The frequencies of calcium oscillations are optimized for efficient calcium-mediated activation of Ras and the ERK/MAPK cascade

Neural Development and Repair Induced by Femtosecond Laser Stimulation

Dendritic spines function as postsynaptic sites, receiving excitatory signals from presynaptic axons. The synaptic plasticity of spines underlies the refinement of neuronal circuits. Neural cognitive disorders are commonly associated with the impairment and elimination of dendritic spines. In this study, we report an all-optical method to activate dendritic spine growth and regeneration by a single short flash of femtosecond laser stimulation. The inhibited development and loss of spines can be rescued by a transient illumination of the laser inside a micrometer region of the soma by activating the extracellular signal-regulated kinase (ERK) signaling pathway. The rescued neurons exhibit function. Hence we provide a potential noninvasive method for the regeneration of dendritic spines.

Neuronal enhancers fine-tune adaptive circuit plasticity

Neuronal activity-regulated gene expression plays a crucial role in sculpting neural circuits that underpin adaptive brain function. Transcriptional enhancers are now recognized as key components of gene regulation that orchestrate spatiotemporally precise patterns of gene transcription. We propose that the dynamics of enhancer activation uniquely position these genomic elements to finely tune activity-dependent cellular plasticity. Enhancer specificity and modularity can be exploited to gain selective genetic access to specific cell states, and the precise modulation of target gene expression within restricted cellular contexts enabled by targeted enhancer manipulation allows for fine-grained evaluation of gene function. Mounting evidence also suggests that enduring stimulus-induced changes in enhancer states can modify target gene activation upon restimulation, thereby contributing to a form of cell-wide metaplasticity. We advocate for focused exploration of activity-dependent enhancer function to gain new insight into the mechanisms underlying brain plasticity and cognitive dysfunction.

Purinergic Ca2+ Signaling as a Novel Mechanism of Drug Tolerance in BRAF-Mutant Melanoma

Drug tolerance is a major cause of relapse after cancer treatment. Despite intensive efforts, its molecular basis remains poorly understood, hampering actionable intervention. We report a previously unrecognized signaling mechanism supporting drug tolerance in BRAF-mutant melanoma treated with BRAF inhibitors that could be of general relevance to other cancers. Its key features are cell-intrinsic intracellular Ca2+ signaling initiated by P2X7 receptors (purinergic ligand-gated cation channels) and an enhanced ability for these Ca2+ signals to reactivate ERK1/2 in the drug-tolerant state. Extracellular ATP, virtually ubiquitous in living systems, is the ligand that can initiate Ca2+ spikes via P2X7 channels. ATP is abundant in the tumor microenvironment and is released by dying cells, ironically implicating treatment-initiated cancer cell death as a source of trophic stimuli that leads to ERK reactivation and drug tolerance. Such a mechanism immediately offers an explanation of the inevitable relapse after BRAFi treatment in BRAF-mutant melanoma and points to actionable strategies to overcome it.

Purinergic Ca2+ signaling as a novel mechanism of drug tolerance in BRAF mutant melanoma

Drug tolerance is a major cause of relapse after cancer treatment. In spite of intensive efforts1-9, its molecular basis remains poorly understood, hampering actionable intervention. We report a previously unrecognized signaling mechanism supporting drug tolerance in BRAF-mutant melanoma treated with BRAF inhibitors that could be of general relevance to other cancers. Its key features are cell-intrinsic intracellular Ca2+ signaling initiated by P2X7 receptors (purinergic ligand-gated cation channels), and an enhanced ability for these Ca2+ signals to reactivate ERK1/2 in the drug-tolerant state. Extracellular ATP, virtually ubiquitous in living systems, is the ligand that can initiate Ca2+ spikes via P2X7 channels. ATP is abundant in the tumor microenvironment and is released by dying cells, ironically implicating treatment-initiated cancer cell death as a source of trophic stimuli that leads to ERK reactivation and drug tolerance. Such a mechanism immediately offers an explanation of the inevitable relapse after BRAFi treatment in BRAF-mutant melanoma, and points to actionable strategies to overcome it.

Activating mutations in JAK2 and CALR differentially affect intracellular calcium flux in store operated calcium entry

BACKGROUND

Calcium (Ca2+) signaling regulates various vital cellular functions, including integrin activation and cell migration. Store-operated calcium entry (SOCE) via calcium release-activated calcium (CRAC) channels represents a major pathway for Ca2+ influx from the extracellular space in multiple cell types. The impact of JAK2-V617F and CALR mutations which are disease initiating in myeloproliferative neoplasms (MPN) on SOCE, calcium flux from the endoplasmic reticulum (ER) to the cytosol, and related key signaling pathways in the presence or absence of erythropoietin (EPO) or thrombopoietin (TPO) is poorly understood. Thus, this study aimed to elucidate the effects of these mutations on the aforementioned calcium dynamics, in cellular models of MPN.

METHODS

Intracellular Ca2+ levels were measured over a time frame of 0-1080 s in Fura-2 AM labeled myeloid progenitor 32D cells expressing various mutations (JAK2-WT/EpoR, JAK2-V617F/EpoR; CALR-WT/MPL, CALR-ins5/MPL, and del52/MPL). Basal Ca2+ concentrations were assessed from 0-108 s. Subsequently, cells were stimulated with EPO/TPO in Ca2+-free Ringer solution, measuring Ca2+ levels from 109-594 s (store depletion). Then, 2 mM of Ca2+ buffer resembling physiological concentrations was added to induce SOCE, and Ca2+ levels were measured from 595-1080 s. Fura-2 AM emission ratios (F340/380) were used to quantify the integrated Ca2+ signal. Statistical significance was assessed by unpaired Student's t-test or Mann-Whitney-U-test, one-way or two-way ANOVA followed by Tukey's multiple comparison test.

RESULTS

Following EPO stimulation, the area under the curve (AUC) representing SOCE significantly increased in 32D-JAK2-V617F cells compared to JAK2-WT cells. In TPO-stimulated CALR cells, we observed elevated Ca2+ levels during store depletion and SOCE in CALR-WT cells compared to CALR-ins5 and del52 cells. Notably, upon stimulation, key components of the Ca2+ signaling pathways, including PLCγ-1 and IP3R, were differentially affected in these cell lines. Hyper-activated PLCγ-1 and IP3R were observed in JAK2-V617F but not in CALR mutated cells. Inhibition of calcium regulatory mechanisms suppressed cellular growth and induced apoptosis in JAK2-V617F cells.

CONCLUSIONS

This report highlights the impact of JAK2 and CALR mutations on Ca2+ flux (store depletion and SOCE) in response to stimulation with EPO and TPO. The study shows that the JAK2-V617F mutation strongly alters the regulatory mechanism of EpoR/JAK2-dependent intracellular calcium balance, affecting baseline calcium levels, EPO-induced calcium entry, and PLCγ-1 signaling pathways. Our results reveal an important role of calcium flux in the homeostasis of JAK2-V617F positive cells.

Engineered Silica Nanoparticles for Nucleic Acid Delivery

The development of nucleic acid-based drugs holds great promise for therapeutic applications, but their effective delivery into cells is hindered by poor cellular membrane permeability and inherent instability. To overcome these challenges, delivery vehicles are required to protect and deliver nucleic acids efficiently. Silica nanoparticles (SiNPs) have emerged as promising nanovectors and recently bioregulators for gene delivery due to their unique advantages. In this review, a summary of recent advancements in the design of SiNPs for nucleic acid delivery and their applications is provided, mainly according to the specific type of nucleic acids. First, the structural characteristics and working mechanisms of various types of nucleic acids are introduced and classified according to their functions. Subsequently, for each nucleic acid type, the use of SiNPs for enhancing delivery performance and their biomedical applications are summarized. The tailored design of SiNPs for selected type of nucleic acid delivery will be highlighted considering the characteristics of nucleic acids. Lastly, the limitations in current research and personal perspectives on future directions in this field are presented. It is expected this opportune review will provide insights into a burgeoning research area for the development of next-generation SiNP-based nucleic acid delivery systems.

