Regulation of the protein stability of EMT transcription factors

Post-transcription mediated Snail stabilization is involved in radiation exposure induced invasion and migration of hepatocarcinoma cells

Increasing evidences suggested that radiotherapy can paradoxically promote tumor invasion and metastatic processes, while its detailed mechanism is not well illustrated. Our present study found that radiation can promote the migration and invasion of hepatocellular carcinoma (HCC) cells via induction of epithelial mesenchymal transition (EMT), which was evidenced by the results that radiation induced up regulation of vimentin while down regulation of E-Cadherin. As to the EMT-related transcription factors, radiation increased the expression of Snail, while not Slug, ZEB1 or TWIST. This was confirmed by the results that radiation increased the nuclear translocation of Snail in HCC cells. However, radiation had no effect on the expression or half-life of Snail mRNA. In HCC cells treated by cycloheximide (CHX, the translation inhibitor), radiation significantly increased the half-life of Snail protein, which suggested that radiation increased the expression of Snail via up regulation of its protein stability. Radiation increased the expression of COP9 signalosome 2 (CSN2), which has been reported to block the ubiquitination and degradation of Snail. Silence of CSN2/Snail can attenuate radiation induced cell migration and EMT of HCC cells. Collectively, our data suggested that radiation can promote HCC cell invasion and EMT by stabilization of Snail via CSN2 signals.

RNF113A promotes the proliferation, migration and invasion, and is associated with a poor prognosis of esophageal squamous cell carcinoma

Ring finger protein 113A (RNF113A) possesses a C3HC4 zinc finger domain and this domain is found in E3 ubiquitin ligase and is involved in tumorigenesis. To date, and at least to the best of our knowledge, there are no studies available which have investigated RNF113A in cancer. Thus, this study aimed to explore the role of RNF113A in the development of esophageal squamous cell carcinoma (ESCC). For this purpose, paraffin-embedded samples from 117 patients with ESCC were selected, as well as 41 pairs of fresh-frozen ESCC and adjacent normal tissue samples. RNF113A expression was examined by immunohistochemistry and reverse transcription-quantitative PCR (RT-qPCR). RNF113A was overexpressed or silenced in the EC9706 and Eca109 cells. The cells were examined for cell cycle progression, apoptosis, invasiveness and migration. Xenograft tumors were also created in mice using the Eca109 cells. Tumor differentiation (P=0.008) and T classification (P<0.001) were found to be significantly associated with RNF113A expression. No statistically significant association was observed between RNF113A expression and sex, age, histological type, tumor location and lymph node metastasis (N classification). Kaplan-Meier analysis revealed that the patients with ESCC with ahigh expression of RNF113A had a lower survival rate than those with a low expression (P=0.002). Multivariate analysis revealed that RNF113A expression (HR=2.406; 95% CI, 1.301-4.449, P=0.005) was independently associated with overall survival in patients with ESCC. The overexpression of RNF113A promoted proliferation, migration, and invasiveness of ESCC cell lines in vitro, and RNF113A silencing reversed these malignant behaviors. RNF113A knockdown inhibited tumor growth in vivo. Thus, these results indicate that RNF113A promotes the proliferation, migration and invasiveness of ESCC cell lines. RNF113A expression in ESCC is this associated with a poor prognosis of affected patients.

Proapoptotic PUMA targets stem-like breast cancer cells to suppress metastasis

Breast cancer cells with stem cell properties are key contributors to metastatic disease, and there remains a need to better understand and target these cells in human cancers. Here, we identified rare stem-like cells in patients' tumors characterized by low levels of the proapoptotic molecule p53-upregulated modulator of apoptosis (PUMA) and showed that these cells play a critical role in tumor progression that is independent of clinical subtype. A signaling axis consisting of the integrin αvβ3, Src kinase, and the transcription factor Slug suppresses PUMA in these cells, promoting tumor stemness. We showed that genetic or pharmacological disruption of αvβ3/Src signaling drives PUMA expression, specifically depleting these stem-like tumor cells; increases their sensitivity to apoptosis; and reduces pulmonary metastasis, with no effect on primary tumor growth. Taken together, these findings point to PUMA as a key vulnerability of stem-like cells and suggest that pharmacological upregulation of PUMA via Src inhibition may represent a strategy to selectively target these cells in a wide spectrum of aggressive breast cancers.

