Role of alternative splicing in generating isoform diversity among plasma membrane calcium pumps

Magnesium enhances aurintricarboxylic acid's inhibitory action on the plasma membrane Ca2+-ATPase

Our research aimed to elucidate the mechanism by which aurintricarboxylic acid (ATA) inhibits plasma membrane Ca2+-ATPase (PMCA), a crucial enzyme responsible for calcium transport. Given the pivotal role of PMCA in cellular calcium homeostasis, understanding how it is inhibited by ATA holds significant implications for potentially regulating physiopathological cellular processes in which this pump is involved. Our experimental findings revealed that ATA employs multiple modes of action to inhibit PMCA activity, which are influenced by ATP but also by the presence of calcium and magnesium ions. Specifically, magnesium appears to enhance this inhibitory effect. Our experimental and in-silico results suggest that, unlike those reported in other proteins, ATA complexed with magnesium (ATA·Mg) is the molecule that inhibits PMCA. In summary, our study presents a novel perspective and establishes a solid foundation for future research efforts aimed at the development of new pharmacological molecules both for PMCA and other proteins.

Bile acids modified by the intestinal microbiota promote colorectal cancer growth by suppressing CD8+ T cell effector functions

Concentrations of the secondary bile acid, deoxycholic acid (DCA), are aberrantly elevated in colorectal cancer (CRC) patients, but the consequences remain poorly understood. Here, we screened a library of gut microbiota-derived metabolites and identified DCA as a negative regulator for CD8+ T cell effector function. Mechanistically, DCA suppressed CD8+ T cell responses by targeting plasma membrane Ca2+ ATPase (PMCA) to inhibit Ca2+-nuclear factor of activated T cells (NFAT)2 signaling. In CRC patients, CD8+ T cell effector function negatively correlated with both DCA concentration and expression of a bacterial DCA biosynthetic gene. Bacteria harboring DCA biosynthetic genes suppressed CD8+ T cells effector function and promoted tumor growth in mice. This effect was abolished by disrupting bile acid metabolism via bile acid chelation, genetic ablation of bacterial DCA biosynthetic pathway, or specific bacteriophage. Our study demonstrated causation between microbial DCA metabolism and anti-tumor CD8+ T cell response in CRC, suggesting potential directions for anti-tumor therapy.

Structural characterization and calcium absorption-promoting effect of sucrose-calcium chelate in Caco-2 monolayer cells and mice

Sucrose emerges as a chelating agent to form a stable sucrose-metal-ion chelate that can potentially improve metal-ion absorption. This study aimed to analyze the structure of sucrose-calcium chelate and its potential to promote calcium absorption in both Caco-2 monolayer cells and mice. The characterization results showed that calcium ions mainly chelated with hydroxyl groups in sucrose to produce sucrose-calcium chelate, altering the crystal structure of sucrose (forming polymer particles) and improving its thermal stability. Sucrose-calcium chelate dose dependently increased the amount of calcium uptake, retention, and transport in the Caco-2 monolayer cell model. Compared to CaCl2 , there was a significant improvement in the proportion of absorbed calcium utilized for transport but not retention (93.13 ± 1.75% vs. 67.67 ± 7.55%). Further treatment of calcium channel inhibitors demonstrated the active transport of sucrose-calcium chelate through Cav1.3. Cellular thermal shift assay and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assays indicated that the ability of sucrose-calcium chelate to promote calcium transport was attributed to its superior ability to bind with PMCA1b, a calcium transporter located on the basement membrane, and stimulate its gene expression compared to CaCl2 . Pharmacokinetic analysis of mice confirmed the calcium absorption-promoting effect of sucrose-calcium chelate, as evident by the higher serum calcium level (44.12 ± 1.90 mg/L vs. 37.42 ± 1.88 mmol/L) and intestinal PMCA1b gene expression than CaCl2 . These findings offer a new understanding of how sucrose-calcium chelate enhances intestinal calcium absorption and could be used as an ingredient in functional foods to treat calcium deficiency. PRACTICAL APPLICATION: The development of high-quality calcium supplements is crucial for addressing the various adverse symptoms associated with calcium deficiency. This study aimed to prepare a sucrose-calcium chelate and analyze its structure, as well as its potential to enhance calcium absorption in Caco-2 monolayer cells and mice. The results demonstrated that the sucrose-calcium chelate effectively promoted calcium absorption. Notably, its ability to enhance calcium transport was linked to its strong binding with PMCA1b, a calcium transporter located on the basement membrane, and its capacity to stimulate PMCA1b gene expression. These findings contribute to a deeper understanding of how the sucrose-calcium chelate enhances intestinal calcium absorption and suggest its potential use as an ingredient in functional foods for treating calcium deficiency.

Photo-Controlled Calcium Overload from Endogenous Sources for Tumor Therapy

Designing reactive calcium-based nanogenerators to produce excess calcium ions (Ca2+ ) in tumor cells is an attractive tumor treatment method. However, nanogenerators that introduce exogenous Ca2+ are either overactive incapable of on-demand release, or excessively inert incapable of an overload of calcium rapidly. Herein, inspired by inherently diverse Ca2+ -regulating channels, a photo-controlled Ca2+ nanomodulator that fully utilizes endogenous Ca2+ from dual sources was designed to achieve Ca2+ overload in tumor cells. Specifically, mesoporous silica nanoparticles were used to co-load bifunctional indocyanine green as a photodynamic/photothermal agent and a thermal-sensitive nitric oxide (NO) donor (BNN-6). Thereafter, they were coated with hyaluronic acid, which served as a tumor cell-targeting unit and a gatekeeper. Under near-infrared light irradiation, the Ca2+ nanomodulator can generate reactive oxygen species that stimulate the transient receptor potential ankyrin subtype 1 channel to realize Ca2+ influx from extracellular environments. Simultaneously, the converted heat can induce BNN-6 decomposition to generate NO, which would open the ryanodine receptor channel in the endoplasmic reticulum and allow stored Ca2+ to leak. Both in vitro and in vivo experiments demonstrated that the combination of photo-controlled Ca2+ influx and release could enable Ca2+ overload in the cytoplasm and efficiently inhibit tumor growth.

Intracellular calcium links milk stasis to lysosome-dependent cell death during early mammary gland involution

Involution of the mammary gland after lactation is a dramatic example of coordinated cell death. Weaning causes distension of the alveolar structures due to the accumulation of milk, which, in turn, activates STAT3 and initiates a caspase-independent but lysosome-dependent cell death (LDCD) pathway. Although the importance of STAT3 and LDCD in early mammary involution is well established, it has not been entirely clear how milk stasis activates STAT3. In this report, we demonstrate that protein levels of the PMCA2 calcium pump are significantly downregulated within 2-4 h of experimental milk stasis. Reductions in PMCA2 expression correlate with an increase in cytoplasmic calcium in vivo as measured by multiphoton intravital imaging of GCaMP6f fluorescence. These events occur concomitant with the appearance of nuclear pSTAT3 expression but prior to significant activation of LDCD or its previously implicated mediators such as LIF, IL6, and TGFβ3, all of which appear to be upregulated by increased intracellular calcium. We further demonstrate that increased intracellular calcium activates STAT3 by inducing degradation of its negative regulator, SOCS3. We also observed that milk stasis, loss of PMCA2 expression and increased intracellular calcium levels activate TFEB, an important regulator of lysosome biogenesis through a process involving inhibition of CDK4/6 and cell cycle progression. In summary, these data suggest that intracellular calcium serves as an important proximal biochemical signal linking milk stasis to STAT3 activation, increased lysosomal biogenesis, and lysosome-mediated cell death.

Tubulin Regulates Plasma Membrane Ca2+-ATPase Activity in a Lipid Environment-dependent Manner

Ca2+ plays a crucial role in cell signaling, cytosolic Ca2+ can change up to 10,000-fold in concentration due to the action of Ca2+-ATPases, including PMCA, SERCA and SCR. The regulation and balance of these enzymes are essential to maintain cytosolic Ca2+ homeostasis. Our laboratory has discovered a novel PMCA regulatory system, involving acetylated tubulin alone or in combination with membrane lipids. This regulation controls cytosolic Ca2+ levels and influences cellular properties such as erythrocyte rheology. This review summarizes the findings on the regulatory mechanism of PMCA activity by acetylated tubulin in combination with lipids. The combination of tubulin cytoskeleton and membrane lipids suggests a novel regulatory system for PMCA, which consequently affects cytosolic Ca2+ content, depending on cytoskeletal and plasma membrane dynamics. Understanding the interaction between acetylated tubulin, lipids and PMCA activity provides new insights into Ca2+ signaling and cell function. Further research may shed light on potential therapeutic targets for diseases related to Ca2+ dysregulation. This discovery contributes to a broader understanding of cellular processes and offers opportunities to develop innovative approaches to treat Ca2+-related disorders. By elucidating the complex regulatory mechanisms of Ca2+ homeostasis, we advance our understanding of cell biology and its implications for human health.

