Calcium influx and the Ca2+-calmodulin complex are involved in interferon-gamma-induced expression of HLA class II molecules on HL-60 cells

Repurposing screen identifies Amlodipine as an inducer of PD-L1 degradation and antitumor immunity

Cancer cell expression of PD-L1 leads to T cells exhaustion by transducing co-inhibitory signal, and further understanding the regulation of PD-L1 in cancer cells may provide additional therapeutic strategies. Here by drug repurposing screen, we identified amlodipine as a potent inhibitor of PD-L1 expression in cancer cells. Further survey of calcium-associated pathways revealed calpain-dependent stabilization of the PD-L1 protein. Intracellular calcium delivered an operational signal to calpain-dependent Beclin-1 cleavage, blocking autophagic degradation of PD-L1 accumulated on recycling endosome (RE). Blocking calcium flux by amlodipine depleted PD-L1 expression and increased CD8+ T-cell infiltration in tumor tissues but not in myocardium, causing dose-dependent tumor suppression in vivo. Rescuing PD-L1 expression eliminated the effects of amlodipine, suggesting the PD-L1-dependent effect of amlodipine. These results reveal a calcium-dependent mechanism controlling PD-L1 degradation, and highlight calcium flux blockade as a potential strategy for combinatorial immunotherapy.

Interferon-γ signaling synergizes with LRRK2 in neurons and microglia derived from human induced pluripotent stem cells

Parkinson's disease-associated kinase LRRK2 has been linked to IFN type II (IFN-γ) response in infections and to dopaminergic neuronal loss. However, whether and how LRRK2 synergizes with IFN-γ remains unclear. In this study, we employed dopaminergic neurons and microglia differentiated from patient-derived induced pluripotent stem cells carrying LRRK2 G2019S, the most common Parkinson's disease-associated mutation. We show that IFN-γ enhances the LRRK2 G2019S-dependent negative regulation of AKT phosphorylation and NFAT activation, thereby increasing neuronal vulnerability to immune challenge. Mechanistically, LRRK2 G2019S suppresses NFAT translocation via calcium signaling and possibly through microtubule reorganization. In microglia, LRRK2 modulates cytokine production and the glycolytic switch in response to IFN-γ in an NFAT-independent manner. Activated LRRK2 G2019S microglia cause neurite shortening, indicating that LRRK2-driven immunological changes can be neurotoxic. We propose that synergistic LRRK2/IFN-γ activation serves as a potential link between inflammation and neurodegeneration in Parkinson's disease.

HER-2/neu as a target for cancer vaccines

A novel modality toward the treatment of HER-2/neu-positive malignancies, mostly including breast and, more recently prostate carcinomas, has been the use of vaccines targeting HER-2/neu extracellular and intracellular domains. HER-2/neu-specific vaccines have been demonstrated to generate durable T-cell anti-HER-2/neu immunity when tested in Phase I and II clinical trials with no significant toxicity or autoimmunity directed against normal tissues. Targeting of HER-2/neu in active immunotherapy may involve peptide and DNA vaccines. Moreover, active anti-HER-2/neu immunization could facilitate the ex vivo expansion of HER-2/neu-specific T cells for use in adoptive immunotherapy for the treatment of established metastatic disease. In addition, early data from trials examining the potential use of HER-2/neu-based vaccines in the adjuvant setting to prevent the relapse of breast cancer in high-risk patients have shown promising results. Future approaches include multiepitope preventive vaccines and combinatorial treatments for generating the most efficient protective anti-tumor immunity.

Interferon-gamma-dependent tyrosine phosphorylation of MEKK4 via Pyk2 is regulated by annexin II and SHP2 in keratinocytes

IFNgamma (interferon-gamma) binding to its cognate receptor results, through JAK (Janus kinase), in direct activation of receptor-bound STAT1 (signal transducer and activator of transcription 1), although there is evidence for additional activation of a MAPK (mitogen-activated protein kinase) pathway. In the present paper, we report IFNgamma-dependent activation of the MEKK4 (MAPK/extracellular-signal-regulated kinase kinase kinase 4) pathway in HaCaT human keratinocytes. MEKK4 is tyrosine-phosphorylated and the IFNgamma-dependent phosphorylation requires intracellular calcium. Calcium-dependent phosphorylation of MEKK4 is mediated by Pyk2. Moreover, MEKK4 and Pyk2 co-localize in an IFNgamma-dependent manner in the perinuclear region. Furthermore, the calcium-binding protein, annexin II, and the calcium-regulated kinase, Pyk2, co-immunoprecipitate with MEKK4 after treatment with IFNgamma. Immunofluorescence imaging of HaCaT cells shows an IFNgamma-dependent co-localization of annexin II with Pyk2 in the perinuclear region, suggesting that annexin II mediates the calcium-dependent regulation of Pyk2. Tyrosine phosphorylation of MEKK4 correlates with its activity to phosphorylate MKK6 (MAPK kinase 6) in vitro and subsequent p38 MAPK activation in an IFNgamma-dependent manner. Additional studies demonstrate that the SH2 (Src homology 2)-domain-containing tyrosine phosphatase SHP2 co-immunoprecipitates with MEKK4 in an IFNgamma-dependent manner and co-localizes with MEKK4 after IFNgamma stimulation in the perinuclear region in HaCaT cells. Furthermore, we provide evidence that SHP2 dephosphorylates MEKK4 and Pyk2, terminating the MEKK4-dependent branch of the IFNgamma signalling pathway.

Mycobacterial lipoarabinomannan and related lipoglycans: from biogenesis to modulation of the immune response

The cell wall component lipoarabinomannan (ManLAM) from Mycobacterium tuberculosis is involved in the inhibition of phagosome maturation, apoptosis and interferon (IFN)-gamma signalling in macrophages and interleukin (IL)-12 cytokine secretion of dendritic cells (DC). All these processes are important for the host to mount an efficient immune response. Conversely, LAM isolated from non-pathogenic mycobacteria (PILAM) have the opposite effect, by inducing a potent proinflammatory response in macrophages and DCs. LAMs from diverse mycobacterial species differ in the modification of their terminal arabinose residues. The strong proinflammatory response induced by PILAM correlates with the presence of phospho-myo-inositol on the terminal arabinose. Interestingly, recent work indicates that the biosynthetic precursor of LAM, lipomannan (LM), which is also present in the cell wall, displays strong proinflammatory effects, independently of which mycobacterial species it is isolated from. Results from in vitro assays and knock-out mice suggest that LM, like PILAM, mediates its biological activity via Toll-like receptor 2. We hypothesize that the LAM/LM ratio might be a crucial factor in determining the virulence of a mycobacterial species and the outcome of the infection. Recent progress in the identification of genes involved in the biosynthesis of LAM is discussed, in particular with respect to the fact that enzymes controlling the LAM/LM balance might represent targets for new antitubercular drugs. In addition, inactivation of these genes may lead to attenuated strains of M. tuberculosis for the development of new vaccine candidates.

The immunosuppressive effect of Fusarium mycotoxin as a function of HLA antigens

We examined the blastogenic response to phytohaemaglutinin (PHA) in HLA-B8, DR3 positive and negative subjects in the presence or absence of the immunosuppressive Fusarium mycotoxin. HLA-B8, DR3 haplotype was associated with a depression of the response to mitogen in the absence of the mycotoxin, whereas in the presence of deoxynivalenol we could not detect significant differences among individuals either possessing or lacking this haplotype.

