The annexin protein lipocortin 1 regulates the MAPK/ERK pathway

Translocation of annexin I from cellular membrane to the nuclear membrane in human esophageal squamous cell carcinoma

AIM: To investigate the alteration of the annexin I subcellular localization in esophageal squamous cell carcinoma (ESCC) and the correlation between the translocation and the tumorigenesis of ESCC.

METHODS: The protein localization of annexin I was detected in both human ESCC tissues and cell line via the indirect immunofluorescence strategy.

RESULTS: In the normal esophageal epithelia the annexin I was mainly located on the plasma membrane and formed a consecutive typical trammels net. Annexin I protein also expressed dispersively in cytoplasm and the nuclei without specific localization on the nuclear membrane. In esophageal cancer annexin I decreased very sharply with scattered disappearance on the cellular membrane, however it translocated and highly expressed on the nuclear membrane, which was never found in normal esophageal epithelia. In cultured esophageal cancer cell line annexin I protein was also focused on the nuclear membrane, which was consistent with the result from esophageal cancer tissues.

CONCLUSION: This observation suggests that the translocation of annexin I protein in ESCC may correlate with the tumorigenesis of the esophageal cancer.

Dexamethasone induces the secretion of annexin I in immature lymphoblastic cells by a calcium-dependent mechanism

The mechanisms by which glucocorticoids (GC) regulate annexin I (ANXA1) secretion in different cells are still a matter of debate. The aims of this study were to evaluate the ability of dexamethasone (Dex) to induce ANXA1 secretion and to investigate the roles of the intracellular free Ca2+ concentration ([Ca2+]i), and of the GC receptor, on that process. For this purpose, the human immature lymphoblastic CCRF-CEM cell line was used. Treatment of the cells with Dex, for up to 4 h, significantly reduced the intracellular content of ANXA1 and increased the amount of this protein bound to the outer surface of the plasma membrane, whereas exposure of cells to Dex, for 12 h, induced the synthesis of ANXA1. At the same short time periods, Dex also induced a significant increase in the [Ca2+]i. Incubation of the cells with BAPTA-AM (10 microM), a cell-permeant high affinity Ca2+ chelator, completely inhibited Dex-induced ANXA1 secretion. Furthermore, the Ca2+ ionophore, ionomycin, alone induced ANXA1 cleavage, but not its secretion. Additionally, we used brefeldin A to investigate the involvement of the classical endoplasmic reticulum (ER)-Golgi pathway of protein secretion in the release of ANXA1. The GC receptor antagonist, RU486, neither reverted the Dex-dependent ANXA1 secretion nor inhibited the increase of the [Ca2+]i induced by Dex. Together, our results indicate that Dex induces ANXA1 synthesis and secretion in CCRF-CEM cells. ANXA1 secretion in this cell type show the following characteristics: (i) is unlikely to involve the classical ER-Golgi pathway; (ii) requires a Ca(2+)-dependent cleavage of ANXA1; (iii) involves both Ca(2+)-dependent and independent mechanisms; and (iv) is apparently independent of the GC receptor alpha isoform.

Hoxa 11 is upstream of Integrin alpha8 expression in the developing kidney

Mutation of the functionally redundant Hoxa 11/Hoxd 11 genes gives absent or rudimentary kidneys resulting from a dramatic reduction of the growth and branching of the ureteric bud. To understand better the molecular mechanisms of Hoxa 11/Hoxd 11 function in kidney development, it is necessary to identify the downstream target genes regulated by their encoded transcription factors. To this end, we conducted a screen for Hoxa 11-responsive genes in two kidney cell lines. HEK293 cells, which usually do not express Hoxa 11, were modified to allow inducible Hoxa 11 expression. The mK10 cells, derived specifically for this study from Hoxa 11/Hoxd 11 double-mutant mice, were also modified to give cell populations with and without Hoxa 11 expression. Differential display, Gene Discovery Arrays, and Affymetrix genechip probe arrays were used to screen for genes up- or down-regulated by Hoxa 11. Nine genes, PDGF A, Cathepsin L, annexin A1, Mm.112139, Est2 repressor factor, NrCAM, ZNF192, integrin-associated protein, and GCM1, showed reproducible 3-fold or smaller changes in gene expression in response to Hoxa 11. One gene, the Integrin alpha8, was up-regulated approximately 20-fold after Hoxa 11 expression. The Integrin alpha8 gene is expressed together with Hoxa 11 in metanephric mesenchyme cells, and mutation of Integrin alpha8 gives a bud-branching morphogenesis defect very similar to that observed in Hoxa 11/Hoxd 11 mutant mice. In situ hybridizations showed a dramatic regional reduction in Integrin alpha8 expression in the developing kidneys of Hoxa 11/Hoxd 11 mutant mice. This work suggests that the Integrin alpha8 gene may be a major effector of Hoxa 11/Hoxd 11 function in the developing kidney.

