Interferon-γ stimulates p11-dependent surface expression of annexin A2 in lung epithelial cells to enhance phagocytosis

Annexin A2 Contributes to Release of Extracellular Vimentin in Response to Inflammation

Vimentin, an abundant intracellular cytoskeletal protein, is secreted into the extracellular space, where it can amplify tissue destruction in inflammatory diseases. The mechanisms by which inflammation promotes the release of extracellular vimentin (ECV) are not defined. In human subjects, we found > twofold higher levels of ECV in gingival crevicular fluid from periodontitis sites with inflammation compared with healthy sites. In cultures of human gingival fibroblasts (hGFs) treated with 1% serum or IL-1β (10 ng/mL) to model tissue injury or inflammation, respectively, we found that 1% serum increased ECV release > 11-fold while IL-1β further enhanced release 17-fold. Mass spectrometry of vimentin immunoprecipitates identified Annexin A2 (AnxA2), a Ca2+-dependent phospholipid-binding protein, as a potential binding protein of ECV, which was confirmed by immunoprecipitation of cultured hGFs and immunostaining of inflamed human gingiva. IL-1β treatment enhanced the abundance of AnxA2 and vimentin in membrane fractions prepared by sucrose gradients of hGF lysates. IL-1β increased colocalization of ECV and AnxA2 at the outer aspect of the plasma membrane of intact hGFs. Knockdown of AnxA2 with siRNA or inhibition of the unconventional secretory pathway reduced ECV release from hGFs. These findings indicate that the production of ECV by hGFs in response to inflammation is mediated by an AnxA2-dependent, unconventional secretory pathway that may play a role in amplification of the inflammatory response.

Fabry disease Schwann cells release p11 to induce sensory neuron hyperactivity

Patients with Fabry disease suffer from chronic debilitating pain and peripheral sensory neuropathy with minimal treatment options, but the cellular drivers of this pain are unknown. Here, we propose a mechanism we believe to be novel in which altered signaling between Schwann cells and sensory neurons underlies the peripheral sensory nerve dysfunction we observed in a genetic rat model of Fabry disease. Using in vivo and in vitro electrophysiological recordings, we demonstrated that Fabry rat sensory neurons exhibited pronounced hyperexcitability. Schwann cells probably contributed to this finding because application of mediators released from cultured Fabry Schwann cells induced spontaneous activity and hyperexcitability in naive sensory neurons. We examined putative algogenic mediators using proteomic analysis and found that Fabry Schwann cells released elevated levels of the protein p11 (S100A10), which induced sensory neuron hyperexcitability. Removal of p11 from Fabry Schwann cell media caused hyperpolarization of neuronal resting membrane potentials, indicating that p11 may contribute to the excessive neuronal excitability caused by Fabry Schwann cells. These findings demonstrate that sensory neurons from rats with Fabry disease exhibit hyperactivity caused in part by Schwann cell release of the protein p11.

Extracellular vesicles released by glioma cells are decorated by Annexin A2 allowing for cellular uptake via heparan sulfate

Extracellular vesicles (EVs) play a crucial role in regulating cell behavior by delivering their cargo to target cells. However, the mechanisms underlying EV-cell interactions are not well understood. Previous studies have shown that heparan sulfate (HS) on target cell surfaces can act as receptors for exosomes uptake, but the ligand for HS on EVs has not been identified. In this study, we isolated EVs from glioma cell lines and glioma patients and identified Annexin A2 (AnxA2) on EVs as a key HS-binding ligand and mediator of EV-cell interactions. Our findings suggest that HS plays a dual role in EV-cell interactions, where HS on EVs captures AnxA2, and on target cells, it acts as a receptor for AnxA2. Removal of HS from the EV surface inhibits EV-target cell interaction by releasing AnxA2. Furthermore, we found that AnxA2-mediated binding of EVs to vascular endothelial cells promotes angiogenesis, and that antibody against AnxA2 inhibited the ability of glioma-derived EVs to stimulate angiogenesis by reducing the uptake of EVs. Our study also suggests that the AnxA2-HS interaction may accelerate the glioma-derived EVs-mediated angiogenesis and that combining AnxA2 on glioma cells with HS on endothelial cells may effectively improve the prognosis evaluation of glioma patients.

