Intracellular pH of mitogen-stimulated lymphocytes

Hexamethylene amiloride synergizes with venetoclax to induce lysosome-dependent cell death in acute myeloid leukemia

Tumors maintain an alkaline intracellular environment to enable rapid growth. The proton exporter NHE1 participates in maintenance of this pH gradient. However, whether targeting NHE1 could inhibit the growth of tumor cells remains unknown. Here, we report that the NHE1 inhibitor Hexamethylene amiloride (HA) efficiently suppresses the growth of AML cell lines. Moreover, HA combined with venetoclax synergized to efficiently inhibit the growth of AML cells. Interestingly, lysosomes are the main contributors to the synergism of HA and venetoclax in inhibiting AML cells. Most importantly, the combination of HA and venetoclax also had prominent anti-leukemia effects in both xenograft models and bone marrow samples from AML patients. In summary, our results provide evidence that the NHE1 inhibitor HA or its combination with venetoclax efficiently inhibits the growth of AML in vitro and in vivo.

Differential trafficking of ligands trogocytosed via CD28 versus CTLA4 promotes collective cellular control of co-stimulation

Intercellular communication is crucial for collective regulation of cellular behaviors. While clustering T cells have been shown to mutually control the production of key communication signals, it is unclear whether they also jointly regulate their availability and degradation. Here we use newly developed reporter systems, bioinformatic analyses, protein structure modeling and genetic perturbations to assess this. We find that T cells utilize trogocytosis by competing antagonistic receptors to differentially control the abundance of immunoregulatory ligands. Specifically, ligands trogocytosed via CD28 are shuttled to the T cell surface, enabling them to co-stimulate neighboring T cells. In contrast, CTLA4-mediated trogocytosis targets ligands for degradation. Mechanistically, this fate separation is controlled by different acid-sensitivities of receptor-ligand interactions and by the receptor intracellular domains. The ability of CD28 and CTLA4 to confer different fates to trogocytosed ligands reveals an additional layer of collective regulation of cellular behaviors and promotes the robustness of population dynamics.

mTOR Senses Intracellular pH through Lysosome Dispersion from RHEB

Acidity, generated in hypoxia or hypermetabolic states, perturbs homeostasis and is a feature of solid tumors. That acid peripherally disperses lysosomes is a three-decade-old observation, yet one little understood or appreciated. However, recent work has recognized the inhibitory impact this spatial redistribution has on mechanistic target of rapamycin complex 1 (mTORC1), a key regulator of metabolism. This finding argues for a paradigm shift in localization of mTORC1 activator Ras homolog enriched in brain (RHEB), a conclusion several others have now independently reached. Thus, mTORC1, known to sense amino acids, mitogens, and energy to restrict biosynthesis to times of adequate resources, also senses pH and, via dampened mTOR-governed synthesis of clock proteins, regulates the circadian clock to achieve concerted responses to metabolic stress. While this may allow cancer to endure metabolic deprivation, immune cell mTOR signaling likewise exhibits pH sensitivity, suggesting that suppression of antitumor immune function by solid tumor acidity may additionally fuel cancers, an obstacle potentially reversible through therapeutic pH manipulation.

Roles of pH in control of cell proliferation

Precise spatiotemporal regulation of intracellular pH (pH_i ) is a prerequisite for normal cell function, and changes in pH_i or pericellular pH (pH_e ) exert important signalling functions. It is well established that proliferation of mammalian cells is dependent on a permissive pH_i in the slightly alkaline range (7.0-7.2). It is also clear that mitogen signalling in nominal absence of HCO3- is associated with an intracellular alkalinization (~0.3 pH unit above steady-state pH_i ), which is secondary to activation of Na⁺ /H⁺ exchange. However, it remains controversial whether this increase in pH_i is part of the mitogenic signal cascade leading to cell cycle entry and progression, and whether it is relevant under physiological conditions. Furthermore, essentially all studies of pH_i in mammalian cell proliferation have focused on the mitogen-induced G0-G1 transition, and the regulation and roles of pH_i during the cell cycle remain poorly understood. The aim of this review is to summarize and critically discuss the possible roles of pH_i and pH_e in cell cycle progression. While the focus is on the mammalian cell cycle, important insights from studies in lower eukaryotes are also discussed. We summarize current evidence of links between cell cycle progression and pH_i and discuss possible pH_i - and pH_e sensors and signalling pathways relevant to mammalian proliferation control. The possibility that changes in pH_i during cell cycle progression may be an integral part of the checkpoint control machinery is explored. Finally, we discuss the relevance of links between pH and proliferation in the context of the perturbed pH homoeostasis and acidic microenvironment of solid tumours.

Potassium increases the antitumor effects of ascorbic acid in breast cancer cell lines in vitro

Ascorbic acid (A) has been demonstrated to exhibit anti-cancer activity in association with chemotherapeutic agents. Potassium (K) is a regulator of cellular proliferation. In the present study, the biological effects of A and K bicarbonate, alone or in combination (A+K), on breast cancer cell lines were evaluated. The survival of cancer cells was determined by sulforhodamine B cell proliferation assay, while analysis of the cell cycle distribution was conducted via fluorescence-activated cell sorting. In addition, the expression of signaling proteins was analyzed upon treatment. The results indicated that there was a heterogeneous response of the different cell lines to A and K, and the best effects were achieved by A+K and A treatment. The interaction between A+K indicated an additive or synergistic effect. In addition, A+K increased the percentage of cells in the sub-G1 phase of the cell cycle, and was the most effective treatment in activating the degradation of poly(adenosine diphosphate-ribose) polymerase-1. In the breast cancer cell line MCF-7, A+K induced the appearance of the 18 kDa isoform of B-cell lymphoma-2-associated X protein (Bax), which is a more potent inducer of apoptosis than the full-length Bax-p21. The effects of A and K on the phosphorylation of extracellular signal-regulated kinase (ERK)1 and ERK2 were heterogeneous. In addition, treatment with K, A and A+K inhibited the expression of nuclear factor-κB. Overall, the results of the present study indicated that K potentiated the anti-tumoral effects of A in breast cancer cells in vitro.

