Role of Na+/H+ exchange by interferon-gamma in enhanced expression of JE and I-A beta genes

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.

New therapeutic targets in ulcerative colitis: the importance of ion transporters in the human colon

BACKGROUND

The absorption of water and ions (especially Na(+) and Cl(-)) is an important function of colonic epithelial cells in both physiological and pathophysiological conditions. Despite the comprehensive animal studies, there are only scarce available data on the ion transporter activities of the normal and inflamed human colon.

METHODS

In this study, 128 healthy controls and 69 patients suffering from ulcerative colitis (UC) were involved. We investigated the expressional and functional characteristics of the Na(+)/H(+) exchangers (NHE) 1-3, the epithelial sodium channel (ENaC), and the SLC26A3 Cl(-)/HCO 3- exchanger downregulated in adenoma (DRA) in primary colonic crypts isolated from human biopsy and surgical samples using microfluorometry, patch clamp, and real-time reverse-transcription polymerase chain reaction (RT-PCR) techniques.

RESULTS

Data collected from colonic crypts showed that the activities of electroneutral (via NHE3) and the electrogenic Na(+) absorption (via ENaC) are in inverse ratio to each other in the proximal and distal colon. We found no significant differences in the activity of NHE2 in different segments of the colon. Surface cell Cl(-)/HCO 3- exchange is more active in the distal part of the colon. Importantly, both sodium and chloride absorptions are damaged in UC, whereas NHE1, which has been shown to promote immune response, is upregulated by 6-fold.

CONCLUSIONS

These results open up new therapeutic targets in UC.

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.

Short-term effect on intestinal epithelial Na+/H+ exchanger by Giα1,2-coupled 5-HT1A and Gq/11-coupled 5-HT2 receptors

The present study evaluated the effect of 5-hydroxytryptamine (5-HT) on intestinal Na(+)/H(+) exchanger (NHE) activity and the cellular signaling pathways involved in T84 cells. T84 cells express endogenous NHE1 and NHE2 proteins, detected by immunoblotting, but not NHE3. The rank order for inhibition of NHE activity in acid-loaded T84 cells was 5-(N-ethyl-N-isopropyl)-amiloride (EIPA; IC(50)=519 [465, 579] nM)>cariporide (IC(50)=630 [484, 819] nM)>amiloride (IC(50)=19 [16, 24] microM); the NHE3 inhibitor S3226 was found to be devoid of effect. This different inhibitory sensitivity indicates that both NHE1 and NHE2 isoforms may play an active role in Na(+)-dependent intracellular pH (pH(i)) recovery in T84 cells. Short-term exposure (0.5 h) of T84 cells to 5-HT increased NHE activity in a concentration-dependent manner. The stimulation induced by 5-HT (30 microM) was partially inhibited by both WAY 100135 (300 nM) and ketanserin (300 nM), antagonists of 5-HT(1A) and 5-HT(2) receptors, respectively. NHE activity was significantly increased by 8-OH-DPAT and alpha-methyl-5-HT, agonists of, respectively, 5-HT(1A) and 5-HT(2) receptors. An incubation of T84 cells with anti-G(s) and anti-G(beta) antibodies complexed with lipofectin did not prevent the 5-HT-induced stimulation of NHE activity. Overnight treatment with anti-G(ialpha1,2) and anti-G(q/11) antibodies complexed with lipofectin blocked the stimulatory effect induced by 8-OH-DPAT and alpha-methyl-5-HT, respectively. It is concluded that in T84 cells 5-HT enhances intestinal NHE activity through stimulation of G(ialpha1,2)-coupled 5-HT(1A) and G(q/11)-coupled 5-HT(2) receptors.

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.

Association of plasminogen with dipeptidyl peptidase IV and Na+/H+ exchanger isoform NHE3 regulates invasion of human 1-LN prostate tumor cells

Binding of plasminogen type II (Pg 2) to dipeptidyl peptidase IV (DPP IV) on the surface of the highly invasive 1-LN human prostate tumor cell line induces an intracellular Ca2+ ([Ca2+]i) signaling cascade accompanied by a rise in intracellular pH (pHi). In endothelial cells, Pg 2 regulates intracellular pH via Na+/H+ exchange (NHE) antiporters; however, this mechanism has not been demonstrated in any other cell type including prostate cancer cells. Because the Pg 2 receptor DPP IV is associated with NHE3 in kidney cell plasma membranes, we investigated a similar association in 1-LN human prostate cancer cells and a mechanistic explanation for changes in [Ca2+]i or pHi induced by Pg 2 in these cells. Our results suggest that the signaling cascade initiated by Pg 2 and its receptor proceeds via activation of phospholipase C, which promotes formation of inositol 3,4,5-trisphosphate, an inducer of Ca2+ release from endoplasmic reticulum stores. Furthermore, our results suggest that Pg 2 may regulate pHi via an association with NHE3 linked to DPP IV in these cells. These associations suggest that Pg has the potential to simultaneously regulate calcium signaling pathways and Na+/H+ exchanges necessary for tumor cell proliferation and invasiveness.

