Regulation of GDNF expression in cultured astrocytes by inflammatory stimuli

Astrocytes express increased levels of neurotrophic factors in response to pathological conditions in the CNS such as injury and inflammation. We have examined the effects of lipopolysaccharide (LPS) and inflammatory cytokines on the expression of GDNF by mouse astrocytes and by C6 glial cells. LPS and tumor necrosis factor-alpha (TNF-alpha) induced an increase in level of glial-derived neurotrophic factor (GDNF) mRNA in both cell types. Similarly, the synthesis of GDNF protein was increased by both treatments. Interleukin-1beta (IL-1beta) and interferon-gamma (IFN-gamma) induced similar effects on GDNF production, whereas IL-2 and IL-6 had no significant effects. These results indicate that the expression of GDNF in astrocytes is regulated by inflammatory stimuli and therefore may provide neurotrophic support to injured neurons in inflammatory conditions in the CNS.

Astrocyte activation by Sindbis virus: expression of GFAP, cytokines, and adhesion molecules

Sindbis virus (SV) is a member of the alphaviruses which has served as a model system for studying viral encephalitis. Although astrocytes are reported to be involved in the pathogenesis of various virus-related diseases, the effects of SV on astrocyte function have not been reported. In this study we compared the effects of two strains of SV, SVA, and SVNI, which differ in their neurovirulent properties, on astrocytes with the use of cultured mouse astrocytes and the rat C6 glial cell line. We found that although both strains can similarly infect and replicate in astrocytes, they induced different changes in the function of these cells. The neurovirulent strain, SVNI, induced a decrease in cell number and a marked increase in the expression of GFAP, whereas SVA did not alter these parameters. In addition, SVNI induced the secretion of the cytokines TNF-alpha and IL-6, the expression of adhesion molecules, and the production of the neurotrophic factor NGF. In contrast, SVA induced smaller increases in the secretion of IL-6 and NGF but did not alter the secretion of TNF-alpha and the expression of the adhesion molecules. Neither virus induced the secretion of IL-2, IL-4, IL-10 and IFN-gamma or the expression of iNOS in the cells. These results indicate that astrocytes, similar to neurons, can serve as target cells to SV infection in the CNS. Moreover, the infection of astrocytes by SVNI leads to changes characteristic of reactive astrogliosis which may contribute to the pathogenesis of SV-induced encephalitis by enhancing the local immune response in the CNS.

A selective impairment of the IL-2 system in lymphocytes of patients with glioblastomas: increased level of soluble IL-2R and reduced protein tyrosine phosphorylation

The occurrence of brain tumors is associated with broad suppression of the immune system function; however, the mechanisms involved in this impairment are not fully characterized. In this study, we have examined mechanisms involved in diminished T lymphocyte reactivity in patients with glioblastomas as compared to patients with other types of brain tumors. We found that the proliferative response of T lymphocytes stimulated with phytohemagglutinin or anti-CD3 was significantly reduced in these patients as compared to patients with meningiomas, oligodendrogliomas and healthy individuals. Stimulated T cells appear to express lower levels of the alpha-subunit (p55) of the IL-2 receptor (IL-2R), and increased levels of soluble IL-2R in cell supernatants, whereas no significant differences were observed in the level of the beta (p75)- or gamma-subunits. In addition, we found that competent T cells of glioblastoma patients exhibit lower levels of tyrosine phosphorylation in response to IL-2 as compared with cells of healthy donors. The decrease in the levels of IL-2 and its receptor was selective since no significant changes were observed in the secretion of other Th1- and Th2-derived cytokines (IFN-gamma and IL-4) and the expression of their respective receptors. These results indicate that the diminished response of T cells obtained from patients with glioblastomas may be due to a selective defect in the production of IL-2 and in the expression of functional IL-2R due to a decreased expression of the membranal IL-2R alpha and to lower levels of tyrosine phosphorylation in response to IL-2.

