Nuclear annexin II negatively regulates growth of LNCaP cells and substitution of ser 11 and 25 to glu prevents nucleo-cytoplasmic shuttling of annexin II

Pathobiological functions and clinical implications of annexin dysregulation in human cancers

Annexins are an extensive superfamily of structurally related calcium- and phospholipid-binding proteins, largely conserved and widely distributed among species. Twelve human annexins have been identified, referred to as Annexin A1-13 (A12 remains as of yet unassigned), whose genes are spread throughout the genome on eight different chromosomes. According to their distinct tissue distribution and subcellular localization, annexins have been functionally implicated in a variety of biological processes relevant to both physiological and pathological conditions. Dysregulation of annexin expression patterns and functions has been revealed as a common feature in multiple cancers, thereby emerging as potential biomarkers and molecular targets for clinical application. Nevertheless, translation of this knowledge to the clinic requires in-depth functional and mechanistic characterization of dysregulated annexins for each individual cancer type, since each protein exhibits varying expression levels and phenotypic specificity depending on the tumor types. This review specifically and thoroughly examines the current knowledge on annexin dysfunctions in carcinogenesis. Hence, available data on expression levels, mechanism of action and pathophysiological effects of Annexin A1-13 among different cancers will be dissected, also further discussing future perspectives for potential applications as biomarkers for early diagnosis, prognosis and molecular-targeted therapies. Special attention is devoted to head and neck cancers (HNC), a complex and heterogeneous group of aggressive malignancies, often lately diagnosed, with high mortality, and scarce therapeutic options.

Annexin A2: The Diversity of Pathological Effects in Tumorigenesis and Immune Response

Annexin A2 (ANXA2) is widely used as a marker in a variety of tumors. By regulating multiple signal pathways, ANXA2 promotes the epithelial-mesenchymal transition, which can cause tumorigenesis and accelerate thymus degeneration. The elevated ANXA2 heterotetramer facilitates the production of plasmin, which participates in pathophysiologic processes such as tumor cell invasion and metastasis, bleeding diseases, angiogenesis, inducing the expression of inflammatory factors. In addition, the ANXA2 on the cell membrane mediates immune response via its interaction with surface proteins of pathogens, C1q, toll-like receptor 2, anti-dsDNA antibodies and immunoglobulins. Nuclear ANXA2 plays a role as part of a primer recognition protein complex that enhances DNA synthesis and cells proliferation by acting on the G1-S phase of the cell. ANXA2 reduction leads to the inhibition of invasion and metastasis in multiple tumor cells, bleeding complications in acute promyelocytic leukemia, retinal angiogenesis, autoimmunity response and tumor drug resistance. In this review, we provide an update on the pathological effects of ANXA2 in both tumorigenesis and the immune response. We highlight ANXA2 as a critical protein in numerous malignancies and the immune host response.

Dephosphorylation of annexin A2 by protein phosphatase 1 regulates endothelial cell barrier

Annexin A2 (ANXA2) is a multifunctional protein expressed in nearly all human tissues and cell types, playing a role in various signaling pathways. It is subjected to phosphorylation, but no specific protein phosphatase has been identified in its posttranslational regulation yet. Using pull-down assay followed by liquid chromatography-mass spectrometry analysis we found that ANXA2 interacts with TIMAP (TGF-beta-inhibited membrane-associated protein) in pulmonary artery endothelial cells. TIMAP is highly expressed in endothelial cells, where it acts as a regulatory and targeting subunit of protein phosphatase 1 (PP1). TIMAP plays an important role in the regulation of the endothelial barrier maintenance through the dephosphorylation of its several substrate proteins. In the present work, phosphorylation of Ser25 side chain in ANXA2 by protein kinase C (PKC) was shown both in vivo and in vitro. Phosphorylation level of ANXA2 at Ser25 increased greatly by inhibition of PP1 and by depletion of its regulatory subunit, TIMAP, implying a role of this PP1 holoenzyme in the dephosphorylation of ANXA2. Immunofluorescence staining and subcellular fractionations revealed a diffuse subcellular localization for the endogenous ANXA2, but phospho-Ser25 ANXA2 was mainly detected in the membrane. ANXA2 depletion lowered the basal endothelial barrier and inhibited cell migration, but had no significant effect on cell proliferation or viability. ANXA2 depleted cells failed to respond to PMA treatment, indicating an intimately involvement of phospho-ANXA2 in PKC signaling. Moreover, phosphorylation of ANXA2 disrupted its interaction with S100A10 suggesting a phosphorylation dependent multiple regulatory role of ANXA2 in endothelial cells. Our results demonstrate the pivotal role of PKC-ANXA2-PP1 pathway in endothelial cell signaling, especially in barrier function and cell migration.

Annexin A2-mediated cancer progression and therapeutic resistance in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a head and neck cancer with poor clinical outcomes and insufficient treatments in Southeast Asian populations. Although concurrent chemoradiotherapy has improved recovery rates of patients, poor overall survival and low efficacy are still critical problems. To improve the therapeutic efficacy, we focused on a tumor-associated protein called Annexin A2 (ANXA2). This review summarizes the mechanisms by which ANXA2 promotes cancer progression (e.g., proliferation, migration, the epithelial-mesenchymal transition, invasion, and cancer stem cell formation) and therapeutic resistance (e.g., radiotherapy, chemotherapy, and immunotherapy). These mechanisms gave us a deeper understanding of the molecular aspects of cancer progression, and further provided us with a great opportunity to overcome therapeutic resistance of NPC and other cancers with high ANXA2 expression by developing this prospective ANXA2-targeted therapy.

Functional Association between Regulatory RNAs and the Annexins

Cells respond to pathophysiological states by activation of stress-induced signalling. Regulatory non-coding microRNAs (miRNAs) often form stable feed-forward loops which ensure prolongation of the signal, contributing to sustained activation. Members of the annexin protein family act as sensors for Ca²⁺, pH, and lipid second messengers, and regulate various signalling pathways. Recently, annexins were reported to participate in feedback loops, suppressing miRNA synthesis and attenuating stress-induced dysregulation of gene expression. They can directly or indirectly associate with RNAs, and are transferred between the cells in exosomes and shed microvesicles. The ability of annexins to recruit other proteins and miRNAs into exosomes implicates them in control of cell–cell interactions, affecting the adaptive responses and remodelling processes during disease. The studies summarized in this Review point to an emerging role of annexins in influencing the synthesis, localisation, and transfer of regulatory RNAs.

Protein phosphorylation and its role in the regulation of Annexin A2 function

BACKGROUND

Annexin A2 (AnxA2) is a multifunctional protein involved in endocytosis, exocytosis, membrane domain organisation, actin remodelling, signal transduction, protein assembly, transcription and mRNA transport, as well as DNA replication and repair.

SCOPE OF REVIEW

The current knowledge of the role of phosphorylation in the functional regulation of AnxA2 is reviewed. To provide a more comprehensive treatment of this topic, we also address in depth the phosphorylation process in general and discuss its possible conformational effects. Furthermore, we discuss the apparent limitations of the methods used to investigate phosphoproteins, as exemplified by the study of AnxA2.

