The sub-cellular localization of annexin V in cultured chick-embryo fibroblasts

The Relevance, Predictability, and Utility of Annexin A5 for Human Physiopathology

As an important functional protein molecule in the human body, human annexin A5 (hAnxA5) is widely found in human cells and body fluids. hAnxA5, the smallest type of annexin, performs a variety of biological functions by reversibly and specifically binding phosphatidylserine (PS) in a calcium-dependent manner and plays an important role in many human physiological and pathological processes. The free state hAnxA5 exists in the form of monomers and usually forms a polymer in a specific self-assembly manner when exerting biological activity. This review systematically discusses the current knowledge and understanding of hAnxA5 from three perspectives: physiopathological relevance, diagnostic value, and therapeutic utility. hAnxA5 affects the occurrence and development of many physiopathological processes. Moreover, hAnxA5 can be used independently or in combination as a biomarker of physiopathological phenomena for the diagnosis of certain diseases. Importantly, based on the properties of hAnxA5, many novel drug candidates have been designed and prepared for application in actual medical practice. However, there are also some gaps and shortcomings in hAnxA5 research. This in-depth study will not only expand the understanding of structural and functional relationships but also promote the application of hAnxA5 in the field of biomedicine.

Calcium-dependent and -independent annexin V binding: distinct molecular behaviours at cell membrane interfaces

Distinct annexin V binding behaviours in Ca2+-dependent and Ca2+-independent cases were comparatively investigated using sum frequency generation vibrational spectroscopy. It was discovered that binding affected the molecular arrangement of both membrane leaflets, and the initial Ca2+-independent binding went through a transition with annexin V reorientation to a more stable state upon adding Ca2+.

Hydrogen peroxide is a neuronal alarmin that triggers specific RNAs, local translation of Annexin A2, and cytoskeletal remodeling in Schwann cells

Schwann cells are key players in neuro-regeneration: They sense "alarm" signals released by degenerating nerve terminals and differentiate toward a proregenerative phenotype, with phagocytosis of nerve debris and nerve guidance. At the murine neuromuscular junction, hydrogen peroxide (H₂O₂) is a key signal of Schwann cells' activation in response to a variety of nerve injuries. Here we report that Schwann cells exposed to low doses of H₂O₂ rewire the expression of several RNAs at both transcriptional and translational levels. Among the genes positively regulated at both levels, we identified an enriched cluster involved in cytoskeleton remodeling and cell migration, with the Annexin (Anxa) proteins being the most represented family. We show that both Annexin A2 (Anxa2) transcript and protein accumulate at the tips of long pseudopods that Schwann cells extend upon H₂O₂ exposure. Interestingly, Schwann cells reply to this signal and to nerve injury by locally translating Anxa2 in pseudopods, and undergo an extensive cytoskeleton remodeling. Our results show that, similarly to neurons, Schwann cells take advantage of local protein synthesis to change shape and move toward damaged axonal terminals to facilitate axonal regeneration.

Characterization of platelet aminophospholipid externalization reveals fatty acids as molecular determinants that regulate coagulation

Aminophospholipid (APL) trafficking across the plasma membrane is a key event in cell activation, apoptosis, and aging and is required for clearance of dying cells and coagulation. Currently the phospholipid molecular species externalized are unknown. Using a lipidomic method, we show that thrombin, collagen, or ionophore-activated human platelets externalize two phosphatidylserines (PSs) and five phosphatidylethanolamines (PEs). Four percent of the total cellular PE/PS pool (∼300 ng/2 × 10(8) cells, thrombin), is externalized via calcium mobilization and protease-activated receptors-1 and -4, and 48% is contained in microparticles. Apoptosis and energy depletion (aging) externalized the same APLs in a calcium-dependent manner, and all stimuli externalized oxidized phospholipids, termed hydroxyeicosatetraenoic acid-PEs. Transmembrane protein-16F (TMEM-16F), the protein mutated in Scott syndrome, was required for PE/PS externalization during thrombin activation and energy depletion, but not apoptosis. Platelet-specific APLs optimally supported tissue factor-dependent coagulation in human plasma, vs. APL with longer or shorter fatty acyl chains. This finding demonstrates fatty acids as molecular determinants of APL that regulate hemostasis. Thus, the molecular species of externalized APL during platelet activation, apoptosis, and energy depletion were characterized, and their ability to support coagulation revealed. The findings have therapeutic implications for bleeding disorders and transfusion therapy. The assay could be applied to other cell events characterized by APL externalization, including cell division and vesiculation.

