Annexin II tetramer: structure and function

A lipid-protein hybrid model for tight junction

The epithelial tight junction (TJ) was first described ultrastructurally as a fusion of the outer lipid leaflets of the adjoining cell membrane bilayers (hemifusion). The discovery of an increasing number of integral TJ and TJ-associated proteins has eclipsed the original lipid-based model with the wide acceptance of a protein-centric model for the TJ. In this review, we stress the importance of lipids in TJ structure and function. A lipid-protein hybrid model accommodates a large body of information supporting the lipidic characteristics of the TJ, harmonizes with the accumulating evidence supporting the TJ as an assembly of lipid rafts, and focuses on an important, but relatively unexplored, field of lipid-protein interactions in the morphology, physiology, and pathophysiology of the TJ.

Increased expression of Annexin A2 in oral squamous cell carcinoma

Previously, in vitro cellular carcinogenesis model of oral squamous cell carcinoma (OSCC) was established with a line of human immortalized oral epithelia cells (HIOECs), a line of cancerous HB96 cells, and another kind of cells (HB56 cells) at the early stage of carcinogenesis. In this study, comparative proteomic analysis identified a panel of differentially expressed proteins among these cells, and Annexin A2 shown as one of the significantly up-regulated proteins accompanying cellular transformation. Annexin A2 was further validated for its expression in the three kinds of cells and in the clinical samples of tumour tissues and their adjacent normal epithelia from primary OSCC patients. Western blot analysis and real-time PCR detected increased Annexin A2 protein and mRNA levels in cancerous HB56 and HB96 cells over HIOECs. Immunohistochemistry showed elevated Annexin A2 protein expression in tumour tissues over the adjacent non-malignant epithelia from OSCC patients; however, the mRNA levels between tumour and normal tissues did not change significantly. Interestingly, levels of Annexin A2 protein expression negatively correlated with the tumour differentiation grades. The results presented here suggest that Annexin A2 protein may play important roles in carcinogenesis of OSCC, and it may also serve as a candidate biomarker for pathologic differentiation grade of OSCC.

Analysis of the urine proteome in patients with pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) accounts for over 213 000 deaths worldwide each year, largely due to late diagnosis. One of the risk factors for the development of PDAC is chronic pancreatitis (CP); the intense desmoplastic reaction makes differentiation between the two conditions extremely difficult. In order to identify biomarkers for noninvasive diagnosis, we performed 2-D DIGE analysis of urine samples from healthy individuals and patients with PDAC and CP. Despite considerable intersample heterogeneity, a total of 127 statistically valid (p<0.05), differentially expressed protein spots were detected, 101 of which were identified using MALDI-TOF MS. A number of these, including annexin A2, gelsolin and CD59 have already been associated with PDAC, however, their validation using immunoblotting proved challenging. This is probably due to extensive PTMs and processing thus indicating the need for raising specific antibodies for urinary proteins. Despite this, our study clearly demonstrates that urine is a valid source of noninvasive biomarkers in patients with pancreatic diseases.

Annexin A2 localizes to the basal epithelial layer and is down-regulated in dysplasia and head and neck squamous cell carcinoma

Annexin A2 is a highly expressed gene with important roles in cell membrane physiology and is frequently dysregulated in cancer. The objective of this study was to determine the pattern of expression and prognostic significance of annexin A2 protein in head and neck squamous cell carcinoma. We assessed both quantitative changes and qualitative distribution of annexin A2 mRNA and protein expression in normal and diseased tissues by immunohistochemistry, immunofluorescence and in situ hybridization. Annexin A2 expression was confined to the basal and suprabasal cells of normal epithelium and the protein cellular location was consistently observed at the cell membrane. Expression levels correlated with histopathological grade, showing significant suppression in moderately and poorly differentiated tumours. We conclude that annexin A2 exhibits a characteristic pattern of expression, distinct from other annexins and suggestive of a cell-specific functional role. The marked reduction of annexin A2 in poorly differentiated tumours and dysplastic tissue is expected to result in a loss of function aimed at the coordination of membrane signalling enzyme complexes, actin polymerization and extracellular matrix proteolysis. The phenotypic consequences may become manifest in an alteration of epithelial tissue growth and remodelling with secondary influence on tumour development, progression and metastasis.

[Annexin A2 expression in head and neck squamous cell carcinoma]

OBJECTIVE

Over-expression of annexin A2 (ANXA2) has been reported in various cancers. However, no data are available on the expression of this protein in head and neck squamous cell carcinomas (HNSCC). The objective of this preliminary study is to investigate the expression of ANXA2 in these carcinomas.

MATERIAL AND METHOD

ANXA2 expression was analyzed by immunohistochemistry in paraffin-embedded sections from 9 patients with premalignant lesions and 21 patients with HNSCC.

RESULTS

All dysplastic tissues showed significantly reduced ANXA2 expression compared to normal tissue. In contrast, ANXA2 expression was observed in all but one of the tumours studied. There was a significant correlation of lower ANXA2 expression with a poorer histological differentiation, larger tumours, and nodal metastases.

CONCLUSIONS

Our data show for the first time that ANXA2 is expressed in head and neck squamous cell carcinomas and that its expression seems to be related with the degree of differentiation status of these tumours.

Localization of annexin II in the paranodal regions and Schmidt-Lanterman incisures in the peripheral nervous system

Annexin II (AX II) is a member of the family of calcium-dependent actin- and phospholipid-binding proteins implicated in numerous intracellular functions such as signal transduction, membrane trafficking, and mRNA transport, as well as in the regulation of membrane/cytoskeleton contacts and extracellular functions. AX II is expressed in the central nervous system (CNS) and is upregulated in some pathological conditions. However, expression and localization of this protein in the peripheral nervous system (PNS) is still uncertain. In the present study, we examined the expression and distribution of AX II in the PNS. By western blot analysis, we found that a higher level of AX II was present in sciatic nerve homogenates than in brain homogenates. RT-PCR of total RNA from rat sciatic nerves revealed that AX II was synthesized within the nerves. Immunohistological analysis showed the characteristic distribution of AX II in Schmidt-Lanterman incisures (SLI) as well as in the paranodal regions. Localization of AX II in the PNS was examined in two mutant mouse models, shiverer and cerebroside sulfotransferase knockout mice, both of which show increased numbers of SLI. The paranodal axo-glial junction is also disrupted in the latter. Interestingly, the staining intensities of AX II in these regions were increased markedly in both mutants, suggesting that not only the numbers but also AX II content in each incisure and paranodal loop were affected. From its characteristic distribution and molecular features, AX II may be important for myelin function in the PNS.

In vitro modeling of matrix vesicle nucleation: synergistic stimulation of mineral formation by annexin A5 and phosphatidylserine

Annexins A5, A2, and A6 (Anx-A5, -A2, and -A6) are quantitatively major proteins of the matrix vesicle nucleational core that is responsible for mineral formation. Anx-A5 significantly activated the induction and propagation of mineral formation when incorporated into synthetic nucleation complexes made of amorphous calcium phosphate (ACP) and Anx-A5 or of phosphatidylserine (PS) plus ACP (PS-CPLX) and Anx-A5. Incorporation of Anx-A5 markedly shortened the induction time, greatly increasing the rate and overall amount of mineral formed when incubated in synthetic cartilage lymph. Constructed by the addition of Ca(2+) to PS, emulsions prepared in an intracellular phosphate buffer matched in ionic composition to the intracellular fluid of growth plate chondrocytes, these biomimetic PS-CPLX nucleators had little nucleational activity. However, incorporation of Anx-A5 transformed them into potent nucleators, with significantly greater activity than those made from ACP without PS. The ability of Anx-A5 to enhance the nucleation and growth of mineral appears to stem from its ability to form two-dimensional crystalline arrays on PS-containing monolayers. However, some stimulatory effect also may result from its ability to exclude Mg(2+) and HCO(-)(3) from nucleation sites. Comparing the various annexins for their ability to activate PS-CPLX nucleation yields the following: avian cartilage Anx-A5 > human placental Anx-A5 > avian liver Anx-A5 > or = avian cartilage Anx-A6 >> cartilage Anx-A2. The stimulatory effect of human placental Anx-A5 and avian cartilage Anx-A6 depended on the presence of PS, since in its absence they either had no effect or actually inhibited the nucleation activity of ACP. Anx-A2 did not significantly enhance mineralization.