MAJOR CONCLUSIONS

AnxA2 is subjected to complex regulation by post-translational modifications affecting its cellular functions, with Ser11, Ser25 and Tyr23 representing important phosphorylation sites. Thus, Ser phosphorylation of AnxA2 is involved in the recruitment and docking of secretory granules, the regulation of its association with S100A10, and sequestration of perinuclear, translationally inactive mRNP complexes. By contrast, Tyr phosphorylation of AnxA2 regulates its role in actin dynamics and increases its association with endosomal compartments. Modification of its three main phosphorylation sites is not sufficient to discriminate between its numerous functions. Thus, fine-tuning of AnxA2 function is mediated by the joint action of several post-translational modifications.

GENERAL SIGNIFICANCE

AnxA2 participates in malignant cell transformation, and its overexpression and/or phosphorylation is associated with cancer progression and metastasis. Thus, tight regulation of AnxA2 function is an integral aspect of cellular homeostasis. The presence of AnxA2 in cancer cell-derived exosomes, as well as the potential regulation of exosomal AnxA2 by phosphorylation or other PTMs, are topics of great interest.

Molecular cloning and expression analysis of annexin A2 gene in sika deer antler tip

OBJECTIVE

Molecular cloning and bioinformatics analysis of annexin A2 (ANXA2) gene in sika deer antler tip were conducted. The role of ANXA2 gene in the growth and development of the antler were analyzed initially.

METHODS

The reverse transcriptase polymerase chain reaction (RT-PCR) was used to clone the cDNA sequence of the ANXA2 gene from antler tip of sika deer (Cervus Nippon hortulorum) and the bioinformatics methods were applied to analyze the amino acid sequence of Anxa2 protein. The mRNA expression levels of the ANXA2 gene in different growth stages were examined by real time reverse transcriptase polymerase chain reaction (real time RT-PCR).

RESULTS

The nucleotide sequence analysis revealed an open reading frame of 1,020 bp encoding 339 amino acids long protein of calculated molecular weight 38.6 kDa and isoelectric point 6.09. Homologous sequence alignment and phylogenetic analysis indicated that the Anxa2 mature protein of sika deer had the closest genetic distance with Cervus elaphus and Bos mutus. Real time RT-PCR results showed that the gene had differential expression levels in different growth stages, and the expression level of the ANXA2 gene was the highest at metaphase (rapid growing period).

CONCLUSION

ANXA2 gene may promote the cell proliferation, and the finding suggested Anxa2 as an important candidate for regulating the growth and development of deer antler.

The upregulation of annexin A2 after spinal cord injury in rats may have implication for astrocyte proliferation

Annexin A2 (ANXA2), is a member of the annexin family of proteins that exhibit Ca²⁺-dependent binding to phospholipids. One attractive biological function of ANXA2 is participating in DNA synthesis and cell proliferation. Previous studies have shown that ANXA2 play a role in the development of the central nervous system. However, the biological function of ANXA2 after spinal cord injury (SCI) is still with limited acquaintance. In the present study, we performed a SCI model in adult rats and investigated the dynamic changes of ANXA2 expression in the spinal cord. Western blot analysis indicated a striking expression upregulation of ANXA2 after SCI. Immunohistochemistry further confirmed that ANXA2 immunoactivity was expressed at low levels in normal condition and increased at 5day after SCI. Double immunofluorescence staining prompted that ANXA2 immunoreactivity was found in astrocytes and neurons. Interestingly, ANXA2 expression was increased predominantly in astrocytes. We also examined the expression profiles of proliferating cell nuclear antigen (PCNA), Cyclin D1 and active caspase-3 in the injured spinal cords by western blot. Co-expression of ANXA2/PCNA, ANXA2/Cyclin D1 was detected in glial fibrillary acidic protein. Importantly, double immunofluorescence staining revealed that cell proliferation evaluated by PCNA appeared in many ANXA2-expressing cells and rare caspase-3 was observed in ANXA2-expressing cells after SCI. In addition, ANXA2 knockdown in astrocytes resulted in the increase of PCNA expression after LPS stimulation, showing that ANXA2 inhibited astrocyte proliferation after inflammation. Our data suggested that ANXA2 might play important roles in CNS pathophysiology after SCI.

Reactive oxygen species exert opposite effects on Tyr23 phosphorylation of the nuclear and cortical pools of annexin A2

Annexin A2 (AnxA2) is a multi-functional and -compartmental protein whose subcellular localisation and functions are tightly regulated by its post-translational modifications. AnxA2 and its Tyr23-phosphorylated form (pTyr23AnxA2) are involved in malignant cell transformation, metastasis and angiogenesis. Here, we show that H₂O₂ exerts rapid, simultaneous and opposite effects on the Tyr23 phosphorylation status of AnxA2 in two distinct compartments of rat pheochromocytoma (PC12) cells. Reactive oxygen species induce dephosphorylation of pTyr23AnxA2 located in the PML bodies of the nucleus, whereas AnxA2 associated with F-actin at the cell cortex is Tyr23 phosphorylated. The H₂O₂-induced responses in both compartments are transient and the pTyr23AnxA2 accumulating at the cell cortex is subsequently incorporated into vesicles and then released to the extracellular space. Blocking nuclear export by leptomycin B does not affect the nuclear pool of pTyr23AnxA2, but increases the amount of total AnxA2 in this compartment, indicating that the protein might have several functions in the nucleus. These results suggest that Tyr23 phosphorylation can regulate the function of AnxA2 at distinct subcellular sites.

Summary: Reactive oxygen species cause two opposite and transient Tyr23-based modifications of annexin A2; its dephosphorylation in the nucleus and phosphorylation at the cell cortex, resulting in release of the protein in exosomes.

A novel role of annexin A2 in human type I collagen gene expression

The fibrillar collagen scaffold of the extracellular matrix provides a structural framework for cells in tissues and regulates intercellular communication; its disregulation has been associated with tumour development and progression. Previous work has shown that expression of type I collagen, the most abundant mammalian extracellular matrix protein, is decreased in chemically or virally transformed cells. This negative regulation could be mapped to a proximal COL1A2 promoter element spanning a CME (Collagen Modulating Element) site in SV40‐transformed human fibroblasts (SV‐WI38) that binds an unknown repressing protein. By magnetic bead pull‐down, we observed a multi‐protein complex bound to the CME with preference for single‐stranded over conventional double‐stranded DNA. MALDI‐TOF mass spectrometry of the CME‐binding protein complex revealed involvement of nuclear annexin A2 (AnxA2) which was increased in SV40‐transformed cells. Further EMSA analysis demonstrated that AnxA2 did not directly bind to the DNA but stabilised the complex and led to an increase in protein binding to the CME in SV‐WI38 but not untransformed WI38 cells. Knockdown of AnxA2 by siRNA increased type I collagen production in both WI38 and SV‐WI38 cells; however, these effects were not mediated at the transcriptional level. Rather, our data indicate a novel functional role of AnxA2 in the negative post‐transcriptional regulation of type I collagen synthesis in human fibroblasts. In SV40‐transformed cells, AnxA2 is accumulated at the proximal COL1A2 promoter region, suggesting close association with the transcriptional machinery that possibly facilitates binding to the emerging mRNA, eventually contributing to overall repression of type I collagen protein synthesis. J. Cell. Biochem. 116: 408–417, 2015. © 2014 The Authors. Journal of Cellular Biochemistry published by Wiley Periodicals, Inc.

