Impact of Annexin A 7 Deficiency on FGF23 Plasma Concentrations.

BACKGROUND/AIMS: The release of fibroblast growth factor FGF23, a powerful regulator of 1,25(OH)2D3 formation and mineral metabolism, is stimulated by store-operated Ca2+ entry (SOCE), which is accomplished by the pore forming Ca2+ release activated channel protein Orai1. Regulators of Orai1 and thus FGF23 release include serum & glucocorticoid inducible kinase SGK1, a kinase up-regulated by glucocorticosteroids. Some effects of glucocorticoids require the presence of annexin A7, such as suppression of prostaglandin E2 in gastric glands. The present study thus explored whether annexin A7 impacts on FGF23 plasma levels. METHODS: Comparisons were made between gene targeted mice lacking functional annexin A7 (Anx7-/-) and their wild type littermates (Anx7+/+). Serum C-terminal-FGF23, intact FGF23, 1,25(OH)2D3 and PTH concentrations were measured by ELISA or EIA. The serum and urinary phosphate concentrations were measured by colorimetry, the serum Ca2+ concentration and the urinary Ca2+ concentration by flame photometry. RESULTS: Serum C-terminal FGF23 levels and corticosterone levels were significantly higher and serum 1,25(OH)2 D3 and PTH levels were significantly lower in Anx7-/- than in Anx7+/+ mice. Water intake was slightly but significantly higher in Anx7-/- mice than in Anx7+/+ mice. No significant difference was observed between Anx7-/- and Anx7+/+ mice in urinary fluid excretion, plasma Ca2+ concentration, plasma phosphate concentration and urinary Ca2+ output. The urinary phosphate output was significantly lower in Anx7-/- mice than in Anx7+/+ mice. CONCLUSION: Annexin A7 deficiency upregulates FGF23 plasma levels, an effect paralleled by increased corticosterone plasma levels, as well as decreased 1,25(OH)2 D3 and PTH plasma levels.

The Anx7(+/-) knockout mutation alters electrical and secretory responses to Ca(2+)-mobilizing agents in pancreatic ß-cells.

Insulin secretion from the pancreatic ß-cell is controlled by changes in membrane potential and intracellular Ca(2+). The contribution of intracellular Ca(2+) stores to this process is poorly understood. We have previously shown that ß-cells of mice lacking one copy of the Annexin 7 gene (Anx7(+/-)) express reduced levels of IP(3) receptors and defects in IP(3)-dependent Ca(2+) signaling. To further elucidate the effect of the Anx7(+/-) mutation on signaling related to intracellular Ca(2+) stores in the ß-cell, we measured the effects of Ca(2+) mobilizing agents on electrical activity, intracellular Ca(2+) and insulin secretion in control and mutant ß-cells. We found that the muscarinic agonist carbachol and the ryanodine receptor agonists caffeine and 4-chloro-m-cresol had more potent depolarizing effects on Anx7(+/-) ß-cells compared to controls. Accordingly, glucose-induced insulin secretion was augmented to a greater extent by caffeine in mutant islets. Surprisingly, ryanodine receptor-mediated Ca(2+) mobilization was not affected by the Anx7(+/-) mutation, suggesting that the mechanism underlying the observed differences in electrical and secretory responsiveness does not involve intracellular Ca(2+) stores. Our results provide evidence that both IP3 receptors and ryanodine receptors play important roles in regulating ß-cell membrane potential and insulin secretion, and that the Anx7(+/-) mutation is associated with alterations in the signaling pathways related to these receptors.

Arthritogenicity of annexin VII revealed by phosphoproteomics of rheumatoid synoviocytes.