Beyond epithelial-to-mesenchymal transition: Common suppression of differentiation programs underlies epithelial barrier dysfunction in mild, moderate, and severe asthma

BACKGROUND

Epithelial barrier dysfunction is a central feature in the pathogenesis of allergic disease. Epithelial-to-mesenchymal transition (EMT) has been proposed as one mechanism afflicting barrier in asthma. However, genes and pathways involved in aberrant epithelial-mesenchymal signaling, and their relationship to asthma severity, are poorly understood.

METHODS

We used unbiased gene network analysis to evaluate functional convergence in epithelial gene expression signatures across multiple public access transcriptomics datasets of human asthma, followed by text mining to evaluate functional marker relevance of discovered genes. We objectively confirmed these findings in epithelial brushings and primary asthmatic epithelial cells cultured in different biological contexts.

RESULTS

We found a striking suppression of epithelial differentiation in asthma, overrepresented by insufficiency in insulin and Notch signaling, but with the absence of conventional EMT markers. We identified EFNB2, FGFR1, FGFR2, INSR, IRS2, NOTCH2, TLE1, and NTRK2 as novel markers central to dysregulation of epithelial-mesenchymal signaling, but surprisingly overlooked in asthma research. We found that this "core" signature of asthma is shared by mild, moderate, and severe forms of disease, progressing with severity. Loss of epithelial differentiation induced by insulin deprivation in normal human bronchial epithelial cells cultured in organotypic conditions closely approximated gene expression in asthmatic epithelial brushings.

CONCLUSIONS

The comparative analysis of publically available transcriptomes demonstrated that epithelial barrier dysfunction in asthma is characterized by persistent underlying de-differentiation program with complex etiology. The lasting alteration of the asthmatic epithelial cell transcriptome implicates regulation involving metabolism and epigenetics, beyond EMT driven by injury and repair in chronic inflammation.

Fate tracing of hepatocytes in mouse liver

Hepatocytes perform most of the functions of the liver and are considered terminally differentiated cells. Recently, it has been suggested that hepatocytes might have the potential to transdifferentiate or dedifferentiate under physiological or pathological conditions in vivo. Epithelial-mesenchymal transition of hepatocytes in liver fibrosis has also been proposed. However, these findings have not been fully confirmed. In this study, hepatocytes were genetically labelled for cell fate tracing using lacZ via the tamoxifen-induced CreERT/loxP system. After induction with tamoxifen, alb + cells were permanently marked by lacZ expression, and all progeny lacZ + cells were derived from a single source with no interference. We did not observe transdifferentiation or dedifferentiation of hepatocytes into cholangiocytes or hepatic progenitor cells under conditions of liver homeostasis or following a 2/3 partial hepatectomy. Meanwhile, lacZ/OPN-positive cells were observed in livers of 3,5-diethoxycarbonyl-1,4-dihydrocollidine-fed mice, and lacZ/alpha-smooth muscle actin-positive cells were detected in carbon tetrachloride-induced chronic liver injury models. These results suggested that some existing differentiated alb + cells might have the potential of transdifferentiation/dedifferentiation or epithelial-to-mesenchymal transition in vivo in some liver injury models, but the proportion of these alb + cells in liver was very low, and their significance and actual function during the pathological process remains to be elucidated.

SPSB3 targets SNAIL for degradation in GSK-3β phosphorylation-dependent manner and regulates metastasis

Epithelial-mesenchymal transition (EMT) is a process during which normal epithelial cells acquire mesenchymal characteristics. EMT has a critical role in various human diseases especially in cancer. EMT facilitates tumor initiation and progression by mediating cancer cell stemness and motility. Zinc finger transcription factor SNAIL is one of the most important initiators of EMT. Therefore, it is of great significance to understand the regulating mechanism of SNAIL. In this study, we carried out a luciferase-based genome-wide screening using small interfering RNA library against ~200 of E3 ligases and ubiquitin-related genes and identified SOCS box protein SPSB3 as a novel E3 ligase component that targets SNAIL into polyubiquitination and degradation in response to GSK-3β phosphorylation of SNAIL. Functionally, we observed that SPSB3 overexpression greatly inhibits tumor metastasis by regulating SNAIL degradation both in vitro and in vivo. The expression of SPSB3 and SNAIL are negatively correlated in human esophageal squamous cell carcinoma tissues, and low SPSB3 expression indicates lymph node metastasis. Moreover, high SPSB3 expression indicates good survivals in various kinds of cancer. Collectively, these findings suggest that SPSB3-mediated SNAIL degradation has a vital role in regulating EMT and cancer progression.

