Localization of five annexins in J774 macrophages and on isolated phagosomes

Proximity labeling of host factor ANXA3 in HCV infection reveals a novel LARP1 function in viral entry

Hepatitis C virus (HCV) infection is tightly connected to the lipid metabolism with lipid droplets (LDs) serving as assembly sites for progeny virions. A previous LD proteome analysis identified annexin A3 (ANXA3) as an important HCV host factor that is enriched at LDs in infected cells and required for HCV morphogenesis. To further characterize ANXA3 function in HCV, we performed proximity labeling using ANXA3-BioID2 as bait in HCV-infected cells. Two of the top proteins identified proximal to ANXA3 during HCV infection were the La-related protein 1 (LARP1) and the ADP ribosylation factor-like protein 8B (ARL8B), both of which have been previously described to act in HCV particle production. In follow-up experiments, ARL8B functioned as a pro-viral HCV host factor without localizing to LDs and thus likely independent of ANXA3. In contrast, LARP1 interacts with HCV core protein in an RNA-dependent manner and is translocated to LDs by core protein. Knockdown of LARP1 decreased HCV spreading without altering HCV RNA replication or viral titers. Unexpectedly, entry of HCV particles and E1/E2-pseudotyped lentiviral particles was reduced by LARP1 depletion, whereas particle production was not altered. Using a recombinant vesicular stomatitis virus (VSV)ΔG entry assay, we showed that LARP1 depletion also decreased entry of VSV with VSV, MERS, and CHIKV glycoproteins. Therefore, our data expand the role of LARP1 as an HCV host factor that is most prominently involved in the early steps of infection, likely contributing to endocytosis of viral particles through the pleiotropic effect LARP1 has on the cellular translatome.

TIM-4 orchestrates mitochondrial homeostasis to promote lung cancer progression via ANXA2/PI3K/AKT/OPA1 axis

Mitochondrial function and homeostasis are critical to the proliferation of lung cancer cells. T-cell immunoglobulin and mucin domain-containing molecule 4 (TIM-4) promotes the development and progression of lung cancer. However, the role of TIM-4 in mitochondria homeostasis in tumor cells remains completely unknown. In this study, we found that TIM-4 promoted growth and proliferation of lung cancer cells by the oxidative phosphorylation (OXPHOS) pathway. Consistently, inhibition of OXPHOS reversed TIM-4-induced proliferation of lung cancer cells. Notably, TIM-4 promoted mitochondrial fusion via enhancing L-OPA1 protein expression. Mechanistically, TIM-4 regulated protein of L-OPA1 through the PI3K/AKT pathway, and TIM-4 interacted with ANXA2 to promote the activation of PI3K/AKT signaling. Collectively, TIM-4 promotes oxidative phosphorylation of lung cancer cells to accelerate tumor progress via ANXA2/PI3K/AKT/OPA1 axis, which sheds significant new lights on the potential role of TIM-4 in regulating tumor cell metabolism.

Aptamers against mouse and human tumor-infiltrating myeloid cells as reagents for targeted chemotherapy

Local delivery of anticancer agents has the potential to maximize treatment efficacy and minimize the acute and long-term systemic toxicities. Here, we used unsupervised systematic evolution of ligands by exponential enrichment to identify four RNA aptamers that specifically recognized mouse and human myeloid cells infiltrating tumors but not their peripheral or circulating counterparts in multiple mouse models and from patients with head and neck squamous cell carcinoma (HNSCC). The use of these aptamers conjugated to doxorubicin enhanced the accumulation and bystander release of the chemotherapeutic drug in both primary and metastatic tumor sites in breast and fibrosarcoma mouse models. In the 4T1 mammary carcinoma model, these doxorubicin-conjugated aptamers outperformed Doxil, the first clinically approved highly optimized nanoparticle for targeted chemotherapy, promoting tumor regression after just three administrations with no detected changes in weight loss or blood chemistry. These RNA aptamers recognized tumor infiltrating myeloid cells in a variety of mouse tumors in vivo and from human HNSCC ex vivo. This work suggests the use of RNA aptamers for the detection of myeloid-derived suppressor cells in humans and for a targeted delivery of chemotherapy to the tumor microenvironment in multiple malignancies.

Proteome Profiling of PMJ2-R and Primary Peritoneal Macrophages

In vitro models are often used for studying macrophage functions, including the process of phagocytosis. The application of primary macrophages has limitations associated with the individual characteristics of animals, which can lead to insufficient standardization and higher variability of the obtained results. Immortalized cell lines do not have these disadvantages, but their responses to various signals can differ from those of the living organism. In the present study, a comparative proteomic analysis of immortalized PMJ2-R cell line and primary peritoneal macrophages isolated from C57BL/6 mice was performed. A total of 4005 proteins were identified, of which 797 were quantified. Obtained results indicate significant differences in the abundances of many proteins, including essential proteins associated with the process of phagocytosis, such as Elmo1, Gsn, Hspa8, Itgb1, Ncf2, Rac2, Rack1, Sirpa, Sod1, C3, and Msr1. These findings indicate that outcomes of studies utilizing PMJ2-R cells as a model of peritoneal macrophages should be carefully validated. All MS data are deposited in ProteomeXchange with the identifier PXD022133.

Roles of Annexin A protein family in autophagy regulation and therapy

Annexin A is a kind of calcium-dependent phospholipid-binding proteins, which contributes to the formation of the cell membranes and cytoskeleton and played a part as a membrane skeleton to stabilize lipid bilayer. Autophagy is one of the most important programmed cell death mechanisms. And recently some reports suggest that annexin A family protein is associated with autophagy for annexin A can regulate the formation of vesicular lipid membranes and promote cell exocytosis. In this review, we summarized the roles of annexin A protein family in autophagy regulation and targeted medical treatment for better diagnoses and therapies.

Annexin A1-suppressed autophagy promotes nasopharyngeal carcinoma cell invasion and metastasis by PI3K/AKT signaling activation

Annexin A1 (ANXA1) is dysregulated in the various tumors. However, the role and mechanism of ANXA1 in the cancers are poorly understood. In this study, we first showed a clinically positive correlation between ANXA1 and autophagy-associated protein SQSTM1 expression in nasopharyngeal carcinoma (NPC) and ANXA1-regulating SQSTM1 expression through autophagy, and further demonstrated that ANXA1 inhibited BECN1 and ATG5-dependent autophagy in the NPC cells. Using phospho-kinase antibody array to identify signaling through which ANXA1 regulated NPC cell autophagy, we found that ANXA1-suppressed autophagy was associated with PI3K/AKT signaling activation. We also showed that ANXA1 expression was significantly increased in the NPCs with metastasis relative to NPCs without metastasis and positively correlated with lymphonode and distant metastasis; high ANXA1 expression in the NPC cells promoted in vitro tumor cell migration and invasion and in vivo metastasis. Lastly, we showed that inhibition of autophagy restored the ability of tumor cell migration and invasion, epithelial–mesenchymal transition (EMT)-like alterations and in vivo metastasis in the ANXA1 knockdown NPC cells with autophagy activation; ANXA1-suppresed autophagy induced EMT-like alterations possibly by inhibiting autophagy-mediated degradation of Snail. Our data suggest that ANXA1-suppressed autophagy promotes NPC cell migration, invasion and metastasis by activating PI3K/AKT signaling pathway, highlighting that the activation of autophagy may inhibit metastasis of NPC with high ANXA1 expression.