Tissue plasminogen activator induces pancreatic cancer cell proliferation by a non-catalytic mechanism that requires extracellular signal-regulated kinase 1/2 activation through epidermal growth factor receptor and annexin A2

Tissue plasminogen activator (tPA) is overexpressed in pancreatic ductal carcinoma and is involved in tumor progression. This effect is probably mediated through the activation of angiogenesis, cell invasion, and cell proliferation. Previous studies support the notion that the effects of tPA on cell invasion require its proteolytic activity. Here, we report the molecular mechanism responsible for the proliferative effects of tPA on pancreatic tumor cells. tPA activates the extracellular signal-regulated kinase 1/2 signaling pathway in a manner that is independent of its catalytic activity. We also show that at least two membrane receptors, epidermal growth factor receptor and annexin A2, which are overexpressed in pancreatic cancer, are involved in the transduction of tPA signaling in pancreatic tumors. This observation suggests the establishment of an amplification loop in tumor cell proliferation. Double immunofluorescence experiments showed co-localization of tPA/epidermal growth factor receptor and tPA/annexin A2 in pancreas cancer cells. These results add novel insights into the non-catalytic functions of tPA in cancer and the molecular mechanisms behind the effects of this protease on cell proliferation, including a role for epidermal growth factor receptor.

Physical and functional interactions of SNAP-23 with annexin A2

Lung surfactant is secreted through the fusion of lamellar bodies with the plasma membrane of alveolar epithelial type II cells. Annexin A2, a Ca(2+)- and phospholipid-binding protein, promotes the fusion of lamellar bodies with the plasma membrane. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are known to have an essential role in surfactant secretion. We hypothesized that annexin A2 acts as a Ca(2+) sensor and mediates membrane fusion via its interaction with SNAREs. Both purified or endogenous annexin A2 in type II cells specifically bound with SNAP-23 in a Ca(2+)-dependent manner, as determined by pull-down experiments using recombinant glutathione S-transferase-tagged SNAP-23. A deletion study identified the cysteine-rich region (CRR) of SNAP-23 as the binding site for annexin A2. Mutations of cysteine residues in the CRR dramatically decreased the binding. SNAP-23 also co-immunoprecipitated with annexin A2; however, a SNAP-23 mutant failed to co-immunoprecipitate with annexin A2. Immunofluorescence revealed a co-localization of SNAP-23 and annexin A2 in type II cells. Furthermore, anti-SNAP-23 antibody significantly inhibited annexin A2-mediated fusion between lamellar bodies and the plasma membrane. These data suggest that annexin A2 and SNAP-23 are involved in the same pathway in the regulation of lung surfactant secretion.

Plasminogen binding and activation at the breast cancer cell surface: the integral role of urokinase activity

Introduction

The regulation of extracellular proteolytic activity via the plasminogen activation system is complex, involving numerous activators, inhibitors, and receptors. Previous studies on monocytic and colon cell lines suggest that plasmin pre-treatment can increase plasminogen binding, allowing the active enzyme to generate binding sites for its precursor. Other studies have shown the importance of pre-formed receptors such as annexin II heterotetramer. However, few studies have used techniques that exclusively characterise cell-surface events and these mechanisms have not been investigated at the breast cancer cell surface.

Methods

We have studied plasminogen binding to MCF-7 in which urokinase plasminogen activator receptor (uPAR) levels were upregulated by PMA (12-O-tetradecanoylphorbol-13-acetate) stimulation, allowing flexible and transient modulation of cell-surface uPA. Similar experiments were also performed using MDA-MB-231 cells, which overexpress uPAR/uPA endogenously. Using techniques that preserve cell integrity, we characterise the role of uPA as both a plasminogen receptor and activator and quantify the relative contribution of pre-formed and cryptic plasminogen receptors to plasminogen binding.

Results

Cell-surface plasminogen binding was significantly enhanced in the presence of elevated levels of uPA in an activity-dependent manner and was greatly attenuated in the presence of the plasmin inhibitor aprotinin. Pre-formed receptors were also found to contribute to increased plasminogen binding after PMA stimulation and to co-localise with uPA/uPAR and plasminogen. Nevertheless, a relatively modest increase in plasminogen-binding capacity coupled with an increase in uPA led to a dramatic increase in the proteolytic capacity of these cells.

Conclusion

We show that the majority of lysine-dependent plasminogen binding to breast cancer cells is ultimately regulated by plasmin activity and is dependent on the presence of significant levels of active uPA. The existence of a proteolytic positive feedback loop in plasminogen activation has profound implications for the ability of breast cancer cells expressing high amounts of uPA to accumulate a large proteolytic capacity at the cell surface, thereby conferring invasive potential.

Regulation of nucleo-cytoplasmic shuttling of human annexin A2: a proposed mechanism

Studies have long been focused on the functions of annexin A2 in the cytoplasm. However, the involvement of annexin A2 in DNA replication as a part of primer recognition protein complex and the presence of nuclear export signal (NES) suggest that annexin A2 is also functional in the nucleus, and its localization in the nucleus is under regulation by interaction with other nuclear factors through its N-terminus. During the study of the mechanism of annexin A2 sequestering in the nucleus and the regulation of its export from the nucleus, in this study, we show that endogenous annexin A2 is present in both the cytoplasm and the nucleus in HeLa, PC-3 and DU-145 cells. While exogenously expressed annexin A2 is excluded from nuclei of annexin A2-null LNCaP cells in a CRM1 (Chromosome Maintenance Region 1) mediated nuclear export, endogenous annexin A2 in HeLa, PC-3 and DU-145 cell lines does not undergo the CRM1 mediated nuclear export. While investigating the mechanism of the nuclear retention of annexin A2, we found that an anti-annexin A2 antibody that recognizes the C-terminus of annexin A2 (D1/274.5) cannot recognize nuclear annexin A2, suggesting that the domain recognized by this antibody may be masked in the nuclei. In order to find out the role of annexin A2 C-terminus in the nuclear retention of annexin A2, we transiently transfected green fluorescence protein (GFP)-fused N-terminal 29 amino acids of annexin A2 to LNCaP, PC-3 and DU-145 cells, and determined that the C-terminus is not required for the nuclear retention of annexin A2. Based on the finding described above, we propose a model for nuclear retention of annexin A2 where the regulation sites reside in the N-terminus and are adjacent to the NES, and upon modification, the NES is exposed and annexin A2 is exported from the nucleus.

Expression of annexin A2 in GABAergic interneurons in the normal rat brain

Expression of the Ca(2+)-dependent phospholipids binding protein annexin A2 (ANX2) in the brain is thought to be largely associated with brain pathological conditions such as tumor, inflammation, and neurodegeneration. The recent findings that ANX2 heterotetramer is involved in learning and neuronal activities necessitates a systematic investigation of the physiological expression of ANX2 in the brain. With combination of in situ hybridization and immunohistochemistry, ANX2 mRNA and protein were specifically detected in a group of GABAergic interneurons throughout the brain. Although ANX2 was absent from the interior of pyramidal neurons, it was found on the membrane and seemly the extracellular space of those neurons, where they closely co-localized with glutamate decarboxylase terminals. In cultured developing neurons, ANX2 was present at high concentrations in the growth cones co-distributing with several growth-associated proteins such as growth associated protein 43 (GAP43), turned on after division/Ulip/CRMP (TUC-4), tubulin, and tissue-plasminogen activator. It then became predominantly distributed on the membrane and mostly in axonal branches as neurons grew and extended synaptic networks. ANX2 was also secreted from cultured neurons, in a membrane-bound form that was Ca(2+)-dependent, which was significantly increased by neuronal depolarization. These results may have implications in the function and regulatory mechanism of ANX2 in the normal brain.

