Complete structure of the murine p36 (annexin II) gene. Identification of mRNAs for both the murine and the human gene with alternatively spliced 5' noncoding exons

Annexin A2 Acts as an Adhesion Molecule on the Endometrial Epithelium during Implantation in Mice

To determine the function of Annexin A2 (Axna2) in mouse embryo implantation in vivo, experimental manipulation of Axna2 activities was performed in mouse endometrial tissue in vivo and in vitro. Histological examination of endometrial tissues was performed throughout the reproduction cycle and after steroid treatment. Embryo implantation was determined after blockage of the Axna2 activities by siRNA or anti-Axna2 antibody. The expression of Axna2 immunoreactivies in the endometrial luminal epithelium changed cyclically in the estrus cycle and was upregulated by estrogen. After nidatory estrogen surge, there was a concentration of Axna2 immunoreactivities at the interface between the implanting embryo and the luminal epithelium. The phenomenon was likely to be induced by the implanting embryos as no such concentration of signal was observed in the inter-implantation sites and in pseudopregnancy. Knockdown of Axna2 by siRNA reduced attachment of mouse blastocysts onto endometrial tissues in vitro. Consistently, the number of implantation sites was significantly reduced after infusion of anti-Axna2 antibody into the uterine cavity. Steroids and embryos modulate the expression of Axna2 in the endometrial epithelium. Axna2 may function as an adhesion molecule during embryo implantation in mice.

Annexin A2 heterotetramer: structure and function

Annexin A2 is a pleiotropic calcium- and anionic phospholipid-binding protein that exists as a monomer and as a heterotetrameric complex with the plasminogen receptor protein, S100A10. Annexin A2 has been proposed to play a key role in many processes including exocytosis, endocytosis, membrane organization, ion channel conductance, and also to link F-actin cytoskeleton to the plasma membrane. Despite an impressive list of potential binding partners and regulatory activities, it was somewhat unexpected that the annexin A2-null mouse should show a relatively benign phenotype. Studies with the annexin A2-null mouse have suggested important functions for annexin A2 and the heterotetramer in fibrinolysis, in the regulation of the LDL receptor and in cellular redox regulation. However, the demonstration that depletion of annexin A2 causes the depletion of several other proteins including S100A10, fascin and affects the expression of at least sixty-one genes has confounded the reports of its function. In this review we will discuss the annexin A2 structure and function and its proposed physiological and pathological roles.

Anti-dsDNA antibodies bind to mesangial annexin II in lupus nephritis

Production of anti-dsDNA antibodies is a hallmark of lupus nephritis, but how these antibodies deposit in organs and elicit inflammatory damage remains unknown. In this study, we sought to identify antigens on the surface of human mesangial cells (HMC) that mediate the binding of human anti-dsDNA antibodies and the subsequent pathogenic processes. We isolated anti-dsDNA antibodies from patients with lupus nephritis by affinity chromatography. We used multiple methods to identify and characterize antigens from the plasma membrane fraction of mesangial cells that crossreacted with the anti-dsDNA antibodies. We found that annexin II mediated the binding of anti-dsDNA antibodies to HMC. After binding to the mesangial cell surface, anti-dsDNA antibodies were internalized into the cytoplasm and nucleus. This also led to induction of IL-6 secretion and annexin II synthesis, mediated through activation of p38 MAPK, JNK, and AKT. Binding of anti-dsDNA antibodies to annexin II correlated with disease activity in human lupus nephritis. Glomerular expression of annexin II correlated with the severity of nephritis, and annexin II colocalized with IgG and C3 deposits in both human and murine lupus nephritis. Gene silencing of annexin II in HMC reduced binding of anti-dsDNA antibody and partially decreased IL-6 secretion. In summary, our data demonstrate that annexin II mediates the binding of anti-dsDNA antibodies to mesangial cells, contributing to the pathogenesis of lupus nephritis. This interaction provides a potential target for therapeutic intervention.

Cloning and Characterization of the Annexin II Receptor on Human Marrow Stromal Cells

Annexin II is a heterotetramer, consisting of two 11-kDa (p11) and two 36-kDa (p36) subunits, that is produced by osteoclasts and stimulates osteoclast formation. However, its receptor is unknown. We showed that annexin II binds to normal primary human marrow stromal cells and the Paget's marrow-derived PSV10 stromal cell line to induce osteoclast formation. 125I-Labeled annexin II binding assays with PSV10 cells demonstrated that there was a single class of annexin II receptors with a Kd of 5.79 nm and Bmax of 2.13 x 10(5) receptors/cell. Annexin III or annexin V did not bind this receptor. Using 125I-labeled annexin II binding to screen NIH3T3 transfected with a human marrow cDNA expression library, we identified a putative annexin II receptor clone, which encoded a novel 26-kDa type I membrane receptor protein when expressed in HEK 293 cells. HEK 293 cells transformed with the cloned annexin II receptor cDNA showed a similar binding affinity to annexin II as that observed in PSV10 cells. Chemical cross-linking experiments with biotinylated annexin II and intact PSV10 cells identified a 55-kDa band on Western blot analysis that reacted with both an anti-p11 antibody and streptavidin but not anti-p36 antibody. A rabbit polyclonal antibody raised against the putative recombinant annexin II receptor also recognized the same 26-kDa protein band detected in PSV10 cells. Importantly, the annexin II receptor antibody dose-dependently blocked the stimulatory effects of annexin II on human osteoclast formation, demonstrating that the receptor mediates the effects of annexin II on osteoclast formation.