Phagosome proteomics to study Leishmania's intracellular niche in macrophages

Intracellular pathogens invade their host cells and replicate within specialized compartments. In turn, the host cell initiates a defensive response trying to kill the invasive agent. As a consequence, intracellular lifestyle implies morphological and physiological changes in both pathogen and host cell. Leishmania spp. are medically important intracellular protozoan parasites that are internalized by professional phagocytes such as macrophages, and reside within the parasitophorous vacuole inhibiting their microbicidal activity. Whereas the proteome of the extracellular promastigote form and the intracellular amastigote form have been extensively studied, the constituents of Leishmania's intracellular niche, an endolysosomal compartment, are not fully deciphered. In this review we discuss protocols to purify such compartments by means of an illustrating example to highlight generally relevant considerations and innovative aspects that allow purification of not only the intracellular parasites but also the phagosomes that harbor them and analyze the latter by gel free proteomics.

A novel approach to analyze lysosomal dysfunctions through subcellular proteomics and lipidomics: the case of NPC1 deficiency

Superparamagnetic iron oxide nanoparticles (SPIONs) have mainly been used as cellular carriers for genes and therapeutic products, while their use in subcellular organelle isolation remains underexploited. We engineered SPIONs targeting distinct subcellular compartments. Dimercaptosuccinic acid-coated SPIONs are internalized and accumulate in late endosomes/lysosomes, while aminolipid-SPIONs reside at the plasma membrane. These features allowed us to establish standardized magnetic isolation procedures for these membrane compartments with a yield and purity permitting proteomic and lipidomic profiling. We validated our approach by comparing the biomolecular compositions of lysosomes and plasma membranes isolated from wild-type and Niemann-Pick disease type C1 (NPC1) deficient cells. While the accumulation of cholesterol and glycosphingolipids is seen as a primary hallmark of NPC1 deficiency, our lipidomics analysis revealed the buildup of several species of glycerophospholipids and other storage lipids in selectively late endosomes/lysosomes of NPC1-KO cells. While the plasma membrane proteome remained largely invariable, we observed pronounced alterations in several proteins linked to autophagy and lysosomal catabolism reflecting vesicular transport obstruction and defective lysosomal turnover resulting from NPC1 deficiency. Thus the use of SPIONs provides a major advancement in fingerprinting subcellular compartments, with an increased potential to identify disease-related alterations in their biomolecular compositions.

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.

Transcriptomic analysis of the head kidney of Topmouth culter (Culter alburnus) infected with Flavobacterium columnare with an emphasis on phagosome pathway

Flavobacterium columnare (FC) has caused worldwide fish columnaris disease with high mortality and great economic losses in cultured fish, including Topmouth culter (Culter alburnus). However, the knowledge about the host factors involved in FC infection is little known. In this study, the transcriptomic profiles of the head kidney from Topmouth culter with or without FC infection were obtained using HiSeq™ 2500 (Illumina). Totally 79,641 unigenes with high quality were obtained. Among them, 4037 differently expressed genes, including 1217 up-regulated and 2820 down-regulated genes, were identified and enriched using databases of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). The differently expressed genes were mainly associated with pathways such as immune response, carbohydrate metabolism, amino acid metabolism, and lipid metabolism. Since phagocytosis is a central mechanism of innate immune response by host cells to defense against infectious agents, genes related to the phagosome pathway were scrutinized and 9 differently expressed phagosome-related genes were identified including 3 up-regulated and 6 down-regulated genes. Five of them were further validated by quantitative real-time polymerase chain reaction (qRT-PCR). This transcriptomic analysis of host genes in response to FC infection provides data towards understanding the infection mechanisms and will shed a new light on the prevention of columnaris.

Potential of Ca2+ in Mycobacterium tuberculosis H37Rv Pathogenesis and Survival

The host-pathogen interaction and involvement of calcium (Ca²⁺) signaling in tuberculosis infection is crucial and plays a significant role in pathogenesis. Ca²⁺ is known as a ubiquitous second messenger that could control multiple processes and is included in cellular activities like division, motility, stress response, and signaling. However, Ca²⁺ is thought to be a regulative molecule in terms of TB infection but its binding relation with proteins/substrates molecules which are influenced with Ca²⁺ concentrations in host-pathogen interaction requires attention. So, in this review, our primary goal is to focus on some Ca²⁺ substrates/proteins and their imperative involvement in pathogenesis, which is unclear. We have discussed several Ca²⁺-binding substrate and protein that affect intracellular mechanism of infected host cell. The major involvement of these proteins/substrates including calmodulin (CaM), calpain, annexin, surfactant protein A (SP-A), surfactant protein D (SP-D), calprotectin (MRP8/14), and PE_PGRS family protein are considered to be significant; however, their detailed understanding in mycobacterium infection is limited. In this aspect, this study will help in adding up our understanding in TB biology and additionally in the development of new therapeutic approach to reduce TB pandemic worldwide.

Annexin A1 localization and its relevance to cancer

Annexin A1 (ANXA1) is a Ca(2+)-regulated phospholipid-binding protein involved in various cell processes. ANXA1 was initially widely studied in inflammation resolution, but its overexpression was later reported in a large number of cancers. Further in-depth investigations have revealed that this protein could have many roles in cancer progression and act at different levels (from cancer initiation to metastasis). This is partly due to the location of ANXA1 in different cell compartments. ANXA1 can be nuclear, cytoplasmic and/or membrane associated. This last location allows ANXA1 to be proteolytically cleaved and/or to become accessible to its cognate partners, the formyl-peptide receptors. Indeed, in some cancers, ANXA1 is found at the cell surface, where it stimulates formyl-peptide receptors to trigger oncogenic pathways. In the present review, we look at the different locations of ANXA1 and their association with the deregulated pathways often observed in cancers. We have specifically detailed the non-classic pathways of ANXA1 externalization, the significance of its cleavage and the role of the ANXA1-formyl-peptide receptor complex in cancer progression.