Epstein–Barr virus latent membrane protein 1 mediates phosphorylation and nuclear translocation of annexin A2 by activating PKC pathway

We have previously combined phosphorylation enrichment with proteomics technology to elucidate the novel phosphoproteins in the signaling pathways triggered by Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) and shown that LMP1 can increase the phosphorylation level of annexin A2. Here, we further showed that LMP1 increased the serine, but not tyrosine, phosphorylation of annexin A2 by activating a novel signaling pathway, the protein kinase C (PKC) signaling pathway. However, LMP1 did not affect the level of annexin A2 expression. In addition, we found that LMP1 induced the nuclear entry of annexin A2 in an energy- and temperature-dependent manner, suggesting that the nuclear entry of annexin A2 is an active process. Treatment of LMP1-expressing cells with the PKC inhibitor myr-psiPKC resulted in annexin A2 being present almost exclusively at cell surface, instead of within the nucleus, suggesting that the nuclear entry of annexin A2 was associated with serine phosphorylation mediated by PKC.

Role of Annexin-II in GI cancers: interaction with gastrins/progastrins

The role of the gastrin peptide hormones (G17, G34) and their precursors (progastrins, PG; gly-extended gastrin, G-gly), in gastrointestinal (GI) cancers has been extensively reviewed in recent years [W. Rengifo-Cam, P. Singh, Role of progastrins and gastrins and their receptors in GI and pancreatic cancers: targets for treatment, Curr. Pharm. Des. 10 (19) (2004) 2345-2358; M. Dufresne, C. Seva, D. Fourmy, Cholecystokinin and gastrin receptors, Physiol. Rev. 86 (3) (2006) 805-847; A. Ferrand, T.C. Wang, Gastrin and cancer: a review, Cancer Lett. 238 (1) (2006) 15-29]. A possible important role of progastrin peptides in colon carcinogenesis has become evident from experiments with transgenic mouse models [W. Rengifo-Cam, P. Singh, (2004); A. Ferrand, T.C. Wang, (2006)]. It is now known that growth stimulatory and co-carcinogenic effects of gastrin/PG peptides are mediated by both proliferative and anti-apoptotic effects of the peptides on target cells [H. Wu, G.N. Rao, B. Dai, P. Singh, Autocrine gastrins in colon cancer cells Up-regulate cytochrome c oxidase Vb and down-regulate efflux of cytochrome c and activation of caspase-3, J. Biol. Chem. 275 (42) (2000) 32491-32498; H. Wu, A. Owlia, P. Singh, Precursor peptide progastrin(1-80) reduces apoptosis of intestinal epithelial cells and upregulates cytochrome c oxidase Vb levels and synthesis of ATP, Am. J. Physiol. Gastrointest. Liver Physiol. 285 (6) (2003) G1097-G1110]. Several receptor subtypes have been described that mediate growth effects of gastrin peptides [W. Rengifo-Cam, P. Singh (2004); M. Dufresne, C. Seva, D. Fourmy, (2006)]. Recently, we identified Annexin II as a high affinity binding protein for gastrin/PG peptides [P. Singh, H. Wu, C. Clark, A. Owlia, Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells, Oncogene (2006), doi:10.1038/sj.onc.1209798]. Importantly, the expression of Annexin II was required for mediating growth stimulatory effects of gastrin and PG peptides on intestinal epithelial and colon cancer cells [P. Singh, H. Wu, C. Clark, A. Owlia, Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells, Oncogene (2006), doi:10.1038/sj.onc.1209798], suggesting that Annexin-II may represent the elusive novel receptor for gastrin/PG peptides. The importance of this finding in relation to the structure and function of Annexin-II, especially in GI cancers, is described below. Since this surprising finding represents a new front in our understanding of the mechanisms involved in mediating growth effects of gastrin/PG peptides in GI cancers, our current understanding of the role of Annexin-II in proliferation and metastasis of cancer cells is additionally reviewed.

Crystallographic analysis of calcium-dependent heparin binding to annexin A2

Annexin A2 and heparin bind to one another with high affinity and in a calcium-dependent manner, an interaction that may play a role in mediating fibrinolysis. In this study, three heparin-derived oligosaccharides of different lengths were co-crystallized with annexin A2 to elucidate the structural basis of the interaction. Crystal structures were obtained at high resolution for uncomplexed annexin A2 and three complexes of heparin oligosaccharides bound to annexin A2. The common heparin-binding site is situated at the convex face of domain IV of annexin A2. At this site, annexin A2 binds up to five sugar residues from the nonreducing end of the oligosaccharide. Unlike most heparin-binding consensus patterns, heparin binding at this site does not rely on arrays of basic residues; instead, main-chain and side-chain nitrogen atoms and two calcium ions play important roles in the binding. Especially significant is a novel calcium-binding site that forms upon heparin binding. Two sugar residues of the heparin derivatives provide oxygen ligands for this calcium ion. Comparison of all four structures shows that heparin binding does not elicit a significant conformational change in annexin A2. Finally, surface plasmon resonance measurements were made for binding interactions between annexin A2 and heparin polysaccharide in solution at pH 7.4 or 5.0. The combined data provide a clear basis for the calcium dependence of heparin binding to annexin A2.

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

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

Proteomics-based identification of autoantibodies in the sera of healthy Chinese individuals from Beijing

The identification of panels of tumor antigens that elicit an antibody response may have utility in cancer screening, diagnosis and in establishing prognosis. However, autoantibodies normally exist in sera of healthy individuals and are enormously diversified. To explore the reservoir of autoantibody in healthy population, we performed a proteomics investigation of autoantibody profiles in the sera of 36 healthy Chinese individuals from Beijing, which may provide valuable reference information to the identification of disease-specific autoantibodies. The results showed that autoantibody profiles varied individually, but some autoantibodies were identified at a high frequency in the healthy population. The autoantibodies against alpha-enolase and those against heterogeneous nuclear ribonucleoprotein L were positive in more than 50% of the sera samples. The autoantibodies identified in more than 20% of samples included those against annexin II, F-actin capping protein beta subunit and calreticulin. Some of these autoantibodies have been previously reported to be involved in autoimmune conditions and cancers. Autoantibodies in the healthy population are important as a foundation from which disease-specific autoantibodies can be defined. Thus our report on autoantibodies in healthy individuals may be useful as a reference for defining new autoantibody biomarkers.

HIV accomplices and adversaries in macrophage infection

Cell surface and intracellular proteins in macrophages influence various steps in the life cycle of lentiviruses. Characterization of these restriction and/or cofactors is essential to understanding how macrophages become unwitting HIV hosts and in fact, can coexist with a heavy viral burden. Although many of the cellular pathways co-opted by HIV in macrophages mimic those seen in CD4+ T cells, emerging evidence reveals cellular constituents of the macrophage, which may be uniquely usurped by HIV. For example, in addition to CD4 and CCR5, membrane annexin II facilitates early steps in infection of macrophages, but not in T cells. Blockade of this pathway effectively diminishes macrophage infection. Viral binding engages a macrophage-centric signaling pathway and a transcriptional profile, including genes such as p21, which benefit the virus. Once inside the cell, multiple host cell molecules are engaged to facilitate virus replication and assembly. Although the macrophage is an enabler, it also possesses innate antiviral mechanisms, including apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3) family DNA-editing enzymes to inhibit replication of HIV. Differential expression of these enzymes, which are largely neutralized by HIV to protect its rebirth, is associated with resistance or susceptibility to the virus. Higher levels of the cytidine deaminases endow potential HIV targets with a viral shield, and IFN-alpha, a natural inducer of macrophage APOBEC expression, renders macrophages tougher combatants to HIV infection. These and other manipulatable pathways may give the macrophage a fighting chance in its battle against the virus.

Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells

We and others have reported the presence of novel progastrin (PG)/gastrin receptors on normal and cancerous intestinal cells. We had earlier reported the presence of 33-36 kDa gastrin-binding proteins on cellular membranes of colon cancer cells. The goal of the current study was to identify the protein(s) in the 33-36 kDa band, and analyse its functional significance. A carbodiimide crosslinker was used for crosslinking radio-labeled gastrins to membrane proteins from gastrin/PG responsive cell lines. Native membrane proteins, crosslinked to the ligand, were solubulized and enriched by >1000-fold, and analysed by surface-enhanced laser desorption/ionization-time of flight-mass spectrometry. The peptide masses were researched against the NCBInr database using the ProFound search engine. Annexin II (ANX II) was identified, and confirmed by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry. As HCT-116 cells express autocrine PG, the in situ association of PG with ANX II was demonstrated in pulldown assays. Direct binding of PG with ANX II was confirmed in an in vitro binding assay. In order to confirm a functional importance of these observations, sense and anti-sense (AS) ANX II RNA-expressing clones of intestinal epithelial (IEC-18) and human colon cancer (HCT-116) cell lines were generated. AS clones demonstrated a significant loss in the growth response to exogenous (IEC-18) and autocrine (HCT-116) PG. We have thus discovered that membrane-associated ANX II binds PG/gastrins, and partially mediates growth factor effects of the peptides.

Identification of phosphoproteins associated with maintenance of transformed state in temperature-sensitive Rous sarcoma-virus infected cells by proteomic analysis

To identify phosphotyrosine-containing proteins essential for maintaining the transformed state, we studied the tyrosine phosphorylation profile of temperature-sensitive mutant of Rous sarcoma virus, tsNY68, infected cells (68N7). Shifting the temperature from 39 degrees C (nonpermissive) to 32 degrees C (permissive) markedly increased the expression of phosphotyrosine-containing cell membrane proteins of approximately 40kDa, as assessed by SDS-PAGE. Membrane and nuclear proteins were separated by two-dimensional gel electrophoresis and immunoblotted with anti-phosphotyrosine antibody. Proteins showing temperature-dependent changes in phosphorylation profile were subjected to in-gel digestion with trypsin and analyzed by mass spectrometry. Five proteins were identified: heterogeneous nuclear ribonucleoprotein (hnRNP) A3, hnRNP A2, annexin II, phosphoglycerate mutase 1, and triosephosphate isomerase 1. hnRNP A3 was phosphorylated at serine residues and had both serine and tyrosine phosphorylated sites. These results suggest an important complementary role for proteomics in identifying molecular abnormalities associated with tumor progression that may be attractive candidates for tumor diagnosis.

Identification of metaphase II-specific gene transcripts in porcine oocytes and their expression in early stage embryos

Annealing control primer (ACP)-based GeneFishing polymerase chain reaction (PCR) was used to identify the genes that are specifically or prominently expressed in porcine oocytes at the metaphase II (MII) and germinal vesicle (GV) stages. By using 60 ACPs, 13 differentially expressed genes (DEGs) were identified. The cloned genes or expressed sequence tags (ESTs) showed sequence similarity with known genes or ESTs of other species in GenBank. The mRNA expression during oocyte maturation and early embryonic development in both pigs and mice of four of these genes (namely transcription factor TZP, annexin A2, hypoxia-inducible protein 2, and ATPase 6) was further characterised by real-time quantitative reverse transcription-PCR. All four genes were markedly upregulated in pig and mouse MII oocytes compared with GV-stage oocytes. The expression levels of the four genes decreased gradually during early cleavage. Thus, these genes may play important roles during oocyte maturation and/or early cleavage in mammals. Although the detailed functions of these genes remain to be determined, their identification in the present study provides insights into meiotic maturation and fertilisation.

Actin microfilament aggregation induced by withaferin A is mediated by annexin II

The actin cytoskeleton supports diverse cellular processes such as endocytosis, oriented growth, adhesion and migration. The dynamic nature of the cytoskeleton, however, has made it difficult to define the roles of the many accessory molecules that modulate actin organization, especially the multifunctional adapter protein annexin II. We now report that the compound withaferin A (1) can alter cytoskeletal architecture in a previously unknown manner by covalently binding annexin II and stimulating its basal F-actin cross-linking activity. Drug-mediated disruption of F-actin organization is dependent on annexin II expression by cells and markedly limits their migratory and invasive capabilities at subcytotoxic concentrations. Given the extensive ethnobotanical history of withaferin-containing plant preparations in the treatment of cancer and inflammatory and neurological disorders, we suggest that annexin II represents a feasible, previously unexploited target for therapeutic intervention by small-molecule drugs.

Phosphoinositide specificity of and mechanism of lipid domain formation by annexin A2-p11 heterotetramer

Annexin A2 is a phospholipid-binding protein that forms a heterotetramer (annexin II-p11 heterotetramer; A2t) with p11 (S100A10). It has been reported that annexin A2 is involved in binding to phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) and in inducing membrane microdomain formation. To understand the mechanisms underlying these findings, we determined the membrane binding properties of annexin A2 wild type and mutants both as monomer and as A2t. Our results from surface plasmon resonance analysis showed that A2t and annexin A2 has modest selectivity for PtdIns(4,5)P2 over other phosphoinositides, which is conferred by conserved basic residues, including Lys279 and Lys281, on the convex surface of annexin A2. Fluorescence microscopy measurements using giant unilamellar vesicles showed that A2t of wild type, but not (K279A)2-(p11)2 or (K281A)2-(p11)2, specifically induced the formation of 1-microm-sized PtdIns(4,5)P2 clusters, which were stabilized by cholesterol. Collectively, these studies elucidate the structural determinant of the PtdIns(4,5)P2 selectivity of A2t and suggest that A2t may be involved in the regulation of PtdIns(4,5)P2 clustering in the cell.

Application of fluorescence difference gel electrophoresis saturation labelling for the analysis of microdissected precursor lesions of pancreatic ductal adenocarcinoma

In order to identify new molecular markers for pancreatic intra-epithelial neoplasias (PanINs), the precursor lesions of pancreatic ductal adenocarcinoma, we established a proteomics approach analysing microdissected PanIN cells. Due to the limited amount of proteins available from microdissection, we developed a procedure including fluorescence dye saturation labelling in combination with high resolution two-dimensional gel electrophoresis. With this procedure we were able to analyse proteins extracted from 1000 microdissected cells with a high resolution of up to 2500 protein spots. Using protein lysates from the pancreatic carcinoma tissue as a reference proteome, we were able to successfully identify the proteins. Thus, we could match approximately 2200 protein spots (92%) of the microdissected sample proteome to the reference proteome for protein identification using matrix-assisted laser desorption/ionisation-time of flight mass spectrometry and nanoliquid chromatography-electrospray ionisation tandem mass spectrometry after in-gel digestion. The first proteome analysis of microdissected PanIN-2 grades revealed eight differentially expressed proteins. The differential expression of the three actin filament-associated proteins--transgelin, vimentin and MRCL3 as well as actin itself--indicates a relevant role of the actin cytoskeleton during pancreatic tumour progression. Additionally, two members of the annexin family (annexin A2 and A4) implicate a functional contribution of exocytotic and endocytotic pathways at that stage.

