Localization and quantitation of cardiac annexins II, V, and VI in hypertensive guinea pigs

Annexins are characterized by Ca2+-dependent binding to phospholipids. Annexin II mainly participates in cell-cell adhesion and signal transduction, whereas annexins V and VI also seem to regulate intracellular calcium cycling. Their abundance and localization were determined in left ventricle (LV) and right ventricle (RV) from hypertensive guinea pigs, during the transition from compensatory hypertrophy to heart failure. Immunoblot analysis of annexins II, V, and VI revealed an increased accumulation (2.6-, 1.45-, and 2.3-fold, respectively) in LV from hypertensive guinea pigs and no modification in RV. Immunofluorescent labeling of annexins II, V, and VI; of Na+-K+-ATPase; and of sarcomeric alpha-actinin showed that in control LV and RV, 1) annexin II is present in nonmuscle cells; 2) annexins V and VI are mainly observed in the sarcolemma and intercalated disks of myocytes; 3) annexins II, V, and VI strongly label endothelial cells and adventitia of coronary arteries; and 4) annexin VI is present in the media. At the onset of heart failure, the most striking changes are the increased protein accumulation in LV and the very strong labeling of annexins II, V, and VI in interstitial tissue, suggesting a role in fibrosis development and cardiac remodeling.

Annexin II and bleeding in acute promyelocytic leukemia

BACKGROUND

Acute promyelocytic leukemia (APL) is associated with a hemorrhagic disorder of unknown cause that responds to treatment with all-trans-retinoic acid.

METHODS

We studied a newly described receptor for fibrinolytic proteins, annexin II, in cells from patients with APL or other leukemias. We examined initial rates of in vitro generation of plasmin by tissue plasminogen activator (t-PA) in the presence of APL cells that did or did not have the characteristic translocation of APL, t(15;17). We also determined the effect of all-trans-retinoic acid on the expression of annexin II and the generation of cell-surface plasmin.

RESULTS

The expression of annexin II, as detected by a fluorescein-tagged antibody, was greater on leukemic cells from patients with APL than on other types of leukemic cells (mean fluorescence intensity, 6.9 and 2.9, respectively; P<0.01). The t(15;17)-positive APL cells stimulated the generation of cell-surface, t-PA-dependent plasmin twice as efficiently as the t(15;17)-negative cells. This increase in plasmin was blocked by an anti-annexin II antibody and was induced by transfection of t(15;17)-negative cells with annexin II complementary DNA. The t(15;17)-positive APL cells contained abundant messenger RNA for annexin II, which disappeared through a transcriptional mechanism after treatment with all-trans-retinoic acid.

CONCLUSIONS

Abnormally high levels of expression of annexin II on APL cells increase the production of plasmin, a fibrinolytic protein. Overexpression of annexin II may be a mechanism for the hemorrhagic complications of APL.

The Npc1 mutation causes an altered expression of caveolin-1, annexin II and protein kinases and phosphorylation of caveolin-1 and annexin II in murine livers

We have previously demonstrated (1) an increased expression of caveolin-1 in murine heterozygous and homozygous Niemann-Pick type C (NPC) livers, and (2) an increased concentration of unesterified cholesterol in a detergent insoluble caveolae-enriched fraction from homozygous livers. To define further the relationship between caveolin-1 function and the cholesterol trafficking defect in NPC, we examined the expression and distribution of additional caveolar and signal transduction proteins. The expression of annexin II was significantly increased in homozygous liver homogenates and the Triton X-100 insoluble floating fraction (TIFF). Phosphoamino acid analysis of caveolin-1 and annexin II from the homozygous TIFF demonstrated an increase in serine and tyrosine phosphorylation, respectively. To determine the basis for increased phosphorylation of these proteins, the expression and distribution of several protein kinases was examined. The expression of PKCalpha, PKCzeta and pp60-src (protein kinases) were significantly increased in both heterozygous and homozygous liver homogenates, while PKCdelta was increased only in homozygous livers. Of the protein kinases analyzed, only CK IIalpha was significantly enriched in the heterozygous TIFF. Finally, the concentration of diacylglycerol in the homozygous TIFF was significantly increased and this elevation may modulate PKC distribution and function. These results provide additional evidence for involvement of a caveolin-1 containing cellular fraction in the pathophysiology of NPC and also suggest that the Npc1 gene product may directly or indirectly, regulate the expression and distribution of signaling molecules.

Calcium-dependent interaction of annexin I with annexin II and mapping of the interaction sites

Annexins are multifunctional intracellular proteins with Ca2+- and phospholipid-binding properties. Their structures consist of four conserved repeat domains that form the core and a diverse N-terminal tail, from which their functional differences may arise. We searched for cellular proteins that interact with the N-terminal tail plus domain I of annexin I (ANX1) by using the yeast two-hybrid method. Screening of a HeLa cell cDNA library yielded annexin II (ANX2) cDNA. The interaction between ANX1 and ANX2 also occurred in vitro in a Ca2+-dependent manner. Mapping of the interaction sites revealed that interaction between domain I of ANX1 and domain IV of ANX2 was stronger than the other combinations.

The crystal structure of a complex of p11 with the annexin II N-terminal peptide

The aggregation and membrane fusion properties of annexin II are modulated by the association with a regulatory light chain called p11.p11 is a member of the S100 EF-hand protein family, which is unique in having lost its calcium-binding properties. We report the first structure of a complex between p11 and its cognate peptide, the N-terminus of annexin II, as well as that of p11 alone. The basic unit for p11 is a tight, non-covalent dimer. In the complex, each annexin II peptide forms hydrophobic interactions with both p11 monomers, thus providing a structural basis for high affinity interactions between an S100 protein and its target sequence. Finally, p11 forms a disulfide-linked tetramer in both types of crystals thus suggesting a model for an oxidized form of other S100 proteins that have been found in the extracellular milieu.

The p11 subunit of the annexin II tetramer plays a key role in the stimulation of t-PA-dependent plasminogen activation

Annexin II tetramer (AIIt) is an important endothelial cell surface protein receptor for plasminogen and t-PA. AIIt, a heterotetramer, is composed of two p36 subunits (called annexin II) and two p11 subunits. In this report, we have compared the ability of the isolated p36 and p11 subunits to stimulate t-PA-dependent [Glu]plasminogen activation. The fluid-phase recombinant p11 subunit stimulated the rate of t-PA-dependent activation of [Glu]plasminogen about 46-fold compared to an approximate stimulation of 2-fold by the recombinant p36 subunit and 77-fold by recombinant AIIt. The stimulation of t-PA-dependent activation of [Glu]plasminogen by the p11 subunit was Ca2+-independent and inhibited by epsilon-aminocaproic acid. [Glu]Plasminogen bound to a p11 subunit affinity column and could be eluted with epsilon-aminocaproic acid. Both AIIt and the p11 subunit protected t-PA and plasmin from inactivation by PAI-1 and alpha2-antiplasmin, respectively. A peptide to the C terminus of the p11 subunit (85-Y-F-V-V-H-M-K-Q-K-G-K-K-96) inhibited the p11-dependent stimulation of t-PA-dependent plasminogen activation. In addition, a deletion mutant of the p11 subunit, missing the last two C-terminal lysine residues, retained only about 15% of the activity of the wild-type p11 subunit. Similarly, a mutant AIIt composed of the wild-type p36 subunit and the p11 subunit deletion mutant possessed about 12% of the wild-type activity. These results, therefore, suggest that the C-terminal lysine residues of the p11 subunit bind plasminogen and participate in the stimulation of t-PA-dependent activation of plasminogen by AIIt.

