TRPM7 triggers Ca2+ sparks and invadosome formation in neuroblastoma cells

Transient Receptor Potential Melastatin 7 (TRPM7) Ion Channel Inhibitors: Preliminary SAR and Conformational Studies of Xenicane Diterpenoids from the Hawaiian Soft Coral Sarcothelia edmondsoni

Waixenicin A, a xenicane diterpene from the octocoral Sarcothelia edmondsoni, is a selective, potent inhibitor of the TRPM7 ion channel. To study the structure-activity relationship (SAR) of waixenicin A, we isolated and assayed related diterpenes from S. edmondsoni. In addition to known waixenicins A (1) and B (2), we purified six xenicane diterpenes, 7S,8S-epoxywaixenicins A (3) and B (4), 12-deacetylwaixenicin A (5), waixenicin E (6), waixenicin F (7), and 20-acetoxyxeniafaraunol B (8). We elucidated the structures of 3-8 by NMR and MS analyses. Compounds 1, 2, 3, 4, and 6 inhibited TRPM7 activity in a cell-based assay, while 5, 7, and 8 were inactive. A preliminary SAR emerged showing that alterations to the nine-membered ring of 1 did not reduce activity, while the 12-acetoxy group, in combination with the dihydropyran, appears to be necessary for TRPM7 inhibition. The bioactive compounds are proposed to be latent electrophiles by formation of a conjugated oxocarbenium ion intermediate. Whole-cell patch-clamp experiments demonstrated that waixenicin A inhibition is irreversible, consistent with a covalent inhibitor, and showed nanomolar potency for waixenicin B (2). Conformational analysis (DFT) of 1, 3, 7, and 8 revealed insights into the conformation of waixenicin A and congeners and provided information regarding the stabilization of the proposed pharmacophore.

The Role of TRPM7 in Oncogenesis

This review summarizes the current understanding of the role of transient receptor potential melastatin-subfamily member 7 (TRPM7) channels in the pathophysiology of neoplastic diseases. The TRPM family represents the largest and most diverse group in the TRP superfamily. Its subtypes are expressed in virtually all human organs playing a central role in (patho)physiological events. The TRPM7 protein (along with TRPM2 and TRPM6) is unique in that it has kinase activity in addition to the channel function. Numerous studies demonstrate the role of TRPM7 chanzyme in tumorigenesis and in other tumor hallmarks such as proliferation, migration, invasion and metastasis. Here we provide an up-to-date overview about the possible role of TRMP7 in a broad range of malignancies such as tumors of the nervous system, head and neck cancers, malignant neoplasms of the upper gastrointestinal tract, colorectal carcinoma, lung cancer, neoplasms of the urinary system, breast cancer, malignant tumors of the female reproductive organs, prostate cancer and other neoplastic pathologies. Experimental data show that the increased expression and/or function of TRPM7 are observed in most malignant tumor types. Thus, TRPM7 chanzyme may be a promising target in tumor therapy.

Mechanosensitive Ion Channels: Their Physiological Importance and Potential Key Role in Cancer

Mechanosensitive ion channels comprise a broad group of proteins that sense mechanical extracellular and intracellular changes, translating them into cation influx to adapt and respond to these physical cues. All cells in the organism are mechanosensitive, and these physical cues have proven to have an important role in regulating proliferation, cell fate and differentiation, migration and cellular stress, among other processes. Indeed, the mechanical properties of the extracellular matrix in cancer change drastically due to high cell proliferation and modification of extracellular protein secretion, suggesting an important contribution to tumor cell regulation. In this review, we describe the physiological significance of mechanosensitive ion channels, emphasizing their role in cancer and immunity, and providing compelling proof of the importance of continuing to explore their potential as new therapeutic targets in cancer research.

STIM1 signals through NFAT1 independently of Orai1 and SOCE to regulate breast cancer cell migration

Store-operated calcium entry (SOCE) contributes to several physiological and pathological conditions including transcription, secretion, immunodeficiencies, and cancer. SOCE has been shown to be important for breast cancer cell migration where knockdown of SOCE components (STIM1 or Orai1) decreases cancer metastasis. Here we show unexpectedly that complete knockout of STIM1 (STIM1-KO) using gene editing in metastatic MDA-MB-231 breast cancer cells results in faster migration and enhanced invasion capacity. In contrast, Orai1-KO cells, which have similar levels of SOCE inhibition as STIM1-KO, migrate slower than the parental cell line. This shows that the enhanced migration phenotype of STIM1-KO cells is not due to the loss of Ca2+ entry through SOCE, rather it involves transcriptional remodeling as elucidated by RNA-seq analyses. Interestingly, NFAT1 is significantly downregulated in STIM1-KO cells and overexpression of NFAT1 reversed the enhanced migration of STIM1-KO cells. STIM1 knockout in other breast cancer cells, independent of their metastatic potential, also enhanced cell migration while reducing NFAT1 expression. These data argue that in breast cancer cells STIM1 modulates NFAT1 expression and cell migration independently of its role in SOCE.

Drugs acting at TRPM7 channels inhibit seizure-like activity

Transient receptor potential cation subfamily M7 (TRPM7) channels are ion channels permeable to divalent cations. They are abundantly expressed with particularly high expression in the brain. Previous studies have highlighted the importance of TRPM7 channels in brain diseases such as stroke and traumatic brain injury, yet evidence for a role in seizures and epilepsy is lacking. Here, we show that carvacrol, a food additive that inhibits TRPM7 channels, and waixenicin A, a novel selective and potent TRPM7 inhibitor, completely suppressed seizure-like activity in rodent hippocampal-entorhinal brain slices exposed to pentylenetetrazole or low magnesium. These findings support inhibition of TRPM7 channels as a novel target for antiseizure medications.

Structural insights into regulation of CNNM-TRPM7 divalent cation uptake by the small GTPase ARL15

Cystathionine-β-synthase (CBS)-pair domain divalent metal cation transport mediators (CNNMs) are an evolutionarily conserved family of magnesium transporters. They promote efflux of Mg2+ ions on their own and influx of divalent cations when expressed with the transient receptor potential ion channel subfamily M member 7 (TRPM7). Recently, ADP-ribosylation factor-like GTPase 15 (ARL15) has been identified as CNNM-binding partner and an inhibitor of divalent cation influx by TRPM7. Here, we characterize ARL15 as a GTP and CNNM-binding protein and demonstrate that ARL15 also inhibits CNNM2 Mg2+ efflux. The crystal structure of a complex between ARL15 and CNNM2 CBS-pair domain reveals the molecular basis for binding and allowed the identification of mutations that specifically block binding. A binding deficient ARL15 mutant, R95A, failed to inhibit CNNM and TRPM7 transport of Mg2+ and Zn2+ ions. Structural analysis and binding experiments with phosphatase of regenerating liver 2 (PRL2 or PTP4A2) showed that ARL15 and PRLs compete for binding CNNM to coordinate regulation of ion transport by CNNM and TRPM7.

