Transmembrane linkage between surface glycoproteins and components of the cytoplasm in neutrophil leukocytes

Protrusive and Contractile Forces of Spreading Human Neutrophils

Human neutrophils are mediators of innate immunity and undergo dramatic shape changes at all stages of their functional life cycle. In this work, we quantified the forces associated with a neutrophil's morphological transition from a nonadherent, quiescent sphere to its adherent and spread state. We did this by tracking, with high spatial and temporal resolution, the cell's mechanical behavior during spreading on microfabricated post-array detectors printed with the extracellular matrix protein fibronectin. Two dominant mechanical regimes were observed: transient protrusion and steady-state contraction. During spreading, a wave of protrusive force (75 ± 8 pN/post) propagates radially outward from the cell center at a speed of 206 ± 28 nm/s. Once completed, the cells enter a sustained contractile state. Although post engagement during contraction was continuously varying, posts within the core of the contact zone were less contractile (-20 ± 10 pN/post) than those residing at the geometric perimeter (-106 ± 10 pN/post). The magnitude of the protrusive force was found to be unchanged in response to cytoskeletal inhibitors of lamellipodium formation and myosin II-mediated contractility. However, cytochalasin B, known to reduce cortical tension in neutrophils, slowed spreading velocity (61 ± 37 nm/s) without significantly reducing protrusive force. Relaxation of the actin cortical shell was a prerequisite for spreading on post arrays as demonstrated by stiffening in response to jasplakinolide and the abrogation of spreading. ROCK and myosin II inhibition reduced long-term contractility. Function blocking antibody studies revealed haptokinetic spreading was induced by β2 integrin ligation. Neutrophils were found to moderately invaginate the post arrays to a depth of ∼1 μm as measured from spinning disk confocal microscopy. Our work suggests a competition of adhesion energy, cortical tension, and the relaxation of cortical tension is at play at the onset of neutrophil spreading.

Perfluorocarbon attenuates response of concanavalin A-stimulated mononuclear blood cells without altering ligand-receptor interaction

Intrapulmonary application of perfluorocarbons (PFC) in acute lung injury is associated with anti-inflammatory effects. A direct impact on leukocytic function may be involved. To further elucidate PFC effects on cellular activation, we compared in an in vitro model the response of concanavalin A (ConA)-stimulated lymphocytes and monocytes exposed to perfluorohexane. We hypothesized that perfluorohexane attenuates the action of the lectin ConA by altering stimulant-receptor interaction on the cell surface. Mononuclear blood cells were stimulated by incubation with ConA in the presence of different amounts of perfluorohexane. The response of lymphocytes and monocytes was determined by means of IL-2 secretion and tissue factor (TF) expression, respectively. The influence of perfluorohexane on cell-surface binding of fluorescence-labeled ConA was studied using flow cytofluorometry and fluorescence microscopy. Perfluorohexane itself did not induce a cellular activation but significantly inhibited both monocytic TF expression and, to a far greater extent, IL-2 secretion of ConA-stimulated mononuclear blood cells. The effect of perfluorohexane was due neither to an alteration of cell viability nor to a binding of the stimulant. The amount of cell surface-bound ConA was not altered by perfluorohexane, and the overall pattern of ConA receptor rearrangement did not differ between controls and treated cells. In the present study, we provide further evidence for an anti-inflammatory effect of PFC that might be beneficial in states of pulmonary hyperinflammation. A PFC-induced alteration of stimulant-receptor interaction on the surface membrane does not seem to be the cause of attenuated cell activation.

Calcium signal transduction from caveolae

Caveolae are specialized membrane microdomains that are found on the plasma membrane of most cells. Recent studies indicate that a variety of signaling molecules are highly organized in caveolae, where their interactions initiate specific signaling cascades. Molecules enriched in this membrane include G protein-coupled receptors, heterotrimeric GTP binding proteins, IP3 receptor-like protein, Ca2+ ATPase, eNOS, and several PKC isoforms. Direct measurements of calcium changes in endothelial cells suggest that caveolae may be sites that regulate intracellular Ca2+ concentration and Ca2+ dependent signal transduction. This review will focus on the role of caveolae in controlling the spatial and temporal pattern of intracellular Ca2+ signaling.

Protein Kinase C (PKC) Isoforms Translocate to Triton-Insoluble Fractions in Stimulated Human Neutrophils: Correlation of Conventional PKC with Activation of NADPH Oxidase

The responses of human neutrophils (PMN) involve reorganization and phosphorylation of cytoskeletal components. We investigated the translocation of protein kinase C (PKC) isoforms to PMN cytoskeletal (Triton-insoluble) fractions, in conjunction with activation of the respiratory burst enzyme NADPH oxidase. In resting PMN, PKC-δ (29%) and small amounts of PKC-α (0.6%), but not PKC-βII, were present in cytoskeletal fractions. Upon stimulation with the PKC agonist PMA, the levels of PKC-α, PKC-βII, and PKC-δ increased in the cytoskeletal fraction, concomitant with a decrease in the noncytoskeletal (Triton-soluble) fractions. PKC-δ maximally associated with cytoskeletal fractions at 160 nM PMA and then declined, while PKC-α and PKC-βII plateaued at 300 nM PMA. Translocation of PKC-δ was maximal by 2 min and sustained for at least 10 min. Translocation of PKC-α and PKC-βII was biphasic, plateauing at 2–3 min and then increasing up to 10 min. Under maximal stimulation conditions, PKC isoforms were entirely cytoskeletal associated. Translocation of the NADPH oxidase component p47phox to the cytoskeletal fraction correlated with translocation of PKC-α and PKC-βII, but not with translocation of PKC-δ. Oxidase activity in cytoskeletal fractions paralleled translocation of PKC-α, PKC-βII, and p47phox. Stimulation with 1,2-dioctanoylglycerol resulted in little translocation of PKC isoforms or p47phox, and in minimal oxidase activity. We conclude that conventional PKC isoforms (PKC-α and/or PKC-βII) may regulate PMA-stimulated cytoskeletal association and activation of NADPH oxidase. PKC-δ may modulate other PMN responses that involve cytoskeletal components.

