The curvature and cholesterol content of phospholipid bilayers alter the transbilayer distribution of specific molecular species of phosphatidylethanolamine

The curvature, cholesterol content, and transbilayer distribution of phospholipids significantly influence the functional properties of cellular membranes, yet little is known of how these parameters interact. In this study, the transbilayer distribution of phosphatidylethanolamine (PE) is determined in vesicles with large (98 nm) and small (19 nm) radii of curvature and with different proportions of PE, phosphatidylcholine, and cholesterol. It was found that the mean diameters of both types of vesicles were not influenced by their lipid composition, and that the amino-reactive compound 2,4,6-trinitrobenzenesulphonic acid (TNBS) was unable to cross the bilayer of either type of vesicle. When large vesicles were treated with TNBS, approximately 40% of the total membrane PE was derivatized; in the small vesicles 55% reacted. These values are interpreted as representing the percentage of total membrane PE residing in the outer leaflet of the vesicle bilayer. The large vesicles likely contained approximately 20% of the total membrane lipid as internal membranes. Therefore, in both types of vesicles, PE as a phospholipid class was randomly distributed between the inner and outer leaflets of the bilayer. The proportion of total PE residing in the outer leaflet was unaffected by changes in either the cholesterol or PE content of the vesicles. However, the transbilayer distributions of individual molecular species of PE were not random, and were significantly influenced by radius of curvature, membrane cholesterol content, or both. For example, palmitate- and docosahexaenoate-containing species of PE were preferentially located in the outer leaflet of the bilayer. Membrane cholesterol content affected the transbilayer distributions of stearate-, oleate-, and linoleate-containing species. The transbilayer distributions of palmitate-, docosahexaenoate-, and stearate-containing species were significantly influenced by membrane curvature, but only in the presence of high levels of cholesterol. Thus, differences in membrane curvature and cholesterol content alter the array of PE molecules present on the surfaces of phospholipid bilayers. In cells and organelles, these differences could have profound effects on a number of critical membrane functions and processes.

The immunological synapse and the actin cytoskeleton: molecular hardware for T cell signaling

The actin cytoskeleton seems to play two critical roles in the activation of T cells. One of these roles is T cell shape development and movement, including formation of the immunological synapse. The other is the formation of a scaffold for signaling components. This review focuses on the recent convergence of cell biology and immunology studies to explain the role of the actin cytoskeleton in creating the molecular basis for immunological synapse formation and T cell signaling.

Vertebrates have conserved capping protein alpha isoforms with specific expression patterns

Capping protein (CP), a ubiquitous actin binding protein composed of an alpha and a beta subunit, is important for actin assembly and cell motility. Lower organisms have one gene and one isoform of each subunit. Chickens have two very similar alpha-subunit isoforms. To determine if vertebrates in general contain multiple alpha isoforms and if those alpha isoforms have conserved sequences, we isolated and analyzed alpha subunit cDNA's in mice and humans. Both mice and humans also have two alpha isoforms. Phylogenetic analysis of the alpha isoform sequences reveals that vertebrates have two highly conserved subfamilies, alpha1 and alpha2. The alpha1 and alpha2 subfamilies are very similar to each other but can be defined and distinguished from each other by a small number of key amino acid residues. In addition, 3' untranslated cDNA sequences are conserved within the isoform subfamilies. To investigate the function of the alpha isoforms, we examined their expression in mouse cells and tissues. Endothelial cells contain only the alpha2 isoform, and erythrocytes contain almost exclusively the alpha1 isoform. Most tissues have both alpha1 and alpha2 isoforms but the ratio of alpha1:alpha2 varies widely. Together, these findings support the hypothesis that the CP alpha isoforms have conserved, unique and essential roles in vertebrates.