A pan-cancer-bioinformatic-based literature review of TRPM7 in cancers

TRPM7, a divalent cation-selective channel with kinase domains, has been widely reported to potentially affect cancers. In this study, we conducted multiple bioinformatic analyses based on open databases and reviewed articles that provided evidence for the effects of TRPM7 on cancers. The purposes of this paper are 1) to provide a pan-cancer overview of TRPM7 in cancers; 2) to summarize evidence of TRPM7 effects on cancers; 3) to identify potential future studies of TRPM7 in cancer. Bioinformatics analysis revealed that no cancer-related TRPM7 mutation was found. TRPM7 is aberrantly expressed in most cancer types but the cancer-noncancer expression pattern varies across cancer types. TRPM7 was not associated with survival, TMB, or cancer stemness in most cancer types. TRPM7 affected drug sensitivity and tumor immunity in some cancer types. The in vitro evidence, preclinical in vivo evidence, and clinical evidence for TRPM7 effects on cancers as well as TRPM7 kinase substrate and TRPM7-targeting drugs associated with cancers were summarized to facilitate comparison. We matched the bioinformatics evidence to literature evidence, thereby unveiling potential avenues for future investigation of TRPM7 in cancers. We believe that this paper will help orient research toward important and relevant aspects of the role of TRPM7 in cancers.

Evidence of Metallic and Polyether Ionophores as Potent Therapeutic Drug Candidate in Cancer Management

Cancer remains one of the most crucial human malignancies with a higher mortality rate globally, and is predicted to escalate soon. Dysregulated ion homeostasis in cancerous cells prompted the researchers to investigate further ion homeostasis impeding agents as potent anticancerous agents. Reutilization of FDA-approved non-cancerous drugs has emerged as a practical approach to developing potent, cost-effective drugs for cancer treatment. Across the globe, most nations are incapable of fulfilling the medical demands of cancer patients due to costlier cancerous drugs. Therefore, we have inclined our review towards emphasizing recent advancements in cancer therapies involving ionophores utilization in exploring potent anticancer drugs. Numerous research reports have established the significant anticancerous potential of ionophores in several pre-clinical reports via modulating aberrant cell signaling pathways and enhancing antitumor immunity in immune cells. This review has mainly summarized the most significant ion homeostasis impeding agents, including copper, zinc, calcium, and polyether, that presented remarkable potential in cancer therapeutics via enhanced antitumor immunity and apoptosis induction. Altogether, this study could provide a robust future perspective for developing cost-effective anticancerous drugs rapidly and cost-effectively, thereby combating the limitations of currently available drugs used in cancer treatment.

CNNM proteins selectively bind to the TRPM7 channel to stimulate divalent cation entry into cells

Magnesium is essential for cellular life, but how it is homeostatically controlled still remains poorly understood. Here, we report that members of CNNM family, which have been controversially implicated in both cellular Mg²⁺ influx and efflux, selectively bind to the TRPM7 channel to stimulate divalent cation entry into cells. Coexpression of CNNMs with the channel markedly increased uptake of divalent cations, which is prevented by an inactivating mutation to the channel’s pore. Knockout (KO) of TRPM7 in cells or application of the TRPM7 channel inhibitor NS8593 also interfered with CNNM-stimulated divalent cation uptake. Conversely, KO of CNNM3 and CNNM4 in HEK-293 cells significantly reduced TRPM7-mediated divalent cation entry, without affecting TRPM7 protein expression or its cell surface levels. Furthermore, we found that cellular overexpression of phosphatases of regenerating liver (PRLs), known CNNMs binding partners, stimulated TRPM7-dependent divalent cation entry and that CNNMs were required for this activity. Whole-cell electrophysiological recordings demonstrated that deletion of CNNM3 and CNNM4 from HEK-293 cells interfered with heterologously expressed and native TRPM7 channel function. We conclude that CNNMs employ the TRPM7 channel to mediate divalent cation influx and that CNNMs also possess separate TRPM7-independent Mg²⁺ efflux activities that contribute to CNNMs’ control of cellular Mg²⁺ homeostasis.

Magnesium is essential for cellular life, but how is it homeostatically controlled? This study shows that proteins of the CNNM family bind to the TRPM7 channel to stimulate divalent cation entry into cells, independent of their function in regulating magnesium ion efflux.

Modulators of TRPM7 and its potential as a drug target for brain tumours

TRPM7 is a non-selective divalent cation channel with an alpha-kinase domain. Corresponding with its broad expression, TRPM7 has a role in a wide range of cell functions, including proliferation, migration, and survival. Growing evidence shows that TRPM7 is also aberrantly expressed in various cancers, including brain cancers. Because ion channels have widespread tissue distribution and result in extensive physiological consequences when dysfunctional, these proteins can be compelling drug targets. In fact, ion channels comprise the third-largest drug target type, following enzymes and receptors. Literature has shown that suppression of TRPM7 results in inhibition of migration, invasion, and proliferation in several human brain tumours. Therefore, TRPM7 presents a potential target for therapeutic brain tumour interventions. This article reviews current literature on TRPM7 as a potential drug target in the context of brain tumours and provides an overview of various selective and non-selective modulators of the channel relevant to pharmacology, oncology, and ion channel function.

TRPM7 Ion Channel: Oncogenic Roles and Therapeutic Potential in Breast Cancer

Simple Summary

Breast cancer is the most frequently diagnosed malignant tumor and the second leading cause of cancer death in women worldwide. The risk of developing breast cancer is 12.8%, i.e., 1 in 8 people, and a woman’s risk of dying is approximately 1 in 39. Calcium signals play an important role in various cancers and transport calcium ions may have altered expression in breast cancer, such as the TRPM7 calcium permeant ion channel, where overexpression may be associated with a poor prognosis. This review focuses on the TRPM7 channel, and the oncogenic roles studied so far in breast cancer. The TRPM7 ion channel is suggested as a potential and prospective target in the diagnosis and treatment of breast cancer.

Abstract

The transient receptor potential melastatin-subfamily member 7 (TRPM7) is a divalent cations permeant channel but also has intrinsic serine/threonine kinase activity. It is ubiquitously expressed in normal tissues and studies have indicated that it participates in important physiological and pharmacological processes through its channel-kinase activity, such as calcium/magnesium homeostasis, phosphorylation of proteins involved in embryogenesis or the cellular process. Accumulating evidence has shown that TRPM7 is overexpressed in human pathologies including breast cancer. Breast cancer is the second leading cause of cancer death in women with an incidence rate increase of around 0.5% per year since 2004. The overexpression of TRPM7 may be associated with a poor prognosis in breast cancer patients, so more efforts are needed to research a new therapeutic target. TRPM7 regulates the levels of Ca²⁺, which can alter the signaling pathways involved in survival, cell cycle progression, proliferation, growth, migration, invasion, epithelial-mesenchymal transition and thus determines cell behavior, promoting tumor development. This work provides a complete overview of the TRPM7 ion channel and its main involvements in breast cancer. Special consideration is given to the modulation of the channel as a potential target in breast cancer treatment by inhibition of proliferation, migration and invasion. Taken together, these data suggest the potential exploitation of TRPM7 channel-kinase as a therapeutic target and a diagnostic biomarker.

