Participation of calmodulin in immunoglobulin capping

Distribution of activated calmodulin in the chloronema tip cells of the moss Funaria hygrometrica

Auxin (indole-3-acetic acid) regulates caulonema differentiation as a result of gradual transitional events in the chloronema tip cells in moss protonema. This auxin action in the moss Funaria hygrometrica involves a rapid influx of calcium ions from the extracellular medium. This investigation demonstrates spatial and temporal changes in calmodulin (CaM) activation (formation of Ca(2+)-CaM complex) in the chloronema tip cells subjected to auxin treatment. Photomicroscopic localisation of the fluorescence (excitation at 365 nm and emission of 397 nm) from the tricomplex of Ca(2+)-CaM with trifluoperazine (TFP, a blocker of Ca(2+)-CaM action) shows a tip to base (tip high) gradient of Ca(2+)-CaM in the chloronema tip cells. Comparison of Ca(2+)-CaM-TFP fluorescence over time in the chloronema tip cells of wild type Funaria with the response in an auxin overproducer mutant (86.1) and an auxin deficient mutant (87.13) reveals the involvement of auxin in calmodulin activation as a rapid response prior to cell differentiation.

Characterisation of isolated egg cells, in vitro fusion products and zygotes of Zea mays L. using the technique of image analysis and confocal laser scanning microscopy

Changes in membrane Ca2+, calcium receptor protein calmodulin, endoplasmic reticulum (ER), mitochondria and cellulose in unfixed, living, isolated egg cells and fusion products of pairs of one egg and one sperm cell of Zea mays L. have been investigated using chlorotetracycline, fluphenazine, immunocytochemical techniques, 3,3'-dihexyloxa-carbocyanine iodide (DiOC6(3)) and calcofluor white in conjunction with computer-controlled video image analysis. In addition, confocal laser scanning microscopy has been used in conjunction with ethidium bromide to detect the nature and location of the sperm cell nuclear chromatin before and after karyogamy. Digitised video images of chlorotetracycline (CTC) fluorescence reveal that egg cells contain high levels of membrane Ca2+ in organelles present around the nucleus while the cytosolic signal is relatively low. Intense CTC fluorescence is invariably present just below the plasma membrane of egg cells and a certain degree of regionalised distribution of Ca2+ in cytoplasm is also discernible. Similarly, the fluphenazine (FPZ)-detectable calmodulin (CaM) and that localised immunocytochemically using monoclonal anti-CaM antibodies reveal high levels of CaM in the vicinity of the nucleus in egg cells. Only a few ER profiles and mitochondria could be visualised in the egg cell and no calcofluor fluorescence could be detected. Following in vitro fertilisation of single isolated eggs substantial changes in the Ca2+ levels occur which include an increase in the membrane Ca2+ of the fusion product, particularly in the cytosol and around the nucleus. Unlike in the eggs the fine CTC fluorescence signal below the plasma membrane is not detectable in the fusion products.(ABSTRACT TRUNCATED AT 250 WORDS)

Confocal image analysis of spatial variations in immunocytochemically identified calmodulin during pollen hydration, germination and pollen tube tip growth in Nicotiana tabacum L

Using monoclonal anti-calmodulin antibodies in conjunction with confocal scanning laser microscopy we have analysed the spatial variations in the distribution pattern of calmodulin (CaM) during the sequential events of pollen hydration, germination and tube growth in Nicotiana tabacum. These immunocytochemical observations have been complemented by immunochemical studies wherein the anti-calmodulin antibody raised against pea CaM recognises a polypeptide of c. 18 kDa in the pollen extracts. Digitisation of confocally acquired optical sections of immunofluorescence images reveals that in hydrated pollen a high level of CaM is consistently present in the region of the germinal apertures. Subsequently, with the onset of germination a high CaM concentration was found associated with the plasma membrane of the germination bubble and in the cytoplasm in its vicinity, while in the vegetative cytoplasm a weak diffuse and intense punctate signal was registered. CaM immunostain was also detected in association with the plasma membrane of the tube tips in both short and long pollen tubes. Furthermore, the cytosol of the tubes invariably manifested an apically focused CaM gradient. We were, however, unable to detect any vacuolar association of CaM in the older regions of the pollen tubes. Although punctate immunostain was obvious across the pollen tube numerous punctate structures were invariably present in the extreme tip. The possible implications of these findings in development of cell polarity, polarised growth, maintenance of calcium homeostasis and CaM interactions with other mechanochemical motor proteins in effecting propulsion of organelles during pollen hydration, germination and pollen tube growth are discussed.

