can promote skin wound healing by stimulating keratinocyte migration and, moreover, can protect cells from excessive oxidative stress that often accompanies and impairs the wound healing process, particularly in chronic wounds, by stimulating an antioxidant response.

G-protein-coupled receptor kinase 2 safeguards epithelial phenotype in head and neck squamous cell carcinomas

Head and neck squamous cell carcinoma (HNSCC) arises from the mucosal lining of the upper aerodigestive tract and display few treatment options in advanced stages. Despite increased knowledge of HNSCC molecular biology, the identification of new players involved in triggering HNSCC recurrence and metastatic disease is needed. We uncover that G-protein-coupled receptor kinase-2 (GRK2) expression is reduced in undifferentiated, high-grade human HNSCC tumors, whereas its silencing in model human HNSCC cells is sufficient to trigger epithelial-to-mesenchymal transition (EMT) phenotypic features, an EMT-like transcriptional program and enhanced lymph node colonization from orthotopic tongue tumors in mice. Conversely, enhancing GRK2 expression counteracts mesenchymal cells traits by mechanisms involving phosphorylation and decreased functionality of the key EMT inducer Snail1. Our results suggest that GRK2 safeguards the epithelial phenotype, whereas its downregulation contributes to the activation of EMT programs in HNSCC.

Targeting SCF E3 Ligases for Cancer Therapies

SKP1-cullin-1-F-box-protein (SCF) E3 ubiquitin ligase complex is responsible for the degradation of proteins in a strictly regulated manner, through which it exerts pivotal roles in regulating various key cellular processes including cell cycle and division, apoptosis, and differentiation. The substrate specificity of the SCF complex largely depends on the distinct F-box proteins, which function in either tumor promotion or suppression or in a context-dependent manner. Among the 69 F-box proteins identified in human genome, FBW7, SKP2, and β-TRCP have been extensively investigated among various types of cancer in respective of their roles in cancer development, progression, and metastasis. Moreover, several specific inhibitors have been developed to target those E3 ligases, and their efficiency in tumors has been determined. In this review, we provide a summary of the roles of SCF E3 ligases in cancer development, as well as the potential application of miRNA or specific inhibitors for cancer therapy.

The basics of epithelial-mesenchymal transition (EMT): A study from a structure, dynamics, and functional perspective

Epithelial-mesenchymal transition (EMT) is a key step in transdifferentiation process in solid cancer development. Forthcoming evidence suggest that the stratified program transforms polarized, immotile epithelial cells to migratory mesenchymal cells associated with enhancement of breast cancer stemness, metastasis, and drug resistance. It involves primarily several signaling pathways, such as transforming growth factor-β (TGF-β), cadherin, notch, plasminogen activator protein inhibitor, urokinase plasminogen activator, and WNT/beta catenin pathways. However, current understanding on the crosstalk of multisignaling pathways and assemblies of key transcription factors remain to be explored. In this review, we focus on the crosstalk of signal transduction pathways linked to the current therapeutic and drug development strategies. We have also performed the computational modeling on indepth the structure and conformational dynamic studies of regulatory proteins and analyze molecular interactions with their associate factors to understand the complicated process of EMT in breast cancer progression and metastasis. Electrostatic potential surfaces have been analyzed that help in optimization of electrostatic interactions between the protein and its ligand. Therefore, understanding the biological implications underlying the EMT process through molecular biology with biocomputation and structural biology approaches will enable the development of new therapeutic strategies to sensitize tumors to conventional therapy and suppress their metastatic phenotype.

FAM83A signaling induces epithelial-mesenchymal transition by the PI3K/AKT/Snail pathway in NSCLC

Family with sequence similarity 83, member A (FAM83A), as a potential tumor promoter, was reported to contribute to the progression of several malignant tumors. However, the significance of FAM83A in invasion and metastasis of non-small cell lung cancer (NSCLC) remains largely unknown. In this study, we found that FAM83A expression was significantly increased in NSCLC tissues. High expression of FAM83A was positively associated with tumor metastasis and poor survival of NSCLC patients. Functional experiments revealed that FAM83A knockdown could suppress NSCLC cell migration and invasion both in vivo and in vitro. While opposite results were observed in FAM83A-transfected cells. Mechanically, we found that FAM83A promoted NSCLC cell migration and invasion by inducing epithelial-mesenchymal transition (EMT) via PI3K/ATK/Snail signaling. Rescue experiment demonstrated that inhibition of either AKT or Snail could partially counteract the promoting effect of FAM83A overexpression in NSCLC metastasis. Taken together, our findings are the first time to demonstrate that increased expression of FAM83A in NSCLC was correlated with EMT and tumor metastasis, which may provide a novel therapeutic target in NSCLC treatment.