A guide to ERK dynamics, part 1: mechanisms and models

Extracellular signal-regulated kinase (ERK) has long been studied as a key driver of both essential cellular processes and disease. A persistent question has been how this single pathway is able to direct multiple cell behaviors, including growth, proliferation, and death. Modern biosensor studies have revealed that the temporal pattern of ERK activity is highly variable and heterogeneous, and critically, that these dynamic differences modulate cell fate. This two-part review discusses the current understanding of dynamic activity in the ERK pathway, how it regulates cellular decisions, and how these cell fates lead to tissue regulation and pathology. In part 1, we cover the optogenetic and live-cell imaging technologies that first revealed the dynamic nature of ERK, as well as current challenges in biosensor data analysis. We also discuss advances in mathematical models for the mechanisms of ERK dynamics, including receptor-level regulation, negative feedback, cooperativity, and paracrine signaling. While hurdles still remain, it is clear that higher temporal and spatial resolution provide mechanistic insights into pathway circuitry. Exciting new algorithms and advanced computational tools enable quantitative measurements of single-cell ERK activation, which in turn inform better models of pathway behavior. However, the fact that current models still cannot fully recapitulate the diversity of ERK responses calls for a deeper understanding of network structure and signal transduction in general.

Activation of MAP2K signaling by genetic engineering or HF-rTMS promotes corticospinal axon sprouting and functional regeneration

Facilitating axon regeneration in the injured central nervous system remains a challenging task. RAF-MAP2K signaling plays a key role in axon elongation during nervous system development. Here, we show that conditional expression of a constitutively kinase-activated BRAF in mature corticospinal neurons elicited the expression of a set of transcription factors previously implicated in the regeneration of zebrafish retinal ganglion cell axons and promoted regeneration and sprouting of corticospinal tract (CST) axons after spinal cord injury in mice. Newly sprouting axon collaterals formed synaptic connections with spinal interneurons, resulting in improved recovery of motor function. Noninvasive suprathreshold high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) activated the BRAF canonical downstream effectors MAP2K1/2 and modulated the expression of a set of regeneration-related transcription factors in a pattern consistent with that induced by BRAF activation. HF-rTMS enabled CST axon regeneration and sprouting, which was abolished in MAP2K1/2 conditional null mice. These data collectively demonstrate a central role of MAP2K signaling in augmenting the growth capacity of mature corticospinal neurons and suggest that HF-rTMS might have potential for treating spinal cord injury by modulating MAP2K signaling.

Autonomous rhythmic activity in glioma networks drives brain tumour growth

Diffuse gliomas, particularly glioblastomas, are incurable brain tumours¹. They are characterized by networks of interconnected brain tumour cells that communicate via Ca²⁺ transients^2-6. However, the networks' architecture and communication strategy and how these influence tumour biology remain unknown. Here we describe how glioblastoma cell networks include a small, plastic population of highly active glioblastoma cells that display rhythmic Ca²⁺ oscillations and are particularly connected to others. Their autonomous periodic Ca²⁺ transients preceded Ca²⁺ transients of other network-connected cells, activating the frequency-dependent MAPK and NF-κB pathways. Mathematical network analysis revealed that glioblastoma network topology follows scale-free and small-world properties, with periodic tumour cells frequently located in network hubs. This network design enabled resistance against random damage but was vulnerable to losing its key hubs. Targeting of autonomous rhythmic activity by selective physical ablation of periodic tumour cells or by genetic or pharmacological interference with the potassium channel KCa3.1 (also known as IK1, SK4 or KCNN4) strongly compromised global network communication. This led to a marked reduction of tumour cell viability within the entire network, reduced tumour growth in mice and extended animal survival. The dependency of glioblastoma networks on periodic Ca²⁺ activity generates a vulnerability⁷ that can be exploited for the development of novel therapies, such as with KCa3.1-inhibiting drugs.

Cholesterol-induced robust Ca oscillation in astrocytes required for survival and lipid droplet formation in high-cholesterol condition

Cholesterol, one of the major cell membrane components, stabilizes membrane fluidity and regulates signal transduction. Beside its canonical roles, cholesterol has been reported to directly activate signaling pathways such as hedgehog (Hh). We recently found that astrocytes, one of the glial cells, respond to Hh pathway stimulation by Ca signaling. These notions led us to test if extracellularly applied cholesterol triggers Ca signaling in astrocytes. Here, we found that cholesterol application induces robust Ca oscillation only in astrocytes with different properties from the Hh-induced Ca response. The Ca oscillation has a long delay which corresponds to the onset of cholesterol accumulation in the plasma membrane. Blockade of the Ca oscillation resulted in enhancement of astrocytic cell death and disturbance of lipid droplet formation, implying a possibility that the cholesterol-induced Ca oscillation plays important roles in astrocytic survival and cholesterol handling under pathological conditions of cholesterol load such as demyelination.

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Robust Ca oscillation by cholesterol in astrocytes but not in neurons and microglia

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Cholesterol-induced Ca oscillation relates to membrane cholesterol accumulation

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The Ca oscillation is driven via the PLC-IP₃ signaling pathway

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Ca oscillation inhibition leads to astrocytic death and lipid droplet malformation

High-specificity protection against radiation-induced bone loss by a pulsed electromagnetic field

Radiotherapy increases tumor cure and survival rates; however, radiotherapy-induced bone damage remains a common issue for which effective countermeasures are lacking, especially considering tumor recurrence risks. We report a high-specificity protection technique based on noninvasive electromagnetic field (EMF). A unique pulsed-burst EMF (PEMF) at 15 Hz and 2 mT induces notable Ca²⁺ oscillations with robust Ca²⁺ spikes in osteoblasts in contrast to other waveforms. This waveform parameter substantially inhibits radiotherapy-induced bone loss by specifically modulating osteoblasts without affecting other bone cell types or tumor cells. Mechanistically, primary cilia are identified as major PEMF sensors in osteoblasts, and the differentiated ciliary expression dominates distinct PEMF sensitivity between osteoblasts and tumor cells. PEMF-induced unique Ca²⁺ oscillations depend on interactions between ciliary polycystins-1/2 and endoplasmic reticulum, which activates the Ras/MAPK/AP-1 axis and subsequent DNA repair Ku70 transcription. Our study introduces a previously unidentified method against radiation-induced bone damage in a noninvasive, cost-effective, and highly specific manner.

Independently paced Ca2+ oscillations in progenitor and differentiated cells in an ex vivo epithelial organ

Cytosolic Ca2+ is a highly dynamic, tightly regulated and broadly conserved cellular signal. Ca2+ dynamics have been studied widely in cellular monocultures, yet organs in vivo comprise heterogeneous populations of stem and differentiated cells. Here, we examine Ca2+ dynamics in the adult Drosophila intestine, a self-renewing epithelial organ in which stem cells continuously produce daughters that differentiate into either enteroendocrine cells or enterocytes. Live imaging of whole organs ex vivo reveals that stem-cell daughters adopt strikingly distinct patterns of Ca2+ oscillations after differentiation: enteroendocrine cells exhibit single-cell Ca2+ oscillations, whereas enterocytes exhibit rhythmic, long-range Ca2+ waves. These multicellular waves do not propagate through immature progenitors (stem cells and enteroblasts), of which the oscillation frequency is approximately half that of enteroendocrine cells. Organ-scale inhibition of gap junctions eliminates Ca2+ oscillations in all cell types - even, intriguingly, in progenitor and enteroendocrine cells that are surrounded only by enterocytes. Our findings establish that cells adopt fate-specific modes of Ca2+ dynamics as they terminally differentiate and reveal that the oscillatory dynamics of different cell types in a single, coherent epithelium are paced independently.