Association of annexin A2 with cancer development (Review)

Annexin A2 (ANXA2) is a well-known calcium-dependent phospholipid binding protein widely distributed in the nucleus, cytoplasm and extracellular surface of various eukaryotic cells. It has been recognized as a pleiotropic protein affecting a wide range of molecular and cellular processes. Dysregulation and abnormal expression of ANXA2 are linked to a large number of prevalent diseases, including autoimmune and neurodegenerative disease, antiphospholipid syndrome, inflammation, diabetes mellitus and a series of cancers. Accumulating data suggest that ANXA2 is aberrantly expressed in a wide spectrum of cancers, and exerts profound effects on tumor cell adhesion, proliferation, apoptosis, invasion and metastasis as well as tumor neovascularization via different modes of action. However, despite significant research, our knowledge of the mechanism by which ANXA2 participates in cancer development remains fragmented. The present review systematically summarizes the effects of ANXA2 on tumor progression, in an attempt to gain an improved understanding of the underlying mechanisms and to provide a potential effective target for cancer therapy.

Annexin A2 complexes with S100 proteins: structure, function and pharmacological manipulation

Annexin A2 (AnxA2) was originally identified as a substrate of the pp60v-src oncoprotein in transformed chicken embryonic fibroblasts. It is an abundant protein that associates with biological membranes as well as the actin cytoskeleton, and has been implicated in intracellular vesicle fusion, the organization of membrane domains, lipid rafts and membrane-cytoskeleton contacts. In addition to an intracellular role, AnxA2 has been reported to participate in processes localized to the cell surface including extracellular protease regulation and cell-cell interactions. There are many reports showing that AnxA2 is differentially expressed between normal and malignant tissue and potentially involved in tumour progression. An important aspect of AnxA2 function relates to its interaction with small Ca²⁺-dependent adaptor proteins called S100 proteins, which is the topic of this review. The interaction between AnxA2 and S100A10 has been very well characterized historically; more recently, other S100 proteins have been shown to interact with AnxA2 as well. The biochemical evidence for the occurrence of these protein interactions will be discussed, as well as their function. Recent studies aiming to generate inhibitors of S100 protein interactions will be described and the potential of these inhibitors to further our understanding of AnxA2 S100 protein interactions will be discussed.

Annexin A2 autoantibodies in thrombosis and autoimmune diseases

Antiphospholipid syndrome (APS) is an autoimmune disease characterized by arterial, venous or small-vessel thrombotic events, and recurrent miscarriages or fetal loss. APS diagnosis is based on the repeated detection of anti-phospholipid (PL) antibodies (Ab), typically associated with anti-β2 glycoprotein I (β2GPI)-Ab. Recent studies suggest that anti-β2GPI Ab activity involves a protein complex including β2GPI and annexin A2 (ANXA2). Anti-ANXA2 Ab recognizes this complex, and these Ab can effectively promote thrombosis by inhibiting plasmin generation, and by activating endothelial cells. Therefore, anti-ANXA2 Ab represent a new biomarker, which can be detected in up to 25% of APS patients. Moreover, anti-ANXA2 Ab have been detected, in thrombotic associated diseases including pre-eclampsia, in other autoimmune diseases, and in cancer.

Nuclear accumulation of annexin A2 contributes to chromosomal instability by coilin-mediated centromere damage

Most human cancers show chromosomal instability (CIN), but the precise mechanisms remain uncertain. Annexin A2 is frequently overexpressed in human cancers, and its relationship to tumorigenesis is poorly understood. We found that annexin A2 is overexpressed in the nuclei of CIN cells compared with cells with microsatellite instability (MIN). Ectopic annexin A2 expression in MIN cells results in a high level of aneuploidy and induces lagging chromosomes; suppression of annexin A2 in CIN cells reduces such CIN signatures with apoptosis of highly aneuploid cells. Ectopic expression of annexin A2 in MIN cells reduces the expression of centromere proteins. Conversely, annexin A2-knockdown in CIN cells increases the expression of centromere proteins. Moreover, the endogenous expression levels of centromere proteins in CIN cells were greatly reduced compared with MIN cell lines. The reduced expression of centromere proteins likely occurred due to aberrant centromere localization of coilin, a major component of the Cajal bodies. These results suggest that nuclear accumulation of annexin A2 has a crucial role in CIN by disrupting centromere function.

Effect of serine phosphorylation and Ser25 phospho-mimicking mutations on nuclear localisation and ligand interactions of annexin A2

Annexin A2 (AnxA2) interacts with numerous ligands, including calcium, lipids, mRNAs and intracellular and extracellular proteins. Different post-translational modifications participate in the discrimination of the functions of AnxA2 by modulating its ligand interactions. Here, phospho-mimicking mutants (AnxA2-S25E and AnxA2-S25D) were employed to investigate the effects of Ser25 phosphorylation on the structure and function of AnxA2 by using AnxA2-S25A as a control. The overall α-helical structure of AnxA2 is not affected by the mutations, since the thermal stabilities and aggregation tendencies of the mutants differ only slightly from the wild-type (wt) protein. Unlike wt AnxA2, all mutants bind the anxA2 3' untranslated region and β-γ-G-actin with high affinity in a Ca(2+)-independent manner. AnxA2-S25E is not targeted to the nucleus in transfected PC12 cells. In vitro phosphorylation of AnxA2 by protein kinase C increases its affinity to mRNA and inhibits its nuclear localisation, in accordance with the data obtained with the phospho-mimicking mutants. Ca(2+)-dependent binding of wt AnxA2 to phosphatidylinositol, phosphatidylinositol-3-phosphate, phosphatidylinositol-4-phosphate and phosphatidylinositol-5-phosphate, as well as weaker but still Ca(2+)-dependent binding to phosphatidylserine and phosphatidylinositol-3,5-bisphosphate, was demonstrated by a protein-lipid overlay assay, whereas binding of AnxA2 to these lipids, as well as its binding to liposomes, is inhibited by the Ser25 mutations. Thus, introduction of a modification (mutation or phosphorylation) at Ser25 appears to induce a conformational change leading to increased accessibility of the mRNA- and G-actin-binding sites in domain IV independent of Ca(2+) levels, while the Ca(2+)-dependent binding of AnxA2 to phospholipids is attenuated.

