Expression and localisation of annexin VII (synexin) isoforms in differentiating myoblasts

The potential mechanism of action of Sorcin and its interacting proteins

Sorcin (Soluble resistance-related calcium binding protein) is a calcium binding oncoprotein. Sorcin is overexpressed in several human tumors and cancer cells lines which confers multidrug resistance (MDR) to these cells. This review summarizes the biochemical functions of Sorcin which includes modulation of calcium homeostasis, apoptosis, and cancer metastasis. Sorcin is involved in various biological processes by interacting with other proteins, such as p-glycoprotein, programmed cell death protein 6, tumor necrosis factor receptor-associated protein 1, Annexin A7, polo-like kinase 1, HCV nonstructural 5A, signal transducer and activator of transcription 3, presenilin 2, α-synuclein, Ca²⁺-release channel and others. A deeper look into the function and interacting partners of Sorcin sheds more light on the possible effects of its physical activity and more elaborately, exploring the role of Sorcin in future research prospects.

A Lipid-Nanosphere-Small MyoD Activating RNA-Bladder Acellular Matrix Graft Scaffold [NP(saMyoD)/BAMG] Facilitates Rat Injured Bladder Muscle Repair and Regeneration [NP(saMyoD)/BAMG]

Background

Bladder tissue engineering is an excellent alternative to conventional gastrointestinal bladder enlargement in the treatment of various acquired and congenital bladder abnormalities. We constructed a nanosphere-small MyoD activating RNA-bladder acellular matrix graft scaffold NP(saMyoD)/BAMG inoculated with adipose-derived stem cells (ADSC) to explore its effect on smooth muscle regeneration and bladder repair function in a rat augmentation model.

Methods

We performed many biotechniques, such as reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot, MTT assay, HE staining, masson staining, and immunohistochemistry in our study. Lipid nanospheres were transfected into rat ADSCs after encapsulate saRNA-MyoD as an introduction vector. Lipid nanospheres encapsulated with saRNA-MyoD were transfected into rat ADSCs. The functional transfected rat ADSCs were called ADSC-NP(saMyoD). Then, Rat models were divided into four groups: sham group, ADSC-BAMG group, ADSC-NP(saMyoD)/BAMG group, and ADSC-NP(saMyoD)/SF(VEGF)/BAMG group. Finally, we compared the bladder function of different models by detecting the bladder histology, bladder capacity, smooth muscle function in each group.

Results

RT-PCR and Western blot results showed that ADSCs transfected with NP(saMyoD) could induce high expression of α-SMA, SM22α, and Desmin. At the same time, MTT analysis showed that NP(saMyoD) did not affect the activity of ADSC cells, suggesting little toxicity. HE staining and immunohistochemistry indicated that the rat bladder repair effect (smooth muscle function, bladder capacities) was better in the ADSC-NP(saMyoD)/BAMG group, ADSC-NP(saMyoD)/SF(VEGF)/BAMG group than in the control group.

Conclusions

Taken together, our results demonstrate that the NP(saMyoD)/SF(VEGF)/BAMG scaffold seeded with ADSCs could promote bladder morphological regeneration and improved bladder urinary function. This strategy of ADSC-NP(saMyoD)/SF(VEGF)/BAMG may has a potential to repair bladder defects in the future.

Annexin A7 expression is downregulated in late-stage gastric cancer and is negatively correlated with the differentiation grade and apoptosis rate

Annexin A7 is a member of the Annexin A family, which participates in various biological processes. Accumulating evidence has demonstrated that Annexin A7 serves an important role in tumorigenesis and is dysregulated in multiple types of cancer. However, the role of Annexin A7 in the tumorigenesis of gastric cancer remains to be determined. The present study revealed that Annexin A7 expression is downregulated in late-stage gastric cancer and is negatively correlated with the differentiation grade and apoptosis. There was a significant difference in Annexin A7 mRNA and protein expression in gastric cancer samples with distinct differentiation grades, with the lowest expression being observed in the highly differentiated cases. A terminal deoxynucleotidyl-transferase-mediated dUTP nick end labelling assay demonstrated that the apoptosis indices of highly, moderately and poorly differentiated gastric cancers were 18.12±2.40, 9.73±1.73 and 4.13±0.83%, respectively, with statistical significance (P<0.05). Flow cytometric analysis demonstrated that the apoptosis rates of gastric cancer MKN74, SGC7901 and BGC823 cells were 10.07±1.21, 7.11±1.04 and 4.25±1.02%, respectively, with statistical significance (P<0.05). Spearman's rank correlation analysis revealed that the Annexin A7 mRNA and protein levels were negatively correlated with the differentiation grade of the gastric cancer tissues, while the apoptosis index was positively correlated with the differentiation grade of the gastric cancer tissues. Furthermore, the apoptosis index was negatively correlated with Annexin A7 mRNA and protein expression. Similar associations were observed among Annexin A7 expression, differentiation grades and apoptosis in gastric cancer cell lines. The results of the present study demonstrated that Annexin A7 expression is downregulated, while apoptosis is upregulated, with the progression of gastric adenocarcinoma. These observations suggested that Annexin A7 may inhibit apoptosis during tumorigenesis and that it is a potential biomarker for the diagnosis, prognosis and treatment of gastric adenocarcinoma.