Anion exchanger 2 is critical for CD8(+) T cells to maintain pHi homeostasis and modulate immune responses

Mitogenic stimulation of lymphocytes involves alkalinization of intracellular pH (pHi ). Subsequent pHi regulation may involve HCO3 (-) extrusion through Cl(-) /HCO3 (-) exchangers and/or Na(+) -HCO3 (-) co-transporters with acid-loading capability. Abnormalities in these mechanisms could result in immune dysfunctions, as suggested by the CD8(+) T-cell expansion encountered in mice lacking Ae2 (a widely expressed acid loader with electroneutral and Na(+) -independent Cl(-) /HCO3 (-) anion-exchange activity). Here we report that CD8(+) T cells but not CD4(+) T cells or other lymphocyte populations, are crucially dependent on Ae2 for pHi regulation. While total lymphocytes (including isolated CD4(+) T cells) exhibit Ae1 expression and Na(+) -HCO3 (-) co-transport with acidifying potential, CD8(+) T cells lack these acid-loading mechanisms. In Ae2-KO mice, CD4(+) but not CD8(+) T cells upregulate these potential Ae2 surrogates. As a consequence, Ae2-KO CD8(+) T cells exhibit alkalinized pHi , and dramatically increase their pHi upon CD3 stimulation. Moreover, stimulated Ae2-deficient CD8(+) T cells show enhanced intracellular production of IL-2 and membrane expression of its receptor IL-2Rα, together with increased cell proliferation and activation. These findings demonstrate that CD8(+) T cells are critically dependent on Ae2 for pHi homeostasis and tuning of cell proliferation and activation. Ae2 thus constitutes a novel target to modulate CD8(+) T-cell responses.

Role of AE2 for pHi regulation in biliary epithelial cells

The Cl⁻/HCO⁻₃anion exchanger 2 (AE2) is known to be involved in intracellular pH (pH_i) regulation and transepithelial acid-base transport. Early studies showed that AE2 gene expression is reduced in liver biopsies and blood mononuclear cells from patients with primary biliary cirrhosis (PBC), a disease characterized by chronic non-suppurative cholangitis associated with antimitochondrial antibodies (AMA) and other autoimmune phenomena. Microfluorimetric analysis of the Cl⁻/HCO⁻₃ anion exchange (AE) in isolated cholangiocytes showed that the cAMP-stimulated AE activity is diminished in PBC compared to both healthy and diseased controls. More recently, it was found that miR-506 is upregulated in cholangiocytes of PBC patients and that AE2 may be a target of miR-506. Additional evidence for a pathogenic role of AE2 dysregulation in PBC was obtained with Ae2^−/−_a,b mice, which develop biochemical, histological, and immunologic alterations that resemble PBC (including development of serum AMA). Analysis of HCO⁻₃ transport systems and pH_i regulation in cholangiocytes from normal and Ae2^−/−_a,b mice confirmed that AE2 is the transporter responsible for the Cl⁻/HCO⁻₃exchange in these cells. On the other hand, both Ae2^+/+_a,b and Ae2^−/−_a,b mouse cholangiocytes exhibited a Cl⁻-independent bicarbonate transport system, essentially a Na⁺-bicarbonate cotransport (NBC) system, which could contribute to pH_i regulation in the absence of AE2.

Proton channels in non-phagocytic cells of the immune system

Proton channels are expressed in all cells of the immune system to various degrees. While their function in phagocytic cells, immune cells that engulf bacteria and cell debris for clearance, has been the object of extensive research, the function of proton channels in non-phagocytic cells has remained more elusive until recently. Further studies have been helped by the discovery of the gene coding for the mammalian proton channel, HVCN1, which has prompted a new wave of research in this area. Recent findings show how proton channels regulate cell function in non-phagocytic cells of the immune system such as basophils and lymphocytes.

Effects of Zizyphus lotus L. (Desf.) polyphenols on Jurkat cell signaling and proliferation

We assessed the effects of Zizyphus lotus L. (Desf.) polyphenols (ZLP) on T-cell signaling and proliferation. Our results showed that ZLP exerted no effect on the increases in intracellular free calcium concentrations, [Ca(2+)]i, in human Jurkat T-cells. However, ZLP modulated the thapsigargin-induced increases in [Ca(2+)]i in these cells. ZLP treatment was found to decrease the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). In addition, ZLP induced a rapid (t1/2=33s) and dose-dependent decrease in intracellular pH (pHi) in human Jurkat T-cells. Furthermore, ZLP significantly curtailed T-cell proliferation by diminishing their progression from S to G2/M phase of cell cycle, and the expression of interleukin-2 (IL-2) mRNA. Taken together, the results of the present study demonstrate that ZLP modulate cell signaling and exert immunosuppressive effects in human T-cells.

In vitro chromatin self-association and its relevance to genome architecture

Chromatin in a eukaryotic nucleus is condensed through 3 hierarchies: primary, secondary, and tertiary chromatin structures. In vitro, when induced with cations, chromatin can self-associate and form large oligomers. This self-association process has been proposed to mimic processes involved in the assembly and maintenance of tertiary chromatin structures in vivo. In this article, we review 30 years of studies of chromatin self-association, with an emphasis on the evidence suggesting that this in vitro process is physiologically relevant.

The non-genomic effects on Na+/H+-exchange 1 by progesterone and 20α-hydroxyprogesterone in human T cells

Progesterone is an endogenous immunomodulator and can suppress T-cell activation during pregnancy. We have previously shown that the non-genomic effects of progesterone, especially acidification, are exerted via plasma membrane sites and suppress cellular genomic responses to mitogens. This study aimed to show that acidification is due to a non-genomic inhibition of Na(+)/H(+)-exchange 1 (NHE1) by progesterone and correlate this with immunosuppressive phytohemagglutinin (PHA)-induced T-cell proliferation. The presence of amiloride-sensitive NHE 1 was identified in T cells. The activity of NHE1 was inhibited by progesterone but not by 20alpha-hydroxyprogesterone (20alpha-OHP). Furthermore, 20alpha-OHP was able to compete with progesterone and release the inhibitory effect on the NHE1. The inhibition of NHE1 activity by progesterone-BSA demonstrated non-genomic action via plasma membrane sites. Finally, co-stimulation with PHA and progesterone or amiloride, (5-(N, N-dimethyl)-amiloride, DMA), inhibited PHA-induced T-cell proliferation, but this inhibition did not occur with 20alpha-OHP and PHA co-stimulation. However, when DMA was applied 72 h after PHA stimulation, it was able to suppress PHA-induced T-cell proliferation. This is the first study to show that progesterone causes a rapid non-genomic inhibition of plasma membrane NHE1 activity in T cells within minutes which is released by 20alpha-OHP. The inhibition of NHE1 leads to immunosuppressive T-cell proliferation and suggests that progesterone might exert a major rapid non-genomic suppressive effect on NHE1 activity at the maternal-fetal interface in vivo and that 20alpha-OHP may possibly be able to quickly release the suppression when T cells circulated away from the interface.