Interferon-gamma acutely induces calcium influx in human microglia

The acute actions of the cytokine, interferon-gamma (IFN-gamma), on intracellular calcium [Ca(2+)](i) levels in human microglia were investigated. In the presence of a calcium-containing physiological solution (Ca(2+)-PSS), IFN-gamma caused a progressive increase in [Ca(2+)](i) to a plateau level with a mean rate of increase of 0.81 +/- 0.17 nM/s and mean amplitude of 102 +/- 12 nM (n = 67 cells). Washout of the cytokine did not alter the plateau established with IFN-gamma in Ca(2+)-PSS; however, introduction of a Ca(2+)-free PSS diminished [Ca(2+)](i) to baseline levels. The decrease in [Ca(2+)](i) with Ca(2+)-free PSS would indicate that the response to IFN-gamma was mediated by an influx pathway. This result was confirmed in separate experiments showing the lack of an induced change in [Ca(2+)](i) with IFN-gamma applied in Ca(2+)-free PSS. The increase in [Ca(2+)](i) induced in Ca(2+)-PSS was reduced to near baseline levels when the external solution contained low Cl(-) in the maintained presence of IFN-gamma suggesting that cellular depolarization inhibited the cytokine mediated entry pathway. The compound SKF96365, which blocks store operated influx of Ca(2+) in human microglia, was ineffective in altering the increase in [Ca(2+)](i), however, La(3+) completely inhibited the Ca(2+) response induced by IFN-gamma. Whole-cell patch clamp studies showed no effect of IFN-gamma to alter outward currents and inward rectifier K(+) currents. The influx of Ca(2+) may serve a signaling role in microglia linking IFN-gamma to functional responses of the cells to infiltrating T lymphocytes into the central nervous system (CNS) during inflammatory processes.

Requirement of Ca2+ and CaMKII for Stat1 Ser-727 phosphorylation in response to IFN-gamma

In response to IFN-gamma, the latent cytoplasmic protein signal transducers and activators of transcription 1 (Stat1) becomes phosphorylated on Y701, dimerizes, and accumulates in the nucleus to activate transcription of IFN-gamma-responsive genes. For maximal gene activation, S727 in the transcription activation domain of Stat1 also is inducibly phosphorylated by IFN-gamma. We previously purified a group of nuclear proteins that interact specifically with the Stat1 transcription activation domain. In this report, we identified one of them as the multifunctional Ca(2+)/calmodulin-dependent kinase (CaMK) II. We demonstrate that IFN-gamma mobilizes a Ca(2+) flux in cells and activates CaMKII. CaMKII can interact directly with Stat1 and phosphorylate Stat1 on S727 in vitro. Inhibition of Ca(2+) flux or CaMKII results in a lack of S727 phosphorylation and Stat1-dependent gene activation, suggesting in vivo phosphorylation of Stat1 S727 by CaMKII. Thus two different cellular signaling events, IFN-gamma receptor occupation and Ca(2+) flux, are required for Stat1 to achieve maximal transcriptional activation through regulation of phosphorylation.

Beta-amyloid-induced calcium influx induces apoptosis in culture by oxidative stress rather than tau phosphorylation

Beta-amyloid (betaA) toxicity in culture is accompanied by multiple events culminating in apoptosis. Calcium influx may represent the initial event, since calcium chelation prevents all subsequent events, while subsequent events include increased generation of reactive oxygen species (ROS) and hyperphosphorylation of tau. In the present study, we undertook to determine whether ROS generation or tau hyperphosphorylation mediate betaA-induced apoptosis. The anti-oxidant vitamin E or the kinase inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenslfonamide (W7) was added following brief treatment of differentiated SH-SY-5Y human neuroblastoma cells with 22 microM betaA. Under these conditions, vitamin E prevented ROS generation and apoptosis, but did not prevent intracellular calcium accumulation or tau phosphorylation. W7 prevented tau phosphorylation but did not block betaA-induced calcium influx, ROS generation or apoptosis. While these studies do not address the long-term consequences of PHF formation, they indicate that ROS generation, rather than tau hyperphosphorylation, leads to apoptosis following betaA-induced calcium influx into cultured cells.

Prostaglandin F2 alpha upregulates intercellular adhesion molecule-1 expression in human gingival fibroblasts

Prostaglandin F2 alpha (PGF2 alpha) is a bioactive lipid mediator, which has been suggested to be involved in the pathogenesis of periodontal disease. However, the roles of PGF2 alpha in the disease are not well understood. In the present study, we investigated the effect of PGF2 alpha on intercellular adhesion molecule-1 (ICAM-1) expression in human gingival fibroblasts (HGF) and the effect of PGF2 alpha on ICAM-1 expression elicited by proinflammatory cytokines, interferon-gamma (IFN-gamma) and tumour necrosis factor alpha (TNF alpha) in the cells. PGF2 alpha-stimulated HGF expressed ICAM-1 expression in a time- and dose-dependent manner. IFN-gamma-elicited ICAM-1 expression was synergistically increased by PGF2 alpha, whereas TNF alpha-induced ICAM-1 expression was slightly inhibited by PGF2 alpha. Fluprostenol, a selective FP receptor agonist, could mimic PGF2 alpha-induced effect on ICAM-1 expression. Furthermore, signal transduction for the regulation of ICAM-1 by PGF2 alpha was investigated using N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W-7), a calcium calmodulin antagonist, and 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine (H-7), an inhibitor of protein kinase C (PKC). W-7 and H-7, remarkably, suppressed PGF2 alpha-induced ICAM-1 expression and synergistic increase of ICAM-1 expression by combination of PGF2 alpha and IFN-gamma, while IFN-gamma-elicited ICAM-1 expression was only partially inhibited by W-7 and H-7. From these data, we suggest that PGF2 alpha upregulates ICAM-1 expression in HGF and synergistically enhances IFN-gamma-induced ICAM-1 expression through FP receptor by calcium calmodulin-dependent and PKC-dependent pathways. PGF2 alpha may be involved in the pathology of periodontal disease by upregulating ICAM-1 expression in HGF.

Interferon-gamma elicits a G-protein-dependent Ca2+ signal in human neutrophils after depletion of intracellular Ca2+ stores

Interferon-gamma (IFN-gamma) has multiple effects on Ca2+ signalling in polymorphonuclear neutrophils (PMNs), including evoked cytosolic Ca2+ transients, increased capacitative calcium influx and increased sequestration of Ca2+ in intracellular stores. The present study was conducted to elucidate the mechanism behind the Ca2+ transients. As observed before, the IFN-gamma-evoked Ca2+ signals were apparent when extracellular Ca2+ was removed. A new finding was that the proportion of responding cells and the extent of calcium release increased with increasing time in EGTA buffer. As assessed by N-formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated Ca2+ release, the intracellular stores were depleted during this incubation period, and the extent of depletion correlated well with the appearance of IFN-gamma-induced Ca2+ signals. This store dependence of the IFN-gamma-induced Ca2+ signals was confirmed by the appearance of IFN-gamma-evoked Ca2+ signals in the presence of extracellular Ca2+ after store depletion by thapsigargin. The appearance of IFN-gamma-mediated Ca2+-signals in the presence of EGTA indicates that IFN-gamma stimulates Ca2+ release from intracellular stores. This was confirmed by the inability of the calcium transportation blocker La3+ to abolish the IFN-gamma response and the total abrogation of the response by the phospholipase C inhibitor U73122. Although these latter results imply a role for inositol 1,4,5-trisphosphate(IP3) in IFN-gamma signalling, comparison of IFN-gamma-evoked responses with fMLP responses revealed clear differences that suggest different signal-transduction pathways. However, responses to fMLP and IFN-gamma were both depressed by pertussis toxin, and the IFN-gamma responses were, in addition, inhibited by the tyrosine kinase inhibitor genistein. Further evidence of the involvement of tyrosine kinase was a slight stimulatory effect of the protein tyrosine phosphatase inhibitor sodium orthovanadate. The PI-3K activity was of minor importance. In conclusion, we present evidence of a novel signal-transduction mechanism for IFN-gamma in PMNs, dependent on tyrosine kinase activity, a pertussis toxin-sensitive G protein and phospholipase C activity.