Potential roles of annexin A7 GTPase in autophagy, senescence and apoptosis

This review covers the roles of ANXA7 GTPase in orchestrating autophagy, senescence and apoptosis interactive networks in various cell types.

Influence of annexin A7 on insulin sensitivity of cellular glucose uptake

Insulin sensitivity is decreased by prostaglandin E2 (PGE2), a major product of cyclooxygenase (COX). As shown in erythrocytes, PGE2 formation is inhibited by annexin A7. The present study defined the role of annexin A7 in glucose metabolism. Gene-targeted mice lacking annexin A7 (annexin7 (-/-)) were compared to wild-type mice (annexin7 (+/+)). The serum 6-Keto-prostaglandin-F1α (6-Keto-PGF1α) concentration was measured by ELISA and hepatic COX activity determined by an enzyme assay. Expression of COX-1, COX-2, prostaglandin E synthase, GLUT-4, and insulin receptor was determined by Western blotting. Glucose and insulin serum concentrations were analyzed following an intraperitoneal glucose load and glucose serum levels after intraperitoneal injection of insulin. Experiments were done without and with pretreatment of the mice with COX-inhibitor aspirin. The serum 6-Keto-PGF1α level and hepatic COX activity were significantly higher in annexin7 (-/-) than in annexin7 (+/+) mice. Hepatic COX-1 expression was higher in annexin7 (-/-) mice. Glucose tolerance was decreased in annexin7 (-/-) mice. Intraperitoneal insulin injection decreased the serum glucose level in both genotypes, an effect significantly less pronounced in annexin7 (-/-) mice. Glucose-induced insulin secretion was higher in annexin7 (-/-) mice. GLUT-4 expression in skeletal muscle from annexin7 (-/-) mice was reduced. Aspirin pretreatment lowered the increase in insulin concentration following glucose injection in both genotypes and virtually abrogated the differences in serum insulin between the genotypes. Aspirin pretreatment improved glucose tolerance in annexin7 (-/-) mice. In conclusion, annexin A7 influences insulin sensitivity of cellular glucose uptake and thus glucose tolerance. These effects depend on COX activity.

Annexin A7 deficiency potentiates cardiac NFAT activity promoting hypertrophic signaling

Annexin A7 (Anxa7) is a cytoskeletal protein interacting with Ca(2+) signaling which in turn is a crucial factor for cardiac remodeling following cardiac injury. The present study explored whether Anxa7 participates in the regulation of cardiac stress signaling. To this end, mice lacking functional Anxa7 (anxa7(-/-)) and wild-type mice (anxa7(+/+)) were investigated following pressure overload by transverse aortic constriction (TAC). In addition, HL-1 cardiomyocytes were silenced with Anxa7 siRNA and treated with isoproterenol. Transcript levels were determined by quantitative RT-PCR, transcriptional activity by luciferase reporter assay and protein abundance by Western blotting and confocal microscopy. As a result, TAC treatment increased the mRNA and protein levels of Anxa7 in wild-type mice. Moreover, TAC increased heart weight to body weight ratio and the cardiac mRNA levels of αSka, Nppb, Col1a1, Col3a1 and Rcan1, effects more pronounced in anxa7(-/-) mice than in anxa7(+/+) mice. Silencing of Anxa7 in HL-1 cardiomyocytes significantly increased nuclear localization of Nfatc1. Furthermore, Anxa7 silencing increased NFAT-dependent transcriptional activity as well as αSka, Nppb, and Rcan1 mRNA levels both, under control conditions and following β-adrenergic stimulation by isoproterenol. These observations point to an important role of annexin A7 in the regulation of cardiac NFAT activity and hypertrophic response following cardiac stress conditions.

Identification of a small molecule preventing BMSC senescence in vitro by improving intracellular homeostasis via ANXA7 and Hmbox1

ABO was discovered to be a novel anti-aging chemical in cultured BMSCs by improving intracellular homeostasis.

Annexin A7 suppresses lymph node metastasis of hepatocarcinoma cells in a mouse model

Background

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer death in China. This study investigated the effects of Annexin A7 (ANXA7) on the inhibition of HCC lymph node metastasis in a mouse model.

Methods

The stable knockup and knockdown of Annexin A7-expressing HCC cells using Annexin A7 cDNA and shRNA vectors, respectively, were injected into a mouse footpad to establish primary and metastatic tumors in mice. On the 14th, 21st, and 28th days after HCC cells inoculation, the mice were sacrificed for inspection of primary and secondary tumors and immunohistochemistry of Annexin A7 expression.

Results

The lymph node metastasis rate of the F_{ANXA7-control} group was 77%, and the lymph node metastasis rate of the F_ANXA7-down group was 100% (p < 0.05). In contrast, the lymph node metastasis rate of the P_ANXA7-up group was 0% and that of the P_{ANXA7-control} group was 36% (p < 0.05). Furthermore, immunohistochemistry experiments revealed that the subcellular localization of Annexin A7 protein in both primary and lymph node-metastasized tumors was mainly in the cytosol. In addition, the expression of the 47 kDa and 51 kDa isoforms of Annexin A7 protein changed during tumor progression.