Role of actin and Myo2p in polarized secretion and growth of Saccharomyces cerevisiae

We examined the role of the actin cytoskeleton in secretion in Saccharomyces cerevisiae with the use of several quantitative assays, including time-lapse video microscopy of cell surface growth in individual living cells. In latrunculin, which depolymerizes filamentous actin, cell surface growth was completely depolarized but still occurred, albeit at a reduced level. Thus, filamentous actin is necessary for polarized secretion but not for secretion per se. Consistent with this conclusion, latrunculin caused vesicles to accumulate at random positions throughout the cell. Cortical actin patches cluster at locations that correlate with sites of polarized secretion. However, we found that actin patch polarization is not necessary for polarized secretion because a mutant, bee1Delta(las17Delta), which completely lacks actin patch polarization, displayed polarized growth. In contrast, a mutant lacking actin cables, tpm1-2 tpm2Delta, had a severe defect in polarized growth. The yeast class V myosin Myo2p is hypothesized to mediate polarized secretion. A mutation in the motor domain of Myo2p, myo2-66, caused growth to be depolarized but with only a partial decrease in the level of overall growth. This effect is similar to that of latrunculin, suggesting that Myo2p interacts with filamentous actin. However, inhibition of Myo2p function by expression of its tail domain completely abolished growth.

The Arf GTPase-activating protein ASAP1 regulates the actin cytoskeleton

Arf family GTP-binding proteins are best characterized as regulators of membrane traffic, but recent studies indicate an additional role in cytoskeletal organization. An Arf GTPase-activating protein of the centaurin beta family, ASAP1 (also known as centaurin beta4), binds Arf and two other known regulators of the actin cytoskeleton, the tyrosine kinase Src and phosphatidylinositol 4,5-bisphosphate. In this paper, we show that ASAP1 localizes to focal adhesions and cycles with focal adhesion proteins when cells are stimulated to move. Overexpression of ASAP1 altered the morphology of focal adhesions and blocked both cell spreading and formation of dorsal ruffles induced by platelet-derived growth factor (PDGF). On the other hand, ASAP1, with a mutation that disrupted GTPase-activating protein activity, had a reduced effect on cell spreading and increased the number of cells forming dorsal ruffles in response to PDGF. These data support a role for an Arf GTPase-activating protein, ASAP1, as a regulator of cytoskeletal remodeling and raise the possibility that the Arf pathway is a target for PDGF signaling.

Attenuation of interleukin-8 production by inhibiting nuclear factor-kappaB translocation using decoy oligonucleotides

Interleukin-8 (IL-8), a monocyte-derived neutrophil chemoattractant factor, is a polymorphonuclear neutrophil chemotaxin that is involved in a number of inflammatory disorders. Transcription of the IL-8 gene is controlled by regulatory proteins, including nuclear factor-kappaB (NF-kappaB), a family of proteins that is important in the transcriptional control of a number of genes. When cells are activated, NF-kappaB translocates from the cytoplasm to the nucleus, where it activates transcription by binding to a specific sequence within the 5' untranslated region of the gene. During translocation, NF-kappaB is potentially susceptible to diversion by oligonucleotides that contain the binding sequence for this protein. In the current study, we produced phosphorothioate-modified oligonucleotides containing the specific DNA sequence that NF-kappaB binds within the IL-8 gene. We then investigated the effects of transfection of monocytes with these oligonucleotides on interleukin-1beta (IL-1beta)-stimulated IL-8 production, IL-8 mRNA expression, and NF-kappaB binding activity. We found that transfection with these oligonucleotides significantly inhibited monocyte IL-8 production. A single-stranded oligonucleotide with two copies of the NF-kappaB-binding sequence was the most potent of those tested. This single-stranded oligonucleotide also inhibited IL-1beta-induced translocation of NF-kappaB to the nucleus and reduced IL-8 mRNA expression. These studies demonstrated that monocyte production of IL-8 can be attenuated using a single-stranded oligonucleotide that binds a transcriptional activating protein before it translocates to the cell nucleus. This approach ultimately may be useful in the control of inflammation involved in a number of diseases.