Cardiomyocytes in culture--a model to study the cellular actions of amiodarone

The extensive use of amiodarone as an anti-arrhythmic drug is hampered by numerous side effects and by insufficient knowledge of its cellular action. The use of cell cultures for studying the mechanism of amiodarone action has been questioned, since available information has indicated that the doses employed for the experiments induce cell damage. We have defined conditions to obtain the amiodarone effect on cardiac cells in culture with no detectable damage. Amiodarone, 1 microg/ml, a concentration comparable to serum levels of the drug in acute and chronically treated humans and rats, reduces cell contractions, modifies membrane electrical properties accordingly, increases ATP content, but does not alter cell substructure or change enzyme activities. We strongly support the use of cell cultures for studying the cellular action(s) of amiodarone and offer conditions suitable for such experiments.

Induction of apoptosis and p53 expression in immature thymocytes by direct interaction with thymic epithelial cells

Apoptosis of normal thymocytes was shown to be triggered by several mechanisms (e.g. glucocorticoids, gamma-irradiation). In the present study the authors report on thymocyte apoptosis that is induced by thymic epithelial cells. The thymocytes undergo a massive apoptotic death within 24 h of cocultivation with thymic epithelial cell monolayers derived from primary cultures (PTEC) or from a thymic epithelial cell line (TEC). Non-thymic monolayers were inactive. Apoptosis induction in this experimental model requires direct contact between the thymocytes and the thymic epithelial monolayer and can be blocked by anti-CD2 and anti-LFA-1 antibodies. The immature CD3-/+dull CD4+CD8+ thymocytes were the cells which undergo apoptosis. The fact that the authors are dealing with a massive apoptotic process of immature cells in the absence of exogenous antigen suggests that it involves the nonselected thymocytes. The apoptotic pathway selected by thymocytes following their culturing on TEC involves p53 expression. Indeed it was found that TEC-induced apoptosis, led to the accumulation of p53 protein that preceded the step of DNA fragmentation in freshly isolated thymocytes as well as in a glucocorticoid resistant thymoma cell line. Since glucocorticoid-induced thymocyte apoptosis is p53-independent, glucocorticoids are conceivably not involved in TEC-induced thymocyte death. The in vitro experimental model presented here may reflect the physiological sequence of events leading to thymocyte death in the thymus.

Differential effects of Th1 and Th2 derived cytokines on NGF synthesis by mouse astrocytes

During the course of brain injury and inflammation there is an increased secretion of neurotrophic substances by astrocytes. We have examined the effect of the Th2-derived cytokine IL-10 and the Th1-derived cytokines Il-2 and IFN-gamma on the secretion of NGF by mouse astrocytes. IL-10 induced a dose-dependent increase in NGF secretion which was blocked by anti-IL-10 antibody. In contrast, the Th1-derived cytokines IFN-gamma and IL-2 did not induce NGF synthesis. Moreover, INF-gamma completely inhibited the increase in NGF secretion induced by IL-10 whereas it had no effect on the induction of NGF by TNF-alpha. These results indicate that IL-10 similarly to other Th2-derived cytokines may provide a neurotrophic support to injured neurons via the induction of NGF synthesis, whereas the Th1-derived cytokine IFN-gamma antagonizes this effect.

Nerve growth factor signal transduction in human B lymphocytes is mediated by gp140trk

Nerve growth factor (NGF) plays an important role in the regulation of the immune system. Recent studies from this laboratory demonstrated the presence of functional NGF receptors on human B lymphocytes; in addition, NGF has been shown to enhance B lymphocyte proliferation. NGF caused both concentration- and time-dependent increases in tyrosine phosphorylation of five proteins of 140, 110, 85, 60 and 42 kDa, which were identified as phospholipase C-gamma 1, phosphatidylinositol-3 kinase and mitogen-activated protein kinase. To elucidate the contribution of the Trk family of tyrosine kinases to the phosphorylation events induced by NGF, we identified gp140trk in human B cells and in human B cell lines. Analysis of specific gp140trk immunoprecipitates indicated that addition of NGF to B cells induced a rapid increase in the tyrosine phosphorylation of gp140trk and inhibition of this phosphorylation prevented the tyrosine phosphorylation of other proteins. These data identify the central role of gp40trk in NGF signaling of human B lymphocytes.

