The nuclear location of annexin V in the human osteosarcoma cell line MG-63 depends on serum factors and tyrosine kinase signaling pathways

Annexins A2 and A5 are potential early biomarkers of hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is a highly lethal liver cancer with late diagnosis; therefore, the identification of new early biomarkers could help reduce mortality. We determine the tissue and plasma status of five annexins during hepatocarcinogenesis by diethylnitrosamine-induced cirrhosis-HCC. We found that Anxa5 was the earliest upregulated gene at week 12 after HCC initiation, while Anxa1 and Anxa2 were upregulated in advanced HCC stages (weeks 18 and 22). Furthermore, the protein level of Annexin A1, A2, A5 and A10 was increased from the early stages. Immunofluorescence and subcellular fractionation revealed Annexin A1, A2, and A5 in the cytoplasm and nuclei of tumor cells. Notably, increased plasma levels of Annexin A5 significantly (r² = 0.8203) correlated with Annexin A5 levels in liver tissue from week 12 and gradually increased until week 22. Using the TCGA database, we found that the expression of ANXA2 (HR = 1.7, p = 0.0046) and ANXA5 (HR = 1.8, p = 0.00077) was associated with poor survival in HCC patients. In conclusion, we have identified Annexin A1 and A5 as potentially useful early biomarkers for poor prognosis in HCC patients.

Age-dependent Effects of 17β-estradiol on the dynamics of estrogen receptor β (ERβ) protein-protein interactions in the ventral hippocampus

Recent clinical evidence suggests that the neuroprotective and beneficial effects of hormone therapy may be limited by factors related to age and reproductive status. The patient's age and length of time without circulating ovarian hormones are likely to be key factors in the specific neurological outcomes of hormone therapy. However, the mechanisms underlying age-related changes in hormone efficacy have not been determined. We hypothesized that there are intrinsic changes in estrogen receptor β (ERβ) function that determine its ability to mediate the actions of 17β-estradiol (E2) in brain regions such as the ventral hippocampus. In this study, we identified and quantified a subset of ERβ protein interactions in the ventral hippocampus that were significantly altered by E2 replacement in young and aged animals, using two-dimensional differential gel electrophoresis coupled with liquid chromatography-electrospray ionization-tandem mass spectrometry. This study demonstrates quantitative changes in ERβ protein-protein interactions with E2 replacement that are dependent upon age in the ventral hippocampus and how these changes could alter processes such as transcriptional regulation. Thus, our data provide evidence that changes in ERβ protein interactions are a potential mechanism for age-related changes in E2 responsiveness in the brain after menopause.

Dietary flavonoids bind to mono-ubiquitinated annexin A1 in nuclei, and inhibit chemical induced mutagenesis

In order to investigate the mechanisms of anti-mutagenic action by dietary flavonoids, we investigated if they inhibit mutation of the thymidine kinase (tk) gene in L5178Ytk(±) lymphoma cells. Silibinin, quercetin and genistein suppressed mutation of the tk gene induced in L5178Ytk(±) lymphoma cells by methyl methanesulfonate (MMS) and As(3+). Flavone and flavonol were less effective. To establish that mutation of the tk gene in L5178Ytk(±) lymphoma cells by MMS and As(3+) is mediated through mono-ubiquitinated annexin A1, L5178Ytk(±) lymphoma cells were treated with annexin A1 anti-sense oligonucleotide. The treatment reduced mRNA as well as protein levels of annexin A1, and suppressed mutation of the tk gene. Nuclear extracts from L5178Ytk(±) lymphoma cells catalyzed translesion DNA synthesis with an oligonucleotide template containing 8-oxo-guanosine in an annexin A1 dependent manner. This translesion DNA synthesis was inhibited by the anti-mutagenic flavonoids, silibinin, quercetin and genistein, in a concentration dependent manner, but only slightly by flavone and flavonol. Because these observations implicate involvement of annexin A1 in mutagenesis, we examined if flavonoids suppress nuclear annexin A1 helicase activity. Silibinin, quercetin and genistein inhibited ssDNA binding, DNA chain annealing and DNA unwinding activities of purified nuclear mono-ubiquitinated annexin A1. Flavone and flavonol were ineffective. The apparent direct binding of anti-mutagenic flavonoids to the annexin A1 molecule was supported by fluorescence quenching. Taken together, these findings illustrate that nuclear annexin A1 may be a novel and productive target protein of prevention for DNA damage induced gene mutation, ultimately conferring cancer chemoprevention.

