Pertussis toxin inhibits chemotactic peptide-stimulated generation of inositol phosphates and lysosomal enzyme secretion in human leukemic (HL-60) cells

Bi-component HlgC/HlgB and HlgA/HlgB γ-hemolysins from S. aureus: Modulation of Ca2+ channels activity through a differential mechanism

Staphylococcal bi-component leukotoxins known as *pore-forming toxins* induce upon a specific binding to membrane receptors, two independent cellular events in human neutrophils. First, they provoke the opening of pre-existing specific ionic channels including Ca²⁺ channels. Then, they form membrane pores specific to monovalent cations leading to immune cells death. Among these leukotoxins, HlgC/HlgB and HlgA/HlgB γ-hemolysins do act in synergy to induce the opening of different types of Ca²⁺ channels in the absence as in the presence of extracellular Ca²⁺. Here, we investigate the mechanism underlying the modulation of Ca²⁺-independent Ca²⁺ channels in response to both active leukotoxins in human neutrophils. In the absence of extracellular Ca²⁺, the Mn²⁺ has been used as a Ca²⁺ surrogate to determine the activity of Ca²⁺-independent Ca²⁺ channels. Our findings provide new insights about different mechanisms involved in the staphylococcal γ-hemolysins activity to regulate three different types of Ca²⁺-independent Ca²⁺ channels. We conclude that (i) HlgC/HlgB stimulates the opening of La³⁺-sensitive Ca²⁺ channels, through a cholera toxin-sensitive G protein, (ii) HlgA/HlgB stimulates the opening of Ca²⁺ channels not sensitive to La³⁺, through a G protein-independent process, and (iii) unlike HlgA/HlgB, HlgC/HlgB toxins prevent the opening of a new type of Ca²⁺ channels by phosphorylation/de-phosphorylation-dependent mechanisms.

A Worldwide Competition to Compare the Speed and Chemotactic Accuracy of Neutrophil-Like Cells

Chemotaxis is the ability to migrate towards the source of chemical gradients. It underlies the ability of neutrophils and other immune cells to hone in on their targets and defend against invading pathogens. Given the importance of neutrophil migration to health and disease, it is crucial to understand the basic mechanisms controlling chemotaxis so that strategies can be developed to modulate cell migration in clinical settings. Because of the complexity of human genetics, Dictyostelium and HL60 cells have long served as models system for studying chemotaxis. Since many of our current insights into chemotaxis have been gained from these two model systems, we decided to compare them side by side in a set of winner-take-all races, the Dicty World Races. These worldwide competitions challenge researchers to genetically engineer and pharmacologically enhance the model systems to compete in microfluidic racecourses. These races bring together technological innovations in genetic engineering and precision measurement of cell motility. Fourteen teams participated in the inaugural Dicty World Race 2014 and contributed cell lines, which they tuned for enhanced speed and chemotactic accuracy. The race enabled large-scale analyses of chemotaxis in complex environments and revealed an intriguing balance of speed and accuracy of the model cell lines. The successes of the first race validated the concept of using fun-spirited competition to gain insights into the complex mechanisms controlling chemotaxis, while the challenges of the first race will guide further technological development and planning of future events.

Moving towards a paradigm: common mechanisms of chemotactic signaling in Dictyostelium and mammalian leukocytes

Chemotaxis, or directed migration of cells along a chemical gradient, is a highly coordinated process that involves gradient sensing, motility, and polarity. Most of our understanding of chemotaxis comes from studies of cells undergoing amoeboid-type migration, in particular the social amoeba Dictyostelium discoideum and leukocytes. In these amoeboid cells the molecular events leading to directed migration can be conceptually divided into four interacting networks: receptor/G protein, signal transduction, cytoskeleton, and polarity. The signal transduction network occupies a central position in this scheme as it receives direct input from the receptor/G protein network, as well as feedback from the cytoskeletal and polarity networks. Multiple overlapping modules within the signal transduction network transmit the signals to the actin cytoskeleton network leading to biased pseudopod protrusion in the direction of the gradient. The overall architecture of the networks, as well as the individual signaling modules, is remarkably conserved between Dictyostelium and mammalian leukocytes, and the similarities and differences between the two systems are the subject of this review.

Measurement of second messengers in signal transduction: cAMP and inositol phosphates

cAMP acts as an intracellular mediator of hormone action and the importance of accurate quantitative determination of cAMP levels in cells and tissues is widely recognized. The most utilized procedures for the determination of adenylate cyclase activity in membranes are described here for measuring the conversion of [alpha-(32)P]ATP into [(32)P]cAMP after a two-step chromatographic separation. Also critical in signal transduction is phosphoinositide turnover, which is linked to receptor activation resulting from changes in cytosolic calcium concentrations. Phosphoinositide turnover can be measured as described in this unit by labeling phospholipid pools with [(3)H]-inositol and then analyzing for tritiated inositol phosphates.

Identification of an alternative G{alpha}q-dependent chemokine receptor signal transduction pathway in dendritic cells and granulocytes

CD38 controls the chemotaxis of leukocytes to some, but not all, chemokines, suggesting that chemokine receptor signaling in leukocytes is more diverse than previously appreciated. To determine the basis for this signaling heterogeneity, we examined the chemokine receptors that signal in a CD38-dependent manner and identified a novel "alternative" chemokine receptor signaling pathway. Similar to the "classical" signaling pathway, the alternative chemokine receptor pathway is activated by Galpha(i2)-containing Gi proteins. However, unlike the classical pathway, the alternative pathway is also dependent on the Gq class of G proteins. We show that Galpha(q)-deficient neutrophils and dendritic cells (DCs) make defective calcium and chemotactic responses upon stimulation with N-formyl methionyl leucyl phenylalanine and CC chemokine ligand (CCL) 3 (neutrophils), or upon stimulation with CCL2, CCL19, CCL21, and CXC chemokine ligand (CXCL) 12 (DCs). In contrast, Galpha(q)-deficient T cell responses to CXCL12 and CCL19 remain intact. Thus, the alternative chemokine receptor pathway controls the migration of only a subset of cells. Regardless, the novel alternative chemokine receptor signaling pathway appears to be critically important for the initiation of inflammatory responses, as Galpha(q) is required for the migration of DCs from the skin to draining lymph nodes after fluorescein isothiocyanate sensitization and the emigration of monocytes from the bone marrow into inflamed skin after contact sensitization.

Expansion of signal transduction by G proteins. The second 15 years or so: from 3 to 16 alpha subunits plus betagamma dimers

The first 15 years, or so, brought the realization that there existed a G protein coupled signal transduction mechanism by which hormone receptors regulate adenylyl cyclases and the light receptor rhodopsin activates visual phosphodiesterase. Three G proteins, Gs, Gi and transducin (T) had been characterized as alphabetagamma heterotrimers, and Gsalpha-GTP and Talpha-GTP had been identified as the sigaling arms of Gs and T. These discoveries were made using classical biochemical approaches, and culminated in the purification of these G proteins. The second 15 years, or so, are the subject of the present review. This time coincided with the advent of powerful recombinant DNA techniques. Combined with the classical approaches, the field expanded the repertoire of G proteins from 3 to 16, discovered the superfamily of seven transmembrane G protein coupled receptors (GPCRs) -- which is not addressed in this article -- and uncovered an amazing repertoire of effector functions regulated not only by alphaGTP complexes but also by betagamma dimers. Emphasis is placed in presenting how the field developed with the hope of conveying why many of the new findings were made.

