Na+/H+ exchange involvement in colony-stimulating factor-1-stimulated macrophage proliferation. Evidence for a requirement during late G1 of the cell cycle but not for early growth factor responses

Membrane androgen receptor sensitive Na+/H+ exchanger activity in prostate cancer cells

Membrane androgen receptors (mAR) are expressed in several tumors. mAR activation by testosterone albumin conjugates (TAC) suppresses tumor growth and migration. mAR signaling involves phosphoinositide-3-kinase (PI3K) and Rho-associated protein kinase (ROCK). PI3K stimulates serum- and glucocorticoid-inducible kinase SGK1, which in turn activates Na(+)/H(+)-exchangers (NHE). In prostate cancer cells cytosolic pH (pHi) was determined utilizing 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein-fluorescence and NHE-activity utilizing Na(+)-dependent cytosolic realkalinization following an ammonium pulse. TAC (100 nM) significantly increased pHi and NHE-activity, effects abrogated by NHE1-inhibitor cariporide (10 μM), SGK1-inhibitors EMD638683 (50 μM) and GSK650349 (10 μM) and ROCK-inhibitors Y-27632 (10 μM) and fasudil (100 μM). TAC treatment rapidly and significantly increased cell volume and actin polymerization, effects abolished in the presence of cariporide. Thus, mAR-activation activates cariporide-sensitive Na(+)/H(+)-exchangers, an effect requiring SGK1 and ROCK activity.

OSR1-sensitive regulation of Na+/H+ exchanger activity in dendritic cells

The oxidative stress-responsive kinase 1 (OSR1) is activated by WNK (with no K kinases) and in turn stimulates the thiazide-sensitive Na-Cl cotransporter (NCC) and the furosemide-sensitive Na-K-2Cl cotransporter (NKCC), thus contributing to transport and cell volume regulation. Little is known about extrarenal functions of OSR1. The present study analyzed the impact of decreased OSR1 activity on the function of dendritic cells (DCs), antigen-presenting cells linking innate and adaptive immunity. DCs were cultured from bone marrow of heterozygous WNK-resistant OSR1 knockin mice (osr(KI)) and wild-type mice (osr(WT)). Cell volume was estimated from forward scatter in FACS analysis, ROS production from 2',7'-dichlorodihydrofluorescein-diacetate fluorescence, cytosolic pH (pH(i)) from 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein fluorescence, and Na(+)/H(+) exchanger activity from Na(+)-dependent realkalinization following ammonium pulse and migration utilizing transwell chambers. DCs expressed WNK1, WNK3, NCC, NKCC1, and OSR1. Phosphorylated NKCC1 was reduced in osr(KI) DCs. Cell volume and pH(i) were similar in osr(KI) and osr(WT) DCs, but Na(+)/H(+) exchanger activity and ROS production were higher in osr(KI) than in osr(WT) DCs. Before LPS treatment, migration was similar in osr(KI) and osr(WT) DCs. LPS (1 μg/ml), however, increased migration of osr(WT) DCs but not of osr(KI) DCs. Na(+)/H(+) exchanger 1 inhibitor cariporide (10 μM) decreased cell volume, intracellular reactive oxygen species (ROS) formation, Na(+)/H(+) exchanger activity, and pH(i) to a greater extent in osr(KI) than in osr(WT) DCs. LPS increased cell volume, Na(+)/H(+) exchanger activity, and ROS formation in osr(WT) DCs but not in osr(KI) DCs and blunted the difference between osr(KI) and osr(WT) DCs. Na(+)/H(+) exchanger activity in osr(WT) DCs was increased by the NKCC1 inhibitor furosemide (100 nM) to values similar to those in osr(KI) DCs. Oxidative stress (10 μM tert-butyl-hydroperoxide) increased Na(+)/H(+) exchanger activity in osr(WT) DCs but not in osr(KI) DCs and reversed the difference between genotypes. Cariporide virtually abrogated Na(+)/H(+) exchanger activity in both genotypes and blunted LPS-induced cell swelling and ROS formation in osr(WT) mice. In conclusion, partial OSR1 deficiency influences Na(+)/H(+) exchanger activity, ROS formation, and migration of dendritic cells.

