Serotonin storage pools in basophil leukemia and mast cells: characterization of two types of serotonin binding protein and radioautographic analysis of the intracellular distribution of [3H]serotonin

We studied binding of serotonin to protein(s) derived from rat basophil leukemia (RBL) cells and mast cells. We found two types of serotonin binding protein in RBL cells. These proteins differed from one another in molecular weight and eluted in separate peaks from sephadex G-200 columns. Peak I protein (KD = 1.9 X 10(-6) M) was a glycoprotein that bound to concanavalin A (Con A); Peak II protein (KD1 = 4.5 X 10(-8) M; KD2 = 3.9 X 10(-6) M) did not bind to Con A. Moreover, binding of [3H]serotonin to protein of peak I was sensitive to inhibition by reserpine, while binding of [3H]serotonin to protein of peak II resisted inhibition by that drug. Other differences between the two types of binding protein were found, the most significant of which was the far more vigorous conditions of homogenization required to extract peak I than peak II protein. Neither peak I nor peak II protein resembled the serotonin binding protein (SBP) that is found in serotonergic neurons of the brain and gut. Electron microscope radioautographic analysis of the intracellular distribution of [3H]serotonin taken up in vitro by RBL cells or in vivo by murine mast cells indicated that essentially all of the labeled amine was located in cytoplasmic granules. No evidence for a pool in the cytosol was found and all granules were capable of becoming labeled. The presence of two types of intracellular serotonin binding proteins in these cells may indicate that there are two intracellular storage compartments for the amine. Both may be intragranular, but peak I protein may be associated with the granular membrane while peak II protein may be more free within the granular core. Different storage proteins may help to explain the differential release of amines from mast cell granules.     

Study of the transit of an integral membrane protein from secretory granules through the plasma membrane of secreting rat basophilic leukemia cells using a specific monoclonal antibody

The monoclonal antibody 5G10 reacted specifically with an 80-kD integral membrane protein in rat basophilic leukemia (RBL) cells. Immunofluorescence microscopy studies of RBL cells, fixed and permeabilized, revealed that the 80-kD protein was located in the membrane of cytoplasmic vesicles. The vesicles were identified as secretory granules by their content in immunoreactive serotonin. Expression of the 5G10 antigen on the surface of unstimulated RBL cells was low. However, RBL cells stimulated to secrete with anti-dinitrophenyl IgE followed by dinitrophenyl-bovine serum albumin or with the Ca2+ ionophore A-23187 displayed an increased expression of the antigen on their surface. Surface exposure of the 5G10 antigen was maximal at 5 min after stimulation of secretion. Removal of dinitrophenyl-bovine serum albumin from the incubation medium resulted in internalization of 50% of the antigen within 10 min.     

Specific uptake of serotonin by murine macrophages

In view of the reported immunomodulatory properties of the monoaminergic neurotransmitter, serotonin (5HT), this study aimed to assess whether 5HT specifically associates with immunocompetent cells. Although murine splenocytes appear to lack high-affinity membrane binding sites for 5HT, they do possess a specific, active, 5HT uptake system similar in affinity (Km = 40 nM) to that described in platelets. This uptake system appears to be confined to macrophages. Further, macrophages rapidly metabolize 5HT to its 5-hydroxyindole acetic acid metabolite. Specific uptake of serotonin by macrophages may thus constitute an important mechanism whereby this amine is able to regulate immune function.     

Immunologically activated chloride channels involved in degranulation of rat mucosal mast cells.

