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The receptor tyrosine kinase RET plays an essential role during embryogenesis in regulating cell proliferation, differentiation, and migration. Upon glial cell line-derived neurotrophic factor (GDNF) stimulation, RET can trigger multiple intracellular signaling pathways that in concert activate various downstream effectors. Here we report that the RET receptor induces calcium (Ca(2+)) signaling and regulates neocortical neuronal progenitor migration through the Phospholipase-C gamma (PLCγ) binding domain Tyr1015. This signaling cascade releases Ca(2+) from the endoplasmic reticulum through the inositol 1,4,5-trisphosphate receptor and stimulates phosphorylation of ERK1/2 and CaMKII. A point mutation at Tyr1015 on RET or small interfering RNA gene silencing of PLCγ block the GDNF-induced signaling cascade. Delivery of the RET mutation to neuronal progenitors in the embryonic ventricular zone using in utero electroporation reveal that Tyr1015 is necessary for GDNF-stimulated migration of neurons to the cortical plate. These findings demonstrate a novel RET mediated signaling pathway that elevates cytosolic Ca(2+) and modulates neuronal migration in the developing neocortex through the PLCγ binding domain Tyr1015.

Developmental exposure to food contaminants, such as polychlorinated biphenyls (PCBs), has been considered as a possible cause of neurodevelopmental disorders. We have investigated the effects of noncytotoxic concentrations of PCBs 153 and 180 on spontaneous differentiation of rat embryonic neural stem cells (NSCs). Upon removal of basic fibroblast growth factor to induce spontaneous differentiation, cells were exposed to 100 nM of the selected PCBs for 48 h and analyzed after 5 days. Both PCBs 153 and 180 induced a significant increase in the number of neurite-bearing Tuj1-positive cells with a concomitant decrease in proliferating cells, as detected by FUCCI transfection and EdU staining. Measurements of spontaneous Ca²⁺ oscillations showed a decreased number of cells with Ca²⁺ activity after PCB exposure, further confirming the increase in neuronal cells. Conversely, exposure to methylmercury (MeHg), which we evaluated in parallel, led to an increased number of cells with Ca²⁺ activity, in agreement with the previously observed inhibition of neuronal differentiation. Analysis with quantitative PCR of the Notch pathway revealed that PCBs have a repressive action on Notch signaling, whereas MeHg activates it. Altogether, the data indicate that nanomolar concentrations of the selected non-dioxin-like PCBs and MeHg interfere in opposite directions with neuronal spontaneous differentiation of NSCs through Notch signaling. Combined exposures to PCBs and MeHg resulted in an induction of apoptosis and an antagonistic interaction on spontaneous neuronal differentiation. NSCs are further proven to be a valuable in vitro model to identify potential developmental neurotoxicants.

Oscillatory fluctuations in the cytosolic concentration of free calcium ions (Ca(2+)) are considered a ubiquitous mechanism for controlling multiple cellular processes. Inositol 1,4,5-trisphosphate (IP(3)) receptors (IP(3)R) are intracellular Ca(2+) release channels that mediate Ca(2+) release from endoplasmic reticulum (ER) Ca(2+) stores. The three IP(3)R subtypes described so far exhibit differential structural, biophysical, and biochemical properties. Subtype specific regulation of IP(3)R by the endogenous modulators IP(3), Ca(2+), protein kinases and associated proteins have been thoroughly examined. In this article we will review the contribution of each IP(3)R subtype in shaping cytosolic Ca(2+) oscillations.

Mitochondrial morphology is controlled by two opposing processes: fusion and fission. Drp1 (dynamin-related protein 1) and hFis1 are two key players of mitochondrial fission, but how Drp1 is recruited to mitochondria and how Drp1-mediated mitochondrial fission is regulated in mammals is poorly understood. Here, we identify the vertebrate-specific protein MIEF1 (mitochondrial elongation factor 1; independently identified as MiD51), which is anchored to the outer mitochondrial membrane. Elevated MIEF1 levels induce extensive mitochondrial fusion, whereas depletion of MIEF1 causes mitochondrial fragmentation. MIEF1 interacts with and recruits Drp1 to mitochondria in a manner independent of hFis1, Mff (mitochondrial fission factor) and Mfn2 (mitofusin 2), but inhibits Drp1 activity, thus executing a negative effect on mitochondrial fission. MIEF1 also interacts with hFis1 and elevated hFis1 levels partially reverse the MIEF1-induced fusion phenotype. In addition to inhibiting Drp1, MIEF1 also actively promotes fusion, but in a manner distinct from mitofusins. In conclusion, our findings uncover a novel mechanism which controls the mitochondrial fusion-fission machinery in vertebrates. As MIEF1 is vertebrate-specific, these data also reveal important differences between yeast and vertebrates in the regulation of mitochondrial dynamics.