Genetic profile identification and clinicopathologic characteristics analysis of the thyroid-like low-grade nasopharyngeal papillary adenocarcinoma

Thyroid-like low-grade nasopharyngeal papillary adenocarcinoma (TL-LGNPPA) is an extremely rare malignancy bearing histomorphological similarities to papillary thyroid carcinoma with good prognosis. It's important to distinguish TL-LGNPPA from other papillary tumors including nasopharyngeal papillary adenocarcinoma (NPPA), metastatic and ectopic papillary thyroid cancer, and metastasized adenocarcinomas, etc. To date, only 48 cases of TL-LGNPPA have been reported in the English literatures. Here, we reported the genomic characteristics of additional 4 cases and reviewed other reports to clarify the clinicopathological features of this tumor. In this study, 41 mutations were detected by whole-exome sequencing, but no typical driver mutations were found. Two sample with Copy Number Variations (CNV) were found (7 q22. 17 q12), of which the segment spanned the regions of RASA4, POLR2J2, SPDYE2, CCL3, CCL4, etc. Additionally, no MSI and HLA LOH were found. To our knowledge, we are the first to reveal the genetic underpinnings of this rare tumor. The clinicopathological features of TL-LGNPPA were characterized, shedding more light on the essential difference between TL-LGNPPA with other papillary tumors.

Jaw1/LRMP increases Ca2+ influx upon GPCR stimulation with heterogeneous effect on the activity of each ITPR subtype

Ca²⁺ influx upon G protein-coupled receptor (GPCR) stimulation is observed as a cytosolic Ca²⁺ concentration oscillation crucial to initiating downstream responses including cell proliferation, differentiation, and cell–cell communication. Although Jaw1 is known to interact with inositol 1,4,5-triphosphate receptor (ITPRs), Ca²⁺ channels on the endoplasmic reticulum, the function of Jaw1 in the Ca²⁺ dynamics with physiological stimulation remains unclear. In this study, using inducible Jaw1-expressing HEK293 cells, we showed that Jaw1 increases Ca²⁺ influx by GPCR stimulation via changing the Ca²⁺ influx oscillation pattern. Furthermore, we showed that Jaw1 increases the Ca²⁺ release activity of all ITPR subtypes in a subtly different manner. It is well known that the Ca²⁺ influx oscillation pattern varies from cell type to cell type, therefore these findings provide an insight into the relationship between the heterogeneous Ca²⁺ dynamics and the specific ITPR and Jaw1 expression patterns.

Optogenetic actuator - ERK biosensor circuits identify MAPK network nodes that shape ERK dynamics

Combining single-cell measurements of ERK activity dynamics with perturbations provides insights into the MAPK network topology. We built circuits consisting of an optogenetic actuator to activate MAPK signaling and an ERK biosensor to measure single-cell ERK dynamics. This allowed us to conduct RNAi screens to investigate the role of 50 MAPK proteins in ERK dynamics. We found that the MAPK network is robust against most node perturbations. We observed that the ERK-RAF and the ERK-RSK2-SOS negative feedback operate simultaneously to regulate ERK dynamics. Bypassing the RSK2-mediated feedback, either by direct optogenetic activation of RAS, or by RSK2 perturbation, sensitized ERK dynamics to further perturbations. Similarly, targeting this feedback in a human ErbB2-dependent oncogenic signaling model increased the efficiency of a MEK inhibitor. The RSK2-mediated feedback is thus important for the ability of the MAPK network to produce consistent ERK outputs, and its perturbation can enhance the efficiency of MAPK inhibitors.

In vitro differentiation of W8B2+ human cardiac stem cells: gene expression of ionic channels and spontaneous calcium activity

Background

Human cardiac stem cells expressing the W8B2 marker (W8B2⁺ CSCs) were recently identified and proposed as a new model of multipotent CSCs capable of differentiating into smooth muscle cells, endothelial cells and immature myocytes. Nevertheless, no characterization of ion channel or calcium activity during the differentiation of these stem cells has been reported.

Methods

The objectives of this study were thus to analyze (using the TaqMan Low-Density Array technique) the gene profile of W8B2⁺ CSCs pertaining to the regulation of ion channels, transporters and other players involved in the calcium homeostasis of these cells. We also analyzed spontaneous calcium activity (via the GCaMP calcium probe) during the in vitro differentiation of W8B2⁺ CSCs into cardiac myocytes.

Results

Our results show an entirely different electrophysiological genomic profile between W8B2⁺ CSCs before and after differentiation. Some specific nodal genes, such as Tbx3, HCN, ICaT, L, KV, and NCX, are overexpressed after this differentiation. In addition, we reveal spontaneous calcium activity or a calcium clock whose kinetics change during the differentiation process. A pharmacological study carried out on differentiated W8B2⁺ CSCs showed that the NCX exchanger and IP3 stores play a fundamental role in the generation of these calcium oscillations.

Conclusions

Taken together, the present results provide important information on ion channel expression and intrinsic calcium dynamics during the differentiation process of stem cells expressing the W8B2 marker.

The Oscillation Amplitude, Not the Frequency of Cytosolic Calcium, Regulates Apoptosis Induction

Although a rising concentration of cytosolic Ca²⁺ has long been recognized as an essential signal for apoptosis, the dynamical mechanisms by which Ca²⁺ regulates apoptosis are not clear yet. To address this, we constructed a computational model that integrates known biochemical reactions and can reproduce the dynamical behaviors of Ca²⁺-induced apoptosis as observed in experiments. Model analysis shows that oscillating Ca²⁺ signals first convert into gradual signals and eventually transform into a switch-like apoptotic response. Via the two processes, the apoptotic signaling pathway filters the frequency of Ca²⁺ oscillations effectively but instead responds acutely to their amplitude. Collectively, our results suggest that Ca²⁺ regulates apoptosis mainly via oscillation amplitude, rather than frequency, modulation. This study not only provides a comprehensive understanding of how oscillatory Ca²⁺ dynamically regulates the complex apoptotic signaling network but also presents a typical example of how Ca²⁺ controls cellular responses through amplitude modulation.

Targeting the Calcium Signalling Machinery in Cancer

Cancer is caused by excessive cell proliferation and a propensity to avoid cell death, while the spread of cancer is facilitated by enhanced cellular migration, invasion, and vascularization. Cytosolic Ca²⁺ is central to each of these important processes, yet to date, there are no cancer drugs currently being used clinically, and very few undergoing clinical trials, that target the Ca²⁺ signalling machinery. The aim of this review is to highlight some of the emerging evidence that targeting key components of the Ca²⁺ signalling machinery represents a novel and relatively untapped therapeutic strategy for the treatment of cancer.