Crosslinking of type I Fc epsilon receptors (Fc epsilon RI) on the surface of basophils or mast cells initiates a cascade of processes leading to the secretion of inflammatory mediators. We report here a correlation between mediator secretion and the activation of Cl- channels in rat mucosal-type mast cells (line RBL-2H3). Stimulation of RBL cells by either IgE and antigen or by a monoclonal antibody specific for the Fc epsilon RI, resulted in the activation of Cl- ion channels as detected by the patch-clamp technique. Channel activation occurred slowly, within minutes after stimulation. The channel has a slope conductance of 32 pS at potentials between 0 and -100 mV, and an increasing open-state probability with increasing depolarization. Activation of apparently the same Cl- channels could be mimicked without stimulation by isolating inside-out membrane patches in tyrode solution. Parallel inhibition of both Cl- channel activity and mediator secretion, as monitored by serotonin release, was observed by two compounds, the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and the anti-allergic drug cromolyn. NPPB inhibited both the antigen-induced Cl- current and the serotonin release, where half-maximal inhibition occurred at similar doses, at 52 microM and 77 microM, respectively. The drug cromolyn, recently found to inhibit immunologically induced mediator secretion from RBL cells upon intracellular application, also blocks Cl- channels (IC50 = 15 microM) when applied to the cytoplasmic side of an inside-out membrane patch. The observed Cl- channel activation upon immunological stimulation and the parallel inhibition of channel current and of serotonin release suggests a functional role for this Cl- channel in mediator secretion from the mast cells studied.     

Interaction of late apoptotic and necrotic cells with vitronectin

Background

Vitronectin is an abundant plasma glycoprotein identified also as a part of extracellular matrix. Vitronectin is substantially enriched at sites of injured, fibrosing, inflamed, and tumor tissues where it is believed to be involved in wound healing and tissue remodeling. Little is known about the mechanism of vitronectin localization into the damaged tissues.

Methodology/Principal Findings

2E12 antibody has been described to bind a subset of late apoptotic cells. Using immunoisolation followed by mass spectrometry, we identified the antigen recognized by 2E12 antibody as vitronectin. Based on flow cytometry, we described that vitronectin binds to the late apoptotic and necrotic cells in cell cultures in vitro as well as in murine thymus and spleen in vivo. Confocal microscopy revealed that vitronectin binds to an intracellular cytoplasmic structure after the membrane rupture.

Conclusions/Significance

We propose that vitronectin could serve as a marker of membrane disruption in necrosis and apoptosis for flow cytometry analysis. Moreover, we suggest that vitronectin binding to dead cells may represent one of the mechanisms of vitronectin incorporation into the injured tissues.     

Mutation analysis of the short cytoplasmic domain of the cell-cell adhesion molecule CEACAM1 identifies residues that orchestrate actin binding and lumen formation

CEACAM1-4S (carcinoembryonic antigen cell adhesion molecule 1, with 4 ectodomains and a short, 12-14 amino acid cytoplasmic domain) mediates lumen formation via an apoptotic and cytoskeletal reorganization mechanism when mammary epithelial cells are grown in a three-dimensional model of mammary morphogenesis. We show by quantitative yeast two-hybrid, BIAcore, NMR HSQC and STD, and confocal analyses that amino acids phenylalanine (Phe(454)) and lysine (Lys(456)) are key residues that interact with actin orchestrating the cytoskeletal reorganization. A CEACAM1 membrane model based on vitamin D-binding protein that predicts an interaction of Phe(454) at subdomain 3 of actin was supported by inhibition of binding of actin to vitamin D-binding protein by the cytoplasmic domain peptide. We also show that residues Thr(457) and/or Ser(459) are phosphorylated in CEACAM1-transfected cells grown in three-dimensional culture and that mutation analysis of these residues (T457A/S459A) or F454A blocks lumen formation. These studies demonstrate that a short cytoplasmic domain membrane receptor can directly mediate substantial intracellular signaling.     

Cellular uptake and intracellular trafficking of long chain fatty acids.

While aspects of cellular fatty acid uptake have been studied as early as 50 years ago, recent developments in this rapidly evolving field have yielded new functional insights on the individual mechanistic steps in this process. The extremely low aqueous solubility of long chain fatty acids (LCFA) together with the very high affinity of serum albumin and cytoplasmic fatty acid binding proteins for LCFA have challenged the limits of technology in resolving the individual steps of this process. To date no single mechanism alone accounts for regulation of cellular LCFA uptake. Key regulatory points in cellular uptake of LCFA include: the aqueous solubility of the LCFA; the driving force(s) for LCFA entry into the cell membrane; the relative roles of diffusional and protein mediated LCFA translocation across the plasma membrane; cytoplasmic LCFA binding protein-mediated uptake and/or intracellular diffusion; the activity of LCFA-CoA synthetase; and cytoplasmic protein mediated targeting of LCFA or LCFA-CoAs toward specific metabolic pathways. The emerging picture is that the cell has multiple, overlapping mechanisms that assure adequate uptake and directed intracellular movement of LCFA required for maintenance of physiological functions. The upcoming challenge is to take advantage of new advances in this field to elucidate the differential interactions between these pathways in intact cells and in tissues.     