Early telencephalic development is dependent on the spatially and temporally coordinated regulation by essential signaling factors. For example, members of the Bone Morphogenetic Protein (BMP) family, such as BMP4, are crucial for proper development of dorsal telencephalic structures. Stimulation of multipotent telencephalic neural stem cells (NSCs) with BMP4 induces differentiation primarily into astrocytic and mesenchymal cells. However, BMP4-mediated mesenchymal differentiation is inhibited at certain culture conditions of NSCs, corresponding to in vivo developmental contexts. These inhibitory mechanisms are not fully understood and the terminal fate of non-astrocytic BMP4 treated NSCs under these conditions is unclear. Here we show that secreted factors inhibited BMP4-mediated mesenchymal differentiation of telencephalic NSCs. BMP4 mediated a dramatic and direct up-regulation of endogenous noggin levels, that in turn exerted a concentration-dependent inhibition of BMP4-mediated mesenchymal differentiation of NSCs. Instead, BMP4 exposure of NSCs induced neuronal differentiation in mesenchyme-preventing conditions, whereas treatment with recombinant noggin alone did not. Wnt signaling is known to be essential for the development of neurons derived from the dorsal telencephalon, and co-stimulation of NSCs with BMP4+Wnt3a resulted in a synergistic effect yielding significantly increased number of mature neurons compared to stimulation with each factor alone. Thus whereas only a subset of BMP4-induced neurons derived from telencephalic NSCs, responded to glutamate receptor (GluR) agonists, over 80% of BMP4+Wnt3a-induced neurons responded appropriately to GluR-agonists. Our results increase the understanding of the role for BMP4 in differentiation of telencephalic multipotent progenitors, and reveal novel implications for noggin and Wnt3a in these events., (Copyright © 2011 Elsevier Inc. All rights reserved.)

ATP-Binding Cassette (ABC) transporters are efflux pumps frequently associated with multidrug resistance in many biological systems, including malaria. Antimalarial drug-resistance involves an ABC transporter, PfMDR1, a homologue of P-glycoprotein in humans. Twenty years of research have shown that several single nucleotide polymorphisms in pfmdr1 modulate in vivo and/or in vitro drug susceptibility. The underlying physiological mechanism of the effect of these mutations remains unclear. Here we develop structural models for PfMDR1 in different predicted conformations, enabling the study of transporter motion. Such analysis of functional polymorphisms allows determination of their potential role in transport and resistance. The bacterial MsbA ABC pump is a PfMDR1 homologue. MsbA crystals in different conformations were used to create PfMDR1 models with Modeller software. Sequences were aligned with ClustalW and analysed by Ali2D revealing a high level of secondary structure conservation. To validate a potential drug binding pocket we performed antimalarial docking simulations. Using aminoquinoline as probe drugs in PfMDR1 mutated parasites we evaluated the physiology underlying the mechanisms of resistance mediated by PfMDR1 polymorphisms. We focused on the analysis of well known functional polymorphisms in PfMDR1 amino acid residues 86, 184, 1034, 1042 and 1246. Our structural analysis suggested the existence of two different biophysical mechanisms of PfMDR1 drug resistance modulation. Polymorphisms in residues 86/184/1246 act by internal allosteric modulation and residues 1034 and 1042 interact directly in a drug pocket. Parasites containing mutated PfMDR1 variants had a significant altered aminoquinoline susceptibility that appears to be dependent on the aminoquinoline lipophobicity characteristics as well as vacuolar efflux by PfCRT. We previously described the in vivo selection of PfMDR1 polymorphisms under antimalarial drug pressure. Now, together with recent PfMDR1 functional reports, we contribute to the understanding of the specific structural role of these polymorphisms in parasite antimalarial drug response.