Phosphoinositide 3-kinase-dependent regulation of Na+/H+ exchanger in dendritic cells

Dendritic cells (DCs), antigen-presenting cells that are able to initiate primary immune responses and to establish immunological memory, are activated by exposure to bacterial lipopolysaccharides (LPS), which leads to cell swelling, triggering ROS formation and stimulating migration. The function of DCs is regulated by the phosphoinositide 3 (PI3) kinase pathway. On the other hand, PI3 kinase is an important regulator of diverse transporters including the Na(+)/H(+) exchanger (NHE). The present study was performed to elucidate the role of PI3 kinase in NHE activity, cell volume, ROS formation, and migration. To this end, DCs were isolated from murine bone marrow, cytosolic pH (pH(i)) determined utilizing 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein fluorescence, Na(+)/H(+) exchanger activity from the Na(+)-dependent realkalinization after an ammonium pulse, cell volume from forward scatter in fluorescence-activated cell sorter analysis, ROS production from 2',7'-dichlorodihydrofluorescein diacetate fluorescence, and migration utilizing transwell migration assays. Exposure of DCs to LPS led within 4 h to a gradual cytosolic acidification paralleled by a transient time- and dose-dependent increase of Na(+)/H(+) exchanger activity, cell swelling, enhanced ROS production, and stimulation of migration. The PI3K inhibitors Wortmannin (1 μM) or LY294002 (10 μM) significantly blunted the effects of LPS on NHE activity, cell volume, ROS production, and migration. The present observations disclose a critical role of PI3K signaling in the regulation of DC function following exposure to LPS.

Inhibition of Lipopolysaccharide-Induced Prostaglandin E2Production and Inflammation by the Na+/H+Exchanger Inhibitors

We analyzed the effects of the Na+/H+ exchanger (NHE) inhibitor 3,5-diamino-6-chloro-N-(diaminomethylidene)pyrazine-2-carboxamide hydrochloride (amiloride) and its analogs 5-(N,N-dimethyl)-amiloride (DMA) and 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) on the lipopolysaccharide (LPS)-induced production of prostaglandin (PG) E2 in vitro and in vivo. In the mouse macrophage-like cell line RAW 264, these inhibitors suppressed the LPS (1 microg/ml)-induced production of PGE2 at 8 h in a concentration-dependent manner. They also reduced the LPS-induced release of arachidonic acid from membrane phospholipids at 4 h and the LPS-induced increase in the level of cyclooxygenase (COX)-2 protein at 6 h, but not the level of COX-2 mRNA at 3 h. The LPS-induced phosphorylation of mitogen-activated protein kinases and degradation of inhibitor of kappaB-alpha were not inhibited by these drugs. In an air pouch-type LPS-induced inflammation model in mice 30 mg/kg amiloride and 10 mg/kg EIPA as well as the COX inhibitor indomethacin (10 mg/kg), significantly reduced the level of PGE2 in the pouch fluid at 8 h and the vascular permeability from 4 to 8 h. The accumulation of pouch fluid and leukocytes in the pouch fluid at 8 h was significantly inhibited by amiloride and EIPA but not by indomethacin. These findings suggested that the NHE inhibitors suppress the production of PGE2 through inhibiting the release of arachidonic acid and the increase in COX-2 protein levels and thus induce anti-inflammatory activity.

The sodium/hydrogen exchanger: a possible mediator of immunity

Immune cells such as macrophages and neutrophils provide the first line of defence of the immune system using phagocytosis, cytokine and chemokine synthesis and release, as well as Reactive Oxygen Species (ROS) generation. Many of these functions are positively coupled with cytoplasmic pH (pHi) and/or phagosomal pH (pHp) modification; an increase in pHi represents an important signal for cytokine and chemokine release, whereas a decrease in pHp can induce an efficient antigen presentation. However, the relationship between pHi and ROS generation is not well understood. In immune cells two main transport systems have been shown to regulate pHi: the Na+/H+ Exchanger (NHE) and the plasmalemmal V-type H+ ATPase. NHE is a family of proteins which exchange Na+ for H+ according to their concentration gradients in an electroneutral manner. The exchanger also plays a key role in several other cellular functions including proliferation, differentiation, apoptosis, migration, and cytoskeletal organization. Since not much is known on the relationship between NHE and immunity, this review outlines the contribution of NHE to different aspects of innate and adaptive immune responses such as phagosomal acidification, NADPH oxidase activation and ROS generation, cytokine and chemokine release as well as T cell apoptosis. The possibility that several pro-inflammatory diseases may be modulated by NHE activity is evaluated.

Current research of hepatic cirrhosis in China

Hepatic cirrhosis is a common disease that poses a serious threat to public health, and is characterized by chronic, progressive and diffuse hepatic lesions preceded by hepatic fibrosis regardless of the exact etiologies. In recent years, considerable achievements have been made in China in research of the etiopathogenesis, diagnosis and especially the treatment of hepatic fibrosis, resulting in much improved prognosis of hepatic fibrosis and cirrhosis. In this paper, the authors review the current status of research in hepatic fibrosis, cirrhosis and their major complications.

