Cell density-dependent changes in intracellular Ca2+ mobilization via the P2Y2 receptor in rat bone marrow stromal cells

Calcium response of spatially arranged cell networks to shear stress by confined single cell patterned microfluidic chips

Osteoblasts in multicellular organisms are sensitive to fluid shear stress (Fss) and respond smartly with versatile patterns of intracellular calcium signal ([Ca²⁺]_i). In this study, a spatial-single cell patterning method was developed by combining micro-contact printing (μCP) and reversible microfluidic chip mounted with vacuum together. Based on this well-defined patterning platform, it's possible to investigate calcium response to Fss modulated by spatial factors, and to characterize multiple calcium patterns quantitatively in terms of cell spacing and cell orientation. The result showed that the Fss-induced [Ca²⁺]_i profiles revealed oscillational signal patterns in non-connected cells such as those in physical-contacted cells. Close-arrayed osteoblasts showed remarkably more [Ca²⁺]_i oscillations than sparse-arrayed cells. The circular shape of the cells was sensitive to oscillational [Ca²⁺]_i as a potential major cause. The consistency of cell orientation and shear stress promoted temporal homogeneity of calcium oscillations.

Targeting Purinergic Signaling and Cell Therapy in Cardiovascular and Neurodegenerative Diseases

Extracellular purines exert several functions in physiological and pathophysiological mechanisms. ATP acts through P2 receptors as a neurotransmitter and neuromodulator and modulates heart contractility, while adenosine participates in neurotransmission, blood pressure, and many other mechanisms. Because of their capability to differentiate into mature cell types, they provide a unique therapeutic strategy for regenerating damaged tissue, such as in cardiovascular and neurodegenerative diseases. Purinergic signaling is pivotal for controlling stem cell differentiation and phenotype determination. Proliferation, differentiation, and apoptosis of stem cells of various origins are regulated by purinergic receptors. In this chapter, we selected neurodegenerative and cardiovascular diseases with clinical trials using cell therapy and purinergic receptor targeting. We discuss these approaches as therapeutic alternatives to neurodegenerative and cardiovascular diseases. For instance, promising results were demonstrated in the utilization of mesenchymal stem cells and bone marrow mononuclear cells in vascular regeneration. Regarding neurodegenerative diseases, in general, P2X7 and A_2A receptors mostly worsen the degenerative state. Stem cell-based therapy, mainly through mesenchymal and hematopoietic stem cells, showed promising results in improving symptoms caused by neurodegeneration. We propose that purinergic receptor activity regulation combined with stem cells could enhance proliferative and differentiation rates as well as cell engraftment.

The ectonucleoside triphosphate diphosphohydrolase-2 (NTPDase2) in human endometrium: a novel marker of basal stroma and mesenchymal stem cells

The human endometrium undergoes repetitive regeneration cycles in order to recover the functional layer, shed during menses. The basal layer, which remains in charge of endometrial regeneration in every cycle, contains adult stem or progenitor cells of epithelial and mesenchymal lineage. Some pathologies such as adenomyosis, in which endometrial tissue develops within the myometrium, originate from this layer. It is well known that the balance between adenosine triphosphate (ATP) and adenosine plays a crucial role in stem/progenitor cell physiology, influencing proliferation, differentiation, and migration. The extracellular levels of nucleotides and nucleosides are regulated by the ectonucleotidases, such as the nucleoside triphosphate diphosphohydrolase 2 (NTPDase2). NTPDase2 is a membrane-expressed enzyme found in cells of mesenchymal origin such as perivascular cells of different tissues and the stem cells of adult neurogenic regions. The aim of this study was to characterize the expression of NTPDase2 in human nonpathological cyclic and postmenopausic endometria and in adenomyosis. We examined proliferative, secretory, and atrophic endometria from women without endometrial pathology and also adenomyotic lesions. Importantly, we identified NTPDase2 as the first marker of basal endometrium since other stromal cell markers such as CD10 label the entire stroma. As expected, NTPDase2 was also found in adenomyotic stroma, thus becoming a convenient tracer of these lesions. We did not record any changes in the expression levels or the localization of NTPDase2 along the cycle, thus suggesting that the enzyme is not influenced by the female sex hormones like other previously studied ectoenzymes. Remarkably, NTPDase2 was expressed by the Sushi Domain containing 2 (SUSD2)⁺ endometrial mesenchymal stem cells (eMSCs) found perivascularly, rendering it useful as a cell marker to improve the isolation of eMSCs needed for regenerative medicine therapies.