Schwann cell release of p11 induces sensory neuron hyperactivity in Fabry disease

Patients with Fabry disease suffer from chronic debilitating pain and peripheral sensory neuropathy with minimal treatment options, but the cellular drivers of this pain are unknown. Here, we propose a novel mechanism by which altered signaling between Schwann cells and sensory neurons underlies the peripheral sensory nerve dysfunction we observe in a genetic rat model of Fabry disease. Using in vivo and in vitro electrophysiological recordings, we demonstrate that Fabry rat sensory neurons exhibit pronounced hyperexcitability. Schwann cells likely contribute to this finding as application of mediators released from cultured Fabry Schwann cells induces spontaneous activity and hyperexcitability in naïve sensory neurons. We examined putative algogenic mediators using proteomic analysis and found that Fabry Schwann cells release elevated levels of the protein p11 (S100-A10) which induces sensory neuron hyperexcitability. Removal of p11 from Fabry Schwann cell media causes hyperpolarization of neuronal resting membrane potential, indicating that p11 contributes to the excessive neuronal excitability caused by Fabry Schwann cells. These findings demonstrate that rats with Fabry disease exhibit sensory neuron hyperexcitability caused in part by Schwann cell release of the protein p11.

Aspergillus fumigatus hijacks human p11 to redirect fungal-containing phagosomes to non-degradative pathway

The decision whether endosomes enter the degradative or recycling pathway in mammalian cells is of fundamental importance for pathogen killing, and its malfunctioning has pathological consequences. We discovered that human p11 is a critical factor for this decision. The HscA protein present on the conidial surface of the human-pathogenic fungus Aspergillus fumigatus anchors p11 on conidia-containing phagosomes (PSs), excludes the PS maturation mediator Rab7, and triggers binding of exocytosis mediators Rab11 and Sec15. This reprogramming redirects PSs to the non-degradative pathway, allowing A. fumigatus to escape cells by outgrowth and expulsion as well as transfer of conidia between cells. The clinical relevance is supported by the identification of a single nucleotide polymorphism in the non-coding region of the S100A10 (p11) gene that affects mRNA and protein expression in response to A. fumigatus and is associated with protection against invasive pulmonary aspergillosis. These findings reveal the role of p11 in mediating fungal PS evasion.

Pseudorabies Virus Regulates the Extracellular Translocation of Annexin A2 To Promote Its Proliferation

Pseudorabies virus (PRV) infection causes enormous economic losses to the pork industry and severe health consequences in many hosts. Annexin A2 (ANXA2) is a membrane-associated protein with various intracellular functions associated with many viral infections. However, the role of ANXA2 in alphaherpesvirus replication is still not explored. In the present study, we identified the interaction between ANXA2 and PRV US3. The deficiency of ANXA2 significantly restricted PRV proliferation. PRV infection or US3 overexpression led to ANXA2 extracellular translocation. Furthermore, we confirmed that PRV or US3 could lead to the phosphorylation of the Tyr23 ANXA2 and Tyr419 Src kinase, which was associated with the ANXA2 cell surface transposition. US3 can also bind to Src in an ANXA2-independent manner and enhance the interaction between Src and ANXA2. Additionally, inhibitors targeting ANXA2 (A2ti-1) or Src (PP2) could remarkably inhibit PRV propagation in vitro and protect mice from PRV infection in vivo. Collectively, our findings broaden our understanding of the molecular mechanisms of ANXA2 in alphaherpesvirus pathogenicity and suggest that ANXA2 is a potential therapeutic target for treating alphaherpesvirus-induced infectious diseases. IMPORTANCE PRV belongs to the alphaherpesvirus and has recently re-emerged in China, causing severe economic losses. Recent studies also indicate that PRV may pose a potential public health challenge. ANXA2 is a multifunctional calcium- and lipid-binding protein implicated in immune function, multiple human diseases, and viral infection. Herein, we found that ANXA2 was essential to PRV efficient proliferation. PRV infection resulted in the extracellular translocation of ANXA2 through phosphorylation of ANXA2 and Src. ANXA2 and Src formed a complex with PRV US3. Importantly, inhibitors targeting ANXA2 or Src prevented PRV infection in vitro and in vivo. Therefore, our studies reveal a novel strategy by which alphaherpesvirus modifies ANXA2 to promote its replication and highlight ANXA2 as a target in developing novel promising antivirus agents in viral therapy.