Tailorable hierarchical structures of biomimetic hydroxyapatite micro/nano particles promoting endocytosis and osteogenic differentiation of stem cells

Hydroxyapatite (HA) micro/nano particles show great promise as artificial bone and dental substitutes, or drug carrier systems. However, the precise regulation of hydroxyapatite micro/nano particles with controllable physicochemical properties (such as hierarchical structure, particle size, potential and crystallinity) is still a challenge. Furthermore, the effects of different hierarchical structures on biological responses have been rarely reported. Herein, the HA particles with a precisely tailored micro/nano hierarchical structure have been developed using an elaborate biomimetic synthesis technology. Three representative particles, namely, micro/nano needle-like HA particles, micro/nano rod-like HA particles, and micro/nano flake-like HA particles, were featured to evaluate their biological responses to stem cells. The pore structure facilitated the adsorption of serum adhesive proteins, which together with the unique hierarchical architecture of micro/nano flake-like HA particles remarkably promoted the endocytosis efficiency in a concentration-dependent manner. The qRT-PCR together with RNA-seq and western blot analyses showed that micro/nano flake-like HA particles more significantly up-regulated the expression of genes and production of proteins related to osteogenic differentiation among the three particles through the activated ERK/MAPK signalling pathway. RNA-seq further revealed a complex mechanism of cell interface events, suggesting that the hierarchical architecture of HA particles is of crucial importance for the regulation of actin cytoskeleton involved in the modulation of cell adhesion which positively stimulated osteogenic differentiation of stem cells. Moreover, the endocytosis of particles into lysosomes resulted in an increase in the intracellular Ca²⁺ levels, which activated possible intracellular Ca²⁺-mediated signaling cascades (Ras/cAMP/Rap1/MAPK signaling pathways) related to osteogenic differentiation of stem cells. Our findings shed light on the effects of different hierarchical structures of HA particles on stem cell differentiation and contribute to the optimal design of implant materials.

Wnt-PLC-IP3-Connexin-Ca2+ axis maintains ependymal motile cilia in zebrafish spinal cord

Ependymal cells (ECs) are multiciliated neuroepithelial cells that line the ventricles of the brain and the central canal of the spinal cord (SC). How ependymal motile cilia are maintained remains largely unexplored. Here we show that zebrafish embryos deficient in Wnt signaling have defective motile cilia, yet harbor intact basal bodies. With respect to maintenance of ependymal motile cilia, plcδ3a is a target gene of Wnt signaling. Lack of Connexin43 (Cx43), especially its channel function, decreases motile cilia and intercellular Ca²⁺ wave (ICW) propagation. Genetic ablation of cx43 in zebrafish and mice diminished motile cilia. Finally, Cx43 is also expressed in ECs of the human SC. Taken together, our findings indicate that gap junction mediated ICWs play an important role in the maintenance of ependymal motile cilia, and suggest that the enhancement of functional gap junctions by pharmacological or genetic manipulations may be adopted to ameliorate motile ciliopathy.

Ependymal cells are supporting cells in the central nervous system. Here the authors elucidate a signalling axis in zebrafish spinal cord ependymal cells that is important for motile cilia assembly and maintenance, demonstrating that it depends on intercellular propagation of calcium ions via connexin 43.

Loss of RDM1 enhances hepatocellular carcinoma progression via p53 and Ras/Raf/ERK pathways

Hepatocellular carcinoma (HCC), with its ineffective therapeutic options and poor prognosis, represents a global threat. In the present study, we show that RAD52 motif 1 (RDM1), a key regulator of DNA double‐strand break repair and recombination, is downregulated in HCC tissues and suppresses tumor growth. In clinical HCC samples, low expression of RDM1 correlates with larger tumor size, poor tumor differentiation, and unfavorable survival. In vitro and in vivo data demonstrate that knockdown of RDM1 increases HCC cell proliferation, colony formation, and cell population at G2/M phase, whereas RDM1 overexpression results in the opposite phenotypes. Mechanistically, RDM1 binds to the tumor suppressor p53 and enhances its protein stability. In the presence of p53, RDM1 suppresses the phosphorylation of Raf and ERK. Overexpression of p53 or treatment with ERK inhibitor significantly abolishes cell proliferation induced by the depletion of RDM1. In addition, overexpression of methyltransferase‐like 3 markedly induces N6‐methyladenosine modification of RDM1 mRNA and represses its expression. Taken together, our study indicates that RDM1 functions as a tumor suppressor and may be a potential prognostic and therapeutic factor for HCC.

TRPC3 Regulates the Proliferation and Apoptosis Resistance of Triple Negative Breast Cancer Cells through the TRPC3/RASA4/MAPK Pathway

Currently, there is no effective molecular-based therapy for triple-negative breast cancer (TNBC). Canonical transient receptor potential isoform 3 (TRPC3) was previously shown to be upregulated in breast cancer biopsy tissues when compared to normal breast tissues. However, the biological role of TRPC3 in breast cancer still remains to be elucidated. In this study, subcellular fractionation followed by Western blot and immunocytochemistry showed that TRPC3 was over-expressed on the plasma membrane of TNBC line MDA-MB-231 when compared to an estrogen receptor-positive cell line MCF-7. TRPC3 blocker Pyr3 and dominant negative of TRPC3 attenuated proliferation, induced apoptosis and sensitized cell death to chemotherapeutic agents in MDA-MB-231 as measured by proliferation assays. Interestingly, Ras GTPase-activating protein 4 (RASA4), a Ca²⁺-promoted Ras-MAPK pathway suppressor, was found to be located on the plasma membrane of MDA-MB-231. Blocking TRPC3 decreased the amount of RASA4 located on the plasma membrane, with concomitant activation of MAPK pathways. Our results suggest that, in TNBC MDA-MB-231 cells, Ca²⁺ influx through TRPC3 channel sustains the presence of RASA4 on the plasma membrane where it inhibits the Ras-MAPK pathway, leading to proliferation and apoptosis resistance. Our study reveals the novel TRPC3-RASA4-MAPK signaling cascade in TNBC cells and suggests that TRPC3 may be exploited as a potential therapeutic target for TNBC.

Regulator of G Protein Signaling Protein 12 (Rgs12) Controls Mouse Osteoblast Differentiation via Calcium Channel/Oscillation and Gαi-ERK Signaling

Bone homeostasis intimately relies on the balance between osteoblasts (OBs) and osteoclasts (OCs). Our previous studies have revealed that regulator of G protein signaling protein 12 (Rgs12), the largest protein in the Rgs super family, is essential for osteoclastogenesis from hematopoietic cells and OC precursors. However, how Rgs12 regulates OB differentiation and function is still unknown. To understand that, we generated an OB-targeted Rgs12 conditional knockout (CKO) mice model by crossing Rgs12fl/fl mice with Osterix (Osx)-Cre transgenic mice. We found that Rgs12 was highly expressed in both OB precursor cells (OPCs) and OBs of wild-type (WT) mice, and gradually increased during OB differentiation, whereas Rgs12-CKO mice (OsxCre/+ ; Rgs12fl/fl ) exhibited a dramatic decrease in both trabecular and cortical bone mass, with reduced numbers of OBs and increased apoptotic cell population. Loss of Rgs12 in OPCs in vitro significantly inhibited OB differentiation and the expression of OB marker genes, resulting in suppression of OB maturation and mineralization. Further mechanism study showed that deletion of Rgs12 in OPCs significantly inhibited guanosine triphosphatase (GTPase) activity and cyclic adenosine monophosphate (cAMP) level, and impaired Calcium (Ca2+ ) oscillations via restraints of major Ca2+ entry sources (extracellular Ca2+ influx and intracellular Ca2+ release from endoplasmic reticulum), partially contributed by the blockage of L-type Ca2+ channel mediated Ca2+ influx. Downstream mediator extracellular signal-related protein kinase (ERK) was found inactive in OBs of OsxCre/+ ; Rgs12fl/fl mice and in OPCs after Rgs12 deletion, whereas application of pertussis toxin (PTX) or overexpression of Rgs12 could rescue the defective OB differentiation via restoration of ERK phosphorylation. Our findings reveal that Rgs12 is an important regulator during osteogenesis and highlight Rgs12 as a potential therapeutic target for bone disorders. © 2018 American Society for Bone and Mineral Research.

