[Immunobiological properties of Bordetella pertussis lipopolysaccharide in the acellular pertussis vaccine].

AIM: Study of Bordetella pertussis lipopolysaccharide (LPS) immunobiological properties in the acellular pertussis vaccine. MATERIALS AND METHODS: Experimental series of acellular pertussis vaccines (APV), lyophilized LPS were used. Antibody titers against LPS in mice sera were evaluated by using EIA with peroxidase conjugate of anti-species antibodies against mice IgG. LPS activity in B. pertussis antigen complex preparations was determined in quantitative chromogenic LAL-test by end point. APV protective activity was determined in mice test during intracerebral infection by B. pertussis strain No. 18323 virulent culture. APV safety was determined in the mice body weight change test. RESULTS: The presence of LPS in APV was shown in immune electrophoresis with purified B. pertussis LPS preparation as a control. Formalin treatment changes immunochemical properties of APV LPS that lead to the shift of precipitation bands with pertussis agglutinating sera from the start zone into cathode. The quantity of LPS in pertussis culture supernatants was on average 49050 +/- 6774 endotoxin units per ml (EU/ml). In APV preparations the quantity of LPS was on average 906 +/- 90 EU/ml, i.e. decreased by more than 50 times. An increase of antibody titers against B. pertussis LPS in mice sera after the APV immunization was shown in EIA, which gives evidence of its presence in immunogenic form in the complex preparations. The preclinical studies carried out show protective activity and specific safety of the experimental APV series. CONCLUSION: Formalin-neutralized APV preparation is a complex of protein antigens in association with LPS. Formalin treatment results in modification of LPS molecule that retains antigenic properties but is significantly less toxic.

The receptor for the orexigenic peptide melanin-concentrating hormone is a G-protein-coupled receptor.

Gene-knockout studies of melanin-concentrating hormone (MCH) and its effect on feeding and energy balance have firmly established MCH as an orexigenic (appetite-stimulating) peptide hormone. Here we identify MCH as the ligand for the orphan receptor SLC-1. The rat SLC-1 is activated by nanomolar concentrations of MCH and is coupled to the G protein G alpha i/o. The pattern of SLC-1 messenger RNA expression coincides with the distribution of MCH-containing nerve terminals and is consistent with the known central effects of MCH. Our identification of an MCH receptor could have implications for the development of new anti-obesity therapies.

Active movement of T cells away from a chemokine.

Movement towards or away from a given stimulus guides the directional migration of prokaryotes, simple eukaryotes and neurons. As bi-directional cues may influence entry and exit of immune effector cells from tissue sites, we evaluated the migratory responses of T-cell subsets to varying concentrations of the chemokine stromal cell derived factor-1 (SDF-1). There was selective repulsion of subpopulations of T cells at high concentrations of recombinant SDF-1 or naturally occurring bone marrow-derived SDF-1, which could be inhibited by pertussis toxin and antibody against the chemokine receptor CXCR4. Distinct sensitivity profiles to genistein, herbimycin and 8-Br-cAMP biochemically distinguished movement of cells towards or away from an SDF-1 gradient. In vivo, antigen-induced T-cell recruitment into the peritoneal cavity was reversed by high but not low concentrations of SDF-1. The phenomenon of movement away from a chemokine represents a previously unknown mechanism regulating the localization of mature T cells. It adds to the functional repertoire of chemokines that may participate in immune physiology and may be applied therapeutically to alter the immune response.

The V3 domain of the HIV-1 gp120 envelope glycoprotein is critical for chemokine-mediated blockade of infection.

