Transient Receptor Potential Melastatin 7 Channel Research Articles

TRPM7 facilitates fibroblast-like synoviocyte proliferation, metastasis and inflammation through increasing IL-6 stability via the PKCα-HuR axis in rheumatoid arthritis

Transient receptor potential melastatin 7 (TRPM7) is a cation channel that plays a role in the progression of rheumatoid arthritis (RA), yet its involvement in synovial hyperplasia and inflammation has not been determined. We previously reported that TRPM7 affects the destruction of articular cartilage in RA. Herein, we further confirmed the involvement of TRPM7 in fibroblast-like synoviocyte (FLS) proliferation, metastasis and inflammation. We observed increased TRPM7 expression in FLSs derived from human RA patients. Pharmacological inhibition of TRPM7 protected primary RA-FLSs from proliferation, metastasis and inflammation. Furthermore, we found that TRPM7 contributes to RA-FLS proliferation, metastasis and inflammation by increasing the intracellular Ca2+ concentration. Mechanistically, the PKCα-HuR axis was demonstrated to respond to Ca2+ influx, leading to TRPM7-mediated RA-FLS proliferation, metastasis and inflammation. Moreover, HuR was shown to bind to IL-6 mRNA after nuclear translocation, which could be weakened by TRPM7 channel inhibition. Additionally, adeno-associated virus 9-mediated TRPM7 silencing is highly effective at alleviating synovial hyperplasia and inflammation in adjuvant-induced arthritis rats. In conclusion, our findings unveil a novel regulatory mechanism involved in the pathogenesis of RA and suggest that targeting TRPM7 might be a potential strategy for the prevention and treatment of RA.

Lianmei Qiwu Decoction relieves diabetic cardiac autonomic neuropathy by regulating AMPK/TrkA/TRPM7 signaling pathway

This study investigated the effect of Lianmei Qiwu Decoction(LMQWD) on the improvement of cardiac autonomic nerve remodeling in the diabetic rat model induced by the high-fat diet and explored the underlying mechanism of LMQWD through the AMP-activated protein kinase(AMPK)/tropomyosin receptor kinase A(TrkA)/transient receptor potential melastatin 7(TRPM7) signaling pathway. The diabetic rats were randomly divided into a model group, an LMQWD group, an AMPK agonist group, an unloaded TRPM7 adenovirus group(TRPM7-N), an overexpressed TRPM7 adenovirus group(TRPM7), an LMQWD + unloaded TRPM7 adenovirus group(LMQWD+TRPM7-N), an LMQWD + overexpressed TRPM7 adenovirus group(LMQWD+TRPM7), and a TRPM7 channel inhibitor group(TRPM7 inhibitor). After four weeks of treatment, programmed electrical stimulation(PES) was employed to detect the arrhythmia susceptibility of rats. The myocardial cell structure and myocardial tissue fibrosis of myocardial and ganglion samples in diabetic rats were observed by hematoxylin-eosin(HE) staining and Masson staining. The immunohistochemistry, immunofluorescence, real-time quantitative polymerase chain reaction(RT-PCR), and Western blot were adopted to detect the distribution and expression of TRPM7, tyrosine hydroxylase(TH), choline acetyltransferase(ChAT), growth associated protein-43(GAP-43), nerve growth factor(NGF), p-AMPK/AMPK, and other genes and related neural markers. The results showed that LMQWD could significantly reduce the arrhythmia susceptibility and the degree of fibrosis in myocardial tissues, decrease the levels of TH, ChAT, and GAP-43 in the myocardium and ganglion, increase NGF, inhibit the expression of TRPM7, and up-regulate p-AMPK/AMPK and p-TrkA/TrkA levels. This study indicated that LMQWD could attenuate cardiac autonomic nerve remodeling in the diabetic state, and its mechanism was associated with the activation of AMPK, further phosphorylation of TrkA, and inhibition of TRPM7 expression.