Ion channels as key partners of cytoskeleton in cancer disease

Several processes occur during tumor development including changes in cell morphology, a reorganization of the expression and distribution of the cytoskeleton proteins as well as ion channels. If cytoskeleton proteins and ion channels have been widely investigated in understanding cancer mechanisms, the interaction between these two elements and the identification of the associated signaling pathways are only beginning to emerge. In this review, we summarize the work published over the past 15 years relating to the roles played by ion channels in these mechanisms of reorganization of the cellular morphology, essential to metastatic dissemination, both through the physical interactions with elements of the cytoskeleton and by intracellular signaling pathways involved.

TRP Channels Interactome as a Novel Therapeutic Target in Breast Cancer

Breast cancer is one of the most frequent cancer types worldwide and the first cause of cancer-related deaths in women. Although significant therapeutic advances have been achieved with drugs such as tamoxifen and trastuzumab, breast cancer still caused 627,000 deaths in 2018. Since cancer is a multifactorial disease, it has become necessary to develop new molecular therapies that can target several relevant cellular processes at once. Ion channels are versatile regulators of several physiological- and pathophysiological-related mechanisms, including cancer-relevant processes such as tumor progression, apoptosis inhibition, proliferation, migration, invasion, and chemoresistance. Ion channels are the main regulators of cellular functions, conducting ions selectively through a pore-forming structure located in the plasma membrane, protein–protein interactions one of their main regulatory mechanisms. Among the different ion channel families, the Transient Receptor Potential (TRP) family stands out in the context of breast cancer since several members have been proposed as prognostic markers in this pathology. However, only a few approaches exist to block their specific activity during tumoral progress. In this article, we describe several TRP channels that have been involved in breast cancer progress with a particular focus on their binding partners that have also been described as drivers of breast cancer progression. Here, we propose disrupting these interactions as attractive and potential new therapeutic targets for treating this neoplastic disease.

Store Operated Calcium Entry in Cell Migration and Cancer Metastasis

Ca²⁺ signaling is ubiquitous in eukaryotic cells and modulates many cellular events including cell migration. Directional cell migration requires the polarization of both signaling and structural elements. This polarization is reflected in various Ca²⁺ signaling pathways that impinge on cell movement. In particular, store-operated Ca²⁺ entry (SOCE) plays important roles in regulating cell movement at both the front and rear of migrating cells. SOCE represents a predominant Ca²⁺ influx pathway in non-excitable cells, which are the primary migrating cells in multicellular organisms. In this review, we summarize the role of Ca²⁺ signaling in cell migration with a focus on SOCE and its diverse functions in migrating cells and cancer metastasis. SOCE has been implicated in regulating focal adhesion turnover in a polarized fashion and the mechanisms involved are beginning to be elucidated. However, SOCE is also involved is other aspects of cell migration with a less well-defined mechanistic understanding. Therefore, much remains to be learned regarding the role and regulation of SOCE in migrating cells.

Waixenicin A, a marine-derived TRPM7 inhibitor: a promising CNS drug lead

Ion channels are the third largest class of targets for therapeutic drugs. The pharmacology of ion channels is an important research area for identifying new treatment options for human diseases. The past decade or so has seen increasing interest in an ion channel protein belonging to the transient receptor potential (TRP) family, namely the melastatin subfamily member 7 (TRPM7), as an emerging drug target. TRPM7 is a bifunctional protein with a magnesium and calcium-conducting divalent ion channel fused with an active kinase domain. TRPM7 is ubiquitously expressed in human tissues, including the brain, and regulates various cell biology processes such as magnesium and calcium homeostasis, cell growth and proliferation, and embryonic development. TRPM7 provides a link between cellular metabolic status and intracellular calcium homeostasis in neurons due to TRPM7's unique sensitivity to fluctuating intracellular Mg·ATP levels. Thus, the protein plays a key role in ischemic and hypoxic neuronal cell death and brain injury, and is one of the key nonglutamate mechanisms in cerebral ischemia and stroke. Currently, the most potent and specific TRPM7 inhibitor is waixenicin A, a xenicane diterpenoid from the Hawaiian soft coral Sarcothelia edmondsoni. Using waixenicin A as a pharmacological tool, we demonstrated that TRPM7 is involved in promoting neurite outgrowth in vitro. Most recently, we found that waixenicin A reduced hypoxic-ischemic brain injury and preserved long-term behavioral outcomes in mouse neonates. We here suggest that TRPM7 is an emerging drug target for CNS diseases and disorders, and waixenicin A is a viable drug lead for these disorders.

TRPV6 calcium channel directs homeostasis of the mammary epithelial sheets and controls epithelial mesenchymal transition

Epithelial integrity is lost upon cancer progression as cancer cells detach from the primary tumor site and start to invade to the surrounding tissues. Invasive cancers of epithelial origin often express altered levels of TRP-family cation channels. Upregulation of TRPV6 Ca2+-channel has been associated with a number of human malignancies and its high expression in breast cancer has been linked to both proliferation and invasive disease. The mechanisms behind the potential of TRPV6 to induce invasive progression have, however, not been well elucidated. Here we show that TRPV6 is connected to both E-cadherin-based adherens junctions and intracellular cytoskeletal structures. Loss of TRPV6 from normal mammary epithelial cells led to disruption of epithelial integrity and abnormal 3D-mammo sphere morphology. Furthermore, expression level of TRPV6 was tightly linked to the levels of common EMT markers, suggesting that TRPV6 may have a role in the mesenchymal invasion of breast cancer cells. Thus, either too low or too high TRPV6 levels compromise homeostasis of the mammary epithelial sheets and may promote the progression of pathophysiological conditions.

TRPM6 and TRPM7: Novel players in cell intercalation during vertebrate embryonic development

A common theme in organogenesis is how the final structure of organs emerge from epithelial tube structures, with the formation of the neural tube being one of the best examples. Two types of cell movements co-occur during neural tube closure involving the migration of cells toward the midline of the embryo (mediolateral intercalation or convergent extension) as well as the deep movement of cells from inside the embryo to the outside of the lateral side of the neural plate (radial intercalation). Failure of either type of cell movement will prevent neural tube closure, which can produce a range of neural tube defects (NTDs), a common congenital disease in humans. Numerous studies have identified signaling pathways that regulate mediolateral intercalation during neural tube closure. Less understood are the pathways that govern radial intercalation. Using the Xenopus laevis system, our group reported the identification of transient receptor potential (TRP) channels, TRPM6 and TRPM7, and the Mg2+ ion they conduct, as novel and key factors regulating both mediolateral and radial intercalation during neural tube closure. Here we broadly discuss tubulogenesis and cell intercalation from the perspective of neural tube closure and the respective roles of TRPM7 and TRPM6 in this critical embryonic process.

