The transcription factors Slug (SNAI2) and Snail (SNAI1) regulate phospholipase D (PLD) promoter in opposite ways towards cancer cell invasion

Significance of epithelial-to-mesenchymal transition inducing transcription factors in predicting distance metastasis and survival in patients with colorectal cancer: A systematic review and meta-analysis

Background:

The clinical relevance of epithelial-to-mesenchymal transition (EMT) in colorectal cancer (CRC) progression has been highlighted over the last decade. Several EMT-inducing transcription factors (EMT-TFs) have been implicated in the regulation of EMT, including Twist, Snail1, Slug, ZEB1, and ZEB2. Here, this meta-analysis aimed to predict the risk of distance metastasis and overall survival in CRC patients with high expression of EMT-TFs.

Materials and Methods:

All eligible studies were searched in PubMed, Scopus, and Web of Science databases. The search was carried out to include literatures published as late as September 1, 2018. In overall, 16 studies that investigated the relationship between EMT-TFs with distance metastasis and survival in CRC patients were included. In meta-analysis, a pooled hazard ratio (HR) and odds ratio (OR) were estimated for associations.

Results:

The results of this review indicated that expressions of all EMT-TFs are significantly correlated with poor overall survival in CRC. Moreover, there are a significant association between Twist (OR, 1.46; 95% confidence interval [CI], 1.03–2.09), Slug (OR, 3.43; 95% CI, 1.98–5.93), and ZEB2 (OR, 2.42; 95% CI, 1.09–5.40) expression with distance metastatic in CRC patients.

Conclusion:

These findings suggest that the overexpression of EMT-TFs plays a key role in increasing the risk of distance metastasis as well as decreasing overall survival in CRC patients.

APN-mediated phosphorylation of BCKDK promotes hepatocellular carcinoma metastasis and proliferation via the ERK signaling pathway

Hepatocellular carcinoma (HCC) is one of the most prevalent human malignancies worldwide and has high morbidity and mortality. Elucidating the molecular mechanisms underlying HCC recurrence and metastasis is critical to identify new therapeutic targets. This study aimed to determine the roles of aminopeptidase N (APN, also known as CD13) in HCC proliferation and metastasis and its underlying mechanisms. We detected APN expression in clinical samples and HCC cell lines using immunohistochemistry, flow cytometry, real-time PCR, and enzyme activity assays. The effects of APN on HCC metastasis and proliferation were verified in both in vitro and in vivo models. RNA-seq, phosphoproteomic, western blot, point mutation, co-immunoprecipitation, and proximity ligation assays were performed to reveal the potential mechanisms. We found that APN was frequently upregulated in HCC tumor tissues and high-metastatic cell lines. Knockout of APN inhibited HCC cell metastasis and proliferation in vitro and in vivo. Functional studies suggested that a loss of APN impedes the ERK signaling pathway in HCC cells. Mechanistically, we found that APN might mediate the phosphorylation at serine 31 of BCKDK (BCKDKS31), promote BCKDK interacting with ERK1/2 and phosphorylating it, thereby activating the ERK signaling pathway in HCC cells. Collectively, our findings indicate that APN mediates the phosphorylation of BCKDKS31 and activates its downstream pathway to promote HCC proliferation and metastasis. Therefore, the APN/BCKDK/ERK axis may serve as a new therapeutic target for HCC therapy, and these findings may be helpful to identify new biomarkers in HCC progression.

MDA-9/Syntenin (SDCBP): Novel gene and therapeutic target for cancer metastasis

The primary cause of cancer-related death from solid tumors is metastasis. While unraveling the mechanisms of this complicated process continues, our ability to effectively target and treat it to decrease patient morbidity and mortality remains disappointing. Early detection of metastatic lesions and approaches to treat metastases (both pharmacological and genetic) are of prime importance to obstruct this process clinically. Metastasis is complex involving both genetic and epigenetic changes in the constantly evolving tumor cell. Moreover, many discrete steps have been identified in metastatic spread, including invasion, intravasation, angiogenesis, attachment at a distant site (secondary seeding), extravasation and micrometastasis and tumor dormancy development. Here, we provide an overview of the metastatic process and highlight a unique pro-metastatic gene, melanoma differentiation associated gene-9/Syntenin (MDA-9/Syntenin) also called syndecan binding protein (SDCBP), which is a major contributor to the majority of independent metastatic events. MDA-9 expression is elevated in a wide range of carcinomas and other cancers, including melanoma, glioblastoma multiforme and neuroblastoma, suggesting that it may provide an appropriate target to intervene in metastasis. Pre-clinical studies confirm that inhibiting MDA-9 either genetically or pharmacologically profoundly suppresses metastasis. An additional benefit to blocking MDA-9 in metastatic cells is sensitization of these cells to a second therapeutic agent, which converts anti-invasion effects to tumor cytocidal effects. Continued mechanistic and therapeutic insights hold promise to advance development of truly effective therapies for metastasis in the future.

