G protein regulation of receptor signalling

Differential role of gpaB and sidA gene expressions in relation to virulence in Aspergillus species from patients with invasive aspergillosis

The virulence genes in invasive aspergillosis (IA) have not been analyzed adequately. The present study was designed to evaluate the expression of gpaB and sidA genes, which are important virulence genes in Aspergillus spp. from bronchoalveolar lavage (BAL) samples. Direct examination and culture on Czapek Agar and Sabouraud Dextrose Agar media were performed for 600 BAL specimens isolated from patients with possible aspergillosis. A Galactomannan ELISA assay was also carried out. The expression levels of the gpaB and sidA genes in isolates were analyzed using quantitative real-time PCR (qRT-PCR). We identified 2 species, including Aspergillus flavus (A. flavus) and Aspergillus fumigatus (A. fumigatus) in 25 positive samples for invasive aspergillosis as validated using GM-ELISA. A. flavus is the main pathogen threatening transplant recipients and cancer patients worldwide. In this study, A. flavus had low levels of the gpaB gene expression compared to A. fumigatus (p = 0.006). The highest sidA expression was detected in transplant recipients (p = 0.05). There was no significant correlation between sidA expression and underlying disease (p = 0.15). The sidA and gpaB gene expression patterns may provide evidence that these virulence genes play important roles in the pathogenicity of Aspergillus isolates; however, there are several regulatory genes responsible for the unexpressed sidA and gpaB genes in the isolates.

The putative guanine nucleotide exchange factor RicA mediates upstream signaling for growth and development in Aspergillus

Heterotrimeric G proteins (G proteins) govern growth, development, and secondary metabolism in various fungi. Here, we characterized ricA, which encodes a putative GDP/GTP exchange factor for G proteins in the model fungus Aspergillus nidulans and the opportunistic human pathogen Aspergillus fumigatus. In both species, ricA mRNA accumulates during vegetative growth and early developmental phases, but it is not present in spores. The deletion of ricA results in severely impaired colony growth and the total (for A. nidulans) or near (for A. fumigatus) absence of asexual sporulation (conidiation). The overexpression (OE) of the A. fumigatus ricA gene (AfricA) restores growth and conidiation in the ΔAnricA mutant to some extent, indicating partial conservation of RicA function in Aspergillus. A series of double mutant analyses revealed that the removal of RgsA (an RGS protein of the GanB Gα subunit), but not sfgA, flbA, rgsB, or rgsC, restored vegetative growth and conidiation in ΔAnricA. Furthermore, we found that RicA can physically interact with GanB in yeast and in vitro. Moreover, the presence of two copies or OE of pkaA suppresses the profound defects caused by ΔAnricA, indicating that RicA-mediated growth and developmental signaling is primarily through GanB and PkaA in A. nidulans. Despite the lack of conidiation, brlA and vosA mRNAs accumulated to normal levels in the ΔricA mutant. In addition, mutants overexpressing fluG or brlA (OEfluG or OEbrlA) failed to restore development in the ΔAnricA mutant. These findings suggest that the commencement of asexual development requires unknown RicA-mediated signaling input in A. nidulans.

Lovastatin inhibits G1/S transition of normal human B-lymphocytes independent of apoptosis

Lovastatin is a potent inhibitor of protein prenylation, and it has been reported to have pleiotropic cellular effects. In the present study we have elucidated the effects of lovastatin on cell cycle progression and apoptosis of normal human B-lymphocytes. When added to B-lymphocytes stimulated with anti-immunoglobulin (anti-mu) and SAC, lovastatin (20 microM) inhibited the cells in the late G1 phase of the cell cycle. Thus, no early activation parameters such as Ca(2+) flux or MYC induction were affected by lovastatin, whereas progression of cells into the second cell cycle as well as DNA synthesis was markedly reduced. We therefore examined the effects of lovastatin on components of the cell cycle machinery responsible for regulating the G1/S transition. We demonstrated that pRB phosphorylation, cdk2 activity needed for this phosphorylation, and the levels of cyclin A, D, and E were inhibited after 24 h of lovastatin treatment, while the levels of p27(Kip1) were elevated. There was no effect on p21(Cip1), cyclin D2, cdk4, and cdk6. These data are consistent with the cells being inhibited by lovastatin between 24 and 32 h into G1. Lovastatin added to stimulated B-cells in late G1 still inhibited the DNA synthesis by 60%, but at this point only minor effects were noted on the cell cycle machinery. We therefore looked for induced apoptosis as an explanation for reduced S-phase entry of the cells. However, despite the ability to enhance the apoptosis of unstimulated B-cells from 48 to 61% as judged by the TUNEL method, lovastatin only marginally affected apoptosis when administered to stimulated B-cells. Thus, it appears that accelerated apoptosis cannot account for the effect of lovastatin on cell cycle progression.

The N-formyl methionyl peptide, formyl-methionyl-leucyl phenylalanine (fMLF) increases the lateral diffusion of complement receptor 1 (CR1/CD35) in human neutrophils; a causative role for oxidative metabolites?

The effects of the N-formyl methionyl peptide, formyl-methionyl-leucyl phenylalanine (fMLF) on the lateral mobility of the complement receptor type 1 (CR1/CD35) in glass-adherent human neutrophils were investigated, using fluorescence recovery after photobleaching (FRAP) and confocal microscopy (CSLM). It was found that addition of 0.1-1 microM fMLF increased the diffusion constant (D) of CR1/CD35 to 167-228% of controls. No effect was observed on the receptor distribution or the mobile fraction of receptors. The effect of fMLF on the lateral diffusion of CR1/CD35 could be totally inhibited by addition of pertussis toxon (PD, 250 ng/ml) or of the free radical scavenger enzymes superoxide dismutase (SOD, 2000 U/ml) and catalase (CAT, 200 U/ml), added together the results show that oxidative metabolites produced by neutrophils in response to fMLF can modulate CR1/CD35 diffusion, and indicate a regulatory role for oxygen radicals in phagocytosis.

