Biophysical and molecular properties of annexin-formed channels

Annexin A family: A new perspective on the regulation of bone metabolism

Osteoblast-mediated bone formation and osteoclast-mediated bone resorption are critical processes in bone metabolism. Annexin A, a calcium-phospholipid binding protein, regulates the proliferation and differentiation of bone cells, including bone marrow mesenchymal stem cells, osteoblasts, and osteoclasts, and has gradually become a marker gene for the diagnosis of osteoporosis. As calcium channel proteins, the annexin A family members are closely associated with mechanical stress, which can target annexins A1, A5, and A6 to promote bone cell differentiation. Despite the significant clinical potential of annexin A family members in bone metabolism, few studies have reported on these mechanisms. Therefore, based on a review of relevant literature, this article elaborates on the specific functions and possible mechanisms of annexin A family members in bone metabolism to provide new ideas for their application in the prevention and treatment of bone diseases, such as osteoporosis.

Molecular characterization and functional implications on mouse peripheral blood mononuclear cells of annexin proteins from Echinococcus granulosus sensu lato

BACKGROUND

Cystic echinococcosis (CE) is a life-threatening zoonotic disease caused by the larval stage of Echinococcus granulosus sensu lato, which employs various strategies to evade the host immune system for survival. Recent advances have revealed the role of annexins as excretory/secretory products, providing new insights into the immune regulation by these proteins in the pathogenesis of CE.

METHODS

Echinococcus granulosus annexin B proteins EgANXB2, EgANXB18, EgANXB20, and EgANXB23 were cloned, expressed, and analyzed using bioinformatic tools. Membrane binding analysis was used to assess their bioactivity, while their immunoreactivity and tissue distribution characteristics were determined experimentally using western blotting and immunofluorescence staining, respectively. Furthermore, quantitative real-time reverse transcription PCR (qRT-PCR) was used to analyze the mRNA expression profiles of EgANXBs in different developmental stages of E. granulosus. Finally, immunofluorescence staining, cell counting kit 8 assays, flow cytometry, transwell migration assays, and qRT-PCR were used to evaluate the functional effects of rEgANXB18 and rEgANXB20 on mouse peripheral blood mononuclear cells (PBMCs).

RESULTS

In this study, we identified four EgANXBs with conserved protein structures and calcium-dependent phospholipid binding activities. rEgANXBs were recognized by serum from sheep infected with E. granulosus and distributed in the germinal layer of fertile cysts. Interestingly, transcription levels of the four EgANXBs were significantly higher in protoscoleces than in 28-day strobilated worms. Moreover, we demonstrated that rEgANXB18 and rEgANXB20 were secretory proteins that could bind to PBMCs and regulate their function. Specifically, rEgANXB18 inhibited cell proliferation and migration while promoting cell apoptosis, NO production, and cytokine profile shifting. In contrast, rEgANXB20 showed limited effects on apoptosis but inhibited NO production.

CONCLUSIONS

Our findings suggested that among the four identified EgANXBs, EgANXB2 and EgANXB23 might play a pivotal role for the development of protoscoleces, while EgANXB18 and EgANXB20, as secretory proteins, appeared to participate in the host-parasite interaction by regulating the function of immune cells.

Analysis of Dysferlin Direct Interactions with Putative Repair Proteins Links Apoptotic Signaling to Ca2+ Elevation via PDCD6 and FKBP8

Quantitative surface plasmon resonance (SPR) was utilized to determine binding strength and calcium dependence of direct interactions between dysferlin and proteins likely to mediate skeletal muscle repair, interrupted in limb girdle muscular dystrophy type 2B/R2. Dysferlin canonical C2A (cC2A) and C2F/G domains directly interacted with annexin A1, calpain-3, caveolin-3, affixin, AHNAK1, syntaxin-4, and mitsugumin-53, with cC2A the primary target and C2F lesser involved, overall demonstrating positive calcium dependence. Dysferlin C2 pairings alone showed negative calcium dependence in almost all cases. Like otoferlin, dysferlin directly interacted via its carboxy terminus with FKBP8, an anti-apoptotic outer mitochondrial membrane protein, and via its C2DE domain with apoptosis-linked gene (ALG-2/PDCD6), linking anti-apoptosis with apoptosis. Confocal Z-stack immunofluorescence confirmed co-compartmentalization of PDCD6 and FKBP8 at the sarcolemmal membrane. Our evidence supports the hypothesis that prior to injury, dysferlin C2 domains self-interact and give rise to a folded, compact structure as indicated for otoferlin. With elevation of intracellular Ca2+ in injury, dysferlin would unfold and expose the cC2A domain for interaction with annexin A1, calpain-3, mitsugumin 53, affixin, and caveolin-3, and dysferlin would realign from its interactions with PDCD6 at basal calcium levels to interact strongly with FKBP8, an intramolecular rearrangement facilitating membrane repair.

Role of calcium-sensor proteins in cell membrane repair

Cell membrane repair is a critical process used to maintain cell integrity and survival from potentially lethal chemical, and mechanical membrane injury. Rapid increases in local calcium levels due to a membrane rupture have been widely accepted as a trigger for multiple membrane-resealing models that utilize exocytosis, endocytosis, patching, and shedding mechanisms. Calcium-sensor proteins, such as synaptotagmins (Syt), dysferlin, S100 proteins, and annexins, have all been identified to regulate, or participate in, multiple modes of membrane repair. Dysfunction of membrane repair from inefficiencies or genetic alterations in these proteins contributes to diseases such as muscular dystrophy (MD) and heart disease. The present review covers the role of some of the key calcium-sensor proteins and their involvement in membrane repair.

Annexin A protein family: Focusing on the occurrence, progression and treatment of cancer

The annexin A (ANXA) protein family is a well-known tissue-specific multigene family that encodes Ca²⁺ phospholipid-binding proteins. A considerable amount of literature is available on the abnormal expression of ANXA proteins in various malignant diseases, including cancer, atherosclerosis and diabetes. As critical regulatory molecules in cancer, ANXA proteins play an essential role in cancer progression, proliferation, invasion and metastasis. Recent studies about their structure, biological properties and functions in different types of cancers are briefly summarised in this review. We further discuss the use of ANXA as new class of targets in the clinical diagnosis and treatment of cancer.

Pine defense against eggs of an herbivorous sawfly is elicited by an annexin-like protein present in egg-associated secretion

Known elicitors of plant defenses against eggs of herbivorous insects are low-molecular-weight organic compounds associated with the eggs. However, previous studies provided evidence that also proteinaceous compounds present in secretion associated with eggs of the herbivorous sawfly Diprion pini can elicit defensive responses in  Pinus sylvestris. Pine responses induced by the proteinaceous secretion are known to result in enhanced emission of (E)-β-farnesene, which attracts egg parasitoids killing the eggs. Here, we aimed to identify the defense-eliciting protein and elucidate its function. After isolating the defense-eliciting protein from D. pini egg-associated secretion by ultrafiltration and gel electrophoresis, we identified it by MALDI-TOF mass spectrometry as an annexin-like protein, which we named 'diprionin'. Further GC-MS analyses showed that pine needles treated with heterologously expressed diprionin released enhanced quantities of (E)-β-farnesene. Our bioassays confirmed attractiveness of diprionin-treated pine to egg parasitoids. Expression of several pine candidate genes involved in terpene biosynthesis and regulation of ROS homeostasis was similarly affected by diprionin and natural sawfly egg deposition. However, the two treatments had different effects on expression of pathogenesis-related genes (PR1, PR5). Diprionin is the first egg-associated proteinaceous elicitor of indirect plant defense against insect eggs described so far.