The ability of CD8 T cells derived from human immunodeficiency virus (HIV)-infected patients to produce soluble HIV-suppressive factor(s) (HIV-SF) has been suggested as an important mechanism of control of HIV infection in vivo. The C-C chemokines RANTES, MIP-1 alpha and MIP-1 beta were recently identified as the major components of the HIV-SF produced by both immortalized and primary patient CD8 T cells. Whereas they potently inhibit infection by primary and macrophage-tropic HIV-1 isolates, T-cell line-adapted viral strains tend to be insensitive to their suppressive effects. Consistent with this discrepancy, two distinct chemokine receptors, namely, CXCR4 (ref. 7) and CCR5 (ref. 8), were recently identified as potential co-receptors for T-cell line-adapted and macrophage-tropic HIV-1 isolates, respectively. Here, we demonstrate that the third hypervariable domain of the gp 120 envelope glycoprotein is a critical determinant of the susceptibility of HIV-1 to chemokines. Moreover, we show that RANTES, MIP-1 alpha and MIP-1 beta block the entry of HIV-1 into cells and that their antiviral activity is independent of pertussis toxin-sensitive signal transduction pathways mediated by chemokine receptors. The ability of the chemokines to block the early steps of HIV infection could be exploited to develop novel therapeutic approaches for AIDS.

Rapid G protein-regulated activation event involved in lymphocyte binding to high endothelial venules.

The homing of blood borne lymphocytes into lymph nodes and Peyer's patches is mediated in part by recognition and binding to specialized high endothelial venules (HEV). Here we demonstrate that a rapid pertussis toxin-sensitive lymphocyte activation event can participate in lymphocyte recognition of HEV. In situ video microscopic analyses of lymphocyte interactions with HEV in exteriorized mouse Peyer's patches reveal that pertussis toxin has no effect on an initial "rolling" displayed by many lymphocytes, but inhibits an activation-dependent "sticking" event required for lymphocyte arrest. This is the first demonstration that physiologic lymphocyte-endothelial interactions can involve sequential rolling, activation, and activation-dependent arrest, previously shown only for neutrophils. The inhibitory effect of the toxin is dependent on its G protein-modifying ADP-ribosyltransferase activity and can be reversed by phorbol myristic acetate, which bypasses cell surface receptors to trigger activation-dependent adhesion. Lymphocyte sticking can occur within 1-3 s after initiation of rolling. We conclude that a rapid receptor-mediated activation event involving G protein signaling can trigger stable lymphocyte attachment to HEV in vivo, and may play a critical role in regulating lymphocyte homing.

Monocyte chemotactic protein 1 is a potent activator of human basophils.

Cytokines belonging to the RANTES/SIS family are highly induced in a number of pathophysiological processes such as autoimmune disorders, cancers, atherosclerosis, and chronic inflammation. However, apart from their chemotactic activity on monocytes and particular lymphocyte types, the biological activities in the human system of this recently discovered cytokine family are largely unknown. Here we report that one family member, described as monocyte chemotactic protein 1 (MCP-1), strongly activates mature human basophils in a pertussis toxin-sensitive manner. MCP-1 causes a rise in the cytosolic free calcium level in basophils and monocytes, but not in other blood leukocyte types, and triggers basophil degranulation at low concentrations (ED50 = 3-10 nM). Thus, MCP-1 is a cytokine capable of directly inducing histamine release by basophils. Furthermore, MCP-1 promotes the formation of leukotriene C4 by basophils pretreated with interleukin 3 (IL-3), IL-5, or granulocyte/macrophage colony-stimulating factor. MCP-1-induced basophil mediator release may play an important role in allergic inflammation and other pathologies expressing MCP-1.

Pertussis toxin inhibits migration of B and T lymphocytes into splenic white pulp cords.

