Intracellular Magnesium Research Articles

Inhibition of PRL-2·CNNM3 Protein Complex Formation Decreases Breast Cancer Proliferation and Tumor Growth

The oncogenic phosphatase of regenerating liver 2 (PRL-2) has been shown to regulate intracellular magnesium levels by forming a complex through an extended amino acid loop present in the Bateman module of the CNNM3 magnesium transporter. Here we identified highly conserved residues located on this amino acid loop critical for the binding with PRL-2. A single point mutation (D426A) of one of those critical amino acids was found to completely disrupt PRL-2·human Cyclin M 3 (CNNM3) complex formation. Whole-cell voltage clamping revealed that expression of CNNM3 influenced the surface current, whereas overexpression of the binding mutant had no effect, indicating that the binding of PRL-2 to CNNM3 is important for the activity of the complex. Interestingly, overexpression of the CNNM3 D426A-binding mutant in cancer cells decreased their ability to proliferate under magnesium-deprived situations and under anchorage-independent growth conditions, demonstrating a PRL-2·CNNM3 complex-dependent oncogenic advantage in a more stringent environment. We further confirmed the importance of this complex in vivo using an orthotopic xenograft breast cancer model. Finally, because molecular modeling showed that the Asp-426 side chain in CNNM3 buries into the catalytic cavity of PRL-2, we showed that a PRL inhibitor could abrogate complex formation, resulting in a decrease in proliferation of human breast cancer cells. In summary, we provide evidence that this fundamental regulatory aspect of PRL-2 in cancer cells could potentially lead to broadly applicable and innovative therapeutic avenues.

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.

Magnesium homeostasis goes awry in chemoresistance -TRPM6, TRPM7 and MagT1 in colon carcinoma LoVo cells

Chemoresistance is one of the most significant factors impeding the progress of cancer therapy (1). It is known that neoplastic cells accumulate magnesium and frequently upregulate one of its transporters, i.e.TRPM7 (2). We have investigated magnesium homeostasis in a model of chemoresistance i.e. colon carcinoma LoVo cells sensitive (LoVo-S) or resistant to doxorubicin (LoVo-R). We observed that LoVo-R have higher amount of total intracellular magnesium than LoVo-S. We studied the expression of some magnesium transporter (TRPM6, TRPM7 and MagT1) by Real Time PCR and Western Blot and found that TRPM6 and 7 are overexpressed in LoVo-S, while MagT1 is upregulated in LoVo-R. In LoVo-S, silencing TRPM7 retards cell growth and shifts the phenotype to one more similar to resistant cells. On the other hand, calpeptin, a calpain inhibitor, upregulates TRPM7, stimulated proliferation and enhances the sensitivity to doxorubicin of LoVo-R. Silencing MagT1 in LoVo-R markedly inhibited cell growth without affecting the response to doxorubicin. We conclude that alterations of magnesium homeostasis play a role in drug resistance.

Magnesium: A Mineral Essential for Health Yet Generally Underestimated or Even Ignored

Magnesium is the fourth most common mineral in the human body after calcium, potassium and sodium. Magnesium must be continuously replenished through foods and water intake because it is not synthesizable. Chronic inadequate intake of magnesium over long period of time can manifest as latent magnesium deficiency with symptoms such as muscle weakness, cramps, fatigue, neurological and cardiovascular dysfunctions, reduced bone mineralization and strength. Reports published by WHO have estimated that ~two thirds of Americans and French have magnesium intake below the recommended amounts but only a small numbers are overtly depleted. The authorities in Finland were concerned of the negative impact of geochemical magnesium deficiency in the eastern region of Finland and its adverse effect on heart health. A program was initiated to increase magnesium intake though supplementation; this has contributed to progressive fall of death rate due to heart-related issues. Restoring and sustaining adequate magnesium store are easy and inexpensive. Some 40% of total body magnesium is intracellular and ~60% in bone and teeth with less than 1% in circulation. Intracellular magnesium deficiency may or may not be reflected as overt hypomagnesaemia making measurement of plasma/serum magnesium potentially misleading when “normal” plasma/serum concentration is “interpreted” to exclude deficiency. In this review, the role of magnesium at cellular level, its homeostasis and major clinical conditions associated with magnesium deficiency in adults will be briefly discussed. Assessment of magnesium status and its potential deficiency by examining individual’s “modus vivendi” and/or the use of laboratory tests will be highlighted. Finally, various therapeutic modalities and monitoring of treatment will be summarized.