Plasmodium berghei ookinetes bind to Anopheles gambiae and Drosophila melanogaster annexins

Using a proteomic approach we identified polypeptides from Anopheles gambiae and Drosophila melanogaster protein extracts that selectively bind purified Plasmodium berghei ookinetes in vitro; these were two and three distinct polypeptides, respectively, with an apparent molecular weight of about 36 kDa. Combining two-dimensional electrophoresis and MALDI-TOF (matrix-associated laser desorption ionization time of flight) mass spectrometry we determined that the polypeptides correspond to isomorphs of the annexin B11 protein of the fruit fly. When protein extracts derived from A. gambiae and D. melanogaster tissue culture cells were further fractionated, the binding activity matching the annexin protein could be localized in the fraction derived from cell membranes in both diptera. Antibody staining showed that annexin also binds to ookinetes during the invasion of the mosquito midgut. Finally, inclusion of antiannexin antisera in a mosquito blood meal impaired parasite development, suggesting a facilitating role for annexins in the infection of the mosquito by Plasmodium.

Annexin II cell surface and mRNA expression in human acute myeloid leukaemia cell lines

INTRODUCTION

Acute promyelocytic leukaemia (APL) (M3) is associated with both a characteristic t(15;17) and severe bleeding diathesis caused by disseminated intravascular coagulation (DIC) and/or hyperfibrinolysis. It has been suggested that annexin II, a coreceptor for tissue plasminogen activator (t-PA) and plasminogen (PLG), is overexpressed on the surface of promyelocytes, leading to an increased fibrinolytic potential.

MATERIALS AND METHODS

This study examined the level of annexin II cell surface and mRNA expression in a range of acute myeloid leukaemia (AML) cell lines. The evidence that annexin II levels are higher in APL would lend support to the hypothesis that the bleeding disorder seen in APL is caused by hyperfibrinolysis.

RESULTS

Cell surface annexin II was found to be expressed at higher levels on NB4 (promyelocytic) cells than on either KG1a (early myeloid) or HL60 (myelocytic) cells. However, even higher levels were found on U937 and MM6 (histo-monocytic) and HEL (erythroid) cells (p<0.01). MM6 cells showed a threefold increase in annexin II mRNA compared to any of the other cell lines.

CONCLUSIONS

These findings do not fully support the concept of the coagulopathy associated with APL being caused by hyperfibrinolysis alone. Further investigations are required to identify the significance of annexin II expression and regulation in leukaemia.

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.

Secretory leukocyte protease inhibitor binds to annexin II, a cofactor for macrophage HIV-1 infection

The distribution of secretory leukocyte protease inhibitor (SLPI) at entry portals indicates its involvement in defending the host from pathogens, consistent with the ability of SLPI to inhibit human immunodeficiency virus (HIV)-1 infection by an unknown mechanism. We now demonstrate that SLPI binds to the membrane of human macrophages through the phospholipid-binding protein, annexin II. Based on the recent identification of human cell membrane phosphatidylserine (PS) in the outer coat of HIV-1, we define a novel role for annexin II, a PS-binding moiety, as a cellular cofactor supporting macrophage HIV-1 infection. Moreover, this HIV-1 PS interaction with annexin II can be disrupted by SLPI or other annexin II–specific inhibitors. The PS–annexin II connection may represent a new target to prevent HIV-1 infection.

Annexin II is a novel receptor for Pseudomonas aeruginosa

Infections with Pseudomonas aeruginosa (P. aeruginosa) are critical in ventilated and poly-traumatized patients. Most important, these bacteria cause frequent and chronic pulmonary infections in patients with cystic fibrosis. Therefore, identification of molecular mechanisms that mediate the infection of mammalian cells with P. aeruginosa is urgently required. Here, we aimed to identify novel receptors that are involved in internalization of P. aeruginosa into mammalian epithelial cells. Employing SDS-PAGE purification and mass spectrometry we demonstrate that annexin II specifically binds to P. aeruginosa. The significance of the interaction of annexin II with P. aeruginosa for the infection of mammalian cells is indicated by the finding that neutralization of the ligands on P. aeruginosa by incubation of the bacteria with recombinant, soluble annexin II prevents internalization of P. aeruginosa into human epithelial cells.

Novel role for Na,K-ATPase in phosphatidylinositol 3-kinase signaling and suppression of cell motility

The Na,K-ATPase, consisting of alpha- and beta-subunits, regulates intracellular ion homeostasis. Recent studies have demonstrated that Na,K-ATPase also regulates epithelial cell tight junction structure and functions. Consistent with an important role in the regulation of epithelial cell structure, both Na,K-ATPase enzyme activity and subunit levels are altered in carcinoma. Previously, we have shown that repletion of Na,K-ATPase beta1-subunit (Na,K-beta) in highly motile Moloney sarcoma virus-transformed Madin-Darby canine kidney (MSV-MDCK) cells suppressed their motility. However, until now, the mechanism by which Na,K-beta reduces cell motility remained elusive. Here, we demonstrate that Na,K-beta localizes to lamellipodia and suppresses cell motility by a novel signaling mechanism involving a cross-talk between Na,K-ATPase alpha1-subunit (Na,K-alpha) and Na,K-beta with proteins involved in phosphatidylinositol 3-kinase (PI3-kinase) signaling pathway. We show that Na,K-alpha associates with the regulatory subunit of PI3-kinase and Na,K-beta binds to annexin II. These molecular interactions locally activate PI3-kinase at the lamellipodia and suppress cell motility in MSV-MDCK cells, independent of Na,K-ATPase ion transport activity. Thus, these results demonstrate a new role for Na,K-ATPase in regulating carcinoma cell motility.

Reorganization of cytoskeleton during surfactant secretion in lung type II cells: a role of annexin II

The secretion of lung surfactant requires the movement of lamellar bodies to the plasma membrane through cytoskeletal barrier at the cell cortex. We hypothesized that the cortical cytoskeleton undergoes a transient disassembly/reassembly in the stimulated type II cells, therefore allowing lamellar bodies access to the plasma membrane. Stabilization of cytoskeleton with Jasplakinolinde (JAS), a cell permeable actin microfilament stabilizer, caused a dose-dependent inhibition of lung surfactant secretion stimulated by terbutaline. This inhibition was also observed in ATP-, phorbol 12-myristate 13-acetate (PMA)- or Ca(2+) ionophore A23187-stimulated surfactant secretion. Stimulation of type II cells with terbutaline exhibited a transient disassembly of filamentous actin (F-actin) as determined by staining with Oregon Green 488 Phalloidin. The protein kinase A inhibitor, H89, abolished the terbutaline-induced F-actin disassembly. Western blot analysis using anti-actin and anti-annexin II antibodies showed a transient increase of G-actin and annexin II in the Triton X-100 soluble fraction of terbutaline-stimulated type II cells. Furthermore, introduction of exogenous annexin II tetramer (AIIt) into permeabilized type II cells caused a disruption in the cortical actin. Treatment of type II cells with N-ethylmaleimide (NEM) resulted in a disruption of the cortical actin. NEM also inhibited annexin II's abilities to bundle F-actin. The results suggest that cytoskeleton undergoes reorganization in the stimulated type II cells, and annexin II tetramer plays a role in this process.