Biochemical analysis of glucocorticoid-induced inhibition of IgE-mediated histamine release from mouse mast cells

Pretreatment of mouse mast cells with 10(-7) to 10(-6) M dexamethasone (DM) during overnight sensitization with mouse IgE antibody resulted in inhibition of antigen-induced histamine release and degranulation. The inhibition of both degranulation and histamine release increased linearly with the duration of the treatment; maximal inhibition was obtained after approximately 16 hr with DM. The addition of DM to sensitized mast cells immediately before antigen challenge did not affect the antigen-induced histamine release. DM interacted directly with mast cells by binding to DM-specific cytoplasmic receptors. The treatment of mast cells with DM did not affect the binding of IgE to mast cells or intracellular cAMP levels. Bridging of cell-bound IgE anti-DNP antibody on mouse mast cells either by multivalent DNP-HSA or by anti-IgE induced phospholipid methylation at the plasma membrane and Ca++ influx into the cells. Pretreatment of mast cells with DM inhibited the antigen-induced phospholipid methylation and Ca++ uptake but failed to affect histamine release by Ca++ ionophore A23187. The results suggest that DM treatment inhibits histamine release by the inhibition of the early stage of biochemical processes leading to opening Ca++ channels but does not affect the process distal to Ca++ influx or the binding of IgE molecules to IgE receptors.     

Intracellular development of membrane protein of influenza virus.

The intracellular development of membrane protein (MP) of influenza A virus was investigated by immunofluorescent staining. Monospecific antiserum was prepared by immunizing rabbits with MP eluted from SDS-polyacrylamide gels of SDS-disrupted NWS virions. In the productive infection in clone 1-5C-4 cells, MP antigen was first detected over the whole cell at 4 hr after infection, concomitantly with the appearance of hemagglutinin (HA) antigen in the cytoplasm, and bright nuclear fluorescence was then observed. Nucleoprotein (NP) antigen was detected in the nucleus prior to the appearance of fluorescence of MP antigen and thereafter the cytoplasmic fluorescence developed. Late in infection, all of these three antigens were observed predominantly in the cytoplasm with stronger fluorescence at the cell surface. Essentially similar findings were obtained in the abortive infections in L cells and BHK cells. The above results suggest that the membrane protein of influenza A virus is present in the nucleus as well as in the cytoplasm of infected cells.     

Anti-Yo Antibody Uptake and Interaction with Its Intracellular Target Antigen Causes Purkinje Cell Death in Rat Cerebellar Slice Cultures: A Possible Mechanism for Paraneoplastic Cerebellar Degeneration in Humans with Gynecological or Breast Cancers

Anti-Yo antibodies are immunoglobulin G (IgG) autoantibodies reactive with a 62 kDa Purkinje cell cytoplasmic protein. These antibodies are closely associated with paraneoplastic cerebellar degeneration in the setting of gynecological and breast malignancies. We have previously demonstrated that incubation of rat cerebellar slice cultures with patient sera and cerebrospinal fluid containing anti-Yo antibodies resulted in Purkinje cell death. The present study addressed three fundamental questions regarding the role of anti-Yo antibodies in disease pathogenesis: 1) Whether the Purkinje cell cytotoxicity required binding of anti-Yo antibody to its intraneuronal 62 kDa target antigen; 2) whether Purkinje cell death might be initiated by antibody-dependent cellular cytotoxicity rather than intracellular antibody binding; and 3) whether Purkinje cell death might simply be a more general result of intracellular antibody accumulation, rather than of specific antibody-antigen interaction. In our study, incubation of rat cerebellar slice cultures with anti-Yo IgG resulted in intracellular antibody binding, and cell death. Infiltration of the Purkinje cell layer by cells of macrophage/microglia lineage was not observed until extensive cell death was already present. Adsorption of anti-Yo IgG with its 62 kDa target antigen abolished both antibody accumulation and cytotoxicity. Antibodies to other intracellular Purkinje cell proteins were also taken up by Purkinje cells and accumulated intracellularly; these included calbindin, calmodulin, PCP-2, and patient anti-Purkinje cell antibodies not reactive with the 62 kDa Yo antigen. However, intracellular accumulation of these antibodies did not affect Purkinje cell viability. The present study is the first to demonstrate that anti-Yo antibodies cause Purkinje cell death by binding to the intracellular 62 kDa Yo antigen. Anti-Yo antibody cytotoxicity did not involve other antibodies or factors present in patient serum and was not initiated by brain mononuclear cells. Purkinje cell death was not simply due to intraneuronal antibody accumulation.     