Zebrafish as a model system for characterization of nanoparticles against cancer

Therapeutic nanoparticles (NPs) have great potential to deliver drugs against human diseases. Encapsulation of drugs in NPs protects them from being metabolized, while they are delivered specifically to a target site, thereby reducing toxicity and other side-effects. However, non-specific tissue accumulation of NPs, for example in macrophages, especially in the spleen and liver is a general problem with many NPs being developed for cancer therapy. To address the problem of non-specific tissue accumulation of NPs we describe the development of the zebrafish embryo as a transparent vertebrate system for characterization of NPs against cancer. We show that injection of human cancer cells results in tumor-like structures, and that subsequently injected fluorescent NPs, either made of polystyrene or liposomes can be imaged in real-time. NP biodistribution and general in vivo properties can be easily monitored in embryos having selective fluorescent labeling of specific tissues. We demonstrate in vitro, by using optical tweezer micromanipulation, microscopy and flow cytometry that polyethylene glycol (PEG) coating of NPs decreases the level of adhesion of NPs to macrophages, and also to cancer cells. In vivo in zebrafish embryos, PEG coating resulted in longer NP circulation times, decreased macrophage uptake, and reduced adhesion to the endothelium. Importantly, liposomes were observed to accumulate passively and selectively in tumor-like structures comprised of human cancer cells. These results show that zebrafish embryo is a powerful system for microscopy-based screening of NPs on the route to preclinical testing.

Calcium signaling in membrane repair

Resealing allows cells to mend damaged membranes rapidly when plasma membrane (PM) disruptions occur. Models of PM repair mechanisms include the "lipid-patch", "endocytic removal", and "macro-vesicle shedding" models, all of which postulate a dependence on local increases in intracellular Ca(2+) at injury sites. Multiple calcium sensors, including synaptotagmin (Syt) VII, dysferlin, and apoptosis-linked gene-2 (ALG-2), are involved in PM resealing, suggesting that Ca(2+) may regulate multiple steps of the repair process. Although earlier studies focused exclusively on external Ca(2+), recent studies suggest that Ca(2+) release from intracellular stores may also be important for PM resealing. Hence, depending on injury size and the type of injury, multiple sources of Ca(2+) may be recruited to trigger and orchestrate repair processes. In this review, we discuss the mechanisms by which the resealing process is promoted by vesicular Ca(2+) channels and Ca(2+) sensors that accumulate at damage sites.

Membrane Repair: Mechanisms and Pathophysiology

Eukaryotic cells have been confronted throughout their evolution with potentially lethal plasma membrane injuries, including those caused by osmotic stress, by infection from bacterial toxins and parasites, and by mechanical and ischemic stress. The wounded cell can survive if a rapid repair response is mounted that restores boundary integrity. Calcium has been identified as the key trigger to activate an effective membrane repair response that utilizes exocytosis and endocytosis to repair a membrane tear, or remove a membrane pore. We here review what is known about the cellular and molecular mechanisms of membrane repair, with particular emphasis on the relevance of repair as it relates to disease pathologies. Collective evidence reveals membrane repair employs primitive yet robust molecular machinery, such as vesicle fusion and contractile rings, processes evolutionarily honed for simplicity and success. Yet to be fully understood is whether core membrane repair machinery exists in all cells, or whether evolutionary adaptation has resulted in multiple compensatory repair pathways that specialize in different tissues and cells within our body.

ANXA1Ac₂₋₂₆ peptide reduces ID1 expression in cervical carcinoma cultures

Cervical cancer is the second most frequent cancer in women worldwide and is associated with genetic alterations, infection with human papilloma virus (HPV), angiogenesis and inflammatory processes. The idea that inflammation is involved in tumorigenesis is supported by the frequent appearance of cancer in areas of chronic inflammation. On the other hand, the inflammatory response is controlled by the action of anti-inflammatory mediators, among these mediators, annexin A1 (ANXA1), a 37 kDa protein was detected as a modulator of inflammatory processes and is expressed by tumor cells. The study was carried out on the epithelial cancer cell line (SiHa) treated with the peptide of annexin A1 (ANXA1Ac2-26). We combined subtraction hybridization approach, Ingenuity Systems software and quantitative PCR, in order to evaluate gene expression influenced by ANXA1. We observed that ANXA1Ac2-26 inhibited proliferation in SiHa cells after 72h. In these cells, 55 genes exhibited changes in expression levels in response to peptide treatment. Six genes were selected and the expression results of 5 up-regulated genes (TPT1, LDHA, NCOA3, HIF1A, RAB13) and one down-regulated gene (ID1) were research by real time quantitative PCR. Four more genes (BMP4, BMPR1B, SMAD1 and SMAD4) of the ID1 pathway were investigated and only one (BMPR1B) shows the same down regulation. The data indicate the involvement of ANXA1Ac2-26 in the altered expression of genes involved in tumorigenic processes, which could potentially be applied as a therapeutic indicator of cervical cancer.

Caspase-1-mediated pathway promotes generation of thromboinflammatory microparticles

Extracellular ATP is a signal of tissue damage and induces macrophage responses that amplify inflammation and coagulation. Here we demonstrate that ATP signaling through macrophage P2X7 receptors uncouples the thioredoxin (TRX)/TRX reductase (TRXR) system and activates the inflammasome through endosome-generated ROS. TRXR and inflammasome activity promoted filopodia formation, cellular release of reduced TRX, and generation of extracellular thiol pathway-dependent, procoagulant microparticles (MPs). Additionally, inflammasome-induced activation of an intracellular caspase-1/calpain cysteine protease cascade degraded filamin, thereby severing bonds between the cytoskeleton and tissue factor (TF), the cell surface receptor responsible for coagulation activation. This cascade enabled TF trafficking from rafts to filopodia and ultimately onto phosphatidylserine-positive, highly procoagulant MPs. Furthermore, caspase-1 specifically facilitated cell surface actin exposure, which was required for the final release of highly procoagulant MPs from filopodia. Together, the results of this study delineate a thromboinflammatory pathway and suggest that components of this pathway have potential as pharmacological targets to simultaneously attenuate inflammation and innate immune cell-induced thrombosis.