Annexin 2 is a phosphatidylinositol (4,5)-bisphosphate binding protein recruited to actin assembly sites at cellular membranes

Annexin 2 is a Ca(2+)-regulated membrane protein and an F-actin-binding protein enriched at actin assembly sites both, on the plasma membrane and on endosomal vesicles. Here, we identify annexin 2 as a phosphatidylinositol (4,5)-bisphosphate (PtdIns(4,5)P(2))-interacting protein, thereby explaining this specific membrane association. Using the pleckstrin-homology (PH) domain of phospholipase Cdelta1 fused to yellow fluorescent protein as a marker for PtdIns(4,5)P(2), we show that annexin 2 and its ligand p11 (S100A10) are targeted to sites of PtdIns(4,5)P(2) enrichment where F-actin accumulates. At the plasma membrane, adhesion of pedestal-forming enteropathogenic Escherichia coli induces a recruitment of 1-phosphatidylinositol-4-phosphate 5-kinase (PtdIns4P 5-kinase) and an enrichment of PtdIns(4,5)P(2) and annexin 2-p11 at sites of bacterial adhesion. Induction of PtdIns(4,5)P(2)-enriched ruffles and PtdIns(4,5)P(2)-positive, actin-coated vacuoles by Arf6-mediated activation of PtdIns4P 5-kinase also leads to a concomitant accumulation of the annexin 2-p11 complex and the PH domain. Binding studies with immobilized phosphoinositides and phosphoinositide-containing liposomes reveal that the purified annexin 2-p11 complex directly and specifically binds to PtdIns(4,5)P(2) with an affinity comparable to that of the PH domain of phospholipase Cdelta1. Experiments using individual subunits identify annexin 2 as the PtdIns(4,5)P(2)-binding entity. Thus, the direct interaction of annexin 2 with PtdIns(4,5)P(2) is a means of specifically recruiting the annexin 2-p11 complex to sites of membrane-associated actin assembly.

Mutant K-ras regulates cathepsin B localization on the surface of human colorectal carcinoma cells

Cathepsin B protein and activity are known to localize to the basal plasma membrane of colon carcinoma cells following the appearance of K-ras mutations. Using immunofluorescence and subcellular fractionation techniques and two human colon carcinoma cell lines - one with a mutated K-ras allele (HCT 116) and a daughter line in which the mutated allele has been disrupted (HKh-2)-we demonstrate that the localization of cathepsin B to caveolae on the surface of these carcinoma cells is regulated by mutant K-ras. In HCT 116 cells, a greater percentage of cathepsin B was distributed to the caveolae, and the secretion of cathepsin B and pericellular (membrane-associated and secreted) cathepsin B activity were greater than observed in HKh-2 cells. Previous studies established the light chain of annexin II tetramer, p11, as a binding site for cathepsin B on the surface of tumor cells. The deletion of active K-ras in HKh-2 cells reduced the steady-state levels of p11 and caveolin-1 and the distribution of p11 to caveolae. Based upon these results, we speculate that cathepsin B, a protease implicated in tumor progression, plays a functional role in initiating proteolytic cascades in caveolae as downstream components of this cascade (e.g., urokinase plasminogen activator and urokinase plasminogen activator receptor) are also present in HCT 116 caveolae.

Annexin A2 Is a Novel RNA-binding Protein

Annexin A2 (ANXA2) is a Ca(2+)-binding protein that is up-regulated in virally transformed cell lines and in human tumors. Here, we show that ANXA2 binds directly to both ribonucleotide homopolymers and human c-myc RNA. ANXA2 was shown to bind specifically to poly(G) with high affinity (K(d) = 60 nM) and not to poly(A), poly(C), or poly(U). The binding of ANXA2 to poly(G) required Ca(2+) (A(50%) = 10 microM). The presence of RNA in the immunoprecipitates of ANXA2 isolated from HeLa cells established that ANXA2 formed a ribonucleoprotein complex in vivo. Sucrose gradient analysis showed that ANXA2 associates with ribonucleoprotein complexes and not with polyribosomes. Reverse transcriptase-PCR identified c-myc mRNA as a component of the ribonucleoprotein complex formed by ANXA2 in vivo, and binding studies confirmed a direct interaction between ANXA2 and c-myc mRNA. Transfection of LNCaP cells with the ANXA2 gene resulted in the up-regulation of c-Myc protein. These findings identify ANXA2 as a Ca(2+)-dependent RNA-binding protein that interacts with the mRNA of the nuclear oncogene, c-myc.

Cell Surface-Dependent Generation of Angiostatin4.5

Angiostatin4.5 (AS4.5) is a naturally occurring human angiostatin isoform, consisting of plasminogen kringles 1-4 plus 85% of kringle 5 (amino acids Lys78 to Arg529). Prior studies indicate that plasminogen is converted to AS4.5 in a two-step reaction. First, plasminogen is activated to plasmin. Then plasmin undergoes autoproteolysis within the inner loop of kringle 5, which can be induced by a free sulfhydryl donor or an alkaline pH. We now demonstrate that plasminogen can be converted to AS4.5 in a cell membrane-dependent reaction. Actin was shown previously to be a surface receptor for plasmin(ogen). We now show that beta-actin is present on the extracellular membranes of cancer cells (PC-3, HT1080, and MDA-MB231), and beta-actin can mediate plasmin binding to the cell surface and autoproteolysis to AS4.5. In the presence of beta-actin, no small molecule-free sulfhydryl donor is needed for generation of AS4.5. Antibodies to actin reduced membrane-dependent generation of AS4.5 by 70%. In a cell-free system, addition of actin to in vitro-generated plasmin resulted in stoichiometric conversion to AS4.5. Annexin II and alpha-enolase have been reported to be plasminogen receptors, but we did not demonstrate a role for these proteins in conversion of plasminogen to AS4.5. Our data indicate that membrane-associated beta-actin, documented previously as a plasminogen receptor, is a key cell membrane receptor capable of mediating conversion of plasmin to AS4.5. This conversion may serve an important role in regulating tumor angiogenesis, invasion, and metastasis, and surface beta-actin may also serve as a prognostic marker to predict tumor behavior.

Quantitative expression analysis of blastocyst-derived gene transcripts in preimplantation developmental stages of in vitro-produced bovine embryos using real-time polymerase chain reaction technology

The main objective of the present study was to analyse the quantitative expression pattern of genes from a subtracted blastocyst transcriptome throughout the preimplantation developmental stages of in vitro-produced bovine oocytes and embryos. For this purpose, Day 5 morula (M) cDNAs were subtracted from Day 7 blastocyst (B) cDNAs (B–M) and used to establish a B–M subtracted cDNA library, as reported previously. From the total generated clones, 19 were analysed quantitatively. The mRNA samples isolated from pools of immature oocytes (n = 150), mature oocytes (n = 150) and two-cell (n = 80), four-cell (n = 40), eight-cell (n = 20), morula (n = 6) and blastocyst (n = 3) embryos were reverse transcribed and subjected to real-time polymerase chain reaction (PCR) using sequence-specific primers and SYBR green as the DNA dye. A relative standard curve method was used to analyse the real-time data taking the morula stage as a calibrator. Applying suppression subtractive hybridisation (SSH), a total of 71 clones, which represent 33 different expressed sequence tags, were generated and available for analysis. Most transcripts were analysed for the first time in bovine embryogenesis. The real-time PCR has validated the results of SSH positively for 84% (16/19) of transcripts, whereas 16% (3/19) showed deviation in the expression pattern from the one seen during SSH. Several transcript-specific expression patterns were observed for genes that play decisive roles in bovine embryogenesis. In addition to identification, accurately quantifying the expression profiles of transcripts during development will pave the way towards understanding the molecular mechanisms of embryogenesis and their potential role in early embryo development. Most importantly, the present study has contributed to the enrichment of bovine embryo gene collection by generating new transcripts involved in bovine embryo development.