Multiple calcium patterns of rat osteoblasts under fluidic shear stress

The intracellular calcium ([Ca²⁺ ]_i ) response induced by external forces can be diverse and complex. Using primary osteoblasts from Wistar rats, we found multiple patterns of [Ca²⁺ ]_i responses induced by fluidic shear stress (Fss), including homogeneous non-oscillation and heterogeneous oscillations. These multiple-patterned [Ca²⁺ ]_i responses could be influenced by Fss intensity, cell density, and cell differentiation. Our real-time measurements with free calcium, ATP, ATP without calcium, suramin, apyrase, and thapsigargin confirmed homogeneous [Ca²⁺ ]_i patterns and/or heterogeneous [Ca²⁺ ]_i oscillations with respect to the combined degree of external Ca²⁺ influx, and intracellular Ca²⁺ release. Our theoretical model supported diverse Fss-induced calcium activities as well. We concluded that a singular factor of Ca²⁺ influx or release dominated to produce smooth homogeneous patterns, but combined factors produced oscillatory heterogeneous patterns. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2039-2051, 2018.

ATP-induced Ca2+-signalling mechanisms in the regulation of mesenchymal stem cell migration

The ability of cells to migrate to the destined tissues or lesions is crucial for physiological processes from tissue morphogenesis, homeostasis and immune responses, and also for stem cell-based regenerative medicines. Cytosolic Ca²⁺ is a primary second messenger in the control and regulation of a wide range of cell functions including cell migration. Extracellular ATP, together with the cognate receptors on the cell surface, ligand-gated ion channel P2X receptors and a subset of G-protein-coupled P2Y receptors, represents common autocrine and/or paracrine Ca²⁺ signalling mechanisms. The P2X receptor ion channels mediate extracellular Ca²⁺ influx, whereas stimulation of the P2Y receptors triggers intracellular Ca²⁺ release from the endoplasmic reticulum (ER), and activation of both type of receptors thus can elevate the cytosolic Ca²⁺ concentration ([Ca²⁺]_c), albeit with different kinetics and capacity. Reduction in the ER Ca²⁺ level following the P2Y receptor activation can further induce store-operated Ca²⁺ entry as a distinct Ca²⁺ influx pathway that contributes in ATP-induced increase in the [Ca²⁺]_c. Mesenchymal stem cells (MSC) are a group of multipotent stem cells that grow from adult tissues and hold promising applications in tissue engineering and cell-based therapies treating a great and diverse number of diseases. There is increasing evidence to show constitutive or evoked ATP release from stem cells themselves or mature cells in the close vicinity. In this review, we discuss the mechanisms for ATP release and clearance, the receptors and ion channels participating in ATP-induced Ca²⁺ signalling and the roles of such signalling mechanisms in mediating ATP-induced regulation of MSC migration.

