Annexinopathies

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.

Polimorfismos e necrose avascular em pacientes com doença falciforme – Uma revisão sistemática

Resumo Objetivo: Estabelecer, de modo sistemático, se existe associação entre polimorfismos e a necrose avascular em pacientes com doença falciforme. Fontes de dados: A revisão, conduzida segundo as diretrizes Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) e registrada no International Prospective Register of Systematic Reviews (PROSPERO), foi baseada na busca de estudos nas bases de dados PubMed, Scientific Electronic Library Online (SciELO), Literatura Latino-Americana e do Caribe em Ciências da Saúde (LILACS), Biblioteca Virtual em Saúde (BVS) e na literatura cinza (Google Scholar e Open Gray) até junho de 2020. A análise da qualidade dos artigos foi baseada nos critérios do Strengthening the Reporting of Observational Studies in Epidemiology (STROBE). Síntese dos dados: Dez artigos foram selecionados nas bases de dados e dois incluídos por meio da busca manual, totalizando 12 estudos elencados. As amostras resultaram em 2.362 pacientes incluídos. Com base na iniciativa STROBE, sete estudos atenderam total e/ou parcialmente mais de 70% dos itens essenciais e dois atingiram menos que 60% deles, com variação geral de 86,4–54,5%. Os resultados mostram que os polimorfismos nos genes da proteína morfogenética óssea 6 (BMP6), da Klotho (KL) e da Anexina A2 (ANXA2) podem ter associação com osteonecrose no contexto da doença falciforme. Seis artigos estudaram o polimorfismo no gene da enzima MTHFR, mas apenas um obteve associação positiva. Os polimorfismos associados ao receptor DARC, ao gene ITGA4, ao CD36 e aos genes de proteínas trombofílicas não demonstraram associação em nenhum dos estudos. Conclusões: Os polimorfismos nos genes BMP6, KL e ANXA2 estão possivelmente associados com a necrose avascular em indivíduos com doença falciforme. Entretanto, para a confirmação dessas alterações genéticas como fatores de risco, é necessário que mais estudos com maior poder estatístico e com maior rigor metodológico sejam realizados.

Polymorphisms and avascular necrosis in patients with sickle cell disease – A systematic review

Objective:

To systematically establish whether there is an association between polymorphisms and avascular necrosis in patients with sickle cell disease.

Data source:

The review, conducted according to PRISMA guidelines and registered with PROSPERO, was based on research of studies in PubMed, SciELO, LILACS, BVS databases and in the gray literature (Google Scholar and Open Gray) published until June 2020. The STROBE initiative was used to analyze the articles’ quality.

Data synthesis:

Ten articles were selected from the databases and two were included through manual search, totaling 12 studies. All samples gathered 2,362 patients. According to STROBE, seven studies fully and/or partially covered more than 70% of the essential items and two studies reached less than 60%, with an overall variation of 86.4–54.5%. The results indicate that polymorphisms in the genes of the bone morphogenetic protein 6 (BMP6), Klotho (KL) and Annexin A2 (ANXA2) may be associated with osteonecrosis in the context of sickle cell disease. Six articles addressed the polymorphism in the MTHFR enzyme gene, but only one found a positive association. Polymorphisms associated with the DARC receptor, the ITGA4 gene, CD36 and thrombophilia protein genes were not associated in any of the studies.

Conclusions:

The results indicate that the polymorphisms in BMP6, Klotho and ANXA2 genes may be associated with avascular necrosis in patients with sickle cell disease. However, in order to confirm these genetic changes as risk factors, further studies with greater statistical power and methodological rigor are needed.

Annexin Animal Models-From Fundamental Principles to Translational Research

Routine manipulation of the mouse genome has become a landmark in biomedical research. Traits that are only associated with advanced developmental stages can now be investigated within a living organism, and the in vivo analysis of corresponding phenotypes and functions advances the translation into the clinical setting. The annexins, a family of closely related calcium (Ca²⁺)- and lipid-binding proteins, are found at various intra- and extracellular locations, and interact with a broad range of membrane lipids and proteins. Their impacts on cellular functions has been extensively assessed in vitro, yet annexin-deficient mouse models generally develop normally and do not display obvious phenotypes. Only in recent years, studies examining genetically modified annexin mouse models which were exposed to stress conditions mimicking human disease often revealed striking phenotypes. This review is the first comprehensive overview of annexin-related research using animal models and their exciting future use for relevant issues in biology and experimental medicine.