An Importance of Magnesium Deficiency in the Formation of Vegetative Disadaptation in Children and Adolescents with Digestive Tract Pathology

Aim. In the study of magnesium deficiency, a distinction is made between magnesium hypoelementosis and magnesium deficit. As a result, detection of the magnesium deficiency and its influence on vegetative disadaptation progression can help to correct damages in early stages and to decrease frequency of chronization of digestive tract disorders in children. Methods and results. 48 children at the ages from 7 to 17 years with complaints on sickliness, stomachache, dyspeptic symptoms were under the care. The first group contained of 28 children with organic digestive system disorders, the second – 20 children with functional digestive system disorders. In both groups serum and intracellular concentration of Mg, Holter monitoring of ECG were carried out. Conclusion. Among children and adolescents with digestive tract pathology, 4,3% of patients had magnesium deficit. Hypoelementosis was detected in 18,7% of cases, that demonstrates great prevalence of latent magnesium deficiency and the necessity of the intracellular content study. Indices of both intracellular (p≤0,05) and extracellular (p ≤0,001) magnesium in children from the 1st group were much lower than in children from the 2nd group. This demonstrates mutual influence of organic digestive tract pathology and magnesium deficit on the development and severity of pathologies. Direct and strong correlation line between intracellular magnesium level lowering and lowered indices of HRV time-line analysis was detected in the 1st group. Correlation absence in the 2nd group demonstrates the influence of magnesium deficiency on vegetative disadaptation development and provides change of digestive tract functional disorders to organic.

Mesendogen, a novel inhibitor of TRPM6, promotes mesoderm and definitive endoderm differentiation of human embryonic stem cells through alteration of magnesium homeostasis

The homo- and hetero-tetrameric channel complexes formed by transient receptor potential cation channel, subfamily M, member 6 (TRPM6) and 7 (TRPM7) (collectively referred to as TRPM6/TRPM7 channels in this study) are the major regulators of cellular magnesium uptake, yet the exact roles of TRPM6/TRPM7 channels and cellular magnesium homeostasis during development are poorly understood. Here, we report a novel small molecule Mesendogen (MEG) which robustly induces nearly homogeneous (≥85%) mesoderm and definitive endoderm (DE) differentiations of human embryonic stem cells (hESCs) in combination with growth factors. A kinome screen followed by loss-of-function experiments identified TRPM6 as the biological target of MEG. We demonstrated that MEG functions by inhibiting TRPM6/TRPM7 magnesium channel activity, as MEG reduced intracellular magnesium level, while TRPM6/TRPM7 channel modulation and magnesium-withdrawal phenocopied MEG at enhancing mesoderm and DE differentiations. This study discovers a robust chemical enhancer of hESC directed differentiation, and uncovers a novel regulatory role of cellular magnesium homeostasis during early embryonic cell fate specification.

Magnesium homeostasis in colon carcinoma LoVo cells sensitive or resistant to doxorubicin.