Deciphering Master Gene Regulators and Associated Networks of Human Mesenchymal Stromal Cells

Mesenchymal Stromal Cells (MSC) are multipotent cells characterized by self-renewal, multilineage differentiation, and immunomodulatory properties. To obtain a gene regulatory profile of human MSCs, we generated a compendium of more than two hundred cell samples with genome-wide expression data, including a homogeneous set of 93 samples of five related primary cell types: bone marrow mesenchymal stem cells (BM-MSC), hematopoietic stem cells (HSC), lymphocytes (LYM), fibroblasts (FIB), and osteoblasts (OSTB). All these samples were integrated to generate a regulatory gene network using the algorithm ARACNe (Algorithm for the Reconstruction of Accurate Cellular Networks; based on mutual information), that finds regulons (groups of target genes regulated by transcription factors) and regulators (i.e., transcription factors, TFs). Furtherly, the algorithm VIPER (Algorithm for Virtual Inference of Protein-activity by Enriched Regulon analysis) was used to inference protein activity and to identify the most significant TF regulators, which control the expression profile of the studied cells. Applying these algorithms, a footprint of candidate master regulators of BM-MSCs was defined, including the genes EPAS1, NFE2L1, SNAI2, STAB2, TEAD1, and TULP3, that presented consistent upregulation and hypomethylation in BM-MSCs. These TFs regulate the activation of the genes in the bone marrow MSC lineage and are involved in development, morphogenesis, cell differentiation, regulation of cell adhesion, and cell structure.

Phospholipase D as a key modulator of cancer progression

The phospholipase D (PLD) family has a ubiquitous expression in cells. PLD isoforms (PLDs) and their hydrolysate phosphatidic acid (PA) have been demonstrated to engage in multiple stages of cancer progression. Aberrant expression of PLDs, especially PLD1 and PLD2, has been detected in various cancers. Inhibition or elimination of PLDs activity has been shown to reduce tumour growth and metastasis. PLDs and PA also serve as downstream effectors of various cell-surface receptors, to trigger and regulate propagation of intracellular signals in the process of tumourigenesis and metastasis. Here, we discuss recent advances in understanding the functions of PLDs and PA in discrete stages of cancer progression, including cancer cell growth, invasion and migration, and angiogenesis, with special emphasis on the tumour-associated signalling pathways mediated by PLDs and PA and the functional importance of PLDs and PA in cancer therapy.

Mammalian phospholipase D: Function, and therapeutics

Despite being discovered over 60 years ago, the precise role of phospholipase D (PLD) is still being elucidated. PLD enzymes catalyze the hydrolysis of the phosphodiester bond of glycerophospholipids producing phosphatidic acid and the free headgroup. PLD family members are found in organisms ranging from viruses, and bacteria to plants, and mammals. They display a range of substrate specificities, are regulated by a diverse range of molecules, and have been implicated in a broad range of cellular processes including receptor signaling, cytoskeletal regulation and membrane trafficking. Recent technological advances including: the development of PLD knockout mice, isoform-specific antibodies, and specific inhibitors are finally permitting a thorough analysis of the in vivo role of mammalian PLDs. These studies are facilitating increased recognition of PLD's role in disease states including cancers and Alzheimer's disease, offering potential as a target for therapeutic intervention.