Iron chelator triggers inflammatory signals in human intestinal epithelial cells: involvement of p38 and extracellular signal-regulated kinase signaling pathways

Competition for cellular iron (Fe) is a vital component of the interaction between host and pathogen. Most bacteria have an obligate requirement for Fe to sustain infection, growth, and survival in host. To obtain iron required for growth, many bacteria secrete iron chelators (siderophores). This study was undertaken to test whether a bacterial siderophore, deferoxamine (DFO), could trigger inflammatory signals in human intestinal epithelial cells as a single stimulus. Incubation of human intestinal epithelial HT-29 cells with DFO increased the expression of IL-8 mRNA, as well as the release of IL-8 protein. The signal transduction study revealed that both p38 and extracellular signal-regulated kinase-1/2 were significantly activated in response to DFO. Accordingly, the selective inhibitors for both kinases, either alone or in combination, completely abolished DFO-induced IL-8 secretion, indicating an importance of mitogen-activated protein kinases pathway. These proinflammatory effects of DFO were, in large part, mediated by activation of Na(+)/H(+) exchangers, because selective blockade of Na(+)/H(+) exchangers prevented the DFO-induced IL-8 production. Interestingly, however, DFO neither induced NF-kappaB activation by itself nor affected IL-1beta- or TNF-alpha-mediated NF-kappaB activation, suggesting a NF-kappaB-independent mechanism in DFO-induced IL-8 production. Global gene expression profiling revealed that DFO significantly up-regulates inflammation-related genes including proinflammatory genes, and that many of those genes are down-modulated by the selective mitogen-activated protein kinase inhibitors. Collectively, these results demonstrate that, in addition to bacterial products or cell wall components, direct chelation of host Fe by infected bacteria may also contribute to the evocation of host inflammatory responses.

The voltage-dependent anion channel is a receptor for plasminogen kringle 5 on human endothelial cells

Human plasminogen contains structural domains that are termed kringles. Proteolytic cleavage of plasminogen yields kringles 1-3 or 4 and kringle 5 (K5), which regulate endothelial cell proliferation. The receptor for kringles 1-3 or 4 has been identified as cell surface-associated ATP synthase; however, the receptor for K5 is not known. Sequence homology exists between the plasminogen activator streptokinase and the human voltage-dependent anion channel (VDAC); however, a functional relationship between these proteins has not been reported. A streptokinase binding site for K5 is located between residues Tyr252-Lys283, which is homologous to the primary sequence of VDAC residues Tyr224-Lys255. Antibodies against these sequences react with VDAC and detect this protein on the plasma membrane of human endothelial cells. K5 binds with high affinity (Kd of 28 nm) to endothelial cells, and binding is inhibited by these antibodies. Purified VDAC binds to K5 but only when reconstituted into liposomes. K5 also interferes with mechanisms controlling the regulation of intracellular Ca2+ via its interaction with VDAC. K5 binding to endothelial cells also induces a decrease in intracellular pH and hyperpolarization of the mitochondrial membrane. These studies suggest that VDAC is a receptor for K5.

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.

Na+/H+ exchanger blockade inhibits enterocyte inflammatory response and protects against colitis

Na+/H+ exchangers (NHEs) are integral transmembrane proteins found in all mammalian cells. There is substantial evidence indicating that NHEs regulate inflammatory processes. Because intestinal epithelial cells express a variety of NHEs, we tested the possibility that NHEs are also involved in regulation of the epithelial cell inflammatory response. In addition, since the epithelial inflammatory response is an important contributor to mucosal inflammation in inflammatory bowel disease (IBD), we examined the role of NHEs in the modulation of disease activity in a mouse model of IBD. In human gut epithelial cells, NHE inhibition using a variety of agents, including amiloride, 5-(N-methyl-N-isobutyl)amiloride, 5-(N-ethyl-N-isopropyl)- amiloride, harmaline, clonidine, and cimetidine, suppressed interleukin-8 (IL-8) production. The inhibitory effect of NHE inhibition on IL-8 was associated with a decrease in IL-8 mRNA accumulation. NHE inhibition suppressed both activation of the p42/p44 mitogen-activated protein kinase and nuclear factor-kappaB. Finally, NHE inhibition ameliorated the course of IBD in dextran sulfate-treated mice. Our data demonstrate that inhibition of NHEs may be an approach worthy of pursuing for the treatment of IBD.

Lithium induces NF-kappa B activation and interleukin-8 production in human intestinal epithelial cells

Lithium has been documented to regulate apoptosis and apoptotic gene expression via NF-kappa B and mitogen-activated protein (MAP) kinase-dependent mechanisms. Since both NF-kappa B and MAP kinases are also important mediators of inflammatory gene expression, we investigated the effect of lithium on NF-kappa B- and MAP kinase-mediated inflammatory gene expression. Incubation of human intestinal epithelial cells with lithium induced both enhanced NF-kappa B DNA binding and NF-kappa B-dependent transcriptional activity. In addition, lithium stimulated activation of both the p38 and p42/44 MAP kinases. This lithium-induced up-regulation of NF-kappa B and MAP kinase activation was associated with an enhancement of interleukin-8 mRNA accumulation as well as an increase in interleukin-8 protein release. These proinflammatory effects of lithium were, in large part, mediated by activation of Na(+)/H(+) exchangers, because selective blockade of Na(+)/H(+) exchangers prevented the lithium-induced intestinal cell inflammatory response. These results demonstrate that lithium stimulates inflammatory gene expression via NF-kappa B and MAP kinase activation.

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.

Differential induction of JE/MCP-1 in subclones from a murine macrophage cell line, RAW 264.7: role of kappaB-3 binding protein

The JE/MCP-1 gene is an immediate-early gene, and its product is a CC chemokine that attracts monocytes, basophils and T lymphocytes. JE/MCP-1 gene expression is induced by various inflammatory stimuli, but its transcriptional mechanism is not fully understood. To address this question, we obtained two subclones from a parental RAW264.7 cell line, one subline with low JE/MCP-1-producing capacity (named RAW.c11) and the other with high JE/MCP-1-producing capacity (named RAW.c25), in response to lipopolysaccharide (LPS). These subclones have no significant differences in CD14 expression, nitric oxide production, or production of other cytokines, including TNF-alpha or IL-1alpha/beta. In electrophoretic mobility shift assays (EMSA), there were no significant differences in DNA binding to the NF-kappaB-consensus sequence and interferon regulatory factor (IRF)-1,2 binding sequences. However, significantly higher binding activity to the NF-kappaB-like sequence (kappaB-3), which is located in the promoter region of the JE/MCP-1 gene, was shown by a high producer subclone than by a low producer subclone. Transient transfection analysis using deletion mutants of a 0.5-kb region from -467 to +59 identified an LPS-responsive region in a kappaB-3 site (from -169 to -132) in the high producer subclone. Mutation of this site markedly reduced sensitivity to LPS in the high producer subclone. These data suggest that a yet undefined nuclear factor may be involved in differential JE/MCP-1 gene transcription.

