Calcium Pump Activity Research Articles

AKT Regulation of ORAI1-Mediated Calcium Influx in Breast Cancer Cells.

Simple SummaryA remodeling in calcium homeostasis and the protein kinase AKT signaling pathway often promotes tumorigenic traits in cancer cells. Changes in calcium signaling can be mediated through altered expression or activity of calcium channels and pumps, which constitute a class of targetable therapeutic targets. Currently, the interplay between the two signaling pathways in breast cancer cells is unclear. A better understanding of the association between calcium and AKT signaling, and the molecular players involved may identify novel therapeutic strategies for breast cancers with abnormal AKT signaling. Using fluorescence calcium imaging and gene silencing/knockout techniques, we showed that increased AKT activation results in increased calcium entry, and that this is mediated through ORAI1 calcium channels. Future studies exploring therapeutic strategies to target PTEN-deficient or hyperactivated AKT cancers should consider this novel correlation between AKT activation and ORAI1-mediated calcium influx.Although breast cancer cells often exhibit both abnormal AKT signaling and calcium signaling, the association between these two pathways is unclear. Using a combination of pharmacological tools, siRNA and CRISPR/Cas9 gene silencing techniques, we investigated the association between PTEN, AKT phosphorylation and calcium signaling in a basal breast cancer cell line. We found that siRNA-mediated PTEN silencing promotes AKT phosphorylation and calcium influx in MDA-MB-231 cells. This increase in AKT phosphorylation and calcium influx was phenocopied by the pharmacological AKT activator, SC79. The increased calcium influx associated with SC79 is inhibited by silencing AKT2, but not AKT1. This increase in calcium influx is suppressed when the store-operated calcium channel, ORAI1 is silenced. The results from this study open a novel avenue for therapeutic targeting of cancer cells with increased AKT activation. Given the association between ORAI1 and breast cancer, ORAI1 is a possible therapeutic target in cancers with abnormal AKT signaling.

Calcium cycling as a mediator of thermogenic metabolism in adipose tissue.

Canonical non-shivering thermogenesis (NST) in brown and beige fat relies on uncoupling protein 1 (UCP1)-mediated heat generation, although alternative mechanisms of NST have been identified, including sarcoplasmic reticulum (SR)-calcium cycling. Intracellular calcium is a crucial cell signaling molecule for which compartmentalization is tightly regulated, and the sarco-endoplasmic calcium ATPase (SERCA) actively pumps calcium from the cytosol into the SR. In this review, we discuss the capacity of SERCA-mediated calcium cycling as a significant mediator of thermogenesis in both brown and beige adipocytes. Here, we suggest two primary mechanisms of SR calcium mediated thermogenesis. The first mechanism is through direct uncoupling of the ATPase and calcium pump activity of SERCA, resulting in the energy of ATP catalysis being expended as heat in the absence of calcium transport. Regulins, a class of SR membrane proteins, act to decrease the calcium affinity of SERCA and uncouple the calcium transport function from ATPase activity, but remain largely unexplored in adipose tissue thermogenesis. A second mechanism is through futile cycling of SR calcium whereby SERCA-mediated SR calcium influx is equally offset by SR calcium efflux, resulting in ATP consumption without a net change in calcium compartmentalization. A fuller understanding of the functional and mechanistic role of calcium cycling as a mediator of adipose tissue thermogenesis and how manipulation of these pathways can be harnessed for therapeutic gain remains unexplored. Significance Statement Enhancing thermogenic metabolism in brown or beige adipose tissue may be of broad therapeutic utility to reduce obesity and metabolic syndrome. Canonical BAT-mediated thermogenesis occurs via uncoupling protein 1 (UCP1). However, UCP1-independent pathways of thermogenesis, such as sarcoplasmic (SR) calcium cycling, have also been identified, but the regulatory mechanisms and functional significance of these pathways remain largely unexplored. Thus, this mini-review discusses the state of the field with regard to calcium cycling as a thermogenic mediator in adipose tissue.