Roles of the Phosphorylation of Transcriptional Factors in Epithelial-Mesenchymal Transition

Epithelial-to-mesenchymal transition (EMT) is the first step in the development of the invasive and migratory properties of cancer metastasis. Since the transcriptional reprogramming of a number of genes occurs in EMT, the regulation of EMT transcription factors has been intensively investigated. EMT transcriptional factors are commonly classified by the direct or indirect repression of E-cadherin because one of hallmarks of EMT is the loss of E-cadherin. This facilitates the expression of genes for EMT, tumor invasion, and metastasis. The posttranslational modification of EMT transcriptional factors, such as Snail and Slug, directly regulates their functions, including their stability, nuclear localization, protein-protein interaction, and ubiquitination for the promotion or termination of EMT at the specific points. Here, we discuss how posttranslational modifications regulate gene expression in a dynamic and reversible manner by modifying upstream signaling pathways, focusing in particular on the posttranslational modifications of Snail, Slug, ZEB1, ZEB2, and TWIST1. This review demonstrates that EMT transcription factors regulate metastasis through their posttranslational modifications and that the flexibility and reversibility of EMT can be modified by phosphorylation.

Snail1: A Transcriptional Factor Controlled at Multiple Levels

Snail1 transcriptional factor plays a key role in the control of epithelial to mesenchymal transition and fibroblast activation. As a consequence, Snail1 expression and function is regulated at multiple levels from gene transcription to protein modifications, affecting its interaction with specific cofactors. In this review, we describe the different elements that control Snail1 expression and its activity both as transcriptional repressor or activator.

C-terminal domain small phosphatase-like 2 promotes epithelial-to-mesenchymal transition via Snail dephosphorylation and stabilization

The epithelial-to-mesenchymal transition (EMT) is a cellular reprogramming process converting epithelial cells into mesenchymal cell morphology. Snail is a critical regulator of EMT by both suppressing epithelial gene expression and promoting mesenchymal gene expression. Expression and activity of Snail are tightly controlled at transcriptional and post-translational levels. It has previously been reported that Snail undergoes phosphorylation and ubiquitin-dependent proteasome degradation. Here, we report nuclear phosphatase SCP4/CTDSPL2 acts as a novel Snail phosphatase. SCP4 physically interacts with and directly dephosphorylates Snail. SCP4-mediated dephosphorylation of Snail suppresses the ubiquitin-dependent proteasome degradation of Snail and consequently enhances TGFβ-induced EMT. The knockdown of SCP4 in MCF10A mammary epithelial cells leads to attenuated cell migration. Collectively, our finding demonstrates that SCP4 plays a critical role in EMT through Snail dephosphorylation and stabilization.

Hypoxia-induced Slug SUMOylation enhances lung cancer metastasis

Background

The Slug-E-cadherin axis plays a critical role in non-small-cell lung cancers (NSCLCs) where aberrant upregulation of Slug promotes cancer metastasis. Now, the post-translational modifications of Slug and their regulation mechanisms still remain unclear in lung cancer. Hence, exploring the protein linkage map of Slug is of great interest for investigating the scenario of how Slug protein is regulated in lung cancer metastasis.

Methods

The Slug associated proteins, Ubc9 and SUMO-1, were identified using yeast two-hybrid screening; and in vitro SUMOylation assays combined with immunoprecipitation and immunoblotting were performed to explore the detail events and regulations of Slug SUMOylation. The functional effects of SUMOylation on Slug proteins were examined by EMSA, reporter assay, ChIP assay, RT-PCR, migration and invasion assays in vitro, tail vein metastatic analysis in vivo, and also evaluated the association with clinical outcome of NSCLC patients.

Results

Slug protein could interact with Ubc9 and SUMO-1 and be SUMOylated in cells. Amino acids 130–212 and 33–129 of Slug are responsible for its binding to Ubc9 and protein inhibitor of activated STAT (PIAS)y, respectively. SUMOylation could enhance the transcriptional repression activity of Slug via recruiting more HDAC1, resulting in reduced expression of downstream Slug target genes and enhanced lung cancer metastasis. In addition, hypoxia could increase Slug SUMOylation through attenuating the interactions of Slug with SENP1 and SENP2. Finally, high expression Slug and Ubc9 levels were associated with poor overall survival among NSCLC patients.

Conclusions

Ubc9/PIASy-mediated Slug SUMOylation and subsequent HDAC1 recruitment may play a crucial role in hypoxia-induced lung cancer progression, and these processes may serve as therapeutic targets for NSCLC.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0996-8) contains supplementary material, which is available to authorized users.

ZNF259 promotes breast cancer cells invasion and migration via ERK/GSK3β/snail signaling

Purpose

Zinc finger protein 259 (ZNF259), also known as ZPR1, is a zinc finger-containing protein that can bind the intracellular tyrosine kinase domain of EGFR. At present, our knowledge on ZNF259 in cancers is limited. Here, we aimed to explore the biological functions of ZNF259 in breast cancer and reveal their mechanisms.

Patients and methods

The expression of ZNF259 was measured in 133 cases of breast cancer by immunohistochemistry. The online database Kaplan–Meier (KM) Plotter Online Tool was used to analyze the relationship between ZNF259 expression and breast cancer patient survival prognosis. Plasmid transfection and small interfering RNA and inhibitor treatments were carried out to explore the functions of ZNF259 in breast cancer cell lines and its potential mechanism. Matrigel invasion and wound healing assays were performed to detect the invasion and migration ability of cancer cells. In addition, protein expressions in tissues and cells were determined by Western blotting.