Role of TGF‑β in the motility of ShcD‑overexpressing 293 cells

The newly identified Src homology and collagen (Shc) family member ShcD was observed to be upregulated in 50% of vertical growth phase and metastatic melanomas. The aim of the present study was to investigate the mechanism by which ShcD mediates cell motility. 293 cell lines were altered to stably express GFP (GF) or GFP‑ShcD (G5). Treatment of the cells with transforming growth factor (TGF)β2 promoted extracellular signal‑regulated kinase (ERK) phosphorylation and, to a lesser extent, Smad2 phosphorylation in GFP‑ShcD‑expressing cells but not in GFP‑overexpressing cells. GFP‑ShcD‑expressing cells exhibited upregulated expression of certain epithelial‑mesenchymal transition‑related genes, such as snail family transcriptional repressor 1 and SLUG, than GFP‑expressing cells. Higher levels of ERK were found in the nuclear fraction of GFP‑ShcD‑expressing cells than that of GFP‑expressing cells. Overall, GFP‑ShcD‑expressing cells demonstrated enhanced migration compared with GFP‑expressing cells. A slight increase in cell migration was observed in both cell lines (GF and G5) when the cells were allowed to migrate towards conditioned medium derived from TGFβ2‑treated GFP‑ShcD expressing cells. Collectively, ShcD upregulation was proposed to induce cell migration by affecting the expression of certain epithelial‑mesenchymal transition‑related genes. Thus, our findings may improve understanding of the role of ShcD in cell migration.

Epithelial-mesenchymal plasticity-engaging stemness in an interplay of phenotypes

Cancer is a genetic disease which results in a functional imbalance between tumour-repressive and oncogenic signals. The WHO highlights the burden of this indomitable disease, listing it as the second leading cause of death globally. The major cause of cancer-related death is rarely the effect of the primary tumour itself, but rather, the devastating spread of cancer cells in metastases. Epithelial-mesenchymal plasticity (EMP)-termed as the ability of cells to maintain its plasticity and transit between epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) states-plays a fundamental role in cancer metastasis. These cell transitions allow them migrate from the primary tumour and invade the secondary site. EMP is associated with migration, invasion, colonisation, self-renewal and drug resistance. This review briefly elucidates the mechanism of EMP and the association between cancer stem cells (CSCs) and circulating tumour cells (CTCs), biomarkers and signalling pathways involved in EMP as well as drug resistance and therapeutic targeting.

Differential responses of epithelial cells from urinary and biliary tract to eggs of Schistosoma haematobium and S. mansoni

Chronic urogenital schistosomiasis can lead to squamous cell carcinoma of the bladder. The International Agency for Research on Cancer classifies the infection with S. haematobium as a group 1 carcinogen, a definitive cause of cancer. By contrast, hepatointestinal schistosomiasis due to the chronic infection with S. mansoni or S. japonicum associated with liver periportal fibrosis, does not apparently lead to malignancy. The effects of culturing human epithelial cells, HCV29, established from normal urothelium, and H69, established from cholangiocytes, in the presence of S. haematobium or S. mansoni eggs were investigated. Cell growth of cells co-cultured with schistosome eggs was monitored in real time, and gene expression analysis of oncogenesis, epithelial to mesenchymal transition and apoptosis pathways was undertaken. Schistosome eggs promoted proliferation of the urothelial cells but inhibited growth of cholangiocytes. In addition, the tumor suppressor P53 pathway was significantly downregulated when exposed to schistosome eggs, and downregulation of estrogen receptor was predicted in urothelial cells exposed only to S. haematobium eggs. Overall, cell proliferative responses were influenced by both the tissue origin of the epithelial cells and the schistosome species.

SNAI1 recruits HDAC1 to suppress SNAI2 transcription during epithelial to mesenchymal transition

Aberrant activation of epithelial to mesenchymal transition (EMT) associated factors were highly correlated with increased mortality in cancer patients. SNAIL family of transcriptional repressors comprised of three members, each of which were essentially associated with gastrulation and neural crest formation. Among which, SNAI1 and SNAI2 were efficiently induced during EMT and their expressions were correlated with poor clinical outcome in patients with breast, colon and ovarian carcinoma. In an ovarian cancer cell lines panel, we identified that SNAI1 and SNAI2 expressions were mutually exclusive, where SNAI1 predominantly represses SNAI2 expression. Detailed analysis of SNAI2 promoter region revealed that SNAI1 binds to two E-box sequences that mediated transcriptional repression. Through epigenetic inhibitor treatments, we identified that inhibition of histone deacetylase (HDAC) activity in SNAI1 overexpressing cells partially rescued SNAI2 expression. Importantly, we demonstrated a significant deacetylation of histone H3 and significant enrichments of HDAC1 and HDAC2 corepressors in both E-box regions of SNAI2 promoter. Our results suggested that SNAI1 repression on SNAI2 expression was predominantly mediated through the recruitment of the histone deacetylation machinery. Utilization of HDAC inhibitors would require additional profiling of SNAI1 activity and combined targeting of SNAI1 and HDACs might render efficient cancer treatment.