The normal migration route of B cells into follicular areas of spleen and lymph nodes is altered in the case of autoreactive cells that have bound self-antigen. To begin characterizing the molecular requirements for B cell migration into follicles, cells were treated with pertussis toxin (PTX), an inhibitor of signaling by many G protein-coupled chemokine receptors. Lymphocyte accumulation in the spleen is not inhibited by PTX and, therefore, the distribution of transferred cells was examined in this tissue. In contrast to untreated cells that localized predominantly in follicular areas within white pulp cords, PTX-treated B cells failed to enter white pulp areas altogether and accumulated in the splenic red pulp. T cells were also excluded from white pulp cords and in the case of both cell types, the adenosine diphosphate-ribosylating subunit of the toxin was required to block white pulp entry. These findings implicate a G protein-coupled receptor in lymphocyte migration into splenic white pulp cords. Exclusion of PTX-treated cells from all organized areas of secondary lymphoid tissues raises the possibility that the association observed between PTX treatment and predisposition to autoimmune disease results from inhibition of tolerance mechanisms that normally operate within secondary lymphoid tissues.

Role in host cell invasion of Trypanosoma cruzi-induced cytosolic-free Ca2+ transients.

Trypanosoma cruzi enters cells by a unique mechanism, distinct from phagocytosis. Invasion is facilitated by disruption of host cell actin microfilaments, and involves recruitment and fusion of host lysosomes at the site of parasite entry. These findings implied the existence of transmembrane signaling mechanisms triggered by the parasites in the host cells before invasion. Here we show that infective trypomastigotes or their isolated membranes, but not the noninfective epimastigotes, induce repetitive cytosolic-free Ca2+ transients in individual normal rat kidney fibroblasts, in a pertussis toxin-sensitive manner. Parasite entry is inhibited by buffering or depleting host cell cytosolic-free Ca2+, or by pretreatment with Ca2+ channel blockers or pertussis toxin. In contrast, invasion is enhanced by brief exposure of the host cells to cytochalasin D. These results indicate that a trypomastigote membrane factor triggers cytosolic-free Ca2+ transients in host cells through a G-protein-coupled pathway. This signaling event may promote invasion through modulation of the host cell actin cytoskeleton.

Increased intracellular cyclic adenosine monophosphate inhibits T lymphocyte-mediated cytolysis by two distinct mechanisms.

Cholera toxin (CT), but not pertussis toxin (PT), treatment of cloned murine CTL inhibited target cell lysis in a dose-dependent fashion. The effects of CT were mimicked by forskolin and cyclic adenosine monophosphate (cAMP) analogues. Inhibition of cytotoxicity by CT and cAMP analogs was mediated in part by attenuation of conjugate formation. Additionally, both CT and cAMP analogs blocked the increase in intracellular Ca2+ induced by stimulation of the TCR complex by mAbs. These findings indicate that cAMP inhibits the activity of CTL by two distinct mechanisms and suggests a role for this second messenger in CTL-mediated cytolysis.

Site-specific alterations in the B oligomer that affect receptor-binding activities and mitogenicity of pertussis toxin.

Pertussis toxin plays a major role in the pathogenesis of whooping cough and is considered an important constituent of vaccines against this disease. It is composed of five different subunits associated in a molar ratio 1S1:1S2:1S3:2S4:1S5. The S1 subunit is responsible for the ADP-ribosyltransferase activity of the toxin. The B moiety, composed of S2 through S5, recognizes and binds to the target cell receptors and has some ADP-ribosyltransferase-independent activities such as mitogenicity. Site-directed mutagenesis of subunits S2 and S3 allowed us to identify amino acid residues involved in receptor binding. Of all the modifications generated, the deletion of Asn 105 in S2 and of Lys 105 in S3 resulted in the more drastic reduction of binding to haptoglobin and CHO cells, respectively. A holotoxin carrying both deletions presented a mitogenicity reduced to an undetectable level. The combination of these B oligomer mutations with two substitutions in the S1 subunit led to the production of a toxin analog with reduced ADP-ribosyltransferase-dependent and -independent activities including mitogenicity. As shown by immunoprecipitation with various monoclonal antibodies, the mutant holotoxin was correctly assembled and antigenically similar to the native toxin. This toxin analog induced toxin-neutralizing antibodies at the same level as the holotoxin carrying only mutations in the S1 subunit, and may therefore be considered a useful candidate for the development of a new generation vaccine against whooping cough.