Evolutionary adaptation of plant annexins has diversified their molecular structures, interactions and functional roles

Annexins are an homologous, structurally related superfamily of proteins known to associate with membrane lipid and cytoskeletal components. Their involvement in membrane organization, vesicle trafficking and signaling is fundamental to cellular processes such as growth, differentiation, secretion and repair. Annexins exist in some prokaryotes and all eukaryotic phyla within which plant annexins represent a monophyletic clade of homologs descended from green algae. Genomic, proteomic and transcriptomic approaches have provided data on the diversity, cellular localization and expression patterns of different plant annexins. The availability of 35 complete plant genomes has enabled systematic comparative analysis to determine phylogenetic relationships, characterize structures and observe functional specificity between and within individual subfamilies. Short amino termini and selective erosion of the canonical type 2 calcium coordinating sites in domains 2 and 3 are typical of plant annexins. The convergent evolution of alternate functional motifs such as 'KGD', redox-sensitive Cys and hydrophobic Trp/Phe residues argues for their functional relevance and contribution to mechanistic diversity in plant annexins. This review examines recent findings and advances in plant annexin research with special focus on their structural diversity, cellular and molecular interactions and their potential integrated functions in the broader context of physiological responses.

Annexin A5 stimulates autophagy and inhibits endocytosis

Macroautophagy is a major lysosomal catabolic process activated particularly under starvation in eukaryotic cells. A new organelle, the autophagosome, engulfs cytoplasmic substrates, which are degraded after fusion with endosomes and/or lysosomes. During a shotgun proteome analysis of purified lysosomal membranes from mouse fibroblasts, a Ca(2+)-dependent phospholipid-binding protein, annexin A5, was found to increase on lysosomal membranes under starvation. This suggests a role for this protein, an abundant annexin with a still unknown intracellular function, in starvation-induced lysosomal degradation. Transient overexpression and silencing experiments showed that annexin A5 increased lysosomal protein degradation, and colocalisation experiments, based on GFP sensitivity to lysosomal acidic pH, indicated that this was mainly the result of inducing autophagosome-lysosome fusion. Annexin A5 also inhibited the endocytosis of a fluid-phase marker and cholera toxin, but not receptor-mediated endocytosis. Therefore, we propose a double and opposite role of annexin A5 in regulating the endocytic and autophagic pathways and the fusion of autophagosomes with lysosomes and endosomes.

PHOSPHATIDYLSERINE SYNTHASE1 is required for microspore development in Arabidopsis thaliana