Annexin1 regulates DC efferocytosis and cross-presentation during Mycobacterium tuberculosis infection

The phagocytosis of apoptotic cells and associated vesicles (efferocytosis) by DCs is an important mechanism for both self tolerance and host defense. Although some of the engulfment ligands involved in efferocytosis have been identified and studied in vitro, the contributions of these ligands in vivo remain ill defined. Here, we determined that during Mycobacterium tuberculosis (Mtb) infection, the engulfment ligand annexin1 is an important mediator in DC cross-presentation that increases efferocytosis in DCs and intrinsically enhances the capacity of the DC antigen-presenting machinery. Annexin1-deficient mice were highly susceptible to Mtb infection and showed an impaired Mtb antigen-specific CD8+ T cell response. Importantly, annexin1 expression was greatly downregulated in Mtb-infected human blood monocyte-derived DCs, indicating that reduction of annexin1 is a critical mechanism for immune evasion by Mtb. Collectively, these data indicate that annexin1 is essential in immunity to Mtb infection and mediates the power of DC efferocytosis and cross-presentation.

Modeling the calcium sequestration system in isolated guinea pig cardiac mitochondria

Under high Ca(2+) load conditions, Ca(2+) concentrations in the extra-mitochondrial and mitochondrial compartments do not display reciprocal dynamics. This is due to a paradoxical increase in the mitochondrial Ca(2+) buffering power as the Ca(2+) load increases. Here we develop and characterize a mechanism of the mitochondrial Ca(2+) sequestration system using an experimental data set from isolated guinea pig cardiac mitochondria. The proposed mechanism elucidates this phenomenon and others in a mathematical framework and is integrated into a previously corroborated model of oxidative phosphorylation including the Na(+)/Ca(2+) cycle. The integrated model reproduces the Ca(2+) dynamics observed in both compartments of the isolated mitochondria respiring on pyruvate after a bolus of CaCl2 followed by ruthenium red and a bolus of NaCl. The model reveals why changes in mitochondrial Ca(2+) concentration of Ca(2+) loaded mitochondria appear significantly mitigated relative to the corresponding extra-mitochondrial Ca(2+) concentration changes after Ca(2+) efflux is initiated. The integrated model was corroborated by simulating the set-point phenomenon. The computational results support the conclusion that the Ca(2+) sequestration system is composed of at least two classes of Ca(2+) buffers. The first class represents prototypical Ca(2+) buffering, and the second class encompasses the complex binding events associated with the formation of amorphous calcium phosphate. With the Ca(2+) sequestration system in mitochondria more precisely defined, computer simulations can aid in the development of innovative therapeutics aimed at addressing the myriad of complications that arise due to mitochondrial Ca(2+) overload.

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.

Propofol inhibits the activation of p38 through up-regulating the expression of annexin A1 to exert its anti-inflammation effect

Inflammatory response is a kind of nonspecific immune response, with the central link of vascular response, which is mainly manifested by changes in neutrophils and vascular endothelial cells. In recent years, the in vivo and in vitro role of intravenous anesthetic propofol in inhibiting inflammatory response has been attracting more and more attention, but the anti-inflammatory mechanisms of propofol for mononuclear cells still remain undefined. In this study, proteomics analysis was applied to investigate protein expression profile changes in serum mononuclear cells following intervention of rats with endotoxemia using propofol. After two-dimensional electrophoresis and mass spectrometric identification, it has been found that the protein Annexin A1 was up-regulated in the propofol intervention group. Annexin A1 is a glucocorticoid-dependent anti-inflammatory protein. After detection using ELISA and Western blot assays, it has also been found that propofol can not only promote the expression of Annexin A1, but also inhibit the phosphorylation level of p38 and release of inflammatory factors (IL-1β, IL-6 and TNF-α) in rats with endotoxemia. In order to further determine the role of up-regulated expression of Annexin A1 in anti-inflammation of propofol, this gene was silenced in vitro in human THP-1 cells, to detect the phosphorylation status of p38 and release of inflammatory factors. The results show that Annexin A1 can negatively regulate phosphorylation of p38 and release of IL-1β, IL-6 and TNF-α in THP-1 cells following propofol intervention and lipopolysaccharide (LPS) stimulation. Our results clearly indicate that propofol can up-regulate Annexin A1 to inhibit the phosphorylation level of p38 and release of IL-1β, IL-6 and TNF-α, so as to inhibit inflammatory response. Therefore, it can be speculated that Annexin A1 might be the key signaling protein in the in vivo and in vitro anti-inflammatory mechanisms of propofol.

The S100A10-annexin A2 complex provides a novel asymmetric platform for membrane repair

Membrane repair is mediated by multiprotein complexes, such as that formed between the dimeric EF-hand protein S100A10, the calcium- and phospholipid-binding protein annexin A2, the enlargeosome protein AHNAK, and members of the transmembrane ferlin family. Although interactions between these proteins have been shown, little is known about their structural arrangement and mechanisms of formation. In this work, we used a non-covalent complex between S100A10 and the N terminus of annexin A2 (residues 1-15) and a designed hybrid protein (A10A2), where S100A10 is linked in tandem to the N-terminal region of annexin A2, to explore the binding region, stoichiometry, and affinity with a synthetic peptide from the C terminus of AHNAK. Using multiple biophysical methods, we identified a novel asymmetric arrangement between a single AHNAK peptide and the A10A2 dimer. The AHNAK peptide was shown to require the annexin A2 N terminus, indicating that the AHNAK binding site comprises regions on both S100A10 and annexin proteins. NMR spectroscopy was used to show that the AHNAK binding surface comprised residues from helix IV in S100A10 and the C-terminal portion from the annexin A2 peptide. This novel surface maps to the exposed side of helices IV and IV' of the S100 dimeric structure, a region not identified in any previous S100 target protein structures. The results provide the first structural details of the ternary S100A10 protein complex required for membrane repair.

The Fc receptor-cytoskeleton complex from human neutrophils

The Fc receptor complex and its associated phagocytic cytoskeleton machinery were captured from the surface of live cells by IgG coated microbeads and identified by mass spectrometry. The random and independently sampled intensity values of peptides were similar in the control and IgG samples. After log transformation, the parent and fragment intensity values showed a normal distribution where ≥99.9% of the data was well above the background noise. Some proteins showed significant differences in intensity between the IgG and control samples by ANOVA followed by the Tukey-Kramer honestly significant difference test. However many proteins were specific to the IgG beads or the control beads. The set of detected cytoskeleton proteins, binding proteins and enzymes detected on the IgG beads were used to predict the network of actin-associated regulatory factors. Signaling factors/proteins such as PIK3, PLC, GTPases (such CDC42, Rho GAPs/GEFs), annexins and inositol triphosphate receptors were all identified as being specific to the activated receptor complex by mass spectrometry. In addition, the tyrosine kinase Fak was detected with the IgG coated beads. Hence, an activated receptor cytoskeleton complex and its associated regulatory proteins were captured from the surface of live human primary leukocytes.