Inhibitory effect of salicylate on 2,4-dinitrophenol and diethyl maleate in isolated rat intestinal epithelial cells

Studies on the mechanism of chemically induced intestinal epithelial injury were carried out using isolated, rat small intestinal epithelial cells. Compounds such as 2,4-dinitrophenol (DNP) and diethyl maleate (DEM), caused NADH loss, an increase in cytosolic Ca2+ concentration and protein thiol loss. Further, these compounds accelerated cell aggregation and decreased cell viability. Calmodulin antagonists inhibited protein thiol loss induced by either of the compound, inhibited cell aggregation and prolonged cell viability, but did not influence NADH loss. It has been reported that the calmodulin-binding protein may regulate cytoskeletal activity. Therefore, the inhibition of protein thiol loss by calmodulin antagonist may be due to a dissociation of calmodulin-binding proteins from cytoskeletal elements. Salicylate also inhibited protein thiol loss induced by DNP and DEM, and inhibited cell aggregation. However, salicylate may have a direct effect in reducing the cytosolic free Ca2+ concentration by complexation and subsequent facilitated release of Ca2+ from cells. Further, in the present study, the induction of cell aggregation may be caused by the appearance of specific sites on the cell membrane surface to which arsenazo III could adsorb, since adsorption of arsenazo III to the isolated epithelial cells seemed to correlate with increased cell aggregation.

Lymphocyte activation and capping of hormone receptors

In this study both a ligand-dependent treatment [concanavalin A (Con A)] and a ligand-independent treatment [high-voltage pulsed galvanic stimulation (HVPGS)] have been used to initiate lymphocyte activation via a transmembrane signaling process. Our results show that both treatments cause the exposure of two different hormone [insulin and interleukin-2 (IL-2)] receptors within the first 5 min of stimulation. When either insulin or IL-2 is present in the culture medium, the stimulated lymphocytes undergo the following responses: (1) increased free intracellular Ca2+ activity; (2) aggregation of insulin or IL-2 receptors into patch/cap structures; (3) tyrosine-kinase-specific phosphorylation of a 32-kd membrane protein; and finally (4) induction of DNA synthesis. Further analysis indicates that hormone receptor capping is inhibited by (1) cytochalasin D, suggesting the involvement of microfilaments; (2) sodium azide, indicating a requirement for ATP production; and (3) W-5, W-7, and W-12 drugs, implying a need for Ca2+/calmodulin activity. Treatment with these metabolic or cytoskeletal inhibitors also prevents both the tyrosine-kinase-specific protein phosphorylation and DNA synthesis which normally follow hormone receptor capping. Double immunofluorescence staining shows that actomyosin, Ca2+/calmodulin, and myosin light-chain kinase are all closely associated with the insulin and IL-2 receptor cap structures. These findings strongly suggest that an actomyosin-mediated contractile system (regulated by Ca2+, calmodulin, and myosin light-chain kinase in an energy-dependent manner) is required not only for the collection of insulin and IL-2 receptors into patch and cap structures but also for the subsequent activation of tyrosine kinase and the initiation of DNA synthesis. We, therefore, propose that the exposure and subsequent patching/capping of at least one hormone receptor are required for the activation of mouse splenic T-lymphocytes.

Anticalmodulin autoantibody in liver diseases: a new antibody against a cytoskeleton-related protein

An ELISA has been developed for detection of auto-antibodies against calmodulin. There was a significantly increased frequency (63.1%) of autoantibodies against calmodulin in 103 patients with chronic liver diseases as compared to that (30%) of patients with systemic lupus erythematosus and to that (6.9%) of normal subjects (p less than 0.01). IgG autoantibodies against calmodulin were detected in the patients with acute hepatitis (37.9%), chronic liver disease (45.6%) and also in the patients with systemic lupus erythematosus (30%). IgM autoantibodies against calmodulin were frequently found in patients with liver cirrhosis (52.2%), primary biliary cirrhosis (50%) and autoimmune chronic active hepatitis (38.7%), but rarely in patients with acute hepatitis (13.8%), chronic persistent hepatitis (9.5%) and systemic lupus erythematosus (0%). IgA autoantibodies against calmodulin were frequently found in liver cirrhosis (33.3%), primary biliary cirrhosis (42.9%) and autoimmune chronic active hepatitis (53.6%), but rarely in chronic persistent hepatitis (15.8%), chronic active hepatitis (14.3%) and systemic lupus erythematosus (0%). The occurrences of autoantibodies against calmodulin correlated neither with those of antismooth muscle antibody, antinuclear antibody and antimitochondrial antibody, nor with serum IgG concentrations. Autoantibodies against calmodulin did not cross-react with troponin, myosin light chain, calf thymus DNA and actin. The titer of autoantibodies against calmodulin was decreased by absorption of serum with calmodulin and the liver plasma membrane fraction. The immunoblotting experiment revealed the binding of autoantibodies against calmodulin to calmodulin. IgG fraction from a patient with autoimmune chronic active hepatitis inhibited the activation of phosphodiesterase by calmodulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Calmodulin in lymphocyte mitogenic stimulation and in lymphoid cell line growth

Calmodulin levels are elevated three- to fourfold in the dividing cells, resulting from the lectin-induced stimulation of fresh human lymphocytes. This increase in calmodulin appears to be related mainly to progression into S phase and supports the hypothesis that calmodulin might be crucial in regulating the progression of lymphoblasts through their division cycle. Calmodulin levels are higher in a lymphoid cell line derived from human acute lymphoblastic leukemia blood cells than in a lymphoid cell line derived from normal human blood cells, suggesting that calmodulin could be an important mediator of the leukemogenetic process.

