Effects of the myosin inhibitor 2,3-butanedione monoxime (BDM) on cell shape, locomotion and fluid pinocytosis in human polymorphonuclear leucocytes

The role of actin, actomyosin and microtubules in defining cell shape during the differentiation of Naegleria amebae into flagellates

Differentiation of Naegleria amebae into flagellates was used to examine the interaction between actin, actomyosin and microtubules in defining cell shape. Amebae, which lack microtubules except during mitosis, differentiate into flagellates with a fixed shape and a complex microtubule cytoskeleton in 120 min. Based on earlier models of ameboid motility it has been suggested that actomyosin is quiescent in flagellates. This hypothesis was tested by following changes in the cytoskeleton using three-dimensional reconstructions prepared by confocal microscopy of individual cells stained with antibodies against actin and tubulin as well as with phalloidin and DNase I. F-actin as defined by phalloidin staining was concentrated in expanding pseudopods. Most phalloidin staining was lost as cells rounded up before the onset of flagellum formation. Actin staining with a Naegleria-specific antibody that recognizes both F- and G-actin was confined to the cell cortex of both amebae and flagellates. DNase I demonstrated G-actin throughout all stages. Most of the actin in the cortex was not bound by phalloidin yet was resistant to detergent extraction suggesting that it was polymerized. The microtubule cytoskeleton of flagellates was intimately associated with this actin cortex. Treatment of flagellates with cytochalasin D produced a rapid loss of flagellate shape and the appearance of phalloidin staining while latrunculin A stabilized the flagellate shape. These results suggest that tension produced by an actomyosin network is required to maintain the flagellate shape. The rapid loss of the flagellate shape induced by drugs, which specifically block myosin light chain kinase, supports this hypothesis.

Interaction of non-adherent suspended neutrophils to complement opsonized pathogens: a new assay using optical traps

Phagocytosis of opsonized pathogens by circulating non-adherent neutrophils is an essential step in host defense, which when overwhelmed contributes to sepsis. To investigate the role played by ligation of complement receptors CR3 and CR4 in non-adherent neutrophils, we designed a novel assay system utilizing dual optical traps, respectively, holding a suspended unactivated cell and presenting a specific ligand-coated bead to the cell surface. We chose anti-CD18 as an example ligand, mimicking the bacterial opsonizing complement fragment iC3b. Presentation of anti-CD18-coated beads elicited both pseudopodial protrusion and subsequent phagocytosis. This is in sharp contrast to previously reported responses of adherent neutrophils, which phagocytize opsonized particles without pseudopod formation. We used this same new assay to probe actomyosin pathways in the neutrophil's pseudopodial and phagocytic response. Disruption of actin or inhibition of myosin light-chain kinase dose-dependently reduced pseudopod formation and phagocytosis rates. In summary, i) the new dual trap assay can be used to study the responses of suspended neutrophils to a variety of ligands, and ii) in a first application of this technique, we found that local ligation of CR3/4 in unactivated neutrophils in suspension induces pseudopod formation and phagocytosis at that site, and that these events occur via an actomyosin-dependent pathway.

A role for microfilament-based contraction in branching morphogenesis of the ureteric bud

BACKGROUND

Branching morphogenesis of the ureteric bud/collecting duct epithelium is an important feature of kidney development. Recent work has identified many transcription factors and paracrine signaling molecules that regulate branching, but the physical mechanisms by which these signals act remain largely unknown. The actin cytoskeleton is a common component of mechanisms of morphogenesis. We have therefore studied the expression of, and requirement for actin filaments in the ureteric bud, a branching epithelium of the mammalian kidney.

METHODS

Embryonic kidney rudiments were grown in organ culture. Actin expression in kidneys growing normally and those in which branching was inhibited was examined using labeled phalloidin. The morphogenetic effects of inhibiting actin organization and tension using cytochalasin D, butanedione monoxime, and Rho kinase ROCK inhibitors were assessed using immunofluorescence.