Evaluation of a needle-free injection system for local anaesthesia prior to venous cannulation

We evaluated a single-use, disposable, carbon-dioxide-powered, needleless injector (J-Tip, National Medical Products Inc., CA, USA), which is claimed to deliver a virtually painless, subcutaneous injection. Seventy-two patients undergoing various types of surgery had a large-bore intravenous cannula inserted prior to induction of general anaesthesia. Three minutes beforehand, a subcutaneous injection of 0.3 ml of 1% plain lidocaine was administered. Subjects were randomly allocated to receive the lidocaine either by the needleless injector or from a conventional syringe and a 25 G needle. Pain scores were recorded on injection of the lidocaine and on insertion of the cannula. There was significantly less pain on injection with the needleless injector than with the 25 G needle (p < 0.001) but, surprisingly, there was more pain on cannulation (p < 0. 001). We conclude that the device certainly delivers a less painful subcutaneous injection than a 25 G needle, but perhaps provides less effective skin anaesthesia for venous cannulation at sites where the subcutaneous space is small; its use might be better suited to areas where the subcutaneous space is deeper.

Dynein-dependent movements of the mitotic spindle in Saccharomyces cerevisiae Do not require filamentous actin

In budding yeast, the mitotic spindle is positioned in the neck between the mother and the bud so that both cells inherit one nucleus. The movement of the mitotic spindle into the neck can be divided into two phases: (1) Kip3p-dependent movement of the nucleus to the neck and alignment of the short spindle, followed by (2) dynein-dependent movement of the spindle into the neck and oscillation of the elongating spindle within the neck. Actin has been hypothesized to be involved in all these movements. To test this hypothesis, we disrupted the actin cytoskeleton with the use of mutations and latrunculin A (latrunculin). We assayed nuclear segregation in synchronized cell populations and observed spindle movements in individual living cells. In synchronized cell populations, no actin cytoskeletal mutant segregated nuclei as poorly as cells lacking dynein function. Furthermore, nuclei segregated efficiently in latrunculin-treated cells. Individual living cell analysis revealed that the preanaphase spindle was mispositioned and misaligned in latrunculin-treated cells and that astral microtubules were misoriented, confirming a role for filamentous actin in the early, Kip3p-dependent phase of spindle positioning. Surprisingly, mispositioned and misaligned mitotic spindles moved into the neck in the absence of filamentous actin, albeit less efficiently. Finally, dynein-dependent sliding of astral microtubules along the cortex and oscillation of the elongating mitotic spindle in the neck occurred in the absence of filamentous actin.

Haemostatic and lipid determinants of prothrombin fragment F1.2 and D-dimer in plasma

The determinants of plasma levels of prothrombin fragment F1.2 (F1.2) and D-dimer in different populations are unclear and this may complicate their interpretation as predictors of thrombotic risk, particularly in the case of D-dimer. We therefore measured F1.2 and D-dimer levels together with a number of other haemostatic and lipid variables in a cross-sectional community-based study of 150 healthy adults (73 male, 77 female), age range 23-80 years, identified from the list of a general practice by stratified random sampling within sex and decade of age. Plasma F1.2 was significantly higher in females than males and was independently and positively associated with age, factor VII activity (FVIIc) and C1 inhibitor, and inversely associated with high density lipoprotein (HDL) cholesterol. Plasma D-dimer showed a quadratic association with age (p <0.0001). In those < or =55 years D-dimer was inversely associated with dilute clot lysis time (DCLT) and activated protein C (APC) ratio. In those >55 years it was significantly higher in females than males and associated positively with age, fibrinogen and, in males, activated factor XII (FXIIa). In a multiple-linear model which combined both age groups, F1.2 and D-dimer were independently associated with each other (r = 0.22, p = 0.03). Thus, thrombin generation and fibrin turnover/fibrinolysis are associated in healthy subjects. HDL cholesterol (inversely) and FVIIc are associated with basal thrombin generation (i.e. F1.2). Determinants of D-dimer differ according to age and interpretation of the biological significance of D-dimer levels in epidemiological studies may therefore not be straightforward.

