Plasma membrane ion channels and epithelial to mesenchymal transition in cancer cells

Aberrations in ion channels interacting with lipid metabolism and epithelial-mesenchymal transition in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is the most prevalent malignant gastrointestinal tumor. Ion channels contribute to tumor growth and progression through interactions with their neighboring molecules including lipids. The dysregulation of membrane ion channels and lipid metabolism may contribute to the epithelial-mesenchymal transition (EMT), leading to metastatic progression. Herein, transcriptome profiles of patients with ESCC were analyzed by performing differential gene expression and weighted gene co-expression network analysis to identify the altered ion channels, lipid metabolism- and EMT-related genes in ESCC. A total of 1,081 differentially expressed genes, including 113 ion channels, 487 lipid metabolism-related, and 537 EMT-related genes, were identified in patients with ESCC. Thereafter, EMT scores were correlated with altered co-expressed genes. The altered co-expressed genes indicated a correlation with EMT signatures. Interactions among 22 ion channels with 3 hub lipid metabolism- and 13 hub EMT-related proteins were determined using protein-protein interaction networks. A pathway map was generated to depict deregulated signaling pathways including insulin resistance and the estrogen receptor-Ca²⁺ signaling pathway in ESCC. The relationship between potential ion channels and 5-year survival rates in ESCC was determined using Kaplan-Meier plots and Cox proportional hazard regression analysis. Inositol 1,4,5-trisphosphate receptor type 3 (ITPR3) was found to be associated with poor prognosis of patients with ESCC. Additionally, drugs interacting with potential ion channels, including GJA1 and ITPR3, were identified. Understanding alterations in ion channels with lipid metabolism and EMT in ESCC pathophysiology would most likely provide potential targets for the better treatment of patients with ESCC.

Intersection between calcium signalling and epithelial-mesenchymal plasticity in the context of cancer

Epithelial-mesenchymal transition (EMT) is a form of cellular phenotypic plasticity and is considered a crucial step in the progression of many cancers. The calcium ion (Ca²⁺) acts as a ubiquitous second messenger and is implicated in many cellular processes, including cell death, migration, invasion and more recently EMT. Throughout this review, the complex interplay between Ca²⁺ signalling and EMT will be explored. An overview of the Ca²⁺ pathways that are remodelled as a consequence of EMT is provided and the role of Ca²⁺ signalling in regulating EMT and its significance is considered. Ca²⁺ signalling pathways may represent a therapeutic opportunity to regulate EMT. However, as will be described in this review, the complexity of these signalling pathways represents significant challenges that must be considered if Ca²⁺ signalling is to be manipulated with the aim of therapeutic intervention in cancer.

Epithelial-to-mesenchymal transition as a learning paradigm of cell biology

Epithelial-to-mesenchymal transition (EMT) is a complex biological process that occurs during normal embryogenesis and in certain pathological conditions, particularly in cancer. EMT can be viewed as a cell biology-based process, since it involves all the cellular components, including the plasma membrane, cytoskeleton and extracellular matrix, endoplasmic reticulum, Golgi apparatus, lysosomes, and mitochondria, as well as cellular processes, such as regulation of gene expression and cell cycle, adhesion, migration, signaling, differentiation, and death. Therefore, we propose that EMT could be used to motivate undergraduate medical students to learn and understand cell biology. Here, we describe and discuss the involvement of each cellular component and process during EMT. To investigate the density with which different cell biology concepts are used in EMT research, we apply a bibliometric approach. The most frequent cell biology topics in EMT studies were regulation of gene expression, cell signaling, cell cycle, cell adhesion, cell death, cell differentiation, and cell migration. Finally, we suggest that the study of EMT could be incorporated into undergraduate disciplines to improve cell biology understanding among premedical, medical and biomedical students.

Glucose and Inositol Transporters, SLC5A1 and SLC5A3, in Glioblastoma Cell Migration

(1) Background: The recurrence of glioblastoma multiforme (GBM) is mainly due to invasion of the surrounding brain tissue, where organic solutes, including glucose and inositol, are abundant. Invasive cell migration has been linked to the aberrant expression of transmembrane solute-linked carriers (SLC). Here, we explore the role of glucose (SLC5A1) and inositol transporters (SLC5A3) in GBM cell migration. (2) Methods: Using immunofluorescence microscopy, we visualized the subcellular localization of SLC5A1 and SLC5A3 in two highly motile human GBM cell lines. We also employed wound-healing assays to examine the effect of SLC inhibition on GBM cell migration and examined the chemotactic potential of inositol. (3) Results: While GBM cell migration was significantly increased by extracellular inositol and glucose, it was strongly impaired by SLC transporter inhibition. In the GBM cell monolayers, both SLCs were exclusively detected in the migrating cells at the monolayer edge. In single GBM cells, both transporters were primarily localized at the leading edge of the lamellipodium. Interestingly, in GBM cells migrating via blebbing, SLC5A1 and SLC5A3 were predominantly detected in nascent and mature blebs, respectively. (4) Conclusion: We provide several lines of evidence for the involvement of SLC5A1 and SLC5A3 in GBM cell migration, thereby complementing the migration-associated transportome. Our findings suggest that SLC inhibition is a promising approach to GBM treatment.