Indication that intracellular fluorescence polarization of T lymphocytes is cell cycle dependent

The degree of depolarization of fluorescence light emitted from an organic dye, used as a molecular probe, is a powerful tool in probing the microenvironment. Polarization measurements of intracellular exogenous fluorescein have been shown to reflect the physiological state of the cells. The relationship between intracellular fluorescein fluorescence polarization (IFFP) and cell cycle, was investigated in the leukemia T-lymphocyte Jurkat cell line. Jurkat T cells were cultured in increasing cell densities, their cell cycle progression cytometrically monitored and the IFFP measured. At the highest cell density, the subpopulation of cells at the resting phases the (Gzero/G1) predominated, and the mean IFFP was 0.186 +/- 0.015. At the lowest density, with diminished proportion of cells in the G1/G2 stages the mean IFFP decreased to 0.126 +/- 0.01. Treatment of the Jurkat T cell line with phase arrested agents 1 microM hydroxyurea, or 1 microM nocodazole, arrests the cells in the S and G2/M phases, respectively. These treated cells exhibit significantly lower IFFP values, mean polarization value 0.140, as compared to 0.171 +/- 0.009 in control cells. Preincubation of Jurkat cells in buffer in accumulation of the cells in the Gzero/G1 phases as well as a parallel increase in IFFP. A characteristic decrease in IFFP was demonstrated upon triggering these cells with Phytohaemagglutinin (PHA). High correlation (Pearson correlation = 0.942) was found between percentage of cells in the Gzero/G1 phases and the mean IFFP of the measured cell population. These results may indicate that the intracellular microviscosity of Jurkat T cells as measured by IFFP, is changing over the cell cycle.

Nerve growth-factor and anti-CD40 provide opposite signals for the production of IgE in interleukin-4-treated lymphocytes

Nerve growth factor (NGF) is a well-known neurotrophic factor acting on both the peripheral and the central nervous systems. In addition, it has been shown to play a role in the function of the immune system through specific receptors. Both high-affinity and low-affinity NGF receptors (NGFR) are expressed on human B lymphocytes. The low-affinity NGFR has been shown to have structural homology with another specific B cell surface molecule, CD40, which plays an important role in IgE production. In view of the structural similarities of the p75 NGFR and CD40 we examined whether NGF may also be involved in the regulation of IgE production. We found that NGF and anti-CD40 exerted opposite effects on the induction of IgE by IL-4 in peripheral blood mononuclear cells. NGF inhibited the induction of IgE by IL-4 and this inhibition was not mediated through blocking of the induction of CD23 nor through inhibition of IL-4R expression. The inhibition of IL-4-dependent IgE production was observed on surface (s)IgE+ and sIgE-/sIgM+ B lymphocytes. Anti-CD40 on the other hand, exerted an enhancing effect on IgE production and its addition to IL-4 provided a signal that was resistant to the inhibitory effect of NGF. Antagonistic effects of NGF and IL-4 were also observed for other Ig isotypes since IL-4 prevented the increase in IgA and IgM production induced by NGF. These data indicate that although NGFR and CD40 belong to the same receptor superfamily and exert similar proliferative effects on B lymphocytes, they interact differently with IL-4 in the regulation of IgE production.

Ouabain induces inhibition of the progression phase in human T-cell proliferation

Ouabain, a specific inhibitor of the Na-K ATPase, has been shown to exert immunosuppressive effects. The goals of this study were to define the stage of the proliferative response which is sensitive to ouabain and to correlate the inhibitory action of ouabain on cell proliferation with its effect on Na-K ATPase activity. We found that ouabain inhibited T-cell proliferation in a dose-dependent manner and this inhibition was similar in CD4+ and CD8+ T cells. To define the role of the Na-K ATPase in early activation of T lymphocytes, we examined the effects of ouabain on the induction of competence (acquisition of responsiveness to interleukin (IL)-2 or IL-4) by phytohemagglutinin (PHA) or the combination of phorbol dibutyrate/ionomycin. Ouabain, at concentrations that completely inhibited the enzyme activity, did not interfere with the induction of competence, suggesting that although activated cells express increased activity of Na-K ATPase, this enzyme activity does not play a role in early activation pathways. In contrast, ouabain inhibited the progression phase to DNA synthesis in a dose-dependent manner even at concentrations that had little or no effect on Na-K ATPase activity. This inhibition was not due to a decrease in the production of IL-2 but rather to an inhibition of the expression of the p55 and p75 subunits of the IL-2 receptor (IL-2R). The inhibition of p55 appeared to occur at the mRNA level. These results indicate that the activity of the Na-K ATPase is not essential for the induction of competence or early activation. On the other hand, inhibition of cell proliferation and transcription of IL-2R subunits by low concentrations of ouabain may be related to changes in intracellular K+ concentrations or to inhibition of membranal phospholipid metabolism secondary to alteration in Na-K ATPase activity.