Neoplastic cells accumulate magnesium, an event which provides selective advantages and is frequently associated with TRPM7overexpression. Little is known about magnesium homeostasis in drug-resistant cancer cells. Therefore, we used the colon cancer LoVo cell model and compared doxorubicin-resistant to sensitive cells. In resistant cells the concentration of total magnesium is higher while its influx capacity is lower than in sensitive cells. Accordingly, resistant cells express lower amounts of the TRPM6 and 7, both involved in magnesium transport. While decreased TRPM6 levels are due to transcriptional regulation, post-transcriptional events are involved in reducing the amounts of TRPM7. Indeed, the calpain inhibitor calpeptin markedly increases the levels of TRPM7 in resistant cells. In doxorubicin-sensitive cells, silencing TRPM7 shifts the phenotype to one more similar to resistant cells, since in these cells silencing TRPM7 significantly decreases the influx of magnesium, increases its intracellular concentration and increases resistance to doxorubicin. On the other hand, calpain inhibition upregulates TRPM7, decreases intracellular magnesium and enhances the sensitivity to doxorubicin of resistant LoVo cells. We conclude that in LoVo cells drug resistance is associated with alteration of magnesium homeostasis through modulation of TRPM7. Our data suggest that TRPM7 expression may be an additional undisclosed player in chemoresistance.

Impact of Magnesium L-Lactate on Occurrence of Ventricular Arrhythmias in Patients with Implantable Cardioverter Defibrillators: A Randomized, Placebo-Controlled Trial.

Background:We evaluated the antiarrhythmic efficacy and quality of life (QoL) impact of oral magnesium Llactate on patients with an implantable cardioverter defibrillator (ICD).Methods:This prospective, double-blind, placebo-controlled trial randomized 70 patients with an ICD to receive oral magnesium L-lactate 3 tablets twice daily (504mg elemental magnesium daily) or matching placebo for 12 months. Patients were seen at baseline, 12, 24, 36, and 52 weeks. The primary endpoints were the cumulative occurrence of ICD therapy [either shock or anti-tachycardia pacing (ATP)] or QoL between the groups.Results:Among the 70 randomized patients with a mean ± SD follow-up of 6.4 ± 4.1 months, 10 patients in the placebo group and 8 in the magnesium group experienced either ICD shock or ATP [HR 0.84, 95% CI 0.33 to 2.12; p=0.706]. Without significant arrhythmia suppression, only minimal effects on QoL were seen. Eighty six percent of all patients had serum intracellular magnesium deficiency.Conclusion:In our underpowered trial, patients with ICDs had intracellular magnesium deficiency but oral magnesium Llactate only nonsignificantly reduced the occurrence of ICD therapies and had little impact on HrQoL.

Effects of transdermal magnesium chloride on quality of life for patients with fibromyalgia: a feasibility study

BackgroundFibromyalgia is a syndrome characterized by chronic pain, fatigue, depression, and sleep disturbances. Its primary cause is unclear. Several studies have reported decreased intracellular magnesium levels in patients with fibromyalgia and have found negative correlation between magnesium levels and fibromyalgia symptoms. ObjectiveTo gather preliminary data on whether transdermal magnesium can improve quality of life for women who have fibromyalgia. Design, setting, participants and interventionsThis is a patient questionnaires and survey in a fibromyalgia clinic at a tertiary medical center. Forty female patients with the diagnosis of fibromyalgia were enrolled. Each participant was provided a spray bottle containing a transdermal magnesium chloride solution and asked to apply 4 sprays per limb twice daily for 4 weeks. Participants were asked to complete the Revised Fibromyalgia Impact Questionnaire, SF-36v2 Health Survey, and a quality-of-life analog scale at baseline, week 2, and week 4. Main outcome measureQuestionnaire and survey scores, evaluated through intent-to-treat and per-protocol analyses. ResultsTwenty-four patients completed the study (mean [SD] age, 57.2 [7.6] years; white, 95%; mean body mass index, 31.3 kg/m2). With intention-to-treat analysis, Revised Fibromyalgia Impact Questionnaire subscale and total scores were significantly improved at week 2 and week 4 (total score, P = 0.001). Per-protocol analysis results were similar: all subscales of the Revised Fibromyalgia Impact Questionnaire were significantly improved at week 2 and week 4 (total score, P = 0.001). ConclusionThis pilot study suggests that transdermal magnesium chloride applied on upper and lower limbs may be beneficial to patients with fibromyalgia. Trial registrationClinicalTrials.gov. ldentifier NCT01968772.