Zooming into the Dark Side of Human Annexin-S100 Complexes: Dynamic Alliance of Flexible Partners

Annexins and S100 proteins form two large families of Ca²⁺-binding proteins. They are quite different both structurally and functionally, with S100 proteins being small (10–12 kDa) acidic regulatory proteins from the EF-hand superfamily of Ca²⁺-binding proteins, and with annexins being at least three-fold larger (329 ± 12 versus 98 ± 7 residues) and using non-EF-hand-based mechanism for calcium binding. Members of both families have multiple biological roles, being able to bind to a large cohort of partners and possessing a multitude of functions. Furthermore, annexins and S100 proteins can interact with each other in either a Ca²⁺-dependent or Ca²⁺-independent manner, forming functional annexin-S100 complexes. Such functional polymorphism and binding indiscrimination are rather unexpected, since structural information is available for many annexins and S100 proteins, which therefore are considered as ordered proteins that should follow the classical “one protein–one structure–one function” model. On the other hand, the ability to be engaged in a wide range of interactions with multiple, often unrelated, binding partners and possess multiple functions represent characteristic features of intrinsically disordered proteins (IDPs) and intrinsically disordered protein regions (IDPRs); i.e., functional proteins or protein regions lacking unique tertiary structures. The aim of this paper is to provide an overview of the functional roles of human annexins and S100 proteins, and to use the protein intrinsic disorder perspective to explain their exceptional multifunctionality and binding promiscuity.

Frequent Alteration of Annexin A9 and A10 in HPV-Negative Head and Neck Squamous Cell Carcinomas: Correlation with the Histopathological Differentiation Grade

The annexin protein superfamily has been implicated in multiple physiological and pathological processes, including carcinogenesis. Altered expression of various annexins has frequently been observed and linked to the development and progression of various human malignancies. However, information is lacking on the expression and clinical significance of annexin A9 (ANXA9) and A10 (ANXA10) in head and neck squamous cell carcinomas (HNSCC). ANXA9 and ANXA10 expression was evaluated in a large cohort of 372 surgically treated HPV-negative HNSCC patients and correlated with the clinicopathologic parameters and disease outcomes. Down-regulation of ANXA9 expression was found in 42% of HNSCC tissue samples, compared to normal epithelia. ANXA9 expression in tumors was significantly associated with oropharyngeal location and histological differentiation grade (P < 0.001). In marked contrast, ANXA10 expression was absent in normal epithelium, but variably detected in the cytoplasm of cancer cells. Positive ANXA10 expression was found in 64% of tumors, and was significantly associated with differentiation grade (P < 0.001), being also more frequent in oropharyngeal tumors (P = 0.019). These results reveal that the expression of both ANXA9 and ANXA10 is frequently altered in HNSCC and associated to the tumor differentiation grade, suggesting that they could be implicated in the pathogenesis of these cancers.

Annexin A6 regulates catabolic events in articular chondrocytes via the modulation of NF-κB and Wnt/ß-catenin signaling

Annexin A6 (AnxA6) is expressed in articular chondrocytes at levels higher than in other mesenchymal cell types. However, the role of AnxA6 in articular chondrocytes is not known. Here we show that complete lack of AnxA6 functions resulted in increased ß-catenin activation in Wnt3a-treated murine articular chondrocytes, whereas AnxA6 expressing articular chondrocytes showed decreased ß-catenin activation. High expression of AnxA6 in human articular chondrocytes showed the highest inhibition of Wnt/ß-catenin signaling. Inhibition of Wnt/ß-catenin signaling activity by AnxA6 together with cytosolic Ca2+ was achieved by interfering with the plasma membrane association of the Wnt signaling complex. AnxA6 also affected the cross-talk between Wnt/ß-catenin signaling and NF-κB signaling by decreasing ß-catenin activity and increasing NF-κB activity in Wnt3a-, interleukin-1beta (IL-1ß)-, and combined Wnt3a/IL-1ß-treated cells. Wnt3a treatment increased the mRNA levels of catabolic markers (cyclooxygenase-2, interleukin-6, inducible nitric oxide synthase) to a much lesser degree than IL-1ß treatment in human articular chondrocytes, and decreased the mRNA levels of matrix metalloproteinase-13 (MMP-13) and articular cartilage markers (aggrecan, type II collagen). Furthermore, Wnt3a decreased the mRNA levels of catabolic markers and MMP-13 in IL-1ß-treated human articular chondrocytes. High expression of AnxA6 resulted in decreased mRNA levels of catabolic markers, and increased MMP-13 and articular cartilage marker mRNA levels in Wnt3a-treated human articular chondrocytes, whereas leading to increased mRNA levels of catabolic markers and MMP-13 in human articular chondrocytes treated with IL-1ß, or combined Wnt3a and IL-1ß. Our findings define a novel role for AnxA6 in articular chondrocytes via its modulation of Wnt/ß-catenin and NF-κB signaling activities and the cross-talk between these two signaling pathways.

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.