Effect of Static Pressure on Early Apoptosis of Condylar Chondrocytes by Activating Transient Receptor Potential Melastatin 7 (TRPM7) Channel

Background: This study is to detect the Ca2+ permeability of transient receptor potential melastatin 7 (TRPM7) channel under Static pressure, and to verify the effection of pressure on cell apoptosis through TRPM7 channel mediated Ca2+ influx. Materials and Methods: Rat condylar chondrocytes cells are divided into control group, pressure group and FTY720 group. TRPM7 protein content is detected by westernblot. Calcium current is detected by colorimetry, and flow cytometry is used to detect apoptotic cells. Results: The cell morphology is spindle or spindle shape with clear boundary. The nucleus is oval and located in the center of the cell. Compared with the control group, the protein content of TRPM7, the calcium concentration was significantly higher (P <0.05). apoptosis in the pressure group is significantly increased than that in the control group (P <0.05). Conclusion: Static pressure upregulates the expression of TRPM7 in chondrocytes, resulting in the increase of intracellular Ca2+ concentration, which leads to apoptosis through signal pathway.

Clinical and Prognostic Values of TRPM7 in Colon and Rectal Cancers.

Background and Objectives: Transient receptor potential melastatin 7 (TRPM7) is a unique channel protein, and functionally responsible for transportation of calcium and magnesium. Physiologically, the TRPM7 channel is involved in homeostasis of calcium and magnesium, and cell survival. TRPM7 expression is up-regulated in many cancers as malignant behaviors of cancer cells, and its deficiency suppresses their growth. Materials and Methods: In this study, we aimed to analyze clinical and prognostic characteristics of TRPM7 expression in colorectal cancers (CRC) using The Cancer Genome Atlas. Results: High expression of TRPM7 was observed in younger patients with rectal cancer (p = 0.0002). By quantitative correlation analysis, TRPM7 was negatively correlated with age (R = -0.239, p = 0.003) and p53 (R = -0.240, p = 0.002). Furthermore, it was positively correlated with APC expression (R = 0.534, p < 0.001) and KRAS expression (R = 0.319, p < 0.001). In colon cancer, there were no variables that showed a significant correlation with TRPM7. Survival analysis found that TRPM7 expression did not have any prognostic value in colon and rectal cancers. Conclusions: Our study highlights that TRPM7 expression in CRC, particularly in rectal cancer, may be a potential marker. Future studies are needed to provide deeper insights into the role of TRPM7 in rectal cancer.

TRPM7 channel inhibition attenuates rheumatoid arthritis articular chondrocyte ferroptosis by suppression of the PKCα-NOX4 axis

A role for ferroptosis in articular cartilage destruction associated with rheumatoid arthritis (RA) has not been identified. We previously reported transient receptor potential melastatin 7 (TRPM7) expression was correlated with RA cartilage destruction. Herein, we further characterized a role for TRPM7 in chondrocyte ferroptosis. The expression of TRPM7 was found to be elevated in articular chondrocytes derived from adjuvant arthritis (AA) rats, human RA patients, and cultured chondrocytes treated with the ferroptosis inducer, erastin. TRPM7 knockdown or pharmacological inhibition protected primary rat articular chondrocytes and human chondrocytes (C28/I2 cells) from ferroptosis. Moreover, TRPM7 channel activity was demonstrated to contribute to chondrocyte ferroptosis by elevation of intracellular Ca2+. Mechanistically, the PKCα-NOX4 axis was found to respond to stimulation with erastin, which resulted in TRPM7-mediated chondrocyte ferroptosis. Meanwhile, PKCα was shown to directly bind to NOX4, which could be reduced by TRPM7 channel inhibition. Adeno-associated virus 9-mediated TRPM7 silencing or TRPM7 blockade with 2-APB alleviated articular cartilage destruction in AA rats and inhibited chondrocyte ferroptosis. Collectively, both genetic and pharmacological inhibitions of TRPM7 attenuated articular cartilage damage and chondrocyte ferroptosis via the PKCα-NOX4 axis, suggesting that TRPM7-mediated chondrocyte ferroptosis is a promising target for the prevention and treatment of RA.

Suppression of Transient Receptor Potential Melastatin 7 by Carvacrol Protects against Injured Spinal Cord by Inhibiting Blood-Spinal Cord Barrier Disruption.