Molecular pathogenesis, epidemiology, and clinical manifestations of respiratory infections due to Bordetella pertussis and other Bordetella subspecies

Bordetella respiratory infections are common in people (B. pertussis) and in animals (B. bronchiseptica). During the last two decades, much has been learned about the virulence determinants, pathogenesis, and immunity of Bordetella. Clinically, the full spectrum of disease due to B. pertussis infection is now understood, and infections in adolescents and adults are recognized as the reservoir for cyclic outbreaks of disease. DTaP vaccines, which are less reactogenic than DTP vaccines, are now in general use in many developed countries, and it is expected that the expansion of their use to adolescents and adults will have a significant impact on reducing pertussis and perhaps decrease the circulation of B. pertussis. Future studies should seek to determine the cause of the unique cough which is associated with Bordetella respiratory infections. It is also hoped that data gathered from molecular Bordetella research will lead to a new generation of DTaP vaccines which provide greater efficacy than is provided by today's vaccines.

Antibody-mediated neutralization of pertussis toxin-induced mitogenicity of human peripheral blood mononuclear cells

Antibody-mediated neutralization of pertussis toxin-induced proliferation of human peripheral blood mononuclear cells (PBMC) was assessed using alamarBlue and compared with results from the Chinese hamster ovary (CHO) cell assay using sera from vaccinated adults and convalescent children. Neutralization values for the CHO assay were similar for vaccinated and convalescent subjects; however. the convalescent group had higher titers in the PBMC assay. Results for pertussis toxin neutralization with the CHO assay appear to be distinct from those with the PBMC assay.

Low levels of occupational exposure to arsenic and antimony: effects on lysosomal glycohydrolase levels in plasma of exposed workers and in lymphocyte cultures

BACKGROUND

Heavy metals have been shown to alter the mechanism and release of lysosomal enzymes. In the present study, the activities of lysosomal glycohydrolases were determined in order to evaluate the asymptomatic toxic effects of low levels of exposure to arsenic (As) and antimony (Sb) in art glass workers.

METHODS

N-acetyl-beta-D-glucosaminidase (NAG), beta-D-glucuronidase (GCR), alpha- and beta-D-galactosidase, alpha-D-glucosidase, and alpha-D-mannosidase were determined by a fluorimetric assay in the plasma of 26 art glass workers. Lymphocytes cultured in the presence of different species of As and Sb served as an in vitro model for the study of the protective action of selenium and zinc.

RESULTS

No significant difference in the plasma levels of the various enzymes was detected in art glass workers or control subjects. The in vitro experiments demonstrated that secretion of lysosomal glycohydrolases was increased by Sb (225%) and decreased by As (57%) at the same concentration of elements (200 microg/L). The addition of bivalent selenium to the culture neutralized the effects of both metals, while zinc chloride did not show any protective effect.

CONCLUSIONS

As for the plasma glycohydrolases, no praecox signs of toxicity related to a low concentration of As and Sb was evident in art glass workers. This may be due to the antagonistic effects demonstrated by these two metals in vitro. Their different mechanism of action on release of glycohydrolases is being discussed.

The human formyl peptide receptor as model system for constitutively active G-protein-coupled receptors

According to the two-state model of G-protein-coupled receptor (GPCR) activation, GPCRs isomerize from an inactive (R) state to an active (R*) state. In the R* state, GPCRs activate G-proteins. Agonist-independent R/R* isomerization is referred to as constitutive activity and results in an increase in basal G-protein activity, i.e. GDP/GTP exchange. Agonists stabilize the R* state and further increase, whereas inverse agonists stabilize the R state and decrease, basal G-protein activity. Constitutive activity is observed in numerous wild-type GPCRs and disease-causing GPCR mutants with increased constitutive activity. The human formyl peptide receptor (FPR) exists in several isoforms (FPR-26, FPR-98 and FPR-G6) and activates chemotaxis and cytotoxic cell functions of phagocytes through G(i)-proteins. Studies in HL-60 leukemia cell membranes demonstrated inhibitory effects of Na(+) and pertussis toxin on basal G(i)-protein activity, suggesting that the FPR is constitutively active. However, since HL-60 cells express several constitutively active chemoattractant receptors, analysis of constitutive FPR activity was difficult. Sf9 insect cells do not express chemoattractant receptors and G(i)-proteins and provide a sensitive reconstitution system for FPR/G(i)-protein coupling. Such expression studies showed that FPR-26 is much more constitutively active than FPR-98 and FPR-G6 as assessed by the relative inhibitory effects of Na(+) and of the inverse agonist cyclosporin H on basal G(i)-protein activity. Site-directed mutagenesis studies suggest that the E346A exchange in the C-terminus critically determines dimerization and constitutive activity of FPR. Moreover, N-glycosylation of the N-terminus seems to be important for constitutive FPR activity. Finally, we discuss some future directions of research.

Involvement of G(q/11) in signal transduction in the mammalian vomeronasal organ

Social behaviors of most mammals are profoundly affected by pheromones. Pheromones are detected by G-protein coupled receptors in the vomeronasal organ (VNO). To investigate the role of G alpha(q/11) in vomeronasal signal transduction pathways, microvillar membranes from murine VNO were prepared. Incubation of such membranes from prepubertal females with adult male urine results in an increase in production of inositol-(1,4,5)-trisphosphate (IP(3)). This stimulation is mimicked by GTP gamma S, blocked by GDP beta S and is tissue specific. Furthermore, use of bacterial toxins such as pertussis that lead to ADP-ribosylation of the G-protein alpha subunits of G(o) and G(i2) do not block the increase in IP(3) levels but U-73122, a PLC inhibitor, blocks the production of IP(3). Studies with monospecific antibodies revealed the presence of three G-proteins, G alpha(o), G alpha(i2) and G alpha(q/11)-related protein, in vomeronasal neurons, concentrated on their microvilli. Our observations indicate that pheromones in male urine act on vomeronasal neurons in the female VNO via a receptor-mediated, G alpha(q/11)-protein-dependent increase in IP(3) levels.

High constitutive activity of the human formyl peptide receptor

The formyl peptide receptor (FPR) couples to pertussis toxin (PTX)-sensitive Gi-proteins to activate chemotaxis and exocytosis in neutrophils. PTX reduces not only formyl peptide-stimulated but also agonist-independent ("basal") Gi-protein activity, suggesting that the FPR is constitutively active. We aimed at identifying an inverse FPR agonist, i.e. a compound that suppresses constitutive FPR activity. In Sf9 insect cell membranes, the G-protein heterotrimer Gialpha2beta1gamma2 reconstituted N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP)-stimulated guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) binding and GTPgammaS-sensitive high affinity [3H]FMLP binding. The FPR "antagonist" cyclosporin H (CsH) potently and efficiently reduced basal GTPgammaS binding in Sf9 membranes. Another FPR antagonist, N-t-butoxycarbonyl-L-phenylalanyl-L-leucyl-L-phenylalanyl-L-leucyl-L- phenylalanine did not inhibit basal GTPgammaS binding but blocked the inhibitory effect of CsH on GTPgammaS binding. Na+ reduced basal GTPgammaS binding and eliminated the inhibitory effect of CsH. Similar effects of FMLP, CsH, and Na+ as in Sf9 membranes were observed with FPR expressed in the mammalian cell line HEK293. Our data show that the human FPR possesses high constitutive activity. CsH is an inverse FPR agonist and stabilizes the FPR in an inactive state. Na+ also stabilizes the FPR in an inactive state and, thereby, diminishes inverse agonist efficacy.