Expression of P2 Purinergic Receptors in Mesenchymal Stem Cells and Their Roles in Extracellular Nucleotide Regulation of Cell Functions

Extracellular ATP and other nucleotides induce autocrine and/or paracrine purinergic signalling via activation of the P2 receptors on the cell surface, which represents one of the most common signalling mechanisms. Mesenchymal stem cells (MSC) are a type of multipotent adult stem cells that have many promising applications in regenerative medicine. There is increasing evidence to show that extracellular nucleotides regulate MSC functions and P2 receptor-mediated purinergic signalling plays an important role in such functional regulation. P2 receptors comprise ligand-gated ion channel P2X receptors and G-protein-coupled P2Y receptors. In this review, we provide an overview of the current understanding with respect to expression of the P2X and P2Y receptors in MSC and their roles in mediating extracellular nucleotide regulation of MSC proliferation, migration and differentiation. J. Cell. Physiol. 232: 287-297, 2017. © 2016 Wiley Periodicals, Inc.

Purinergic and Store-Operated Ca(2+) Signaling Mechanisms in Mesenchymal Stem Cells and Their Roles in ATP-Induced Stimulation of Cell Migration

ATP is an extrinsic signal that can induce an increase in the cytosolic Ca(2+) level ([Ca(2+) ]c ) in mesenchymal stem cells (MSCs). However, the cognate intrinsic mechanisms underlying ATP-induced Ca(2+) signaling in MSCs is still contentious, and their importance in MSC migration remains unknown. In this study, we investigated the molecular mechanisms underlying ATP-induced Ca(2+) signaling and their roles in the regulation of cell migration in human dental pulp MSCs (hDP-MSCs). RT-PCR analysis of mRNA transcripts and interrogation of agonist-induced increases in the [Ca(2+) ]c support that P2X7, P2Y1 , and P2Y11 receptors participate in ATP-induced Ca(2+) signaling. In addition, following P2Y receptor activation, Ca(2+) release-activated Ca(2+) Orai1/Stim1 channel as a downstream mechanism also plays a significant role in ATP-induced Ca(2+) signaling. ATP concentration-dependently stimulates hDP-MSC migration. Pharmacological and genetic interventions of the expression or function of the P2X7, P2Y1 and P2Y11 receptors, and Orai1/Stim1 channel support critical involvement of these Ca(2+) signaling mechanisms in ATP-induced stimulation of hDP-MSC migration. Taken together, this study provide evidence to show that purinergic P2X7, P2Y1 , and P2Y11 receptors and store-operated Orai1/Stim1 channel represent important molecular mechanisms responsible for ATP-induced Ca(2+) signaling in hDP-MSCs and activation of these mechanisms stimulates hDP-MSC migration. Such information is useful in building a mechanistic understanding of MSC homing in tissue homeostasis and developing more efficient MSC-based therapeutic applications. Stem Cells 2016;34:2102-2114.

Specific profiles of ion channels and ionotropic receptors define adipose- and bone marrow derived stromal cells

Adherent, fibroblastic cells from different tissues are thought to contain subsets of tissue-specific stem/progenitor cells (often called mesenchymal stem cells). These cells display similar cell surface characteristics based on their fibroblastic nature, but also exhibit differences in molecular phenotype, growth rate, and their ability to differentiate into various cell phenotypes. The mechanisms underlying these differences remain poorly understood. We analyzed Ca(2+) signals and membrane properties in rat adipose-derived stromal cells (ADSCs) and bone marrow stromal cells (BMSCs) in basal conditions, and then following a switch into medium that contains factors known to modify their character. Modified ADSCs (mADSCs) expressed L-type Ca(2+) channels whereas both L- and P/Q- channels were operational in mBMSCs. Both mADSCs and mBMSCs possessed functional endoplasmic reticulum Ca(2+) stores, expressed ryanodine receptor-1 and -3, and exhibited spontaneous [Ca(2+)]i oscillations. The mBMSCs expressed P2X7 purinoceptors; the mADSCs expressed both P2X (but not P2X7) and P2Y (but not P2Y1) receptors. Both types of stromal cells exhibited [Ca(2+)]i responses to vasopressin (AVP) and expressed V1 type receptors. Functional oxytocin (OT) receptors were, in contrast, expressed only in modified ADSCs and BMSCs. AVP and OT-induced [Ca(2+)]i responses were dose-dependent and were blocked by their respective specific receptor antagonists. Electrophysiological data revealed that passive ion currents dominated the membrane conductance in ADSCs and BMSCs. Medium modification led to a significant shift in the reversal potential of passive currents from -40 to -50mV in cells in basal to -80mV in modified cells. Hence membrane conductance was mediated by non-selective channels in cells in basal conditions, whereas in modified medium conditions, it was associated with K(+)-selective channels. Our results indicate that modification of ADSCs and BMSCs by alteration in medium formulation is associated with significant changes in their Ca(2+) signaling and membrane properties.