Results

ZNF259 expression was much higher in breast cancer cells than in the adjacent normal breast duct glandular epithelial cells (75.94% vs 7.52%, P<0.001) and was closely related to the breast cancer patients’ TNM stages (P=0.013) and lymph node metastasis (P=0.021). Knockdown of ZNF259 could downregulate p-ERK, p-GSK3β, and Snail expression, and upregulate the expression of E-cadherin and ZO-1, and then it also inhibited invasion and migration by the breast cancer cell lines MCF-7 and MDA-MB-231. Correspondingly, ZNF259 transfection could upregulate p-ERK, p-GSK3β, and Snail expression, and downregulate E-cadherin and ZO-1 expression, which led to stronger invasion and migration abilities of cancer cells. Furthermore, the ERK inhibitor U0126 could reverse all these effects induced by ZNF259 transfection.

Conclusion

ZNF259 could promote breast cancer cell invasion and migration by activating the ERK/GSK3β/Snail signaling pathway.

TMEM17 promotes malignant progression of breast cancer via AKT/GSK3β signaling

Purpose

Current knowledge of TMEM17, a recently identified protein of the transmembrane (TMEM) family, is limited, especially with respect to its expression and biological functions in malignant tumors. This study analyzed TMEM17 expression in invasive breast cancer tissue and breast cell lines and its relevance to clinicopathological factors, and investigated the mechanisms underlying the biological effects of TMEM17 on breast cancer cells.

Patients and methods

TMEM17 protein expression was determined in 20 freshly harvested specimens (tumor and paired normal tissues) by Western blotting. Immunohistochemical analysis was performed to determine the expression and subcellular localization of TMEM17 in samples from 167 patients (mean age, 49 years) diagnosed with invasive ductal carcinoma (38 with triple-negative breast cancer; 129 with non-triple-negative breast cancer) who underwent complete resection in the First Affiliated Hospital of China Medical University between 2011 and 2013. Furthermore, TMEM17 was knocked down by small interfering RNAs in breast cancer cell lines.

Results

TMEM17 was found to be significantly upregulated in breast cancer tissues compared to the corresponding normal breast tissues by Western blotting (p=0.015). Immunohistochemical analysis revealed that TMEM was significantly upregulated in invasive breast cancer cells compared to adjacent normal breast duct glandular epithelial cells (10.78% vs 76.05%, p<0.001), and its expression was closely related to the patient’s T-stage (p=0.022), advanced TNM stages (p=0.007), and lymph node metastasis (p=0.012). After TMEM17 knockdown or overexpression in breast cancer cell lines, TMEM17 upregulated p-AKT, p-GSK3β, active β-catenin, and Snail, and downstream target proteins c-myc and cyclin D1, and downregulated E-cadherin, resulting in increased cancer cell proliferation, invasion, and migration. These effects were reversed by the AKT inhibitor LY294002.

Conclusion

Our results indicate that TMEM17 is upregulated in breast cancer tissues and can promote malignant progression of breast cancer cells by activating the AKT/GSK3β signaling pathway.

A partnership with the proteasome; the destructive nature of GSK3

Glycogen Synthase Kinase-3 (GSK3) was originally reported as a key enzyme of glucose homeostasis through regulation of the rate of glycogen synthesis. It has subsequently been found to influence most cellular processes, including growth, differentiation and death, as part of its role in modulating response to hormonal, nutritional and cellular stress stimuli. More than 100 protein targets for GSK3 have been proposed although only a small fraction of these have been convincingly validated in physiological cell systems. The effects of GSK3 phosphorylation on substrates include alteration of enzyme activity, protein localisation, protein:protein interaction and protein stability. This latter form of regulation of GSK3 substrates is the focus of this review. There is an ever-growing list of GSK3 substrates that upon phosphorylation are targeted to the beta-transducin repeat containing protein (β-TrCP), thereby allowing ubiquitination of bound protein by cullin-1 and so initiating destruction at the proteasome. We propose the existence of a GSK3-β-TrCP ‘destruction hit-list’ that allows co-ordinated removal (or stabilisation) of a set of proteins with a common physiological purpose, through control of GSK3. We identify 29 proteins where there is relatively strong evidence for regulation by a GSK3-β-TrCP axis and note common features of regulation and pathophysiology. Furthermore, we assess the potential of pre-phosphorylation (priming) of these targets (normally a prerequisite for GSK3 recognition) to provide a second layer of regulation delineated by the priming kinase that allows GSK3 to mark them for destruction. Finally, we discuss whether this knowledge improves options for therapeutic intervention.

Stability of the PHF10 subunit of PBAF signature module is regulated by phosphorylation: role of β-TrCP

The PBAF chromatin-remodeling complexes are multi-protein machines, regulating expression of genes involved in proliferation and differentiation. PHF10 is a subunit of the PBAF essential for its association with chromatin. Mammalian PHF10 is expressed as four ubiquitous isoforms, which are alternatively incorporated in the complex and differ by their influence on transcription of target genes. PHF10 have different domain structure and two of them (PHF10-S isoforms) lack C-terminal PHD domains, which enables their phosphorylation by CK-1. Here we have found that PBAF subunits have low turnover rate, except for PHF10 which has much lower half-life, and is degraded by β-TrCP. The β-TrCP knockdown stabilizes PBAF core subunits - BRG1 and BAF155 and specific subunits - PHF10, BAF200, BAF180 and BRD7. PHF10 isoforms contain two non-canonical β-TrCP degrons and are degraded by β-TrCP in a phospho-dependent manner. But phosphorylation of PHF10-S degrons by CK-1, contrary to previously described degrons, prevents their degradation. Targeted molecular docking demonstrated that phosphorylated forms of PHF10 bind to β-TrCP with much lower affinity than non-phosphorylated ones, contrary to previously described degrons. This unorthodox mechanism proposes that phosphorylation of β-TrCP degrons by CK-1 could not only degrade a set of proteins, but also stabilize a different set of targets.