Cellular calcium uptake is a controlled physiological process mediated by multiple ion channels. The exposure of cells to either one of the protein kinase C (PKC) inhibitors, staurosporine (STS) or PKC412, can trigger Ca²(+) influx leading to cell death. The precise molecular mechanisms regulating these events remain elusive. In this study, we report that the PKC inhibitors induce a prolonged Ca²(+) import through hyperpolarization-activated cyclic nucleotide-gated channel 2 (HCN2) in lung carcinoma cells and in primary culture of cortical neurons, sufficient to trigger apoptosis-inducing factor (AIF)-mediated apoptosis. Downregulation of HCN2 prevented the drug-induced Ca²(+) increase and subsequent apoptosis. Importantly, the PKC inhibitors did not cause Ca²(+) entry into HEK293 cells, which do not express the HCN channels. However, introduction of HCN2 sensitized them to STS/PKC412-induced apoptosis. Mutagenesis of putative PKC phosphorylation sites within the C-terminal domain of HCN2 revealed that dephosphorylation of Thr⁵⁴⁹ was critical for the prolonged Ca²(+) entry required for AIF-mediated apoptosis. Our findings demonstrate a novel role for the HCN2 channel by providing evidence that it can act as an upstream regulator of cell death triggered by PKC inhibitors.

Perception of the environment relies on somatosensory neurons. Mechanosensory, proprioceptor and many nociceptor subtypes of these neurons have specific mechanosensitivity profiles to adequately differentiate stimulus patterns. Nevertheless, the cellular basis of differential mechanosensation remains largely elusive. Successful transduction of sensory information relies on the recruitment of sensory neurons and mechanosensation occurring at their peripheral axonal endings in vivo. Conspicuously, existing in vitro models aimed to decipher molecular mechanisms of mechanosensation test single sensory neuron somata at any one time. Here, we introduce a compartmental in vitro chamber design to deliver precisely controlled mechanical stimulation of sensory axons with synchronous real-time imaging of Ca(2+) transients in neuronal somata that reliably reflect action potential firing patterns. We report of three previously not characterized types of mechanosensitive neuron subpopulations with distinct intrinsic axonal properties tuned specifically to static indentation or vibration stimuli, showing that different classes of sensory neurons are tuned to specific types of mechanical stimuli. Primary receptor currents of vibration neurons display rapidly adapting conductance reliably detected for every single stimulus during vibration and are consistently converted into action potentials. This result allows for the characterization of two critical steps of mechanosensation in vivo: primary signal detection and signal conversion into specific action potential firing patterns in axons.

Human embryonic stem (hES) cell differentiation into dopamine neurons is considered a promising strategy for cell replacement therapy in Parkinson's disease, yet the functional properties of hES cell-derived dopamine neurons remain poorly defined. The objective of this study was to characterize intracellular calcium (Ca(2+)) and sub-plasma membrane cyclic AMP-signaling properties in hES cell-derived dopamine neurons. We found that hES cell-derived dopamine neurons and neural progenitors raised Ca(2+) from intra- and extracellular compartments in response to depolarization, glutamate, ATP, and dopamine D(2) receptor activation, while undifferentiated hES cells only mobilized Ca(2+) from intracellular stores in response to ATP and D(2) receptor-induced activation. Interestingly, we also found that hES cell-derived dopamine neurons in addition to primary ventral midbrain dopamine neurons were more prone to release Ca(2+) from intracellular stores than non-dopamine neurons following treatment with the neuropeptide neurotensin. Furthermore, hES cell-derived dopamine neurons showed cAMP elevations in response to forskolin and 3-isobutyl-methylxanthine, similar to primary dopamine neurons. Taken together, these results unravel the temporal sequence by which hES cells acquire Ca(2+) and cAMP signaling competence during dopamine differentiation.

Cytosolic calcium (Ca2+) oscillations are vastly flexible cell signals that convey information regulating numerous cellular processes. The frequency and amplitude of the oscillating signal can be varied infinitely by concerted actions of Ca2+ transporters and Ca2+-binding proteins to encode specific messages that trigger downstream molecular events. High frequency cytosolic Ca2+ oscillations regulate fast responses, such as synaptic transmission and secretion, whereas low frequency oscillations regulate slow processes, such as fertilization and gene transcription. Thus, the cell exploits Ca2+ oscillations as a signalling carrier to transduce vital information that controls its behaviour. Here, we review the underlying biochemical mechanisms responsible for generating and discriminating cytosolic Ca2+ oscillations., (2010 Elsevier Inc. All rights reserved.)