Role of vacuolar H(+)-ATPase in interferon-induced inhibition of viral glycoprotein transport

We have shown previously that interferon-beta (IFN-beta) induces the alkalinization of trans-Golgi network (TGN) and inhibits the transport of G protein of vesicular stomatitis virus (VSV) in L(B) cells and gD protein of herpes simplex virus (HSV-1) in LMtk- cells transfected with gD cDNA. The vacuolar H(+)-ATPase (V-ATPase) is responsible for maintaining pH in TGN, and V-ATPase-mediated acidification is required for normal transport of proteins. To examine whether alkalinization caused by IFN is mediated through V-ATPase, the activity of V-ATPase was determined in IFN-treated cells by coupling ATP hydrolysis to NADH oxidation. Bafilomycin (Baf) was used as positive control, as it specifically inhibits V-ATPase. The activity of V-ATPase was reduced in IFN-treated or Baf-treated cells compared with untreated cells. Doses of IFN-beta or Baf that neither alter pHi nor inhibit the transport of viral glycoproteins concomitantly inhibited the transport of G and gD proteins in TGN, as demonstrated by indirect immunofluorescence studies, and raised the pH of TGN as demonstrated by a decrease in the uptake of DAMP. Further, the effect of Baf on IFN-induced antiviral activity against VSV was examined to correlate the biologic significance of these findings. Data showed that Baf significantly enhances (5-50-fold) the IFN-induced antiviral activity as demonstrated by viral titers from supernatants. These findings suggest that the inhibition of transport of G and gD proteins by IFN-beta, may be related to the inhibition of V-ATPase-mediated acidification of TGN.

Interferon-gamma, bacterial lipopolysaccharide, and tumor necrosis factor-alpha induce CD11a mRNA and protein via Na+/H+ exchange and protein kinase C-dependent mechanisms in tissue macrophages

Previously CD11a or leukocyte function-associated antigen alpha-1 was found to be induced at the surface protein level in thioglycolate-elicited peritoneal macrophages by bacterial lipopolysaccharide and interferon-gamma. To investigate this induction further, Northern blotting and enzyme-linked immunosorbent assays were used to examine the role of second messengers in CD11a gene product induction by these agents. Here I report that CD11a RNA and cell surface protein induced by bacterial lipopolysaccharide and tumor necrosis factor-alpha are sensitive to inhibition of protein kinase C, while insensitive to inhibition of Na+/H+ exchange. CD11a induction by interferon-gamma conversely is sensitive to inhibition of Na+/H+ exchange and insensitive to inhibition of protein kinase C. These observations indicate that CD11a may be induced by multiple and separate second messenger systems in primary macrophages.

Kinase inhibitors abrogate IFN-gamma-induced class II transactivator and class II MHC gene expression in astroglioma cell lines

Multiple kinase events, involving both tyrosine (tyr) kinase and serine/threonine (ser/thr) kinase activity, are required for IFN-gamma-induced class II MHC mRNA and protein expression in primary rat astrocytes. In this study, we examined the necessity of ser/thr and tyr kinase activity for IFN-gamma-induced stimulation of class II MHC gene expression in the human astroglioma cell lines CRT and CH235, as well as the involvement of these kinases in IFN-gamma-induced expression of the class II transactivator (CIITA), a protein critical for IFN-gamma-induced transcription of class II MHC genes. We show that general ser/thr kinase inhibitors, inhibitors of the ser/thr kinase mitogen-activated protein kinase (MAPK), and tyr kinase inhibitors reduce IFN-gamma-induced class II MHC mRNA and protein expression in a dose-dependent manner. As well, these inhibitors abrogate IFN-gamma-induced CIITA mRNA expression in the astroglioma cell lines. We have further demonstrated that cells constitutively expressing the CIITA protein (2fTGH.CIITA) show no decrease in CIITA or class II MHC mRNA expression in the presence of ser/thr and tyr kinase inhibitors. Collectively, these data indicate that ser/thr kinase activity, possibly MAPK, and tyr kinase activity are required for IFN-gamma-induced expression of CIITA mRNA, and the subsequent expression of class II MHC genes.

Ouabain enhances the lipopolysaccharide-induced nitric oxide production by rat peritoneal macrophages

Incubation of rat peritoneal macrophages with the bacterial product lipopolysaccharide (LPS) caused significant increases in the production of nitrite, a stable endproduct of nitric oxide (NO). Addition of the digitalis-derived glycoside ouabain, which alone is without effect, significantly enhanced the stimulating effects of LPS. The Na+ ionophore monensin was without any effect, while the Ca2+ ionophore A23187, like ouabain, enhanced the effect of LPS. Thus ouabain may enhance the LPS-stimulated NO production in rat peritoneal macrophages via still unknown mechanisms in which Ca2+ ions are most likely involved.

Leukocyte migration and activation by murine chemokines

Chemokines are a family of chemotactic cytokines which attract different types of leukocytes. This property, combined with some additional inflammatory and growth-regulatory activities, demonstrate their crucial role in the immune system. Chemokines are low molecular weight proteins and possess a typical positioning of four conserved cysteines. This family is further subdivided in two subfamilies depending on whether the first two cysteines are adjacent or not (CC and CXC chemokines, respectively). The CXC chemokines (including interleukin-8) predominantly attract neutrophils, whereas CC chemokines induce migration of monocytes, as well as other leukocyte cell types. In this article, the general characteristics of chemokines are reviewed. Furthermore, the murine CC chemokines, JE/MCP-1, MCP-3/MARC, MIP-1 alpha, MIP-1 beta, RANTES, TCA3, C10/MRP-1, MRP-2, and eotaxin, are discussed more in detail.