NHE blockade inhibits chemokine production and NF-kappaB activation in immunostimulated endothelial cells

Na(+)/H(+) exchanger (NHE) activation has been documented to contribute to endothelial cell injury caused by inflammatory states. However, the role of NHEs in regulation of the endothelial cell inflammatory response has not been investigated. The present study tested the hypothesis that NHEs contribute to endothelial cell inflammation induced by endotoxin or interleukin (IL)-1beta. NHE inhibition using amiloride, 5-(N-ethyl-N-isopropyl)-amiloride, and 5-(N-methyl-N-isobutyl)amiloride as well as the non-amiloride NHE inhibitors cimetidine, clonidine, and harmaline suppressed endotoxin-induced IL-8 and monocyte chemoattractant protein (MCP)-1 production by human umbilical endothelial vein cells (HUVECs). The suppressive effect of amiloride on endotoxin-induced IL-8 production was associated with a decreased accumulation of IL-8 mRNA. NHE inhibitors suppressed both inhibitory (I)kappaB degradation and nuclear factor (NF)-kappaB DNA binding, suggesting that a decrease in activation of the IkappaB-NF-kappaB system contributed to the suppression of HUVEC inflammatory response by NHE blockade. NHE inhibition decreased also the IL-1beta-induced HUVEC inflammatory response, because amiloride suppressed IL-1beta-induced E-selectin expression on HUVECs. These results demonstrate that maximal activation of the HUVEC inflammatory response requires a functional NHE.

Inhibition of the Na(+)/H(+) antiporter suppresses IL-12 p40 production by mouse macrophages

The amiloride-inhibitable Na(+)/H(+) antiporter plays an important role in macrophage activation. The intracellular pathways leading to interleukin (IL)-12 p40 production by activated macrophages are incompletely understood. In the present study, we examined the contribution of the Na(+)/H(+) antiporter to the production of IL-12 p40. Amiloride or its analogs decreased the production of IL-12 p40 in macrophages stimulated with bacterial lipopolysaccharide and interferon-gamma. The order of potency of amiloride analogs was consistent with the proposition that the effect of amiloride is mediated by the inhibition of the Na(+)/H(+) antiporter. The effect of amiloride was post-transcriptional, as IL-12 p40 mRNA levels induced by lipopolysaccharide and interferon-gamma were not affected by this inhibitor. Furthermore, the inhibitory effect of amiloride on IL-12 p40 production was not a result of interference with the activation of the p38 and p42/44 mitogen-activated protein kinases or c-Jun kinase. In summary, the production of IL-12 p40 requires a functional Na(+)/H(+) antiporter.

Targeted disruption of the Nhe1 gene fails to inhibit beta(1)-adrenergic receptor-induced parotid gland hypertrophy

Chronic beta(1)-adrenergic receptor activation results in hypertrophy and hyperplasia of rodent salivary gland acinar cells. Na(+)/H(+) exchanger isoform 1 (NHE1) regulates cell volume and the induction of cell proliferation in many tissues. To investigate the relationship between NHE1 and the response of parotid glands to beta(1)-adrenergic agonists, we examined by Northern blot analysis NHE1 expression in saline-treated mice and mice 30 min and 2, 6, and 24 h after isoproterenol injection. NHE1 transcripts increased approximately 50% by 2 h, and a more than twofold increase was noted at 24 h. Isoproterenol did not acutely increase Na(+)/H(+) exchanger activity; however, exchanger activity was significantly elevated by 24 h. To test whether NHE1 activity is essential for inducing salivary gland hypertrophy in vivo, mice with targeted disruption of Nhe1 were treated with isoproterenol. Na(+)/H(+) exchanger activity was absent in acinar cells from Nhe1(-/-) mice, nevertheless, the lack of NHE1 failed to inhibit isoproterenol-induced hypertrophy. These data directly demonstrate that acinar cell hypertrophy induced by chronic beta(1)-adrenergic receptor stimulation occurs independently of NHE1 activity.

Inhibition of the NA(+)/H(+) exchanger reduces rat hepatic stellate cell activity and liver fibrosis: an in vitro and in vivo study

BACKGROUND & AIMS

The Na(+)/H(+) exchanger is the main intracellular pH (pH(i)) regulator in hepatic stellate cells (HSCs) and plays a key role in regulating proliferation and gene expression. We evaluated the effect of specific inhibition of this exchanger on HSC proliferation and collagen synthesis in vivo and in vitro.