Initial Characterization of the Vitamin D Binding Protein (Gc-Globulin) Binding Site on the Neutrophil Plasma Membrane: Evidence for a Chondroitin Sulfate Proteoglycan

The vitamin D binding protein (DBP) is a multifunctional plasma protein that can modulate certain immune and inflammatory responses. The diverse cellular functions of DBP appear to require cell surface binding to mediate these processes. Numerous reports have detected DBP bound to the surface of several cell types and would support the concept of a cell surface binding site for DBP. However, direct evidence for such a molecule has been lacking and essentially nothing is known about its basic biochemical properties. In the present study, radioiodinated DBP was used as a probe to characterize biochemically the neutrophil DBP binding site. Radiolabeled DBP binds to and remains associated with the plasma membrane and is not degraded. Quantitation of DBP binding to either intact cells or purified plasma membranes showed nonsaturable (linear) binding with positive cooperativity, possibly suggesting DBP oligomer formation. Solubilization of cell bound 125I-DBP with various nonionic and zwitterionic detergents demonstrated that DBP binds to a membrane macromolecule that partitions to the detergent insoluble fraction. Moreover, this molecule does not associate with the cytoskeleton. Cross-linking of radiolabeled DBP bound to plasma membranes increased the amount of protein that partitioned to the insoluble fraction, and analysis of these complexes by SDS-PAGE revealed that they may be very large since they did not enter the gel. Finally, treatment of plasma membranes with either proteases or chondroitinase ABC completely abrogated membrane binding of DBP, suggesting that the protein binds to a chondroitin sulfate proteoglycan.

Moesin becomes linked to the plasma membrane in attached neutrophil granulocytes

Following 35 min of adhesion to a plastic surface, an 80-kDa F-actin-binding protein was shown to be enriched in the plasma membrane fractions of porcine neutrophils by protein blotting with labeled F-actin. This protein was almost undetectable in membrane fractions of free floating neutrophils, while it was present in total cell samples. The 80-kDa protein appeared to be a major high molecular mass component of the isolated actin-cytoskeleton of both control and attached cells. The studied F-actin-binding protein was recognized by anti-moesin antibodies. Our results suggest that moesin is translocated to the plasma membrane upon adhesion of neutrophils to the extracellular surface.

The mechanism of diatom locomotion. I. An ultrastructural study of the motility apparatus

Observations of raphe-associated cell structure of the diatomNavicula cuspidatasuggest the involvement in cell locomotion of secretory vesicles, the locally specialized plasmalemma opposite the raphe, microfilamentous bundles and strands of mucilage in the raphe. It is proposed th at diatoms are propelled by the flow of adhesive strands of mucilage that project from the raphe, powered and controlled by a membrane-associated microfilamentous system.

Effect of cytochalasin D on the mechanical properties and morphology of passive human neutrophils

The actin-rich cortex plays a major role in neutrophil chemotaxis and phagocytosis. In passive neutrophils, 30-50% of the actin molecules are in the F (filamentous) form, and it is the shifting of equilibrium with its monomeric G (globular) form that controls cell motility and phagocytosis. Cytochalasins have been shown to inhibit cell phagocytosis and ruffling. In purified actin, cytochalasins have been shown to decrease the amount of F-actin by capping the fast-growth end of actin filaments. Recent studies with intact cells, however, reveal that the most potent cytochalasin, cytochalasin D (CD), actually increases F-actin content suggesting that CD disrupts the actin network so as to increase the number of actin-filament ends for further actin polymerization. In this paper, we report the effects of CD on the passive mechanical behavior and morphology of human neutrophils with 1, 2, 10, and 20 microM CD. At 1 and 2 microM CD, the cells remain spherical. However, in the presence of 10 and 20 microM CD, cells are severely deformed and "blebby" as shown by light and scanning electron microscopy. After 1 and 2 microM CD treatment, the cells show a decrease of 43 and 66%, respectively, in cortical tension when measured by static micropipet aspiration experiments. Similarly, the cytoplasmic viscosities of 1 and 2 microM CD-treated cells are decreased, but only by 17 and 24%, respectively. A proportionally greater effect on the cortical tension suggests that CD acts mainly on the actin-rich cortex by disrupting the filament network.

Moesin, ezrin, and p205 are actin-binding proteins associated with neutrophil plasma membranes

Actin-binding proteins in bovine neutrophil plasma membranes were identified using blot overlays with 125I-labeled F-actin. Along with surface-biotinylated proteins, membranes were enriched in major actin-binding polypeptides of 78, 81, and 205 kDa. Binding was specific for F-actin because G-actin did not bind. Further, unlabeled F-actin blocked the binding of 125I-labeled F-actin whereas other acidic biopolymers were relatively ineffective. Binding also was specifically inhibited by myosin subfragment 1, but not by CapZ or plasma gelsolin, suggesting that the membrane proteins, like myosin, bind along the sides of the actin filaments. The 78- and 81-kDa polypeptides were identified as moesin and ezrin, respectively, by co-migration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoprecipitation with antibodies specific for moesin and ezrin. Although not present in detectable amounts in bovine neutrophils, radixin (a third and closely related member of this gene family) also bound 125I-labeled F-actin on blot overlays. Experiments with full-length and truncated bacterial fusion proteins localized the actin-binding site in moesin to the extreme carboxy terminus, a highly conserved sequence. Immunofluorescence micrographs of permeabilized cells and cell "footprints" showed moesin co-localization with actin at the cytoplasmic surface of the plasma membrane, consistent with a role as a membrane-actin-linking protein.

Passive mechanical behavior of human neutrophils: effect of cytochalasin B

Actin is a ubiquitous protein in eukaryotic cells. It plays a major role in cell motility and in the maintenance and control of cell shape. In this article, we intend to address the contribution of actin to the passive mechanical properties of human neutrophils. As a framework for assessing this contribution, the neutrophil is modeled as a simple viscous fluid drop with a constant cortical ("surface") tension. The reagent cytochalasin B (CTB) was used to disrupt the F-actin structure, and the neutrophil cortical tension and cytoplasmic viscosity were evaluated by single-cell micropipette aspiration. The cortical tension was calculated by simple force balance, and the viscosity was calculated according to a numerical analysis of the cell entry into the micropipette. CTB reduced the cell cortical tension in a dose-dependent fashion: by 19% at a concentration of 3 microM and by 49% at 30 microM. CTB also reduced the cytoplasmic viscosity by approximately -25% at a concentration of 3 microM and by approximately 65% at a concentration of 30 microM when compared at the same aspiration pressures. All three groups of neutrophils, normal cells, and cells treated with either 3 or 30 microM CTB, exhibited non-Newtonian behavior, in that the apparent viscosity decreased with increasing shear rate. The dependence of the cytoplasmic viscosity on deformation rate can be described empirically by mu = mu c(gamma m/gamma c)-b, where mu is cytoplasmic viscosity, gamma m is mean shear rate, mu c is the characteristic viscosity at the characteristic shear rate gamma c, and b is a material coefficient. The shear rate dependence of the cytoplasmic viscosity was reduced by CTB treatment. This is reflected by the changes in the material coefficients. When gamma c was set to 1 s-1, pc = 130 +/- 23 Pa.s and b = 0.52 +/- 0.09 for normal neutrophils and pc = 54 +/- 15 Pa.S and b = 0.26 +/- 0.05 for cells treated with 30 micro M CTB. These results provide the first quantitative assessment of the role that Pa-s-actin structure plays in the passive mechanical properties of human neutrophils.