Tyrosine kinase but not phospholipid/Ca2+ signaling pathway is involved in interferon-gamma stimulation of Ia expression in macrophages

The specific signal transduction pathway(s) involved in the induction of the expression of the MHC class II molecule, Ia, on macrophages by interferon-gamma (IFN-gamma) is unclear. In this paper, we assessed the role of several signal transduction pathways including calcium mobilization, phospholipase C, protein kinase C and cyclic nucleotide-dependent protein kinase, and the tyrosine kinase pathways. IFN-gamma was unable to mobilize intracellular calcium, unlike platelet-activating factor, which stimulated a threefold increase in cytosolic Ca2+ concentration in macrophages. Inhibition of the phospholipase C pathway by U73122 or ET-180CH3 and of phosphatidic acid phosphohydrolase by propranolol did not suppress IFN-gamma-induced Ia expression. In addition, inhibition of protein kinase C by calphostin C or cyclic nucleotide-dependent protein kinase by HA1004 did not suppress Ia expression. However, IFN-gamma-induced Ia expression was significantly suppressed when the tyrosine kinase pathway was inhibited with herbimycin A and genestein. In addition, those two inhibitors suppressed tyrosine phosphorylation of several proteins in macrophages that may or may not be involved in the induction of Ia expression. Thus, IFN-gamma used only the tyrosine kinase signaling pathway, but not the phospholipid/Ca2+ signaling pathways, to induce Ia expression in macrophages.

Ligation of the alpha 2-macroglobulin signalling receptor on macrophages induces protein phosphorylation and an increase in cytosolic pH

We have recently described an alpha 2-macroglobulin (alpha 2M) signalling receptor which is distinct from the low-density lipoprotein-related protein/alpha 2M receptor (LRP/alpha 2MR). Ligation of the macrophage signalling receptor by alpha 2M-methylamine stimulates production of several second messengers and involves a pertussis toxin-insensitive G-protein. We now report that binding of alpha 2M-methylamine, or the cloned M(r) = 20,000 receptor-binding fragment from rat alpha 1M, to macrophage alpha 2M signalling receptors induces protein phosphorylation. By use of a monoclonal antibody to phospholipase C gamma l (PLC gamma l) we were able to identify it as one target for protein phosphorylation. Phosphorylation was time and concentration dependent, being optimal at about 60 s of incubation and a 100-200 nM ligand concentration. By use of a second monoclonal antibody directed against phosphotyrosine, we were able to demonstrate that at least a portion of the label was incorporated into one or more tyrosine residues. PLC gamma l phosphorylation was then studied in membrane preparations at 4 degrees C in order to minimize serine or threonine modification. Preincubation of macrophage membranes with genistein, a tyrosine kinase inhibitor, drastically reduced phosphorylation of PLC gamma l. Receptor-associated protein, which blocks alpha 2M binding to LRP/alpha 2MR but not to the alpha 2M signalling receptor, had no effect on alpha 2M-methylamine-induced tyrosine phosphorylation of PLC gamma l. Binding of lactoferrin to LRP/alpha 2MR failed to induce phosphorylation of PLC gamma l, further supporting the hypothesis that the alpha 2M signalling receptor and LRP/alpha 2MR are distinct entities. Growth factors which induce tyrosine phosphorylation typically cause a rise in cytosolic pH. Binding of a2M-methylamine to macrophages also gradually increased the intracellular pH in a concentration-dependent manner, being optimal at a 200 nM ligand concentration. The increase in pH was amiloride sensitive. We propose that receptor-recognized forms of a2M may function like growth factors with regard to macrophage regulation.

Activation of the c-fos promoter by increased internal pH

Changes in intracellular pH (pHin) take part in the mitogenic response. Their importance has been stressed by the finding that mouse fibroblasts expressing a yeast proton pumping ATPase (PMA1) exhibit a transformed phenotype and are tumorigenic. These cells do maintain a higher pHin, supporting the idea that elevated pHin may act as a proliferative trigger. Here we show that cells constitutively expressing PMA1 have higher levels of the AP-1 transcription factor. The use of stable transfectants and transient transfection assays show that PMA1 activity induces transactivation of the c-fos promoter. The activation of the promoter is mediated throughout the serum response element (SRE). The use of protein kinase C inhibitors suggests that AP-1 activation is achieved through a pathway independent of protein kinase C.

Establishment of new interferon-gamma-resistant mutant cells with dominant phenotypes

We established interferon-gamma-resistant (IGR) cells from a human colon adenocarcinoma cell line, LoVo. Their resistance was extremely high, and the ED50 values of IFN-gamma were > 10(5) IU/ml. Interestingly, although IGR-5 cells were still sensitive to the antiproliferative effect of IFN-alpha, the cells lost responsiveness to the antiviral effects of both IFN-alpha and gamma. Another clone, IGR-53, was unresponsive to both the antiproliferative and antiviral effects of either IFN-alpha or gamma. Furthermore, the IFN-gamma-resistant phenotypes of IGR cells were apparently dominant to the parental LoVo cells based on complementation tests. Although IGR-53 cells lack IFN-gamma receptors, IGR-5 cells seemed to have functional IFN-gamma receptors and processing mechanisms of IFN-gamma bound to the receptors. Northern analysis showed that IGR-5 cells responded to IFN-gamma and alpha, but the enhancement of IRF-1 expression by IFN-gamma was markedly suppressed.