Non-genomic immunosuppressive actions of progesterone inhibits PHA-induced alkalinization and activation in T cells

Progesterone is an endogenous immunomodulator, and can suppress T-cell activation during pregnancy. When analyzed under a genome time scale, the classic steroid receptor pathway does not have any effect on ion fluxes. Therefore, the aim of this study was to investigate whether the non-genomic effects on ion fluxes by progesterone could immunosuppress phytohemagglutinin (PHA)-induced human peripheral T-cell activation. The new findings indicated that, first, only progesterone stimulated both [Ca2+]i elevation and pHi decrease; in contrast, estradiol or testosterone stimulated [Ca2+]i elevation and hydrocortisone or dexamethasone stimulated pHi decrease. Secondly, the [Ca2+]i increase by progesterone was dependent on Ca2+ influx, and the acidification was blocked by Na+/H+ exchange (NHE) inhibitor, 3-methylsulphonyl-4-piperidinobenzoyl, guanidine hydrochloride (HOE-694) but not by 5-(N,N-dimethyl)-amiloride (DMA). Thirdly, progesterone blocked phorbol 12-myristate 13-acetate (PMA) or PHA-induced alkalinization, but PHA did not prevent progesterone-induced acidification. Fourthly, progesterone did not induce T-cell proliferation; however, co-stimulation progesterone with PHA was able to suppress PHA-induced IL-2 or IL-4 secretion and proliferation. When progesterone was applied 72 h after PHA stimulation, progesterone could suppress PHA-induced T-cell proliferation. Finally, immobilization of progesterone by conjugation to a large carrier molecule (BSA) also stimulated a rapid [Ca2+]i elevation, pHi decrease, and suppressed PHA-induced proliferation. These results suggested that the non-genomic effects of progesterone, especially acidification, are exerted via plasma membrane sites and suppress the genomic responses to PHA. Progesterone might act directly through membrane specific nonclassical steroid receptors to cause immunomodulation and suppression of T-cell activation during pregnancy.

Docosahexaenoic acid and other fatty acids induce a decrease in pHi in Jurkat T-cells

1. Docosahexaenoic acid (DHA) induced rapid (t1/2=33 s) and dose-dependent decreases in pHi in BCECF-loaded human (Jurkat) T-cells. Addition of 5-(N,N-dimethyl)-amiloride, an inhibitor of Na+/H+ exchanger, prolonged DHA-induced acidification as a function of time, indicating that the exchanger is implicated in pHi recovery. 2. Other fatty acids like oleic acid, arachidonic acid, eicosapentaenoic acid, but not palmitic acid, also induced a fall in pHi in these cells. 3. To assess the role of calcium in the DHA-induced acidification, we conducted experiments in Ca2+-free (0% Ca2+) and Ca2+-containing (100% Ca2+) buffer. We observed that there was no difference in the degree of DHA-induced transient acidification in both the experimental conditions, though pHi recovery was faster in 0% Ca2+ medium than that in 100% Ca2+ medium. 4. In the presence of BAPTA, a calcium chelator, a rapid recovery of DHA-induced acidosis was observed. Furthermore, addition of CaCl2 into 0% Ca2+ medium curtailed DHA-evoked rapid pHi recovery. In 0% Ca2+ medium, containing BAPTA, DHA did not evoke increases in [Ca2+]i, though this fatty acid still induced a rapid acidification in these cells. These observations suggest that calcium is implicated in the long-lasting DHA-induced acidosis. 5. DHA-induced rapid acidification may be due to its deprotonation in the plasma membrane (flip-flop model), as suggested by the following observations: (1) DHA with a -COOH group induced intracellular acidification, but this fatty acid with a -COOCH3 group failed to do so, and (2) DHA, but not propionic acid, -induced acidification was completely reversed by addition of fatty acid-free bovine serum albumin in these cells. 6. These results suggest that DHA induces acidosis via deprotonation and Ca2+ mobilization in human T-cells.

Regulation of T-cell apoptosis by reactive oxygen species

To ensure that a constant number of T cells are preserved in the peripheral lymphoid organs, the production and proliferation of T cells must be balanced out by their death. Newly generated T cells exit the thymus and are maintained as resting T cells. Transient disruption of homeostasis occurs when naïve T cells undergo antigen-induced expansion, a process involving intracellular signaling events that lead to T cell proliferation, acquisition of effector functions, and, ultimately, either apoptosis or differentiation into long-lived memory cells. The last decision point (death vs. differentiation) is a crucial one: it resets lymphoid homeostasis, promotes protective immunity, and limits autoimmunity. Despite its importance, relatively little is known about the molecular mechanisms involved in this cell fate decision. Although multiple mechanisms are likely involved, recent data suggest an underlying regulatory role for reactive oxygen species in controlling the susceptibility of T cells to apoptosis. This review focuses on recent advances in our understanding of how reactive oxygen species modulate T-cell apoptosis.

The pathogenesis of Barrett's esophagus

Significant progress has been made in clinicians' understanding of the molecular pathogenesis of BE, and the laboratory findings are beginning to lead to hypothesis-driven clinical studies; however, the following questions remain unanswered: (1) how can clinicians identify the persons most at risk for the development of esophageal adenocarcinoma, (2) what are the environmental gene interactions in esophageal carcinogenesis, and (3) can clinicians prevent the development of esophageal adenocarcinoma in the population at risk? As esophageal adenocarcinoma starts to reach epidemic proportions, further research in these areas is urgently required. With the advent of the genomic era and an explosion in studies in BE, significant progress can be made.