Influence of calcium and other divalent cations on protein turnover in rat skeletal muscle

When rat muscles were incubated in Ca2+-free media, their rates of protein break-down were significantly lower than in complete medium (2.58 mM Ca2+). Dantrolene and 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester, inhibitors of Ca2+ release from the sarcoplasmic reticulum, also reduced muscle proteolysis. When Ca2+ was added (up to 5.16 mM), proteolysis increased progressively up to 70% in the intact soleus and extensor digitorum longus muscles and up to 300% in the cut diaphragm preparation. Addition of Ca2+ did not affect the muscles' ATP or phosphocreatine content and increased protein synthesis slightly or not at all. Sr2+, Ba2+, and Mn2+ also increased proteolysis, but were less effective than Ca2+. Mg2+ inhibited the enhancement of proteolysis by Ca2+. This stimulation by Ca2+ was not affected by inhibitors of voltage-dependent Ca2+ channels, calmodulin, metalloendoproteases, microfilament or microtubule formation, or mersalyl. High Ca2+ levels also increased prostaglandin (PG) E2 production, although a rise in PGE2 did not appear essential for the increased proteolysis. The proteolysis induced by Ca2+ was prevented in muscles treated with Ep-475 or leupeptin. By contrast, these inhibitors of thiol proteases did not affect protein breakdown in Ca2+-free medium. Thus extracellular Ca2+ activates and Mg2+ inhibits a proteolytic pathway involving thiol proteases.

Trifluoperazine and W-7 inhibit mating in Chlamydomonas at an early stage of gametic interaction

Gametic mating by Chlamydomonas reinhardi is inhibited in a dose-dependent and reversible manner by the calmodulin antagonists trifluoperazine (TFP) and W-7, but not by W-5, an analog of W-7 having lower affinity for calmodulin. Quantitation of the sequential steps of mating showed that TFP and W-7 both allow normal levels of flagellar agglutination but prevent all subsequent steps. Gametes agglutinate aberrantly and do not form mating pairs. Further, both of these drugs prevent the translocation of latex beads along the flagellar surface. Our observations suggest that calmodulin may play an integral role in the translocation of flagellar adhesion sites during the tip-locking stage of the Chlamydomonas mating reaction. Flagellar surface motility may be crucial to the transduction of signals during mating and may share regulatory mechanisms with other forms of surface motility.

In vivo interaction of antibodies with cell surface proteins used as antigens

Antibody interactions with cell membrane glycoproteins in vivo exhibit features of aggregation and capping with resultant shedding similar to those events described in several in vitro isolated cell systems. Requirements for divalent ligand binding and participation of cytoskeletal elements are demonstrated in vivo as well. Persistence of antigen in immune complexes with complement interaction in situ appear to be necessary to induce an inflammatory response in vivo. Abrogation of this response occurs when circumstances permit antigenic modulation with disappearance of the immune complex.

Insulin receptor capping and its correlation with calmodulin-dependent myosin light chain kinase

Both fluorescence microscopy and fluorometric analysis techniques have been used to characterize insulin receptor capping in IM-9 human lymphoblastoid cells. Morphologically, insulin caps appear similar to lectin or antiimmunoglobulin-induced caps displaying a preferential accumulation of actin, myosin, and actin-binding protein directly underneath the cap structure. Using the fluorescent calcium indicator quin2 we have detected no change in the calcium activity following insulin stimulation. However, in the presence of a number of calmodulin inhibitors, such as W-5, W-7, W-12, and trifluoperazine (TFP), insulin capping is significantly inhibited, which implies that a calmodulin-regulated process is involved. Using double immunofluorescence microscopy, we have found that the calmodulin-dependent myosin light chain kinase (MLCK) is concentrated directly beneath insulin caps. Upon treatment with trifluoperazine (TFP), the redistribution of both MLCK and insulin receptors are inhibited concomitantly. Our data indicate that the calmodulin-dependent myosin light chain kinase may be directly responsible for the activation of actomyosin-mediated contractility during insulin receptor capping.