Evaluation of a needle-free injection system for local anaesthesia prior to venous cannulation

We evaluated a single-use, disposable, carbon-dioxide-powered, needleless injector (J-Tip, National Medical Products Inc., CA, USA), which is claimed to deliver a virtually painless, subcutaneous injection. Seventy-two patients undergoing various types of surgery had a large-bore intravenous cannula inserted prior to induction of general anaesthesia. Three minutes beforehand, a subcutaneous injection of 0.3 ml of 1% plain lidocaine was administered. Subjects were randomly allocated to receive the lidocaine either by the needleless injector or from a conventional syringe and a 25 G needle. Pain scores were recorded on injection of the lidocaine and on insertion of the cannula. There was significantly less pain on injection with the needleless injector than with the 25 G needle (p < 0.001) but, surprisingly, there was more pain on cannulation (p < 0. 001). We conclude that the device certainly delivers a less painful subcutaneous injection than a 25 G needle, but perhaps provides less effective skin anaesthesia for venous cannulation at sites where the subcutaneous space is small; its use might be better suited to areas where the subcutaneous space is deeper.

Autonomic dysfunction is related to impaired pancreatic beta cell function in patients with coronary artery disease

OBJECTIVE

To assess the role of beta cell failure in the development of autonomic dysfunction in patients with coronary artery disease.

DESIGN

Autonomic function was measured by standard clinical methods and by heart rate variability in 24 type II diabetic and 24 non-diabetic subjects with coronary artery disease. Quantitative estimates of pancreatic beta cell function (%beta) and insulin resistance were made from basal plasma glucose and insulin concentrations using a computer solved model. Fasting proinsulin levels provided an independent measure of beta cell function.

RESULTS

The circadian rhythm of sympathovagal balance (ratio of low to high frequency spectral components of heart rate variability) was significantly attenuated in patients with below median (%beta </= 63. 3) compared with above median pancreatic beta cell function. Multiple measures of autonomic function showed positive associations with %beta (low frequency: r = 0.41, p = 0.004; high frequency: r = 0.27, p = 0.07; lying/standing fall in systolic pressure: r = -0.30, p = 0.04) and negative associations with proinsulin (low frequency: r = -0.35, p = 0.03; high frequency: r = -0.36, p = 0.02; standard deviation of RR intervals: r = -0.43, p = 0.007). Associations tended to be stronger in non-diabetic than diabetic patients. In contrast, there was no association between insulin resistance and either autonomic function or the circadian rhythm of sympathovagal balance, regardless of diabetes status.

CONCLUSIONS

The data are consistent with the hypothesis that beta cell failure plays a pathogenic role in the development of autonomic dysfunction in patients with coronary artery disease.

Control of actin assembly and disassembly at filament ends

The most important discovery in the field is that the Arp2/3 complex nucleates assembly of actin filaments with free barbed ends. Arp2/3 also binds the sides of actin filaments to create a branched network. Arp2/3's nucleation activity is stimulated by WASP family proteins, some of which mediate signaling from small G-proteins. Listeria movement caused by actin polymerization can be reconstituted in vitro using purified proteins: Arp2/3 complex, capping protein, actin depolymerizing factor/cofilin, and actin. actin depolymerizing factor/cofilin increases the rate at which actin subunits leave pointed ends, and capping protein caps barbed ends.

In vivo adenovirus-mediated endothelial nitric oxide synthase gene transfer ameliorates lung allograft ischemia-reperfusion injury

OBJECTIVE

Nitric oxide regulates vascular tone, inhibits platelet aggregation, and inhibits leukocyte adhesion, all of which are important modulators of ischemia-reperfusion injury. This study aimed to determine the effects of endothelial constitutive nitric oxide synthase gene transfer on ischemia-reperfusion injury in a rat lung transplant model.