Translocation of annexin B1 in response to the stimulation of PMA and ionomycin in cervical cancer cells

Annexin B1 is a novel member of the annexin superfamily which was isolated from a Cysticercus cellulosae cDNA library. To investigate the physiological roles of annexin B1, we firstly performed immunohistochemical analysis on frozen Cysticercus cellulosae sections and found that annexin B1 was present not only in the tegument of the bladder wall, but also in the host-derived inflammatory layer; In addition, ELISA analysis revealed that annexin B1 could be detected in the cystic fluid of Cysticercus cellulosae and the sera of pigs with cysticercosis. These findings indicated that annexin B1 might be a secretary protein. We further constructed a pEGFP-annexin B1 plasmid and transfected it into SiHa cells. We found that GFP-annexin B1 was stimulated to translocate to the plasma membrane by phorbol 12-myristate 13-acetate (PMA). By contrast, it was induced to distribute at the plasma and nuclear membranes by treatment with calcium ionophore ionomycin. PMA increased annexin B1 membrane binding, which might facilitate exocytosis. Moreover, translocation of the protein to the plasma and nuclear membranes after stimulated by ionomycin, was predicted to be related to an additional function.

Stimulation-dependent recruitment of cytosolic phospholipase A2-alpha to EA.hy.926 endothelial cell membranes leads to calcium-independent association

Cytosolic phospholipase A2-alpha (cPLA2-alpha) is a calcium-activated enzyme involved in agonist-induced arachidonic acid release. In endothelial cells, free arachidonic acid is predominantly converted into prostacyclin, a potent vasodilator and inhibitor of platelet activation. As the rate-limiting step in prostacyclin production is the generation of free arachidonic acid by cPLA2-alpha, this enzyme has become an attractive pharmacological target and the focus of many studies. Following stimulation with calcium-mobilizing agonists, cPLA2-alpha translocates to intracellular phospholipid membranes via its C2 domain. In this study, the calcium-induced association of cPLA2-alpha with EA.hy.926 endothelial cell membranes was investigated. Subcellular fractionation and immunofluorescence studies showed that following stimulation with histamine, thrombin or the calcium ionophore A23187, cPLA2-alpha relocated to intracellular membranes. Treatment of A23187-stimulated cells with EGTA or BAPTA-AM demonstrated that a substantial pool of cPLA2-alpha remained associated with membrane fractions in a calcium-independent manner. Furthermore, immunofluorescence microscopy studies revealed that cells stimulated for periods of greater than 10 min showed a high proportion of calcium-independent membrane-associated cPLA2-alpha. Calcium-independent membrane association of cPLA2-alpha was not due to hydrophobic or cytoskeletal interactions. Finally, the recombinant C2 domain of cPLA2-alpha exhibited calcium-independent membrane binding to membranes isolated from A23187-stimulated cells but not those isolated from nonstimulated cells. These findings suggest that novel mechanisms involving accessory proteins at the target membrane play a role in the regulation of cPLA2-alpha. Such regulatory associations could enable the cell to discriminate between the varying levels of cytosolic calcium induced by different stimuli.