When the blood-spinal cord barrier (BSCB) is disrupted after a spinal cord injury (SCI), several pathophysiological cascades occur, including inflammation and apoptotic cell death of neurons and oligodendrocytes, resulting in permanent neurological deficits. Transient receptor potential melastatin 7 (TRPM7) is involved in the pathological processes in many neuronal diseases, including traumatic brain injury, amyotrophic lateral sclerosis, parkinsonism dementia, and Alzheimer's disease. Further, carvacrol (CAR), a TRPM7 inhibitor, is known to protect against SCI by reducing oxidative stress and inhibiting the endothelial nitric oxide synthase pathway. However, the functions of TRPM7 in the regulation of BSCB homeostasis after SCI have not been examined. Here, we demonstrated that TRPM7, a calcium-mediated non-selective divalent cation channel, plays a critical role after SCI in rats. Rats were contused at T9 and given CAR (50 mg/kg) intraperitoneally immediately and 12 h after SCI, and then given the same dose once a day for 7 days. TRPM7 was found to be up-regulated after SCI in both in vitro and in vivo studies, and it was expressed in blood vessels alongside neurons and oligodendrocytes. Additionally, CAR treatment suppressed BSCB disruption by inhibiting the loss of tight junction (TJ) proteins and preserved TJ integrity. CAR also reduced apoptotic cell death and improved functional recovery after SCI by preventing BSCB disruption caused by blood infiltration and inflammatory responses. Based on these findings, we propose that blocking the TRPM7 channel can inhibit the destruction of the BSCB and it is a potential target in therapeutic drug development for use in SCI.

NSAIDs Naproxen, Ibuprofen, Salicylate, and Aspirin Inhibit TRPM7 Channels by Cytosolic Acidification.

Non-steroidal anti-inflammatory drugs (NSAIDs) are used for relieving pain and inflammation accompanying numerous disease states. The primary therapeutic mechanism of these widely used drugs is the inhibition of cyclooxygenase 1 and 2 (COX1, 2) enzymes that catalyze the conversion of arachidonic acid into prostaglandins. At higher doses, NSAIDs are used for prevention of certain types of cancer and as experimental treatments for Alzheimer’s disease. In the immune system, various NSAIDs have been reported to influence neutrophil function and lymphocyte proliferation, and affect ion channels and cellular calcium homeostasis. Transient receptor potential melastatin 7 (TRPM7) cation channels are highly expressed in T lymphocytes and are inhibited by Mg2+, acidic pH, and polyamines. Here, we report a novel effect of naproxen, ibuprofen, salicylate, and acetylsalicylate on TRPM7. At concentrations of 3–30mM, they reversibly inhibited TRPM7 channel currents. By measuring intracellular pH with the ratiometric indicator BCECF, we found that at 300μM to 30mM, these NSAIDs reversibly acidified the cytoplasm in a concentration-dependent manner, and propose that TRPM7 channel inhibition is a consequence of cytosolic acidification, rather than direct. NSAID inhibition of TRPM7 channels was slow, voltage-independent, and displayed use-dependence, increasing in potency upon repeated drug applications. The extent of channel inhibition by salicylate strongly depended on cellular PI(4,5)P2 levels, as revealed when this phospholipid was depleted with voltage-sensitive lipid phosphatase (VSP). Salicylate inhibited heterologously expressed wildtype TRPM7 channels but not the S1107R variant, which is insensitive to cytosolic pH, Mg2+, and PI(4,5)P2 depletion. NSAID-induced acidification was also observed in Schneider 2 cells from Drosophila, an organism that lacks orthologous COX genes, suggesting that this effect is unrelated to COX enzyme activity. A 24-h exposure to 300μM–10mM naproxen resulted in a concentration-dependent reduction in cell viability. In addition to TRPM7, the described NSAID effect would be expected to apply to other ion channels and transporters sensitive to intracellular pH.

Cardioprotective effect of fingolimod against calcium paradox-induced myocardial injury in the isolated rat heart.