METHODS

In group I, donor animals were injected intravenously with 5 x 10(9) pfu of adenovirus-encoding endothelial constitutive nitric oxide synthase. Groups II and III served as controls, whereby donor animals were injected with either 5 x 10(9) pfu of adenovirus encoding beta-galactosidase or saline solution, respectively. Twenty-four hours after injection, left lungs were harvested and preserved for 18 hours at 4 degrees C, then implanted into isogeneic recipients, which were put to death 24 hours later. Recombinant endothelial constitutive nitric oxide synthase gene expression was evaluated by Western blotting and immunohistochemistry. Lung grafts were assessed by measuring arterial oxygenation, myeloperoxidase activity, and wet/dry weight ratios.

RESULTS

Western blotting confirmed the overexpression of endothelial constitutive nitric oxide synthase in lungs so transfected compared with controls. Twenty-four hours after reperfusion, mean arterial oxygenation was significantly improved in group I compared with group II and III controls (189.4 +/- 47.1 mm Hg vs 71.7 +/- 8.9 mm Hg and 67.8 +/- 12.2 mm Hg, P =.02, P =.01, respectively). Myeloperoxidase activity, a reflection of tissue neutrophil sequestration, was also significantly reduced in group I compared with groups II and III (0.136 +/- 0.038 DeltaOD/mg/min vs 0. 587 +/- 0.077 and 0.489 +/- 0.126 DeltaOD/mg/min, P =.001, P =.01, respectively).

CONCLUSION

Adenovirus-mediated gene transfer with endothelial constitutive nitric oxide synthase ameliorates ischemia-reperfusion injury as manifested by significantly improved oxygenation and decreased neutrophil sequestration in transplanted lung isografts. Endothelial constitutive nitric oxide synthase gene transfer may reduce acute lung dysfunction after lung transplantation.

Listeria monocytogenes ActA protein interacts with phosphatidylinositol 4,5-bisphosphate in vitro

The N-terminal region of the Listeria monocytogenes ActA protein, in conjunction with host cell factors, is sufficient for actin polymerization at the bacterial surface. Previous data suggested that ActA could protect barbed ends from capping proteins. We tested this hypothesis by actin polymerization experiments in the presence of the ActA N-terminal fragment and capping protein. ActA does not protect barbed ends from capping protein. In contrast, this polypeptide prevents PIP(2) from inhibiting the capping activity of capping protein. Gel filtration and tryptophan fluorescence experiments showed that the purified ActA N-terminal fragment binds to PIP(2) and PIP, defining phosphoinositides as novels ligands for this functional domain of ActA. Phosphoinositide binding to the N-terminal region of ActA may induce conformational changes in ActA and/or facilitate binding of other cell components, important for ActA-induced actin polymerization.

Direct binding of Reelin to VLDL receptor and ApoE receptor 2 induces tyrosine phosphorylation of disabled-1 and modulates tau phosphorylation

The large extracellular matrix protein Reelin is produced by Cajal-Retzius neurons in specific regions of the developing brain, where it controls neuronal migration and positioning. Genetic evidence suggests that interpretation of the Reelin signal by migrating neurons involves two neuronal cell surface proteins, the very low density lipoprotein receptor (VLDLR) and the apoE receptor 2 (ApoER2) as well as a cytosolic adaptor protein, Disabled-1 (Dab1). We show that Reelin binds directly and specifically to the ectodomains of VLDLR and ApoER2 in vitro and that blockade of VLDLR and ApoER2 correlates with loss of Reelin-induced tyrosine phosphorylation of Disabled-1 in cultured primary embryonic neurons. Furthermore, mice that lack either Reelin or both VLDLR and ApoER2 exhibit hyperphosphorylation of the microtubule-stabilizing protein tau. Taken together, these findings suggest that Reelin acts via VLDLR and ApoER2 to regulate Disabled-1 tyrosine phosphorylation and microtubule function in neurons.