Monomeric α-synuclein activates the plasma membrane calcium pump

Alpha-synuclein (aSN) is a membrane-associated and intrinsically disordered protein, well known for pathological aggregation in neurodegeneration. However, the physiological function of aSN is disputed. Pull-down experiments have pointed to plasma membrane Ca2+ -ATPase (PMCA) as a potential interaction partner. From proximity ligation assays, we find that aSN and PMCA colocalize at neuronal synapses, and we show that calcium expulsion is activated by aSN and PMCA. We further show that soluble, monomeric aSN activates PMCA at par with calmodulin, but independent of the autoinhibitory domain of PMCA, and highly dependent on acidic phospholipids and membrane-anchoring properties of aSN. On PMCA, the key site is mapped to the acidic lipid-binding site, located within a disordered PMCA-specific loop connecting the cytosolic A domain and transmembrane segment 3. Our studies point toward a novel physiological role of monomeric aSN as a stimulator of calcium clearance in neurons through activation of PMCA.

The function of alternative splicing in the proteome: rewiring protein interactomes to put old functions into new contexts

Alternative splicing affects more than 95% of multi-exon genes in the human genome. These changes affect the proteome in a myriad of ways. Here, we review our understanding of the breadth of these changes from their effect on protein structure to their influence on interactions. These changes encompass effects on nucleic acid binding in the nucleus to protein-carbohydrate interactions in the extracellular milieu, altering interactions involving all major classes of biological molecules. Protein isoforms have profound influences on cellular and tissue physiology, for example, by shaping neuronal connections, enhancing insulin secretion by pancreatic beta cells and allowing for alternative viral defense strategies in stem cells. More broadly, alternative splicing enables repurposing proteins from one context to another and thereby contributes to both the evolution of new traits as well as the creation of disease-specific interactomes that drive pathological phenotypes. In this Review, we highlight this universal character of alternative splicing as a central regulator of protein function with implications for almost every biological process.

Intracellular Calcium links Milk Stasis to Lysosome Dependent Cell Death by Activating a TGFβ3/TFEB/STAT3 Pathway Early during Mammary Gland Involution

Involution of the mammary gland after lactation is a dramatic example of coordinated cell death. Weaning causes distension of the alveolar structures due to the accumulation of milk, which, in turn, activates STAT3 and initiates a caspase-independent but lysosome-dependent cell death (LDCD) pathway. Although the importance of STAT3 and LDCD in early mammary involution is well established, it has not been entirely clear how milk stasis activates STAT3. In this report, we demonstrate that protein levels of the PMCA2 calcium pump are significantly downregulated within 2-4 hours of experimental milk stasis. Reductions in PMCA2 expression correlate with an increase in cytoplasmic calcium in vivo as measured by multiphoton intravital imaging of GCaMP6f fluorescence. These events occur concomitant with the appearance of nuclear pSTAT3 expression but prior to significant activation of LDCD or its previously implicated mediators such as LIF, IL6 and TGFβ3, all of which appear to be upregulated by increased intracellular calcium. We also observed that milk stasis, loss of PMCA2 expression and increased intracellular calcium levels activate TFEB, an important regulator of lysosome biogenesis. This is the result of increased TGFβ signaling and inhibition of cell cycle progression. Finally, we demonstrate that increased intracellular calcium activates STAT3 by inducing degradation of its negative regulator, SOCS3, a process which also appears to be mediated by TGFβ signaling. In summary, these data suggest that intracellular calcium serves as an important proximal biochemical signal linking milk stasis to STAT3 activation, increased lysosomal biogenesis, and lysosome-mediated cell death.

Genetic variations in human ATP2B4 gene alter Plasmodium falciparum in vitro growth in RBCs from Gambian adults

BACKGROUND

Polymorphisms in ATP2B4 coding for PMCA4b, the primary regulator of erythrocyte calcium concentration, have been shown by GWAS and cross-sectional studies to protect against severe malaria but the mechanism remains unknown.

METHODS

Using a recall-by-genotype design, we investigated the impact of a common haplotype variant in ATP2B4 using in vitro assays that model erythrocyte stage malaria pathogenesis. Ninety-six donors representing homozygote (carriers of the minor allele, C/C), heterozygote (T/C) and wildtype (T/T) carriers of the tagging SNP rs1541252 were selected from a cohort of over 12,000 participants in the Keneba Biobank.

RESULTS

Red blood cells (RBCs) from homozygotes showed reduced PMCA4b protein expression (mean fluorescence intensities (MFI = 2428 ± 124, 3544 ± 159 and 4261 ± 283], for homozygotes, heterozygotes and wildtypes respectively, p < 0.0001) and slower rates of calcium expulsion (calcium t_½ ± SD = 4.7 ± 0.5, 1.8 ± 0.3 and 1.9 ± 0.4 min, p < 0.0001). Growth of a Plasmodium falciparum laboratory strain (FCR3) and two Gambian field isolates was decreased in RBCs from homozygotes compared to heterozygotes and wildtypes (p < 0.01). Genotype group did not affect parasite adhesion in vitro or var-gene expression in malaria-infected RBCs. Parasite growth was inhibited by a known inhibitor of PMCA4b, aurintricarboxylic acid (IC₅₀ = 122uM CI: 110-134) confirming its sensitivity to calcium channel blockade.

CONCLUSION

The data support the hypothesis that this ATP2B4 genotype, common in The Gambia and other malaria-endemic areas, protects against severe malaria through the suppression of parasitaemia during an infection. Reduction in parasite density plays a pivotal role in disease outcome by minimizing all aspects of malaria pathogenesis. Follow up studies are needed to further elucidate the mechanism of protection and to determine if this ATP2B4 genotype carries a fitness cost or increases susceptibility to other human disease.

The distinguishing electrical properties of cancer cells

In recent decades, medical research has been primarily focused on the inherited aspect of cancers, despite the reality that only 5-10% of tumours discovered are derived from genetic causes. Cancer is a broad term, and therefore it is inaccurate to address it as a purely genetic disease. Understanding cancer cells' behaviour is the first step in countering them. Behind the scenes, there is a complicated network of environmental factors, DNA errors, metabolic shifts, and electrostatic alterations that build over time and lead to the illness's development. This latter aspect has been analyzed in previous studies, but how the different electrical changes integrate and affect each other is rarely examined. Every cell in the human body possesses electrical properties that are essential for proper behaviour both within and outside of the cell itself. It is not yet clear whether these changes correlate with cell mutation in cancer cells, or only with their subsequent development. Either way, these aspects merit further investigation, especially with regards to their causes and consequences. Trying to block changes at various levels of occurrence or assisting in their prevention could be the key to stopping cells from becoming cancerous. Therefore, a comprehensive understanding of the current knowledge regarding the electrical landscape of cells is much needed. We review four essential electrical characteristics of cells, providing a deep understanding of the electrostatic changes in cancer cells compared to their normal counterparts. In particular, we provide an overview of intracellular and extracellular pH modifications, differences in ionic concentrations in the cytoplasm, transmembrane potential variations, and changes within mitochondria. New therapies targeting or exploiting the electrical properties of cells are developed and tested every year, such as pH-dependent carriers and tumour-treating fields. A brief section regarding the state-of-the-art of these therapies can be found at the end of this review. Finally, we highlight how these alterations integrate and potentially yield indications of cells' malignancy or metastatic index.

The ataxia-linked E1081Q mutation affects the sub-plasma membrane Ca2+-microdomains by tuning PMCA3 activity

Calcium concentration must be finely tuned in all eukaryotic cells to ensure the correct performance of its signalling function. Neuronal activity is exquisitely dependent on the control of Ca²⁺ homeostasis: its alterations ultimately play a pivotal role in the origin and progression of many neurodegenerative processes. A complex toolkit of Ca²⁺ pumps and exchangers maintains the fluctuation of cytosolic Ca²⁺ concentration within the appropriate threshold. Two ubiquitous (isoforms 1 and 4) and two neuronally enriched (isoforms 2 and 3) of the plasma membrane Ca²⁺ATPase (PMCA pump) selectively regulate cytosolic Ca²⁺ transients by shaping the sub-plasma membrane (PM) microdomains. In humans, genetic mutations in ATP2B1, ATP2B2 and ATP2B3 gene have been linked with hearing loss, cerebellar ataxia and global neurodevelopmental delay: all of them were found to impair pump activity. Here we report three additional mutations in ATP2B3 gene corresponding to E1081Q, R1133Q and R696H amino acids substitution, respectively. Among them, the novel missense mutation (E1081Q) immediately upstream the C-terminal calmodulin-binding domain (CaM-BD) of the PMCA3 protein was present in two patients originating from two distinct families. Our biochemical and molecular studies on PMCA3 E1081Q mutant have revealed a splicing variant-dependent effect of the mutation in shaping the sub-PM [Ca²⁺]. The E1081Q substitution in the full-length b variant abolished the capacity of the pump to reduce [Ca²⁺] in the sub-PM microdomain (in line with the previously described ataxia-related PMCA mutations negatively affecting Ca²⁺ pumping activity), while, surprisingly, its introduction in the truncated a variant selectively increased Ca²⁺ extrusion activity in the sub-PM Ca²⁺ microdomains. These results highlight the importance to set a precise threshold of [Ca²⁺] by fine-tuning the sub-PM microdomains and the different contribution of the PMCA splice variants in this regulation.