Voltage-activated proton currents in human lymphocytes

Voltage-activated proton currents are reported for the first time in human peripheral blood T and B lymphocytes and in the human leukaemic T cell line Jurkat E6-1. The properties of H(+) currents studied using tight-seal voltage-clamp recording techniques were similar in all cells. Changing the pH gradient by one unit caused a 47 mV shift in the reversal potential, demonstrating high selectivity of the channels for protons. H(+) current activation upon membrane depolarisation had a sigmoidal time course that could be fitted by a single exponential function after a brief delay. Increasing pH(o) shifted the activation threshold to more negative potentials, and increased both the H(+) current amplitude and the rate of activation. In lymphocytes studied at pH(i) 6.0, the activation threshold was more negative and the H(+) current density was three times larger than at pH(i) 7.0. Increasing the intracellular Ca(2+) concentration to 1 microM did not change H(+) current amplitude or kinetics detectably. Extracellularly applied Zn(2+) and Cd(2+) inhibited proton currents, slowing activation and shifting the voltage-activation curve to more positive potentials. The H(+) current amplitude was 100 times larger in CD19+ B lymphocytes and in Jurkat E6-1 cells than in CD3+ T lymphocytes. Following stimulation with the phorbol ester PMA, the H(+) current density in peripheral blood T lymphocytes and Jurkat T cells increased. In contrast, the H(+) current density of phorbol ester (PMA)-stimulated B lymphocytes was reduced and activation became slower. The pattern of expression of H(+) channels in lymphocytes appears well suited to their proposed role of charge compensation during the respiratory burst.

Proliferation, not apoptosis, alters epithelial cell migration in small intestine of CFTR null mice

Expression of a mutated cystic fibrosis transmembrane conductance regulator (CFTR) has been shown to enhance proliferation within CF airways, and cells expressing a mutated CFTR have been shown to be less susceptible to apoptosis. Because the CFTR is expressed in the epithelial cells lining the gastrointestinal tract and all CF mouse models are characterized by gastrointestinal obstruction, we hypothesized that CFTR null mice would have increased epithelial cell proliferation and reduced apoptosis within the small intestine. The rate of intestinal epithelial cell migration from crypt to villus was increased in CFTR null mice relative to mice expressing the wild-type CFTR. This difference in migration could be explained by an increase in epithelial cell proliferation but not by a difference in apoptosis within the crypts of Lieberkühn. In addition, using two independent sets of CF cell lines, we found that epithelial cell susceptibility to apoptosis was unrelated to the presence of a functional CFTR. Thus increased proliferation but not alterations in apoptosis within epithelial cells might contribute to the pathophysiology of CF.

Response of alkalinization or acidification by phytohemagglutinin is dependent on the activity of protein kinase C in human peripheral T Cells

The increase of intracellular free calcium concentration ([Ca(2+)](i)) and protein kinase C (PKC) activity are two major early mitogenic signals to initiate proliferation of human T cells. However, a rapid change in intracellular pH (pH(i)), acidification or alkalinization during the activation, is also associated after these two signals. The aim of this study was to define whether the change in pH(i) is affected by calcium and protein kinase C (PKC), in phytohemagglutinin (PHA)-stimulated T cells. T cells were isolated from human peripheral blood. The [Ca(2+)](i) and the pH(i) were measured using, respectively, the fluorescent dyes, Fura-2, and BCECF. In addition, down-regulation of PKC activity by PMA (1 microM, 18 h) was confirmed in these cells using a protein kinase assay. The results indicated that, (1) alkalinization was induced by PHA or PMA in T cells; the results of alkalinization was PKC-dependent and Ca(2+)-independent, (2) in PKC down-regulated T cells, PHA induced acidification; this effect was enhanced by pre-treating the cells with the Na(+)/H(+) exchange inhibitor, 5-(N,N-dimethyl)-amiloride, (DMA, 10 microM, 20 min), (3) the acidification was dependent on the Ca(2+) influx and blocked by removal of extracellular calcium or the addition of the inorganic channel blocker, Ni(2+), and (4) Thapsigargin (TG), a Ca(2+)-ATPase inhibitor, confirmed that acidification by the Ca(2+) influx occurred in T cells in which PKC was not down-regulated. These findings indicate two mechanisms, alkalinization by PKC and acidification by Ca(2+) influx, exist in regulating pH(i) in T cells. This is the first report that PHA stimulates the acidification by Ca(2+) influx but not alkalinization in T cells after down-regulation of PKC. In conclusion, the activity of PKC in T cells determines the response in alkalinization or acidification by PHA.

Current status of flow cytometry in cell and molecular biology

This review summarizes recent developments in flow cytometry (FC). It gives an overview of techniques currently available, in terms of apparatus and sample handling, a guide to evaluating applications, an overview of dyes and staining methods, an introduction to internet resources, and a broad listing of classic references and reviews in various fields of interest, as well as some recent interesting articles.

Plasma membrane NADH-oxidoreductase system: a critical review of the structural and functional data

The observation in the early 1970s that ferricyanide can replace transferrin as a growth factor highlighted the major role plasma membrane proteins can play within a mammalian cell. Ferricyanide, being impermeant to the cell, was assumed to act at the level of the plasma membrane. Since that time, several enzymes isolated from the plasma membrane have been described, which, using NADH as the intracellular electron donor, are capable of reducing ferricyanide. However, their exact modes of action, and their physiological substrates and functions have not been solved to date. Numerous hypotheses have been proposed for the role of such redox enzymes within the plasma membrane. Examples include the regulation of cell signaling, cell growth, apoptosis, proton pumping, and ion channels. All of these roles may be a result of the function of these enzymes as cellular redox sensors. The emergence of many diverse roles for ferricyanide utilizing redox enzymes present in the plasma membrane might also, in part, be due to the numerous redox enzymes present within the membrane; the poor molecular characterization of the enzymes may be the reason for some of the diverging results reported in the literature as various researchers may be working on different enzymes. Here we review the diverse proposals given for structure and function to the plasma membrane NADH-oxidoreductase system(s) with a specific focus on those enzyme activities which can couple ferricyanide and NADH. Although they are still ill-defined enzymes, evidence is rising that they are of utmost significance for cellular regulation.