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.

DNA chain unwinding and annealing reactions of lipocortin (annexin) I heterotetramer: regulation by Ca(2+) and Mg(2+)

Lipocortin I-S100 (calcyclin) heterotetramer exhibited ATPase activity in the presence of dsDNA but not ssDNA. To demonstrate its helicase activity, an 80-mer polynucleotide complementary to the replication origin of M13mp18 was synthesized, and the oligonucleotide, (dC)(20), was ligated to either its 5'- or 3'- end for binding to lipocortin. Lipocortin I heterotetramer displaced chains of the partially Y-shaped duplexes with a dC-tail at either the 5'- or 3'- end. The chain displacement required ATP and Mg(2+). Nonhydrolyzable ATP analogues were not effective. Lipocortin I heterotetramer also catalyzed annealing of the polynucleotides to M13mp18. Ca(2+) and phospholipids but not ATP and Mg(2+) were essential for this reaction. Since the chain displacing and annealing reactions were inhibited by monospecific anti-lipocortin I or anti-S100 antibodies, the present observations suggest that the lipocortin I heterotetramer regulates unwinding and annealing of DNA by Mg(2+) (plus ATP) and Ca(2+) (and phospholipids), respectively.

Molecular monitoring of bleomycin-induced pulmonary fibrosis by cDNA microarray-based gene expression profiling

Pulmonary fibrosis is a progressive disorder whose molecular pathology is poorly understood. Here we developed an in-house cDNA microarray ("lung chip") originating from a lung-normalized cDNA library. By using this lung chip, we analyzed global gene expression in a murine model of bleomycin-induced fibrosis and selected 82 genes that differed by more than twofold intensity in at least one pairwise comparison with controls. Cluster analysis of these selected genes showed that the expression of genes associated with inflammation reached maximum levels at 5 days after bleomycin administration, while genes involved in the development of fibrosis increased gradually up to 14 days after bleomycin treatment. These changes in gene expression signature were well correlated with observed histopathological changes. The results show that microarray analysis of animal disease models is a powerful approach to understanding the gene expression programs that underlie these disorders.

Annexin-1 is abnormally expressed in fragile X syndrome: two-dimensional electrophoresis study in lymphocytes

The search for targets of FMRP (the product of FMR1, the mutated gene in Fragile X syndrome) has predominantly focused on identifying transcripts that are regulated by this RNA-binding protein. This study introduces the use of two-dimensional gel electrophoresis (2D PAGE) as a novel approach for demonstrating changes in protein synthesis secondary to FMRP deficit. By a standardized 2D PAGE protocol, we studied leukocyte homogenates from 30 males with different patterns of FMR1 mutation and different levels of FMRP. Samples from these subjects were compared to those of 12 normal control males and eight subjects with other mental retardation-associated conditions (i.e., Rett and Down syndromes). We found an abnormal pattern of a major leukocytic protein, identified by 2D PAGE datasets and immunoblotting as annexin-1 (Anx-1). Anx-1 appeared in subjects with Fragile X as multiple rather than 1-2 spots, at approximately 37 kd, in the pI 5-7 range. The presence and intensity of this Anx-1 pattern was relatively independent of Anx-1 levels and inversely related to total and high MW FMRP immunoreactivities. Based on the 2D PAGE pattern, without obvious MW change, and on dephosphorylation assays, we concluded that Anx-1's abnormality represents an aberrant posttranslational modification other than phosphorylation. Comparisons of our data with published cytoskeletal protein 2D profiles suggest that Anx-1 may be abnormally acetylated and, consequently, incapable of establishing appropriate N-terminal protein-protein interactions. In addition to its peripheral anti-inflammatory function, Anx-1 mediates glucocorticoid inhibition of the hypothalamo-pituitary-adrenal axis. As the latter seems to be disrupted in Fragile X syndrome, the reported Anx-1 abnormality could be responsible for some aspects of the Fragile X neurobehavioral phenotype. Our data also emphasize the feasibility of using 2D PAGE for disclosing molecular abnormalities in Fragile X and other genetic disorders.