Plasma Membrane Ca2+ ATPase Activity Enables Sustained Store-operated Ca2+ Entry in the Absence of a Bulk Cytosolic Ca2+ Rise

In many cell types, the rise in cytosolic Ca2+ due to opening of Ca2+ release-activated Ca2+ (CRAC) channels drives a plethora of responses, including secretion, motility, energy production, and gene expression. The amplitude and time course of the cytosolic Ca2+ rise is shaped by the rates of Ca2+ entry into and removal from the cytosol. However, an extended bulk Ca2+ rise is toxic to cells. Here, we show that the plasma membrane Ca2+ ATPase (PMCA) pump plays a major role in preventing a prolonged cytosolic Ca2+ signal following CRAC channel activation. Ca2+ entry through CRAC channels leads to a sustained sub-plasmalemmal Ca2+ rise but bulk Ca2+ is kept low by the activity of PMCA4b. Despite the low cytosolic Ca2+, membrane permeability to Ca2+ is still elevated and Ca2+ continues to enter through CRAC channels. Ca2+-dependent NFAT activation, driven by Ca2+ nanodomains near the open channels, is maintained despite the return of bulk Ca2+ to near pre-stimulation levels. Our data reveal a central role for PMCA4b in determining the pattern of a functional Ca2+ signal and in sharpening local Ca2+ gradients near CRAC channels, whilst protecting cells from a toxic Ca2+ overload.

Exosomal MiR-4261 mediates calcium overload in RBCs by downregulating the expression of ATP2B4 in multiple myeloma

Background

Hypercalcemia induced by multiple myeloma (MM) affects the biological functions of excitable and non-excitable cells. However, red blood cells (RBCs) regulatory effect on calcium in hypercalcemia is still not fully understood.

Methods

A total of 113 patients with MM osteolytic lesions were studied retrospectively. Flow cytometry and atomic absorption spectroscopy were used to detect calcium content. Immunofluorescence and Western blotting were used to investigate protein expression. GEO and miRNA databases were used to screen miRNAs. Exosomal miR-4261 migration was investigated by Transwell assay. Dual-luciferase assays confirmed the targeting relationship between miR-4261 and ATP2B4. An RBC oxidative stress model was constructed, and Omega-Agatoxin IVA was used to study the role of plasma membrane Ca²⁺-ATPase 4 (PMCA4) in RBCs.

Results

The results showed that MM RBCs had calcium overload, and serum calcium levels increased as the number of RBCs decreased. The expression of PMCA4 in MM RBCs was significantly lower than in normal RBCs. The exosomal miR-4261 produced by MM cells could be transferred to RBCs to downregulate the expression of ATP2B4.

Conclusions

Studies have confirmed that RBCs experience calcium overload in MM with osteolytic lesions, which is related to the downregulation of ATP2B4 by MM exosomal miR-4261.

Caloxin-derived peptides for the inhibition of plasma membrane calcium ATPases

Plasma membrane calcium ATPases (PMCAs) are a family of transmembrane proteins responsible for the extrusion of cytosolic Ca²⁺ to the extracellular milieu. They are important players of the calcium homeostasis possibly implicated in some important diseases. The reference inhibitors of PMCA extruding activity are on one hand ortho-vanadate (IC₅₀ in the 30 mM range), and on the other a series of 12- to 20-mer peptides named caloxins (IC₅₀ in the 100 µM scale). As for all integral membrane proteins, biochemistry and pharmacology are difficult to study on isolated and/or purified proteins. Using a series of reference blockers, we assessed a pharmacological window with which we could study the functionality of PMCAs in living cells. Using this system, we screened for alternative versions of caloxins, aiming at shortening the peptide backbone, introducing non-natural amino acids, and overall trying to get a glimpse at the structure-activity relationship between those new peptides and the protein in a cellular context. We describe a short series of equipotent 5-residue long analogues with IC₅₀ in the low µM range.

Treatment with specific and pan-plasma membrane calcium ATPase (PMCA) inhibitors reduces malaria parasite growth in vitro and in vivo

Background

Rapid emergence of Plasmodium resistance to anti-malarial drug mainstays has driven a continual effort to discover novel drugs that target different biochemical pathway (s) during infection. Plasma membrane Calcium + 2 ATPase (PMCA4), a novel plasma membrane protein that regulates Calcium levels in various cells, namely red blood cell (RBC), endothelial cell and platelets, represents a new biochemical pathway that may interfere with susceptibility to malaria and/or severe malaria.

Methods

This study identified several pharmacological inhibitors of PMCA4, namely ATA and Resveratrol, and tested for their anti-malarial activities in vitro and in vivo using the Plasmodium falciparum 3D7 strain, the Plasmodium berghei ANKA strain, and Plasmodium yoelii 17XL strain as model.

Results

In vitro propagation of P. falciparum 3D7 strain in the presence of a wide concentration range of the inhibitors revealed that the parasite growth was inhibited in a dose-dependent manner, with IC₅₀s at 634 and 0.231 µM, respectively.

Results

The results confirmed that both compounds exhibit moderate to potent anti-malarial activities with the strongest parasite growth inhibition shown by resveratrol at 0.231 µM. In vivo models using P. berghei ANKA for experimental cerebral malaria and P. yoelii 17XL for the effect on parasite growth, showed that the highest dose of ATA, 30 mg/kg BW, increased survival of the mice. Likewise, resveratrol inhibited the parasite growth following 4 days intraperitoneal injection at the dose of 100 mg/kg BW.

Conclusion

The findings indicate that the PMCA4 of the human host may be a potential target for novel anti-malarials, either as single drug or in combination with the currently available effective anti-malarials.

The PLEKHA7-PDZD11 complex regulates the localization of the calcium pump PMCA and calcium handling in cultured cells

The plasma membrane calcium ATPase (PMCA) extrudes calcium from the cytosol to the extracellular space to terminate calcium-dependent signaling. Although the distribution of PMCA is crucial for its function, the molecular mechanisms that regulate the localization of PMCA isoforms are not well understood. PLEKHA7 is implicated by genetic studies in hypertension and the regulation of calcium handling. PLEKHA7 recruits the small adapter protein PDZD11 to adherens junctions, and together they control the trafficking and localization of plasma membrane associated proteins, including the Menkes copper ATPase. Since PDZD11 binds to the C-terminal domain of b-isoforms of PMCA, PDZD11 and its interactor PLEKHA7 could control the localization and activity of PMCA. Here, we test this hypothesis using cultured cell model systems. We show using immunofluorescence microscopy and a surface biotinylation assay that KO of either PLEKHA7 or PDZD11 in mouse kidney collecting duct epithelial cells results in increased accumulation of endogenous PMCA at lateral cell–cell contacts and PDZ-dependent ectopic apical localization of exogenous PMCA4x/b isoform. In HeLa cells, coexpression of PDZD11 reduces membrane accumulation of overexpressed PMCA4x/b, and analysis of cytosolic calcium transients shows that PDZD11 counteracts calcium extrusion activity of overexpressed PMCA4x/b, but not PMCA4x/a, which lacks the PDZ-binding motif. Moreover, KO of PDZD11 in either endothelial (bEnd.3) or epithelial (mouse kidney collecting duct) cells increases the rate of calcium extrusion. Collectively, these results suggest that the PLEKHA7–PDZD11 complex modulates calcium homeostasis by regulating the localization of PMCA.