The zebrafish band 4.1 member Mir is involved in cell movements associated with gastrulation

Cellular processes rely on dynamic events occurring between the cortical cytoskeleton and plasma membrane. Members of the Band 4.1 superfamily, which are best known for their ability to tether the cytoskeleton to the plasma membrane, play prominent structural and regulatory roles that influence cell-cell and cell-substrate interactions, endo- and exocytosis, cell polarity, migration, proliferation, and differentiation. We have identified a new member of the zebrafish Band 4.1 superfamily, which is the homolog of human myosin regulatory light chain interacting protein (MIR), and have examined its role in embryonic development. Zebrafish Mir contains the conserved amino-terminal plasma membrane-binding FERM (Band 4.1/ezrin/radixin/moesin) domain as well as other putative protein-protein interacting domains, including a RING finger. Overall, zebrafish Mir is 71% identical to human MIR located at chromosome 6p23-p22.3, and maps on linkage group 19 to a region of synteny with human chromosome 6. In situ hybridization and RT-PCR revealed that mir is expressed maternally and ubiquitously throughout development. Blocking Mir translation using a mir-specific, morpholino-based, knock-down strategy or expressing Mir constructs lacking the RING finger domain disrupts gastrulation and leads to subsequent trunk and tail defects. In severe cases, morphants exogastrulate. The synergistic effect seen when two mir-specific morpholinos are used in conjunction reflects the specific knock-down of mir. In addition, morphant phenotypes induced by mir-specific morpholinos are rescued by overexpression of the full-length Mir. In situ hybridization analysis with mesodermal- and neural-specific markers shows that morphants exhibit a delay in cell movements associated with gastrulation, epiboly, convergence, and extension. A yeast two-hybrid analysis was performed to identify binding partners that may participate with Mir during gastrulation, and Annexin V, a calcium channel protein, was isolated. At early developmental stages, annexin V transcripts colocalize with mir, but after gastrulation, annexin V mRNA becomes localized to the distal tail region and an area in the olfactory placode. At the protein level, Mir colocalizes with Annexin V when expressed in COS cells. Together, these results indicate that Mir is essential for embryonic development and that its role in early embryonic development likely involves calcium-dependent mechanisms essential during the extensive cell movements associated with gastrulation.

Phospholipid signalling in the nucleus. Een DAG uit het leven van de inositide signalering in de nucleus

Diverse methodologies, ranging from activity measurements in various nuclear subfractions to electron microscopy, have been used to demonstrate and establish that many of the key lipids and enzymes responsible for the metabolism of inositol lipids are resident in nuclei. PtdIns(4)P, PtdIns(4,5)P2 and PtdOH are all present in nuclei, as well as the corresponding enzyme activities required to synthesise and metabolise these compounds. In addition other non-inositol containing phospholipids such as phosphatidylcholine constitute a significant percentage of the total nuclear phospholipid content. We feel that it is pertinent to include this lipid in our discussion as it provides an alternative source of 1, 2-diacylglycerol (DAG) in addition to the hydrolysis of PtdIns(4, 5)P2. We discuss at length data related to the sources and possible consequences of nuclear DAG production as this lipid appears to be increasingly central to a number of general physiological functions. Data relating to the existence of alternative pathways of inositol phospholipid synthesis, the role of 3-phosphorylated inositol lipids and lipid compartmentalisation and transport are reviewed. The field has also expanded to a point where we can now also begin to address what role these lipids play in cellular proliferation and differentiation and hopefully provide avenues for further research.

Ovariectomy enhances the expression and nuclear translocation of annexin 5 in rat anterior pituitary gonadotrophs

An observation of abundant annexin 5, a novel calcium and phospholipid binding protein, in gonadotrophs of the anterior pituitary gland of ovariectomized rats (Kawaminami et al., 1997 (in press)) led us to investigate the effect of ovariectomy on the subcellular distribution and synthesis of annexin 5. Gonadotrophs, which were identified by immunocytochemistry with anti LHbeta antiserum, dramatically increased their size three weeks after ovariectomy. These 'castration cells' were shown to contain abundant annexin 5 associated with the plasma membrane, nuclear envelope and nucleoplasm. True localization within the nucleus was shown by optical sectioning with a confocal microscope. Northern blot analysis showed that annexin 5 mRNA in the anterior pituitary gland was increased 24 h after ovariectomy. It further increased in parallel with LHbeta mRNA at three weeks and it decreased in parallel with LHbeta mRNA when estradiol (250 microg/animal per day) was given for 3 days. These results show that the expression of pituitary annexin 5 is controlled by ovarian estradiol and imply that annexin 5 plays a physiological role in the nucleus of activated gonadotrophs.