Modulation of annexin II by homocysteine: implications for atherothrombosis

Recent evidence indicates a potential role for the plasmin/plasminogen activator system in the prevention of atherosclerotic vascular disease. Fibrin deposition is a common histologic feature of the tissues of mice that are genetically deficient in one or more key components of the fibrinolytic system. Cell surface receptors may support fibrinolytic surveillance in both intravascular and extravascular locations by stimulating the efficiency plasmin generation and by protecting plasmin from its inhibitors. In vitro studies suggest that the endothelial cell receptor, annexin II, which independently binds both plasminogen and t-PA, could play a key role in the process. Binding of plasminogen to annexin II is specifically inhibited in the presence of excess concentrations of the atherogenic LDL-like particle Lp(a). Similarly, t-PA binding to annexin II is blocked by homocysteine, a sulfhydryl-containing amino acid that is associated with atherogenesis and that directly derivatizes the t-PA binding domain of annexin II. Elucidation of the precise role of annexin II in fibrinolytic surveillance, however, will await in vivo study.

Differential expression of annexins I, II and IV in human tissues: an immunohistochemical study

Annexins constitute a family of Ca2+- and phospholipid-binding proteins. Although their functions are still not clearly defined, several members of the annexin family have been implicated in membrane-related events along exocytotic and endocytotic pathways. To elucidate a possible correlation of those functional proposals with the tissue distribution of annexins, we analysed immunohistochemically the expression of annexins I, II and IV in a broad variety of human tissues. Annexins I and II were chosen for this study since their functionally relevant N-terminal domains are structurally closely related, whilst annexin IV is structurally less related to the former two proteins. The study revealed distinct expression patterns of annexins I, II and IV throughout the body. Annexin I was found in leucocytes of peripheral blood, tissue macrophages and T-lymphocytes and in certain epithelial cells (respiratory and urinary system, superficial cells of non-keratinised squamous epithelium), annexin II in endothelial cells, myoepithelial cells and certain epithelial cells (mainly respiratory and urinary system), whereas annexin IV was almost exclusively found in epithelial cells. Epithelia of the upper respiratory system, Bowman's capsule, urothelial cells, mesothelial cells, peripheral nerves, the choroid plexus, ependymal cells and pia mater and arachnoid of meninges generally strongly expressed all three annexins investigated. The characteristic expression in different tissues and the intracellular distribution indicates that the three annexins investigated are involved in aspects of differentiation and/or physiological functions specific to these tissues.

Induction of acute translational response genes by homocysteine. Elongation factors-1alpha, -beta, and -delta

The thiol amino acid homocysteine (HC) accumulates in homocystinuria and homocyst(e)inemia, and is associated with a wide variety of clinical manifestations. To determine whether HC influences the cell's program of gene expression, vascular endothelial cells were treated with HC for 6-42 h and analyzed by differential display. We found a 3-7-fold, time-dependent induction of a 220-base pair fragment, which demonstrated complete sequence identity with elongation factor-1delta (EF-1delta), a member of the multimeric complex regulating mRNA translation. Fibroblasts from cystathionine beta-synthase -/- individuals also showed up to 3.0-fold increased levels of mRNA for EF-1alpha, -beta, and -delta when compared with normal cells, and treatment of normal cells with the HC precursor, methionine, induced a 1.5-2.0-fold increase in EF-1alpha, -beta, and -delta mRNA. This induction was completely inhibited by cycloheximide and reflected a doubling in the rate of gene transcription in nuclear run-on analyses. In HC-treated endothelial cells, pulse-chase studies revealed a doubling in the rate of synthesis of the thiol-containing protein, annexin II, but no change in synthesis of the cysteineless protein, plasminogen activator inhibitor-1. Thus, HC induces expression of a family of acute translational response genes through a protein synthesis-dependent transcriptional mechanism. This process may mediate accelerated synthesis of free thiol-containing proteins in response to HC-induced oxidative stress.

[Fc gamma receptors in human placenta]

This review summarizes the status of our knowledge on the structure, expression and function of Fc gamma R in the placenta. The discovery in syncytiotrophoblast of an MHC class I--related FcR, of the type responsible for intestinal uptake of milk IgG in suckling rats and mice is also described.

The phosphotyrosine phosphatase SHP-2 participates in a multimeric signaling complex and regulates T cell receptor (TCR) coupling to the Ras/mitogen-activated protein kinase (MAPK) pathway in Jurkat T cells

Src homology 2 (SH2) domain-containing phosphotyrosine phosphatases (SHPs) are increasingly being shown to play critical roles in protein tyrosine kinase-mediated signaling pathways. The role of SHP-1 as a negative regulator of T cell receptor (TCR) signaling has been established. To further explore the function of the other member of this family, SHP-2, in TCR-mediated events, a catalytically inactive mutant SHP-2 was expressed under an inducible promoter in Jurkat T cells. Expression of the mutant phosphatase significantly inhibited TCR-induced activation of the extracellular-regulated kinase (ERK)-2 member of the mitogen-activated protein kinase (MAPK) family, but had no effect on TCR-zeta chain tyrosine phosphorylation or TCR-elicited Ca2+ transients. Inactive SHP-2 was targeted to membranes resulting in the selective increase in tyrosine phosphorylation of three membrane-associated candidate SHP-2 substrates of 110 kD, 55-60 kD, and 36 kD, respectively. Analysis of immunoprecipitates containing inactive SHP-2 also indicated that the 110-kD and 36-kD Grb-2-associated proteins were putative substrates for SHP-2. TCR-stimulation of Jurkat T cells expressing wild-type SHP-2 resulted in the formation of a multimeric cytosolic complex composed of SHP-2, Grb-2, phosphatidylinositol (PI) 3'-kinase, and p110. A significant proportion of this complex was shown to be membrane associated, presumably as a result of translocation from the cytosol. Catalytically inactive SHP-2, rather than the wild-type PTPase, was preferentially localized in complex with Grb-2 and the p85 subunit of PI 3'-kinase, suggesting that the dephosphorylating actions of SHP-2 may regulate the association of these signaling molecules to the p110 complex. Our results show that SHP-2 plays a critical role in linking the TCR to the Ras/MAPK pathway in Jurkat T cells, and also provide some insight into the molecular interactions of SHP-2 that form the basis of this signal transduction process.

Tissue plasminogen activator binding to the annexin II tail domain. Direct modulation by homocysteine

Tissue plasminogen activator binds to endothelial cells via the calcium-regulated phospholipid-binding protein annexin II, an interaction that is inhibited by the prothrombotic amino acid homocysteine. We sought to identify the tissue plasminogen activator binding domain of annexin II and to determine the mechanism of its modulation by homocysteine. Tissue plasminogen activator binding to immobilized annexin II was inhibited by intact fluid phase annexin II but not by its "core" fragment (residues 25-339). Two overlapping "tail" peptides specifically blocked 65-75% of binding. Localization of the tissue plasminogen activator binding domain was confirmed upon specific inhibition by the hexapeptide LCKLSL (residues 7-12). Expressed C9G annexin II protein failed to support tissue plasminogen activator binding, while binding to C133G, C262G, and C335G was equivalent to that of wild type annexin II. Upon exposure to homocysteine, annexin II underwent a 135 +/- 4-Da increase in mass localizing specifically to Cys9 and a 60-66% loss in tissue plasminogen activator-binding capacity (I50 = 11 microM). Upon treatment of cultured endothelial cells with [35S]homocysteine, the dithiothreitol-sensitive label was recovered by immunoprecipitation with anti-annexin II IgG. These data provide a potential mechanism for the prothrombotic effect of homocysteine by demonstrating direct blockade of the tissue plasminogen activator binding domain of annexin II.