Intracellular magnesium level determines cell viability in the MPP+ model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder resulting from mitochondrial dysfunction in dopaminergic neurons. Mitochondria are believed to be responsible for cellular Mg2+ homeostasis. Mg2+ is indispensable for maintaining ordinal cellular functions, hence perturbation of the cellular Mg2+ homeostasis may be responsible for the disorders of physiological functions and diseases including PD. However, the changes in intracellular Mg2+ concentration ([Mg2+]i) and the role of Mg2+ in PD have still been obscure. In this study, we investigated [Mg2+]i and its effect on neurodegeneration in the 1-methyl-4-phenylpyridinium (MPP+) model of PD in differentiated PC12 cells. Application of MPP+ induced an increase in [Mg2+]i immediately via two different pathways: Mg2+ release from mitochondria and Mg2+ influx across cell membrane, and the increased [Mg2+]i sustained for more than 16h after MPP+ application. Suppression of Mg2+ influx decreased the viability of the cells exposed to MPP+. The cell viability correlated highly with [Mg2+]i. In the PC12 cells with suppressed Mg2+ influx, ATP concentration decreased and the amount of reactive oxygen species (ROS) increased after an 8h exposure to MPP+. Our results indicate that the increase in [Mg2+]i inhibited cellular ROS generation and maintained ATP production, which resulted in the protection from MPP+ toxicity.

Hydrophobic Gating of Ion Permeation in Magnesium Channel CorA.

Ion channels catalyze ionic permeation across membranes via water-filled pores. To understand how changes in intracellular magnesium concentration regulate the influx of Mg2+ into cells, we examine early events in the relaxation of Mg2+ channel CorA toward its open state using massively-repeated molecular dynamics simulations conducted either with or without regulatory ions. The pore of CorA contains a 2-nm-long hydrophobic bottleneck which remained dehydrated in most simulations. However, rapid hydration or “wetting” events concurrent with small-amplitude fluctuations in pore diameter occurred spontaneously and reversibly. In the absence of regulatory ions, wetting transitions are more likely and include a wet state that is significantly more stable and more hydrated. The free energy profile for Mg2+ permeation presents a barrier whose magnitude is anticorrelated to pore diameter and the extent of hydrophobic hydration. These findings support an allosteric mechanism whereby wetting of a hydrophobic gate couples changes in intracellular magnesium concentration to the onset of ionic conduction.

Mitochondrial magnesium to the rescue.

A paper recently published in BBA Molecular Cell Research by Cui Y. et al.[1] captured our attention. It reports the identification of a novel yeast mitochondrial Mg2+ transporter, with exciting implications for a better characterization of mitochondrial magnesium homeostasis and its role in cellular (patho)physiology.The idea that mitochondria may serve as functional intracellular magnesium stores, from or to where it can be mobilized in response to (patho)physiological stimuli, is not unprecedented. [...]

Transcription closed and open complex dynamics studies reveal balance between genetic determinants and co-factors

In E. coli, promoter closed and open complexes are key steps in transcription initiation, where magnesium-dependent RNA polymerase catalyzes RNA synthesis. However, the exact mechanism of initiation remains to be fully elucidated. Here, using single mRNA detection and dual reporter studies, we show that increased intracellular magnesium concentration affects Plac initiation complex formation resulting in a highly dynamic process over the cell growth phases. Mg2+ regulates transcription transition, which modulates bimodality of mRNA distribution in the exponential phase. We reveal that Mg2+ regulates the size and frequency of the mRNA burst by changing the open complex duration. Moreover, increasing magnesium concentration leads to higher intrinsic and extrinsic noise in the exponential phase. RNAP-Mg2+ interaction simulation reveals critical movements creating a shorter contact distance between aspartic acid residues and Nucleotide Triphosphate residues and increasing electrostatic charges in the active site. Our findings provide unique biophysical insights into the balanced mechanism of genetic determinants and magnesium ion in transcription initiation regulation during cell growth.

