Calcium-dependent regulation of actin filament bundling by lipocortin-85

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.

Changes in the cellular distribution of lipocortin-1 (Annexin-1) in C6 glioma cells after exposure to dexamethasone

Glucocorticoid-induced changes in cellular levels of Lipocortin-1 (LC-1) (Annexin 1) in C6 glioma cells were determined by electrotransfer and immunoblotting techniques. Separate cell protein fractions were prepared to study the influence of the glucocorticoid steroid, dexamethasone, on LC-1 localisation. Cells were grown in steroid-depleted medium and exposed to dexamethasone (10(-8) and 10(-7) M) for 2, 6, and 16 hr. The glucocorticoid-dependent changes in cellular content of LC-1 were both dose- and time-related. Increases above control levels in intracellular and extracellular LC-1 content were detected with the greatest changes occurring at the cell surface. The glucocorticoid-dependent alteration in LC-1 distribution in C6 glioma cells was attenuated by the protein synthesis inhibitor, cycloheximide, indicating the involvement of de novo LC-1 synthesis. The significance of these results is discussed in relation to the current concept that some of the anti-inflammatory effect of glucocorticoids occurs through the action of extracellular LC-1.

Annexin II tetramer: structure and function

The annexins are a family of proteins that bind acidic phospholipids in the presence of Ca2+. The interaction of these proteins with biological membranes has led to the suggestion that these proteins may play a role in membrane trafficking events such as exocytosis, endocytosis and cell-cell adhesion. One member of the annexin family, annexin II, has been shown to exist as a monomer, heterodimer or heterotetramer. The ability of annexin II tetramer to bridge secretory granules to plasma membrane has suggested that this protein may play a role in Ca(2+)-dependent exocytosis. Annexin II tetramer has also been demonstrated on the extracellular face of some metastatic cells where it mediates the binding of certain metastatic cells to normal cells. Annexin II tetramer is a major cellular substrate of protein kinase C and pp60src. Phosphorylation of annexin II tetramer is a negative modulator of protein function.

The annexins: specific markers of midline structures and sensory neurons in the developing murine central nervous system

The annexins are a family of cytoplasmic proteins that have been shown to have numerous actions within a cell. Recent evidence suggests that at least one of these proteins plays a role in the development of the central nervous system (CNS). The present study examines the temporal expression and spatial distribution of annexins I, II, IV, V, and VI during development and at maturity in the murine CNS by immunocytochemical analysis. The results demonstrate that annexins I, II and IV exhibit clear immunolabeling in the murine CNS with distinct patterns of temporal and spatial expression. Annexin IV is the first annexin to be expressed on embryonic day (E) 9.5 while annexin I is the last to be expressed (E11.5). Annexins I, II and IV are found in the floor plate region, but to differing rostrocaudal extents. Annexin I has a very restricted distribution, only present in the midline raphe of the brainstem. Annexin II is present in the spinal cord, brainstem and mesencephalon. Annexin IV has the widest midline distribution, being observed in the floor and roof plates of the developing CNS. Additionally, antibodies against annexin II and IV immunolabel most dorsal root and sensory ganglion cells and their axons. During early postnatal development, immunolabeling with each antibody gradually disappears in many structures, and only first order sensory neurons and their fibers are immunopositive for annexins II and IV at weaning. Three functions of the annexins are suggested by the present findings: (1) to help establish the midline structures of the floor and roof plates, (2) to help direct the decussation of sensory fibers, and (3) to regulate some aspect of sensory neuron processing, such as signal transduction.

Annexin VI isoforms are differentially expressed in mammalian tissues

Purified annexin VI migrates as a closely spaced doublet when separated by SDS-PAGE. Immunolocalization of annexin VI in heart demonstrates staining at different defined subcellular compartments. Moss et al. identified two cDNAs, one having an insert of 18 bases encoding VAAEIL at the beginning of repeat domain seven. We have identified the splicing site of the murine annexin VI gene. It contains a single small exon of 18 bases. PCR amplification of reverse transcribed (RT) mRNA demonstrates that, in all tissues tested, the mRNA isoform containing the insert is predominant. Site-directed antibody was produced and affinity purified against peptides reflecting the insert and deletion sequences. The steady-state isoform ratio of the annexin VI protein is consistent with the RT-PCR data. Chromatographic experiments demonstrate that the annexin VI protein isoforms have biochemical differences. These differences may target the individual isoforms to unique cellular compartments or alter functional properties.