Phosphatidylserine (PS) has many important biological roles, but little is known about its role in plants, partly because of its low abundance. We show here that PS is enriched in Arabidopsis floral tissues and that genetic disruption of PS biosynthesis decreased heterozygote fertility due to inhibition of pollen maturation. At1g15110, designated PSS1, encodes a base-exchange-type PS synthase. Escherichia coli cells expressing PSS1 accumulated PS in the presence of l-serine at 23°C. Promoter-GUS assays showed PSS1 expression in developing anther pollen and tapetum. A few seeds with pss1-1 and pss1-2 knockout alleles escaped embryonic lethality but developed into sterile dwarf mutant plants. These plants contained no PS, verifying that PSS1 is essential for PS biosynthesis. Reciprocal crossing revealed reduced pss1 transmission via male gametophytes, predicting a rate of 61.6%pss1-1 pollen defects in PSS1/pss1-1 plants. Alexander's staining of inseparable qrt1-1 PSS1/pss1-1 quartets revealed a rate of 42% having three or four dead pollen grains, suggesting sporophytic pss1-1 cell death effects. Analysis with the nuclear stain 4',6-diamidino-2-phenylindole (DAPI) showed that all tetrads from PSS1/pss1-1 anthers retain their nuclei, whereas unicellular microspores were sometimes anucleate. Transgenic Arabidopsis expressing a GFP-LactC2 construct that binds PS revealed vesicular staining in tetrads and bicellular microspores and nuclear membrane staining in unicellular microspores. Hence, distribution and/or transport of PS across membranes were dynamically regulated in pollen microspores. However, among unicellular microspores from PSS1/pss1-2 GFP-LactC2 plants, all anucleate microspores showed little GFP-LactC2 fluorescence, suggesting that pss1-2 microspores are more sensitive to sporophytic defects or show partial gametophytic defects.

The annexins: spatial and temporal coordination of signaling events during cellular stress

Annexins are a family of structurally related, Ca2+-sensitive proteins that bind to negatively charged phospholipids and establish specific interactions with other lipids and lipid microdomains. They are present in all eukaryotic cells and share a common folding motif, the "annexin core", which incorporates Ca2+- and membrane-binding sites. Annexins participate in a variety of intracellular processes, ranging from the regulation of membrane dynamics to cell migration, proliferation, and apoptosis. Here we focus on the role of annexins in cellular signaling during stress. A chronic stress response triggers the activation of different intracellular pathways, resulting in profound changes in Ca2+ and pH homeostasis and the production of lipid second messengers. We review the latest data on how these changes are sensed by the annexins, which have the ability to simultaneously interact with specific lipid and protein moieties at the plasma membrane, contributing to stress adaptation via regulation of various signaling pathways.

Annexin A1 subcellular expression in laryngeal squamous cell carcinoma

AIMS

Annexin A1 (ANXA1) is a soluble cytoplasmic protein, moving to membranes when calcium levels are elevated. ANXA1 has also been shown to move to the nucleus or outside the cells, depending on tyrosine-kinase signalling, thus interfering in cytoskeletal organization and cell differentiation, mostly in inflammatory and neoplastic processes. The aim was to investigate subcellular patterns of immunohistochemical expression of ANXA1 in neoplastic and non-neoplastic samples from patients with laryngeal squamous cell carcinomas (LSCC), to elucidate the role of ANXA1 in laryngeal carcinogenesis.

METHODS AND RESULTS

Serial analysis of gene expression experiments detected reduced expression of ANXA1 gene in LSCC compared with the corresponding non-neoplastic margins. Quantitative polymerase chain reaction confirmed ANXA1 low expression in 15 LSCC and eight matched normal samples. Thus, we investigated subcellular patterns of immunohistochemical expression of ANXA1 in 241 paraffin-embedded samples from 95 patients with LSCC. The results showed ANXA1 down-regulation in dysplastic, tumourous and metastatic lesions and provided evidence for the progressive migration of ANXA1 from the nucleus towards the membrane during laryngeal tumorigenesis.

CONCLUSIONS

ANXA1 dysregulation was observed early in laryngeal carcinogenesis, in intra-epithelial neoplasms; it was not found related to prognostic parameters, such as nodal metastases.

Capacitative calcium entry and proliferation of human osteoblast-like MG-63 cells

Adult bone tissue is continuously being remodelled and bone mass is maintained by a balance between osteoclastic bone resorption and osteoblastic bone formation. Alteration of osteoblastic cell proliferation may account in part for lack of balance between these two processes in bone loss of osteoporosis. There is calcium (Ca2+) control in numerous cellular functions; however, involvement of capacitative Ca2+ entry (CCE) in proliferation of bone cells is less well investigated.