Cationic lipid guided short-hairpin RNA interference of annexin A2 attenuates tumor growth and metastasis in a mouse lung cancer stem cell model

The role of side populations (SP) or cancer stem-like cells (CSC) in promoting the resistance phenotype presents a viable anticancer target. Human-derived H1650 SP cells over-express annexin A2 (AnxA2) and SOX2, and are resistant to conventional cytotoxic chemotherapeutics. AnxA2 and SOX2 bind to proto-oncogenes, c-Myc and c-Src, and AnxA2 forms a functional heterotetramer with S100A10 to promote tumor motility. However, the combined role of AnxA2, S100A10 and SOX2 in promoting the resistant phenotype of SP cells has not been investigated. In the current studies, we examined for the first time a possible role of AnxA2 in regulating SA100A10 and SOX2 in promoting a resistant phenotype of lung tumors derived from H1650 SP cells. The resistance of H1650 SP cells to chemotherapy compared to H1650 MP cells was investigated by cell viability studies. A short hairpin RNA targeting AnxA2 (shAnxA2) was formulated in a liposomal (cationic ligand-guided, CLG) carrier and characterized for size, charge and entrapment and loading efficiencies; CLG carrier uptake by H1650 SP cells was demonstrated by fluorescence microscopy, and knockdown of AnxA2 confirmed by qRT-PCR and Western blot. Targeting of xenograft and orthotopic lung tumors was demonstrated with fluorescent (DiR) CLG carriers in mice. The therapeutic efficacy of CLG-AnxA2, compared to that of placebo, was investigated after 2 weeks of treatment in terms of tumor weights and tumor burden in vivo. Compared to mixed population cells, H1650 SP cells showed exponential resistance to docetaxel (15-fold), cisplatin (13-fold), 5-fluorouracil (31-fold), camptothecin (7-fold), and gemcitabine (16-fold). CLG carriers were nanoparticulate (199nm) with a slight positive charge (21.82mV); CLG-shAnx2 was of similar size (217nm) with decreased charge (12.11mV), and entrapment and loading efficiencies of 97% and 6.13% respectively. Fluorescence microscopy showed high uptake of CLG-shAnxA2 in H1650 SP cells after 2h resulting in a 6-fold reduction in AnxA2 mRNA expression and 92% decreased protein expression. Fluorescence imaging confirmed targeting of tumors and lungs by DiR-CLG carriers with sustained localization up to 4h in mice. CLG-shAnxA2 treatment of mice significantly reduced the weights of lung tumors derived from H1650 SP cells and tumor burden was reduced to only 19% of controls. The loss in tumor weights in response to CLG-shAnxA2 was associated with a significant loss in the relative levels of AnxA2, SOX2, total β-catenin and S100A10, both at the RNA and protein levels. These results suggest the intriguing possibility that AnxA2 may directly or indirectly regulate relative levels of β-catenin, S100A10 and SOX2, and that the combination of these factors may contribute to the resistant phenotype of H1650 SP cells. Thus down-regulating AnxA2 using RNAi methods may provide a useful method for targeting cancer stem cells and help advance therapeutic efficacy against lung cancers.

Annexin A2: its molecular regulation and cellular expression in cancer development

Annexin A2 (ANXA2) orchestrates multiple biologic processes and clinical associations, especially in cancer progression. The structure of ANXA2 affects its cellular localization and function. However, posttranslational modification and protease-mediated N-terminal cleavage also play critical roles in regulating ANXA2. ANXA2 expression levels vary among different types of cancers. With some cancers, ANXA2 can be used for the detection and diagnosis of cancer and for monitoring cancer progression. ANXA2 is also required for drug-resistance. This review discusses the feasibility of ANXA2 which is active in cancer development and can be a therapeutic target in cancer management.

The tumor suppressor annexin A10 is a novel component of nuclear paraspeckles

Annexin A10 is the latest identified member of the annexin family of Ca(2+)- and phospholipid-binding proteins. In previous studies, downregulation of annexin A10 was correlated with dedifferentiation, invasion, and tumor progression, pointing to a possible tumor suppressor role. However, the biochemical characteristics and functions of annexin A10 remain unknown. We show that annexin A10 displays biochemical characteristics atypical for an annexin, indicating a Ca(2+)- and membrane-binding-independent function. Annexin A10 co-localizes with the mRNA-binding proteins SFPQ and PSPC1 at paraspeckles, an only recently discovered nuclear body, and decreases paraspeckle numbers when overexpressed in HeLa cells. In addition, annexin A10 relocates to dark perinucleolar caps upon transcriptional inhibition of RNA polymerase II. We mapped the cap-binding function of annexin A10 to the proximal part of the core domain, which is missing in the short isoform of annexin A10, and show its independence from the remaining functional type II Ca(2+)-binding site. In contrast to this, paraspeckle recruitment required additional core regions and was negatively affected by the mutation of the last type II Ca(2+)-binding site. Additionally, we show that overexpression of annexin A10 in HeLa cells increases their sensitivity to apoptosis and reduces colony formation. The identification of unique nuclear and biochemical characteristics of annexin A10 points towards its membrane-independent role in paraspeckle-associated mRNA regulation or processing.

p11 and its role in depression and therapeutic responses to antidepressants

Studies of the multifunctional protein p11 (also known as S100A10) are shedding light on the molecular and cellular mechanisms underlying depression. Here, we review data implicating p11 in both the amplification of serotonergic signalling and the regulation of gene transcription. We summarize studies demonstrating that levels of p11 are regulated in depression and by antidepressant regimens and, conversely, that p11 regulates depression-like behaviours and/or responses to antidepressants. Current and future studies of p11 may provide a molecular and cellular framework for the development of novel antidepressant therapies.

Annexin A2 and S100A10 regulate human papillomavirus type 16 entry and intracellular trafficking in human keratinocytes

Human papillomaviruses (HPVs) cause benign and malignant tumors of the mucosal and cutaneous epithelium. The initial events regulating HPV infection impact the establishment of viral persistence, which is requisite for malignant progression of HPV-infected lesions. However, the precise mechanisms involved in HPV entry into host cells, including the cellular factors regulating virus uptake, are not clearly defined. We show that HPV16 exposure to human keratinocytes initiates epidermal growth factor receptor (EGFR)-dependent Src protein kinase activation that results in phosphorylation and extracellular translocation of annexin A2 (AnxA2). HPV16 particles interact with AnxA2 in association with S100A10 as a heterotetramer at the cell surface in a Ca(2+)-dependent manner, and the interaction appears to involve heparan-sulfonated proteoglycans. We show multiple lines of evidence that this interaction promotes virus uptake into host cells. An antibody to AnxA2 prevents HPV16 internalization, whereas an antibody to S100A10 blocks infection at a late endosomal/lysosomal site. These results suggest that AnxA2 and S100A10 have separate roles during HPV16 binding, entry, and trafficking. Our data additionally imply that AnxA2 and S100A10 may be involved in regulating the intracellular trafficking of virus particles prior to nuclear delivery of the viral genome.

Annexin A2 heterotetramer: structure and function

Annexin A2 is a pleiotropic calcium- and anionic phospholipid-binding protein that exists as a monomer and as a heterotetrameric complex with the plasminogen receptor protein, S100A10. Annexin A2 has been proposed to play a key role in many processes including exocytosis, endocytosis, membrane organization, ion channel conductance, and also to link F-actin cytoskeleton to the plasma membrane. Despite an impressive list of potential binding partners and regulatory activities, it was somewhat unexpected that the annexin A2-null mouse should show a relatively benign phenotype. Studies with the annexin A2-null mouse have suggested important functions for annexin A2 and the heterotetramer in fibrinolysis, in the regulation of the LDL receptor and in cellular redox regulation. However, the demonstration that depletion of annexin A2 causes the depletion of several other proteins including S100A10, fascin and affects the expression of at least sixty-one genes has confounded the reports of its function. In this review we will discuss the annexin A2 structure and function and its proposed physiological and pathological roles.