The seesaw between normal function and protein aggregation: How functional interactions may increase protein solubility

Protein aggregation has been studied for at least 3 decades, and many of the principles that regulate this event are relatively well understood. Here, however, we present a different perspective to explain why proteins aggregate: we argue that aggregation may occur as a side-effect of the lack of one or more natural partners that, under physiologic conditions, would act as chaperones. This would explain why the same surfaces that have evolved for functional purposes are also those that favour aggregation. In the course of reviewing this field, we substantiate our hypothesis with three paradigmatic examples that argue for the generality of our proposal. An obvious corollary of this hypothesis is, of course, that targeting the physiological partners of a protein could be the most direct and specific approach to designing anti-aggregation molecules. Our analysis may thus inform a different strategy for combating diseases of protein aggregation and misfolding.

Populus euphratica annexin1 facilitates cadmium enrichment in transgenic Arabidopsis

Phytoremediation offers a great potential for affordable remediation of heavy metal (HM)-polluted soil and water. Screening and identifying candidate genes related to HM uptake and transport is prerequisite for improvement of phytoremediation by genetic engineering. Using the cadmium (Cd)-hypersensitive Populus euphratica, an annexin encoding gene facilitating Cd enrichment was identified in this study. With a 12 h exposure to CdCl₂ (50-100 μM), P. euphratica cells down-regulated transcripts of annexin1 (PeANN1). PeANN1 was homologue to Arabidopsis annexin1 (AtANN1) and localized mainly to the plasma membrane (PM) and cytosol. Compared with wild type and Atann1 mutant, PeANN1 overexpression in Arabidopsis resulted in a more pronounced decline in survival rate and root length after a long-term Cd stress (10 d, 50 μM), due to a higher cadmium accumulation in roots. PeANN1-transgenic roots exhibited enhanced influx conductance of Cd²⁺ under cadmium shock (30 min, 50 μM) and short-term stress (12 h, 50 μM). Noteworthy, the PeANN1-facilitated Cd²⁺ influx was significantly inhibited by a calcium-permeable channel (CaPC) inhibitor (GdCl₃) but was promoted by 1 mM H₂O₂, indicating that Cd²⁺ entered root cells via radical-activated CaPCs in the PM. Therefore, PeANN1 can serve as a candidate gene for improvement of phytoremediation by genetic engineering.

ANXC7 Is a Mitochondrion-Localized Annexin Involved in Controlling Conidium Development and Oxidative Resistance in the Thermophilic Fungus Thermomyces lanuginosus

Annexins (ANXs) are widely expressed and structurally related proteins which play multiple biological roles in animals, plants, and fungi. Although ANXs have been localized to the cytosol and the cell membrane and the molecular basis of the four annexin repeats is well established, the in vivo roles of these proteins are still far from clear, particularly with regard to the filamentous fungi. Thermomyces lanuginosus, a thermophilic fungus, is widely used in the fermentation industry; however, the role of ANX in this organism is unknown. In this study, a single ANX homologue (ANXC7) was identified and characterized in T. lanuginosus. The expression pattern indicated that ANXC7 is closely associated to conidium development, and it accumulated in the mitochondria of the forming conidia. The deletion of ANXC7 (ΔANXC7) resulted in no obvious phenotype related to colony growth on solid CM medium. However, when ΔANXC7 was grown in CM liquid culture, the mycelium masses appeared to be larger and looser compared to the wild-type. Additionally, the dry weight of the mutant mycelia was significantly increased. Under conditions that compromise cell-wall integrity, ΔANXC7 was less vulnerable than the wild-type with regard to such damage. Moreover, based on a surface hydrophobicity test, the ΔANXC7 strain was clearly less hydrophobic. The growth of ΔANXC7 was inhibited when grown under selected stress conditions, particularly with regard to salt stress; however, the oxidative resistance to exogenous H₂O₂ in ΔANXC7 was increased, and endogenous H₂O₂ levels within the ΔANXC7 were lower than in the wild-type, thereby suggesting that the ANXC7 specifically controls oxidative resistance. Based on microscopic observation, 4-day-conidia were more prevalent than 5-day conidia on the conidiophore stalk of ΔANXC7, even though the ΔANXC7 demonstrated an increased production of conidia during these days, indicating precocious conidial maturation and shedding from the conidiophore stalk in this strain. Taken together, our data indicate that ANXC7 localizes to the mitochondria and is involved in controlling conidium development and oxidative resistance in T. lanuginosus.

Inhibition of somatosensory mechanotransduction by annexin A6

Mechanically activated, slowly adapting currents in sensory neurons have been linked to noxious mechanosensation. The conotoxin NMB-1 (noxious mechanosensation blocker-1) blocks such currents and inhibits mechanical pain. Using a biotinylated form of NMB-1 in mass spectrometry analysis, we identified 67 binding proteins in sensory neurons and a sensory neuron-derived cell line, of which the top candidate was annexin A6, a membrane-associated calcium-binding protein. Annexin A6-deficient mice showed increased sensitivity to mechanical stimuli. Sensory neurons from these mice showed increased activity of the cation channel Piezo2, which mediates a rapidly adapting mechano-gated current linked to proprioception and touch, and a decrease in mechanically activated, slowly adapting currents. Conversely, overexpression of annexin A6 in sensory neurons inhibited rapidly adapting currents that were partially mediated by Piezo2. Furthermore, overexpression of annexin A6 in sensory neurons attenuated mechanical pain in a mouse model of osteoarthritis, a disease in which mechanically evoked pain is particularly problematic. These data suggest that annexin A6 can be exploited to inhibit chronic mechanical pain.