The neutrophil-activating protein (HP-NAP) of Helicobacter pylori is a protective antigen and a major virulence factor.

Helicobacter pylori infection induces the appearance of inflammatory infiltrates, consisting mainly of neutrophils and monocytes, in the human gastric mucosa. A bacterial protein with neutrophil activating activity (HP-NAP) has been previously identified, but its role in infection and immune response is still largely unknown. Here, we show that vaccination of mice with HP-NAP induces protection against H. pylori challenge, and that the majority of infected patients produce antibodies specific for HP-NAP, suggesting an important role of this factor in immunity. We also show that HP-NAP is chemotactic for human leukocytes and that it activates their NADPH oxidase to produce reactive oxygen intermediates, as demonstrated by the translocation of its cytosolic subunits to the plasma membrane, and by the lack of activity on chronic granulomatous disease leukocytes. This stimulating effect is strongly potentiated by tumor necrosis factor alpha and interferon gamma and is mediated by a rapid increase of the cytosolic calcium concentration. The activation of leukocytes induced by HP-NAP is completely inhibited by pertussis toxin, wortmannin, and PP1. On the basis of these results, we conclude that HP-NAP is a virulence factor important for the H. pylori pathogenic effects at the site of infection and a candidate antigen for vaccine development.

Histidyl-tRNA synthetase and asparaginyl-tRNA synthetase, autoantigens in myositis, activate chemokine receptors on T lymphocytes and immature dendritic cells.

Autoantibodies to histidyl-tRNA synthetase (HisRS) or to alanyl-, asparaginyl-, glycyl-, isoleucyl-, or threonyl-tRNA synthetase occur in approximately 25% of patients with polymyositis or dermatomyositis. We tested the ability of several aminoacyl-tRNA synthetases to induce leukocyte migration. HisRS induced CD4(+) and CD8(+) lymphocytes, interleukin (IL)-2-activated monocytes, and immature dendritic cells (iDCs) to migrate, but not neutrophils, mature DCs, or unstimulated monocytes. An NH(2)-terminal domain, 1-48 HisRS, was chemotactic for lymphocytes and activated monocytes, whereas a deletion mutant, HisRS-M, was inactive. HisRS selectively activated CC chemokine receptor (CCR)5-transfected HEK-293 cells, inducing migration by interacting with extracellular domain three. Furthermore, monoclonal anti-CCR5 blocked HisRS-induced chemotaxis and conversely, HisRS blocked anti-CCR5 binding. Asparaginyl-tRNA synthetase induced migration of lymphocytes, activated monocytes, iDCs, and CCR3-transfected HEK-293 cells. Seryl-tRNA synthetase induced migration of CCR3-transfected cells but not iDCs. Nonautoantigenic aspartyl-tRNA and lysyl-tRNA synthetases were not chemotactic. Thus, autoantigenic aminoacyl-tRNA synthetases, perhaps liberated from damaged muscle cells, may perpetuate the development of myositis by recruiting mononuclear cells that induce innate and adaptive immune responses. Therefore, the selection of a self-molecule as a target for an autoantibody response may be a consequence of the proinflammatory properties of the molecule itself.

Pertussis toxin inhibits activation-induced cell death of human thymocytes, pre-B leukemia cells and monocytes.