In adrenocortical tissue, annexins II and VI are attached to clathrin coated vesicles in a calcium-independent manner

We have previously characterized three populations of clathrin coated vesicles (CCVs) isolated from bovine adrenocortical tissue and designated them as large, medium and small coated vesicles, i.e., LCV, MCV and SCV, respectively. Here, we show that annexins II and VI, two of the annexins involved in membrane traffic, are present in the three populations of CCVs but with different distributions between coat proteins (CP) and lipidic vesicle membrane. Annexin VI is only associated with the membrane, whatever the CCV population. In contrast, annexin II is differently distributed between coat and membrane, depending on the CCV population. Both annexins are bound to membranes in a calcium-independent manner and solubilization studies in Triton X114 (TX114) suggest that they interact poorly with lipids by hydrophobic interactions. Ligand blotting experiments show that both annexins bind to CCV proteins: annexin II to a 200-kDa component in all CCVs and annexin VI to a 100-kDa component in LCV and SCV identified as dynamin, a GTPase essential for endocytic CCV pinching off. Dynamin is tightly associated to annexin VI only in LCVs, the endocytic [transferrin (Tf) positive] vesicles. Our data suggest that annexins II and VI could define specific protein-lipid interaction microdomains that could play a role in the different functions of the CCVs.

Annexin V inhibits protein kinase C activity via a mechanism of phospholipid sequestration

In this study, we assessed the role of annexin V, a Ca2+-dependent phospholipid-binding protein, as a regulator of protein kinase C (PKC) and characterized its mechanism of inhibition. Several mutants obtained by oligonucleotide site-directed mutagenesis were tested in vitro on PKC activity in cytosolic fractions from Jurkat cells and on purified PKCalpha. Annexin V inhibited phosphorylation of annexin II by endogenous PKC and phosphorylation of myelin basic protein by PKCalpha. In both systems, the use of single Ca2+-binding-site mutants of annexin V led to a partial reversal of inhibition, and the Ca2+-binding site located in the first domain of annexin V was found to have the most important role. An increase in the number of mutated Ca2+-binding sites led to a greater loss of inhibition. These results corroborated those showing the progressive loss of binding of these mutants to phospholipid liposomes. In conclusion, we show that PKC inhibition by annexin V is the consequence of a mechanism involving phospholipid sequestration by annexin V, and that the Ca2+-binding site located in domain 1 of annexin V plays a predominant role in this process. In addition, we show that the R122AIK site, which may act analogously to a PKC-inhibitory pseudosubstrate site, is not involved in PKC inhibition, and that a peptide corresponding to the C-terminal tail of annexin V inhibits PKC activity but to a lesser extent than annexin V itself.

Altered cardiac annexin mRNA and protein levels in the left ventricle of patients with end-stage heart failure

Annexins are a unique family of membrane-associated, Ca2+ and phospholipid-binding proteins found in various tissues. Among the 12 isoforms, Annexin II, V and VI exist in heart tissue in the highest amounts. Annexin VI has been shown to affect intracellular Ca2+ cycling and contractility in isolated cardiomyocytes. Annexin V is present in both cardiomyocytes and non-myocyte cell types in the heart and may play a role in the regulation of cellular ion fluxes, organization and secretion, while the cardiac effects of annexin II are unclear. To identify changes in annexin II, V and VI isoforms that might occur in human heart failure, we measured mRNA and protein levels of these three annexins in transplanted left ventricular tissue of 12 patients with end-stage congestive heart failure due to coronary artery disease (CAD, n=6) or idiopathic dilated cardiomyopathy (DCM, n=6) who underwent cardiac transplantation. Normal heart tissue (C, n=6) was used as a control. Northern blot analyses showed a significant decrease (61%) in annexin VI mRNA levels in heart failure patients compared with controls (1.08+/-0.16 v 2.79+/-0.20 A.U.C. unit, determined by laser densitometry, mean+/-s.e.). In contrast, we found a 67% increase (2. 32+/-0.27 v 3.88+/-0.29) in annexin II mRNA levels and a two-fold increase (1.00+/-0.24 v 2.21+/-0.29) in annexin V mRNA levels in cardiomyopathic hearts as compared to normal hearts. Western blot analyses demonstrated a corresponding decrease (46.1%) in annexin VI protein levels in the heart failure group as compared to controls (2. 63+/-0.22 v 4.88+/-0.52), while annexin II protein levels showed a significant 40.7% increase in patients with heart failure compared to those in normal hearts (5.08+/-0.67 v 3.61+/-0.32). Annexin V protein levels were also significantly increased (45%) in heart failure patients compared with normal (2.14+/-0.19 v 1.48+/-0.11). No difference in either annexins II, V or VI mRNA and protein levels were found between CAD and DCM patients. We conclude that human end-stage heart failure is associated with a down regulation of annexin VI and up regulation of annexin II and V proteins. Coordinate changes were observed in steady-state mRNA levels. These results suggest that these annexin isoforms may contribute to the regulation of intracellular Ca2+ homeostasis in the cardiomyopathic heart.

Profibrinolytic properties characterize a stably transformed human endothelial cell line

A stable immortalized venous endothelial cell (IVEC) line, obtained by transfection of human umbilical vein endothelial cells (HUVEC), retains many normal differentiated endothelial characteristics. We compared the fibrinolytic activities of IVEC and HUVEC, and observed that IVEC express a more profibrinolytic phenotype than HUVEC, since they bind and activate plasminogen more efficiently, produce more tissue plasminogen activator and urokinase-type plasminogen activator antigens, and secrete less plasminogen activator inhibitor-1 antigen both under basal conditions and after stimulation with lipopolysaccharide, phorbol ester and tumor necrosis factor. Moreover, immunostaining and Western blotting of IVEC for the plasminogen/tissue plasminogen activator receptor annexin II, as well as Northern blotting of annexin II mRNA, revealed similar patterns of surface expression in IVEC and HUVEC. Plasminogen activator inhibitor-2 is expressed similarly in both cell types. IVEC may be a useful human model for functional and pharmacological explorations and modulations of fibrinolytic system components.

The role of annexin II tetramer in the activation of plasminogen

Annexin II tetramer (AIIt) is a major Ca2+-binding protein of endothelial cells which has been shown to exist on both the intracellular and extracellular surfaces of the plasma membrane. In this report, we demonstrate that AIIt stimulates the activation of plasminogen by facilitating the tissue plasminogen activator (t-PA)-dependent conversion of plasminogen to plasmin. Fluid-phase AIIt stimulated the rate of activation of [Glu]plasminogen about 341-fold compared with an approximate 6-fold stimulation by annexin II. AIIt bound to [Glu]plasminogen(S741C-fluorescein) with a Kd of 1. 26 +/- 0.04 microM (mean +/- S.D., n = 3) and this interaction resulted in a large conformational change in [Glu]plasminogen. Kinetic analysis established that AIIt produces a large increase of about 190-fold in the kcat, app and a small increase in the Km,app which resulted in a 90-fold increase in the catalytic efficiency (kcat/Km) of t-PA for [Glu]plasminogen. AIIt also stimulated the t-PA-dependent activation of [Lys]plasminogen about 28-fold. Furthermore, other annexins such as annexin I, V, or VI did not produce comparable activation of t-PA-dependent conversion of [Glu]plasminogen to plasmin. The stimulation of the activation of [Glu]plasminogen by AIIt was Ca2+-independent and inhibited by epsilon-aminocaproic acid. AIIt bound to human 293 cells potentiated t-PA-dependent plasminogen activation. AIIt that was bound to phospholipid vesicles or heparin also stimulated the activation of [Glu]plasminogen 5- or 11-fold, respectively. Furthermore, immunofluorescence labeling of nonpermeabilized HUVEC revealed a punctated distribution of AIIt subunits on the cell surface. These results therefore identify AIIt as a potent in vitro activator of plasminogen.