Regulation of CD18 expression in human neutrophils as related to shape changes

The study analyses the distribution and quantitative expression of surface CD18 of neutrophils exposed to distinct stimuli that produce different types of continuous shape changes, including types that are associated with locomotion and others that are not. The chemotactic peptide N-formyl-L-norleucyl-L-leucyl-L-phenylalanine, colchicine and nocodazole were used to induce a polarized locomotor morphology, phorbol myristate acetate, 1,2-dioctanoylglycerol and 1-oleoyl-2-acetyl-glycerol to induce non-polar motile cells ruffling all over the surface and 2H2O to induce non-polar cells performing circus movements as have been previously described. Except for colchicine and nocodazole, these stimuli increased surface expression of CD18. Thus, stimulated shape changes are frequently, though not always, associated with increased surface expression of CD18. High concentrations (10(−7) to 10(−5) M) of phorbol myristate acetate but not of chemotactic peptide induced down-regulation of surface CD18. Cytochalasin D (10(−4) M) stimulated CD18 expression even though it inhibited shape changes. The surface distribution of CD18 determined by light microscopy was uniform in unstimulated cells or in various forms of stimulation except for cells treated with 10(−5) M cytochalasin D. Cytochalasin D (10(−5) M) produced CD18 accumulation at the pole opposite the F-actin cap. Experiments with colchicine, nocodazole, 2H2O and cytochalasin D suggest that microtubules as well as microfilaments modulate surface expression of CD18. The results suggest that protein kinase C and phosphatases play a role in regulating surface expression of CD18 in neutrophils.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of human platelets with concanavalin A involves phospholipase C activation

In response to concanavalin A, cytoplasmic calcium movement was observed in human platelets, both in the presence of 1 mM Ca2+ or 1 mM EGTA in the medium. Concanavalin A also caused the activation of inositide turnover and the production of inositol phosphates, suggesting that activation of phospholipase C occurs. The mechanism by which concanavalin A stimulates phospholipase C does not depend on GTP-binding transducers, because it was not inhibited by GDP beta S, while experiments performed in the presence of cytochalasin B suggested a role for membrane glycoprotein IIb-IIIa-cytoskeleton interaction in this process. Ca(2+)-proteases and Na+/H+ antiport also seemed to be related to concanavalin A-induced phospholipase C activation, as suggested by experiments performed in the presence of leupeptin and amiloride.

Surface glycoconjugates of cynomolgus monkey trabecular cells

Non-ionic detergent-soluble and detergent-resistant cynomolgus monkey trabecular cell surface glycoconjugates have been identified using three radiolabeling procedures and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The cell surface glycoconjugates were radiolabeled with tritiated sodium borohydride after treatment with: (1) neuraminidase/galactose oxidase; (2) galactose oxidase; or (3) sodium metaperiodate. The non-ionic detergent soluble components were removed by treatment of the monolayer cell culture with 1% Triton X-100 in hypotonic buffer. The radiolabeled trabecular cell surface glycoconjugates in the Triton X-100 soluble and insoluble fractions were resolved by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing conditions and visualized by fluorography. Treatment of the monkey trabecular cells with neuraminidase/galactose oxidase/tritiated sodium borohydride resulted in the radiolabeling of five components ranging in apparent molecular weight from 128,000 to 39,000 in the Triton X-100 soluble fractions, while 12 radiolabeled glycoconjugates with apparent molecular weights ranging from 240,000 to 26,000 were resolved in the Triton X-100 resistant fraction.

Detection of transmembrane linkages between immunoglobulin or complement receptors and the neutrophil's cortical microfilaments by resonance energy transfer microscopy

By exploiting the 1/r4 (where r is the separation distance between fluorochromes) dependence of energy transfer between parallel lamellae, we have observed transmembrane energy transfer between membrane receptors and cortical microfilaments. Receptors were labeled with donor- or acceptor-conjugated Fab fragments, whereas microfilaments were labeled with acceptor- or donor-conjugated phalloidin reagents. Energy transfer was imaged by optical microscopy. We report that cell surface receptors can be constitutively unlinked, linked or inducibly linked to microfilaments.

Concanavalin A induces a cytoskeletal association of T200 molecules in T lymphocytes

A recent report indicated that T200 molecules interact with elements of the cytoskeleton in BW5147 T lymphoma cells. We have confirmed the cytoskeletal association of T200 by examining nonionic detergent-soluble and detergent-insoluble fractions of murine T cell tumor cell lines, cloned cytotoxic T lymphocyte lines, and thymocytes. Concanavalin A (Con A)-treated and untreated cells were extracted with 0.5% Triton X-100 and the remaining insoluble material was extracted under conditions allowing actin depolymerization. In the absence of Con A treatment, little T200 could be recovered from the depolymerized insoluble fraction. However, in T cells treated with capping concentrations of Con A, a considerable amount of T200 was rendered insoluble in nonionic detergent, and T200 could be recovered from the insoluble fraction by a buffer which dissociates actin polymers. A lesser, but still significant, amount of T200 associated with the detergent-insoluble fraction of thymocytes treated with concentrations of Con A and succinyl Con A, which are mitogenic for T cells. We also found that in T cells treated with mitogenic concentrations of succinyl Con A, more T200 associated with cytoskeleton than did H-2 or LFA-1 molecules. Because T200 is such a predominant molecule on the surface of T cells, such translocations of the molecule may have a major impact on the physiology of the cell, especially if T200 functions as a protein tyrosine phosphatase as recent evidence by others suggests.

Characterization and cytoskeletal association of a major cell surface glycoprotein, GP 140, in human neutrophils

The binding of specific ligands to neutrophil cell surface receptors and the association of these receptors with the cytoskeleton may represent an essential step in activation. To identify surface proteins that are linked to the cytoskeleton during activation, neutrophil 125I-surface labeled plasma membranes were extracted with Triton X-100, and the soluble and insoluble (cytoskeleton) fractions analyzed by SDS-PAGE and autoradiography. The major cell surface proteins recruited to the cytoskeleton after activation with Con A, FMLP, zymosan-activated serum, or immune complexes possessed a relative molecular mass in the range of 80 to 13 kD. In addition to these proteins, WGA stimulates the recruitment of a 140-kD protein (GP 140) to the cytoskeletal fraction. That GP 140 is a WGA-binding protein was verified by Western blotting and WGA-Sepharose affinity chromatography. The Coomassie blue staining pattern of the WGA cytoskeletal fraction revealed major protein bands at apparent molecular weights of greater than 200 (approximately 250, 240, 235), 200, 115, 82/78 (a doublet), 56, 43, 36, and 18 kD. Labeling cells with 32PO4 before WGA treatment indicated that the cytoskeletal proteins with molecular weights of 115, 82/78, and 72 kD, and a 40-kD detergent soluble protein, are phosphorylated during activation. The 78 kD cytoskeletal phosphoprotein co-migrates with the lower subunit of erythrocyte (RBC) band 4.1 and shows strong cross-reactivity with RBC anti-band 4.1 antibody. Phosphorylation of cytoskeletal proteins like 4.1 may be involved in the regulation of interactions between GP 140 and the actin-containing cytoskeleton. Unlike the C3bi receptor, GP 140 is a major surface component of unactivated PMNs, has no stoichiometrically related 95-kD subunit, and has two isoforms with pIs in the range of 6.4 to 6.6. Under conditions that result in an increased expression of the C3bi receptor (such as treatment with the Ca2+ ionophore A23187), the amount of GP 140 on the PMN cell surface appears to be significantly reduced. The interaction of GP 140 with the cytoskeleton during activation suggests that GP 140 may play an important role in neutrophil functional responses.

