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

AnnexinA6: a potential therapeutic target gene for extracellular matrix mineralization

The mineralization of the extracellular matrix (ECM) is an essential and crucial process for physiological bone formation and pathological calcification. The abnormal function of ECM mineralization contributes to the worldwide risk of developing mineralization-related diseases; for instance, vascular calcification is attributed to the hyperfunction of ECM mineralization, while osteoporosis is due to hypofunction. AnnexinA6 (AnxA6), a Ca2+-dependent phospholipid-binding protein, has been extensively reported as an essential target in mineralization-related diseases such as osteoporosis, osteoarthritis, atherosclerosis, osteosarcoma, and calcific aortic valve disease. To date, AnxA6, as the largest member of the Annexin family, has attracted much attention due to its significant contribution to matrix vesicles (MVs) production and release, MVs-ECM interaction, cytoplasmic Ca2+ influx, and maturation of hydroxyapatite, making it an essential target in ECM mineralization. In this review, we outlined the recent advancements in the role of AnxA6 in mineralization-related diseases and the potential mechanisms of AnxA6 under normal and mineralization-related pathological conditions. AnxA6 could promote ECM mineralization for bone regeneration in the manner described previously. Therefore, AnxA6 may be a potential osteogenic target for ECM mineralization.

Annexin-phospholipid interactions. Functional implications

Annexins constitute an evolutionary conserved multigene protein superfamily characterized by their ability to interact with biological membranes in a calcium dependent manner. They are expressed by all living organisms with the exception of certain unicellular organisms. The vertebrate annexin core is composed of four (eight in annexin A6) homologous domains of around 70 amino acids, with the overall shape of a slightly bent ring surrounding a central hydrophilic pore. Calcium- and phospholipid-binding sites are located on the convex side while the N-terminus links domains I and IV on the concave side. The N-terminus region shows great variability in length and amino acid sequence and it greatly influences protein stability and specific functions of annexins. These proteins interact mainly with acidic phospholipids, such as phosphatidylserine, but differences are found regarding their affinity for lipids and calcium requirements for the interaction. Annexins are involved in a wide range of intra- and extracellular biological processes in vitro, most of them directly related with the conserved ability to bind to phospholipid bilayers: membrane trafficking, membrane-cytoskeleton anchorage, ion channel activity and regulation, as well as antiinflammatory and anticoagulant activities. However, the in vivo physiological functions of annexins are just beginning to be established.

A novel calcium-dependent proapoptotic effect of annexin 1 on human neutrophils

The glucocorticoid-inducible protein annexin (ANXA) 1 is an anti-inflammatory mediator that down-regulates the host response. Endogenously, ANXA1 is released in large amounts from adherent polymorphonuclear neutrophils (PMN) and binds to their cell surface to inhibit their extravasation into inflamed tissues. The present study determined the effects of exogenous ANXA1 on several functions of human PMN in vitro. Addition of 0.1-1 microM human recombinant ANXA1 to the PMN provoked rapid and transient changes in intracellular Ca2+ concentrations that were blocked by the Ca2+ channel inhibitor SKF-96365. Although ANXA1 did not affect oxidant production and only minimally affected PMN chemotactic properties, the ANXA1-promoted Ca2+ influx was associated with two important functional effects: shedding of L-selectin and acceleration of PMN apoptosis. The latter effect was confirmed using three distinct technical procedures, namely, cell cycle, Hoechst staining, and ANXA5 binding assay. ANXA1-induced PMN apoptosis was insensitive to inhibitors of L-selectin shedding, whereas it appeared to be associated with dephosphorylation of the proapoptotic intracellular mediator BAD. In conclusion, exogenous ANXA1 displayed selective actions on human PMN. We propose that the new proapoptotic effect reported here may be part of the spectrum of ANXA1-mediated events involved in the resolution of acute inflammation.

Clinical significance of measurement of plasma annexin V concentration of patients in the emergency room

Annexin V, a calcium-binding protein, is widely present in various organs and tissues. In the present study, plasma annexin V concentration was measured in 158 patients who were brought to the emergency room, including 25 patients suffering from acute myocardial infarction (AMI), 14 with cerebrovascular disease, 11 with trauma of the extremities, 11 with severe trauma associated with visceral damage, and 35 with witnessed cardiac arrest. Annexin V concentration in normal healthy individuals (n=110) was 1.9+/-0.7 ng/ml. Annexin V concentration in AMI and cardiac arrest patients was 11.0+/-4.9 and 15.3+/-7.9 ng/ml, respectively, being significantly higher than that in patients with cerebrovascular disease (5.4+/-2.7 ng/ml). The value in severe trauma patients was 15.9+/-9.4 ng/ml, being significantly higher than that in patients with trauma of the extremities (5.6+/-1.2 ng/ml). Annexin V concentrations in the cardiac arrest and AMI patients who survived more than 24 h after admission were lower than those in patients who died within 24 h after the onset of symptoms. Annexin V content in the lungs and myocardium in normal rats was extremely high in comparison to that in brain and skeletal muscle. These results suggest that the high levels of plasma annexin V in patients with AMI, cardiac arrest and severe trauma reflect the severity of damage of the myocardium and/or other visceral organs, and measurement of plasma annexin V concentration may help to assess the prognosis of patients brought to the emergency room.