Intracellular calcium and calmodulin involvement in protoplast fusion

(45)Ca(2+) uptake was compared between fusogenic and nonfusogenic Daucus carota L. protoplasts. Fusogenic protoplasts took 10 minutes to reach calcium equilibrium compared to 5 minutes in the nonfusogenic protoplasts. Intracellular stores of calcium were manipulated by isolating protoplasts in different calcium regimes. Lowering of intracellular calcium lowered fusion potential, while raising intracellular stores of calcium enhanced fusion potential. Regardless of the amount of calcium sequestered in a store, mobilization with A23187 increased fusion levels within 10 minutes. Calmodulin antagonists were potent inhibitors of protoplast fusion. This inhibition was obtained by treating cells with the calmodulin antagonists during protoplast isolation. A23187, however, only allowed a partial recovery from this inhibition, indicating that calcium flux alone was not sufficient for maximum fusion potential. On the basis of the evidence presented, we propose that calcium fluxes during protoplast isolation activate a calmodulin-mediated biochemical process that is necessary for the formation or maintenance of a fusion permissive state.

Calcium-dependent association of a protein complex with the lymphocyte plasma membrane: probable identity with calmodulin-calcineurin

A protein complex is shown to participate in a calcium-dependent association with plasma membranes purified either from pig mesenteric lymph node lymphocytes or from human lymphoblastoid cell lines. Plasma membranes prepared in the presence of calcium possess this complex; those prepared in the absence of calcium (5 mM EGTA) do not. The complex associates itself with the inner cytoplasmic surface of the plasma membrane. This complex is referred to as the "acidic protein band" because of its location during migration upon alkaline-urea gel electrophoresis. The complex dissociates from the plasma membrane during electrophoresis on 8-M urea gels, irrespective of calcium levels during electrophoresis; at intermediate urea concentrations (4-6 M), the complex is not dissociated in the presence of calcium. Upon purification of the acidic protein band, SDS acrylamide gel electrophoresis, immunoblotting, and radioimmunoassay techniques suggest that the acidic protein band is composed of at least four peptides (designated 68K, 59K, 20K, 20K): two of these (68K, 20K) are immunopositive for calcineurin and one (20K) is immunopositive for calmodulin. Immunoblots of urea gels also indicate that the calcineurin heavy chain (68K) can also appear at three different locations on the urea gel. Patches and caps induced in human peripheral blood lymphocytes by fluorescein-conjugated goat anti-human IgG are not coincident with the location of calcineurin, which remains distributed throughout the cell.

Lymphocyte mechanical response triggered by cross-linking surface receptors

Using a recently developed method (Petersen, N. O., W. B. McConnaughey, and E. L. Elson, 1982, Proc. Natl. Acad. Sci. USA., 79:5327-5331), we have measured changes in the deformability of lymphocytes triggered by cross-linking cell surface proteins. Our study was motivated by two previously demonstrated phenomena: the redistribution ("capping") of cross-linked surface immunoglobulin (sIg) on B lymphocytes and the inhibition of capping and lateral diffusion ("anchorage modulation") of sIg by the tetravalent lectin Concanavalin A (Con A). Both capping and anchorage modulation are initiated by cross-linking cell surface proteins and both require participation of the cytoskeleton. We have shown that the resistance of lymphocytes to deformation strongly increased when sIg or Con A acceptors were cross-linked. We have measured changes in deformability in terms of an empirical "stiffness" parameter, defined as the rate at which the force of cellular compression increases with the extent of compression. For untreated cells the stiffness was approximately 0.15 mdyn/micron; for cells treated with antibodies against sIg or with Con A the stiffness increased to approximately 0.6 or 0.4 mdyn/micron, respectively. The stiffness decreased after completion of the capping of sIg. The increases in stiffness could be reversed to various extents by cytochalasin D and by colchicine. The need for cross-linking was demonstrated by the failure both of monovalent Fab' fragments of the antibodies against sIg and of succinylated Con A (a poor cross-linker) to cause an increase in stiffness. We conclude that capping and anchorage modulation involve changes in the lymphocyte cytoskeleton and possibly other cytoplasmic properties, which increase the cellular viscoelastic resistance to deformation. Similar increases in cell stiffness could be produced by exposing cells to hypertonic medium, azide ions, and to a calcium ionophore in the presence of calcium ions. These results shed new light on the capabilities of the lymphocyte cytoskeleton and its role in capping and anchorage modulation. They also demonstrate that measurements of cellular deformability can characterize changes in cytoskeletal functions initiated by signals originating at the cell surface.