Conclusion

This study indicated that Annexin A7 expression was able to inhibit HCC lymph node metastasis, whereas knockdown of Annexin A7 expression significantly induced HCC metastasis to local lymph nodes.

Adhesion of annexin 7 deficient erythrocytes to endothelial cells

Annexin 7 deficiency has previously been shown to foster suicidal death of erythrocytes or eryptosis, which is triggered by increase of intracellular Ca(2+) concentration ([Ca(2+)](i)) and characterized by cell shrinkage and cell membrane scrambling with subsequent phosphatidylserine exposure at the cell surface. Eryptosis following increase of [Ca(2+)](i) by Ca(2+) ionophore ionomycin, osmotic shock or energy depletion was more pronounced in erythrocytes from annexinA7-deficient mice (anxA7(-/-)) than in erythrocytes from wild type mice (anxA7(+/+)). As phosphatidylserine exposure is considered to mediate adhesion of erythrocytes to the vascular wall, the present study explored adhesion of erythrocytes from anx7(-/-) and anx7(+/+)-mice following increase of [Ca(2+)](i) by Ca(2+) ionophore ionomycin (1 µM for 30 min), hyperosmotic shock (addition of 550 mM sucrose for 2 hours) or energy depletion (removal of glucose for 12 hours). Phosphatidylserine exposing erythrocytes were identified by annexin V binding, cell volume estimated from forward scatter in FACS analysis and adhesion to human umbilical vein endothelial cells (HUVEC) utilizing a flow chamber. As a result, ionomycin, sucrose addition and glucose removal all triggered phosphatidylserine-exposure, decreased forward scatter and enhanced adhesion of erythrocytes to human umbilical vein endothelial cells (HUVEC), effects significantly more pronounced in anx7(-/-) than in anx7(+/+)-erythrocytes. Following ischemia, morphological renal injury was significantly higher in anx7(-/-) than in anx7(+/+)-mice. The present observations demonstrate that enhanced eryptosis of annexin7 deficient cells is paralleled by increased adhesion of erythrocytes to the vascular wall, an effect, which may impact on microcirculation during ischemia.

Extracellular annexins and dynamin are important for sequential steps in myoblast fusion

Annexins A1 and A5 are important for initial lipid mixing, whereas subsequent stages of myoblast fusion depend on dynamin, phosphatidylinositol(4,5)bisphosphate, and cellular metabolism.

Myoblast fusion into multinucleated myotubes is a crucial step in skeletal muscle development and regeneration. Here, we accumulated murine myoblasts at the ready-to-fuse stage by blocking formation of early fusion intermediates with lysophosphatidylcholine. Lifting the block allowed us to explore a largely synchronized fusion. We found that initial merger of two cell membranes detected as lipid mixing involved extracellular annexins A1 and A5 acting in a functionally redundant manner. Subsequent stages of myoblast fusion depended on dynamin activity, phosphatidylinositol(4,5)bisphosphate content, and cell metabolism. Uncoupling fusion from preceding stages of myogenesis will help in the analysis of the interplay between protein machines that initiate and complete cell unification and in the identification of additional protein players controlling different fusion stages.

Strumpellin is a novel valosin-containing protein binding partner linking hereditary spastic paraplegia to protein aggregation diseases

Mutations of the human valosin-containing protein gene cause autosomal-dominant inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia. We identified strumpellin as a novel valosin-containing protein binding partner. Strumpellin mutations have been shown to cause hereditary spastic paraplegia. We demonstrate that strumpellin is a ubiquitously expressed protein present in cytosolic and endoplasmic reticulum cell fractions. Overexpression or ablation of wild-type strumpellin caused significantly reduced wound closure velocities in wound healing assays, whereas overexpression of the disease-causing strumpellin N471D mutant showed no functional effect. Strumpellin knockdown experiments in human neuroblastoma cells resulted in a dramatic reduction of axonal outgrowth. Knockdown studies in zebrafish revealed severe cardiac contractile dysfunction, tail curvature and impaired motility. The latter phenotype is due to a loss of central and peripheral motoneuron formation. These data imply a strumpellin loss-of-function pathogenesis in hereditary spastic paraplegia. In the human central nervous system strumpellin shows a presynaptic localization. We further identified strumpellin in pathological protein aggregates in inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia, various myofibrillar myopathies and in cortical neurons of a Huntington's disease mouse model. Beyond hereditary spastic paraplegia, our findings imply that mutant forms of strumpellin and valosin-containing protein may have a concerted pathogenic role in various protein aggregate diseases.

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.