Biomedical applications of maghemite ferrofluid

The use of cell-targeted ferrofluid in the characterization of modifications of cell membranes is reviewed. Maghemite ferrofluid was synthesized by the Massart method, complexed with dimercaptosuccinic acid (FF). Cell targeting by FF was developed by coupling FF to various biological effectors such as antibodies, lectins, etc, which enabled magnetic cell sorting. Modifications in erythrocyte membranes were studied using FF bound to recombinant human annexin V (AnxFF) which is very sensitive, compared to other Anx-based reagents, in the early detection of phosphatidylserine (PS) exposition on the outer leaflet of the plasma membrane. Thus PS exposition on mouse RBC was detected already after a 24-h storage at 4 degrees C and, transiently, 24 h after their infection by Plasmodium parasites, at which time the parasites are still confined to the liver, thus leading to the recruitment of young RBC and the accumulation of a species, intermediate between reticulocytes and erythrocytes, and the actual RBC target of plasmodial invasion. AnxFF revealed PS exposition on RBC from sickle cell anemia patients, following various inflammations and already after 20 days of human blood storage under blood bank conditions. Such a sensitive detection should be similar to that of macrophages which recognize exposed PS on cells and bring about the latter's elimination from the circulation. AnxFF binding determination was combined with that of cell electrophoretic mobility, glycerol resistance and filterability to characterize RBC membrane modifications in Alzheimer's disease patients which suggested a continuous damage and regeneration in RBC of these patients. A logistic analysis suggested that several three-parameter combinations could permit diagnosis of Alzheimer's disease with up to 95% accuracy. THP1 cells and macrophages, derived themselves by incubation with retinoic acid, were bound to FF and placed in a radio frequency alternating magnetic field. Magnetocytolysis was associated with FF attachment to the cells without damage to non-bound cells and without heating of the surrounding solution.

Differential expression and localization of annexin V in cardiac myocytes during growth and hypertrophy

Recently it was shown that annexin V is the most prominent member of the annexin family in the adult heart [1]. Amongst others, annexin V has been suggested to play a role in developmental processes. The aim of the present study was to explore whether in the heart annexin V content and localization change during maturational and hypertrophic growth, in order to obtain indications that annexin V is involved in cardiac growth processes. First, in the intact rat heart annexin V content and localization were studied during perinatal development. It was clearly demonstrated that annexin V content in total heart transiently increased in the first week after birth, from 0.79 +/- 0.06 microg/mg protein at 1 day before birth to a peak value of 1.24 +/- 0.08 microg/mg protein 6 days after birth, whereafter annexin V protein levels declined to a value of 0.70 +/- 0.06 microg/mg protein at 84 days after birth (p < 0.05). Differences in annexin V content were also observed between myocytes isolated from neonatal and adult hearts [0.81 +/- 0.09 and 0.17 +/- 0.08 microg/mg protein, respectively (p < 0.05)]. Moreover, during cardiac maturational growth the subcellular localization of annexin V might change from a cytoplasmic to a more prominent sarcolemmal localization. Second, in vivo hypertrophy induced by aortic coarctation resulted in a marked degree of hypertrophy (22% increase in ventricular weight), but was not associated with a change in annexin V localization or content. The quantitative results obtained with intact hypertrophic rat hearts are supported by findings in neonatal ventricular myocytes, in which hypertrophy was induced by phenylephrine (10(-5) M). In the latter model no changes in annexin V content could be observed either. In conclusion, the marked alterations in annexin V content during the maturational growth in the heart suggest a possible involvement of this protein in this process. In contrast, the absence of changes in annexin V content and localization in hypertrophied hearts compared to age matched control hearts suggests that annexin V does not play a crucial role in the maintenance of the hypertrophic phenotype of the cardiac muscle cell. This notion is supported by observations in phenylephrine-induced hypertrophied neonatal cardiomyocytes.