OBJECTIVE: To identify novel proteins involved in the pathogenesis of rheumatoid arthritis (RA) and to characterise the identified proteins based on pathogenic and therapeutic aspects. METHODS: The authors applied differential phosphoproteomic analysis to articular synoviocytes between RA and osteoarthritis (OA) to identify proteins differently phosphorylated between RA and OA. Focusing on annexin VII (Anx7), one of the highly phosphorylated proteins in RA, the authors prepared Anx7-transgenic C57BL/6 (Anx7-Tg-B6) mice to evaluate their susceptibility to collagen-induced arthritis (CIA). In addition, the authors examined the effect of anti-Anx7 antibodies (Abs) on CIA and serum levels of cytokines in wild-type DBA/1J mice, which are known to be susceptible to CIA, and in Anx7-Tg-B6 mice. In vitro, the authors examined the effect of the Anx7 knockdown by small interfering RNA on the secretion of cytokines in rheumatoid synoviocytes and the human synovial sarcoma cell line SW982. RESULTS: The Anx7 transgene altered the CIA-resistant B6 mice to CIA-susceptible ones. The Abs treatment suppressed CIA even in the wild-type DBA/1J mice. The serum levels of cytokines including interleukin 6 (IL-6) and TNFα were not altered by the Abs treatment in vivo. On the other hand, the knockdown of Anx7 by small interfering RNA caused downregulation of IL-8 secretion in vitro. CONCLUSIONS: These results indicate that Anx7 participates in the pathogenesis of RA partly through the secretion of IL-8. The study data have demonstrated the pathogenic roles and therapeutic significance of Anx7 in RA for the first time.

Enhanced eryptosis of erythrocytes from gene-targeted mice lacking annexin A7.

Annexin A7 is a ubiquitously expressed Ca(2+)- and phospholipid-binding protein. Erythrocytes from mice lacking annexin A7 (anxA7(-/-)) are deformed and relatively resistant to osmotic swelling. In normal erythrocytes, hyperosmotic shock, Cl(-) removal, and energy depletion (glucose removal) trigger PGE(2) formation, which stimulates Ca(2+)-permeable cation channels, increases cytosolic Ca(2+) activity ([Ca(2+)](i)), and thus triggers suicidal death of erythrocytes or eryptosis, characterized by scrambling of the cell membrane with phosphatidylserine exposure at the cell surface. The present experiments explored the influence of annexin A7 deficiency on eryptosis. In erythrocytes from annexin A7-deficient mice (anxA7(-/-)) and wild-type mice (anxA7(+/+)), PGE(2) formation was determined utilizing an immunoassay, ion channel activity by whole-cell patch clamp recording, [Ca(2+)](i) by fluo3 fluorescence, and phosphatidylserine exposure by binding of annexin A5 in fluorescence activated cell sorter (FACS) analysis. Erythrocyte number and hematocrit were significantly smaller in blood from anx7(-/-) than in anx7(+/+) mice. Cl(-)-removal (replacement with gluconate) stimulated PGE(2)-formation, activated cation currents, increased [Ca(2+)](i), and triggered phosphatidylserine exposure, effects significantly more pronounced in anx7(-/-) than in anx7(+/+) erythrocytes. Hyperosmotic shock (addition of 400 mM sucrose) and glucose depletion (removal of glucose) similarly increased cytosolic Ca(2+) activity and triggered phosphatidylserine exposure, effects again significantly more pronounced in anx7(-/-) than in anx7(+/+) erythrocytes. The effects of Cl(-) removal on PGE(2) formation and the cation current, as well as the effect of hypertonic cell shrinkage on [Ca(2+)](i) and cell membrane scrambling, were blunted following inhibition of cyclooxygenase by aspirin or diclofenac. In conclusion, lack of annexin A7 sensitizes the erythrocytes for "proapoptotic" Ca(2+) overload, an effect shortening the life span of the affected erythrocytes and, thus, leading to anemia.

Enhanced heterogeneity of myocardial conduction and severe cardiac electrical instability in annexin A7-deficient mice.