Propagation of Oscillating Chemical Signals through Reaction Networks

Akin to electronic systems that can tune to and process signals of select frequencies, systems/networks of chemical reactions also "propagate" time-varying concentration inputs in a frequency-dependent manner. Whereas signals of low frequencies are transmitted, higher frequency inputs are dampened and converted into steady-concentration outputs. Such behavior is observed in both idealized reaction chains as well as realistic signaling cascades, in the latter case explaining the experimentally observed responses of such cascades to input calcium oscillations. These and other results are supported by numerical simulations within the freely available Kinetix web application we developed to study chemical systems of arbitrary architectures, reaction kinetics, and boundary conditions.

Ca2+ Requirements for Long-Term Depression Are Frequency Sensitive in Purkinje Cells

Cerebellar long-term depression (LTD) is a form of synaptic plasticity dependent on postsynaptic Ca²⁺ changes. One fundamental question is how LTD is selectively induced by specific numbers of Ca²⁺ pulses and which are the frequency and duration of this train of pulses required for LTD induction. The molecular mechanism which leads the integration of postsynaptic Ca²⁺ pulses in the LTD signaling network has not been elucidated either. Recent publications have shown that Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is required for LTD induction. Additionally, protein kinase C (PKC), CaMKII, and MAPK play an important role to transduce the frequency of Ca²⁺ pulses into their enzymatic activity levels; however, it is still unknown which enzymes are involved in decoding Ca²⁺ pulses in LTD. We have extended a stochastic model of LTD by adding the molecular network regulating CaMKII activity and its activation. We solved this model with stochastic engine for pathway simulation to include the effect of biochemical noise in LTD. We systematically investigated the dependence of LTD induction on stimulus frequencies, and we found that LTD is selectively induced by a specific number of Ca²⁺ spikes at different frequencies. We observed that CaMKII is essential to induce LTD, and LTD is only weakly induced when its Thr286 phosphorylation site has been deleted. We found that CaMKII decodes the frequency of Ca²⁺ spikes into different amounts of kinase activity during LTD induction. In addition, PKC and ERK enzyme activity is highly sensitive to the frequency and the number of Ca²⁺ pulses and this sensitivity has an important effect on LTD activation. This research predicts the postsynaptic Ca²⁺ requirements to induce LTD using a typical synaptic activation sequence and explains how LTD is selectively induced by specific number of Ca²⁺ pulses at different frequencies.

A far-red fluorescent probe based on a phospha-fluorescein scaffold for cytosolic calcium imaging

The far-red emissive fluorescent probe CaPF-1 based on a phospha-fluorescein scaffold enables the detection of cytosolic calcium ions in living cells. The probe can be excited in the red region (λ_abs = 636 nm) and exhibits a sufficiently high fluorescence turn-on response in the far-red region (λ_em = 663 nm) upon complexation with calcium ions. The hydrophilic and anionic characteristics of this phospha-fluorescein fluorophore allowed the cytosolic localization of CaPF-1. Moreover, it was possible to visualize histamine-induced calcium oscillation in HeLa cells using CaPF-1.

TRPC3-mediated Ca2+ signals as a promising strategy to boost therapeutic angiogenesis in failing hearts: The role of autologous endothelial colony forming cells

Endothelial progenitor cells (EPCs) are a sub-population of bone marrow-derived mononuclear cells that are released in circulation to restore damaged endothelium during its physiological turnover or rescue blood perfusion after an ischemic insult. Additionally, they may be mobilized from perivascular niches located within larger arteries' wall in response to hypoxic conditions. For this reason, EPCs have been regarded as an effective tool to promote revascularization and functional recovery of ischemic hearts, but clinical application failed to exploit the full potential of patients-derived cells. Indeed, the frequency and biological activity of EPCs are compromised in aging individuals or in subjects suffering from severe cardiovascular risk factors. Rejuvenating the reparative phenotype of autologous EPCs through a gene transfer approach has, therefore, been put forward as an alternative approach to enhance their therapeutic potential in cardiovascular patients. An increase in intracellular Ca²⁺ concentration constitutes a pivotal signal for the activation of the so-called endothelial colony forming cells (ECFCs), the only known truly endothelial EPC subset. Studies from our group showed that the Ca²⁺ toolkit differs between peripheral blood- and umbilical cord blood (UCB)-derived ECFCs. In the present article, we first discuss how VEGF uses repetitive Ca²⁺ spikes to regulate angiogenesis in ECFCs and outline how VEGF-induced intracellular Ca²⁺ oscillations differ between the two ECFC subtypes. We then hypothesize about the possibility to rejuvenate the biological activity of autologous ECFCs by transfecting the cell with the Ca²⁺ -permeable channel Transient Receptor Potential Canonical 3, which selectively drives the Ca²⁺ response to VEGF in UCB-derived ECFCs.

Determining the Limitations and Benefits of Noise in Gene Regulation and Signal Transduction through Single Cell, Microscopy-Based Analysis

Stochastic fluctuations, termed "noise," in the level of biological molecules can greatly impact cellular functions. While biological noise can sometimes be detrimental, recent studies have provided an increasing number of examples in which biological noise can be functionally beneficial. Rather than provide an exhaustive review of the growing literature in this field, in this review, we focus on single-cell studies based on quantitative microscopy that have generated a deeper understanding of the sources, characteristics, limitations, and benefits of biological noise. Specifically, we highlight studies showing how noise can help coordinate the expression of multiple downstream target genes, impact the channel capacity of signaling networks, and interact synergistically with oscillatory dynamics to enhance the sensitivity of signal processing. We conclude with a discussion of current challenges and future opportunities.

Sexual pheromone modulates the frequency of cytosolic Ca2+ bursts in Saccharomyces cerevisiae

Transient and highly regulated elevations of cytosolic Ca²⁺ control a variety of cellular processes. Bulk measurements using radioactive Ca²⁺ and the luminescent sensor aequorin have shown that in response to pheromone, budding yeast cells undergo a rise of cytosolic Ca²⁺ that is mediated by two import systems composed of the Mid1-Cch1-Ecm7 protein complex and the Fig1 protein. Although this response has been widely studied, there is no treatment of Ca²⁺ dynamics at the single-cell level. Here, using protein calcium indicators, we show that both vegetative and pheromone-treated yeast cells exhibit discrete and asynchronous Ca²⁺ bursts. Most bursts reach maximal amplitude in 1-10 s, range between 7 and 30 s, and decay in a way that fits a single-exponential model. In vegetative cells, bursts are scarce but preferentially occur when cells are transitioning G1 and S phases. On pheromone presence, Ca²⁺ burst occurrence increases dramatically, persisting during cell growth polarization. Pheromone concentration modulates burst frequency in a mechanism that depends on Mid1, Fig1, and a third, unidentified, import system. We also show that the calcineurin-responsive transcription factor Crz1 undergoes nuclear localization bursts during the pheromone response.

TrpC5 regulates differentiation through the Ca2+/Wnt5a signalling pathway in colorectal cancer

Transient receptor potential channel 5 (TrpC5) is a member of the TrpC subgroup, and it forms a receptor-activated, non-selective Ca²⁺ channel. The architecture of the TrpC5 channel is poorly understood. In the present study, we report that TrpC5 is a key factor in regulating differentiation in colorectal cancer (CRC). Through a study of specimens from a large cohort of patients with CRC, we found that TrpC5 was highly expressed and its cellular level correlated with tumour grade. We showed further that up-regulated TrpC5 caused a robust rise in intracellular calcium concentration [Ca²⁺]_i, increased Wnt5a expression and the nuclear translocation of β-catenin, leading to a reduction in cancer differentiation and an increase in cancer cell stemness. Notably, patients with tumours that expressed high levels of TrpC5 showed significantly poorer disease-free and overall survival. Therefore, our findings suggest that TrpC5 is an independent adverse prognostic factor for death in CRC, reducing differentiation through the Ca²⁺/Wnt5a signalling pathway.