Elevated testosterone concentrations induce cardiac hypertrophy but the molecular mechanisms are poorly understood. Anabolic properties of testosterone involve an increase in protein synthesis. The mammalian target of rapamycin complex 1 (mTORC1) pathway is a major regulator of cell growth, but the relationship between testosterone action and mTORC1 in cardiac cells remains unknown. Here, we investigated whether the hypertrophic effects of testosterone are mediated by mTORC1 signaling in cultured cardiomyocytes. Testosterone increases the phosphorylation of mTOR and its downstream targets 40S ribosomal protein S6 kinase 1 (S6K1; also known as RPS6KB1) and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1). The S6K1 phosphorylation induced by testosterone was blocked by rapamycin and small interfering RNA to mTOR. Moreover, the hormone increased both extracellular-regulated kinase (ERK1/2) and protein kinase B (Akt) phosphorylation. ERK1/2 inhibitor PD98059 blocked the testosterone-induced S6K1 phosphorylation, whereas Akt inhibition (Akt-inhibitor-X) had no effect. Testosterone-induced ERK1/2 and S6K1 phosphorylation increases were blocked by either 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid-acetoxymethylester or by inhibitors of inositol 1,4,5-trisphosphate (IP(3)) pathway: U-73122 and 2-aminoethyl diphenylborate. Finally, cardiomyocyte hypertrophy was evaluated by, the expression of beta-myosin heavy chain, alpha-skeletal actin, cell size, and amino acid incorporation. Testosterone increased all four parameters and the increase being blocked by mTOR inhibition. Our findings suggest that testosterone activates the mTORC1/S6K1 axis through IP(3)/Ca(2+) and MEK/ERK1/2 to induce cardiomyocyte hypertrophy.

Rationale: We have previously shown that angiomotin (Amot) is essential for endothelial cell migration during mouse embryogenesis. However, approximately 5% of Amot knockout mice survived without any detectable vascular defects. Angiomotin-like protein 1 (AmotL1) potentially compensates for the absence of Amot as it is 62% homologous to Amot and exhibits similar expression pattern in endothelial cells., Objective: Here, we report the identification of a novel isoform of AmotL1 that controls endothelial cell polarization and directional migration., Methods and Results: Small interfering RNA-mediated silencing of AmotL1 in mouse aortic endothelial cells caused a significant reduction in migration. In confluent mouse pancreatic islet endothelial cells (MS-1), AmotL1 colocalized with Amot to tight junctions. Small interfering RNA knockdown of both Amot and AmotL1 in MS-1 cells exhibited an additive effect on increasing paracellular permeability compared to that of knocking down either Amot or AmotL1, indicating both proteins were required for proper tight junction activity. Moreover, as visualized using high-resolution 2-photon microscopy, the morpholino-mediated knockdown of amotl1 during zebrafish embryogenesis resulted in vascular migratory defect of intersegmental vessels with strikingly decreased junction stability between the stalk cells and the aorta. However, the phenotype was quite distinct from that of amot knockdown which affected polarization of the tip cells of intersegmental vessels. Double knockdown resulted in an additive phenotype of depolarized tip cells with no or decreased connection of the stalk cells to the dorsal aorta., Conclusions: These results cumulatively validate that Amot and AmotL1 have similar effects on endothelial migration and tight junction formation in vitro. However, in vivo Amot appears to control the polarity of vascular tip cells whereas AmotL1 mainly affects the stability of cell-cell junctions of the stalk cells.

Dendritic growth is pivotal in the neurogenesis of cortical neurons. The sodium pump, or Na,K-ATPase, is an evolutionarily conserved protein that, in addition to its central role in establishing the electrochemical gradient, has recently been reported to function as a receptor and signaling mediator. Although a large body of evidence points toward a dual function for the Na,K-ATPase, few biological implications of this signaling pathway have been described. Here we report that Na,K-ATPase signal transduction triggers dendritic growth as well as a transcriptional program dependent on cAMP response element binding protein (CREB) and cAMP response element (CRE)-mediated gene expression, primarily regulated via Ca(2+)/calmodulin-dependent protein (CaM) kinases. The signaling cascade mediating dendritic arbor growth also involves intracellular Ca(2+) oscillations and sustained phosphorylation of mitogen-activated protein (MAP) kinases. Thus, our results suggest a novel role for the Na,K-ATPase as a modulator of dendritic growth in developing neurons.