Mechanical Stretch Triggers Epithelial-Mesenchymal Transition in Keratinocytes Through Piezo1 Channel

The epithelial-mesenchymal transition (EMT) process has emerged as a central regulator of embryonic development, tissue repair and tumor malignancy. In recent years, researchers have specifically focused on how mechanical signals drive the EMT program in epithelial cells. However, how epithelial cells specifically leverage mechanical force to control the EMT process remains unclear. Here, we show that the bona fide mechanically activated cation channel Piezo1 plays a critical role in the EMT. The Piezo1 is expressed in human primary epidermal keratinocytes (HEKs) and is responsible for the mechanical stretch-induced Ca2+ concentration. Inhibition of Piezo1 activation by the inhibitor GsMTx4 or by siRNA-mediated Piezo1 knockdown influenced the morphology and migration of HEKs. Moreover, Piezo1 activity also altered EMT-correlated markers expression in response to mechanical stretch. We propose that the mechanically activated cation channel Piezo1 is an important determinant of mechanical force-induced EMT in keratinocytes and might play similar roles in other epithelial cells.

In Silico Analysis of Ion Channels and Their Correlation with Epithelial to Mesenchymal Transition in Breast Cancer

Simple Summary

Breast cancer involves changes in the healthy cells of the breast resulting in rapid and abnormal division of cells that later spread to other parts of the body through the process of metastasis, which involves epithelial mesenchymal transition (EMT). Ion channels play a significant role in the switch from epithelial to mesenchymal transition through their contributions to cellular motility, cell volume regulation and cell cycle progression. Comprehensive computational analyses were performed to understand the role of ion channels in tumor/metastatic samples of breast cancer and their correlation with EMT.

Abstract

Uncontrolled growth of breast cells due to altered gene expression is a key feature of breast cancer. Alterations in the expression of ion channels lead to variations in cellular activities, thus contributing to attributes of cancer hallmarks. Changes in the expression levels of ion channels were observed as a consequence of EMT. Additionally, ion channels were reported in the activation of EMT and maintenance of a mesenchymal phenotype. Here, to identify altered ion channels in breast cancer patients, differential gene expression and weighted gene co-expression network analyses were performed using transcriptomic data. Protein–protein interactions network analysis was carried out to determine the ion channels interacting with hub EMT-related genes in breast cancer. Thirty-two ion channels were found interacting with twenty-six hub EMT-related genes. The identified ion channels were further correlated with EMT scores, indicating mesenchymal phenotype. Further, the pathway map was generated to represent a snapshot of deregulated cellular processes by altered ion channels and EMT-related genes. Kaplan–Meier five-year survival analysis and Cox regressions indicated the expression of CACNA1B, ANO6, TRPV3, VDAC1 and VDAC2 to be potentially associated with poor survival. Deregulated ion channels correlate with EMT-related genes and have a crucial role in breast cancer-associated tumorigenesis. Most likely, they are potential candidates for the determination of prognosis in patients with breast cancer.

Alterations of Ion Homeostasis in Cancer Metastasis: Implications for Treatment

We have previously reported that metastases from all malignancies are characterized by a core program of gene expression that suppresses extracellular matrix interactions, induces vascularization/tissue remodeling, activates the oxidative metabolism, and alters ion homeostasis. Among these features, the least elucidated component is ion homeostasis. Here we review the literature with the goal to infer a better mechanistic understanding of the progression-associated ionic alterations and identify the most promising drugs for treatment. Cancer metastasis is accompanied by skewing in calcium, zinc, copper, potassium, sodium and chloride homeostasis. Membrane potential changes and water uptake through Aquaporins may also play roles. Drug candidates to reverse these alterations are at various stages of testing, with some having entered clinical trials. Challenges to their utilization comprise differences among tumor types and the involvement of multiple ions in each case. Further, adverse effects may become a concern, as channel blockers, chelators, or supplemented ions will affect healthy and transformed cells alike.

Calcium signaling induces a partial EMT

Epithelial plasticity, or epithelial-to-mesenchymal transition (EMT), is a well-recognized form of cellular plasticity, which endows tumor cells with invasive properties and alters their sensitivity to various agents, thus representing a major challenge to cancer therapy. It is increasingly accepted that carcinoma cells exist along a continuum of hybrid epithelial-mesenchymal (E-M) states and that cells exhibiting such partial EMT (P-EMT) states have greater metastatic competence than those characterized by either extreme (E or M). We described recently a P-EMT program operating in vivo by which carcinoma cells lose their epithelial state through post-translational programs. Here, we investigate the underlying mechanisms and report that prolonged calcium signaling induces a P-EMT characterized by the internalization of membrane-associated E-cadherin (ECAD) and other epithelial proteins as well as an increase in cellular migration and invasion. Signaling through Gαq-associated G-protein-coupled receptors (GPCRs) recapitulates these effects, which operate through the downstream activation of calmodulin-Camk2b signaling. These results implicate calcium signaling as a trigger for the acquisition of hybrid/partial epithelial-mesenchymal states in carcinoma cells.