RESULTS

F-actin is expressed particularly strongly in the apical domains of cells at the tips of branching ureteric bud, but this expression depends on the bud actively growing and branching. Blocking the polymerization of actin using cytochalasin D inhibits ureteric bud branching reversibly, as does blocking myosin function using butadiene monoxime. Inhibiting the activation of ROCK, a known activator of myosin, with the drugs Y27632 or with H1152 inhibits the expression of strong actin bundles in the ureteric bud tips and inhibits ureteric bud branching without inhibiting other aspects of renal development.

CONCLUSION

The formation of tension-bearing actin-myosin complexes is essential for branching morphogenesis in the developing kidney.

Development of a wound dressing targeting neutrophil function

Earlier studies show that neutrophils are virtually unable to kill Staphylococcus aureus in vitro. However, upon addition of 10 mM N-acetylcysteine (NAC) or reduced glutathione (GSH) the neutrophil bacterial killing ability becomes excellent. We want to exploit this phenomenon to develop a wound dressing material that will improve neutrophil function. To study the mechanisms behind the downregulation of neutrophil elimination of bacteria, we used different markers for neutrophil function on surface-adhering neutrophils in contact with S. aureus with or without addition of the antioxidants NAC or GSH. Analysis by scanning electron microscopy showed cell shrinkage and numerous cytoplasmic processes on surface-adhering neutrophils exposed to S. aureus. In cells exposed to S. aureus and GSH, the cells were of normal size and the cytoplasm was spread as in normal attachment. Staining for intracellular GSH, a hallmark of oxidative stress, showed little difference between the experimental groups, indicating that the cells were not damaged by traditional oxidative stress. The H(2)O(2) production of neutrophils, measured by Amplex red, was correlated to bacterial exposure and was not affected by the addition of scavengers. The intracellular and extracellular production of ROS was measured by luminol-amplified chemiluminescence. The apparent ROS-production was mostly intracellular and decreased in the presence of scavengers. However, extracellular production of ROS was not affected by the addition of NAC. The production of nitric oxide (NO) was measured spectrophotometrically as the production of nitrate apparently decreased in the presence of scavengers, probably as a result of interference with the reagents in the test system. In conclusion, differences between leukocytes that were able to eliminate S. aureus and those that were not were mainly seen in the morphology of the cells and in cell viability. The morphological findings point to a difference in NO signaling in the absence and presence of ROS scavengers.

Myosin II is present in gastric parietal cells and required for lamellipodial dynamics associated with cell activation

Nonmuscle myosin II has been shown to participate in organizing the actin cytoskeleton in polarized epithelial cells. Vectorial acid secretion in cultured parietal cells involves translocation of proton pumps from cytoplasmic vesicular membranes to the apical plasma membrane vacuole with coordinated lamellipodial dynamics at the basolateral membrane. Here we identify nonmuscle myosin II in rabbit gastric parietal cells. Western blots with isoform-specific antibodies indicate that myosin IIA is present in both cytosolic and particulate membrane fractions whereas the IIB isoform is associated only with particulate fractions. Immunofluorescent staining demonstrates that myosin IIA is diffusely located throughout the cytoplasm of resting parietal cells. However, after stimulation, myosin IIA is rapidly redistributed to lamellipodial extensions at the cell periphery; virtually all the cytoplasmic myosin IIA joins the newly formed basolateral membrane extensions. 2,3-Butanedione monoximine (BDM), a myosin-ATPase inhibitor, greatly diminishes the lamellipodial dynamics elicited by stimulation and retains the pattern of myosin IIA cytoplasmic staining. However, BDM had no apparent effect on the stimulation associated redistribution of H,K-ATPase from a cytoplasmic membrane compartment to apical membrane vacuoles. The myosin light chain kinase inhibitor 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-7) also did not alter the stimulation-associated recruitment of H,K-ATPase to apical membrane vacuoles, but unlike BDM it had relatively minor inhibitory effects on lamellipodial dynamics. We conclude that specific disruption of the basolateral actomyosin cytoskeleton has no demonstrable effect on recruitment of H,K-ATPase-rich vesicles into the apical secretory membrane. However, myosin II plays an important role in regulating lamellipodial dynamics and cortical actomyosin associated with parietal cell activation.