Endogenous TRPV1 stimulation leads to the activation of the inositol phospholipid pathway necessary for sustained Ca2+ oscillations

Sensory neuron subpopulations as well as breast and prostate cancer cells express functional transient receptor potential vanilloid type 1 (TRPV1) ion channels; however little is known how TRPV1 activation leads to biological responses. Agonist-induced activation of TRPV1 resulted in specific spatiotemporal patterns of cytoplasmic Ca²⁺ signals in breast and prostate cancer-derived cells. Capsaicin (CAPS; 50μM) evoked intracellular Ca²⁺ oscillations and/or intercellular Ca²⁺ waves in all cell lines. As evidenced in prostate cancer Du 145 cells, oscillations were largely dependent on the expression of functional TRPV1 channels in the plasma membrane, phospholipase C activation and on the presence of extracellular Ca²⁺ ions. Concomitant oscillations of the mitochondrial matrix Ca²⁺ concentration resulted in mitochondria energization evidenced by increased ATP production. CAPS-induced Ca²⁺ oscillations also occurred in a subset of sensory neurons, yet already at lower CAPS concentrations (1μM). Stimulation of ectopically expressed TRPV1 channels in CAPS-insensitive NIH-3T3 cells didn't provoke CAPS-triggered Ca²⁺ oscillations; rather it resulted in low-magnitude, long-lasting elevations of the cytosolic Ca²⁺ concentration. This indicates that sole TRPV1 activation is not sufficient to generate Ca²⁺ oscillations. Instead the initial TRPV1-mediated signal leads to the activation of the inositol phospholipid pathway. This in turn suffices to generate a biologically relevant frequency-modulated Ca²⁺ signal.

Cellular Architecture Regulates Collective Calcium Signaling and Cell Contractility

A key feature of multicellular systems is the ability of cells to function collectively in response to external stimuli. However, the mechanisms of intercellular cell signaling and their functional implications in diverse vascular structures are poorly understood. Using a combination of computational modeling and plasma lithography micropatterning, we investigate the roles of structural arrangement of endothelial cells in collective calcium signaling and cell contractility. Under histamine stimulation, endothelial cells in self-assembled and microengineered networks, but not individual cells and monolayers, exhibit calcium oscillations. Micropatterning, pharmacological inhibition, and computational modeling reveal that the calcium oscillation depends on the number of neighboring cells coupled via gap junctional intercellular communication, providing a mechanistic basis of the architecture-dependent calcium signaling. Furthermore, the calcium oscillation attenuates the histamine-induced cytoskeletal reorganization and cell contraction, resulting in differential cell responses in an architecture-dependent manner. Taken together, our results suggest that endothelial cells can sense and respond to chemical stimuli according to the vascular architecture via collective calcium signaling.

Endothelial mitochondria regulate the intracellular Ca2+ response to fluid shear stress

Shear stress is known to stimulate an intracellular free calcium concentration ([Ca(2+)]i) response in vascular endothelial cells (ECs). [Ca(2+)]i is a key second messenger for signaling that leads to vasodilation and EC survival. Although it is accepted that the shear-induced [Ca(2+)]i response is, in part, due to Ca(2+) release from the endoplasmic reticulum (ER), the role of mitochondria (second largest Ca(2+) store) is unknown. We hypothesized that the mitochondria play a role in regulating [Ca(2+)]i in sheared ECs. Cultured ECs, loaded with a Ca(2+)-sensitive fluorophore, were exposed to physiological levels of shear stress. Shear stress elicited [Ca(2+)]i transients in a percentage of cells with a fraction of them displaying oscillations. Peak magnitudes, percentage of oscillating ECs, and oscillation frequencies depended on the shear level. [Ca(2+)]i transients/oscillations were present when experiments were conducted in Ca(2+)-free solution (plus lanthanum) but absent when ECs were treated with a phospholipase C inhibitor, suggesting that the ER inositol 1,4,5-trisphosphate receptor is responsible for the [Ca(2+)]i response. Either a mitochondrial uncoupler or an electron transport chain inhibitor, but not a mitochondrial ATP synthase inhibitor, prevented the occurrence of transients and especially inhibited the oscillations. Knockdown of the mitochondrial Ca(2+) uniporter also inhibited the shear-induced [Ca(2+)]i transients/oscillations compared with controls. Hence, EC mitochondria, through Ca(2+) uptake/release, regulate the temporal profile of shear-induced ER Ca(2+) release. [Ca(2+)]i oscillation frequencies detected were within the range for activation of mechanoresponsive kinases and transcription factors, suggesting that dysfunctional EC mitochondria may contribute to cardiovascular disease by deregulating the shear-induced [Ca(2+)]i response.

Band-pass processing in a GPCR signaling pathway selects for NFAT transcription factor activation

Many biological processes are rhythmic and proper timing is increasingly appreciated as being critical for development and maintenance of physiological functions. To understand how temporal modulation of an input signal influences downstream responses, we employ microfluidic pulsatile stimulation of a G-protein coupled receptor, the muscarinic M3 receptor, in single cells with simultaneous real-time imaging of both intracellular calcium and NFAT nuclear localization. Interestingly, we find that reduced stimulation with pulses of ligand can give more efficient transcription factor activation, if stimuli are timed appropriately. Our experiments and computational analyses show that M3 receptor-induced calcium oscillations form a low pass filter while calcium-induced NFAT translocation forms a high pass filter. The combination acts as a band-pass filter optimized for intermediate frequencies of stimulation. We demonstrate that receptor desensitization and NFAT translocation rates determine critical features of the band-pass filter and that the band-pass may be shifted for different receptors or NFAT dynamics. As an example, we show that the two NFAT isoforms (NFAT4 and NFAT1) have shifted band-pass windows for the same receptor. While we focus specifically on the M3 muscarinic receptor and NFAT translocation, band-pass processing is expected to be a general theme that applies to multiple signaling pathways.

Noise facilitates transcriptional control under dynamic inputs

Cells must respond sensitively to time-varying inputs in complex signaling environments. To understand how signaling networks process dynamic inputs into gene expression outputs and the role of noise in cellular information processing, we studied the immune pathway NF-κB under periodic cytokine inputs using microfluidic single-cell measurements and stochastic modeling. We find that NF-κB dynamics in fibroblasts synchronize with oscillating TNF signal and become entrained, leading to significantly increased NF-κB oscillation amplitude and mRNA output compared to non-entrained response. Simulations show that intrinsic biochemical noise in individual cells improves NF-κB oscillation and entrainment, whereas cell-to-cell variability in NF-κB natural frequency creates population robustness, together enabling entrainment over a wider range of dynamic inputs. This wide range is confirmed by experiments where entrained cells were measured under all input periods. These results indicate that synergy between oscillation and noise allows cells to achieve efficient gene expression in dynamically changing signaling environments.

The functional contribution of calcium ion flux heterogeneity in T cells

The role of intracellular calcium ion oscillations in T-cell physiology is being increasingly appreciated by studies that describe how unique temporal and spatial calcium ion signatures can control different signalling pathways. Within this review, we provide detailed mechanisms of calcium ion oscillations, and emphasise the pivotal role that calcium signalling plays in directing crucial events pertaining to T-cell functionality. We also describe methods of calcium ion quantification, and take the opportunity to discuss how a deeper understanding of calcium signalling combined with new detection and quantification methodologies can be used to better design immunotherapies targeting T-cell responses.