Down-regulation of annexin A1 in the urothelium decreases cell survival after bacterial toxin exposure

PURPOSE

We examined the role of annexins in bladder urothelium. We characterized expression and distribution in normal bladders, biopsies from patients with bladder pain syndrome, cultured human urothelium and urothelial TEU-2 cells.

MATERIALS AND METHODS

Annexin expression in bladder layers was analyzed by quantitative reverse transcriptase-polymerase chain reaction and immunofluorescence. We assessed cell survival after exposure to the pore forming bacterial toxin streptolysin O by microscopy and alamarBlue® assay. Bladder dome biopsies were obtained from 8 asymptomatic controls and 28 patients with symptoms of bladder pain syndrome.

RESULTS

Annexin A1, A2, A5 and A6 were differentially distributed in bladder layers. Annexin A6 was abundant in detrusor smooth muscle and low in urothelium, while annexin A1 was the highest in urothelium. Annexin A2 was localized to the lateral membrane of umbrella cells but excluded from tight junctions. TEU-2 cell differentiation caused up-regulation of annexin A1 and A2 and down-regulation of annexin A6 mRNA. Mature urothelium dedifferentiation during culture caused the opposite effect, decreasing annexin A1 and increasing annexin A6. Annexin A2 influenced TEU-2 cell epithelial permeability. siRNA mediated knockdown of annexin A1 in TEU-2 cells caused significantly decreased cell survival after streptolysin O exposure. Annexin A1 was significantly reduced in biopsies from patients with bladder pain syndrome.

CONCLUSIONS

Several annexins are expressed in human bladder and TEU-2 cells, in which levels are regulated during urothelial differentiation. Annexin A1 down-regulation in patients with bladder pain syndrome might decrease cell survival and contribute to compromised urothelial function.

Genotoxic agents promote the nuclear accumulation of annexin A2: role of annexin A2 in mitigating DNA damage

Annexin A2 is an abundant cellular protein that is mainly localized in the cytoplasm and plasma membrane, however a small population has been found in the nucleus, suggesting a nuclear function for the protein. Annexin A2 possesses a nuclear export sequence (NES) and inhibition of the NES is sufficient to cause nuclear accumulation. Here we show that annexin A2 accumulates in the nucleus in response to genotoxic agents including gamma-radiation, UV radiation, etoposide and chromium VI and that this event is mediated by the nuclear export sequence of annexin A2. Nuclear accumulation of annexin A2 is blocked by the antioxidant agent N-acetyl cysteine (NAC) and stimulated by hydrogen peroxide (H₂O₂), suggesting that this is a reactive oxygen species dependent event. In response to genotoxic agents, cells depleted of annexin A2 show enhanced phospho-histone H2AX and p53 levels, increased numbers of p53-binding protein 1 nuclear foci and increased levels of nuclear 8-oxo-2′-deoxyguanine, suggesting that annexin A2 plays a role in protecting DNA from damage. This is the first report showing the nuclear translocation of annexin A2 in response to genotoxic agents and its role in mitigating DNA damage.

Annexin A2 modulates radiation-sensitive transcriptional programming and cell fate

We previously established annexin A2 as a radioresponsive protein associated with anchorage independent growth in murine epidermal cells. In this study, we demonstrate annexin A2 nuclear translocation in human skin organotypic culture and murine epidermal cells after exposure to X radiation (10-200 cGy), supporting a conserved nuclear function for annexin A2. Whole genome expression profiling in the presence and absence of annexin A2 [shRNA] identified fundamentally altered transcriptional programming that changes the radioresponsive transcriptome. Bioinformatics predicted that silencing AnxA2 may enhance cell death responses to stress in association with reduced activation of pro-survival signals such as nuclear factor kappa B. This prediction was validated by demonstrating a significant increase in sensitivity toward tumor necrosis factor alpha-induced cell death in annexin A2 silenced cells, relative to vector controls, associated with reduced nuclear translocation of RelA (p65) following tumor necrosis factor alpha treatment. These observations implicate an annexin A2 niche in cell fate regulation such that AnxA2 protects cells from radiation-induced apoptosis to maintain cellular homeostasis at low-dose radiation.

Annexin A2 silencing induces G2 arrest of non-small cell lung cancer cells through p53-dependent and -independent mechanisms

Annexin A2 (ANXA2) overexpression is required for cancer cell proliferation; however, the molecular mechanisms underlying ANXA2-mediated regulation of the cell cycle are still unknown. ANXA2 is highly expressed in non-small cell lung cancer (NSCLC) and is positively correlated with a poor prognosis. NSCLC A549 cells lacking ANXA2 exhibited defects in tumor growth in vivo and in cell proliferation in vitro without cytotoxicity. ANXA2 knockdown induced cell cycle arrest at G(2) phase. Unexpectedly, ANXA2 silencing increased the expression of p53 and its downstream genes, which resulted in p53-dependent and -independent G(2) arrest. Aberrant JNK inactivation, which was observed in ANXA2-deficient cells, inhibited cell proliferation following G(2) arrest. A lack of ANXA2 caused a loss of JNK-regulated c-Jun expression, resulting in an increase in p53 transcription. These results demonstrate a novel role for ANXA2 in NSCLC cell proliferation by facilitating the cell cycle partly through the regulation of p53 via JNK/c-Jun.

The association of annexin A2 and cancers

Annexins are a group of calcium- and phospholipid-dependent proteins. As a member of the annexin, annexin A2 (Anxa2) is widely distributed in nucleus, cytoplasm and extracellular surface and mainly expressed in human endothelial cells, mononuclear cells, macrophages, marrow cells and some tumor cells. Accumulated evidences indicated that Anxa2 deregulation was associated with the occurrence, invasion and metastasis of cancers. Anxa2 up-regulation was related to the development, invasion, metastasis and drug resistance of hepatocellular carcinoma, colorectal cancer, breast cancer, pancreatic cancer, acute promyelocytic leukemia and renal cell carcinoma; while Anxa2 down-regulation was associated with prostate cancer, esophageal squamous carcinoma and nasopharyngeal carcinoma and sinonasal adenocarcinoma. The association between Anxa2 and malignant tumors as well as the potential action mechanisms were summarized in current work. Anxa2 might be used as a potential biomarker for the diagnosis, treatment and prognosis of certain tumors.

