Adenosine arrests breast cancer cell motility by A3 receptor stimulation

In neutrophils, adenosine triphosphate (ATP) release and autocrine purinergic signaling regulate coordinated cell motility during chemotaxis. Here, we studied whether similar mechanisms regulate the motility of breast cancer cells. While neutrophils and benign human mammary epithelial cells (HMEC) form a single leading edge, MDA-MB-231 breast cancer cells possess multiple leading edges enriched with A3 adenosine receptors. Compared to HMEC, MDA-MB-231 cells overexpress the ectonucleotidases ENPP1 and CD73, which convert extracellular ATP released by the cells to adenosine that stimulates A3 receptors and promotes cell migration with frequent directional changes. However, exogenous adenosine added to breast cancer cells or the A3 receptor agonist IB-MECA dose-dependently arrested cell motility by simultaneous stimulation of multiple leading edges, doubling cell surface areas and significantly reducing migration velocity by up to 75 %. We conclude that MDA-MB-231 cells, HMEC, and neutrophils differ in the purinergic signaling mechanisms that regulate their motility patterns and that the subcellular distribution of A3 adenosine receptors in MDA-MB-231 breast cancer cells contributes to dysfunctional cell motility. These findings imply that purinergic signaling mechanisms may be potential therapeutic targets to interfere with the motility of breast cancer cells in order to reduce the spread of cancer cells and the risk of metastasis.     

Cyclic 3',5'-adenosine monophosphate modulates vascular endothelial cell migration in vitro

Using a modified Boyden chamber assay, we have examined the effect of cyclic nucleotides on bovine aortic endothelial cell migration in vitro. Dibutyrl cyclic 3',5'-adenosine monophosphate (5 mM) inhibited endothelial cell random migration by 67% and inhibited fibronectin-induced chemotaxis by 75%. Agents which significantly stimulated adenylate cyclase activity in endothelial cell membranes were also effective inhibitors of endothelial cell migration. Timolol blocked both the isoproterenol-induced stimulation of adenylate cyclase and the ability of isoproterenol to inhibit endothelial cell migration. Caffeine and isoproterenol together had a greater inhibitory effect on endothelial cell motility than either alone. These data suggest that cAMP may modulate vascular endothelial cell migration in an inhibitory fashion.     

Chemotactic activity of extracellular nucleotideson human immune cells.

Purinergic P2 receptors are a class of plasma membrane receptors that are express in many tissues and are ligated by extracellular nucleotides [such as adenosine triphosphate (ATP), adenosine diphosphate (ADP), uridine 5'-triphosphate (UTP) and uridine 5'-diphosphate (UDP)], which are released as a consequence of cell damage, cell stress, bacterial infection or other noxious stimuli. According to the molecular structure, P2 receptors are divided into two subfamilies: P2X and P2Y receptors. The P2X receptors are ligand-gated channels, whereas P2Y receptors are G-protein-coupled seven-membrane-spanning receptors. Several studies indicate that nucleotides play an important role in immune response modulation through their action on multiple cell types, including monocytes, mast cells, dendritic cells, neutrophils, and eosinophils. Recent work by our group and others identified extracellular nucleotides as chemotaxins for various human immune cells, including eosinophils, neutrophils and dendritic cells. In this review, we summarise recent findings in this field and put forward a hypothesis on the role of P2 receptors in the early recruitment of human immune cells to the site of inflammation.     