MDA-9/Syntenin: An emerging global molecular target regulating cancer invasion and metastasis

With few exceptions, metastasis is the terminal stage of cancer with limited therapeutic options. Metastasis consists of numerous phenotypic and genotypic alterations of cells that are directly and indirectly induced by multiple intrinsic (cellular) and extrinsic (micro-environmental) factors. To metastasize, a cancer cell often transitions from an epithelial to mesenchymal morphology (EMT), modifies the extracellular matrix, forms emboli and survives in the circulation, escapes immune surveillance, adheres to sites distant from the initial tumor and finally develops a blood supply (angiogenesis) and colonizes in a secondary niche (a micrometastasis). Scientific advances have greatly enhanced our understanding of the precise molecular and genetic changes, operating independently or collectively, that lead to metastasis. This review focuses on a unique gene, melanoma differentiation associated gene-9 (also known as Syntenin-1; Syndecan Binding Protein (sdcbp); mda-9/syntenin), initially cloned and characterized from metastatic human melanoma and shown to be a pro-metastatic gene. In the last two decades, our comprehension of the diversity of actions of MDA-9/Syntenin on cellular phenotype has emerged. MDA-9/Sytenin plays pivotal regulatory roles in multiple signaling cascades and orchestrates both metastatic and non-metastatic events. Considering the relevance of this gene in controlling cancer invasion and metastasis, approaches have been developed to uniquely and selectively target this gene. We also provide recent updates on strategies that have been successfully employed in targeting MDA-9/Syntenin resulting in profound pre-clinical anti-cancer activity.

E-cadherin and Snail Immunoexpression in Colorectal Adenocarcinomas

Epithelial-mesenchymal transition (EMT) is a fundamental process which governs invasiveness. E-cadherin plays a major role in development, organogenesis and tissue formation, but also in tumor progression. Snail is a transcription factor described as a direct repressor of E-cadherin during development and in carcinogenesis. In this study we analyzed E-cadherin and Snail immunoexpression in 47 cases of colorectal adenocarcinoma (CRC) in comparison with some histopathological prognostic factors. The majority of cases were G2 tumors in stages II and III, with vascular and perineural invasion. All cases showed positive cytoplasmic signal for E-cadherin and Snail. E-cadherin reactions were intense with the highest composite score (CS) values in CRC G1. CS values of E-cadherin decreased with the advancement in tumor stage and the association with vascular and perineural invasion was statistically significant. Snail immunoreaction was intense with the highest values of CS in CRC G3, being more evident with the increase of tumor staging, aspect which was statistically significant. CS and Snail association demonstrated a statistically significant aspect related to vascular invasion. We found a negative linear correlation of E-cadherin and Snail expression. The obtained results indicate the implication of Snail and E-cadherin in EMT of CRC, aspect which is useful in the evaluation and stratification of patients with CRC for the targeted specific therapy.