Sheep-erythrocyte-capping by human T-lymphocytes. Pharmacological inhibition by phenothiazine drugs

In our previous studies it was found that E-rosette dissociation and sheep-erythrocyte capping were active processes involving the cytoskeleton. These cellular functions are now shown to be very sensitive to phenothiazine-drugs whose activities can be differentiated as follows: trifluoperazine greater than chlorpromazine greater than sulfoxide derivatives, suggesting a role for calmodulin-mediated events. These findings are in contradiction to prior reports pointing to the inefficacy of chlorpromazine to inhibit slow kinetic capping. However, no co-capping of trifluoperazine fluorescence (as a probe of calmodulin) and sheep erythrocytes could be observed. No requirement in extracellular calcium was evident for E-rosette formation and dissociation.

Quantitative radioautographic study of intracellular localization of calmodulin antagonist, W-7, in Chinese-hamster ovary cells

The purpose of the present study was to analyse quantitatively the localization of calmodulin antagonist, n-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7) in CHO-Kl cells. The cultured CHO-Kl cells were labelled with 1 (16.7 microM), 2 (33.4 microM), 5 (83.5 microM) and 10 microCi/ml (167 microM) tritiated W-7. Some cells were preincubated in 10, 50 and 100 microM unlabelled W-7 for 30 min and then labelled with 2 or 5 microCi/ml tritiated W-7 for 1 h. The cells were doubly fixed in glutaraldehyde and osmium-tetroxide solution, and embedded in Epon. For light-microscopic radioautography, 2 micron-thick sections were wet mounted with radioautographic emulsion and exposed for 1 month. The radioautograms showed that large numbers of silver grains were mainly localized in the cytoplasm as well as in the nucleus. Quantitative analysis demonstrated that, in both the cytoplasm and nucleus, the number of silver grains was dependent on the concentration of the administered tritiated W-7 and the number was dramatically decreased by the pretreatment of unlabelled W-7. These results show that, in CHO-Kl cells, the W-7 binding sites are saturable. It is concluded that W-7 may get into CHO-Kl cells and be bound to a specific protein that may be calmodulin protein.

Cross-linking surface immunoglobulin increases the stiffness of lymphocytes

Cross-linking surface immunoglobulin (sIg) on B-lymphocytes causes a substantial increase in the mechanical stiffness of the cells. This has been demonstrated using a new method for measuring cellular deformability. The method is based on a device, the "Cell Poker", which we use to determine the force required slightly to indent or compress a cell adherent to a rigid substrate in culture. Cross-linking of sIg by bivalent anti-sIg antibodies is necessary to elicit the increase in stiffness; binding of monovalent Fab fragments is insufficient. The increase in stiffness is partially reversed by cytochalasin D and by completion of the capping of the cross-linked sIg. The modulation of cellular deformability and the induction of cellular dynamic processes such as capping are similar in their requirements for cross-linking sIg and in their sensitivity to cytochalasins. This suggests that both kinds of responses stem from similar cellular processes and structures. These results emphasize the mechanical capability of lymphocytes and suggest that the physiological functions of these cells are likely to employ this capability.

A transmembranous NADH-dehydrogenase in human erythrocyte membranes

Evidence is presented for a transmembranous NADH-dehydrogenase in human erythrocyte plasma membrane. We suggest that this enzyme is responsible for the ferricyanide reduction by intact cells. This NADH-dehydrogenase is distinctly different from the NADH-cytochrome b5 reductase on the cytoplasmic side of the membrane. Pretreatment of erythrocytes with the nonpenetrating inhibitor diazobenzene sulfonate (DABS) results in a 35% loss of NADH-ferricyanide reductase activity in the isolated plasma membrane. Since NADH and ferricyanide are both impermeable, the transmembrane enzyme can only be assayed in open membrane sheets with both surfaces exposed, and not in closed vesicles. The transmembrane dehydrogenase has affinity constants of 90 microM for NADH and 125 microM for ferricyanide. It is inhibited by p-chloromercuribenzoate, bathophenanthroline sulfonate, and chlorpromazine.

A kinetic study of membrane immunoglobulin capping by flow cytometry

A flow cytometric procedure has been developed for performing kinetic studies on the capping of membrane immunoglobulin (mIg) on B lymphocytes. Mouse B cells were stained with fluorescein-conjugated antimouse-Ig antisera and subjected to pulse-shape (width, peak, and area) analyses prior to, during, and after ligand-induced redistribution of mIg. It was found that ring-stained, patched, and capped cells could be discriminated based on the width of the electronic signal curve generated as the cells passed through the laser beam. Additionally, endocytosis and or shedding of the cap could be correlated with a change in the area under the curve. Using these two parameters (width and area), the effects of temperature, cross-linking, and several pharmacological agents on the capping process were examined. Through the use of flow cytometry, the inhibitory effects of various perturbants could be localized to discrete stages of the capping process.