Homologous cardiac calcium pump regulators phospholamban and sarcolipin adopt distinct oligomeric states in the membrane

Phospholamban (PLN) and Sarcolipin (SLN) are homologous membrane proteins that belong to the family of proteins that regulate the activity of the cardiac calcium pump (sarcoplasmic reticulum Ca2+-ATPase, SERCA). PLN and SLN share highly conserved leucine zipper motifs that control self-association;consequently, it has been proposed that both PLN and SLN assemble into stablepentamers in the membrane.In this study, we used molecular dynamics (MD) simulations and Western blot analysis to investigate the precise molecular architecture of the PLN and SLN oligomers. Analysis showed that the PLN pentamer is the predominant oligomer present in mouse ventricles and ventricle-like human iPSC-derived cardiomyocytes, in agreement with the MD simulations showing stable leucine zipper interactions across all protomer-protomer interfaces and MD replicates. Interestingly, we found that the PLN pentamer populates an asymmetric structure of the transmembrane region, which is likely anintrinsicfeature of the oligomer in a lipid bilayer. The SLN pentamer is not favorably formed across MD replicates and species of origin;instead, SLN from human and mouse atria primarily populate coexisting dimeric and trimeric states. In contrast to previous studies, our findings indicate that the SLN pentamer is not the predominant oligomeric state populated in the membrane. We conclude that despite their structural homology, PLN and SLN adopt distinct oligomeric states in the membrane. We propose that the distinct oligomeric states populated by PLN and SLN may contribute to tissue-specific SERCA regulation via differences in protomer–oligomer exchange, oligomer–SERCA dynamics, and noise filtering during β-adrenergic stimulation in the heart.

Arsenic and Protein Expression: It might help to know the mechanism of As toxicity

Arsenic and Protein Expression: It might help to know the mechanism of As toxicity

Regulation of transgelin and GST-pi proteins in the tissues of hamsters exposed to sodium arsenite

Regulation of transgelin and GST-pi proteins in the tissues of hamsters exposed to sodium arsenite

Calcium and Redox Liaison: A Key Role of Selenoprotein N in Skeletal Muscle.

Selenoprotein N (SEPN1) is a type II glycoprotein of the endoplasmic reticulum (ER) that senses calcium levels to tune the activity of the sarcoplasmic reticulum calcium pump (SERCA pump) through a redox-mediated mechanism, modulating ER calcium homeostasis. In SEPN1-depleted muscles, altered ER calcium homeostasis triggers ER stress, which induces CHOP-mediated malfunction, altering excitation–contraction coupling. SEPN1 is localized in a region of the ER where the latter is in close contact with mitochondria, i.e., the mitochondria-associated membranes (MAM), which are important for calcium mobilization from the ER to mitochondria. Accordingly, SEPN1-depleted models have impairment of both ER and mitochondria calcium regulation and ATP production. SEPN1-related myopathy (SEPN1-RM) is an inherited congenital muscle disease due to SEPN1 loss of function, whose main histopathological features are minicores, i.e., areas of mitochondria depletion and sarcomere disorganization in muscle fibers. SEPN1-RM presents with weakness involving predominantly axial and diaphragmatic muscles. Since there is currently no disease-modifying drug to treat this myopathy, analysis of SEPN1 function in parallel with that of the muscle phenotype in SEPN1 loss of function models should help in understanding the pathogenic basis of the disease and possibly point to novel drugs for therapy. The present essay recapitulates the novel biological findings on SEPN1 and how these reconcile with the muscle and bioenergetics phenotype of SEPN1-related myopathy.

CaM-stimulated Ca2+-ATPase activity on the symbiosome membrane from broad bean root nodules and its sensitivity to chlorpromazine

Relatively recently, we provided preliminary evidence for stimulating action of CaM on the activity of the symbiosome membrane (SM) Ca2+-ATPase from broad bean root nodules functioning, as to date found by us, as ATP-driven Ca2+/nH+ exchanger. In the present work, CaM effects on the enzyme studied in much more detail by following its catalytic and transport activities. It was found that the kinetics of both ITP hydrolysis by the SM vesicles and symbiosomes and two processes involved in the transport cycle of the Ca2+-ATPase, namely, Ca2+ uptake by symbiosomes and development within them of alkaline pH shift, is markedly accelerated in the presence of CaM and inhibited by its antagonist, chlorpromazine (CP). Based on the data obtained, it was concluded that under selected experimental conditions the observed modulation by CaM of the calcium pump activities is largely caused by the increase in Vmax of the enzyme rather than its apparent Km for Ca2+. These results are discussed in the light of the available literature data showing that the mechanism of CaM action on Ca2+-ATPases in eukaryotic cell membranes may be based not only on dissociation in the presence of Ca2+-CaM complex of the CaM-binding auto-inhibitory domain from their active center but also the use of some other mechanisms not involving any significant structural changes of CaM-binding target proteins.

Understanding doxorubicin associated calcium remodeling during triple-negative breast cancer treatment: an in silico study.