Effect of Cytoskeletal Disruption on Mechanotransduction of Hydrostatic Pressure by C3H10T1/2 Murine Fibroblasts

Cyclic hydrostatic pressure of physiological magnitude (< 10 MPa) stimulates chondrogenic differentiation of mesenchymal stem cells, but mechanotransduction mechanisms are not well understood. It was hypothesized that an intact cytoskeleton would be required for uninhibited mechanotransduction of hydrostatic pressure. Therefore we examined the effects of drugs which selectively interfere with actin and tubulin polymerization on pressure-induced upregulation of aggrecan and col2a1 (type II collagen) mRNA expression. C3H10T1/2 cells were cultured as pellets in either 4µM cytochalasin D or 4µM nocodazole and subjected to 3 days of cyclic hydrostatic compression (1 Hz, 5 MPa, 2 h per day). Phalloidin staining and indirect immunostaining with anti α-tubulin antibody confirmed disruption of microfilament and microtubule assemblies, respectively. Real time RT-PCR revealed that both drugs substantially lowered the basal level of aggrecan and col2a1 mRNA, but that neither drug prevented a pressure-stimulated increase in gene expression relative to the altered basal state. Thus upregulation of macromolecular gene expression by cyclic hydrostatic pressure did not require a completely intact cytoskeleton.

Calcium- and pH-dependent localization of annexin A6 isoforms in Balb/3T3 fibroblasts reflecting their potential participation in vesicular transport

Annexin A6 (AnxA6), calcium- and membrane-binding protein, is involved in membrane dynamics. It exists in the cell in two isoforms, AnxA6-1 and AnxA6-2, varying only by the VAAEIL sequence. In most cells, AnxA6-1 predominates. A limited number of observations suggests that both isoforms differ from each other functionally. The EGF-dependent Ca(2+) influx in A431 cells is inhibited only by AnxA6-1. Moreover, AnxA6-2 was found to exhibit higher affinity for Ca(2+). In this report we addressed the potential significance of the VAAEIL deletion in AnxA6-2. For this purpose, we expressed AnxA6 isoform cDNAs in bacteria or mouse Balb/3T3 fibroblasts. The recombinant AnxA6-2 was characterized by a less extended molecular shape than that of AnxA6-1 and required a narrower [Ca(2+)] range to bind liposomes. Upon lowering pH in the presence of EGTA recombinant AnxA6-2 became less hydrophobic than AnxA6-1 as revealed by the Triton X-114 partition. Furthermore, AnxA6-2 revealed stronger F-actin binding than that of AnxA6-1. Immunofluorescence microscopy showed that the EGFP-tagged AnxA6 isoforms expressed in Balb/3T3 fibroblasts relocate in a Ca(2+)- and H(+)-sensitive manner to the vesicular structures in a perinuclear region or in cytosol. Cell fractionation showed that in resting conditions AnxA6-1 is associated with early endosomes and AnxA6-2 with late endosomes, and an increase in [Ca(2+)] and/or [H(+)] induced their opposite distribution. These findings suggest a potentially independent regulation, localization, and function of AnxA6 isoforms in Balb/3T3 fibroblasts. More generally, our findings suggest distinct functions of AnxA6 isoforms in membrane dynamics.

Localization and cellular distribution of CPNE5 in embryonic mouse brain

CPNE5 is one of the ubiquitous Ca(2+)-dependent, phospholipid-binding proteins that are highly conserved in animals. It was cloned in the fetal human brain with no exact functions identified yet. We have examined the distribution pattern of CPNE5 mRNA and protein in the developing murine brain by using in situ hybridization, western blotting and immunocytochemistry. Expression of CPNE5 mRNA remains high from embryonic day 9.5 (E9.5) to E15.5 in the developing murine brain. Whole-mount in situ hybridization with the E11.5 and E12.5 embryos showed the strong positive signals in the central nervous system. Western-blot analysis showed that CPNE5 protein is expressed in the developing but not in the adult murine brain. In situ hybridization and immunohistochemistry analysis on the embryonic brain sections indicated that both at RNA and protein levels CPNE5 is mainly expressed in frontal cortex, medial nasal prominence, ganglionic eminence and medulla, particularly in the ventricular zones. Further investigation revealed the co-localization of CPNE5 with Tuj1 and Nestin on embryonic brain sections. In addition to the slight expression in primary cultured neural progenitor cells, CPNE5 is found in soma and neurite projections of primary cultured neurons where Tuj1 is co-localized. Our results demonstrate that CPNE5 is expressed in both neural progenitor cells and the differentiated neurons during the neural development, which suggests that CPNE5 might play an important role in the development of murine central nervous system.

CREB-1alpha is recruited to and mediates upregulation of the cytochrome c promoter during enhanced mitochondrial biogenesis accompanying skeletal muscle differentiation

To further understand pathways coordinating the expression of nuclear genes encoding mitochondrial proteins, we studied mitochondrial biogenesis during differentiation of myoblasts to myotubes. This energy-demanding process was accompanied by a fivefold increase of ATP turnover, covered by an eightfold increase of mitochondrial activity. While no change in mitochondrial DNA copy number was observed, mRNAs as well as proteins for nucleus-encoded cytochrome c, cytochrome c oxidase subunit IV, and mitochondrial transcription factor A (TFAM) increased, together with total cellular RNA and protein levels. Detailed analysis of the cytochrome c promoter by luciferase reporter, binding affinity, and electrophoretic mobility shift assays as well as mutagenesis studies revealed a critical role for cyclic AMP responsive element binding protein 1 (CREB-1) for promoter activation. Expression of two CREB-1 isoforms was observed by using specific antibodies and quantitative reverse transcription-PCR, and a shift from phosphorylated CREB-1Delta in myoblasts to phosphorylated CREB-1alpha protein in myotubes was shown, while mRNA ratios remained unchanged. Chromatin immunoprecipitation assays confirmed preferential binding of CREB-1alpha in situ to the cytochrome c promoter in myotubes. Overexpression of constitutively active and dominant-negative forms supported the key role of CREB-1 in regulating the expression of genes encoding mitochondrial proteins during myogenesis and probably also in other situations of enhanced mitochondrial biogenesis.