Store-operated Ca2+ influx and stimulation of exocytosis in HL-60 granulocytes

This study addresses the role of store-operated Ca2+ influx in the regulation of exocytosis in inflammatory cells. In HL-60 granulocytes, which do not possess voltage-operated Ca2+ channels, the chemotactic peptide fMet-Leu-Phe (fMLP) was able to stimulate store-operated Ca2+ influx and to trigger exocytosis of primary granules. An efficient triggering of exocytosis by fMLP required the presence of extracellular Ca2+ and was inhibited by blockers of store-operated Ca2+ influx. However, receptor-independent activation of store-operated Ca2+ influx through thapsigargin did not trigger exocytosis. fMLP was unable to stimulate exocytosis in the absence of cytosolic free Ca2+ concentration [Ca2+]c elevations. However, a second signal generated by fMLP synergized with store-operated Ca2+ influx to trigger exocytosis and led to a left shift of the exocytosis/[Ca2+]c relationship in ionomycin-stimulated cells. The synergistic fMLP-generated signaling cascade was long-lasting, involved a pertussis toxin-sensitive G protein and a phosphatidylinositol 3-kinase. In summary, store-operated Ca2+ influx is crucial for the efficient triggering of exocytosis in HL-60 granulocytes, but, as opposed to Ca2+ influx through voltage-operated Ca2+ channels in neurons, it is not a sufficient stimulus by itself and requires synergistic receptor-generated signals.

Protein kinases A and C positively regulate G protein-dependent activation of phosphatidylinositol-specific phospholipase C by tumor necrosis factor-alpha in MC3T3-E1 osteoblasts

The role(s) of protein kinases in the regulation of G protein-dependent activation of phosphatidylinositol-specific phospholipase C by tumor necrosis factor-alpha was investigated in the osteoblast cell line MC3T3-E1. We have previously reported the stimulatory effects of tumor necrosis factor-alpha and A1F4-, an activator of G proteins, on this phospholipase pathway documented by a decrease in mass of PI and release of diacylglycerol. In this study, we further explored the mechanism(s) by which the tumor necrosis factor or A1F4(-)-promoted breakdown of phosphatidylinositol and the polyphosphoinositides by phospholipase C is regulated. Tumor necrosis factor-alpha was found to elicit a 4-5-fold increase in the formation of [3H]inositol-1,4-phosphate and [3H]inositol-1,4,5-phosphate; and a 36% increase in [3H]inositol-1-phosphate within 5 min in prelabeled cells. [3H]inositol-4-phosphate, a metabolite of [3H]inositol-1,4-phosphate and [3H]inositol-1,4,5-phosphate, was found to be the predominant phosphoinositol product of tumor necrosis factor-alpha and A1F4(-)-activated phospholipase C hydrolysis after 30 min. In addition, the preincubation of cells with pertussis toxin decreased the tumor necrosis factor-induced release of inositol phosphates by 53%. Inhibitors of protein kinase C, including Et-18-OMe and H-7, dramatically decreased the formation of [3H]inositol phosphates stimulated by either tumor necrosis factor-alpha or A1F4- by 90-100% but did not affect basal formation. The activation of cAMP-dependent protein kinase, or protein kinase A, by the treatment of cells with forskolin or 8-BrcAMP augmented basal, tumor necrosis factor-alpha and A1F4(-)-induced [3H]inositol phosphate formation. Therefore, we report that protein kinases can regulate tumor necrosis factor-alpha-initiated signalling at the cell surface in osteoblasts through effects on the coupling between receptor, G-protein and phosphatidylinositol-specific phospholipase C.

Pertussis toxin-sensitive activation of phospholipase C by the C5a and fMet-Leu-Phe receptors

Signal transduction pathways that mediate C5a and fMet-Leu-Phe (fMLP)-induced pertussis toxin (PTx)-sensitive activation of phospholipase C (PLC) have been investigated using a cotransfection assay system in COS-7 cells. The abilities of the receptors for C5a and fMLP to activate PLC beta2 and PLC beta3 through the Gbetagamma subunits of endogenous Gi proteins in COS-7 cells were tested because both PLC beta2 and PLC beta3 were shown to be activated by the betagamma subunits of G proteins in in vitro reconstitution assays. Neither of the receptors can activate endogenous PLC beta3 or recombinant PLC beta3 in transfected COS-7 cells. However, both receptors can clearly activate PLC beta2 in a PTx-sensitive manner, suggesting that the receptors may interact with endogenous PTx-sensitive G proteins and activate PLC beta2 probably through the Gbetagamma subunits. These findings were further corroborated by the results that PLC beta3 could only be slightly activated by Gbeta1gamma1 or Gbeta1gamma5 in the cotransfection assay, whereas the Gbetagamma subunits strongly activated PLC beta2 under the same conditions. PLC beta3 can be activated by Galphaq, Galpha11, and Galpha16 in the cotransfection assay. In addition, the Ggamma2 and Ggamma3 mutants with substitution of the C-terminal Cys residue by a Ser residue, which can inhibit wild type Gbetagamma-mediated activation of PLC beta2, were able to inhibit C5a or fMLP-mediated activation of PLC beta2. These Ggamma mutants, however, showed little effect on m1-muscarinic receptor-mediated PLC activation, which is mediated by the Gq class of G proteins. These results all confirm that the Gbetagamma subunits are involved in PLC beta2 activation by the two chemoattractant receptors and suggest that in COS-7 cells activation of PLC beta3 by Gbetagamma may not be the primary pathway for the receptors.

Potentiation of Gi-mediated phospholipase C activation by retinoic acid in HL-60 cells. Possible role of G gamma 2

Differentiated HL-60 cells acquire responsiveness to fMet-Leu-Phe (fMLP), which activates phospholipase C and O2- generation in a pertussis toxin-sensitive manner. Addition of retinoic acid (RA) for the last 24 h during dimethyl sulfoxide (Me2SO)-induced differentiation enhanced fMLP-dependent signals and interaction between fMLP receptor and G(i). RA modifies both the function and subunit composition of G(i)2, the predominant G(i) of HL-60 membranes, as shown by comparing purified G(i)2 from membranes of Me2SO-treated cells (D-G(i)2) to G(i)2 from membranes of cells treated with both Me2SO and RA (DR-G(i)2). As compared to D-G(i)2, DR-G(i)2 induced more fMLP binding when added to membranes of pertussis toxin-treated HL-60 cells and, in the presence of GTP gamma S, stimulated beta gamma-sensitive phospholipase C in extracts of HL-60 cells to a much greater extent at a lower concentrations. Immunoblasts revealed that RA induced expression of the gamma 2 subunit, which was otherwise undetectable in G(i)2 purified from HL-60 cells or in HL-60 membranes. Possibly by inducing expression of gamma 2, RA alters two functions of the G(i) beta gamma subunit, modulation of fMLP receptor-G(i)2 coupling and activation of the effector, Phospholipase C.