IFN-gamma induces calcium transients and increases the capacitative calcium entry in human neutrophils

We have previously reported that long-term priming of human polymorphonuclear neutrophilic granulocytes (PMN) with interferon-gamma (IFN-gamma) increased the fMLP-stimulated calcium influx. We now show that also after short-term incubation with IFN-gamma, PMN calcium metabolism is modulated. Single adherent cells in three different calcium-containing buffers (high, normal, and low [Ca2+]) were stimulated with the bacterial peptide fMLP or the Ca-ATPase inhibitor thapsigargin (Tg) after about 5 min preincubation with IFN-gamma. The results of this protocol indicated that IFN-gamma increases both calcium influx and calcium sequestration. Store dependent Ca2+ influx, directly measured on readdition of calcium to Tg-treated cells incubated in EGTA buffer, was significantly enhanced in IFN-gamma-treated cells. This effect of IFN-gamma was enhanced by the tyrosine kinase inhibitor herbimycin A. Strikingly, in low extracellular calcium concentrations, IFN-gamma induced calcium transients in 20%-60% of the cells. The proportion of PMN responding with Ca2+ transients increased with decreasing extracellular calcium concentration. Average lagtime from addition of IFN-gamma to a response that could be measured was 7.3 sec, and average increase in [Ca2+] above the basal level was 790 nM. These IFN-gamma-induced transients could not be depressed by herbimycin A. Thus, IFN-gamma can increase capacitative calcium influx, induce calcium transients, and possibly affect calcium sequestration in human PMN.

Effect of propranolol and IFN-beta on the induction of MHC class II expression and cytokine production by IFN-gamma IN THP-1 human monocytic cells

This study was undertaken to investigate the effects of propranolol, IFN-beta, and the protein kinase modulators on IFN-gamma induction of MHC class II antigen expression and cytokine production in THP-1 human monocytic cells. IFN-gamma induced expression of HLA-DR and DQ molecules and secretion of the monokines IL-1 beta and TNF-alpha in THP-1 cells in a time and dose-dependent manner. The effect of INF-gamma on class II HLA antigens was dose-dependently inhibited by IFN-beta. H-7, phloretin, staurosporine as well as GF 109203X are selective enzyme inhibitors of protein kinase C (PKC), down-regulating IFN-gamma induced MHC class II expression and cytokine production. Stimulators of PKC, like PMA, replaced IFN-gamma in the induction of monokines in THP-1 cells, whereas the addition of HA 1004 or arachidonic acid to the culture had no effect on IFN-gamma mediated changes. Blocking of phospholipase D (PLD)-derived diacylglycerol (DAG) formation by propranolol abrogated IFN-gamma increased HLA class II expression and IL-1 beta secretion, but had little effect on IFN-gamma induced TNF-alpha production. These findings appear to suggest that PLD-derived phosphatidate is not the primary source of DAG production in IFN-gamma-induced TNF-alpha secretion, but may be necessary for IFN-gamma-mediated MHC class II induction and IL-1 beta production in human monocytes, whereas phospholipase A2 may not be required for IFN-gamma activation of PKC in the process.

Differential regulation of cytokine-induced major histocompatibility complex class II expression and nitric oxide release in rat microglia and astrocytes by effectors of tyrosine kinase, protein kinase C, and cAMP

Two glial cell populations of the CNS, astrocytes and microglia, were examined for expression of two immunologically important molecules, MHC class II and nitric oxide (NO), following treatment with cytokines. IFN-gamma induced both molecules in microglia at substantially higher levels than astrocytes. The addition of TNF-alpha to IFN-gamma elevated class II expression and NO in both cells. Genistein, an inhibitor of tyrosine kinases, and calphostin, an inhibitor of protein kinase C, diminished cytokine induction of class II MHC and NO in both glial populations. Forskolin was most effective in inhibiting class II MHC expression, but had little inhibitory effect on NO production. These results indicate microglia are more effective than astrocytes in producing cell-associated and secreted immune mediators in response to IFN-gamma and or TNF-alpha and multiple parallel, but distinct, signaling events are required for cytokine induced class II MHC or NO production.

Arachidonic Acid Mediates Interferon-γ–Induced Sphingomyelin Hydrolysis and Monocytic Marker Expression in HL-60 Cell Line

The biochemical signaling mechanisms involved in transducing the effects of interferon-γ (IFN-γ) on human leukemia-derived HL-60 cell differentiation are not completely understood. Recent studies established the existence of a sphyngomyelin (SM) cycle that operates in response to the action of IFN-γ on HL-60 cells, but the mechanisms by which IFN-γ induces the SM hydrolysis remain unexplored. In this study, biochemical events mediating IFN-γ effects on SM turnover and their specificity and role in HL-60 differentiation were investigated. The activation of the SM cycle by IFN-γ occurred rapidly, with a decrease of approximately 20% in the SM level observed after 60 minutes with a concomitant increase in ceramide level. Treatment of HL-60 cells with IFN-γ did not influence the 1,2-diacylglycerol concentration, intracellular Ca2+ concentration, or phospholipase D activity. IFN-γ stimulated a rapid release of arachidonic acid (AA) from HL-60 cells; the effect was abolished by the pretreatment of cells with pertussis toxin, suggesting a role for a pertussis-toxin–sensitive G protein in IFN-γ–mediated activation of phospholipase A2 (PLA2 ). At 4 to 120 hours after the stimulation of the cells with IFN-γ, a significant increase in the particulate and soluble PLA2 activity was observed, corresponding to an increase in the level of immunoreactive cPLA2 in both cytosol and membrane fractions. The treatment of cells with tyrosine kinase inhibitor herbimycin A completely abolished the effect of IFN-γ on PLA2 activity in membrane and cytosolic fractions, but had no effect on IFN-γ–mediated early AA release suggesting dual mechanism of PLA2 activation. Melittin, potent activator of PLA2 , and AA mimicked the effect of IFN-γ on SM hydrolysis. Pretreatment of HL-60 cells with the PLA2 inhibitor, bromophenacyl bromide (BPB), or pertussis toxin abolished the effect of IFN-γ on SM hydrolysis; exogenous addition of AA overcame the effects of BPB and pertussis toxin. Long-term exposure (5 days) of HL-60 cells to IFN-γ caused an increase in nitroblue tetrazolium (NBT)-reducing and nonspecific esterase (NSE) activity and induced expression of FcγRI (CD64) without significant effects on cell number, adherence, or fagocytic activity. The treatment of cells with AA or melittin induced NBT, NSE, and CD64 expression to the level similar to that observed with IFN-γ, and no further increase was observed with the combination of IFN-γ and AA or IFN-γ and melittin. Treatment of HL-60 cells with indomethacin, an inhibitor of cyclo-oxygenase, and nordihydroguaiaretic acid (NDGA), an inhibitor of lipoxygenase, had no effects on IFN-γ–mediated induction of CD64 expression. These studies indicate a key role for the phospholipase A2/AA pathway, as an early biochemical signal elicited by the occupation of IFN-γ–receptor, in mediating IFN-γ induction of the SM cycle and phenotypic changes associated with differentiation of HL-60 along monocytic lineage.