Calpactin I binds to the glial fibrillary acidic protein (GFAP) and cosediments with glial filaments in a Ca(2+)-dependent manner: implications for concerted regulatory effects of calpactin I and S100 protein on glial filaments

Calpactin I, a heterotetrameric, cytoskeletal protein complex composed of two copies of annexin II cross-linked by two copies of p11, an S100-like protein, binds to the glial fibrillary acidic protein (GFAP) and cosediments with glial filaments (GF) in a Ca(2+)-dependent manner, apparently without affecting GFAP polymerization under the present experimental conditions. Cosedimentation of calpactin I with GF, which occurs at micromolar free Ca2+ concentrations, is proportional to the concentrations of both calpactin I and GFAP and does not occur under conditions where GFAP assembly is maximally inhibited by, e.g., S100 protein. Annexin II also cosediments with GF and binds to GFAP, although to much smaller extents. Other annexins, such as annexins I, V, and VI, or p11 do not bind to either GF or GFAP. Calpactin I and S100 protein bind to different sites on GFAP, as investigated by fluorescence spectroscopy using acrylodan-labeled GFAP. Calpactin I and S100 protein might act, in the presence of Ca2+, in a concerted manner to determine the number and topography of GF in differentiating and/or mature glial cells.

Effect of 67 kDa calcimedin on caldesmon functioning

Interaction of smooth muscle caldesmon with calmodulin, troponin C, S-100 protein and 67 kDa calcimedin was analyzed. Native gel electrophoresis and crosslinking revealed the complex formation between caldesmon and three EF-hand Ca-binding proteins, whereas calcimedin did not interact with caldesmon. In the presence of Ca2+, calcimedin binds to actin-tropomyosin without affecting the interaction of caldesmon with this complex. Although calcimedin reversed the inhibitory action of caldesmon on the actomyosin ATPase activity at a lower concentration than three other Ca-binding proteins, this effect only slightly depends on Ca2+ and was observed at the concentration of calcimedin comparable to that of actin. It is concluded that calcimedin itself cannot be responsible for Ca-dependent regulation of caldesmon functioning, but actin bundling induced by calcimedin (or by other actin binding proteins) decreases the inhibitory action of caldesmon on the actomyosin ATPase activity.

Structure-function correlations of calcium binding and calcium channel activities based on 3-dimensional models of human annexins I, II, III, V and VII

The annexins are a family of calcium-dependent phospholipid-binding proteins which share a high degree of primary sequence similarity. Using a model of the crystal structure of annexin V as a template, 3-dimensional models of human annexins I, II, III and VII were constructed by homology modeling (J. Greer, J. Mol. Biol. 153, 1027-1042, 1981; J.M. Chen, G. Lee, R.B. Murphy, R.P. Carty, P.W. Brant-Rauf, E. Friedman and M.R. Pincus, J. Biomolec. Str. Dyn. 6, 859-87, 1989) for the 316 amino acid portions corresponding to the annexin V structure published by Huber et al. (J. Mol. Biol. 223, 683-704, 1992). These methods were used to study structure-function correlations for calcium ion binding and calcium channel activity. Published experimental data are specifically shown to be consistent with the annexin models. Possible intramolecular disulfide bridges were identified in annexin I (between Cys297 and Cys316) and in annexins II and VII (between Cys115 and Cys243). Each of the annexin models have 3 postulated calcium binding sites, usually via a Gly-Xxx-Gly-Thr loop with an acidic Glu or Asp residue 42 positions C-terminal to the first Gly. Despite a nonconserved binding site sequence, annexins I and II are able to coordinate calcium in domain 3 since the residue in the second loop position is directed toward the solvent away from the binding pocket. This finding also suggests a mechanism for a conformational change upon binding calcium. Highly conserved Arg and acidic sidechains stabilize the channel pore structure; annexin channels probably exist in a closed state normally. Arg271 may be involved in channel opening upon activation: basic residue 254 can stabilize Glu112, which allows Arg271 to interact with residue 95 instead of Glu112. Residue 267, found on the convex surface at the pore opening, may also be important in modifying channel activity.