Influence of ion channel modulation on in vitro interferon-gamma induced MHC class I and II expression on macrophages

The in vitro effect of K+ channel blockers quinidine and verapamil, anion channel blocker SITS and K+ channel openers diazoxide, pinacidil, and BRL 38227 on interferon-gamma (IFN-gamma) induced MHC class I and II expression of Lewis rat peritoneal macrophages was investigated by cell ELISA assay. MHC class I expression was significantly enhanced by diazoxide at concentrations of 10(-5)M to 10(-6)M and by pinacidil and BRL 38227 at the concentration of 10(-6)M. MHC class II expression was enhanced by pinacidil and BRL 38227 at concentrations of 10(-5)M to 10(-6)M. The enhancing effect of pinacidil could be blocked by inhibitors of the protein kinases PKA and PKC suggesting that activation of both is required for optimum induction of MHC molecule expression. K+ and anion channel blockers were less active in modulation of MHC molecule expression. Verapamil had no influence, quinidine suppressed MHC class I expression at concentrations of 10(-4)M to 10(-5)M, and SITS suppressed MHC class I expression at the concentration of 10(-3)M. Since MHC class II expression is essential for efficient antigen presentation to T helper cells and MHC class I expression is required for target cell lysis by cytotoxic T cells, ion channel modulating drugs may be potential candidates for immunopharmacological intervention in inflammatory diseases.

K+ ionophores inhibit nerve growth factor-induced neuronal differentiation in rat adrenal pheochromocytoma PC12 cells

Incubation with a K+/H+ ionophore nigericin attenuated the nerve growth factor (NGF)-induced neurite outgrowth in rat pheochromocytoma PC12 cells. However, a Na+/H+ ionophore monensin and a Ca2+ ionophore A23187 did not inhibited the neurite outgrowth. Nigericin also inhibited the NGF-caused induction of acetylcholinesterase and suppression of cell proliferation. These changes were dependent on the amount of the ionophore added to the culture. In addition, a distinct K+ ionophore, valinomycin, similarly inhibited the NGF-induced neuronal differentiation. These results suggest the presence of the K+ ionophore-sensitive mechanism in the NGF-induced differentiation system in PC12 cells.

Inhibition of IFN-gamma induction of class II MHC genes by cAMP and prostaglandins

Triggering of the cyclic AMP (cAMP) signal transduction pathway inhibits the the interferon gamma (IFN-gamma)-mediated induction of class II major histocompatibility (MHC) genes. We have investigated the mechanism of the inhibition of IFN-gamma induction of the murine A alpha class II MHC gene by cAMP and E series prostaglandins (PGEs). 151 base pairs of the A alpha promoter were sufficient to confer positive regulation by IFN-gamma and negative regulation by cAMP which accurately mirrored the regulation of the endogenous A alpha gene. cAMP also inhibited the IFN-gamma activation of the Fc gamma receptor I (Fc gamma RI) gene promoter, an "early" promoter which is activated immediately after treatment of cells with IFN-gamma. PGEs, which cause an elevation in intracellular cAMP, inhibited the induction of the A alpha promoter, and inhibition was greater in the presence of tumor necrosis factor alpha (TNF alpha). A mutational analysis of the A alpha promoter showed that all four conserved class II promoter elements, the S, X1, X2, and Y boxes, play a role in mediating A alpha promoter activation by IFN-gamma. Mutations in these elements did not diminish the cAMP inhibition of promoter activation by IFN-gamma. Thus, conserved class II promoter sequences which mediate most known examples of positive and negative regulation, including cAMP inhibition of constitutive class II expression, do not mediate cAMP inhibition of IFN-gamma activation of the A alpha promoter. We suggest that this inhibition may be mediated by a novel class II promoter element or by disruption of an early step in the IFN-gamma signal transduction pathway.

MCP-1 mRNA expression in basal keratinocytes of psoriatic lesions

In addition to hyperproliferation of keratinocytes, psoriasis is characterized by pronounced leukocytic infiltration. In contrast to the epidermal localization of neutrophils and T lymphocytes, macrophages are almost exclusively restricted to the dermal compartment. By immunohistologic analysis, these dermal macrophages were mainly encountered in the papillary dermis and arranged along the rete ridges in close proximity to proliferating keratinocytes. Monocyte chemoattractant protein (MCP-1) anti-sense RNA probes yielded abundant signals over the proliferating basal keratinocytes of the tips of the rete ridges, and, to a lesser extent, in cells in the papillae. Thus, the strongest MCP-1 message in psoriatic lesions is found above the dermal-epidermal junction and this may explain the characteristic sub-basal distribution of dermal macrophages. These results suggest that MCP-1 is important in regulating the interaction between proliferating keratinocytes and dermal macrophages in psoriasis pathogenesis.

The generation of nitric oxide participates in gamma IFN-induced MHC class II antigen expression by cultured astrocytoma cells

The effects of interferon gamma (gamma IFN) on the MHCII antigen expression by human cultured astrocytoma cells were investigated. The co-incubation of gamma IFN with T67 astrocytoma cells produced a dose-dependent increase of MHCII antigen expression as evaluated by flow cytometric (FACS) analysis and confocal laser microscopy analysis. The number of MHCII molecules expressed by gamma IFN-pretreated astrocytoma cells was reduced by co-incubation with N omega-nitro-L-arginine methyl ester (L-NAME), a selective inhibitor of the nitric oxide (NO)-synthesizing enzyme. In addition, methylene blue, which inhibits the biological activity of NO acting at the guanylate cyclase level, strongly antagonized the MHCII antigen expression on astrocytoma cells induced by gamma IFN. Furthermore, gamma IFN increased the activity of the inducible isoform of NO-synthase as well as the concentration of nitrite, one of the breakdown products of NO and the antiplatelet activity of astrocytoma cells. In conclusion, the present data show that gamma IFN increases the synthesis and release of NO by cultured astrocytoma cells and this could co-participate in the MHCII antigen expression by this cell type. Therefore, the generation of NO by cultured astrocytoma cells may represent an important step in the development of the immunocompetent activity of astrocytes.