Is there a Role of Intracellular Magnesium in Prevention of Heart Failure?

Heart failure, characterized by the reduction in left and /or right ventricular function, is the most common cause of mortality and morbidity in almost around the world. This syndrome is induced by β1-adrenergic receptor (β1-AR) desensitization, which in turn is caused by the reduction in cellular cAMP concentration. Cellular cAMP concentration is modulated by adenylyl cyclases (ACs), a family of enzymes that are strongly activated by intracellular magnesium and circulating levels of the stress-related hormones. Short-term activation of β1-AR signalling pathway by increased levels of these hormones induces an increase in intracellular Mg2+ and cAMP concentrations, which improves cardiac function. Nevertheless, long-term activation of β1-AR signalling pathway by elevated levels of these hormones reduces intracellular Mg2+ and cAMP levels, which deteriorates cardiac function. Intracellular cAMP signalling has a circadian rhythm (CR) in mammals, and CR may modulate diverse phenomena. The loss of CR may per se be a cause of severe diseases. Magnesium can regulate intracellular cAMP production and through this may modulate the CR. Here we propose that longterm activation of β1-AR signalling pathway, and /or the use of diuretics, can induce a progressive reduction of intracellular of magnesium and a subsequent gradual reduction of intracellular cAMP levels. This in turn can cause β1-AR desensitization, the loss of CR of the hormones related with HF, and, finally, HF development. We suggest the therapeutic implications of this mechanism in the prevention of HF.

Magnesium and type 2 diabetes.

Type 2 diabetes is frequently associated with both extracellular and intracellular magnesium (Mg) deficits. A chronic latent Mg deficit or an overt clinical hypomagnesemia is common in patients with type 2 diabetes, especially in those with poorly controlled glycemic profiles. Insulin and glucose are important regulators of Mg metabolism. Intracellular Mg plays a key role in regulating insulin action, insulin-mediated-glucose-uptake and vascular tone. Reduced intracellular Mg concentrations result in a defective tyrosine-kinase activity, postreceptorial impairment in insulin action and worsening of insulin resistance in diabetic patients. A low Mg intake and an increased Mg urinary loss appear the most important mechanisms that may favor Mg depletion in patients with type 2 diabetes. Low dietary Mg intake has been related to the development of type 2 diabetes and metabolic syndrome. Benefits of Mg supplementation on metabolic profiles in diabetic patients have been found in most, but not all clinical studies and larger prospective studies are needed to support the potential role of dietary Mg supplementation as a possible public health strategy in diabetes risk. The aim of this review is to revise current evidence on the mechanisms of Mg deficiency in diabetes and on the possible role of Mg supplementation in the prevention and management of the disease.

Small for Gestational Age and Magnesium: Intrauterine magnesium deficiency may induce metabolic syndrome in later life.

Magnesium deficiency during pregnancy as a result of insufficient or low intake of magnesium is common in developing and developed countries. Previous reports have shown that intracellular magnesium of cord blood platelets is lower among small for gestational age (SGA) groups than that of appropriate for gestational age (AGA) groups, suggesting that intrauterine magnesium deficiency may result in SGA. Additionally, the risk of adult-onset diseases such as insulin resistance syndrome is greater among children whose mothers were malnourished during pregnancy, and who consequently had a low birth weight. In a number of animal models, poor nutrition during pregnancy leads to offspring that exhibit pathophysiological changes similar to human diseases. The offspring of pregnant rats fed a magensium restricted diet have developed hypermethylation in the hepatic 11β-hydroxysteroid dehydrogenase-2 promoter. These findings indicate that maternal magnesium deficiencies during pregnancy influence regulation of non-imprinted genes by altering the epigenetic regulation of gene expression, thereby inducing different metabolic phenotypes. Magnesium deficiency during pregnancy may be responsible for not only maternal and fetal nutritional problems, but also lifelong consequences that affect the offspring throughout their life. Epidemiological, clinical, and basic research on the effects of magnesium deficiency now indicates underlying mechanisms, especially epigenetic processes.