Cllmodulin in tip-growing plant cells, visualized by fluorescing calmodulin-binding phenothiazines

Calmodulin (CaM) was visualized light-microscopically by the fluorescent CaM inhibitors fluphenazine and chlorpromazine, both phenothiazines, during polar tip growth of pollen tubes of Lilium longiflorum, root hairs of Lepidium sativum, moss caulonema of Funaria hygrometrica, fungal hyphae of Achlya spec. and in the alga Acetabularia mediterranea, as well as during multipolar tip growth in Micrasterias denticulata. Young pollen tubes and root hairs showed tip fluorescence; at later stages and in the growing parts of the other subjects the fluorescence was almost uniform. After treatment with cytochalasin B, punctuate fluorescence occurred in the clear zone adjacent to the tip of pollen tubes. The observations indicate that there is CaM in all our tested systems detectable with this method. It may play a key role in starting polar growth. As in pollen tubes, CaM might be in part associated with the microfilament network at the tip, and thus regulate vesicle transport and cytoplasmic streaming.

Effects of trifluoperazine, a calmodulin antagonist, on rabbit T- and B-cell responses to mitogens and antigen

Trifluoperazine (TFP), an inhibitor of the calcium-binding protein, calmodulin (CaM), was used to assess the role of calmodulin in the responses of rabbit lymphoid cells to stimulation with mitogen and antigen. After binding goat anti-rabbit Fab antibody, rabbit B cells lose their surface immunoglobulin (Ig) through endocytosis and then reexpress this protein during the next 24 hr. This reexpression was markedly inhibited by TFP. The brief and early addition of TFP markedly inhibited the increased [3H]thymidine (Tdr) uptake by rabbit T cells treated with concanavalin A and B cells exposed to anti-Fab. TFP greatly inhibited the induction by keyhole limpet hemocyanin (KLH) of the in vitro syntheses of antibody, Ig, and protein by KLH-primed lymph node cells (LNC). The earlier the TFP the greater was the inhibition of induction of these syntheses. However, once induced, synthesis and secretion of antibody were not inhibited by TFP. In striking contrast to the inhibition by TFP of the mitogenic and antigenic responses of lymphoid cells was the lack of effect of this drug on resting lymphocytes. Since TFP was not cytotoxic for either resting or mitogen- or antigen-stimulated LNC, it is highly unlikely that the observed inhibitory effects of this drug were due to its cytotoxicity. We postulate that an early signal for the activation of LNC proliferation, differentiation, and the syntheses of antibody, Ig, and protein involves a calcium-CaM-mediated reaction. Based on this work and that of others, the calcium-CaM complex may mediate an interaction between the ligand-occupied surface receptor and the cytoskeleton.

Infection of B lymphocytes by a human herpesvirus, Epstein-Barr virus, is blocked by calmodulin antagonists

Epstein-Barr virus (EBV) is a human herpesvirus that selectively binds to and infects human B lymphocytes (B cells). In the studies presented here, we found that several phenothiazines, including trifluoperazine, chlorpromazine, prochlorpromazine, and promethazine, blocked EBV infectivity of isolated adult human B cells as measured either by outgrowth of transformed cell colonies or by [3H]thymidine incorporation. Trifluoperazine, chlorpromazine, and prochlorpromazine were equally effective with 20 microM fully inhibiting infectivity, whereas 100 microM promethazine was required for a comparable effect. Inhibition by trifluoperazine was partially reversible. Studies with radiolabeled EBV demonstrated that the inhibitors did not impair virus binding to B cells. Electron microscopic examination of B lymphocytes revealed that trifluoperazine reduced the number of large uncoated cell vacuoles and the number of membrane microvilli, indicating that this agent interfered with cell pinocytosis. This process was accompanied by inhibition of EBV endocytosis into B cells. Phenothiazines bind to and inhibit calmodulin, an intracellular calcium-binding protein that regulates several key enzymes, some of which directly affect cytoskeletal elements, although they also may interact nonspecifically with other cellular constituents. In this regard, haloperidol, a non-phenothiazine calmodulin antagonist, and R24571, a derivative of the antimycotic miconazole, which is a potent and highly specific calmodulin inhibitor, also blocked EBV infection. These studies suggest that calmodulin or a calmodulin-regulated cellular enzyme(s) is involved in normal cellular endocytic processes in B lymphocytes and thereby in the early stages of EBV infection.