Dissection of lymphocyte function-associated antigen 1-dependent adhesion and signal transduction in human natural killer cells shown by the use of cholera or pertussis toxin

The effect of the guanosine triphosphate-binding protein (G-protein) inhibitors cholera toxin (Ctx) and pertussis toxin (Ptx) has been analyzed on lymphocyte function-associated antigen 1 (LFA-1)-dependent adhesion and signal transduction in human natural killer (NK) cells. Ctx, but not Ptx, inhibited the LFA-1-dependent adhesion of NK cells to tumor target cells which constitutively express the intercellular cell adhesion molecule-1 (ICAM-1) and to NIH/3T3 mouse fibroblasts stably transfected with human ICAM-1. This effect was detectable only by the use of the entire Ctx but not of the Ctx B subunit. In addition, Ctx could inhibit both NK cell binding and spreading to purified ICAM-1 protein. NK cell treatment with Ctx modified neither the surface expression of LFA-1 nor its Mg2+ binding site. These findings, together with the absence of any detectable effect of Ctx on the constitutive phosphorylation of LFA-1 alpha, suggests that this toxin modifies the avidity of LFA-1 for ICAM-1 by acting on LFA-1-cytoskeletal protein association. Unlike Ctx, Ptx did not affect NK cell adhesion. The effects of Ctx and Ptx are unlikely to depend on intracellular levels of cyclic adenosine 3',5'-monophosphate (cAMP), since a strong increase of cAMP was induced by both toxins. Moreover, this was confirmed by the observation that the LFA-1-dependent adhesion was not inhibited by the adenylate cyclase activator forskolin (FSK), the phosphodiesterase inhibitor isobutyl-1-methylxanthine (IBMX), or both, which increase intracellular cAMP levels. Unlike the differential effect on cell adhesion, both the intracellular calcium [Ca2+]i increase and phosphoinositide breakdown mediated via LFA-1 were consistently inhibited in a dose-dependent manner by both Ctx and Ptx. Also in this case, the inhibitory effect did not depend on an increase of intracellular cAMP as indicated by NK cell treatment with FSK, IBMX, or both. Further evidence of the involvement of G-proteins in LFA-1-mediated signal transduction was the inhibitory effect of the GDP analog guanosine-5'-O-2-thiodiphosphate (GDP beta S) on LFA-1-mediated calcium mobilization. Taken together, our data provide evidence that the LFA-1-mediated NK cell adhesion and signal transduction are partially independent phenomena which may be regulated by different G-proteins.

Pertussis toxin-sensitive GTP-binding proteins regulate activation-induced apoptotic cell death of human natural killer cells

Apoptosis of natural killer (NK) cells can be induced by non-specific physical damage (UV irradiation, heat shock) or by simultaneous ligation of the CD16 and the interleukin-2 receptor (IL-2R) molecules, but not with either anti-CD16 or IL-2 alone. Whereas blockade of GTP-binding protein (G protein)-mediated signal transduction using ADP-ribosylating bacterial toxins or the GTPase-resistant GTP analog guanosine 5'-0-(3-thiotriphosphate (GTP gamma S) does not affect non-specific induction of NK cell apoptosis, such interventions do inhibit induction of apoptosis by anti-CD16/IL-2. The G proteins involved in the regulation of activation-induced NK apoptosis are sensitive to pertussis toxin (PTX) and to the non-specific GTP analog GTP gamma S but not to cholera toxin, Pseudomonas exotoxin A or diphtheria toxin. A pertussis toxin mutant that lacks ADP-ribosylating activity, but conserves the membrane translocating and T cell-mitogenic effects of the native molecule, fails to inhibit NK apoptosis. To exert their apoptosis-inhibitory effect, PTX and GTP gamma S must be employed before cells are activated. Later addition has no effect, suggesting the implication of G proteins in the transmission of apoptosis-inducing signals, but not in the effector stage of apoptosis. Pre-incubation with PTX or GTP gamma S does not affect the activation of NK cells by CD16 cross-linking, IL-2 stimulation- or both, as assessed by the induction of CD69 expression, protein tyrosine phosphorylation and calcium mobilization. Moreover, neither PTX nor GTP gamma S compromise the effector function of NK cells or the susceptibility of target cells to NK-mediated lysis. These data suggest apoptosis as a novel mechanism by which NK responses may be controlled in vivo, as well as an experimental and therapeutical strategy to counteract endogenous down-regulation of NK responses.

Synergy between signal transduction pathways is obligatory for expression of c-fos in B and T cell lines: implication for c-fos control via surface immunoglobulin and T cell antigen receptors

Expression of the protooncogene c-fos is controlled by three main regulatory pathways involving kinase C, cAMP, and calcium. Kinase C mediates its effects via phosphorylation of serum response factor (SRF) which interacts with the serum response element (SRE); cAMP and calcium mediate their effects via phosphorylation of CREB (cAMP regulatory element binding protein) presumably by activation of a protein kinase A or calmodulin-regulated kinase. We have examined the function of these elements in Burkitt's lymphoma cells (Ramos and Daudi) as well as a T lymphocytic cell line (Jurkat). We have found that stimulation of any one of these pathways alone has little or no effect on c-fos induction. However, kinase C activation (PMA stimulation) combined with either cAMP (forskolin plus MIX) or calcium stimulation (ionophore) leads to greatly enhanced c-fos induction. By contrast, cAMP in the presence of calcium shows no synergy in c-fos induction. Okadaic acid augments PMA- as well as calcium-mediated activation of c-fos, and has little or no effect when combined with cAMP. The main difference between Ramos (B cells) and Jurkat (T cells) in the regulation of c-fos is that cAMP plus calcium is strongly synergistic in Jurkat and is without effect in Ramos. Analysis of AP-1 activity using gel mobility shift assays confirms that the requirements for synergy in c-fos mRNA induction are paralleled by requirements for synergy in induction of AP-1 activity. Signaling in B cells due to anti-Ig stimulation involves both kinase C activation and release of intracellular calcium, and results in c-fos mRNA induction. Our results indicate that synergy between the kinase C activation and calcium is needed for efficient c-fos induction since neither of these two alone induces c-fos well. That synergy of signaling pathways is relevant for the anti-Ig induction of c-fos is supported by the fact that cAMP-inducing agents and okadaic acid further enhance anti-Ig induction of c-fos. These results suggest that cell-specific patterns of synergy are an essential feature for c-fos induction and may be relevant for c-fos control through B and T cell antigen receptors.