The annexins of Dictyostelium

Annexins are a highly conserved ubiquitous family of Ca2+- and phospholipid-binding proteins present in nearly all eukaryotic cells. Analysis of the Dictyostelium genome revealed the presence of two annexin genes, the annexin C1 gene (nxnA) giving rise to two isoforms of 47 and 51 kDa (previously synexin), and the annexin C2 gene (nxnB) coding for a 56-kDa protein with 33% sequence identity to annexin C1. Annexin C2 is expressed at very low and constant levels throughout development. Quantification by real-time PCR indicated that it is present in about 35-fold lower amounts compared to annexin C1. We have used a GFP-tagged annexin C2 to study its cellular distribution and dynamics. In cell fractionation studies, annexin C2 cofractionates with annexin C1 and is enriched in the 100,000 g pellet. Like annexin C1, GFP-AnxC2 stains the plasma membrane. In addition it is present in the perinuclear region and overlaps to some degree with the Golgi apparatus, whereas annexin C1 is present on intracellular membranes resembling endosomal membranes and in the nucleus. Annexin C2 is not observed in the nucleus. An annexin C1 mutant (SYN-) which shows a defect during multicellular development can be rescued by full-length annexin C1, whereas overexpression of GFP-AnxC2 did not rescue the developmental defect The data support the concept that annexins, although having a highly conserved structure, participate in different functions in a cell.

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.

Statin therapy induces ultrastructural damage in skeletal muscle in patients without myalgia

Muscle pain and weakness are frequent complaints in patients receiving 3-hydroxymethylglutaryl coenzymeA (HMG CoA) reductase inhibitors (statins). Many patients with myalgia have creatine kinase levels that are either normal or only marginally elevated, and no obvious structural defects have been reported in patients with myalgia only. To investigate further the mechanism that mediates statin-induced skeletal muscle damage, skeletal muscle biopsies from statin-treated and non-statin-treated patients were examined using both electron microscopy and biochemical approaches. The present paper reports clear evidence of skeletal muscle damage in statin-treated patients, despite their being asymptomatic. Though the degree of overall damage is slight, it has a characteristic pattern that includes breakdown of the T-tubular system and subsarcolemmal rupture. These characteristic structural abnormalities observed in the statin-treated patients were reproduced by extraction of cholesterol from skeletal muscle fibres in vitro. These findings support the hypothesis that statin-induced cholesterol lowering per se contributes to myocyte damage and suggest further that it is the specific lipid/protein organization of the skeletal muscle cell itself that renders it particularly vulnerable.

α-Actinin 4 and BAT1 interaction with the Cytochrome c promoter upon skeletal muscle differentiation

To identify common regulatory features of nuclear genes encoding mitochondrial proteins we searched for regulatory elements in the Cytochrome c promoter during skeletal muscle differentiation in cell culture. A consensus element with the sequence GCTGCCGCAC-(N4-20)-GGSCGYGGG was found in both rat Cyt c and coxIV promoters. This new sequence element with yet undescribed function, but high abundance in promoters of nuclear genes encoding mitochondrial proteins available from the databases, showed a striking change in protein binding in electromobility shift assays when myoblasts were compared to myotubes. Proteins involved in the observed protein-DNA complexes were isolated from myotubes and identified by MALDI-TOF as BAT1, a DEAD-box protein of yet unknown function, heat shock protein HSP84, and alpha-actinin 4, a non-muscle isoform of the structural protein alpha-actinin. alpha-actinin 4 was found to be preferentially localized in the nucleus upon induction of myogenesis, suggesting a signaling function during muscle differentiation. In conclusion, the analyzed sequence motif may be a new candidate for common regulatory elements specific for nuclear encoded mitochondrial genes, and alpha-actinin 4 may be involved in their regulation.

Nuclear localization of Annexin A7 during murine brain development

BACKGROUND

Annexin A7 is a member of the annexin protein family, which is characterized by its ability to interact with phospholipids in the presence of Ca2+-ions and which is thought to function in Ca2+-homeostasis. Results from mutant mice showed altered Ca2+-wave propagation in astrocytes. As the appearance and distribution of Annexin A7 during brain development has not been investigated so far, we focused on the distribution of Annexin A7 protein during mouse embryogenesis in the developing central nervous system and in the adult mouse brain.