Annexins-Coordinators of Cholesterol Homeostasis in Endocytic Pathways

The spatiotemporal regulation of calcium (Ca2+) storage in late endosomes (LE) and lysosomes (Lys) is increasingly recognized to influence a variety of membrane trafficking events, including endocytosis, exocytosis, and autophagy. Alterations in Ca2+ homeostasis within the LE/Lys compartment are implicated in human diseases, ranging from lysosomal storage diseases (LSDs) to neurodegeneration and cancer, and they correlate with changes in the membrane binding behaviour of Ca2+-binding proteins. This also includes Annexins (AnxA), which is a family of Ca2+-binding proteins participating in membrane traffic and tethering, microdomain organization, cytoskeleton interactions, Ca2+ signalling, and LE/Lys positioning. Although our knowledge regarding the way Annexins contribute to LE/Lys functions is still incomplete, recruitment of Annexins to LE/Lys is greatly influenced by the availability of Annexin bindings sites, including acidic phospholipids, such as phosphatidylserine (PS) and phosphatidic acid (PA), cholesterol, and phosphatidylinositol (4,5)-bisphosphate (PIP2). Moreover, the cytosolic portion of LE/Lys membrane proteins may also, directly or indirectly, determine the recruitment of Annexins to LE. Strikingly, within LE/Lys, AnxA1, A2, A6, and A8 differentially contribute to cholesterol transport along the endocytic route, in particular, cholesterol transfer between LE and other compartments, positioning Annexins at the centre of major pathways mediating cellular cholesterol homeostasis. Underlying mechanisms include the formation of membrane contact sites (MCS) and intraluminal vesicles (ILV), as well as the modulation of LE-cholesterol transporter activity. In this review, we will summarize the current understanding how Annexins contribute to influence LE/Lys membrane transport and associated functions.

Annexins: Ca2+ Effectors Determining Membrane Trafficking in the Late Endocytic Compartment

Despite the discovery of annexins 40 years ago, we are just beginning to understand some of the functions of these still enigmatic proteins. Defined and characterized by their ability to bind anionic membrane lipids in a Ca²⁺-dependent manner, each annexin has to be considered a multifunctional protein, with a multitude of cellular locations and diverse activities. Underlying causes for this considerable functional diversity include their capability to associate with multiple cytosolic and membrane proteins. In recent years, the increasingly recognized establishment of membrane contact sites between subcellular compartments opens a new scenario for annexins as instrumental players to link Ca²⁺ signalling with the integration of membrane trafficking in many facets of cell physiology. In this chapter, we review and discuss current knowledge on the contribution of annexins in the biogenesis and functioning of the late endocytic compartment, affecting endo- and exocytic pathways in a variety of physiological consequences ranging from membrane repair, lysosomal exocytosis, to cell migration.

Fungal annexins: a mini review

The large family of annexins is composed of more than a thousand members which are typically phospholipid-binding proteins. Annexins act in a number of signalling networks and membrane trafficking events which are fundamental to cell physiology. Annexins exert their functions mainly through their calcium-dependent membrane binding abilities; however, some calcium-independent interactions have been documented in the literature. Although mammalian and plant annexins have been well characterized, little is known about this family in fungi. This mini review summarizes the available data on fungal annexins.

Down-regulating annexin gene GhAnn2 inhibits cotton fiber elongation and decreases Ca2+ influx at the cell apex

Cotton fiber is a single cell that differentiates from the ovule epidermis and undergoes synchronous elongation with high secretion and growth rate. Apart from economic importance, cotton fiber provides an excellent single-celled model for studying mechanisms of cell-growth. Annexins are Ca(2+)- and phospholipid-binding proteins that have been reported to be localized in multiple cellular compartments and involved in control of vesicle secretions. Although several annexins have been found to be highly expressed in elongating cotton fibers, their functional roles in fiber development remain unknown. Here, 14 annexin family members were identified from the fully sequenced diploid G. raimondii (D5 genome), half of which were expressed in fibers of the cultivated tetraploid species G. hirsutum (cv. YZ1). Among them, GhAnn2 from the D genome of the tetraploid species displayed high expression level in elongating fiber. The expression of GhAnn2 could be induced by some phytohormones that play important roles in fiber elongation, such as IAA and GA3. RNAi-mediated down-regulation of GhAnn2 inhibited fiber elongation and secondary cell wall synthesis, resulting in shorter and thinner mature fibers in the transgenic plants. Measurement with non-invasive scanning ion-selective electrode revealed that the rate of Ca(2+) influx from extracellular to intracellular was decreased at the fiber cell apex of GhAnn2 silencing lines, in comparison to that in the wild type. These results indicate that GhAnn2 may regulate fiber development through modulating Ca(2+) fluxes and signaling.

Interactomics of Qa-SNARE in Arabidopsis thaliana

Membrane trafficking in plants is involved in cellular development and the adaptation to various environmental changes. SNARE (soluble N-ethylmaleimide-sensitive factor attachment receptor) proteins mediate the fusion between vesicles and organelles to facilitate transport cargo proteins in cells. To characterize further the SNARE protein networks in cells, we carried out interactome analysis of SNARE proteins using 12 transgenic Arabidopsis thaliana plants expressing green fluorescent protein (GFP)-tagged Qa-SNAREs (SYP111, SYP121, SYP122, SYP123, SYP132, SYP21, SYP22, SYP31, SYP32, SYP41, SYP42 and SYP43). Microsomal fractions were prepared from each transgenic root, and subjected to immunoprecipitation (IP) using micromagnetic beads coupled to anti-GFP antibodies. To identify Qa-SNARE-interacting proteins, all immunoprecipitated products were then subjected to mass spectrometric (IP-MS) analysis. The IP-MS data revealed not only known interactions of SNARE proteins, but also unknown interactions. The IP-MS results were next categorized by gene ontology analysis. The data revealed that categories of cellular component organization, the cytoskeleton and endosome were enriched in the SYP2, SYP3 and SYP4 groups. In contrast, transporter activity was classified specifically in the SYP132 group. We also identified a novel interaction between SYP22 and VAMP711, which was validated using co-localization analysis with confocal microscopy and IP. Additional novel SNARE-interacting proteins play roles in vesicle transport and lignin biosynthesis, and were identified as membrane microdomain-related proteins. We propose that Qa-SNARE interactomics is useful for understanding SNARE interactions across the whole cell.

Calcium and reactive oxygen species rule the waves of signaling

Calcium signaling and reactive oxygen species signaling are directly connected, and both contribute to cell-to-cell signal propagation in plants.

Cotton AnnGh3 encoding an annexin protein is preferentially expressed in fibers and promotes initiation and elongation of leaf trichomes in transgenic Arabidopsis

The annexins are a multifamily of calcium-regulated phospholipid-binding proteins. To investigate the roles of annexins in fiber development, four genes encoding putative annexin proteins were isolated from cotton (Gossypium hirsutum) and designated AnnGh3, AnnGh4, AnnGh5, and AnnGh6. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) results indicated that AnnGh3, AnnGh4, and AnnGh5 were preferentially expressed in fibers, while the transcripts of AnnGh6 were predominantly accumulated in roots. During fiber development, the transcripts of AnnGh3/4/5 genes were mainly accumulated in rapidly elongating fibers. With fiber cells further developed, their expression activity was dramatically declined to a relatively low level. In situ hybridization results indicated that AnnGh3 and AnnGh5 were expressed in initiating fiber cells (0-2 DPA). Additionally, their expression in fibers was also regulated by phytohormones and [Ca(2+)]. Subcellular localization analysis discovered that AnnGh3 protein was localized in the cytoplasm. Overexpression of AnnGh3 in Arabidopsis resulted in a significant increase in trichome density and length on leaves of the transgenic plants, suggesting that AnnGh3 may be involved in fiber cell initiation and elongation of cotton.