Membrane sodium-proton exchange and primary hypertension

Recent studies have revealed that an enhancement of sodium-proton exchange is a frequently observed ion transport abnormality in essential hypertension. An altered antiport activity not only is measurable in blood cells of hypertensive subjects ex vivo but also is detectable in skeletal muscle in vivo. Several lines of argument suggest that the altered antiport activity is not an epiphenomenon of hypertension: 1) the increased activity is found only in a subgroup of patients with high blood pressure, 2) it is not tightly correlated to the severity or duration of hypertension, and 3) high sodium-proton exchange activity persists over time and is not affected by antihypertensive treatment. Available evidence suggests that enhanced sodium-proton exchange is associated with or a cause for the structural alterations found in resistance vessels of hypertensive individuals (media hypertrophy) and left ventricular hypertrophy. This review summarizes some of the physiological properties and roles of the sodium-proton exchanger and discusses its kinetic properties in essential hypertension. Furthermore, the reasons for the enhanced antiport activity and its potential implications regarding the pathogenesis of hypertension are discussed.

Structural analysis of the human interferon gamma receptor: a small segment of the intracellular domain is specifically required for class I major histocompatibility complex antigen induction and antiviral activity

Mutations of the human interferon gamma (IFN-gamma) receptor intracellular domain have permitted us to define a restricted region of that domain as necessary for both induction of class I major histocompatibility complex antigen by IFN-gamma and protection against encephalomyocarditis virus. This region consists of five amino acids (YDKPH), all of which are conserved in the human and murine receptors. Tyr-457 and His-461 are essential for activity. Approximately 80% of the amino acids of the intracellular domain of the receptor is not required for major histocompatibility complex class I antigen induction or for antiviral protection against encephalomyocarditis virus. The observation that there was no protection by IFN-gamma against vesiculostomatitis virus indicates that other factors, in addition to chromosome 21 accessory factor(s), are required to generate the full complement of transduction signals from the human IFN-gamma receptor.

Modulation of the anti-proliferative signal of interferon-alpha by tamoxifen in U937 cells

Several clinical protocols are attempting to utilize the combined anti-proliferative signal of interferon-alpha (INF-alpha) and tamoxifen on cancer cells. We demonstrated here that the effect of these two agents on the growth of the premacrophage U937 cells is antagonistic. This antagonistic effect is paralleled by the ability of tamoxifen to modulate the INF-alpha-induced hyperpolarization in these cells. INF-alpha-induced hyperpolarization was shown before to be an integral part of the anti-proliferative signal of this agent. Tamoxifen liberates Ca2+ from intracellular stores of U937 cells but this effect of the drug is not the cause of its antagonistic effect with the anti-proliferative signal of IFN-alpha. We suggest therefore, that the combined effect of these two anti-cancer drugs could also be advantageous for macrophage proliferation.

Downregulation of JE and KC genes by glucocorticoids does not prevent the G0----G1 transition in BALB/3T3 cells

The effects of glucocorticoid hormones on the expression of the growth factor-inducible genes JE, KC, and c-myc were analyzed in parental BALB/3T3 and polyomavirus middle-T antigen-transfected cell lines. Northern (RNA) blot hybridization and run-on transcription analysis showed that (i) glucocorticoid hormones selectively inhibit JE and KC expression at the transcriptional level and (ii) the downregulatory effect of glucocorticoids on JE and KC expression is partial for serum-stimulated and middle T antigen-transformed cells and total for quiescent and exponentially growing cells. Gel mobility assays using AP-1 oligonucleotides showed a positive correlation between glucocorticoid downregulating effect and presence of the AP-1 complex. JE and KC downregulation by means of the AP-1 complex may play a role in the actions of glucocorticoids as anti-inflammatory and antitumor agents. The ability of glucocorticoids to downregulate JE and KC was used to investigate the relevance of these genes to the mitogenic response to serum growth factors. Hydrocortisone did not alter the basal DNA synthesis level displayed by quiescent 3T3 cells, but it potentiated both the mitogenic effect of platelet-derived growth factor and c-myc induction by serum growth factors. Upon serum restimulation, untreated and dexamethasone-treated quiescent 3T3 cultures entered the S phase after an identical time lag (G1). These results suggest that (i) JE and KC are not necessary for the G0----G1----S transition and (ii) c-myc overexpression is likely to be the basis for the potentiating effect of glucocorticoids on serum growth factors.

Tyrosine phosphorylation is an early and requisite signal induced by interferon-gamma in HL-60 cells

Interferon-gamma (IFN gamma) is a potent immunomodulatory cytokine. However, the early mechanisms which mediate the pleiotropic effects of IFN gamma on different cells are as yet poorly understood. Therefore, we tested the role of tyrosine phosphorylation in signalling induced by IFN gamma. IFN gamma was found to induce rapid tyrosine phosphorylation of several proteins in HL-60 cells. This effect was detectable by 2 min, reached a maximum by about 4-16 min and thereafter declined. Tyrosine phosphorylation was dependent on receptor occupation and was maximally stimulated by 10 ng/ml IFN gamma. Treatment of HL-60 cells with the tyrosine kinase inhibitors, genistein and herbimycin A, inhibited both IFN gamma-stimulated tyrosine phosphorylation and IFN gamma-induced Fc receptor expression. Thus, increased tyrosine phosphorylation appears to be an obligatory early and proximal signal mediating at least some of the later cellular responses induced by IFN gamma in HL-60 cells.