Angiotensin II induces peroxisome proliferator-activated receptor gamma in PC12W cells via angiotensin type 2 receptor activation

The angiotensin type 2 (AT2) receptor has been previously demonstrated to exert neuroprotective actions possibly by inducing neuronal cell differentiation involving neurite outgrowth. The nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPARgamma) is an important transcriptional regulator of cell differentiation. The aim of the present study was to clarify whether PPARgamma is involved in AT2-receptor-mediated morphological neuronal cell differentiation. To investigate AT2-receptor-mediated morphological neuronal cell differentiation, rat pheochromocytoma cells (PC12W cells) expressing AT2 but not AT1 receptors, were stimulated with angiotensin II (Ang II, 100 nmol/L) +/- the PPARgamma antagonists GW9662 (3 micromol/L) and bisphenol A diglycidyl ether (BADGE, 1 micromol/L), and neurite outgrowth of these cells was assessed. Ang II induced neurite outgrowth by 19 +/- 1.6-fold (p < 0.01). Antagonizing PPARgamma activity by GW9662 or BADGE potently blocked Ang II-induced neurite outgrowth (Ang II + GW9662: 6.6 +/- 1.5-fold, p < 0.05; Ang II + BADGE: 1.3 +/- 0.7-fold, p < 0.01). AT2 receptor activation by Ang II markedly induced mRNA and protein expression of the PPARgamma2 isoform and enhanced ligand-induced PPARgamma activity in transactivation assays. In conclusion, the present study demonstrates that Ang II induces PPARgamma expression and ligand-mediated PPARgamma activity via AT2 receptor activation, which appears to be a crucial process in AT2 receptor mediated neurite outgrowth. AT2 receptor/PPARgamma-dependent neurite outgrowth may play an important role during neuroprotective processes.

Structural and functional characterisation of the mouse annexin A9 promoter

Annexin A9 is an atypical member of the annexin family of Ca(2+) and phospholipid-binding proteins, initially identified in EST data bases. Its amino acid sequences responsible for calcium coordination are mutated suggesting an atypical, Ca(2+)-independent cellular function in comparison to other family members. In line with a specialized function of annexin A9 is the restricted presence of its cDNA in EST libraries from different tissues. To identify elements mediating this regulation of annexin A9 transcription, we have cloned the mouse homolog of the human annexin A9 gene and characterised its promoter. By employing 2.5 kb of the most 5' flanking region of the gene, containing 5' non-coding sequence, exon I and intron I in luciferase reporter assays in annexin A9 positive HEPA 1-6 cells, we reveal the existence of a minimal promoter located at the 3' flank of intron I. The sequence covering this minimal promoter contains a binding site consensus for the transcription factor GATA-1 whose binding were verified by electrophoretic mobility shift assays (EMSA). Further mapping analysis also identified two elements in exon I with a negative regulatory function on gene transcription. This suggests that the entire region containing the non-protein coding exon I and the adjacent intron I is involved in the regulation of mouse annexin A9 transcription.

Identification of cJun-responsive genes in Rat-1a cells using multiple techniques: increased expression of stathmin is necessary for cJun-mediated anchorage-independent growth

cJun is a major component of the transcription factor AP-1 and mediates a diverse set of biologic properties including proliferation, differentiation, and apoptosis. To identify cJun-responsive genes, we inducibly expressed cJun in Rat-1a cells and observed two distinct phenotypes: changes in cellular morphology with adherent growth and anchorage-independent growth. The biologic effects of cJun were entirely reversible demonstrating that they require the continued presence of cJun. To determine the genes, which mediate the biologic effects of cJun, we employed multiple methods including differential gene analysis, suppression subtractive hybridization, and cDNA microarrays. We identified 38 cJun-responsive genes including three uncharacterized genes under adherent and/or nonadherent conditions. Half of the known 36 genes were cytoskeleton- and adhesion-related genes, suggesting a major role of cJun in the regulation of the genes related to cell morphology. As proof of the principle that this approach could identify genes whose upregulation was necessary for nonadherent growth, we investigated one gene, stathmin whose upregulation by cJun was observed only under these conditions. Although overexpression of stathmin did not result in nonadherent growth, inhibition of stathmin protein expression by antisense oligonucleotides in cJun-induced Rat-1a cells prevented nonadherent growth. These results suggest that stathmin plays an essential role in anchorage-independent growth by cJun and may be a potential target for specific inhibitors for AP-1-dependent processes involved in carcinogenesis.