METHODS

Rat HSCs were incubated in the presence of platelet-derived growth factor (PDGF), transforming growth factor (TGF)-beta1, iron ascorbate (FeAsc), and ferric nitrilotriacetate solution (FeNTA) with or without the Na(+)/H(+) exchanger inhibitor 5-N-ethyl-N-isopropyl-amiloride (EIPA). pH(i) and Na(+)/H(+) exchanger activity, cell proliferation, and type I collagen accumulation were measured by using the fluorescent dye 2',7'-bis-(carboxyethyl)-5(6)-carboxyfluorescein, by immunohistochemistry for bromodeoxyuridine, and by enzyme-linked immunosorbent assay, respectively. In vivo liver fibrosis was induced by dimethylnitrosamine administration and bile duct ligation (BDL) in rats treated or not treated with amiloride.

RESULTS

PDGF, FeAsc, and FeNTA increased Na(+)/H(+) exchange activity and induced HSC proliferation. TGF-beta1 had no effect on the Na(+)/H(+) exchanger and was able, as for FeAsc and FeNTA, to induce type I collagen accumulation. EIPA inhibited all the effects determined by PDGF, FeAsc, and FeNTA and had no effect on TGF-beta1-induced collagen accumulation. In vivo, amiloride reduced HSC proliferation, activation, collagen deposition, and collagen synthesis.

CONCLUSIONS

The Na(+)/H(+) exchanger can play a key role in the development of liver fibrosis and in HSC activation in vivo.

High-capacity redox control at the plasma membrane of mammalian cells: trans-membrane, cell surface, and serum NADH-oxidases

The high capacity of proliferating mammalian cells to transfer electrons from cytosolic NADH to extracellular electron acceptors like oxygen is poorly understood and not widely recognized. Nevertheless, trans-plasma membrane electron transport (plasma membrane redox control) probably ranks alongside the Na+/H+ antiport system (pH control) and glucose transport in facilitating cellular responses to physiological stimuli. These plasma membrane transport systems are acutely responsive to receptor ligation by growth factors, polypeptide hormones, and other cell activators. A novel tetrazolium-based cell proliferation assay that we have shown to measure an NADH-oxidoreductase component of the trans-plasma membrane electron transport system has allowed direct comparisons with NADH:ferricyanide-oxidoreductase and respiratory burst NADPH-oxidoreductase. In addition, an NAD(P)H-oxidase at the cell surface and an NADH-oxidase activity in body fluids can be measured by modifying the basic cell proliferation assay. As determined by reduction of the cell-impermeable tetrazolium reagent, WST-1, electron transfer across the plasma membrane of dividing cells can exceed that of fully activated human peripheral blood neutrophils. Cellular reduction of WST-1 is dependent on the presence of an intermediate electron acceptor and is inhibited by superoxide dismutase (SOD) and by oxygen, implying indirect involvement of superoxide in WST-1 reduction. Cell-surface NAD(P)H-oxidase and serum NADH-oxidase are shown to be distinct from trans-plasma membrane NADH-oxidoreductase by their differential sensitivity to capsaicin and pCMBS. The glycolytic metabolism of cancer cells may be linked to changes in trans-plasma membrane NADH:WST-1-oxidoreductase activity and to increased serum NADH-oxidase in cancer.

Intracellular pathways mediating Na+/H+ exchange activation by platelet-derived growth factor in rat hepatic stellate cells

BACKGROUND & AIMS

The Na+/H+ exchanger is the main intracellular pH regulator in hepatic stellate cells (HSCs), and its activity is increased by platelet-derived growth factor (PDGF). Amiloride, an Na+/H+ exchange inhibitor, reduces PDGF-induced HSC proliferation, suggesting that the Na+/H+ exchanger plays a role in regulating HSC proliferative response. The aim of this study was to characterize the intracellular pathways mediating activation of the Na+/H+ exchanger by PDGF in HSCs.

METHODS

The activity of the Na+/H+ exchanger and HSC proliferation rate were evaluated under control condition and after incubation with PDGF in the absence or presence of specific inhibitors of the main intracellular pathways of signal transduction. Na+/H+ exchange protein expression was evaluated by means of Western blot.

RESULTS

PDGF induced a significant increase in the activity of the Na+/H+ exchanger without modifying protein expression. Inhibition of the calcium/calmodulin- and protein kinase C-dependent pathways resulted in a significant inhibition of both Na+/H+ exchange activity and of PDGF-induced HSC proliferation. The involvement of the two pathways was confirmed by showing that incubation of HSCs with both phorbol-12-myristate-13-acetate, a potent protein kinase C activator, and thapsigargin, which increases intracellular calcium levels, significantly increased both the Na+/H+ exchanger activity and HSC proliferation rate. Inhibition of the protein kinase A pathway did not modify either PDGF-induced Na+/H+ exchange activation or PDGF-induced HSC proliferation. On the contrary, inhibition of the mitogen-activated protein kinase- and of phosphatidylinositol 3-kinase-dependent pathways significantly reduced PDGF-induced HSC proliferation without affecting the activity of the Na+/H+ exchanger.