Calcium Signalling in Medulloblastoma: An In Silico Analysis of the Expression of Calcium Regulating Genes in Patient Samples

Dysregulation in calcium signalling is implicated in several cancer-associated processes, including cell proliferation, migration, invasion and therapy resistance. Modulators of specific calcium-regulating proteins have been proposed as promising future therapeutic agents for some cancers. Alterations in calcium signalling have been extensively studied in some cancers; however, this area of research is highly underexplored in medulloblastoma (MB), the most common paediatric malignant brain tumour. Current MB treatment modalities are not completely effective and can result in several long-lasting mental complications. Hence, new treatment strategies are needed. In this study, we sought to probe the landscape of calcium signalling regulators to uncover those most likely to be involved in MB tumours. We investigated the expression of calcium signalling regulator genes in MB patients using publicly available datasets. We stratified the expression level of these genes with MB molecular subgroups, tumour metastasis and patient survival to uncover correlations with clinical features. Of particular interest was CACNA1 genes, in which we were able to show a developmentally-driven change in expression within the cerebellum, MB's tissue of origin, highlighting a potential influence on tumour incidence. This study lays a platform for future investigations into molecular regulators of calcium signalling in MB formation and progression.

Auto-inhibitory intramolecular S5/S6 interaction in the TRPV6 channel regulates breast cancer cell migration and invasion

TRPV6, a Ca-selective channel, is abundantly expressed in the placenta, intestine, kidney and bone marrow. TRPV6 is vital to Ca homeostasis and its defective expression or function is linked to transient neonatal hyperparathyroidism, Lowe syndrome/Dent disease, renal stone, osteoporosis and cancers. The fact that the molecular mechanism underlying the function and regulation of TRPV6 is still not well understood hampers, in particular, the understanding of how TRPV6 contributes to breast cancer development. By electrophysiology and Ca imaging in Xenopus oocytes and cancer cells, molecular biology and numerical simulation, here we reveal an intramolecular S5/S6 helix interaction in TRPV6 that is functionally autoinhibitory and is mediated by the R532:D620 bonding. Predicted pathogenic mutation R532Q within S5 disrupts the S5/S6 interaction leading to gain-of-function of the channel, which promotes breast cancer cell progression through strengthening of the TRPV6/PI3K interaction, activation of a PI3K/Akt/GSK-3β cascade, and up-regulation of epithelial-mesenchymal transition and anti-apoptosis.

Transient Receptor Potential Channels in the Epithelial-to-Mesenchymal Transition

The epithelial-to-mesenchymal transition (EMT) is a strictly regulated process that is indispensable for normal development, but it can result in fibrosis and cancer progression. It encompasses a complete alteration of the cellular transcriptomic profile, promoting the expression of genes involved in cellular migration, invasion and proliferation. Extracellular signaling factors driving the EMT process require secondary messengers to convey their effects to their targets. Due to its remarkable properties, calcium represents an ideal candidate to translate molecular messages from receptor to effector. Therefore, calcium-permeable ion channels that facilitate the influx of extracellular calcium into the cytosol can exert major influences on cellular phenotype. Transient receptor potential (TRP) channels represent a superfamily of non-selective cation channels that decode physical and chemical stimuli into cellular behavior. Their role as cellular sensors renders them interesting proteins to study in the context of phenotypic transitions, such as EMT. In this review, we elaborate on the current knowledge regarding TRP channel expression and activity in cellular phenotype and EMT.

Store-operated Ca2+ entry as a key oncogenic Ca2+ signaling driving tumor invasion-metastasis cascade and its translational potential

Tumor metastasis is the primary cause of treatment failure and cancer-related deaths. Store-operated Ca²⁺ entry (SOCE), which is mediated by stromal interaction molecules (STIM) and ORAI proteins, has been implicated in the tumor invasion-metastasis cascade. Epithelial-mesenchymal transition (EMT) is a cellular program that enables tumor cells to acquire the capacities needed for migration and invasion and the formation of distal metastases. Tumor-associated angiogenesis contributes to metastasis because aberrantly developed vessels offer a path for tumor cell dissemination as well as supply sufficient nutrients for the metastatic colony to develop into metastasis. Recently, increasing evidence has indicated that SOCE alterations actively participate in the multi-step process of tumor metastasis. In addition, the dysregulated expression of STIM/ORAI has been reported to be a predictor of poor prognosis. Herein, we review the latest advances about the critical role of SOCE in the tumor metastasis cascade and the underlying regulatory mechanisms. We emphasize the contributions of SOCE to the EMT program, tumor cell migration and invasion, and angiogenesis. We further discuss the possibility of modulating SOCE or intervening in the downstream signaling pathways as a feasible targeting therapy for cancer treatment.