Co-stimulation of T cells via CD28 inhibits human IgE production; reversal by pertussis toxin

In lymphocyte cultures, IgE production was achieved by stimulating T cells with anti-CD2 and IL-2. Here we show that anti-CD28, in the presence or absence of IL-2, reduces this IgE production approximately 10-fold. This inhibition of IgE production was almost completely reversed by Pertussis toxin (PT). PT had no effect on IgE production when the cells were stimulated in the absence of anti-CD28. No major effects of PT were found on IgM production. PT had no effect on purified B cells, stimulated with IL-4 and anti-CD40. In the presence of saturating amounts of rIL-4 similar results were obtained, albeit the absolute amounts of IgE produced were higher in all situations. Furthermore, PT-induced IgE production was still dependent on IL-4, as was evident from experiments in which anti-IL-4 was added to the culture. The IgE enhancing effect was dependent on the adenosine diphosphate (ADP)-ribosyltransferase activity of PT, because a mutant molecule lacking this activity was not able to restore anti-CD28-induced inhibition of IgE synthesis. Thus, we show that co-stimulation with anti-CD28 causes an inhibition of T cell-dependent IgE production by B cells, which inhibition can be specifically overcome by PT. An analysis of the molecular pathways underlying this phenomenon may contribute to our understanding of the regulation of IgE synthesis in (patho)physiological conditions.

Signaling pathways activated by protein tyrosine phosphorylation in lymphocytes

Antigen and cytokine receptors induce rapid tyrosine phosphorylation of receptor subunits, other membrane proteins, and signaling components. Each receptor induces phosphorylation of a number of proteins. Although there is often overlap between targets of different receptors, any given receptor only induces phosphorylation of a subset of possible targets. How this choice of targets is achieved for these receptors is not yet understood. The cellular events downstream of some signaling components are beginning to come into view. Recent progress in these areas is discussed.

Mechanisms of nonopsonic phagocytosis of Pseudomonas aeruginosa

The interaction of the macrophage cell line P388D1 with Pseudomonas aeruginosa in the absence of stimulators or opsonins led to substantial association of bacteria, as judged by visual counting and FACScan assays. This association was observable within 5 min of addition of bacteria, could not be disturbed by exhaustive washing, and occurred with pilus- or flagellum-deficient mutants but not with rpoN mutants, which have been proposed to lack a secondary adhesin. In contrast, specific antibody was capable of causing similar enhancement of bacterial uptake regardless of the rpoN phenotype. Fibronectin stimulated uptake of bacteria with the pilus as an adhesin, and stimulation was observable within 5 min. Both fibronectin-enhanced and antibody-opsonized uptake were susceptible to inhibition by pertussis toxin but not by cholera toxin. The influence of fibronectin on P388D1 cells was distinguishable from that of lipopolysaccharide, which caused substantial morphological changes in cells. Although lipopolysaccharide stimulated bacterial uptake, it actually suppressed fibronectin-mediated enhancement of uptake at high concentrations.

Agonistic and antagonistic effects of cholera toxin on human B lymphocyte proliferation

In our attempts to elucidate the mechanisms regulating the IL2- and IL4-induced proliferation of human B lymphocytes, we studied the effects of cholera toxin (CT) and other agents increasing adenosine 3', 5'-cyclic monophosphate (cAMP) levels on tonsil B cells activated through their antigen receptors. CT enhanced proliferation of anti-IgM-costimulated B cells in a dose-dependent fashion (1 ng/ml to 10 micrograms/ml), a property shared in part by other agents inducing cAMP, such as forskolin, prostaglandin E2 and dibutyryl-cAMP, but not by the purified B subunit of CT. However, when cytokine-dependent proliferation was studied, CT and cAMP-increasing agents inhibited IL2-induced DNA synthesis of anti-IgM-activated B cells. This blockade was not due to a modification of the kinetics of proliferation, but was rather a consequence of partial inhibition of IL2 receptor expression. In contrast CT and cAMP-elevating agents enhanced the latest phases of the IL4-induced DNA synthesis of anti-IgM-activated B cells. These results indicate that CT displays agonistic and antagonistic effects on human B cell proliferation, most of these effects being reproduced by cAMP-elevating agents. Thus limited activation of the cAMP pathway in B cells may facilitate the development of TH2-type immune responses.

Multiple forms of the G protein-related beta subunit in Daudi lymphoblastoid cells

We have explored the forms of the G protein-related beta subunit which are present in Daudi lymphoblastoid cells. Northern blotting with labeled beta-1 and beta-2 probes indicates that two messages of 3.3 kb and 1.7 kb are present for both beta-1 and beta-2, implying that multiple forms of the beta subunit are present. Antibodies were raised against two peptides of the beta subunit (residues 1-23 and 127-145). Both antibodies detected subunits at 35 kDa and 31 kDa, of which the 35-kDa form predominates in the membrane fraction and the 31-kDa one in the cell cytosol. Crosslinking of the membrane fraction with the cleavable crosslinker (DTSSP) caused a simultaneous diminution in the 31-kDa form while increasing the amount of the 35-kDa form--a pattern which was reversed upon the reduction of these crosslinks with DTT. Studies of the soluble form indicate that this is truly a soluble protein since centrifugation at 200,000 x g for 2 h did not diminish the levels of the protein in the soluble fraction. Sedimentation analysis indicates that the soluble beta-homologue is found in fractions which overlap with those which contain the mu chain of immunoglobulin at a position clearly distinct from the expected positions of free mu or free beta. Our results suggest that at least two forms of a subunit which is closely related to, or identical with, the beta subunit of G proteins are present in Daudi cells.