β-transducin repeat-containing E3 ubiquitin protein ligase inhibits migration, invasion and proliferation of glioma cells

β-transducin repeat-containing E3 ubiquitin protein ligase (β-TrCP) serves as the substrate recognition subunit for the Skp1-Cullin1-F-box protein E3 ubiquitin ligase, which recognizes the double phosphorylated DSG (X)_2+nS destruction motif in various substrates that are essential for numerous aspects of tumorigenesis and regulates several important signaling pathways. However, the biological significance of β-TrCP in glioma progression remains largely unknown. A previous study by the authors demonstrated that the levels of β-TrCP protein expression in brain glioma tissues were significantly lower compared with non-tumorous tissues and that higher grades of gliomas exhibited lower levels of β-TrCP expression in comparison with lower glioma grades. In addition, low β-TrCP expression was associated with poor prognosis in patients with glioma. Subsequently, the present study aimed to investigate the effect of β-TrCP on migratory, invasive and proliferative abilities of glioma cells. β-TrCP plasmids were transfected into cultured U251 and U87 glioma cells, and changes in migration, invasion and proliferation were analyzed using wound healing, Transwell and EdU assays. It was identified that the overexpression of β-TrCP inhibited migration, invasion and proliferation in glioma cells. In summary, these results indicate that β-TrCP may serve a protective role against the progression of glioma by suppressing cell migration, invasion and proliferation. The potential mechanism of β-TrCP I glioma cells requires additional investigation.

CK1δ/GSK3β/FBXW7α axis promotes degradation of the ZNF322A oncoprotein to suppress lung cancer progression

Overexpression of Cys2His2 zinc-finger 322A (ZNF322A) oncogenic transcription factor is associated with lung tumorigenesis. However, the mechanism of ZNF322A overexpression remains poorly understood. Here, we discover that protein stability of ZNF322A is regulated by coordinated phosphorylation and ubiquitination through the CK1δ/GSK3β/FBXW7α axis. CK1δ and GSK3β kinases sequentially phosphorylate ZNF322A at serine-396 and then serine-391. Moreover, the doubly phosphorylated ZNF322A protein creates a destruction motif for the ubiquitin ligase FBXW7α leading to ZNF322A protein destruction. Overexpression of FBXW7α induces ZNF322A protein degradation, thereby blocks ZNF322A transcription activity and suppresses ZNF322A-induced tumor growth and metastasis in vitro and in vivo. Clinically, overexpression of ZNF322A correlates with low FBXW7α or defective CK1δ/GSK3β-mediated phosphorylation in lung cancer patients. Multivariate Cox regression analysis indicates that patients with ZNF322A high/FBXW7 low expression profile can be used as an independent factor to predict the clinical outcome in lung cancer patients. Our results reveal a new mechanism of ZNF322A oncoprotein destruction regulated by the CK1δ/GSK3β/FBXW7α axis. Deregulation of this signaling axis results in ZNF322A overexpression and promotes cancer progression.

Therapeutic Targeting of Epithelial Plasticity Programs: Focus on the Epithelial-Mesenchymal Transition

Mounting data points to epithelial plasticity programs such as the epithelial-mesenchymal transition (EMT) as clinically relevant therapeutic targets for the treatment of malignant tumors. In addition to the widely realized role of EMT in increasing cancer cell invasiveness during cancer metastasis, the EMT has also been implicated in allowing cancer cells to avoid tumor suppressor pathways during early tumorigenesis. In addition, data linking EMT to innate and acquired treatment resistance further points towards the desire to develop pharmacological therapies to target epithelial plasticity in cancer. In this review we organized our discussion on pathways and agents that can be used to target the EMT in cancer into 3 groups: (1) extracellular inducers of EMT, (2) the transcription factors that orchestrate the EMT transcriptome, and (3) the downstream effectors of EMT. We highlight only briefly specific canonical pathways known to be involved in EMT, such as the signal transduction pathways TGFβ, EFGR, and Axl-Gas6. We emphasize in more detail pathways that we believe are emerging novel pathways and therapeutic targets such as epigenetic therapies, glycosylation pathways, and immunotherapy. The heterogeneity of tumors and the dynamic nature of epithelial plasticity in cancer cells make it likely that targeting only 1 EMT-related process will be unsuccessful or only transiently successful. We suggest that with greater understanding of epithelial plasticity regulation, such as with the EMT, a more systematic targeting of multiple EMT regulatory networks will be the best path forward to improve cancer outcomes.