Efficient nanoparticle mediated sustained RNA interference in human primary endothelial cells

Endothelium forms an important target for drug and/or gene therapy since endothelial cells play critical roles in angiogenesis and vascular functions and are associated with various pathophysiological conditions. RNA mediated gene silencing presents a new therapeutic approach to overcome many such diseases, but the major challenge of such an approach is to ensure minimal toxicity and effective transfection efficiency of short hairpin RNA (shRNA) to primary endothelial cells. In the present study, we formulated shAnnexin A2 loaded poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles which produced intracellular small interfering RNA (siRNA) against Annexin A2 and brought about the downregulation of Annexin A2. The per cent encapsulation of the plasmid within the nanoparticle was found to be 57.65%. We compared our nanoparticle based transfections with Lipofectamine mediated transfection, and our studies show that nanoparticle based transfection efficiency is very high (~97%) and is more sustained compared to conventional Lipofectamine mediated transfections in primary retinal microvascular endothelial cells and human cancer cell lines. Our findings also show that the shAnnexin A2 loaded PLGA nanoparticles had minimal toxicity with almost 95% of cells being viable 24 h post-transfection while Lipofectamine based transfections resulted in only 30% viable cells. Therefore, PLGA nanoparticle based transfection may be used for efficient siRNA transfection to human primary endothelial and cancer cells. This may serve as a potential adjuvant treatment option for diseases such as diabetic retinopathy, retinopathy of prematurity and age related macular degeneration besides various cancers.

Annexin A2 binds RNA and reduces the frameshifting efficiency of infectious bronchitis virus

Annexin A2 (ANXA2) is a protein implicated in diverse cellular functions, including exocytosis, DNA synthesis and cell proliferation. It was recently proposed to be involved in RNA metabolism because it was shown to associate with some cellular mRNA. Here, we identified ANXA2 as a RNA binding protein (RBP) that binds IBV (Infectious Bronchitis Virus) pseudoknot RNA. We first confirmed the binding of ANXA2 to IBV pseudoknot RNA by ultraviolet crosslinking and showed its binding to RNA pseudoknot with ANXA2 protein in vitro and in the cells. Since the RNA pseudoknot located in the frameshifting region of IBV was used as bait for cellular RBPs, we tested whether ANXA2 could regulate the frameshfting of IBV pseudoknot RNA by dual luciferase assay. Overexpression of ANXA2 significantly reduced the frameshifting efficiency from IBV pseudoknot RNA and knockdown of the protein strikingly increased the frameshifting efficiency. The results suggest that ANXA2 is a cellular RBP that can modulate the frameshifting efficiency of viral RNA, enabling it to act as an anti-viral cellular protein, and hinting at roles in RNA metabolism for other cellular mRNAs.

A competitive hexapeptide inhibitor of annexin A2 prevents hypoxia-induced angiogenic events

Extracellular proteolysis is an indispensable requirement for the formation of new blood vessels during neovascularization and is implicated in the generation of several angiogenic regulatory molecules. Anti-proteolytic agents have become attractive therapeutic strategies in diseases associated with excessive neovascularization. Annexin A2 (AnxA2) is an endothelial cell-surface receptor for the generation of active proteolytic factors, such as plasmin. Here, we show that AnxA2 is abundantly expressed in the neovascular tufts in a murine model of neovascularization. Exposure to hypoxic conditions results in elevation of AnxA2 and tissue plasminogen activator (tPA) in human retinal microvascular endothelial cells (RMVECs). We show that the hexapeptide competitive inhibitor LCKLSL, which targets the N-terminal tPA-binding site of AnxA2, binds efficiently to cell-surface AnxA2 compared with binding of the control peptide LGKLSL. Treatment with the competitive peptide inhibits the generation of plasmin and suppresses the VEGF-induced activity of tPA under hypoxic conditions. Application of the competitive peptide in two in vivo models of angiogenesis demonstrated suppression of the angiogenic responses, which was also associated with significant changes in the vascular sprouting. These results suggest that AnxA2-mediated plasmin generation is an important event in angiogenesis and is inhibited by a specific competitive peptide that inhibits the binding of tPA to AnxA2.

Signal transducer and activator of transcription 6 (STAT6) is a novel interactor of annexin A2 in prostate cancer cells

Annexin A2 (AnxA2) is a multifunctional Ca(2+)-dependent phospholipid-binding protein, and its overexpression is implicated in malignant transformation of several cancers. In prostate cancer, however, the expression of AnxA2 is lost in prostate intraepithelial neoplasia and reappears in the high-grade tumors, suggesting a complex regulation of AnxA2 in the prostate microenvironment. Since a majority of the biological functions of AnxA2 are mediated by its interaction with other proteins, we performed a yeast two-hybrid assay to search for novel interactors of AnxA2. Our studies revealed that signal transducer and activator of transcription 6 (STAT6), a member of the STAT family of transcription factors, is a binding partner of AnxA2. We confirmed AnxA2-STAT6 interaction by in vitro co-immunoprecipitation and fluorescence resonance energy transfer (FRET) studies and demonstrated that AnxA2 interacts with phosphorylated STAT6. Furthermore, chromatin immunoprecipitation (ChIP) assay revealed that AnxA2 is associated with the STAT6 DNA-binding complex, and luciferase reporter assays demonstrated that AnxA2 upregulates the activity of STAT6. Upon interleukin-4 treatment, AnxA2 stabilizes the cytosolic levels of phosphorylated STAT6 and promotes its nuclear entry. These findings suggest that AnxA2-STAT6 interactions could have potential implications in prostate cancer progression. This report is the first to demonstrate the interaction of AnxA2 with STAT6 and suggests a possible mechanism by which AnxA2 contributes to the metastatic processes of prostate cancer.

Phosphoproteome study reveals Hsp27 as a novel signaling molecule involved in GDNF-induced neurite outgrowth

Glial-cell-line-derived neurotrophic factor (GDNF) is a most potent survival factor for dopaminergic neurons. In addition, GDNF was also found to promote neurite outgrowth in dopaminergic neurons. However, despite the potential clinical and physiological importance of GDNF, its mechanism of action is unclear. Therefore, we employed a state-of-the-art proteomic technique, DIGE (Difference in two-dimensional gel electrophoresis), to quantitatively compare profiles of phosphoproteins of PC12-GFRalpha1-RET cells (that stably overexpress GDNF receptor alpha1 and RET) 0.5 and 10 h after GDNF challenge with control. A total of 92 differentially expressed proteins were successfully identified by mass spectrometry. Among them, the relative levels of phosphorylated Hsp27 increased significantly both in 0.5 and 10 h GDNF-treated PC12-GFRalpha1-RET cells. Confocal microscopy and Western blot results showed that the phosphorylation of Hsp27 after GDNF treatment was accompanied by its nuclear translocation. After the mRNA of Hsp27 was interfered, neurite outgrowth of PC12-GFRalpha1-RET cells induced by GDNF was significantly blocked. Furthermore, the percentage of neurite outgrowth induced by GDNF was also reduced by the expression of dominant-negative mutants of Hsp27, in which specific serine phosphorylation residues (Ser15, Ser78 and Ser82) were substituted with alanine. Our data also revealed that p38 MAPK and ERK are the upstream regulators of Hsp27 phosphorylation. Hence, in addition to the numerous novel proteins that are potentially important in GDNF mediated differentiation of dopaminergic cells revealed by our study, our data has indicated that Hsp27 is a novel signaling molecule involved in GDNF-induced neurite outgrowth of dopaminergic neurons.