Fingolimod (FTY720) inhibits Ca2+-permeable, Mg2+-sensitive channels called transient receptor potential melastatin 7 (TRPM7), but its effects on Ca2+ paradox (CP) - induced myocardial damage has not been evaluated. We studied the effect of FTY720 on CP-induced myocardial damage and used other TRPM7 channel inhibitors nordihydroguaiaretic acid (NDGA) and Mg2+ to test if any effect of FTY720 was via TRPM7 inhibition. Langendorff-perfused Wistar rat hearts were treated with FTY720 or NDGA and subjected to a CP protocol consisting of Ca2+ depletion followed by Ca2+ repletion. Hearts of rats pre-treated with MgSO4 were also subjected to CP. Hemodynamic parameters were measured using an intraventricular balloon, and myocardial infarct size was quantified using triphenyltetrazolium chloride stain. TRPM7 proteins in ventricular tissue were detected using immunoblot analysis. FTY720, but not NDGA, decreased CP-induced infarct size. Both FTY720 and NDGA minimized the CP-induced elevation of left ventricular end-diastolic pressure, but only FTY720 ultimately improved ventricular developed pressure. Mg2+ pre-treatment had no effect on CP-induced infarct size, nor hemodynamic parameters during CP, nor the level of TRPM7 protein expression in ventricular tissue. Overall, FTY720 attenuated CP-induced myocardial damage, with potential therapeutic implications on Ca2+-mediated cardiotoxicity; however, the cardioprotective mechanism of FTY720 seems to be unrelated to TRPM7 channel modulation.

CCT128930 is a novel and potent antagonist of TRPM7 channel

Transient receptor potential melastatin 7 (TRPM7) channels represent a major magnesium (Mg2+)-uptake component in mammalian cells and are negatively modulated by internal Mg2+. However, few TRPM7 modulators were identified so far, which hindered the understanding of the TRPM7 channel functions. In this study, we identified that CCT128930, an ATP-competitive protein kinase B inhibitor reported previously, was a potent TRPM7 channel antagonist. The inhibition of CCT128930 on TRPM7 was independent of intracellular Mg2+. In the absence and presence of 300 μM Mg2+ in pipette solution, the IC50 values were 0.86 ± 0.11 μM and 0.63 ± 0.09 μM, respectively. Subtype selectivity data showed that CCT128930 preferentially inhibited TRPM7 channels compared to TRPM6 and TRPM8 isoforms. In addition, CCT128930 was found to be able to reduce the endogenous TRPM7-like currents in SH-SY5Y neuroblastoma cells. At last, multiple residues in the superficial part of the TRPM7 selectivity filter were identified to be critical for the inhibitory activity of CCT128930 which are different from the determinants of Mg2+ and reported TRPM7 antagonists. Our results indicated that CCT128930 is a novel and potent TRPM7 channel antagonist.

Phagocytic activity of splenic macrophages is enhanced and accompanied by cytosolic alkalinization in TRPM7 kinase-dead mice.

Transient receptor potential melastatin 7 (TRPM7) is a unique protein functioning as a cation channel as well as a serine/threonine kinase and is highly expressed in immune cells such as lymphocytes and macrophages. TRPM7 kinase-dead (KD) mouse model has been used to investigate the role of this protein in immune cells; these animals display moderate splenomegaly and ectopic hemopoiesis. The basal TRPM7 current magnitudes in peritoneal macrophages isolated from KD mice were higher; however, the maximum currents, achieved after cytoplasmic Mg2+ washout, were not different. In the present study, we investigated the consequences of TRPM7 kinase inactivation in splenic and peritoneal macrophages. We measured the basal phagocytic activity of splenic macrophages using fluorescent latex beads, pHrodo zymosan bioparticles, and opsonized red blood cells. KD macrophages phagocytized more efficiently and had slightly higher baseline calcium levels compared to WT cells. We found no obvious differences in store-operated Ca2+ entry between WT and KD macrophages. By contrast, the resting cytosolic pH in KD macrophages was significantly more alkaline than in WT. Pharmacological blockade of sodium hydrogen exchanger 1 (NHE1) reversed the cytosolic alkalinization and reduced phagocytosis in KD macrophages. Basal TRPM7 channel activity in KD macrophages was also reduced after NHE1 blockade. Cytosolic Mg2+ sensitivity of TRPM7 channels measured in peritoneal macrophages was similar in WT and KD mice. The higher basal TRPM7 channel activity in KD macrophages is likely due to alkalinization. Our results identify a novel role for TRPM7 kinase as a suppressor of basal phagocytosis and a regulator of cellular pH.

The TRPM7 Channel in the Nervous and Cardiovascular Systems.