Calcium-dependent conformational rearrangements and protein stability in chicken annexin A5

The conformational rearrangements that take place after calcium binding in chicken annexin A5 and a mutant lacking residues 3-10 were analyzed, in parallel with human annexin A5, by circular dichroism (CD), infrared spectroscopy (IR), and differential scanning calorimetry. Human and chicken annexins present a slightly different shape in the far-UV CD and IR spectra, but the main secondary-structure features are quite similar (70-80% alpha-helix). However, thermal stability of human annexin is significantly lower than its chicken counterpart (approximately 8 degrees C) and equivalent to the chicken N-terminally truncated form. The N-terminal extension contributes greatly to stabilize the overall annexin A5 structure. Infrared spectroscopy reveals the presence of two populations of alpha-helical structures, the canonical alpha-helices (approximately 1650 cm(-1)) and another, at a lower wavenumber (approximately 1634 cm(-1)), probably arising from helix-helix interactions or solvated alpha-helices. Saturation with calcium induces: alterations in the environment of the unique tryptophan residue of the recombinant proteins, as detected by near-UV CD spectroscopy; more compact tertiary structures that could account for the higher thermal stabilities (8 to 12 degrees C), this effect being higher for human annexin; and an increase in canonical alpha-helix percentage by a rearrangement of nonperiodical structure or 3(10) helices together with a variation in helix-helix interactions, as shown by amide I curve-fitting and 2D-IR.

Retinoic acid stimulates annexin-mediated growth plate chondrocyte mineralization

Biomineralization is a highly regulated process that plays a major role during the development of skeletal tissues. Despite its obvious importance, little is known about its regulation. Previously, it has been demonstrated that retinoic acid (RA) stimulates terminal differentiation and mineralization of growth plate chondrocytes (Iwamoto, M., I.M. Shapiro, K. Yagumi, A.L. Boskey, P.S. Leboy, S.L. Adams, and M. Pacifici. 1993. Exp. Cell Res. 207:413-420). In this study, we provide evidence that RA treatment of growth plate chondrocytes caused a series of events eventually leading to mineralization of these cultures: increase in cytosolic calcium concentration, followed by up-regulation of annexin II, V, and VI gene expression, and release of annexin II-, V-, VI- and alkaline phosphatase-containing matrix vesicles. Cotreatment of growth plate chondrocytes with RA and BAPTA-AM, a cell permeable Ca2+ chelator, inhibited the up-regulation of annexin gene expression and mineralization of these cultures. Interestingly, only matrix vesicles isolated from RA-treated cells that contained annexins, were able to take up Ca2+ and mineralize, whereas vesicles isolated from untreated or RA/BAPTA-treated cells, that contained no or only little annexins were not able to take up Ca2+ and mineralize. Cotreatment of chondrocytes with RA and EDTA revealed that increases in the cytosolic calcium concentration were due to influx of extracellular calcium. Interestingly, the novel 1,4-benzothiazepine derivative K-201, a specific annexin Ca2+ channel blocker, or antibodies specific for annexin II, V, or VI inhibited the increases in cytosolic calcium concentration in RA-treated chondrocytes. These findings indicate that annexins II, V, and VI form Ca2+ channels in the plasma membrane of terminally differentiated growth plate chondrocytes and mediate Ca2+ influx into these cells. The resulting increased cytosolic calcium concentration leads to a further up-regulation of annexin II, V, and VI gene expression, the release of annexin II-, V-, VI- and alkaline phosphatase-containing matrix vesicles, and the initiation of mineralization by these vesicles.