Localization of annexin V in the adult and neonatal heart

Annexins are a major family of intracellular Ca2+-binding proteins which have been implicated in a variety of cellular functions. Several conflicting reports have been published on the location of annexin V in the heart. In this paper we have used confocal microscopy to demonstrate that annexin V is associated with the sarcolemma and intercalated discs of cardiac myocytes in sections of adult porcine and rat heart. In addition, we have used confocal microscopy of isolated rat myocytes to show that this association is stable even after cells were treated with the intracellular calcium chelator BAPTA-AM, to reduce cytosolic calcium levels to very low levels. This demonstrates that annexin V associates tightly with the sarcolemma and suggests that components in addition to phospholipid are involved in binding annexin V to the membrane. Furthermore, we show that, in sections of the neonatal rat left ventricle, annexin V has a different subcellular location than that observed in the terminally differentiated adult myocyte. In these differentiating neonatal cells, annexin V is also located in the nucleoplasm and at the periphery of the nucleus. These results demonstrate that the subcellular location of annexin V is differentially regulated and suggest that annexin V regulates calcium-dependent processes at both the sarcolemma and the nucleus.

The nuclear location of annexin V in the human osteosarcoma cell line MG-63 depends on serum factors and tyrosine kinase signaling pathways

Serum starvation of MG-63 cells increases their doubling time from 24 h to 4 days. Cells grown in medium containing 10% fetal calf serum contain high levels of annexin V in the cell nucleus, whereas growth for 4 days in the absence of serum results in loss of nuclear annexin V from 72 +/- 4% of cells. Many of the cells which still have nuclear annexin V under these conditions seem to have recently finished dividing. Refeeding cells with medium containing serum restores annexin V to nuclei within 5 h. Charcoal treatment removes factors from serum that are required to allow annexin V to return to the nucleus. Protein synthesis is not required for annexin V to return to nuclei since inhibition of protein synthesis with cycloheximide does not prevent the serum-induced return of annexin V to nuclei. This, and other evidence, indicates that the presence of annexin V in nuclei reflects translocation rather than catabolism and resynthesis. Inhibition of tyrosine kinase activities with genistein attenuates the relocation of annexin V from the cytoplasm to the nucleus. Thus, the nuclear location of annexin V is controlled by signaling pathways involving serum factors and tyrosine kinases. The results argue for an important role for annexin V in the cell nucleus.

Localization of five annexins in J774 macrophages and on isolated phagosomes

Annexins are a family of structurally related proteins which bind phospholipids in a calcium-dependent manner. Although the precise functions of annexins are unknown, there is an accumulating set of data arguing for a role for some of them in vesicular transport and, specifically, in membrane-membrane or membrane-cytoskeletal interactions during these processes. Here we describe our qualitative and quantitative analysis of the localization of annexins I-V in J774 macrophages that had internalized latex beads, both with and without IgG opsonization. Our results show that whereas all these annexins are present on both the plasma membrane and on phagosomes, the localization on other organelles differs. Annexins I, II, III and V were detected on early endosomes, while only annexin V was seen on late endocytic organelles and mitochondria. Annexins I and II distributed along the plasma membrane non-uniformly and co-localized with F-actin at the sites of membrane protrusions. We also investigated by western blot analysis the association of annexins with purified phagosomes isolated at different time-points after latex bead internalization. While the amounts of annexins I, II, III and V associated with phagosomes were similar at all times after their formation, the level of annexin IV was significantly higher on older phagosomes. Whereas annexins I, II, IV and V could be removed from phagosome membranes with a Ca2+ chelator they remained membrane bound under low calcium conditions. In contrast, annexin III was removed under these conditions and needed a relatively high Ca2+ concentration to remain phagosome bound. Because of their purity and ease of preparation we suggest that phagosomes are a powerful system to study the potential role of annexins in membrane traffic.