RESULTS

Annexin A7 is expressed in cells of the developing brain where a change in its subcellular localization from cytoplasm to nucleus was observed. In the adult CNS, the subcellular distribution of Annexin A7 depends on the cell type. By immunohistochemistry analysis Annexin A7 was detected in the cytosol of undifferentiated cells at embryonic days E5-E8. At E11-E15 the protein is still present in the cytosol of cells predominantly located in the ventricular germinative zone surrounding the lateral ventricle. Later on, at embryonic day E16, Annexin A7 in cells of the intermediate and marginal zone of the neopallium translocates to the nucleus. Neuronal cells of all areas in the adult brain present Annexin A7 in the nucleus, whereas glial fibrillary acidic protein (GFAP)-positive astrocytes exhibit both, a cytoplasmic and nuclear staining. The presence of nuclear Annexin A7 was confirmed by extraction of the nucleoplasm from isolated nuclei obtained from neuronal and astroglial cell lines.

CONCLUSION

We have demonstrated a translocation of Annexin A7 to nuclei of cells in early murine brain development and the presence of Annexin A7 in nuclei of neuronal cells in the adult animal. The role of Annexin A7 in nuclei of differentiating and mature neuronal cells remains elusive.

Annexin expression in inflammatory myopathies

The pathogenesis of the inflammatory myopathies is still unclear, making their treatment largely empirical. Improved understanding of the molecular mechanisms of inflammatory muscle injury may, however, lead to the development of more specific immunotherapies. To elucidate a possible pathogenic contribution of calcium-binding proteins such as the annexins, we immunohistochemically investigated muscle biopsy specimens from patients with dermatomyositis (10 cases), polymyositis (9 cases), and inclusion-body myositis (4 cases), compared to control cases comprising sarcoid myopathy (3 cases), Duchenne muscular dystrophy (DMD; 4 cases), and normal muscle (3 cases). We found expression of annexins A1, A2, A4, and A6 in the vascular endothelium of all cases. Myofibers expressed annexins A5, A6, and A7 diffusely and weakly in the cytosol, whereas annexins A5 and A7 were also particularly localized to the sarcolemma. In the inflammatory myopathies, in areas of myonecrosis in DMD, and in granulomatous lesions of sarcoid myopathy, reactivity of annexins A1, A2, A4, A5, and A6 was observed in macrophages and T-lymphocytes. Whereas the latter annexins appear to be nonspecific indicators of activation, annexin A1 upregulation may represent endogenous anti-inflammatory mechanisms that merit further investigation.

Enaptin, a giant actin-binding protein, is an element of the nuclear membrane and the actin cytoskeleton

Enaptin belongs to a family of recently identified giant proteins that associate with the F-actin cytoskeleton as well as the nuclear membrane. It is composed of an N-terminal alpha-actinin type actin-binding domain (ABD) followed by a long coiled coil rod and a transmembrane domain at the C-terminus. The ABD binds to F-actin in vivo and in vitro and leads to bundle formation. The human Enaptin gene spreads over 515 kb and gives rise to several splicing isoforms (Nesprin-1, Myne-1, Syne-1, CPG2). The longest assembled cDNA encompasses 27,669 bp and predicts a 1014 kDa protein. Antibodies against the ABD of Enaptin localise the protein at F-actin-rich structures throughout the cell and in focal contacts as well as at the nuclear envelope. In COS7 cells, the protein is also present within the nuclear compartment. With the discovery of the actin-binding properties of Enaptin and the highly homologous Nuance, we define a family of proteins that integrate the cytoskeleton with the nucleoskeleton.

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.

Information transfer in the penta-EF-hand protein sorcin does not operate via the canonical structural/functional pairing. A study with site-specific mutants

Sorcin is a typical penta-EF-hand protein that participates in Ca2+-regulated processes by translocating reversibly from cytosol to membranes, where it interacts with different target proteins in different tissues. Binding of two Ca2+/monomer triggers translocation, although EF1, EF2, and EF3 are potentially able to bind calcium at micromolar concentrations. To identify the functional pair, the conserved bidentate -Z glutamate in these EF-hands was mutated to yield E53Q-, E94A-, and E124A-sorcin, respectively. Limited structural perturbations occur only in E124A-sorcin due to involvement of Glu-124 in a network of interactions that comprise the long D helix connecting EF3 to EF2. The overall affinity for Ca2+ and for two sorcin targets, annexin VII and the ryanodine receptor, follows the order wild-type > E53Q- > E94A- > E124A-sorcin, indicating that disruption of EF3 has the largest functional impact and that disruption of EF2 and EF1 has progressively smaller effects. Based on this experimental evidence, EF3 and EF2, which are not paired in the canonical manner, are the functional EF-hands. Sorcin is proposed to be activated upon Ca2+ binding to EF3 and transmission of the conformational change at Glu-124 via the D helix to EF2 and from there to EF1 via the canonical structural/functional pairing. This mechanism may be applicable to all penta-EF-hand proteins.