Isolation and characterization of annexin 2 pseudogene in Rattus norvegicus

Annexin 2 is a calcium-regulated, phospholipid-binding protein present in endothelial cells, macrophages and some tumor cells. Annexin 2 is a substrate for a variety of protein kinases, and plays roles in the regulation of endocytosis, exocytosis and thrombolysis. We have determined the nucleotide sequence of a rat genomic DNA fragment that hybridized to a rat annexin 2 DNA complementary to RNA (cDNA) probe. Sequence analysis revealed that it was an intronless rat annexin 2, consisting of a start-to-stop-codon-length copy of the processed transcript. This pseudogene contained 33 point mutations and two deletion sites in the coding region as compared with the cDNA, and thus displayed typical features of a retroposon. Transitions were more frequent than transversions, and the most frequent type of mutation was G to A transition. We isolated a phage clone that contained a functional rat annexin 2 genomic fragment including coding exons 3 and 4. Polymerase chain reaction and subsequent sequence analysis revealed an intron of approximately 4 kbp at the same site as in humans and mice. Whereas the annexin 2 gene or its cDNA homologues have been detected in various species from Xenopus to humans, its pseudogene has been reported only in humans. In the present study, we demonstrated the presence of an annexin 2 pseudogene in rats.

Identification of novel peroxisome proliferator-activated receptor alpha (PPARalpha) target genes in mouse liver using cDNA microarray analysis

Peroxisome proliferators, which function as peroxisome proliferator-activated receptor-alpha (PPARalpha) agonists, are a group of structurally diverse nongenotoxic hepatocarcinogens including the fibrate class of hypolipidemic drugs that induce peroxisome proliferation in liver parenchymal cells. Sustained activation of PPARalpha by these agents leads to the development of liver tumors in rats and mice. To understand the molecular mechanisms responsible for the pleiotropic effects of these agents, we have utilized the cDNA microarray to generate a molecular portrait of gene expression in the liver of mice treated for 2 weeks with Wy-14,643, a potent peroxisome proliferator. PPARalpha activation resulted in the stimulation of expression (fourfold or greater) of 36 genes and decreased the expression (fourfold or more decrease) of 671 genes. Enhanced expression of several genes involved in lipid and glucose metabolism and many other genes associated with peroxisome biogenesis, cell surface function, transcription, cell cycle, and apoptosis has been observed. These include: CYP2B9, CYP2B10, monoglyceride lipase, pyruvate dehydrogenase-kinase-4, cell death-inducing DNA-fragmentation factor-alpha, peroxisomal biogenesis factor 11beta, as well as several cell recognition surface proteins including annexin A2, CD24, CD39, lymphocyte antigen 6, and retinoic acid early transcript-gamma, among others. Northern blotting of total RNA extracted from the livers of PPARalpha-/- mice and from mice lacking both PPARalpha and peroxisomal fatty acyl-CoA oxidase (AOX), that were fed control and Wy-14,643-containing diets for 2 weeks, as well as time course of induction following a single dose of Wy-14,643, revealed that upregulation of genes identified by microarray procedure is dependent upon peroxisome proliferation vis-à-vis PPARalpha. However, cell death-inducing DNA-fragmentation factor-alpha mRNA, which is increased in the livers of wild-type mice treated with peroxisome proliferators, was not enhanced in AOX-/- mice with spontaneous peroxisome proliferation. These observations indicate that the activation of PPARalpha leads to increased and decreased expression of many genes not associated with peroxisomes, and that delayed onset of enhanced expression of some genes may be the result of metabolic events occurring secondary to PPARalpha activation and alterations in lipid metabolism.

Mechanical strain stimulates nitric oxide production by rapid activation of endothelial nitric oxide synthase in osteocytes

Previous studies have indicated that physiological levels of dynamic mechanical strain produce rapid increases in nitric oxide (NO) release from rat ulna explants and primary cultures of osteoblast-like cells and embryonic chick osteocytes derived from long bones. To establish the mechanism by which loading-induced NO production may be regulated, we have examined: nitric oxide synthase (NOS) isoform mRNA and protein expression, the effect of mechanical loading in vivo on NOS mRNA expression, and the effect of mechanical strain on NO production by bone cells in culture. Using Northern blot analyses, in situ hybridization, and immunocytochemistry we have established that the predominant NOS isoform expressed in rat long bone periosteal osteoblasts and in a distinct population of cortical bone osteocytes is the endothelial form of NOS (eNOS), with little or no expression of the inducible NOS or neuronal NOS isoforms. In contrast, in non-load-bearing calvariae there are no detectable levels of eNOS in osteocytes and little in osteoblasts. Consistent with these observations, ulnar explants release NO rapidly in response to loading in vitro, presumably through the activation of eNOS, whereas calvarial explants do not. The relative contribution of different bone cells to these rapid increases in strain-induced NO release was established by assessment of medium nitrite (stable NO metabolite) concentration, which showed that purified populations of osteocytes produce significantly greater quantities of NO per cell in response to mechanical strain than osteoblast-like cells derived from the same bones. Using Northern blot hybridization, we have also shown that neither a single nor five consecutive daily periods of in vivo mechanical loading produced any significant effect on different NOS isoform mRNA expression in rat ulnae. In conclusion, our results indicate that eNOS is the prevailing isoform expressed by cells of the osteoblast/osteocyte lineage and that strain produces increases in the activity of eNOS without apparently altering the levels of eNOS mRNA.