Annexins I and II bind to lipid A: a possible role in the inhibition of endotoxins

Annexins are Ca2+-dependent phospholipid-binding proteins with anti-inflammatory properties that are present on the surfaces of, and released from, certain cell types, such as leukocytes and secretory epithelia. The present study investigated the possibility that annexins may bind directly to bacterial endotoxin, inhibiting its interactions with cellular receptors or accessory binding proteins. An enzyme-linked immunoassay demonstrated calcium-dependent binding of low nanomolar concentrations of annexin-I and annexin-II p36/p11 heterotetramer to lipid A. In contrast, little or no annexin binding to lipopolysaccharide (LPS) was detected under similar conditions. LPS-binding protein binding to lipid A was blocked by annexin-I, and the annexins inhibited nitrite generation in RAW 264.7 cells induced by lipid A but not that induced by LPS. The data suggest that direct binding of annexins to lipid A may represent a mechanism for suppressing cellular and systemic responses to endotoxin.

[The receptor and pathways for human cytomegalovirus entry]

The cellular receptor for human cytomegalovirus(HCMV) entry has not been identified. To date, heparan sulfate proteoglycan, annexin II, and CD13(aminopeptidase N) are reported to be associated with HCMV entry into human fibroblast cells. A recombinant HCMV that can express a marker protein on the infected cell was generated and used to assess relationship between HCMV entry and expression of heparan sulfate and CD13. The recombinant virus could infect to two human neuroblastoma-derived cell lines that do not express CD13 but do heparan sulfate on the surface. In addition, a human malignant melanoma-derived cell line that expresses CD13 did not allow HCMV entry. HCMV appears to enter into neuroectodermal tissue-derived cells via a CD13-independent pathway.

Direct interaction between human cytomegalovirus glycoprotein B and cellular annexin II

Cellular annexin II has been shown to specifically bind human cytomegalovirus (HCMV) and be a component of highly purified virions. In this report, we characterize the interaction of annexin II with HCMV. We found that the binding of annexin II to the HCMV envelope occurs partially through the calcium-dependent phospholipid-binding ability of annexin II since some annexin II was dissociated from virions with chelating agents. However, a substantial proportion of virion-associated annexin II was resistant to chelation, which suggested a calcium-independent interaction between annexin II and an HCMV envelope component. The search for a nonphospholipid component to account for this binding led to the discovery that HCMV glycoprotein B (gpUL55) (gB) can physically interact with annexin II. We present three lines of evidence to support the conclusion that HCMV gB can bind host cell annexin II.

Suppressive effect on lymphoproliferation in vitro by soluble annexin II released from isolated placental membranes

PROBLEM

Syncytiotrophoblast microvillous plasma membranes (StMPM) are potent suppressors of lymphoproliferation in vitro. We have previously shown that soluble annexin II (AII) is present at higher levels in retroplacental serum (RPS) than in peripheral serum, and that soluble AII has an immunosuppressive effect. The aims of this study were to determine whether AII can be released from StMPM and whether soluble AII from StMPM exerts any immunosuppressive effect.

METHOD OF STUDY

Isolated StMPM were incubated in growth medium for 18 hr and supernatants were prepared by ultracentrifugation. Soluble AII was detected by immunoblotting. StMPM, StMPM supernatant, and affinity-purified AII were analysed in a lymphoproliferation assay for immunomodulating activity.

RESULTS

AII heavy chain and its p11 light chain were detected both in StMPM supernatant and in RPS after removal of StMPM particles by ultracentrifugation. StMPM, StMPM supernatant, and purified AII suppressed lymphoproliferation in a dose-dependent manner. Absorption of AII from StMPM supernatant reduced the suppressive activity. The suppressive effect of StMPM supernatant and purified AII was completely reversed by heating at 100 degrees C for 30 min or by adding recombinant interleukin-2 at 100 units/ml. Although StMPM and affinity-purified AII suppressed the proliferation of lymphocytes from all donors tested, StMPM supernatant suppressed the proliferation of lymphocytes from 12 of 23 donors. Six of eight female non-suppressed donors were multiparae, whereas five of five female suppressed donors were nulliparae.

CONCLUSIONS

Annexin II is released by isolated placental membranes in vitro and is present in RPS, indicating in vivo release of AII at the fetomaternal interface, probably as AII heterotetramer. AII has immunosuppressive activity and may be important in fetal allograft survival.

Structural analysis of junctions formed between lipid membranes and several annexins by cryo-electron microscopy

The (annexin II-p11)2 tetramer has been proposed to participate in exocytosis and several other members of the annexin superfamily have been reported to aggregate liposomes in vitro. In this context, the Ca2+-dependent binding of several annexins to chromaffin granules and liposomes was investigated by cryo-electron microscopy. The Ca2+-dependent aggregation of lipid membranes by (annexin II-p11)2 results from the spontaneous self-organization of the protein into two-dimensional plaques, which are visualized in projection as characteristic junctions. The junctions have a constant thickness of 210(+/-10) A and present a symmetrical distribution of electron-dense material arranged into seven stripes. They were observed over a wide range of Ca2+ concentrations, down to 2 microM. The molecular components corresponding to the seven electron-dense stripes were assigned as follows: the two associated membranes give rise to two outer stripes each and the three central stripes correspond to the (annexin II-p11)2 tetramer. Each annexin II molecule interacts with the outer lipid leaflet of one membrane, giving rise to one stripe, while the central stripe is due to the (p11)2 dimer with which both annexin II molecules interact. Both annexin II and annexin I also induced the Ca2+-dependent aggregation of liposomes via junctions that lack the central (p11)2 moiety and present only six high-density stripes. As expected, both annexin V and annexin III bind to liposomes without inducing their aggregation.

Presence and comparison of Ca2+ transport activity of annexins I, II, V, and VI in large unilamellar vesicles

This study evaluated whether annexins I, II and VI possess Ca2+ transport activity in phospholipid membranes by the burst method, and the activity of each was compared with that of annexin V. Briefly, in the presence of 400 microM Ca2+, each annexin at 50 nM was added to large unilamellar vesicles (LUV) which were then burst in fura-2 solution with 0.2% Triton X-100, followed by examination of Ca2+ signals. Annexins I, II, V and VI were all shown to express, each to a different degree, Ca2+ activity toward phosphatidylserine/phosphatidyl- ethanolamine-LUV. Ca2+ signal intensity increased dependent on annexin concentration, and the Ca2+ transport activity of annexin V and VI was higher than that of annexin I and II. However, none of annexin I, II, V and VI expressed Ca2+ transport activity in LUV produced using phosphatidylcholine. Ca(2+)-incorporated LUV with no annexin showed signals whose intensity was proportional to Ca2+ concentration. The Ca2+ transport activity of the annexins could be effectively measured by the burst method. Ca2+ signal intensity would thus appear to be unique for each of the annexins and to be determined by the particular function and specificity of each of those considered in this study.

P11, a unique member of the S100 family of calcium-binding proteins, interacts with and inhibits the activity of the 85-kDa cytosolic phospholipase A2

Using a two hybrid system screen of a human cDNA library, we have found that p11, a unique member of the S100 family of calcium-binding proteins, interacts with the carboxyl region of the 85-kDa cytosolic phospholipase A2 (cPLA2). p11 synthesized in a cell-free system interacts with cPLA2 in vitro. The p11-cPLA2 complex is detectable from a human bronchial epithelial cell line (BEAS 2B). Furthermore, p11 inhibits cPLA2 activity in vitro. Selective inhibition of p11 expression in the BEAS 2B cells by antisense RNA results in an increased PLA2 activity as well as an increased release of prelabeled arachidonic acid. This study demonstrates a novel mechanism for the regulation of cPLA2 by an S100 protein.