Exosomes, autophagy and ER stress pathways in human diseases: Cross-regulation and therapeutic approaches

Exosomal release pathway and autophagy together maintain homeostasis and survival of cells under stressful conditions. Autophagy is a catabolic process through which cell entities, such as malformed biomacromolecules and damaged organelles, are degraded and recycled via the lysosomal-dependent pathway. Exosomes, a sub-type of extracellular vesicles (EVs) formed by the inward budding of multivesicular bodies (MVBs), are mostly involved in mediating communication between cells. The unfolded protein response (UPR) is an adaptive response that is activated to sustain survival in the cells faced with the endoplasmic reticulum (ER) stress through a complex network that involves protein synthesis, exosomes secretion and autophagy. Disruption of the critical crosstalk between EVs, UPR and autophagy may be implicated in various human diseases, including cancers and neurodegenerative diseases, yet the molecular mechanism(s) behind the coordination of these communication pathways remains obscure. Here, we review the available information on the mechanisms that control autophagy, ER stress and EV pathways, with the view that a better understanding of their crosstalk and balance may improve our knowledge on the pathogenesis and treatment of human diseases, where these pathways are dysregulated.

The encephalomyocarditis virus Leader promotes the release of virions inside extracellular vesicles via the induction of secretory autophagy

Naked viruses can escape host cells before the induction of lysis via release in extracellular vesicles (EVs). These nanosized EVs cloak the secreted virus particles in a host-derived membrane, which alters virus-host interactions that affect infection efficiency and antiviral immunity. Currently, little is known about the viral and host factors regulating this form of virus release. Here, we assessed the role of the encephalomyocarditis virus (EMCV) Leader protein, a 'viral security protein' that subverts the host antiviral response. EV release upon infection with wildtype virus or a Leader-deficient mutant was characterized at the single particle level using high-resolution flow cytometry. Inactivation of the Leader abolished EV induction during infection and strongly reduced EV-enclosed virus release. We demonstrate that the Leader promotes the release of virions within EVs by stimulating a secretory arm of autophagy. This newly discovered role of the EMCV Leader adds to the variety of mechanisms via which this protein affects virus-host interactions. Moreover, these data provide first evidence for a crucial role of a non-structural viral protein in the non-lytic release of picornaviruses via packaging in EVs.

Annexin A2 acts as an adherent molecule under the regulation of steroids during embryo implantation

We previously showed that annexin A2 (Axna2) was transiently expressed at the embryo-uterine luminal epithelium interface during the window of implantation and was involved in mouse embryo implantation. At the same time, Axna2 was reported to be upregulated in human receptive endometrium, which was critical for embryo attachment as an intracellular molecule. Here, we identified Axna2 as a membrane-bound molecule on human endometrial epithelial cells and trophoblast cells, and the outer surface membrane-bound Axna2 was involved in human embryo attachment. In addition, physiological levels of estrogen and progesterone increased the expression of overall Axna2 as well as that in the extracellular surface membrane protein fraction in human endometrial cells. Furthermore, p11 (or S100A10, a member of the S100 EF-hand family protein, molecular weight 11 kDa) was involved in the translocation of Axna2 to the outer surface membrane of endometrial epithelial cells without affecting its overall expression. Finally, the surface relocation of Axna2 was also dependent on cell-cell contact and calcium binding. A better understanding of the function and regulation of Axna2 in human endometrium may help us to identify a potential therapeutic target for subfertile and infertile patients.

Inflammation, Infection and Venous Thromboembolism

The association between inflammation, infection, and venous thrombosis has long been recognized; yet, only in the last decades have we begun to understand the mechanisms through which the immune and coagulation systems interact and reciprocally regulate one another. These interconnected networks mount an effective response to injury and pathogen invasion, but if unregulated can result in pathological thrombosis and organ damage. Neutrophils, monocytes, and platelets interact with each other and the endothelium in host defense and also play critical roles in the formation of venous thromboembolism. This knowledge has advanced our understanding of both human physiology and pathophysiology, as well as identified mechanisms of anticoagulant resistance and novel therapeutic targets for the prevention and treatment of thrombosis. In this review, we discuss the contributions of inflammation and infection to venous thromboembolism.