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.

Proteomic analysis of male zebrafish livers chronically exposed to perfluorononanoic acid

Perfluorononanoic acid (PFNA), a synthetic perfluorinated carboxylic acid and fluorosurfactant, is a known environmental contaminant found in people and wildlife. To understand the hepatotoxicity mechanism of PFNA, male zebrafish (n=200) were exposed to differing concentrations of PFNA (0, 0.1, 0.5, and 1.0 mg/L) for 180 days. A two-dimensional difference gel electrophoresis (2-D DIGE) approach coupled with MALDI-TOF-MS/MS analysis was employed to detect and identify the differential expressed proteins. A total of 57 proteins were successfully identified and categorized into functional classes that included metabolism (amino acid metabolism, TCA cycle and pyruvate metabolism, gluconeogenesis and glycolysis, protein metabolism and modification, and nucleotides metabolism), structure and motility, stress and defense, signal transduction, and cell communication. Our proteomic analyses added new perspective to PFNA hepatotoxicity in zebrafish. Results regarding mRNA levels demonstrated that the involvement of peroxisome proliferator-activated receptors (PPARs) could not sufficiently explain the hepatotoxicity mechanism of PFAAs in zebrafish. The extensive protein variations indicated that multiple cellular pathways were involved in and suggested that multiple protein molecules should be simultaneously targeted as an effective strategy to counter PFNA toxicity. Other potential modes should be further investigated.

Control of kidney development by calcium ions

From the formation of a simple kidney in amphibian larvae, the pronephros, to the formation of the more complex mammalian kidney, the metanephros, calcium is present through numerous steps of tubulogenesis and nephron induction. Several calcium-binding proteins such as regucalcin/SMP-30 and calbindin-D28k are commonly used to label pronephric tubules and metanephric ureteral epithelium, respectively. However, the involvement of calcium and calcium signalling at various stages of renal organogenesis was not clearly delineated. In recent years, several studies have pinpointed an unsuspected role of calcium in determination of the pronephric territory and for conversion of metanephric mesenchyme into nephrons. Influx of calcium and calcium transients have been recorded in the pool of renal progenitors to allow tubule formation, highlighting the occurrence of calcium-dependent signalling events during early kidney development. Characterization of nuclear calcium signalling is emerging. Implication of the non-canonical calcium/NFAT Wnt signalling pathway as an essential mechanism to promote nephrogenesis has recently been demonstrated. This review examines the current knowledge of the impact of calcium ions during embryonic development of the kidney. It focuses on Ca(2+) binding proteins and Ca(2+) sensors that are involved in renal organogenesis and briefly examines the link between calcium-dependent signals and polycystins.

Annexins

Annexins are multifunctional lipid-binding proteins. Plant annexins are expressed throughout the life cycle and are under environmental control. Their association or insertion into membranes may be governed by a range of local conditions (Ca(2+), pH, voltage or lipid identity) and nonclassical sorting motifs. Protein functions include exocytosis, actin binding, peroxidase activity, callose synthase regulation and ion transport. As such, annexins appear capable of linking Ca(2+), redox and lipid signalling to coordinate development with responses to the biotic and abiotic environment. Significant advances in plant annexin research have been made in the past 2 yr. Here, we review the basis of annexin multifunctionality and suggest how these proteins may operate in the life and death of a plant cell.

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.

Differences in pig muscle proteome according to HAL genotype: implications for meat quality defects

Bidimensional electrophoresis was used to compare sarcoplasmic protein profiles of early post-mortem pig semimembranosus muscles, sampled from pigs of different HAL genotypes (RYR1 mutation 1841T/C): 6 NN, 6 Nn, 6 nn. ANOVA showed that 55 (18%) of the total of 300 matched protein spots were influenced by genotype, and hierarchical clustering analysis identified 31 (10% of the matched proteins) additional proteins coregulated with these proteins. Fold-changes of differentially expressed proteins were between 1.3 and 21.8. Peptide mass fingerprinting identification of 78 of these 86 proteins indicates that faster pH decline of nn pigs was not explained by higher abundance of glycolytic enzymes. Results indicate further that nn muscles contained fewer proteins of the oxidative metabolic pathway, fewer antioxidants, and more protein fragments. Lower abundance of small heat shock proteins and myofibrillar proteins in nn muscles may at least partly be explained by the effect of pH on their extractability. Possible consequences of lower levels of antioxidants and repair capacities, increased protein fragmentation, and lower extractability of certain proteins in nn muscles on meat quality are discussed.

Zea mays annexins modulate cytosolic free Ca2+ and generate a Ca2+-permeable conductance

Regulation of reactive oxygen species and cytosolic free calcium ([Ca(2+)](cyt)) is central to plant function. Annexins are small proteins capable of Ca(2+)-dependent membrane binding or membrane insertion. They possess structural motifs that could support both peroxidase activity and calcium transport. Here, a Zea mays annexin preparation caused increases in [Ca(2+)](cyt) when added to protoplasts of Arabidopsis thaliana roots expressing aequorin. The pharmacological profile was consistent with annexin activation (at the extracellular plasma membrane face) of Arabidopsis Ca(2+)-permeable nonselective cation channels. Secreted annexins could therefore modulate Ca(2+) influx. As maize annexins occur in the cytosol and plasma membrane, they were incorporated at the intracellular face of lipid bilayers designed to mimic the plasma membrane. Here, they generated an instantaneously activating Ca(2+)-permeable conductance at mildly acidic pH that was sensitive to verapamil and Gd(3+) and had a Ca(2+)-to-K(+) permeability ratio of 0.36. These results suggest that cytosolic annexins create a Ca(2+) influx pathway directly, particularly during stress responses involving acidosis. A maize annexin preparation also demonstrated in vitro peroxidase activity that appeared independent of heme association. In conclusion, this study has demonstrated that plant annexins create Ca(2+)-permeable transport pathways, regulate [Ca(2+)](cyt), and may function as peroxidases in vitro.

Serum ferritin and transferrin levels as serologic markers of methylene diphenyl diisocyanate-induced occupational asthma

BACKGROUND

Although methylene diphenyl diisocyanate (MDI) may induce occupational asthma in the workplace, the pathogenic mechanisms are unclear.

OBJECTIVES

By using bronchoalveolar lavage fluid, we sought to identify proteins that were differentially expressed between subjects with MDI-induced occupational asthma (MDI-OA) and asymptomatic exposed controls (AECs).

METHODS

To find proteins that were differentially expressed between the MDI-OA and AEC groups, 2-dimensional electrophoresis was performed by using bronchoalveolar lavage fluid obtained from subjects after MDI-specific inhalation challenge. The selected protein spots were then identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The clinical relevance of the differentially expressed spots was compared by ELISA using sera from the MDI-OA/eosinophilic bronchitis, AEC, and unexposed healthy control groups. Receiver operating characteristic curves were then plotted, and the sensitivity and specificity were determined.