A new cis-acting motif is required for the axonal SMN-dependent Anxa2 mRNA localization

Spinal muscular atrophy (SMA) is caused by mutations and/or deletions of the survival motor neuron gene (SMN1). Besides its function in the biogenesis of spliceosomal snRNPs, SMN might possess a motor neuron specific role and could function in the transport of axonal mRNAs and in the modulation of local protein translation. Accordingly, SMN colocalizes with axonal mRNAs of differentiated NSC-34 motor neuron-like cells. We recently showed that SMN depletion gives rise to a decrease in the axonal transport of the mRNAs encoding Annexin A2 (Anxa2). In this work, we have characterized the structural features of the Anxa2 mRNA required for its axonal targeting by SMN. We found that a G-rich motif located near the 3'UTR is essential for axonal localization of the Anxa2 transcript. We also show that mutations in the motif sequence abolish targeting of Anxa2 reporter mRNAs in axon-like structures of differentiated NSC-34 cells. Finally, localization of both wild-type and mutated Anxa2 reporters is restricted to the cell body in SMN-depleted cells. Altogether, our studies show that this G-motif represents a novel and essential determinant for axonal localization of the Anxa2 mRNA mediated by the SMN complex.

Unconventional Transport Routes of Soluble and Membrane Proteins and Their Role in Developmental Biology

Many proteins and cargoes in eukaryotic cells are secreted through the conventional secretory pathway that brings proteins and membranes from the endoplasmic reticulum to the plasma membrane, passing through various cell compartments, and then the extracellular space. The recent identification of an increasing number of leaderless secreted proteins bypassing the Golgi apparatus unveiled the existence of alternative protein secretion pathways. Moreover, other unconventional routes for secretion of soluble or transmembrane proteins with initial endoplasmic reticulum localization were identified. Furthermore, other proteins normally functioning in conventional membrane traffic or in the biogenesis of unique plant/fungi organelles or in plasmodesmata transport seem to be involved in unconventional secretory pathways. These alternative pathways are functionally related to biotic stress and development, and are becoming more and more important in cell biology studies in yeast, mammalian cells and in plants. The city of Lecce hosted specialists working on mammals, plants and microorganisms for the inaugural meeting on “Unconventional Protein and Membrane Traffic” (UPMT) during 4–7 October 2016. The main aim of the meeting was to include the highest number of topics, summarized in this report, related to the unconventional transport routes of protein and membranes.

TNF-alpha and annexin A2: inflammation in thrombotic primary antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by thromboses and/or pregnancy losses. Laboratory criterion for the diagnosis of APS is the presence of antiphospholipid antibodies (anticardiolipin, anti-beta2-glycoprotein I (aβ2gpI) and lupus anticoagulant). On the one hand, the latest classification criteria for the diagnosis of APS emphasized that thrombotic manifestations of the syndrome should be without any signs of an inflammatory process, while on the other hand, some recent reports have suggested that APS is a "pro-inflammatory state." This article is focused on the importance of TNF-alpha and annexin A2 (anxA2) for patients with vascular (thrombotic) manifestations of the primary APS. The classic antithrombotic and antiplatelet therapy does not protect APS patients from the development of recurrent thrombosis. Therefore, an urgent need for the introduction of new therapeutic approaches in the treatment of APS patients is obvious. This review provides a rationale for the necessity for the use of immunomodulatory medications that could interfere with β2gpI binding to its receptor(s), such as anxA2, and/or inhibit TNF-alpha activity.

Why Calcium? How Calcium Became the Best Communicator

Calcium carries messages to virtually all important functions of cells. Although it was already active in unicellular organisms, its role became universally important after the transition to multicellular life. In this Minireview, we explore how calcium ended up in this privileged position. Most likely its unique coordination chemistry was a decisive factor as it makes its binding by complex molecules particularly easy even in the presence of large excesses of other cations, e.g. magnesium. Its free concentration within cells can thus be maintained at the very low levels demanded by the signaling function. A large cadre of proteins has evolved to bind or transport calcium. They all contribute to buffer it within cells, but a number of them also decode its message for the benefit of the target. The most important of these "calcium sensors" are the EF-hand proteins. Calcium is an ambivalent messenger. Although essential to the correct functioning of cell processes, if not carefully controlled spatially and temporally within cells, it generates variously severe cell dysfunctions, and even cell death.

Atorvastatin protects endothelial colony‑forming cells against H2O2‑induced oxidative damage by regulating the expression of annexin A2

Endothelial dysfunction and injury are central events in the pathogenesis of ischemic vascular disorders. Endothelial progenitor cells (EPCs) are mobilized from the bone marrow into the peripheral circulation, where they locate to sites of injured endothelium and are involved in endothelial repair and vascular regeneration. During these processes, EPCs are exposed to oxidative stress, a crucial pathological condition, which occurs during vascular injury and limits the efficacy of EPCs in the repair of injured endothelium. Statins are effective inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase, and are commonly used to manage and prevent ischemic vascular disease by reducing plasma cholesterol levels. In addition to lowering cholesterol, statins have also been reported to exert pleiotropic actions, including anti-inflammatory and anti-oxidative activities. The present study aimed to investigate the ability of atorvastatin to protect endothelial colony-forming cells (ECFCs), a homogeneous subtype of EPCs, from hydrogen peroxide (H₂O₂)-induced oxidative damage, and to determine the mechanism underlying this protective action. MTT assay, acridine orange/ethidium bromide staining, reactive oxygen species assay, western blot analysis and tube formation assay were employed. The results demonstrated that H₂O₂ induced cell death and decreased the tube-forming ability of the ECFCs, in a concentration-dependent manner; however, these effects were partially attenuated following administration of atorvastatin. The reversion of the quantitative and qualitative impairment of the H₂O₂-treated ECFCs appeared to be mediated by the regulation of annexin A2, as the expression levels of annexin A2 were decreased following treatment with H₂O₂ and increased following treatment with atorvastatin. These results indicated that annexin A2 may be involved in the H₂O₂-induced damage of ECFCs, and in the protective activities of atorvastatin in response to oxidative stress.