OBJECTIVES: Annexin A7 is involved in cardiomyocyte membrane organization and Ca(2+)-dependent signalling processes. We investigated the impact of annexin A7 on cardiac electrophysiological properties using an annexin A7-deficient mouse strain (annexin A7(-/-)). METHODS: Nineteen adult annexin A7(-/-) and 14 wild-type mice were examined electrophysiologically in vivo by transvenous catheterization. Hearts were additionally perfused by the Langendorff method and epicardial activation mapping was performed. RESULTS: The susceptibility to induction of atrial fibrillation was elevated in annexin A7(-/-) mice. Ten deficient animals showed atrial fibrillation (AF) episodes > or =1 min and sustained AF > or =30 min was observed in 4 annexin A7(-/-) mice, but in none of the wild-type mice. The incidence of ventricular tachycardia (VT) was higher in annexin A7(-/-) mice and VT duration was prolonged. Epicardial mapping showed elevated anisotropy and inhomogeneity of conduction, leading to conduction blocks in the deficient mice. Besides alterations of intracellular calcium homeostasis, electron microscopy showed a homogeneous, electron-dense material that filled the myocardial intercellular compartments and accumulated at the basement membranes. This led to expansion of the extracellular spaces, which was the most probable substrate factor responsible for the disturbances of electrical communication. CONCLUSIONS: Annexin A7 deficiency causes severe electrical instability in the murine heart, including conduction disturbances and anisotropy of impulse propagation, which is accompanied by disturbed calcium handling and intercellular deposits.

Annexin 7 mobilizes calcium from endoplasmic reticulum stores in brain.

Mobilization of intracellular calcium from inositol-1,4,5-triphosphate (IP3)-sensitive endoplasmic reticulum (ER) stores plays a prominent role in brain function. Mice heterozygous for the annexin A7 (Anx7) gene have a profound reduction in IP3 receptor function in pancreatic islets along with defective insulin secretion. We examined IP3-sensitive calcium pools in the brains of Anx7 (+/-) mice by utilizing ATP/Mg(2+)-dependent (45)Ca(2+) uptake into brain membrane preparations and tissue sections. Although the Anx7 (+/-) mouse brain displayed similar levels of IP3 binding sites and thapsigargin-sensitive (45)Ca(2+) uptake as that seen in wild-type mouse brain, the Anx7 (+/-) mouse brain Ca(2+) pools showed markedly reduced sensitivity to IP3. A potent and saturable Ca(2+)-releasing effect of recombinant ANX7 protein was demonstrated in mouse and rat brain membrane preparations, which was additive with that of IP3. We propose that ANX7 mobilizes Ca(2+) from an endoplasmic reticulum-like pool, which can be recruited to enhance IP3-mediated Ca(2+) release.

Influence of the Anx7 (+/-) knockout mutation and fasting stress on the genomics of the mouse adrenal gland.

The Anx7 gene codes for a Ca(2+)/GTPase with calcium channel and membrane fusion properties that has been proposed to regulate exocytotic secretion in chromaffin and other cell types. We have previously reported that the homozygous Anx7 (+/-) knockout mouse has an embryonically lethal phenotype. However, the viable heterozygous Anx7 (+/-) mouse displays a complex phenotype that includes adrenal gland hypertrophy, chromaffin cell hyperplasia, and defective IP(3) receptor (IP(3)R) expression. To search for a molecular basis for this phenotype, we have used cDNA microarray technology and have challenged control and mutant mice with fed or fasting conditions. We report that in the absence of the Anx7/IP(3)R signaling system, the cells in the adrenal gland are unable to discriminate between the fed and fasted states, in vivo. In control chromaffin cells, fasting is accompanied by an increased expression of structural genes for chromaffin cell contents, including chromogranin A and B, and DbetaH. There are also genes whose expression is specifically reduced. However, the Anx7 (+/-) mutation results in sustained expression of these nutritionally sensitive genes. We hypothesize that the calcium signaling defect due to the missing IP(3)R may be responsible for the global effects of the mutation on nutritionally sensitive genes. We further hypothesize that the tonically elevated expression of chromogranin A, a reportedly master control "switch" for dense core granule formation, may contribute to the process driving glandular hypertrophy and chromaffin cell hyperplasia in the Anx7 (+/-) mutant mouse.

Function, expression and localization of annexin A7 in platelets and red blood cells: insights derived from an annexin A7 mutant mouse.