Activation of human thymocytes and pre-B cells via the CD3/T cell receptor (TCR) complex or the IgM/B cell receptor complex, respectively, results in apoptotic cell death. Similarly, cross-linking of the activation marker CD69, which belongs to the natural killer complex, causes apoptosis of lipopolysaccharide-preactivated monocytes. Here we show that pertussis toxin (PTX) inhibits the activation-induced apoptosis of these three cell types, though it fails to prevent the programmed cell death that follows exposure of cells to the synthetic glucocorticoid dexamethasone (thymocytes, pre-B cells) or to interleukin 4 (monocytes). The capacity of pertussis toxin to suppress activation-induced death is not due to quenching of the activation signal, because thymocytes exposed to PTX are still capable of mobilizing Ca2+ after TCR-alpha/beta cross-linking and proliferate in response to costimulation with PTX and CD3/TCR ligation. The apoptosis-inhibitory effect of PTX depends on the presence of an intact adenosine diphosphate (ADP)-ribosylating moiety, since a mutant pertussis toxin molecule that lacks enzymatic activity, but still possesses the membrane translocating activity, fails to interfere with activation-induced cell death. A toxin that induces a different spectrum of ADP ribosylation than PTX, cholera toxin, fails to inhibit apoptosis. To suppress apoptosis, the intact PTX holotoxin must be added to cells before the lethal activation step; its addition 30 min after initial activation remains without effect on apoptosis. These data unravel a PTX sensitive signal transduction event that intervenes during an early step of activation-induced cell death of immune cells.

Tumor necrosis factor/cachectin increases permeability of endothelial cell monolayers by a mechanism involving regulatory G proteins.

Endothelium is an important target of tumor necrosis factor/cachectin (TNF), a central mediator of the host response in endotoxemia and Gram-negative sepsis. In this report, TNF is shown to increase the permeability of endothelial cell monolayers to macromolecules and lower molecular weight solutes by a mechanism involving a pertussis toxin-sensitive regulatory G protein. Within 1-3 h of exposure to TNF (5 nM), changes in cell shape/cytoskeleton occurred that led to disruption of monolayer continuity with the formation of intercellular gaps. Correlated with these structural changes was an increase in endothelial permeability to macromolecular and lower molecular weight tracers; time-dependent, reversible increases in passage of these tracers, evident by 1-3 h, were observed after addition of TNF to cultures. Perturbation of barrier function by TNF also depended on the dose of TNF added being half-maximal by approximately 0.4 nM. Only a brief exposure (15 min) of TNF to endothelium was required to induce an increase in permeability, and this was not prevented by the presence of cycloheximide or actinomycin D. Preincubation of monolayers with pertussis toxin blocked in parallel TNF-induced increased passage of solutes and cell shape/cytoskeletal perturbation, indicating the close correlation between these changes in endothelial cell function. In contrast, pertussis toxin did not alter TNF-induced modulation of two endothelial cell coagulant properties. These data provide evidence for two intracellular pathways of TNF action that are distinguishable by pertussis toxin and provide insight into a mechanism underlying loss of solute from the intravascular space mediated by TNF: alteration in endothelial cell barrier function.

Chemoattractant-induced activation of c-fos gene expression in human monocytes.

Human monocytes use the products of phosphoinositide hydrolysis (1,2-diacylglycerol and inositol 1,4,5-triphosphate) as second messengers to trigger rapid cellular activation during the occupancy of chemoattractant receptors. The effect of chemoattractants on modulation of gene expression in monocytes was examined in this study. The chemoattractants FMLP and platelet-activating factor induced the progressive increase of c-fos RNA to 6-15-fold over those of control within 30 min after treatment. Similar kinetics of c-fos gene activation was also observed when cells were treated with PMA or sn-1,2-dioctanoylglycerol, but not with the calcium mobilizer ionomycin, suggesting a role for protein kinase C in gene regulation by chemoattractant receptors. Activation of c-fos gene expression by FMLP is mediated through a pertussis toxin-sensitive G protein, since pertussis toxin treatment of the cells blocked the induction of the c-fos gene by FMLP but not PMA. The level of c-myc RNA was slightly decreased after 1 h of treatment with chemoattractants, but not with PMA or diacylglycerol. This implies that chemoattractant receptor occupancy generates signals beyond protein kinase C activation that are capable of selectively downregulating monocyte gene expression. The effect of FMLP and PMA on the accumulation of c-fos RNA appears to result from altering both the rate of transcription and message stability. These observations indicate that signals generated through chemoattractant receptor occupancy may regulate monocyte function at the genetic level.

Monocyte selectivity and tissue localization suggests a role for breast and kidney-expressed chemokine (BRAK) in macrophage development.