Microfilament association of ASGP-2, the concanavalin A-binding glycoprotein of the cell-surface sialomucin complex of 13,762 rat mammary ascites tumor cells

Microfilament-associated proteins and membrane-microfilament interactions are being investigated in microvilli isolated from 13,762 rat mammary ascites tumor cells. "Phalloidin shift" analyses on velocity sedimentation gradients of Triton X-100 extracts of [3H]-glucosamine-labeled microvilli identified a 120-kDa cell-surface glycoprotein associated with the microvillar microfilament core. The identification was verified by concanavalin A (Con A) blots of one- and two-dimensional (2D) electrophoresis gels of sedimented microfilament cores. By 2D-electrophoresis and lectin analyses the 120-kDa protein appeared to be a fraction of ASGP-2, the major Con A-binding glycoprotein of the sialomucin complex of the 13,762 cells. This identity was confirmed by immunoblot analyses using immunoblot-purified anti-ASGP-2 from anti-membrane serum prepared against microvillar membranes. Proteolysis of the microvilli with subtilisin or trypsin resulted in an increase in the amount of ASGP-2 associated with the microfilament cores. An increase was also observed with sialidase treatment of the microvilli, suggesting that negative charges, probably present on the highly sialated sialomucin ASGP-1 of the ASGP-1/ASGP-2 sialomucin complex, reduce ASGP-2 association with the microfilament core. Proteolysis of isolated microvillar membranes, which contain actin but not microfilaments, also increased the association of ASGP-2 with a Triton-insoluble, actin-containing membrane fraction. Purified ASGP-2 does not bind to microfilaments in sedimentation assays. Since the Triton-insoluble membrane residue is enriched in an actin-containing transmembrane complex, which contains a different glycoprotein, we suggest that the ASGP-2 is binding indirectly via this complex to the microfilament core in the intact microvilli.

Signal transduction by glycophorin A: role of extracellular and cytoplasmic domains in a modulatable process

Binding of ligands to the extracellular region of the erythrocyte transmembrane protein glycophorin A induces a decrease in membrane deformability. Since the property of membrane deformability is regulated by the skeletal proteins on the cytoplasmic side of the membrane, this suggests that ligand binding may initiate a transmembrane signal. To further study this process, we examined which domains of the extracellular region of glycophorin are involved in signal transduction and whether the cytoplasmic domain of the molecule is necessary for transmitting the signal. Using the ektacytometer, we compared the effect on deformability of four monoclonal antibodies that detect different epitopes on glycophorin A. We found that 9A3 (which recognized the amino terminus of glycophorin) caused a 5.8-fold increase in rigidity, R-10 and 10F7 (which recognized epitopes in the mid-region of the extracellular domain) caused a 10.8-fold increase in rigidity and B14 (which binds to glycophorin close to the membrane) caused a 18-fold increase in rigidity. Further, a direct relationship was observed between the degree of antibody-induced rigidity and the amount of glycophorin A that became associated with the skeletal proteins in a Triton shell assay. In Miltenberger V erythrocytes, which contain a hybrid sialoglycoprotein with no cytoplasmic domain, antibody binding did not induce an increase in rigidity. These results imply that glycophorin A is capable of a modulatable form of transmembrane signaling that is determined by the extracellular domain to which the ligand binds, and the cytoplasmic domain of glycophorin A is crucial for this process.

Purified cytochrome b from human granulocyte plasma membrane is comprised of two polypeptides with relative molecular weights of 91,000 and 22,000

A new method has been developed for purification of cytochrome b from stimulated human granulocytes offering the advantage of high yields from practical quantities of whole blood. Polymorphonuclear leukocytes were treated with diisopropylfluorophosphate, degranulated and disrupted by nitrogen cavitation. Membranes enriched in cytochrome b were prepared by differential centrifugation. Complete solubilization of the cytochrome from the membranes was achieved in octylglucoside after a 1-M salt wash. Wheat germ agglutinin-conjugated Sepharose 4B specifically bound the solubilized cytochrome b and afforded a threefold purification. Eluate from the immobilized wheat germ agglutinin was further enriched by chromatography on immobilized heparin. The final 260-fold purification of the b-type cytochrome with a 20-30% yield was achieved by velocity sedimentation in sucrose density gradients. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the purified preparation revealed two polypeptides of Mr 91,000 and Mr 22,000. Treatment of the 125I-labeled, purified preparation with peptide:N-glycosidase F, which removes N-linked sugars, decreased relative molecular weight of the larger species to approximately 50,000, whereas beta-elimination, which removes O-linked sugars, had little or no effect on the mobility of the Mr-91,000 polypeptide. Neither of the deglycosylation conditions had any effect on electrophoretic mobility of the Mr-22,000 polypeptide. Disuccinimidyl suberate cross-linked the two polypeptides to a new Mr of 120,000-135,000 by SDS-PAGE. Antibody raised to the purified preparation immunoprecipitated spectral activity and, on Western blots, bound to the Mr-22,000 polypeptide but not the Mr-91,000 polypeptide. Western blot analysis of granulocytes from patients with X-linked chronic granulomatous disease revealed a complete absence of the Mr-22,000 polypeptide. These results (a) suggest that the two polypeptides are in close association and are part of the cytochrome b, (b) provide explanation for the molecular weight discrepancies previously reported for the protein, and (c) further support the involvement of the cytochrome in superoxide production in human neutrophils.

Plasma membrane proteins from human normal and chronic myeloid leukemic granulocytes: identification and partial characterization of the concanavalin A-binding and detergent resistant proteins

In this work granulocytes from normal human donors and patients suffering from chronic myeloid leukemia (CML) were externally labeled with 125Iodine, using the Iodogen method. 125Iodine labeled Concanavalin A binding proteins (CBP) and detergent-resistant proteins (DRP) were isolated from the cell lysates and characterized by one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (1D- and 2D-SDS-PAGE). Autoradiographs of the 2D-gels of DRP show seven proteins with Mr 118,000 (spot 1 a), Mr 112,000 (spot 1b), Mr 78,000-85,000 (spot 2), Mr 85,000 (spot 4), Mr 52,000 (spot 3, 3 a and 3 b). Of this set, spot 1 b, 2 and 4 are also present in the autoradiographs of 2D-gels of CBP and, hence, may be considered to be transmembrane components. Spot 4 is expressed more intensely in the normal granulocytes while spots 3 a and 3 b are mainly expressed on the leukemic granulocytes.

