Calcium-induced translocation of annexins to subcellular organelles of human neutrophils

Role of S100A8/A9 for Cytokine Secretion, Revealed in Neutrophils Derived from ER-Hoxb8 Progenitors

S100A9, a Ca²⁺-binding protein, is tightly associated to neutrophil pro-inflammatory functions when forming a heterodimer with its S100A8 partner. Upon secretion into the extracellular environment, these proteins behave like damage-associated molecular pattern molecules, which actively participate in the amplification of the inflammation process by recruitment and activation of pro-inflammatory cells. Intracellular functions have also been attributed to the S100A8/A9 complex, notably its ability to regulate nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation. However, the complete functional spectrum of S100A8/A9 at the intracellular level is far from being understood. In this context, we here investigated the possibility that the absence of intracellular S100A8/A9 is involved in cytokine secretion. To overcome the difficulty of genetically modifying neutrophils, we used murine neutrophils derived from wild-type and S100A9^−/− Hoxb8 immortalized myeloid progenitors. After confirming that differentiated Hoxb8 neutrophil-like cells are a suitable model to study neutrophil functions, our data show that absence of S100A8/A9 led to a dysregulation of cytokine secretion after lipopolysaccharide (LPS) stimulation. Furthermore, we demonstrate that S100A8/A9-induced cytokine secretion was regulated by the nuclear factor kappa B (NF-κB) pathway. These results were confirmed in human differentiated HL-60 cells, in which S100A9 was inhibited by shRNAs. Finally, our results indicate that the degranulation process could be involved in the regulation of cytokine secretion by S100A8/A9.

Calcium signaling and regulation of neutrophil functions: Still a long way to go

Neutrophils are the most abundant leukocytes in blood and disruption in their functions often results in an increased risk of serious infections and inflammatory autoimmune diseases. Following recent discoveries in their influence over disease progression, a resurgence of interest for neutrophil biology has taken place. The multitude of signaling pathways activated by the engagement of numerous types of receptors, with which neutrophils are endowed, reflects the functional complexity of these cells. It is therefore not surprising that there remains a huge lack in the understanding of molecular mechanisms underlining neutrophil functions. Moreover, studies on neutrophils are undoubtedly limited by the difficulty to efficiently edit the cell's genome. Over the past 30 years, compelling evidence has clearly highlighted that Ca²⁺ -signaling is governing the key processes associated with neutrophil functions. The confirmation of the role of an elevation of intracellular Ca²⁺ concentration has come from studies on NADPH oxidase activation and phagocytosis. In this review, we give an overview and update of our current knowledge on the role of Ca²⁺ mobilization in the regulation of pro-inflammatory functions of neutrophils. In particular, we stress the importance of Ca²⁺ in the formation of NETs and cytokine secretion in the light of newest findings. This will allow us to embrace how much further we have to go to understand the complex dynamics of Ca²⁺ -dependent mechanisms in order to gain more insights into the role of neutrophils in the pathogenesis of inflammatory diseases. The potential for therapeutics to regulate the neutrophil functions, such as Ca²⁺ influx inhibitors to prevent autoimmune and chronic inflammatory diseases, has been discussed in the last part of the review.

Annexin A6 contributes to the invasiveness of breast carcinoma cells by influencing the organization and localization of functional focal adhesions

The interaction of annexin A6 (AnxA6) with membrane phospholipids and either specific extracellular matrix (ECM) components or F-actin suggests that it may influence cellular processes associated with rapid plasma membrane reorganization such as cell adhesion and motility. Here, we examined the putative roles of AnxA6 in adhesion-related cellular processes that contribute to breast cancer progression. We show that breast cancer cells secrete annexins via the exosomal pathway and that the secreted annexins are predominantly cell surface-associated. Depletion of AnxA6 in the invasive BT-549 breast cancer cells is accompanied by enhanced anchorage-independent cell growth but cell-cell cohesion, cell adhesion/spreading onto collagen type IV or fetuin-A, cell motility and invasiveness were strongly inhibited. To explain the loss in adhesion/motility, we show that vinculin-based focal adhesions in the AnxA6-depleted BT-549 cells are elongated and randomly distributed. These focal contacts are also functionally defective because the activation of focal adhesion kinase and the phosphoinositide-3 kinase/Akt pathway were strongly inhibited while the MAP kinase pathway remained constitutively active. Compared with normal human breast tissues, reduced AnxA6 expression in breast carcinoma tissues correlates with enhanced cell proliferation. Together this suggests that reduced AnxA6 expression contributes to breast cancer progression by promoting the loss of functional cell-cell and/or cell-ECM contacts and anchorage-independent cell proliferation.