OBJECTIVES

The study described here was aimed to investigate roles of CCE in the proliferation of osteoblast-like MG-63 cells.

MATERIALS AND METHODS

Pharmacological characterizations of CCE were undertaken in parallel, with evaluation of the expression of transient receptor potential canonical (TRPC) channels and of cell proliferation.

RESULTS

Intracellular Ca2+ store depletion by thapsigargin induced CCE in MG-63 cells; this was characterized by a rapid transient increase of intracellular Ca2+ followed by significant CCE, induced by conditions that stimulated cell proliferation, namely serum and platelet-derived growth factor. Inhibitors of store-operated Ca2+ channels (2-APB and SKF-96365) prevented CCE, while voltage-dependent Ca2+ channel blockers had no effect. Expression of various TRPC channels was shown in the cells, some having been shown to be responsible for CCE. Voltage-dependent Ca2+ channel blockers had no effect on osteoblast proliferation while thapsigargin, 2-APB and SKF-96395, inhibited it. Cell cycle analysis showed that 2-APB and SKF-96395 lengthen the S and G2/M phases, which would account for the reduction in cell proliferation.

CONCLUSIONS

Our results indicate that CCE, likely attributed to the activation of TRPCs, might be the main route for Ca2+ influx involved in osteoblast proliferation.

Annexins: linking Ca2+ signalling to membrane dynamics

Eukaryotic cells contain various Ca(2+)-effector proteins that mediate cellular responses to changes in intracellular Ca(2+) levels. A unique class of these proteins - annexins - can bind to certain membrane phospholipids in a Ca(2+)-dependent manner, providing a link between Ca(2+) signalling and membrane functions. By forming networks on the membrane surface, annexins can function as organizers of membrane domains and membrane-recruitment platforms for proteins with which they interact. These and related properties enable annexins to participate in several otherwise unrelated events that range from membrane dynamics to cell differentiation and migration.

Annexin V disruption impairs mechanically induced calcium signaling in osteoblastic cells

The mechanical environment of the skeleton plays an important role in the establishment and maintenance of structurally competent bone. Biophysical signals induced by mechanical loading elicit a variety of cellular responses in bone cells, however, little is known about the underlying mechanotransduction mechanism. We hypothesized that bone cells detect and transduce biophysical signals into biological responses via a mechanism requiring annexin V (AnxV). AnxV, a calcium-dependent phospholipid binding protein, has several attributes, which suggest it is ideally suited for a role as a mechanosensor, possibly a mechanosensitive ion channel. These include the ability to function as a Ca2+ selective ion channel, and the ability to interact with both extracellular matrix proteins and cytoskeletal elements. To test the hypothesis that AnxV has a role in mechanosensing, we studied the response of osteoblastic cells to oscillating fluid flow, a physiologically relevant physical signal in bone, in the presence and absence of AnxV inhibitors. In addition, we investigated the effects of oscillating flow on the cellular location of AnxV. Oscillating fluid flow increased both [Ca2+]i levels and c-fos protein levels in osteoblasts. Disruption of AnxV with blocking antibodies or a pharmacological inhibitor, K201 (JTV-519), significantly inhibited both responses. Additionally, our data show that the cellular location of AnxV was modulated by oscillating fluid flow. Exposure to oscillating fluid flow resulted in a significant increase in AnxV at both the cell and nuclear membranes. In summary, our data suggest that AnxV mediates flow-induced Ca2+ signaling in osteoblastic cells. These data support the idea of AnxV as a Ca2+ channel, or a component of the signaling pathway, in the mechanism by which mechanical signals are transduced into cellular responses in the osteoblast. Furthermore, the presence of a highly mobile pool of AnxV may provide cells with a powerful mechanism by which cellular responses to mechanical loading might be amplified and regulated.