Annexin A2 is SUMOylated on its N-terminal domain: regulation by insulin

Insulin receptor (IR) endocytosis requires a remodelling of the actin cytoskeleton. We show here that ANXA2 is SUMOylated at the K10 located in a non-consensus SUMOylation motif in the N-terminal domain. The Y24F mutation decreased the SUMOylation signal, whereas insulin stimulation increased ANXA2 SUMOylation. A survey of protein SUMOylation in hepatic Golgi/endosome (G/E) fractions after insulin injections revealed the presence of a SUMOylation pattern and confirmed the SUMOylation of ANXA2. The construction of an IR/ANXA2/SUMO network (IRASGEN) in the G/E context reveals the presence of interacting nodes whereby SUMO1 connects ANXA2 to actin and microtubule-mediated changes in membrane topology. Heritable variants associated with type 2 diabetes represent 41% of the IRASGEN thus pointing out the physio-pathological importance of this subnetwork.

The discoidin domain receptor 2/annexin A2/matrix metalloproteinase 13 loop promotes joint destruction in arthritis through promoting migration and invasion of fibroblast-like synoviocytes

OBJECTIVE

Discoidin domain receptor 2 (DDR-2)/matrix metalloproteinase (MMP) signaling is an important pathway involved in cartilage destruction in rheumatoid arthritis (RA). However, the molecular mechanisms of this pathway have not been clearly identified. This study was undertaken to screen key molecules involved in this pathway and evaluate their biologic functions in synovium invasion of RA.

METHODS

DDR-2-interacting proteins were examined in vitro by immunoprecipitation and mass spectrometry, and annexin A2 was acquired. The effects of annexin A2 on fibroblast-like synoviocyte (FLS) migration were evaluated using a Transwell invasion assay and an Erasion trace test. In Ddr2(-/-) mice with collagen-induced arthritis (CIA), hematoxylin and eosin (H&E) staining, immunohistochemical analysis, and Western blot analysis were used to assess expression of DDR-2, annexin A2, and MMP-13, as well as synovial hyperplasia. Rats with CIA were treated with lentivirus annexin A2 small interfering RNA (siRNA), and annexin A2 siRNA effects on joint damage were analyzed based upon arthritis index scores and results of micro-computed tomography and H&E staining. The differences between annexin A2 expression in clinical samples from RA and osteoarthritis patients were compared using Western blotting.

RESULTS

Annexin 2 was identified for the first time as a DDR-2 binding protein. It may be phosphorylated by phospho-DDR-2, leading to MMP-13 secretion. The annexin A2 phosphorylation level and MMP-13 expression level were decreased and collagen-induced joint damage greatly reduced in Ddr2(-/-) mice. Joint damage in rats with CIA was significantly ameliorated when annexin A2 was down-regulated. Annexin A2 expression and phosphorylation were elevated in human RA synovial tissue.

CONCLUSION

Annexin A2 is a key molecule in the DDR-2/annexin A2/MMP-13 loop, the activation of which contributes to joint destruction in RA, mainly through promoting invasion of FLS. Annexin A2 might therefore become a novel clinical target for RA treatment.

Fhit delocalizes annexin a4 from plasma membrane to cytosol and sensitizes lung cancer cells to paclitaxel

Fhit protein is lost or reduced in a large fraction of human tumors, and its restoration triggers apoptosis and suppresses tumor formation or progression in preclinical models. Here, we describe the identification of candidate Fhit-interacting proteins with cytosolic and plasma membrane localization. Among these, Annexin 4 (ANXA4) was validated by co-immunoprecipitation and confocal microscopy as a partner of this novel Fhit protein complex. Here we report that overexpression of Fhit prevents Annexin A4 translocation from cytosol to plasma membrane in A549 lung cancer cells treated with paclitaxel. Moreover, paclitaxel administration in combination with AdFHIT acts synergistically to increase the apoptotic rate of tumor cells both in vitro and in vivo experiments.