Lipid raft proteome of the human neutrophil azurophil granule

Detergent-resistant membrane domains (DRMs) are present in the membranes of azurophil granules in human neutrophils (Feuk-Lagerstedt et al., J. Leukoc. Biol. 2002, 72, 970). Using a proteomic approach, we have now identified 106 proteins in a DRM preparation from these granule membranes. Among these proteins were the lipid raft structural proteins flotillin-1 and -2, cytoskeletal proteins such as actin, vimentin and tubulin, and membrane fusion promoting proteins like annexins and dysferlin. Our results suggest that the azurophil granule membrane, in similarity to the plasma membrane, is an elaborate structure that takes part in intracellular signaling and functions other than the mere delivery of bactericidal effector molecules to the phagosome.

Annexin expression in inflammatory myopathies

The pathogenesis of the inflammatory myopathies is still unclear, making their treatment largely empirical. Improved understanding of the molecular mechanisms of inflammatory muscle injury may, however, lead to the development of more specific immunotherapies. To elucidate a possible pathogenic contribution of calcium-binding proteins such as the annexins, we immunohistochemically investigated muscle biopsy specimens from patients with dermatomyositis (10 cases), polymyositis (9 cases), and inclusion-body myositis (4 cases), compared to control cases comprising sarcoid myopathy (3 cases), Duchenne muscular dystrophy (DMD; 4 cases), and normal muscle (3 cases). We found expression of annexins A1, A2, A4, and A6 in the vascular endothelium of all cases. Myofibers expressed annexins A5, A6, and A7 diffusely and weakly in the cytosol, whereas annexins A5 and A7 were also particularly localized to the sarcolemma. In the inflammatory myopathies, in areas of myonecrosis in DMD, and in granulomatous lesions of sarcoid myopathy, reactivity of annexins A1, A2, A4, A5, and A6 was observed in macrophages and T-lymphocytes. Whereas the latter annexins appear to be nonspecific indicators of activation, annexin A1 upregulation may represent endogenous anti-inflammatory mechanisms that merit further investigation.

Stimulus-specific defect in the phagocytic pathways of annexin 1 null macrophages

The role of the glucocorticoid-regulated protein annexin 1 during the process of phagocytosis has been studied using annexin 1 null peritoneal macrophages. Wild type and annexin 1 null macrophages were incubated with several distinct phagocytic targets. No differences were observed in rate or the maximal response with respect to IgG complexes or opsonised zymosan phagocytosis, as assessed by monitoring the production of reactive oxygen species. When annexin 1 null macrophages were incubated with non-opsonised zymosan particles, they exhibited impaired generation of reactive oxygen species, which was linked to a defect in binding of cells to the particles, as determined with fluorescent zymosan. This phenomenon was further confirmed by electron microscopy analysis, where annexin 1 null macrophages internalised fewer non-opsonised zymosan particles. Specific alterations in macrophage plasma membrane markers were observed in the annexin 1 null cells. Whereas no differences in dectin-1 and FcgammaR II/III expression were measured between the two genotypes, decreased membrane CD11b and F4/80 levels were measured selectively in macrophages lacking annexin 1. These cells also responded with an enhanced release of PGE(2) and COX-2 protein expression following addition of the soluble stimulants, LPS and heat-activated IgG. In conclusion, these results suggest that participation of endogenous annexin 1 during zymosan phagocytosis is critical and that this protein plays a tonic inhibitory role during macrophage activation.

Annexin 2 binding to phosphatidylinositol 4,5-bisphosphate on endocytic vesicles is regulated by the stress response pathway

Annexin 2 is a Ca(2+)-binding protein that has an essential role in actin-dependent macropinosome motility. We show here that macropinosome rocketing can be induced by hyperosmotic shock, either alone or synergistically when combined with phorbol ester or pervanadate. Rocketing was blocked by inhibitors of phosphatidylinositol-3-kinase(s), p38 mitogen-activated protein (MAP) kinase, and calcium, suggesting the involvement of phosphoinositide signaling. Since various phosphoinositides are enriched on inwardly mobile vesicles, we examined whether or not annexin 2 binds to any of this class of phospholipid. In liposome sedimentation assays, we show that recombinant annexin 2 binds to phosphatidylinositol 4,5-bisphosphate (PtdIns-4,5P(2)) but not to other poly- and mono-phosphoinositides. The affinity of annexin 2 for PtdIns-4,5P(2) (K(D) approximately 5 microm) is comparable with those reported for a variety of PtdIns-4,5P(2)-binding proteins and is enhanced in the presence of Ca(2+). Although annexin 1 also bound to PtdIns-4,5P(2), annexin 5 did not, indicating that this is not a generic annexin property. To test whether annexin 2 binds to PtdIns-4,5P(2) in vivo, we microinjected rat basophilic leukemia cells stably expressing annexin 2-green fluorescent protein (GFP) with fluorescently tagged antibodies to PtdIns-4,5P(2). Annexin 2-GFP and anti-PtdIns-4,5P(2) IgG co-localize at sites of pinosome formation, and annexin 2-GFP relocalizes to intracellular membranes in Ptk cells microinjected with Arf6Q67L, which has been shown to stimulate PtdIns-4,5P(2) synthesis on pinosomes through activation of phosphatidylinositol 5 kinase. These results establish a novel phospholipid-binding specificity for annexin 2 consistent with a role in mediating the interaction between the macropinosome surface and the polymerized actin tail.