Interaction in vitro of type III intermediate filament proteins with Z-DNA and B-Z-DNA junctions

The selection of DNA fragments containing simple d(GT)(n) and composite d(GT)(m). d(GA)(n) microsatellites during affinity binding of mouse genomic DNA to type III cytoplasmic intermediate filaments (cIFs) in vitro, and the detection of such repeats, often as parts of nuclear matrix attachment region (MAR)-like DNA, in SDS-stable DNA-vimentin crosslinkage products isolated from intact fibroblasts, prompted a detailed study of the interaction of type III cIF proteins with left-handed Z-DNA formed from d(GT)(17) and d(CG)(17) repeats under the topological tension of negatively supercoiled plasmids. Although d(GT)(n) tracts possess a distinctly lower Z-DNA-forming potential than d(CG)(n) tracts, the filament proteins produced a stronger electrophoretic mobility shift with a plasmid carrying a d(GT)(17) insert than with plasmids containing different d(CG)(n) inserts, consistent with the facts that the B-Z transition of d(GT)(n) repeats requires a higher negative superhelical density than that of d(CG)(n) repeats and the affinity of cIF proteins for plasmid DNA increases with its superhelical tension. That both types of dinucleotide repeat had indeed undergone B-Z transition was confirmed by S1 nuclease and chemical footprinting analysis of the plasmids, which also demonstrated efficient protection by cIF proteins from nucleolytic and chemical attack of the Z-DNA helices as such, as well as of the flanking B-Z junctions. The analysis also revealed sensibilization of nucleotides in the center of one of the two strands of a perfect d(CG)(17) insert toward S1 nuclease, indicating cIF protein-induced bending of the repeat. In all these assays, vimentin and glial fibrillary acidic protein (GFAP) showed comparable activities, versus desmin, which was almost inactive. In addition, vimentin and GFAP exhibited much higher affinities for the Z-DNA conformation of brominated, linear d(CG)(25) repeats than for the B-DNA configuration of the unmodified oligonucleotides. While double-stranded DNA was incapable of chasing the Z-DNA from its protein complexes, and Holliday junction and single-stranded (ss)DNA were distinguished by reasonable competitiveness, phosphatidylinositol (PI) and, particularly, phosphatidylinositol 4,5-diphosphate (PIP(2)) turned out to be extremely potent competitors. Because PIP(2) is an important member of the nuclear PI signal transduction cascade, it might exert a regulatory influence on the binding of cIF proteins to Z- and other DNA conformations. From this interaction of cIF proteins with Z- and bent DNA and their previously detected affinities for MAR-like, ss, triple helical, and four-way junction DNA, it may be concluded that the filament proteins play a general role in such nuclear matrix-associated processes as DNA replication, recombination, repair, and transcription.

A potential endogenous ligand of annexin IV in the exocrine pancreas. Carbohydrate structure of GP-2, a glycosylphosphatidylinositol-anchored glycoprotein of zymogen granule membranes

We demonstrated previously that annexins IV, V, and VI, proteins of the calcium/phospholipid-binding annexin family, have glycosaminoglycan binding properties (Ishitsuka, R., Kojima, K., Utsumi, H., Ogawa, H., and Matsumoto, I. (1998) J. Biol. Chem. 273, 9935-9941). In this study, we investigated the endogenous ligands of annexin IV in the exocrine pancreas. Immunohistochemical study of bovine pancreas showed that annexin IV localized in the apical cytoplasmic region of pancreatic acinar cells where zymogen granules are concentrated. Because it is the major component of the zymogen granule membrane, the glycosylphosphatidylinositol-anchored glycoprotein GP-2 was suggested to play a role in apical sorting and secretion of zymogens. We isolated GP-2 from porcine pancreas extract and determined the structure of its N-linked oligosaccharides by two-dimensional mapping. The major carbohydrate structures of porcine GP-2 were trisialo-triantennary and tetrasialo-tetra-antennary complex-type oligosaccharides. Dot-blot assay showed that annexin IV interacts with GP-2 in the presence of calcium and that it recognizes the terminal sialic acid residues linked through alpha2-3 linkages to the carbohydrate of GP-2. Lectin blot assay showed that Maackia amurensis mitogen, a plant lectin specific for the trisaccharide sequence Sia(alpha)2-3Galbeta1-4GlcNAc of N-linked oligosaccharides, has strong affinity for GP-2. Thus, M. amurensis mitogen was used as a specific probe for GP-2 in the histochemical staining of the bovine pancreas. GP-2 was found to localize exclusively in the same apical cytoplasmic region of pancreatic acinar cells as annexin IV does. These results suggest that GP-2 is an endogenous ligand of annexin IV in the exocrine pancreas.