Transient receptor potential melastatin 7 (TRPM7), along with the closely related TRPM6, are unique channels that have dual operations: cation permeability and kinase activity. In contrast to the limited tissue distribution of TRPM6, TRPM7 is widely expressed among tissues and is therefore implicated in a variety of cellular functions physiologically and pathophysiologically. The discovery of TRPM7's unique structure imparting dual ion channel and kinase activities shed light onto novel and peculiar biological functions, such as Mg2+ homeostasis, cellular Ca2+ flickering, and even intranuclear transcriptional regulation by a cleaved kinase domain translocated to nuclei. Interestingly, at a higher level, TRPM7 participates in several biological processes in the nervous and cardiovascular systems, in which excitatory responses in neurons and cardiomyocytes are critical for their function. Here, we review the roles of TRPM7 in cells involved in the nervous and cardiovascular systems and discuss its potential as a future therapeutic target.

Isoproterenol-Dependent Activation of TRPM7 Protects Against Neurotoxin-Induced Loss of Neuroblastoma Cells.

Neuronal function and their survival depend on the activation of ion channels. Loss of ion channel function is known to induce neurodegenerative diseases such as Parkinson’s that exhibit loss of dopaminergic neurons; however, mechanisms that could limit neuronal loss are not yet fully identified. Our data suggest that neurotoxin-mediated loss of neuroblastoma SH-SY5Y cells is inhibited by the addition of β-adrenergic receptor (β-AR) agonist isoproterenol. The addition of isoproterenol to SHSY-5Y cells showed increased Mg2+ influx and cell survival in the presence of neurotoxin especially at higher concentration of isoproterenol. Importantly, isoproterenol potentiated transient receptor potential melastatin-7 (TRPM7) channel activation that leads to an increase in intracellular Mg2+ levels. The addition of 2APB, which is a known TRPM7 channel blocker, significantly decreased the TRPM7 function and inhibited isoproterenol-mediated protection against neurotoxins. Moreover, neurotoxins inhibited TRPM7 expression and function, but the restoration of TRPM7 expression increased neuroblastoma cell survival. In contrast, TRPM7 silencing increased cell loss, decreased Mg2+ homeostasis, and inhibited mitochondrial function. Moreover, isoproterenol treatment prevented neurotoxin-mediated loss of TRPM7 expression and inhibited Bax expression that induces cell survival. These effects were dependent on the neurotoxin-induced increase in oxidative stress, which inhibits TRPM7 expression and function. Together, our results suggest a positive role for β-AR in activating TRPM7 channels that regulate Mg2+ homeostasis and are essential for the survival of SH-SY5Y cells from neurotoxin.

The Role of Transient Receptor Potential Melastatin 7 (TRPM7) in Cell Viability: A Potential Target to Suppress Breast Cancer Cell Cycle.

The divalent cation-selective channel transient receptor potential melastatin 7 (TRPM7) channel was shown to affect the proliferation of some types of cancer cell. However, the function of TRPM7 in the viability of breast cancer cells remains unclear. Here we show that TRPM inhibitors suppressed the viability of TRPM7-expressing breast cancer cells. We first demonstrated that the TRPM7 inhibitors 2-aminoethyl diphenylborinate (2-APB), ginsenoside Rd (Gin Rd), and waixenicin A preferentially suppressed the viability of human embryonic kidney HEK293 overexpressing TRPM7 (HEK-M7) cells over wildtype HEK293 (WT-HEK). Next, we confirmed the effects of 2-APB on the TRPM7 channel functions by whole-cell currents and divalent cation influx. The inhibition of the viability of HEK-M7 cells by 2-APB was not mediated by the increase in cell death but by the interruption of the cell cycle. Similar to HEK-M7 cells, the viability of TRPM7-expressing human breast cancer MDA-MB-231, AU565, and T47D cells were also suppressed by 2-APB by arresting the cell cycle in the S phase. Furthermore, in a novel TRPM7 knock-out MDA-MB-231 (KO-231) cell line, decreased divalent influx and reduced proliferation were observed compared to the wildtype MDA-MB-231 cells. 2-APB and Gin Rd preferentially suppressed the viability of wildtype MDA-MB-231 cells over KO-231 by affecting the cell cycle in wildtype but not KO-231 cells. Our results suggest that TRPM7 regulates the cell cycle of breast cancers and is a potential therapeutic target.