Arachidonic Acid Mediates Interferon-γ–Induced Sphingomyelin Hydrolysis and Monocytic Marker Expression in HL-60 Cell Line

The biochemical signaling mechanisms involved in transducing the effects of interferon-γ (IFN-γ) on human leukemia-derived HL-60 cell differentiation are not completely understood. Recent studies established the existence of a sphyngomyelin (SM) cycle that operates in response to the action of IFN-γ on HL-60 cells, but the mechanisms by which IFN-γ induces the SM hydrolysis remain unexplored. In this study, biochemical events mediating IFN-γ effects on SM turnover and their specificity and role in HL-60 differentiation were investigated. The activation of the SM cycle by IFN-γ occurred rapidly, with a decrease of approximately 20% in the SM level observed after 60 minutes with a concomitant increase in ceramide level. Treatment of HL-60 cells with IFN-γ did not influence the 1,2-diacylglycerol concentration, intracellular Ca2+ concentration, or phospholipase D activity. IFN-γ stimulated a rapid release of arachidonic acid (AA) from HL-60 cells; the effect was abolished by the pretreatment of cells with pertussis toxin, suggesting a role for a pertussis-toxin–sensitive G protein in IFN-γ–mediated activation of phospholipase A2 (PLA2 ). At 4 to 120 hours after the stimulation of the cells with IFN-γ, a significant increase in the particulate and soluble PLA2 activity was observed, corresponding to an increase in the level of immunoreactive cPLA2 in both cytosol and membrane fractions. The treatment of cells with tyrosine kinase inhibitor herbimycin A completely abolished the effect of IFN-γ on PLA2 activity in membrane and cytosolic fractions, but had no effect on IFN-γ–mediated early AA release suggesting dual mechanism of PLA2 activation. Melittin, potent activator of PLA2 , and AA mimicked the effect of IFN-γ on SM hydrolysis. Pretreatment of HL-60 cells with the PLA2 inhibitor, bromophenacyl bromide (BPB), or pertussis toxin abolished the effect of IFN-γ on SM hydrolysis; exogenous addition of AA overcame the effects of BPB and pertussis toxin. Long-term exposure (5 days) of HL-60 cells to IFN-γ caused an increase in nitroblue tetrazolium (NBT)-reducing and nonspecific esterase (NSE) activity and induced expression of FcγRI (CD64) without significant effects on cell number, adherence, or fagocytic activity. The treatment of cells with AA or melittin induced NBT, NSE, and CD64 expression to the level similar to that observed with IFN-γ, and no further increase was observed with the combination of IFN-γ and AA or IFN-γ and melittin. Treatment of HL-60 cells with indomethacin, an inhibitor of cyclo-oxygenase, and nordihydroguaiaretic acid (NDGA), an inhibitor of lipoxygenase, had no effects on IFN-γ–mediated induction of CD64 expression. These studies indicate a key role for the phospholipase A2/AA pathway, as an early biochemical signal elicited by the occupation of IFN-γ–receptor, in mediating IFN-γ induction of the SM cycle and phenotypic changes associated with differentiation of HL-60 along monocytic lineage.

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.

Potentiation by thyroxine of interferon-gamma-induced HLA-DR expression is protein kinase A- and C-dependent

L-Thyroxine (T4) and 3,3',5-L-triiodothyronine (T3) potentiate the antiviral state induced by interferon-gamma(IFN-gamma) in homologous cells by a mechanism that is dependent upon calcium/phospholipid-dependent protein kinase (PKC). L-T4 and T3 also potentiate induction by IFN-gamma of MHC class II HLA-DR antigen expression in HeLa cells. In the present studies of HLA-DR expression, the PKC inhibitor staurosporine (0.1-1 nM) enhanced the expression of HLA-DR when the inhibitor was added simultaneously with IFN-gamma, 100 IU/ml. In the presence of IFN-gamma and 10(-7) M T4, the same concentrations of staurosporine inhibited potentiation of HLA-DR expression by thyroid hormone. A more specific PKC inhibitor, CGP41251 (0.5-5 nM), similarly enhanced HLA-DR expression in the presence of IFN-gamma but inhibited thyroid hormone potentiation of antigen expression. Both actions of CGP41251 were suppressed when cells were also treated with phorbol 12-myristate 13-acetate (PMA). A phospholipase C inhibitor, U73122 (1-1000 nM), did not alter the potentiating ability of T4, although it inhibited in a concentration-dependent manner the expression of HLA-DR induced by IFN-gamma. The potentiating effect of T4 was much more sensitive to a cyclic AMP-dependent protein kinase (PKA) inhibitor,KT5720 (1-1000nM), than was the induction of HLA-DR by IFN-gamma. The inhibitory effects of KT5720 were reversed by concurrent 8-bromo-cAMP treatment. The calmodulin antagonist W-7 (5-50 microM) did not alter IFN-gamma induction of HLA-DR in either the presence or absence of T4. HLA-DR expression in HeLa cells appears to be under PKC-associated inhibition; IFN-gamma reverses this inhibition to promote the appearance of the DR antigen. In contrast, potentiation by T4 of induction of HLA-DR by IFN-gamma requires activation of PKC. PKA is involved both in DR induction by IFN-gamma and in potentiation of the latter by T4. Thus, PKA and PKC have discrete roles in IFN-gamma-induced MHC class II antigen expression and its modulation by thyroid hormone.

Interferon-gamma affects protein kinase C activity in human neutrophils

Interferon-gamma (IFN-gamma) is a priming agent of polymorphonuclear neutrophilic granulocyte (PMN) oxygen metabolism, and protein kinase C (PKC) is traditionally believed to play a central role in activation of this oxygen metabolism. In the present study, we have shown that the PKC activity in PMN is affected by IFN-gamma. After only 2 minutes exposure to IFN-gamma (100 U/ml), PKC activity was significantly increased in the noncytosolic fraction of the cells. This increase was transient, but toward the end of the priming period of 2 h, the membrane-associated PKC activity increased again to about 152% of control. In the cytosolic fraction, a small and hardly detectable decrease in PKC activity was observed. Treatment of PMN with granulocyte-macrophage colony-stimulating factor (GM-CSF), another PMN priming agent, showed no significant effects on the PKC activity. When the cells were stimulated with the bacterial peptide fMLP after a priming period with IFN-gamma or GM-CSF for 2 h, no significant difference between treated and control cells could be observed. PMN oxygen metabolism, measured by flow cytometry as an accumulation of the fluorescent compound dichlorofluorescein, was in these experiments significantly primed by IFN-gamma, both at baseline and when stimulated with fMLP. The protein kinase C inhibitors H7 and Ro31-8220 blocked the fMLP responses to some extent, but not completely. However, no significant difference between fMLP responses in control and IFN-gamma-treated cells could be detected after administration of inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Sphingomyelin-ceramide turnover in CD28 costimulatory signaling

When the CD28 membrane glycoprotein of T cells binds to its ligand, a signal is transmitted that is required for T cell receptor-induced proliferation and cytokine secretion: T cells are not stimulated by the CD28 signal alone. Ligation of CD28 initiated sphingomyelin hydrolysis and generated ceramide. Treatment of T cells with either exogenous sphingomyelinase or a cell-permeable ceramide analogue. C6-ceramide, mimicked the CD28 signal by inducing T cell proliferation and interleukin-2 gene transcription. Stabilization of interleukin-2 mRNA was also observed in C6-ceramide-treated cells. Thus, the sphingomyelin-ceramide pathway is a candidate for mediating the costimulatory signal.