Bacterial lipopolysaccharide activates protein kinase C, but not intracellular calcium elevation, in human peripheral T cells

The increase of intracellular free calcium concentration ([Ca(2+)](i)) and protein kinase C (PKC) activity are two major early mitogenic signals to initiate proliferation of human peripheral T cells. Bacterial lipopolysaccharide (LPS) is nonmitogenic in human T cells. However, in the presence of monocytes, LPS becomes mitogenic to proliferate T cells. The aim of this study was to define the incompetency of LPS on two mitogenic signals in human peripheral T cells. T cells were isolated from human peripheral blood. [Ca(2+)](i) and pH(i) were determined by loading the cells with the fluorescent dyes, Fura-2 acetoxymethyl ester (Fura-2/AM) and 2',7'-bis(2-carboxyethyl)-5-(and 6)carboxyfluorescein acetoxymethyl ester (BCECF/AM). PKC activity was determined by protein kinase assay and cell proliferation was estimated from the incorporation of [(3)H]-thymidine. The results indicated that (1) LPS (10 microg/ml) stimulated PKC activity significantly within 5 min, reached a plateau at 30 min, and maintained that level for at least 2 h; and (2) LPS stimulated cytoplasmic alkalinization but did not affect the levels of [Ca(2+)](i) and [(3)H]-thymidine incorporation into T cells. Moreover, the combination of calcium ionophore A23187 with LPS significantly stimulated [(3)H]-thymidine incorporation into T cells. Thus, the results demonstrate that LPS failed to proliferate T cells, probably because of a lack of the machinery necessary to stimulate the mitogenic signal on [Ca(2+)](i) elevation.

Acid modulation of HT29 cell growth and differentiation. An in vitro model for Barrett's esophagus

Cell proliferation and differentiation are influenced by environmental factors, including the extracellular pH. We recently showed, using an ex vivo organ culture system of human mucosal Barrett's esophageal biopsies, that acid has a highly variable effect on cell proliferation and differentiation depending on the pattern of acid exposure. Study of the mechanisms underlying these dynamic effects of acid on this premalignant intestinal-like epithelium is hampered by lack of an immortalized cell line. We therefore investigated the effect of acid exposure on the human colonic carcinoma cell line HT29, chosen because of its intestinal cell derivation and its ability to differentiate in vitro. HT29 cells exposed to pH 5 medium either continuously (up to 3 weeks), or as a short (1 hour) pulse, were compared with cells cultured at pH 7.4. Villin expression was induced only by long term acid exposure, and correlated with the development of differentiated polarized cells that contain a brush border and microvillus inclusions. Chronic acid exposure arrested cell proliferation, whereas a 1 hour acid-pulse enhanced cell proliferation, as determined by [3H]thymidine incorporation assays and proliferating cell nuclear antigen expression. Serum starvation attenuated the hyperproliferative effect of an acid-pulse. In addition, the doubling time of at least the first cell cycle after an acid-pulse was shortened. The Na/H exchanger is likely to play a role since the hyperproliferative acid-induced response was blocked by amiloride; and the activity of the exchanger was increased at acidic pH as determined by 22Na uptake. These results support a role for extracellular pH on cell proliferation and differentiation of HT29 cells. Furthermore, these findings parallel the dynamic effects of acid on Barrett's esophagus, and suggest that HT29 cells could serve as an in vitro model for studying the mechanism of acid modulation in Barrett's esophagus.

Abnormalities in CD69 expression, cytosolic pH and Ca2+ during activation of lymphocytes from patients with systemic lupus erythematosus

Several immuno-regulatory abnormalities have been described in SLE patients. T cell dysfunction in SLE includes defective in vitro proliferative responses to several stimuli, reduced IL-2 production and a poor helper function. It has been widely proposed that this defective T cell immunoregulatory function has a key role in the hyperactivity of B cells and auto-antibody production in SLE. However, it has not been elucidated whether or not this cell dysfunction is intrinsic to lymphocytes or is due to other factors such as anti-lymphocyte auto-antibodies. In this study we have evaluated some important early cell activation events in T and non-T lymphocytes from patients with systemic lupus erythematosus (SLE). Peripheral blood lymphocytes from SLE patients and controls were isolated. The intracellular pH (pHi), cytosolic calcium (Ca2+i) and CD69 expression were determined by spectrofluorometry and flow cytometry. Modifications of these parameters in response to protein kinase C (PKC) activators, mitogenic lectins and calcium ionophores were also studied. We found a significant reduction in the increase of pHi in response to PKC activators (PMA) in SLE cells. In addition, the induction of CD69 expression by PMA was significantly lower in T cells from SLE patients. By contrast, freshly isolated non-stimulated SLE cells exhibited a significantly higher pHi, as well as an increased baseline expression of the early cell activation antigen CD69. On the other hand, the increase in Ca2+i in response to a Ca2+ ionophore (4Br-A23187) or thapsigargin in Ca(2+)-free solutions, was smaller in SLE lymphocytes. We concluded that T cells from SLE patients exhibit abnormalities in several key early cell activation events (pHi, Ca2+i and CD69 expression). These abnormalities could have an important role in the T cell dysfunction observed in SLE. The presence of T cells with a preactivated phenotype in the peripheral blood of SLE patients, could be a reflection of the ongoing autoimmune phenomena that is occurring in these patients.

Studies of human tumors by MRS: a review

The literature describing 31P, 1H, 13C, 23Na and 19F MRS in vivo in human cancers is reviewed. Cancers have typical metabolic characteristics in 31P and 1H MRS including high levels of phospholipid metabolites and a cellular pH more alkaline than normal. These alone are not specific for cancer but are diagnostic in appropriate clinical settings. Some metabolic characteristics appear to be prognostic indices and correlation with treatment response is emerging as an important potentially cost-effective use of MRS in oncology. 19F MRS examines pharmacokinetics of 5-fluorouracil and by demonstrating its retention predicts response of a cancer to treatment. Current needs include improvement of diagnostic specificity by use of techniques like multivoxel MRS, proton decoupling of 31P, short echo time and fat-suppressed 1H MRS, 13C MRS direct or via 1H-observe, and statistical analysis of multiple spectral features. Trials in large populations in well defined clinical settings are needed to determine if MRS can provide independent prognostic indices useful in cancer management.

D-glyceraldehyde-3-phosphate dehydrogenase from HeLa cells--1. Purification and properties of the enzyme

1. D-GPDH from HeLa cells was isolated and purified. 2. Some basic kinetic constants are reported. 3. Sodium dodecyl polyacrylamide gel electrophoresis gave a single band with a molecular weight of approximately 36 K. 4. ATP and NADH inhibit competitively enzyme activity. 5. Comparative catalytic properties of GPDH from normal and tumor cells were effectuated.