G-protein involvement in muscarinic receptor-stimulation of inositol phosphates in longitudinal smooth muscle from the small intestine of the guinea-pig

1. Aluminium fluoride (AlF), pertussis toxin (PTX) and cholera toxin (ChTX) have been used to examine the involvement of G-proteins during muscarinic acetylcholine receptor (AChR) stimulation of inositol phospholipid hydrolysis in fragments of longitudinal smooth muscle from the small intestine of the guinea-pig. 2. Carbachol (CCh) induced time- and concentration-dependent increases in [3H]-inositol monophosphates, [3H]-inositol (1,4) bisphosphate, [3H]-inositol (1,3,4) trisphosphate, [3H]-inositol (1,4,5) trisphosphate ([3H]-Ins (1,4,5)P3) and [3H]-inositol tetrakisphosphates measured by h.p.l.c. These increases were inhibited > 95% in the presence of the muscarinic AChR antagonist atropine (0.5 microM). 3. AlF transiently increased the basal levels of [3H]-Ins (1,4,5)P3 but increases in the levels of the other [3H]-inositol phosphates occurred more slowly. CCh-induced increases in the levels of all the [3H]-inositol phosphates were strongly inhibited in the presence of AlF. 4. PTX had no effect on basal levels of any of the [3H]-inositol phosphates but reduced the effects of CCh on these; ChTX had no effects on either basal or CCh-stimulated levels. 5. It was concluded that muscarinic AChR-stimulated increases in the levels of [3H]-inositol phosphates occur via both a PTX-sensitive G-protein and a PTX-insensitive mechanism. The actions of AlF may suggest the involvement of an inhibitory G-protein in the regulation of muscarinic AChR-stimulated inositol phospholipid turnover.

Enhancement of pertussis-toxin-sensitive Na(+)-dependent uridine transporter activity in HL-60 granulocytes by N-formylmethionyl-leucyl-phenylalanine

N-Formyl-Met-Leu-Phe (FMLP), at concentrations as low as 5 nM, caused an increase in intracellular uridine pools in dimethyl sulphoxide (Me2SO)-differentiated HL-60 cells. Intracellular uridine pools were elevated rapidly and reached a maximum within 10 min of exposure to 10 microM FMLP, followed by a gradual decline. This enhancement by FMLP was a consequence of a 3-fold increase in the Vmax of pertussis-toxin-sensitive Na(+)-dependent uridine transport system, with no change in the apparent Km. Km values of 2.67 +/- 0.45 and 3.85 +/- 0.52 microM and Vmax. values of 0.046 +/- 0.017 and 0.125 +/- 0.020 microM/s were obtained for untreated and FMLP-treated Me2SO-differentiated cells respectively. The effect of FMLP on the Na(+)-dependent transport of uridine in Me2SO-differentiated HL-60 cells was specific, as the facilitated transport of uridine was unaffected. Furthermore, this phenomenon was not observed in undifferentiated, phorbol 12-myristate 13-acetate (PMA)-differentiated or pertussis-toxin-treated Me2SO-differentiated HL-60 cells. Removal of extracellular Ca2+ with EGTA abolished the FMLP enhancement of uridine transport in a reversible manner, suggesting the involvement of Ca2+. However, the Ca2+ ionophore A23187 only partially mimicked the effect of FMLP. Similarly, with PMA the transport was sub-optimally enhanced, but a full activation was observed in cells treated with both A23187 and PMA. These findings suggest that activation of the Na(+)-dependent uridine transporter by FMLP in Me2SO-differentiated HL-60 cells involves a pertussis-toxin-sensitive G-protein with a bifurcating signal-transduction pathway.

Effect of heat shock, [Ca2+]i, and cAMP on inositol trisphosphate in human epidermoid A-431 cells

The basal levels of inositol monophosphate, inositol bisphosphate, and inositol trisphosphate (InsP3) in A-431 cells incubated in Na(+)-Hanks' solution were, respectively, 1.23 +/- 0.18, 0.17 +/- 0.03, and 0.69 +/- 0.07% of the total radioactivity in the cell. When cells were heated, InsP3 increased in a temperature-dependent manner related to the duration of heating. The active form of InsP3, inositol 1,4,5-trisphosphate, increased 237 +/- 17% after heating (45 degrees C, 20 min) then returned to baseline within 15 min after the return to 37 degrees C. The heat-induced increase in InsP3 was not observed in the absence of extracellular Ca2+ or with amiloride treatment. Treatment with the nonhydrolyzable GTP analogue 5'-guanylylimidodiphosphate stimulated that component of the InsP3 increase due to G proteins. U-73122, an inhibitor of phospholipase C-mediated processes, blocked the increase in InsP3 resulting from heat exposure. Both pertussis toxin (30 ng/ml, 24 h), an inhibitor of G inhibitory protein, and cholera toxin (1 microgram/ml, 1 h), a stimulator of G stimulatory protein, increased InsP3 in unheated cells, and heating failed to induce a further increase, suggesting that heat activates G proteins. Likewise, 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), 3-isobutyl-1-methylxanthine, Ro 20-1724, or forskolin increased InsP3 in unheated cells, and heat did not cause an additional increase. The InsP3 increase induced by 8-BrcAMP was inhibited by removal of extracellular Ca2+ or treatment with verapamil, suggesting that an influx of extracellular Ca2+ stimulates InsP3 production.(ABSTRACT TRUNCATED AT 250 WORDS)

Transmembrane signaling changes with aging

Altered immune response and transmembrane signaling with aging has previously been demonstrated. The aim of the present study was to characterize PMNLs and lymphocyte G proteins and to determine whether their relative amounts are altered with aging. First we studied the effects of FMLP on PMNLs IP3 formation. It was found that in any group of elderly the PMNLs IP3 formation was significantly decreased compared to that of young subjects. In FMLP receptor binding affinity no measurable difference exists in either low- or high-affinity FMLP receptors. The autoradiogram of 32P-ADP-ribosylated proteins by CT in lymphocytes of young individuals showed a major polypeptide of 40 kDa, and two much less prevalent components of 52 and 45 kDa. In contrast, in lymphocytes of elderly subjects the major polypeptide was 45 kDa, and the two others were very weakly labeled. In PMNLs, CT labeled the 45-kDa band quite strongly, mainly in the elderly, and the 52- and 40-kDa bands were very weakly labeled, mainly in young subjects. When PT was used, no age-related pattern changes could be demonstrated, while differences could be observed between the two types of cells.