CONCLUSIONS

Activation of the Na+/H+ exchanger by PDGF in HSCs is mediated by calcium/calmodulin- and protein kinase C-dependent pathways. PDGF-induced HSC proliferation is mediated by Na+/H+ exchange-dependent and -independent pathways.

The Na+/H+ exchanger modulates the fibrogenic effect of oxidative stress in rat hepatic stellate cells

BACKGROUND/AIMS

Oxidative stress is associated with liver fibrosis in vivo and with hepatic stellate cell (HSC) activation in vitro, but the intracellular mechanisms mediating these effects are mostly unknown. The Na+/H+ exchanger plays a key role in regulating the cell cycle, and is involved in HSC proliferation. Its role in different HSC features, such as collagen accumulation, is still unknown. We thus evaluated if the Na+/H+ exchanger modulates the fibrogenic effect of oxidative stress in rat HSC.

METHODS

HSC were incubated with 0.1 mM ferric nitrilotriacetate complex (FeNTA). Intracellular hydroperoxides and malonildialdehyde (MDA) levels in the culture media were measured by the dichlorofluorescein and TBARS method, respectively. Intracellular pH and Na+/H+ exchanger activity were measured using the fluorescent dye BCECF. Cell proliferation was measured by immunohistochemistry for bromodeoxyuridine incorporation. Collagen type I accumulation in the culture media was measured by ELISA.

RESULTS

HSC incubation with FeNTA resulted in a significant production of intracellular hydroperoxides and MDA, associated with increased Na+/H+ exchange activity and baseline intracellular pH (pHi). Exposure of HSC to FeNTA significantly enhanced the number of proliferating HSC and collagen type I levels in the culture medium. All these effects were reversed by the antioxidant resveratrol and by the Na+/H+ exchanger inhibitor amiloride.

CONCLUSIONS

This study indicates that the Na+/H+ exchanger might represent a common mediator of the different effects induced by oxidative stress on HSC. The reduction in cell proliferation and collagen synthesis induced by amiloride could represent a new therapeutic challenge in liver fibrosis.

CSF-1 and cell cycle control in macrophages

Control of cell proliferation involves a finely interwoven network of positive and negative cell cycle regulators. Signal transduction pathways linking c-fms (CSF-1R) to cellular proliferation and differentiation are being explored. Part of the strategy is to use a series of G1 inhibitors to help pinpoint relevant targets. Several inhibitors-8Br-cAMP, interferon gamma (IFN gamma), INF alpha/beta, lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF alpha), and dimethylamiloride-suppress CSF-1-stimulated proliferation in murine bone marrow-derived macrophages (BMM) even when added in the mid- to late-G1 phase of the cell cycle. The down-modulating effects of the inhibitors on the expression of the following cell cycle regulators have been examined: c-myc, cyclin D1 and D2, cdk4, Rb phosphorylation, E2F binding activity, ribonucleotide reductase subunits, and PCNA. Some differences in the negative control of such regulators were found, for example, in the manner in which IFN gamma and cAMP down-regulate c-myc expression. Using blocking antibodies and BMM from type I IFN receptor knockout mice, it appears that one of these inhibitors, IFN alpha/beta, acts as an endogenous inhibitor in CSF-1-treated BMM and is also responsible, at least in part, for the inhibition of cell cycle progression by LPS and TNF alpha. Another strategy has been to attempt to relate early biochemical changes induced by CSF-1 to later changes in the G1 phase, partly by studying cycling versus noncycling macrophages and partly by using cells expressing c-fms with tyrosine mutations in the intracytoplasmic region. CSF-1-mediated effects on the following signal transduction molecules in these systems will be described: PI3-kinase, myelin basic protein kinases, Erks, and STAT transcription factors.