Annexin V forms calcium-dependent trimeric units on phospholipid vesicles

The quaternary structure of annexin V, a calcium-dependent phospholipid binding protein, was investigated by chemical cross-linking. Calcium was found to induce the formation of trimers, hexamers, and higher aggregates only when anionic phospholipids were present. Oligomerization occurred under the same conditions annexin-vesicle binding. A model is proposed in which cell stimulation leads to calcium-induced organization of arrays of annexin V lining the inner membrane surface, thus altering properties such as permeability and fluidity.

Effects of the expression of mammalian annexins in yeast secretory mutants

The hypothesis that calcium-dependent membrane-binding proteins of the annexin family can influence intracellular membrane trafficking was tested by expressing five mammalian annexins in wild-type yeast cells (Saccharomyces cerevisiae) and in 13 yeast secretory (sec) mutants. Expression of human synexin (annexin VII) inhibited the growth of sec2, sec4 and sec15 mutants at a semi-permissive temperature. These three sec mutants are defective in the final step in the secretory pathway, the process of exocytosis. The inhibition of growth correlated with reduced viability and increased accumulation of internal invertase in these mutants when expressing synexin. Bovine endonexin (annexin IV) partially suppressed the growth defect of a sec2 mutant incubated at a semi-permissive temperature. Human synexin, human lipocortin (annexin I), and murine p68 (annexin VI) reduced the lag time associated with adaptation of sec2 mutants to galactose-containing medium. These interactions suggest that the annexins may influence specific steps in membrane trafficking associated with cell growth, secretion and plasma membrane remodelling.

S-100 protein binds to annexin II and p11, the heavy and light chains of calpactin I

S-100 protein, a dimeric, Ca(2+)-binding protein of the EF-hand type, interacts with annexin II (p36, the heavy chain of the cytoskeletal protein complex, calpactin I), with p11 (the light and regulatory chain of calpactin I) and with the hetero-tetramer annexin II2-p11(2) (calpactin I) in a Ca(2+)-regulated way, but not with annexins I, V and VI. The interaction of S-100 protein with the above proteins was investigated by fluorescence spectroscopy using acrylodan-S-100 protein and acrylodan-annexin II and by cross-linking experiments using the bifunctional cross-linker disuccinimidyl suberate (DSS). S-100 protein binds with the highest affinity to annexin II (Kd approx. 0.4 microM) and with the lowest affinity to calpactin I (Kd approx. 10 microM), with a constant stoichiometry of about 2 mol of protein/S-100 dimer. Thus, S-100 protein could substitute for p11 in regulating the activities of annexin II in cells which do not express p11 and/or act synergistically with p11 in cells expressing both p11 and S-100. The binding of S-100 protein to p11 could reflect the natural tendency of S-100 subunits and p11 to dimerize. Chimeric p11-S-100 alpha and p11-S-100-beta proteins could therefore form in a Ca(2+)-regulated way. The interaction of S-100 protein with calpactin I appears of doubtful physiological importance, because of the low binding affinity, of the small extent of fluorescence changes induced by calpactin I in acrylodan-S-100 protein and of lack of DSS-induced complex formation between the two protein species.

The annexins and exocytosis

The annexins are a group of homologous proteins that bind phospholipids in the presence of calcium. They may provide a major pathway for communication between cellular membranes and their cytoplasmic environment. Annexins have a characteristic "bivalent" activity in the sense that they can draw two membranes together when activated by calcium. This has led to the hypothesis that certain members of this protein family may initiate contact and fusion between a secretory vesicle membrane and the plasma membrane during the process of exocytosis.

Annexins IV (p32) and VI (p68) interact with erythrocyte membrane in a calcium-dependent manner

Purification of annexin IV and VI from porcine liver was achieved by Mono Q ion exchange chromatography at pH 8.9 and pH 7.5, respectively. The isolated proteins interacted with erythrocyte membrane as function of calcium ion and the protein concentration. Half-maximal binding of annexin VI to erythrocyte membrane was found to occur at 8 microM Ca2+. The maximal binding was estimated as 2 micrograms of annexin VI per 1 microgram or erythrocyte membrane protein, in the presence of 100 microM Ca2+. The property of erythrocyte membrane to interact with annexins was utilized in preparation of a affinity-column with polyacrylamide-immobilized erythrocyte membrane.