Proteomic profiling of glucocorticoid-exposed myogenic cells: Time series assessment of protein translocation and transcription of inactive mRNAs

BACKGROUND

Prednisone, one of the most highly prescribed drugs, has well characterized effects on gene transcription mediated by the glucocorticoid receptor. These effects are typically occurring on the scale of hours. Prednisone also has a number of non-transcriptional effects (occurring on minutes scale) on protein signaling, yet these are less well studied. We sought to expand the understanding of acute effects of prednisone action on cell signaling using a combination of SILAC strategy and subcellular fractionations from C2C12 myotubes.

RESULTS

De novo translation of proteins was inhibited in both SILAC labeled and unlabeled C2C12 myotubes. Unlabeled cells were exposed to prednisone while SILAC labeled cells remained untreated. After 0, 5, 15, and 30 minutes of prednisone exposure, labeled and unlabeled cells were mixed at 1:1 ratios and fractionated into cytosolic and nuclear fractions. A total of 534 proteins in the cytosol and 626 proteins in the nucleus were identified and quantitated, using 3 or more peptides per protein with peptide based probability < or = 0.001. We identified significant increases (1.7- to 3.1- fold) in cytoplasmic abundance of 11 ribosomal proteins within 5 minutes of exposure, all of which returned to baseline by 30 min. We hypothesized that these drug-induced acute changes in the subcellular localization of the cell's protein translational machinery could lead to altered translation of quiescent RNAs. To test this, de novo protein synthesis was assayed after 15 minutes of drug exposure. Quantitative fluorography identified 16 2D gel spots showing rapid changes in translation; five of these were identified by MS/MS (pyruvate kinase, annexin A6 isoform A and isoform B, nasopharyngeal epithelium specific protein 1, and isoform 2 of Replication factor C subunit 1), and all showed the 5' terminal oligopyrimidine motifs associated with mRNA sequestration to and from inactive mRNA pools.

CONCLUSION

We describe novel approaches of subcellular proteomic profiling and assessment of acute changes on a minute-based time scale. These data expand the current knowledge of acute, non-transcriptional activities of glucocorticoids, including changes in protein subcellular localization, altered translation of quiescent RNA pools, and PKC-mediated cytoskeleton remodeling.

Proteomic profiling of distinct clonal populations of bone marrow mesenchymal stem cells

Mesenchymal stem cells (MSCs) have attracted immense research interest in the field of regenerative medicine due to their ability to be cultured for successive passages and multi-lineage differentiation. The molecular mechanisms governing MSC self-renewal and differentiation remain largely unknown. The development of sophisticated techniques, in particular clinical proteomics, has enabled researchers in various fields to identify and characterize cell specific biomarkers for therapeutic purposes. This study seeks to understand the cellular and sub-cellular processes responsible for the existence of stem cell populations in bone marrow samples by revealing the whole cell proteome of the clonal cultures of bone marrow-derived MSCs (BMSCs). Protein profiling of the MSC clonal populations was conducted by Two-Dimensional Liquid Chromatography/Matrix-Assisted Laser Desorption/Ionisation (MALDI) Mass Spectrometry (MS). A total of 83 proteins were identified with high confidence of which 11 showed differential expression between subpopulations, which included cytoskeletal and structural proteins, calcium binding proteins, cytokinetic proteins, and members of the intermediate filament family. This study generated a proteome reference map of BMSCs from the clonal populations, which will be valuable to better understand the underlying mechanism of BMSC self-renewal and differentiation.

The roles of HSP27 and annexin II in resistance to UVC-induced cell death: comparative studies of the human UVC-sensitive and -resistant cell lines RSa and APr-1

We have reported that heat shock protein 27 (HSP27) and annexin II are involved in the protection of human cells against UVC-induced cell death. In this study we tried to confirm the combined roles of HSP27 and annexin II in cell death after UVC irradiation. In RSa cells with sensitivity to UVC, expression of annexin II decreased after UVC irradiation, but not in AP(r)-1 cells with increased resistance to UVC. HSP27 siRNA-transfected AP(r)-1 cells were sensitized to UVC lethality and showed decreased annexin II expression after UVC irradiation. In contrast, transfection of RSa cells with HSP27 cDNA increased their resistance to UVC lethality and caused increased annexin II expression. Furthermore, over-production of annexin II in RSa cells resulted in increased resistance to UVC lethality. This study indicates the involvement of cellular HSP27 expression in the UVC susceptibility of human cells, which occurs in association with regulation of annexin II expression.

Annexin A1 subcellular expression in laryngeal squamous cell carcinoma

AIMS

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Annexin A2 positively contributes to the malignant phenotype and secretion of IL-6 in DU145 prostate cancer cells

Several groups, including ours, have reported that annexin A2 (ANXA2) expression is reduced in most prostate cancer (CaP). More recently, however, we reported that ANXA2 is expressed in some high-grade tumors, but the biologic consequence of this is currently unknown. To elucidate the function of ANXA2 in CaP, we reduced its expression in DU145 cells using shRNA and tested the impact on characteristics of malignancy. Reduction of ANXA2 suppressed anchorage-dependent and -independent cell growth without affecting invasiveness. Interestingly, interleukin-6 (IL-6) secretion was reduced concomitantly with the reduction of ANXA2 but independently of S100A10. IL-6 expression was restored when wild type but not mutant ANXA2 was reexpressed in these cells. In a retrospective study of radical prostatectomy specimens from patients with nonmetastatic CaP, 100% of patients with ANXA2-positive tumors (n = 4) had a biochemical relapse while only 50% of patients with ANXA2 negative tumors (n = 20) relapsed, suggesting that ANXA2 expression in prostate tumors may be predictive of biochemical relapse. Significant cytoplasmic staining of ANXA2 was detected in 3 of 4 ANXA2-positive tumors, whereas ANXA2 is localized to the plasma membrane in benign prostatic glands. These finding, taken together, suggests a possible mechanism whereby ANXA2 expression positively contributes to an aggressive phenotype in a subset of CaP and suggest that ANXA2 has markedly different functions depending on its cellular context. Finally, this is the first description of a role for ANXA2 in IL-6 expression, and ANXA2 represents a new therapeutic target for reducing IL-6 in high-grade prostate cancer.

Insight into the location and dynamics of the annexin A2 N-terminal domain during Ca(2+)-induced membrane bridging

Annexin A2 (AnxA2) is a Ca(2+)- and phospholipid-binding protein involved in many cellular regulatory processes. Like other annexins, it is constituted by two domains: a conserved core, containing the Ca(2+) binding sites, and a variable N-terminal segment, containing sites for interactions with other protein partners like S100A10 (p11). A wealth of data exists on the structure and dynamics of the core, but little is known about the N-terminal domain especially in the Ca(2+)-induced membrane-bridging process. To investigate this protein region in the monomeric AnxA2 and in the heterotetramer (AnxA2-p11)(2), the reactive Cys8 residue was specifically labelled with the fluorescent probe acrylodan and the interactions with membranes were studied by steady-state and time-resolved fluorescence. In membrane junctions formed by the (AnxA2-p11)(2) heterotetramer, the flexibility of the N-terminal domain increased as compared to the protein in solution. In "homotypic" membrane junctions formed by monomeric AnxA2, acrylodan moved to a more hydrophobic environment than in the protein in solution and the flexibility of the N-terminal domain also increased. In these junctions, this domain is probably not in close contact with the membrane surface, as suggested by the weak quenching of acrylodan observed with doxyl-PCs, but pairs of N-termini likely interact, as revealed by the excimer-forming probe pyrene-maleimide bound to Cys8. We present a model of monomeric AnxA2 N-terminal domain organization in "homotypic" bridged membranes in the presence of Ca(2+).