Modulation of calcium fluxes in Jurkat T cells by myristic acid. Inhibition is independent of membrane potential and intracellular pH

Treatment of T lymphocytes with mitogenic antibodies against the T-cell receptor/CD3 complex induces within seconds a rise in the concentration of intracellular free Ca2+. We recently reported that free myristic acid, but not its methyl ester, inhibits both the anti-CD3-induced Ca2+ influx across the cell membrane and the Ca2+ release from intracellular stores in Jurkat T cells. Here we show that myristic acid induced a rapid hyperpolarization of the cell membrane potential and a decrease in intracellular pH in Jurkat cells. Lauric acid and palmitic acid caused minor hyperpolarization, whereas other saturated non-esterified fatty acids tested were without effect. Hyperpolarization of the membrane potential in Jurkat cells with valinomycin did not, however, inhibit the anti-CD3-induced Ca2+ signal, and the blocking effect on the Ca2+ signal in myristic acid-treated Jurkat cells was not reversed after normalization of the cell membrane potential by treatment with gramicidin. The inhibitory effect of myristic acid on the Ca2+ fluxes thus cannot be explained by changes in membrane potential. We also present evidence that the blocking effect of myristic acid on the receptor-operated Ca2+ flux is not due to the myristic acid-induced decrease in intracellular pH. Moreover, we demonstrate that myristic acid does not prevent the release of Ca2+ triggered by inositol 1,4,5-trisphosphate from intracellular pools in permeabilized cells. Our findings indicate that myristic acid blocks anti-CD3-induced Ca2+ traffic in Jurkat cells by interfering with the regulation of Ca2+ mobilization, apparently by blocking an early step in signal transduction from the T-cell-antigen receptor/CD3 complex.

Cytotoxic T lymphocyte (CTL)-mediated cytolysis proceeds in the absence of Na+/H+ antiport activity: regulation of cytosolic pH by the Na+/H+ antiport in a cloned CTL

Cytotoxic T lymphocyte (CTL)-mediated cytolysis of specifically bound target cells (TC) is thought to be triggered by cross-linking the T-cell antigen receptor (TcR). Biochemical events associated with TcR cross-linking include increased intracellular calcium levels [Ca2+]i, hydrolysis of phosphatidylinositol (PI), and an increase in intracellular pH [pH]i. Whereas CTL-mediated cytolysis of some TC is calcium-dependent, and PI hydrolysis is speculated to trigger the CTL lethal hit via activation of PKC, little is known about changes in [pH]i relating to activation of the lethal hit stage. We report regulation of [pH]i in a cloned CTL by the electroneutral Na+/H+ antiport during activation with PMA and specific antigen-bearing TC. Furthermore, using 5-(N-methyl-N-isobutyl) amiloride (MIBA), a potent antiport inhibitor, we demonstrate that Na+/H+ exchange is not required for activation of CTL cytolytic activity.

Effects of prostaglandin E2 and F2 alpha on cytoplasmic pH in a clonal osteoblast-like cell line, MOB 3-4

Prostaglandin E2 (PGE2, 5 ng/ml to 5 micrograms/ml) induced a dose-dependent increase in cAMP accumulation, inositol phosphates (IPs) accumulation, and cytoplasmic free Ca2+ ([Ca2+]i) in a clonal osteoblast-like cell line, MOB 3-4. In contrast, prostaglandin F2 alpha (PGF2 alpha, 5 ng/ml to 5 micrograms/ml) stimulated increases in IPs accumulation and [Ca2+]i without stimulating an increase in cAMP accumulation. Both PGE2 (greater than 0.5 micrograms/ml) and PGF2 alpha (greater than or equal to 5 micrograms/ml) increased cytoplasmic pH (pHi) from approximately 7.15 to 7.35 in BCECF-loaded cells. A tumor promotor, phorbol 12-myristate 13-acetate (PMA, 0.1-100 nM) also increased pHi without effect on phosphoinositide hydrolysis. Both PGE2-(5 micrograms/ml) and PMA- (100 nM) induced cytoplasmic alkalinization was inhibited by removal of extracellular Na+, or by pretreatment of the cells with amiloride (0.5 mM), an inhibitor of Na+/H+ exchange, or H-7 (100 microM), a nonspecific inhibitor of protein kinase C. Thus, MOB 3-4 cells appeared to possess PGE2 receptors and PGF2 alpha receptors: the former are coupled to adenylate cyclase and phospholipase C, and the latter are predominantly coupled to phospholipase C. Also the cells appeared to possess an amiloride-sensitive Na+/H+ exchange activity, which increases pHi in response to PGE2 and PGF2 alpha, as well as to PMA. Long-term (48 hr) exposure of the cells to PGE2 at a high concentration (5 micrograms/ml), but not to PGF2 alpha and PMA, decreased DNA synthesis in the serum-deficient medium. Thus, cytoplasmic alkalinization appeared insufficient for cell replication. At least in MOB 3-4 cells, the inhibitory effect of PGE2 on DNA synthesis may be due to the cAMP messenger system.

Cytoplasmic alkalinization produced by the combination of anti-immunoglobulin antibody plus cytochalasin D in murine B lymphocytes

The intracellular pH of murine splenic B lymphocytes was measured using the pH-sensitive fluorescent dye, bis(carboxyethyl)carboxyfluorescein (BCECF). After stimulation of B lymphocytes with anti-immunoglobulin antibody plus cytochalasin D, two agents that act in synergy to promote S-phase entry, a late increase in pH was detected that occurred prior to the onset of DNA synthesis. The degree of alkalinization observed was comparable to that produced by two additional mitogenic regimens. Cytoplasmic alkalinization was not blocked by dimethylamiloride. Cytoplasmic alkalinization represents a sign of, and may play a role in, stimulation of B lymphocytes to enter S phase.

Role of cyclic AMP in proliferation of lung tissue in organ culture

The role of cyclic AMP in cell proliferation and division has been the subject of study by a number of investigators in the past 30 years, but the argument of whether cyclic AMP is a negative or a positive regulator has not been settled. We studied the effect of cyclic AMP on proliferation of normal and postpneumonectomized lung tissues in young adult rats by measuring the incorporation of tritiated thymidine into lung DNA in organ culture. In normal lung tissues the incorporation of [3H]thymidine was increased by exogenous dibutyryl cyclic AMP, or by isoproterenol or forskolin to stimulate adenylate cyclase, or by caffeine, which inhibits cAMP phosphodiesterase. The effect of isoproterenol, but not forskolin, was abolished by the beta-adrenergic blocking agent propranolol. The effect of caffeine on [3H]thymidine incorporation was further enhanced in normal lung tissues in the presence of dibutyryl cyclic AMP and in postpneumonectomized lung tissues. Imidazole, a cAMP phosphodiesterase stimulator, also increased [3H]thymidine incorporation in culture, but the effect was not magnified in the presence of exogenous dibutyryl cyclic AMP, nor in postpneumonectomized lung tissues. The data suggest that cyclic AMP acts as a positive regulator in proliferation of lung tissues.