Effect arylamine N-acetyltransferase 1 on morphology, adhesion, migration, and invasion of MDA-MB-231 cells: role of matrix metalloproteinases and integrin αV

Reducted arylamine N-acetyltransferase (NAT1) in breast cancers is associated with poor patient survival. NAT1 has also been associated with changes in cancer cell survival and invasion both invitro and invivo. Here, we report the effects of NAT1 in cancer cell invasion by addressing its role in adherence, migration, and invasion in vitro. The NAT1 gene was deleted in MDA-MB-231, HT-29 and HeLa cells using CRISPR/Cas9 gene editing. Loss of NAT1 increased adherence to collagen in all three cell-lines but migration was unaffected. NAT1 deletion decreased invasion and induced changes to cell morphology. These effects were independent of matrix metalloproteinases but were related to integrin ITGαV expression. The data suggest NAT1 is important in adhesion and invasion through integrin expression.

Kv3 channels contribute to cancer cell migration via vimentin regulation

Cell migration is a complex and important process in cancer progression. Vimentin has pivotal roles in cancer cell migration, and various signaling pathways including the AKT pathway are involved in cancer cell migration via vimentin regulation. Recent studies have revealed that voltage-gated potassium (Kv) channels have important functions in cancer cell migration; however, the exact mechanism is still unclear. In the present study, we focused on Kv3 channels with vimentin in cancer migration using human cervical cancer cells (HeLa) and canine mammary tumor cells (CHMp). Cancer cell migration was significantly inhibited, and vimentin expression was significantly decreased by Kv3 blocker, BDS-II. The Kv3 blocker also inactivated the AKT pathway in HeLa cells. In addition, reduced expressions of vimentin and Kv3.4 were observed in HeLa cells when treated with AKT blocker, MK2206. These results suggest that Kv3 channels play important roles in cancer cell migration by regulating vimentin and having closely related with the AKT pathway in human cervical cancer cells.

The epithelial sodium channel has a role in breast cancer cell proliferation

PURPOSE

Breast cancer is the most common cancer affecting women worldwide with half a million associated deaths annually. Despite a huge global effort, the pathways of breast cancer progression are not fully elucidated. Ion channels have recently emerged as novel regulators of cancer cell proliferation and metastasis. The epithelial sodium channel, ENaC, made up of α, β and γ subunits is well known for its role in Na⁺ reabsorption in epithelia, but a number of novel roles for ENaC have been described, including potential roles in cancer. A role for ENaC in breast cancer, however, has yet to be described. Therefore, the effects of ENaC level and activity on breast cancer proliferation were investigated.

METHODS

Through the publicly available SCAN-B dataset associations between αENaC mRNA expression and breast cancer subtypes, proliferation markers and epithelial-mesenchymal transition markers (EMT) were assessed. αENaC expression, through overexpression or siRNA-mediated knockdown, and activity, through the ENaC-specific inhibitor amiloride, were altered in MCF7, T47D, BT549, and MDAMB231 breast cancer cells. MTT and EdU cell proliferation assays were used to determine the effect of these manipulations on breast cancer cell proliferation.

RESULTS

High αENaC mRNA expression was associated with less aggressive and less proliferative breast cancer subtypes and with reduced expression of proliferation markers. Decreased αENaC expression or activity, in the mesenchymal breast cancer cell lines BT549 and MDAMB231, increased breast cancer cell proliferation. Conversely, increased αENaC expression decreased breast cancer cell proliferation.

CONCLUSION

αENaC expression is associated with a poor prognosis in breast cancer and is a novel regulator of breast cancer cell proliferation. Taken together, these results identify ENaC as a potential future therapeutic target.

Molecular machineries and physiological relevance of ER-mediated membrane contacts

Membrane contact sites (MCSs) are defined as regions where two organelles are closely apposed, and most MCSs associated with each other via protein-protein or protein-lipid interactions. A number of key molecular machinery systems participate in mediating substance exchange and signal transduction, both of which are essential processes in terms of cellular physiology and pathophysiology. The endoplasmic reticulum (ER) is the largest reticulum network within the cell and has extensive communication with other cellular organelles, including the plasma membrane (PM), mitochondria, Golgi, endosomes and lipid droplets (LDs). The contacts and reactions between them are largely mediated by various protein tethers and lipids. Ions, lipids and even proteins can be transported between the ER and neighboring organelles or recruited to the contact site to exert their functions. This review focuses on the key molecules involved in the formation of different contact sites as well as their biological functions.