Receptors for C3b on the neutrophil surface associate with the cytoskeleton-containing cell residue subsequent to cell lysis with non-ionic detergent. Cytoskeletal-CR1 interactions

Radioiodinated Fab' and F(ab')2 fragments were prepared from 57F monoclonal antibody which is specific for the C3b receptor (CR1) on human cells. We find that both Fab' and F(ab')2 fragments bind to CR1 on human neutrophils and then dissociate, at 0 degree C, with half-lives of 172 and 35 min, respectively. In addition to binding to cell surface CR1, both antibody fragments bind specifically to the isolated non-ionic detergent-insoluble cellular residue (NDIR) which remains after cell lysis and solubilization in Triton X-100. We also find that Fab' and F(ab')2 antibody fragments remain associated with the NDIR after the radiolabeled antibody fragments are allowed to bind to cell surface CR1, the unbound fragments removed, and the cells subsequently lysed in non-ionic detergent. Because the cytoskeletal matrix (together with the cell nucleus) makes up a substantial portion of the NDIR, these results suggest that some fraction of cell surface CR1 may be associated in vivo with the cytoskeletal matrix. However, post-lysis association of cell surface-CR1-antibody fragment complexes to the NDIR occurs. Examination of the binding kinetics of this interaction reveals that less than 10% of cell surface CR1 exists bound to the NDIR prior to cell lysis. While the nature of post-cell lysis association of CR1 with the NDIR is unknown, several modulating effects are noted. For example, binding of bivalent cross-linking agents to CR1 on cells followed by a 37 degrees C incubation is known to induce internalization of cell surface CR1. We find that binding of F(ab')2 antibody fragments under these conditions causes a 50% decrease in association of this 57F fragment to the NDIR. Pretreatment of the cells at 37 degrees C with the chemotactic peptide N-formyl-methionyl-leucylphenylalanine similarly caused a 50% decrease of (Fab'-labeled) CR1 association with the NDIR cell fraction. These results support the hypothesis that chemotactic peptide serves to enhance CR1-mediated adherence to C3b-bearing targets by increasing the density of CR1 on the cell surface rather than by inducing cytoskeletal-dependent, detergent-stable, CR1 redistribution on the cell surface.

Concanavalin A binding induces association of possible mating-type receptors with the cytoskeleton in Tetrahymena

The lectin concanavalin A (conA; 25 micrograms/ml) inhibits conjugation in the ciliate Tetrahymena, and binds to receptors localized at the junction between conjugating cells. We report here that succinyl-conA (30 micrograms/ml) has similar activity, but that two other mannosespecific lectins, lentil and pea lectins, have inhibitory activities more than tenfold lower in this system, indicating that factors other than mannose specificity are essential for biological activity. By using fluorescein-isothiocyanate (FITC)-conA, we have found that extraction of cells with the detergent Triton X-100 removes conA receptors from the extraction-resistant cytoskeleton, but that the binding of conA to its receptor before extraction associates the ligand-receptor complex with the cytoskeleton. Under the hypothesis that the conA receptor may be a mating type receptor, we have used this ligand-induced differential cytoskeletal association, in conjunction with electrophoresis and Western blotting, to identify a glycoprotein with an apparent molecular weight (MW) of 23,000 D which may be a mating type receptor. Our data are consistent with a model in which a direct interaction between the conA receptor and the cytoskeleton, rather than receptor cross-linking, is the biologically significant activity of ligand binding.

Phorbol ester induces rapid actin assembly in neutrophil leucocytes independently of changes in [Ca2+]i and pHi

The phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA), at nanomolar concentrations, induces rapid (t1/2 approximately 30 s) protrusion of multiple petal-shaped lamellae by neutrophil leucocytes. Lamellae are richly endowed with actin filaments as determined by the localization of rhodamine-phalloidin, suggesting extensive assembly at the cell cortex. Direct measurement of the proportion of total cell actin which is polymerized, by using a deoxyribonuclease I inhibition assay, indicates that the proportion of polymerized actin approximately doubles, and that assembly initiated by 30 nM TPA occurs with no obvious lag phase and with a t1/2 of about 30 s. A half-maximal response was induced at 2 nM TPA. Since both actin assembly and protrusion of lamellae are completely inhibited by 10(-6) M cytochalasin D, protrusion of lamellae is presumably dependent on actin filament assembly. To examine whether TPA induces actin assembly via changes in [Ca2+]i or pHi, these parameters were monitored in cells loaded with the fluorescent indicators quin2 and quene1 respectively. Addition of TPA caused no change in [Ca2+]i but a biphasic change in pHi. To examine further the potential role of ionic changes in regulation of actin assembly, the morphological responses of cells to TPA were monitored in severely Ca2+-depleted cells, or cells in which pHi had been experimentally raised or lowered by simultaneous additions of a weak base (NH4Cl) or weak acid (CH3COONa) respectively. The protrusion of lamellae induced by TPA was completely unaffected by these experimental manipulations indicating that TPA can directly regulate actin assembly, and hence morphology, by mechanisms essentially independent of [Ca2+]i and pHi.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial clearance and granulocyte response in experimental peritonitis

Clearance kinetics of Escherichia coli and Bacteroides fragilis from the peritoneal cavity and functional properties of peritoneal and blood polymorphonuclear leukocytes (PMNL) were studied in pigs. The bacteria, approximately 10(10) colony forming units (CFU) of each species, were intraperitoneally injected. Blood and peritoneal exudate were sampled regularly during 24 hr for bacterial quantification and PMNL analysis. The peritoneal concentration of both species fell rapidly in the first 3 hr and then stabilized. Approximately 10(2) CFU/ml remained after 24 hr. Chemotaxis, phagocytosis, and metabolic activation of the peritoneal PMNL showed little change. In some pigs a second bacterial dose was injected 6 hr after the first dose and gave an identical clearance pattern. Exhaustion of the local defence capacity thus was excluded as cause of the impaired bacterial elimination.

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.