Interferon-gamma and lipopolysaccharide reduce cAMP responses in cultured glial cells: reversal by a type IV phosphodiesterase inhibitor

The aim of the present study was to determine whether two classical macrophage activators, bacterial lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) could affect the accumulation of the second messenger cAMP in cultured rat microglia and astrocytes. Purified microglia and astrocyte secondary cultures obtained from the neonatal rat were grown for 3 days in basal medium Eagle (BME) + 10% fetal calf serum (FCS). Exposure of microglia to LPS resulted into a dose- and time-dependent decrease in the accumulation of cAMP induced by receptor-mediated (isoproterenol or prostaglandin E2) or direct (forskolin) activation of adenylate cyclase. The inhibitory effect of LPS was rapid (a 10 min preincubation was sufficient to approach a maximal effect), occurred at low doses (IC50 = 1.2 ng/ml), and was not abrogated by pertussis toxin. A selective inhibitor of type IV phosphodiesterase (rolipram, 100 nM) prevented the effect of LPS on cAMP accumulation, while inhibitors of other forms of phosphodiesterase were unable to do so. IFN-gamma (100 u/ml) also caused a depression of the evoked cAMP accumulation in microglia after a 10 min preincubation, and its effect was prevented by rolipram, as in the case of LPS. Astrocytes differed from microglia in that LPS (1-100 ng/ml) did not inhibit the accumulation of cAMP induced by either isoproterenol or forskolin; on the other hand, IFN-gamma did have an inhibitory effect (though less pronounced than in microglia) that could be prevented by rolipram.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Role of protein kinase C activation in synthesis of complement components C2 and factor B in interferon-gamma-stimulated human fibroblasts, glioblastoma cell line A172 and monocytes

The synthesis of C2 and factor B, the key components of complement system, is performed by various kinds of cells and is also up-regulated by interferon-gamma (IFN-gamma). By using human fibroblasts, human glioblastoma cell line A172 and monocytes, we investigated the signal-transduction mechanism for IFN-gamma-induced synthesis of C2 and factor B. The C2 and factor B synthesis induced by IFN-gamma in all three cell types was inhibited by a protein kinase C (PKC) inhibitor, 1-(5-isoquinolinyl-sulphonyl)-2-methylpiperazine (H-7). The depletion of PKC in these cell types after treatment with phorbol 12-myristate 13-acetate (PMA) resulted in inhibition of IFN-gamma-induced C2 production. In addition, IFN-gamma treatment elicited a decrease in cytoplasmic PKC in A172 cells, indicating that PKC is activated by IFN-gamma. These results suggest that PKC is crucial for IFN-gamma-induced C2 and factor B synthesis. Northern-blot analysis showed that the effects at H-7 were at least partly mediated by modulation of C2 and factor B mRNA abundance in A172 cells. Since treatment of fibroblasts and A172 cells with IFN-gamma had no effect on intracellular Ca2+ concentration, and since neither EGTA nor nifedipine inhibited C2 or factor B synthesis induced by IFN-gamma, we concluded that intracellular Ca2+ mobilization was not involved in the effect of IFN-gamma. In addition, genistein, herbimycin A and N-(6-aminohexyl)-5-chloro-1-naphthalene-sulphonamide (W-7) had no inhibitory effect on IFN-gamma-mediated action in any of the three cell types, which suggests that IFN-gamma acts independently of tyrosine kinases and calmodulin-dependent protein kinases.

Interferon-gamma-induced HLA-DR, but not ICAM-1, expression of human keratinocytes is down-regulated by calmodulin antagonist

Interferon-gamma (IFN-gamma) has been shown to induce or enhance the expression of MHC class II and intercellular adhesion molecule-1 (ICAM-1) in a variety of human and murine cell types, including epidermal keratinocytes (KC). However, the expression of MHC class II and ICAM-1 molecules induced by IFN-gamma is not necessarily coordinated. We investigated the inhibitory effects of the calmodulin antagonist, W-7, and its chlorine deficient inactive analogue, W-5, on the expression of MHC class II (HLA-DR) and ICAM-1 by human KC incubated with IFN-gamma. We found that the IFN-gamma-induced expression of HLA-DR was reproducibly and dose-dependently inhibited by W-7. However, the expression of ICAM-1 was highly resistant to the inhibitory effects of W-7. Neither HLA-DR nor ICAM-1 expression was affected by W-5. These data suggest that the IFN-gamma-induced HLA-DR, but not ICAM-1, expression is mediated, if not exclusively, by calmodulin in human KC.

Interferon-gamma modulates cytosolic free calcium in human neutrophilic granulocytes

To investigate the role of cytosolic free calcium ([Ca2+]i in interferon-gamma (IFN-gamma) pre-activation (priming) of human neutrophilic granulocytes (PMN) we used three different fluorescence methods, i.e. digital imaging of single, adherent, Fura-2 loaded cells, flow cytometric measurements of single, non-adherent, Fluo-3 loaded cells, and spectrofluorometry of Indo-1 loaded PMN in suspension. IFN-gamma increased the [Ca2+]i level in single, adherent PMN during the second phase of the fMLP response. The bacterial peptide fMLP (N-formyl-L-methionyl-L-leucyl-L-phenylalanine) is a known stimulant of the calcium/inositol phosphate system. The [Ca2+]i increase was abolished in Ca(2+)-free test buffer. Furthermore, the baseline [Ca2+]i level was found to be slightly increased in IFN-gamma primed PMN as analysed with flow cytometry. On the other hand, these [Ca2+]i responses were not detectable with the other methods used. We suggest that IFN-gamma increases the plasma membrane permeability for calcium in PMN, and substantiate this by demonstrating compliance with a capacitative model for intracellular calcium regulation. Mathematical modeling also suggested that IFN-gamma primed human PMN may sequester 13% more Ca2+ than unprimed cells in fMLP-insensitive intracellular stores. Thus, the Ca2+ responses to IFN-gamma are modest and not easily detectable with some of the methods currently in use. They nevertheless explain why fMLP elicits brisker responses from PMN after IFN-gamma priming.

Interferon-gamma up-regulates a unique set of proteins in human keratinocytes. Molecular cloning and expression of the cDNA encoding the RGD-sequence-containing protein IGUP I-5111

Treatment of proliferating and quiescent primary human keratinocytes with interferon-gamma (IFN-gamma) (100 U/ml, 23.5 h) followed by two-dimensional gel analysis revealed three proteins, IGUP I-3421 (M(r) = 48,200, pI = 6.06); IGUP I-3524 (M(r) = 56,900, pI = 5.92), a protein homologous to peptide-chain-release factor and tryptophanyl-tRNA synthetase; and IGUP I-5111 (M(r) = 30,400, pI = 5.76) recorded in the keratinocyte protein database (Celis et al., 1991, 1992) that are highly and specifically up-regulated by IFN-gamma among several agents tested including 14 other cytokines, second messengers [dibutyryl cAMP (Bt2cAMP), dibutyryl cGMP (Bt2cGMP)] and compounds known to affect keratinocytes [4 beta-phorbol 12-myristate 13-acetate (PMA), retinoic acid, Ca2+, dexamethasone, lipopolysaccharides, foetal calf serum]. Protein IGUP I-5111 was selected for further studies as its level is affected by simian-virus-40 transformation and because peptide sequences were available in the microsequence database. The cDNA was cloned from a fibroblast cDNA library using degenerate oligodeoxyribonucleotides and expressed in AMA cells using the vaccinia virus expression system. Database searches indicated that the predicted protein, which migrated with the AMA variant of keratinocyte protein IEF SSP 5111, is novel although it exhibits weak similarity to cytoskeletal proteins. IGUP I-5111 contains the RGD sequence found in many extracellular glycoprotein ligands of the integrin receptor family and it is found at least partially in the culture supernatant. Considering the presence of IFN-gamma in psoriatic plaques as well as its putative involvement in the pathophysiology of the disease it was of interest to determine whether the set of proteins was upregulated in these cells. Two-dimensional gel analysis of the protein phenotype of non-cultured, unfractionated psoriatic keratinocytes failed to reveal up-regulation of any of the three IFN-gamma-induced proteins suggesting that the effect of IFN-gamma in vivo may be modulated by the activity of other cytokine(s) or growth factor(s). Psoriatic keratinocytes were equally sensitive to IFN-gamma as their normal counterparts.