Participation of calcium and calmodulin in the formation of acetylcholine receptor clusters

The formation of acetylcholine receptor (AChR) clusters can be experimentally induced in cultured Xenopus myotomal muscle cells by positive polypeptide-coated latex beads (Peng, H.B., P.-C. Cheng, and P.W. Luther, 1981, Nature [Lond.], 292:831-834). This provides a simple procedure for studying the cellular process of AChR clustering. In this study, the involvement of calcium and calmodulin in this process was examined. A deprivation in extracellular calcium by calcium-free medium or by the addition of calcium antagonists such as divalent cations Co2+ and Ni2+ (1-5 mM) or organic compounds verapamil and D-600 (0.1-0.5 mM) suppressed the formation of AChR clusters induced by the latex beads in a largely reversible manner. Antagonists against calmodulin, including trifluoperazine (1-5 microM) and the naphthalene sulfonamide W-7 (20 microM), also suppressed AChR clustering. However, the effect of W-7 was much weaker than that of trifluoperazine (TFP). Although the formation of AChR clusters is inhibited by these drugs, the stability of the existent clusters is relatively insensitive to them. These data suggest that the clustering of AChR involves a Ca2+ and calmodulin-activated process. Immunofluorescence studies using an antibody against calmodulin indicate that calmodulin is diffusely distributed in the cytoplasm in addition to its localization at the I-bands. Thus I propose that a local rise in intracellular calcium caused by a locally applied stimulus, exemplified here by the polypeptide-coated latex beads, may trigger the formation of AChR clusters. Furthermore, the cellular machinery for this process may involve calmodulin and is diffusely distributed in the muscle cell.

Regulation of receptor capping in mouse lymphoma T cells by Ca2+-activated myosin light chain kinase

Several characteristics of receptor capping in lymphocyte membranes suggest similarities with mechanisms underlying control of contraction in smooth muscle fibers. Both capping and contraction are Ca2+ dependent and require metabolic energy. Contractile proteins such as actin and myosin are associated with the cap, as is calmodulin, which mediates the Ca2+ dependence of smooth muscle contraction. Recent studies have shown that myosin light chain kinase (MLCK), which plays a central role in regulation of smooth muscle contraction, is also present in isolated lymphocyte membrane-cytoskeleton complexes. We have explored this analogy further, using mouse lymphoma T cells whose membranes were rendered permeable to small proteins by using a low-Ca2+ EGTA solution similar to that used to chemically skin smooth muscle cells. Permeabilized lymphocytes were then exposed to solutions containing various combinations of high or low Ca2+, ATP, or other nucleotides (5'-adenylyl imidodiphosphate, adenosine 5'-[gamma-thio]triphosphate, guanosine 5'-[gamma-thio]triphosphate, CTP, ITP, UTP, and GTP), calmodulin, Ca2+-insensitive MLCK (MLCK subunit that has been stripped of the Ca2+ binding site), and the catalytic subunit of cAMP-dependent protein kinase that phosphorylates (and thereby inactivates) MLCK. Capping of concanavalin A-labeled receptors in these various test solutions was scored. In all solutions the capping observed in permeable lymphoma cells correlated well with contraction previously observed in similarly treated skinned smooth muscle fibers, providing strong evidence for the involvement of myosin light chain phosphorylation in the regulation of receptor capping.

Trifluoperazine, a calmodulin antagonist, inhibits muscle cell fusion

We investigated the effect of trifluoperazine (TFP), a calmodulin antagonist, on the fusion of chick skeletal myoblasts in culture. TFP was found to inhibit myoblast fusion. This effect occurs at concentrations that have been reported to inhibit Ca2+-calmodulin in vitro, and is reversed upon removal of TFP. In addition, other calmodulin antagonists, including chlorpromazine, N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W7), and N-(6-aminohexyl)-1-naphthalene-sulfonamide (W5), inhibit fusion at doses that correspond closely to the antagonistic effects of these drugs on calmodulin. The expression of surface acetylcholine receptor, a characteristic aspect of muscle differentiation, is not impaired in TFP-arrested myoblasts. Myoblasts inhibited from fusion by 10 microM TFP display impaired alignment. In the presence of the Ca2+ ionophore A23187, the fusion block by 10 microM TFP is partially reversed and myoblast alignment is restored. The presence and distribution of calmodulin in both prefusional myoblasts and fused muscle cells was established by immunofluorescence. We observed an apparent redistribution of calmodulin staining that is temporally correlated with the onset of myoblast fusion. Our findings suggest a possible role for calmodulin in the regulation of myoblast fusion.

Inhibition of measles virus budding by phenothiazines

HeLa cells infected with measles virus show an accumulation of virus-specific strands at the plasma membrane after addition of the anticalmodulin drugs trifluoperazine (TFP) and chlorpromazine (CPZ), whereas spherical virus particles are almost completely absent. At low drug concentrations (10-15 microM TFP; 30-40 microM CPZ) the inhibitory effect is dependent on the presence of extracellular calcium. The strands complete the budding process after removal of the drugs. Restoration of virus budding is not sensitive to cycloheximide and immunoprecipitation experiments give evidence that the viral protein synthesis is not qualitatively altered in the presence of TFP. The data indicate that both drugs arrest the budding process at an intermediate stage at the plasma membrane. The inability of the strands to comigrate with cytochalasin B-induced actin patches suggests that the inhibition of budding is probably the result of an impaired interaction of viral structures with the cytoskeleton.