Membrane and cytoskeletal changes associated with IgE-mediated serotonin release from rat basophilic leukemia cells

Binding of antigen to IgE-receptor complexes on the surface of RBL-2H3 rat basophilic leukemia cells is the first event leading to the release of cellular serotonin, histamine, and other mediators of allergic, asthmatic, and inflammatory responses. We have used dinitrophenol-conjugated bovine serum albumin (DNP-BSA) as well as the fluorescent antigen, DNP-B-phycoerythrin, and the electron-dense antigen, DNP-BSA-gold, to investigate dynamic membrane and cytoskeletal events associated with the release of [3H]serotonin from anti-DNP-IgE-primed RBL-2H3 cells. These multivalent antigens bind rapidly to cell surface IgE-receptor complexes. Their distribution is initially uniform, but within 2 min DNP-BSA-gold is found in coated pits and is subsequently internalized. Antigen internalization occurs in the presence and absence of extracellular Ca2+. The F-actin content of the detergent-extracted cell matrices analyzed by SDS PAGE decreases during the first 10-30 s of antigen binding and then increases by 1 min to almost double the control levels. A rapid and sustained increase is also observed when total F-actin is quantified by flow cytometry after binding of rhodamine-phalloidin. The antigen-stimulated increase in F-actin coincides with (and may cause) the transformation of the cell surface from a finely microvillous to a highly folded or plicated topography. Other early membrane responses include increased cell spreading and a 2-3-fold increase in the uptake of fluorescein-dextran by fluid pinocytosis. The surface and F-actin changes show the same dependence on DNP-protein concentration as stimulated [3H]serotonin release; and both the membrane responses and the release of mediators are terminated by the addition of the non-cross-linking monovalent ligand, DNP-lysine. These data indicate that the same antigen-stimulated transduction pathway controls both the membrane/cytoskeletal and secretory events. However, the membrane and actin responses to IgE-receptor cross-linking are independent of extracellular Ca2+ and are mimicked by phorbol myristate acetate, whereas ligand-dependent mediator release depends on extracellular Ca2+ and is mimicked by the Ca2+ ionophore A23187.     

Subcellular localization of binding sites for cytochalasin D: evidence from activation energies.

The activation energies for binding of tritiated cytochalasin D to HEp-2 cells and isolated plasma membrane were determined by Arrhenius plots. The higher value for intact cells (24 kcal/mol) compared to the plasma membrane fraction (4 kcal/mol at greater than 11.5 degrees C, 18 kcal/mol at less than 11.5 degrees C) was taken as evidence that [3H]cytochalasin D must penetrate the plasma membrane in order to reach its binding sites. The data support the conclusion that binding sites for [3H]cytochalasin D are intracellular, on the cytoplasmic face of the plasma membrane (rather than within the lipid bilayer), and on microsomes (endomembranes).     

Plasmodium falciparum: analysis of the interaction of antigen Pf155/RESA with the erythrocyte membrane

The location of the Plasmodium falciparum vaccine candidate antigen Pf155/RESA in the membrane of infected erythrocytes was analzyed by means of selective surface radioiodination and immunofluorescence of surface-modified cells. The lack of radiolabel in Pf155/RESA as well as its localization by immunofluorescence similar to that of the N-terminal region of erythrocyte band 3 suggests that the antigen is associated with the cytoplasmic phase of the erythrocyte membrane. In concordance with this, Pf155/RESA was detected by immunofluorescence on the surface of inside out membrane vesicles from P. falciparum-infected erythrocytes. Pf155/RESA from spent culture medium also bound to inside out membrane vesicles of normal erythrocytes as well as to cytoskeletal shells of such vesicles, but failed to bind to sealed right-side out membrane vesicles. Depletion of spectrin from the vesicles abolished antigen binding, suggesting that Pf155/RESA association with the erythrocyte cytoskeleton is mediated by spectrin.     