Early Developmental PMCA2b Expression Protects From Ketamine-Induced Apoptosis and GABA Impairments in Differentiating Hippocampal Progenitor Cells

PMCA2 is not expressed until the late embryonic state when the control of subtle Ca²⁺ fluxes becomes important for neuronal specialization. During this period, immature neurons are especially vulnerable to degenerative insults induced by the N-methyl-D-aspartate (NMDA) receptor blocker, ketamine. As H19-7 hippocampal progenitor cells isolated from E17 do not express the PMCA2 isoform, they constitute a valuable model for studying its role in neuronal development. In this study, we demonstrated that heterologous expression of PMCA2b enhanced the differentiation of H19-7 cells and protected from ketamine-induced death. PMCA2b did not affect resting [Ca²⁺]_c in the presence or absence of ketamine and had no effect on the rate of Ca²⁺ clearance following membrane depolarization in the presence of the drug. The upregulation of endogenous PMCA1 demonstrated in response to PMCA2b expression as well as ketamine-induced PMCA4 depletion were indifferent to the rate of Ca²⁺ clearance in the presence of ketamine. Yet, co-expression of PMCA4b and PMCA2b was able to partially restore Ca²⁺ extrusion diminished by ketamine. The profiling of NMDA receptor expression showed upregulation of the NMDAR1 subunit in PMCA2b-expressing cells and increased co-immunoprecipitation of both proteins following ketamine treatment. Further microarray screening demonstrated a significant influence of PMCA2b on GABA signaling in differentiating progenitor cells, manifested by the unique regulation of several genes key to the GABAergic transmission. The overall activity of glutamate decarboxylase remained unchanged, but Ca²⁺-induced GABA release was inhibited in the presence of ketamine. Interestingly, PMCA2b expression was able to reverse this effect. The mechanism of GABA secretion normalization in the presence of ketamine may involve PMCA2b-mediated inhibition of GABA transaminase, thus shifting GABA utilization from energetic purposes to neurosecretion. In this study, we show for the first time that developmentally controlled PMCA expression may dictate the pattern of differentiation of hippocampal progenitor cells. Moreover, the appearance of PMCA2 early in development has long-standing consequences for GABA metabolism with yet an unpredictable influence on GABAergic neurotransmission during later stages of brain maturation. In contrast, the presence of PMCA2b seems to be protective for differentiating progenitor cells from ketamine-induced apoptotic death.

Basal Vascular Smooth Muscle Cell Tone in eNOS Knockout Mice Can Be Reversed by Cyclic Stretch and Is Independent of Age

Introduction and Aims: Endothelial nitric oxide synthase (eNOS) knockout mice develop pronounced cardiovascular disease. In the present study, we describe the alterations in aortic physiology and biomechanics of eNOS knockout and C57Bl/6 control mice at 2–12 months of age, including a thorough physiological investigation of age and cyclic stretch-dependent VSMC contractility and aortic stiffness.

Methods and Results: Peripheral blood pressure and aortic pulse wave velocity were measured in vivo, and aortic biomechanical studies and isometric contractions were investigated ex vivo. Age-dependent progression of aortic stiffness, peripheral hypertension, and aortic contractility in eNOS knockout mice was absent, attenuated, or similar to C57Bl/6 control mice. Voltage-gated calcium channel (VGCC)-dependent calcium influx inversely affected isometric contraction and aortic stiffening by α₁-adrenergic stimulation in eNOS knockout mice. Baseline aortic stiffness was selectively reduced in eNOS knockout mice after ex vivo cyclic stretch exposure in an amplitude-dependent manner, which prompted us to investigate cyclic stretch dependent regulation of aortic contractility and stiffness. Aortic stiffness, both in baseline conditions and after activation of vascular smooth muscle cell (VSMC) contraction, was reduced with increasing cyclic stretch amplitude. This cyclic stretch dependency was attenuated with age, although aged eNOS knockout mice displayed better preservation of cyclic stretch-dependency compared to C57Bl/6 control mice. Store operated calcium entry-medicated aortic stiffening as induced by inhibiting sarcoplasmic reticulum calcium ATPase pumps with 10 µM CPA was most pronounced in the aorta of aged mice and at low cyclic stretch amplitude, but independent of eNOS. Basal aortic tonus and VSMC depolarization were highly dependent on eNOS, and were most pronounced at low cyclic stretch, with attenuation at increasing cyclic stretch amplitude.

Conclusion: eNOS knockout mice display attenuated progression of arterial disease as compared to C57Bl/6 control mice. Basal VSMC tone in eNOS knockout mice could be reduced by ex vivo exposure to cyclic stretch through stretch-dependent regulation of cytosolic calcium. Both baseline and active aortic stiffness were highly dependent on cyclic stretch regulation, which was more pronounced in young versus aged mice. Other mediators of VSMC contraction and calcium handling were dependent on cyclic stretch mechanotransduction, but independent of eNOS.

Structure, Function and Regulation of the Plasma Membrane Calcium Pump in Health and Disease

In this review, I summarize the present knowledge of the structural and functional properties of the mammalian plasma membrane calcium pump (PMCA). It is outlined how the cellular expression of the different spliced isoforms of the four genes are regulated under normal and pathological conditions.

Plasma Membrane Calcium ATPase-Neuroplastin Complexes Are Selectively Stabilized in GM1-Containing Lipid Rafts

The recent identification of plasma membrane (Ca²⁺)-ATPase (PMCA)-Neuroplastin (Np) complexes has renewed attention on cell regulation of cytosolic calcium extrusion, which is of particular relevance in neurons. Here, we tested the hypothesis that PMCA-Neuroplastin complexes exist in specific ganglioside-containing rafts, which could affect calcium homeostasis. We analyzed the abundance of all four PMCA paralogs (PMCA1-4) and Neuroplastin isoforms (Np65 and Np55) in lipid rafts and bulk membrane fractions from GM2/GD2 synthase-deficient mouse brains. In these fractions, we found altered distribution of Np65/Np55 and selected PMCA isoforms, namely PMCA1 and 2. Cell surface staining and confocal microscopy identified GM1 as the main complex ganglioside co-localizing with Neuroplastin in cultured hippocampal neurons. Furthermore, blocking GM1 with a specific antibody resulted in delayed calcium restoration of electrically evoked calcium transients in the soma of hippocampal neurons. The content and composition of all ganglioside species were unchanged in Neuroplastin-deficient mouse brains. Therefore, we conclude that altered composition or disorganization of ganglioside-containing rafts results in changed regulation of calcium signals in neurons. We propose that GM1 could be a key sphingolipid for ensuring proper location of the PMCA-Neuroplastin complexes into rafts in order to participate in the regulation of neuronal calcium homeostasis.

The regulation roles of Ca2+ in erythropoiesis: What have we learned?

Calcium (Ca²⁺) is an important second messenger molecule in the body, regulating cell cycle and fate. There is growing evidence that intracellular Ca²⁺ levels play functional roles in the total physiological process of erythroid differentiation, including the proliferation and differentiation of erythroid progenitor cells, terminal enucleation, and mature red blood cell aging and clearance. Moreover, recent research on the pathology of erythroid disorders has made great progress in the past decades, indicating that calcium ion hemostasis is closely related to ineffective erythropoiesis and increased sensitivity to stress factors. In this review, we summarized what is known about the functional roles of intracellular Ca²⁺ in erythropoiesis and erythrocyte-related diseases, with an emphasis on the regulation of the intracellular Ca²⁺ homeostasis during erythroid differentiation. An understanding of the regulation roles of Ca²⁺ homeostasis in erythroid differentiation will facilitate further studies and eventually molecular identification of the pathways involved in the pathological process of erythroid disorders, providing new therapeutic opportunities in erythrocyte-related disease.

Tri-ortho-cresyl phosphate exposure leads to low egg production and poor eggshell quality via disrupting follicular development and shell gland function in laying hens

Tri-ortho-cresyl phosphate (TOCP) has been used commercially as a plasticizer and a flame retardant, which has been reported to cause multiple toxicities in humans and other animals. However, the effect of TOCP on female reproductive system is still unclear. The aim of this investigation was to evaluate the reproductive toxicity of TOCP in female avian and investigate its molecular mechanism. In the current study, 50 adult hens were given a single oral dose of TOCP (750 mg/kg). Egg laid by the hens were harvested and counted. Egg quality is assessed by determining the shell strength and thickness. Samples of ovary, shell gland, and serum were collected on day 0, 2, 7, and 21 after the administration. The morphological and pathological changes in tissues were examined. Cell death, follicular development, and steroidogenesis were determined to assess the toxicity of TOCP on laying hens. The results showed that egg production, egg weight, and eggshell strength significantly decreased after TOCP exposure. The calcium levels in serum and eggshell decreased and the expression levels of the eggshell formation-related genes calbindin-D28k (CaBP-D28k) and carbonic anhydrase 2 (CA2) were downregulated. The inhibitory effects of TOCP on follicular development and steroidogenesis were observed with changes in the levels of the related proteins such as forkhead box O1 (FoxO1) and mothers against decapentaplegic homolog 2/3 (Smad2/3). Cell death was identified, which might lead to follicular development disorder. Taken together, TOCP reduced the quantity and quality of the eggs laid by the hens through disrupting follicular development, steroidogenesis, and shell gland function.