Proteomics analysis of starved cells revealed Annexin A1 as an important regulator of autophagic degradation

Macroautophagy is involved in the bulk degradation of long-lived cytosolic proteins and subcellular organelles, which is important for the survival of cells during starvation. To identify potential players of the autophagy process, we subjected HCT116 cells cultured in complete medium and in Earle's balanced salt solution to proteomics analysis. In approximately 1500 protein spots detected, we characterized 52 unique proteins, whose expression levels were significantly changed following starvation. Notably, we found that Annexin A1 was significantly upregulated following starvation at both mRNA and protein levels. Inhibition of Annexin A1 expression with specific siRNA did not alter starvation-induced autophagy as measured by the level of lipidated LC3, but significantly reversed autophagy degradation as measured by the level of p62/SQSTM 1. Thus Annexin A1 seemed to be positively upregulated during starvation to promote autophagic degradation. Overall, the data presented in this study established a expression profile of the proteome in starved cells, which allowed the identification of proteins with potential significance in starvation-induced autophagy.

Changes of cell-surface thiols and intracellular signaling in human monocytic cell line THP-1 treated with diphenylcyclopropenone

Changes of cell-surface thiols induced by chemical treatment may affect the conformations of membrane proteins and intracellular signaling mechanisms. In our previous study, we found that a non-toxic dose of diphenylcyclopropene (DPCP), which is a potent skin sensitizer, induced an increase of cell-surface thiols in cells of a human monocytic cell line, THP-1. Here, we examined the influence of DPCP on intracellular signaling. First, we confirmed that DPCP induced an increase of cell-surface thiols not only in THP-1 cells, but also in primary monocytes. The intracellular reduced-form glutathione/oxidized-form glutathione ratio (GSH/GSSG ratio) was not affected by DPCP treatment. By means of labeling with a membrane-impermeable thiol-reactive compound, Alexa Fluor 488 C5 maleimide (AFM), followed by two-dimensional gel electrophoresis and analysis by liquid chromatography coupled with electrospray tandem mass spectrometry (LC/MS/MS), we identified several proteins whose thiol contents were modified in response to DPCP. These proteins included cell membrane components, such as actin and β-tubulin, molecular chaperones, such as heat shock protein 27A and 70, and endoplasmic reticulum (ER) stress-inducible proteins. Next, we confirmed the expression in DPCP-treated cells of spliced XBP1, a known marker of ER stress. We also detected the phosphorylation of SAPK/JNK and p38 MAPK, which are downstream signaling molecules in the IRE1α-ASK1 pathway, which is activated by ER stress. These data suggested that increase of cell-surface thiols might be associated with activation of ER stress-mediated signaling.

Analysis of phagosomal proteomes: from latex-bead to bacterial phagosomes

Phagosomal proteome characterization has contributed significantly to the understanding of host-pathogen interaction and the mechanism of infectious diseases caused by intracellular bacteria. The latex bead-containing phagosome has been widely used as a model system to study phagosomal proteomes at a global level. In contrast, the study of bacteria-containing phagosomes at a similar level has just begun. A number of intracellular microbial species are studied for their proteomes during the invasion of a host, providing insight into their metabolic adaptation in host cells and interaction with host-cell antimicrobial environments. In this review, we attempt to summarize the most recent advancements in the proteomic study of microbial phagosomes, especially those originating from mouse or human cells. We also briefly describe the proteomics of latex bead-containing phagosomes because they are often used as model phagosomes for study. We provide descriptions on major biological and technological components in phagosomal proteome studies. We also discuss the role of phagosomal proteome study in the broader horizon of systems biology and the technological challenges in phagosomal proteome characterization.

Annexin A1 is a new functional linker between actin filaments and phagosomes during phagocytosis

Remodelling of the actin cytoskeleton plays a key role in particle internalisation and the phagosome maturation processes. Actin-binding proteins (ABPs) are the main players in actin remodelling but the precise role of these proteins in phagocytosis needs to be clarified. Annexins, a group of ABPs, are known to be present on phagosomes. Here, we identified annexin A1 as a factor that binds to isolated latex bead phagosomes (LBPs) in the presence of Ca(2+) and facilitates the F-actin-LBP interaction in vitro. In macrophages the association of endogenous annexin A1 with LBP membranes was strongly correlated with the spatial and temporal accumulation of F-actin at the LBP. Annexin A1 was found on phagocytic cups and around early phagosomes, where the F-actin was prominently concentrated. After uptake was completed, annexin A1, along with F-actin, dissociated from the nascent LBP surface. At later stages of phagocytosis annexin A1 transiently concentrated only around those LBPs that showed transient F-actin accumulation ('actin flashing'). Downregulation of annexin A1 expression resulted in impaired phagocytosis and actin flashing. These data identify annexin A1 as an important component of phagocytosis that appears to link actin accumulation to different steps of phagosome formation.

Plasma membrane repair and cellular damage control: the annexin survival kit

Plasmalemmal injury is a frequent event in the life of a cell. Physical disruption of the plasma membrane is common in cells that operate under conditions of mechanical stress. The permeability barrier can also be breached by chemical means: pathogens gain access to host cells by secreting pore-forming toxins and phospholipases, and the host's own immune system employs pore-forming proteins to eliminate both pathogens and the pathogen-invaded cells. In all cases, the influx of extracellular Ca(2+) is being sensed and interpreted as an "immediate danger" signal. Various Ca(2+)-dependent mechanisms are employed to enable plasma membrane repair. Extensively damaged regions of the plasma membrane can be patched with internal membranes delivered to the cell surface by exocytosis. Nucleated cells are capable of resealing their injured plasmalemma by endocytosis of the permeabilized site. Likewise, the shedding of membrane microparticles is thought to be involved in the physical elimination of pores. Membrane blebbing is a further damage-control mechanism, which is triggered after initial attempts at plasmalemmal resealing have failed. The members of the annexin protein family are ubiquitously expressed and function as intracellular Ca(2+) sensors. Most cells contain multiple annexins, which interact with distinct plasma membrane regions promoting membrane segregation, membrane fusion and--in combination with their individual Ca(2+)-sensitivity--allow spatially confined, graded responses to membrane injury.