Acceleration of intracellular targeting of antigen by the B-cell antigen receptor: importance depends on the nature of the antigen-antibody interaction.

The B-cell antigen receptor (BCR) internalizes bound antigen such that antigen-derived peptides become associated with emigrating major histocompatibility complex (MHC) class II molecules for presentation to T cells. Experiments with B-cell transfectants reveal that BCR confers a specificity of intracellular targeting since chimeric antigen receptors which internalize antigen by virtue of a heterologous cytoplasmic domain do not necessarily give rise to presentation. In contrast, however, previous studies have shown that antigen binding to irrelevant cell surface molecules (e.g. transferrin receptor, MHC class I) can ultimately lead to presentation. The solution to this paradox appears to be that the intracellular targeting by BCR actually reflects an acceleration of antigen delivery. Depending on the nature of the BCR-antigen interaction, this accelerated targeting can be essential in determining whether or not internalization leads to significant presentation. Physiologically, the accelerated delivery of antigen by BCR could prove of particular importance early in the immune response when antigen-BCR interaction is likely to be poor.     

Association of gelsolin with actin filaments and cell membranes of macrophages and platelets

Recent evidence that polyphosphoinositides regulate the function of the actin-modulating protein gelsolin in vitro raises the possibility that gelsolin interacts with cell membranes. This paper reports ultrastructural immunohistochemical data revealing that gelsolin molecules localize with plasma and intracellular membranes, including rough endoplasmic reticulum, cortical vesicles and mitochondria of macrophages, and blood platelets. Anti-gelsolin gold also labeled the surface and interior of secondary lysosomes presumably representing plasma gelsolin ingested by these cells from the lung surface by endocytosis. Gelsolin molecules, visualized with colloidal gold in replicas of the cytoplasmic side of the substrate-adherent plasma membrane of mechanically unroofed and rapidly frozen and freeze-dried macrophages, associated with the ends of short actin filaments sitting on the cytoplasmic membrane surface. A generalized distribution of gelsolin molecules in thin sections of resting platelets rapidly became peripheral, and plasmalemma association increased following thrombin stimulation. At later times the distribution reverted to the cytoplasmic distribution of resting cells. These findings provide the first evidence for gelsolin binding to actin filament ends in cells and indicate that gelsolin functions in both cytoplasmic and membrane domains.     

Nonlabeled secondary antibodies augment/maintain the binding of primary, specific antibodies to cell membrane antigens.

BACKGROUND: In studies on surface membrane antigen expression using immunofluorescence techniques, it is commonly observed that direct staining gives weaker signals than the signals following indirect staining with fluorochrome-conjugated secondary antibodies. This is most marked when cells have also been permeabilized in order to stain intracellular protein. The commonly accepted explanation for this observation is that fluorochrome-conjugated secondary antibodies bind to a higher number of binding sites on the primary antibody, as compared to the binding of conjugated primary antibodies to the membrane antigens. Another hypothesis might be that the antibody/antibody complexes formed on the membranes when using the indirect technique may have an augmented ability to bind the membrane epitopes. The present study was performed in order to check this hypothesis. MATERIALS AND METHODS: Peripheral blood mononuclear cells were stained with fluorochrome-conjugated anti-CD antibodies directly without or with a second-step application of nonconjugated goat anti-mouse IgG antibodies, followed by different fixation and permeabilization methods. The cells were analyzed by flow cytometry. RESULTS: A second-step application of nonconjugated goat anti-mouse IgG antibodies following direct staining with fluorochrome-conjugated anti-CD antibodies gave a significant increase in membrane antigen expression on permeabilized cells as compared to direct staining alone. The secondary antibody must be bivalent, since whole IgG or F(ab')(2) fragments of the goat anti-mouse antibodies showed effects, while Fab fragments did not. CONCLUSIONS: Nonlabeled secondary antibodies are able to influence the binding of primary, specific antibodies to cell membrane antigens on cells treated with permeabilizing agents necessary for staining intracellular proteins. The improved membrane antigen expression seems to be due to the formation of a network of primary and secondary antibodies on the cell surface, with increased ability for maintaining binding to CD antigens.     