Gold Compounds Inhibit the Ca2+-ATPase Activity of Brain PMCA and Human Neuroblastoma SH-SY5Y Cells and Decrease Cell Viability

Plasma membrane calcium ATPases (PMCA) are key proteins in the maintenance of calcium (Ca2+) homeostasis. Dysregulation of PMCA function is associated with several human pathologies, including neurodegenerative diseases, and, therefore, these proteins are potential drug targets to counteract those diseases. Gold compounds, namely of Au(I), are well-known for their therapeutic use in rheumatoid arthritis and other diseases for centuries. Herein, we report the ability of dichloro(2-pyridinecarboxylate)gold(III) (1), chlorotrimethylphosphinegold(I) (2), 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidenegold(I) chloride (3), and chlorotriphenylphosphinegold(I) (4) compounds to interfere with the Ca2+-ATPase activity of pig brain purified PMCA and with membranes from SH-SY5Y neuroblastoma cell cultures. The Au(III) compound (1) inhibits PMCA activity with the IC50 value of 4.9 µM, while Au(I) compounds (2, 3, and 4) inhibit the protein activity with IC50 values of 2.8, 21, and 0.9 µM, respectively. Regarding the native substrate MgATP, gold compounds 1 and 4 showed a non-competitive type of inhibition, whereas compounds 2 and 3 showed a mixed type of inhibition. All gold complexes showed cytotoxic effects on human neuroblastoma SH-SY5Y cells, although compounds 1 and 3 were more cytotoxic than compounds 2 and 4. In summary, this work shows that both Au (I and III) compounds are high-affinity inhibitors of the Ca2+-ATPase activity in purified PMCA fractions and in membranes from SH-SY5Y human neuroblastoma cells. Additionally, they exert strong cytotoxic effects.

Progress on Genetic Basis of Primary Aldosteronism

Primary aldosteronism (PA) is a heterogeneous group of disorders caused by the autonomous overproduction of aldosterone with simultaneous suppression of plasma renin activity (PRA). It is considered to be the most common endocrine cause of secondary arterial hypertension (HT) and is associated with a high rate of cardiovascular complications. PA is most often caused by a bilateral adrenal hyperplasia (BAH) or aldosterone-producing adenoma (APA); rarer causes of PA include genetic disorders of steroidogenesis (familial hyperaldosteronism (FA) type I, II, III and IV), aldosterone-producing adrenocortical carcinoma, and ectopic aldosterone-producing tumors. Over the last few years, significant progress has been made towards understanding the genetic basis of PA, classifying it as a channelopathy. Recently, a growing body of clinical evidence suggests that mutations in ion channels appear to be the major cause of aldosterone-producing adenomas, and several mutations within the ion channel encoding genes have been identified. Somatic mutations in four genes (KCNJ5, ATP1A1, ATP2B3 and CACNA1D) have been identified in nearly 60% of the sporadic APAs, while germline mutations in KCNJ5 and CACNA1H have been reported in different subtypes of familial hyperaldosteronism. These new insights into the molecular mechanisms underlying PA may be associated with potential implications for diagnosis and therapy.

Circadian miR-449c-5p regulates uterine Ca2+ transport during eggshell calcification in chickens

Background

miRNAs regulate circadian patterns by modulating the biological clocks of animals. In our previous study, we found that the clock gene exhibited a cosine expression pattern in the fallopian tube of chicken uterus. Clock-controlled miRNAs are present in mammals and Drosophila; however, whether there are clock-controlled miRNAs in the chicken uterus and, if so, how they regulate egg-laying rhythms is unclear. In this study, we selected 18 layer hens with similar ovipositional rhythmicity (each of three birds were sacrificed for study per 4 h throughout 24 h); their transcriptomes were scanned to identify the circadian miRNAs and to explore regulatory mechanisms within the uterus of chickens.

Results

We identified six circadian miRNAs that are mainly associated with several biological processes including ion trans-membrane transportation, response to calcium ion, and enrichment of calcium signaling pathways. Verification of the experimental results revealed that miR-449c-5p exhibited a cosine expression pattern in the chicken uterus. Ca²⁺-transporting ATPase 4 (ATP2B4) in the plasma membrane is the predicted target gene of circadian miR-449c-5p and is highly enriched in the calcium signaling pathway. We speculated that clock-controlled miR-449c-5p regulated Ca²⁺ transportation during eggshell calcification in the chicken uterus by targeting ATP2B4. ATP2B4 mRNA and protein were rhythmically expressed in the chicken uterus, and dual-luciferase reporter gene assays confirmed that ATP2B4 was directly targeted by miR-449c-5p. The expression of miR-449c-5p showed an opposite trend to that of ATP2B4 within a 24 h cycle in the chicken uterus; it inhibited mRNA and protein expression of ATP2B4 in the uterine tubular gland cells. In addition, overexpression of ATP2B4 significantly decreased intracellular Ca²⁺ concentration (P < 0.05), while knockdown of ATP2B4 accelerated intracellular Ca²⁺ concentrations. We found similar results after ATP2B4 knockdown by miR-449c-5p. Taken together, these results indicate that ATP2B4 promotes uterine Ca²⁺ trans-epithelial transport.

Conclusions

Clock-controlled miR-449c-5p regulates Ca²⁺ transport in the chicken uterus by targeting ATP2B4 during eggshell calcification.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08074-3.

Plasma Membrane Ca2+ Pump PMCA4z Is More Active Than Splicing Variant PMCA4x

The plasma membrane Ca²⁺ pumps (PMCA) are P-ATPases that control Ca²⁺ signaling and homeostasis by transporting Ca²⁺ out of the eukaryotic cell. Humans have four genes that code for PMCA isoforms (PMCA1-4). A large diversity of PMCA isoforms is generated by alternative mRNA splicing at sites A and C. The different PMCA isoforms are expressed in a cell-type and developmental-specific manner and exhibit differential sensitivity to a great number of regulatory mechanisms. PMCA4 has two A splice variants, the forms "x" and "z". While PMCA4x is ubiquitously expressed and relatively well-studied, PMCA4z is less characterized and its expression is restricted to some tissues such as the brain and heart muscle. PMCA4z lacks a stretch of 12 amino acids in the so-called A-M3 linker, a conformation-sensitive region of the molecule connecting the actuator domain (A) with the third transmembrane segment (M3). We expressed in yeast PMCA4 variants "x" and "z", maintaining constant the most frequent splice variant "b" at the C-terminal end, and obtained purified preparations of both proteins. In the basal autoinhibited state, PMCA4zb showed a higher ATPase activity and a higher apparent Ca²⁺ affinity than PMCA4xb. Both isoforms were stimulated by calmodulin but PMCA4zb was more strongly activated by acidic lipids than PMCA4xb. The results indicate that a PMCA4 intrinsically more active and more responsive to acidic lipids is produced by the variant "z" of the splicing site A.

Role of calcium oscillations in sperm physiology

Intracellular Ca²⁺ is a key regulator of cell signaling and sperm are not the exception. Cells often use cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) oscillations as a means to decodify external and internal information. [Ca²⁺]_i oscillations faster than those usually found in other cells and correlated with flagellar beat were the first to be described in sperm in 1993 by Susan Suarez, in the boar. More than 20 years passed before similar [Ca²⁺]_i oscillations were documented in human sperm, simultaneously examining their flagellar beat in three dimensions by Corkidi et al. 2017. On the other hand, 10 years after the discovery of the fast boar [Ca²⁺]_i oscillations, slower ones triggered by compounds from the egg external envelope were found to regulate cell motility and chemotaxis in sperm from marine organisms. Today it is known that sperm display fast and slow spontaneous and agonist triggered [Ca²⁺]_i oscillations. In mammalian sperm these Ca²⁺ transients may act like a multifaceted tool that regulates fundamental functions such as motility and acrosome reaction. This review covers the main sperm species and experimental conditions where [Ca²⁺]_i oscillations have been described and discusses what is known about the transporters involved, their regulation and the physiological purpose of these oscillations. There is a lot to be learned regarding the origin, regulation and physiological relevance of these Ca²⁺ oscillations.

Ca2+ roles in electroporation-induced changes of cancer cell physiology: From membrane repair to cell death

The combination of Ca²⁺ ions and electroporation has gained attention as potential alternative to electrochemotherapy. Ca²⁺ is an important component of the cell membrane repair system and its presence directly influences the dynamics of the pore cycle after electroporation which can be exploited for cancer therapies. Here, the influence of Ca²⁺ concentration is investigated on small molecule electrotransfer and release of Calcein from 4T1, MX-1, B16F10, U87 cancer cells after cell exposure to microsecond electric pulses. Moreover, we investigated simultaneous molecule electrotransfer and intracellular calcium ion influx when media was supplemented with different Ca²⁺ concentrations. Results show that increased concentrations of calcium ions reduce the electrotransfer of small molecules to different lines of cancer cells as well as the release of Calcein. These effects are related with an enhanced membrane repair mechanism. Overall, we show that the efficiency of molecular electrotransfer can be controlled by regulating Ca²⁺ concentration in the electroporation medium. For the first time, the cause of cancer cell death in vitro from 1 mM CaCl₂ concentrations is related to the irreversible loss of Ca²⁺ homeostasis after cell electroporation. Our findings provide fundamental insight on the mechanisms of Ca²⁺ electroporation that might lead to improved therapeutic outcomes.