Phosphorylation of the inhibitory guanine-nucleotide-binding protein as a possible mechanism of inhibition by protein kinase C of agonist-induced Ca2+ mobilization in human platelet

Increases in the intracellular Ca2+ concentration of human platelets caused by receptor agonists, such as thrombin, 9,11-epithio-11,12-methanothromboxane A2 (STA2), platelet-activating factor (PAF) and arginine-vasopressin, were inhibited by prior addition of 12-O-tetradecanoylphorbol 13-acetate (TPA) in time-dependent and concentration-dependent manners. The inhibitions were mostly reversed by staurosporine, and inhibitor of protein kinase C, added 1 min before TPA. Prior treatment of platelets with thrombin or STA2, the efficacious Ca2+ mobilizer, suppressed the increase in the intracellular Ca2+ concentration of the cells to other agonists, but treatment with less efficacious PAF or vasopressin did not. The heterologous receptor desensitizations were also reversed by staurosporine. The antibody, directed against the carboxy-terminal region of the alpha subunits 1 and 2 of the inhibitory guanine-nucleotide-binding proteins (Gi1 alpha and Gi2 alpha), was raised in rabbit and was used to immunoprecipitate Gi alpha in 32P-labeled platelets. The radioactivity was detected in Gi alpha after incubation of 32P-labeled platelets with TPA, thrombin or STA2, but not in the cells incubated with PAF or vasopressin. The time-dependency or concentration-dependency of TPA-induced phosphorylation of Gi alpha was similar to the dependency of its inhibitory action on agonist-induced Ca2+ mobilization. Thus, strong activation of Ca2+/phospholipid-dependent protein kinase C by phorbol ester or agonists of certain Ca(2+)-mobilizing receptors leads to phosphorylation of the alpha subunit of guanine-nucleotide-binding protein, thereby impairing the coupling of the G protein to receptors as a feedback regulatory component of the receptor-triggered intracellular Ca(2+)-mobilizing system.

Autocrine motility factor and its receptor: role in cell locomotion and metastasis

The ability to locomote and migrate is fundamental to the acquisition of invasive and metastatic properties by tumor cells. Autocrine motility factor (AMF) is a 55 kD cytokine produced by various tumor cells which stimulates their in vitro motility and in vivo lung colonizing ability. AMF stimulates cell motility via a receptor-mediated signalling pathway. Signal transduction following binding of AMF to its receptor, a cell surface glycoprotein of 78 kD (gp78) homologous to p53, is mediated by a pertussis toxin sensitive G protein, inositol phosphate production and the phosphorylation of gp78. Cell surface gp78 is localized to the leading and trailing edges of motile cells but following cell permeabilization is found within an extended network of intracellular tubulovesicles. Gp78 tubulovesicles colocalize with microtubules and extension of the tubulovesicular network to the cell periphery is dependent on the presence of intact microtubules. Gp78 labeled vesicles can be induced to translocate between the cell center and periphery by altering intracellular pH as previously described for tubulovesicles labeled by fluid phase uptake. Anti-gp78 mAb added to viable motile cells is localized to large multivesicular bodies which, with time, relocate to the leading edge. Binding of AMF to its receptor induces signal transduction, similar to chemotactic stimulation of neutrophil mobility, as well as the internalization and transport of its receptor to the leading edge stimulating pseudopodial protrusion and cell motility.

A guanine nucleotide-binding regulatory protein in human sperm mediates acrosomal exocytosis induced by the human zona pellucida

Guanine nucleotide-binding regulatory proteins play key intermediary roles in regulating zona pellucida-mediated acrosomal exocytosis in mouse and bull sperm. Since human sperm possess a Gi-like protein and undergo the acrosome reaction in response to the human zona pellucida, we investigated whether this G protein plays a regulatory role in this exocytotic process. Zonae pellucidae isolated from eggs that had been inseminated but had shown no signs of fertilization after retrieval for in vitro fertilization and embryo transfer were pooled into groups of greater than or equal to 50 in order to reduce variability in biological responses due to the possible presence of ZP that had undergone modifications associated with the polyspermy block. Acid-solubilized zonae pellucidae were incubated with capacitated sperm, and the sperm then assessed for the acrosome reaction using both the P. sativum agglutinin and chlortetracycline fluorescence assays; both assays gave similar results. Sperm incubated with solubilized zonae pellucidae at a final concentration of 2, 4, or 6 ZP/microliter underwent acrosomal exocytosis to a similar extent as compared with A-23187. Sperm were incubated with 1 microgram/ml pertussis toxin during capacitation to functionally inactivate the Gi-like protein. Pertussis toxin treatment of sperm did not affect sperm motility and the ability of the cells to bind to structurally intact zonae pellucidae. Pertussis toxin, however, completely inhibited the percentage acrosome reactions induced by solubilized zonae pellucidae. By contrast, the A-23187-induced acrosome reaction was insensitive to PT treatment. Pertussis toxin inhibition of the zona pellucida-induced acrosome reaction occurred in a concentration-dependent manner with maximal effects observed at 100 ng/ml PT.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor class desensitization of leukocyte chemoattractant receptors

To better define their regulation, formylpeptide and C5a chemoattractant receptor cDNAs were transiently expressed with high efficiency (approximately 35-54%) in human kidney cells. As in neutrophils, both receptors were active in elevating intracellular calcium (ED50 approximately 0.5-1 nM). Agonist-specific desensitization for calcium elevation was observed for both chemoattractant receptors at doses of approximately 1 nM. Heterologous desensitization of formylpeptide, C5a, and alpha 1-adrenergic receptors required high doses of phorbol ester (100 nM phorbol 12-myristate 13-acetate). To further study the phenomenon of desensitization, formylpeptide and C5a receptor cDNAs were cotransfected resulting in approximately 80% of receptor-positive cells expressing both receptors. These cells also possessed endogenous alpha 1-adrenergic receptors. Interestingly, chemoattractant receptors were cross-desensitized by pretreatment with low doses of either C5a or formylmethionylleucylphenylalanine (10 nM) but not by the alpha 1-adrenergic agonist norepinephrine (up to 10 microM). Neither chemoattractant desensitized alpha 1-adrenergic receptors. This phenomenon was reproduced in human neutrophils. These data suggest a previously uncharacterized mechanism of receptor regulation, which is intermediate between homologous and heterologous desensitization. Class desensitization of chemoattractant receptors is less selective than homologous desensitization but is far more efficient and specific than heterologous desensitization. Receptor class desensitization may affect functional classes of receptors via modification of either the receptor or the shared guanine nucleotide-binding regulatory protein.

The superoxide-generating oxidase of phagocytic cells. Physiological, molecular and pathological aspects

Professional phagocytes (neutrophils, eosinophils, monocytes and macrophages) possess an enzymatic complex, the NADPH oxidase, which is able to catalyze the one-electron reduction of molecular oxygen to superoxide, O2-. The NADPH oxidase is dormant in non-activated phagocytes. It is suddenly activated upon exposure of phagocytes to the appropriate stimuli and thereby contributes to the microbicidal activity of these cells. Oxidase activation in phagocytes involves the assembly, in the plasma membrane, of membrane-bound and cytosolic components of the oxidase complex, which were diassembled in the resting state. One of the membrane-bound components in resting phagocytes has been identified as a low-potential b-type cytochrome, a heterodimer composed of two subunits of 22-kDa and 91-kDa. The link between NADPH and cytochrome b is probably a flavoprotein whose subcellular localization in resting phagocytes remains to be determined. Genetic defects in the cytochrome b subunits and in the cytosolic factors have been shown to be the molecular basis of chronic granulomatous disease, a group of inherited disorders in the host defense, characterized by severe, recurrent bacterial and fungal infections in which phagocytic cells fail to generate O2- upon stimulation. The present review is focused on recent data concerning the signaling pathway which leads to oxidase activation, including specific receptors, the production of second messengers, the organization of the oxidase complex and the molecular defects responsible for granulomatous disease.