Translocation of cytosolic annexin 2 to a Triton-insoluble membrane subdomain upon nicotine stimulation of chromaffin cultured cells

To gain a better understanding of the function of annexin 2, we have investigated the subcellular distribution of the monomeric and heterotetrameric forms of annexin 2 and their relationship to the cytoskeleton upon stimulation of chromaffin cells. Quantitative immunoblotting has revealed that in resting cells a large amount of annexin 2 is monomeric and cytosolic. Upon nicotine stimulation 80% of total annexin 2 becomes associated with a Triton-X100-insoluble fraction where the monomeric and the heterotetrameric forms are found. The translocation of monomeric annexin 2 is Ca2+-dependent and complete at 1 microM free Ca2+. We have shown that about 66% of the annexin 2 associated with the Triton-X100-insoluble fraction is soluble in octylglucoside while the remnants are insoluble in the detergent and remain likely associated with actin filaments and associated cytoskeleton proteins. The octylglucoside-soluble fraction contains integral proteins from the plasma membrane and from granule membrane, but does not contain caveolin. Moreover, upon nicotine stimulation, a redistribution of proteins was detected in this fraction. These dynamic processes appear concomitantly with the phosphorylation of annexin 2 in this compartment and with catecholamine release. It is suggested that the soluble octylglucoside fraction may represent a special lipidic membrane compartment where the NSF attachment proteins and the cytosolic proteins like annexin 2 and rab3a may become concentrated upon stimulation of the cell. The presence of annexin 2 is consistent with its proposed function on granule and target membrane proteins required for the close apposition of two distinct membranes and supports its functional role in the regulated exocytosis/endocytosis process.

Inhibition of lung surfactant secretion from alveolar type II cells and annexin II tetramer-mediated membrane fusion by phenothiazines

We investigated the effects of phenothiazines on lung surfactant secretion from rat alveolar epithelial type II cells and on annexin II tetramer (Anx IIt)-mediated membrane fusion. Trifluoperazine and promethazine inhibited ATP-stimulated phosphatidylcholine (PC) secretion from type II cells in a dose-dependent manner. Concentrations that cause 50% inhibition (IC50) were approximately 3 and 25 microM for trifluoperazine and promethazine, respectively. Promethazine also inhibited PC secretion of type II cells stimulated by other secretagogues, including calcium ionophore A23187, phorbol 12-myristate 13-acetate, and terbutaline that are known to stimulate PC secretion via different signal transduction pathways. Since we have recently determined that Anx IIt is involved in PC secretion of type II cells, we examined whether phenothiazines influence Anx IIt's activity. Trifluoperazine and promethazine inhibited Anx IIt's ability to aggregate phosphatidylserine (PS) liposomes, to fuse PS/phosphatidylethanolamine (PE) liposomes, and to fuse PS/PE liposomes with lamellar bodies. These results suggest a relationship between lung surfactant secretion and Anx IIt-mediated membrane fusion.

Characterization of the heparin binding properties of annexin II tetramer

In this report, we have characterized the interaction of heparin with the Ca2+- and phospholipid-binding protein annexin II tetramer (AIIt). Analysis of the circular dichroism spectra demonstrated that the Ca2+-dependent binding of AIIt to heparin caused a large decrease in the alpha-helical content of AIIt from approximately 44 to 31%, a small decrease in the beta-sheet content from approximately 27 to 24%, and an increase in the unordered structure from 20 to 29%. The binding of heparin also decreased the Ca2+ concentration required for a half-maximal conformational change in AIIt from 360 to 84 microM. AIIt bound to heparin with an apparent Kd of 32 +/- 6 nM (mean +/- S.D., n = 3) and a stoichiometry of 11 +/- 0.9 mol of AIIt/mol of heparin (mean +/- S.D., n = 3). The binding of heparin to AIIt was specific as other sulfated polysaccharides did not elicit a conformational change in AIIt. A region of the p36 subunit of AIIt (Phe306-Ser313) was found to contain a Cardin-Weintraub consensus sequence for glycosaminoglycan recognition. A peptide to this region underwent a conformational change upon heparin binding. Other annexins contained the Cardin-Weintraub consensus sequence, but did not undergo a substantial conformational change upon heparin binding.

The Cdk-like protein PCTAIRE-1 from mouse brain associates with p11 and 14-3-3 proteins

PCTAIRE-1 is a member of the cyclin-dependent kinase (cdk)-like class of proteins, and is localized mainly in the mammalian brain. Using the yeast two-hybrid system we screened a mouse brain cDNA library with PCTAIRE-1 as bait, and isolated several clones coding for the mouse homologs of the following proteins: p11 (also known as calpactin I light chain) and the eta, theta (also known as tau) and zeta isoforms of 14-3-3 proteins. We confirmed that these four proteins interact with PCTAIRE-1 by demonstrating the biochemical interactions using the pure recombinant proteins. The fact that 14-3-3 proteins are known to interact with many other intracellular proteins (such as C-kinase, Raf, Bcr, P13-kinase) and p11 with annexin II (a major pp60(v-src) and C-kinase substrate) suggests that PCTAIRE-1 might be part of multiple signal transduction cascades and cellular protein networks.

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.

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.

Phosphorylation by protein kinase C of annexin 2 in chromaffin cells stimulated by nicotine

Annexin 2 phosphorylated in vitro by protein kinase C has been shown to restore partially catecholamine secretion in streptolysin O-permeabilized chromaffin cells depleted of their protein kinase C activity. This result suggested a phosphorylation of annexin 2 in stimulated cells. Nicotine stimulation induced an increase of 32P incorporation in annexin 2 heavy chain concomitant with catecholamine release. This incorporation results from phosphorylation by protein kinase C because (a) serine was the only phosphorylated residue, (b) 32P incorporation was inhibited by the protein kinase inhibitors H7, GF 109203X, and staurosporine, and (c) activators of this enzyme, 12-O-tetradecanoylphorbol 13-acetate and 1,2-dioctanoylglycerate, increased the incorporation of radioactivity. The phosphorylated heavy chain had an electrophoretic mobility lower than that of the unmodified one, thus allowing determination of the fraction of phosphorylated protein. In the resting state, a significant fraction of annexin 2 heavy chain was phosphorylated, and nicotine stimulation resulted in an activation of both phosphorylation and dephosphorylation. Phosphorylation was largely increased in the presence of okadaic acid, indicating the involvement of type 1 and 2A phosphatases.