Expression of the SNAI2 transcriptional repressor is regulated by C16-ceramide

Ceramide synthase 6 (CerS6) is an enzyme that preferentially generates pro-apoptotic C₁₆-ceramide in the sphingolipid metabolic pathway. Reduced expression of CerS6 has been associated with apoptosis resistance and recent studies point to a role for CerS6 in epithelial mesenchymal transition (EMT). Because cells that undergo EMT are also more resistant to apoptosis, we hypothesized that reduced expression of CerS6 could induce changes that are associated with EMT. We found that shRNA-mediated knockdown of CerS6 increases expression of the EMT transcription factor SNAI2 but not SNAI1 or TWIST. Treatment with C₆-ceramide nanoliposomes (CNL) resulted in a preferential increase in C₁₆-ceramide and suppressed SNAI2 transcriptional activation and protein expression. The increase in C₁₆-ceramide following CNL treatment was dependent on CerS activity and occurred even when CerS6 shRNA was expressed. shRNA against CerS5, which like CerS6 preferentially generates C₁₆-ceramide, also decreased transcriptional activation of SNAI2, suggesting a role for C₁₆-ceramide rather than a specific enzyme in the regulation of this transcription factor. While loss of CerS6 has been associated with apoptosis resistance, we found that cells lacking this protein are more susceptible to the effects CNL. In summary, our study identifies SNAI2 as a novel target whose expression can be influenced by C₁₆-ceramide levels. The potential of CNL to suppress SNAI2 expression has important clinical implications, since elevated expression of this transcription factor has been associated with an aggressive phenotype or poor outcomes in several types of solid tumors.

A novel SRC-2-dependent regulation of epithelial-mesenchymal transition in breast cancer cells

Steroid receptor coactivator 2 (SRC-2) is a nuclear receptor coactivator, important for the regulation of estrogen receptor alpha (ERα)-mediated transcriptional activity in breast cancer cells. However, the transcriptional role of SRC-2 in breast cancer is still ambiguous. Here we aimed to unravel a more precise transcriptional role of SRC-2 and uncover unique target genes in MCF-7 breast cancer cells, as opposed to the known oncogene SRC-3. Gene expression analyses of cells depleted of either SRC-2 or SRC-3 showed that they transcriptionally regulate mostly separate gene sets. However, individual unique gene sets were implicated in some of the same major gene ontology biological processes, such as cellular structure and development. This finding was supported by three-dimensional cell cultures, demonstrating that depletion of SRC-2 and SRC-3 changed the morphology of the cells into epithelial-like hollow acinar structures, indicating that both SRC proteins are involved in maintaining the hybrid E/M phenotype. In clinical ER-positive, HER2-negative breast cancer samples the expression of SRC-2 was negatively correlated with the expression of MCF-7-related luminal, cell cycle and cellular morphogenesis genes. Finally, elucidating SRC-2 unique transcriptional effects, we identified Lyn kinase (an EMT biomarker) to be upregulated exclusively after SRC-2 depletion. In conclusion, we show that both SRC-2 and SRC-3 are essential for the EMT in breast cancer cells, controlling different transcriptional niches.

The EBV-Encoded Oncoprotein, LMP1, Induces an Epithelial-to-Mesenchymal Transition (EMT) via Its CTAR1 Domain through Integrin-Mediated ERK-MAPK Signalling

The Epstein–Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) oncogene can induce profound effects on epithelial growth and differentiation including many of the features of the epithelial-to-mesenchymal transition (EMT). To better characterise these effects, we used the well-defined Madin Darby Canine Kidney (MDCK) epithelial cell model and found that LMP1 expression in these cells induces EMT as defined by characteristic morphological changes accompanied by loss of E-cadherin, desmosomal cadherin and tight junction protein expression. The induction of the EMT phenotype required a functional CTAR1 domain of LMP1 and studies using pharmacological inhibitors revealed contributions from signalling pathways commonly induced by integrin–ligand interactions: extracellular signal-regulated kinases/mitogen-activated protein kinases (ERK-MAPK), PI3-Kinase and tyrosine kinases, but not transforming growth factor beta (TGFβ). More detailed analysis implicated the CTAR1-mediated induction of Slug and Twist in LMP1-induced EMT. A key role for β1 integrin signalling in LMP1-mediated ERK-MAPK and focal adhesion kianse (FAK) phosphorylation was observed, and β1 integrin activation was found to enhance LMP1-induced cell viability and survival. These findings support an important role for LMP1 in disease pathogenesis through transcriptional reprogramming that enhances tumour cell survival and leads to a more invasive, metastatic phenotype.