Staurosporine induces astrocytic phenotypes and differential expression of specific PKC isoforms in C6 glial cells

In this study we examined the effects of staurosporine, a potent inhibitor of protein kinase C (PKC), on the differentiation of C6 glial cells and on the expression and cellular distribution of specific PKC isoforms. Staurosporine reduced cell proliferation and induced distinctive changes in the morphological appearance of the cells to that characteristic of cells exhibiting astrocytic phenotypes. The differentiative effect of staurosporine was further indicated by the increased expression of two proteins related to astrocytic phenotypes, glial fibrillary acidic protein (GFAP) and glutamine synthetase. Thus, staurosporine induced a dose-dependent increase both in GFAP immunoreactivity and in the activity and protein levels of glutamine synthetase. Staurosporine also induced a decrease in the expression of PKC-beta 2 and an increase in that of PKC-gamma. In addition, it induced translocation of PKC-epsilon from the membrane to the cytosol, whereas no differences were observed in the distribution of the other PKC isoforms. The results of our study indicate that staurosporine induced astrocytic phenotypes in glial cells and that changes in the expression and cellular distribution of these PKC isoforms may be related to astrocytic differentiation.

T lymphocyte subpopulations and activation markers correlate with severity of Alzheimer's disease

In this study we investigated immune-associated antigens of peripheral lymphocytes from patients with Alzheimer's disease (AD). The patients were divided into two groups--mild and moderately severe--according to severity of disease stage, and their lymphocytes were compared to those of elderly controls. In the mild stage of the disease we observed a slight increase in the HLA-DR marker (9.5 +/- 2.4% vs 6.5 +/- 1.1%; P = 0.06), but no changes in the CD4, CD8, and interleukin-2 receptor (IL-2R) markers. In the moderately severe stage, we observed a significant increase in the HLA-DR (18.5 +/- 2.7%) and CD4 markers (55.2 +/- 3.5% vs 43.5 +/- 2.1%, P < 0.01), and a slight decrease in the CD8 subset (19.5 +/- 1.4% vs 22.3 +/- 1.3%, P = 0.05). In the same group, following stimulation with the mitogen PHA, we observed a marked reduction in IL-2R expression (30.9 +/- 4.7% vs 41.1 +/- 2.7%, P = 0.05) and in the proliferative ability of lymphocytes (21131 +/- 4676 cpm vs 47909 +/- 1107 cpm, P < 0.04). However, mitogen-induced IL-2 secretion levels from the same lymphocytes were significantly elevated (17.4 +/- 4.8 U/ml vs 8.6 +/- 4.3 U/ml, P < 0.01). Marked changes in immunological parameters in the moderately severe group support the hypothesis of a peripheral immune reaction in AD which may be correlated with the clinical stage of the disease.

Nerve growth factor induces activation of MAP-kinase and p90rsk in human B lymphocytes

A previous report from this laboratory demonstrated that human B lymphocytes expressed nerve growth factor (NGF) receptors on their surface. On the basis of NGF enhancement of B cell proliferation these receptors are presumed to be functional. We have now characterized one of the signaling pathways that NGF may utilize in the functional activation of B lymphocytes. Stimulation of three different human B-lymphoblastoid cell lines with NGF induced the tyrosine phosphorylation and activation of the p42erk-2 isoform of MAP-kinase (MAPK). In addition, NGF induced shifts in the mobility of p90 ribosomal S6 kinase (p90rsk) on immunoblots and increased p90rsk kinase activity in immunoprecipitates. NGF-induced shifts in p90rsk mobility displayed similar dose and time kinetics as NGF-induced MAPK activation. Activation of both MAPK and p90rsk occurred with doses of NGF as low as 400 pg/ml. Preincubation of NGF with anti-NGF Ab inhibited NGF-induced activation of MAPK and p90rsk. These results demonstrate that the interaction of NGF with its receptor on human B cells results in the stimulation of major components of the signaling pathway also initiated by NGF-receptor ligation in cells of neuronal origin.