Motility and ramification of human fetal microglia in culture: an investigation using time-lapse video microscopy and image analysis

Microglia are mononuclear phagocytes of the central nervous system and are considered to derive from circulating bone marrow progenitors that colonize the developing human nervous system in the second trimester. They first appear as ameboid forms and progressively differentiate to process-bearing "ramified" forms with maturation. Signals driving this transformation are known to be partly derived from astrocytes. In this investigation we have used cocultures of astrocytes and microglia to demonstrate the relationship between motility and morphology of microglia associated with signals derived from astrocytes. Analysis of progressive cultures using time-lapse video microscopy clearly demonstrates the dynamic nature of microglia. We observe that ameboid microglial cells progressively ramify when cocultured with astrocytes, mirroring the "differentiation" of microglia in situ during development. We further demonstrate that individual cells undergo morphological transformations from "ramified" to "bipolar" to "tripolar" and "ameboid" states in accordance with local environmental cues associated with astrocytes in subconfluent cultures. Remarkably, cells are still capable of migration at velocities of 20-35 microm/h in a fully ramified state overlying confluent astrocytes, as determined by image analysis of motility. This is in keeping with the capacity of microglia for a rapid response to inflammatory cues in the CNS. We also demonstrate selective expression of the chemokines MIP-1alpha and MCP-1 by confluent human fetal astrocytes in cocultures and propose a role for these chemotactic cytokines as regulators of microglial motility and differentiation. The interchangeable morphological continuum of microglia supports the view that these cells represent a single heterogeneous population of resident mononuclear phagocytes capable of marked plasticity.     

Purine and pyrimidine nucleotides potentiate activation of NADPH oxidase and degranulation by chemotactic peptides and induce aggregation of human neutrophils via G proteins

Whereas the chemotactic peptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe), induced NADPH-oxidase-catalyzed superoxide (O2-) formation in human neutrophils, purine and pyrimidine nucleotides per se did not stimulate NADPH oxidase but enhanced O2- formation induced by submaximally and maximally stimulatory concentrations of fMet-Leu-Phe up to fivefold. On the other hand, FMet-Leu-Phe primed neutrophils to generate O2- upon exposure to nucleotides. At a concentration of 100 microM, purine nucleotides enhanced O2- formation in the effectiveness order adenosine 5'-O-[3-thio]triphosphate (ATP[gamma S]) greater than ITP greater than guanosine 5'-O-[3-thio]triphosphate (GTP[gamma S]) greater than ATP = adenosine 5'-O-[2-thio]triphosphate (Sp-diastereomer) = GTP = guanosine 5'-O-[2-thio]diphosphate (GDP[beta S] = ADP greater than adenosine 5'-[beta, gamma-imido]triphosphate = adenosine 5'-O-[2-thio]triphosphate] (Rp-diastereomer). Pyrimidine nucleotides stimulated fMet-Leu-Phe-induced O2- formation in the effectiveness order uridine 5'-O-[3-thio]triphosphate (UTP[gamma S]) = UTP greater than CTP. Uracil (UDP[beta S]) = uridine 5'-O[2-thio]triphosphate (Rp-diastereomer) (Rp)-UTP[beta S]) = UTP greater than CTP. Uracil nucleotides were similarly effective potentiators of O2- formation as the corresponding adenine nucleotides. GDP[beta S] and UDP[beta S] synergistically enhanced the stimulatory effects of ATP[gamma S], GTP[gamma S] and UTP[gamma S]. Purine and pyrimidine nucleotides did not induce degranulation in neutrophils but potentiated fMet-Leu-Phe-induced release of beta-glucuronidase with similar nucleotide specificities as for O2- formation. In contrast, nucleotides per se induced aggregation of neutrophils. Treatment with pertussis toxin prevented aggregation induced by both nucleotides and fMet-Leu-Phe. Our results suggest that purine and pyrimidine nucleotides act via nucleotide receptors, the nucleotide specificity of which is different from nucleotide receptors in other cell types. Neutrophil nucleotide receptors are coupled to guanine-nucleotide-binding proteins. As nucleotides are released from cells under physiological and pathological conditions, they may play roles as intercellular signal molecules in neutrophil activation.     