Apoptosis-inducing factor (AIF), a flavoprotein with NADH oxidase activity anchored to the mitochondrial inner membrane, is known to be involved in complex I maintenance. During apoptosis, AIF can be released from mitochondria and translocate to the nucleus, where it participates in chromatin condensation and large-scale DNA fragmentation. The mechanism of AIF release is not fully understood. Here, we show that a prolonged ( approximately 10 min) increase in intracellular Ca(2+) level is a prerequisite step for AIF processing and release during cell death. In contrast, a transient ATP-induced Ca(2+) increase, followed by rapid normalization of the Ca(2+) level, was not sufficient to trigger the proteolysis of AIF. Hence, import of extracellular Ca(2+) into staurosporine-treated cells caused the activation of a calpain, located in the intermembrane space of mitochondria. The activated calpain, in turn, cleaved membrane-bound AIF, and the soluble fragment was released from the mitochondria upon outer membrane permeabilization through Bax/Bak-mediated pores or by the induction of Ca(2+)-dependent mitochondrial permeability transition. Inhibition of calpain, or chelation of Ca(2+), but not the suppression of caspase activity, prevented processing and release of AIF. Combined, these results provide novel insights into the mechanism of AIF release during cell death.

Increasing evidence suggests that alpha-chemokines serve several important functions in the nervous system, including regulation of neuroimmune responses, neurotransmission, neuronal survival, and central nervous system development. In this study, we first examined the function of two alpha-chemokines, chemokine ligand (CXCL) 6 and CXCL8, and their receptors, CXCR1 and CXCR2, in the developing rat ventral midbrain (VM). We found that CXCR2 and CXCL6 are regulated during VM development and that CXCL6 promotes the differentiation of nurr77-related receptor (Nurr1)+ precursors into dopaminergic (DA) neurons in vitro. Intriguingly, CXCL8, a ligand expressed only in Homo sapiens, enhanced progenitor cell division, neurogenesis, and tyrosine hydroxylase-positive (TH+) cell number in rodent precursor and neurosphere cultures. CXCL1, the murine ortholog of CXCL8, was developmentally regulated in the VM and exhibited activities similar but not identical to those of CXCL8. TH+ cells derived from chemokine-treated VM neurospheres coexpressed Nurr1 and VMAT and were functionally active, as shown by calcium (Ca(2+)) fluxes in response to AMPA. In conclusion, our data demonstrate that CXCL1, CXCL6, and CXCL8 increase the number of DA neurons in VM precursor and neurosphere cultures by diverse mechanisms. Thus, alpha-chemokines may find an application in the preparation of cells for drug development or Parkinson's disease cell replacement therapy.

Calcium (Ca2+) oscillations play fundamental roles in various cell signaling processes and have been the subject of numerous modeling studies. Here we have implemented a general mathematical model to simulate the impact of store-operated Ca2+ entry on intracellular Ca2+ oscillations. In addition, we have compared two different models of the inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) and their influences on intracellular Ca2+ oscillations. Store-operated Ca2+ entry following Ca2+ depletion of endoplasmic reticulum (ER) is an important component of Ca2+ signaling. We have developed a phenomenological model of store-operated Ca2+ entry via store-operated Ca2+ (SOC) channels, which are activated upon ER Ca2+ depletion. The depletion evokes a bi-phasic Ca2+ signal, which is also produced in our mathematical model. The IP3R is an important regulator of intracellular Ca2+ signals. This IP3 sensitive Ca2+ channel is also regulated by Ca2+. We apply two IP3R models, the Mak-McBride-Foskett model and the De Young and Keizer model, with significantly different channel characteristics. Our results show that the two separate IP3R models evoke intracellular Ca2+ oscillations with different frequencies and amplitudes. Store-operated Ca2+ entry affects the oscillatory behavior of these intracellular Ca2+ oscillations. The IP3 threshold is altered when store-operated Ca2+ entry is excluded from the model. Frequencies and amplitudes of intracellular Ca2+ oscillations are also altered without store-operated Ca2+ entry. Under certain conditions, when intracellular Ca2+ oscillations are absent, excluding store-operated Ca2+ entry induces an oscillatory response. These findings increase knowledge concerning store-operated Ca2+ entry and its impact on intracellular Ca2+ oscillations.