TRPM7 channel inhibition exacerbates pulmonary arterial hypertension through MEK/ERK pathway.

Cellular senescence is an important mechanism of autonomous tumor suppression, while its consequence such as the senescence-associated secretory phenotype (SASP) may drive tumorigenesis and age-related diseases. Therefore, controlling the cell fate optimally when encountering senescence stress is helpful for anti-cancer or anti-aging treatments. To identify genes essential for senescence establishment or maintenance, we carried out a CRISPR-based screen with a deliberately designed single-guide RNA (sgRNA) library. The library comprised of about 12,000 kinds of sgRNAs targeting 1378 senescence-associated genes selected by integrating the information of literature mining, protein-protein interaction network, and differential gene expression. We successfully detected a dozen gene deficiencies potentially causing senescence bypass, and their phenotypes were further validated with a high true positive rate. RNA-seq analysis showed distinct transcriptome patterns of these bypass cells. Interestingly, in the bypass cells, the expression of SASP genes was maintained or elevated with CHEK2, HAS1, or MDK deficiency; but neutralized with MTOR, CRISPLD2, or MORF4L1 deficiency. Pathways of some age-related neurodegenerative disorders were also downregulated with MTOR, CRISPLD2, or MORF4L1 deficiency. The results demonstrated that disturbing these genes could lead to distinct cell fates as a consequence of senescence bypass, suggesting that they may play essential roles in cellular senescence.

Prostaglandin E2 increases migration and proliferation of human glioblastoma cells by activating transient receptor potential melastatin 7 channels.

Recent studies showed that both prostaglandin E2 (PGE2) and transient receptor potential melastatin 7 (TRPM7) play important roles in migration and proliferation of human glioblastoma cells. In this study, we tested the association between PGE2 and TRPM7. We found that PGE2 increased TRPM7 currents in HEK293 and human glioblastoma A172 cells. The PGE2 EP3 receptor antagonist L‐798106 abrogated the PGE2 stimulatory effect, while EP3 agonist 17‐phenyl trinor prostaglandin E2 (17‐pt‐PGE2) mimicked the effect of PEG2 on TRPM7. The TRPM7 phosphotransferase activity‐deficient mutation, K1646R had no effect on PGE2 induced increase of TRPM7 currents. Inhibition of protein kinase A (PKA) activity by Rp‐cAMP increased TRPM7 currents. TRPM7 PKA phosphorylation site mutation S1269A abolished the PGE2 effect on TRPM7 currents. PGE2 increased both mRNA and membrane protein expression of TRPM7 in A172 cells. Knockdown of TRPM7 by shRNA abrogated the PGE2 stimulated migration and proliferation of A172 cells. Blockage of TRPM7 with 2‐aminoethoxydiphenyl borate (2‐APB) or NS8593 had a similar effect as TRPM7‐shRNA. In conclusion, our results demonstrate that PGE2 activates TRPM7 via EP3/PKA signalling pathway, and that PGE2 enhances migration and proliferation of human glioblastoma cells by up‐regulation of the TRPM7 channel.

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.

The kinase activity of the channel-kinase protein TRPM7 regulates stability and localization of the TRPM7 channel in polarized epithelial cells.

The channel-kinase transient receptor potential melastatin 7 (TRPM7) is a bifunctional protein with ion channel and kinase domains. The kinase activity of TRPM7 has been linked to the regulation of a broad range of cellular activities, but little is understood as to how the channel itself is regulated by its own kinase activity. Here, using several mammalian cell lines expressing WT TRPM7 or kinase-inactive variants, we discovered that compared with the cells expressing WT TRPM7, cells in which TRPM7's kinase activity was inactivated had faster degradation, elevated ubiquitination, and increased intracellular retention of the channel. Mutational analysis of TRPM7 autophosphorylation sites further revealed a role for Ser-1360 of TRPM7 as a key residue mediating both TRPM7 stability and intracellular trafficking. Additional trafficking roles were uncovered for Ser-1403 and Ser-1567, whose phosphorylation by TRPM7's kinase activity mediated the interaction of the channel with the signaling protein 14-3-3θ. In summary, our results point to a critical role for TRPM7's kinase activity in regulating proteasome-mediated turnover of the TRPM7 channel and controlling its cellular localization in polarized epithelial cells. Overall, these findings improve our understanding of the significance of TRPM7's kinase activity for functional regulation of its channel activity.