Degradation of extracellular nucleotides and their analogs in HeLa and HUVEC cell cultures

The use of nucleotides and their analogs in the pharmacological studies of nucleotide receptors (P2 class) should be preceded by detailed studies on their degradation connected with ecto-enzymes of a given cell type. In the present studies we have analyzed stability of some phosphorothioate and phosphonate analogs of ATP and ADP in the HeLa epitheloid carcinoma and endothelial HUVEC cells cultures. Our studies have revealed that ecto-nucleotide pyrophosphatase (E-NPP) is one of the main enzymes involved in the extracellular degradation of ATP and other nucleotides in the HeLa cells. On the other hand, the ecto-ATPDase is responsible for the hydrolysis of extracellular nucleotides in human endothelial cell cultures, while the E-NPP-like enzymes of the HUVEC cells are not essential to this degradation. The concerted action of the aforementioned ecto-enzymes and nucleotide pyrophosphatase, 5'-nucleotidase and adenosine deaminase present in fetal bovine serum (FBS) supplied to the culture medium, results in partial or complete degradation of the phosphorothioate (ATPgammaS) and phosphonate analogs of adenosine nucleotides (alpha,beta-methylene-ATP and beta,gamma-methylene-ATP) in the cell cultures. Only ADPbetaS appears to be resistant to these enzymes. The influence of some nucleotides and their analogs on the proliferation of the HeLa cells in presence or absence of FBS is also discussed.     

The role of nucleotides in the neuron--glia communication responsible for the brain functions

Accumulating findings indicate that nucleotides play an important role in cell-to-cell communication through P2 purinoceptors, even though ATP is recognized primarily to be a source of free energy and nucleotides are key molecules in cells. P2 purinoceptors are divided into two families, ionotropic receptors (P2X) and metabotropic receptors (P2Y). P2X receptors (7 types; P2X(1)-P2X(7)) contain intrinsic pores that open by binding with ATP. P2Y (8 types; P2Y(1, 2, 4, 6, 11, 12, 13,) and (14)) are activated by nucleotides and couple to intracellular second-messenger systems through heteromeric G-proteins. Nucleotides are released or leaked from non-excitable cells as well as neurons in physiological and pathophysiological conditions. One of the most exciting cells in non-excitable cells is the glia cells, which are classified into astrocytes, oligodendrocytes, and microglia. Astrocytes express many types of P2 purinoceptors and release the 'gliotransmitter' ATP to communicate with neurons, microglia and the vascular walls of capillaries. Microglia also express many types of P2 purinoceptors and are known as resident macrophages in the CNS. ATP and other nucleotides work as 'warning molecules' especially through activating microglia in pathophysiological conditions. Microglia play a key role in neuropathic pain and show phagocytosis through nucleotide-evoked activation of P2X(4) and P2Y(6) receptors, respectively. Such strong molecular, cellular and system-level evidence for extracellular nucleotide signaling places nucleotides in the central stage of cell communications in glia/CNS.     

Ecto-nucleoside triphosphate diphosphohydrolase 1 (E-NTPDase1/CD39) regulates neutrophil chemotaxis by hydrolyzing released ATP to adenosine

Polymorphonuclear neutrophils release ATP in response to stimulation by chemoattractants, such as the peptide N-formyl-methionyl-leucyl-phenylalanine. Released ATP and the hydrolytic product adenosine regulate chemotaxis of neutrophils by sequentially activating purinergic nucleotide and adenosine receptors, respectively. Here we show that that ecto-nucleoside triphosphate diphosphohydrolase 1 (E-NTPDase1, CD39) is a critical enzyme for hydrolysis of released ATP by neutrophils and for cell migration in response to multiple agonists (N-formyl-methionyl-leucyl-phenylalanine, interleukin-8, and C5a). Upon stimulation of human neutrophils or differentiated HL-60 cells in a chemotactic gradient, E-NTPDase1 tightly associates with the leading edge of polarized cells during chemotaxis. Inhibition of E-NTPDase1 reduces the migration speed of neutrophils but not their ability to detect the orientation of the gradient field. Studies of neutrophils from E-NTPDase1 knock-out mice reveal similar impairments of chemotaxis in vitro and in vivo. Thus, E-NTPDase1 plays an important role in regulating neutrophil chemotaxis by facilitating the hydrolysis of extracellular ATP.     