Evidence that annexin II Is not a putative membrane receptor for 1?,25(OH)2-vitamin D3

The seco-steroid hormone 1alpha,25(OH)(2)-vitamin D(3) (1,25-D(3)) is known to generate biological responses via both genomic and non-genomic rapid signal transduction pathways. The calcium regulated annexin II/p11 heterotetramer (AII(2)/p11(2)] was proposed by Baran and co-authors to be the membrane receptor responsible for mediating non-genomic, rapid actions of 1,25-D(3), based on ligand affinity labeling, competition, and saturation analysis experiments. Given the cytosolic presence of both the monomeric and heterotetrameric form of AII and their functional regulation by intracellular calcium concentrations, which are known to be affected by 1,25-D(3) rapid, non-genomic activities, we investigated in vitro the affinity of [(3)H]1,25-D(3) for the AII monomer and AII(2)/p11(2) in the absence and presence of calcium using saturation analysis and gel-filtration chromatography. Using two different techniques for separating bound from free ligand (perchlorate and hydroxylapatite (HAP)) over a series of 30 experiments, no evidence for specific binding of [(3)H]1,25-D(3) was obtained with or without the presence of 700 nM exogenous calcium, using either the AII monomer or AII(2)/p11(2). However saturable binding of [(3)H]1,25-D(3) to the lipid raft/caveolae enriched rat intestinal fraction was consistently observed (K(d) = 3.0 nM; B(max) = 45 fmols/mg total protein). AII was detected in lipid raft/caveolae enriched fractions from rat and mouse intestine and ROS 17/2.8 and NB4 cells by Western blot, but incubation in the presence of exogenous calcium did not ablate 1,25-D(3) binding as reported by Baran et al. Our results suggest that AII does not bind 1,25-D(3) in a physiologically relevant manner; however, recent studies linking AII(2)/p11(2) phosphorylation to vesicle fusion and its calcium regulated localization may make AII a possible down-stream substrate for 1,25-D(3) induced rapid cellular effects.

Expresión de las anexinas a1 y a2 en la mucosa del tracto aerodigestivo superior

INTRODUCTION

Annexins A1 and A2 have been related with the maintenance of tissue integrity. They have been identified in a wide variety of tissues, but little is known regarding their expression in upper the aerodigestive tract. The aim of this work is to describe the expression of these proteins in the mucosa of the upper aerodigestive tract.

MATERIAL AND METHODS

Tissue samples from respiratory (nasal and laryngeal) and digestive (oral and pharyngeal) mucosa from non-oncological patients were studied. Annexin A1 and A2 expression was determined by immunohistochemistry.

RESULTS

Both annexins were expressed in the ciliated and in the stratified non-keratinized epithelia, but with a different pattern; ANXA1 was expressed in the more differentiated cells whereas ANXA2 was expressed in the less differentiated ones (with the exception of the cilia of ciliated cells).

CONCLUSION

Although annexins A1 and A2 are structurally and philogenetically related its expression pattern in the upper aerodigestive tract suggests that they have different functions.

Novel organization and properties of annexin 2-membrane complexes

Annexin 2 belongs to the annexin family of proteins that bind to phospholipid membranes in a Ca(2+)-dependent manner. Here we show that, under mild acidic conditions, annexin 2 binds to and aggregates membranes containing anionic phospholipids, a fact that questions the mechanism of its interaction with membranes via Ca(2+) bridges only. The H(+) sensitivity of annexin 2-mediated aggregation is modulated by lipid composition (i.e. cholesterol content). Cryo-electron microscopy of aggregated liposomes revealed that both the monomeric and the tetrameric forms of the protein form bridges between the liposomes at acidic pH. Monomeric annexin 2 induced two different organizations of the membrane junctions. The first resembled that obtained at pH 7 in the presence of Ca(2+). For the tetramer, the arrangement was different. These bridges seemed more flexible than the Ca(2+)-mediated junctions allowing the invagination of membranes. Time-resolved fluorescence analysis at mild acidic pH and the measurement of Stokes radius revealed that the protein undergoes conformational changes similar to those induced by Ca(2+). Labeling with the lipophilic probe 3-(trifluoromethyl)-3-(m-[(125)I]iodophenyl)diazirine indicated that the protein has access to the hydrophobic part of the membrane at both acidic pH in the absence of Ca(2+) and at neutral pH in the presence of Ca(2+). Models for the membrane interactions of annexin 2 at neutral pH in the presence of Ca(2+) and at acidic pH are discussed.

Regulation of annexin A2 by reversible glutathionylation

The annexin A2-S100A10 heterotetramer (AIIt) is a multifunctional Ca(2+)-dependent, phospholipid-binding, and F-actin-binding phosphoprotein composed of two annexin A2 subunits and two S100A10 subunits. It was reported previously that oxidative stress from exogenous hydrogen peroxide or generated in response to tumor necrosis factor-alpha results in the glutathionylation of Cys(8) of annexin A2. In this study, we demonstrate that AIIt is an oxidatively labile protein whose level of activity is regulated by the redox status of its sulfhydryl groups. Oxidation of AIIt by diamide resulted in a time- and concentration-dependent loss of the ability of AIIt to interact with phospholipid liposomes and F-actin. The inhibitory effect of diamide on the activity of AIIt was partially reversed by dithiothreitol. In addition, incubation of AIIt with diamide and GSH resulted in the glutathionylation of AIIt in vitro. Mass spectrometry established the incorporation of 2 mol of GSH/mol of annexin A2 subunit at Cys(8) and Cys(132). Glutathionylation potentiated the inhibitory effects of diamide on the activity of AIIt. Furthermore, AIIt could be deglutathionylated by glutaredoxin (thiol transferase). Thus, we show for the first time that AIIt can undergo functional reactivation by glutaredoxin, therefore establishing that AIIt is regulated by reversible glutathionylation.

CEACAM1, a Cell-Cell Adhesion Molecule, Directly Associates with Annexin II in a Three-dimensional Model of Mammary Morphogenesis

The epithelial cell adhesion molecule CEACAM1 (carcinoembryonic antigen cell adhesion molecule-1) is down-regulated in colon, prostate, breast, and liver cancer. Here we show that CEACAM1-4S, a splice form with four Ig-like ectodomains and a short cytoplasmic domain (14 amino acids), directly associates with annexin II, a lipid raft-associated molecule, which is also down-regulated in many cancers. Annexin II was identified using a glutathione S-transferase pull-down assay in which the cytoplasmic domain of CEACAM-4S was fused to glutathione S-transferase, the fusion protein was incubated with cell lysates, and isolated proteins were sequenced by mass spectrometry. The interaction was confirmed first by reciprocal immunoprecipitations using anti-CEACAM1 and anti-annexin II antibodies and second by confocal laser microscopy showing co-localization of CEACAM1 with annexin II in mammary epithelial cells grown in Matrigel. In addition, CEACAM1 co-localized with p11, a component of the tetrameric AIIt complex at the plasma membrane, and with annexin II in secretory vesicles. Immobilized, oriented peptides from the cytoplasmic domain of CEACAM1-4S were shown to directly associate with bovine AIIt, which is 98% homologous to human AIIt, with average KD values of about 30 nM using surface plasmon resonance, demonstrating direct binding of functionally relevant AIIt to the cytoplasmic domain of CEACAM1-4S.