RESULTS

Twenty-three protein spots were identified that distinguished the subjects with MDI-OA from those in the AEC group. Among them, ferritin expression was downregulated whereas transferrin expression was upregulated in subjects with MDI-OA compared with AEC; these results were validated by ELISA using sera from the MDI-OA/EB and AEC groups. To identify subjects with MDI-OA, the optimal serum cutoff levels were 69.84 ng/mL for ferritin and 2.48 microg/mL for transferrin. When these 2 parameters were combined, the sensitivity was 71.43% and the specificity was 85.71%.

CONCLUSION

Serum ferritin and transferrin levels are associated with the phenotype of MDI-OA.

Group IVA cytosolic phospholipase A2 (cPLA2alpha) and integrin alphaIIbbeta3 reinforce each other's functions during alphaIIbbeta3 signaling in platelets

Group IVA cytosolic phospholipase A(2) (cPLA(2)alpha) catalyzes release of arachidonic acid from glycerophospholipids, leading to thromboxane A(2) (TxA(2)) production. Some platelet agonists stimulate cPLA(2)alpha, but others require fibrinogen binding to alphaIIbbeta3 to elicit TxA(2). Therefore, relationships between cPLA(2)alpha and alphaIIbbeta3 were examined. cPLA(2)alpha and a cPLA(2)alpha binding partner, vimentin, coimmunoprecipitated with alphaIIbbeta3 from platelets, independent of fibrinogen binding. Studies with purified proteins and with recombinant proteins expressed in CHO cells determined that the interaction between cPLA(2)alpha and alphaIIbbeta3 was indirect and was dependent on the alphaIIb and beta3 cytoplasmic tails. Fibrinogen binding to alphaIIbbeta3 caused an increase in integrin-associated cPLA(2)alpha activity in normal platelets, but not in cPLA(2)alpha-deficient mouse platelets or in human platelets treated with pyrrophenone, a cPLA(2)alpha inhibitor. cPLA(2)alpha activation downstream of alphaIIbbeta3 had functional consequences for platelets in that it was required for fibrinogen-dependent recruitment of activated protein kinase Cbeta to the alphaIIbbeta3 complex and for platelet spreading. Thus, cPLA(2)alpha and alphaIIbbeta3 interact to reinforce each other's functions during alphaIIbbeta3 signaling. This provides a plausible explanation for the role of alphaIIbbeta3 in TxA(2) formation and in the defective hemostatic function of mouse or human platelets deficient in cPLA(2)alpha.

An increase in intracellular Ca2+ is involved in pronephric tubule differentiation in the amphibian Xenopus laevis

The pronephros is the first kidney to develop and is the functional embryonic kidney in lower vertebrates. It has previously been shown that pronephric tubules can be induced to form ex vivo in ectodermal tissue by treatment with activin A and retinoic acid. In this study, we investigated the role of Ca(2+) signaling in the formation of the pronephric tubules both in intact Xenopus embryos and ex vivo. In the ex vivo system, retinoic acid but not activin A stimulated the generation of Ca(2+) transients during tubule formation. Furthermore, tubule differentiation could be induced by agents that increase the concentration of intracellular Ca(2+) in activin A-treated ectoderm. In addition, tubule formation was inhibited by loading the ectodermal tissue with the Ca(2+) chelator, BAPTA-AM prior to activin A/retinoic acid treatment. In intact embryos, Ca(2+) transients were also recorded during tubule formation, and photo-activation of the caged Ca(2+) chelator, diazo-2, localized to the pronephric domain, produced embryos with a shortened and widened tubule phenotype. In addition, the location of the Ca(2+) transients observed, correlated with the expression pattern of the specific pronephric tubule gene, XSMP-30. These data indicate that Ca(2+) might be a necessary signal in the process of tubulogenesis both ex vivo and in intact embryos.

Annexins: multifunctional components of growth and adaptation

Plant annexins are ubiquitous, soluble proteins capable of Ca(2+)-dependent and Ca(2+)-independent binding to endomembranes and the plasma membrane. Some members of this multigene family are capable of binding to F-actin, hydrolysing ATP and GTP, acting as peroxidases or cation channels. These multifunctional proteins are distributed throughout the plant and throughout the life cycle. Their expression and intracellular localization are under developmental and environmental control. The in vitro properties of annexins and their known, dynamic distribution patterns suggest that they could be central regulators or effectors of plant growth and stress signalling. Potentially, they could operate in signalling pathways involving cytosolic free calcium and reactive oxygen species.

Proteome analysis of human gastric cardia adenocarcinoma by laser capture microdissection

Background

The incidence of gastric cardiac adenocarcinoma (GCA) has been increasing in the past two decades in China, but the molecular changes relating to carcinogenesis have not been well characterised.

Methods

In this study, we used a comparative proteomic approach to analyse the malignant and nonmalignant gastric cardia epithelial cells isolated by navigated laser capture microdissection (LCM) from paired surgical specimens of human GCA.

Results

Twenty-seven spots corresponding to 23 proteins were consistently differentially regulated. Fifteen proteins were shown to be up-regulated, while eight proteins were shown to be down-regulated in malignant cells compared with nonmalignant columnar epithelial cells. The identified proteins appeared to be involved in metabolism, chaperone, antioxidation, signal transduction, apoptosis, cell proliferation, and differentiation. In addition, expressions of HSP27, 60, and Prx-2 in GCA specimens were further confirmed by immunohistochemical and western blot analyses.

Conclusion

These data indicate that the combination of navigated LCM with 2-DE provides an effective strategy for discovering proteins that are differentially expressed in GCA. Such proteins may contribute in elucidating the molecular mechanisms of GCA carcinogenesis. Furthermore, the combination provides potential clinical biomarkers that aid in early detection and provide potential therapeutic targets.

Potential Role of Annexin AnnAt1 from Arabidopsis thaliana in pH-Mediated Cellular Response to Environmental Stimuli

Plant annexins, Ca(2+)- and membrane-binding proteins, are probably implicated in the cellular response to stress resulting from acidification of cytosol. To understand how annexins can contribute to cellular ion homeostasis, we investigated the pH-induced changes in the structure and function of recombinant annexin AnnAt1 from Arabidopsis thaliana. The decrease of pH from 7.0 to 5.8 reduced the time of the formation of ion channels by AnnAt1 in artificial lipid membranes from 3.5 h to 15-20 min and increased their unitary conductance from 32 to 63 pS. These changes were accompanied by an increase in AnnAt1 hydrophobicity as revealed by hydrophobicity predictions, by an increase in fluorescence of 2-(p-toluidino)naphthalene-6-sulfonic acid (TNS) bound to AnnAt1 and fluorescence resonance energy transfer from AnnAt1 tryptophan residues to TNS. Concomitant lipid partition of AnnAt1 at acidic pH resulted in its partial protection from proteolytic digestion. Secondary structures of AnnAt1 determined by circular dichroism and infrared spectroscopy were also affected by lowering the pH from 7.2 to 5.2. These changes were characterized by an increase in beta-sheet content at the expense of alpha-helical structures, and were accompanied by reversible formation of AnnAt1 oligomers as probed by ultracentrifugation in a sucrose gradient. A further decrease of pH from 5.2 to 4.5 or lower led to the formation of irreversible aggregates and loss of AnnAt1 ionic conductance. Our findings suggest that AnnAt1 can sense changes of the pH milieu over the pH range from 7 to 5 and respond by changes in ion channel conductance, hydrophobicity, secondary structure of the protein and formation of oligomers. Further acidification irreversibly inactivated AnnAt1. We suggest that the pH-sensitive ion channel activity of AnnAt1 may play a role in intracellular ion homeostasis.