MicroRNA-135a inhibits cardiac fibrosis induced by isoproterenol via TRPM7 channel

BackgroundCardiac fibrosis is a crucial factor of heart failure. It has been reported that several microRNAs (miRNAs, miRs) were involved in cardiac fibrosis, however, the role and possible regulatory mechanism of microRNA-135a (miR-135a) in cardiac fibrosis have not been investigated. Here, we explored the regulation mechanism of miR-135a on cardiac fibrosis. Methods and ResultsIn vitro, cardiac fibroblasts (CFs) from neonatal rats were treated by isoproterenol (ISO) at the final concentration of 10 μM for 24 h and miR-135a expression was decreased obviously. A miR-135a mimic inhibited CFs proliferation and differentiation by down-regulating transient receptor potential melastatin 7 (TRPM7) expression and current, whose effects were reversed by either the addition of miR-135a mimic or silencing TRPM7. In vivo, adult SD rat cardiac fibrosis was induced by subcutaneous administration of ISO (5 mg/kg/day) for 10 days. The expression of Collagen I, α-smooth muscle actin (α-SMA) and TRPM7 were up-regulated while miR-135a was down-regulated. In summary, our results illustrated that TRPM7 channel played an essential role in regulating fibrosis and that miR-135a protected against ISO-induced cardiac fibrosis via TRPM7 channel. ConclusionMiR-135a inhibits cardiac fibrosis via miR-135a- TRPM7-collagen production pathway.

The crucial role of the TRPM7 kinase domain in the early stage of amelogenesis

Transient receptor potential melastatin-7 (TRPM7) is a bi-functional protein containing a kinase domain fused to an ion channel. TRPM7 is highly expressed in ameloblasts during tooth development. Here we show that TRPM7 kinase-inactive knock-in mutant mice (TRPM7 KR mice) exhibited small enamel volume with opaque white-colored incisors. The TRPM7 channel function of ameloblast-lineage cells from TRPM7 KR mice was normal. Interestingly, phosphorylation of intracellular molecules including Smad1/5/9, p38 and cAMP response element binding protein (CREB) was inhibited in ameloblasts from TRPM7 KR mice at the pre-secretory stage. An immunoprecipitation assay showed that CREB was bound to TRPM7, suggesting that direct phosphorylation of CREB by TRPM7 was inhibited in ameloblast-lineage cells from TRPM7 KR mice. These results indicate that the function of the TRPM7 kinase domain plays an important role in ameloblast differentiation, independent of TRPM7 channel activity, via phosphorylation of CREB.

Activation of transient receptor potential melastatin 7 (TRPM7) channel increases basal autophagy and reduces amyloid β-peptide

Cerebral accumulation of amyloid β-peptide (Aβ), which is produced from amyloid precursor protein (APP), is the primary cause of Alzheimer's disease (AD). Autophagy recycles cellular components and digests intracellular components including Aβ. The Ca2+- and Mg2+-permeable transient receptor potential melastatin 7 (TRPM7) channel underlies the constitutive Ca2+ influx in some cells. Since we already reported that TRPM7 channel-mediated Ca2+ influx regulates basal autophagy, we hypothesize that the activation of TRPM7 channel could increase basal autophagy and consequently decrease Aβ. In this study, we showed that naltriben (NTB), a specific TRPM7 channel activator, induced Ca2+ influx and activated autophagic signaling in neuroblastoma SH-SY5Y cells. NTB also promoted co-localization of LC3 and APP, and reduced Aβ. Furthermore, we found that an early-onset familial AD-associated presenilin1 ΔE9 (PS1 ΔE9) mutant cells had attenuated basal autophagy. NTB was able to recover autophagy and decrease Aβ in PS1 ΔE9 cells. Our results show that the activating TRPM7 channel may prevent AD-related Aβ neuropathology via modulating Ca2+-regulated basal autophagy.