Translocation of annexin I from cellular membrane to the nuclear membrane in human esophageal squamous cell carcinoma

AIM: To investigate the alteration of the annexin I subcellular localization in esophageal squamous cell carcinoma (ESCC) and the correlation between the translocation and the tumorigenesis of ESCC.

METHODS: The protein localization of annexin I was detected in both human ESCC tissues and cell line via the indirect immunofluorescence strategy.

RESULTS: In the normal esophageal epithelia the annexin I was mainly located on the plasma membrane and formed a consecutive typical trammels net. Annexin I protein also expressed dispersively in cytoplasm and the nuclei without specific localization on the nuclear membrane. In esophageal cancer annexin I decreased very sharply with scattered disappearance on the cellular membrane, however it translocated and highly expressed on the nuclear membrane, which was never found in normal esophageal epithelia. In cultured esophageal cancer cell line annexin I protein was also focused on the nuclear membrane, which was consistent with the result from esophageal cancer tissues.

CONCLUSION: This observation suggests that the translocation of annexin I protein in ESCC may correlate with the tumorigenesis of the esophageal cancer.

Plasminogen-mediated matrix invasion and degradation by macrophages is dependent on surface expression of annexin II

Genetic evidence demonstrates the importance of plasminogen activation in the migration of macrophages to sites of injury and inflammation, their removal of necrotic debris, and their clearance of fibrin. These studies identified the plasminogen binding protein annexin II on the surface of macrophages and determined its role in their ability to degrade and migrate through extracellular matrices. Calcium-dependent binding of annexin II to RAW264.7 macrophages was shown using flow cytometry and Western blot analysis of EGTA eluates. Ligand blots demonstrated that annexin II comigrates with one of several proteins in lysates and membranes derived from RAW264.7 macrophages that bind plasminogen. Preincubation of RAW264.7 macrophages with monoclonal anti-annexin II IgG inhibited (35%) their binding of 125I-Lys-plasminogen. Likewise, plasmin binding to human monocyte-derived macrophages and THP-1 monocytes was inhibited (50% and 35%, respectively) when cells were preincubated with anti-annexin II IgG. Inhibition of plasminogen binding to annexin II on RAW264.7 macrophages significantly impaired their ability to activate plasminogen and degrade [3H]-glucosamine-labeled extracellular matrices. The migration of THP-1 monocytes through a porous membrane, in response to monocyte chemotactic protein-1, was blocked when the membranes were coated with extracellular matrix. The addition of plasminogen to the monocytes restored their ability to migrate through the matrix-coated membrane. Preincubation of THP-1 monocytes with anti-annexin II IgG inhibited (60%) their plasminogen-dependent chemotaxis through the extracellular matrix. These studies identify annexin II as a plasminogen binding site on macrophages and indicate an important role for annexin II in their invasive and degradative phenotype.

Redistribution of annexin in gravistimulated pea plumules

We used immunocytochemistry to investigate the effects of gravistimulation on annexin localization in etiolated pea plumule shoots. In longitudinal sections, an asymmetric annexin immunostaining pattern was observed in a defined group of cells located just basipetal to apical meristems at the main shoot apex and at all of the axillary buds, an area classically referred to as the leaf gap. The pattern was observed using both protein-A-purified anti-annexin and affinity-purified anti-annexin antibodies for the immunostaining. A subset of the cells with the annexin staining also showed an unusually high level of periodic acid Schiff (PAS) staining in their cell walls. Prior to gravistimulation, the highest concentration of annexin was oriented toward the direction of gravity along the apical end of these immunostained cells. In contrast, both at 15 and 30 min after gravistimulation, the annexin immunostain became more evenly distributed all around the cell and more distinctly cell peripheral. The asymmetry along the lower wall of these cells was no longer evident. In accord with current models of annexin action, we interpret the results to indicate that annexin-mediated secretion in the leaf gap area is preferentially toward the apical meristem prior to gravistimulation, and that gravistimulation results in a redirection of this secretion. These data are to our knowledge the first to show a correlation between the vector of gravity and the distribution of annexins in the cells of flowering plants.

Endogenous cleavage of annexin I generates a truncated protein with a reduced calcium requirement for binding to neutrophil secretory vesicles and plasma membrane

We have earlier shown that an N-terminal truncated annexin I molecule, annexin I(des1-8), is generated in human neutrophils through cleavage by a membrane localized metalloprotease. The truncated protein showed differences in membrane binding among the neutrophil granule populations as compared to full-length annexin I. In this study, we investigated the cleavage capabilities of isolated neutrophil secretory vesicles and plasma membrane, and the binding of full-length annexin I and annexin I(des1-8) to these membrane fractions. Translocations were performed in vitro to secretory vesicles and plasma membrane, respectively, at different Ca(2+) concentrations. We show that the annexin I-cleaving membrane localized metalloprotease is present both in the secretory vesicles and the plasma membrane. The N-terminal truncation of annexin I gives rise to a molecule with a decreased Ca(2+) requirement for binding, both to secretory vesicles and plasma membrane. There was, thus, no difference in binding of either full-length annexin I or annexin I(des1-8) to the secretory vesicles as compared to the plasma membrane.