Purification of novel calcium binding proteins from Trypanosoma brucei: properties of 22-, 24- and 38-kilodalton proteins

The present study was undertaken to systematically purify calcium binding proteins (CaBPs) from homogenates of Trypanosoma brucei. This work is important since CaBPs either serve as intracellular calcium buffers or mediate cellular response to calcium signals. Disruption of either process should be lethal to trypanosomes. We report that the 45Ca-gel overlay assay can be used to detect CaBPs following fractionation on DE-52, phenyl-Sepharose, Mono-Q, and Superose 12. Specific CaBPs of 22, 24, and 38 kDa were purified. Each of these proteins associated with 45Ca under denaturing and non-denaturing conditions. An approximate Kd for calcium of 8 microM was calculated for 22-kDa CaBP. None of the trypanosome CaBPs were related to known calcium binding protein families. They did not associate with hydrophobic interaction columns or cellular membranes in a calcium-dependent way, nor cross-react with 2 separate antibodies against annexin consensus sequences. A synthetic peptide corresponding to amino terminal residues 16-30 of 22-kDa CaBP was used to generate polyclonal antibodies. Immunoblots identified 22-kDa CaBP in African trypanosomes but not in other Kinetoplastidae or mammalian cells. Nonetheless, significant homology (58%) was observed between the amino terminal 37 residues of 22-kDa CaBP and the amino terminus of translationally controlled p21 from mammalian tumor cells. The present study is the first to apply systemic fractionation techniques to identify the complement of CaBPs in T. brucei. We conclude that novel CaBPs other than calmodulin and annexin family members contribute towards calcium pathways in these organisms.

Inhibition of protein kinase C by annexin V

Annexin V is a protein of unknown biological function that undergoes Ca(2+)-dependent binding to phospholipids located on the cytosolic face of the plasma membrane. Preliminary results presented herein suggest that a biological function of annexin V is the inhibition of protein kinase C (PKC). In vitro assays showed that annexin V was a specific high-affinity inhibitor of PKC-mediated phosphorylation of annexin I and myosin light chain kinase substrates, with half-maximal inhibition occurring at approximately 0.4 microM. Annexin V did not inhibit epidermal growth factor receptor/kinase phosphorylation of annexin I or cAMP-dependent protein kinase phosphorylation of the Kemptide peptide substrate. Since annexin V purified from both human placenta and recombinant bacteria inhibited protein kinase C activity, it is not likely that the inhibitor activity was associated with a minor contaminant of the preparations. The following results indicated that the mechanism of inhibition did not involve annexin V sequestration of phospholipid that was required for protein kinase C activation: similar inhibition curves were observed as phospholipid concentration was varied from 0 to 800 micrograms/mL; the extent of inhibition was not significantly affected by the order of addition of phospholipid, substrate, or PKC, and the core domain of annexin I was not a high-affinity inhibitor of PKC even though it had similar Ca2+ and phospholipid binding properties as annexin V. These data indirectly indicate that inhibition occurred by direct interaction between annexin V and PKC. Since the concentration of annexin V in many cell types exceeds the amounts required to achieve PKC inhibition in vitro, it is possible that annexin V inhibits PKC in a biologically significant manner in intact cells.

Membrane-bound annexin V isoforms (CaBP33 and CaBP37) and annexin VI in bovine tissues behave like integral membrane proteins

The distribution of annexin V isoforms (CaBP33 and CaBP37) and of annexin VI in bovine lung, heart, and brain subfractions was investigated with special reference to the fractions of these proteins which are membrane-bound. In addition to EGTA-extractable pools of the above proteins, membranes from lung, heart, and brain contain EGTA-resistant annexins V and VI which can be solubilized with detergents (Triton X-100 or Triton X-114). A strong base like Na2CO3, which is usually effective in extracting membrane proteins, only partially solubilizes the membrane-bound, EGTA-resistant annexins analyzed here. Also, only 50-60% of the Triton X-114-soluble annexins partition in the aqueous phase, the remaining fractions being recovered in the detergent-rich phase. Altogether, these findings suggest that, by an as yet unknown mechanism, following Ca(2+)-dependent association of annexin V isoforms and annexin VI with membranes, substantial fractions of these proteins remain bound to membranes in a Ca(2+)-independent way and behave like integral membrane proteins. These results further support the possibility that the above annexins might play a role in membrane trafficking and/or in the regulation of the structural organization of membranes.