The presence of professional phagocytes dictates the number of host cells targeted for Yop translocation during infection

Type III secretion systems deliver effector proteins from Gram‐negative bacterial pathogens into host cells, where they disarm host defences, allowing the pathogens to establish infection. Although Yersinia pseudotuberculosis delivers its effector proteins, called Yops, into numerous cell types grown in culture, we show that during infection Y. pseudotuberculosis selectively targets Yops to professional phagocytes in Peyer's patches, mesenteric lymph nodes and spleen, although it colocalizes with B and T cells as well as professional phagocytes. Strikingly, in the absence of neutrophils, the number of cells with translocated Yops was significantly reduced although the bacterial loads were similar, indicating that Y. pseudotuberculosis did not arbitrarily deliver Yops to the available cells. Using isolated splenocytes, selective binding and selective targeting to professional phagocytes when bacteria were limiting was also observed, indicating that tissue architecture was not required for the tropism for professional phagocytes. In isolated splenocytes, YadA and Invasin increased the number of all cells types with translocated Yops, but professional phagocytes were still preferentially translocated with Yops in the absence of these adhesins. Together these results indicate that Y. pseudotuberculosis discriminates among cells it encounters during infection and selectively delivers Yops to phagocytes while refraining from translocation to other cell types.     

Sphingosine 1-phosphate signaling: providing cells with a sense of direction

Sphingosine 1-phosphate (S1P) is a sphingolipid metabolite that regulates diverse biological functions. S1P has been identified as a high-affinity ligand for a family of five G-protein-coupled receptors, known as the S1P receptors. The physiological role of the S1P receptor S1P(1) in vascular maturation was recently revealed by gene disruption in mice. In addition to other cellular processes, the binding of S1P to its receptors regulates motility and directional migration of a variety of cell types, including endothelial cells and vascular smooth muscle cells. This review focuses on the important role of S1P and its receptors in cell migration and describes a new paradigm for receptor cross-communication in which transactivation of S1P(1) by a receptor tyrosine kinase (PDGFR) is crucial for cell motility.     

Collective dynamics of cancer cells confined in a confluent monolayer of normal cells

Tumorigenesis often involves specific changes in cell motility and intercellular adhesion. Understanding the collective cancer cell behavior associated with these specific changes could facilitate the detection of malignant characteristics during tumor growth and invasion. In this study, a cellular vertex model is developed to investigate the collective dynamics of a disk-like aggregate of cancer cells confined in a confluent monolayer of normal cells. The effects of intercellular adhesion and cell motility on tumor progression are examined. It is found that the stresses in both the cancer cells and the normal cells increase with tumor growth, resulting in a crowded environment and enhanced cell apoptosis. The intercellular adhesion between cancer cells and normal cells is revealed to promote tumor growth and invasion. The tumor invasion dynamics hinges on the motility of cancer cells. The cancer cells could orchestrate into different collective migration modes, e.g., directional migration and rotational oscillations, dictated by the competition between cell persistence and local coordination. Phase diagrams are established to reveal the competitive mechanisms. This work highlights the role of mechanics in regulating tumor growth and invasion.     

Real-time imaging reveals that P2Y2 and P2Y12 receptor agonists are not chemoattractants and macrophage chemotaxis to complement C5a is phosphatidylinositol 3-kinase (PI3K)- and p38 mitogen-activated protein kinase (MAPK)-independent