Inhibition of Annexin A2 gene transcription is a promising molecular target for hepatoma cell proliferation and metastasis

Hepatocyte Annexin A2 (ANXA2) expression is associated with the progression and metastasis of hepatocellular carcinoma (HCC). Circulating ANXA2 levels in HCC patients are significantly higher compared with that of patients with benign liver disease. ANXA2 levels have been found to correlate with hepatitis B virus infection, extrahepatic metastasis and portal vein thrombus. By contrast, ANXA2 levels do not correlate with tumour size and AFP levels. However, the underlying mechanisms of ANXA2 remain obscure. The results of the current study identified that abnormalities in hepatic ANXA2 expression were localised to the cell membrane and cytoplasm of HCC tissues and mainly in the cytoplasm of para-cancerous tissues. ANXA2 was overexpressed in MHCC97-H cells which have high metastatic potential. Following specific ANXA2-small hairpin RNA (shRNA) transfection in vitro, ANXA-2 was effectively inhibited and the S phase ratio of cells was 27.76%, compared with 36.14% in mock-treated cells. In addition, the invading cell ratio was reduced in the shRNA-treated group (52.16%) compared with the mock-treated group (86.14%). The growth and volume of xenograft tumours in vivo was significantly suppressed (P<0.05) in the shRNA group compared with that of the mock group, indicating that ANXA2 may be a novel and useful target for elucidating molecular mechanisms involving the proliferation and metastasis of HCC.

Pilot study identifying myosin heavy chain 7, desmin, insulin-like growth factor 7, and annexin A2 as circulating biomarkers of human heart failure

In-depth proteomic analyses offer a systematic way to investigate protein alterations in disease and, as such, can be a powerful tool for the identification of novel biomarkers. Here, we analyzed proteomic data from a transgenic mouse model with cardiac-specific overexpression of activated calcineurin (CnA), which results in severe cardiac hypertrophy. We applied statistically filtering and false discovery rate correction methods to identify 52 proteins that were significantly different in the CnA hearts compared to controls. Subsequent informatic analysis consisted of comparison of these 52 CnA proteins to another proteomic dataset of heart failure, three available independent microarray datasets, and correlation of their expression with the human plasma and urine proteome. Following this filtering strategy, four proteins passed these selection criteria, including myosin heavy chain 7, insulin-like growth factor-binding protein 7, annexin A2, and desmin. We assessed expression levels of these proteins in mouse plasma by immunoblotting, and observed significantly different levels of expression between healthy and failing mice for all four proteins. We verified antibody cross-reactivity by examining human cardiac explant tissue by immunoblotting. Finally, we assessed protein levels in plasma samples obtained from four unaffected and four heart failure patients and demonstrated that all four proteins increased between twofold and 150-fold in heart failure. We conclude that MYH7, IGFBP7, ANXA2, and DESM are all excellent candidate plasma biomarkers of heart failure in mouse and human.

Annexin A2 system in human biology: cell surface and beyond

Annexin A2 (A2) is a multicompartmental, multifunctional protein that orchestrates a growing spectrum of biologic processes. At the endothelial cell surface, A2 and S100A10 (p11) form a heterotetramer, which accelerates tissue plasminogen activator-dependent activation of the fibrinolytic protease, plasmin. In antiphospholipid syndrome, anti-A2 antibodies are associated with clinical thrombosis, whereas overexpression of A2 in acute promyelocytic leukemia promotes hyperfibrinolytic bleeding. A2 is upregulated in hypoxia, and mice deficient in A2 are resistant to oxygen-induced retinal neovascularization, suggesting a role for A2 in human retinal vascular proliferation. In solid malignancies, the (A2•p11)(2) tetramer may promote cancer cell invasion, whereas in multiple myeloma A2 enables malignant plasmacyte growth and predicts prognosis. In the central nervous system, the p11 enables membrane insertion of serotonin receptors that govern mood. In the peripheral nervous system, p11 directs sodium channels to the plasma membrane, enabling pain perception. In cerebral cortex neurons, A2 stabilizes the microtubule-associated tau protein, which, when mutated, is associated with frontotemporal dementia. In inflammatory dendritic cells, A2 maintains late endosomal/lysosomal membrane integrity, thus modulating inflammasome activation and cytokine secretion in a model of aseptic arthritis. Together, these findings suggest an emerging, multifaceted role for A2 in human health and disease.

Loss of maternal annexin A5 increases the likelihood of placental platelet thrombosis and foetal loss

Antiphospholipid syndrome is associated with an increased risk of thrombosis and pregnancy loss. Annexin A5 (Anxa5) is a candidate autoantigen. It is not known, however, whether endogenous Anxa5 prevents foetal loss during normal pregnancy. We found significant reductions in litter size and foetal weight in Anxa5-null mice (Anxa5-KO). These changes occurred even when only the mother was Anxa5-KO. A small amount of placental fibrin deposition was observed in the decidual tissues, but did not noticeably differ between wild-type and Anxa5-KO mice. However, immunoreactivity for integrin beta 3/CD61, a platelet marker, was demonstrated within thrombi in the arterial canals only in Anxa5-KO mothers. Subcutaneous administration of the anticoagulant heparin to pregnant Anxa5-KO mice significantly reduced pregnancy loss, suggesting that maternal Anxa5 is crucial for maintaining intact placental circulation. Hence, the presence of maternal Anxa5 minimises the risk of thrombosis in the placental circulation and reduces the risk of foetal loss.