DIGE-based protein expression analysis of B[a]P-exposed hepatoma cells reveals a complex stress response including alterations in oxidative stress, cell cycle control, and cytoskeleton motility at toxic and subacute concentrations

Although the effects of high concentrations of the carcinogen benzo[a]pyrene (B[a]P) have been studied extensively, little is known about its effects at subacute toxic concentrations, which are typical for environmental pollutants. We exposed murine Hepa1c1c7 cells to a toxic concentration (5 μM) and a subacute concentration (50 nM) of B[a]P over a period of 2-24 h to differentiate between acute and pseudochronic effects and conducted a time-course analysis of B[a]P-influenced protein expression by DIGE. In total, a set of 120 spots were found to be significantly altered due to B[a]P exposure of which 112 were subsequently identified by mass spectrometry. Clustering and principal component analysis were conducted to identify sets of proteins responding in a concerted manner to the exposure. Our results indicate an immediate response to the contaminant at the protein level and demonstrate that B[a]P exposure alters the cellular response by disturbing proteins involved in oxidative stress, cell cycle regulation, apoptosis, and cytoskeleton organization. Furthermore, network analysis of protein-protein interactions revealed a complex network of interacting, B[a]P-regulated proteins mostly belonging to the cytoskeleton organization and several signal transduction pathways.

Effects of exogenous annexin-1 on lipopolysaccharide-induced proliferation and reactive oxygen species production partially through modulation of CRAC channels but independent of NF-kappaB pathway

OBJECTIVE

To investigate the effects of exogenous annexin-1 (ANXA1) on lipopolysaccharide(LPS)-induced proliferation, reactive oxygen species (ROS) production, and calcium signal transduction in RAW264.7 macrophages.

METHODS

RAW264.7 macrophages were treated with or without LPS in the absence or presence of ANXA1. The proliferation effects were detected by Cell Counting Kit-8 assay. ROS were quantified by flow cytometry and fluorescence microscopy. Intracellular Ca(2+) concentration ([Ca(2+)](i)) was analyzed by laser confocal scanning microscopy. IkappaBalpha degradation and NF-kappaB translocation were tested by Western blot.

RESULTS

Exogenous ANXA1 inhibited LPS-induced proliferation and ROS production in a dose-dependent manner. LPS evoked [Ca(2+)](i) increase through CRAC channels, and ANXA1 suppressed LPS-induced [Ca(2+)](i) increase in a dose-dependent manner. The CRAC channels were associated with LPS-induced proliferation and ROS production. Exogenous ANXA1 had no effect on LPS-induced IkappaB degradation and NF-kappaB translocation.

CONCLUSIONS

ANXA1 inhibited LPS-induced proliferation and ROS production in RAW264.7 macrophages partially through modulation of CRAC channels but independent of the NF-kappaB pathway.

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 A2 regulates phagocytosis of photoreceptor outer segments in the mouse retina

The daily phagocytosis of shed photoreceptor outer segments by pigment epithelial cells is critical for the maintenance of the retina. In a subtractive polymerase chain reaction analysis, we found that functional differentiation of human ARPE19 retinal pigment epithelial (RPE) cells is accompanied by up-regulation of annexin (anx) A2, a major Src substrate and regulator of membrane-cytoskeleton dynamics. Here, we show that anx A2 is recruited to the nascent phagocytic cup in vitro and in vivo and that it fully dissociates once the phagosome is internalized. In ARPE19 cells depleted of anx A2 by using small interfering RNA and in ANX A2(-/-) mice the phagocytosis of outer segments was impaired, and in ANX A2(-/-) mice there was an accumulation of phagocytosed outer segments in the RPE apical processes, indicative of retarded phagosome transport. We show that anx A2 is tyrosine phosphorylated at the onset of phagocytosis and that the synchronized activation of focal adhesion kinase and c-Src is abnormal in ANX A2(-/-) mice. These findings reveal that anx A2 is involved in the circadian regulation of outer segment phagocytosis, and they provide new insight into the protein machinery that regulates phagocytic function in RPE cells.

Proteomic profiling of rat lung epithelial cells induced by acrolein

AIMS

Acrolein is a highly toxic unsaturated aldehyde and is also an endogenous byproduct produced from lipid peroxidation. It can be formed from the breakdown of certain pollutants in outdoor air or from burning tobacco or gasoline. Inhalation and dermal exposure to acrolein are extremely toxic to human tissue. Although it is known that acrolein is toxic to lung tissue, no studies have attempted to address the changes induced by acrolein on a global scale.

MAIN METHODS

In the present study we have attempted to address the changes in global protein expression induced by acrolein using proteomics analysis in rat lung epithelial cells.

KEY FINDINGS

Our analysis reveals a comprehensive profiling of the proteins that includes a heterogeneous class of proteins and this compels one to consider that the toxic response to acrolein is very complex. There were 34 proteins that showed changes between the control cells and after acrolein treatment. The expression of 18 proteins was increased and the expression of 16 proteins was decreased following exposure to acrolein. We have further validated two differentially expressed proteins namely annexin II (ANXII) and prohibitin (PHB) in lung epithelial cells treated with acrolein.

SIGNIFICANCE

Based on the results of the overall proteomic analysis, acrolein appears to induce changes in a diverse range of proteins suggesting a complex mechanism of acrolein-induced toxicity in lung epithelial cells.

On the adaptive nature of annexin-A1

Studies over the last decade have provided us with a wealth of evidence showing that Annexin-1 is a homeostatic endogenous anti-inflammatory mediator of the innate immune system. However, as in Robert Louis Stevenson's novel 'The Strange Case of Dr Jekyll and Mr Hyde', recent investigations on the role of this protein in the adaptive immune response have revealed a previous unknown 'dark side' as positive modulator of T cell activation. This review will be focusing on these recent findings providing further evidences for the promising therapeutic potential of drugs targeting Annexin-1.

Decreased expression of annexin A1 during the progression of cervical neoplasia

The aim of this study was to evaluate whether the expression of annexin A1 (ANXA1) is associated with the progression of cervical neoplasia. ANXA1 expression was examined by immunohistochemistry in paraffin-embedded cervical tissue samples (n = 234), comprising 52 samples of normal cervical epithelia, 30 of cervical intraepithelial neoplasia (CIN) I, 27 of CIN II, 32 of CIN III, and 93 of invasive squamous cell carcinoma (ISCC). ANXA1 expression was strong in normal cervical squamous epithelium and significantly reduced with increasing progression of cervical neoplasia. Moreover, a close association was observed between ANXA1 expression and tumour cell differentiation in ISCC. These preliminary results indicate that ANXA1 may be an effective candidate for detecting CIN lesions and for evaluating tumour cell differentiation in squamous cell carcinoma of the cervix.