The microRNA expression signature of pancreatic ductal adenocarcinoma by RNA sequencing: anti-tumour functions of the microRNA-216 cluster

We analysed the RNA sequence-based microRNA (miRNA) signature of pancreatic ductal adenocarcinoma (PDAC). Aberrantly expressed miRNAs were successfully identified in this signature. Using the PDAC signature, we focused on 4 clustered miRNAs, miR-216a-5p, miR-216a-3p, miR-216b-5p and miR-216b-3p on human chromosome 2p16.1. All members of the miR-216 cluster were significantly reduced in PDAC specimens. Ectopic expression of these miRNAs suppressed cancer cell aggressiveness, suggesting miR-216 cluster as anti-tumour miRNAs in PDAC cells. The impact of miR-216b-3p (passenger strand of pre-miR-216b) on cancer cells is still ambiguous. Forkhead box Q1 (FOXQ1) was directly regulated by miR-216b-3p and overexpression of FOXQ1 was confirmed in clinical specimens. High expression of FOXQ1 predicted a shorter survival of patients with PDAC by Kaplan-Meier analysis. Loss-of-function assays showed that cancer cell migration and invasion activities were significantly reduced by siFOXQ1 transfectants. We investigated pathways downstream from FOXQ1 by using genome-wide gene expression analysis. Identification of the miR-216-3p/FOXQ1-mediated network in PDAC should enhance understanding of PDAC aggressiveness at the molecular level.

Stabilization of the transcription factors slug and twist by the deubiquitinase dub3 is a key requirement for tumor metastasis

The epithelial-mesenchymal transition (EMT) represents a cellular de-differentiation process that provides cells with the increased plasticity required during embryonic development, tissue remodeling, wound healing and metastasis. Slug and Twist are two key EMT transcription factors (EMT-TFs) that are tightly regulated via ubiquitination and degradation. How Slug and Twist escape degradation and become stabilized in cancer cells remains unclear. One plausible mechanism of Slug and Twist stabilization involves removal of ubiquitin by deubiquitinases (DUBs). In this study, we identified Dub3 as a novel DUB for both Slug and Twist. We further found that Dub3 overexpression increased Slug and Twist protein levels in a dose-dependent manner, whereas Dub3-knockdown decreased their protein levels. Of importance, Dub3 interacted with Slug and Twist and prevented them from degradation, thereby promoting migration, invasion, and cancer stem cell (CSC)-like properties of breast cancer cells. Intriguingly, Dub3 was identified as an early response gene that was upregulated after exposure to inflammatory cytokines such as IL-6, which plays a critical role in the growth and metastasis of breast cancer cells, as well as the maintenance of breast CSCs. We found that Dub3 played an essential role in IL-6 induced EMT through stabilization of Slug and Twist. Our study has uncovered an IL-6-Dub3-Slug/Twist signaling axis during EMT and suggests potential approaches that could target Dub3 to prevent metastatic breast tumor.

DHEA increases epithelial markers and decreases mesenchymal proteins in breast cancer cells and reduces xenograft growth

Breast cancer is one of the most common neoplasias and the leading cause of cancer death in women worldwide. Its high mortality rate is linked to a great metastatic capacity associated with the epithelial-mesenchymal transition (EMT). During this process, a decrease in epithelial proteins expression and an increase of mesenchymal proteins are observed. On the other hand, it has been shown that dehydroepiandrosterone (DHEA), the most abundant steroid in human plasma, inhibits migration of breast cancer cells; however, the underlying mechanisms have not been elucidated. In this study, the in vitro effect of DHEA on the expression pattern of some EMT-related proteins, such as E-cadherin (epithelial), N-cadherin, vimentin and Snail (mesenchymal) was measured by Western blot and immunofluorescence in MDA-MB-231 breast cancer cells with invasive, metastatic and mesenchymal phenotype. Also, the in vivo effect of DHEA on xenograft tumor growth in nude mice (nu^-/nu^-) and on expression of the same epithelial and mesenchymal proteins in generated tumors was evaluated. We found that DHEA increased expression of E-cadherin and decreased N-cadherin, vimentin and Snail expression both in MD-MB-231 cells and in the formed tumors, possibly by DHEA-induced reversion of mesenchymal phenotype. These results were correlated with a tumor size reduction in mouse xenografts following DHEA administration either a week earlier or concurrent with breast cancer cells inoculation. In conclusion, DHEA could be useful in the treatment of breast cancer with mesenchymal phenotype.