Adenosine 5'-triphosphate (ATP) has been implicated in the recruitment of professional phagocytes (neutrophils and macrophages) to sites of infection and tissue injury in two distinct ways. First, ATP itself is thought to be a chemotactic "find me" signal released by dying cells, and second, autocrine ATP signaling is implicated as an amplifier mechanism for chemotactic navigation to end-target chemoattractants, such as complement C5a. Here we show using real-time chemotaxis assays that mouse peritoneal macrophages do not directionally migrate to stable analogs of ATP (adenosine-5'-(γ-thio)-triphosphate (ATPγS)) or its hydrolysis product ADP (adenosine-5'-(β-thio)-diphosphate (ADPβS)). HPLC revealed that these synthetic P2Y(2) (ATPγS) and P2Y(12) (ADPβS) receptor ligands were in fact slowly degraded. We also found that ATPγS, but not ADPβS, promoted chemokinesis (increased random migration). Furthermore, we found that photorelease of ATP or ADP induced lamellipodial membrane extensions. At the cell signaling level, C5a, but not ATPγS, activated Akt, whereas both ligands induced p38 MAPK activation. p38 MAPK and Akt activation are strongly implicated in neutrophil chemotaxis. However, we found that inhibitors of phosphatidylinositol 3-kinase (PI3K; upstream of Akt) and p38 MAPK (or conditional deletion of p38α MAPK) did not impair macrophage chemotactic efficiency or migration velocity. Our results suggest that PI3K and p38 MAPK are redundant for macrophage chemotaxis and that purinergic P2Y(2) and P2Y(12) receptor ligands are not chemotactic. We propose that ATP signaling is strictly autocrine or paracrine and that ATP and ADP may act as short-range "touch me" (rather than long-range find me) signals to promote phagocytic clearance via cell spreading.     

Purinergic mechanisms in the control of gastrointestinal motility

For many years, ATP and adenosine have been implicated in movement regulation of the gastrointestinal tract. They act through three major receptor subtypes: adenosine or P1 receptors, P2X receptors and P2Y receptors. Each of these major receptor types can be subdivided into several different classes and is widely distributed amongst various neurons, muscle types, glia and interstitial cells that regulate intestinal functions. Several key roles for the different receptors and their endogenous ligands have been identified in physiological and pharmacological studies. For example, adenosine acting at A(1) receptors appears to inhibit intestinal motility in various pathological conditions. Similarly, ATP acting at P2Y receptors is an important component of inhibitory neuromuscular transmission, acting as a cotransmitter with nitric oxide. ATP acting at P2X and P2Y(1) receptors is important for synaptic transmission in simple descending excitatory and inhibitory reflex pathways. Some P2Y receptor subtypes prefer uridine nucleotides over purine nucleotides. Thus, roles for UTP and UDP as enteric transmitters in place of ATP cannot be excluded. ATP also appears to be important for sensory transduction, especially in chemosensitive pathways that initiate local inhibitory reflexes. Despite this evidence, data are lacking about the roles of either adenosine or ATP in more complex motility patterns such as segmentation or the interdigestive migrating motor complex. Clarification of roles for purinergic transmission in these common, but understudied, motility patterns will depend on the use of subtype-specific antagonists that in some cases have not yet been developed.     

Adenine nucleotide metabolism by chondrocytes in vitro: Role of ATP in chondrocyte maturation and matrix mineralization

The objective of the investigation was to explore the notion that chondrocytes in the growth plate secrete nucleotides and that these compounds are used to regulate cell maturation and matrix mineralization. Chondrocytes were isolated from the cephalic region of chick embryo sterna and maintained in culture until confluent. To promote expression of the mature phenotype, cultures were then treated with retinoic acid. During the culture period, medium was removed and analyzed for nucleotides using a modified reverse-phase high-performance liquid chromatography (HPLC) procedure. We found that culture medium, conditioned by the chondrocytes, contained significant quantities of nucleotides. Moreover, the nucleotide concentrations were similar in magnitude to levels reported for media conditioned by other cell types. In terms of species, adenosine diphosphate (ADP) was the major nucleotide present in the conditioned medium; adenosine monophosphate (AMP) was present, but at a lower concentration than ADP. To examine the possibility that adenosine triphosphate (ATP) was released by the cultured chondrocytes, but was rapidly degraded into ADP and AMP, we examined the kinetics of ATP breakdown by chondrocytes. We found that chondrocytes degraded over 70% of exogenous ATP within 15 minutes. Similar experiments performed with ADP and AMP indicated that these nucleotides were also degraded by the cells, but at a slower rate than ATP. To determine whether the extracellular nucleotides modulate cartilage development, we examined the effect of exogenous ATP on four major determinants of chondrocyte function: alkaline phosphatase activity, cell proliferation rate, anaerobic metabolism, and mineral deposition. We found that ATP caused only minimum alterations in cell number and alkaline phosphatase activity; however, it increased the lactate content of the medium probably by stimulating anaerobic glycolysis. We noted that ATP had a significant effect on the amount and type of mineral deposited into chondrocyte cultures. Compared with untreated controls, ATP stimulated formation of a small amount of poorly crystallized calcium phosphate. The results of the study show for the first time that chondrocytes release nucleotides into the extracellular milieu. Although they are rapidly degraded, they serve to regulate both mineral formation and energy metabolism. © 1995 Wiley-Liss Inc.     