Calcium signaling: breast cancer's approach to manipulation of cellular circuitry

Calcium is a versatile element that participates in cell signaling for a wide range of cell processes such as death, cell cycle, division, migration, invasion, metabolism, differentiation, autophagy, transcription, and others. Specificity of calcium in each of these processes is achieved through modulation of intracellular calcium concentrations by changing the characteristics (amplitude/frequency modulation) or location (spatial modulation) of the signal. Breast cancer utilizes calcium signaling as an advantage for survival and progression. This review integrates evidence showing that increases in expression of calcium channels, GPCRs, pumps, effectors, and enzymes, as well as resulting intracellular calcium signals, lead to high calcium and/or an elevated calcium- mobilizing capacity necessary for malignant functions such as migratory, invasive, proliferative, tumorigenic, or metastatic capacities.

Activation of the Ion Channel TRPV4 Induces Epithelial to Mesenchymal Transition in Breast Cancer Cells

Epithelial to mesenchymal transition (EMT) in cancer is important in therapeutic resistance and invasiveness. Calcium signaling is key to the induction of EMT in breast cancer cells. Although inhibition of specific calcium-permeable ion channels regulates the induction of a sub-set of EMT markers in breast cancer cells, it is still unclear if activation of a specific calcium channel can be a driver for the induction of EMT events. In this study, we exploited the availability of a selective pharmacological activator of the calcium-permeable ion channel TRPV4 to assess the direct role of calcium influx in EMT marker induction. Gene association studies revealed a link between TRPV4 and gene-ontologies associated with EMT and poorer relapse-free survival in lymph node-positive basal breast cancers. TRPV4 was an important component of the calcium influx phase induced in MDA-MB-468 breast cancer cells by the EMT inducer epidermal growth factor (EGF). Pharmacological activation of TRPV4 then drove the induction of a variety of EMT markers in breast cancer cells. These studies demonstrate that calcium influx through specific pathways appears to be sufficient to trigger EMT events.

TRPV4 Overexpression Promotes Metastasis Through Epithelial-Mesenchymal Transition in Gastric Cancer and Correlates with Poor Prognosis

Purpose

Transient receptor potential vanilloid 4 (TRPV4) has been reported to be involved in the progression of several human tumors. Nevertheless, clinical significance and molecular mechanism of TRPV4 in gastric cancer (GC) remain poorly defined.

Patients and Methods

Immunohistochemistry assays were used to investigate the correlation between the expression of TRPV4 and epithelial–mesenchymal transition (EMT) markers in human GC tissues. The correlations between TRPV4 expression and clinicopathological features and between TRPV4 expression and survival rates were also examined. TRPV4 knockdown was performed by using small interfering RNAs. In vitro, Cell Counting Kit-8 (CCK-8) assay, colony formation assay, and transwell assay were employed to further explore the biological functions of TRPV4, and Western blotting was used to evaluate the changes in the expression of TRPV4 protein and EMT-related proteins in HGC-27 and MGC-803 human GC cell lines.

Results

TRPV4 expression was upregulated in GC tissues and cell lines. TRPV4 overexpression was associated with greater depth of tumor invasion, lymph node metastasis, higher TNM stage, poor overall survival, and worse disease-free survival. TRPV4 expression was inversely correlated with E-cadherin expression and positively correlated with vimentin expression. In vitro, knockdown of TRPV4 inhibited GC cell proliferation, colony formation, and invasion. Furthermore, the knockdown of TRPV4 modulated EMT by upregulating E-cadherin expression and downregulating the expression of N-cadherin and vimentin. In addition, the EMT-related transcription factor Snail was downregulated, whereas the expression levels of other transcription factors such as Slug and Twist did not change.

Conclusion

TRPV4 was upregulated in human GC and the overexpression of TRPV4 could promote GC progression, partially through Snail-mediated EMT.

Potassium and Calcium Channel Complexes as Novel Targets for Cancer Research

The intracellular Ca²⁺ concentration is mainly controlled by Ca²⁺ channels. These channels form complexes with K⁺ channels, which function to amplify Ca²⁺ flux. In cancer cells, voltage-gated/voltage-dependent Ca²⁺ channels and non-voltage-gated/voltage-independent Ca²⁺ channels have been reported to interact with K⁺ channels such as Ca²⁺-activated K⁺ channels and voltage-gated K⁺ channels. These channels are activated by an increase in cytosolic Ca²⁺ concentration or by membrane depolarization, which induces membrane hyperpolarization, increasing the driving force for Ca²⁺ flux. These complexes, composed of K⁺ and Ca²⁺ channels, are regulated by several molecules including lipids (ether lipids and cholesterol), proteins (e.g. STIM), receptors (e.g. S1R/SIGMAR1), and peptides (e.g. LL-37) and can be targeted by monoclonal antibodies, making them novel targets for cancer research.

EMT signaling: potential contribution of CRISPR/Cas gene editing

Epithelial to mesenchymal transition (EMT) is a complex plastic and reversible cellular process that has critical roles in diverse physiological and pathological phenomena. EMT is involved in embryonic development, organogenesis and tissue repair, as well as in fibrosis, cancer metastasis and drug resistance. In recent years, the ability to edit the genome using the clustered regularly interspaced palindromic repeats (CRISPR) and associated protein (Cas) system has greatly contributed to identify or validate critical genes in pathway signaling. This review delineates the complex EMT networks and discusses recent studies that have used CRISPR/Cas technology to further advance our understanding of the EMT process.