Fusion of lamellar body with plasma membrane is driven by the dual action of annexin II tetramer and arachidonic acid

Annexin II has been implicated in membrane fusion during the exocytosis of lamellar bodies from alveolar epithelial type II cells. Most previous studies were based on the fusion assays by using model membranes. In the present study, we investigated annexin II-mediated membrane fusion by using isolated lamellar bodies and plasma membrane as determined by the relief of octadecyl rhodamine B (R18) self-quenching. Immunodepletion of annexin II from type II cell cytosol reduced its fusion activity. Purified annexin II tetramer (AIIt) induced the fusion of lamellar bodies with the plasma membrane in a dose-dependent manner. This fusion is Ca2+-dependent and is highly specific to AIIt because other annexins (I and II monomer, III, IV, V, and VI) were unable to induce the fusion. Modification of the different functional residues of AIIt by N-ethylmaleimide, nitric oxide, or peroxynitrite abolished AIIt-mediated fusion. Arachidonic acid enhanced AIIt-mediated fusion and reduced its Ca2+ requirement to an intracellularly achievable level. This effect is due to membrane-bound arachidonic acid, not free arachidonic acid. Other fatty acids including linolenic acid, palmitoleic acid, myristoleic acid, stearic acid, palmitic acid, and myristic acid had little effect. AIIt-mediated fusion was suppressed by the removal of arachidonic acid from lamellar body and plasma membrane using bovine serum albumin. The addition of arachidonic acid back to the arachidonic acid-depleted membranes restored its fusion activity. Our results suggest that the fusion between lamellar bodies with the plasma membrane is driven by the synergistic action of AIIt and arachidonic acid.

Thrombin induces endothelial cell-surface exposure of the plasminogen receptor annexin 2

Cell-surface annexin 2 (A2) and its ligand p11 have been implicated in fibrinolysis because of their ability to accelerate tissue plasminogen activator (tPA)-mediated activation of plasminogen to plasmin. Because thrombin is a potent cell modulator obligately produced at the site of clot formation, we hypothesized that the amount of cell-surface A2 and p11 might be altered by thrombin with consequent effects on plasmin generation. In support of this hypothesis, immunofluorescence microscopy and hydrophilic biotinylation experiments showed that both A2 and p11 were significantly increased on the surface of human umbilical vein endothelial cells (HUVECs) treated with thrombin (0.8-8 nM) for 5 minutes followed by 1 hour at 37 degrees C. Intracellular immunofluorescence microscopy and immunoblot analyses of whole cell extracts revealed increased p11 but unchanged A2 in response to thrombin, suggesting that transbilayer trafficking of A2 might be controlled by p11. The thrombin receptor-activating peptide (TRAP) similarly affected cells, demonstrating that cell signaling at least involved the type-1 protease activated receptor (PAR-1). An effect on the fibrinolysis pathway after treatment of HUVECs with thrombin was shown by increased fluorescein-labeled plasminogen binding to cells, which was inhibited by an antibody specific for p11. This was confirmed by observing that thrombin pretreatment of HUVECs increased biotin-modified plasminogen binding. Utilizing a chromogenic assay, pretreatment of HUVECs by thrombin further enhanced activation of the Glu and Lys forms of plasminogen by tPA. These data suggest a novel mechanism that links the coagulation and fibrinolysis pathways by thrombin-mediated feedback.

Characterization of the human p11 promoter sequence

p11 is expressed in many different cell types, and serves a variety of regulatory functions. In order to better understand the transcriptional control of this protein, the 5' promoter region of the human p11 gene was cloned and sequenced. After confirming the transcription start point (TSP) using 5' rapid amplification of cDNA ends analysis, the 5' promoter was analysed. The sequence lacks a TATA box, but contains a variety of putative regulatory elements. There are two GAS sites, two AP-1 sites, two overlapping Sp-1 sites, and a gamma-IRE site clustered between -1080 and -1450. There is another cluster of putative regulatory sites between the TSP and -550 which contains two Sp-1 sites, two AP-2 sites, one GAS site, one NF-kappaB site, an incomplete CAAT box (8/9) and an overlapping Sp-1/AP-2 site at -17 to -26. Reporter gene constructs containing 4225 and 1498 bases 5' of the TSP demonstrated excellent unidirectional transcriptional activity in both constructs. Reporter genes containing serial 5' deletions were compared to the -1498 construct. The reporter gene which contained base pairs (bp) -36 to +89 had almost no activity. The reporter gene containing -188 to +89 had 50% of the -1498 construct, indicating that this sequence contains at least the minimal promoter. The Sp-1/AP-2 site near the transcription start site was studied by electrophoretic mobility shift and reporter gene assays. Addition of HeLa cell nuclear extract to labeled double-stranded (ds) oligonucleotide containing this sequence resulted in a gel shift which was inhibited by excess unlabeled ds oligonucleotide and by a consensus cold Sp-1 ds oligonucleotide, indicating specific Sp-1 binding. Excess AP-2 or NF-kappaB ds oligonucleotide had no effect on nuclear protein binding to the sequence. Mutation of the p11 wild-type Sp-1/AP-2 sequence eliminated both nuclear protein binding and the sequences ability to compete with native sequence for nuclear binding protein. A -1048 to +89 reporter construct containing a mutated Sp-1/AP-2 site resulted in a 40% decrease in transcriptional activity. Therefore, the 5' flanking sequence of the p11 gene exhibits promoter activity which may be localized to a variety of controlling regions, of which the proximal Sp-1/AP-2 site appears to be important for basal activity via its Sp-1 binding ability.

Annexin II/p11 is up-regulated in Purkinje cells in EAE and MS

The sensory neuron specific sodium channel Na(v)1.8 is normally detectable at only very low levels within cerebellar Purkinje cells. Annexin II light chain (p11) binds to the amino terminus of Na(v)1.8 and facilitates its functional expression within the cell membrane. We previously demonstrated that expression of Na(v)1.8 is up-regulated in cerebellar Purkinje cells in experimental allergic encephalomyelitis (EAE) and multiple sclerosis (MS). In this study we demonstrate that expression of p11 is significantly up-regulated in Purkinje cells in EAE (71 +/- 9.0% vs 21.3 +/- 4.9% in controls) and in MS(65.5 +/- 1.6% vs 21.8 +/- 6.2% in controls). We also demonstrate a high degree of co-expression of p11 and Na(v)1.8 (84.8 +/- 8.9%). Together with earlier results which show that experimental expression of Na(v)1.8 within Purkinje cells perturbs the temporal pattern of impulse generation in these cells, our results extend the evidence for an acquired channelopathy which interferes with cerebellar function in MS.

Interferon-gamma induces p11 gene and protein expression in human epithelial cells through interferon-gamma-activated sequences in the p11 promoter

The effect of interferon (IFN)-gamma on p11 expression was studied in two human epithelial cell lines (BEAS-2B and HeLa). Treatment with IFN-gamma resulted in increased steady-state levels of p11 mRNA and protein expression, with a time-dependent and dose-dependent effect. Transient transfection experiments of a reporter gene construct containing 1498 bp of the 5'-flanking region of the p11 promoter demonstrated that IFN-gamma induced p11 gene expression at the transcriptional level. These effects were inhibited at the promoter and protein levels by a specific JAK-2 kinase inhibitor, AG-490. Functional analysis of the p11 promoter indicates that two gamma-activated sequence elements (GAS) located at positions 1219 and 1090 are important for the induction of the p11 promoter by IFN-gamma. Transfection of mutated reporter constructs demonstrated that the mutation at the GAS-2 site (1090) inhibited the p11 promoter activity, with a reduction of about approximately 73% and mutation at the GAS-3 site (1219) eliminated about 26% of the p11 promoter activity. A STAT1 dominant negative mutant vector at Tyr-701 (JAK kinase phosphorylation site) blocked the effect of IFN-gamma on the p11 promoter activity. IFN-gamma induced a rapid tyrosine phosphorylation and nuclear translocation of STAT1 protein, which is involved in the binding to the GAS-2 site in the p11 promoter by EMSA analysis. These data suggest that IFN-gamma-induced p11 expression is mediated through the binding of STAT1 to GAS sites in the p11 promoter. Inhibition of p11 expression by inhibitory antisense RNAs (iRNA) treatment resulted in enhanced IFN-gamma and calcium ionophore-stimulated arachidonic acid release suggesting that at least in part IFN-gamma-stimulated p11 expression may serve a counterregulatory role.