Modulation of paclitaxel resistance by annexin IV in human cancer cell lines

A recurring problem with cancer therapies is the development of drug resistance. While investigating the protein profile of cells resistant to a novel antimitotic compound (A204197), we discovered an increase in annexin IV expression. When we examined the annexin IV protein expression level in a paclitaxel-resistant cell line (H460/T800), we found that annexin IV was also overexpressed. Interestingly a closely related protein, annexin II, was not overexpressed in H460/T800 cells. Immunostaining with either annexin II or IV antibody revealed that annexin IV was primarily located in the nucleus of paclitaxel-resistant H460/T800 cells. Short-term treatment of H460 cells with 10 nM paclitaxel for up to 4 days resulted in induction of annexin IV, but not annexin II expression. In addition, there was an increase in annexin IV staining in the nucleus starting at day 1. Furthermore, cells pretreated with 10 nM paclitaxel for 4 days resulted in cells becoming approximately fivefold more resistant to paclitaxel. Transfection of annexin IV cDNA into 293T cells revealed that there was a threefold increase in paclitaxel resistance. Thus our results indicate that annexin IV plays a role in paclitaxel resistance in this cell line and it is among one of the earliest proteins that is induced in cells in response to cytotoxic stress such as antimitotic drug treatment.

Regulated exocytosis in immune function: are SNARE-proteins involved?

Inflammation is an important feature in the pathogenesis of most chronic lung diseases. It is characterized by tissue infiltration with various inflammatory cells, including eosinophils, mast cells, basophils, macrophages, neutrophils, T- and B-lymphocytes and dendritic cells (1). In the tissue granulocytes release their toxic granule proteins after being stimulated by soluble mediators released by other inflammatory cells (2). Therefore, it is important to characterize the intracellular mechanisms regulating the transport of the granule contents in inflammatory cells. Intracellular vesicle-traffic in mammalian cells is mediated by transport vesicles that emerge from donor compartments and are specifically targeted to acceptor compartments where they deliver their contents after membrane fusion (3). This traffic leads to three types of fusion: vesicle-intracellular membranes, vesicle-vesicle or vesicle-plasma membrane. The process leading to fusion of vesicle-plasma membrane is called exocytosis, and it delivers proteins to the cell surface (receptors e.g. CD11b, CD18) and exports soluble molecules (mediators e.g. ECP) from the cell. A number of key proteins involved in regulated exocytosis have been identified from inflammatory cells. This review is a brief summary of these proteins and it includes recent results from studies on regulated exocytosis in inflammatory cells.

Subcellular fractionation of human neutrophils on Percoll density gradients

Subcellular fractionation has been an important tool in the investigation of neutrophil structural organization including granule heterogeneity, composition and mobilization. The resolution of organelles obtained by subcellular fractionation was improved considerably after the introduction of nitrogen cavitation as an efficient but gentle means of disrupting neutrophils and with Percoll as a density medium. This paper describes in detail the methodology of subcellular fractionation of nitrogen cavitated neutrophils on one-, two-, and three-layer Percoll density gradients. Appropriate marker proteins are presented for neutrophil organelles including azurophil, specific and gelatinase granules, in addition to secretory vesicles and plasma membranes. The dynamics of granule and secretory vesicle exocytosis is demonstrated by subcellular fractionation of resting and activated human neutrophils. Finally, the paper describes the applications of subcellular fractionation in the investigation of the localization of neutrophil constituents, in protein purification schemes and in the study of translocation of cytosolic proteins to isolated neutrophil organelles.

Exocytosis of neutrophil granulocytes

Neutrophil granulocytes play an important role in the defense mechanisms of mammalian organisms against bacterial invaders. The combat arsenal of neutrophils consists of engulfing and endocytosing the foreign particle, producing toxic oxygen compounds, and liberating substances stored in intracellular vesicles. At least four different types of granules are formed during maturation of neutrophil granulocytes in the bone marrow. Functional properties of release from the different granule populations differ in several respects from characteristics of neurotransmitter release, the best understood secretory process in mammals. The available data indicate that several key proteins of the exocytotic machinery identified in neural tissue either are absent from neutrophil granulocytes or their subcellular localization is different. Furthermore, in a human disease (Chédiak-Higashi syndrome), the defect of the secretory pathway affects mainly the cells of the haemopoietic lineage. Taken together, these data suggest that regulated exocytosis from neutrophil granulocytes (or perhaps also from other haemopoietic cells) may represent a specific case of the general mechanism of secretion.