Modulation of K+ currents in human lymphocytes by pH

1. Using whole-cell patch-clamp techniques, we found that the voltage-dependent K+ conductance in human peripheral blood T lymphocytes is enhanced threefold at alkaline intracellular pH (pHi) compared to acid pHi. This pH dependence can be described by a model having two strongly co-operative proton binding sites with pka 7.15. A similar pHi sensitivity exists for K+ conductance in mitogen-activated cells. 2. The reversal potential, threshold voltage for activation of the K+ conductance, and voltage dependence of steady-state inactivation are not affected by pHi. Activation and inactivation kinetics are also unchanged. 3. Single-channel measurements made in whole-cell patch-clamp mode indicate that the effect of intracellular pH on the amplitudes of single-channel events parallels, but does not wholly account for, the effect of pHi on the macroscopic currents. 4. Lowering extracellular pH (pHo) shifts the threshold for activation of the K+ current to a more depolarized voltage, consistent with a surface charge screening effect. Apparent changes in peak current and activation kinetics at acid pHo can be accounted for by this voltage shift. An additional slowing of inactivation kinetics at low pHo does occur. 5. The relevance of the pH sensitivity of the voltage-gated K+ conductance to lymphocyte mitogenesis and volume regulation is discussed.

Effect of cyclosporin A and ionophores on the intracellular pH of lymphocytes as measured by flow cytometry

Because of the known importance of pHi changes on the biology of cells, we have investigated the effect of CsA, the clinically important immunomodulator, on the pHi of resting mouse spleen and human peripheral blood lymphocytes. We have found that pharmacological doses (0.8 microM) of CsA caused no change in the pHi in these cells. Similarly, the Ca2+ ionophore, A23187, up to 5 microns concentration, had no effect on the pHi of these cells, in contrast to previous reports. However, higher doses of CsA (2.4-8.0 microM) did change the pHi transiently or permanently. These results were obtained with flow cytometric measurements of fluorescence intensity of the pH-sensitive dye, BCECF.

Voltage-dependent potassium channels in mouse Schwann cells

1. Ionic currents in Schwann cells cultured from enzymatically dissociated sciatic nerves of newborn mice were recorded by the whole-cell variation of the patch-clamp technique. 2. In these cells only the voltage-dependent K+ currents were recorded. The K+ current was suppressed by quinine, 4-aminopyridine (4-AP) or tetraethylammonium (TEA), their half-suppression concentrations being 22 microM, 0.3 mM and 15 mM, respectively. 3. The peak amplitudes and density of the K+ currents in these Schwann cells increased rapidly during the first 2 days of the culture. 4. In an investigation of the linkage between K+ channels and Schwann cell proliferation, three different K+ channel blockers (quinine, 4-AP and TEA) were added to the medium at different stages of the culture. In media containing sublethal doses of quinine or 4-AP, the start of cell proliferation was delayed when these drugs were added at 12 h or on day 3. The same doses of these drugs applied on day 6, when the Schwann cells were proliferating, did not affect cell proliferation. TEA showed a discrepancy between the dose-dependent blocking of K+ channels and cell proliferation because of its additional cytotoxic effects. 5. It is concluded that voltage-dependent K+ channels in mouse Schwann cells are similar to those observed in human and murine T lymphocytes. These K+ channels are suggested to be involved in Schwann cell proliferation at early stages of development.

Methotrexate: studies on cellular metabolism. III.--Effect on the transplasma-membrane redox activity and on ferricyanide-induced proton extrusion by HeLa cells

The effect of methotrexate (MTX) on transplasma-membrane electron transport and ferricyanide-induced proton extrusion by HeLa cells was studied. Both systems were inhibited by MTX. It is suggested that inhibition of electron transport and proton extrusion caused by MTX could be associated with other metabolic alterations such as response to the increase in NADH levels and decrease in intracellular pH.

The role of potassium channels in Schwann cell proliferation in Wallerian degeneration of explant rabbit sciatic nerves

1. Patch clamp studies of whole-cell ionic currents and biochemical studies of proliferation were carried out on Schwann cells of myelinated axons in explant segments of sciatic nerves of adult rabbit maintained in culture for 0-10 days. 2. Schwann cell proliferation, as assayed by [3H]thymidine incorporation and by electron microscopic autoradiography, showed an increase following nerve explant. Proliferation proceeded in parallel with a gradual hyperpolarization of the resting potential and an increase in K+ currents in Schwann cells of myelinated axons. 3. The relation between K+ channels and proliferation was studied by incubating explant nerves in the presence of various K+ channel blockers. Quinine, TEA and 4-aminopyridine (4-AP), which blocked K+ currents in Schwann cells, were found also to block Schwann cell proliferation in a dose-dependent fashion and over similar concentrations. Electron microscopy showed that TEA did not retard myelin and axonal break-down which is thought to be the source of mitogens for Schwann cell proliferation. 4. The relation between resting potential and proliferation was studied by incubating explant nerves in depolarizing culture media. Depolarizing monovalent cations (K+ and Rb+) led to a marked inhibition of Schwann cell proliferation. However, Cs+ and NH4+, which did not depolarize Schwann cells in patch clamp studies, also inhibited proliferation. Gramicidin and veratridine also inhibited proliferation. 5. The results suggest that the expression of K+ channels is functionally important for Schwann cell proliferation in Wallerian degeneration. A possible link between K+ channel and proliferation might be via a hyperpolarization of the resting membrane potential which occurs when Schwann cells proliferate.

Transmembrane ferricyanide reductase activity in Ehrlich ascites tumor cells

A transmembrane ferricyanide reductase activity was assayed in intact Ehrlich ascites tumor cells. Kinetic measurements gave a Km of 0.14 mM and a Vmax of 0.31 mumol/min per 10(6) cells. In short-term batch experiments, this activity was enhanced in the presence of 10 mM lactate, a source of cytosolic NADH. The transmembrane redox activity was accompanied by alkalinization of the cytosol. Both ferricyanide reduction and proton extrusion were diminished in the presence of 0.2 mM amiloride. Several cytotoxic drugs significantly inhibited the ferricyanide reductase activity at concentrations at which they show antineoplastic activity.