TRPC6 regulates cell cycle progression by modulating membrane potential in bone marrow stromal cells

BACKGROUND AND PURPOSE

Ca(2+) influx is important for cell cycle progression, but the mechanisms involved seem to vary. We investigated the potential roles of transient receptor potential (TRP) channels and store-operated Ca(2+) entry (SOCE)-related molecules STIM (stromal interaction molecule)/Orai in the cell cycle progression of rat bone marrow stromal cells (BMSCs), a reliable therapeutic resource for regenerative medicine.

EXPERIMENTAL APPROACH

PCR and immunoblot analyses were used to examine mRNA and protein levels, fluorescence imaging and patch clamping for Ca(2+) influx and membrane potential measurements, and flow cytometry for cell cycle analysis.

KEY RESULTS

Cell cycle synchronization of BMSCs revealed S phase-specific enhancement of TRPC1, STIM and Orai mRNA and protein expression. In contrast, TRPC6 expression decreased in the S phase and increased in the G1 phase. Resting membrane potential (RMP) of BMSCs was most negative and positive in the S and G1 phases, respectively, and was accompanied by an enhancement and attenuation of SOCE respectively. Chemically depolarizing/hyperpolarizing the membrane erased these differences in SOCE magnitude during the cell cycle. siRNA knockdown of TRPC6 produced a negative shift in RMP, increased SOCE and caused redistribution of BMSCs with increased populations in the S and G2 /M phases and accumulation of cyclins A2 and B1. A low concentration of Gd(3+) (1 μM) suppressed BMSC proliferation at its concentration to inhibit SOC channels relatively specifically.

CONCLUSIONS AND IMPLICATIONS

TRPC6, by changing the membrane potential, plays a pivotal role in controlling the SOCE magnitude, which is critical for cell cycle progression of BMSCs. This finding provides a new therapeutic strategy for regulating BMSC proliferation.

P2Y13 receptor-mediated rapid increase in intracellular calcium induced by ADP in cultured dorsal spinal cord microglia

P2Y receptors have been implicated in the calcium mobilization by the response to neuroexcitatory substances in neurons and astrocytes, but little is known about P2Y receptors in microglia cells. In the present study, the effects of ADP on the intracellular calcium concentration ([Ca(2+)]i) in cultured dorsal spinal cord microglia were detected with confocal laser scanning microscopy using fluo-4/AM as a calcium fluorescence indicator that could monitor real-time alterations of [Ca(2+)]i. Here we show that ADP (0.01-100 μM) causes a rapid increase in [Ca(2+)]i with a dose-dependent manner in cultured microglia. The action of ADP on [Ca(2+)]i was significantly blocked by MRS2211 (a selective P2Y13 receptor antagonist), but was unaffected by MRS2179 (a selective P2Y1 receptor antagonist) or MRS2395 (a selective P2Y12 receptor antagonist), which suggest that P2Y13 receptor may be responsible for ADP-evoked Ca(2+) mobilization in cultured microglia. P2Y13-evoked Ca(2+) response can be obviously inhibited by BAPTA-AM and U-73122, respectively. Moreover, removal of extracellular Ca(2+) (by EGTA) also can obvious suppress the Ca(2+) mobilization. These results means both intracellular calcium and extracellular calcium are potentially important mechanisms in P2Y13 receptor-evoked Ca(2+) mobilization. However, P2Y13 receptor-evoked Ca(2+) response was not impaired after CdCl2 and verapamil administration, which suggest that voltage-operated Ca(2+) channels may be not related with P2Y13-evoked Ca(2+) response. In addition, Ca(2+) mobilization induced by ADP was abolished by different store-operated Ca(2+) channels (SOCs) blocker, 2-APB (50 μM) and SKF-96365 (1 mM), respectively. These observations suggest that the activation of P2Y13 receptor might be involved in the effect of ADP on [Ca(2+)]i in cultured dorsal spinal cord microglia. Furthermore, our results raise a possibility that P2Y13 receptor activation causes Ca(2+) release from Ca(2+) store, which leads to the opening of SOCs.