Plasmin and Plasminogen System in the Tumor Microenvironment: Implications for Cancer Diagnosis, Prognosis, and Therapy

Simple Summary

In this review, we present a detailed discussion of how the plasminogen-activation system is utilized by tumor cells in their unrelenting attack on the tissues surrounding them. Plasmin is an enzyme which is responsible for digesting several proteins that hold the tissues surrounding solid tumors together. In this process tumor cells utilize the activity of plasmin to digest tissue barriers in order to leave the tumour site and spread to other parts of the body. We specifically focus on the role of plasminogen receptor—p11 which is an important regulatory protein that facilitates the conversion of plasminogen to plasmin and by this means promotes the attack by the tumour cells on their surrounding tissues.

Abstract

The tumor microenvironment (TME) is now being widely accepted as the key contributor to a range of processes involved in cancer progression from tumor growth to metastasis and chemoresistance. The extracellular matrix (ECM) and the proteases that mediate the remodeling of the ECM form an integral part of the TME. Plasmin is a broad-spectrum, highly potent, serine protease whose activation from its precursor plasminogen is tightly regulated by the activators (uPA, uPAR, and tPA), the inhibitors (PAI-1, PAI-2), and plasminogen receptors. Collectively, this system is called the plasminogen activation system. The expression of the components of the plasminogen activation system by malignant cells and the surrounding stromal cells modulates the TME resulting in sustained cancer progression signals. In this review, we provide a detailed discussion of the roles of plasminogen activation system in tumor growth, invasion, metastasis, and chemoresistance with specific emphasis on their role in the TME. We particularly review the recent highlights of the plasminogen receptor S100A10 (p11), which is a pivotal component of the plasminogen activation system.

Coupling of Integrin α5 to Annexin A2 by Flow Drives Endothelial Activation

RATIONALE

Atherosclerosis preferentially occurs at specific sites of the vasculature where endothelial cells (ECs) are exposed to disturbed blood flow. Translocation of integrin α5 to lipid rafts promotes integrin activation and ligation, which is critical for oscillatory shear stress (OSS)-induced EC activation. However, the underlying mechanism of OSS promoted integrin α5 lipid raft translocation has remained largely unknown.

OBJECTIVE

The objective of this study was to specify the mechanotransduction mechanism of OSS-induced integrin α5 translocation and subsequent EC activation.

METHODS AND RESULTS

Mass spectrometry studies identified endothelial ANXA2 (annexin A2) as a potential carrier allowing integrin α5β1 to traffic in response to OSS. Interference by siRNA of AnxA2 in ECs greatly decreased OSS-induced integrin α5β1 translocation to lipid rafts, EC activation, and monocyte adhesion. Pharmacological and genetic inhibition of PTP1B (protein tyrosine phosphatase 1B) blunted OSS-induced integrin α5β1 activation, which is dependent on Piezo1-mediated calcium influx in ECs. Furthermore, ANXA2 was identified as a direct substrate of activated PTP1B by mass spectrometry. Using bioluminescence resonance energy transfer assay, PTP1B-dephosphorylated ANXA2 at Y24 was found to lead to conformational freedom of the C-terminal core domain from the N-terminal domain of ANXA2. Immunoprecipitation assays showed that this unmasked ANXA2-C-terminal core domain specifically binds to an integrin α5 nonconserved cytoplasmic domain but not β1. Importantly, ectopic lentiviral overexpression of an ANXA2^Y24F mutant increased and shRNA against Ptp1B decreased integrin α5β1 ligation, inflammatory signaling, and progression of plaques at atheroprone sites in apolipoprotein E (ApoE)^-/- mice. However, the antiatherosclerotic effect of Ptp1B shRNA was abolished in AnxA2^-/-ApoE^-/- mice.