Immunoisolation and partial characterization of endothelial plasmalemmal vesicles (caveolae)

Plasmalemmal vesicles (PVs) or caveolae are plasma membrane invaginations and associated vesicles of regular size and shape found in most mammalian cell types. They are particularly numerous in the continuous endothelium of certain microvascular beds (e.g., heart, lung, and muscles) in which they have been identified as transcytotic vesicular carriers. Their chemistry and function have been extensively studied in the last years by various means, including several attempts to isolate them by cell fractionation from different cell types. The methods so far used rely on nonspecific physical parameters of the caveolae and their membrane (e.g., size-specific gravity and solubility in detergents) which do not rule out contamination from other membrane sources, especially the plasmalemma proper. We report here a different method for the isolation of PVs from plasmalemmal fragments obtained by a silica-coating procedure from the rat lung vasculature. The method includes sonication and flotation of a mixed vesicle fraction, as the first step, followed by specific immunoisolation of PVs on anticaveolin-coated magnetic microspheres, as the second step. The mixed vesicle fraction, is thereby resolved into a bound subfraction (B), which consists primarily of PVs or caveolae, and a nonbound subfraction (NB) enriched in vesicles derived from the plasmalemma proper. The results so far obtained indicate that some specific endothelial membrane proteins (e.g., thrombomodulin, functional thrombin receptor) are distributed about evenly between the B and NB subfractions, whereas others are restricted to the NB subfraction (e.g., angiotensin converting enzyme, podocalyxin). Glycoproteins distribute unevenly between the two subfractions and antigens involved in signal transduction [e.g., annexin II, protein kinase C alpha, the G alpha subunits of heterotrimeric G proteins (alpha s, alpha q, alpha i2, alpha i3), small GTP-binding proteins, endothelial nitric oxide synthase, and nonreceptor protein kinase c-src] are concentrated in the NB (plasmalemma proper-enriched) subfraction rather than in the caveolae of the B subfraction. Additional work should show whether discrepancies between our findings and those already recorded in the literature represent inadequate fractionation techniques or are accounted for by chemical differentiation of caveolae from one cell type to another.

Modification of annexin II expression in PC12 cell lines does not affect Ca(2+)-dependent exocytosis

The Ca2+/phospholipid/cytoskeletal-binding protein annexin II has been proposed to play an important role in Ca(2+)-dependent exocytosis; however, the evidence for this role is inconclusive. More direct evidence obtained by manipulating annexin II levels in cells is still required. We have attempted to do this by generating stably transfected PC12 cell lines expressing proteins which elevate or lower functional annexin II levels and using these cell lines to investigate Ca(2+)-dependent exocytosis. Three cell lines were generated: one expressing an annexin II mutant which aggregates annexin II in at least a proportion of the cells, thereby removing functional protein from the cell; a mixed clonal cell line constitutively overexpressing human annexin II; and a clonal cell line capable of over-expressing annexin II in the presence of sodium butyrate. After digitonin permeabilization, Ca(2+)-dependent dopamine release from these cell lines was compared with that from control nontransfected cells, and, in addition, release was compared in induced to uninduced cells. There were no significant differences in Ca(2+)-dependent exocytosis between any of the transfected cell lines before or after induction and the control cells. In addition, nontransfected PC12 cells treated with nerve growth factor, which elevates annexin II levels severalfold, failed to increase Ca(2+)-dependent exocytosis after digitonin permeabilization, compared with control cells. We conclude that annexin II is not an important regulator of Ca(2+)-dependent exocytosis in PC12 cells.

Specific release of membrane-bound annexin II and cortical cytoskeletal elements by sequestration of membrane cholesterol

Annexin II is an abundant protein which is present in the cytosol and on the cytoplasmic face of plasma membrane and early endosomes. It is generally believed that this association occurs via Ca(2+)-dependent binding to lipids, a mechanism typical for the annexin protein family. Although previous studies have shown that annexin II is involved in early endosome dynamics and organization, the precise biological role of the protein is unknown. In this study, we found that approximately 50% of the total cellular annexin was associated with membranes in a Ca(2+)-independent manner. This binding was extremely tight, since it resisted high salt and, to some extent, high pH treatments. We found, however, that membrane-associated annexin II could be quantitatively released by low concentrations of the cholesterol-sequestering agents filipin and digitonin. Both treatments released an identical and limited set of proteins but had no effects on other membrane-associated proteins. Among the released proteins, we identified, in addition to annexin II itself, the cortical cytoskeletal proteins alpha-actinin, ezrin and moesin, and membrane-associated actin. Our biochemical and immunological observations indicate that these proteins are part of a complex containing annexin II and that stability of the complex is sensitive to cholesterol sequestering agents. Since annexin II is tightly membrane-associated in a cholesterol-dependent manner, and since it seems to interact physically with elements of the cortical actin cytoskeleton, we propose that the protein serves as interface between membranes containing high amounts of cholesterol and the actin cytoskeleton.

Characterization of human recombinant annexin II tetramer purified from bacteria: role of N-terminal acetylation

Annexin II tetramer (AIIt) is a Ca2+-dependent, phosphatidylserine-binding, and F-actin-bundling phosphoprotein which is localized to both the extracellular and cytoplasmic surfaces of the plasma membrane. The tetramer is composed of two p36 heavy chains and two p11 light chains. We have produced prokaryotic cDNA expression constructs for both p36 and p11. Both proteins were expressed in large amounts in Escherichia coli upon induction with IPTG. Electrospray ionization mass spectrometry and amino acid sequence analysis of purified recombinant p36 (rp36) and recombinant p11 (rp11) suggested that the recombinant proteins were identical to their native counterparts except for the lack of N-terminal acetylation of rp36. Furthermore, the non-acetylated rp36 bound rp11 and formed AIIt. The circular dichroism spectra and urea denaturation profiles of acetylated AIIt and non-acetylated rAIIt were identical. In addition, both the acetylated AIIt and non-acetylated rAIIt were similar in their Ca2+ dependence and concentration dependence of phospholipid liposome aggregation, chromaffin granule aggregation, and F-actin bundling. These results suggest that N-terminal acetylation of p36 is not in fact necessary for binding of the protein to p11 and that N-terminal acetylation does not affect the conformational stability of AIIt or the in vitro activities of AIIt. The availability of large amounts of rAIIt will facilitate further characterization of the structure-function relationships of the protein.

Tyrosine phosphorylation of annexin II tetramer is stimulated by membrane binding

In the present article we have examined if the interaction of the Ca2+-binding protein, annexin II tetramer (AIIt) with the plasma membrane phospholipids or with the submembranous cytoskeleton, effects the accessibility of the tyrosine phosphorylation site of AIIt. In the presence of Ca2+, pp60(c-src) catalyzed the incorporation of 0.22 +/- 0.05 mol of phosphate/mol of AIIt (mean +/- S.D., n = 5). The Ca2+-dependent binding of AIIt to purified adrenal medulla plasma membrane or phosphatidylserine vesicles stimulated the pp60(c-src)-dependent phosphorylation of AIIt to 0.62 +/- 0.04 mol of phosphate/mol of AIIt (mean +/- S.D., n = 5) or 0.93 +/- 0.07 mol of phosphate/mol of AIIt (mean +/- S.D., n = 5), respectively. Phosphatidylserine- or phosphatidylinositol-containing vesicles but not vesicles composed of phosphatidylcholine or phosphatidylethanolamine, stimulated the phosphorylation of AIIt. In contrast, the binding of AIIt to F-actin resulted in the incorporation of only 0.04 +/- 0.04 mol of phosphate/mol of AIIt (mean +/- S.D., n = 5). These results suggest that the interaction of AIIt with plasma membrane and not the submembranous cytoskeleton, activates the tyrosine phosphorylation of AIIt by inducing a conformational change in the protein resulting in the enhanced exposure or accessibility of the tyrosine-phosphorylation site.