Localization of immunoreactive lipocortin-1 in the brain and pituitary gland of the rat. Effects of adrenalectomy, dexamethasone and colchicine treatment

The presence and localization of endogenous lipocortin-1 (LC-1, a protein which has been proposed to mediate the anti-inflammatory actions of the glucocorticoids) was studied by immunohistochemical techniques in rat brain and pituitary. A polyclonal antiserum specific for a fragment of lipocortin-1 (alpha alpha 1-188) was used to visualize immunoreactive LC-1 (iLC-1) in both neuronal and non-neuronal cell structures. Neuronal staining, which was independent of microtubular axonal transport mechanisms (in that it was not affected by blockade of axonal transport), was found in varicose nerve fibres in various regions of the brain. In addition, iLC-1 was found in the cytoplasm of neuronal cells throughout the brain. Of all brain regions which showed iLC-1, only the hippocampal neurons showed a reduced staining intensity after adrenalectomy. However, iLC-1 was not affected by dexamethasone treatment. Non-neuronal iLC-1 was found in ependymocytes lining the cerebral ventricles and aqueduct. In addition, iLC-1 was found in tanycytes in all circumventricular organs studied and in the ventral walls of the third ventricle, where some of the branching tail processes appeared to envelop local capillaries and neuronal cell bodies. A tancycyte-mediated release of LC-1 from varicose nerve fibres into the portal vasculature is proposed.

Biochemical characterization of annexins I and II isolated from pig nervous tissue

Five proteins having molecular masses of 90, 67, 37, 36, and 32 kDa (p90, p67, p37, p36, and p32, respectively) were identified in the particulate fractions of pig brain cortex and pig spinal cord prepared in the presence of 0.2 mM Ca2+ and further purified using a protocol previously described for the purification of calpactins. Proteins p90, p37, and p36 are related to annexins I and II. Annexin II, represented by p90, is found as an heterotetramer, composed of two heavy chains of 36 kDa and two light chains of 11 kDa, and as a monomer of 36 kDa. Protein p37, which differs immunologically from p36, is a monomer and could be related to annexin I. All three proteins are Ca(2+)-dependent phospholipid- and F-actin-binding proteins; they are phosphorylated on a serine and on a tyrosine residue by protein kinases associated with synaptic plasma membranes. Purified p36 monomer and p36 heterotetramer proteins bind to actin at millimolar Ca2+ concentrations. The stoichiometry of p36 binding to F-actin at saturation is 1:2, corresponding to one tetramer or monomer of calpactin for two actin monomers (KD, 3 x 10(-6) M). Synaptic plasma membranes supplemented with the monomeric or tetrameric forms of p36 phosphorylate the proteins on a serine residue. The monomer is phosphorylated on a serine residue by a Ca(2+)-independent protein kinase, whereas the heterotetramer is phosphorylated on a serine residue and a tyrosine residue by Ca(2+)-dependent protein kinases. Antibodies to brain p37 and p36 together with antibodies to lymphocytes lipocortins 1 and 2 were used to follow the distribution of these proteins in nervous tissues. Polypeptides of 37, 34, and 36 kDa cross-react with these antibodies. Anti-p37 and antilipocortin 1 cross-react on the same 37- and 34-kDa polypeptides; anti-p36 and antilipocortin 2 cross-react only on the 36-kDa polypeptides.

Regulation of the sarcoplasmic reticulum Ca(2+)-release channel requires intact annexin VI

Annexin VI has eight highly conserved repeated domains; all other annexins have four. Díaz-Muñoz et al. (J Biol Chem 265:15894, 1990) reported that annexin VI alters the gating properties of the ryanodine-sensitive Ca(2+)-release channel isolated from sarcoplasmic reticulum. The investigate the domain structure of rat annexin VI (67 kDa calcimedin) required for this channel regulation, various proteolytic digestions were performed. In each case, protease-resistant core polypeptides were produced. Annexin VI was digested with V8 protease and two core polypeptides were purified by Ca(2+)-dependent phospholipid binding followed by HPLC. The purified fragments were shown to be derived from the N- and C-terminal halves of annexin VI, and demonstrated differential immunoreactivity with monoclonal antibodies to rat annexin VI. While both core polypeptides retained their ability to bind phospholipids in a Ca(2+)-dependent manner, they did not regulate the sarcoplasmic reticulum Ca(2+)-dependent manner, they did not regulate the sarcoplasmic reticulum Ca(2+)-release channel as did intact annexin VI.