Scrutinizing calcium flux oscillations in T lymphocytes to deduce the strength of stimulus

The capture and activation of individual T cells on functionalised surfaces enables real-time analyses of the magnitude and rhythm of intracellular calcium release. Application of Haarlet transformations generate a calcium flux ‘threshold’, with the frequency of the ‘threshold crossings’ correlating with the strength of the original T cell stimulus. These findings represent a new method to evaluate graduations in T cell activation in real time, and at a single-cell level.

Physiological epidermal growth factor concentrations activate high affinity receptors to elicit calcium oscillations

Signaling mediated by the epidermal growth factor (EGF) is crucial in tissue development, homeostasis and tumorigenesis. EGF is mitogenic at picomolar concentrations and is known to bind its receptor on high affinity binding sites depending of the oligomerization state of the receptor (monomer or dimer). In spite of these observations, the cellular response induced by EGF has been mainly characterized for nanomolar concentrations of the growth factor, and a clear definition of the cellular response to circulating (picomolar) concentrations is still lacking. We investigated Ca2+ signaling, an early event in EGF responses, in response to picomolar doses in COS-7 cells where the monomer/dimer equilibrium is unaltered by the synthesis of exogenous EGFR. Using the fluo5F Ca2+ indicator, we found that picomolar concentrations of EGF induced in 50% of the cells a robust oscillatory Ca2+ signal quantitatively similar to the Ca2+ signal induced by nanomolar concentrations. However, responses to nanomolar and picomolar concentrations differed in their underlying mechanisms as the picomolar EGF response involved essentially plasma membrane Ca2+ channels that are not activated by internal Ca2+ store depletion, while the nanomolar EGF response involved internal Ca2+ release. Moreover, while the picomolar EGF response was modulated by charybdotoxin-sensitive K+ channels, the nanomolar response was insensitive to the blockade of these ion channels.

Calmodulin-controlled spatial decoding of oscillatory Ca2+ signals by calcineurin

Calcineurin is responsible for mediating a wide variety of cellular processes in response to dynamic calcium (Ca(2+)) signals, yet the precise mechanisms involved in the spatiotemporal control of calcineurin signaling are poorly understood. Here, we use genetically encoded fluorescent biosensors to directly probe the role of cytosolic Ca(2+) oscillations in modulating calcineurin activity dynamics in insulin-secreting MIN6 β-cells. We show that Ca(2+) oscillations induce distinct temporal patterns of calcineurin activity in the cytosol and plasma membrane vs at the ER and mitochondria in these cells. Furthermore, we found that these differential calcineurin activity patterns are determined by variations in the subcellular distribution of calmodulin (CaM), indicating that CaM plays an active role in shaping both the spatial and temporal aspects of calcineurin signaling. Together, our findings provide new insights into the mechanisms by which oscillatory signals are decoded to generate specific functional outputs within different cellular compartments.

Gambierol inhibition of voltage-gated potassium channels augments spontaneous Ca2+ oscillations in cerebrocortical neurons

Gambierol is a marine polycyclic ether toxin produced by the marine dinoflagellate Gambierdiscus toxicus and is a member of the ciguatoxin toxin family. Gambierol has been demonstrated to be either a low-efficacy partial agonist/antagonist of voltage-gated sodium channels or a potent blocker of voltage-gated potassium channels (Kvs). Here we examined the influence of gambierol on intact cerebrocortical neurons. We found that gambierol produced both a concentration-dependent augmentation of spontaneous Ca(2+) oscillations, and an inhibition of Kv channel function with similar potencies. In addition, an array of selective as well as universal Kv channel inhibitors mimicked gambierol in augmenting spontaneous Ca(2+) oscillations in cerebrocortical neurons. These data are consistent with a gambierol blockade of Kv channels underlying the observed increase in spontaneous Ca(2+) oscillation frequency. We also found that gambierol produced a robust stimulation of phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2). Gambierol-stimulated ERK1/2 activation was dependent on both inotropic [N-methyl-d-aspartate (NMDA)] and type I metabotropic glutamate receptors (mGluRs) inasmuch as MK-801 [NMDA receptor inhibitor; (5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate], S-(4)-CGP [S-(4)-carboxyphenylglycine], and MTEP [type I mGluR inhibitors; 3-((2-methyl-4-thiazolyl)ethynyl) pyridine] attenuated the response. In addition, 2-aminoethoxydiphenylborane, an inositol 1,4,5-trisphosphate receptor inhibitor, and U73122 (1-[6-[[(17b)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione), a phospholipase C inhibitor, both suppressed gambierol-induced ERK1/2 activation, further confirming the role of type I mGluR-mediated signaling in the observed ERK1/2 activation. Finally, we found that gambierol produced a concentration-dependent stimulation of neurite outgrowth that was mimicked by 4-aminopyridine, a universal potassium channel inhibitor. Considered together, these data demonstrate that gambierol alters both Ca(2+) signaling and neurite outgrowth in cerebrocortical neurons as a consequence of blockade of Kv channels.

Purinergic signalling is required for calcium oscillations in migratory chondrogenic progenitor cells

Osteoarthritis (OA) is the most common form of chronic musculoskeletal disorders. A migratory stem cell population termed chondrogenic progenitor cells (CPC) with in vitro chondrogenic potential was previously isolated from OA cartilage. Since intracellular Ca(2+) signalling is an important regulator of chondrogenesis, we aimed to provide a detailed understanding of the Ca(2+) homeostasis of CPCs. In this work, CPCs immortalised by lentiviral administration of the human telomerase reverse transcriptase (hTERT) and grown in monolayer cultures were studied. Expressions of all three IP3Rs were confirmed, but no RyR subtypes were detected. Ca(2+) oscillations observed in CPCs were predominantly dependent on Ca(2+) release and store replenishment via store-operated Ca(2+) entry; CPCs express both STIM1 and Orai1 proteins. Expressions of adenosine receptor mRNAs were verified, and adenosine elicited Ca(2+) transients. Various P2 receptor subtypes were identified; P2Y1 can bind ADP; P2Y4 is targeted by UTP; and ATP may evoke Ca(2+) transients via detected P2X subtypes, as well as P2Y1 and P2Y2. Enzymatic breakdown of extracellular nucleotides by apyrase completely abrogated Ca(2+) oscillations, suggesting that an autocrine/paracrine purinergic mechanism may drive Ca(2+) oscillations in these cells. As CPCs possess a broad spectrum of functional molecular elements of Ca(2+) signalling, Ca(2+)-dependent regulatory mechanisms can be supposed to influence their differentiation potential.

Calcium-dependent regulation of glucose homeostasis in the liver

A major role of the liver is to integrate multiple signals to maintain normal blood glucose levels. The balance between glucose storage and mobilization is primarily regulated by the counteracting effects of insulin and glucagon. However, numerous signals converge in the liver to ensure energy demand matches the physiological status of the organism. Many circulating hormones regulate glycogenolysis, gluconeogenesis and mitochondrial metabolism by calcium-dependent signaling mechanisms that manifest as cytosolic Ca(2+) oscillations. Stimulus-strength is encoded in the Ca(2+) oscillation frequency, and also by the range of intercellular Ca(2+) wave propagation in the intact liver. In this article, we describe how Ca(2+) oscillations and waves can regulate glucose output and oxidative metabolism in the intact liver; how multiple stimuli are decoded though Ca(2+) signaling at the organ level, and the implications of Ca(2+) signal dysregulation in diseases such as metabolic syndrome and non-alcoholic fatty liver disease.