Formation of inositol polyphosphates in cultured adrenal chromaffin cells

Formation of inositol polyphosphates has been characterized in cultured bovine adrenal chromaffin cells in terms of calcium dependency and isomers of inositol polyphosphates. There are two distinct pathways of generation of InsP3. Stimulants such as high K+ induce InsP3 accumulation by a calcium uptake-dependent mechanism. Stimulants such as Ang II induce InsP3 accumulation by a calcium uptake-independent mechanism. Both mechanisms are involved in nicotinic stimulation. These results suggest that calcium entry as well as receptor-mediated mechanisms play a significant role in phosphoinositides hydrolysis through phospholipase C in adrenal chromaffin cells. Nicotinic receptor stimulation induces a rapid and transient increase in Ins(1,4,5)P3 accumulation followed by a slower accumulation of Ins(1,3,4)P3. Moreover, nicotine induces a large and rapid increase in Ins(1,3,4,5,6)P5 accumulation with an extent and time course similar to Ins(1,4,5)P3, which peaks at 15 sec after stimulation. Nicotine also induced Ins(1,3,4,5)P4 and InsP6 accumulation with a slower time course and a lesser magnitude than Ins(1,3,4,5,6)P5. These results indicate that adrenal chromaffin cells possess fine regulation of inositol polyphosphates metabolism and that inositol polyphosphates are involved with the control of cellular function in these cells.

Tumor cell autocrine motility factor receptor

The ability to locomote and migrate is fundamental to the acquisition of invasive and metastatic properties by tumor cells. Autocrine motility factor (AMF) is a cytokine produced by various tumor cells which stimulates their in vitro motility and in vivo lung-colonizing ability. AMF stimulates cell motility via a receptor-mediated signalling pathway. Signal transduction following binding of AMF to its receptor, a cell surface glycoprotein of 78 kD (gp78), is mediated by a pertussis toxin sensitive G protein, inositol phosphate production and the phosphorylation of gp78. AMF induces gp78 internalization to intracellular tubulovesicles and transport to the leading edge stimulating pseudopodial protrusion and cell motility.

Internalization pathway of C3b receptors in human neutrophils and its transmodulation by chemoattractant receptors stimulation

On the surface of phagocytes, C3b receptors (CR1) bind C3b-coated particles and promote their ingestion after activation by appropriate stimuli such as lymphokines or the chemoattractant formyl methionyl leucyl phenylalanine (fMLP) and fibronectin. The aims of the present study were 1) to define at the electron microscopic level the nature of the process responsible for CR1 internalization and 2) to dissect the mechanism by which a physiological activator (fMLP) stimulates this process. CR1 was visualized either by the immunogold technique or by quantitative electron microscopic autoradiography using a monoclonal anti-CR1 antibody. Both techniques revealed that after anti-CR1 binding, CR1 cluster on the neutrophil surface in a time-, temperature-, and antibody-dependent fashion, but do not concentrate in coated pits. CR1 internalization requires receptor cross-linking (does not occur in the presence of Fab fragments of anti-CR1) and intact microfilaments. It results in the association of the internalized material with large flattened vacuoles, organized in stacks. Together with the surface localization of CR1 close to cytoplasmic projections (ruffles), these observations suggest that uptake of CR1 occurs through a macropinocytotic process. Eventually, CR1 concentrate in lysosomal structures. fMLP markedly stimulates this pattern of CR1 internalization without affecting their clustering or their lack of association with coated pits. Stimulation by fMLP is inhibited by pertussis toxin, unaffected by preventing receptor-triggered cytosolic free calcium [Ca2+]i elevations, and mimicked by phorbol myristate acetate. Taken together our data demonstrate 1) that, in neutrophils, CR1 is internalized via a coated pit independent macropinocytotic process, dependent on intact microfilaments and receptor cross-linking; 2) that, in the same cells, fMLP is internalized via the classical coated pits pathway; and 3) that fMLP amplifies CR1 uptake possibly via protein kinase C stimulation.

Bradykinin induces phosphoinositide turnover, 1,2-diglyceride formation, and growth in cultured adult human keratinocytes

The effects of bradykinin on activation of phosphoinositide turnover, 1,2-diglyceride formation, and growth of cultured adult human keratinocytes were investigated. Keratinocytes specifically bound [3H]bradykinin with high affinity (kd = 3.4 nM) and displayed 1.5 X 10(5) binding sites/cell. Bradykinin caused a rapid dose-dependent increase in inositol trisphosphate (IP3) inositol bisphosphate, and inositol monophosphate. IP3 was maximally increased (fivefold) at 30 s and remained elevated for at least 10 min. Half maximal stimulation of IP3 formation was observed at 27 nM bradykinin. IP3 accumulation was equally elevated by bradykinin and lys-bradykinin but was not stimulated by des-Arg9-bradykinin, indicating that phospholipase C in cultured keratinocytes is coupled to B2 bradykinin receptors. Treatment of keratinocytes with active phorbol ester (TPA) caused a significant inhibition (50%) of bradykinin-induced IP3 accumulation, suggesting negative regulation of phospholipase C by protein kinase C. Bradykinin also caused a significant elevation in 1,2-diacylglycerol (DAG) content. DAG content was maximally elevated (twofold) at 1 min and remained elevated for at least 10 min. Bradykinin also caused a significant (twofold, p less than 0.02) increase in keratinocyte growth. These data demonstrate that bradykinin is a potent agonist of the phospholipase C/protein kinase C signal transduction system in cultured adult human keratinocytes and that activation of this pathway by bradykinin is associated with increased keratinocyte growth.

Possible interaction of alpha 1-adrenergic receptor with pertussis-toxin-sensitive guanine-nucleotide-binding regulatory proteins (G proteins) responsible for phospholipase C activation in rat liver plasma membranes

Islet-activating protein (IAP; pertussis toxin) was employed to test the hypothesis that IAP-sensitive GTP-binding regulatory proteins (G proteins) are coupled with alpha 1-adrenergic receptor in rat liver plasma membranes. The high-affinity state of the binding of alpha 2-adrenergic agonist, which is known to be coupled with IAP-sensitive G protein, was abolished in IAP-treated plasma membranes. IAP treatment of plasma membranes could also diminish the high-affinity state of the alpha 1-adrenergic receptor for the agonist. Restoration of the high-affinity state of the alpha 1-adrenergic receptor for the agonist occurred on reconstitution of the bovine brain IAP-sensitive G proteins. The alpha 1-adrenergic receptor agonist stimulated inositol triphosphate (InsP3) production from [3H]inositol-labeled liver plasma membranes in a concentration-dependent manner. IAP treatment also decreased alpha 1-adrenergic-agonist-induced InsP3 production but not completely. From these results, we concluded that there is a possibility that both IAP-sensitive and IAP-insensitive G proteins were involved in alpha 1-adrenergic-receptor-stimulated phospholipase C activation in rat liver plasma membranes.