Pharmacological Treatment may Impair Mineral Status in Blood

Hematological and biochemical blood parameters are rather stable in healthy subjects. However, there are many factors that can influence mineral status in blood, including diseases, diet, and drugs. It has been found that several medicines can alter both mineral concentrations and other mineral-status-related parameters in blood. In experimental and human studies, it has been shown that hypotension therapy disturbs zinc status in the body [1]. Some of our results suggest that indapamide and amlodipine treatment can decrease zinc concentration in serum and erythrocytes. Moreover, the decrease in zinc is accompanied by an increase in glucose serum levels [2]. In our experimental study, we observed that treatment with indapamide and amlodipine was associated with increased red blood cell counts and hematocrit values in the serum of spontaneously hypertensive rats [3]. In patients, high hematocrit could reflect the increase in red blood cell mass resulting from the reduction in plasma volume due to treatment with thiazide-type diuretics. Long-term therapy with captopril and enalapril may lead to zinc depletion in erythrocytes and monocytes. Preliminary data suggest that indapamide can cause a slight elevation in blood calcium levels. Several results indicate that loop diuretics, especially furosemide, reduce serum calcium and magnesium levels. It has also been observed that beta-blockers may induce hypocalcemia and hypomagnesemia [4]. Antiepileptic therapy with valproic acid may cause abnormalities in serum copper concentration. Some authors have found that therapy with valproic acid can diminish copper levels in erythrocytes and serum in epileptic patients [5,6]. Nonsteroidal anti-inflammatory drugs, when taken regularly, may cause bleeding from the gastrointestinal tract and iron loss with the blood. The use of aspirin and other medicines belonging to this group of drugs may therefore increase the risk of iron deficiency, which can be identified as a low hemoglobin and serum ferritin concentration [4,7]. In patients with digoxin therapy, a decrease in intracellular magnesium levels and a relatively low level of magnesium in serum were observed [8]. The long-term use of corticosteroids, cisplatin, cyclosporine is also associated with a depletion of magnesium in the serum and an increase in the risk of hypomagnesemia [4,9]. It is known that dietary restriction may impair mineral status; however, pharmacological treatment of obesity may also alter the concentration of minerals in the blood. In our clinical study, we found that 12 weeks of sibutramine therapy decreases zinc and increases magnesium concentrations in the serum, leading to mineral imbalances in obese women [10]. Oral contraceptives (OCs) are among the most commonly used drugs in developed countries. One of the side effects of this group of drugs is their influence on the mineral status in women. In several studies, it was observed that the use of oral contraceptives is associated with decreased zinc, magnesium, and selenium serum concentrations, and with increased copper levels in serum. It has also been found that oral contraceptives can increase ferritin and iron levels, TIBC, and mean corpuscular hemoglobin in serum, while decreasing red blood cells and hematocrit in whole blood in women. The results of human studies suggest that the effect of OCs on mineral status can vary with the form, dose, concomitant agents, and patient characteristics [4,11]. The mechanisms behind the observed interactions between drugs and minerals cannot always be explained. Some may be associated with changes in the excretion of minerals in the urine. Drugs may also influence the absorption and/or distribution of minerals in the body [4 ]. In conclusion, many drugs influence mineral status in the blood. Pharmacological treatment may require the monitoring of mineral concentrations in blood. Moreover, the interpretation of the results of morphological and biochemical analyses in blood requires a consideration of the drugs being used by the patient.

X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection, and neoplasia disease: a combined immune deficiency with magnesium defect.