Proteomic identification of an upregulated isoform of annexin A3 in the rat brain following reversible cerebral ischemia

We used proteomics to identify regulated proteins following cerebral ischemia in a rat model. Young rats were subjected to reversible middle cerebral artery (MCA) occlusion and proteins were extracted from the peri-infarcted and the corresponding contralateral area at days 3 and 14 postischemia. Proteins were analyzed by two-dimensional polyacrylamide gel electrophoresis followed by mass spectrometry. We report for the first time that an isoform of annexin A3 (ANXA3) was among the upregulated proteins in the postischemic rat brain. The results were confirmed by real-time PCR and by western blotting. Double- and triple-immunostaining with neuronal and microglia/macrophagic markers demonstrated that ANXA3 is produced by resting microglia in control tissue and by activated microglial/macrophage cells in the infarcted area. 3D-images of the infarcted area suggest that ANXA3 is associated with a phagocytic phenotype. Our study identifies ANXA3 as a novel marker of brain microglia, which should be of substantial value in future studies of microglial cells and its role in the postischemic brain.

Proteomic analysis of pycnogenol effects in RAW 264.7 macrophage reveals induction of cathepsin D expression and enhancement of phagocytosis

Pycnogenol, polyphenolic compounds extracted from the pine bark, is beneficial for human health. To understand more of its effects, the present study is to explore the protein expression pattern induced by pycnogenol in RAW 264.7 cells. Global analysis using two-dimensional gel electrophoresis indicated that treatment with pycnogenol induces upregulation of four proteins, whose identities were revealed by mass spectrometry as cathepsin D, keratinocyte lipid-binding protein, proteasome subunit alpha type 1, and annexin IV. The pycnogenol effect displayed a time- and concentration-dependent manner. Unlike pycnogenol, N-acetyl cysteine and vitamin C had no effect on cathepsin D expression. Further studies showed that cathepsin D induction is correlated with an increase of lysosomal staining and enhancement of phagocytosis. These results reveal the novel effects of pycnogenol on protein expression and phagocytic functions and illustrate the advantage of proteomics-based strategy in unveiling the molecular basis of phytochemicals.

Identification of a novel interaction between the Ca2+-binding protein S100A11 and the Ca2+- and phospholipid-binding protein annexin A6

S100A11 is a member of the S100 family of EF-hand Ca2+-binding proteins, which is expressed in smooth muscle and other tissues. Ca2+binding to S100A11 induces a conformational change that exposes a hydrophobic surface for interaction with target proteins. Affinity chromatography with immobilized S100A11 was used to isolate a 70-kDa protein from smooth muscle that bound to S100A11 in a Ca2+-dependent manner and was identified by mass spectrometry as annexin A6. Direct Ca2+-dependent interaction between S100A11 and annexin A6 was confirmed by affinity chromatography of the purified bacterially expressed proteins, by gel overlay of annexin A6 with purified S100A11, by chemical cross-linking, and by coprecipitation of S100A11 with annexin A6 bound to liposomes. The expression of S100A11 and annexin A6 in the same cell type was verified by RT-PCR and immunocytochemistry of isolated vascular smooth muscle cells. The site of binding of S100A11 on annexin A6 was investigated by partial tryptic digestion and deletion mutagenesis. The unique NH2terminal head region of annexin A6 was not required for S100A11 binding, but binding sites were identified in both NH2- and COOH-terminal halves of the molecule. We hypothesize that an agonist-induced increase in cytosolic free [Ca2+] leads to formation of a complex of S100A11 and annexin A6, which forms a physical connection between the plasma membrane and the cytoskeleton, or plays a role in the formation of signaling complexes at the level of the sarcolemma.

Actin deficiency induces cofilin phosphorylation: proteome analysis of HeLa cells after beta-actin gene silencing

Actin-binding proteins regulate the dynamic structure and function of actin filaments in the cell. Much is known about how manipulation of the actin-binding proteins affects the structure and function of actin filaments; however, little is known about how manipulation of actin in the cell affects actin-binding proteins. We addressed this question by utilizing two technologies: RNA interference and 2-dimensional gel electrophoresis. We knocked down beta-actin expression in HeLa cells using short interfering RNA and applied 2-DGE to examine alterations in the HeLa cell proteome. We revealed a 2-5 fold increases of four protein spots on 2-D gels and identified these proteins by mass spectrometry. Three of the four proteins were actin-binding proteins, including cofilin, which promotes both disassembly and assembly of actin filaments but becomes inactivated when phosphorylated. Further examination revealed that the cofilin total protein level barely increased, but the phosphorylated cofilin level increased dramatically in HeLa cells after beta-actin siRNA treatment. These results suggest that in response to siRNA-induced beta-actin deficiency HeLa cells inactivate cofilin by phosphorylation rather than down-regulate its protein expression level. This study also demonstrates that the combination of RNA interference and 2-dimensional gel electrophoresis technologies provides a valuable method to study protein interactions in a specific cellular pathway.

Annexin 1: Differential expression in tumor and mast cells in human larynx cancer

Annexin 1 protein (ANXA1) expression was evaluated in tumor and mast cells in human larynx cancer and control epithelium. The effect of the exogenous ANXA1 (peptide Ac 2-26) was also examined during the cellular growth of the Hep-2 human larynx epidermoid carcinoma cell line. This peptide inhibited the proliferation of the Hep-2 cells within 144 hr. In surgical tissue specimens from 20 patients with larynx cancer, ultrastructural immunocytochemistry analysis showed in vivo down-regulation of ANXA1 expression in the tumor and increased in mast cells and Hep-2 cells treated with peptide Ac2-26. Combined in vivo and in vitro analysis demonstrated that ANXA1 plays a regulatory role in laryngeal cancer cell growth. We believe that a better understanding of the regulatory mechanisms of ANXA1 in tumor and mast cells may lead to future biological targets for the therapeutic intervention of human larynx cancer.

Annexin 1 Negatively Regulates IL-6 Expression via Effects on p38 MAPK and MAPK Phosphatase-1

Annexin 1 (Anx-1) is a mediator of the anti-inflammatory actions of glucocorticoids, but the mechanism of its anti-inflammatory effects is not known. We investigated the role of Anx-1 in the regulation of the proinflammatory cytokine, IL-6. Lung fibroblast cell lines derived from Anx-1(-/-) and wild-type (WT) mice were treated with dexamethasone and/or IL-1. IL-6 mRNA and protein were measured using real-time PCR and ELISA, and MAPK pathway activation was studied. Compared with WT cells, unstimulated Anx-1(-/-) cells exhibited dramatically increased basal IL-6 mRNA and protein expression. In concert with this result, Anx-1 deficiency was associated with increased basal phosphorylated p38, JNK, and ERK1/2 MAPKs. IL-1-inducible phosphorylated p38 was also increased in Anx-1(-/-) cells. The increase in IL-6 release in Anx-1(-/-) cells was inhibited by inhibition of p38 MAPK. Anx-1(-/-) cells were less sensitive to dexamethasone inhibition of IL-6 mRNA expression than WT cells, although inhibition by dexamethasone of IL-6 protein was similar. MAPK phosphatase-1 (MKP-1), a glucocorticoid-induced negative regulator of MAPK activation, was up-regulated by dexamethasone in WT cells, but this effect of dexamethasone was significantly impaired in Anx-1(-/-) cells. Treatment of Anx-1(-/-) cells with Anx-1 N-terminal peptide restored MKP-1 expression and inhibited p38 MAPK activity. These data demonstrate that Anx-1 is an endogenous inhibitory regulator of MAPK activation and IL-6 expression, and that Anx-1 is required for glucocorticoid up-regulation of MKP-1. Therapeutic manipulation of Anx-1 could provide glucocorticoid-mimicking effects in inflammatory disease.