Inhibition of cytosolic phospholipase A2 by annexin V in differentiated permeabilized HL-60 cells. Evidence of crucial importance of domain I type II Ca2+-binding site in the mechanism of inhibition

Annexin V belongs to a family of proteins that interact with phospholipids in a Ca2+-dependent manner. This protein has been demonstrated to have anti-phospholipase A2 activity. However, this effect has never yet been reported with the 85-kDa cytosolic PLA2 (cPLA2). We studied, in a model of differentiated and streptolysin O-permeabilized HL-60 cells, the effect of annexin V on cPLA2 activity after stimulation by calcium, GTPgammaS (guanosine 5'-O-(3-thiotriphosphate)), formyl-Met-Leu-Phe, or phorbol 12-myristate 13-acetate. Both recombinant and human placental purified annexin V inhibit cPLA2 activity whatever the stimulus used. The decrease of arachidonic acid release is of 40 and 50%, respectively, at [Ca2+] of 3 and 10 microM. The mechanism of inhibition was also analyzed. cPLA2 requires calcium and protein kinase C (PKC) or mitogen-activated protein kinase phosphorylation for its activation. As annexin V was shown to be an endogenous inhibitor of PKC, PKC-stimulated cPLA2 activity was analyzed. Using GF109203x, a specific PKC inhibitor, we demonstrated that this pathway is of minor importance in our model. cPLA2 inhibition by annexin V is not linked to PKC inhibition. To test the hypothesis of phospholipid depletion, mutants of annexin V were constructed using mutagenesis directed to Ca2+ site. We demonstrate that the Ca2+ site located in domain I is necessary for the inhibitory effect of annexin V on cPLA2 activity. The site in domain IV is also involved but with less efficiency. In contrast, mutations in site II and III do not modify this effect. Moreover, annexin V mutated on all sites does not inhibit cPLA2. Thus, we propose a predominant role of module (I/IV) in the biological action of annexin V, which, in physiological conditions, may control cPLA2 activity by depletion of the phospholipid substrate.

Subcellular localization of annexin V in human foreskin fibroblasts: nuclear localization depends on growth state

Annexin V is a major intracellular calcium-binding protein in human foreskin fibroblasts. Immunocytochemistry revealed that annexin V was localized in the nucleus and throughout the cytoplasm in human foreskin fibroblasts. The presence of annexin V in the nucleus was variable depending on the growth state. Nuclear staining was strongest in proliferating cells immediately after sub-culture, and decreased on prolonged culture without changing the culture medium. The cytoplasmic location of annexin V was not greatly affected by the same conditions. Refeeding cells with fresh serum restored annexin V to the nuclei of all cells within 24 h indicating that nuclear localization of annexin V is dependent on serum factors.

Differential expression of annexins I-VI in the rat dorsal root ganglia and spinal cord

The annexins are a family of Ca(2+)-dependent phospholipid-binding proteins. In the present study, the spatial expression patterns of annexins I-VI were evaluated in the rat dorsal root ganglia (DRG) and spinal cord (SC) by using indirect immunofluorescence. Annexin I is expressed in small sensory neurons of the DRG, by most neurons of the SC, and by ependymal cells lining the central canal. Annexin II is expressed by most sensory neurons of the DRG but is primarily expressed in the SC by glial cells. Annexin III is expressed by most sensory neurons, regardless of size, by endothelial cells lining the blood vessels, and by the perineurium. In the SC, annexin III is primarily expressed by astrocytes. In the DRG and the SC, annexin IV is primarily expressed by glial cells and at lower levels by neurons. In the DRG, annexin V is expressed in relatively high concentrations in small sensory neurons in contrast to the SC, where it is expressed mainly by ependymal cells and by small-diameter axons located in the superficial laminae of the dorsal horn areas. Annexin VI is differentially expressed by sensory neurons of the DRG, being more concentrated in small neurons. In the SC, annexin VI has the most striking distribution. It is concentrated subjacent to the plasma membrane of motor neurons and their processes. The differential localization pattern of annexins in cells of the SC and DRG could reflect their individual biological roles in Ca(2+)-signal transduction within the central nervous system.