Sulphasalazine inhibition of human granulocyte activation by inhibition of second messenger compounds

The effects of sulphasalazine on the production of second messenger compounds in human granulocytes have been characterised by various stimuli. The increases in cytosolic calcium, inositol trisphosphate, diacylglycerol, and phosphatidic acid (all important mediators of intracellular signal transduction) triggered by stimulation were inhibited by sulphasalazine. The metabolites 5-amino-salicylic acid and sulphapyridine were less potent inhibitors than the mother compound. It is concluded that sulphasalazine inhibits the synthesis of phosphoinositide derived second messenger compounds at the level of phospholipase C or its regulatory guanosine 5'-triphosphate (GTP) binding protein. Inhibition of phosphatidic acid synthesis was either due to the same mechanism, or to interaction with a phospholipase D regulating GTP binding protein.

Tyrosine phosphorylation and the mechanism of signal transduction by the B-lymphocyte antigen receptor

Lymphocytes provide a powerful defense against infectious agents with their exquisite ability to distinguish between macromolecules of the host and macromolecules of foreign invaders. This ability derives from the antigen receptors, which are created from precursor minigenes by a series of genetic-recombination reactions [1, 2] and from cellular mechanisms that inactivate lymphocytes expressing self-reactive antigen receptors [3, 4]. Central to the problem of distinguishing self from non-self is the means by which these antigen receptors recognize antigen and transmit the information of that recognition to the interior of the cell. This information ultimately leads to lymphocyte activation or inactivation, depending upon the context. In this review, I shall summarize recent advances in understanding the structural elements of the antigen receptor complex of B lymphocytes and in understanding the signal-transduction events initiated by this receptor.

The role of G-proteins versus protein tyrosine kinases in the regulation of lymphocyte activation

The relative roles of G-proteins and protein tyrosine kinases (PTKs) in the regulation of antigen receptor-mediated signalling in B and T cells is controversial. As they, and the biochemical events they control, are potential targets for intervention in various immune dysfunctions, the resolution of the controversy is of great interest. Here, Margaret Harnett and Kevin Rigley provide a timely assessment of current understanding, and propose a model for the interaction of G-proteins and PTKs in antigen receptor-mediated signalling.

Inhibition or activation of human T cell receptor transfectants is controlled by defined, soluble antigen arrays

We present evidence that direct T cell receptor (TCR) occupancy by antigen can either activate or inhibit T cells, depending upon whether or not a threshold number of local TCRs are crosslinked by multivalent arrays of the antigen. Variants of Jurkat cells were previously transfected with TCR alpha and beta chains that bind fluorescein, yielding FL-TCR+ human T cells. The transfectants are activated upon binding soluble multivalent antigen arrays at concentrations well below those required for monovalent interactions. This activation, measured by calcium fluxes and interleukin 2 (IL-2) production, indicates the superior binding avidity of multivalent ligands. Smaller, less multivalent arrays do not activate the cells, but antagonize larger arrays, demonstrating that antigen can bind TCR as either agonist or antagonist. The balance between activation and inhibition depends upon antigen array size, ligand valence, and concentration, indicating that a threshold extent of receptor crosslinking, and not individual perturbations of single TCR, is required for activation by antigen. Approximately 100 stimulatory arrays specifically bind per FL-TCR+ cell at concentrations where IL-2 production is half-maximal.

Evidence for defective transmembrane signaling in B cells from patients with Wiskott-Aldrich syndrome

B lymphocytes from patients expressing the X chromosome-linked immune deficiency disorder, Wiskott-Aldrich syndrome (WAS), fail to produce antibodies in response to stimulation with polysaccharides and other type-2 T cell-independent antigens. To investigate whether this abnormality reflects a defect in the signal transduction cascade normally triggered by ligation of surface immunoglobulin (sIg) on B cells, we have examined early signaling events induced by anti-Ig antibody stimulation of EBV B lymphoblastoid cell lines from WAS patients and healthy controls. Despite the expression of comparable levels of sIg and sIgM on WAS and control EBV B cells, WAS cells failed to manifest the increased proliferation in response to anti-Ig treatment observed in the control cell lines. WAS and control EBV B cells also differed in the magnitude of the change in cytosolic free calcium ([Ca2+]i) induced by sIg ligation; WAS cells showed either markedly diminished or no changes in [Ca2+]i levels whereas control EBV B cells consistently showed increases in [Ca2+]i. Anti-Ig-induced changes in inositol phosphate release were also markedly reduced in WAS compared with control cells. As protein tyrosine phosphorylation is thought to represent a proximal event in the activation of B cells, inducing increases in [Ca2+]i by virtue of tyrosine phosphorylation of phospholipase C (PLC)-gamma, profiles of protein tyrosine phosphorylation and expression of tyrosine-phosphorylated PLC-gamma 1 were compared between WAS and normal EBV B cells before and after sIg cross-linking. These studies revealed that in addition to defective mobilization of Ca2+, the WAS cells manifested little or no increase in tyrosine phosphorylation of PLC-gamma 1 or other intracellular proteins after sIg ligation. Together these results indicate the association of WAS with a defect in the coupling of sIg to signal transduction pathways considered prerequisite for B cell activation, likely at the level of tyrosine phosphorylation. The abnormalities observed in these early transmembrane signaling events in WAS EBV B cells may play a role not only in the nonresponsiveness of WAS patient B cells to certain T independent antigens, but also in the genesis of some of the other cellular deficits exhibited by these patients.