Differential engagement of ORAI1 and TRPC1 in the induction of vimentin expression by different stimuli

The Ca²⁺ signal is essential in both hypoxia- and epidermal growth factor (EGF)-mediated epithelial to mesenchymal transition (EMT) in MDA-MB-468 breast cancer cells. This finding suggests that Ca²⁺-permeable ion channels participate in the induction of expression of some mesenchymal markers such as vimentin. However, the ion channels involved in vimentin expression induction have not been fully characterized. This work sought to define how differential modulation of the calcium signal effects the induction of vimentin and the Ca²⁺ influx pathways involved. We identified that the intracellular Ca²⁺ chelator EGTA-AM, cytochalasin D (a modulator of cytoskeletal dynamics and cell morphology), and the sarco/endoplasmic reticulum ATPase inhibitor thapsigargin are all inducers of vimentin in MDA-MB-468 breast cancer cells. EGTA-AM- and thapsigargin-mediated induction of vimentin expression in MDA-MB-468 cells involves store-operated Ca²⁺ entry, as evidenced by sensitivity to silencing of the molecular components of this pathway, STIM1 and ORAI1. In stark contrast, cytochalasin D-mediated vimentin induction was insensitive to silencing of ORAI1, despite sensitivity to silencing of its canonical activator the endoplasmic reticulum Ca²⁺ sensor STIM1. Cytochalasin D-mediated vimentin induction was, however, sensitive to silencing of another reported STIM1 target, TRPC1. Subsequent studies identified that EGTA-AM-induced vimentin expression also partially involved a TRPC1-dependent pathway. These studies define a complex interplay between vimentin expression in this model and the specific Ca²⁺-permeable ion channels involved. The complexity in the engagement of different Ca²⁺ influx pathways that regulate vimentin induction are opportunities but also potential challenges in targeting Ca²⁺ signaling to block EMT in cancer cells. Our findings further highlight the need to identify potential indispensable ion channels that can regulate induction of specific mesenchymal markers via different stimuli.

High-throughput screening identified miR-7-2-3p and miR-29c-3p as metastasis suppressors in gallbladder carcinoma

BACKGROUND

Gallbladder carcinoma (GBC) is one of the most aggressive and lethal tumors, with extremely high metastatic activity and poor prognosis. Previously we have studied miRNAs that promote metastasis and progression of GBC, the aim of present study was to systematically elucidate the metastasis suppressor miRNAs in GBC.

METHODS

A novel designed high-throughput screening method that combined high content screening (HCS) and miRNA microarray analysis was conducted to filter out anti-metastatic miRNAs of GBC. Frozen samples were analyzed for the expression of goal miRNAs by real-time PCR. The biological functions of miRNAs were studied by transwell, immunoblot. Liver metastasis model via spleen injection was further examined in nude mice. Kaplan-Meier and Cox regression analyses were used to analyze the effect of goal miRNAs on overall survival. The target genes and interaction network of goal miRNAs were determined by whole transcriptome genome sequencing.

RESULTS

Out of the miRNAs library, a series of prominent metastatic suppressor miRNA candidates were filtered out. Among them, miR-7-2-3p and miR-29c-3p were discovered downregulated in GBC, and upregulation of them could reverse epithelial-mesenchymal transition and decrease the metastasis ability of GBC cells in vitro and in vivo, which was dominated by the miRNA-mRNA-lncRNA co-expression network. And DCLK1 and SLC36A1 are the direct target genes of miR-7-2-3p and miR-29c-3p. Moreover, the deficiency of miR-7-2-3p and miR-29c-3p was closely associated with poor prognosis of GBC patients.

CONCLUSIONS

Our findings indicate that miR-7-2-3p and miR-29c-3p play crucial roles in the pathogenesis and worse prognosis of GBCs, which may serve as prognosis biomarkers and promise potential therapeutic targets in the future.

A Novel Calcium-Mediated EMT Pathway Controlled by Lipids: An Opportunity for Prostate Cancer Adjuvant Therapy

The composition of periprostatic adipose tissue (PPAT) has been shown to play a role in prostate cancer (PCa) progression. We recently reported an inverse association between PCa aggressiveness and elevated PPAT linoleic acid (LA) and eicosapentaenoic acid (EPA) content. In the present study, we identified a new signaling pathway with a positive feedback loop between the epithelial-to-mesenchymal transition (EMT) transcription factor Zeb1 and the Ca²⁺-activated K⁺ channel SK3, which leads to an amplification of Ca²⁺ entry and cellular migration. Using in vitro experiments and ex vivo cultures of human PCa slices, we demonstrated that LA and EPA exert anticancer effects, by modulating Ca²⁺ entry, which was involved in Zeb1 regulation and cancer cellular migration. This functional approach using human prostate tumors highlights the clinical relevance of our observations, and may allow us to consider the possibility of targeting cancer spread by altering the lipid microenvironment.