Stapled peptides: providing the best of both worlds in drug development

Peptide-based drug discovery has experienced a remarkable resurgence within the past decade due to the emerging class of inhibitors known as stapled peptides. Stapled peptides are therapeutic protein mimetics that have been locked within a specific conformational structure by hydrocarbon stapling. These peptides are highly important in selectively impairing disease-relevant protein–protein interactions and exhibit significant pharmacokinetic advantages over other forms of therapeutics in terms of affinity, specificity, size, synthetic accessibility and resistance to proteolytic degradation. A series of stapled peptides are currently in development, and the potential successes of these peptides, either as single-agent treatments or as combinational treatments with other therapeutic modalities, could potentially change the landscape of protein therapeutic development. Here, we provide examples of successful discovery efforts to illustrate the research strategies of stapled peptides in drug design and development.

EBV-miR-BART10-3p facilitates epithelial-mesenchymal transition and promotes metastasis of nasopharyngeal carcinoma by targeting BTRC

Epstein-Barr virus (EBV) infection is closely associated with tumorigenesis and development of nasopharyngeal carcinoma (NPC), but the underlying molecular mechanisms remain poorly understood. It has been recently reported that EBV encodes 44 mature miRNAs, some of which were found to promote tumor development by targeting virus-infected host genes or self-viral genes. However, few targets of EBV encoded-miRNAs that are related to NPC development have been identified to date. In this study, we revealed that in NPC cells, EBV-miR-BART10-3p directly targets BTRC gene that encodes βTrCP (beta-transducin repeat containing E3 ubiquitin protein ligase). We found that EBV-miR-BART10-3p expression in clinical samples from a cohort of 106 NPC patients negatively correlated with BTRC expression levels. Over-expression of EBV-miR-BART10-3p and down-regulation of BTRC were associated with poor prognosis in NPC patients. EBV-miR-BART10-3p promoted the invasion and migration cabilities of NPC cells through the targeting of BTRC and regulation of the expression of the downstream substrates β-catenin and Snail. As a result, EBV-miR-BART10-3p facilitated epithelial-mesenchymal transition of NPC. Our study presents an unreported mechanism underlying EBV infection in NPC carcinogenesis, and provides a potential novel biomarker for NPC diagnosis, treatment and prognosis.

Hijacking the Hexosamine Biosynthetic Pathway to Promote EMT-Mediated Neoplastic Phenotypes

The epithelial-mesenchymal transition (EMT) is a highly conserved program necessary for orchestrating distant cell migration during embryonic development. Multiple studies in cancer have demonstrated a critical role for EMT during the initial stages of tumorigenesis and later during tumor invasion. Transcription factors (TFs) such as SNAIL, TWIST, and ZEB are master EMT regulators that are aberrantly overexpressed in many malignancies. Recent evidence correlates EMT-related transcriptomic alterations with metabolic reprograming in cancer. Metabolic alterations may allow cancer to adapt to environmental stressors, supporting the irregular macromolecular demand of rapid proliferation. One potential metabolic pathway of increasing importance is the hexosamine biosynthesis pathway (HBP). The HBP utilizes glycolytic intermediates to generate the metabolite UDP-GlcNAc. This and other charged nucleotide sugars serve as the basis for biosynthesis of glycoproteins and other glycoconjugates. Recent reports in the field of glycobiology have cultivated great curiosity within the cancer research community. However, specific mechanistic relationships between the HBP and fundamental pathways of cancer, such as EMT, have yet to be elucidated. Altered protein glycosylation downstream of the HBP is well positioned to mediate many cellular changes associated with EMT including cell-cell adhesion, responsiveness to growth factors, immune system evasion, and signal transduction programs. Here, we outline some of the basics of the HBP and putative roles the HBP may have in driving EMT-related cancer processes. With novel appreciation of the HBP's connection to EMT, we hope to illuminate the potential for new therapeutic targets of cancer.

β-TrCP-mediated ubiquitination and degradation of liver-enriched transcription factor CREB-H

CREB-H is an endoplasmic reticulum-resident bZIP transcription factor which critically regulates lipid homeostasis and gluconeogenesis in the liver. CREB-H is proteolytically activated by regulated intramembrane proteolysis to generate a C-terminally truncated form known as CREB-H-ΔTC, which translocates to the nucleus to activate target gene expression. CREB-H-ΔTC is a fast turnover protein but the mechanism governing its destruction was not well understood. In this study, we report on β-TrCP-dependent ubiquitination and proteasomal degradation of CREB-H-ΔTC. The degradation of CREB-H-ΔTC was mediated by lysine 48-linked polyubiquitination and could be inhibited by proteasome inhibitor. CREB-H-ΔTC physically interacted with β-TrCP, a substrate recognition subunit of the SCF^β-TrCP E3 ubiquitin ligase. Forced expression of β-TrCP increased the polyubiquitination and decreased the stability of CREB-H-ΔTC, whereas knockdown of β-TrCP had the opposite effect. An evolutionarily conserved sequence, SDSGIS, was identified in CREB-H-ΔTC, which functioned as the β-TrCP-binding motif. CREB-H-ΔTC lacking this motif was stabilized and resistant to β-TrCP-induced polyubiquitination. This motif was a phosphodegron and its phosphorylation was required for β-TrCP recognition. Furthermore, two inhibitory phosphorylation sites close to the phosphodegron were identified. Taken together, our work revealed a new intracellular signaling pathway that controls ubiquitination and degradation of the active form of CREB-H transcription factor.