Nerve growth factor induces activation of MAP-kinase and p90rsk in human B lymphocytes

A previous report from this laboratory demonstrated that human B lymphocytes expressed nerve growth factor (NGF) receptors on their surface. On the basis of NGF enhancement of B cell proliferation these receptors are presumed to be functional. We have now characterized one of the signaling pathways that NGF may utilize in the functional activation of B lymphocytes. Stimulation of three different human B-lymphoblastoid cell lines with NGF induced the tyrosine phosphorylation and activation of the p42erk-2 isoform of MAP-kinase (MAPK). In addition, NGF induced shifts in the mobility of p90 ribosomal S6 kinase (p90rsk) on immunoblots and increased p90rsk kinase activity in immunoprecipitates. NGF-induced shifts in p90rsk mobility displayed similar dose and time kinetics as NGF-induced MAPK activation. Activation of both MAPK and p90rsk occurred with doses of NGF as low as 400 pg/ml. Preincubation of NGF with anti-NGF Ab inhibited NGF-induced activation of MAPK and p90rsk. These results demonstrate that the interaction of NGF with its receptor on human B cells results in the stimulation of major components of the signaling pathway also initiated by NGF-receptor ligation in cells of neuronal origin.

Rapid stimulatory effect of insulin on binding of glycolytic enzymes to cytoskeleton of C-6 glial cells, and the antagonistic action of calmodulin inhibitors

Insulin was shown in our previous experiments to induce an increase in binding of glycolytic enzymes to muscle cytoskeleton. We show here the same stimulatory effect of insulin in C-6 glial cells in culture. In these cells, like in muscle, a short time of incubation with insulin (1-10 min) induced an increase in cytoskeleton bound phosphofructokinase and aldolase. This stimulatory effect of insulin could be prevented by treatment with calmodulin antagonists trifluoperazine, thioridazine or CGS 9343 B (a potent and selective inhibitor of calmodulin activity), which strongly suggests that calmodulin is involved in this action of insulin. Our previous experiments have shown that growth factors and Ca(2+) also induce a rapid, calmodulin-mediated stimulation of binding of glycolytic enzymes to cytoskeleton. The present and previous results suggest that the rapid binding of glycolytic enzymes to cytoskeleton, may be a general mechanism, in different cells, in signal transduction of insulin, growth factors and other Ca(2+) -mobilizing hormones. The accelerated cytoskeletal glycolysis will supply local ATP, which is required for the rapid cytoskeletal-membrane rearrangements following the binding of hormone to its receptor.

Platelet activating factor induces nerve growth factor production by rat astrocytes

During the course of brain injury and inflammation there is an enhanced secretion of neurotrophic substances. We have examined the effect of platelet activating factor (PAF), which has been associated with various pathological conditions in the central nervous system, on the secretion of nerve growth factor (NGF) by astrocytes. Enriched cultures of rat cortical astrocytes were treated with various concentrations of PAF for different periods of time. PAF induced a dose-dependent increase in NGF secretion, the maximal increase of 120% obtained with 50 nM PAF after 48 h of treatment. This effect was blocked by the specific antagonist WEB 2086 and was not related to a proliferative response of the cells to PAF. Concomitant treatment of the cells with PAF and tumor necrosis factor-alpha resulted in a synergistic increase in NGF secretion. These results indicate that PAF may provide a neurotrophic signal to injured neurons and may cooperate with TNF-alpha in this effect.

Interleukin-4 modulates the proliferation and differentiation of glial cells

We examined the effects of the T cell-derived cytokine, interleukin (IL)-4 on the proliferation and differentiation of C6 glial cells. IL-4 exerted a biphasic effect on cell proliferation, increasing cell proliferation at concentrations ranging from 10 to 50 ng/ml and inhibiting at higher concentrations. Inhibition of cell proliferation was associated with differentiation of the cells to express astrocytic phenotypes as evidenced by morphology, increased glial fibrillary acidic protein (GFAP) immunoreactivity and elevated glutamine synthetase expression. IL-4 also induced the secretion of nerve growth factor by these cells. These results suggest an important role for IL-4 during instances of CNS trauma and inflammation.