Galpha12 and Galpha13 regulate extracellular signal-regulated kinase and c-Jun kinase pathways by different mechanisms in COS-7 cells

Many growth factors and agonists for G protein-coupled receptors activate mitogen-activated protein (MAP) kinase pathways, including the extracellular signal-regulated kinase (ERK) pathway and the c-Jun kinase (JNK) pathway. Transient transfection of dominant negative and constitutively active pathway components in COS-7 cells shows that two G protein subunits, Galpha12 and Galpha13, inhibit the ERK pathway and stimulate the JNK pathway. Constitutively active (GTPase-deficient) Galpha12 and Galpha13 both inhibit ERK pathway activation by epidermal growth factor. A Galpha13/alphaz chimera, which responds to stimulation by Gi-coupled receptors, mediates inhibition of ERK via such a receptor, the dopamine-2 receptor. In addition, expression of a dominant negative mutant of the GTPase, Cdc42, blocks activation of the JNK pathway by Galpha12 and Galpha13 but does not alter inhibition of ERK activation by the same Galpha proteins; conversely, mutationally activated Cdc42 stimulates the JNK pathway but has no effect on the ERK pathway. Our results show that different mechanisms mediate two effects of Galpha12 and Galpha13: the ERK pathway inhibition is mediated at the level of MAP kinase kinase in a Ras- and Raf-independent fashion, whereas the JNK pathway stimulation is mediated by Cdc42.

G alpha 13 stimulates Na+-H+ exchange through distinct Cdc42-dependent and RhoA-dependent pathways

Activity of the ubiquitously expressed Na+-H+ exchanger subtype NHE1 is stimulated upon activation of receptor tyrosine kinases and G protein-coupled receptors. The intracellular signaling pathways mediating receptor regulation of the exchanger, however, are poorly understood. Using transient expression of dominant interfering and constitutively active alleles in CCL39 fibroblasts, we determined that the GTPases Ha-Ras and Galpha 13 stimulate NHE1 through distinct signaling cascades. Exchange activity stimulated by constitutively active RasV12 occurs through a Rafl- and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase kinase (MEK)-dependent mechanism. Constitutively active Galpha 13QL, recently shown to stimulate the Jun kinase cascade, activates NHE1 through a Cdc42- and MEK kinase (MEKK1)-dependent mechanism that is independent of Rac1. Constitutively active Rac1V12 does stimulate NHE1 through a MEKK1-dependent mechanism, but dominant interfering Rac1N17 does not inhibit Galpha 13QL-mediated or constitutively active Cdc42V12-mediated stimulation of the exchanger. Conversely, Cdc42NI7 does not inhibit Rac1V12 activation of NHE1, suggesting that Rae I and Cdc42 independently regulate a MEKK1-dependent activation of the exchanger. Rapid (<10 min) stimulation of NHE1 with a Ga13/Gaz chimera also was inhibited by a kinase-inactive MEKK. Galpha 13QL, but not RasV12, also stimulates NHE1 through a RhoA-dependent pathway that is independent of MEKK, and microinjection of mutationally active Galpha 13 results in a Rho phenotype of increased stress fiber formation. These findings indicate a new target for Rho-like proteins: the regulation of H+ ex- change and intracellular pH. Our findings also suggest that a MEKK cascade diverges to regulate effectors other than transcription factors.

An early transient increase of intracellular Na+ may be one of the first components of the mitogenic signal. Direct detection by 23Na-NMR spectroscopy in quiescent 3T3 mouse fibroblasts stimulated by growth factors

23Na-NMR spectroscopy was designed to allow for continuous recording of intracellular Na+ in 3T3 fibroblasts stimulated by serum growth-factors in the presence of ion transport inhibitors. The metabolic state of cells at rest and following stimulation was monitored by 31P-NMR spectra of ATP and related high-energy phosphates. The study demonstrates that early activation of ion transporters by addition of serum is marked by the appearance of transient increase of the intracellular Na+, beginning 3 min after addition of serum to quiescent culture and lasting approx. 20 min. The initial rise in cellular Na+ results from an increased activity of the bumetanide-sensitive Na+/K+/Cl- cotransport and of the amiloride-sensitive Na+/H+ antiport. It is suppressed by any one of these inhibitors. Subsequent activation of the ouabain-sensitive Na+/K(+)-ATPase results in an increased Na+ efflux, leading to a return of intracellular Na+ to its initial baseline. Previous work had shown that the early activation of bumetanide-sensitive and amiloride sensitive ion-transporters by growth-factors was essential for induction of cell division, at least in some cell types. Preventing ion activation by adding ion-transport inhibitors lead to the inhibition of DNA synthesis 18 h later. This process was reversible upon elimination of these inhibitors. Even though alternative non-specific effects of these inhibitors cannot be ruled out, the observed transient peak in intracellular Na+ may be one of the earliest components of the mitogenic signal. On the basis of previous works, its effect seems to be related to the activation of Ca(2+)-dependent and cyclic AMP second messenger pathways. The different mechanisms whereby the activated Na+/K+/Cl- cotransport and the Na+/H+ antiport contribute to this signal need to be further investigated.