Overcoming Resistance to Endocrine Therapy in Breast Cancer: New Approaches to a Nagging Problem

In the majority of women, breast cancer progresses through increased transcriptional activity due to over-expressed oestrogen receptors (ER). Therapeutic strategies include: (i) reduction of circulating ovarian oestrogens or of peripherally produced oestrogen (in postmenopausal women) with aromatase inhibitors and (ii) application of selective ER modulators for receptor blockade. The success of these interventions is limited by the variable but persistent onset of acquired resistance and by an intrinsic refractiveness which manifests despite adequate levels of ER in about 50% of patients with advanced metastatic disease. Loss of functional ER leads to endocrine insensitivity, loss of cellular adhesion and polarity, and increased migratory potential due to trans-differentiation of the epithelial cancer cells into a mesenchymal-like phenotype (epithelial-mesenchymal transition; EMT). Multiple mechanisms contributing to therapeutic failure have been proposed: (i) loss or modification of ER expression including epigenetic mechanisms, (ii) agonistic actions of selective ER modulators that may be enhanced through an increased expression of co-activators, (iii) attenuation of the tamoxifen metabolism through expression of genetic variants of P450 cytochromes which leads to more or less active metabolites and (iv) increased growth factor signalling particularly through epidermal growth factor receptor activation of pathways involving keratinocyte growth factor, platelet-derived growth factor, and nuclear factor x03BA;B. In addition, the small non-coding microRNAs, recently recognized as critical gene regulators, exhibit differential expression in tamoxifen-sensitive versus resistant cell lines. Several studies suggest the potential of using these either as targets or as therapeutic agents to modulate EMT regulators as a means of reversing the aggressive metastatic phenotype by reversal of the EMT, with the added benefit of re-sensitization to anti-oestrogens.

F-box protein interactions with the hallmark pathways in cancer

F-box proteins (FBP) are the substrate specifying subunit of Skp1-Cul1-FBP (SCF)-type E3 ubiquitin ligases and are responsible for directing the ubiquitination of numerous proteins essential for cellular function. Due to their ability to regulate the expression and activity of oncogenes and tumour suppressor genes, FBPs themselves play important roles in cancer development and progression. In this review, we provide a comprehensive overview of FBPs and their targets in relation to their interaction with the hallmarks of cancer cell biology, including the regulation of proliferation, epigenetics, migration and invasion, metabolism, angiogenesis, cell death and DNA damage responses. Each cancer hallmark is revealed to have multiple FBPs which converge on common signalling hubs or response pathways. We also highlight the complex regulatory interplay between SCF-type ligases and other ubiquitin ligases. We suggest six highly interconnected FBPs affecting multiple cancer hallmarks, which may prove sensible candidates for therapeutic intervention.

Deciphering the insights of poly(ADP-ribosylation) in tumor progression

Poly (ADP-ribose) polymerase (PARP) inhibitors are particularly efficient against tumors with defects in the homologous recombination repair pathway. Nonetheless poly(ADP-ribosylation) (PARylation) modulates prometastasic activities and adaptation of tumor to a hostile microenvironment. Modulation of metastasis-promoting traits is possible through the alteration of key transcription factors involved in the regulation of the hypoxic response, the recruitment of new vessels (or angiogenesis), and the stimulation of epithelial to mesenchymal transition (EMT). In this review, we summarized some of the findings that focalize on PARP-1's action on tumor aggressiveness, suggesting new therapeutic opportunities against an assembly of tumors not necessarily bearing DNA repair defects. Metastasis accounts for the vast majority of mortality derived from solid cancer. PARP-1 is an active player in tumor adaptation to metastasis and PARP inhibitors, recognized as promising therapeutic agents against homologous recombination deficient tumors, has novel properties responsible for the antimetastatic actions in different tumor settings.

Targeting the ubiquitin pathway for cancer treatment

Proteasome-mediated degradation is a common mechanism by which cells renew their intracellular proteins and maintain protein homeostasis. In this process, the E3 ubiquitin ligases are responsible for targeting specific substrates (proteins) for ubiquitin-mediated degradation. However, in cancer cells, the stability and the balance between oncoproteins and tumor suppressor proteins are disturbed in part due to deregulated proteasome-mediated degradation. This ultimately leads to either stabilization of oncoprotein(s) or increased degradation of tumor suppressor(s), contributing to tumorigenesis and cancer progression. Therefore, E3 ubiquitin ligases including the SCF types of ubiquitin ligases have recently evolved as promising therapeutic targets for the development of novel anti-cancer drugs. In this review, we highlighted the critical components along the ubiquitin pathway including E1, E2, various E3 enzymes and DUBs that could serve as potential drug targets and also described the available bioactive compounds that target the ubiquitin pathway to control various cancers.

Snail is an independent prognostic indicator for predicting recurrence and progression in non-muscle-invasive bladder cancer

OBJECTIVE

Snail, an inducer of the epithelial-to-mesenchymal transition, increases motility and invasiveness of cancer cells by repressing E-cadherin expression. We investigate the relationship between Snail expression and clinicopathological parameters and evaluate its prognostic significance in patients with non-muscle-invasive bladder cancer (NMIBC).