Oligomerization, F-actin interaction, and membrane association of the ubiquitous mammalian coronin 3 are mediated by its carboxyl terminus

Coronin 3 is a ubiquitously expressed member of the coronin protein family in mammals. In fibroblasts and HEK 293 cells, it is localized both in the cytosol and in the submembranous cytoskeleton, especially at lamellipodia and membrane ruffles. The carboxyl terminus of all coronins contains a coiled coil suggested to mediate dimerization. We show here that in contrast to other coronin homologues, the recombinant human coronin 3 carboxyl terminus forms oligomers rather than dimers, and that this part is sufficient to bind to and cross-link F-actin in vitro. The carboxyl terminus alone also conferred membrane association in vivo, and removal of the coiled coil abolished membrane localization but not in vitro F-actin binding. Coronin 3 is exclusively extracted as an oligomer from both the cytosol and the membrane fraction. Because oligomerization was not reported for other coronins, it might be a key feature governing coronin 3-specific functions. Cytosolic coronin 3 showed a high degree of phosphorylation, which is likely to regulate the subcellular localization of the protein.

Kinetics and thermodynamics of annexin A1 binding to solid-supported membranes: a QCM study

By means of the quartz crystal microbalance (QCM) technique, the interaction of annexin A1 with lipid membranes was quantified using solid-supported bilayers immobilized on gold electrodes deposited on 5 MHz quartz plates. Solid-supported lipid bilayers were composed of a first octanethiol monolayer chemisorbed on gold and a physisorbed phospholipid monolayer obtained from vesicle fusion. This experimental setup enabled us to determine for the first time rate constants and affinity constants of annexin A1 binding to phosphatidylserine-containing layers as a function of the calcium ion concentration in solution and the cholesterol content within the outer leaflet of the solid-supported bilayer. The results reveal that a decrease in Ca(2+) concentration from 1 mM to 100 microM significantly increases the rate of annexin A1 binding to the membrane independent of the cholesterol content. However, the presence of cholesterol in the membrane altered the affinity constants considerably. While the association constant decreases with decreasing Ca(2+) concentration in the case of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine (POPS) membranes lacking cholesterol, it remains high in the presence of cholesterol.

Ca(++)-dependent vesicle release from erythrocytes involves stomatin-specific lipid rafts, synexin (annexin VII), and sorcin

Cytosolic Ca(++) induces the shedding of microvesicles and nanovesicles from erythrocytes. Atomic force microscopy was used to determine the sizes of these vesicles and to resolve the patchy, fine structure of the microvesicle membrane. The vesicles are highly enriched in glycosyl phosphatidylinositol-linked proteins, free of cytoskeletal components, and depleted of the major transmembrane proteins. Both types of vesicles contain 2 as-yet-unrecognized red cell proteins, synexin and sorcin, which translocate from the cytosol to the membrane upon Ca(++) binding. In nanovesicles, synexin and sorcin are the most abundant proteins after hemoglobin. In contrast, the microvesicles are highly enriched in stomatin. The membranes of both microvesicles and nanovesicles contain lipid rafts. Stomatin is the major protein of the microvesicular lipid rafts, whereas synexin and sorcin represent the major proteins of the nanovesicular rafts in the presence of Ca(++). Interestingly, the raft proteins flotillin-1 and flotillin-2 are not found in the vesicles but remain in the red cell membrane. These data indicate the presence of different types of lipid rafts in the erythrocyte membrane with distinct fates after Ca(++) entry. Synexin, which is known to be vital to the process of membrane fusion, is suggested to be a key component in the process of vesicle release from erythrocytes.

Annexins: from structure to function

Annexins are Ca2+ and phospholipid binding proteins forming an evolutionary conserved multigene family with members of the family being expressed throughout animal and plant kingdoms. Structurally, annexins are characterized by a highly alpha-helical and tightly packed protein core domain considered to represent a Ca2+-regulated membrane binding module. Many of the annexin cores have been crystallized, and their molecular structures reveal interesting features that include the architecture of the annexin-type Ca2+ binding sites and a central hydrophilic pore proposed to function as a Ca2+ channel. In addition to the conserved core, all annexins contain a second principal domain. This domain, which NH2-terminally precedes the core, is unique for a given member of the family and most likely specifies individual annexin properties in vivo. Cellular and animal knock-out models as well as dominant-negative mutants have recently been established for a number of annexins, and the effects of such manipulations are strikingly different for different members of the family. At least for some annexins, it appears that they participate in the regulation of membrane organization and membrane traffic and the regulation of ion (Ca2+) currents across membranes or Ca2+ concentrations within cells. Although annexins lack signal sequences for secretion, some members of the family have also been identified extracellularly where they can act as receptors for serum proteases on the endothelium as well as inhibitors of neutrophil migration and blood coagulation. Finally, deregulations in annexin expression and activity have been correlated with human diseases, e.g., in acute promyelocytic leukemia and the antiphospholipid antibody syndrome, and the term annexinopathies has been coined.