Mounting evidence suggests that the ion pump, Na,K-ATPase, can, in the presence of ouabain, act as a signal transducer. A prominent binding motif linking the Na,K-ATPase to intracellular signaling effectors has, however, not yet been identified. Here we report that the N-terminal tail of the Na,K-ATPase catalytic alpha-subunit (alphaNT-t) binds directly to the N terminus of the inositol 1,4,5-trisphosphate receptor. Three amino acid residues, LKK, conserved in most species and most alpha-isoforms, are essential for the binding to occur. In wild-type cells, low concentrations of ouabain trigger low frequency calcium oscillations that activate NF-kappaB and protect from apoptosis. All of these effects are suppressed in cells overexpressing a peptide corresponding to alphaNT-t but not in cells overexpressing a peptide corresponding to alphaNT-t deltaLKK. Thus we have identified a well conserved Na,K-ATPase motif that binds to the inositol 1,4,5-trisphosphate receptor and can trigger an anti-apoptotic calcium signal.

Gain-of-function mutations in SHP-2/PTPN11 cause Noonan syndrome, a human developmental disorder. Noonan syndrome is characterized by proportionate short stature, facial dysmorphia, increased risk of leukemia, and congenital heart defects in approximately 50% of cases. Congenital heart abnormalities are common in Noonan syndrome, but the signaling pathway(s) linking gain-of-function SHP-2 mutants to heart disease is unclear. Diverse cell types coordinate cardiac morphogenesis, which is regulated by calcium (Ca2+) and the nuclear factor of activated T-cells (NFAT). It has been shown that the frequency of Ca2+ oscillations regulates NFAT activity. Here, we show that in fibroblasts, Ca2+ oscillations in response to FGF-2 require the phosphatase activity of SHP-2. Conversely, gain-of-function mutants of SHP-2 enhanced FGF-2-mediated Ca2+ oscillations in fibroblasts and spontaneous Ca2+ oscillations in cardiomyocytes. The enhanced frequency of cardiomyocyte Ca2+ oscillations induced by a gain-of-function SHP-2 mutant correlated with reduced nuclear translocation and transcriptional activity of NFAT. These data imply that gain-of-function SHP-2 mutants disrupt the Ca2+ oscillatory control of NFAT, suggesting a potential mechanism for congenital heart defects in Noonan syndrome.

Epithelial cells are vital to sense the presence of bacteria, thereby initiating a proper innate immune response. This occurs via different mechanisms, e.g. recognition by pattern recognition receptors (TLR), or alteration of the cellular Ca2+ homeostasis. The Escherichia coli toxin cytolysin A (ClyA) is naturally delivered to target cells as active pore assemblies within outer membrane vesicles (OMVs), and we here investigate a possible role of ClyA-containing OMVs (ClyA+ (OMV)) for induction of proinflammatory responses via the above-mentioned mechanisms. We report that low, sublytic concentrations of ClyA+ (OMV) affect the Ca2+ homeostasis in epithelial cells by induction of slow, intracellular Ca2+ oscillations, while increased concentrations act cytolytically. Thus, ClyA belongs to the novel group of pore-forming toxins shown to elicit such biphasic responses. Ca2+ waves in the minute range have been shown to regulate gene transcription of, e.g. interleukin (IL)-6 and -8. While the periodicity of ClyA+ (OMV)-induced Ca2+ waves (22.9 +/- 0.9 min) fail to induce an IL-8 response, our data fit to the general concept of frequency-specific gene expression. Molecular investigations of the signal transduction pathway reveals that ClyA+ (OMV) utilize a different one as compared with those previously reported for other toxins causing Ca2+ waves. The ClyA protein per se and ClyA pore assemblies are non-immunogenic, while lipopolysaccharide present on the OMVs induces a TLR4-dependent proinflammatory response as expected. Additional membrane components of the OMV, e.g. OmpW, was also found to elicit proinflammatory responses that was independent of TLR4 and Ca2+ signalling.

Calcium (Ca2+) oscillations are universal signals exploited by cells to regulate a vast number of cellular processes. Frequency and amplitude, the key features of oscillating waves, can yield information that can be decoded by intracellular processes. Analysis and quantification of Ca2+ oscillations are crucial for understanding the general concept of Ca2+ signaling. This protocol presents a method for performing spectral analysis of Ca2+ oscillations using MATLAB software.