MATERIALS AND METHODS

A total of 332 patients treated with transurethral resection of the bladder tumor between October 2002 and July 2010 were histopathologically confirmed to be NMIBC. Tumor recurrence and progression were followed up in all patients. Immunohistochemical staining of 332 slices was performed. The expression of Snail was evaluated by ICH and graded for intensity and area of staining. We correlated Snail scores with clinical and pathological variables, and association of Snail staining with tumor recurrence and progression was evaluated by univariate, multivariate analysis and Kaplan-Meier survival curves.

RESULTS

Of 332 patients with NMIBC, there was Snail positivity in 104 tumors (31.3 %), and Snail expression correlated with age, multifocality, carcinoma in situ, tumor stage and tumor grade (each p < 0.05, respectively). A multivariate Cox regression model revealed that Snail expression was an independent predictor of tumor recurrence [hazard ratio (HR) 1.95, p = 0.001] and progression (HR 2.34, p = 0.014) in patients with NMIBC. Kaplan-Meier estimates showed that Snail expression was significantly associated with recurrence and progression (log-rank test, p < 0.0001, respectively).

CONCLUSIONS

Analysis of Snail expression in 332 NMIBC tissue specimens revealed its potential usefulness as a biomarker to predict the NMIBC prognosis.

Helicobacter pylori CagA promotes Snail-mediated epithelial-mesenchymal transition by reducing GSK-3 activity

Cytotoxin-associated gene A (CagA) is an oncoprotein and a major virulence factor of H. pylori. CagA is delivered into gastric epithelial cells via a type IV secretion system and causes cellular transformation. The loss of epithelial adhesion that accompanies the epithelial-mesenchymal transition (EMT) is a hallmark of gastric cancer. Although CagA is a causal factor in gastric cancer, the link between CagA and the associated EMT has not been elucidated. Here, we show that CagA induces the EMT by stabilizing Snail, a transcriptional repressor of E-cadherin expression. Mechanistically we show that CagA binds GSK-3 in a manner similar to Axin and causes it to shift to an insoluble fraction, resulting in reduced GSK-3 activity. We also find that the level of Snail protein is increased in H. pylori infected epithelium in clinical samples. These results suggest that H. pylori CagA acts as a pathogenic scaffold protein that induces a Snail-mediated EMT via the depletion of GSK-3.

The CK1 Family: Contribution to Cellular Stress Response and Its Role in Carcinogenesis

Members of the highly conserved and ubiquitously expressed pleiotropic CK1 family play major regulatory roles in many cellular processes including DNA-processing and repair, proliferation, cytoskeleton dynamics, vesicular trafficking, apoptosis, and cell differentiation. As a consequence of cellular stress conditions, interaction of CK1 with the mitotic spindle is manifold increased pointing to regulatory functions at the mitotic checkpoint. Furthermore, CK1 is able to alter the activity of key proteins in signal transduction and signal integration molecules. In line with this notion, CK1 is tightly connected to the regulation and degradation of β-catenin, p53, and MDM2. Considering the importance of CK1 for accurate cell division and regulation of tumor suppressor functions, it is not surprising that mutations and alterations in the expression and/or activity of CK1 isoforms are often detected in various tumor entities including cancer of the kidney, choriocarcinomas, breast carcinomas, oral cancer, adenocarcinomas of the pancreas, and ovarian cancer. Therefore, scientific effort has enormously increased (i) to understand the regulation of CK1 and its involvement in tumorigenesis- and tumor progression-related signal transduction pathways and (ii) to develop CK1-specific inhibitors for the use in personalized therapy concepts. In this review, we summarize the current knowledge regarding CK1 regulation, function, and interaction with cellular proteins playing central roles in cellular stress-responses and carcinogenesis.

HNRNPAB induces epithelial-mesenchymal transition and promotes metastasis of hepatocellular carcinoma by transcriptionally activating SNAIL

Expression of heterogeneous nuclear ribonucleoprotein AB (HNRNPAB) has been reported to be dysregulated in tumors, but its specific contributions to tumor formation and progression are not fully understood. Here, we demonstrate that HNRNPAB is overexpressed in highly metastatic cells and tumor tissues from patients with hepatocellular carcinoma (HCC) with recurrence. We found that HNRNPAB overexpression promoted epithelial-mesenchymal transition (EMT) in a manner associated with HCC metastasis in vitro and in vivo. RNA interference-mediated silencing of the EMT factor SNAIL attenuated HNRNPAB-enhanced cell invasion in vitro and lung metastasis in vivo. Mechanistically, HNRNPAB acted to transactivate SNAIL1 transcription, which in turn inhibited transcription of the pivotal SNAIL target gene E-cadherin. Overexpression of HNRNPAB in HCC samples correlated with higher SNAIL levels, shorter overall survival, and higher tumor recurrence. HNRNPAB overexpression, alone or in combination with SNAIL, was found to be a significant independent risk factor for recurrence and survival after curative resection. In conclusion, our findings define HNRNPAB as an activator of EMT and metastasis in HCC that predicts poor clinical outcomes.