Cleavage of annexin I in human neutrophils is mediated by a membrane-localized metalloprotease

A truncated form of annexin I, formed during Ca2+-induced translocation to neutrophil specific granules and secretory vesicles/plasma membranes, is generated through the action of an endogenous membrane protease. The cleavage of annexin I is inhibited by the metalloprotease inhibitor 1,10-phenanthroline as well as by Triton X-100 and dithiothreitol, classifying the protease as a membrane-bound, thiol-dependent metalloprotease. The cleavage site is located close to the N-terminal of annexin I, leaving a truncated form of the molecule, des1-8 annexin I, that contains the Ca2+-binding sites, as well as a number of phosphorylation sites of importance for the function of the protein. When assessing binding capacity to different neutrophil organelles, full-length annexin I bound to azurophil granules, specific granules, and secretory vesicles/plasma membranes, while des1-8 annexin I only bound to specific granules and secretory vesicles/plasma membranes, but not to azurophil granules (C. Sjölin, C. Dahlgren, Biochim. Biophys. Acta 1281 (1996) 227-234). This implies that there are different mechanisms of binding to neutrophil organelles of full-length annexin I and the truncated form, and that cleavage of annexin I might be of regulatory importance for the degranulation process.

Identification by differential display of transcripts regulated during hematopoietic differentiation

The polymerase chain reaction-based differential display method (DDRT-PCR) was used to identify mRNAs differentially expressed during the maturation of human CD34+ progenitor cells stimulated to differentiate in vitro towards granulomonocytic or erythroid lineages with a mixture of hemopoietins (kit ligand + interleukin 3 + GM-CSF in the absence or presence of erythropoietin, respectively). Three cDNA transcripts (B32, B41, and B56) display differential expression during cytokine-induced maturation of CD34+ cells. These clones have no homology with already-described sequences. Primer extension cofirmed the presence of the corresponding mRNA. The levels of mRNA corresponding to B32 are enhanced in the later phases of the granulomonocytic as well as in the erythroid differentiation of CD34+ cells. The mRNA identified by B41 was induced by a late stage in only granulomonocytic differentiation of CD34+ cells. The mRNA corresponding to B56 was instead present in nonstimulated CD34+ cells, declined in the early stages of differentiation, and reappeared at later stages in cells treated with both combinations of cytokines. Expression of these genes was detected in a number of acute myelogenous leukemias, as well as in some leukemic cell lines. B32 and B41 were downregulated in KG-1 cells induced to differentiate towards the monocytic lineage, whereas the levels of B56 were unchanged. In K562 cells, clones B41 and B56 were downregulated only in the late phases of PMA-induced megakaryocytic differentiation and during erythroid differentiation. B32 was rapidly downregulated when K562 cells were induced to differentiate towards either megakaryocytic or erythroid phenotypes. These transcripts represent novel hematopoietic cDNAs that should prove of value for the study of human blood cells and their disorders.

Exocytosis in chromaffin cells of the adrenal medulla

The chromaffin cell has been used as a model to characterize releasable components present in secretory granules and to understand the cellular mechanisms involved in catecholamine release. Recent physiological and biochemical developments have revealed that molecular mechanisms implicated in granule trafficking are conserved in all eukaryotic species: a rise in intracellular calcium triggers regulated exocytosis, and highly conserved proteins are essential elements which interact with each other to form a molecular scaffolding, ensuring the docking of granules at the plasma membrane, and perhaps membrane fusion. However, the mechanisms regulating secretion are multiple and cell specific. They operate at different steps along the life of a granule, from the time of granule biosynthesis up to the last step of exocytosis. With regard to cell specificity, noradrenaline and adrenaline chromaffin cells display different receptor and signaling characteristics that may be important to exocytosis. Characterization of regulated exocytosis in chromaffin cells provides not only fundamental knowledge of neurosecretion but is of additional importance as these cells are used for therapeutic purposes.

Subcellular fractionation of polarized epithelial cells and identification of organelle-specific proteins by two-dimensional gel electrophoresis

Protein targeting and sorting is accomplished by complex vesicular transport processes that are tightly regulated within a cell. This is especially important for epithelial cells because correct delivery of newly synthesized proteins as well as recycling and sorting of internalized membrane proteins is essential for the establishment and preservation of cellular polarity. Many transport events, linking various subcellular compartments, have been analyzed, but many transport mechanisms still remain unresolved. In this study we attempted to identify proteins specifically associated with distinct organelles in murine mammary epithelial cells (EpH4). We isolated subcellular compartments by continuous sucrose gradient centrifugation in order to further analyze their protein composition by high-resolution two-dimensional gel electrophoresis (2-DE). The successful separation of late endosomes (LE), early endosomes (EE) and most of the rough endoplasmic reticulum (RER) was confirmed by subsequent analysis of gradient fractions for compartment-specific enzymes and marker proteins. Both Golgi and plasma membrane (PM) were found to partially co-purify with EE in such gradients. Characteristic polypeptide patterns were revealed on 2-DE gels for fractions enriched in membranes of different origin. Based on improved sample preparation and loading techniques (this issue, C. Pasquali et al., Electrophoresis, 1997, 18, 2573-2581), we were able to identify several proteins by immunoblotting or microsequencing of Coomassie-stained spots. This will be the basis for a further characterization of organelle-specific molecules in epithelial cells as well as for the establishment of a 2-DE reference map of membrane proteins from murine mammary epithelium.