Elimination from peripheral lymphoid tissues of self-reactive B lymphocytes recognizing membrane-bound antigens

The long-standing hypothesis that tolerance to self antigens is mediated by either elimination or functional inactivation (anergy) or self-reactive lymphocytes is now accepted, but little is known about the factors responsible for initiating one process rather than the other. In the B-cell lineage, tolerant self-reactive cells persist in the peripheral lymphoid organs of transgenic mice expressing lysozyme and anti-lysozyme immunoglobulin genes, but are eliminated in similar transgenic mice expressing anti-major histocompatibility complex immunoglobulin genes. By modifying the structure of the lysozyme transgene and the isotype of the anti-lysozyme immunoglobulin genes, we demonstrate here that induction of anergy or deletion is not due to differences in antibody affinity or isotype, but to recognition of monomeric or oligomeric soluble antigen versus highly multivalent membrane-bound antigen. Our findings indicate that the degree of receptor crosslinking can have qualitatively distinct signalling consequences for lymphocyte development.

A 32-kD GTP-binding protein associated with the CD4-p56lck and CD8-p56lck T cell receptor complexes

The guanosine triphosphate (GTP)-binding proteins include signal-transducing heterotrimeric G proteins (for example, Gs, Gi), smaller GTP-binding proteins that function in protein sorting, and the oncogenic protein p21ras. The T cell receptor complexes CD4-p56lck and CD8-p56lck were found to include a 32- to 33-kilodalton phosphoprotein (p32) that was recognized by an antiserum to a consensus GTP-binding region in G proteins. Immunoprecipitated CD4 and CD8 complexes bound GTP and hydrolyzed it to guanosine diphosphate (GDP). The p32 protein was covalently linked to [alpha-32P]GTP by ultraviolet photoaffinity labeling. These results demonstrate an interaction between T cell receptor complexes and an intracellular GTP-binding protein.

Roles of human peripheral blood leukocyte protein kinase C and G proteins in inflammatory mediator release by isogenic Escherichia coli strains

The signal transduction pathway (protein kinase C [PKC], calcium influx, and G protein involvement) was studied with isogenic Escherichia coli strains expressing different types of adhesins (MSH+/- MS-Fim+/-, P-MRH+/- P-Fim+/-, and S-MRH+/- S-Fim+/-) or varying only in the expression of E. coli alpha-hemolysin. As target cells, human polymorphonuclear granulocytes (PMN) and a lymphocyte-monocyte-basophil (LMB) cell suspension were used. The alpha-hemolysin-producing (Hly+) strain E. coli K-12(pANN5211) induced calcium influx in a dose-dependent manner in both cell types. No calcium influx was detected after stimulation with the hemolysin-negative (Hly-) E. coli bacteria independent of the type of fimbriae. With Hly+ bacteria, a dose-dependent activation of PKC was observed in both cell types. The Hly- E. coli K-12 induced PKC to a lesser degree, expressing kinetics different from those of E. coli K-12(pANN5211) (Hly+). E. coli MSH+ MS-Fim+ was the most potent activator for PKC. Membrane preparations from leukocytes stimulated with Hly+ E. coli K-12(pANN5211) showed increased binding of [3H]guanylylimidodiphosphate, a nonhydrolyzable GTP analog, and increased GTPase activity compared with leukocytes stimulated with Hly- E. coli K-12. The amounts of GTPase activation and [3H]guanylylimidodiphosphate binding were similar for all Hly- E. coli bacteria in human PMN as well as in human LMB; no activation was obtained for E. coli bacteria without any type of fimbriae. GTP-gamma-S, a nonhydrolyzable GTP analog, inhibited the leukotriene B4 (LTB4) generation from human PMN by Hly- bacteria, unlike E. coli K-12(pANN5211). However, in the presence of NaF, a predominant activator of Gi, LTB4 generation by Hly+ and by Hly- bacteria was significantly enhanced. For LMBs only LTB4 generation by Hly+ bacteria was increased in the presence of GTP-gamma-S. NaF decreased the chemiluminescence induced by all E. coli strains. Our results thus indicate that (i) Hly+ and Hly- bacteria induce the activation of distinct G proteins, e.g., Gi, to different degrees, (ii) LTB4 generation and chemiluminescence response are differently regulated, and (iii) in comparison with PMN, a different signal transduction pathway is activated by E. coli bacteria in LMBs.

NF-kappa B activation by tumor necrosis factor alpha in the Jurkat T cell line is independent of protein kinase A, protein kinase C, and Ca(2+)-regulated kinases

NF-kappa B is a DNA-binding regulatory factor able to control transcription of a number of genes, including human immunodeficiency virus (HIV) genes. In T cells, NF-kappa B is activated upon cellular treatment by phorbol esters and the cytokine tumor necrosis factor alpha (TNF alpha). In the present work, we investigated the molecular events leading to NF-kappa B activation by TNF alpha in a human T cell line (Jurkat) and its subclone JCT6, which presents a deficiency in the PKA transduction pathway. We found that in both cell lines, both phorbol ester and TNF alpha were able to activate NF-kappa B. Phorbol activation was positively modulated by Ca2+ influx while TNF alpha activation was not. Furthermore, while PMA activation was inhibited by the PKC inhibitor staurosporin, the TNF alpha effect was unchanged. TNF alpha did not activate cAMP production and its signal was not modulated by cAMP activators. Moreover, cAMP activators did not activate NF-kappa B in Jurkat cells. Thus, TNF alpha-induced NF-kappa B activation was found to be mediated by none of the major signal-mediating kinases such as protein kinase C (PKC), protein kinase A, or Ca(2+)-regulated kinases. Furthermore, we found that cytoplasmic acidification facilitated NF-kappa B activation by both TNF alpha and PKC, by a mechanism that increases NF-kappa B/I kappa B dissociation without affecting the NF-kappa B translocation step.