Epithelial-to-mesenchymal transition transcription factors in cancer-associated fibroblasts

Beyond inducing epithelial‐to‐mesenchymal transcription (EMT), transcriptional factors of the Snail, ZEB and Twist families (EMT‐TFs) control global plasticity programmes affecting cell stemness and fate. Literature addressing the reactivation of these factors in adult tumour cells is very extensive, as they enable cancer cell plasticity and fuel both tumour initiation and metastatic spread. Incipient data reveal that EMT‐TFs are also expressed in fibroblasts, providing these with additional properties. Here, I will review recent reports on the expression of EMT‐TFs in cancer‐associated fibroblasts (CAFs). The new model suggests that EMT‐TFs can be envisioned as essential metastasis and chemoresistance‐promoting molecules, thereby enabling coordinated plasticity programmes in parenchyma and stroma–tumour compartments.

Nicotinic acid inhibits glioma invasion by facilitating Snail1 degradation

Malignant glioma is a formidable disease that commonly leads to death, mainly due to the invasion of tumor cells into neighboring tissues. Therefore, inhibition of tumor cell invasion may provide an effective therapy for malignant glioma. Here we report that nicotinic acid (NA), an essential vitamin, inhibits glioma cell invasion in vitro and in vivo. Treatment of the U251 glioma cells with NA in vitro results in reduced invasion, which is accompanied by a loss of mesenchymal phenotype and an increase in cell-cell adhesion. At the molecular level, transcription of the adherens junction protein E-cadherin is upregulated, leading to accumulation of E-cadherin protein at the cell-cell boundary. This can be attributed to NA's ability to facilitate the ubiquitination and degradation of Snail1, a transcription factor that represses E-cadherin expression. Similarly, NA transiently inhibits neural crest migration in Xenopus embryos in a Snail1-dependent manner, indicating that the mechanism of action for NA in cell migration is evolutionarily conserved. We further show that NA injection blocks the infiltration of tumor cells into the adjacent brain tissues and improves animal survival in a rat model of glioma. These results suggest that NA treatment may be developed into a potential therapy for malignant glioma.

DAPK loss in colon cancer tumor buds: implications for migration capacity of disseminating tumor cells

Defining new therapeutic strategies to overcome therapy resistance due to tumor heterogeneity in colon cancer is challenging. One option is to explore the molecular profile of aggressive disseminating tumor cells. The cytoskeleton-associated Death-associated protein kinase (DAPK) is involved in the cross talk between tumor and immune cells at the invasion front of colorectal cancer. Here dedifferentiated tumor cells histologically defined as tumor budding are associated with a high risk of metastasis and poor prognosis. Analyzing samples from 144 colorectal cancer patients we investigated immunhistochemical DAPK expression in different tumor regions such as center, invasion front, and buds. Functional consequences for tumor aggressiveness were studied in a panel of colon tumor cell lines using different migration, wound healing, and invasion assays. DAPK levels were experimentally modified by siRNA transfection and overexpression as well as inhibitor treatments. We found that DAPK expression was reduced towards the invasion front and was nearly absent in tumor buds. Applying the ECIS system with HCT116 and HCT116 stable lentiviral DAPK knock down cells (HCTshDAPK) we identified an important role for DAPK in decreasing the migratory capacity whereas proliferation was not affected. Furthermore, the migration pattern differed with HCTshDAPK cells showing a cluster-like migration of tumor cell groups. DAPK inhibitor treatment revealed that the migration rate was independent of DAPK's catalytic activity. Modulation of DAPK expression level in SW480 and DLD1 colorectal cancer cells significantly influenced wound closure rate. DAPK seems to be a major player that influences the migratory capability of disseminating tumor cells and possibly affects the dynamic interface between pro- and anti-survival factors at the invasion front of colorectal cancer. This interesting and new finding requires further evaluation.