Identification of a calmodulin-binding and inhibitory peptide domain in the HIV-1 transmembrane glycoprotein

A number of studies suggest a critical role of the HIV-1 envelope glycoprotein in cytopathogenesis, but the detailed mechanisms of cell injury remain to be defined. HIV-1 envelope proteins associate with the host cell membrane, and studies have demonstrated that HIV perturbs membrane structure and function. We describe here a structurally conserved region of the HIV-1 transmembrane protein (TM) that displays functional properties of target regions of proteins that interact directly with calcium-saturated calmodulin as part of cellular response cascades. The synthetic peptide homolog encompassing the carboxyl terminus (amino acid residues 828-855) of HIV-1 TM protein (LLP-1) is shown in standard in vitro assays to bind efficiently to purified calmodulin (CaM) and to inhibit in vitro CaM-mediated stimulation of phosphodiesterase activity. This suggests that this peptide homolog binds to CaM at affinities similar to those reported for a reference CaM-binding peptide. In addition, the CaM-dependent process of phospholipid synthesis can be inhibited in cell cultures by exogenous addition of the LLP-1. Finally, we have shown that the full-length TM protein binds CaM, whereas a truncated TM protein lacking the LLP-1 segment does not bind CaM. These results suggest a novel mechanism of viral cytopathogenesis mediated by the interaction of HIV-1 TM protein with cellular CaM, that could lead to an uncoupling of critical cellular signal transduction pathways.

Specific suppression of major histocompatibility complex class I and class II genes in astrocytes by brain-enriched gangliosides

The effect of brain-enriched gangliosides on constitutive and cytokine-inducible expression of major histocompatibility complex (MHC) class I and II genes in cultured astrocytes was studied. Before treatment with gangliosides, astrocytes expressed constitutive MHC class I but not class II molecules, however, the expression of both MHC class I and II cell surface molecules on astrocytes was induced to high levels by interferon gamma (IFN-gamma). Constitutive and IFN-gamma-inducible expression of MHC class I and II molecules was suppressed by treatment of astrocytes with exogenous bovine brain gangliosides in a dose-dependent manner. Constitutive and induced MHC class I and II mRNA levels were also suppressed by gangliosides, indicating control through transcriptional mechanisms. This was consistent with the ability of gangliosides to suppress the binding activity of transcription factors, especially NF-kappa B-like binding activity, important for the expression of both MHC class I and II genes. These studies may be important for understanding mechanisms of central nervous system (CNS)-specific regulation of major histocompatibility molecules in neuroectodermal cells and the role of gangliosides in regulating MHC-restricted antiviral and autoimmune responses within the CNS.

Interferon-gamma-stimulated and GTP-binding-proteins-mediated phospholipase A2 activation in human neuroblasts

Interferon-gamma (IFN-gamma) is a potent growth-inhibitory cytokine also endowed with differentiating activity on neural cells. Binding of IFN-gamma to its high-affinity receptor induces a rapid and transient activation of phospholipase A2 (PLA2). The mechanism coupling the IFN-gamma receptor (IFN-gamma-R) to PLA2 activation is not clearly defined, and no information is available on this mechanism in neuroblast cells. We have tested the hypothesis that GTP-binding proteins (G-proteins) may couple the IFN-gamma-R to PLA2 in the human neuroblastoma (NB) cell line LAN-5. Incubation of NB cells with IFN-gamma resulted in a rapid increase in [3H]arachidonic acid (AA) release, and this effect was blocked by pretreatment with anti-IFN-gamma antibodies. IFN-gamma-stimulated AA release was still observed in permeabilized cells that were blocked by pretreatment with anti-IFN-gamma-R antibodies. Exposure of permeabilized LAN-5 cells to guanosine 5'-[gamma-thio]triphosphate (GTP[S]), a non-hydrolysable GTP analogue, induced a dose-dependent release of [3H]AA. A non-specific nucleotide effect was excluded, since similar stimulatory effects on AA mobilization were not observed by GTP, ATP, CTP, ADP and GDP. IFN-gamma-stimulated AA release was completely blocked by the guanine nucleotide analogue that inhibits G-protein function, guanosine 5'-[beta-thio]diphosphate (GDP[S]). A role for G-proteins in IFN-gamma-R coupling to PLA2 was further supported by the inhibition of IFN-gamma-induced [3H]AA release by treatment of permeabilized cells with pertussis toxin and with the antiserum against the common alpha-subunits of G-proteins. To determine a possible contribution to AA mobilization by the phospholipase C and diacyglycerol lipase pathway or by protein kinase C activation, the effects of neomycin, a phospholipase C inhibitor, and PMA (phorbol 12-myristate 13-acetate), a direct activator of protein kinase C, were investigated. Neither neomycin nor PMA affected either basal or IFN-gamma-stimulated AA release. Ca2+ concentration, which has been shown to regulate the activity of some PLA2s, does not appear to play an important role in the regulation of the IFN-gamma-stimulated PLA2 activity, since incubating permeabilized cells in different concentrations of Ca2+ induced AA release without affecting the IFN-gamma response. Altogether, these findings suggest the existence of IFN-gamma-R, which couples a Ca(2+)-independent PLA2 activation via pertussis-toxin-sensitive G-proteins.

Modulation of leukocyte cyclic AMP phosphodiesterase activity by recombinant interferon-gamma: evidence for a differential effect on atopic monocytes

Mechanisms of interferon-gamma (IFN-gamma) effects on monocytes are poorly defined. Evidence for altered IFN-gamma responses and increased monocyte cyclic AMP phosphodiesterase (PDE) activity in atopic dermatitis (AD) suggested a possible relationship. PDE activity in response to IFN-gamma was assessed in normal and atopic monocytes to evaluate the IFN-gamma regulatory role in cell function. Adherence-isolated peripheral blood monocytes were exposed to recombinant human IFN-gamma at 0.1-300 U/ml in Gey's balanced salt solution for varying time periods. Anti-IFN-gamma was used as control. PDE activity was measured by radioenzyme assay using 1 microM cyclic AMP as final substrate concentration. IFN-gamma caused a dose-dependent increase in PDE activity of normal monocytes and the effect was neutralized by anti-IFN-gamma. By contrast, in atopic monocytes, PDE activity was not affected by IFN-gamma at low dose, while at concentrations greater than 200 U/ml, it significantly reduced phosphodiesterase activity. IFN-gamma of PDE activity may alter normal monocyte functions by decreasing cyclic AMP levels. Paradoxical PDE unresponsiveness probably reflects maximal PDE activation in atopic monocytes. This elevated PDE activity is inhibited by high IFN-gamma levels. Reduction of atopic monocyte PDE activity may help to normalize immune function and could account for recent reports of therapeutic efficacy of IFN-gamma in AD.

Stimulation of MHC class I transcription by interferon-gamma involves a non-A, non-C kinase in addition to protein kinase C

The signal pathways by which interferon-gamma (IFN-gamma) is able to up-regulate major histocompatibility complex (MHC) class I transcription were studied in two human hematopoietic tumor cell lines, K562 and Ramos. These studies suggest that the IFN-gamma signal is transduced via an H7- and staurosporine-sensitive kinase that is distinct from protein kinase C (PKC) and protein kinase A (PKA) in both cell types. Ramos cells appear to utilize an additional pathway involving double-stranded RNA-dependent protein kinase. PKC and possibly PKA appear to be involved in one or more intersecting pathways by which agonists of these kinases are able to act synergistically with IFN-gamma, but activation of these latter pathways is neither necessary nor sufficient for induction of MHC class I transcription. Modulation of G-protein- and Ca2+-calmodulin-associated pathways and arachidonic acid metabolism had no effect on constitutive or IFN-gamma-stimulated class I transcription. The class I stimulatory factor produced in response to IFN-gamma treatment appears to have a short t1/2. The identity of this factor is unknown, but is likely to be distinct from known mediators of IFN-stimulated transcription. Gene and cell-type specificity in the signal transduction pathways utilized by IFN-gamma implies that such pathways may be useful targets for experimental and therapeutic manipulation.