Transfection of annexin 1 in monocytic cells produces a high degree of spontaneous and stimulated apoptosis associated with caspase-3 activation

Transfection of the pre-monomyelocytic U937 cell line with a plasmid coding for full-length annexin 1 (ANX1, 347 amino acid) leads to cell death by promoting apoptosis. In addition, over-expression of the N-terminal and the first domain of the protein (144 amino acids, clone ANX1-S), which does not contain the Ca2+ binding sites, gives susceptibility to cell apoptosis following activation by either 5 ng ml(-1) tumour necrosis factor (TNF)-alpha or 1 - 40 microg ml-1 etoposide. This was demonstrated by using the fluorescent labelled annexin V, cell cycle and nuclear staining analyses. Transfection with an empty plasmid (clone CMV) or with a plasmid carrying the cDNA antisense for ANX1 (clone ANX1-AS) did not alter U937 cells to the degree of apoptosis promoted by either stimulant. Treatment of CMV U937 cells with TNF-alpha increased ANX1 mRNA and protein expression in a time-dependent manner, with maximal increases at 3 and 6 h, respectively. Clone ANX1-S showed higher constitutive (more than 2 fold) and activated caspase-3 activity, associated with higher phospholipase A2 (PLA2) activity (in the region of +50 - 100%), whereas expression of cytosolic PLA2 Bax and Bcl-2 were similar in all cell clones, as determined by Western blotting. In conclusion, this study demonstrates a complex regulatory role of cell apoptosis for ANX1, at least with regards to cells of the myelo-monocytic lineage.

UDP hydrolase activity associated with the porcine liver annexin fraction

In the crude fraction of porcine liver annexins, we identified annexin IV (AnxIV), AnxII and AnxVI of MW (molecular weight) of 32, 36 and 68 kDa, respectively, an albumin of MW of 61.5 kDa and an UDP hydrolase (UDPase) of MW of 62 kDa, related to the human UDPase from Golgi membranes. The latter enzyme exhibits its highest specificity towards UDP and GDP but not ADP and CDP, and it is stimulated by Mg(2+) and Ca(2+). AnxVI itself, although it binds purine nucleotides, does not exhibit hydrolytic activity towards nucleotides. Taken together, these results suggest that AnxVI may interact in vivo with a nucleotide-utilizing enzyme, UDPase. This is in line with observations made by other investigators that various annexins are able to interact with nucleotide-utilizing proteins, such as protein kinases, GTPases, cytoskeletal proteins and p120(GAP). Such interactions could be of particular importance in modulating the biological activities of these proteins in vivo.

Two proteins modulating transendothelial migration of leukocytes recognize novel carboxylated glycans on endothelial cells

We recently showed that a class of novel carboxylated N:-glycans was constitutively expressed on endothelial cells. Activated, but not resting, neutrophils expressed binding sites for the novel glycans. We also showed that a mAb against these novel glycans (mAbGB3.1) inhibited leukocyte extravasation in a murine model of peritoneal inflammation. To identify molecules that mediated these interactions, we isolated binding proteins from bovine lung by their differential affinity for carboxylated or neutralized glycans. Two leukocyte calcium-binding proteins that bound in a carboxylate-dependent manner were identified as S100A8 and annexin I. An intact N terminus of annexin I and heteromeric assembly of S100A8 with S100A9 (another member of the S100 family) appeared necessary for this interaction. A mAb to S100A9 blocked neutrophil binding to immobilized carboxylated glycans. Purified human S100A8/A9 complex and recombinant human annexin I showed carboxylate-dependent binding to immobilized bovine lung carboxylated glycans and recognized a subset of mannose-labeled endothelial glycoproteins immunoprecipitated by mAbGB3.1. Saturable binding of S100A8/A9 complex to endothelial cells was also blocked by mAbGB3.1. These results suggest that the carboxylated glycans play important roles in leukocyte trafficking by interacting with proteins known to modulate extravasation.