Neutrophil extracted lipocortin inhibits corticotropin secretion in the AtT-20 D16:16 clonal mouse pituitary cell line. Lipocortin inhibition of ACTH release in vitro

The mechanism of short-term glucocorticoid (GC) inhibition of the hypothalamic-pituitary-adrenal axis is not well understood. The direct anti-inflammatory activities of lipocortins (LCs) have suggested a role for them as extra- and intracellular mediators of the biological effects of GCs. It has been reported that recombinant human (rh) LC1 inhibits corticotropin (ACTH) release from pituitary tissue in vitro but not from AtT-20 D16:16 corticotrophs. Using the same cell line we have tested whether other exogenous rhLCs or native LC extracted from polymorphonucleate neutrophils (neLC), likely LC1, have an effect on ACTH secretion. It is shown that: (1) basal release was not affected by a short-term incubation with neLC; (2) secretion induced by corticotropin-releasing factor (CRF) and other secretagogues (phorbol ester, potassium ion or calcium ionophore) was inhibited by neLC; (3) GC inhibition of CRF-stimulated release was reverted by a monoclonal anti-neLC antibody; (4) rhLC2, rhLC5 and the fragment 212-234 of rhLC5 were without effect. Thus, only neLC is effective on AtT-20 D16:16 cells, suggesting for this annexin a role in the early phase GC inhibition of ACTH secretion.

A rise in ionized calcium activates the neutrophil NADPH-oxidase but is not sufficient to directly translocate cytosolic p47phox or p67phox to b cytochrome containing membranes

Neutrophil production of reactive oxygen species is dependent on an assembly process that involves a translocation of the cytosolic NADPH-oxidase components (p47phox; p67phox; Rac2) to a b cytochrome containing membrane. Based on the fact that an intracellular Ca2+ rise can activate the oxidase without any extracellular release of reactive oxygen species, we suggest that the oxidase can be assembled in a membrane distinct from the plasma membrane. Disintegrated cells were used to monitor Ca2+ dependent membrane binding of neutrophil cytosolic proteins. Membranes containing the b cytochrome part of the oxidase, i.e., specific granules and plasma membranes/secretory vesicles, were used in the translocation experiments. Several cytosolic proteins were found to translocate to specific granules as well as the plasma membranes/secretory vesicles, one of them being annexin I. Using antibodies in the blotting assay against the cytosolic oxidase components p47phox and p67phox, we could show that no Ca2+ dependent translocation of these cytosolic proteins occur to neither of the b cytochrome containing membranes.

Translocation of annexin XI to neutrophil subcellular organelles

In an earlier study, annexin XI was found to be present in the cytosol of neutrophil granulocytes (Blood (1996) 87, 4817). The protein was isolated by calcium-dependent translocation to specific granules and was found to be a 42-kDa truncated form of annexin XI. Using human autoantibodies directed against annexin XI we have now reinvestigated the ability of full size annexin XI to translocate to different neutrophil organelles isolated by subcellular fractionation. The autoantisera used recognised a protein of 55-kDa in neutrophil cytosol and comparison with a whole cell lysate indicated that the larger portion of the cellular content of this protein is localised to the cytosol. Azurophil granules, specific granules and secretory vesicles/plasma membrane were isolated by subcellular fractionation on Percoll gradients, mixed respectively with neutrophil cytosol and the calcium concentration was raised. Immunoblotting showed that annexin XI translocated to specific granules and secretory vesicles/plasma membrane at 100 micromol/l calcium. When raising the concentration of calcium to 1 mmol/l, annexin XI translocated to the azurophil granules as well. Periphagosomal translocation of annexin XI occurred during phagocytosis of yeast particles, implying that this protein plays a role in the events associated with the phagocytic process.

Annexin II binds to the membrane of A549 cells in a calcium-dependent and calcium-independent manner

We investigated the nature of annexin II binding to the biological membranes using a lung epithelium-derived cell line A549. The cytosolic and membrane fractions of A549 cells were separated in the presence of 5 mM EGTA. Both fractions contain annexin II monomer and tetramer as evaluated by western blots using specific monoclonal antibodies against p36 and p11 subunits of annexin II. A substantial amount of annexin II was associated with the membrane fraction even after extensive washing with EGTA buffer, indicating the presence of two pools of annexin II. The EGTA-resistant membrane-bound annexin II could be partially extracted by 1% Triton X-100 or 60 mM n-octyl-beta-D-glucopyranoside, and completely by 30 mM CHAPS or 0.1% deoxycholate. This fraction of annexin II was also extracted by 0.1 M Na2CO3, pH 11 and partitioned into the aqueous phase after being treated with Triton X-114, demonstrating that the EGTA-resistant annexin II is a peripheral membrane protein. When the cells were lysed in varying concentrations of Ca2+, annexin II translocated from cytosolic fraction to membrane fraction at 4-25 microM Ca2+. To identify proteins closely associated with annexin II the membrane fraction was treated with the bifunctional chemical cross-linker disulfosuccinimidyl tartarate, followed by western blot analysis using anti-p36 or anti-p11 antibodies. We find that both p36 and p11 were cross-linked to a 51 kDa protein. In addition, p11 also binds to several proteins with molecular mass of 91, 65, 40 and 36 kDa. Our results suggest that annexin II may bind to the A549 cell membranes via specific membrane-associated proteins.