Induction of interleukin-8 synthesis integrates effects on transcription and mRNA degradation from at least three different cytokine- or stress-activated signal transduction pathways

A hallmark of inflammation is the burst-like formation of certain proteins, initiated by cellular stress and proinflammatory cytokines like interleukin 1 (IL-1) and tumor necrosis factor, stimuli which simultaneously activate different mitogen-activated protein (MAP) kinases and NF-kappaB. Cooperation of these signaling pathways to induce formation of IL-8, a prototype chemokine which causes leukocyte migration and activation, was investigated by expressing active and inactive forms of protein kinases. Constitutively active MAP kinase kinase 7 (MKK7), an activator of the stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) pathway, induced IL-8 synthesis and transcription from a minimal IL-8 promoter. Furthermore, MKK7 synergized in both effects with NF-kappaB-inducing kinase (NIK). Activation of the IL-8 promoter by either of the kinases required functional NF-kappaB and AP-1 sites. While NIK and MKK7 did not affect degradation of IL-8 mRNA, an active form of MKK6, which selectively activates p38 MAP kinase, induced marked stabilization of the transcript and further increased IL-8 protein formation induced by NIK plus MKK7. Consistently, the MAP kinase kinase kinase MEKK1, which can activate NF-kappaB, SAPK/JNK, and p38 MAP kinases, most potently induced IL-8 formation. These results provide evidence that maximal IL-8 gene expression requires the coordinate action of at least three different signal transduction pathways which cooperate to induce mRNA synthesis and suppress mRNA degradation.

Cdc42-induced actin filaments are protected from capping protein

Each actin filament has a pointed and a barbed end, however, filament elongation occurs primarily at the barbed end. Capping proteins, by binding to the barbed end, can terminate this elongation. The rate of capping depends on the concentration of capping protein [1], and thus, if capping terminates elongation, the length of filaments should vary inversely with the concentration of capping protein. In cell extracts, such as those derived from neutrophils, new actin filaments can be nucleated by addition of GTPgammaS-activated Cdc42 (a small GTPase of the Rho family). To determine whether elongation of these filaments is terminated by capping, we manipulated the concentration of capping protein, the major calcium-independent capping protein in neutrophils, and observed the effects on filament lengths. Depletion of 70% of the capping protein from extracts increased the mean length of filaments elongated from spectrin-actin seeds (very short actin filaments with free barbed ends) but did not increase the mean length of filaments induced by Cdc42. Furthermore, doubling the concentration of capping protein in cell extracts by adding pure capping protein did not decrease the mean length of filaments induced by Cdc42. These results suggest that the barbed ends of Cdc42-induced filaments are protected from capping by capping protein.

Formation of Ephemeral Bedform Turrets in Coastal Foredunes

Rare, erosional turret bedforms are described in a coastal foredune environment. These ephemeral structures are formed as a result of moist columns of sand being sculpted by aeolian action of saltating particles. Mature formation of these features appears to be facilitated by the action of an advancing foredune ridge, first preserving and then isolating the turrets for further enhanced erosion within a dune environment. It is envisaged that these structures may be preserved in dune stratigraphy.

The disabled 1 phosphotyrosine-binding domain binds to the internalization signals of transmembrane glycoproteins and to phospholipids

Disabled gene products are important for nervous system development in drosophila and mammals. In mice, the Dab1 protein is thought to function downstream of the extracellular protein Reln during neuronal positioning. The structures of Dab proteins suggest that they mediate protein-protein or protein-membrane docking functions. Here we show that the amino-terminal phosphotyrosine-binding (PTB) domain of Dab1 binds to the transmembrane glycoproteins of the amyloid precursor protein (APP) and low-density lipoprotein receptor families and the cytoplasmic signaling protein Ship. Dab1 associates with the APP cytoplasmic domain in transfected cells and is coexpressed with APP in hippocampal neurons. Screening of a set of altered peptide sequences showed that the sequence GYXNPXY present in APP family members is an optimal binding sequence, with approximately 0.5 microM affinity. Unlike other PTB domains, the Dab1 PTB does not bind to tyrosine-phosphorylated peptide ligands. The PTB domain also binds specifically to phospholipid bilayers containing phosphatidylinositol 4P (PtdIns4P) or PtdIns4,5P2 in a manner that does not interfere with protein binding. We propose that the PTB domain permits Dab1 to bind specifically to transmembrane proteins containing an NPXY internalization signal.