Annexins as nucleotide-binding proteins: facts and speculations

Annexins are ubiquitous multifunctional Ca2+ and phospholipid-binding proteins whose mechanism of function remains largely unknown. The accumulated in vitro experimental evidence indicates that ATP and GTP are functional ligands for nucleotide-sensitive annexin isoforms. Such nucleotide binding could modulate Ca2+ homeostasis, vesicular transport and/or signal transduction pathways and link them to cellular energy metabolism. Alternatively, since annexins are able to interact with other nucleotide-utilizing proteins, such as various kinases, GTPases and structural proteins, these proteins could influence the guanine nucleotide exchange metabolism and/or control the activity of various G proteins. The nucleotide-binding properties of annexins may affect the development or maintenance of some pathologies and diseases in which changes in physiological concentrations of purine nucleotides or disruption of Ca2+ homeostasis are crucial targets.

Mechanism of annexin I-mediated membrane aggregation

It has been proposed that annexin I has two separate interaction sites that are involved in membrane binding and aggregation, respectively. To better understand the mechanism of annexin I-mediated membrane aggregation, we investigated the properties of the inducible secondary interaction site implicated in membrane aggregation. X-ray specular reflectivity measurements showed that the thickness of annexin I layer bound to the phospholipid monolayer was 31 +/- 2 A, indicating that annexin I binds membranes as a protein monomer or monolayer. Surface plasmon resonance measurements of annexin I, V, and mutants, which allowed evaluation of membrane aggregation activity of annexin I separately from its membrane binding, revealed direct correlation between the relative membrane aggregation activity and the relative affinity of the secondary interaction site for the secondary membrane. The secondary binding was driven primarily by hydrophobic interactions, unlike calcium-mediated electrostatic primary membrane binding. Chemical cross-linking of membrane-bound annexin I showed that a significant degree of lateral association of annexin I molecules precedes its membrane aggregation. Taken together, these results support a hypothetical model of annexin I-mediated membrane aggregation, in which a laterally aggregated monolayer of membrane-bound annexin I directly interacts with a secondary membrane via its induced hydrophobic interaction site.

Annexin-I inhibits PMA-induced c-fos SRE activation by suppressing cytosolic phospholipase A2 signal

Annexin-I (ANX-I) is a 37-kDa protein with a calcium-dependent phospholipid-binding property. Previously we have observed the inhibition of cytosolic phospholipase A2 (cPLA2) by ANX-I in the studies using purified recombinant ANX-I, and proposed a specific interaction model for the mechanism of cPLA2 inhibition by ANX-I [Kim et al. (1994) FEBS Lett. 343, 251-255]. Here we have studied the role of ANX-I in the cPLA2 signaling pathway by transient transfection assay. The stimulation of Rat2 fibroblast cells with phorbol 12-myristate 13-acetate (PMA) induced the c-fos serum response element (SRE). The SRE stimulation by PMA was dramatically reduced by (1) pretreatment with a cPLA2-specific inhibitor, arachidonyltrifluoromethyl ketone, or (2) co-transfection with antisense cPLA2 oligonucleotide, indicating that the SRE activation was through cPLA2 activation. Co-transfection with an ANX-I expression vector also reduced the SRE stimulation by PMA, suggesting the inhibition of cPLA2 by ANX-I. The active domain of ANX-I was mapped using various deletion mutants. ANX-I(1-113) and ANX-I(34-346) were fully active, whereas ANX-I(114-346) abolished the activity. Therefore the activity was in the amino acid 34 to 113 region, which corresponds to the conserved domain I of ANX-I.