PT pretreatment inhibits 48/80-induced activation of Ca(+)-permeable channels in rat peritoneal mast cells

We recently reported that the secretagogue, compound 48/80, activated Ca2(+)-permeable channels of mast cells possibly via a second messenger [Kuno, Okada, and Shibata. Am. J. Physiol. 256 (Cell Physiol. 25): C560-C568, 1989]. The effects of pretreatment with pertussis toxin (PT) on compound 48/80 (48/80)-induced activation of the Ca2(+)-permeable channel have now been investigated by measuring Ca2+ signals of cell suspensions using the Ca2+ indicator fura-2 and by recording Ba2+ currents through the channel using the patch-clamp technique. In the presence of extracellular Ca2+, the fluorescence change was biphasic, with an immediate rise and a delayed peak at room temperature. The delayed peak, mainly due to Ca2+ entry through plasma membranes, was greatly reduced by pretreatment with PT. The quenching of the fluorescence by 48/80-induced Mn2+ influx was also decreased by PT, whereas the Ca2+ transients due to Ca2+ release from the intracellular stores apparently did not change. In patch-clamp recordings from cell-attached patches with pipettes containing isotonic Ba2+, the 48/80-induced Ba2+ currents were either suppressed or delayed in the PT-treated cells, under conditions where degranulation was absent. These results suggest that PT-sensitive GTP-binding protein is involved in activating the Ca2(+)-permeable channel in mast cells during stimulus-secretion coupling.

Guanosine 5'-[gamma-thio]triphosphate-stimulated hydrolysis of phosphatidylinositol 4,5-bisphosphate in HL-60 granulocytes. Evidence that the guanine nucleotide acts by relieving phospholipase C from an inhibitory constraint

Myeloid differentiated human leukaemia (HL-60) cells contain a soluble phospholipase C that hydrolysed phosphatidylinositol 4.5-bisphosphate and was markedly stimulated by the metabolically stable GTP analogue guanosine 5'-[gamma-thio]triphosphate (GTP[S]). Half-maximal and maximal (up to 5-fold) stimulation of inositol phosphate formation by GTP[S] occurred at 1.5 microM and 30 microM respectively. Other nucleotides (GTP, GDP, GMP, guanosine 5'-[beta-thio]diphosphate. ATP, adenosine 5'-[gamma-thio]triphosphate, UTP) did not affect phospholipase C activity, GTP[S] stimulation of inositol phosphate accumulation was inhibited by excess GDP, but not by ADP. The effect of GTP[S] on inositol phosphate formation was absolutely dependent on and markedly stimulated by free Ca2+ (median effective concn. approximately 100 nM). Analysis of inositol phosphates by anion-exchange chromatography revealed InsP3 as the major product of GTP[S]-stimulated phospholipase C activity. In the absence of GTP[S], specific phospholipase C activity was markedly decreased when tested at high protein concentrations, whereas GTP[S] stimulation of the enzyme was markedly enhanced under these conditions. As both basal and GTP[S]-stimulated inositol phosphate formation were linear with time whether studied at low or high protein concentration, these results suggest that (a) phospholipase C is under an inhibitory constraint and (b) GTP[S] relieves this inhibition, most likely by activating a soluble GTP-binding protein.

Muscarinic cholinergic stimulation of inositol phosphate production in cultured embryonic chick atrial cells. Evidence for a role of two guanine-nucleotide-binding proteins

These studies demonstrate a novel mechanism for the coupling of the muscarinic receptor to phospholipase C activity in embryonic chick atrial cells. In monolayer cultures of atrial cells from hearts of embryonic chicks at 14 days in ovo, carbamylcholine stimulated the sequential appearance of InsP3, InsP2 and InsP1 with an EC50 (concn. causing 50% of maximal stimulation) of 30 microM. In the presence of 15 mM-Li, a 5 min exposure to carbamylcholine (0.1 mM) increased InsP3 levels to a maximum of 47 +/- 12% over basal, InsP2 to 108 +/- 13% over basal and InsP1 to 42 +/- 5% over basal. This effect was blocked by 5 microM-atropine. Incubation of these cells with pertussis toxin (15 h; 0.5 ng/ml) inhibited carbamylcholine-stimulated InsP3, InsP2 and InsP1 formation by 42 +/- 7%, 30 +/- 3% and 48 +/- 7% respectively. The IC50 (concn. causing 50% inhibition) for pertussis toxin inhibition of all three inositol phosphates was 0.01 ng/ml, with a half-time of 6 h at 0.5 ng/ml. This partial sensitivity to pertussis toxin was not due to incomplete ADP-ribosylation of the guanine-nucleotide-binding protein (G-protein), since autoradiography of polyacrylamide gels of cell homogenates incubated with [32P]NAD+ in the presence of pertussis toxin demonstrated that incubation of cells with 0.5 ng of pertussis toxin/ml for 15 h resulted in complete ADP-ribosylation of pertussis toxin substrates by endogenous NAD+. In cells permeabilized with saponin (10 micrograms/ml), 0.1 mM-GTP[S] (guanosine 5'-[gamma-thio]triphosphate) stimulated InsP1 by 102 +/- 15% (mean +/- S.E.M., n = 4), InsP2 by 421 +/- 67% and InsP3 by 124 +/- 33% above basal. Incubation of cells for 15 h with 0.5 ng of pertussis toxin/ml decreased GTP[S]-stimulated InsP1 production in saponin-treated cells by 30 +/- 10% (n = 3), InsP2 production by 45 +/- 7% (n = 4) and InsP3 production by 49 +/- 6% (n = 4). These data demonstrate that in embryonic chick atrial cells at least two independent G-proteins, a pertussis toxin-sensitive G-protein and a pertussis toxin-insensitive G-protein, play a role in coupling muscarinic agonist binding to phospholipase C activation and to inositol phosphate production.

Involvement of GTP-binding proteins in actin polymerization in human neutrophils

The motility of human neutrophils, which is of vital importance for the role of these cells in host defense, is based on rapid and dynamic changes of the filamentous actin F-actin) network. Consequently, to understand how neutrophils move and ingest particles, we need to know how polymerization and depolymerization of actin are regulated. Previous studies by several investigators have, based on indirect evidence obtained with pertussis toxin, suggested a role for GTP-binding protein(s) (G protein) in chemotaxis-induced, but not phagocytosis-induced, reorganization of the F-actin network. The aim of the present investigation was to study the effects of directly activated G proteins (i.e., without prior ligand-receptor complex formation) on the F-actin content in human neutrophils. AlF4- induced a pronounced and sustained increase in F-actin in intact neutrophils. This effect coincided with an increase in cytosolic free Ca2+, indicating that phospholipase C and the subsequent transduction mechanism were also activated. Inhibition of phospholipase C activity by extensive depression of the cytosolic free Ca2+ level (less than 20 nM) only marginally affected the AlF4(-)-induced rise in F-actin content. The major part of the AlF4(-)-induced rise in F-actin content was also resistant to pertussis toxin, suggesting that pertussis toxin-insensitive G proteins in neutrophils are also able to trigger actin polymerization. The specificity of AlF4- in activating G proteins was also tested in permeabilized cells. In this case the effect was more rapid and could be totally abolished by guanosine 5'-[beta-thio]diphosphate. In analogy, in permeabilized cells guanosine 5'-[gamma-thio]triphosphate mimicked the effect of AlF4- on actin polymerization, and the effect induced by this nonhydrolyzable GTP analogue could also be totally abolished by guanosine 5'-[beta-thio]diphosphate. In summary, the present data support our previous hypothesis that G proteins are intimately linked to actin polymerization in human neutrophils.