Regulation of the protein stability of EMT transcription factors

The epithelial to mesenchymal transition (EMT) consists of a rapid change of cell phenotype, characterized by the loss of epithelial characteristics and the acquisition of a more invasive phenotype. Transcription factors regulating EMT (Snail, Twist and Zeb) are extremely labile proteins, rapidly degraded by the proteasome system. In this review we analyze the current mechanisms controlling degradation of EMT transcription factors, focusing on the role of new E3 ubiquitin-ligases involved in EMT. We also summarize the regulation of the stability of these EMT transcription factors, specially observed in different stress conditions, such as hypoxia, chemotherapeutic drugs, oxidative stress or γ-irradiation.

Nuclear ubiquitination by FBXL5 modulates Snail1 DNA binding and stability

The zinc finger transcription factor Snail1 regulates epithelial to mesenchymal transition, repressing epithelial markers and activating mesenchymal genes. Snail1 is an extremely labile protein degraded by the cytoplasmic ubiquitin-ligases β-TrCP1/FBXW1 and Ppa/FBXL14. Using a short hairpin RNA screening, we have identified FBXL5 as a novel Snail1 ubiquitin ligase. FBXL5 is located in the nucleus where it interacts with Snail1 promoting its polyubiquitination and affecting Snail1 protein stability and function by impairing DNA binding. Snail1 downregulation by FBXL5 is prevented by Lats2, a protein kinase that phosphorylates Snail1 precluding its nuclear export but not its polyubiquitination. Actually, although polyubiquitination by FBXL5 takes place in the nucleus, Snail1 is degraded in the cytosol. Finally, FBXL5 is highly sensitive to stress conditions and is downregulated by iron depletion and γ-irradiation, explaining Snail1 stabilization in these conditions. These results characterize a novel nuclear ubiquitin ligase controlling Snail1 protein stability and provide the molecular basis for understanding how radiotherapy upregulates the epithelial to mesenchymal transition-inducer Snail1.

DYRK2 controls the epithelial-mesenchymal transition in breast cancer by degrading Snail

The epithelial-mesenchymal transition (EMT) plays a fundamental role in the early stages of breast cancer invasion. Snail, a zinc finger transcriptional repressor, is an important regulator of EMT. Snail is phosphorylated by GSK3β and is subsequently degraded by βTrCP-mediated ubiquitination. We identified an additional kinase, DYRK2, that regulates Snail stability. Knockdown of DYRK2 promoted EMT and cancer invasion in vitro and in vivo. Consistent with these results, DYRK2 was found to be down-regulated in human breast cancer tissue. Patients with low DYRK2-expressing tumors had a worse outcome than those with high DYRK2-expressing tumors. These findings revealed that DYRK2 regulates cancer invasion and metastasis by degrading Snail.

Role of fucosyltransferase IV in epithelial-mesenchymal transition in breast cancer cells

Epithelial–mesenchymal transition (EMT) is a crucial step in tumor progression and has an important role during cancer invasion and metastasis. Although fucosyltransferase IV (FUT4) has been implicated in the modulation of cell migration, invasion and cancer metastasis, its role during EMT is unclear. This study explores the molecular mechanisms of the involvement of FUT4 in EMT in breast cancer cells. Breast cancer cell lines display increased expression of FUT4, which is accompanied by enhanced appearance of the mesenchymal phenotype and which can be reversed by knockdown of endogenous FUT4. Moreover, FUT4 induced activation of phosphatidylinositol 3-kinase (PI3K)/Akt, and inactivation of GSK3β and nuclear translocation of NF-κB, resulting in increased Snail and MMP-9 expression and greater cell motility. Taken together, these findings indicate that FUT4 has a role in EMT through activation of the PI3K/Akt and NF-κB signaling systems, which induce the key mediators Snail and MMP-9 and facilitate the acquisition of a mesenchymal phenotype. Our findings support the possibility that FUT4 is a novel regulator of EMT in breast cancer cells and a promising target for cancer therapy.

Regulation of protein degradation by O-GlcNAcylation: crosstalk with ubiquitination

The post-translational modification of intracellular proteins by O-linked N-acetylglucosamine (O-GlcNAc) regulates essential cellular processes such as signal transduction, transcription, translation, and protein degradation. Misfolded, damaged, and unwanted proteins are tagged with a chain of ubiquitin moieties for degradation by the proteasome, which is critical for cellular homeostasis. In this review, we summarize the current knowledge of the interplay between O-GlcNAcylation and ubiquitination in the control of protein degradation. Understanding the mechanisms of action of O-GlcNAcylation in the ubiquitin-proteosome system shall facilitate the development of therapeutics for human diseases such as cancer, metabolic syndrome, and neurodegenerative diseases.

Regulatory networks defining EMT during cancer initiation and progression

Epithelial to mesenchymal transition (EMT) is essential for driving plasticity during development, but is an unintentional behaviour of cells during cancer progression. The EMT-associated reprogramming of cells not only suggests that fundamental changes may occur to several regulatory networks but also that an intimate interplay exists between them. Disturbance of a controlled epithelial balance is triggered by altering several layers of regulation, including the transcriptional and translational machinery, expression of non-coding RNAs, alternative splicing and protein stability.