Purinergic receptors and nucleotide processing ectoenzymes: Their roles in regulating mesenchymal stem cell functions

Human mesenchymal stem cells (MSCs) are a rare population of non-hematopoietic stem cells with multilineage potential, originally identified in the bone marrow. Due to the lack of a single specific marker, MSCs can be recognized and isolated by a series of features such as plastic adherence, a panel of surface markers, the clonogenic and the differentiation abilities. The recognized role of MSCs in the regulation of hemopoiesis, in cell-degeneration protection and in the homeostasis of mesodermal tissues through their differentiation properties, justifies the current interest in identifying the biochemical signals produced by MSCs and their active crosstalk in tissue environments. Only recently have extracellular nucleotides (eNTPs) and their metabolites been included among the molecular signals produced by MSCs. These molecules are active on both ionotropic and metabotropic receptors present in most cell types. MSCs possess a significant display of these receptors and of nucleotide processing ectoenzymes on their plasma membrane. Thus, from their niche, MSCs give a significant contribution to the complex signaling network of eNTPs and its derivatives. Recent studies have demonstrated the multifaceted aspects of eNTP metabolism and their signal transduction in MSCs and revealed important roles in specifying differentiation lineages and modulating MSC physiology and communication with other cells. This review discusses the roles of eNTPs, their receptors and ectoenzymes, and the relevance of the signaling network and MSC functions, and also focuses on the importance of this emerging area of interest for future MSC-based cell therapies.

Role of ecto-NTPDases on UDP-sensitive P2Y(6) receptor activation during osteogenic differentiation of primary bone marrow stromal cells from postmenopausal women

This study aimed at investigating the expression and function of uracil nucleotide-sensitive receptors (P2Y(2), P2Y(4), and P2Y(6)) on osteogenic differentiation of human bone marrow stromal cells (BMSCs) in culture. Bone marrow specimens were obtained from postmenopausal female patients (68 ± 5 years old, n = 18) undergoing total hip arthroplasty. UTP and UDP (100 µM) facilitated osteogenic differentiation of the cells measured as increases in alkaline phosphatase (ALP) activity, without affecting cell proliferation. Uracil nucleotides concentration-dependently increased [Ca(2+)](i) in BMSCs; their effects became less evident with time (7 > 21 days) of the cells in culture. Selective activation of P2Y(6) receptors with the stable UDP analog, PSB 0474, mimicked the effects of both UTP and UDP, whereas UTPγS was devoid of effect. Selective blockade of P2Y(6) receptors with MRS 2578 prevented [Ca(2+)](i) rises and osteogenic differentiation caused by UDP at all culture time points. BMSCs are immunoreactive against P2Y(2), P2Y(4), and P2Y(6) receptors. While the expression of P2Y(6) receptors remained fairly constant (7∼21 days), P2Y(2) and P2Y(4) became evident only in less proliferative and more differentiated cultures (7 < 21 days). The rate of extracellular UTP and UDP inactivation was higher in less proliferative and more differentiated cell populations. Immunoreactivity against NTPDase1, -2, and -3 rises as cells differentiate (7 < 21 days). Data show that uracil nucleotides are important regulators of osteogenic cells differentiation predominantly through the activation of UDP-sensitive P2Y(6) receptors coupled to increases in [Ca(2+)](i) . Endogenous actions of uracil nucleotides may be balanced through specific NTPDases determining whether osteoblast progenitors are driven into proliferation or differentiation.