Localization of annexin V in rat normal kidney and experimental glomerulonephritis

The localization of annexin V, a calcium binding protein, was immunochemically and immunohistologically studied in experimental rat glomerulonephritis using annexin V polyclonal antibody. Plasma and urinary annexin V levels were measured by a sandwich enzyme-linked immunosorbent assay (ELISA). Urinary annexin V level, which was correlated with urinary L-lactate dehydrogenase activity, N-acetyl-beta-D-glucosaminidase activity and protein level, increased time-dependently after the injection of nephritogenic antigen (bovine glomerular basement membrane), progressively increasing to attain a peak level at 4 weeks of 51.5 +/- 11.3 ng/h. However, plasma annexin V level showed no increase during the study period. Normal kidneys showed strong staining for annexin V in distal tubules, being particularly strong in tubules of the inner stripe of the outer medulla, but could not be detected in proximal tubules. Annexin V was seen in visceral epithelial cells. Bowman's capsule of the glomerulus, the vascular endothelium of arterioles and interlobular arteries, and vascular smooth muscle. In nephritis, the lumen of distal tubules and the luminal cell membrane were deeply stained, with leakage of annexin V being observed from tubular cells. In the present study, renal annexin V was markedly excreted into urine, and its urinary level reflected the severity of damage of renal tissue and the progression of nephritis. These changes of annexin V in the distal tubule and visceral epithelial cells may be of significance in cell injury of the kidney.

The roles of annexins and types II and X collagen in matrix vesicle-mediated mineralization of growth plate cartilage

Annexins II, V, and VI are major components of matrix vesicles (MV), i.e. particles that have the critical role of initiating the mineralization process in skeletal tissues. Furthermore, types II and X collagen are associated with MV, and these interactions mediated by annexin V stimulate Ca(2+) uptake and mineralization of MV. However, the exact roles of annexin II, V, and VI and the interaction between annexin V and types II and X collagen in MV function and initiation of mineralization are not well understood. In this study, we demonstrate that annexin II, V, or VI mediate Ca(2+) influx into phosphatidylserine (PS)-enriched liposomes, liposomes containing lipids extracted from authentic MV, and intact authentic MV. The annexin Ca(2+) channel blocker, K-201, not only inhibited Ca(2+) influx into fura-2-loaded PS-enriched liposomes mediated by annexin II, V, or VI, but also inhibited Ca(2+) uptake by authentic MV. Types II and X collagen only bound to liposomes in the presence of annexin V but not in the presence of annexin II or VI. Binding of these collagens to annexin V stimulated its Ca(2+) channel activities, leading to an increased Ca(2+) influx into the liposomes. These findings indicate that the formation of annexin II, V, and VI Ca(2+) channels in MV together with stimulation of annexin V channel activity by collagen (types II and X) binding can explain how MV are able to rapidly take up Ca(2+) and initiate the formation of the first crystal phase.

Regulatory roles of zinc in matrix vesicle-mediated mineralization of growth plate cartilage

Zinc (Zn2+) has long been known to play important roles in mineralization and ossification of skeletal tissues, but the mechanisms of Zn2+ action are not well understood. In this study we investigated the effects of Zn2+ on mineralization in a cell culture system in which terminal differentiation and mineralization of hypertrophic growth plate chondrocytes was induced by retinoic acid (RA) treatment. Addition of Zn2+ to RA-treated cultures decreased mineralization in a dose-dependent manner without affecting alkaline phosphatase (APase) activity. Characterization of matrix vesicles (MVs), particles that initiate the mineralization process, revealed that vesicles isolated from RA-treated and RA/Zn2+-treated cultures showed similar APase activity, but vesicles from RA/Zn2+-treated cultures contained significantly less Ca2+ and Pi. MVs isolated from RA-treated cultures were able to take up Ca2+ and mineralize in vitro, whereas vesicles isolated from RA/Zn2+-treated cultures were not able to do so. Detergent treatment, which ruptures the MV membrane and exposes preformed intravesicular Ca2+-Pi-phospholipid complexes, did not restore the Ca2+ uptake abilities of MVs isolated from RA/Zn2+-treated cultures, suggesting that vesicles from RA/Zn2+-treated cultures did not contain functional Ca2+-Pi-phospholipid complexes. Zn2+ treatment did not affect the content of annexins II, V, and VI in MVs or the Ca2+-dependent, EDTA-reversible binding of these molecules to the membrane surface. However, Zn2+ treatment did affect the EDTA-nonreversible binding of these molecules to the MV membrane, suggesting that Zn2+ interferes with the assembly of annexins in the MV membrane. In addition, Zn2+ inhibited annexin II-, V-, and VI-mediated Ca2+ influx into liposomes. In conclusion, Zn2+ inhibits the mineralizing competence of intravesicular Ca2+-Pi-phospholipid complexes and function of annexin channels, thereby controlling Ca2+ influx into MVs, the formation of the first crystal phase inside the vesicles and initiation of mineralization.