Modification of some lymphocyte functions in vitro by opioid receptor agonists and antagonist in chronic uremic patients and healthy subjects

In ten chronic uremic patients on regular hemodialysis treatment in vitro experiments revealed that stimulation of opioid receptors with morphine did not significantly change the mitogen-induced proliferative response of peripheral blood lymphocytes and interleukin-2 (IL-2) receptor expression on PHA-stimulated lymphocytes, while it appreciably decreased surface transferrin (Trf) receptor expression on PHA-stimulated lymphocytes. However, metenkephalin inhibited mitogen-induced proliferation and surface Trf receptor expression on uremic lymphocytes without affecting IL-2 receptor expression on PHA-stimulated cells. In ten healthy subjects opioid receptor agonists did not significantly affect mitogen-induced proliferation of lymphocytes, except for the inhibitory effect of 10(-8) M morphine in relation to lymphocytes stimulated with an optimal pokeweed mitogen (PWM) concentration. At the same time, opioid receptor agonists depressed surface IL-2 and Trf receptor expression on PHA-stimulated normal lymphocytes. In most of our experiments naloxone itself, a non-selective competitive opioid receptor antagonist, decreased mitogen-induced lymphocyte proliferation and IL-2 and Trf receptor expression on PHA-stimulated lymphocytes. Moreover, most frequently naloxone did not reverse inhibitory effects of opioid receptor agonists on lymphocytes. The results seem to indicate that opioid receptor stimulation by high metenkephalin concentrations, which are observed in the uremic blood plasma, may share the responsibility for immunodeficiency in chronic uremic patients. Next, in the presence of opioid receptor agonists directions of changes in the mitogen-induced proliferative response may not follow the alterations of IL-2 and Trf receptor expression on both uremic and normal lymphocytes. Finally the results also suggest that naloxone may possibly exert effects which are independent of its action on opioid receptors on lymphocytes.

Mutations of immunoglobulin transmembrane and cytoplasmic domains: effects on intracellular signaling and antigen presentation

The membrane-bound form of immunoglobulin serves as an antigen-specific receptor for B cells mediating signal transduction and antigen presentation. We have developed an assay that reconstitutes both these physiologic responses with respect to the antigen phosphorylcholine. By introducing specific mutations in the human Ig mu chain gene, we have shown that certain transmembrane residues and the short cytoplasmic domain are crucial for these two activities. Moreover, elimination of a single transmembrane hydroxyl group severely inhibits antigen presentation without affecting signal transduction, suggesting that these two functions are mediated by different protein interactions.

Characterization of functional GTP binding proteins in Jurkat T cell mutants lacking either CD3-Ti or CD2 surface receptors

G proteins are membrane-bound molecules involved in coupling of surface receptors with signal transduction effector systems in multiple cell types including T lymphocytes. Given that mature T cells which lack antigen receptors (CDl-Ti) are refractory to stimulation through CD2 or other accessory molecules, T cell receptor components likely play a critical role in coupling surface receptors with signal transduction effectors. It has recently been proposed that modulation of T cell receptor components with MAbs results in a physical loss or functional inactivation of G protein(s). In view of the importance of the T cell activation process, we herein examined G proteins in untreated or antibody-modulated Jurkat T cells as well as in genetic variants lacking either CD3-Ti or CD2 surface receptors. 43- and 41-kDa G protein alpha chains are ADP ribosylated with cholera (CTX) and pertussis (PTX) toxins, respectively, in wild type and receptor minus cell populations. In the wild type Jurkat cell line as well as in CD3- and CD2- variants, AlF4- can activate the G protein(s) presumably associated with phospholipase C to generate polyphosphoinositide turnover as well as an increase in cytoplasmic free calcium ions. Furthermore, G protein(s) linked to adenylylcyclase, a pathway which inhibits T lymphocyte activation, can be directly activated with CTX in the absence of CD3-Ti or CD2 on the membrane. Importantly, AlF4- can also induce polyphosphoinositide turnover in Jurkat cells whose T cell receptor proteins have been modulated with anti-CD3 MAb. These data provide functional and biochemical evidence that at least certain G proteins are intact in the absence of surface expression of CD3-Ti or CD2 molecules and imply that CD3-Ti desensitization is not singularly due to G protein loss.

Interleukin (IL)-8-induced in vitro human lymphocyte migration is inhibited by cholera and pertussis toxins and inhibitors of protein kinase C

To further investigate the intracellular mechanisms involved in IL-8-induced human mixed peripheral blood lymphocyte (PBL) migration, the effects of pertussis toxin (PTX), cholera toxin (CTX), and protein kinase C (pkC) inhibitors were investigated. Potent inhibition of IL-8-induced PBL migration was observed following exposure of PBL to PTX and CTX (1 pM to 0.1 microM), 8-bromo cyclic adenosine monophosphate (cAMP; 1 nM to 1 microM), H7 (1 pM to 0.1 microM), sphingosine (0.1 microM to 100 microM) and the novel pkC inhibitors Ro 31-7549 and Ro 31-8220 (10 pM to 1 microM) for 10 min. Following incubation of the lymphocytes for 30 min in the presence of the direct activators of pkC, 1-oleoyl-2-acetyl-sn-glycerol (OAG) and 1,2-dioctanoyl-sn-glycerol (DOG; 10nM to 100 microM), there was a reversal of the effects of a suboptimal dose of the specific pkC inhibitors Ro 31-7549 and Ro 31-8220. These results suggest that intracellular signals transduced during IL-8-induced in vitro PBL migration may involve pertussis and cholera toxin-sensitive G protein subunits and activation of pkC, processes which are characteristically linked to receptor binding.

Pertussis toxin B-subunit-induced Ca2(+)-fluxes in Jurkat human lymphoma cells: the action of long-term pre-treatment with cholera and pertussis holotoxins