Aim: Triple-negative breast cancer (TNBC) is the most malignant subtype of breast cancer with high heterogeneity, rapid progression, and paucity of treatment options. The most effective chemotherapeutic drug used to treat TNBC is doxorubicin (Doxo) which is an anthracycline antibiotic. However, Doxo treatment alters cytosolic calcium dynamics leading to drug-resistance condition. The aim of this study is to capture the alterations in the activity of various calcium channels and pumps during Doxo treatment and their consequences on cytosolic calcium dynamics that ultimately result in drug resistance.Methods: In the present study, a mathematical model is proposed to capture the complex dynamical landscape of intracellular calcium during Doxo treatment. This study provides an insight into Doxo remodeling of calcium dynamics and associated drug-resistance effect. The model was first analyzed analytically and then explored through numerical simulation using techniques like global sensitivity analysis, parameter recalibration, etc.Results: The model is used to predict the potential combination therapy for Doxo that can overcome Doxo associated drug resistance. The results show targeting the dysregulated Ca2+ channels and pumps might provide efficient chemotherapy in TNBC. It was also observed that the indispensability of calcium influx rate is paramount in the Doxo drug resistance. Finally, three drugs were identified from existing literature that could be used as a combination therapy along with Doxo.Conclusions: The investigation highlights the importance of integrating the calcium signaling of various calcium regulating compounds for their effective anti-tumor effects deliverance along with chemotherapeutic agents. The results from this study might provide a new direction to the experimental biologists to explore different combination therapies with Doxo to enhance its anti-tumor effect.

Long-Time Phase Correlations Reveal Regulation of Beating Cardiomyocytes.

Spontaneous contractions of cardiomyocytes are driven by calcium oscillations due to the activity of ionic calcium channels and pumps. The beating phase is related to the time-dependent deviation of the oscillations from their average frequency, due to noise and the resulting cellular response. Here, we demonstrate experimentally that, in addition to the short-time (1-2Hz), beat-to-beat variability, there are long-time correlations (tens of minutes) in the beating phase dynamics of isolated cardiomyocytes. Our theoretical model relates these long-time correlations to cellular regulation that restores the frequency to its average, homeostatic value in response to stochastic perturbations.

Cardiomyocyte Calcium Ion Oscillations-Lessons From Physics.

We review a theoretical, coarse-grained description for cardiomyocytes calcium dynamics that is motivated by experiments on RyR channel dynamics and provides an analogy to other spontaneously oscillating systems. We show how a minimal model, that focuses on calcium channel and pump dynamics and kinetics, results in a single, easily understood equation for spontaneous calcium oscillations (the Van-der-Pol equation). We analyze experiments on isolated RyR channels to quantify how the channel dynamics depends both on the local calcium concentration, as well as its temporal behavior (“adaptation”). Our oscillator model analytically predicts the conditions for spontaneous oscillations, their frequency and amplitude, and how each of those scale with the small number of relevant parameters related to calcium channel and pump activity. The minimal model is easily extended to include the effects of noise and external pacing (electrical or mechanical). We show how our simple oscillator predicts and explains the experimental observations of synchronization, “bursting” and reduction of apparent noise in the beating dynamics of paced cells. Thus, our analogy and theoretical approach provides robust predictions for the beating dynamics, and their biochemical and mechanical modulation.

Calumenin-1 Interacts with Climp63 to Cooperatively Determine the Luminal Width and Distribution of Endoplasmic Reticulum Sheets.

SummaryThe ER is composed of distinct structures like tubules, matrices, and sheets, all of which are important for its various functions. However, how these distinct ER structures, especially the perinuclear ER sheets, are formed remains unclear. We report here that the ER membrane protein Climp63 and the ER luminal protein calumenin-1 (Calu1) collaboratively maintain ER sheet morphology. We show that the luminal length of Climp63 is positively correlated with the luminal width of ER sheets. Moreover, the lumen-only mutant of Climp63 dominant-negatively narrows the lumen of ER sheets, demonstrating that Climp63 acts as an ER luminal bridge. We also reveal that Calu1 specifically interacts with Climp63 and antagonizes Climp63 in terms of both ER sheet distribution and luminal width. Together, our data provide insight into how the structure of ER sheets is maintained and regulated.

Activity of the SPCA1 Calcium Pump Couples Sphingomyelin Synthesis to Sorting of Secretory Proteins in the Trans-Golgi Network

How the principal functions of the Golgi apparatus-protein processing, lipid synthesis, and sorting ofmacromolecules-are integrated to constitute cargo-specific trafficking pathways originating from the trans-Golgi network (TGN) is unknown. Here, we show that the activity of the Golgi localized SPCA1 calcium pump couples sorting and export of secreted proteins to synthesis of new lipid in the TGN membrane. A secreted Ca2+-binding protein, Cab45, constitutes the core component of a Ca2+-dependent, oligomerization-driven sorting mechanism whereby secreted proteins bound to Cab45 are packaged into a TGN-derived vesicular carrier whose membrane is enriched in sphingomyelin, a lipid implicated in TGN-to-cell surface transport. SPCA1 activity is controlled by the sphingomyelin content of the TGN membrane, such that local sphingomyelin synthesis promotes Ca2+ flux into the lumen of the TGN, which drives secretory protein sorting and export, thereby establishing a protein- and lipid-specific secretion pathway.