The clinical and immunologic features of pulmonary fibrosis in sarcoidosis

Sarcoidosis is a multisystem, granulomatous disease that most often affects the lungs. The clinical course is highly variable; many patients undergo spontaneous remission, but up to a third of patients progresses to a chronic disease course. The development of pulmonary fibrosis (PF) in a subset of patients with chronic disease has a negative impact on morbidity and mortality. While sarcoidosis-associated PF can be progressive, it is often referred to as "burnt out" disease, a designation reflecting inactive granulomatous inflammation. The immune mechanisms of sarcoidosis-associated PF are not well understood. It is not clear if fibrotic processes are active from the onset of sarcoidosis in predisposed individuals, or whether a profibrotic state develops as a response to ongoing inflammation. Transforming growth factor β (TGF-β) is an important profibrotic cytokine, and in sarcoidosis, distinct genotypes of TGF-β have been identified in those with PF. The overall cytokine profile in sarcoidosis-associated PF has not been well characterized, although a transition from a T helper 1 to a T helper 2 signature has been proposed. Macrophages have important regulatory interactions with fibroblasts, and the role of alveolar macrophages in sarcoidosis-associated PF is a compelling target for further study. Elucidating the natural history of sarcoidosis-associated PF will inform our understanding of the fundamental derangements, and will enhance prognostication and the development of therapeutic strategies.

Proteomics-based analysis of invasion-related proteins in malignant gliomas

One of the insidious biological features of gliomas is their potential to extensively invade normal brain tissue, yet molecular mechanisms that dictate this locally invasive behavior remain poorly understood. To investigate the molecular basis of invasion by malignant gliomas, proteomic analysis was performed using a pair of canine glioma subclones - J3T-1 and J3T-2 - that show different invasion phenotypes in rat brains but have similar genetic backgrounds. Two-dimensional protein electrophoresis of whole-cell lysates of J3T-1 (angiogenesis-dependent invasion phenotype) and J3T-2 (angiogenesis-independent invasion phenotype) was performed. Twenty-two distinct spots were recognized when significant alteration was defined as more than 1.5-fold change in spot intensity between J3T-1 and J3T-2. Four proteins that demonstrated increased expression in J3T-1, and 14 proteins that demonstrated increased expression in J3T-2 were identified using liquid chromatography-mass spectrometry analysis. One of the proteins identified was annexin A2, which was expressed at higher levels in J3T-1 than in J3T-2. The higher expression of annexin A2 in J3T-1 was corroborated by quantitative RT-PCR of the cultured cells and immunohistochemical staining of the rat brain tumors. Moreover, immunohistochemical analysis of human glioblastoma specimens showed that annexin A2 was expressed at high levels in the tumor cells that formed clusters around dilated vessels. These results reveal differences in the proteomic profiles between these two cell lines that might correlate with their different invasion profiles. Thus, annexin A2 may be related to angiogenesis-dependent invasion.

The annexin A2/S100A10 system in health and disease: emerging paradigms

Since its discovery as a src kinase substrate more than three decades ago, appreciation for the physiologic functions of annexin A2 and its associated proteins has increased dramatically. With its binding partner S100A10 (p11), A2 forms a cell surface complex that regulates generation of the primary fibrinolytic protease, plasmin, and is dynamically regulated in settings of hemostasis and thrombosis. In addition, the complex is transcriptionally upregulated in hypoxia and promotes pathologic neoangiogenesis in the tissues such as the retina. Dysregulation of both A2 and p11 has been reported in examples of rodent and human cancer. Intracellularly, A2 plays a critical role in endosomal repair in postarthroplastic osteolysis, and intracellular p11 regulates serotonin receptor activity in psychiatric mood disorders. In human studies, the A2 system contributes to the coagulopathy of acute promyelocytic leukemia, and is a target of high-titer autoantibodies in patients with antiphospholipid syndrome, cerebral thrombosis, and possibly preeclampsia. Polymorphisms in the human ANXA2 gene have been associated with stroke and avascular osteonecrosis of bone, two severe complications of sickle cell disease. Together, these new findings suggest that manipulation of the annexin A2/S100A10 system may offer promising new avenues for treatment of a spectrum of human disorders.