Chemotactically directed redistribution of alpha-actinin precedes morphological polarization and reversal of polarity in human polymorphonuclear leucocytes (PMNs)

We have determined the temporal and spatial relationship between cell polarization and alpha-actinin localization by analysing the redistribution of alpha-actinin and F-actin in spherical PMNs developing polarity and in polarized cells reversing polarity following localized stimulation with chemotactic peptide using micropipettes. Initially spherical PMNs develop a one-sided accumulation of alpha-actinin before lamellipodia enriched in alpha-actinin are formed. In polarized cells, alpha-actinin is concentrated at the leading front. When polarity is reversed, alpha-actinin redistribution to the uropod precedes reversal of morphological polarity and formation of new lamellipodia at the uropod. Later, lamellipodia enriched in F-actin and alpha-actinin develop at the former uropod to form a new front. The data document that redistribution of alpha-actinin is a very early event in the development of polarity, which precedes formation of lamellipodia.

Induction of nephrotoxic serum nephritis in inbred mice and suppressive effect of colchicine on the development of this nephritis

Accelerated nephrotoxic serum (NTS) nephritis is successfully produced in C57BL/6 mice, using anti-murine glomerular basement membrane (GBM) rabbit antiserum. Anti-murine GBM rabbits antiserum was obtained by immunization of New Zealand white rabbit with trypsinized GBM antigen from normal C57BL/6 mice. Preimmunization with normal rabbit IgG and injection with 150 microl of NTS induced typical NTS nephritis with cellular proliferation in glomeruli, occlusion of glomerular loops, crescents, tubulointerstitial changes and hyperazotemia within 14 days. Polymorphonuclear leucocytes (PMN) have an important role in induction and development of NTS nephritis. Furthermore, clinically used colchicine is thought to suppress functions of PMN. Therefore, the therapeutic effect of colchicine on NTS nephritis was examined. The histological score (HS) of the group treated with 60 microg kg (-1) of colchicine (2.8 +/- 0.5) was significantly lower than that of positive control group (4.03 +/- 0.3).The direct immunofluorescent microscopic study revealed that there is no quantitative difference in the deposition of rabbit IgG, mouse IgG and C3 in GBM between these two groups. Urinary protein excretion and hyperazotemia were significantly suppressed by treatment with 60 microg kg (-1) of colchicine. A NTS nephritis model was established, it was found that colchicine may have a suppressive effect on the development of glomerular nephritis.

Intercellular transfer and supramolecular organization of human leukocyte antigen C at inhibitory natural killer cell immune synapses

After accumulation of target cell human leukocyte antigen (HLA)-C at inhibitory natural killer (NK) cell immune synapses, some HLA-C transfers from target cells to NK cell plasma membranes and cytoplasm. This unexpected intercellular transfer of HLA-C is dependent on NK receptor recognition, since HLA-Cw6 or -Cw4 but not -Cw3 transfer to an NK transfectant expressing killer Ig-like receptor (KIR)2DL1. Strikingly, live-cell time-lapse laser scanning confocal microscopy shows vesicles containing target cell green fluorescent protein-tagged HLA-C migrating away from immune synapses into NK cells. Unlike clustering of HLA-C at the immune synapse, intercellular transfer of HLA-C is dependent on NK cell ATP, but not target cell ATP. However, the intercellular transfer of HLA-C is not dependent on active polymerization of the actin cytoskeleton. In addition, different arrangements of HLA-C are seen at inhibitory NK immune synapses, and these alter as NK synapses mature, but in a fashion distinct from that seen upon T cell activation.