Effect of pteridine derivatives on intracellular calcium concentration in human monocytic cells

Pteridines are heterocyclic compounds which are synthesized and released by human monocytes/macrophages following stimulation by interferon-gamma. Their concentration in various body fluids proved to be indicative for the stimulation of the cellular immune system, and determination of pteridines has become an important diagnostic tool. We show that pteridine derivatives, namely neopterin (N), 7,8-dihydroneopterin (NH2), and 5,6,7,8-tetrahydrobiopterin (BH4) increase intracellular calcium (Cai) in human monocytic cells. Significant increases of Cai are observed at 10 nmol/l NH2, at 100 nmol/l BH4 and at 1 mol/l N, i.e. at concentrations encountered in vivo. At a concentration of 1 mumol/l, Cai is increased (from a control value of 145 +/- 7 nmol/l) to 464 +/- 62 nmol/l (NH2), 340 +/- 41 nmol/l (BH4) and 344 +/- 46 nmol/l (N), respectively. The increase of Cai depends on the presence of extracellular calcium and is likely to be due to activation of a calcium channel. We show that the absence of extracellular calcium or the addition of lanthanum ions to the extracellular fluid fully reverses the pteridine-induced increase of Cai. According to these observations, pteridines may mimic the effects of other inflammatory mediators on monocytic cells and seem to be involved in the crosstalk of immunocompetent cells.

Modulation of the antigenic phenotype of human melanoma cells by differentiation-inducing and growth-suppressing agents

Tumor cells often display alterations in their normal program of cellular differentiation. A promising approach for the treatment of cancer involves the induction of terminal differentiation and a loss of proliferative capacity in cancer cells. In human melanoma cells, the combination of mezerein (MEZ) and fibroblast interferon (IFN-beta), results in a rapid and irreversible suppression of cell growth with a concomitant increase in the synthesis of melanin. The induction of terminal differentiation is associated with alterations in the expression of several cellular genes, including fibronectin, ISG-15 and ISG-54, and changes in the expression of specific cell surface antigens, including intercellular adhesion molecule-1 (ICAM-1) and HLA Class I antigens. In the HO-1 human melanoma cell line, induction of terminal differentiation by MEZ plus IFN-beta results in an induction and/or increased expression of ICAM-1, HLA Class I antigens and HLA Class II antigens. IFN-beta and MEZ alone can modulate expression of these antigens to a lower extent than does the combination of compounds. Induction of terminal differentiation and the irreversible suppression of cell growth is not a prerequisite for antigenic modulation in HO-1 cells. This is indicated by the inability of immune interferon (IFN-gamma), a strong inducer of ICAM-1, HLA Class I antigens and HLA Class II antigens synthesis, or the combination of IFN-beta plus IFN-gamma which synergistically but reversibly suppresses HO-1 growth, to induce melanin synthesis or terminal differentiation in HO-1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Stimulation of receptor-coupled phospholipase A2 by interferon-gamma

The biomolecular mechanisms that mediate signal transduction by type II (gamma) interferon (IFN) are poorly understood. IFN-gamma is a potent growth inhibitory cytokine also endowed with antiviral, immunomodulatory, and differentiating activities on various cell targets, including neural cells. IFN-gamma induced a rapid and transient activation of phospholipase A2 in LAN-5, a human neuroblastoma cell line. A consequence of phospholipase A2 activation was the release of arachidonic acid and the generation of lysophospholipids from membrane phospholipids. Treatment of pre-labeled LAN-5 cells with a receptor-saturating concentration of IFN-gamma led to a time-dependent release of [3H]arachidonic acid into the culture media and generation of [32P]lysophosphatidylcholine. Pretreatment of cultures with the phospholipase A2 inhibitor, bromophenacyl bromide, markedly inhibited both [3H]arachidonic acid release and lysophosphatidylcholine production induced by IFN-gamma treatment. Pretreatment of LAN-5 cells with nordihydroguaiaretic acid, a lipoxygenase inhibitor, or with indomethacin, a cyclooxygenase inhibitor, amplified the release of [3H]arachidonic acid and production of lysophosphatidylcholine induced by non-saturating concentrations of IFN-gamma. In parallel, and with the same time-dependent effect, a significant decrease in phosphatidylcholine labeling was observed in IFN-gamma-treated cells, further indicating that a potential signal transduction mechanism of IFN-gamma is the hydrolysis of membrane phosphatidylcholine by phospholipase A2.

The effects of interferon-beta on phorbol ester or calcium ionophore-induced intercellular adhesion molecule-I expression in epidermal carcinoma cells

Keratinocyte intercellular adhesion molecule (ICAM)-I expression is induced by interferon (IFN)-gamma. It has been previously reported that IFN-beta suppresses IFN-gamma-induced ICAM-I expression in A431 cells, a human squamous cell carcinoma cell line. In this study, the suppression mechanisms were investigated at the post second messenger level. Both 12-O-tetradecanoylphorbol-13-acetate (TPA) and calcium ionophore (A23187) induce ICAM-I expression in A431 cells. ICAM-I expression induced by either was not suppressed with cotreatment with IFN-beta. Furthermore, IFN-beta did not inhibit the translocation of protein kinase C (PKC) by TPA. It appears that the pathways involved in ICAM-I expression induced by activation of PKC or increased in intracellular Ca++ are not affected by IFN-beta.

Interferon-gamma induces phosphorylation of multiple small-molecular-weight proteins in U937 cells

This study examines the hypothesis that interferon-gamma (IFN-gamma) induces protein phosphorylation as part of the signal transduction pathway used to activate U937 cells. U937 cells labeled with 32Pi were treated with IFN-gamma, proteins were separated by two-dimensional polyacrylamide gel electrophoresis, and the pattern of protein phosphorylation was determined by autoradiography and computer-assisted two-dimensional densitometry. IFN-gamma (100 U/ml) induced phosphorylation of multiple proteins between 15 and 60 min, and the proteins were all dephosphorylated by 120 min. The pattern of proteins phosphorylated in the presence of ionomycin or PMA differed from that of IFN-gamma. Inhibition of protein kinase C activity by 1-(5-isoquinolinesulfonyl)2-methyl piperazine (H-7), inhibition of calcium-calmodulin-dependent protein kinase by N-(6-aminohexyl)-5-chloro-naphthalenesulfonamide (W-7), and inhibition of calcium redistribution by 8-(diethylamino)-octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8) did not inhibit the majority of IFN-gamma-induced protein phosphorylation. These data indicate that IFN-gamma induces protein phosphorylation in U937 cells by activation of a kinase different from, or in addition to, protein kinase C or calcium-calmodulin-dependent kinase.

Biphasic effect of camp-elevating agents on ICAM-1 expression stimulated by retinoic acid and interferonγ

Incubation of the human glioma cell line HS 683 in the presence of IFN-gamma or retinoic acid strongly stimulates the cell-surface expression of the intercellular adhesion molecule ICAM-1. We have investigated the role of the cAMP-mediated signal transduction pathway in this process and report that pharmacological agents which increased the intracellular levels of cAMP exhibited a biphasic action on ICAM-1 expression in human glioma cell line HS 683. Treatment for 1 hr with 25 microM forskolin or 1 mM isobutylmethylxanthine, or for 12 hr with 100 ng/ml pertussis toxin or 50 micrograms/ml cholera toxin transiently stimulated ICAM-1 expression with a maximal level of expression 8 hr post treatment, after which time ICAM-1 expression returned to the basal level. On the other hand, such pretreatments inhibited the inducing effects of either retinoic acid or IFN-gamma. Indeed, 24 hr after treatment with cAMP-elevating agents, both the retinoic-acid- and the IFN-gamma-induced ICAM-1 expression were inhibited by 60 to 80%, with a maximal 90 to 100% inhibition 72 hr post treatment. This inhibition of the cell-surface expression of ICAM-1 was confirmed at the mRNA level. The intracytoplasmic levels of cAMP were also quantified following treatments with forskolin, retinoic acid or IFN-gamma. In response to forskolin, cAMP levels increased 30-fold within 5 min, whereas a 10-fold increase occurred 60 min following treatment with 10 microM retinoic acid. Interferon gamma, in contrast, did not induce cAMP accumulation. These results were also correlated with an in vitro activation of adenylyl cyclase activity by retinoic acid and inhibition of this activity by IFN-gamma, in a dose-dependent and a GTP-dependent manner. Our results suggest that the suppression of IFN-gamma-induced ICAM-1 expression, obtained upon pre-treatment with cAMP-elevating agents, is due to direct antagonism with IFN-gamma action on adenylyl cyclase. However, the inhibition of retinoic-acid-induced ICAM-1 expression cannot be explained by the same mechanisms. The timing of adenylyl cyclase stimulation and cAMP accumulation, as well as the levels of cAMP accumulation, are probably involved in this inhibition. Our results also emphasize the fact that the induction of ICAM-1 expression is a multi-step process implicating different transductional signals among which cAMP might be involved as a second messenger.