细胞运动、细胞迁移与细胞骨架研究进展

细胞定向运动与细胞骨架的动态循环密切相关。运动细胞在其伪足前沿依靠细胞骨架的不断聚合推动细胞膜的前进,在基部靠近细胞体部位通过细胞骨架的不断解聚收缩拖拉细胞体向前运动,细胞骨架的聚合与解聚通过伪足与支撑表面的吸附与解吸附而偶连。肌动蛋白组成的微丝骨架是大多数运动细胞的主要成分。外界刺激引起微丝细胞骨架动态变化的信号通路已逐步明了。线虫精子细胞的运动行为与阿米巴变形运动相似,但是在线虫精子细胞中没有肌动蛋白,而是以精子主要蛋白为基础形成细胞骨架驱动精子细胞的运动。与肌动蛋白不同,精子主要蛋白没有分子极性、ATP结合位点和马达蛋白。通过比较研究以上两种运动体系将有助于在分子水平上进一步阐明细胞运动的机理。     

Some thoughts on the evolutionary basis for the prominent role of ATP and ADP in cellular energy metabolism

The predominance of the adenosine triphosphate/adenosine diphosphate (ATP/ADP) couple in cellular phosphorylation reactions, including those that form the basis for cellular energy metabolism, cannot be explained on thermodynamic grounds since a variety of "high energy phosphate" compounds (including ADP itself) found in the cell would, based on thermodynamic considerations, be at least as effective as ATP in serving as a phosphoryl donor. How then did present-day organisms come to rely on the ATP/ADP couple as the principal mediator of phosphorylation reactions? The early appearance of adenine compounds in the prebiotic environment is suggested by experiments indicating that, relative to other purine or pyridimine compounds, adenine derivatives are preferentially synthesized under simulated prebiotic conditions (Ponnamperuma et al., 1963). In addition to the roles of adenine nucleotides in phosphorylation reactions, other adenine derivatives (e.g. Coenzyme A, flavin adenine dinucleotide, puridine nucleotides) are employed in a variety of metabolic roles. The principal function of the adenine moiety in these latter cases is in the binding of these derivatives to the relevant enzyme. The capability for binding of the adenine moiety appears to have arisen early in evolution and been exploited in a multitude of contexts, a suggestion consistent with observed similarities between the binding sites of several enzymes employing adenine derivatives as substrate. The early availability of suitable adenine compounds in the biosphere and development of complementary binding sites on cellular proteins, coupled with the expected advantages in having a limited number of metabolites as central mediators of endergonic and exergonic metabolism could readily have led to the observed pre-eminence of adenine nucleotides in cellular energy metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lysophosphatidic acid receptor activation affects the C13NJ microglia cell line proteome leading to alterations in glycolysis,motility, and cytoskeletal architecture