Diverse effects of different neutrophil organelles on truncation and membrane-binding characteristics of annexin I

A neutrophil annexin I-related protein, detected after translocation of cytosolic proteins to specific granules and secretory vesicles/plasma membrane (Sjölin et al. (1994) Biochem. J. 300, 325-330), has been characterized with respect to origin and organelle-binding properties. The annexin I-related protein is formed as a result of annexin I cleavage, and this occurs during translocation of annexin I to the specific granules and secretory vesicles/plasma membrane, but not when annexin I is translocated to azurophil granules. The cleavage required calcium and it was facilitated in the presence of specific granules or secretory vesicles/plasma membrane, but not in the presence of azurophil granules. We conclude that the membranes of specific granules and secretory vesicles/plasma membrane contain a protease which is able to cleave annexin I into a truncated 38 kDa fragment, which retains the ability to bind to these organelles. The azurophil granules lack the capacity to cleave annexin I as well as the ability to bind the 38 kDa fragment. These findings may implicate a role for annexin I in the divergent regulation of exocytosis of the different neutrophil granules.

Annexin II in exocytosis: catecholamine secretion requires the translocation of p36 to the subplasmalemmal region in chromaffin cells

Annexin II is a Ca(2+)-dependent membrane-binding protein present in a wide variety of cells and tissues. Within cells, annexin II is found either as a 36-kD monomer (p36) or as a heterotetrameric complex (p90) coupled with the S-100-related protein, p11. Annexin II has been suggested to be involved in exocytosis as it can restore the secretory responsiveness of permeabilized chromaffin cells. By quantitative confocal immunofluorescence, immunoreplica analysis and immunoprecipitation, we show here the translocation of p36 from the cytosol to a subplasmalemmal Triton X-100 insoluble fraction in chromaffin cells following nicotinic stimulation. A synthetic peptide corresponding to the NH2-terminal domain of p36 which contains the phosphorylation sites was microinjected into individual chromaffin cells and catecholamine secretion was monitored by amperometry. This peptide blocked completely the nicotine-induced recruitment of p36 to the cell periphery and strongly inhibited exocytosis evoked by either nicotine or high K+. The light chain of annexin II, p11, was selectively expressed by adrenergic chromaffin cells, and was only present in the subplasmalemmal Triton X-100 insoluble protein fraction of both resting and stimulated cells. p11 can modify the Ca(2+)- and/or the phospholipid-binding properties of p36. We found that loss Ca2+ was required to stimulate the translocation of p36 and to trigger exocytosis in adrenergic chromaffin cells. Our findings suggest that the translocation of p36 to the subplasmalemmal region is an essential event in regulated exocytosis and support the idea that the presence of p11 in adrenergic cells may confer a higher Ca2+ affinity to the exocytotic pathway in these cells.

Translocation of annexin I to plasma membranes and phagosomes in human neutrophils upon stimulation with opsonized zymosan: possible role in phagosome function

Annexin I in the cytosol of resting neutrophils was translocated to the plasma membranes upon addition of opsonized zymosan (OZ). Maximum translocation could be detected 1 min after stimulation with OZ, and decreased thereafter. Subcellular fractionation studies demonstrated that annexin I could not be detected in the granule fractions in either resting or activated cells, but was found in association with the phagosome fraction. The marked translocation of annexin I was unique to OZ, since formyl-Met-Leu-Phe induced only slight translocation of annexin I to the plasma membranes, and phorbol 12-myristate 13-acetate had no effect at all. The mechanism regulating the translocation of annexin I is not clear. Annexin I is not phosphorylated in resting or stimulated cells. The correlation between the elevation in the intracellular calcium ion concentration ([Ca2+]i) and the degree of translocation of annexin I to the plasma membranes induced by the different stimuli, together with the inhibition of these processes by the addition of EGTA, indicate that the translocation of annexin I can probably be attributed to the rise in [Ca2+]i. However, this cannot be the sole mechanism since ionomycin, which caused an increase in [CA2+]i similar to that induced by OZ, was less efficient than OZ in inducing translocation of annexin I. The induction of annexin I translocation to the plasma membrane by OZ, which was the only agent that induced phagosome formation, and the detection of annexin I in the phagosome fraction, suggest that annexin I participates in phagosome function.