Hyperglycemia-induced cardiac contractile dysfunction in the diabetic heart.

The development of a diabetic cardiomyopathy is a multifactorial process, and evidence is accumulating that defects in intracellular free calcium concentration [Ca2+]i or its homeostasis are related to impaired mechanical performance of the diabetic heart leading to a reduction in contractile dysfunction. Defects in ryanodine receptor, reduced activity of the sarcoplasmic reticulum calcium pump (SERCA) and, along with reduced activity of the sodium-calcium exchanger (NCX) and alterations in myofilament, collectively cause a calcium imbalance within the diabetic cardiomyocytes. This in turn is characterized by cytosolic calcium overloading or elevated diastolic calcium leading to heart failure. Numerous studies have been performed to identify the cellular, subcellular, and molecular derangements in diabetes-induced cardiomyopathy (DCM), but the precise mechanism(s) is still unknown. This review focuses on the mechanism behind DCM, the onset of contractile dysfunction, and the associated changes with special emphasis on hyperglycemia, mitochondrial dysfunction in the diabetic heart. Further, management strategies, including treatment and emerging therapeutic modalities, are discussed.

Reduction of calcium flux from the extracellular region and endoplasmic reticulum by amorphous nano-silica particles owing to carboxy group addition on their surface

Several studies have reported that amorphous nano-silica particles (nano-SPs) modulate calcium flux, although the mechanism remains incompletely understood. We thus analyzed the relationship between calcium flux and particle surface properties and determined the calcium flux route. Treatment of Balb/c 3T3 fibroblasts with nano-SPs with a diameter of 70nm (nSP70) increased cytosolic calcium concentration, but that with SPs with a diameter of 300 or 1000nm did not. Surface modification of nSP70 with a carboxy group also did not modulate calcium flux. Pretreatment with a general calcium entry blocker almost completely suppressed calcium flux by nSP70. Preconditioning by emptying the endoplasmic reticulum (ER) calcium stores slightly suppressed calcium flux by nSP70. These results indicate that nSP70 mainly modulates calcium flux across plasma membrane calcium channels, with subsequent activation of the ER calcium pump, and that the potential of calcium flux by nano-SPs is determined by the particle surface charge.

CARDIAC CONTRACTILITY MODULATION FOR TREATMENT OF CHRONIC HEART FAILURE

The review article describes the current role of phospholambane in the regulation of ATP-dependent calcium pump activity and the number of cardiomyocytes, and the possibilities of cardiac contractility modulation as a novel method for treatment of chronic heart failure.

Protective effects of agmatine on doxorubicin-induced chronic cardiotoxicity in rat

The detrimental cardio-toxic effect of doxorubicin, an effective chemotherapeutic agent, limited its clinical use. It has been claimed that doxorubicin cardio-toxicity occurs through calcium ions (Ca2+) overload and reactive oxygen species production. Agmatine, an endogenous imidazoline receptor agonist, induce uptake of cytosolic Ca2+ and cause an increase in activity of calcium pumps, including Ca2+-ATPase. Also it shows self-scavenging effect against reactive oxygen species production. Therefore, present study was designed to investigate the effects of agmatine against chronic cardio-toxicity of doxorubicin in rats.Male wistar rats were intraperitoneally injected with doxorubicin and agmatine four times a week for a month. Agmatine significantly alleviate the adverse effect of doxorubicin on left ventricular papillary muscle stimulation threshold and contractibility. Chronic co-administration of agmatine with doxorubicin blocked electrocardiographic changes induced by doxorubicin. In addition, agmatine improved body weight and decreased the mortality rate of animals by doxorubicin. Moreover, reversing the doxorubicin induced myocardial lesions was observed in animals treated by agmatine. A significant rise in the total antioxidant capacity of rat plasma was achieved in agmatine-treated animals in comparison to doxorubicin.To conclude, agmatine may improve therapeutic outcomes of doxorubicin since it exerts protective effects against doxorubicin-induced chronic cardiotoxicity in rats.