BACKGROUND: Annexin A7 is a Ca2+- and phospholipid-binding protein expressed as a 47 and 51 kDa isoform, which is thought to be involved in membrane fusion processes. Recently the 47 kDa isoform has been identified in erythrocytes where it was proposed to be a key component in the process of the Ca2+-dependent vesicle release, a process with which red blood cells might protect themselves against an attack by for example complement components. RESULTS: The role of annexin A7 in red blood cells was addressed in erythrocytes from anxA7-/- mice. Interestingly, the Ca2+-mediated vesiculation process was not impaired. Also, the membrane organization appeared not to be disturbed as assessed using gradient fractionation studies. Instead, lack of annexin A7 led to an altered cell shape and increased osmotic resistance of red blood cells. Annexin A7 was also identified in platelets. In these cells its loss led to a slightly slower aggregation velocity which seems to be compensated by an increased number of platelets. The results appear to rule out an important role of annexin A7 in membrane fusion processes occurring in red blood cells. Instead the protein might be involved in the organization of the membrane cytoskeleton. Red blood cells may represent an appropriate model to study the role of annexin A7 in cellular processes. CONCLUSION: We have demonstrated the presence of both annexin A7 isoforms in red blood cells and the presence of the small isoform in platelets. In both cell types the loss of annexin A7 impairs cellular functions. The defects observed are however not compatible with a crucial role for annexin A7 in membrane fusion processes in these cell types.

Expression and localization of annexin A7 in the rat lithium-pilocarpine model of acquired epilepsy.

BACKGROUND: Annexin A7 (synexin, ANXA7) is a member of annexins, which plays an essential role in the regulation of calcium homeostasis. Considerable evidence shows that the pathogenetic mechanism of acquired epilepsy (AE) has been related to the imbalance of calcium homeostasis. The aim of this study was to investigate ANXA7 expression and cellular localization in the cortex and hippocampus in the rat lithium-pilocarpine model of AE. METHODS: Totally 81 adult healthy male Wistar rats were randomly divided into control group (n = 9) and experimental group (n = 72), the experimental group contained eight subgroups according to sacrifice time (n = 9) (6-hour, 24-hour, 48-hour, 72-hour, 7-day, 15-day, 1-month, and 2-month). In the experimental group, rats were intraperitoneally injected by lithium-pilocarpine to induce AE model. We examined the expression and localization of ANXA7 via immunohistochemistry, double-label immunofluorescence with the use of neuron specific enolase (NSE) antibody, glial fibrillary acidic protein (GFAP) antibody and propidium iodide (PI), respectively. The data of optical density value were analyzed by analysis of variance. RESULTS: ANXA7 expression increased significantly in the experimental groups especially in the acute period (6 hours, 24 hours, and 48 hours after the onset of seizure) using immunohistochemistry. Double-label immunofluorescence and confocal microscopy disclosed that ANXA7 localized in the neurons but not in astrocytes and did not localize in the nucleus, which were performed with anti-NSE, anti-GFAP and PI respectively. CONCLUSION: ANXA7 may play a potential role in the pathogenetic mechanisms of the rat lithium-pilocarpine model of AE.

Antiviral effect of Phyllanthus nanus ethanolic extract against hepatitis B virus (HBV) by expression microarray analysis.

Ethanolic extract of Phyllanthus nanus (P. nanus) treatment exhibited potent antiviral activity against Hepatitis B virus (HBV). The effects of these extracts on HBV in the HBV genome integrated cell lines--Alexander cells and HepG2 2.2.15 cells were examined. Experimental results showed that the ethanolic extract of P. nanus produced suppressive effect on HBsAg secretion and HBsAg mRNA expression. The extract also inhibited HBV replication as measured by HBV DNA level in vitro. In addition, using a duck HBV (DHBV) primary culture model, the P. nanus ethanolic extract suppressed viral replication of DHBV in DHBV infected primary duck hepatocytes. The gene expression pattern in Alexander cells that had been treated with the ethanolic extract of P. nanus was also revealed by microarray techniques. The microarray results indicated that there was up-regulation of expression of several genes, including annexin A7 (Axn7). The subcellular localization of Axn7 and anti-HBV effect of Axn7 over-expression in Alexander cells were also investigated. Results showed that expression of Axn7-GFP fusion protein are localized around the secretory vesicles and could cause a decrease in HBsAg secretion in Alexander cells. Axn7 protein might play an important role in the medicinal effect of the active principle(s) of P. nanus.