Survival of the myeloid progenitor cell line FDC-P1 is prolonged by interferon-gamma or interleukin-4

Continuous proliferation of the immortalized myeloid progenitor cell line FDC-P1 depends on stimulation with either interleukin-3 (IL-3) or granulocyte-macrophage colony stimulating factor (GM-CSF). Two other cytokines, interferon-gamma (IFN-gamma) and IL-4, were found to prolong FDC-P1 survival for several days. Surviving cells incorporated [3H]thymidine and a minority completed up to 3 cell divisions before dying. This transient proliferative response was a direct effect of IFN-gamma and IL-4 since these cytokines did not induce production of detectable IL-3 or GM-CSF and the response was unaffected by cell concentration. IL-6, a constitutive product of FDC-P1 cells whose secretion was increased by IL-3, GM-CSF and IL-4 but not by IFN-gamma, was not responsible for the proliferative response. FDC-P1 lines that constitutively expressed the cell cycle-associated oncogene myc or the survival-associated oncogene bcl-2 also responded only transiently to IFN-gamma or IL-4, indicating that expression of these genes did not complement the signals delivered by IFN-gamma or IL-4. By contrast, the protein kinase C activator phorbol 12-myristate 13-acetate (PMA) prolonged survival of FDC-P1 cells on its own and potentiated the response to IFN-gamma or IL-4, although the combination of stimuli did not support long-term growth. It is concluded that IFN-gamma and IL-4 trigger only some of the signalling events that lead to mitogenesis; these events are complemented by stimulation with PMA but additional signals are required for sustained proliferation.

Modulation of the antigenic phenotype of human breast carcinoma cells by modifiers of protein kinase C activity and recombinant human interferons

In the present study we have analyzed the effect of a synthetic protein kinase C (PKC) activator 3-(N-acetylamino)-5-(N-decyl-N-methylamino)-benzyl alcohol (ADMB) and the natural PKC-activating tumor-promoting agents 12-O-tetradecanoylphorbol 13-acetate (TPA) and mezerein on the antigenic phenotype of T47D human breast carcinoma cells. All three agents increased the surface expression of the tumor-associated antigen BCA 225 and various cellular antigens, including HLA class II antigens, intercellular adhesion molecule 1 (ICAM-1) and c-erbB-2. Expression of the same antigens was also upregulated to various extents in T47D cells by recombinant fibroblast (IFN beta) and immune (IFN gamma) interferon. Shedding of BCA 225 from T47D cells was induced by TPA, mezerein, IFN beta and IFN gamma, whereas ADMB did not display this activity. The ability of ADMB, TPA and mezerein to modulate the antigenic phenotype of T47D cells appears to involve a PKC-mediated pathway, since the PKC inhibitor, H-7, eliminates antigenic modulation. In contrast, the ability of IFN beta and IFN gamma to enhance the synthesis, expression and shedding of BCA 225, as well as to enhance HLA class II antigens, c-erbB-2 and ICAM-1 expression, was either unchanged or modestly reduced by simultaneous exposure to H-7. Analysis of steady-state mRNA levels for HLA class I antigens, HLA class II-DR beta antigen, ICAM-1 and c-erbB-2 indicated that the ability of H-7 to inhibit expression of these antigens in TPA-, mezerein- and ADMB-treated cells was not a consequence of a reduction in the steady-state levels of mRNAs for these antigens. The results of the present investigation indicate that the biochemical pathways mediating enhanced antigenic expression in T47D cells induced by TPA, mezerein and the synthetic PKC activator ADMB are different from those induced by recombinant interferons. Furthermore, up-regulation of antigenic expression in T47D cells can occur by a PKC-dependent or a PKC-independent pathway.

Effect of cytokines and lipopolysaccharide on CD14 antigen expression in human monocytes and macrophages

The 52 kD myeloid membrane glycoprotein CD14 represents the receptor for complexes of lipopolysaccharide (LPS) and LPS binding protein (LBP); it is involved in LPS induced tumor necrosis factor-alpha production. Expression of CD14 increases in monocytes differentiating into macrophages, and it is reduced by rIFNg in monocytes in vitro. In the present study CD14 membrane antigen expression was investigated in cultures of human mononuclear leucocytes (PBL), in elutriated, purified monocytes, and in blood monocyte derived Teflon cultured macrophages. Cells were incubated for 15 or 45 h with rIL-1, rIL-2, rIL-3, rIL-5, rIL-6, rTNFa, rGM-CSF, rM-CSF, rTGFb1, rIFNa, lipopolysaccharide (LPS), and, as a control, rIFNg. The monoclonal antibodies Leu-M3 and MEM 18 were used for labelling of CD14 antigen by indirect immunofluorescence and FACS analysis of scatter gated monocytes or macrophages. IFNg concentrations were determined in PBL culture supernatants by ELISA. rIFNa and rIL-2 reduced CD14 in 15 and 45 h PBL cultures, an effect mediated by endogenous IFNg, since it was abolished by simultaneous addition of an anti-IFNg antibody. rIFNa and rIL-2 were ineffective in purified monocytes or macrophages. rIL-4 strongly reduced CD14 in PBL and purified monocytes after 45 h, whereas in macrophages the decrease was weak, although measurable after 15 h. The other cytokines investigated did not change CD14 antigen expression. Cycloheximide alone reduced CD14, but when added in combination with rIFNg the effect on CD14 downregulation was more pronounced. The effect of rIFNg on CD14 in PBL cultures was dose-dependently inhibited by rIL-4 and this inhibition is probably due to an IL-4 mediated blockade of IFNg secretion. LPS at a low dose increased CD14, at a high dose it produced a variable decrease of CD14 in PBL, which was probably due to LPS induced IFNg secretion. LPS strongly enhanced CD14 in 45 h cultures of purified monocytes. The results, showing that CD14 antigen expression is upregulated by LPS and downregulated by rIFNg and rIL-4, suggest that the LPS-LBP receptor is involved in the feedback response of IFNg and IL-4 to LPS stimulation.

Protein kinase C is involved in the early signals of interferon-alpha but not of interferon-gamma in U937 cells

Increasing interest is being focused on the role of protein kinase C (PKC) in the mode of action of interferons (IFNs). Here we report that IFN-alpha induced a transient translocation of PKC from the cytosol to the particulate fraction of U937 cells. In contrast, after IFN-gamma treatment, no significant change in PKC activity could be observed. IFN-induced changes in membrane potential were also examined by means of a potential sensitive oxonal dye and flow cytometry. Hyperpolarization was induced by both IFN-alpha and IFN-gamma. The protein kinase inhibitor H-7 blocked the hyperpolarization induced by IFN-alpha but not by IFN-gamma. These concordant results suggest that PKC is involved in the early signals of IFN-alpha but not of IFN-gamma in U937 cells.