Microglia, the immunocompetent cells of the CNS, are rapidly activated in response to injury and microglia migration towards and homing at damaged tissue plays a key role in CNS regeneration. Lysophosphatidic acid (LPA) is involved in signaling events evoking microglia responses through cognate G protein‐coupled receptors. Here we show that human immortalized C13NJ microglia express LPA receptor subtypes LPA₁, LPA₂, and LPA₃ on mRNA and protein level. LPA activation of C13NJ cells induced Rho and extracellular signal‐regulated kinase activation and enhanced cellular ATP production. In addition, LPA induced process retraction, cell spreading, led to pronounced changes of the actin cytoskeleton and reduced cell motility, which could be reversed by inhibition of Rho activity. To get an indication about LPA‐induced global alterations in protein expression patterns a 2‐D DIGE/LC‐ESI‐MS proteomic approach was applied. On the proteome level the most prominent changes in response to LPA were observed for glycolytic enzymes and proteins regulating cell motility and/or cytoskeletal dynamics. The present findings suggest that naturally occurring LPA is a potent regulator of microglia biology. This might be of particular relevance in the pathophysiological context of neurodegenerative disorders where LPA concentrations can be significantly elevated in the CNS.     

A generalized transport model for biased cell migration in an anisotropic environment

 A generalized transport model is derived for cell migration in an anisotropic environment and is applied to the specific cases of biased cell migration in a gradient of a stimulus (taxis; e.g., chemotaxis or haptotaxis) or along an axis of anisotropy (e.g., contact guidance). The model accounts for spatial or directional dependence of cell speed and cell turning behavior to predict a constitutive cell flux equation with drift velocity and diffusivity tensor (termed random motility tensor) that are explicit functions of the parameters of the underlying random walk model. This model provides the connection between cell locomotion and the resulting persistent random walk behavior to the observed cell migration on longer time scales, thus it provides a framework for interpreting cell migration data in terms of underlying motility mechanisms. Received: 8 April 1999     

P2Y purinergic signaling in prostate cancer: Emerging insights into pathophysiology and therapy

Despite recent advances in the treatment landscape for prostate cancer, many challenges still remain. A more profound understanding of prostate cancer pathogenesis and the underlying mechanisms is critical to developing novel therapeutics strategies. Extracellular nucleotides play a central role in the growth and progression of a variety of cancer types – almost all tumor cells and immune cells express purinergic membrane receptors for extracellular nucleotides (ATP, ADP, UTP, UDP, UDP-sugar) and their metabolic nucleoside products (e.g., adenosine). Herein we review the pathological and immunomodulatory roles of P2Y purinergic nucleotide receptors in prostate cancer and their potential as therapeutic targets to address some of the clinical limitations in prostate cancer treatment.     

Regulation of adenine nucleotide concentration at endothelium-fluid interface by viscous shear flow.

The action of adenine nucleotides on vascular endothelial cells is apparently mediated by the local flow conditions. Because nucleotides are sequentially degraded from ATP-->ADP-->AMP-->adenosine by ecto-enzymes at the endothelial surface, it has been hypothesized that the observed flow effect is caused by the flow-dependent change of nucleotide concentration at the cell surface. In this study, we have calculated the concentration profiles of adenine nucleotides at the cell surface under flow conditions encountered in an in vitro parallel-plate flow system, as has been used in several related experimental studies. When medium containing uniformly distributed ATP is perfused over endothelial monolayers, our results show that ATP concentration in the cell vicinity gradually decreases in the streamwise direction as a result of enzymatic degradation. This hydrolysis of ATP results in the generation of ADP, and ADP concentration in turn gradually increases at the cell surface. The concentration profiles of nucleotides are dependent on the levels of applied wall shear rate. As the corresponding shear stress increases from 0.1 to 30 dynes/cm2, ATP concentration at the cell surface at the center of coverslip increases from 0.66 to 0.93. Under no-flow conditions, our model predicts a steady decline of ATP concentration and a transient increase of ATP-derived ADP, comparable to the published results of previous experiments. These numerical results, combined with our recent experimental data, provide insights into the cellular mechanisms by which hemodynamic flow modulates the effects of vasoactive agents on endothelium.