Prediction of functional sites based on the fuzzy oil drop model

A description of many biological processes requires knowledge of the 3-D structure of proteins and, in particular, the defined active site responsible for biological function. Many proteins, the genes of which have been identified as the result of human genome sequencing, and which were synthesized experimentally, await identification of their biological activity. Currently used methods do not always yield satisfactory results, and new algorithms need to be developed to recognize the localization of active sites in proteins. This paper describes a computational model that can be used to identify potential areas that are able to interact with other molecules (ligands, substrates, inhibitors, etc.). The model for active site recognition is based on the analysis of hydrophobicity distribution in protein molecules. It is shown, based on the analyses of proteins with known biological activity and of proteins of unknown function, that the region of significantly irregular hydrophobicity distribution in proteins appears to be function related.

Classifications of ovarian cancer tissues by proteomic patterns

Ovarian cancer is a morphologically and biologically heterogeneous disease. The identification of type-specific protein markers for ovarian cancer would provide the basis for more tailored treatments, as well as clues for understanding the molecular mechanisms governing cancer progression. In the present study, we used a novel approach to classify 24 ovarian cancer tissue samples based on the proteomic pattern of each sample. The method involved fractionation according to pI using chromatofocusing with analytical columns in the first dimension followed by separation of the proteins in each pI fraction using nonporous RP HPLC, which was coupled to an ESI-TOF mass analyzer for molecular weight (MW) analysis. A 2-D mass map of the protein content of each type of ovarian cancer tissue samples based upon pI versus intact protein MW was generated. Using this method, the clear cell and serous ovarian carcinoma samples were histologically distinguished by principal component analysis and clustering analysis based on their protein expression profiles and subtype-specific biomarker candidates of ovarian cancers were identified, which could be further investigated for future clinical study.

Mapping Functional Domains of Chloride Intracellular Channel (CLIC) Proteins in Vivo

Chloride intracellular channel (CLIC) proteins are small proteins distantly related to the omega family of glutathione S-transferases (GSTs). CLIC proteins are expressed in a wide variety of tissues in multicellular organisms and are targeted to specific cellular membranes. Members of this family are capable in vitro of changing conformation from a globular, soluble state to a membrane-inserted state in which they provide chloride conductance. The structural basis for in vivo CLIC protein function, however, is not well understood. We have mapped the functional domains of CLIC family members using an in vivo assay for membrane localization and function of CLIC proteins in the nematode Caenorhabditis elegans. A<70 amino acid N-terminal domain is a key determinant of membrane localization and function of invertebrate CLIC proteins. This domain, which we term the ''PTM'' domain, named after an amphipathic putative transmembrane helix contained within it, directs distinct C. elegans CLIC homologs to distinct subcellular membranes. We find that within the PTM region, the cysteine residues required for GST-type activity are unnecessary for invertebrate CLIC function, but that specific residues within the proposed transmembrane helix are necessary for correct targeting and protein function. We find that among all tested invertebrate CLIC proteins, function appears to be completely conserved despite striking differences in the charged residues contained within the amphipathic helix. This indicates that these residues do not contribute to anion selectivity as previously suggested. We find that outside the PTM region, the remaining three-quarters of CLIC protein sequence is functionally equivalent not only among vertebrate and invertebrate CLIC proteins, but also among the more distantly related GST-omega and GST-sigma proteins. The PTM region thus provides both targeting information and CLIC functional specificity, possibly adapting GST-type proteins to function as ion channels.

Effects of mutagenesis of W343 in human annexin A6 isoform 1 on its interaction with GTP: nucleotide-induced oligomer formation and ion channel activity

Accumulated experimental evidence suggests that annexin A6 (AnxA6) is involved in ion transport in various tissues. Such a biological function is related either to the modulation of ion transport systems by AnxA6 or to the ion channel activity of the protein. While AnxA6 channel activity at low pH seems to be associated with a large conformational transition in the protein, the mechanism of GTP-induced ion channel formation remains obscure. This activity is not accompanied by changes in protein structure. The existence of a domain binding the phosphate groups of GTP in AnxA6 [Bandorowicz-Pikula, J., Kirilenko, A., van Deursen, R., Golczak, M., Kuhnel, M., Lancelin, J. M., Pikula, S., and Buchet, R. (2003) Biochemistry 42, 9137-9146] may provide some clues about the molecular mechanisms of GTP-induced ion channel formation. In addition, we observed that one of the AnxA6 tryptophan residues, W192 or W343, may be involved in GTP binding. Therefore, we created several site-directed mutants of AnxA6 in which selected amino acid residues within a consensus sequence of a putative nucleotide-binding domain of AnxA6 were replaced with other amino acid residues without affecting the overall structure of protein as examined by circular dichroism and infrared spectroscopies. Their properties were analyzed and compared to those of the native protein. In contrast to mutant W192S and wild-type annexin, mutant W343S neither bound GTP nor exhibited GTP-induced ion channel activity. In addition, we detected the likely formation of AnxA6 trimers in the presence of GTP. The ability of mutant W343S to form trimers was significantly impaired. Our findings suggest that W343 participates in the formation of AnxA6 trimers. We hypothesize that such trimers could lead to a functional unit of the GTP-induced ion channels formed by the annexin molecules.

Annexin A4 self-association modulates general membrane protein mobility in living cells

Annexins are Ca2+-regulated phospholipid-binding proteins whose function is only partially understood. Annexin A4 is a member of this family that is believed to be involved in exocytosis and regulation of epithelial Cl- secretion. In this work, fluorescent protein fusions of annexin A4 were used to investigate Ca2+-induced annexin A4 translocation and self-association on membrane surfaces in living cells. We designed a novel, genetically encoded, FRET sensor (CYNEX4) that allowed for easy quantification of translocation and self-association. Mobility of annexin A4 on membrane surfaces was investigated by FRAP. The experiments revealed the immobile nature of annexin A4 aggregates on membrane surfaces, which in turn strongly reduced the mobility of transmembrane and plasma membrane associated proteins. Our work provides mechanistic insight into how annexin A4 may regulate plasma membrane protein function.