[Mechanism and significance of arteriolar media hypertrophy/ hyperplasia in arterial hypertension. Role of the Na+/H+ antiport]

The most common haemodynamic abnormality in human essential hypertension is an increase in systemic vascular resistance. Morphologic substrate for increased flow resistance is a narrowing of the lumen of arteriolar resistance vessels. During the course of essential hypertension, this is associated with an increase in wall (mainly media) thickness due to hypertrophy and hyperplasia of vascular smooth muscle cells. In contrast to concepts interpreting media thickening strictly as structural adaptation to increased perfusion pressure, various lines of evidence also point to pressure independent factors. In this context, extracellular factors such as "growth factors" as well as alterations in the activity of intracellular messenger systems must be considered. Recent studies suggest that substances generally known to act as vasoconstrictors such as angiotensin II, noradrenaline and arginine-vasopressin may also stimulate vascular smooth muscle cell growth and proliferation. Intracellular messenger systems with possible significance in the response to trophins and/or mitogens of vascular smooth muscle cells are phospholipase C, protein kinase C and the Na+/H+-antiport. These systems have been demonstrated to be altered in hypertension supporting the concept that one endogenous factor in human essential hypertension with pathophysiological significance, at least in a subgroup of patients, may be an enhanced reactivity of vascular smooth muscle cells to trophic and mitogenic stimuli. In this context, intracellular messenger systems such as phospholipase C, protein kinase C and/or the Na+/H+-antiport may play an important pathophysiological role.

Acidic intracellular pH shift during Caenorhabditis elegans larval development

During recovery from the developmentally arrested, nonfeeding dauer stage of the nematode Caenorhabditis elegans, metabolic activation is accompanied by a decrease in intracellular pH (pHi). Phosphorus-31 nuclear magnetic resonance (31P NMR) analyses of perchloric acid extracts show that inorganic phosphate predominates in dauer larvae, whereas ATP and other high-energy metabolites are abundant within 6 hr after dauer larvae have been placed in food to initiate development. Although metabolic activation has been associated with an alkaline pHi shift in other organisms, in vivo 31P NMR analysis of recovering dauer larvae shows a pHi decrease from approximately 7.3 to approximately 6.3 within 3 hr after the animals encounter food. This shift occurs before feeding begins, and it coincides with, or soon follows, the developmental commitment to recover from the dauer stage, suggesting that control of pHi may be important in the regulation of larval development in nematodes.

Luminescence spectroscopic approaches in studying cell surface dynamics

The major elements of membranes, such as proteins, lipids and polysaccharides, are in dynamic interaction with each other (Albertset al.1983). Protein diffusion in the lipid matrix of the membrane, the lipid diffusion and dynamic domain formation below and above their transition temperature from gel to fluid state, have many functional implications. This type of behaviour of membranes is often summarized in one frequently used word membrane fluidity (coined by Shinitzky & Henkart, 1979). The dynamic behaviour of the cell membrane includes rotational, translational and segmental movements of membrane elements (or their domain-like associations) in the plane of, and perpendicular to the membrane. The ever changing proximity relationships form a dynamic pattern of lipids, proteins and saccharide moieties and are usually described as ‘cell-surface dynamics’ (Damjanovichet al.1981). The knowledge about the above defined behaviour originates from experiments performed mostly on cytoplasmic membranes of eukaryotic cells. Nevertheless numerous data are available also on the mitochondrial and nuclear membranes, as well as endo (sarco-)plasmic reticulum (Martonosi, 1982; Slater, 1981; Siekevitz, 1981).

PET in clinical oncology

Positron Emission Tomography (PET) is an imaging technique that produces cross sectional images based on tissue biochemical and physiological processes. PET complements other anatomic imaging techniques such as x-ray CT and magnetic resonance imaging (MRI). Fundamental processes such as glucose metabolism, oxygen metabolism, and blood flow can be imaged and quantified with PET, in addition to many other processes of both clinical and investigative interest. PET is now emerging as a clinical tool in oncology and is useful in noninvasively grading tumors, in determining tumor activity and recurrence, and in monitoring the effects of a variety of therapeutic interventions with tumors. While most of the applications of PET in oncology to date have been in brain tumors, the technique is now being applied in tumor evaluations outside of the central nervous system.

Changes in intracellular pH and cell volume during the early phase of DMSO-induced differentiation of Friend erythroleukemia cells

Changes in intracellular pH and water volume were measured after treatment of Friend erythroleukemia cells with 1.5% DMSO. It was found that a continuous decrease in pHi occurred, beginning 1 h after induction and a decline in pHi of 0.18 was measured after 9 h. In addition a decline in cellular water volume, of 12% only 15 min after induction, and 23% after 9 h, was observed.

Amiloride-induced suppression of lymphocyte proliferation: inhibition of IL 2 receptor expression after blockade of early sodium influx

Increased rates of monovalent cation fluxes are implicated in the activation of lymphocytes by mitogens. Our report shows that amiloride and dimethylamiloride, two inhibitors of the Na+/H+ antiport, dose dependently prevent the proliferation of mitogen-activated human peripheral blood lymphocytes. The action of these drugs follows several mechanisms, since their inhibitory effect can be reversed by extensive washing when they are used at low concentrations (150 microM for amiloride, 40 microM for dimethylamiloride), while at higher non cytotoxic concentrations this reversibility is no longer observed. We have studied the mechanism whereby amiloride inhibits the blastogenesis by measuring their effect on: 1) IL 2 production, 2) acquisition of IL 2 responsiveness and induction of IL 2 receptors, 3) IL 2-induced proliferation. Unlike the expression of IL 2 receptors, IL 2 production and IL 2-dependent proliferation were not inhibited by the low drug concentrations which indeed prevent blastogenesis. Moreover under these conditions, an enhanced accumulation of IL 2 was observed in the supernatants of stimulated cells. These results show that the drugs interact differently with the different cell populations involved in T cell proliferation: increase of an amiloride-dependent sodium influx is an obligatory step required to induce the early increase of the ouabain-dependent potassium influx which is needed for the expression of IL 2 receptors. On the contrary, the influx of potassium necessary for the IL 2-dependent proliferation does not seem to be controlled by the amiloride-dependent sodium flux.