Functional PAF receptors in glia cells: binding parameters and regulation of expression

Platelet activating factor is a unique phosphoglycerine which possesses a variety of biological functions exerting its biological effects via specific surface receptors. In the central nervous system, platelet activating factor has been suggested to play a role during injury especially in conditions of ischemia and trauma-induced neuronal damage. The specific cell populations expressing platelet activating factor receptor, however, have not been identified. In this study, the binding properties of platelet activating factor receptors in C6 glioma cells and primary cultures of astrocytes and oligodendrocytes were characterized by using the ligand [3H]WEB 2086. Early-passage glial cells which exhibit oligodendrocytic phenotype, expressed lower levels of [3H]WEB 2086 binding than either late-passage cells which exhibit astrocytic phenotypes or primary astroglia cells. No specific binding was observed in primary cultures of oligodendrocytes. The Bmax (136 +/- 15.3 fmol/mg protein) and Kd (29 +/- 3.2 nM) levels obtained for primary astroglia cells were similar to those described for other cell types. The expression of platelet activating factor receptor in early-passage glia cells was up-regulated by treatment with insulin which induces astrocytic differentiation. In contrast, db-cyclic AMP exerted an inhibitory effect on the level of platelet activating factor receptor in both early- and late-passage cells. The level of functional platelet activating factor receptor in C6 cells as measured by the ability of platelet activating factor to induce 45Ca2+ influx was increased in cells expressing astrocytic phenotypes and was decreased in db-cyclic AMP-treated cells. In accordance with lack of specific [3H]WEB 2086 binding, platelet activating factor did not induce a detectable response of Ca2+ influx in cultures of oligodendrocytes. This report provides the first direct demonstration of selective expression of functional platelet activating factor receptors and their properties in astroglia cells. The findings support the suggestion that platelet activating factor may play an important role as a mediator of injury and immune responses in the nervous system.

Correlation of cytokine secretion by mononuclear cells of Alzheimer patients and their disease stage

Cytokine secretion by human mononuclear cells (MNC) was investigated in age-matched controls and in patients with Alzheimer's disease (AD). AD patients were divided into two study groups: 'mild' and 'moderately severe'. A significant increase in interleukin-2 (IL-2) and gamma interferon (IFN-gamma) secretion was found in AD patients in the moderately severe stage of the disease, whereas in the mild stage of the disease there was a significant decrease in interleukin-3 activity (IL-3) and tumor necrosis factor (TNF) levels. No significant differences were found in the level of production of interleukin-1 (IL-1 beta). Our results demonstrate the existence of defective immune functions in AD patients which are correlated with the clinical condition of these patients.

Regulation of immunoglobulin production by nerve growth factor: comparison with anti-CD40

Nerve growth factor (NGF) is a well-known neurotrophic factor acting on both the peripheral and the central nervous systems. In addition, it has been shown to play a role in the function of the immune system through specific receptors. The low-affinity NGF receptor (NGFR) is present on human B lymphocytes and has been shown to have structural homology with another specific B cell surface molecule, CD40. NGF and anti-CD40 have been shown to modulate B-cell proliferation and Immunoglobulin (Ig) secretion. However, there have been no studies directly comparing the properties of these putative B-cell growth factors, particularly similarities in receptor expression or their role in B cell function. In this study, we examined the expression of NGFR and CD40 in a number of B-lymphoblastoid cell lines, representative of various stages of differentiation. We found that NGFR and CD40 are expressed on all B-cell lines to various degrees with the exception of plasma cells. Using two Ig secreting cell lines, both NGF and anti-CD40 decreased Ig secretion in a dose-dependent manner. The interaction of NGF and anti-CD40 with interleukin-4 (IL-4) was surprisingly different. Whereas IL-4 reversed the inhibitory effect of NGF on Ig secretion, it did not reverse that of anti-CD40. In addition, differences were observed at the level of receptor expression; IL-4 decreased the expression of NGFR, but increased that of CD40. These data indicate that although NGFR and CD40 are expressed in a co-ordinate fashion on B cells and exert similar effects on Ig secretion, differences in interaction with other growth factors may be important in their activities at different stages of B-cell differentiation.