TRPM7/RPSA Complex Regulates Pancreatic Cancer Cell Migration

Pancreatic ductal adenocarcinoma (PDAC) is a malignancy with a very poor prognosis due to highly metastatic profile. Cell migration is an essential step of the metastatic cascade allowing cancer cells to spread toward target tissues. Recent studies strongly suggest that bioactive elastin peptides, also named elastokines or elastin-derived peptides (EDPs), are released in the extracellular microenvironment during tumoral remodeling of the stroma. EDPs stimulate cancer cell migration by interacting with their membrane receptor, ribosomal protein SA (RPSA). Others membrane proteins like ion channels are also involved in cancer cell migration. It has been recently shown that the transient receptor potential melastatin-related 7 (TRPM7) channel regulates PDAC cell migration and invasion. The objective of this work was to study the effect of EDPs on TRPM7 channel in human pancreatic cancer cells. We showed that EDPs promote MIA PaCa-2 cell migration using Boyden chamber assay. Cells transfected with a siRNA targeting TRPM7 were not able to migrate in response to EDPs indicating that TRPM7 regulated cell migration induced by these peptides. Moreover, EDPs were able to stimulate TRPM7 currents recorded by Patch-Clamp. Finally, we showed that TRPM7 channels and RPSA receptors are colocalized at the plasma membrane of human pancreatic cancer cells. Taken together, our data suggest that TRPM7/RPSA complex regulated human pancreatic cancer cell migration. This complex may be a promising therapeutic target in PDAC.

Insights and perspectives on calcium channel functions in the cockpit of cancerous space invaders

Development of metastasis causes the most serious clinical consequences of cancer and is responsible for over 90 % of cancer-related deaths. Hence, a better understanding of the mechanisms that drive metastasis formation appears critical for drug development designed to prevent the spread of cancer and related mortality. Metastasis dissemination is a multistep process supported by the increased motility and invasiveness capacities of tumor cells. To succeed in overcoming the mechanical constraints imposed by the basement membrane and surrounding tissues, cancer cells reorganize their focal adhesions or extend acto-adhesive cellular protrusions, called invadosomes, that can both contact the extracellular matrix and tune its degradation through metalloprotease activity. Over the last decade, accumulating evidence has demonstrated that altered Ca²⁺ channel activities and/or expression promote tumor cell-specific phenotypic changes, such as exacerbated migration and invasion capacities, leading to metastasis formation. While several studies have addressed the molecular basis of Ca²⁺ channel-dependent cancer cell migration, we are still far from having a comprehensive vision of the Ca²⁺ channel-regulated mechanisms of migration/invasion. This is especially true regarding the specific context of invadosome-driven invasion. This review aims to provide an overview of the current evidence supporting a central role for Ca²⁺ channel-dependent signaling in the regulation of these dynamic degradative structures. It will present available data on the few Ca²⁺ channels that have been studied in that specific context and discuss some potential interesting actors that have not been fully explored yet.

Cadmium exposure enhances cell migration and invasion through modulated TRPM7 channel expression

Cadmium is a xenobiotic involved in neoplastic transformation. Cadmium enters the cells through divalent cation transporters including the Transient Receptor Potential Melastatin-related 7 (TRPM7) which is known to be involved in cancer cell fate. This work aimed to study the role of TRPM7 in neoplastic transformation induced by cadmium exposure in non-cancer epithelial cells. Non-cancer epithelial cells were chronically exposed to low-dose of cadmium. TRPM7 expression and function were studied by Western-Blot, Patch-Clamp and calcium and magnesium imaging. Finally, cell migration and invasion were studied by Boyden chamber assays. Chronic cadmium exposure induced TRPM7 overexpression and increased the membrane currents (P < 0.001). Cells exposed to cadmium had higher intracellular calcium and magnesium levels (P < 0.05). TRPM7 silencing restored calcium levels but strongly decreased intracellular magnesium concentration (P < 0.001). Moreover, cadmium exposure enhanced both cell migration and invasion, but TRPM7 silencing strongly decreased these features (P < 0.001). Furthermore, mammary epithelial cells exposed to cadmium became rounded and had less cell-to-cell junctions. Cadmium exposure decreased epithelial markers while the mesenchymal ones were increased. Importantly, TRPM7 silencing was able to reverse these phenotypic modifications (P < 0.05). To summarize, our data show that chronic cadmium exposure enhanced TRPM7 expression and activity in non-cancer epithelial cells. TRPM7 overexpression induced intracellular magnesium increase and stimulated cell migration and invasion. These neoplastic properties could be linked to a TRPM7-dependent epithelial-to-mesenchymal transition reprogramming in cell exposed to cadmium. These findings provide new insights into the regulation of cell fates by cadmium exposure.

Regulation of Membrane Calcium Transport Proteins by the Surrounding Lipid Environment

Calcium ions (Ca2+) are major messengers in cell signaling, impacting nearly every aspect of cellular life. Those signals are generated within a wide spatial and temporal range through a large variety of Ca2+ channels, pumps, and exchangers. More and more evidences suggest that Ca2+ exchanges are regulated by their surrounding lipid environment. In this review, we point out the technical challenges that are currently being overcome and those that still need to be defeated to analyze the Ca2+ transport protein-lipid interactions. We then provide evidences for the modulation of Ca2+ transport proteins by lipids, including cholesterol, acidic phospholipids, sphingolipids, and their metabolites. We also integrate documented mechanisms involved in the regulation of Ca2+ transport proteins by the lipid environment. Those include: (i) Direct interaction inside the protein with non-annular lipids; (ii) close interaction with the first shell of annular lipids; (iii) regulation of membrane biophysical properties (e.g., membrane lipid packing, thickness, and curvature) directly around the protein through annular lipids; and (iv) gathering and downstream signaling of several proteins inside lipid domains. We finally discuss recent reports supporting the related alteration of Ca2+ and lipids in different pathophysiological events and the possibility to target lipids in Ca2+-related diseases.

Targeting Ca2+ signalling through phytomolecules to combat cancer

Cancer is amongst the life-threatening public health issue worldwide, hence responsible for millions of death every year. It is affecting human health regardless of their gender, age, eating habits, and ecological location. Many drugs and therapies are available for its cure still the need for effective targeted drugs and therapies are of paramount importance. In the recent past, Ca²⁺ signalling (including channels/transporters/pumps) are being studied as a plausible target for combating the cancer menace. Many evidence has shown that the intracellular Ca²⁺ homeostasis is altered in cancer cells and the remodelling is linked with tumor instigation, angiogenesis, progression, and metastasis. Focusing on these altered Ca²⁺ signalling tool kit for cancer treatment is a cross-cutting and emerging area of research. In addition, there are numerous phytomolecules which can be exploited as a potential Ca²⁺ (channels/transporters/ pumps) modulators in the context of targeting Ca²⁺ signalling in the cancer cell. In the present review, a list of plant-based potential Ca²⁺ (channel/transporters/pumps) modulators has been reported which could have application in the framework of repurposing the potential drugs to target Ca²⁺ signalling pathways in cancer cells. This review also aims to gain attention in and support for prospective research in this field.