The glycosyl phosphatidylinositol-linked Fc gamma RIIIPMN mediates transmembrane signaling events distinct from Fc gamma RII

To investigate the ability of FcgammaRIII(PMN), the GPI-anchored isoform of FcgammaRIII (CD16) in polymorphonuclear leukocytes (PMN), to mediate transmembrane signaling events, we measured changes in membrane potential with DiOC(5) and in intracellular calcium with indo-1. FcgammaR were ligated by anti-FcgammaRIII mAb 3G8 (IgG and Fab), anti-FcgammaRII mAb IV.3 (IgG and Fab), and human IgG aggregates. Cell bound mAbs were also crosslinked by goat F(ab')(2) anti-mouse IgG. 3G8 IgG elicited a rapid change in [Ca(2+)](i), which was unaffected by EGTA, Vibrio cholerae toxin (CT), or Bordetella pertussis toxin (PT), and was abolished by BAPTA . Univalent receptor binding with 3G8 Fab gave no response but crosslinking with F(aV)2 GAM gave a rapid [Ca2,](i) response. Neither IV.3 Fab, IV.3 IgG, nor crosslinking of IV.3 Fab elicited a calcium signal. PI-PLC-treated PMN with the density of FcgammaRIII(PMN) reduced to that of FcgammaRII showed an unattenuated change in [Ca(2+)](i), with a 3G8 stimulus. The effects of IgG aggregates paralleled those of 3G8 mAb. These data indicate that multivalent ligation of FcgammaRIII(PMN) initiates an increase in [Ca(2+)];, derived from intracellular stores, that is distinct from both the FMLP- and FcgammaRII-induced responses. Ligand-dependent interaction with FcgammaRII is not required. Since FcgammaRIII(PMN) can internalize the FcgammaRIII-specific probe Con A-opsonized E and lyse anti-FcgammaRIII heteroantibody-opsonized chick E, this GPI-anchored molecule mediates both signal transduction and integrated cell responses.

Agonist-sensitive binding of a photoreactive GTP analog to a G-protein alpha-subunit in membranes of HL-60 cells

Myeloid-differentiated HL-60 cells were used to study the activation of G-proteins by receptor agonists. Following incubation of membranes with the photoreactive GTP analog. [alpha-32P]GTP azidoanilide, and subsequent exposure to ultraviolet light (254 nm), photolabeling of 40 kDa proteins comigrating with the Gi2 alpha-subunit was observed. Photolabeling in the absence or presence of the chemoattractant, N-formyl-methionyl-leucyl-phenylalanine (FMLP), absolutely required Mg2+; FMLP stimulated photolabeling at all Mg2+ concentrations employed (up to 30 mM). Addition of GDP (3-50 microM) reduced basal photolabeling to a greater extent than photolabeling stimulated by FMLP. FMLP did not stimulate photolabeling of proteins modified by pertussis toxin. Leukotriene B4 and C5a also stimulated photolabeling of 40 kDa proteins. The results indicate that (i) the major G-protein in HL-60 cells, Gi2, requires Mg2+ for basal and receptor-stimulated activity, (ii) effective receptor-mediated activation of G-proteins is observed at mM concentrations of Mg2+, and (iii) receptor agonists apparently reduce the affinity of G-proteins for GDP.

Chemotactic peptide receptor-cytoskeletal interactions and functional correlations in differentiated HL-60 cells and human polymorphonuclear leukocytes

We studied the chemotactic peptide receptor/cytoskeletal interactions in HL-60 cells induced to differentiate with different agents and attempted to correlate these observations with the acquisition of different functional responses. Dibutyryl cyclic AMP-treated cells showed rapid superoxide anion production in response to N-formyl-methionyl-leucyl-phenylalanine (FMLP) and slow, sustained response to phorbol myristate acetate (PMA). Retinoic acid-induced cells showed a slow, sustained response to both FMLP and PMA. Interferon-gamma-treated cells produced no superoxide anion on stimulation with FMLP, whereas tumor necrosis factor (TNF)-treated cells showed a slight response. Chemotactic peptide receptor association was the same in the HL-60 cells treated with different agents, despite marked differences in the superoxide anion generation and actin polymerization responses to FMLP and PMA in these cells. In mature neutrophils chemotactic peptide receptor association with the cytoskeleton was not affected by either pertussis or cholera toxin. However, both toxins inhibited FMLP-induced actin polymerization and superoxide anion generation. This suggested involvement of a G-protein similar to Gt, rather than Gi or Gs. Neither toxin had any effect on PMA-induced superoxide anion generation. These observations indicate that receptor association with the cytoskeleton may not have a significant role in affecting signal recognition and response. Among the several possible roles suggested, clearance of the occupied receptors may be the most important role of the cytoskeletal association. HL-60 cells induced to differentiate with different agents (because of their varied functional responses) might prove very useful in dissecting the molecular mechanisms regulating stimulus-induced activation of neutrophils.

Influence of bacterial toxins and forskolin upon vasopressin-induced inositol phosphate accumulation in WRK 1 cells

The accumulation of inositol phosphates in WRK 1 cells, stimulated with a range of vasopressin concentrations, was diminished by prior exposure to cholera toxin or forskolin, whilst that observed in the presence of maximal concentrations of the hormone was enhanced in pertussis-toxin-treated cells. In the presence of [32P]NAD+, both cholera toxin and pertussis toxin provoked the labelling of peptides with approximate Mrs of 45,000 and 41,000 respectively in the membranes of WRK 1 cells. Exposure to cholera toxin or forskolin for 15-18 h enhanced cyclic AMP accumulation in these cells. The concentrations of these agents which provoked half-maximal cyclic AMP accumulation were similar to those required to diminish receptor-mediated inositol phosphate accumulation by 50%. In contrast, half-maximal ADP-ribosylation of the 45,000Mr peptide needed 100-fold greater concentrations of the toxin than were effective in provoking half-maximal inhibition of inositol phosphate accumulation. Cholera toxin or forskolin also reduced the maximal specific binding, to intact WRK 1 cells, of both [3H][Arg8]vasopressin and the V1a antagonist [3H][beta-mercapto-beta,beta-cyclopentamethylenepropionic acid,O-methyl-Tyr2, Arg8]vasopressin. The kinetics for the loss of this binding capacity following cholera-toxin treatment were very similar to those describing the diminution of vasopressin-stimulated inositol phosphate accumulation in the same cells.