Evidence that phorbol ester interferes with stimulated Ca2+ redistribution by activating Ca2+ efflux in neutrophil leucocytes

The free calcium ion concentration, [Ca2+]i, in the cytoplasmic matrix of quin2-loaded neutrophil leucocytes increases rapidly after addition of concanavalin A. This increase is effectively abolished by a short (3 min) preincubation with 10 nM-TPA (12-O-tetradecanoylphorbol 13-acetate). TPA also inhibits a [Ca2+]i rise of similar magnitude induced by low concentrations (10 nM) of calcium ionophore A23187, suggesting that phorbol ester does not interfere with a physiological influx mechanism. To investigate the effects of TPA further, cells were depleted of Ca2+ during quin2 loading and then re-equilibrated with normal extracellular [Ca2+]. The return to a stable [Ca2+]i value was preceded by a transient overshoot in [Ca2+]i, implying delayed activation of an efflux mechanism by rising [Ca2+]i. TPA abolished the transient, suggesting preactivation by TPA of the efflux mechanism before Ca2+ influx. TPA also stimulates net Ca2+ efflux from neutrophils and neutrophil cytoplasts. These observations are consistent with the thesis that TPA stimulates a Ca2+-efflux mechanism in these cells.

Reciprocal transmembranous receptor-cytoskeleton interactions in concanavalin A-activated platelets

Concanavalin A (Con A) has been used to activate platelets, inducing a specific interaction between the glycoprotein IIb-IIIa complex and the cytoskeleton of the activated platelet. In agreement with this, we have shown that Con A activates human platelets, initiating phosphorylation, secretion, and cytoskeletal formation. Con A and cytochalasin B were used to demonstrate a reciprocal interaction of the glycoprotein complex with the platelet cytoskeleton. Additionally, we have shown that a similar reciprocity is provided by the multivalent fibrin-fibrinogen platelet interaction found in the thrombin-induced clot. Con A differs from other activators in precipitating an apparent cytoskeletal core despite a complete inhibition of platelet activation by prostaglandin E1. We suggest, from this result, that Con A may be cross-linking a membrane-associated cytoskeletal complex present in the unactivated platelet.

A T-lymphoma transmembrane glycoprotein (gp180) is linked to the cytoskeletal protein, fodrin

A major mouse T-lymphoma surface glycoprotein (gp180) has been identified by labeling cells with 125I and [3H]glucosamine. After ligand-induced receptor patching and/or capping, the amount of gp 180 in the membrane-associated cytoskeleton fraction increases in direct proportion to the percentage of patched/capped cells. There is a parallel increase in the amount of fodrin in the membrane-associated cytoskeleton fraction. Evidence is presented that gp180 is the same as or very similar to the T-lymphocyte-specific glycoprotein T-200. An immunobinding assay of Nonidet P-40-solubilized plasma membrane selectively co-isolates gp180 and fodrin. After induction of receptor rearrangement, double-label immunofluorescence reveals that fodrin accumulated directly beneath gp180 patches and caps. Membrane extraction with Triton X-114 followed by sucrose gradient centrifugation permits isolation of a gp180-fodrin complex with a 1:1 molar ratio and sedimentation coefficient(s) of approximately 20. This complex remains stable during isoelectric focusing and exhibits a pl in the range of 5.2-5.7. On the basis of our results we conclude that gp180, an integral membrane glycoprotein, and fodrin, a component of the membrane-associated cytoskeleton, are closely associated into a complex. Furthermore, we contend that, through fodrin's association with actin, this complex is of functional significance in ligand-induced patching and capping of gp180. We also propose that, through lateral interactions in the plane of the membrane, the gp180-fodrin complex might be responsible for linking other surface receptors to the intracellular microfilament network during lymphocyte patching and capping.

Erythrocyte membrane rigidity induced by glycophorin A-ligand interaction. Evidence for a ligand-induced association between glycophorin A and skeletal proteins

Erythrocyte skeletal proteins are known to play an important role in determining membrane deformability. In order to see whether transmembrane proteins also influence deformability and, if so, whether this influence is mediated by an interaction with the membrane skeleton, we examined the effect on deformability of ligands specific for transmembrane proteins. We found membrane deformability markedly reduced in erythrocytes that were pretreated with glycophorin A-specific ligands. In contrast, ligands specific for band 3 and A and B blood group antigens had no effect. The increase in membrane rigidity appeared to depend upon a transmembrane event and not upon a rigidity-inducing lattice on the outside surface of the cell in that a monovalent Fab of antiglycophorin IgG caused decreased deformability. We therefore looked for a ligand-induced association of glycophorin and the skeletal proteins and found, in Triton X-100-insoluble residues, a partitioning of glycophorin with the skeletal proteins only after preincubation with a ligand specific for glycophorin. We then studied cells and resealed membranes with skeletal protein abnormalities. In spectrin-deficient and protein 4.1-deficient erythrocytes and in 2,3-diphosphoglycerate-treated resealed membranes, the antiglycophorin IgG was only one-third as effective in decreasing deformability as it was in normal cells. Thus, normal skeletal proteins appear to be essential for liganded glycophorin to affect membrane deformability maximally. Taken together, these observations indicate that there is a ligand-induced interaction between glycophorin A and skeletal proteins and that this interaction can directly influence membrane deformability.

Isolation of a subpopulation of glycoprotein IIb-III from platelet membranes that is bound to membrane actin

Triton X-100-insoluble residues, or skeletons, of plasma membrane-rich vesicles obtained from unstimulated human platelets were isolated by high speed centrifugation. About 10-15% of the total surface iodinatable glycoproteins IIb and III (GPIIb and GPIII, respectively) co-isolated with the insoluble fraction. After sonication and centrifugation the solubilized material was further purified by affinity chromatography on Lens culinaris lectin-Sepharose. SDS PAGE analysis of this material revealed the presence of at least three major proteins, which were shown to be GPIIb, GPIII, and membrane actin, as judged by their electrophoretic properties and on the basis of immunological criteria. Antibodies directed against platelet surface glycoproteins and antibodies directed against rabbit actin were able to immunoprecipitate all three proteins, which indicates that they were noncovalently associated with one another. Gel filtration of the Lens lectin-purified Triton-insoluble complex on Ultrogel AcA 22 showed that greater than 85% of the total surface GPIIb and III was associated with an actin-rich peak that eluted in the void volume. In contrast, the form of GPIIb-III present in the Triton-soluble membrane fraction behaved as monomeric species when chromatographed under identical conditions. Finally, the GPIIb-III membrane actin complex bound with high efficiency to rabbit f-actin in vitro in a Ca++-independent manner, whereas the monomeric forms found in the Triton-soluble fraction did not bind to actin. These results indicate that two forms of GPIIb and III exist: one that binds directly to endogenous membrane actin and one that does not.

Activation of protein kinase C in neutrophil cytoplasts. Localization of protein substrates and possible relationship with stimulus-response coupling

Treatment of enucleated, granule-free neutrophil cytoplasts with the protein kinase C activator phorbol 12-O-myristate-13-acetate (PMA) causes an increased 32P-incorporation into a variety of polypeptides. Permeabilization of PMA-stimulated, 32P-labeled cytoplasts by 0.01% digitonin fully releases the majority of these phosphorylated proteins. A statistically significant correlation is found between the extent of PMA-induced activation of generation of superoxide anion (O2-) and the phosphorylation of a cytosolic polypeptide with an apparent Mr of 46,000, whose 32P-labeling is also enhanced by the treatment of cytoplasts with 1-oleyl-2-acetylglycerol, the Ca2+ ionophore ionomycin or latex beads. Furthermore, treatment of cytoplasts with the protein kinase C inhibitor trifluoperazine markedly inhibits the 32P-labeling of proteins in the 40 000 Mr range, including the 46 kDa polypeptide, and almost totally abolishes the activation of O2- production by PMA.