Identification and characterization of a novel type of annexin-membrane interaction: Ca2+ is not required for the association of annexin II with early endosomes

Annexin II, a member of a family of Ca2+ and membrane binding proteins, has been implicated in regulating membrane organization and membrane transport during endocytosis and Ca2+ regulated secretion. To characterize the mechanistic aspects of the annexin. II action we studied parameters which determine the endosomal association of annexin II. Immunoblot analysis of subcellular membrane fractions prepared from BHK cells in the presence of a Ca2+ chelating agent reveals that annexin II remains associated with endosomal membranes under such conditions. This annexin II behaviour is atypical for the Ca2+ regulated annexins and is corroborated by the finding that ectopically expressed annexin II mutants with inactivated Ca2+ binding sites continue to co-fractionate with endosomal membranes. The Ca(2+)-independent membrane association of annexin II is also not affected by introducing mutations interfering with the complex formation of annexin II with its intracellular protein ligand p11. However, a deletion of the unique N-terminal domain of annexin II, in particular the sequence spanning residues 15 to 24, abolishes the Ca(2+)-independent association of the protein with endosomes. These results describe a novel, Ca(2+)-independent type of annexin-membrane interaction and provide a first explanation for the observed preference of different annexins for different cellular membranes. In the case of annexin II this specificity could be mediated through specific membrane receptors interacting with a unique sequence in the annexin II molecule.

In vivo modulation of annexins I, II and V expression by thyroxine and methylthiouracil

Regulation of annexin concentration and localization were investigated in thyroid tissues of hypothyroid [methylthiouracil (MeSur) treatment], euthyroid (control) and hyperthyroid [thyroxine (T4) treatment] rats. A low level of circulating thyroid hormones induces a decrease of total thyroid calcium-binding protein concentration when compared with the concentration in unstimulated animals. Conversely, concentrations of annexins I, II and V increase. The accumulation of these proteins in two subcellular compartments (cytosolic and particulate fractions) can be reversed by addition of thyroid hormones. The finding of a specific increase in annexins concentration in thyroid-hormone-deficient rats, with a general decrease of the total calcium-binding protein content points to a very important role of these proteins in the cells. Furthermore, hyperthyroidisnt gives opposite results. To investigate the transduction pathway of annexins I-, II- and V-induced biosynthesis by thyroid hormones in thyroid glands, we used cultured pig thyroid cells as in vitro model system. In previous work [16], we have shown that annexin concentrations and localization are under TSH control via the adenylate cyclase pathway. In the presence of MeSur (in the culture medium), the protein-binding iodine remains low, indicative of weak thyroid hormone synthesis (data not shown) and that the annexins content is unchanged. These results suggest that, in thyroid tissue, an indirect mechanism links thyroid hormones to annexin expressions via the TSH feed-back loop, and excludes autocrine regulation.

p30, a novel protein target of mouse calcyclin (S100A6)

A novel protein target of mouse calcyclin (S100A6) was detected by a gel overlay method with 125I-labelled calcyclin. Interaction of calcyclin with its 30 kDa target protein (p30) present in Ehrlich ascites tumour (EAT) cells depended on the presence of Ca2+ ions. The binding of p30, evidenced by the reaction with 125I-labelled calcyclin, was found to be of higher affinity than the binding between mouse calcyclin and annexin II or glyceraldehyde-3-phosphate dehydrogenase. Examination of tissue extracts by the gel overlay method has shown that p30 is present not only in the EAT cells but also in mouse brain and spleen. This novel target protein of mouse calcyclin was purified to homogeneity from EAT cells by means of Phenyl-Sepharose chromatography, affinity chromatography and CM-cellulose chromatography. Purified p30 was digested with alpha-chymotrypsin and a partial amino acid sequence of one of the resulting peptides was established. A database search analysis revealed that the sequence is unique, with a similarity of less than 55% to any other known protein sequence.

Annexin II is a novel player in insulin signal transduction. Possible association between annexin II phosphorylation and insulin receptor internalization

Annexin II is a Ca2+-, phospholipid-, and actin- binding protein that was implicated in the regulation of vesicular traffic and endosome fusion. It is a known substrate for protein kinases including the platelet-derived growth factor receptor, src protein-tyrosine kinase, and protein kinase C. In the present study we investigated the possible involvement of annexin II in insulin signal transduction. Phosphorylation of annexin II in response to insulin treatment of intact Chinese hamster ovary (CHO)-T cells was detected by 5 min and reached maximal levels after a 2-3-h incubation with the hormone. However, unlike other receptor substrates, annexin II failed to undergo insulin-induced Tyr phosphorylation under conditions where receptor internalization was inhibited. This was evident in CHO cells, overexpressing the insulin receptor, in which internalization was inhibited either by tyrosine kinase inhibitors or by lowering the temperature to 4 degrees C, and in CHO cells overexpressing various insulin receptor mutants in which normal internalization was impaired. Hence, Tyr phosphorylation of annexin II could be part of the internalization and sorting mechanism of the insulin receptor.

Increased content of annexin II (p36) and p11 in human placenta brush-border membrane vesicles during syncytiotrophoblast maturation and differentiation

Annexins are a group of proteins abundant in placental membranes where they may play diverse functional roles. Annexins are expressed in high levels in mature placenta but little is known about their presence at very early stages of gestation and later. We used the model of brush-border membrane vesicles (BBMV) at different stages of gestation to assess precise localization of some of these proteins in syncytiotrophoblast apical membrane and to determine their appearance along the maturation process of placenta. Here we describe annexins type I, II, IV, V and VI which are present all along gestation in BBMV. Annexin II (p36) is present with the S100 like calcium-binding protein p11 in BBMV, where they can constitute heterotetrameric forms of annexin II linked to cytoskeleton structures. No variation of annexins I, IV and VI content was observed in BBMV along pregnancy. Annexin V undergoes significant decrease after 12th week, which could be related to local anticoagulant activity. Levels of annexin II and p11 increased progressively during gestation suggesting that heterotetrameric forms of annexin II play a role in the differentiation process of placenta and in function of the mature microvilli.

Characterization of type III intermediate filament regulatory protein target epitopes: S-100 (beta and/or alpha) binds the N-terminal head domain; annexin II2-p11(2) binds the rod domain

We have investigated the interaction of S-100 proteins (beta and/or alpha) and annexin II2-p11(2) with glial fibrillary acidic protein (GFAP) and desmin to have further information on the mechanisms whereby S-100 proteins and annexin II2-p11(2) affect assembly/disassembly of GFAP and desmin intermediate filaments (IFs). Analyses were conducted on either native IF subunits, GFAP or desmin rod domain, or headless GFAP or desmin. Our data indicate that: (i) S-100 proteins bind to GFAP and desmin N-terminal head domain; (ii) annexin II2-p11(2) binds to GFAP rod domain; (iii) annexin II2-p11(2) does not interact with desmin nor affects desmin assembly. The present data suggest that the ability of S-100 proteins to inhibit GFAP and desmin assemblies and to promote the disassembly of preformed GFAP and desmin IFs depends on occupation of a site on the N-terminal head domain of these IF subunit. It is known that the N-terminal head domain is critical for the progression from the stage of GFAP and desmin dimers/tetramers to that of large oligomers. On the other hand, the ability of annexin II2-p11(2) to stimulate GFAP assembly under conditions where this latter is normally hampered (e.g., at alkaline pH values) might depend on annexin II2-p11(2)-induced changes in the structure of GFAP rod domain, possibly as a consequence of charge modifications. By contrast, the inability of annexin II2-p11(2) to bind to desmin would depend on desmin resistance to charge modifications.

Mapping of a regulatory important site for protein kinase C phosphorylation in the N-terminal domain of annexin II

Annexin II is a Ca(2+)-regulated membrane- and cytoskeleton-binding protein implicated in membrane transport events along the Ca(2+)-regulated secretory and the early endocytic pathway. Biochemical properties of this annexin and its intracellular distribution are regulated by complex formation with p11 (S100A10), a member of the S100 protein family. The annexin II-p11 interaction is mediated through the unique N-terminal domain of annexin II and is inhibited by protein kinase C phosphorylation of a serine residue in annexin II. To map this regulatory serine phosphorylation site we developed a baculovirus-mediated expression system for wild-type annexin II and for a series of annexin II mutants which contained substitutions in one or more serine residues present in the N-terminal domain. The different mutant derivatives were purified and shown to display the same biochemical properties as recombinant wild-type annexin II and the authentic protein purified from porcine intestine. However, significant differences in phosphate incorporation were observed when the individual serine mutants were subjected to phosphorylation by protein kinase C. A comparison of the phosphorylation patterns obtained identified Ser-II as the protein kinase C site responsible for regulating the annexin II-p11 interaction. Ser-II lies within the sequence mediating p11 binding, i.e. amino-acid residues 1 to 14 of annexin II, and phosphorylation at this site most likely leads to a direct spatial interference with p11 binding.