Signal transducer and activator of transcription-6 (STAT6) is a constitutively expressed survival factor in human prostate cancer

BACKGROUND

Signal transducer and activator of transcription (STAT)-6 is a member of the STAT family of latent transcription factors. In this investigation, we examined STAT6 expression in clinical prostate cancer tissue specimen and determined its role in prostate cell proliferation and migration.

METHODS

STAT6 expression in cell lines and tissues was analyzed by RT-PCR, IHC and/or immunoblot analyses. Down-regulation of STAT6 expression was achieved by STAT6 siRNA and its effect on cell migration and apoptosis was measured.

RESULTS

STAT6 is highly expressed in the fibromuscular stroma of prostate cancer specimens. STAT6 is also expressed in the malignant epithelial layer and prostate intraepithelial neoplasia (PIN). STAT6 expression was significantly correlated with high histological grades of prostate cancer as well as with tumor size. Our data indicate deregulated STAT6 mRNA and protein expression in prostate cancer cells with high levels in the non-cancerous HPV 18C-1 and cancerous DU145 cell lines and low levels in PC3 and LNCaP cells. Phosphorylated STAT6 was expressed in all three cancer cell lines DU145, PC3, and LNCaP. Down-regulation of STAT6 using siRNA leads to the induction of early apoptosis in DU145 cells and inhibits migration of these cells. Significant reduction in cell viability and transcriptional down-regulation of the anti-apoptotic protein Bcl-X(L) was observed followed by STAT6 down-regulation in DU145 cells. Interestingly STAT6 also regulates transcription of 15-lipoxygenase-1 gene in DU145 cells.

CONCLUSIONS

Our data suggest that STAT6 is a survival factor in prostate cancer and regulates the genetic transcriptional program that is responsible for prostate cancer progression.

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.

Annexin II binds to SHP2 and this interaction is regulated by HSP70 levels

The protein tyrosine phosphatase SHP2 is a positive effector of EGFR signaling. To improve our understanding of SHP2's function, we searched for additional binding proteins of SHP2. We found that Annexin II is an SHP2-binding protein. Physical interactions of SHP2 with Annexin II were confirmed in vivo. Furthermore, binding of SHP2 with Annexin II was regulated somewhat by EGF treatment and the extracellular Ca2+ chelator, EGTA. Previously, we reported that HSP70 levels can influence the binding of SHP2 with EGFR. Interestingly, increased HSP70 levels also inhibited the binding of SHP2 with Annexin II after EGF treatment in vivo. In addition, immunostaining experiments indicated that a fraction of SHP2 and Annexin II co-localized in the cell membrane region after EGF treatment. Our findings indicate that Annexin II is binding partner of SHP2 and the binding of SHP2 with Annexin II is affected by EGF stimulation, extracellular calcium levels, and the levels of HSP70.

Probing early growth response 1 interacting proteins at the active promoter in osteoblast cells using oligoprecipitation and mass spectrometry

Current advances in proteomics have allowed for a rapidly expanding integration of associated methodologies with more traditional molecular and biochemical approaches to the study of cell function. Recent studies on the role of inorganic phosphate have suggested this ion is a novel signaling molecule capable of altering the function of numerous cell types. Elevated inorganic phosphate generated in the extracellular microenvironment by differentiating osteoblasts has recently been determined to act through a largely uncharacterized mechanism as an important signaling molecule responsible for altering the transcription of various genes during osteoblast differentiation. The transcription factor, early growth response protein 1 (EGR1), has previously been shown to be involved in the early response of osteoblasts to inorganic phosphate. To elucidate the role of EGR1 as a potential early regulator of transcription in the inorganic phosphate response, an oligoprecipitation procedure was optimized to capture the DNA bound, transcriptionally active form of EGR1. The interacting proteins thusly captured were identified using mass spectrometry (MS). Proteins involved in transcription, RNA processing, and chromatin modification were identified by this approach. The combined oligoprecipitation-MS approach presented here is highly effective for isolating and characterizing entire transcriptional complexes in the DNA bound state and is broadly extendable to the identification of both known and unknown transcription factor protein complexes.

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.

Dual localization: proteins in extracellular and intracellular compartments

The goal of this article is to provide a comprehensive catalog of those proteins documented to exhibit dual localization, being found in both the extracellular compartment (cell surface and extracellular medium) as well as the intracellular compartment (cytosol and nucleus). A large subset of these proteins that show dual localization is found both in the nucleus and outside of cells. Proteins destined to be secreted out of the cell or to be expressed at the cell surface usually enter the endomembrane pathway on the basis of a signal sequence that targets them into the endoplasmic reticulum. Proteins destined for import into the nucleus, on the other hand, usually carry a nuclear localization signal. We have organized our catalog in terms of the presence and absence of these trafficking signals: (a) proteins that contain a signal sequence but no nuclear localization signal; (b) proteins that contain both a signal sequence as well as a nuclear localization signal; (c) proteins that contain a nuclear localization signal but lack a signal sequence; and (d) proteins containing neither a signal sequence nor a nuclear localization signal. Novel insights regarding the activities of several classes of proteins exhibiting dual localization can be derived when one targeting signal is experimentally abrogated. For example, the mitogenic activity of both fibroblasts growth factor-1 and schwannoma-derived growth factor clearly requires nuclear localization, independent of the activation of the receptor tyrosine kinase signaling pathway. In addition, there is a growing list of integral membrane receptors that undergo translocation to the nucleus, with bona fide nuclear localization signals and transcription activation activity. The information provided in this descriptive catalog will, hopefully, stimulate investigations into the pathways and mechanisms of transport between these compartments and the physiological significance of dual localization.

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.

Annexin A2 recognises a specific region in the 3'-UTR of its cognate messenger RNA

Annexin A2 is a multifunctional Ca(2+)- and lipid-binding protein. We previously showed that a distinct pool of cellular Annexin A2 associates with mRNP complexes or polysomes associated with the cytoskeleton. Here we report in vitro and in vivo experiments showing that Annexin A2 present in this subset of mRNP complexes interacts with its cognate mRNA and c-myc mRNA, but not with beta(2)-microglobulin mRNA translated on membrane-bound polysomes. The protein recognises sequence elements within the untranslated regions, but not within the coding region, of its cognate mRNA. Alignment of the Annexin A2-binding 3'-untranslated regions of annexin A2 mRNA from several species reveals a five nucleotide consensus sequence 5'-AA(C/G)(A/U)G. The Annexin A2-interacting region of the 3'-untranslated region can be mapped to a sequence of about 100 nucleotides containing two repeats of the consensus sequence. The binding elements appear to involve both single and double stranded regions, indicating that a specific higher order mRNA structure is required for binding to Annexin A2. We suggest that this type of interaction is representative for a group of mRNAs translated on cytoskeleton-bound polysomes.