Association of specific cell-surface glycoproteins with a triton X-100-resistant complex of plasma membrane proteins isolated from T-lymphoma cells (P1798)

A non-ionic detergent-resistant complex of membrane-associated proteins and cell-surface glycoproteins has been isolated by gel filtration and isopyknic centrifugation of purified plasma membranes from the murine T-lymphoma P 1798. This complex elutes as a high molecular weight peak (greater than 15 X 10(6) D) and contains two specific sets of (1) cell-surface glycoproteins; (2) membrane-associated proteins. The cell-surface glycoproteins consist of two vectorially labelled major components present in a fixed molar ratio: The Thy-1 glycoprotein and a non-H-2 glycoprotein of 55 kD. Minor but significant amounts of the class I histocompatibility antigen Qa-2 are also contained in the detergent-resistant complex. The membrane-associated proteins are not vectorially labelled, and form a complex group of proteins in the 30-70 kD range. Since actin is not detectable among these polypeptides, they probably constitute a plasma membrane-associated structure that is distinct from actin-containing, submembranous cytoskeletal elements.

Retention of the glycoprotein IIb-IIIa complex in the isolated platelet cytoskeleton. Effects of separable assembly of platelet pseudopodal and contractile cytoskeletons

To investigate the association of the putative platelet fibrinogen receptor (glycoprotein IIb-III(a) with the cytoskeleton, 125I-surface labeled human platelets washed by gel-filtration were activated under conditions which allow selective assembly of the platelet cytoskeleton. The four conditions were activation with arachidonate or phorbol 12-myristate 13-acetate (PMA) with and without pretreatment with cytochalasin E. Activation with arachidonate generates a complete cytoskeletal core (pseudopodal and contractile elements) while PMA activation forms only an actin plus actin-binding protein pseudopodal core. Pretreatment with cytochalasin E leads to actomyosin contractile core formation if arachidonate activated, and essentially blocks cytoskeletal development if PMA activated. Cytoskeletal cores from arachidonate or PMA-activated platelets retained 26 (+/- 3%) of the total 125I-IIIa. Pretreatment with cytochalasin E followed by arachidonate or PMA activation reduced the 125I-IIIa retention to near control levels (unactivated platelets: 4 +/- 2%). The role of aggregation vs. receptor occupancy in the retention of IIb-IIIa was assessed by activation of platelets with arachidonate in the presence of fibrinogen fragment D (0.6-12 mg/ml). Aggregation was blocked by increasing concentrations of fragment D reagent while cytoskeletal assembly was not altered. The IIIa retention correlated with extent of aggregation with maximal retention corresponding to full aggregation. To determine if cytoskeletal development is necessary for the expression of the fibrinogen binding site, binding studies were performed with unlabeled platelets and 125I-fibrinogen. The mean number of binding sites and the mean dissociation constant were not significantly different among the four activation conditions. Although the development of a platelet cytoskeletal core is not required for the expression of the fibrinogen binding site, the retention of the glycoprotein IIb-IIIa complex is dependent on fibrinogen-supported aggregation as well as the formation of the pseudopodal cytoskeleton.

A cell surface integral membrane glycoprotein of 85,000 mol wt (gp85) associated with triton X-100-insoluble cell skeleton

The Triton X-100-insoluble skeleton of baby hamster kidney BHK cells consists of the nucleus, intermediate-size filaments, and actin fibers. By transmission electron microscopy, membrane fragments were found to be associated with these insoluble structures. When radioiodinated or [3H]glucosamine-labeled cells were extracted with 0.5% Triton, most plasma membrane glycoproteins were solubilized except for a glycoprotein with a molecular weight of 85,000 (gp85) that remained associated with the insoluble skeletons. Immunoprecipitation with a specific antiserum indicated that the gp85 is not a proteolytic degradation product of fibronectin, an extracellular matrix glycoprotein insoluble in detergent. A monoclonal antibody of BHK cells specific for gp85 was produced. Immunofluorescence analysis with this monoclonal antibody indicated that gp85 is not associated with the extracellular matrix, but is confined to the cell membrane. Both in fixed and unfixed intact cells, fluorescence was concentrated in dots preferentially aligned in streaks on the cell surface. Gp85 was found to behave as an integral membrane protein interacting with the hydrophobic core of the lipid bilayer since it was extracted from membrane preparations by ionic detergents such as SDS, but not by 0.1 N NaOH (pH 12) in the absence of detergents, a condition known to release peripheral molecules. Association of gp85 with the cell skeleton was unaffected by increasing the Triton concentration up to 5%, but it was affected when actin filaments were dissociated or when a protein-denaturing agent (6 M urea) was used in the presence of Triton, suggesting that protein-protein interactions are involved in the association of gp85 with the cell skeleton. We conclude that gp85 is an integral plasma membrane glycoprotein that might have a role in cell surface-cytoskeleton interaction.

Nonidet P-40 extraction of lymphocyte plasma membrane. Characterization of the insoluble residue

Purified preparations of lymphocyte plasma membrane were extracted exhaustively with Nonidet P-40 in Dulbecco's phosphate-buffered saline medium. The insoluble fraction, as defined by sedimentation at 10(6) g-min, contained about 10% of the membrane protein as well as cholesterol and phospholipid. The lipid/protein ratio, cholesterol/phospholipid ratio and sphingomyelin content were increased in the residue. Density-gradient centrifugation suggested that the lipid and protein form a common entity. As judged by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the Nonidet P-40-insoluble fractions of the plasma membranes of human B lymphoblastoid cells and pig mesenteric lymph-node lymphocytes possessed similar qualitative polypeptide compositions but differed quantitatively. Both residues comprised major polypeptides of Mr 28 000, 33 000, 45 000 and 68 000, together with a prominent band of Mr 120 000 in the human and of Mr 200 000 in the pig. The polypeptides of Mr 28 000, 33 000, 68 000 and 120 000 were probably located exclusively in the Nonidet P-40-insoluble residue, which also possessed a 4-fold increase in 5'-nucleotidase specific activity. The results indicate that a reproducible fraction of lymphocyte plasma membrane is insoluble in non-ionic detergents and that this fraction possesses a unique polypeptide composition. By analogy with similar studies with erythrocyte ghosts, it appears likely that the polypeptides are located on the plasma membrane's cytoplasmic face.