Annexin V counteracts apoptosis while inducing Ca(2+) influx in human lymphocytic T cells

We have previously shown that when annexin V is present during the execution of a cell death program, apoptosis is delayed. This is reflected by the inhibition of DNA cleavage and of the release of apoptotic membrane particles, and by reduction of the proteolytic processing of caspase-3. Here, we have studied the mechanism(s) through which annexin V counteracts apoptosis in the human CEM T cell line. The degree of apoptosis inhibition was associated with an increase of intracellular Ca(2+) concentration ([Ca(2+)](i)). Reduction of the extracellular Ca(2+) concentration by EGTA abolished the anti-apoptotic effect, suggesting that annexin V favors Ca(2+) influx and that Ca(2+) acts as an inhibitor rather than an activator of apoptosis in CEM T cells. The effects on apoptosis and [Ca(2+)](i) of several modified annexins with different electrophysiological properties indicate that the N-terminal domain of annexin V is necessary for the Ca(2+)-dependent anti-apoptotic action of annexin V. These results suggest that annexin V regulates membrane Ca(2+) permeability and is protective against apoptosis by increasing [Ca(2+)](i) in CEM T cells.

ATP-Binding site of annexin VI characterized by photochemical release of nucleotide and infrared difference spectroscopy

Structural changes induced by nucleotide binding to porcine liver annexin VI (AnxVI) were probed by reaction-induced difference spectroscopy (RIDS). Photorelease of the nucleotide from ATP[Et(PhNO2)] produced RIDS of AnxVI characterized by reproducible changes in the amide I region. The magnitude of the infrared change was comparable to RIDS of other ATP-binding proteins, such as Ca(2+)-ATPase and creatine and arginine kinases. Analysis of RIDS revealed the existence of ATP-binding site(s) (K(d) < 1 microM) within the AnxVI molecule, comprising five to six amino acid residues located in the C-terminal portion of the protein molecule. The binding stoichiometry of ATP:AnxVI was determined as 1:1 (mol/mol). ATP, in the presence of Ca2+, induced changes in protein secondary structure reflected by a 5% decrease in alpha-helix content of the protein in favor of unordered structure. Such changes may influence the affinity of AnxVI for Ca2+ and modulate its interaction with membranes.

Protective effect of JTV519, a new 1,4-benzothiazepine derivative, on prolonged myocardial preservation

BACKGROUND

JTV519 is know to protect cardiomyocytes from calcium overloading-induced damage. The aim of this study was to investigate the potential protective effect of JTV519 on myocardium subjected to prolonged ischemia and the underlying mechanism of such protection. The effect of JTV519 was also compared with that of diltiazem, a 1,5-benzothiazepine derivative.

METHODS

Isolated rat hearts were randomly divided into three groups. Control hearts were arrested with histidine-tryptophan-ketoglutarat (HTK) cardioplegic solution alone. In the JTV519 group of hearts, cardiac arrest was achieved with JTV519 (10(-3) mmol/L) in the HTK solution. Hearts in the diltiazem group were arrested with diltiazem (0.5 mmol/L) in the HTK solution. All the hearts were then subjected to 6-hour storage in HTK solution at 4 degrees C.

RESULTS

After a 30-minute reperfusion, the left ventricular developed pressure in the JTV519 and diltiazem groups were improved significantly compared with the control group. There was a significantly lower left ventricular end-diastolic pressure level and higher recovery of coronary flow in the JTV519 group than in the control group. The postischemic intracellular calcium concentration was attenuated by adding JTV519 or diltiazem to HTK cardioplegia.

CONCLUSION

As an adjunct to cardioplegia, JTV519 showed a significant protective effect on myocardium undergoing 6 hours of ischemia. The beneficial protective effects of JTV519 are correlated with its ability to inhibit the postischemic rise in intracellular calcium.

Localization of the apoptosis-inducing activity of lupus anticoagulant in an annexin V-binding antibody subset

Lupus anticoagulant (LAC) is associated with arterial and venous thrombosis, thrombocytopenia, and recurrent fetal loss. We have reported previously that plasma with LAC activity induces apoptosis in endothelial cells and binds annexin V (Nakamura, N., Y. Shidara, N. Kawaguchi, C. Azuma, N. Mitsuda, S. Onishi, K. Yamaji, and Y. Wada. 1994. Biochem. Biophys. Res. Commun. 205:1488-1493). In this study, we separated two IgG antibody fractions, one with and one without affinity for annexin V, from 10 patients with LAC. LAC and apoptotic activities were localized in the annexin V-binding fraction in all 10 patients. DNA fragmentation was dose-dependent, paralleling the amount of IgG added to the human umbilical vein endothelial cell culture medium, and was inhibited by preincubation with annexin V. Removal of the antiphospholipid antibodies from patient IgG with phospholipid liposomes did not abolish the apoptosis-inducing activities or binding to annexin V. These results imply that patients with LAC often have antibodies that do not bind phospholipids and are responsible for the induction of apoptosis in endothelial cells.