Isolation and characterization of an anticoagulant protein from human placenta

A convenient method for preparation of the calcium ion-binding protein annexin V

This study presents a novel method for the production and purification of annexin V using cation exchange chromatography in the presence of calcium ions at neutral or alkaline pH. This method enables the handling of a large quantity of sample at one time without deterioration of the adsorption capacity of the cation exchange carrier by contaminating proteins, as well as the production of the calcium ion-binding protein annexin V with high purity on an industrial scale from both recombinant products and native products.

Antiphospholipid Antibodies Accelerate Plasma Coagulation by Inhibiting Annexin-V Binding to Phospholipids: A “Lupus Procoagulant” Phenomenon

The antiphospholipid syndrome is a thrombophilic condition marked by antibodies that recognize anionic phospholipid-protein cofactor complexes. We recently reported that exposure to IgG fractions from antiphospholipid patients reduces the level of annexin-V, a phospholipid-binding anticoagulant protein, on cultured trophoblasts and endothelial cells and accelerates coagulation of plasma exposed to these cells. Therefore, we asked whether antiphospholipid antibodies might directly reduce annexin-V binding to noncellular phospholipid substrates. Using ellipsometry, we found that antiphospholipid IgGs reduce the quantity of annexin-V bound to phospholipid bilayers; this reduction is dependent on the presence of β2-glycoprotein I. Also, exposure to plasmas containing antiphospholipid antibodies reduces annexin-V binding to phosphatidyl serine-coated microtiter plates, frozen thawed washed platelets, activated partial thromboplastin time (aPTT) reagent and prothrombin time reagent and reduces the anticoagulant effect of the protein. These studies show that antiphospholipid antibodies interfere with the binding of annexin-V to anionic phospholipid and with its anticoagulant activity. This acceleration of coagulation, due to reduced binding of annexin V, stands in marked contrast to the “lupus anticoagulant effect” previously described in these patients. These results are the first direct demonstration of the displacement of annexin-V and the consequent acceleration of coagulation on noncellular phospholipid surfaces by antiphospholipid antibodies.

© 1998 by The American Society of Hematology.

Antiphospholipid Antibodies Accelerate Plasma Coagulation by Inhibiting Annexin-V Binding to Phospholipids: A “Lupus Procoagulant” Phenomenon

The antiphospholipid syndrome is a thrombophilic condition marked by antibodies that recognize anionic phospholipid-protein cofactor complexes. We recently reported that exposure to IgG fractions from antiphospholipid patients reduces the level of annexin-V, a phospholipid-binding anticoagulant protein, on cultured trophoblasts and endothelial cells and accelerates coagulation of plasma exposed to these cells. Therefore, we asked whether antiphospholipid antibodies might directly reduce annexin-V binding to noncellular phospholipid substrates. Using ellipsometry, we found that antiphospholipid IgGs reduce the quantity of annexin-V bound to phospholipid bilayers; this reduction is dependent on the presence of β2-glycoprotein I. Also, exposure to plasmas containing antiphospholipid antibodies reduces annexin-V binding to phosphatidyl serine-coated microtiter plates, frozen thawed washed platelets, activated partial thromboplastin time (aPTT) reagent and prothrombin time reagent and reduces the anticoagulant effect of the protein. These studies show that antiphospholipid antibodies interfere with the binding of annexin-V to anionic phospholipid and with its anticoagulant activity. This acceleration of coagulation, due to reduced binding of annexin V, stands in marked contrast to the “lupus anticoagulant effect” previously described in these patients. These results are the first direct demonstration of the displacement of annexin-V and the consequent acceleration of coagulation on noncellular phospholipid surfaces by antiphospholipid antibodies.

© 1998 by The American Society of Hematology.

Functional and genetic analysis of annexin VI

This study is concerned with the determination of the function of the 68kDa calcium-binding protein, annexin VI. Studies on the structure and regulation of the gene include a detailed analysis of annexin VI expressed heterologously in human A431 carcinoma cells. We have recently discovered that annexin VI is subject to a novel growth dependent post-translational modification. Interestingly, the protein exerts a negative effect on A431 cells. This effect was manifested as a partial reversal of the transformed phenotype. We are currently exploring the hypothesis that the post-translational modification of annexin VI is required for sub-cellular targeting, and that correct localisation within the cell is essential for function.

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.

Expression of annexin VI (p68, 67 kDa-calelectrin) in normal human tissues: evidence for developmental regulation in B- and T-lymphocytes

This paper describes the tissue distribution of annexin VI, a Ca(2+)-dependent phospholipid binding protein, and a member of the annexin super-gene family. In order to determine whether annexin VI expression correlated with a particular functional phenotype, an extensive series of non-pathological human tissues were examined, in which annexin VI was detected either immunohistochemically or by immunofluorescence, using a rabbit polyclonal anti(human annexin VI)-IgG of known specificity. Although most tissues investigated were found to express annexin VI, the protein was usually confined to highly specific cell types within each tissue, the staining generally appearing cytoplasmic and diffuse. There was particularly good correlation between annexin VI expression and hormone secreting cells, with positive staining in the islet cells of the pancreas, the Leydig cells of the testis and the cells of the adrenal cortex. A notable exception was the parathyroid gland, which lacked detectable annexin VI. Although the protein was absent in most epithelia, it was expressed strongly in certain secretory epithelia; e.g. the ductal epithelial cells of the salivary glands and non-lactating breast, and the sweat glands and their ducts. The observation that the epithelial cells of lactating breast failed to stain for annexin VI suggests functional regulation of protein expression in this tissue. However, the most interesting finding was that annexin VI expression appeared to be developmentally regulated in B- and T-lymphocyte differentiation, with negative staining in the proliferating B cells of the germinal centre of the lymph nodes, but strong staining in the mature small lymphocytes of the cortex, mantle zone and paracortex.

Antiphospholipid antibodies and recurrent pregnancy loss

Antiphospholipid antibodies (APA) have recently been linked to a variety of clinical findings including arterial and venous thrombosis, recurrent spontaneous abortions and fetal loss, as well as thrombocytopenia. These observations have stimulated multidisciplinary interest in the laboratory identification of APA and the clinical management of patients with positive tests for APA.