Proteins Regulating Microvesicle Biogenesis and Multidrug Resistance in Cancer

Microvesicles (MV) are emerging as important mediators of intercellular communication. While MVs are important signaling vectors for many physiological processes, they are also implicated in cancer pathology and progression. Cellular activation is perhaps the most widely reported initiator of MV biogenesis, however, the precise mechanism remains undefined. Uncovering the proteins involved in regulating MV biogenesis is of interest given their role in the dissemination of deleterious cancer traits. MVs shed from drug-resistant cancer cells transfer multidrug resistance (MDR) proteins to drug-sensitive cells and confer the MDR phenotype in a matter of hours. MDR is attributed to the overexpression of ABC transporters, primarily P-glycoprotein and MRP1. Their expression and functionality is dependent on a number of proteins. In particular, FERM domain proteins have been implicated in supporting the functionality of efflux transporters in drug-resistant cells and in recipient cells during intercellular transfer by vesicles. Herein, the most recent research on the proteins involved in MV biogenesis and in the dissemination of MV-mediated MDR are discussed. Attention is drawn to unanswered questions in the literature that may prove to be of benefit in ongoing efforts to improve clinical response to chemotherapy and circumventing MDR.

TRPM7 residue S1269 mediates cAMP dependence of Ca2+ influx

The nonspecific divalent cation channel TRPM7 (transient receptor potential-melastatin-like 7) is involved in many Ca²⁺ and Mg²⁺-dependent cellular processes, including survival, proliferation and migration. TRPM7 expression predicts metastasis and recurrence in breast cancer and several other cancers. In cultured cells, it can induce an invasive phenotype by promoting Ca²⁺-mediated epithelial-mesenchymal transition. We previously showed that in neuroblastoma cells that overexpress TRPM7 moderately, stimulation with Ca²⁺-mobilizing agonists leads to a characteristic sustained influx of Ca²⁺. Here we report that sustained influx through TRPM7 is abruptly abrogated by elevating intracellular levels of cyclic adenosine monophosphate (cAMP). Using pharmacological inhibitors and overexpression studies we show that this blockage is mediated by the cAMP effector Protein Kinase A (PKA). Mutational analysis demonstrates that the Serine residue S1269, which is present proximal to the coiled-coil domain within the protein c-terminus, is responsible for sensitivity to cAMP.

Reactive astrocytes in multiple sclerosis impair neuronal outgrowth through TRPM7-mediated chondroitin sulfate proteoglycan production

Multiple sclerosis (MS) is a chronic inflammatory disorder of the central nervous system (CNS), characterized by inflammation‐mediated demyelination, axonal injury and neurodegeneration. The mechanisms underlying impaired neuronal function are not fully understood, but evidence is accumulating that the presence of the gliotic scar produced by reactive astrocytes play a critical role in these detrimental processes. Here, we identified astrocytic Transient Receptor Potential cation channel, subfamily M, member 7 (TRPM7), a Ca²⁺‐permeable nonselective cation channel, as a novel player in the formation of a gliotic scar. TRPM7 was found to be highly expressed in reactive astrocytes within well‐characterized MS lesions and upregulated in primary astrocytes under chronic inflammatory conditions. TRPM7 overexpressing astrocytes impaired neuronal outgrowth in vitro by increasing the production of chondroitin sulfate proteoglycans, a key component of the gliotic scar. These findings indicate that astrocytic TRPM7 is a critical regulator of the formation of a gliotic scar and provide a novel mechanism by which reactive astrocytes affect neuronal outgrowth.

Multiple S100 protein isoforms and C-terminal phosphorylation contribute to the paralog-selective regulation of nonmuscle myosin 2 filaments

Nonmuscle myosin 2 (NM2) has three paralogs in mammals, NM2A, NM2B, and NM2C, which have both unique and overlapping functions in cell migration, formation of cell-cell adhesions, and cell polarity. Their assembly into homo- and heterotypic bipolar filaments in living cells is primarily regulated by phosphorylation of the N-terminally bound regulatory light chain. Here, we present evidence that the equilibrium between these filaments and single NM2A and NM2B molecules can be controlled via S100 calcium-binding protein interactions and phosphorylation at the C-terminal end of the heavy chains. Furthermore, we show that in addition to S100A4, other members of the S100 family can also mediate disassembly of homotypic NM2A filaments. Importantly, these proteins can selectively remove NM2A molecules from heterotypic filaments. We also found that tail phosphorylation (at Ser-1956 and Ser-1975) of NM2B by casein kinase 2, as well as phosphomimetic substitutions at sites targeted by protein kinase C (PKC) and transient receptor potential cation channel subfamily M member 7 (TRPM7), down-regulates filament assembly in an additive fashion. Tail phosphorylation of NM2A had a comparatively minor effect on filament stability. S100 binding and tail phosphorylation therefore preferentially disassemble NM2A and NM2B, respectively. These two distinct mechanisms are likely to contribute to the temporal and spatial sorting of the two NM2 paralogs within heterotypic filaments. The existence of multiple NM2A-depolymerizing S100 paralogs offers the potential for diverse regulatory inputs modulating NM2A filament disassembly in cells and provides functional redundancy under both physiological and pathological conditions.

The vesicular transfer of CLIC1 from glioblastoma to microvascular endothelial cells requires TRPM7

Chloride intracellular channel 1 (CLIC1) is highly expressed and secreted by human glioblastoma cells and cell lines such as U87, initiating cell migration and tumor growth. Here, we examined whether CLIC1 could be transferred to human primary microvascular endothelial cells (HMEC). We previously reported that the oncogenic microRNA, miR-5096, increased the release of extracellular vesicles (EVs) by which it increased its own transfer from U87 to surrounding cells. Thus, we also examined its effect on the CLIC1 transfer. In homotypic cultures, miR-5096 did not increase the expression of CLIC1 in U87 nor in HMEC. However, the endothelial CLIC1 level increased after exposure to EVs released by U87, and even more by miR-5096-loaded U87. The EVs-transferred CLIC1 was active in HMEC, promoting endothelial sprouting in matrigel. Cell exposure to EVs induced cytosolic Ca²⁺ spikes which were dependent on the transient receptor potential melastatin member 7 (TRPM7). TRPM7 silencing prevented Ca²⁺ spikes and the subsequent CLIC1 delivery into HMEC. Our data suggest that the vesicular transfer of CLIC1 between cells requires TRMP7 expression in recipient endothelial cells. How the vesicular transfer of CLIC1 is modulated in cancer therapy is a future challenge.