Fine-mapping in African-American women confirms the importance of the 10p12 locus to sarcoidosis

Sarcoidosis is a chronic granulomatous disease with a wide spectrum of symptoms. Genome-wide association studies in European populations have reported significant associations between sarcoidosis and single nucleotide polymorphisms (SNPs) located in the inter-genic region between the C10ORF67 and OTUD1 genes on chromosome 10p12, and the ANXA11 gene (chromosome 10q22). We carried out fine-mapping at 10p12 and 10q22 to assess associations of genetic variants in those regions with sarcoidosis risk in African American women, based on 486 sarcoidosis cases and 943 age- and geography-matched controls in a nested case-control study within the Black Women’s Health Study. There were no significant associations with variants of the ANXA11 gene (P=0.17). Haplotypic analyses of the C10ORF67-OTUD1 inter-genic region revealed a strong inverse association of the variants rs1398024 and rs11013452 with sarcoidosis (OR=0.52; P=0.01). Both SNPs are located inside a ~300 kb low recombination region of chromosome 10p12, suggesting that both SNPs are tagging the same causal variant. Our top SNP (rs11013452) is located inside a smaller LD block in HapMap YRI, further narrowing the position of the causal SNP to a region of ~ 8kb on chromosome 10p12. The present findings confirm the potential importance of the 10p12 locus in the etiology of sarcoidosis.

Do annexins participate in lipid messenger mediated intracellular signaling? A question revisited

Annexins are physiologically important proteins that play a role in calcium buffering but also influence membrane structure, participate in Ca²⁺-dependent membrane repair events and in remodelling of the cytoskeleton. Thirty years ago several peptides isolated from lung perfusates, peritoneal leukocytes, neutrophiles and renal cells were proven inhibitory to the activity of phospholipase A₂. Those peptides were found to derive from structurally related proteins: annexins AnxA1 and AnxA2. These findings raised the question whether annexins may participate in regulation of the production of lipid second messengers and, therefore, modulate numerous lipid mediated signaling pathways in the cell. Recent advances in the field of annexins made also with the use of knock-out animal models revealed that these proteins are indeed important constituents of specific signaling pathways. In this review we provide evidence supporting the hypothesis that annexins, as membrane-binding proteins and organizers of the membrane lateral heterogeneity, may participate in lipid mediated signaling pathways by affecting the distribution and activity of lipid metabolizing enzymes (most of the reports point to phospholipase A₂) and of protein kinases regulating activity of these enzymes. Moreover, some experimental data suggest that annexins may directly interact with lipid metabolizing enzymes and, in a calcium-dependent or independent manner, with some of their substrates and products. On the basis of these observations, many investigators suggest that annexins are capable of linking Ca²⁺, redox and lipid signaling to coordinate vital cellular responses to the environmental stimuli.

Annexins as organizers of cholesterol- and sphingomyelin-enriched membrane microdomains in Niemann-Pick type C disease

Growing evidence suggests that membrane microdomains enriched in cholesterol and sphingomyelin are sites for numerous cellular processes, including signaling, vesicular transport, interaction with pathogens, and viral infection, etc. Recently some members of the annexin family of conserved calcium and membrane-binding proteins have been recognized as cholesterol-interacting molecules and suggested to play a role in the formation, stabilization, and dynamics of membrane microdomains to affect membrane lateral organization and to attract other proteins and signaling molecules onto their territory. Furthermore, annexins were implicated in the interactions between cytosolic and membrane molecules, in the turnover and storage of cholesterol and in various signaling pathways. In this review, we focus on the mechanisms of interaction of annexins with lipid microdomains and the role of annexins in membrane microdomains dynamics including possible participation of the domain-associated forms of annexins in the etiology of human lysosomal storage disease called Niemann-Pick type C disease, related to the abnormal storage of cholesterol in the lysosome-like intracellular compartment. The involvement of annexins and cholesterol/sphingomyelin-enriched membrane microdomains in other pathologies including cardiac dysfunctions, neurodegenerative diseases, obesity, diabetes mellitus, and cancer is likely, but is not supported by substantial experimental observations, and therefore awaits further clarification.

Proteomics analysis of differentially expressed proteins in chicken trachea and kidney after infection with the highly virulent and attenuated coronavirus infectious bronchitis virus in vivo

BACKGROUND

Infectious bronchitis virus (IBV) is first to be discovered coronavirus which is probably endemic in all regions with intensive impact on poultry production. In this study, we used two-dimensional gel electrophoresis (2-DE) and two-dimensional fluorescence difference gel electrophoresis (2-DIGE), coupled with matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF/TOF-MS), to explore the global proteome profiles of trachea and kidney tissues from chicken at different stages infected in vivo with the highly virulent ck/CH/LDL/97I P5 strain of infectious bronchitis virus (IBV) and the embryo-passaged, attenuated ck/CH/LDL/97I P115 strain.

RESULTS

Fifty-eight differentially expressed proteins were identified. Results demonstrated that some proteins which had functions in cytoskeleton organization, anti-oxidative stress, and stress response, showed different change patterns in abundance from chicken infected with the highly virulent ck/CH/LDL/97I P5 strain and those given the embryo-passaged, attenuated P115 stain. In addition, the dynamic transcriptional alterations of 12 selected proteins were analyzed by the real-time RT-PCR, and western blot analysis confirmed the change in abundance of heat shock proteins (HSP) beta-1, annexin A2, and annexin A5.