The exotoxins of Bordetella pertussis and Vibrio cholera have been used to investigate signal transduction in the human T-cell lymphoma Jurkat. Stimulation of the cells, leading to an increase in cytoplasmic free calcium, could be achieved by the anti-T-cell receptor complex antibody OKT3 and by pertussis holotoxin (PTHT), or its B-subunit (PTB), but not by cholera holotoxin (CTHT) or its B-subunit (CTB). Both holotoxins ADP-ribosylated specifically G-proteins in the plasma membrane of intact cells, while their B-subunits had no ADP-ribosyltransferase activity. Incubation of the cells with CTHT led to a state of unresponsiveness to all stimulants. CTB was without any effect, indicating that the ADP-ribosyltransferase activity of cholera toxin (located in the A-subunit of the holotoxin) was necessary for the inhibition of cellular signalling. The inhibitory effect of cholera toxin on the pertussis toxin action was not due to a blockade of pertussis toxin interaction with the cell surface, because pertussis toxin was still able to ADP-ribosylate membrane proteins in cholera toxin treated intact cells. In addition, the cholera toxin mediated inhibition was not due to elevated levels of cyclic-AMP, as forskolin (a direct activator of the adenylate cyclase) and no inhibitory effect. The stimulating effect of PTHT was independent of its ADP-ribosyltransferase activity, because it could also be obtained by the B-subunit alone. In addition, the increase of cytoplasmic free calcium after stimulation by PTHT clearly preceded the ADP-ribosylation. Pre-treatment with PTHT, PTB or OKT3, led to a long lasting increase in the level of intracellular Ca2+ in Jurkat cells, which could not, therefore, be stimulated further. Inhibition by cholera holotoxin of the stimulation by OKT3 and pertussis toxin (PTHT and PTB) imply that the mitogenic effect of pertussis toxin is perhaps mediated via the T-cell antigen receptor signalling cascade. The presented data do not support the idea that a pertussis toxin-sensitive G-protein is involved in coupling the T-cell antigen receptor to the phospholipase C.

Activation of the respiratory burst in murine phagocytes by certain guanine ribonucleosides modified at the 7 and 8 positions: possible involvement of a pertussis toxin-sensitive G-protein

The capacity of certain guanine ribonucleosides (modified at the 7 and/or 8 positions) to enhance the respiratory burst of murine peritoneal phagocytes was evaluated. The results show that 8-mercaptoguanosine, 8-bromoguanosine, 7-methyl-8-oxoguanosine and 7-thia-8-oxoguanosine, when injected intraperitoneally into mice, induced peritoneal phagocytes to generate reactive oxygen species as early as 1 h after injection. In vivo administration of the nucleosides induced higher levels of phagocyte activation than in vitro treatment with the same nucleosides. However, the addition of interferon alpha/beta in vitro significantly increased the magnitude of phagocyte activation by the nucleosides, suggesting an important role for cytokines/lymphokines in the nucleoside-induced phagocyte activation in vivo. Furthermore, pre-treatment of phagocytes in vitro with Bordetella pertussis toxin, before treatment with the guanosines, inhibited their capacity to induce the respiratory burst. These observations establish these low-molecular-weight compounds as interesting probes for the study of stimulus-response coupling in phagocytes.

Inhibitors of arachidonic acid lipoxygenase impair the stimulation of inositol phospholipid hydrolysis by the T lymphocyte mitogen phytohaemagglutinin

Piriprost and nordihydroguiaretic acid (NDGA), specific inhibitors of arachidonate lipoxygenase, inhibited phytohaemagglutinin (PHA)-stimulated breakdown of inositol lipids in human T lymphocytes. The dual inhibitors eicosatetraynoic acid (ETYA) and BW 755C, which inhibit both lipoxygenase and cyclooxygenase, also had similar actions, whereas indomethacin and acetylsalicyclic acid, which inhibit cyclooxygenase alone, did not. The effects of lipoxygenase inhibitors and dual inhibitors were reversible. These agents did not inhibit phosphatidylinositol-4,5-bisphosphate-specific phospholipase C (PIP2-PLC) in vitro. Bromophenacyl bromide, and irreversible inhibitor of phospholipase A2, also abolished PHA-stimulated inositol lipid breakdown without affecting PIP2-PLC in vitro. The results are consistent with a role for the PHA-stimulated generation of arachidonic acid and its conversion to lipoxygenase metabolites (e.g. leukotrienes and/or hydroxyeicosatetraenoic acids) as intermediate steps in the signal transduction pathway between cell-surface mitogen receptors and the stimulation of PIP2-PLC in lymphocytes.

Analysis of signaling via surface immunoglobulin receptors on B cells from CBA/N mice

CBA/N mice, which carry the xid immunodeficiency, lack a mature subpopulation of B cells. The residual B cells in these mice do not make antibodies to type-2 T-independent antigens, nor do they synthesize DNA in response to mitogenic forms of anti-Ig antibodies. It is therefore an attractive hypothesis that the surface immunoglobulin receptors (sIgR) on xid B cells signal abnormally following cross-linking. We show here that anti-Ig antibodies do cause inositol phospholipid hydrolysis and Ca2+ mobilization in xid B cells. However, the response of these cells are only 40%-50% of those of normal B cells. Studies with permeabilized cells demonstrated that the hyporesponsiveness is not due to ineffective coupling of sIgR to their associated G-protein. Rather it is apparently due to a quantitative and/or qualitative deficiency in the polyphosphoinositide-specific phosphodiesterase which mediates sIgR-induced inositol phospholipid hydrolysis. These observations may provide a biochemical explanation for the immunological abnormalities resulting from the xid mutation.

Modulation of leukotriene generation by pertussis toxin

The purpose of our study was to characterize the properties of the interaction of pertussis toxin with human polymorphonuclear leukocytes for the modulation of leukotriene generation and metabolism. The cells were stimulated with either the Ca ionophore A23187, opsonized zymosan, or the bacterial peptide formyl-methionyl-leucyl phenylalanine. Incubation of the cells with pertussis toxin led to a rapid inhibition of LTB4 generation when formyl-methionyl-leucyl phenylalanine was used as the stimulus, whereas there was no effect with the Ca ionophore and just a low effect with opsonized zymosan. The inhibition of leukotriene generation was dependent on the incubation time, temperature, and pertussis toxin concentration. The effect was not dependent on the presence of calcium. Incubation of the cells with guanosine 5'-O-(3-thiotriphosphate) the stable analog of GTP, led to a time-dependent increase in leukotriene generation induced by formyl-methionyl-leucyl phenylalanine which was abolished by the simultaneous addition of pertussis toxin. Our data suggest that the formyl-methionyl-leucyl phenylalanine-induced generation of leukotrienes is dependent on a GTP-binding protein. The participation of the various G proteins has yet to be elucidated.