TRPM7 channels play a role in high glucose-induced endoplasmic reticulum stress and neuronal cell apoptosis

High-glucose (HG) levels and hyperglycemia associated with diabetes are known to cause neuronal damage. The detailed molecular mechanisms, however, remain to be elucidated. Here, we investigated the role of transient receptor potential melastatin 7 (TRPM7) channels in HG-mediated endoplasmic reticulum stress (ERS) and injury of NS20Y neuronal cells. The cells were incubated in the absence or presence of HG for 48 h. We found that mRNA and protein levels of TRPM7 and of ERS-associated proteins, such as C/EBP homologous protein (CHOP), 78-kDa glucose-regulated protein (GRP78), and inducible nitric-oxide synthase (iNOS), increased in HG-treated cells, along with significantly increased TRPM7-associated currents in these cells. Similar results were obtained in cerebral cortical tissue from an insulin-deficiency model of diabetic mice. Moreover, HG treatment of cells activated ERS-associated proapoptotic caspase activity and induced cellular injury. Interestingly, a NOS inhibitor, l-NAME, suppressed the HG-induced increase of TRPM7 expression and cellular injury. siRNA-mediated TRPM7 knockdown or chemical inhibition of TRPM7 activity also suppressed HG-induced ERS and decreased cleaved caspase-12/caspase-3 levels and cell injury. Of note, TRPM7 overexpression increased ERS and cell injury independently of its kinase activity. Taken together, our findings suggest that TRPM7 channel activities play a key role in HG-associated ERS and cytotoxicity through an apoptosis-inducing signaling cascade involving HG, iNOS, TRPM7, ERS proteins, and caspases.

Spatiotemporal Characteristics of Intercellular Calcium Wave Communication in Micropatterned Assemblies of Single Cells

Micropatterned substrates offer a unique possibility to define and control spatial organization of biological cells at the microscale, which greatly facilitates investigations of the cell-to-cell communication in vitro. Here, we developed a simple micropatterning strategy to resolve various spatiotemporal characteristics of intercellular calcium wave (ICW) communication among isolated BV-2 microglial cells. By using a single-ring assembly, we found that the direction of the initial transmitter secretion was strongly correlated with the site of the cell at which the mechanical stimulus triggering the ICWs was imposed. By using multiring assemblies, we observed that the response ratio of the same outmost cells 160 μm away from the center increased from 0% in the single-ring assembly to 9.6% in the four-ring assembly. This revealed that cells located in the interring acted as regenerative amplifiers for the ICWs generated by the central cell. By using a special oval-type micropattern, we found that calcium mobilization in lamellipodia of a fusiform BV-2 microglia cell occurred 2.9 times faster than that in the middle part of the cell, demonstrating a higher region-specific sensitivity of lamellipodia to the transmitter. Taken together, our micropatterning strategy opened up new experimental prospects to study ICWs and revealed novel spatiotemporal characteristics of ICW communication including stimulation site-dependent secretion, regenerative propagation, and region-specific cell sensitivity.

S100A4 regulates macrophage invasion by distinct myosin-dependent and myosin-independent mechanisms

S100A4, a member of the S100 family of Ca²⁺-binding proteins, is a key regulator of cell migration and invasion. Our previous studies showed that bone marrow–derived macrophages from S100A4^−/− mice exhibit defects in directional motility and chemotaxis in vitro and reduced recruitment to sites of inflammation in vivo. We now show that the loss of S100A4 produces two mechanistically distinct phenotypes with regard to macrophage invasion: a defect in matrix degradation, due to a disruption of podosome rosettes caused by myosin-IIA overassembly, and a myosin-independent increase in microtubule acetylation, which increases podosome rosette stability and is sufficient to inhibit macrophage invasion. Our studies point to S100A4 as a critical regulator of matrix degradation, whose actions converge on the dynamics and degradative functions of podosome rosettes.

TRPM6 and TRPM7 differentially contribute to the relief of heteromeric TRPM6/7 channels from inhibition by cytosolic Mg2+ and Mg·ATP

TRPM6 and its homologue TRPM7 are α-kinase-coupled divalent cation-selective channels activated upon reduction of cytosolic levels of Mg²⁺ and Mg·ATP. TRPM6 is vital for organismal Mg²⁺ balance. However, mechanistically the cellular role and functional nonredundancy of TRPM6 remain incompletely understood. Comparative analysis of native currents in primary cells from TRPM6- versus TRPM7-deficient mice supported the concept that native TRPM6 primarily functions as a constituent of heteromeric TRPM6/7 channels. However, heterologous expression of the human TRPM6 protein engendered controversial results with respect to channel characteristics including its regulation by Mg²⁺ and Mg·ATP. To resolve this issue, we cloned the mouse TRPM6 (mTRPM6) cDNA and compared its functional characteristics to mouse TRPM7 (mTRPM7) after heterologous expression. Notably, we observed that mTRPM6 and mTRPM7 differentially regulate properties of heteromeric mTRPM6/7 channels: In the presence of mTRPM7, the extreme sensitivity of functionally expressed homomeric mTRPM6 to Mg²⁺ is tuned to higher concentrations, whereas mTRPM6 relieves mTRPM7 from the tight inhibition by Mg·ATP. Consequently, the association of mTRPM6 with mTRPM7 allows for high constitutive activity of mTRPM6/7 in the presence of physiological levels of Mg²⁺ and Mg·ATP, thus laying the mechanistic foundation for constant vectorial Mg²⁺ transport specifically into epithelial cells.

TRP channel pores and local calcium signals

Calcium signals control a plethora of essential cellular functions ranging from secretion and contraction to gene expression and sensory signaling cascades. An essential part of intracellular calcium signals originates from the transmembrane flux of calcium ions, which is mainly mediated through different calcium-permeable cation channels with variable calcium selectivity. Opening of individual calcium permeable channels induces a local cytosolic calcium rise that can be highly restricted in time and space. Here, we provide a short overview of the current knowledge about calcium permeation and localized calcium signals in transient receptor potential (TRP) channels. We also present a brief survey of some fundamental theoretical aspects of the local calcium signals generated upon opening of single calcium-permeable channels, and compare theoretical predictions with published experimental data on TRP channel-mediated local calcium signals.

Proteoglycans, ion channels and cell-matrix adhesion

Cell surface proteoglycans comprise a transmembrane or membrane-associated core protein to which one or more glycosaminoglycan chains are covalently attached. They are ubiquitous receptors on nearly all animal cell surfaces. In mammals, the cell surface proteoglycans include the six glypicans, CD44, NG2 (CSPG4), neuropilin-1 and four syndecans. A single syndecan is present in invertebrates such as nematodes and insects. Uniquely, syndecans are receptors for many classes of proteins that can bind to the heparan sulphate chains present on syndecan core proteins. These range from cytokines, chemokines, growth factors and morphogens to enzymes and extracellular matrix (ECM) glycoproteins and collagens. Extracellular interactions with other receptors, such as some integrins, are mediated by the core protein. This places syndecans at the nexus of many cellular responses to extracellular cues in development, maintenance, repair and disease. The cytoplasmic domains of syndecans, while having no intrinsic kinase activity, can nevertheless signal through binding proteins. All syndecans appear to be connected to the actin cytoskeleton and can therefore contribute to cell adhesion, notably to the ECM and migration. Recent data now suggest that syndecans can regulate stretch-activated ion channels. The structure and function of the syndecans and the ion channels are reviewed here, along with an analysis of ion channel functions in cell-matrix adhesion. This area sheds new light on the syndecans, not least since evidence suggests that this is an evolutionarily conserved relationship that is also potentially important in the progression of some common diseases where syndecans are implicated.

