Movement Of Surface Receptors Research Articles

Single particle tracking of surface receptor movement during cell division.

We have used fluorescent latex beads to label membrane receptors on cultured NRK cells. Movement of individual beads during cell division was recorded with digital imaging techniques. Surface-bound beads showed no organized movement during metaphase but started to migrate toward the equator approximately 1 min after anaphase onset, when chromosomes moved out of the equatorial region to create the interzone. The movement was most active in the central region of the cell near separating chromosomes, while beads located near the poles of the cell underwent primarily random motion. Most beads showed a surge in speed upon the passage of chromosomes, suggesting a possible link between chromosome separation and cortical reorganization. Furthermore, treatment of anaphase cells with cytochalasin D induced a rapid, simultaneous collapse of beads and cortical actin filaments into aggregates, indicating that the movement of beads was closely related to the reorganization of the actin cortex. In contrast to normal directional movement, cytochalasin-induced movement occurred in random directions and caused some beads in the equatorial region to move toward poles. Our results indicate that cytokinesis involves contractile activities, not only along the equator, but over a wide area of the actin-containing cortex. In addition, organized cortical activities appear to be temporally activated at anaphase onset, and spatially modulated by the spindle interzone or separating chromosomes.

Effect of the antidepressant drug-Stelazine on lymphocyte capping

The antidepressant agent, Stelazine (trifluoroperazine dihydrochloride), is known to cause inactivation of the calcium-binding protein, calmodulin. We report here that this drug in the concentration range of 5 × 10 −5M to 10 −6M causes remarkable inhibitory effects on ligand-induced T-lymphocyte receptor capping. The possible involvement of calmodulin in the regulation of lymphocyte surface receptor movement is therefore implicated.

Lymphocyte alpha-actinin. Relationship to cell membrane and co-capping with surface receptors.

Mouse spleen lymphocytes synthesize a protein which comigrates with skeletal muscle alpha-actinin on two-dimensional gel electrophoresis and is immunoprecipitated by an antibody directed against skeletal muscle alpha-actinin. Mouse lymphocyte alpha-actinin is present in membrane fractions, and is immunoprecipitated from lymphocyte detergent lysates by an antiserum made against these purified membranes. The anti-alpha-actinin activity of this antiserum is not adsorbed after incubation with fixed intact lymphocytes. Lymphocyte alpha-actinin does not bind concanavalin A and it is inaccessible to lactoperoxidase-catalyzed surface iodination. Double immunofluorescence shows that alpha-actinin moves concurrently along the cell membrane with redistributed surface immunoglobulins and Thy-1 antigen, and remains associated up to 30 min with surface aggregates of these receptors. Our results suggest that lymphocyte alpha-actinin, as defined by molecular weight and cross reactivity with the antibody against the muscle protein, (a) is associated with the cell membrane, (b) is not expressed at the cell surface, and (c) participates in the movement of surface receptors.

Decrease in the Density of Intramembrane Particles Associated with Ligand-Independent Cap Formation

The number and distribution of intramembrane particles (IMPs) were examined on capped lymphocytes and control cells. Simultaneous movement of surface receptors and microvilli during ligand-independent (LI-) cap formation in a hypertonic medium made it possible not only to dis-tinguish between capped and non-capped cells in freeze-fractured specimens but also to detect the region where receptors had accumulated by referring only to their morphology. No accumulation of IMPs in the region of the cap was detected, and the distribution of IMPs was random for both capped and non-capped cells. However, the density of IMPs on the protoplasmic halves of cleaved membranes was slightly, but significantly, lower for capped cells than for non-capped cells, whereas that on the exoplasmic halves did not differ. These results suggest that the majority of IMPs are not composed of mobile receptors such as surface Ig, and surface receptors found as IMPs before cap formation might be changed by this event in the intercalated state into the lipid bilayer and, thus might not be detected as IMPs on cap forming cells.

Correlation between actin polymerization and surface receptor segregation in neuroblastoma cells treated with concanavalin A.

In response to concanavalin A (Con A), neuroblastoma cells undergo marked morphological changes which involve the retraction of neurites and the induction of broad and extensive lamellar regions around the cell periphery. From the use of FITC-Con A it was shown that the membrane formed on the induced lamellar regions lacked receptors to Con A from the onset of lamella formation. These receptors were confined to the cell body; they initially showed a uniform distribution and were subsequently collected into patches and finally into aggregates or caps. When the aggregates occurred on the cell periphery their position coincided with areas free of lamellae. Investigations of the lamellar regions in Triton-extracted cell monolayers showed them to consist of a meshwork of actin filaments containing radiating thin filament bundles or microspikes. With increasing time in the presence of Con A there was a progressive increase in the number of radiating microspikes. Previous studies have shown the actin in these lamellar regions to be singly polarized with respect to the cell body. From the segregation of Con A receptors away from areas of actin polymerization in the lamellae it is concluded that actin is involved in some indirect way in surface receptor movement.