Recent studies indicate novel roles for the ubiquitous ion pump, Na,K-ATPase, in addition to its function as a key regulator of intracellular sodium and potassium concentration. We have previously demonstrated that ouabain, the endogenous ligand of Na,K-ATPase, can trigger intracellular Ca2+ oscillations, a versatile intracellular signal controlling a diverse range of cellular processes. Here we report that Na,K-ATPase and inositol 1,4,5-trisphosphate (InsP3) receptor (InsP3R) form a cell signaling microdomain that, in the presence of ouabain, generates slow Ca2+ oscillations in renal cells. Using fluorescent resonance energy transfer (FRET) measurements, we detected a close spatial proximity between Na,K-ATPase and InsP3R. Ouabain significantly enhanced FRET between Na,K-ATPase and InsP3R. The FRET effect and ouabain-induced Ca2+ oscillations were not observed following disruption of the actin cytoskeleton. Partial truncation of the NH2 terminus of Na,K-ATPase catalytic alpha1-subunit abolished Ca2+ oscillations and downstream activation of NF-kappaB. Ouabain-induced Ca2+ oscillations occurred in cells expressing an InsP3 sponge and were hence independent of InsP3 generation. Thus, we present a novel principle for a cell signaling microdomain where an ion pump serves as a receptor.

The plant-derived steroid, digoxin, a specific inhibitor of Na,K-ATPase, has been used for centuries in the treatment of heart disease. Recent studies demonstrate the presence of a digoxin analog, ouabain, in mammalian tissue, but its biological role has not been elucidated. Here, we show in renal epithelial cells that ouabain, in doses causing only partial Na,K-ATPase inhibition, acts as a biological inducer of regular, low-frequency intracellular calcium ([Ca(2+)](i)) oscillations that elicit activation of the transcription factor, NF-kappa B. Partial inhibition of Na,K-ATPase using low extracellular K(+) and depolarization of cells did not have these effects. Incubation of cells in Ca(2+)-free media, inhibition of voltage-gated calcium channels, inositol triphosphate receptor antagonism, and redistribution of actin to a thick layer adjacent to the plasma membrane abolished [Ca(2+)](i) oscillations, indicating that they were caused by a concerted action of inositol triphosphate receptors and capacitative calcium entry via plasma membrane channels. Blockade of ouabain-induced [Ca(2+)](i) oscillations prevented activation of NF-kappa B. The results demonstrate a new mechanism for steroid signaling via plasma membrane receptors and underline a novel role for the steroid hormone, ouabain, as a physiological inducer of [Ca(2+)](i) oscillations involved in transcriptional regulation in mammalian cells.

Pyelonephritis is one of the most common febrile diseases in children. If not treated appropriately, it causes irreversible renal damage and accounts for a large proportion of end stage renal failures. Renal scarring can occur in the absence of inflammatory cells, indicating that bacteria may have a direct signalling effect on renal cells. Intracellular calcium ([Ca2+]i) oscillations can protect cells from the cytotoxic effects of prolonged increases in intracellular calcium. However, no pathophysiologically relevant protein that induces such oscillations has been identified. Here we show that infection by uropathogenic Escherichia coli induces a constant, low-frequency oscillatory [Ca2+]i response in target primary rat renal epithelial cells induced by the secreted RTX (repeats-in-toxin) toxin alpha-haemolysin. The response depends on calcium influx through L-type calcium channels as well as from internal stores gated by inositol triphosphate. Internal calcium oscillations induced by alpha-haemolysin in a renal epithelial cell line stimulated production of cytokines interleukin (IL)-6 and IL-8. Our findings indicate a novel role for alpha-haemolysin in pyelonephritis: as an inducer of an oscillating second messenger response in target cells, which fine-tunes gene expression during the inflammatory response.

Despite the importance of dopamine signaling, it remains unknown if the two major subclasses of dopamine receptors exist on the same or distinct populations of neurons. Here we used confocal microscopy to demonstrate that virtually all striatal neurons, both in vitro and in vivo, contained dopamine receptors of both classes. We also provide functional evidence for such colocalization: in essentially all neurons examined, fenoldopam, an agonist of the D1 subclass of receptors, inhibited both the Na+/K+ pump and tetrodotoxin (TTX)-sensitive sodium channels, and quinpirole, an agonist of the D2 subclass of receptors, activated TTX-sensitive sodium channels. Thus D1 and D2 classes of ligands may functionally interact in virtually all dopamine-responsive neurons within the basal ganglia.