CD3/T-cell receptor coupling to a pertussis and cholera toxin-insensitive G-protein

We have analyzed the effect of CD3/T-cell receptor stimulation on GTP hydrolysis and GTP binding. We show that stimulation of Jurkat, T-cell, membranes with OKT3 results in a 50% increase in GTP hydrolysis which is specifically inhibited by GDP. Pretreatment of the membranes with neither pertussis toxin nor cholera toxin inhibited the GTP hydrolysis. We also show that stimulation with OKT3 increases the binding of GTP gamma S to Jurkat membranes. These data strongly implicate the involvement of a G-protein in CD3/T-cell receptor signalling.

Interaction of interferon with other cytokines

Interferons interact with other cytokines to exert their antiviral, cell growth regulatory and immunomodulatory activities. Growth factors, tumor necrosis factors, colony stimulating factors, interleukins and interferons have pleiotropic effects and form a parallel network of intercellular signals. These signals are transduced at the cell surface through specific receptors with intrinsic enzymatic activity or with the capacity to regulate intracellular enzymes through interactive effects with G-proteins. This leads to regulated gene transcription of intracellular and secreted, functional and structural proteins. Although much is known about the interaction of cytokines with their receptors and about the regulation of transcription at the genomic level the various steps linking these two phenomena deserve further research.

Physical linkage of a guanine nucleotide-binding protein-related gene to the chicken major histocompatibility complex

Several genes were found closely associated with major histocompatibility class I and class II beta-chain genes in chicken genomic DNA clusters by hybridizing tissue-specific cDNA probes to cosmid clones. A cDNA probe for one of these genes, probe C12.3 isolated from a chicken liver cDNA library, was used to clone the homologous sequence H12.3 from a human B-lymphoblastoid cell line cDNA library. C12.3 and H12.3 encode exactly the same 317-residue-long protein. The sequence of 12.3 shows significant homology with the two known guanine nucleotide-binding protein beta subunits (GP beta 1 and GP beta 2) and other proteins that all share the same segmented structure with seven internal homologous repeats about 45 residues in length. Unlike the chicken gene, the human H12.3 gene and its mouse counterpart are not located on the same chromosome as the major histocompatibility complex. A possible involvement of the C12.3 gene product in major histocompatibility complex-linked control of lymphocyte proliferation in chickens is discussed.

Production of the haemopoietic growth factors GM-CSF and interleukin-3 by mast cells in response to IgE receptor-mediated activation

Mast cells have a central role in allergic diseases mediated by specific immunoglobulin E antibody responses to allergens. The binding of IgE to the high-affinity receptor for IgE (Fc epsilon R) on mast cells and basophils enables these cells to react specifically to allergens. Such contact leads to the activation of mast cells and the release of histamine and other pharmacological mediators, causing an immediate hypersensitivity and acute inflammatory reactions, accompanied by the development of allergic symptoms. Here we show that Fc epsilon R-mediated activation of murine mast cells results in the production of the haemopoietic growth factors granulocyte/macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3). IL-3 and GM-CSF, in addition to their role in bone marrow haemopoiesis, also influence inflammation as they have the capacity to recruit, prime and activate inflammatory cells such as neutrophils, macrophages and eosinophils. Secretion of these factors by mast cells in response to allergens may therefore have an important role in local tissue defense.

Age related impairment in phosphatidylinositol breakdown of polymorphonuclear granulocytes

It is well known that with aging the immune response decreases. Most of the effector functions occur through specific receptors. Thus, we investigated the effects of various stimulants, acting through receptors or directly through the GTP-binding Gi protein, on phosphatidylinositol breakdown in PMNLs of young and elderly subjects and try to modulate it. A marked decrease in inositol phosphate (IP1, IP2, IP3) formation in PMNLs of elderly was found under FMLP stimulation when compared to that of young subjects. Neither GTP gamma S, nor AIF4- could induce an increase of IP3 in PMNLs of elderly comparable to that of young subjects. The results suggest that at least an alteration exists at the GTP-binding Gi protein level, as well as in the mechanism of linkage of the receptor to the G protein.

Nucleoside and nucleotide modulation of genetic expression--a new approach to chemotherapy

Unlike conventional enzymes, receptors that activate G proteins do not catalyze the direct formation or cleavage of covalent bonds but act instead as a catalyst for the exchange of GTP vs GDP, which results in major conformational changes in the alpha subunit of G proteins and dissociation and selective binding of the alpha subunit which provokes direct enzyme activation eventually resulting in stimulation of protein kinase A, B or C. Each of these kinases can phosphorylate specific DNA binding proteins which allow new portions of DNA to be read and expressed. Such a series of events can act as switches to control cellular genetic expression resulting in cellular proliferation, differentiation or hormonal secretion of growth factors (Scheme I). Examples of nucleosides and nucleotides which appear to exert their therapeutic effects via G protein control of cellular proliferation resulting in differentiation are tiazofurin, selenazofurin, and 8-chloro-cAMP which have been synthesized and studied in our laboratories. The clinical application of these nucleosides in cancer treatment is presently underway and offers a viable alternative to chemotherapy with highly cytotoxic agents. The use of these derivatives result in down-regulation of the G protein regulatory pathways responsible for rapid cell division. Alternatively, a series of guanosine analogs prepared in our laboratories, 8-bromoguanosine, 8-mercaptoguanosine, 7-methyl-8-oxoguanosine and 7-thia-8-oxoguanosine, all activate various aspects of the immune response by up-regulation of G protein regulatory pathways in various lymphocyte derived cells. Guanosine-like nucleosides which function in this manner could have major clinical application as antitumor, antiviral and antimetastatic agents providing the desired specificity can be achieved. Specific immune enhancement of the aged might be an attainable goal if suitable orally active guanosine derivatives with high specificity can be achieved. The G protein regulatory pathways for modulation of genetic expression in specific cell types provide a major modern approach to new chemotherapeutic agents.