The plasma membrane calcium ATPase 4 does not influence parasite levels but partially promotes experimental cerebral malaria during murine blood stage malaria

BACKGROUND

Recent genome wide analysis studies have identified a strong association between single nucleotide variations within the human ATP2B4 gene and susceptibility to severe malaria. The ATP2B4 gene encodes the plasma membrane calcium ATPase 4 (PMCA4), which is responsible for controlling the physiological level of intracellular calcium in many cell types, including red blood cells (RBCs). It is, therefore, postulated that genetic differences in the activity or expression level of PMCA4 alters intracellular Ca2+ levels and affects RBC hydration, modulating the invasion and growth of the Plasmodium parasite within its target host cell.

METHODS

In this study the course of three different Plasmodium spp. infections were examined in mice with systemic knockout of Pmca4 expression.

RESULTS

Ablation of PMCA4 reduced the size of RBCs and their haemoglobin content but did not affect RBC maturation and reticulocyte count. Surprisingly, knockout of PMCA4 did not significantly alter peripheral parasite burdens or the dynamics of blood stage Plasmodium chabaudi infection or reticulocyte-restricted Plasmodium yoelii infection. Interestingly, although ablation of PMCA4 did not affect peripheral parasite levels during Plasmodium berghei infection, it did promote slight protection against experimental cerebral malaria, associated with a minor reduction in antigen-experienced T cell accumulation in the brain.

CONCLUSIONS

The finding suggests that PMCA4 may play a minor role in the development of severe malarial complications, but that this appears independent of direct effects on parasite invasion, growth or survival within RBCs.

Proton-coupled cotransporter involves phenanthrene xylem loading in roots

The uptake and translocation of polycyclic aromatic hydrocarbons (PAHs) by staple crops have gained much attention. However, the mechanism on phenanthrene xylem loading across plasma membrane is still unclear. In this study, we investigated the concentration dependence of phenanthrene xylem loading and the relationship between phenanthrene concentration and xylem sap pH. The impacts of metabolic inhibitor, temperature, and dissolved oxygen on phenanthrene concentration in xylem sap were observed as well. The Michaelis-Menten equation fits phenanthrene xylem loading across parenchyma cell membrane well and xylem sap pH decreases with the increase in treated phenanthrene concentration. Metabolic inhibitor, low temperature and low dissolved oxygen can suppress phenanthrene loading into xylem sap. The inhibitory rate of sodium vanadate on xylem sap phenanthrene is between 19.76% and 25.82%. Low temperature reduces phenanthrene concentration in xylem sap by 86.68%. Hypoxia (2 mg L^-1) inhibits phenanthrene loading into xylem by 78.67%. Therefore, it is indicated that H⁺/phenanthrene cotransporter is implicated in phenanthrene loading into xylem. Our work offers a valuable model to understand the mechanism of PAH loading into xylem.

Plasma Membrane Calcium ATPase Regulates Stoichiometry of CD4+ T-Cell Compartments

Immune responses involve mobilization of T cells within naïve and memory compartments. Tightly regulated Ca²⁺ levels are essential for balanced immune outcomes. How Ca²⁺ contributes to regulating compartment stoichiometry is unknown. Here, we show that plasma membrane Ca²⁺ ATPase 4 (PMCA4) is differentially expressed in human CD4⁺ T compartments yielding distinct store operated Ca²⁺ entry (SOCE) profiles. Modulation of PMCA4 yielded a more prominent increase of SOCE in memory than in naïve CD4⁺ T cell. Interestingly, downregulation of PMCA4 reduced the effector compartment fraction and led to accumulation of cells in the naïve compartment. In silico analysis and chromatin immunoprecipitation point towards Ying Yang 1 (YY1) as a transcription factor regulating PMCA4 expression. Analyses of PMCA and YY1 expression patterns following activation and of PMCA promoter activity following downregulation of YY1 highlight repressive role of YY1 on PMCA expression. Our findings show that PMCA4 adapts Ca²⁺ levels to cellular requirements during effector and quiescent phases and thereby represent a potential target to intervene with the outcome of the immune response.

Structural Basis of Substrate-Independent Phosphorylation in a P4-ATPase Lipid Flippase

P4-ATPases define a eukaryotic subfamily of the P-type ATPases, and are responsible for the transverse flip of specific lipids from the extracellular or luminal leaflet to the cytosolic leaflet of cell membranes. The enzymatic cycle of P-type ATPases is divided into autophosphorylation and dephosphorylation half-reactions. Unlike most other P-type ATPases, P4-ATPases transport their substrate during dephosphorylation only, i.e. the phosphorylation half-reaction is not associated with transport. To study the structural basis of the distinct mechanisms of P4-ATPases, we have determined cryo-EM structures of Drs2p-Cdc50p from Saccharomyces cerevisiae covering multiple intermediates of the cycle. We identify several structural motifs specific to Drs2p and P4-ATPases in general that decrease movements and flexibility of domains as compared to other P-type ATPases such as Na⁺/K⁺-ATPase or Ca²⁺-ATPase. These motifs include the linkers that connect the transmembrane region to the actuator (A) domain, which is responsible for dephosphorylation. Additionally, mutation of Tyr380, which interacts with conserved Asp340 of the distinct DGET dephosphorylation loop of P4-ATPases, highlights a functional role of these P4-ATPase specific motifs in the A-domain. Finally, the transmembrane (TM) domain, responsible for transport, also undergoes less extensive conformational changes, which is ensured both by a longer segment connecting TM helix 4 with the phosphorylation site, and possible stabilization by the auxiliary subunit Cdc50p. Collectively these adaptions in P4-ATPases are responsible for phosphorylation becoming transport-independent.

Ciliary Ca2+ pumps regulate intraciliary Ca2+ from the action potential and may co-localize with ciliary voltage-gated Ca2+ channels

Calcium ions (Ca2+) entering cilia through the ciliary voltage-gated calcium channels (CaV) during the action potential causes reversal of the ciliary power stroke and backward swimming in Paramecium tetraurelia. How calcium is returned to the resting level is not yet clear. Our focus is on calcium pumps as a possible mechanism. There are 23 P. tetraurelia genes for calcium pumps that are members of the family of plasma membrane Ca2+ ATPases (PMCAs). They have domains homologous to those found in mammalian PMCAs. Of the 13 pump proteins previously identified in cilia, ptPMCA2a and ptPMCA2b are most abundant in the cilia. We used RNAi to examine which PMCA might be involved in regulating intraciliary Ca2+ after the action potential. RNAi for only ptPMCA2a and ptPMCA2b causes cells to significantly prolong their backward swimming, which indicates that Ca2+ extrusion in the cilia is impaired when these PMCAs are depleted. We used immunoprecipitations (IP) to find that ptPMCA2a and ptPMCA2b are co-immunoprecipitated with the CaV channel α1 subunits that are found only in the cilia. We used iodixanol (OptiPrep) density gradients to show that ptPMCA2a and ptPMCA2b and CaV1c are found in the same density fractions. These results suggest that ptPMCA2a and ptPMCA2b are located in the proximity of ciliary CaV channels.

Development and maintenance of vision's first synapse

Synapses in the outer retina are the first information relay points in vision. Here, photoreceptors form synapses onto two types of interneurons, bipolar cells and horizontal cells. Because outer retina synapses are particularly large and highly ordered, they have been a useful system for the discovery of mechanisms underlying synapse specificity and maintenance. Understanding these processes is critical to efforts aimed at restoring visual function through repairing or replacing neurons and promoting their connectivity. We review outer retina neuron synapse architecture, neural migration modes, and the cellular and molecular pathways that play key roles in the development and maintenance of these connections. We further discuss how these mechanisms may impact connectivity in the retina.

Crosstalk among Calcium ATPases: PMCA, SERCA and SPCA in Mental Diseases

Calcium in mammalian neurons is essential for developmental processes, neurotransmitter release, apoptosis, and signal transduction. Incorrectly processed Ca²⁺ signal is well-known to trigger a cascade of events leading to altered response to variety of stimuli and persistent accumulation of pathological changes at the molecular level. To counterbalance potentially detrimental consequences of Ca²⁺, neurons are equipped with sophisticated mechanisms that function to keep its concentration in a tightly regulated range. Calcium pumps belonging to the P-type family of ATPases: plasma membrane Ca²⁺-ATPase (PMCA), sarco/endoplasmic Ca²⁺-ATPase (SERCA) and secretory pathway Ca²⁺-ATPase (SPCA) are considered efficient line of defense against abnormal Ca²⁺ rises. However, their role is not limited only to Ca²⁺ transport, as they present tissue-specific functionality and unique sensitive to the regulation by the main calcium signal decoding protein—calmodulin (CaM). Based on the available literature, in this review we analyze the contribution of these three types of Ca²⁺-ATPases to neuropathology, with a special emphasis on mental diseases.