Distinct effects of annexin A7 and p53 on arachidonate lipoxygenation in prostate cancer cells involve 5-lipoxygenase transcription.

Tumor suppressor function for Annexin A7 (ANXA7; 10q21) is based on cancer-prone phenotype in Anxa7(+/-) mouse and ANXA7 prognostic role in human cancers. Because ANXA7-caused liposome aggregation can be promoted by arachidonic acid (AA), we hypothesized that the phospholipid-binding tumor suppressor ANXA7 is associated with AA cascade. In a comparative study of ANXA7 versus canonical tumor suppressor p53 effects on AA lipoxygenation pathway in the p53-mutant and androgen-insensitive DU145 prostate cancer cells, both tumor suppressors altered gene expression of major 5-lipoxygenase (LOX) and 15-LOXs, including response to T helper 2 (Th2)-cytokine [interleukin-4 (IL-4)] and endogenous steroids (mimicked by dexamethasone). Wild-type and mutant ANXA7 distinctly affected expression of the dexamethasone-induced 15-LOX-2 (a prostate-specific endogenous tumor suppressor) as well as the IL-4-induced 15-LOX-1. On the other hand, wild-type p53 restored 5-LOX expression in DU145 to levels comparable to benign prostate epithelial cells. Using mass spectrometry of DNA affinity-enriched nuclear proteins, we detected different proteins that were bound to adjacent p53 and estrogen response elements in the 5-LOX promoter in DU145 cells introduced with ANXA7 versus p53. Sex hormone regulator 17-beta hydroxysteroid dehydrogenase 4 was identified under p53 introduction, which induced the 5-LOX expression. Meantime, nuclear proteins bound to the same 5-LOX promoter site under introduction of ANXA7 (that was associated with the repressed 5-LOX) were identified as zinc finger proteins ZNF433 and Aiolos, pyrin domain-containing NALP10, and the p53-regulating DNA repair enzyme APEX1. Thus, ANXA7 and p53 can distinctly regulate LOX transcription that is potentially relevant to the AA-mediated cell growth control in tumor suppression.

Protein kinase C and guanosine triphosphate combine to potentiate calcium-dependent membrane fusion driven by annexin 7.

Exocytotic secretion is promoted by the concerted action of calcium, guanine nucleotide, and protein kinase C. We now show that the calcium-dependent membrane fusion activity of annexin 7 in vitro is further potentiated by the combined addition of guanine nucleotide and protein kinase C. The observed increment involves the simultaneous activation of annexin 7 by these two effectors. Guanosine triphosphate (GTP) and its non-hydrolyzable analogues optimally enhance the phosphorylation of annexin 7 by protein kinase C in vitro. Reciprocally, phosphorylation by protein kinase C significantly potentiates the binding and hydrolysis of GTP by annexin 7. Only protein kinase C-dependent phosphorylation has a significant positive effect on annexin 7 GTPase, although other protein kinases, including cAMP-dependent protein kinase, cGMP-dependent protein kinase, and pp60(c-)(src), have been shown to label the protein with high efficiency. In vivo, the ratio of bound GDP/GTP and phosphorylation of annexin 7 change in direct proportion to the extent of catecholamine release from chromaffin cells in response to stimulation by carbachol, or to inhibition by various protein kinase C inhibitors. These results thus lead us to hypothesize that annexin 7 may serve as a common site of action for calcium, guanine nucleotide, and protein kinase C in the exocytotic membrane fusion process in chromaffin cells.