Control of the nuclear-cytoplasmic partitioning of annexin II by a nuclear export signal and by p11 binding

This study investigated mechanisms controlling the nuclear-cytoplasmic partitioning of annexin II (AnxII). AnxII and its ligand, p11, were localized by immunofluorescence to the cytoplasmic compartment of U1242MG cells, with minimal AnxII or p11 detected within nuclei. Similarly, GFP-AnxII and GFP-p11 chimeras localized to the endogenous proteins. Likewise, GFP-AnxII(1-22) was excluded from nuclei, whereas GFP-AnxII(23-338) and GFP alone were distributed throughout the cells. Immunoprecipitation and biochemical studies showed that GFP-AnxII did not form heteromeric complexes with endogenous p11 and AnxII. Thus, the AnxII N-tail is necessary and sufficient to cause nuclear exclusion of the GFP fusion protein but this does not involve p11 binding. A nuclear export signal consensus sequence was found in the AnxII 3-12 region. The consensus mutant GFP-AnxII(L10A/L12A) confirmed that these residues are necessary for nuclear exclusion. The nuclear exclusion of GFP-AnxII(1-22) was temperature-dependent and reversible, and the nuclear export inhibitor leptomycin B (LmB) caused GFP-AnxII or overexpressed AnxII monomer to accumulate in nuclei. Therefore, AnxII monomer can enter the nucleus and is actively exported. However, LmB had little effect on the localization of AnxII/p11 complex in U1242MG cells, indicating that the complex is sequestered in the cytoplasm. By contrast, LmB treatment of v-src-transformed fibroblasts caused endogenous AnxII to accumulate in nuclei. The LmB-induced nuclear accumulation of AnxII was accelerated by pervanadate and inhibited by genistein, suggesting that phosphorylation promotes nuclear entry of AnxII. Thus, nuclear exclusion of AnxII results from nuclear export of the monomer and sequestration of AnxII/p11 complex, and may be modulated by phosphorylation.

Redistribution of annexin in gravistimulated pea plumules

We used immunocytochemistry to investigate the effects of gravistimulation on annexin localization in etiolated pea plumule shoots. In longitudinal sections, an asymmetric annexin immunostaining pattern was observed in a defined group of cells located just basipetal to apical meristems at the main shoot apex and at all of the axillary buds, an area classically referred to as the leaf gap. The pattern was observed using both protein-A-purified anti-annexin and affinity-purified anti-annexin antibodies for the immunostaining. A subset of the cells with the annexin staining also showed an unusually high level of periodic acid Schiff (PAS) staining in their cell walls. Prior to gravistimulation, the highest concentration of annexin was oriented toward the direction of gravity along the apical end of these immunostained cells. In contrast, both at 15 and 30 min after gravistimulation, the annexin immunostain became more evenly distributed all around the cell and more distinctly cell peripheral. The asymmetry along the lower wall of these cells was no longer evident. In accord with current models of annexin action, we interpret the results to indicate that annexin-mediated secretion in the leaf gap area is preferentially toward the apical meristem prior to gravistimulation, and that gravistimulation results in a redirection of this secretion. These data are to our knowledge the first to show a correlation between the vector of gravity and the distribution of annexins in the cells of flowering plants.