Involvement of Golgi-associated Lyn tyrosine kinase in the translocation of annexin II to the endoplasmic reticulum under oxidative stress

Src-family tyrosine kinases, known to participate in signaling pathways of a variety of receptors at the plasma membrane, are found in cellular endomembranes such as the Golgi apparatus and endosomes. Recently, we showed that Lyn, a member of the Src kinases, accumulates on the Golgi apparatus and then traffics to the plasma membrane. We show here that a majority of endogenous Lyn but not c-Src is accumulated in Golgi-enriched heavy-membrane fractions on a sucrose-density gradient, whereas a small amount of endogenous Lyn is present in light-membrane fractions containing the plasma membrane. Inducible expression of kinase-active Lyn, which biosynthetically reaches the Golgi apparatus, triggers tyrosine phosphorylation of proteins including annexin II. Coimmunoprecipitation analyses reveal that Lyn physically associates with annexin II, and an in vitro kinase assay shows that Lyn phosphorylates annexin II directly. Furthermore, stimulation of cells with H2O2 induces tyrosine phosphorylation of annexin II on the Golgi apparatus in a manner that is dependent on the kinase activity of Src kinases, leading to the translocation of annexin II from the Golgi apparatus to the endoplasmic reticulum. Thus, these results suggest that endomembranes containing the Golgi apparatus where Lyn is anchored can serve as a signaling platform under oxidative stress.

Down-regulation of the anti-inflammatory protein annexin A1 in cystic fibrosis knock-out mice and patients

Cystic fibrosis is a fatal human genetic disease caused by mutations in the CFTR gene encoding a cAMP-activated chloride channel. It is characterized by abnormal fluid transport across secretory epithelia and chronic inflammation in lung, pancreas, and intestine. Because cystic fibrosis (CF) pathophysiology cannot be explained solely by dysfunction of cystic fibrosis transmembrane conductance regulator (CFTR), we applied a proteomic approach (bidimensional electrophoresis and mass spectrometry) to search for differentially expressed proteins between mice lacking cftr (cftr(tm1Unc), cftr-/-) and controls using colonic crypts from young animals, i.e. prior to the development of intestinal inflammation. By analyzing total proteins separated in the range of pH 6-11, we detected 24 differentially expressed proteins (>2-fold). In this work, we focused on one of these proteins that was absent in two-dimensional gels from cftr-/- mice. This protein spot (molecular mass, 37 kDa; pI 7) was identified by mass spectrometry as annexin A1, an anti-inflammatory protein. Interestingly, annexin A1 was also undetectable in lungs and pancreas of cftr-/- mice, tissues known to express CFTR. Absence of this inhibitory mediator of the host inflammatory response was associated with colonic up-regulation of the proinflammatory cytosolic phospholipase A2. More importantly, annexin A1 was down-regulated in nasal epithelial cells from CF patients bearing homozygous nonsense mutations in the CFTR gene (Y122X, 489delC) and differentially expressed in F508del patients. These results suggest that annexin A1 may be a key protein involved in CF pathogenesis especially in relation to the not well defined field of inflammation in CF. We suggest that decreased expression of annexin A1 contributes to the worsening of the CF phenotype.

Annexin A2 expression during cellular differentiation in myeloid cell lines

Annexin A2 is a calcium-dependent, phospholipid-binding protein found on many cell types. It consists of a short hydrophobic tail (Ser(2)-Asn(32)), which dictates its function, and a core domain (Phe(33)-Asp(339)), which is involved in phospholipid binding. Annexin A2 has been implicated in a number of biochemical processes, including cell proliferation, foetal immune tolerance, ion-channel activation, cell-cell interactions and the bridging of membranes. Annexin A2 is reported to be a powerful activator of plasminogen and, therefore, is implicated in many normal and pathological processes such as haemostasis and metastasis. Myeloid cell lines are used, extensively, to study many aspects of cellular proliferation, differentiation and function. In the present study, we have used flow cytometry and real-time PCR to investigate the role of annexin A2 expression in the proliferation and differentiation of a number of myeloid cell lines. The results demonstrated that annexin A2 expression was affected when the cells were induced to differentiate by stimulation with all-trans-retinoic acid. Annexin A2 may, therefore, be an important player in cellular differentiation and its disorders.

Changes in intracellular calcium concentration in response to hypertonicity in bovine articular chondrocytes

Intracellular calcium concentration ([Ca2+]i) in articular chondrocytes changes during mechanical challenges associated with joint movements, because of the fluctuation of the extracellular osmotic environment during joint loading. Matrix synthesis by chondrocytes is modulated by loading patterns, possibly mediated by variations in intracellular composition, including [Ca2+]i. The present study has employed the Ca(2+)-sensitive fluoroprobe Fura-2 to determine the effects of hypertonic shock on intracellular Ca2+ concentration ([Ca2+]i) and to characterise the mechanisms involved in the response for isolated bovine articular chondrocytes. In cells subjected to a hypertonic shock, [Ca2+]i rapidly increased by approximately 300%, reaching a maximal value within 50 s following the hypertonic shock with a recovery of more than 90% towards the initial [Ca2+]i within 5 min. The effect was inhibited by removal of extracellular Ca2+ ions, but not by thapsigargin, indicating that the rise in [Ca2+]i is only a result of influx from the extracellular medium. The rise was insensitive to inhibitors of L-type voltage-activated Ca2+ channels, TRPV channels or stretch-activated cation channels. Non-specific inhibitors of Ca2+ channels like CdCl2, NiCl2, LaCl3 and ZnCl2 significantly attenuated the response, although the extent in which CdCl2 and NiCl2 (both of them inhibitors of annexin-mediated Ca2+ fluxes) inhibited the response was significantly greater. The rise was also sensitive to KBR7943, inhibitor of NCE reverse mode and trifluoperazine, inhibitor of the activity of annexins. Hypertonic shock also produced also hyperpolarisation of chondrocytes (Em measured by means of Di-BA-C4(3), a membrane potential sensitive dye), which was inhibited by TEA-Cl and BaCl, but was not affected by changing the extracellular solution to Ca(2+)-free HBS. Inhibition of hyperpolarisation completely abolished the [Ca2+]i rise following hypertonic shock. Treatment with retinoic acid, which can increase the activity of annexins as Ca2+ transport pathways caused a significant increase in [Ca2+]i. The recovery of [Ca2+] was inhibited by benzamil and was dependent on extracellular Na+, but was unaffected by Na-orthovanadate, an inhibitor of plasma Ca(2+)-ATPase. We conclude that in response to hypertonic shock, NCE reverse mode and annexins are the pathways responsible for the [Ca2+]i increase, while forward mode operation of NCE is responsible for the subsequent extrusion of Ca2+ and recovery of [Ca2+]i towards initial values.