Neuronal plasticity of human Wharton's jelly mesenchymal stromal cells to the dopaminergic cell type compared with human bone marrow mesenchymal stromal cells

BACKGROUND AIMS

Mesenchymal stromal cells (MSC) derived from Wharton's jelly (WJ) of the umbilical cord are increasingly gaining prominence as substitutes for bone marrow (BM) MSC. While MSC isolated from different tissue sources may share common mesenchymal properties, the difference in their plasticity to individual lineages is ill-defined. Thus the focus of this study was to estimate the neuronal plasticity of WJ MSC to the dopaminergic (DA) cell type in comparison with BM MSC.

METHODS

For neuronal differentiation, MSC were exposed to developmentally relevant cues for midbrain DA neurons: sonic hedgehog (SHH) and fibroblast growth factor 8 (FGF8), along with basic fibroblast growth factor (bFGF).

RESULTS

Naive MSC from both sources constitutively expressed neuronal markers. Flow cytometry data revealed that the control WJ MSC shared a signature similar to BM MSC for early neuronal markers (nestin, musashi12 and A2B5) and DA-specific markers [tyrosine hydroxylase (TH) and Nuclear Receptor related protein 1 (Nurr1) but differed for mature neuronal proteins [β-tubulin III and microtubule-associated protein 2 (Map2ab)]. Similar populations of cells in both sources of MSC were positive for the SHH receptors [patched (PTCH) and smoothened (SMO)]. In induced BM and WJ MSC, real-time reverse transcriptase (RT)-polymerase chain reaction (PCR) analysis showed similar levels of DA-related transcription factors Nurr1 and Engrailed (En) 1. Immunocytochemical and flow cytometry analysis showed an increase in mature neuronal marker Map2ab. Kv4.2, a K(+) channel marker, was observed only in the induced MSC. Induced MSC also expressed several DA-specific markers, TH, dopamine and cyclic AMP regulated phosphoprotein (DARPP) 32, paired-like homeodomain transcription factor (PitX) 3 and vesicular monoamine transporter (VMAT) 2, in comparable levels between the two sources. The efficiency (c. 65%) of transdifferentiation of WJ MSC to TH-positive cells was similar to that of induced BM MSC. Constitutive and inducible release of dopamine was found to be similar between induced BM and WJ MSC, as measured by dopamine enzyme-linked immunosorbent assay (ELISA). Interestingly, an adenosine triphosphate (ATP)-stimulated change in intracellular Ca(2+) was observed in both control and induced MSC, but only the induced MSC was capable of releasing dopamine.

CONCLUSIONS

Our data demonstrate that MSC from the two different sources respond similarly to inductive cues to differentiate terminally to a DA cell type, and the neuronal plasticity of human WJ MSC is comparable with that of BM MSC.

Purinergic signaling in embryonic and stem cell development

Nucleotides are of crucial importance as carriers of energy in all organisms. However, the concept that in addition to their intracellular roles, nucleotides act as extracellular ligands specifically on receptors of the plasma membrane took longer to be accepted. Purinergic signaling exerted by purines and pyrimidines, principally ATP and adenosine, occurs throughout embryologic development in a wide variety of organisms, including amphibians, birds, and mammals. Cellular signaling, mediated by ATP, is present in development at very early stages, e.g., gastrulation of Xenopus and germ layer definition of chick embryo cells. Purinergic receptor expression and functions have been studied in the development of many organs, including the heart, eye, skeletal muscle and the nervous system. In vitro studies with stem cells revealed that purinergic receptors are involved in the processes of proliferation, differentiation, and phenotype determination of differentiated cells. Thus, nucleotides are able to induce various intracellular signaling pathways via crosstalk with other bioactive molecules acting on growth factor and neurotransmitter receptors. Since normal development is disturbed by dysfunction of purinergic signaling in animal models, further studies are needed to elucidate the functions of purinoceptor subtypes in developmental processes.