Role of protein kinase C in insulin activation of the Na-K pump in cultured skeletal muscle

Administration of insulin to preparations of skeletal muscle causes an increase in Na(+)-K+ pump activity within 15-30 min. Although several mechanisms have been proposed, such as promotion of Na+ influx and translocation of pumps from intracellular to membrane sites, the early events involved in this effect remain unknown. We have investigated the possibility that activation of protein kinase C (PKC) may be an initial event in Na(+)-K+ pump activation in primary cultures of rat skeletal muscle. Insulin (80-100 mU/ml) and tumor-promoting phorbol esters (10-100 nM) increased Na(+)-K+ pump activity as determined by measurements of ouabain-suppressible 86Rb uptake, electrogenic pump component of membrane potential, and specific [3H]ouabain binding. These effects were not reduced by treatment of myotubes with amiloride, which blocks Na(+)-H+ exchange, or with tetrodotoxin, which blocks voltage-dependent Na+ channels. Effects of insulin and phorbol esters were not additive, suggestive of a common mechanism. Effects of both phorbol esters and insulin were significantly reduced by staurosporine (50-100 nM) and by downregulation of PKC (by pretreatment of myotubes with phorbol ester for 24 h). The findings suggest that insulin may stimulate Na(+)-K+ pump activity in skeletal muscle by activation of PKC.

Enhancement of IgE production by anti-CD40 antibody in atopic dermatitis

It has been recently recognized that the obligate requirement for T cells in the development of IgE responses can be substituted for by anti-CD40 antibody. In this study of patients with atopic dermatitis and high IgE levels, we have analyzed the role of the CD40 molecule in IgE production. Costimulation of peripheral blood mononuclear cells (PBMCs) from normal donors with interleukin-4 (IL-4) and anti-CD40 monoclonal antibody resulted in a selective increase in IgE production; either reagent alone, however, was ineffective. In contrast, addition of anti-CD40 monoclonal antibody alone to PBMCs or B cells from patients with atopic dermatitis markedly increased IgE production, even in the absence of exogenous IL-4. With the use of an ELISA spot assay, this increase in IgE production was attributed to an expansion of IgE-secreting B cells. In anti-IgM-stimulated lymphocyte cultures from patients with atopic dermatitis the costimulation with anti-CD40 induced strong lymphocyte proliferation. Similar results were observed with anti-IgM plus IL-4. The augmentation induced by anti-CD40 was inhibited by addition of anti-IL4 to anti-CD40-treated atopic dermatitis cells. In normal subjects the effects of anti-CD40 alone on IgE production could be observed after pretreatment of normal PBMCs with IL-4 for 3 days. The effects of anti-CD40 in atopic dermatitis may be explained in part by differences in CD40 expression. In freshly isolated PBMCs from patients with atopic dermatitis, the mean fluorescence intensity of CD40 expression on B cells was increased when compared with PBMCs from nonatopic donors, ans stimulation of normal or atopic dermatitis PBMCs with IL-4 increased the intensity of CD40 staining of cells.