The Epithelial-to-Mesenchymal Transition-Like Process in Glioblastoma: An Updated Systematic Review and In Silico Investigation

Glioblastoma multiforme (GBM) is the most aggressive form of brain cancer due to its highly invasive nature that impedes the surgical removal of all tumor cells, making relapse inevitable. However, the mechanisms used by glioma cells to invade the surrounding tissue are still unclear. In this context, epithelial-to-mesenchymal transition (EMT) has emerged as a key regulator of this invasive state and although the real relevance of this program in malignant glioma is still controversial, it has been strongly associated with GBM malignancy. EMT is a very complex process regulated by several families of transcriptional factors through many signaling pathways that form a network that allows cancer cells to acquire invasive properties and penetrate the neighboring stroma, resulting in the formation of an advantageous microenvironment for cancer progression and metastasis. In this systematic review, we focus on the molecular mechanisms of EMT including EMT-factors, drug resistance, miRNA, and new therapeutic strategies. In addition, we address controversial questions about mesenchymal shift in GBMs with a bioinformatics analysis to show that in terms of epithelial and mesenchymal phenotype, the majority of GBMs samples analyzed have a profile more mesenchymal than epithelial. If induced, this phenotype can be shifted toward an even more mesenchymal phenotype in an EMT-like process in glioma cells. A better understanding of the molecular regulation of the EMT during tumor spreading will help to provide potential therapeutic interventions to target this program when treating GBM.

Re-evaluating the role of epithelial-mesenchymal-transition in cancer progression

Epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are essential for embryonic development and also important in cancer progression. In a conventional model, epithelial-like cancer cells transit to mesenchymal-like tumor cells with great motility via EMT transcription factors; these mesenchymal-like cells migrate through the circulation system, relocate to a suitable site and then convert back to an epithelial-like phenotype to regenerate the tumor. However, recent findings challenge this conventional model and support the existence of a stable hybrid epithelial/mesenchymal (E/M) tumor population. Hybrid E/M tumor cells exhibit both epithelial and mesenchymal properties, possess great metastatic and tumorigenic capacity and are associated with poorer patient prognosis. The hybrid E/M model and associated regulatory networks represent a conceptual change regarding tumor metastasis and organ colonization. It may lead to the development of novel treatment strategies to ultimately stop cancer progression and improve disease-free survival.

EMT reversal in human cancer cells after IR knockdown in hyperinsulinemic mice

Type 2 diabetes (T2D) is associated with increased cancer risk and cancer-related mortality. Data herein show that we generated an immunodeficient hyperinsulinemic mouse by crossing the Rag1(-/-) mice, which have no mature B or T lymphocytes, with the MKR mouse model of T2D to generate the Rag1(-/-) (Rag/WT) and Rag1(-/-)/MKR(+/+) (Rag/MKR) mice. The female Rag/MKR mice are insulin resistant and have significantly higher nonfasting plasma insulin levels compared with the Rag/WT controls. Therefore, we used these Rag/MKR mice to investigate the role of endogenous hyperinsulinemia on human cancer progression. In this study, we show that hyperinsulinemia in the Rag/MKR mice increases the expression of mesenchymal transcription factors, TWIST1 and ZEB1, and increases the expression of the angiogenesis marker, vascular endothelial growth factor A (VEGFA). We also show that silencing the insulin receptor (IR) in the human LCC6 cancer cells leads to decreased tumor growth and metastases, suppression of mesenchymal markers vimentin, SLUG, TWIST1 and ZEB1, suppression of angiogenesis markers, VEGFA and VEGFD, and re-expression of the epithelial marker, E-cadherin. The data in this paper demonstrate that IR knockdown in primary tumors partially reverses the growth-promoting effects of hyperinsulinemia as well as highlighting the importance of the insulin receptor signaling pathway in cancer progression, and more specifically in epithelial-mesenchymal transition.

Elongator Protein 3 (Elp3) stabilizes Snail1 and regulates neural crest migration in Xenopus

Elongator protein 3 (Elp3) is the enzymatic unit of the elongator protein complex, a histone acetyltransferase complex involved in transcriptional elongation. It has long been shown to play an important role in cell migration; however, the underlying mechanism is unknown. Here, we showed that Elp3 is expressed in pre-migratory and migrating neural crest cells in Xenopus embryos, and knockdown of Elp3 inhibited neural crest cell migration. Interestingly, Elp3 binds Snail1 through its zinc-finger domain and inhibits its ubiquitination by β-Trcp without interfering with the Snail1/Trcp interaction. We showed evidence that Elp3-mediated stabilization of Snail1 was likely involved in the activation of N-cadherin in neural crest cells to regulate their migratory ability. Our findings provide a new mechanism for the function of Elp3 in cell migration through stabilizing Snail1, a master regulator of cell motility.