Lipocortin (Annexin) I heterotetramer binds to purine RNA and pyrimidine DNA

Lipocortin I-like protein with a molecular weight of 94,000 Da as judged by Western analysis was found to bind to ssDNA rather than to dsDNA in a Ca(2+)-dependent manner. This protein was also bound to [(32)P]poly(rA) and [(32)P]poly(rG) as measured by EMSA. Poly(rG), poly(rA), poly(dC), and poly(dT) were competitive against binding of either [(32)P]poly(rA) or [(32)P]poly(rG), while poly(rC), poly(rU), and poly(dA) were less effective binding competitors. The binding of this protein to poly(rA) or poly(rG) was inhibited by immunoprecipitable anti-lipocortin I (calpactin II) and anti-S100 protein antibodies, but not by an anti-Ig antibody. Phospholipids such as phosphatidylserine and phosphatidylinositol enhanced the binding of lipocortin I to poly(rA). Taken together, our present observations suggest that the lipocortin I-S100 protein heterotetramer binds to either purine RNAs or pyrimidine ssDNAs in a Ca(2+)- and phospholipid-dependent manner.

Lipocortin V may function as a signaling protein for vascular endothelial growth factor receptor-2/Flk-1

Binding of vascular endothelial growth factor (VEGF) to its receptor, VEGFR-2 (Flk-1/KDR), induces dimerization and activation of the tyrosine kinase domain of the receptor, resulting in autophosphorylation of cytoplasmic tyrosine residues used as docking sites for signaling proteins that relay the signals for cell proliferation, migration, and permeability enhancement. We explored the VEGF/receptor signaling pathway by performing a two-hybrid screen of a rat lung cDNA library in yeast using the intracellular domain of rat VEGFR-2 as bait. Two clones encoding lipocortin V were isolated. Subsequent studies with the yeast two-hybrid assay showed that the complete intracellular domain of VEGFR-2 was required for the interaction. Co-immunoprecipitation of translated proteins confirmed the interaction between the VEGF receptor and lipocortin V. VEGF induced a rapid tyrosine phosphorylation of lipocortin V in human umbilical vein endothelial cells (HUVEC). Pretreatment of HUVEC with antisense oligodeoxyribonucleotide (ODN) for lipocortin V significantly inhibited VEGF-induced cell proliferation, which was accompanied by a decrease in protein synthesis and tyrosine phosphorylation of lipocortin V. Our results indicate that lipocortin V may function as a signaling protein for VEGFR-2 by directly interacting with the intracellular domain of the receptor and appears to be involved in regulation of vascular endothelial cell proliferation mediated by VEGFR-2.

Ovariectomy enhances the expression and nuclear translocation of annexin 5 in rat anterior pituitary gonadotrophs

An observation of abundant annexin 5, a novel calcium and phospholipid binding protein, in gonadotrophs of the anterior pituitary gland of ovariectomized rats (Kawaminami et al., 1997 (in press)) led us to investigate the effect of ovariectomy on the subcellular distribution and synthesis of annexin 5. Gonadotrophs, which were identified by immunocytochemistry with anti LHbeta antiserum, dramatically increased their size three weeks after ovariectomy. These 'castration cells' were shown to contain abundant annexin 5 associated with the plasma membrane, nuclear envelope and nucleoplasm. True localization within the nucleus was shown by optical sectioning with a confocal microscope. Northern blot analysis showed that annexin 5 mRNA in the anterior pituitary gland was increased 24 h after ovariectomy. It further increased in parallel with LHbeta mRNA at three weeks and it decreased in parallel with LHbeta mRNA when estradiol (250 microg/animal per day) was given for 3 days. These results show that the expression of pituitary annexin 5 is controlled by ovarian estradiol and imply that annexin 5 plays a physiological role in the nucleus of activated gonadotrophs.