Identification of an AHNAK binding motif specific for the Annexin2/S100A10 tetramer

The Annexin2 tetramer (A2t), which consists of two Annexin2 molecules bound to a S100A10 dimer, is implicated in membrane-trafficking events. Here, we showed using a yeast triple-hybrid experiment and in vitro binding assay that Annexin2 is required for strong binding of S100A10 to the C-terminal domain of the protein Ahnak. We also revealed that this effect involves only the Annexin2 N-terminal tail, which is implicated in S100A10/Annexin2 tetramerization. The minimal A2t binding motif (A2tBP1) in Ahnak was mapped to a 20-amino acid peptide, and this peptide is highly specific for A2t. We also identified a second A2t binding motif (A2tBP2) present in the N-terminal domain of Ahnak, which binds to A2t, albeit with less affinity. When overexpressed as an EGFP fusion protein in MDCK cells, A2tBPs cofractionate in a calcium-dependent manner and co-immunoprecipitate with S100A10 and Annexin2. In living cells, A2tBPs target EGFP to the cytoplasm as does Annexin2. In response to oxidative and mechanical stress, EGFP-A2tBPs relocalize within minutes to the plasma membrane; a behavior shared with Annexin2-GFP. These results suggest that the A2t complex exists within the cytoplasm of resting living cells and that its localization at the plasma membrane relies on cellular signaling. Together, our data demonstrate that A2tBP1 is a specific A2t complex binding domain and may be a powerful tool to help elucidate A2t structure and cellular functions.

The annexins of Dictyostelium

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

Heterogeneity of the intrahepatic biliary epithelium

The objectives of this review are to outline the recent findings related to the morphological heterogeneity of the biliary epithelium and the heterogeneous pathophysiological responses of different sized bile ducts to liver gastrointestinal hormones and peptides and liver injury/toxins with changes in apoptotic, proliferative and secretory activities. The knowledge of biliary function is rapidly increasing because of the recognition that biliary epithelial cells (cholangiocytes) are the targets of human cholangiopathies, which are characterized by proliferation/damage of bile ducts within a small range of sizes. The unique anatomy, morphology, innervation and vascularization of the biliary epithelium are consistent with function of cholangiocytes within different regions of the biliary tree. The in vivo models [e.g., bile duct ligation (BDL), partial hepatectomy, feeding of bile acids, carbon tetrachloride (CCl₄) or α-naphthylisothiocyanate (ANIT)] and the in vivo experimental tools [e.g., freshly isolated small and large cholangiocytes or intrahepatic bile duct units (IBDU) and primary cultures of small and large murine cholangiocytes] have allowed us to demonstrate the morphological and functional heterogeneity of the intrahepatic biliary epithelium. These models demonstrated the differential secretory activities and the heterogeneous apoptotic and proliferative responses of different sized ducts. Similar to animal models of cholangiocyte proliferation/injury restricted to specific sized ducts, in human liver diseases bile duct damage predominates specific sized bile ducts. Future studies related to the functional heterogeneity of the intrahepatic biliary epithelium may disclose new pathophysiological treatments for patients with cholangiopathies.

Mitochondrial proteomic characterization of human normal articular chondrocytes

OBJECTIVE

Mitochondrial dysfunctions have been associated with apoptosis, aging and osteoarthritis (OA). Chondrocyte mitochondrial proteins are attractive targets for the study of the metabolism of cartilage degradation. The copurification of "contaminating" proteins has been the major problem in all phases of mitochondrial proteome research. Therefore, we set up a procedure for the proteomic analysis of human chondrocyte mitochondrial proteins.

METHOD

Four types of protein extracts were obtained from primary cultured chondrocytes isolated from healthy donors: (1) initial total chondrocyte extract (CE), (2) cytosol-enriched supernatant fraction (CY), (3) crude mitochondria fraction (CM), and (4) pure mitochondria fraction (PM). Mitochondria were purified by density gradient ultracentrifugation. Mitochondrial proteins were separated by means of two-dimensional gel electrophoresis (2-DE) and silver stained. Protein spots were then identified by mass spectrometry using MALDI-TOF/TOF technology.

RESULTS

The best 2-DE reference map of mitochondrial proteome was constructed employing PM fraction. Thirty-nine percent of the identified proteins were functionally distributed in the mitochondria, 14% in the endoplasmic reticulum and 36% in the cytoplasm. Examining their biological function, 22% are involved in protein targeting, 12% in signaling, 12% in glycolysis, 10% in RNA, DNA or protein synthesis, 10% in oxidative phosphorylation and 4% in redox. The analysis of mitochondrial Mn-superoxide dismutase (SODM) revealed an age-dependent decrease of this protein.

CONCLUSION

PM fraction allowed the obtention of a high quality proteomic map for the study of mitochondrial proteins in human articular chondrocytes. This proteomic approach may be also efficient to analyze both quantitative and qualitative modulations of the mitochondrial proteome in human chondrocytes during aging and pathological conditions such as OA.

Impaired phagocytic mechanism in annexin 1 null macrophages

The role of the anti-inflammatory protein annexin-A1 (Anx-A1) in the phagocytic process has been investigated using a murine bone marrow culture-derived macrophage model from Anx-A1(+/+) and Anx-A1(-/-) mice. Macrophages prepared from Anx-A1(-/-) mice exhibited a reduced ingestion of zymosan, Neisseria meningitidis or sheep red blood cells, when compared to Anx-A1(+/+) cells and in the case of zymosan this effect was also mirrored by a reduced clearance in vivo when particles were injected into the peritoneal cavity of Anx-A1(-/-) mice. The ablation of the Anx-A1 gene did not cause any apparent cytoskeletal defects associated with particle ingestion but the cell surface expression of the key adhesion molecule CD11b was depressed in the Anx-A1(-/-) cells providing a possible explanation for the attenuated phagocytic potential of these cells. The production of the cytokines TNFalpha and IL-6 was increased in Anx-A1(-/-) macrophages following phagocytosis of all types of particle.