Selective Inhibition of Liver Cancer Cells Using Venom Peptide

Increasingly cancer is being viewed as a channelopathy because the passage of ions via ion channels and transporters mediate the regulation of tumor cell survival, death, and motility. As a result, a potential targeted therapy for cancer is to use venom peptides that are selective for ion channels and transporters overexpressed in tumor cells. Here we describe the selectivity and mechanism of action of terebrid snail venom peptide, Tv1, for treating the most common type of liver cancer, hepatocellular carcinoma (HCC). Tv1 inhibited the proliferation of murine HCC cells and significantly reduced tumor size in Tv1-treated syngeneic tumor-bearing mice. Tv1's mechanism of action involves binding to overexpressed transient receptor potential (TRP) channels leading to calcium dependent apoptosis resulting from down-regulation of cyclooxygenase-2 (COX-2). Our findings demonstrate the importance of modulating ion channels and the unique potential of venom peptides as tumor specific ligands in the quest for targeted cancer therapies.

Calcium Signaling in Brain Cancers: Roles and Therapeutic Targeting

Calcium signaling, in addition to its numerous physiological roles, is also implicated in several pathological conditions including cancer. An increasing body of evidence suggest critical roles of calcium signaling in the promotion of different aspects of cancer, including cell proliferation, therapy resistance and metastatic-related processes. In many cases, this is associated with altered expression and/or activity of some calcium channels and pumps. Brain cancers have also been the subject of many of these studies. In addition to diverse roles of calcium signals in normal brain function, a number of proteins involved in calcium transport are implicated to have specific roles in some brain cancers including gliomas, medulloblastoma, neuroblastoma and meningioma. This review discusses research that has been conducted so far to understand diverse roles of Ca²⁺-transporting proteins in the progression of brain cancers, as well as any attempts to target these proteins towards a therapeutic approach for the control of brain cancers. Finally, some knowledge gaps in the field that may need to be further considered are also discussed.

Pharmacological inhibition of store-operated calcium entry in MDA-MB-468 basal A breast cancer cells: consequences on calcium signalling, cell migration and proliferation

Store-operated Ca²⁺ entry is a pathway that is remodelled in a variety of cancers, and altered expression of the components of store-operated Ca²⁺ entry is a feature of breast cancer cells of the basal molecular subtype. Studies of store-operated Ca²⁺ entry in breast cancer cells have used non-specific pharmacological inhibitors, complete depletion of intracellular Ca²⁺ stores and have mostly focused on MDA-MB-231 cells (a basal B breast cancer cell line). These studies compared the effects of the selective store-operated Ca²⁺ entry inhibitors Synta66 and YM58483 (also known as BTP2) on global cytosolic free Ca²⁺ ([Ca²⁺]_CYT) changes induced by physiological stimuli in a different breast cancer basal cell line model, MDA-MB-468. The effects of these agents on proliferation as well as serum and epidermal growth factor (EGF) induced migration were also assessed. Activation with the purinergic receptor activator adenosine triphosphate, produced a sustained increase in [Ca²⁺]_CYT that was entirely dependent on store-operated Ca²⁺ entry. The protease activated receptor 2 activator, trypsin, and EGF also produced Ca²⁺ influx that was sensitive to both Synta66 and YM58483. Serum-activated migration of MDA-MB-468 breast cancer cells was sensitive to both store-operated Ca²⁺ inhibitors. However, proliferation and EGF-activated migration was differentially affected by Synta66 and YM58483. These studies highlight the need to define the exact mechanisms of action of different store-operated calcium entry inhibitors and the impact of such differences in the control of tumour progression pathways.

Real-time scratch assay reveals mechanisms of early calcium signaling in breast cancer cells in response to wounding

Aggressive cellular phenotypes such as uncontrolled proliferation and increased migration capacity engender cellular transformation, malignancy and metastasis. While genetic mutations are undisputed drivers of cancer initiation and progression, it is increasingly accepted that external factors are also playing a major role. Two recently studied modulators of breast cancer are changes in the cellular mechanical microenvironment and alterations in calcium homeostasis. While many studies investigate these factors separately in breast cancer cells, very few do so in combination. This current work sets a foundation to explore mechano-calcium relationships driving malignant progression in breast cancer. Utilizing real-time imaging of an in vitro scratch assay, we were able to resolve mechanically-sensitive calcium signaling in human breast cancer cells. We observed rapid initiation of intracellular calcium elevations within seconds in cells at the immediate wound edge, followed by a time-dependent increase in calcium in cells at distances up to 500μm from the scratch wound. Calcium signaling to neighboring cells away from the wound edge returned to baseline within seconds. Calcium elevations at the wound edge however, persisted for up to 50 minutes. Rigorous quantification showed that extracellular calcium was necessary for persistent calcium elevation at the wound edge, but intercellular signal propagation was dependent on internal calcium stores. In addition, intercellular signaling required extracellular ATP and activation of P2Y₂ receptors. Through comparison of scratch-induced signaling from multiple cell lines, we report drastic reductions in response from aggressively tumorigenic and metastatic cells. The real-time scratch assay established here provides quantitative data on the molecular mechanisms that support rapid scratch-induced calcium signaling in breast cancer cells. These mechanisms now provide a clear framework for investigating which short-term calcium signals promote long-term changes in cancer cell biology.