Altered expression of annexin II in human B-cell lymphoma cell lines

Annexin II is a growth-regulated gene, whose expression is significantly increased in various human cancers. We examined annexin II expression in II human B-cell lymphoma cell lines and in normal B-cells. Wide variation was observed in the levels of annexin II in these cell lines. Annexin II overexpression was observed in 5 cell lines, while significantly reduced expression was observed in Raji, OMA-BL-1 and REH cell lines. Analysis of the annexin II gene, mRNA and protein in Raji and OMA-BL-1 cell lines indicated that annexin II gene was unaltered and that a low level of annexin II transcripts are produced in these cells. Down-regulation of annexin II expression was at the transcriptional level, and no reexpression of annexin II was observed after treatment of cells with demethylating agents. Thus methylation of the annexin II gene does not appear to be responsible for annexin II down-regulation. A slow migrating altered form of annexin II was detected in Raji and OMA-BL-1 cells, which was detected with the anti-chicken annexin II antiserum, but not with the anti-human annexin II antiserum. The slow migrating annexin II species was found to be sensitive to dephosphorylation by calf intestinal alkaline phosphatase, resulting in reduction of the size of the protein on SDS-polyacrylamide gels. The phosphorylated annexin II was also observed in nuclear extracts of human K562 and HeLa cells. Thus, Raji and OMA-BL-1 cells exclusively produce a phosphorylated form of annexin II, and phosphorylated annexin II may be important for cell survival and proliferation.

Interaction of the fibrinolytic receptor, annexin II, with the endothelial cell surface. Essential role of endonexin repeat 2

Endothelial cells express a cell surface co-receptor for plasminogen and tissue plasminogen activator (t-PA) which we recently identified as annexin II (Hajjar, K. A., Jacovina, A. T., and Chacko, J. (1994) J. Biol. Chem. 269, 21191-21197). This protein enhances the catalytic efficiency of t-PA-dependent plasmin generation by 60-fold (Cesarman, G. M., Guevara, C. A., and Hajjar, K. A. (1994) J. Biol. Chem. 269, 21198-21203). Here, we demonstrate that annexin II is constitutively translocated to the endothelial cell surface within 16 h of biosynthesis, and that cell surface annexin II comprises 4.3 +/- 1.0% of the total cellular pool. Exogenous 125I-annexin II bound to EGTA-washed endothelial cells with high affinity (Kd 49 nM) and in a calcium-dependent (I50 = 3 microM), phospholipid-sensitive manner. Peptides KASMKGLGTDED and YDSMKGKGTRDK, mimicking the calcium-binding "endonexin" motif (KGXGT) of annexin II, blocked its interaction with endothelial cells. Recombinant annexin II, bearing the calcium-binding site substitution D161A of core repeat 2, failed to compete with binding of the wild type protein to the cell surface, while E246A and D321A mutants, corresponding to core repeats 3 and 4, behaved as effective competitors. These data suggest that translocated annexin II interacts with cell surface phospholipid via a high affinity calcium-dependent binding site that includes residues 118-122 (KGLGT) and the coordinating Asp161 of core repeat 2. Thus, calcium-regulated expression of annexin II on the endothelial cell surface may play a central role in control of plasmin-mediated processes.

Annexins in the human neuroblastoma SH-SY5Y: demonstration of relocation of annexins II and V to membranes in response to elevation of intracellular calcium by membrane depolarisation and by the calcium ionophore A23187

The human neuroblastoma SH-SY5Y was found to express annexins I, II, IV, V, and VI by western blot analysis. Calcium-dependent membrane-binding proteins were isolated from SH-SY5Y and analysed by 2-dimensional gel electrophoresis. Proteins with Mr and Pi values similar to those of annexins I, II, III, IV, V, and VI were observed. The identity of annexins II and V was confirmed by western blotting. The membrane association of annexins II and V was studied in cells that had been stimulated to release noradrenaline by K+ depolarisation or by treatment with the ionophore A23187. Annexins II and V were both found to associate with membranes in a manner that was resistant to elution with EGTA and required Triton X-100 for their solubilisation. Homogenisation of cells in calcium-containing buffers also resulted in the formation of EGTA-resistant membrane-associated annexins II and V. The results demonstrate calcium-dependent relocation of annexins II and V to membranes in intact cells and suggest that these annexins bind in a calcium-dependent manner to non-phospholipid components of SH-SY5Y membranes. Examination of cells by immunofluorescence microscopy demonstrated that annexin II was homogeneously associated with the plasma membrane before treatment with ionophore and relocated to discrete patches of staining after treatment. Annexin V was found by immunofluorescence to be present in the cytoplasm and in the nucleus, Stimulation of the cells produced no change in the cytoplasmic staining pattern but resulted in a partial relocation of nuclear annexin V to the periphery of the nucleus. The results argue for a general role for both annexins in calcium signalling at discrete intracellular locations. The results are not consistent with the specific involvement proposed previously for annexin II in membrane fusion at sites of vesicle exocytosis.

Phospholipase A2 activity and calpactin I levels in rat lymphokine-activated killer cells: correlation with the cytotoxic activity

In the present paper we have shown evidence for a significant increase of type II sPLA2 activity in A-LAK cells. The A-LAK-mediated cytotoxicity against YAC-1 target cells was strongly inhibited by two inhibitors of sPLA2, p-BPB and mepacrine, suggesting the involvement of this enzyme in the lytic mechanism of A-LAK. On the other hand, stimuli such as A23187 ionophore and TPA, which were able to induce in control cells an increased AA release, failed to cause this effect in IL-2-treated cells, suggesting that PLA2 was not active in these cells. Thus, we analyzed the levels of calpactin I, which is considered to be involved in the down-regulation of PLA2 activity. HrIL-2 treatment led to an increased expression of calpactin I at both the RNA and the protein level. A substantial portion of calpactin I was associated with the external surface of A-LAK and was able to exert a strong inhibitory effect on a purified porcine pancreatic PLA2 activity in vitro. Our results suggest that the role of calpactin I could be relevant to regulate PLA2 activity, and to protect the effector cells against a possible toxic effect which this enzyme could exert if present at high levels.

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.

The crystal structure and ion channel activity of human annexin II, a peripheral membrane protein

Annexin II binds in a calcium-dependent manner to acidic phospholipids and is a substrate of some protein kinases. An N-terminally shortened form of human annexin II was crystallized and its molecular structure determined. It is very similar to two previously described members of this protein family, annexin I and annexin V. The protein structure is nearly completely alpha-helical organized as four compact domains which consist of five alpha-helices each. The domains surround a hydrophilic pore. The calcium binding sites are located at the convex side of the structure as in annexin V. Recombinant and natural porcine annexin II are active as ion channel with characteristics similar to annexin V, while N-terminally shortened annexin II and the heterotetramer (annexin II-p11)2 are inactive. Two cysteine residues, Cys133 and Cys262, form a disulphide bridge connecting domains II and III, adding further weight to the notion that ion channel activity does not require major structural rearrangements.