Ethanol inhibits early events in T-lymphocyte activation

Ethanol has been reported to be immunosuppressive. We have studied the effects of ethanol on early activation events related to the proliferative response of human T lymphocytes. Ethanol inhibited T-cell proliferation in a dose-dependent manner. To define the target of this ethanol-mediated inhibition of T-cell function we examined its effect on the activation of T lymphocytes or induction of competence (acquisition of responsiveness to interleukin (IL)-2 or IL-4) by phytohemagglutinin (PHA) or the combination of phorbol dibutyrate (PDB)/ionomycin. Ethanol inhibited induction of competence with PHA by up to 50% when compared to control cells. In contrast to the effects on PHA-mediated activation of the cells, ethanol exerted no inhibitory action on the induction of competence by PDB/ionomycin. Ethanol also inhibited the induction of c-fos by PHA but not by PDB/ionomycin. To investigate the basis for these differences, the effects of ethanol on Ca2+ mobilization were examined. Ethanol inhibited PHA-induced Ca2+ mobilization in a dose-dependent manner. This inhibition was exerted mainly on transmembrane Ca2+ influx rather than on release of Ca2+ from intracellular stores. Ethanol did not affect Ca2+ mobilization induced by ionomycin. Co-incubation of ionomycin with PHA, during the induction of competence, abolished the inhibition exerted by ethanol when compared to cells treated with PHA alone. The inability of ethanol to exert complete inhibition on cell proliferation may be due to the activation of Ca(2+)-independent pathways by PHA, since combined treatment with ethanol and the intracellular Ca2+ chelator, BAPTA, did not completely inhibit the proliferative response. The inhibitory effects of ethanol on PHA-induced Ca2+ mobilization and subsequent induction of c-fos indicate that ethanol interferes with Ca(2+)-dependent pathways activated by PHA and this may provide the basis for its immunosuppressive action.

Neuroblastoma sensitivity to growth inhibition by deferrioxamine: evidence for a block in G1 phase of the cell cycle

Iron (Fe) is known to be necessary for cellular proliferation. Previous studies have suggested that neuroblastoma cells appear to be relatively sensitive to growth inhibition by a specific Fe chelator, deferrioxamine (DFO), in vitro. Also, DFO has been recently used for the treatment of neuroblastoma patients. In this paper we demonstrate that neuroblastoma cell proliferation in vitro is extremely sensitive to inhibition by DFO as compared to another cell line with almost identical growth kinetics. Neuroblastoma cells treated with DFO adapt appropriately to Fe chelation as measured by marked upregulation of transferrin receptor mRNA, increased functional transferrin receptor, and decreased cellular ferritin concentration. Further studies that quantitated cellular incorporation of 59Fe from added transferrin-59Fe in the presence of DFO indicated that neuroblastoma cells were more sensitive to inhibition of Fe incorporation by the chelator as compared to the other cell line. Neuroblastoma cells treated with DFO showed a consistent arrest in the G1 phase of the cell cycle. For cells taken from the "resting" state this block occurred before the vast majority of cells had entered S or G2-M phases of the cell cycle. Further evidence that neuroblastoma cells were arrested before the G1-S interface was provided when cells inhibited by DFO and released into aphidicolin exhibit arrest at the G1-S interface, whereas release from aphidicolin into DFO resulted in entry into S phase. Also, DFO-treated cells exhibited a decrease in both p34cdc2 immunoreactive protein as well as kinase activity. The results of these latter studies strongly indicate evidence for a Fe requirement for malignant cell proliferation before the onset of DNA synthesis. Our results also provide a basis for further studies that will better define a therapeutic approach to patients with neuroblastoma utilizing DFO treatment.

Early signals in serum-induced increases in ouabain-sensitive Na(+)-K+ pump activity and in glucose transport in rat skeletal muscle are amiloride-sensitive

The acute effects of serum on sodium-potassium (Na(+)-K+) pump activity and glucose uptake in cultured rat skeletal muscle were studied. Addition of serum to myotubes in phosphate-buffered saline caused Na(+)-K+ pump activity (as measured by changes in the ouabain-sensitive component of both membrane potential and 86Rb uptake) to increase, with peak effects obtained after 30 min. The effect was blocked completely by treatment with amiloride, but not by tetrodotoxin, which blocks voltage-dependent Na+ channels. On transfer of myotubes to Na(+)-free, choline buffer, resting Na(+)-K+ pump activity decreased to about 10% of that in phosphate-buffered saline. Addition of regular serum, but not Na(+)-free serum, caused Na(+)-K+ pump activity to increase slightly. Similar results were obtained with serum on glucose uptake, the peak effect being reached within 15 min. Stimulation of glucose uptake by serum was partially reduced by amiloride and was not altered by tetrodotoxin. Removal of external Na+ also eliminated serum effects on glucose uptake. The results demonstrate that there are similar signals involving Na(+)-H+ exchange for serum-induced increases in Na(+)-K+ pump activity and glucose transport. The lack of complete blockade of serum-induced elevation of glucose transport suggests an additional, as yet undefined, intracellular signal for stimulation of this transport system.