CONCLUSIONS

The proteomic alterations described here may suggest that these changes to protein expression correlate with IBV virus' virulence in chicken, hence provides valuable insights into the interactions of IBV with its host and may also assist with investigations of the pathogenesis of IBV and other coronavirus infections.

Annexin A2 at the interface of actin and membrane dynamics: a focus on its roles in endocytosis and cell polarization

Annexins are a family of calcium- and phospholipid-binding proteins found in nearly all eukaryotes. They are structurally highly conserved and have been implicated in a wide range of cellular activities. In this paper, we focus on Annexin A2 (AnxA2). Altered expression of this protein has been identified in a wide variety of cancers, has also been found on the HIV particle, and has been implicated in the maturation of the virus. Recently, it has also been shown to have an important role in the establishment of normal apical polarity in epithelial cells. We synthesize here the known biochemical properties of this protein and the extensive literature concerning its involvement in the endocytic pathway. We stress the importance of AnxA2 as a platform for actin remodeling in the vicinity of dynamic cellular membranes, in the hope that this may shed light on the normal functions of the protein and its contribution to disease.

Low ANXA10 expression is associated with disease aggressiveness in bladder cancer

Background:

Markers for outcome prediction in bladder cancer are urgently needed. We have previously identified a molecular signature for predicting progression in non-muscle-invasive bladder cancer. ANXA10 was one of the markers included in the signature and we now validated the prognostic relevance of ANXA10 at the protein level.

Methods:

We investigated ANXA10 expression by immunohistochemistry using a tissue microarray with 249 Ta and T1 urothelial carcinomas. The expression of ANXA10 was also investigated in an additional set of 97 more advanced tumours. The functional role of ANXA10 in cell lines was investigated by siRNA-mediated ANXA10 knockdown using wound-healing assays, proliferation assays, and ingenuity pathway analysis.

Results:

Low expression of ANXA10 correlated with shorter progression-free survival in patients with stage Ta and T1 tumours (P<0.00001). Furthermore, patients with more advanced tumours and low ANXA10 expression had an unfavourable prognosis (P<0.00001). We found that ANXA10 siRNA transfected cells grew significantly faster compared with control siRNA transfected cells. Furthermore, a wound-healing assay showed that ANXA10 siRNA transfected cells spread along wound edges faster than control transfected cells.

Conclusion:

We conclude that ANXA10 may be a clinical relevant marker for predicting outcome in both early and advanced stages of bladder cancer.

The influence of PCSK9 polymorphisms on serum low-density lipoprotein cholesterol and risk of atherosclerosis

Pro-protein-convertase-subtilisin-kexin-9 (PCSK9) enhances the degradation of the low-density lipoprotein receptor (LDLR) that plays a major role in cholesterol homeostasis. Recent advances have revealed a large number of genetic variants of PCSK9 that may modulate plasma cholesterol levels either positively or negatively, therefore influencing the risk of atherosclerosis. Recognition of these mutants may have clinical implication in assessing severity of disease, prognosis, or response to drug therapy. PCSK9's expression, secretion, and plasma levels maybe modulated by the proprotein convertase furin, by natural inhibitors (annexin-A2), or influenced by lipid-altering agents such as statins, fibrates, ezetimibe, and berberine. It is now a prime target for therapy, prompting the development of various approaches to reduce its LDLR degrading activity, including antibody neutralization, anti-sense oligonucleotides such as phosphorothioates, locked nucleic acids, and RNA interference, and eventually small molecule inhibitors. Which one will be clinically applicable will depend on long-term effects, cost, and ease of administration.

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

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

Role of annexin A2 in cellular entry of rabbit vesivirus

The mechanisms of calicivirus attachment and internalization are not well understood, mainly due to the lack of a reliable cell-culture system for most of its members. In this study, rabbit vesivirus (RaV) virions were shown to bind annexin A2 (ANXA2) in a membrane protein fraction from HEK293T cells, using a virus overlay protein-binding assay and matrix-assisted laser desorption/ionization time-of-flight analysis. A monoclonal anti-ANXA2 antibody and small interfering RNA-mediated knockdown of ANXA2 expression in HEK293T cells reduced virus infection significantly, further supporting the role of ANXA2 in RaV attachment and/or internalization.

Annexin A2 regulates phagocytosis of photoreceptor outer segments in the mouse retina

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

The role of annexins in tumour development and progression

The annexins are a super-family of closely related calcium and membrane-binding proteins. They have a diverse range of cellular functions that include vesicle trafficking, cell division, apoptosis, calcium signalling and growth regulation. Many studies have shown the annexins to be among the genes whose expression are consistently differentially altered in neoplasia. Some annexins show increased expression in specific types of tumours, while others show loss of expression. Mechanistic studies relating the changes in annexin expression to tumour cell function, particularly tumour invasion and metastasis, angiogenesis and drug resistance, are now also emerging. Changes in the expression of individual annexins are associated with particular types of tumour and hence the annexins may also be useful biomarkers in the clinic.