ATP induces contraction mediated by the P2Y(2) receptor in rat intestinal subepithelial myofibroblasts

Intestinal subepithelial myofibroblasts (IMFs) exist just under the epithelial membrane directly facing the mucosal microvascular capillary surface distributed in the lamina propria. In the gastrointestinal tract, ATP is released from epithelial and endothelial cells in response to mechanical stimuli. Although it has been reported that mechanical stimuli evoke synchronized Ca(2+) waves in cultured IMFs, the contractile responses by ATP stimulation have not been examined. The aim of this study was to clarify the mechanism of the contraction of IMFs in response to ATP. ATP (1-30μM) induced contraction in a concentration-dependent manner. These contractions were inhibited by LaCl(3) (100-300μM) and by Ca(2+)-free solution (0.5mM EGTA). Fura-2/Ca(2+) signals indicated that ATP (1-10μM) elicited transient increases in intracellular Ca(2+) concentration ([Ca(2+)](i)). In addition, αβ-methylene-ATP (10, 30 and 300μM), a broad spectrum P2X agonist at a concentration higher than 100μM, induced neither contraction nor [Ca(2+)](i) rise. UTP (1-30μM), a selective P2Y(2) and P2Y(4) agonist in rodent, induced concentration-dependent contractions and [Ca(2+)](i) increases, whereas ADP and UDP (10μM) did not induce contractions. Pretreatment with suramin (30-100μM), a relatively selective P2Y(2) antagonist, strongly inhibited ATP- and UTP-induced contractions and [Ca(2+)](i) increases. However, pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (PPADS: 10-30μM), a receptor antagonist for several P2X and P2Y but less effective to P2Y(2) receptor, failed to inhibit ATP- and UTP-induced contractions and [Ca(2+)](i) increases. By RT-PCR, mRNA expressions of the P2Y(1) and P2Y(2) receptors, but not P2Y(4) or P2Y(6), were detected in IMFs. These results suggest that ATP induces [Ca(2+)](i)-dependent contraction in IMFs, which is mediated through the P2Y(2) receptor.

Osteoblasts modulate Ca2+ signaling in bone-metastatic prostate and breast cancer cells

Metastatic prostate and breast cancers display a predilection for the skeleton. The high incidence of skeletal metastasis may be a reflection of favorable reciprocal interactions between the bone microenvironment and disseminated cancer cells. Here we show that bone-metastatic PC3-ML prostate cancer cells and MDA-231 breast cancer cells-when co-cultured with human osteoblasts-down-regulate the increase in cytosolic free calcium (Ca(2+)) induced by agonist stimulation. This osteoblast promoted alteration of Ca(2+) signaling develops and reverts in a time-dependent manner. Most importantly, the Ca(2+) responses of cancer cells lacking bone metastatic potential are not affected by osteoblasts. The limited increase in cytosolic Ca(2+) observed in bone-metastatic cells does not result from depleted intracellular Ca(2+) stores but rather a decreased entry of Ca(2+) from the extracellular space. Interestingly, the inhibition of histone deacetylase in cancer cells replicates the changes in Ca(2+) signaling induced by osteoblasts, suggesting the participation of epigenetic mechanisms. Finally, cancer cells harvested from skeletal metastases induced in mice showed Ca(2+) responses identical to cells co-cultured with osteoblasts. However, Ca(2+) signaling in cancer cells recovered from metastases to soft-tissues was not affected, emphasizing the role of the bone microenvironment in regulating the functional behavior of bone-metastatic cells. We propose that osteoblasts protect selected malignant phenotypes from cell death caused by an excessive increase in cytosolic Ca(2+), thereby facilitating their progression into macroscopic skeletal metastases.