Downregulation of JE and KC genes by glucocorticoids does not prevent the G0----G1 transition in BALB/3T3 cells

The effects of glucocorticoid hormones on the expression of the growth factor-inducible genes JE, KC, and c-myc were analyzed in parental BALB/3T3 and polyomavirus middle-T antigen-transfected cell lines. Northern (RNA) blot hybridization and run-on transcription analysis showed that (i) glucocorticoid hormones selectively inhibit JE and KC expression at the transcriptional level and (ii) the downregulatory effect of glucocorticoids on JE and KC expression is partial for serum-stimulated and middle T antigen-transformed cells and total for quiescent and exponentially growing cells. Gel mobility assays using AP-1 oligonucleotides showed a positive correlation between glucocorticoid downregulating effect and presence of the AP-1 complex. JE and KC downregulation by means of the AP-1 complex may play a role in the actions of glucocorticoids as anti-inflammatory and antitumor agents. The ability of glucocorticoids to downregulate JE and KC was used to investigate the relevance of these genes to the mitogenic response to serum growth factors. Hydrocortisone did not alter the basal DNA synthesis level displayed by quiescent 3T3 cells, but it potentiated both the mitogenic effect of platelet-derived growth factor and c-myc induction by serum growth factors. Upon serum restimulation, untreated and dexamethasone-treated quiescent 3T3 cultures entered the S phase after an identical time lag (G1). These results suggest that (i) JE and KC are not necessary for the G0----G1----S transition and (ii) c-myc overexpression is likely to be the basis for the potentiating effect of glucocorticoids on serum growth factors.

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.

A collection of mRNA species that are inducible in the RAW 264.7 mouse macrophage cell line by gamma interferon and other agents

To identify genes induced during macrophage activation, a cDNA library was prepared from cultures of the RAW 264.7 mouse macrophage cell line that had been treated with conditioned medium from mitogen-stimulated spleen cells, and the cDNA library was screened by differential plaque hybridization. Eleven cDNA clones, designated CRG-1 through CRG-11, corresponding to mRNA species inducible in RAW 264.7 cells by the spleen cell conditioned medium, were isolated. Inductions were not blocked by cycloheximide. All of the mRNAs were inducible by gamma interferon, and some were also inducible by alpha and beta interferons, by lipopolysaccharide, by phorbol 12-myristate 13-acetate, and by the calcium ionophore A23187. Sequencing of the cDNAs revealed that CRG-1, CRG-3, and CRG-5 are cDNAs of recently identified transcription factors IRF-1, zif/268, and LRF-1 respectively. As previously reported, CRG-2 and CRG-10 (MIG) encode new members of the platelet factor 4 family of cytokines. CRG-6 corresponds to a new member of a family of interferon-inducible genes clustered on mouse chromosome 1, CRG-9 corresponds to a prostaglandin synthase homolog, CRG-8 corresponds to beta 2-microglobulin, and CRG-4 corresponds to metallothionein II. CRG-11 contains sequences of a truncated L1Md repetitive element as well as nonrepetitive sequences. The nonrepetitive sequence of CRG-11 as well as the sequences of CRG-7 are not closely related to published sequences. The CRG genes and proteins are of interest because of their involvement in macrophage activation, because of their roles as mediators of the effects of gamma interferon and other pleiotropic agents, and because of their usefulness as tools for studying the signal pathways through which gamma interferon and other inducers exert their effects on gene and protein expression.

A collection of mRNA species that are inducible in the RAW 264.7 mouse macrophage cell line by gamma interferon and other agents

To identify genes induced during macrophage activation, a cDNA library was prepared from cultures of the RAW 264.7 mouse macrophage cell line that had been treated with conditioned medium from mitogen-stimulated spleen cells, and the cDNA library was screened by differential plaque hybridization. Eleven cDNA clones, designated CRG-1 through CRG-11, corresponding to mRNA species inducible in RAW 264.7 cells by the spleen cell conditioned medium, were isolated. Inductions were not blocked by cycloheximide. All of the mRNAs were inducible by gamma interferon, and some were also inducible by alpha and beta interferons, by lipopolysaccharide, by phorbol 12-myristate 13-acetate, and by the calcium ionophore A23187. Sequencing of the cDNAs revealed that CRG-1, CRG-3, and CRG-5 are cDNAs of recently identified transcription factors IRF-1, zif/268, and LRF-1 respectively. As previously reported, CRG-2 and CRG-10 (MIG) encode new members of the platelet factor 4 family of cytokines. CRG-6 corresponds to a new member of a family of interferon-inducible genes clustered on mouse chromosome 1, CRG-9 corresponds to a prostaglandin synthase homolog, CRG-8 corresponds to beta 2-microglobulin, and CRG-4 corresponds to metallothionein II. CRG-11 contains sequences of a truncated L1Md repetitive element as well as nonrepetitive sequences. The nonrepetitive sequence of CRG-11 as well as the sequences of CRG-7 are not closely related to published sequences. The CRG genes and proteins are of interest because of their involvement in macrophage activation, because of their roles as mediators of the effects of gamma interferon and other pleiotropic agents, and because of their usefulness as tools for studying the signal pathways through which gamma interferon and other inducers exert their effects on gene and protein expression.