Although numerous chemokines act on monocytes, none of them is specific for these cells. Here, we show that breast and kidney-expressed chemokine (BRAK) is a highly selective monocyte chemoattractant. Migration efficacy and Bordetella pertussis toxin-sensitive Ca(2+) mobilization responses to BRAK were strongly enhanced after treatment of monocytes with the cyclic AMP-elevating agents prostaglandin E(2) and forskolin. BRAK is the first monocyte-selective chemokine, as other types of blood leukocytes or monocyte-derived dendritic cells and macrophages did not respond. Expression in normal skin keratinocytes and dermal fibroblasts as well as lamina propria cells in normal intestinal tissues suggests a homeostatic rather than an inflammatory function for this chemokine. In addition, macrophages were frequently found to colocalize with BRAK-producing fibroblasts. We propose that BRAK is involved in the generation of tissue macrophages by recruiting extravasated precursors to fibroblasts, which are known to secrete essential cytokines for macrophage development.

Primary role for Gi protein signaling in the regulation of interleukin 12 production and the induction of T helper cell type 1 responses.

We explored the role of Gi protein signaling in the regulation of interleukin (IL)-12 production and T helper cell type 1 (Th1) T cell differentiation. In initial studies, we showed that treatment of normal mice with pertussis toxin (PT), which inhibits Gi protein signaling, enhanced the capacity of splenocytes to produce IL-12 in response to both microbial and nonmicrobial stimuli. In addition, PT treatment increased the production of tumor necrosis factor (TNF)-alpha and IL-10 by stimulated cells. These findings were corroborated by the fact that untreated Gi2alpha(2/-) mice exhibited enhanced production of IL-12 and TNF-alpha by splenocytes, and of IL-12 p40 by purified spleen CD8alpha(+) lymphoid dendritic cells. Finally, we showed that while normal BALB/c mice infected with Leishmania major exhibited a nonhealing phenotype, those treated with PT when infection was initiated exhibited a healing phenotype along with an enhancement of leishmania-specific Th1 responses in draining lymph nodes. Further, healing was prevented by coadministration of anti-IL-12 and PT. These data demonstrate that endogenous Gi protein signaling has a primary role in the regulation of IL-12 production and the induction of Th1 responses in vivo.

Identification of human neutrophil-derived cathepsin G and azurocidin/CAP37 as chemoattractants for mononuclear cells and neutrophils.

Macrophage infiltration into inflammatory sites is generally preceded by neutrophils. This suggests neutrophils may be the source of chemotactic factors for monocytes. To identify these putative monocyte attractants, we have systematically prepared neutrophil granules, lysed them, and sequentially purified the released proteins by several reverse phase chromatography procedures. Assays for monocyte chemotactic activity of the chromatography fractions yielded a major peak of activity associated with a protein of 30 kD, according to SDS-PAGE analysis. NH2-terminal sequence of the protein revealed this to be identical to cathepsin G. The monocyte chemotactic activity of human cathepsin G was dose dependent with optimal concentration at 0.5-1 microg/ml. Cathepsin G is chemotactic rather than chemokinetic for monocytes, as demonstrated by checkerboard analysis. Cathepsin G-induced monocyte chemotaxis is partially pertussis toxin sensitive implying the involvement of a G protein-coupled receptor. Enzymatic activity of cathepsin G is associated with its monocyte chemotactic activity, since DFP- or PMSF-inactivated cathepsin G no longer induced monocyte migration. The chemotactic activity of cathepsin G can also be completely blocked by alpha1 antichymotrypsin, a specific inhibitor of chymotrypsin-like proteinases present in human plasma. In addition, cathepsin G is also a potent chemoattractant for neutrophils and a chemokinetic stimulant for T cells. In the course of pursuing these in vitro studies, we established that the T cell chemoattractant, azurocidin/CAP37 from human neutrophil granules, at doses of 0.05 to 5 microg/ml, was chemotactic for monocytes and neutrophils. As predicted from the in vitro chemotactic activity, subcutaneous injection of cathepsin G into BALB/c mice led to infiltration of both mononuclear cells and neutrophils. Thus, the transition of inflammatory exudate from neutrophil to mononuclear cells can be mediated, at least in part, by extracellular release of neutrophil granule proteins such as cathepsin G and azurocidin/CAP37.