Calmodulin-NADH semidehydroascorbate oxidoreductase interactions of clathrin coated vesicles

NADH semidehydroascorbate oxidoreductase activity is present in clathrin coated vesicles isolated from rat liver. The activity of the enzyme on the coated vesicles and Golgi apparatus but not that of endoplasmic reticulum is stimulated by calmodulin and is inhibited by three different drugs which are known inhibitors of calmodulin function including trifluoperizine, pimozide and R24571. Extraction of clathrin from the vesicles causes a decrease in activity which can be partially restored when the extracted clathrin is added back. Added calmodulin also restores much of the activity which is lost when the clathrin is removed and the specific activity of added pure calmodulin is similar to that of the crude clathrin on a protein basis. There is a decrease in enzyme activity if coated vesicles or Golgi apparatus are treated with a calcium antagonist (8-[N,N-diethylamino]-octyl-3,4,5-trimethoxybenzoate) (TMB-8). However, the enzyme activity can be recovered to that of the untreated control if calcium (6.0 mM) is added. An additive stimulatory effect on enzyme activity is also observed when both calcium (1.0 mM) and calmodulin (40 micrograms/ml) are present in the vesicles simultaneously. The results show that the NADH-semidehydroascorbate oxidoreductase of coated vesicles and Golgi apparatus have regulatory properties different from those of the microsomal electron transport system. Calmodulin-calcium control mediated through the semidehydroascorbate reductase, may be among the components that regulate Golgi apparatus secretion.

Receptor capping in mouse T-lymphoma cells: a Ca2+ and calmodulin-stimulated ATP-dependent process

The roles that Ca2+, calmodulin, and ATP play in the redistribution of concanavalin A (Con A) binding sites on the surface of mouse T-lymphoma cells were examined. Membranes of cells labeled with fluorescein-conjugated Con A (Fl-Con A) were made permeable ("skinned") to ions and proteins by incubation in a solution containing no added Ca2+, 7 mM EGTA, and ATP. The intracellular ionic and protein concentrations could then be varied, and the degree of Con A receptor capping monitored simultaneously. A graded increase (9.0 to 30%) was found in the number of capped cells with increasing Ca2+ concentration from 10(-6)-10(-4.9) M. Increasing concentrations of trifluoperazine, chlorpromazine, and promethazine (1.5 x 10(-6) to 1.0 x 10(-4) M) in cell suspensions containing 10(-4) M Ca2+ produced graded inhibition of capping in the same order that the drugs bind to calmodulin. Removal of extracellular Ca2+ dissociated (reversed) some of the caps into patches, thus reducing their number (12%). ATP was required for either capping or cap dissociation to occur. Addition of calmodulin (3.9 x 10(-8)-6.3 x 10(-7) M) to the cell suspension increased the Ca2+ sensitivity. These results provide direct evidence that capping of Con A receptors is a reversible process (i) regulated by intracellular Ca2+ concentrations, (ii) requiring ATP as an energy source, and (iii) susceptible to the influence of calmodulin. These findings are consistent with the hypothesis that the collection of surface receptor patches into cap structures is controlled by the interaction of actomyosin filaments, which in turn is regulated by a Ca2+-calmodulin-activated control system.

Calcium regulation of the actin-mediated cytoskeletal transformation of sea urchin coelomocytes

Coelomocytes from several echinoderm species undergo an actin-mediated cytoskeletal transformation once subjected to hypotonic shock. In this study, coelomocytes from the sea urchins Lytechinus variegatus and Arbacia punctulata were induced to "transform" by treatment with greater than 5 microM of the calcium ionophore A23187 in the presence of external Ca++. The dependence of ionophore transformation on external Ca++ and the lack of chlorotetracycline staining indicates that these cells rely on external Ca++ sources. NBD-phallacidin (7-Nitrobenz-2-oxa-1,3-diazole-phallacidin) staining of lysolecithin permeabilized cells and whole-mount transmission electron microscopy (TEM) show that similar reorganizations of the actin cytoskeleton take place during hypotonic shock and ionophore transformation, although actin filament bundling is less apparent in A23187-treated cells. As has been shown with hypotonic shock transformation, the ionophore elicited shape change is inhibited by anticalmodulin drugs. Greater than 10 microM concentrations of W 13 inhibit filopod formation, while this drug's less active structural analogue, W 12, exhibits no effects. W 13 also appears to disrupt actin filament-membrane associations in the cells. Fluorescent localization of calmodulin using a photooxidized derivative of trifluoperazine indicates a general cytoplasmic distribution with some concentration in filopod core bundles. Coelomocyte transformation may be an example of a cellular shape change regulated by Ca++ through the action of calmodulin modulation of actin-membrane interactions.