Identification and Characterization of the Acidic pH Binding Sites for Growth Regulatory Ligands of Low Density Lipoprotein Receptor-related Protein-1

The type V TGF-beta receptor (TbetaR-V) plays an important role in growth inhibition by IGFBP-3 and TGF-beta in responsive cells. Unexpectedly, TbetaR-V was recently found to be identical to the LRP-1/alpha(2)M receptor; this has disclosed previously unreported growth regulatory functions of LRP-1. Here we demonstrate that, in addition to expressing LRP-1, all cells examined exhibit low affinity but high density acidic pH binding sites for LRP-1 growth regulatory ligands (TGF-beta(1), IGFBP-3, and alpha(2)M(*)). These sites, like LRP-1, are sensitive to receptor-associated protein and calcium depletion but, unlike LRP-1, are also sensitive to chondroitin sulfate and heparin and capable of directly binding ligands, which do not bind to LRP-1. Annexin VI has been identified as a major membrane-associated protein capable of directly binding alpha(2)M(*) at acidic pH. This is evidenced by: 1) structural and Western blot analyses of the protein purified from bovine liver plasma membranes by alpha(2)M(*) affinity column chromatography at acidic pH, and 2) dot blot analysis of the interaction of annexin VI and (125)I-alpha(2)M(*). Cell surface annexin VI is involved in (125)I-TGF-beta(1) and (125)I-alpha(2)M(*) binding to the acidic pH binding sites and (125)I-alpha(2)M(*) binding to LRP-1 at neutral pH as demonstrated by the sensitivity of cells to pretreatment with anti-annexin VI IgG. Cell surface annexin VI is also capable of mediating internalization and degradation of cell surface-bound (125)I-TGF-beta(1) and (125)I-alpha(2)M(*) at pH 6 and of forming ternary complexes with (125)I-alpha(2)M(*) and LRP-1 at neutral pH as demonstrated by co-immunoprecipitation. Trifluoperazine and fluphenazine, which inhibit ligand binding to the acidic pH binding sites, block degradation after internalization of cell surface-bound (125)I-TGF-beta(1) or (125)I-alpha(2)M(*). These results suggest that cell surface annexin VI may function as an acidic pH binding site or receptor and may also function as a co-receptor with LRP-1 at neutral pH.

Increased expression and altered location of annexin IV in renal clear cell carcinoma: a possible role in tumour dissemination

The proteome of renal cell carcinoma and non-neoplastic kidney tissue was analysed from 12 patients by two-dimensional polyacrylamide gel electrophoresis to search for differentially expressed proteins in the tumour. Annexin IV was identified to be up-regulated in tumour cells. These patients and further 11 were characterized by RT-PCR. We found an increased amount of annexin IV mRNA. Immunohistochemical analysis revealed an altered localization of annexin IV in tumour cells. Additionally we demonstrate that over-expressed annexin IV promotes cell migration in a carcinoma model system. From these results above it seems possible that annexin IV plays an important role in the morphological diversification and dissemination of the clear cell renal cell carcinoma.

The deregulation of arachidonic acid metabolism-related genes in human esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is 1 of the most common cancers worldwide. In our study, cDNA microarray comprising 14,803 genes was employed to identify gene-specific expression profile in 6 paired samples of ESCC. Nine genes identified were commonly upregulated and 36 downregulated in tumors, as compared to normal esophageal squamous epithelia. Among these genes, we found that 9 of the altered expression genes were related to arachidonic acid (AA) metabolism, such as annexin-I, annexin-II, S100A8, S100A10, S100P, glutathione peroxidase-3, phosphatidylcholine transfer protein, aldo-keto reductase family 1 and cyclooxygenase-2 (COX-2). To gain insights into the regulation of the AA metabolism pathway involved in the carcinogenesis of ESCC, we investigated the expression of 8 genes related to the AA metabolism by semiquantitative reverse transcript (RT)-PCR and/or Western blot and immunohistochemistry. These genes include annexin-I, annexin-II, COX-2, cyclooxygenase-1 (COX-1) and cytosolic phospholipase A(2) (cPLA(2)), 5-lipoxygenase (5-LOX), 5-lipoxygenase activating protein (FLAP) and 12-lipoxygenase (12-LOX) (not included in the array data). The expression level of annexin-I, annexin-II was downregulated in esophageal cancer, whereas cPLA(2), FLAP, COX-2, 5-LOX and 12-LOX were upregulated. These data suggested that AA metabolism pathway and its altered expression may contribute to esophageal squamous cell carcinogenesis.

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.

Inactivation of annexin II tetramer by S-nitrosoglutathione

We investigated the effect of nitric oxide (NO) donors on the activities of annexin II tetramer (AIIt), a member of the Ca2+- dependent phospholipid-binding protein family. Incubation of purified AIIt with S-nitrosoglutathione (GSNO) led to the inhibition of AIIt-mediated liposome aggregation. This effect was dose-dependent with an IC50 of approximately 100 micro m. Sodium nitroprusside, another NO donor also inhibited AIIt-mediated liposome aggregation, whereas reduced glutathione, nitrate, or nitrite had no effects. GSNO also inhibited AIIt-mediated membrane fusion, but not the binding of AIIt to the membrane. GSNO only has a modest effect on liposome aggregation mediated by annexins I, III or IV. The binding of AIIt to the membrane protected the reactive sites of GSNO on AIIt. GSNO did not inhibit AIIt-mediated liposome aggregation in the presence of dithiothreitol. Taken together, our results suggest that GSNO inactivates AIIt possibly via S-nitrosylation and/or the formation of disulfide bonds.

Genes for calcium-permeable channels in the plasma membrane of plant root cells

In plant cells, Ca(2+) is required for both structural and biophysical roles. In addition, changes in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) orchestrate responses to developmental and environmental signals. In many instances, [Ca(2+)](cyt) is increased by Ca(2+) influx across the plasma membrane through ion channels. Although the electrophysiological and biochemical characteristics of Ca(2+)-permeable channels in the plasma membrane of plant cells are well known, genes encoding putative Ca(2+)-permeable channels have only recently been identified. By comparing the tissue expression patterns and electrophysiology of Ca(2+)-permeable channels in the plasma membrane of root cells with those of genes encoding candidate plasma membrane Ca(2+) channels, the genetic counterparts of specific Ca(2+)-permeable channels can be deduced. Sequence homologies and the physiology of transgenic antisense plants suggest that the Arabidopsis AtTPC1 gene encodes a depolarisation-activated Ca(2+) channel. Members of the annexin gene family are likely to encode hyperpolarisation-activated Ca(2+) channels, based on their corresponding occurrence in secretory or elongating root cells, their inhibition by La(3+) and nifedipine, and their increased activity as [Ca(2+)](cyt) is raised. Based on their electrophysiology and tissue expression patterns, AtSKOR encodes a depolarisation-activated outward-rectifying (Ca(2+)-permeable) K(+) channel (KORC) in stelar cells and AtGORK is likely to encode a KORC in the plasma membrane of other Arabidopsis root cells. Two candidate gene families, of cyclic-nucleotide gated channels (CNGC) and ionotropic glutamate receptor (GLR) homologues, are proposed as the genetic correlates of voltage-independent cation (VIC) channels.