Activation of the B Cell Receptor Leads to Increased Membrane Proximity of the Igα Cytoplasmic Domain

Binding of antigen to the B cell receptor (BCR) induces conformational changes in BCR''s cytoplasmic domains that are concomitant with phosphorylation of the immunoreceptor tyrosine-based activation motifs (ITAMs). Recently, reversible folding of the CD3ε and ξ chain ITAMs into the plasma membrane has been suggested to regulate T cell receptor signaling. Here we show that the Igα and Igβ cytoplasmic domains of the BCR do not associate with plasma membrane in resting B cells. However, antigen binding and ITAM phosphorylation specifically increased membrane proximity of Igα, but not Igβ. Thus, BCR activation is accompanied by asymmetric conformational changes, possibly promoting the binding of Igα and Igβ to differently localized signaling complexes.     

Subcellular localization of IpaC,an invasion plasmid antigen of Shigella dysenteriae type 1 and its in-vitro binding capability to mammalian cells

Invasion plasmid antigen C (IpaC), a 45-kDa protein encoded by an invasion plasmid of Shigella, is associated with the invasion of epithelial cells by the bacteria. Invasive strains of S. dysenteriae type 1 secreted more proteins into the extracellular environment than a non-invasive strain and secreted more IpaC protein. An anti-IpaC mouse monoclonal antibody was used as a probe to determine the subcellular localization of IpaC and its involvement in invasion of mammalian cells. Immunogold labelling of ultrathin sections of invasive bacteria indicated that the IpaC was only present in the cytoplasmic membrane and cytoplasm. There were no gold-IgG particles on the bacterial surface. Immunoblot analysis of different cellular fractions confirmed that the protein was associated with the inner cytoplasmic membrane and cytosolic fraction. The in-vitro binding capability of the IpaC protein was assessed using HeLa and isolated rat intestinal epithelial cells. The binding of the protein to the surface of mammalian cells indicates that it may have a role in the early stages of the infection process. The binding was sensitive to the action of proteolytic enzymes.     

Notch responds differently to Delta and Wingless in cultured Drosophila cells

Notch, a cell surface receptor, is required for producing different types of cells during development of Drosophila melanogaster. Notch activates expression of one set of genes in response to ligand Delta and another set of genes in response to ligand Wingless. The means by which Notch initiates these different intracellular activities was examined in this study. Cultured cells expressing Notch were treated with Delta or Wingless, and the effect on Notch was examined by Western blotting. Treatment of cells with Delta resulted in accumulation of approximately 120-kDa Notch intracellular domain molecules in the cytoplasmic fraction. This form of Notch did not accumulate in cells treated with Wingless, but the approximately 350-kDa full-length Notch molecules accumulated. These results indicate that N responds differently to binding by Delta and Wingless, and suggest that although the Delta signal is transduced by the Notch intracellular domain released from the plasma membrane, the Wingless signal is transduced by the Notch intracellular domain associated with the plasma membrane.     

Immunohistochemical localization of sodium-potassium ATPase in human normal stomach and gastric adenocarcinomas

We studied the expression pattern of Na, K-ATPase beta 1 subunit in human normal stomachs and in gastric adenocarcinomas by using anti-Na, K-ATPase beta 1 subunit-specific monoclonal antibody. Tissue samples were processed in formalin solution or in a cold acetic acid-ethanol solution, routinely processed, embedded in paraffin, and an immunoperoxidase method for Na, K-ATPase beta 1 subunit was performed. After antigen retrieval using a steamer in citrate buffer (pH 6.0), tissue sections initially fixed in cold acetic acid-ethanol showed intense immunoreactivity with the antibody at the lateral or basolateral cytoplasmic membrane of normal gastric epithelial cells, at the cytoplasmic membrane of gastric carcinoma cells according to the level of differentiation, and at the cytoplasmic membrane and in the cytoplasm of Schwann cells and neurons in the mesenteric plexus of the gastric wall. Acetic acid-ethanol and paraffin embedding is a useful method for the investigation of the immunohistochemical localization of Na, K-ATPase in normal and diseased tissues.