To describe the role of the magnesium transporter 1 (MAGT1) in the pathogenesis of 'X-linked immunodeficiency with magnesium defect, Epstein-Barr virus (EBV) infection, and neoplasia' (XMEN) disease and its clinical implications. The magnesium transporter protein MAGT1 participates in the intracellular magnesium ion (Mg) homeostasis and facilitates a transient Mg influx induced by the activation of the T-cell receptor. Loss-of-function mutations in MAGT1 cause an immunodeficiency named 'XMEN syndrome', characterized by CD4 lymphopenia, chronic EBV infection, and EBV-related lymphoproliferative disorders. Patients with XMEN disease have impaired T-cell activation and decreased cytolytic function of natural killer (NK) and CD8 T cells because of decreased expression of the NK stimulatory receptor 'natural-killer group 2, member D' (NKG2D). Patients may have defective specific antibody responses secondary to T cell dysfunction, but B cells have not been shown to be directly affected by mutations in MAGT1. XMEN disease has revealed a novel role for free intracellular magnesium in the immune system. Further understanding of the MAGT1 signaling pathway may lead to new diagnostic and therapeutic approaches.

Functional study of NIPA2 mutations identified from the patients with childhood absence epilepsy.

Recently many genetic mutations that are associated with epilepsy have been identified. The protein NIPA2 (non-imprinted in Prader-Willi/Angelman syndrome region protein 2) is a highly selective magnesium transporter encoded by the gene NIPA2 in which we have found three mutations (p.I178F, p.N244S and p.N334_E335insD) within a population of patients with childhood absence epilepsy (CAE). In this study, immunofluorescence labeling, inductively coupled plasma-optical emission spectroscopy (ICP-OES), MTT metabolic rate detection and computational modeling were utilized to elucidate how these mutations result in CAE. We found in cultured neurons that NIPA2 (wild-type) proteins were localized to the cell periphery, whereas mutant proteins were not effectively trafficked to the cell membrane. Furthermore, we found a decrease in intracellular magnesium concentration in the neurons transfected with mutant NIPA2, but no effect on the survival of neurons. To understand how low intracellular magnesium resulted in hyperexcitability, we built and analyzed a computational model to simulate the effects of mutations. The model suggested that lower intracellular magnesium concentration enhanced synaptic N-methyl-D-aspartate receptor (NMDAR) currents. This study primarily reveals that a selective magnesium transporter NIPA2 may play a role in the pathogenesis of CAE.

Mg2+‐Dependent Modulation of BKCa Channels by Genistein in Rat Arteriolar Smooth Muscle Cells

Genistein, a protein tyrosine kinase (PTK) inhibitor, regulates ion channel activities. However, the mechanism of action of genistein on large-conductance calcium-activated potassium (BK(Ca)) channels is unclear. This study aimed to investigate whether the mechanism of Mg(2+)-dependent modulation of BK(Ca) channel activity in vascular smooth muscle cells involved inhibition of phosphorylation by genistein or direct interaction between genistein and BK(Ca) channels. The whole-cell and inside-out patch-clamp techniques were used to measure BK(Ca) currents and the effects of genistein on BK(Ca) channel activities in rat mesenteric arteriolar smooth muscle cells. We found that the effects of genistein on BK(Ca) currents were Mg(2+)-dependent. Genistein (50 μM) inhibited BK(Ca) currents if the intracellular free magnesium concentration ([Mg(2+)]i) was 2 μM or 20 μM, but amplified BK(Ca) currents if [Mg(2+)]i was 200 μM or 2000 μM. The inhibitory effect of genistein on BK(Ca) currents was reversed by the protein tyrosine phosphatase inhibitor sodium orthovanadate (0.5 mM). Daidzein (50 μM), an inactive analogue of genistein, also amplified BK(Ca) currents, and its amplification was insensitive to orthovanadate. Another PTK inhibitor, tyrphostin 23 (50 μM), reduced the open probability of BK(Ca) channels. This inhibitory effect was weaker at 200 μM [Mg(2+)]i than at 2 μM [Mg(2+) ]i, and was countered by orthovanadate. Our results suggest that genistein amplifies BK(Ca) currents at a high [Mg(2+)]i, but inhibits BK(Ca) currents at a low [Mg(2+)]i. The mechanism of this biphasic effects involves PTK-independent amplification and [Mg(2+)]i -PTK-dependent inhibition.