Membrane fusion protein synexin (annexin VII) as a Ca2+/GTP sensor in exocytotic secretion.

Exocytotic membrane fusion and secretion are promoted by the concerted action of GTP and Ca2+, although the precise site(s) of action in the process are not presently known. However, the calcium-dependent membrane fusion reaction driven by synexin (annexin VII) is an in vitro model for this process, which we have now found to be further activated by GTP. The mechanism of fusion activation depends on the unique ability of synexin to bind and hydrolyze GTP in a calcium-dependent manner, both in vitro and in vivo in streptolysin O-permeabilized chromaffin cells. The required [Ca2+] for GTP binding by synexin is in the range of 50-200 microM, which is known to occur at exocytotic sites in chromaffin cells, neurons, and other cell types. Previous immunolocalization studies place synexin at exocytotic sites in chromaffin cells, and we conclude that synexin is an atypical G protein that may be responsible for both detecting and mediating the Ca2+/GTP signal for exocytotic membrane fusion.

Defects in inositol 1,4,5-trisphosphate receptor expression, Ca(2+) signaling, and insulin secretion in the anx7(+/-) knockout mouse.

The mammalian anx7 gene codes for a Ca(2+)-activated GTPase, which supports Ca(2+)/GTP-dependent secretion events and Ca(2+) channel activities in vitro and in vivo. To test whether anx7 might be involved in Ca(2+) signaling in secreting pancreatic beta cells, we knocked out the anx7 gene in the mouse and tested the insulin-secretory properties of the beta cells. The nullizygous anx7 (-/-) phenotype is lethal at embryonic day 10 because of cerebral hemorrhage. However, the heterozygous anx7 (+/-) mouse, although expressing only low levels of ANX7 protein, is viable and fertile. The anx7 (+/-) phenotype is associated with a substantial defect in insulin secretion, although the insulin content of the islets, is 8- to 10-fold higher in the mutants than in the normal littermate control. We infer from electrophysiological studies that both glucose-stimulated secretion and voltage-dependent Ca(2+) channel functions are normal. However, electrooptical recordings indicate that the (+/-) mutation has caused a change in the ability of inositol 1,4,5-trisphosphate (IP(3))-generating agonists to release intracellular calcium. The principle molecular consequence of lower anx7 expression is a profound reduction in IP(3) receptor expression and function in pancreatic islets. The profound increase in islets, beta cell number, and size may be a means of compensating for less efficient insulin secretion by individual defective pancreatic beta cells. This is a direct demonstration of a connection between glucose-activated insulin secretion and Ca(2+) signaling through IP(3)-sensitive Ca(2+) stores.

The in vivo role of annexin VII (synexin): characterization of an annexin VII-deficient Dictyostelium mutant indicates an involvement in Ca(2+)-regulated processes.

Dictyostelium discoideum cells harbor two annexin VII isoforms of 47 and 51 kDa which are present throughout development. In immunofluorescence and cell fractionation studies annexin VII was found in the cytoplasm and on the plasma membrane. In gene disruption mutants lacking both annexin VII isoforms growth, pinocytosis, phagocytosis, chemotaxis and motility were not significantly impaired under routine laboratory conditions, and the cells were able to complete the developmental cycle on bacterial plates. On non-nutrient agar plates development was delayed by three to four hours and a significant number of aggregates was no longer able to form fruiting bodies. Exocytosis as determined by measuring extracellular cAMP phosphodiesterase, alpha-fucosidase and alpha-mannosidase activity was unaltered, the total amounts of these enzymes were however lower in the mutant than in the wild type. The mutant cells were markedly impaired when they were exposed to low Ca2+ concentrations by adding EGTA to the nutrient medium. Under these conditions growth, motility and chemotaxis were severely affected. The Ca2+ concentrations were similar in mutant and wild-type cells both under normal and Ca2+ limiting conditions; however, the distribution was altered under low Ca2+ conditions in SYN-cells. The data suggest that annexin VII is not required for membrane fusion events but rather contributes to proper Ca2+ homeostasis in the cell.