Constitutive calcium entry and cancer: updated views and insights

Tight control of basal cytosolic Ca²⁺ concentration is essential for cell survival and to fine-tune Ca²⁺-dependent cell functions. A way to control this basal cytosolic Ca²⁺ concentration is to regulate membrane Ca²⁺ channels including store-operated Ca²⁺ channels and secondary messenger-operated channels linked to G-protein-coupled or tyrosine kinase receptor activation. Orai, with or without its reticular STIM partner and Transient Receptor Potential (TRP) proteins, were considered to be the main Ca²⁺ channels involved. It is well accepted that, in response to cell stimulation, opening of these Ca²⁺ channels contributes to Ca²⁺ entry and the transient increase in cytosolic Ca²⁺ concentration involved in intracellular signaling. However, in various experimental conditions, Ca²⁺ entry and/or Ca²⁺ currents can be recorded at rest, without application of any experimental stimulation. This led to the proposition that some plasma membrane Ca²⁺ channels are already open/activated in basal condition, contributing therefore to constitutive Ca²⁺ entry. This article focuses on direct and indirect observations supporting constitutive activity of channels belonging to the Orai and TRP families and on the mechanisms underlying their basal/constitutive activities.

Role of TRPM7 in Cancer: Potential as Molecular Biomarker and Therapeutic Target

The transient receptor potential melastatin-subfamily member 7 (TRPM7) is a ubiquitously expressed ion channel with intrinsic kinase activity. Molecular and electrophysiological analyses of the structure and activity of TRPM7 have revealed functional coupling of its channel and kinase activity. Studies have indicated the important roles of TRPM7 channel-kinase in fundamental cellular processes, physiological responses, and embryonic development. Accumulating evidence has shown that TRPM7 is aberrantly expressed and/or activated in human diseases including cancer. TRPM7 plays a variety of functional roles in cancer cells including survival, cell cycle progression, proliferation, growth, migration, invasion, and epithelial-mesenchymal transition (EMT). Data from a study using mouse xenograft of human cancer show that TRPM7 is required for tumor growth and metastasis. The aberrant expression of TRPM7 and its genetic mutations/polymorphisms have been identified in various types of carcinoma. Chemical modulators of TRPM7 channel produced inhibition of proliferation, growth, migration, invasion, invadosome formation, and markers of EMT in cancer cells. Taken together, these studies suggest the potential value of exploiting TRPM7 channel-kinase as a molecular biomarker and therapeutic target in human malignancies.

The Transient Receptor Potential Melastatin 7 Channel Regulates Pancreatic Cancer Cell Invasion through the Hsp90α/uPA/MMP2 pathway

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy with a very poor prognosis. There is an urgent need to better understand the molecular mechanisms that regulate PDAC cell aggressiveness. The transient receptor potential melastatin 7 (TRPM7) is a nonselective cationic channel that mainly conducts Ca²⁺ and Mg²⁺. TRPM7 is overexpressed in numerous malignancies including PDAC. In the present study, we used the PANC-1 and MIA PaCa-2 cell lines to specifically assess the role of TRPM7 in cell invasion and matrix metalloproteinase secretion. We show that TRPM7 regulates Mg²⁺ homeostasis and constitutive cation entry in both PDAC cell lines. Moreover, cell invasion is strongly reduced by TRPM7 silencing without affecting the cell viability. Conditioned media were further studied, by gel zymography, to detect matrix metalloproteinase (MMP) secretion in PDAC cells. Our results show that MMP-2, urokinase plasminogen activator (uPA), and heat-shock protein 90α (Hsp90α) secretions are significantly decreased in TRPM7-deficient PDAC cells. Moreover, TRPM7 expression in human PDAC lymph node metastasis is correlated to the channel expression in primary tumor. Taken together, our results show that TRPM7 is involved in PDAC cell invasion through regulation of Hsp90α/uPA/MMP-2 proteolytic axis, confirming that this channel could be a promising biomarker and possibly a target for PDAC metastasis therapy.

Function and regulation of TRPM7, as well as intracellular magnesium content, are altered in cells expressing ΔF508-CFTR and G551D-CFTR

Cystic fibrosis (CF), one of the most common fatal hereditary disorders, is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The CFTR gene product is a multidomain adenosine triphosphate-binding cassette (ABC) protein that functions as a chloride (Cl(-)) channel that is regulated by intracellular magnesium [Mg(2+)]i. The most common mutations in CFTR are a deletion of a phenylalanine residue at position 508 (ΔF508-CFTR, 70-80 % of CF phenotypes) and a Gly551Asp substitution (G551D-CFTR, 4-5 % of alleles), which lead to decreased or almost abolished Cl(-) channel function, respectively. Magnesium ions have to be finely regulated within cells for optimal expression and function of CFTR. Therefore, the melastatin-like transient receptor potential cation channel, subfamily M, member 7 (TRPM7), which is responsible for Mg(2+) entry, was studies and [Mg(2+)]i measured in cells stably expressing wildtype CFTR, and two mutant proteins (ΔF508-CFTR and G551D-CFTR). This study shows for the first time that [Mg(2+)]i is decreased in cells expressing ΔF508-CFTR and G551D-CFTR mutated proteins. It was also observed that the expression of the TRPM7 protein is increased; however, membrane localization was altered for both ΔF508del-CFTR and G551D-CFTR. Furthermore, both the function and regulation of the TRPM7 channel regarding Mg(2+) is decreased in the cells expressing the mutated CFTR. Ca(2+) influx via TRPM7 were also modified in cells expressing a mutated CFTR. Therefore, there appears to be a direct involvement of TRPM7 in CF physiopathology. Finally, we propose that the TRPM7 activator Naltriben is a new potentiator for G551D-CFTR as the function of this mutant increases upon activation of TRPM7 by Naltriben.

Inhibition of TRPM7 by carvacrol suppresses glioblastoma cell proliferation, migration and invasion

Glioblastomas are progressive brain tumors with devastating proliferative and invasive characteristics. Ion channels are the second largest target class for drug development. In this study, we investigated the effects of the TRPM7 inhibitor carvacrol on the viability, resistance to apoptosis, migration, and invasiveness of the human U87 glioblastoma cell line.

The expression levels of TRPM7 mRNA and protein in U87 cells were detected by RT-PCR, western blotting and immunofluorescence. TRPM7 currents were recorded using whole-cell patch-clamp techniques. An MTT assay was used to assess cell viability and proliferation. Wound healing and transwell experiments were used to evaluate cell migration and invasion. Protein levels of p-Akt/t-Akt, p-ERK1/2/t-ERK1/2, cleaved caspase-3, MMP-2 and phosphorylated cofilin were also detected.

TRPM7 mRNA and protein expression in U87 cells is higher than in normal human astrocytes. Whole-cell patch-clamp recording showed that carvacrol blocks recombinant TRPM7 current in HEK293 cells and endogenous TRPM7-like current in U87 cells. Carvacrol treatment reduced the viability, migration and invasion of U87 cells. Carvacrol also decreased MMP-2 protein expression and promoted the phosphorylation of cofilin. Furthermore, carvacrol inhibited the Ras/MEK/MAPK and PI3K/Akt signaling pathways.