Assessment of CXC ligand 12-mediated calcium signalling and its regulators in basal-like breast cancer cells

CXC ligand (L)12 is a chemokine implicated in the migration, invasion and metastasis of cancer cells via interaction with its receptors CXC chemokine receptor (CXCR)4 and CXCR7. In the present study, CXCL12-mediated Ca²⁺ signalling was compared with two basal-like breast cancer cell lines, MDA-MB-231 and MDA-MB-468, which demonstrate distinct metastatic potential. CXCL12 treatment induced Ca²⁺ responses in the more metastatic MDA-MB-231 cells but not in the less metastatic MDA-MB-468 cells. Assessment of mRNA levels of CXCL12 receptors and their potential modulators in both cell lines revealed that CXCR4 and CXCR7 levels were increased in MDA-MB-231 cells compared with MDA-MB-468 cells. Cluster of differentiation (CD)24, the negative regulator of CXCL12 responses, demonstrated increased expression in MDA-MB-468 cells compared with MDA-MB-231 cells, and the two cell lines expressed comparable levels of hypoxia-inducible factor (HIF)2α, a CXCR4 regulator. Induction of epithelial-mesenchymal transition (EMT) by epidermal growth factor exhibited opposite effects on CXCR4 mRNA levels compared with hypoxia-induced EMT. Neither EMT inducer exhibited an effect on CXCR7 expression, however hypoxia increased HIF2α expression levels in MDA-MB-468 cells. Analysis of the gene expression profiles of breast tumours revealed that the highest expression levels of CXCR4 and CXCR7 were in the Claudin-Low molecular subtype, which is markedly associated with EMT features.

Hypoxia-induced reactive oxygen species mediate N-cadherin and SERPINE1 expression, EGFR signalling and motility in MDA-MB-468 breast cancer cells

One of the hallmarks of the tumour microenvironment is hypoxia resulting from increased oxygen consumption by proliferative cancer cells and altered vasculature. Hypoxic tension initiates various cellular signals and can drive epithelial to mesenchymal transition (EMT), a process important in cancer progression. In this study, using the antioxidant N-acetylcysteine (NAC), we show that hypoxia-induced reactive oxygen species (ROS) in MDA-MB-468 breast cancer cells, selectively regulate hypoxia-induced increases in N-cadherin and SERPINE1, two proteins involved in cell adhesion. Treatment of cells with NAC also attenuated hypoxia-mediated activation of EGFR, but did not have any effect on hypoxia-mediated induction of HIF1α. Exogenous hydrogen peroxide phenocopied the effects of hypoxia on N-cadherin and SERPINE1 expression and EGFR activation, suggesting its possible involvement in these hypoxia-mediated events. Reflective of their effect on cell adhesion proteins and EGFR (associated with migratory phenotypes), NAC also reduced cell migration under hypoxic conditions, a crucial event in metastasis. Our findings suggest a selective role for redox signalling in the regulation of specific components of the responses to hypoxia and induction of EMT in breast cancer cells. This study provides new evidence supporting the potential of targeting ROS as a therapeutic strategy for the control of breast cancer metastasis.

TRPC1 is a differential regulator of hypoxia-mediated events and Akt signalling in PTEN-deficient breast cancer cells

Hypoxia is a feature of the tumour microenvironment that promotes invasiveness, resistance to chemotherapeutics and cell survival. Our studies identify the transient receptor potential canonical-1 (TRPC1) ion channel as a key component of responses to hypoxia in breast cancer cells. This regulation includes control of specific epithelial to mesenchymal transition (EMT) events and hypoxia-mediated activation of signalling pathways such as activation of the EGFR, STAT3 and the autophagy marker LC3B, through hypoxia-inducible factor-1α (HIF1α)-dependent and -independent mechanisms. TRPC1 regulated HIF1α levels in PTEN-deficient MDA-MB-468 and HCC1569 breast cancer cell lines. This regulation arises from effects on the constitutive translation of HIF1α under normoxic conditions via an Akt-dependent pathway. In further support of the role of TRPC1 in EMT, its expression is closely associated with EMT- and metastasis-related genes in breast tumours, and is enhanced in basal B breast cancer cell lines. TRPC1 expression is also significantly prognostic for basal breast cancers, particularly those classified as lymph node positive. The defined roles of TRPC1 identified here could be therapeutically exploited for the control of oncogenic pathways in breast cancer cells.