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.

New Insights into the Crossroads between EMT and Stemness in the Context of Cancer

The epithelial-mesenchymal transition (EMT) is an example of cellular plasticity, where an epithelial cell acquires a mesenchymal-like phenotype that increases its migratory and invasive properties. Stemness is the ability of stem cells to proliferate in an asymmetric way that allows them to maintain the reservoir of undifferentiated cells with stem cell identity, but also to produce new differentiated cells. Initial works revealed that activation of the EMT program in epithelial cells induces the acquisition of stem cell properties, which in the context of cancer may contribute to the appearance of tumor initiating cells (TIC). However, a number of groups have recently reported that mesenchymal-epithelial transition (MET) is required for efficient metastatic colonization and that EMT may be not necessarily associated with stemness. In this review, we summarize recent findings that extend our knowledge about the crossroads between EMT and stemness and their relevance under physiological or pathological conditions.

Inflammasome-independent NLRP3 is required for epithelial-mesenchymal transition in colon cancer cells

Inflammasome NLRP3 plays a crucial role in the process of colitis and colitis--associated colon cancer. Even though much is known regarding the NLRP3 inflammasome that regulates pro-inflammatory cytokine release in innate immune cells, the role of NLRP3 in non-immune cells is still unclear. In this study, we showed that NLRP3 was highly expressed in mesenchymal-like colon cancer cells (SW620), and was upregulated by tumor necrosis factors-α (TNF-α) and transforming growth factor-β1 (TGF-β1) respectively, during EMT in colon cancer epithelial cells HCT116 and HT29. Knockdown of NLRP3 retained epithelial spindle-like morphology of HCT116 and HT29 cells and reversed the mesenchymal characteristic of SW620 cells, indicated by the decreased expression of vimentin and MMP9 and increased expression of E-cadherin. In addition, knockdown of NLRP3 in colorectal carcinoma cells displayed diminished cell migration and invasion. Interestingly, during the EMT process induced by TNF-α or TGF-β1, the cleaved caspase-1 and ASC speck were not detected, indicating that NLRP3 functions in an inflammasome-independent way. Further studies demonstrated that NLRP3 protein expression was regulated by NF-κB signaling in TNF-α or TGF-β1-induced EMT, as verified by the NF-κB inhibitor Bay 11-7082. Moreover, NLRP3 knockdown reduced the expression of Snail1, indicating that NLRP3 may promote EMT through regulating Snail1. In summary, our results showed that the NLRP3 expression, not the inflammasome activation, was required for EMT in colorectal cancer cells.

A Switch in Akt Isoforms Is Required for Notch-Induced Snail1 Expression and Protection from Cell Death

Notch activation in aortic endothelial cells (ECs) takes place at embryonic stages during cardiac valve formation and induces endothelial-to-mesenchymal transition (EndMT). Using aortic ECs, we show here that active Notch expression promotes EndMT, resulting in downregulation of vascular endothelial cadherin (VE-cadherin) and upregulation of mesenchymal genes such as those for fibronectin and Snail1/2. In these cells, transforming growth factor β1 exacerbates Notch effects by increasing Snail1 and fibronectin activation. When Notch-downstream pathways were analyzed, we detected an increase in glycogen synthase kinase 3β (GSK-3β) phosphorylation and inactivation that facilitates Snail1 nuclear retention and protein stabilization. However, the total activity of Akt was downregulated. The discrepancy between Akt activity and GSK-3β phosphorylation is explained by a Notch-induced switch in the Akt isoforms, whereby Akt1, the predominant isoform expressed in ECs, is decreased and Akt2 transcription is upregulated. Mechanistically, Akt2 induction requires the stimulation of the β-catenin/TCF4 transcriptional complex, which activates the Akt2 promoter. Active, phosphorylated Akt2 translocates to the nucleus in Notch-expressing cells, resulting in GSK-3β inactivation in this compartment. Akt2, but not Akt1, colocalizes in the nucleus with lamin B in the nuclear envelope. In addition to promoting GSK-3β inactivation, Notch downregulates Forkhead box O1 (FoxO1), another Akt2 nuclear substrate. Moreover, Notch protects ECs from oxidative stress-induced apoptosis through an Akt2- and Snail1-dependent mechanism.