Receptor mobility and the cytoskeleton in some human leukemic cells

Introduction. Lymphoid cells will, under certain conditions, exhibit striking exemples of surface receptor movement upon exposure to specific ligands. The receptors will first assemble in a few small surface areas (patching) and eventually aggregate at one pole of the cell (capping), leaving practically no receptors of the same specificity elsewhere on the cell surface. For a number of reasons cytoskeletal elements, like microtubules and microfilaments, are thought to play an important role in the movement of the cell surface receptors. However, the exact mechanism by which the cytoskeleton has its facilitating or inhibiting effect on receptor mobility is still largely a matter of speculation.During an investigation on non-Hodgkin lymphoma's we obtained leukocytes from three patients with clinically different leukemia's, i.e. hairy cell leukemia (HCL), prolymphocytic leukemia (PLL), and chronic lymphocytic leukemia (CLL). These gave different results in capping tests with Concanavalin A (ConA) and with antibodies against total Ig (Alg).

Cytoskeletal regulation of concanavalin A capping in pulmonary alveolar macrophages.

CONCANAVALIN A (con A) capping occurs in polymorphonuclear leukocytes (PMN) and is thought to be dependent on disruption of microtubules with subsequent lateral movement of lectin receptors to a polar region in the plasma membrane1. Capping in PMN is induced by colchicine but is blocked by cytochalasin B, an inhibitor of microfilament assembly2. Based on these observations, a cytoskeletal system that effects transmembrane control of receptor mobility has been proposed. The microtubules system interacts directly or indirectly with membrane components to limit the mobility of surface receptors while the contractile system of microfilaments may enhance the movement of these receptors into caps3. Here we report that capping also occurs in guinea pig alveolar macrophages (AM), and that the factors which regulate AM surface receptor movement differ dramatically from those in PMN. AM are capped by cytochalasin B alone, which is contrary to the experience with the PMN. AM capping is dependent on oxidative phosphorylation and the cap is associated with formation of a striking uropod (Fig. 1).

Inhibition of Antigen-Induced B Lymphocyte Activation in Vitro by Cytochalasin B

Cytochalasin B (CB), a fungal metabolite which disrupts microfilaments. and will inhibit capping and other events requiring membrane movement, suppressed the production of antibody-forming cells (AFC) in both mouse whole spleen cultures immunized with sheep erythrocytes (SRBC) and in mouse B lymphocyte cultures immunized with the thymic independent antigen DNP-Ficoll (DF). CB at a concentration of 1 mug/ml inhibited the AFC response by more than 90% in spleen cell cultures immunized with SRBC. This inhibition was completely reversible by removal of CB up to 24 hr after the start of culture. Spleen cells cultured in the presence of CB for the first 48 to 72 hr had a decreased AFC response similar to that of cultures in which SRBC had been withheld for thocyte the same period of time. Incubating whole spleen cell or B lymphocyte cultures immunized with DF for as short as 6 hr decreased the AFC response more than 60%. Antibody secretion, cell viability, and antigenicity of the SRBC and DF were not affected by CB. The results of these experiments favor the concept that movement of surface receptors is necessary in activating lymphocytes to differentiate into AFC. The differential response to CB observed in SRBC and DF stimulated cultures makes the technique employed a useful tool to study membrane events occuring between antigen interaction with surface receptor and the initiation of differentiative events.

Electron microscopic analysis of the modulation of lymphocyte receptor mobility

The topographic distribution of ferritin-labelled concanavalin A (FT-ConA) bound to the surface membrane of mouse lymphocytes has been analysed by examining ultrathin sections and ghost membranes in the electron microscope. Binding of FT-ConA to lymphocytes at 37 °C did not induce redistribution of ConA receptors at any dose of the labelled lectin. In contrast, in cells treated with colchicine, FT-ConA induced both patch and cap formation. These findings suggest that the modulation of receptor mobility by colchicine occurs at the level of individual receptors. Ultrastructural observations revealed both microtubules and microfilaments in lymphocytes consistent with the suggestion that these cellular structures may be involved in the control of receptor mobility. Analyses using freeze-fracture methods indicated that the distribution of intramembranous particles is not correlated with either the movement of surface receptors or the modulation events. An hypothesis on the modulation of surface receptors by cytoplasmic structures is proposed on the basis of these and previous observations.