Annexins in Paramecium cells. Involvement in site-specific positioning of secretory organelles

Annexins were isolated from Paramecium cell homogenates by standard ethylene glycol tetraacetic acid (EGTA) extraction and 100 000-g centrifugation. Two different antibodies (Abs) against synthetic peptides were used, Call-15 and B15, which in mammalian cells recognize a sequence of annexin II or a common sequence occurring in several annexins (except for annexin II), respectively. With anti-Call-15 Abs, western blots from EGTA extracts showed strongly reactive bands of 44.5 and 46 kDa and of higher values. Some of these bands bound to the 100 000-g pellet fraction when Ca(2+) was added. Immuno- and affinity labelling revealed selective, Ca(2+)-dependent labelling of the cell cortex, with enrichment around trichocyst docking sites (facing subplasmalemmal Ca(2+) stores). Cortical fluorescence labelling decreased in wild-type (7S) cells when trichocyst ghosts were detached after synchronous exocytosis. Similarly, cortical labelling was reduced when intact trichocysts were detached from the cell surface of non-discharge mutant cells (nd9-28 degrees C, showing identical bands on blots), which then contained numerous heavily labelled phagolysosomes. This strongly suggests annexin downregulation. All together, the dynamic labelling of cortical structures we observed strongly supports involvement of calpactin-like annexins in trichocyst docking. Anti-B15 Abs recognized a band of 51 kDa and some of higher values. These Abs selectively labelled the outlines of the cytoproct, the site of spent phagolysosome exocytosis. In conclusion, our data indicate involvement of specific sets of annexins in site-specific positioning and attachment of widely different secretory organelles at the cell surface in Paramecium cells.

Mechanisms of phagocytosis

Recent advances in research on phagocytosis include a better appreciation of the cross-talk between phagocytic receptors, the definition of multiple signaling domains within these receptors, and a deeper understanding of the downstream effector pathways leading to actin polymerization and particle internalization. Phagosome maturation in macrophages proceeds via a series of membrane fusion and fission events, which modify the phagosome in small increments, and appears to be regulated, in part, by GTP-binding proteins and perhaps by protein kinase C. The isolation of dysphagic mutants of Dictyostelium discoideum presages the identification of new genes required for phagocytosis.

The lysosomal membrane glycoproteins Lamp-1 and Lamp-2 are present in mobilizable organelles, but are absent from the azurophil granules of human neutrophils

The subcellular localization of two members of a highly glycosylated protein group present in lysosomal membranes in most cells, the lysosome-associated membrane proteins 1 and 2 (Lamp-1 and Lamp-2), was examined in human neutrophil granulocytes. Antibodies that were raised against purified Lamp-1 adn Lamp-2 gave a distinct granular staining of the cytoplasm upon immunostaining of neutrophils. Subcellular fractionation was used to separate the azurophil and specific granules from a light-membrane fraction containing plasma membranes and secretory vesicles, and Western blotting was used to determine the presence of the Lamps in these fractions. The results show that Lamp-1 and Lamp-2 are present in the specific-granule-enriched fraction and in the light-membrane fraction, but not in the azurophil granules. Separation of secretory vesicles from plasma membranes disclosed that the light-membrane Lamps were present primarily in the secretory-vesicle-enriched fraction. During phagocytosis both Lamp-1 and Lamp-2 became markedly concentrated around the ingested particle and they both appear on the cell surface when the secretory organelles are mobilized.

Serum protects against azurophil granule dependent down-regulation of complement receptor type 1 (CR1) on human neutrophils

We have investigated the effect of gradual degranulation on the expression of functional receptors (CR1 and CR3) on human neutrophils. Incubation with increasing concentrations of fMLP (10(-10) - 10(-7) M) translocated CR1 and CR3 to the cell surface in a similar kinetic pattern. When reaching maximal expression of receptors (10(-7) M fMLP), 78 +/- 10% and 87 +/- 9% of the total pool of CR1 and CR3, respectively, were translocated to the cell surface. To drive the mobilization process further, cytochalasin B was introduced to increase the stimulatory effect of fMLP. No further increase in CR1 surface expression was obtained. However, we found a characteristic time course of surface appearance of CR1 and CR3 with a maximal surface expression within 1 minute, followed by a time-related down-regulation of CR1 but not CR3. In addition, the total pool of CR1 in cytochalasin B treated neutrophils was reduced after 15 minutes stimulation with fMLP measured by flow cytometry and immunoblotting, indicating degradation of CR1. The down-regulation of CR1 was concomitant with a translocation of azurophil granules, in terms of upregulation of CD63. Azurophil, but not specific nor secretory, granule fractions caused a down-regulation of CR1 on fMLP activated neutrophils. The presence of human sera and serine protease inhibitor protected CR1 from down-regulation. Together, these findings indicate that intracellular stored proteases, released in the late part of the sequential mobilization process, alters the expression of functional receptors mobilized in the early part of the mobilization process. The findings also focus on the importance of the microenvironment for the net outcome of neutrophil activation in terms of functional receptor expression.