Targeting the Nuclear Export Protein XPO1/CRM1 Reverses Epithelial to Mesenchymal Transition

Here we demonstrate for the first time that targeted inhibition of nuclear exporter protein exportin 1 (XPO1) also known as chromosome maintenance region 1 (CRM1) by Selective Inhibitor of Nuclear Export (SINE) compounds results in reversal of EMT in snail-transduced primary human mammary epithelial cells (HMECs). SINE compounds selinexor (KPT-330) and KPT-185, leptomycin B (LMB as +ve control) but not KPT-301 (-ve control) reverse EMT, suppress mesenchymal markers and consequently induce growth inhibition, apoptosis and prevent spheroid formation. SINE treatment resulted in nuclear retention of snail regulator FBXL5 that was concurrent with suppression of snail and down-regulation of mesenchymal markers. FBXL5 siRNA or transfection with cys528 mut-Xpo1 (lacking SINE binding site) markedly abrogated SINE activity highlighting an XPO1 and FBXL5 mediated mechanism of action. Silencing XPO1 or snail caused re-expression of FBXL5 as well as EMT reversal. Pathway analysis on SINE treated HMECs further verified the involvement of additional F-Box family proteins and confirmed the suppression of snail network. Oral administration of selinexor (15 mg/kg p.o. QoDx3/week for 3weeks) resulted in complete cures (no tumor rebound at 120 days) of HMLER-Snail xenografts. These findings raise the unique possibility of blocking EMT at the nuclear pore.

Snail1-driven plasticity of epithelial and mesenchymal cells sustains cancer malignancy

The transcription factor Snail1 induces epithelial-to-mesenchymal transition (EMT) in tumor epithelial cells, a process associated with the emergence of stemness, invasion and cancer malignancy. Here, we review recent reports indicating that Snail1 also regulates mesenchymal plasticity and paracrine signaling and propose that Snail1 orchestrates the generation of cancer stem cells (CSCs) and cancer-associated fibroblasts (CAFs). Our view supports the current models for tumorigenesis that consider stemness and tumor microenvironment as retroactive actors for metastasis formation, revealing Snail1 as a regulator of these metastatic forces. This view offers new perspectives for understanding and targeting metastasis.

Nanoparticle-mediated down-regulation of TWIST increases radiosensitivity of nasopharyngeal carcinoma cells via ERK pathway

Evidence suggests that over-expression of TWIST, an epithelial-mesenchymal transition inducer, might have a correlation with cancer progression and chemoresistance. However, its roles in radioresistance of cancer have rarely been reported. High TWIST expression was detected in nasopharyngeal carcinoma (NPC) and associated with poor prognosis. Thus, in the present study, we aimed to determine whether knockdown of TWIST can increase radiosensitivity of NPC cells. Chitosan-encapsulated TWIST-siRNA nanoparticles were constructed and used to silence TWIST expression in CNE2 cells. The cell viability and apoptosis as well as possible MAPKs pathways were assessed after irradiation treatment. The results showed that the nanoparticles successfully suppressed TWIST expression in CNE2 cells, and TWIST depletion significantly sensitized CNE2 cells to irradiation by inducing activation of ERK pathway but not JNK or p-38 pathways. The data suggested that TWIST depletion might be a promising approach sensitizing NPC cells to irradiation. Further investigations are needed to confirm the results.

Epithelial to mesenchymal transition in tumor cells as consequence of phenotypic instability

During the last years many articles have reported epithelial-to-mesenchymal transitions (EMT) induced by a myriad of gene products either when added to the cell medium or when transfected. Molecularly the EMT is characterized by the up-regulation of transcriptional factors (EMT-TFs) repressing the epithelial gene E-cadherin, a protein essential for the maintenance of the epithelial phenotype. These EMT-TFs are subjected to a complex regulation involving binary self-stimulatory loops, allowing the possibility of the amplification of input signals. The capability of EMT-TFs to promote an EMT is controlled by E-cadherin that limits the transcription of mesenchymal genes. We discuss here the differences between normal and tumor epithelial cells; in the latter a partial inactivation of E-cadherin function enables extracellular signals to be amplified and induce an EMT. This tumor cell phenotypic instability is exacerbated in cell culture conditions. Therefore, it is likely that many of the gene products reported to control this transition act only in very specific cell tumor cell lines; thus, in cells with an unstable phenotype due to pre-existing alterations in E-cadherin safeguard mechanism.