Evidence that cell survival is controlled by interleukin-3 independently of cell proliferation

Hemopoietic cell proliferation is controlled by a set of polypeptide growth factors and regulatory molecules that bind to cell surface receptors inducing cellular responses. Maintenance of a viable state, cell growth, DNA synthesis and mitosis are basic properties of proliferating cells, but links between growth factor receptors and each of these cellular outcomes are poorly understood. Most studies have monitored DNA synthesis as a measure of progression through the cell cycle or directly measured viable cell numbers, but cell survival per se as an output of receptor activation by ligand, has received little attention. In this study we have used a bone marrow-derived murine cell line that is dependent on interleukin-3 for growth, to investigate the relationship between DNA synthesis and a biochemical marker of cell survival, reduction of the tetrazolium salt, MTT. We show that at times up to 6 hr, continued DNA synthesis, RNA synthesis, protein synthesis, and mitochondrial respiration are not necessary for background or IL-3-stimulated MTT reduction. Furthermore, dibutyryl cyclic AMP promoted background and IL-3-dependent MTT reduction while simultaneously inhibiting DNA synthesis. These results provide evidence that IL-3 controls events involved in MTT reduction and cell survival independently of DNA synthesis.

Structure-function relations in the inhibition of murine contact hypersensitivity by amiloride

Topical application of amiloride, a potent inhibitor of the Na+/H+ antiport, inhibits cutaneous inflammation induced by ultraviolet radiation or contact hypersensitivity in mice. Amiloride analogues with greater and lesser inhibition of the Na+/H+ exchange were tested to determine whether anti-inflammatory effects correlate with this activity. Structural analogues of amiloride without significant activity at the Na+/H+ antiport (pyrazine, pyrazinamide, and chloropyrazine) failed to inhibit contact hypersensitivity. N-amidino-3-amino-5-dimethyl amino-6-chloropyrazinecarboxamide (DMA) has a 23-fold greater affinity for the Na+/H+ antiport compared to amiloride, but failed to inhibit contact hypersensitivity in this assay. 3,5-diamino-6-chloropyrazine-amido-guanidine (DCG), which has only 7% of the affinity of amiloride for the antiport, suppressed contact hypersensitivity as well as amiloride. Experiments examining the ability of these agents to diffuse through mouse skin revealed amiloride to be superior to both DCG and DMA, which were approximately equal. DMA, with greater inhibition of the Na+/H+ antiport but lesser ability to inhibit contact hypersensitivity, inhibited protein synthesis and induced cell death more than amiloride or DCG. Amiloride and DCG hold promise as topical anti-inflammatory agents. Their anti-inflammatory properties do not correlate with affinity for the Na+/H+ antiport, ability to penetrate murine skin, or inhibition of protein synthesis.

Characterization of signaling pathways to Na+/H+ exchanger activation with epidermal growth factor in hepatocytes

To investigate the signaling pathways to Na+/H+ exchanger activation with epidermal growth factor in hepatocytes, we measured changes in cytosolic free calcium and intracellular pH levels at the single-cell level using digital imaging fluorescence microscopy of fura-2- or BCECF-loaded hepatocytes in primary culture. Epidermal growth factor induced cytosolic free calcium oscillations consisting of periodic trains of spikes with a latency period of up to several minutes. These calcium responses were inhibited by tyrosine kinase inhibitor genistein (100 mumol/L) and abolished by emptying of intracellular Ca2+ pools with 3 mumol/L thapsigargin, an inhibitor of Ca(2+)-ATPase on the endoplasmic reticulum. Epidermal growth factor (1 nmol/L) induced an intracellular pH increase of 0.12 +/- 0.07 units from the basal level of 7.25 +/- 0.09 units after several minutes of latency. This effect was completely abolished by 1 mmol/L amiloride, an inhibitor of the Na+/H+ exchanger. The epidermal growth factor-induced intracellular pH increase was inhibited by pretreatment of hepatocytes with genistein (100 mumol/L), thapsigargin (3 mumol/L) or calmodulin inhibitor W-7 (25 mumol/L), but not with protein kinase C inhibitor H-7 (50 mumol/L) or with cyclic AMP-dependent kinase inhibitor H-8 (60 mumol/L). Phorbol ester PMA (phorbol 12-myristate 13-acetate), a potent activator of protein kinase C, induced a slight intracellular pH increase significantly smaller than that with epidermal growth factor, whereas this effect was completely blocked by pretreatment with H-7, indicating that PMA-induced intracellular pH increase is mediated by protein kinase C pathways, unlike epidermal growth factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical events accompanying macrophage activation and the inhibition of colony-stimulating factor-1-induced macrophage proliferation by tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharide

Agents that can arrest cellular proliferation are now providing insights into mechanisms of growth factor action and how this action may be controlled. It is shown here that the macrophage activating agents tumor necrosis factor-alpha (TNF alpha), interferon-gamma (IFN gamma), and lipopolysaccharide (LPS) can maximally inhibit colony stimulating factor-1 (CSF-1)-induced, murine bone marrow-derived macrophage (BMM) DNA synthesis even when added 8-12 h after the growth factor, a period coinciding with the G1/S-phase border of the BMM cell cycle. This inhibition was independent of autocrine PGE2 production or increased cAMP levels. In order to compare the mode of action of these agents, their effects on a number of other BMM responses in the absence or presence of CSF-1 were examined. All three agents stimulated BMM protein synthesis; TNF alpha and LPS, but not IFN gamma, stimulated BMM Na+/H+ exchange and Na+,K(+)-ATPase activities, as well as c-fos mRNA levels. IFN gamma did not inhibit the CSF-1-induced Na+,K(+)-ATPase activity. TNF alpha and LPS inhibited both CSF-1-stimulated urokinase-type plasminogen activator (u-PA) mRNA levels and u-PA activity in BMM, whereas IFN gamma lowered only the u-PA activity. In contrast, LPS and IFN gamma, but not TNF alpha, inhibited CSF-1-induced BMM c-myc mRNA levels, the lack of effect of TNF alpha dissociating the inhibition of DNA synthesis and decreased c-myc mRNA expression for this cytokine. These results indicate that certain biochemical responses are common to both growth factors and inhibitors of BMM DNA synthesis and that TNF alpha, IFN gamma, and LPS, even though they all have a common action in suppressing DNA synthesis, activate multiple signaling pathways in BMM, only some of which overlap or converge.

Signalling through CSF receptors

The finely regulated process of blood cell formation is under the control of a family of glycoprotein hormones, known as colony-stimulating factors (CSFs), and their receptors. The complexity of the intracellular mechanisms involved in the action of such factors has been appreciated only recently. In this review, Gino Vairo and John Hamilton discuss the biochemistry of CSF action and its relevance to growth control, and examine the possibility that different CSFs may use common control pathways within the one cell type.

GM-CSF and IL-3 stimulate diacylglycerol generation in murine bone marrow-derived macrophages

In murine bone marrow-derived macrophages, prelabeled with either [3H]myristic acid or [3H]arachidonic acid, the mitogenic colony stimulating factors GM-CSF and IL-3 stimulated a transient increase in [3H]diacylglycerol generation. Maximum [3H]diacylglycerol levels were detected at 10-15 min. The stimulation of [3H]diacylglycerol generation was dependent on the concentration of CSF and correlated with their ability to activate a variety of processes in the macrophage, including DNA synthesis. This is the first report to demonstrate that GM-CSF elevates diacylglycerol levels in macrophages and also to show that diacylglycerol generation may be an important signaling mechanism for IL-3 action. In conjunction with our recent demonstration that the mitogenic agents CSF-1, 12-0-tetradecanoylphorbol-13-acetate and exogenous phospholipase C also stimulate diacylglycerol generation in the macrophage (Veis and Hamilton, J.Cell.Physiol., 147, 298-305, 1991), our findings suggest that an increase in diacylglycerol levels is necessary but not sufficient for macrophage proliferation.

Colony stimulating factor-1 stimulates diacylglycerol generation in murine bone marrow-derived macrophages, but not in resident peritoneal macrophages

Colony stimulating factor-1 (CSF-1) stimulates DNA synthesis in murine bone marrow-derived macrophages (BMM); however, unlike BMM, murine resident peritoneal macrophages (RPM) undergo a poor proliferative response. It has previously been shown that phosphatidylinositol-4,5-bisphosphate hydrolysis is not associated with CSF-1 action in BMM. In this report we demonstrate that, despite a lack of inositol trisphosphate generation, CSF-1 transiently elevated both [3H]myristoyl- and [3H]arachidonyl-diacylglycerol (DAG) in BMM in a dose-dependent fashion. CSF-1 failed, however, to stimulate an increase in either species of DAG in RPM. Thus, DAG could be a second messenger for the proliferative action of CSF-1 in macrophages. Other mitogenic agents, 12-0-tetradecanoyl phorbol 13-acetate (TPA) and exogenous phospholipase C, also increased BMM levels of [3H]myristoyl- and [3H]arachidonyl-DAG. The nonmitogenic agents, lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha) and zymosan, had different effects on the generation of either species of DAG in BMM. LPS failed to elevate either form, TNF-alpha increased only [3H]arachidonyl-DAG, while zymosan stimulated levels of both species of DAG. It therefore appears that increased diacylglycerol generation may be necessary, but perhaps not sufficient, for macrophage proliferation.