Sperm ion channels and transporters in male fertility and infertility

Mammalian sperm cells must respond to cues originating from along the female reproductive tract and from the layers of the egg in order to complete their fertilization journey. Dynamic regulation of ion signalling is, therefore, essential for sperm cells to adapt to their constantly changing environment. Over the past 15 years, direct electrophysiological recordings together with genetically modified mouse models and human genetics have confirmed the importance of ion channels, including the principal Ca²⁺-selective plasma membrane ion channel CatSper, for sperm activity. Sperm ion channels and membrane receptors are attractive targets for both the development of contraceptives and infertility treatment drugs. Furthermore, in this era of assisted reproductive technologies, understanding the signalling processes implicated in defective sperm function, particularly those arising from genetic abnormalities, is of the utmost importance not only for the development of infertility treatments but also to assess the overall health of a patient and his children. Future studies to improve reproductive health care and overall health care as a function of the ability to reproduce should include identification and analyses of gene variants that underlie human infertility and research into fertility-related molecules.

The development and hepatotoxicity of acetaminophen: reviewing over a century of progress

Acetaminophen (APAP) was first synthesized in the 1800s, and came on the market approximately 65 years ago. Since then, it has become one of the most used drugs in the world. However, it is also a major cause of acute liver failure. Early investigations of the mechanisms of toxicity revealed that cytochrome P450 enzymes catalyze formation of a reactive metabolite in the liver that depletes glutathione and covalently binds to proteins. That work led to the introduction of N-acetylcysteine (NAC) as an antidote for APAP overdose. Subsequent studies identified the reactive metabolite N-acetyl-p-benzoquinone imine, specific P450 enzymes involved, the mechanism of P450-mediated oxidation, and major adducted proteins. Significant gaps remain in our understanding of the mechanisms downstream of metabolism, but several events appear critical. These events include development of an initial oxidative stress, reactive nitrogen formation, altered calcium flux, JNK activation and mitochondrial translocation, inhibition of mitochondrial respiration, the mitochondrial permeability transition, and nuclear DNA fragmentation. Additional research is necessary to complete our knowledge of the toxicity, such as the source of the initial oxidative stress, and to greatly improve our understanding of liver regeneration after APAP overdose. A better understanding of these mechanisms may lead to additional treatment options. Even though NAC is an excellent antidote, its effectiveness is limited to the first 16 hours following overdose.

ACYP2 contributes to malignant progression of glioma through promoting Ca2+ efflux and subsequently activating c-Myc and STAT3 signals

Background

Acylphosphatase 2 (ACYP2) is involved in cell differentiation, energy metabolism and hydrolysis of intracellular ion pump. It has been reported as a negative regulator in leukemia and a positive regulator in colon cancer, respectively. However, its biological role in glioma remains totally unclear.

Methods

We performed quantitative RT-PCR (qRT-PCR), immunohistochemistry (IHC) and western blot assays to evaluate ACYP2 expression. The functions of ACYP2 in glioma cells were determined by a series of in vitro and in vivo experiments, including cell proliferation, colony formation, cell cycle, apoptosis, migration, invasion and nude mouse tumorigenicity assays. In addition, western blot and co-immunoprecipitation (Co-IP) assays were used to identify its downstream targets.

Results

Knocking down ACYP2 in glioma cells significantly inhibited cell proliferation, colony formation, migration, invasion and tumorigenic potential in nude mice, and induced cell cycle arrest and apoptosis. Conversely, ectopic expression of ACYP2 in glioma cells dramatically promoted malignant phenotypes of glioma cells. Mechanistically, ACYP2 promoted malignant progression of glioma cells through regulating intracellular Ca²⁺ homeostasis via its interaction with PMCA4, thereby activating c-Myc and PTP1B/STAT3 signals. This could be effectively reversed by Ca²⁺ chelator BAPTA-AM or calpain inhibitor calpeptin.

Conclusions

Our data demonstrate that ACYP2 functions as an oncogene in glioma through activating c-Myc and STAT3 signals via the regulation of intracellular Ca²⁺ homeostasis, and indicate that ACYP2 may be a potential therapeutic target and prognostic biomarker in gliomas.

Primary Active Ca2+ Transport Systems in Health and Disease

Calcium ions (Ca²⁺) are prominent cell signaling effectors that regulate a wide variety of cellular processes. Among the different players in Ca²⁺ homeostasis, primary active Ca²⁺ transporters are responsible for keeping low basal Ca²⁺ levels in the cytosol while establishing steep Ca²⁺ gradients across intracellular membranes or the plasma membrane. This review summarizes our current knowledge on the three types of primary active Ca²⁺-ATPases: the sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) pumps, the secretory pathway Ca²⁺- ATPase (SPCA) isoforms, and the plasma membrane Ca²⁺-ATPase (PMCA) Ca²⁺-transporters. We first discuss the Ca²⁺ transport mechanism of SERCA1a, which serves as a reference to describe the Ca²⁺ transport of other Ca²⁺ pumps. We further highlight the common and unique features of each isoform and review their structure-function relationship, expression pattern, regulatory mechanisms, and specific physiological roles. Finally, we discuss the increasing genetic and in vivo evidence that links the dysfunction of specific Ca²⁺-ATPase isoforms to a broad range of human pathologies, and highlight emerging therapeutic strategies that target Ca²⁺ pumps.

Molecular and Electrophysiological Analyses of ATP2B4 Gene Variants in Bilateral Adrenal Hyperaldosteronism

Primary aldosteronism (PA) is the most common cause of secondary hypertension with a high prevalence among patients with resistant hypertension. Despite the recent discovery of somatic variants in aldosterone-producing adenoma (APA)-associated PA, causes for PA due to bilateral aldosterone production (bilateral hyperaldosteronism; BHA) remain unknown. Herein, we identified rare gene variants in ATP2B4, in a cohort of patients with BHA. ATP2B4 belongs to the same family of Ca-ATPases as ATP2B3, which is involved in the pathogenesis of APA. Endogenous ATP2B4 expression was characterized in adrenal tissue, and the gene variants were functionally analyzed for effects on aldosterone synthase (CYP11B2) expression, steroid production in basal and agonist-stimulated conditions, and for changes in biophysical properties of channel properties. Knockdown of ATP2B4 in HAC15 exhibited reduced angiotensin II stimulation in one of four shRNA clones. Stable HAC15 cell lines with doxycycline (dox) - inducible wild-type and variant forms of ATP2B4 - were generated, and dox-induced upregulation of ATP2B4 mRNA and protein was confirmed. However, ATP2B4 variants did not alter basal or agonist-stimulated CYP11B2 expression. Whole-cell recordings in HAC15 cells indicated robust endogenous ATP2B4 conductance in native cells but reduced conductance with overexpressed WT and variant ATP2B4. The previously defined PA-causing ATP2B3 variant served as a positive control and exhibited elevated CYP11B2 mRNA. In conclusion, while this study did not confirm a pathogenic role for ATP2B4 variants in BHA, we describe the sequencing analysis for familial and sporadic BHA and outline a template for the thorough in vitro characterization of gene variants.

Plasma Membrane Ca2+ ATPase Isoform 4 (PMCA4) Has an Important Role in Numerous Hallmarks of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is largely resistant to standard treatments leading to poor patient survival. The expression of plasma membrane calcium ATPase-4 (PMCA4) is reported to modulate key cancer hallmarks including cell migration, growth, and apoptotic resistance. Data-mining revealed that PMCA4 was over-expressed in pancreatic ductal adenocarcinoma (PDAC) tumors which correlated with poor patient survival. Western blot and RT-qPCR revealed that MIA PaCa-2 cells almost exclusively express PMCA4 making these a suitable cellular model of PDAC with poor patient survival. Knockdown of PMCA4 in MIA PaCa-2 cells (using siRNA) reduced cytosolic Ca²⁺ ([Ca²⁺]_i) clearance, cell migration, and sensitized cells to apoptosis, without affecting cell growth. Knocking down PMCA4 had minimal effects on numerous metabolic parameters (as assessed using the Seahorse XF analyzer). In summary, this study provides the first evidence that PMCA4 is over-expressed in PDAC and plays a role in cell migration and apoptotic resistance in MIA PaCa-2 cells. This suggests that PMCA4 may offer an attractive novel therapeutic target in PDAC.