Interleukin-6 induced overexpression of valosin-containing protein (VCP)/p97 is associated with androgen-independent prostate cancer (AIPC) progression

Though Androgen deprivation therapy (ADT) is effective initially, numerous patients become resistant to it and develop castration resistant PCa (CRPC). Cytokines promotes ligand independent activation of AR. Interleukin-6 (IL-6) levels are elevated in CRPC patients and regulate AR activity. However, progression to CRPC is not fully understood. In this study, we analyzed differential protein expression in LNCaP cells treated with IL-6 using proteomics. Results revealed altered expression of 27 proteins and Valosin-containing protein (VCP)/p97 plays a predominant role in co-regulation of altered proteins. Interestingly, IL-6 induced VCP expression through Pim-1 via STAT3 is AR independent there by suggesting a role for VCP in CRPC. Transfection of LNCaP cells for VCP overexpression showed an increased cell proliferation, migration, and invasion where as its inhibition by NMS-873 showed the reverse effect causing cell death. Mechanistic studies demonstrate that cell death occurs due to apoptosis by endoplasmic reticulum (ER) stress, elevated cell cycle inhibitors p21, p27kip1, and active PARP and reduced Bcl-2. VCP promotes cell invasion and migration by altering E-cadherin and Vimentin levels inversely triggering EMT of PCa cells. VCP immunostaining revealed no staining in BPH but strong staining in PCa. This study determines VCP may play an important role in progression to CRPC and it can be a favorable target with to develop new therapies to treat ADT resistant prostate cancer.

Stability of the hybrid epithelial/mesenchymal phenotype

Epithelial-to-Mesenchymal Transition (EMT) and its reverse – Mesenchymal to Epithelial Transition (MET) – are hallmarks of cellular plasticity during embryonic development and cancer metastasis. During EMT, epithelial cells lose cell-cell adhesion and gain migratory and invasive traits either partially or completely, leading to a hybrid epithelial/mesenchymal (hybrid E/M) or a mesenchymal phenotype respectively. Mesenchymal cells move individually, but hybrid E/M cells migrate collectively as observed during gastrulation, wound healing, and the formation of tumor clusters detected as Circulating Tumor Cells (CTCs). Typically, the hybrid E/M phenotype has largely been tacitly assumed to be transient and ‘metastable’. Here, we identify certain ‘phenotypic stability factors’ (PSFs) such as GRHL2 that couple to the core EMT decision-making circuit (miR-200/ZEB) and stabilize hybrid E/M phenotype. Further, we show that H1975 lung cancer cells can display a stable hybrid E/M phenotype and migrate collectively, a behavior that is impaired by knockdown of GRHL2 and another previously identified PSF - OVOL. In addition, our computational model predicts that GRHL2 can also associate hybrid E/M phenotype with high tumor-initiating potential, a prediction strengthened by the observation that the higher levels of these PSFs may be predictive of poor patient outcome. Finally, based on these specific examples, we deduce certain network motifs that can stabilize the hybrid E/M phenotype. Our results suggest that partial EMT, i.e. a hybrid E/M phenotype, need not be ‘metastable’, and strengthen the emerging notion that partial EMT, but not necessarily a complete EMT, is associated with aggressive tumor progression.

The transcription factors Slug (SNAI2) and Snail (SNAI1) regulate phospholipase D (PLD) promoter in opposite ways towards cancer cell invasion

Slug (SNAI2) and Snail (SNAI1) are master regulatory transcription factors for organogenesis and wound healing, and they are involved in the epithelial to mesenchymal transition (EMT) of cancer cells. We found that the activity of phospholipase D isoform 2 (PLD2) is highly increased in cancers with larger size and poor prognosis (MDA-MB-231 versus MCF-7 cells), so we determined if Snail or Slug were responsible for PLD2 gene transcription regulation. Unexpectedly, we found that PLD2 expression was positively regulated by Slug but negatively regulated by Snail. The differential effects are amplified in breast cancer cells over normal cells and with MDA-MB-231 more robustly than MCF-7. Slug putatively binds to the PLD2 promoter and transactivates it, which is negated when Slug and Snail compete with each other. Meanwhile, PLD2 has a negative effect on Snail expression and a positive effect on Slug, thus closing a feedback loop between the lipase and the transcription factors. Further, PA, the product of PLD2 enzymatic reaction, has profound effects on its own and it further regulates the transcription factors. Thus, we show for the first time that the overexpressed PLD2 in human breast tumors is regulated by Slug and Snail transcription factors. The newly uncovered feedback loops in highly invasive cancer cells have important implications in the process of EMT.