Annexins II, IV, V and VI relocate in response to rises in intracellular calcium in human foreskin fibroblasts

Annexins are a family of proteins implicated in a number of cellular processes involving calcium. We studied annexins I, II, IV, V and VI and found that they are all present in human foreskin fibroblasts and, from immunocytochemical studies, have distinct locations in the cell. Only annexin IV and annexin V have unstructured cytoplasmic staining patterns consistent with predominantly cytosolic locations. Annexin VI partially colocalizes with the endoplasmic reticulum. In contrast, annexins I and II are both associated with the plasma membrane with annexin II having a very homogeneous staining compared with the punctate pattern observed for annexin I. Annexins I, IV and V are all present in the nucleus at higher concentrations than in the cytoplasm. Treatment of cells with the calcium ionophore A23187 to raise intracellular calcium, results in relocations of annexin II, IV, V and VI. Intranuclear annexins IV and V relocate to the nuclear membrane whereas the cytosolic pools of these annexins relocate to the plasma membrane. Annexin II relocates to granular structures at the plasma membrane whereas annexin VI relocates to a more homogeneous distribution on the plasma membrane. These results are consistent with an important role for annexins in mediating the calcium signal at the plasma membrane and within the nuclei of fibroblasts.

Calcium-induced relocation of annexins IV and V in the human osteosarcoma cell line MG-63

In cell culture, human osteoblasts and the osteosarcoma cell line MG-63 express annexins I, II, IV, V and VI. Small proportions of annexins IV and V are lost from MG-63 cells into the culture medium in a sedimentable form. however, the bulk of these annexins is intracellular. In non-confluent cells 3 days after passaging, annexin IV and annexin V are strongly present throughout the nucleus and are also present in the cytoplasm. On elevation of the intracellular calcium concentration with the lonophore ionomycin, the intranuclear pools of annexin IV in 38 +/- 4% of cells and annexin V in 70 +/- 5% of cells show relocation to the nuclear membrane within 40 s. Extracellular ATP, which causes a transient increase in the cytosolic free calcium concentration by acting at P2-purinoceptors, also causes relocation of the intranuclear pool of annexin IV in 22 +/- 4% of cells and of annexin V in 38 +/- 8% of cells. After stimulation no significant reversal of the relocation is observed. Elevation of intracellular calcium with ionophore and ATP also causes relocation of the cytoplasmic pools of annexins IV and V. The results support a role for annexins at cellular membranes in response to elevation of cytosolic calcium levels.

Detection of membrane-bound guanylate cyclase activity in rat C6 glioma cells at different growth states following activation by natriuretic peptides

We studied the activity and the ultracytochemical localization of membrane-bound guanylate cyclase (GC) after stimulation with rat atrial natriuretic peptide (rANP), porcine brain natriuretic peptide (pBNP), rat brain natriuretic peptide (rBNP), or porcine C-type natriuretic peptide (CNP) in rat C6 glioma cells during proliferation or following exposure of confluent cells to dibutyryl cyclic AMP (db-cAMP) or retinoic acid (RA). Under our experimental conditions all peptides were activators of GC as demonstrated by the accumulation of cGMP within cells. During proliferation of C6 cells, the amounts of cGMP remained approximately constant. However, at subconfluency, confluency and postconfluency, the GC reaction product was located at different sites in C6 cells. At subconfluency, GC reaction product was on membranes of protoplasmic extensions, at postconfluency, GC reaction product was in association with membranes of cell bodies, and at confluency, both localizations of GC reaction product were detected. Incubation of confluent cells in culture medium containing db-cAMP or RA induced the appearance of long and slender protoplasmic extensions. Under these conditions, the GC reaction product was localized exclusively to these processes. These data suggest that GC is differentially located depending on the state of growth of glial cells, and that in differentiating glial cells GC is preferentially located in cell processes.