Candidate genes of the transcellular and paracellular calcium absorption pathways in the small intestine of laying hens

To meet the high calcium (Ca) demand during eggshell biomineralization (2 g of Ca per egg), laying hens develop specific metabolic regulations to maintain Ca homeostasis. The intake of Ca, its solubilization, and absorption capacity are enhanced at sexual maturity (SM). A better knowledge of the intestinal Ca transporters involved in their variations at this stage could indicate new nutritional strategies to enhance Ca digestive utilization. Transcellular Ca absorption pathway and its major player calbindin-D 28 K (CALB1) mediate a saturable transport, which has been extensively described in this model. Conversely, a contribution by the paracellular pathway involving non-saturable Ca transport through intercellular tight junction has also been suggested. The aim of the present study was to identify candidate genes of these two pathways and their patterns of expression, in immature pullets (12, 15, and 17 wk old) and mature laying hens (23 wk old) in the duodenum, jejunum, and ileum. Using RT-qPCR, this study identifies 3 new candidate genes for transcellular, and 9 for paracellular Ca transport. A total of 5 candidates of the transcellular pathway, transient receptor potential cation channels subfamily C member 1 (TRPC1) and M member 7 (TRPM7); CALB1 and ATPase plasma membrane Ca²⁺ transporting 1 (ATP2B1) and ATPase plasma membrane Ca²⁺ transporting 2 (ATP2B2) were enhanced with age or after SM in the duodenum, the jejunum or all 3 segments. A total of 4 candidates of the paracellular pathway Claudin 2 (CLDN2) and tight junction proteins 1, 2, and 3 (TJP1, TJP2 and TJP3) increased in the small intestine after SM. Additionally, CALB1, ATP2B2, and CLDN2 were overexpressed in the duodenum or the jejunum or both segments after SM. The enhanced expression of candidate genes of the paracellular Ca pathway after SM, supports that the non-saturable transport could be a mechanism of great importance when high concentrations of soluble Ca are observed in the intestinal content during eggshell formation. Both pathways may work cooperatively in the duodenum and jejunum, the main sites of Ca absorption in laying hens.

Reciprocality Between Estrogen Biology and Calcium Signaling in the Cardiovascular System

17β-Estradiol (E₂) is the main estrogenic hormone in the body and exerts many cardiovascular protective effects. Via three receptors known to date, including estrogen receptors α (ERα) and β (ERβ) and the G protein-coupled estrogen receptor 1 (GPER, aka GPR30), E₂ regulates numerous calcium-dependent activities in cardiovascular tissues. Nevertheless, effects of E₂ and its receptors on components of the calcium signaling machinery (CSM), the underlying mechanisms, and the linked functional impact are only beginning to be elucidated. A picture is emerging of the reciprocality between estrogen biology and Ca²⁺ signaling. Therein, E₂ and GPER, via both E₂-dependent and E₂-independent actions, moderate Ca²⁺-dependent activities; in turn, ERα and GPER are regulated by Ca²⁺ at the receptor level and downstream signaling via a feedforward loop. This article reviews current understanding of the effects of E₂ and its receptors on the cardiovascular CSM and vice versa with a focus on mechanisms and combined functional impact. An overview of the main CSM components in cardiovascular tissues will be first provided, followed by a brief review of estrogen receptors and their Ca²⁺-dependent regulation. The effects of estrogenic agonists to stimulate acute Ca²⁺ signals will then be reviewed. Subsequently, E₂-dependent and E₂-independent effects of GPER on components of the Ca²⁺ signals triggered by other stimuli will be discussed. Finally, a case study will illustrate how the many mechanisms are coordinated to moderate Ca²⁺-dependent activities in the cardiovascular system.

Host Calcium Channels and Pumps in Viral Infections

Ca²⁺ is essential for virus entry, viral gene replication, virion maturation, and release. The alteration of host cells Ca²⁺ homeostasis is one of the strategies that viruses use to modulate host cells signal transduction mechanisms in their favor. Host calcium-permeable channels and pumps (including voltage-gated calcium channels, store-operated channels, receptor-operated channels, transient receptor potential ion channels, and Ca²⁺-ATPase) mediate Ca²⁺ across the plasma membrane or subcellular organelles, modulating intracellular free Ca²⁺. Therefore, these Ca²⁺ channels or pumps present important aspects of viral pathogenesis and virus–host interaction. It has been reported that viruses hijack host calcium channels or pumps, disturbing the cellular homeostatic balance of Ca²⁺. Such a disturbance benefits virus lifecycles while inducing host cells’ morbidity. Evidence has emerged that pharmacologically targeting the calcium channel or calcium release from the endoplasmic reticulum (ER) can obstruct virus lifecycles. Impeding virus-induced abnormal intracellular Ca²⁺ homeostasis is becoming a useful strategy in the development of potent antiviral drugs. In this present review, the recent identified cellular calcium channels and pumps as targets for virus attack are emphasized.

The Puzzling Role of Neuron-Specific PMCA Isoforms in the Aging Process

The aging process is a physiological phenomenon associated with progressive changes in metabolism, genes expression, and cellular resistance to stress. In neurons, one of the hallmarks of senescence is a disturbance of calcium homeostasis that may have far-reaching detrimental consequences on neuronal physiology and function. Among several proteins involved in calcium handling, plasma membrane Ca²⁺-ATPase (PMCA) is the most sensitive calcium detector controlling calcium homeostasis. PMCA exists in four main isoforms and PMCA2 and PMCA3 are highly expressed in the brain. The overall effects of impaired calcium extrusion due to age-dependent decline of PMCA function seem to accumulate with age, increasing the susceptibility to neurotoxic insults. To analyze the PMCA role in neuronal cells, we have developed stable transfected differentiated PC12 lines with down-regulated PMCA2 or PMCA3 isoforms to mimic age-related changes. The resting Ca²⁺ increased in both PMCA-deficient lines affecting the expression of several Ca²⁺-associated proteins, i.e., sarco/endoplasmic Ca²⁺-ATPase (SERCA), calmodulin, calcineurin, GAP43, CCR5, IP₃Rs, and certain types of voltage-gated Ca²⁺ channels (VGCCs). Functional studies also demonstrated profound changes in intracellular pH regulation and mitochondrial metabolism. Moreover, modification of PMCAs membrane composition triggered some adaptive processes to counterbalance calcium overload, but the reduction of PMCA2 appeared to be more detrimental to the cells than PMCA3.

Evaluation of Single-Nucleotide Polymorphisms of Transcription Factor 7-Like 2 and ATP2B1 Genes as Cardiovascular Risk Predictors in Chronic Kidney Disease

Introduction:

Cardiovascular disease (CVD) is the primary cause of morbidity and premature mortality in chronic kidney disease (CKD). The transcription factor 7-like 2 (TCF7L2) gene product TCF4 is a transcription factor that acts as a downstream effector in the canonical Wnt signaling pathway and may be important in the development of both type 2 diabetes and renal development and disease. It is, therefore, plausible that mutations in this gene could manifest themselves in reduced kidney function or kidney disease through their effects on hyperglycemia as well as independent of this mechanism. The ATP2B1 gene encodes the plasma membrane calcium ATPase isoform 1, which removes bivalent calcium ions from eukaryotic cells against very large concentration gradients and is responsible for controlling the contraction and dilation of vascular smooth muscles.

Aim and Objectives:

The aims of this study are (1) to evaluate single-nucleotide polymorphisms (SNPs) of TCF7L2 gene as cardiovascular risk predictors in CKD and (2) to evaluate SNPs of ATP2B1 gene as cardiovascular risk predictors in CKD.

Subjects and Methods:

Fifty clinically diagnosed CKD patients in the age group between 20 and 60 years of both genders were selected as cases and fifty healthy participants from the master health checkup department were selected as controls. Genomic DNA was extracted based on the spin column kit method. The DNA samples were stored at −20°C until analysis. Genotyping for TCF7L2 gene rs7903146 (C/T) and ATP2B1 gene rs11105354 (A/G) was carried out through polymerase chain reaction.

Results:

T allele frequency was observed in 12 controls and 23 cases (odds ratio [OR] = 2.2, 95% confidence interval [CI]: 1.0–4.7). CC genotype was observed in 38 controls and 27 cases and CT genotype in 22 cases and 12 controls. A allele was found in 38 cases and 23 controls (OR = 2, 95% CI: 1.1–3.8). The mean values of cholesterol, low-density lipoprotein, triglycerides, glucose, insulin, urea, and creatinine were high in cases when compared to controls.

Conclusion:

T allele of TCF7L2 gene rs7903146 (C/T) and A allele of ATP2B1 (A/G) gene rs11105354 (A/G) are associated with CVD in CKD patients.