Rapid modulation of N-formyl chemotactic peptide receptors on the surface of human granulocytes: formation of high-affinity ligand-receptor complexes in transient association with cytoskeleton

When human granulocytes were exposed to 50 nM N-formyl-Met-Leu-[3H]Phe at 37 degrees C they rapidly formed ligand-receptor complexes that dissociated 50-100 times more slowly than those on cells initially exposed to the peptide at 4 degrees C. These complexes of apparent higher affinity were stable after detergent solubilization of the cells with Triton X-100. The complexes co-isolated with the detergent insoluble cytoskeletal residues and were free of the cytosolic and Golgi markers, lactate dehydrogenase and galactosyl transferase, respectively. After 5 s of exposure to f-Met-Leu-Phe, 2,000-3,000 molecules of ligand per cell were trapped in such complexes. Continued exposure resulted in capture of a maximum of 14,000 molecules per cell by 5 min. Exposure at 15 degrees C, a temperature at which endocytosis of the receptor is prevented, resulted in complex formation at a linear rate for at least 20 min to levels twice those measured at 37 degrees C. At 4 degrees C, complex formation was approximately 10% of the maximum amount formed at 37 degrees C. Pulse-chase experiments revealed that the complex was in transient association with the cytoskeleton with a half life ranging between 30 s to 4 min depending on the length of the original incubation. Electron microscopic autoradiography indicated that after 1 min of incubation at 37 degrees C, the majority of the specific autoradiographic grains were localized to the outer circumference of the cellular cytoskeleton. After 4 min of incubation, the grains were less frequent at the cytoskeleton periphery but still threefold enriched over a random cellular distribution. We conclude that a metabolically controlled modulation of the state of the N-formyl chemotactic peptide receptor occurs in the plasma membrane which may be the result of transient association of ligand-receptor complex and the cell cytoskeleton.

Isolation and characterization of a novel 68,000-Mr Ca2+-binding protein of lymphocyte plasma membrane

A 68 000-Mr protein is a major component of a Nonidet P-40-insoluble fraction of lymphocyte plasma membrane prepared from human B lymphoblastoid cells ( BRI 8) and pig mesenteric lymph nodes. The association of the protein with the detergent-insoluble complex depends on free Ca2+ concentrations of greater than 10 microM. The human and pig 68 000-Mr proteins were purified and appear to be homologous on the basis of amino acid composition and peptide mapping. The protein is monomeric, has pI 5.8 and a single high-affinity Ca2+-binding site (KD 1.2 microM). The results are discussed in terms of the possible role of the 68 000-Mr protein as an intracellular Ca2+ receptor in lymphocytes.

Mechanism of concanavalin A-induced anchorage of the major cell surface glycoproteins to the submembrane cytoskeleton in 13762 ascites mammary adenocarcinoma cells

Concanavalin A (Con A)-induced anchorage of the major cell surface sialoglycoprotein component complex (ASGP-1/ASGP-2) was studied in 13762 rat mammary adenocarcinoma sublines with mobile (MAT-B1 subline) and immobile (MAT-C1 subline) cell surface Con A receptors. Treatment of cells, isolated microvilli, or microvillar membranes with Con A resulted in marked retention of ASGP-1 and ASGP-2, a Con A-binding protein, in cytoskeletal residues of both sublines obtained by extraction with Triton X-100 in PBS. When Con A-treated microvillar membranes were extracted with a buffer containing Triton X-100, the sialoglycoprotein complex was found associated in the residues with a transmembrane complex composed of actin, a 58,000-dalton polypeptide, and a cytoskeleton-associated glycoprotein (CAG), also a Con A-binding protein, in MAT-C1 membranes, and of actin and CAG in MAT-B1 membranes. Untreated membrane Triton residues retained very little ASGP-1/ASGP-2 complex. Association of the sialoglycomembrane complex and the transmembrane complex was also demonstrated in Con A-treated, but not untreated, microvilli by their comigration on CsCl gradients. Association of both complexes with the cytoskeleton of microvilli was shown by sucrose density gradient centrifugation. A fraction of the polymerized actin comigrated with the transmembrane complex alone in the absence of Con A and with both the transmembrane complex and the sialoglycoprotein complex in the presence of Con A. From these results we propose that anchorage of the sialoglycoprotein complex to the cytoskeleton on Con A treatment occurs by cross-linking ASGP-2, the major cell surface Con A-binding component, to CAG of the transmembrane complex, which is natively linked to the cytoskeleton via its actin component. Since Con A-induced anchorage occurs in sublines with mobile and immobile receptors, the anchorage process cannot be responsible for the differences in receptor mobility between the sublines.

Lens actin: purification and localization

Actin was purified from the chick lens using DEAE-52 column chromatography followed by hydroxylapatite chromatography. The antibody produced against the purified actin cross-reacted specifically with lens actin from other species in addition to smooth and skeletal muscle actin and labelled the stress bundles of cultured fibroblasts. Actin was localized, using immunological methods, primarily to the plasma membrane of the epithelial and fiber cells of the chick and human lens. Actin filaments were also identified by HMM S-1 labeling in bovine cortical fiber cells. Using this procedure, the actin filaments were found throughout the fiber cell but were mainly concentrated near the plasma membrane and in cell processes. They formed a population distinct from the beaded filaments. The initial DEAE-52 column chromatography was also useful in the initial purification of lens fiber cell intermediate filament protein and two species of beta-crystallins.

Capping of cholera toxin-ganglioside GM1 complexes on mouse lymphocytes is accompanied by co-capping of alpha-actinin

We used cholera toxin, which binds exclusively and with a high affinity to the ganglioside GM1, as a probe to investigate the distribution of this glycolipid on the surface of mouse lymphocytes. When lymphocytes are incubated with cholera toxin (or its B subunit) and then sequentially with horse anti-toxin and FITC-swine anti-horse Ig at 37 degrees C, the cholera toxin-ganglioside GM1 complex is redistributed to a cap at one pole of the cell. The capping of cholera toxin-GM1 complexes is slower than the capping of surface-Ig complexes, requires two antibodies, and is inhibited at high toxin concentrations. Cholera toxin-GM1, like surface-Ig capping, is an energy-dependent process and is inhibited by sodium azide, low temperatures, or cytochalasin B, but is unaffected by demecolcine. An affinity-purified antibody against alpha-actinin was used to examine the distribution of this cytoskeletal component during the capping process. 88% of the cells that had a surface Ig cap displayed a co-cap of alpha-actinin, and 57% of the cells that had a cholera toxin-GM1 cap displayed a co-cap of alpha-actinin. Time course studies revealed similar kinetics of external ligand cap formation and the formation of alpha-actinin co-caps. We conclude that capping of a cell-surface glycolipid is associated with a reorganization of the underlying cytoskeleton. The implications of such an association are discussed in the context of current models of the mechanism of capping.

The role of cytoskeletal and cytocontractile elements in pathologic processes

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