Systematical bifurcation analysis of an intracellular calcium oscillation model

As a very important second messenger, Ca2+ plays the role of adjusting various cellular physiological processes through calcium oscillations. In this paper, a further theoretical study is conducted to explore the kinetic behavior of the calcium signals based on a mathematical model. At first, the causes behind the appearance and disappearance of calcium oscillations are strictly verified from the theoretical level and a comparative analysis between the improved model and the original model is also made. Then, it is found that with the increase of relaxation time, the second bifurcation point of the system moves towards the increasing direction of the stimulus intensity and the oscillation interval displays gradual increase. It is also found that under given stimulus intensity, with the relaxation time getting longer, both the peak value and the period of the calcium oscillations display significant increase. Combining the results from the comparative analysis between the improved model and the original model with the results from the analysis of the relaxation time, it shows that the calcium pump activity exerts a direct impact on the calcium oscillation interval. Finally, the calcium leakage item is introduced into the improved model and it is found that as the calcium leakage increases, the two Hopf bifurcation points of the system both move towards the decreasing direction of the stimulus intensity and the oscillation interval gradually narrows down. The study also shows that under given stimulus intensity, as the calcium leakage increases, the peak value of the calcium oscillations displays slow increase and the oscillation period displays gradual decline.

Another micropeptide flexes its muscle

Muscle Physiology Genome annotation is a complex but imperfect art. Attesting to its limitations is the growing evidence that certain transcripts annotated as long noncoding RNAs (lncRNAs) in fact code for small peptides with biologically important functions. One such lncRNA-derived micropeptide in mammals is myoregulin, which reduces muscle performance by inhibiting the activity of a key calcium pump. Nelson et al. describe the opposite activity in a second lncRNA-derived micropeptide in mammalian muscle, called DWORF (see the Perspective by Payre and Desplan). This peptide enhances muscle performance by activating the same calcium pump. DWORF may prove to be useful in improving the cardiac muscle function of mammals with heart disease. Science , this issue p. [271][1]; see also p. [226][2] [1]: /lookup/doi/10.1126/science.aad4076 [2]: /lookup/doi/10.1126/science.aad9873

Multilayer network representation of membrane potential and cytosolic calcium concentration dynamics in beta cells

Modern theory of networks has been recognized as a very successful methodological concept for the description and analysis of complex systems. However, some complex systems are more complex than others. For instance, several real-life systems are constituted by interdependent subsystems and their elements are subjected to different types of interactions that can also change with time. Recently, the multilayer network formalism has been proposed as a general theoretical framework for the description and analysis of such multi-dimensional complex systems and is acquiring more and more prominence in terms of a new research direction. In the present study, we use this methodology for the description of functional connectivity patterns and signal propagation between pancreatic beta cells in an islet of Langerhans at the levels of membrane potential (MP) and cytosolic calcium concentration ([Ca2+]c) dynamics to study the extent of overlap in the two networks and to clarify whether time lags between the two signals in individual cells are in any way dependent on the role these cells play in the functional networks. The two corresponding network layers are constructed on the basis of signal directions and pairwise correlations, whereas the interlayer connections represent the time lag between both measured signals. Our results confirm our previous finding that both MP and [Ca2+]c change spread across an islet in the form of a depolarization and a [Ca2+]c wave, respectively. Both types of waves follow nearly the same path and the networks in both layers have a similar but not entirely the same structure. We show that the observed discrepancies are attributed to variability in delays between the depolarization and rise in [Ca2+]c. In particular, high-degree nodes in both layers are found to exhibit a larger time lag between the MP and the [Ca2+]c signal than nodes with less connections. We speculate that this finding reflects a higher activity of endoplasmic reticulum calcium pumps in the most connected cells. Our findings indicate that visualizing and studying the temporal information flow and interaction patterns between beta cells as a multiplex network can provide valuable new insights into the physiology of the complex signaling processes in islets of Langerhans.

Mg2+,ATP-залежна кальцієва помпа плазматичної мембрани гладеньком’язових клітин. 1. Структурна організація та влаcтивоcтi

Tight control of cytoplasm Ca2+ concentration is essential in cell functioning. Changing of Ca2+ concentration is thorough in smooth muscle cells, because it determines relaxation/constraint process. One of key proteins which control Ca2+ concentration in cytoplasm is Mg2+, ATP-dependent plasma membrane calcium pump. Thus, it is important to find compoumds which allowed one to change Mg2+, ATP-dependent plasma membrane calcium pump activity, as long as this topic is of current interest in biochemical research which regards energy and pharmacomechanical coupling mechanism of muscle excitation and contraction. In this article we generalized literatute and own data about properties of smooth muscle cell plasma membrane Ca(2+)-pump. Stuctural oganization, kinetical properties and molecular biology are considered.