Collagen binding activity of recombinant and N-terminally modified annexin V (anchorin CII)

We have cloned the full coding cDNA sequence of chicken annexin V and of a mutant lacking 8 amino acid residues of the N-terminal tail for prokaryotic expression. Both proteins were synthesized in Escherichia coli upon induction with isopropyl thio-beta-D-galactoside, and were purified following two different protocols: one based on the ability of these proteins to interact reversibly with liposomes in the presence of calcium, and the other based on two sequential ion-exchange chromatographic steps. Spectroscopical analysis of recombinant annexin V revealed that binding of calcium did not change the circular dichroism spectra indicating no significant changes on the secondary structure; however, a conformational change affecting the exposition to the solvent of the tryptophan residue 187 was detected by analysis of fluorescence emission spectra. Recombinant annexin V binds with high affinity to collagen types II and X, and with lower affinity to collagen type I in a calcium-independent manner. Heat denaturing of collagen decreases this interaction while pepsin-treatment of collagen almost completely abolishes annexin V binding. Mutated annexin V interacts with collagen in a similar way as the nonmutated recombinant protein, indicating that the N-terminal tail of annexin V is not essential for collagen binding.

A new function of calphobindin I (annexin V). Promotion of both migration and urokinase-type plasminogen activator activity of normal human keratinocytes

Calphobindin I (CPB-I, annexin V) is an anticoagulant protein purified from human placenta; it is a member of the annexin family that binds phospholipids in a calcium-dependent manner. In this study, we discovered and examined a new function of CPB-I: promotion of both the migration and the urokinase-type plasminogen activator (uPA) activity of normal human keratinocytes (NHK). While the treatment of NHK with a 10-micrograms/ml concentration of CPB-I for 24 h or 48 h caused an approximate 30% increase in the migration of NHK (compared with the no treatment), migration was inhibited when anti-CPB-I monoclonal antibodies (i.e. A46 and A180) were added along with the CPB-I. Moreover, while the treatment of NHK with a CPB-I concentration greater than 10 micrograms/ml caused a significant increase in the activity of secreted uPA, reflected in an approximately 40% increase in cell migration, uPA activity was inhibited both by cycloheximide and by monoclonal antibodies. This significant increase of secreted uPA was seen 8 h after the addition of CPB-I. Specific binding of CPB-I to NHK had a Kd value of 95.2 nM (equivalent to a CPB-I had no effect on NHK proliferation. Furthermore, CPB-I enhanced reepithelialization when it was applied locally twice a day to full-thickness cutaneous wounds made in male rats. Our results show that, during an injury, CPB-I helps reepithelialization through the promotion of both uPA synthesis and migration of keratinocytes without stimulating their proliferation.

Cell surface annexin II is a high affinity receptor for the alternatively spliced segment of tenascin-C

We have investigated the binding of soluble tenascin-C (TN-C) to several cell lines using a radioligand binding assay. Specific binding was demonstrated to U-251MG human glioma cells and to a line of bovine aortic endothelial cells, but hamster fibroblasts showed no specific binding. Recombinant proteins corresponding to specific domains of TN-C were used to map the binding site(s) in TN-C. The alternatively spliced segment (TNfnA-D) inhibited the binding of native TN-C most strongly, and itself bound to glioma and endothelial cells. Scatchard analysis of TNfnA-D binding indicated 2-5 x 10(5) binding sites per cell, with an apparent 2 nM dissociation constant. The cell surface receptor for TNfnA-D was identified as a 35-kD protein on the basis of blot binding assays and affinity chromatography of membrane extracts on native TN-C and TNfnA-D columns. Protein sequencing indicated that this 35-kD receptor was annexin II. Annexin II is well characterized as a cytoplasmic protein, so it was surprising to find it as a presumably extracellular receptor for TN-C. To confirm that it was the 35-kD receptor, we obtained purified annexin II and demonstrated its binding to TNfnA-D and TN-C at nM concentrations. Antibodies to annexin II prominently stained the external surface of live endothelial cells and blocked the binding of TNfnA-D to the cells. Thus annexin II appears to be a receptor for the alternatively spliced segment of TN-C, and may mediate cellular responses to soluble TN-C in the extracellular matrix.