Signaling to extracellular signal-regulated kinase from ErbB1 kinase and protein kinase C: feedback, heterogeneity, and gating

Many extracellular signals act via the Raf/MEK/ERK cascade in which kinetics, cell-cell variability, and sensitivity of the ERK response can all influence cell fate. Here we used automated microscopy to explore the effects of ERK-mediated negative feedback on these attributes in cells expressing endogenous ERK or ERK2-GFP reporters. We studied acute rather than chronic stimulation with either epidermal growth factor (ErbB1 activation) or phorbol 12,13-dibutyrate (PKC activation). In unstimulated cells, ERK-mediated negative feedback reduced the population-average and cell-cell variability of the level of activated ppERK and increased its robustness to changes in ERK expression. In stimulated cells, negative feedback (evident between 5 min and 4 h) also reduced average levels and variability of phosphorylated ERK (ppERK) without altering the “gradedness” or sensitivity of the response. Binning cells according to total ERK expression revealed, strikingly, that maximal ppERK responses initially occur at submaximal ERK levels and that this non-monotonic relationship changes to an increasing, monotonic one within 15 min. These phenomena occur in HeLa cells and MCF7 breast cancer cells and in the presence and absence of ERK-mediated negative feedback. They were best modeled assuming distributive (rather than processive) activation. Thus, we have uncovered a novel, time-dependent change in the relationship between total ERK and ppERK levels that persists without negative feedback. This change makes acute response kinetics dependent on ERK level and provides a “gating” or control mechanism in which the interplay between stimulus duration and the distribution of ERK expression across cells could modulate the proportion of cells that respond to stimulation.

Calmodulin transduces Ca2+ oscillations into differential regulation of its target proteins

Diverse physiological processes are regulated differentially by Ca(2+) oscillations through the common regulatory hub calmodulin. The capacity of calmodulin to combine specificity with promiscuity remains to be resolved. Here we propose a mechanism based on the molecular properties of calmodulin, its two domains with separate Ca(2+) binding affinities, and target exchange rates that depend on both target identity and Ca(2+) occupancy. The binding dynamics among Ca(2+), Mg(2+), calmodulin, and its targets were modeled with mass-action differential equations based on experimentally determined protein concentrations and rate constants. The model predicts that the activation of calcineurin and nitric oxide synthase depends nonmonotonically on Ca(2+)-oscillation frequency. Preferential activation reaches a maximum at a target-specific frequency. Differential activation arises from the accumulation of inactive calmodulin-target intermediate complexes between Ca(2+) transients. Their accumulation provides the system with hysteresis and favors activation of some targets at the expense of others. The generality of this result was tested by simulating 60 000 networks with two, four, or eight targets with concentrations and rate constants from experimentally determined ranges. Most networks exhibit differential activation that increases in magnitude with the number of targets. Moreover, differential activation increases with decreasing calmodulin concentration due to competition among targets. The results rationalize calmodulin signaling in terms of the network topology and the molecular properties of calmodulin.

Cyclic ADP ribose is a novel regulator of intracellular Ca2+ oscillations in human bone marrow mesenchymal stem cells

Bone marrow mesenchymal stem cells (MSCs) are a promising cell source for regenerative medicine. However, the cellular biology of these cells is not fully understood. The present study characterizes the cyclic ADP-ribose (cADPR)-mediated Ca(2+) signals in human MSCs and finds that externally applied cADPR can increase the frequency of spontaneous intracellular Ca(2+) (Ca(2+) (i) ) oscillations. The increase was abrogated by a specific cADPR antagonist or an inositol trisphosphate receptor (IP3R) inhibitor, but not by ryanodine. In addition, the cADPR-induced increase of Ca(2+) (i) oscillation frequency was prevented by inhibitors of nucleoside transporter or by inhibitors of the transient receptor potential cation melastatin-2 (TRPM2) channel. RT-PCR revealed mRNAs for the nucleoside transporters, concentrative nucleoside transporters 1/2 and equilibrative nucleoside transporters 1/3, IP3R1/2/3 and the TRPM2 channel, but not those for ryanodine receptors and CD38 in human MSCs. Knockdown of the TRPM2 channel by specific short interference RNA abolished the effect of cADPR on the Ca(2+) (i) oscillation frequency, and prevented the stimulation of proliferation by cADPR. Moreover, cADPR remarkably increased phosphorylated extracellular-signal-regulated kinases 1/2 (ERK1/2), but not Akt or p38 mitogen-activated protein kinase (MAPK). However, cADPR had no effect on adipogenesis or osteogenesis in human MSCs. Our results indicate that cADPR is a novel regulator of Ca(2+) (i) oscillations in human MSCs. It permeates the cell membrane through the nucleoside transporters and increases Ca(2+) oscillation via activation of the TRPM2 channel, resulting in enhanced phosphorylation of ERK1/2 and, thereby, stimulation of human MSC proliferation. This study delineates an alternate signalling pathway of cADPR that is distinct from its well-established role of serving as a Ca(2+) messenger for mobilizing the internal Ca(2+) stores. Whether cADPR can be used clinically for stimulating marrow function in patients with marrow disorders remains to be further studied.

Stromal interaction molecule 2 (STIM2) is frequently overexpressed in colorectal tumors and confers a tumor cell growth suppressor phenotype

Allelic imbalances at chromosome 4p have been largely documented in many different tumor types. In colorectal cancer, loss of heterozygosity (LOH) at 4p15 has been associated with tumor aggressiveness and poor patient outcome, however no target genes in the region have been identified to date. Since stromal interaction molecule 2 (STIM2) is located at 4p15.2 and has been proposed as a candidate gene for this region in glioblastoma multiforme, we aimed at investigating the role of STIM2 in colorectal cancer. We studied STIM2 transcript expression levels in a collection of xenografted primary colorectal tumors (n = 20) and a well-annotated tumor series of colorectal cancer (n = 140). We observed an overexpression of STIM2 in 63.5% of the cases that was associated with a less invasive phenotype. In vitro and in vivo functional studies with colon cancer cell lines revealed that overexpression of STIM2 reduced cell proliferation and tumor growth, respectively. Our work presents several lines of evidence indicating that STIM2 overexpression is a frequent trait in colorectal cancer that results in cell growth suppression, certifying that even in the absence of somatic genetic or epigenetic alterations, recurrent regions of LOH should still be considered a hallmark for the presence of relevant genes for tumorigenesis.

Spatial distribution and dose-response relationship for different operation modes in a reaction-diffusion model of the MAPK cascade

The mitogen-activated protein kinase (MAPK) cascade plays a critical role in the control of cell growth. Deregulation of this pathway contributes to the development of many cancers. To better understand its signal transduction, we constructed a reaction-diffusion model for the MAPK pathway. We modeled the three layers of phosphorylation-dephosphorylation reactions and diffusion processes from the cell membrane to the nucleus. Based on different types of feedback in the MAPK cascade, four operation modes are introduced. For each of the four modes, spatial distributions and dose-response curves of active kinases (i.e. ppMAPK) are explored by numerical simulation. The effects of propagation length, diffusion coefficient and feedback strength on the pathway dynamics are investigated. We found that intrinsic bistability in the MAPK cascade can generate a traveling wave of ppMAPK with constant amplitude when the propagation length is short. ppMAPK in this mode of intrinsic bistability decays more slowly than it does in all other modes as the propagation length increases. Moreover, we examined the global and local responses to Ras-GTP of these four modes, and demonstrated how the shapes of these dose-response curves change as the propagation length increases. Also, we found that larger diffusion constant gives a higher response level on the zero-order regime and makes the ppMAPK profiles flatter under strong Ras-GTP stimulus. Furthermore, we observed that spatial responses of ppMAPK are more sensitive to negative feedback than to positive feedback in the broader signal range. Finally, we showed how oscillatory signals pass through the kinase cascade, and found that high frequency signals are damped faster than low frequency ones.