Loss of annexin A7 leads to alterations in frequency-induced shortening of isolated murine cardiomyocytes

Annexin A7 has been proposed to function in the fusion of vesicles, acting as a Ca(2+) channel and as Ca(2+)-activated GTPase, thus inducing Ca(2+)/GTP-dependent secretory events. To understand the function of annexin A7, we have performed targeted disruption of the Anxa7 gene in mice. Matings between heterozygous mice produced offspring showing a normal Mendelian pattern of inheritance, indicating that the loss of annexin A7 did not interfere with viability in utero. Mice lacking annexin A7 showed no obvious phenotype and were fertile. To assay for exocytosis, insulin secretion from isolated islets of Langerhans was examined. Ca(2+)-induced and cyclic AMP-mediated potentiation of insulin secretion was unchanged in the absence of annexin A7, suggesting that it is not directly implicated in vesicle fusion. Ca(2+) regulation studied in isolated cardiomyocytes, showed that while cells from early embryos displayed intact Ca(2+) homeostasis and expressed all of the components required for excitation-contraction coupling, cardiomyocytes from adult Anxa7(-/-) mice exhibited an altered cell shortening-frequency relationship when stimulated with high frequencies. This suggests a function for annexin A7 in electromechanical coupling, probably through Ca(2+) homoeostasis.

Annexin VII: an astroglial protein exhibiting a Ca2+-dependent subcellular distribution

A fundamental issue in neuronal and glial cells is how intracellular rises in Ca2+ are coupled to signaling cascades and changes in subcellular morphology. We studied the expression and localization of annexin VII (synexin), a Ca(2+)-/GTP-dependent membrane fusion protein, in the human CNS. Here, we demonstrate the presence of two annexin VII isoforms (47 and 51 kDa) in human brain tissue as well as its exclusive expression in astroglial cells. An in vitro study of astrocyte-derived C6 rat glioblastoma cells expressing a GFP tagged annexin VII fusion protein demonstrates a sequential redistribution of the fusion protein in response to rising intracellular Ca2+ concentrations. Our findings indicate a role of annexin VII in the regulation of intracellular Ca(2+)-dependent processes in astroglial cells.

Cholesterol enhances phospholipid binding and aggregation of annexins by their core domain

Annexins are Ca(2+)-dependent phospholipid-binding proteins composed of two domains: A conserved core that is responsible for Ca(2+)- and phospholipid-binding, and a variable N-terminal tail. A Ca(2+)-independent annexin 2-membrane association has been shown to be modulated by the presence of cholesterol in the membranes. Herein, the roles of the core and the N-terminal tail on the cholesterol-enhancement of annexin 2 membrane binding and aggregation were studied. The results show that (i) the cholesterol-mediated increase in membrane binding and in the Ca(2+) sensitivity for membrane aggregation were not modified by a N-terminal peptide (residues 15-26), and were conserved in mutants of the N-terminal end (S11 and S25 substitutions); (ii) cholesterol induced an increase in the Ca(2+)-dependent membrane binding and aggregation of the N-terminally truncated protein (Delta 1-29); and (iii) annexins 5 and 6, two proteins with unrelated N-terminal tails and homologous core domains showed a cholesterol-mediated enhancement of the Ca(2+)-dependent binding to membranes. These data indicate that the core domain is responsible for the cholesterol-mediated effects. A model for the cholesterol effect in membrane organisation, annexin binding and aggregation is discussed.

Parvin, a 42 kDa focal adhesion protein, related to the alpha-actinin superfamily

We have identified and cloned a novel 42-kDa protein termed alpha-parvin, which has a single alpha-actinin-like actin-binding domain. Unlike other members of the alpha-actinin superfamily, which are large multidomain proteins, alpha-parvin lacks a rod domain or any other C-terminal structural modules and therefore represents the smallest known protein of the superfamily. We demonstrate that mouse alpha-parvin is widely expressed as two mRNA species generated by alternative use of two polyadenylation signals. We analyzed the actin-binding properties of mouse alpha-parvin and determined the K(d) with muscle F-actin to be 8.4+/-2.1 microM. The GFP-tagged alpha-parvin co-localizes with actin filaments at membrane ruffles, focal contacts and tensin-rich fibers in the central area of fibroblasts. Domain analysis identifies the second calponin homology domain of parvin as a module sufficient for targeting the focal contacts. In man and mouse, a closely related paralogue beta-parvin and a more distant relative gamma-parvin have also been identified and cloned. The availability of the genomic sequences of different organisms enabled us to recognize closely related parvin-like proteins in flies and worms, but not in yeast and Dictyostelium. Phylogenetic analysis of alpha-parvin and its para- and orthologues suggests, that the parvins represent a new family of alpha-actinin-related proteins that mediate cell-matrix adhesion.

The sorcin-annexin VII calcium-dependent interaction requires the sorcin N-terminal domain

Surface plasmon resonance experiments show that at neutral pH the stability of the complex between sorcin and annexin VII (synexin) increases dramatically between 3 and 6 microM calcium; at the latter cation concentration the K(D) value is 0.63 microM. In turn, the lack of complex formation between the sorcin Ca(2+) binding domain (33-198) and synexin maps the annexin binding site to the N-terminal region of the sorcin polypeptide chain. Annexin VII likewise employs the N-terminal domain, more specifically the first 31 amino acids, to interact with sorcin [Brownawell, A.M. and Creutz, C.E. (1997) J. Biol. Chem. 272, 22182-22190]. The interaction may involve similar structural motifs in the two proteins, namely GGYY and GYGG in sorcin and GYPP in synexin.