Therefore, carvacrol may have therapeutic potential for the treatment of glioblastomas through its inhibition of TRPM7 channels.

Role of TRP ion channels in cancer and tumorigenesis

Transient receptor potential (TRP) channels are recently identified proteins that form a versatile family of ion channels, the majority of which are calcium permeable and exhibit complex regulatory patterns with sensitivity to multiple environmental factors. While this sensitivity has captured early attention, leading to recognition of TRP channels as environmental and chemical sensors, many later studies concentrated on the regulation of intracellular calcium by TRP channels. Due to mutations, dysregulation of ion channel gating or expression levels, normal spatiotemporal patterns of local Ca(2+) distribution become distorted. This causes deregulation of downstream effectors sensitive to changes in Ca(2+) homeostasis that, in turn, promotes pathophysiological cancer hallmarks, such as enhanced survival, proliferation and invasion. These observations give rise to the appreciation of the important contributions that TRP channels make to many cellular processes controlling cell fate and positioning these channels as important players in cancer regulation. This review discusses the accumulated scientific knowledge focused on TRP channel involvement in regulation of cell fate in various transformed tissues.

Rapid and Localized Mechanical Stimulation and Adhesion Assay: TRPM7 Involvement in Calcium Signaling and Cell Adhesion

A cell mechanical stimulation equipment, based on cell substrate deformation, and a more sensitive method for measuring adhesion of cells were developed. A probe, precisely positioned close to the cell, was capable of a vertical localized mechanical stimulation with a temporal frequency of 207 Hz, and strain magnitude of 50%. This setup was characterized and used to probe the response of Human Umbilical Endothelial Vein Cells (HUVECs) in terms of calcium signaling. The intracellular calcium ion concentration was measured by the genetically encoded Cameleon biosensor, with the Transient Receptor Potential cation channel, subfamily M, member 7 (TRPM7) expression inhibited. As TRPM7 expression also regulates adhesion, a relatively simple method for measuring adhesion of cells was also developed, tested and used to study the effect of adhesion alone. Three adhesion conditions of HUVECs on polyacrylamide gel dishes were compared. In the first condition, the substrate is fully treated with Sulfo-SANPAH crosslinking and fibronectin. The other two conditions had increasingly reduced adhesion: partially treated (only coated with fibronectin, with no use of Sulfo-SANPAH, at 5% of the normal amount) and non-treated polyacrylamide gels. The cells showed adhesion and calcium response to the mechanical stimulation correlated to the degree of gel treatment: highest for fully treated gels and lowest for non-treated ones. TRPM7 inhibition by siRNA on HUVECs caused an increase in adhesion relative to control (no siRNA treatment) and non-targeting siRNA, but a decrease to 80% of calcium response relative to non-targeting siRNA which confirms the important role of TRPM7 in mechanotransduction despite the increase in adhesion.

Natural and Synthetic Modulators of the TRPM7 Channel

Transient receptor potential cation channel subfamily M member 7 (TRPM7) is a bi-functional protein comprising a TRP ion channel segment linked to an α-type protein kinase domain. Genetic inactivation of TRPM7 revealed its central role in magnesium metabolism, cell motility, proliferation and differentiation. TRPM7 is associated with anoxic neuronal death, cardiac fibrosis and tumor progression highlighting TRPM7 as a new drug target. Recently, several laboratories have independently identified pharmacological compounds inhibiting or activating the TRPM7 channel. The recently found TRPM7 modulators were used as new experimental tools to unravel cellular functions of the TRPM7 channel. Here, we provide a concise overview of this emerging field.

MycN promotes TRPM7 expression and cell migration in neuroblastoma through a process that involves polyamines

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MycN expression correlates with TRPM7 expression in neuroblastoma (NB) tumors.

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Expression of the transmembrane protein TRPM7 correlates with lower overall survival in NB tumors.

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MycN promotes TRPM7 mRNA and protein expression and increases TRPM7 channel activity.

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TRPM7 regulates NB cell migration.

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Polyamines regulate TRPM7 expression.

Neuroblastoma is an extra-cranial solid cancer in children. MYCN gene amplification is a prognostic indicator of poor outcome in neuroblastoma. Recent studies have shown that the multiple steps involved in cell migration are dependent on the availability of intracellular calcium (Ca²⁺). Although significant advances have been made in understanding the role of Ca²⁺ during migration, little has been achieved towards understanding its impact on the progression of diseases such as cancer. Interestingly, previous studies showed that cancer cell migration is regulated by TRPM7, a calcium-permeable ion channel. The objective of the current study was to elucidate the mechanism by which MycN promotes NB cell migration and the mechanism regulating TRPM7 expression. The results showed that MycN increased TRPM7 expression, induced TRPM7 channel activity, increased intracellular Ca²⁺ signaling, and promoted cell migration in NB cells. The results also showed that inhibition or down-regulation of ornithine decarboxylase (ODC) inhibited TRPM7 expression, a process that was reversed by spermidine. Overall, this study provides evidence that MycN promotes TRPM7 expression and cell migration through a mechanism that involves ODC synthesis of polyamines.

Expression and contributions of TRPM7 and KCa2.3/SK3 channels to the increased migration and invasion of microglia in anti-inflammatory activation states

Microglia rapidly respond to CNS injury and disease and can assume a spectrum of activation states. While changes in gene expression and production of inflammatory mediators have been extensively described after classical (LPS-induced) and alternative (IL4-induced) microglial activation, less is known about acquired de-activation in response to IL10. It is important to understand how microglial activation states affect their migration and invasion; crucial functions after injury and in the developing CNS. We reported that LPS-treated rat microglia migrate very poorly, while IL4-treated cells migrate and invade much better. Having discovered that the lamellum of migrating microglia contains a large ring of podosomes – microscopic structures that are thought to mediate adhesion, migration and invasion – we hypothesized that IL4 and IL10 would differentially affect podosome expression, gene induction, migration and invasion. Further, based on the enrichment of the KCa2.3/SK3 Ca²⁺-activated potassium channel in microglial podosomes, we predicted that it regulates migration and invasion. We found both similarities and differences in gene induction by IL4 and IL10 and, while both cytokines increased migration and invasion, only IL10 affected podosome expression. KCa2.3 currents were recorded in microglia under all three activation conditions and KCNN3 (KCa2.3) expression was similar. Surprisingly then, of three KCa2.3 inhibitors (apamin, tamapin, NS8593), only NS8593 abrogated the increased migration and invasion of IL4 and IL10-treated microglia (and invasion of unstimulated microglia). This discrepancy was explained by the observed block of TRPM7 currents in microglia by NS8593, which occurred under all three activation conditions. A similar inhibition of both migration and invasion was seen with a TRPM7 inhibitor (AA-861) that does not block KCa2.3 channels. Thus, we conclude that TRPM7 (not KCa2.3) contributes to the enhanced ability of microglia to migrate and invade when in anti-inflammatory states. This will be an important consideration in developing TRPM7 inhibitors for treating CNS injury.