JE mRNA accumulates rapidly in aortic injury and in platelet-derived growth factor-stimulated vascular smooth muscle cells

The early response to vascular injury is characterized by migration of inflammatory cells, including monocytes, and platelets to the damaged vessel wall. These inflammatory cells may serve as a source of growth factors and cytokines that stimulate vascular smooth muscle cell (VSMC) migration and proliferation associated with intimal hyperplasia. JE is a platelet-derived growth factor (PDGF)-inducible "early" gene that encodes a monocyte chemoattractant and, as such, could play an important role in inflammation. We now report that JE mRNA levels are increased in intact aorta after balloon injury. The time course of this increase, with maximal levels at 4 hours, is similar to that seen in PDGF-treated cultured rat aortic VSMCs. The accumulation of JE mRNA in cultured VSMCs is accompanied by a marked increase in the secretion of JE protein. The elevation of JE mRNA levels in VSMCs shows specificity for PDGF, because angiotensin II, alpha-thrombin, and epidermal growth factor fail to increase JE mRNA levels. In contrast to 3T3 fibroblasts, the accumulation of JE mRNA in VSMCs in response to PDGF is predominantly due to an increase in JE mRNA stability. The accumulation of JE mRNA in VSMCs stimulated by PDGF appears to occur via a novel pathway(s) independent of Ca2+ mobilization, Na(+)-H+ exchange, protein kinase C activation, or elevation in cAMP levels. These findings suggest that VSMCs may take part in the early inflammatory response after injury through the production of JE, a potent monocyte chemoattractant. Finally, our data suggest that JE may be a marker for PDGF-specific effects on VSMCs, both in vitro and in vivo. Thus, in addition to direct effects on VSMC growth and migration, PDGF may play a role in the early inflammatory response after vascular injury by inducing chemoattractants, such as that encoded by JE.

Interferon-gamma/lipopolysaccharide-treated mouse embryonic fibroblasts are killed by a glycolysis/L-arginine-dependent process accompanied by depression of mitochondrial respiration

Normal mouse embryo fibroblasts (MEF) are killed by treatment with low doses of interferon gamma (IFN-gamma) in combination with lipopolysaccharide (LPS). This cytotoxicity has previously been shown to represent an active suicidal reaction. Here we show that the time period between first contact with IFN-gamma/LPS (t = 0 h) and cell death (t = 48 h) can be separated into two distinct periods, during which glycolytic metabolism of glucose either has a positive (8-24 h) or a negative (30-48 h) effect on cytotoxicity. During the first period (8-24 h), withdrawal of glucose from the culture medium, or inclusion in the medium of the glycolytic inhibitors deoxy-D-glucose, NaF or iodoacetate, prevented later cell death. During the second period (30-48 h), withdrawal of glucose or supplementation of the culture medium with glycolytic inhibitors was no longer protective; instead it was a requirement for cell suicide to occur. Glycolytic activity during the first period was found to be increased twofold in LPS-treated MEF and almost threefold in IFN-gamma/LPS-treated MEF. A variety of agents were found both to protect cells against IFN-gamma/LPS-induced cytotoxicity and to inhibit increased glycolysis in these cells: glucocorticoids, the serine-type protease inhibitor N-acetyl-DL-phenylalanine-beta-naphthyl ester, the ADP-ribosylation inhibitors 3-aminobenzamide and nicotinamide, and the transcription and translation inhibitors actinomycin and cycloheximide. Mitochondrial function, although normal in LPS-treated cells, was markedly depressed in IFN-gamma/LPS-treated MEF. Specifically, malate- and succinate-driven respiration was found to be impaired. Furthermore, IFN-gamma/LPS-treated MEF contained one-third of the ATP level of LPS-treated MEF. Withdrawal of L-arginine from the culture medium prevented cell death in IFN-gamma/LPS-treated MEF. N-Methyl-L-arginine, which is an inhibitor of nitric oxide (NO.) biosynthesis from L-arginine, also inhibited cell death. In conclusion, we propose that cell death in our experiments is due to an L-arginine/glycolysis-dependent impairment of mitochondrial respiration.

BALB/c-3T3 fibroblasts resistant to growth inhibition by beta interferon exhibit aberrant platelet-derived growth factor, epidermal growth factor, and fibroblast growth factor signal transduction

Several lines of evidence now exist to suggest an interaction between the platelet-derived growth factor (PDGF) growth-stimulatory signal transduction pathway and the beta interferon (IFN-beta) growth-inhibitory signal transduction pathway. The most direct examples are inhibition of PDGF-mediated gene induction and mitogenesis by IFN-beta and the effects of activators and inhibitors of the IFN-inducible double-stranded RNA-dependent eIF2 kinase on expression of PDGF-inducible genes. To further investigate the nature of this PDGF/IFN-beta interaction, we selected BALB/c-3T3 cells for resistance to growth inhibition by IFN-beta and analyzed the phenotypes of resulting clonal lines (called IRB cells) with respect to PDGF signal transduction. Although selected only for IFN resistance, the IRB cells were found to be defective for induction of growth-related genes c-fos, c-myc and JE in response to PDGF. This block to signal transduction was not due to loss or inactivation of PDGF receptors, as immunoprecipitation of PDGF receptors with antiphosphotyrosine antibodies showed them to be present at equal levels in the BALB/c-3T3 and IRB cells and to be autophosphorylated normally in response to PDGF. Furthermore, treatment with other peptide growth factors (PDGF-AA, fibroblast growth factor, and epidermal growth factor) also failed to induce c-fos, c-myc, or JE expression in IRB cells. All of these growth factors, however, were able to induce another early growth-related gene, Egr-1. The block to signaling was not due to a defect in inositol phosphate metabolism, as PDGF treatment induced normal calcium mobilization and phosphotidylinositol-3-kinase activation in these cells. Activation of protein kinase C by phorbol esters did induce c-fos, c-myc, and JE in IRB cells, indicating that signalling pathways distal to this enzyme remained intact. We have previously shown that IFN-inducible enzyme activities, including double-stranded RNA-dependent eIF2 kinase and 2',5'-oligoadenylate synthetase, are normal in IRB cells. The finding that the induction of multiple growth-related genes by several independent growth factors is inhibited in these IFN-resistant cells suggests that there is a second messenger common to both growth factor and IFN signaling pathways and that this messenger is defective in these cells.