The B-oligomer of pertussis toxin deactivates CC chemokine receptor 5 and blocks entry of M-tropic HIV-1 strains.

Infection of target cells by HIV-1 requires initial binding interactions between the viral envelope glycoprotein gp120, the cell surface protein CD4, and one of the members of the seven-transmembrane G protein-coupled chemokine receptor family. Most primary isolates (R5 strains) use chemokine receptor CCR5, but some primary syncytium-inducing, as well as T cell line-adapted, strains (X4 strains) use the CXCR4 receptor. Signaling from both CCR5 and CXCR4 is mediated by pertussis toxin (PTX)-sensitive G(i) proteins and is not required for HIV-1 entry. Here, we show that the PTX holotoxin as well as its binding subunit, B-oligomer, which lacks G(i)-inhibitory activity, blocked entry of R5 but not X4 strains into primary T lymphocytes. Interestingly, B-oligomer inhibited virus production by peripheral blood mononuclear cell cultures infected with either R5 or X4 strains, indicating that it can affect HIV-1 replication at both entry and post-entry levels. T cells treated with B-oligomer did not initiate signal transduction in response to macrophage inflammatory protein (MIP)-1beta or RANTES (regulated upon activation, normal T cell expressed and secreted); however, cell surface expression of CCR5 and binding of MIP-1beta or HIV-1 to such cells were not impaired. The inhibitory effect of B-oligomer on signaling from CCR5 and on entry of R5 HIV-1 strains was reversed by protein kinase C (PKC) inhibitors, indicating that B-oligomer activity is mediated by signaling events that involve PKC. B-oligomer also blocked cocapping of CCR5 and CD4 induced by R5 HIV-1 in primary T cells, but did not affect cocapping of CXCR4 and CD4 after inoculation of the cultures with X4 HIV-1. These results suggest that the B-oligomer of PTX cross-deactivates CCR5 to impair its function as a coreceptor for HIV-1.

Intracellular elevations of free calcium induced by activation of histamine H1 receptors in interphase and mitotic HeLa cells: hormone signal transduction is altered during mitosis.

A broad range of membrane functions, including endocytosis and exocytosis, are strongly inhibited during mitosis. The underlying mechanisms are unclear, however, but will probably be important in relation to the mitotic cycle and the regulation of surface phenomena generally. A major unanswered question is whether membrane signal transduction is altered during mitosis; suppression of an intracellular calcium [( Ca2+]i) transient could inhibit exocytosis; [Ca2+]i elevation could disassemble the mitotic spindle. Activation of the histamine H1 receptor interphase in HeLa cells is shown here by Indo-1 fluorescence to produce a transient elevation of [Ca2+]i. The [Ca2+]i transient consists of an initial sharp rise that is at least partially dependent on intracellular calcium followed by an elevated plateau that is absolutely dependent on extracellular calcium. The [Ca2+]i transient is completely suppressed by preincubation with the tumor promoter, phorbol myristate acetate, but is unaffected by preincubation with pertussis toxin (islet-activating protein). In mitotic (metaphase-arrested) HeLa cells, the [Ca2+]i transient is largely limited to the initial peak. Measurement of 45Ca2+ uptake shows that it is stimulated by histamine in interphase cells, but not in mitotics. We conclude that the histamine-stimulated generation of the second messenger, [Ca2+]i, in mitotic cells is limited by failure to activate a sustained calcium influx. The initial phase of calcium mobilization from intracellular stores is comparable to that in interphase cells. Hormone signal transduction thus appears to be altered during mitosis.