CONCLUSIONS

Our data elucidate a novel endothelial mechanotransduction molecular mechanism linking atheroprone flow and activation of integrin α5β1, thereby identifying a class of potential therapeutic targets for atherosclerosis. Graphic Abstract: An graphic abstract is available for this article.

Multiple Biological Roles of Extracellular Vesicles in Lung Injury and Inflammation Microenvironment

Lung injury and inflammation are complex pathological processes. The influence and crosstalk between various cells form a characteristic microenvironment. Extracellular vesicles from different cell sources in the microenvironment carry multiple cargo molecules, which affect the pathological process through different pathways. Here, we mainly discussed the mechanism of crosstalk between alveolar epithelial cells and different immune cells through extracellular vesicles in lung inflammation and reviewed the mechanism of extracellular vesicles released by blood and airways on lung inflammation. Finally, the role of extracellular vesicles in viral infection of the lung was also described.

Co-localization of Interleukin-1α and Annexin A2 at the plasma membrane in response to oxidative stress

Interleukin-1α (IL-1α) and Annexin A2 (AnxA2) are pleiotropic molecules with both intracellular and extracellular roles. They share several characteristics including unconventional secretion aided by S100 proteins, anchoring of the externalized proteins at the outer surface of the plasma membrane and response to oxidative stress. Although IL-1α and AnxA2 have been implicated in a variety of biological processes, including cancer, little is known about the mechanisms of their cellular release. In the present study, employing the non-cancerous breast epithelial MCF10A cells, we demonstrate that IL-1α and AnxA2 establish a close association in response to oxidative stress. Stress conditions lead to translocation of both proteins towards lamellipodia rich in vimentin and association of full-length IL-1α and Tyr23 phosphorylated AnxA2 with the plasma membrane at peripheral sites depleted of F-actin. Notably, membrane-associated IL-1α and AnxA2 preferentially localize to the outer edges of the MCF10A cell islands, suggesting that the two proteins participate in the communication of these epithelial cells with their neighboring cells. Similarly, in U2OS osteosarcoma cell line both endogenous IL-1α and transiently produced IL-1α/EGFP associate with the plasma membrane. While benign MFC10A cells present membrane-associated IL-1α and AnxA2 at the edges of their cell islands, the aggressive cancerous U2OS cells communicate in such manner also with distant cells.

Modulation of Ion Channels and Receptors by p11 (S100A10)

p11 (S100A10, annexin II light chain, calpactin I light chain) is a multifunctional protein that forms a heterotetrameric complex with Annexin A2, particularly at cell membranes. p11, alone or together with Annexin A2, interacts with several ion channels and receptors and regulates their cellular localization and function. Altered levels of p11 are implicated in the pathophysiology of several forms of cancer, psychiatric disorders, and neurodegeneration. Via interactions with ion channels and receptors, p11 modulates therapeutic actions of drugs targeting brain disorders. By serving as a plasminogen receptor, p11 plays an important role in plasmin generation, fibrinolysis, angiogenesis, tumor progression, and metastasis. Here, we review mechanisms whereby p11 regulates functions of ion channels and receptors in health and disease states.

Cell-surface translocation of annexin A2 contributes to bleomycin-induced pulmonary fibrosis by mediating inflammatory response in mice

Bleomycin, a widely used anti-cancer drug, may give rise to pulmonary fibrosis, a serious side effect which is associated with significant morbidity and mortality. Despite the intensive efforts, the precise pathogenic mechanisms of pulmonary fibrosis still remain to be clarified. Our previous study showed that bleomycin bound directly to annexin A2 (ANXA2, or p36), leading to development of pulmonary fibrosis by impeding transcription factor EB (TFEB)-induced autophagic flux. Here, we demonstrated that ANXA2 also played a critical role in bleomycin-induced inflammation, which represents another major cause of bleomycin-induced pulmonary fibrosis. We found that bleomycin could induce the cell surface translocation of ANXA2 in lung epithelial cells through exosomal secretion, associated with enhanced interaction between ANXA2 and p11. Knockdown of ANXA2 or blocking membrane ANXA2 mitigated bleomycin-induced activation of nuclear factor (NF)-κB pathway and production of pro-inflammatory cytokine IL-6 in lung epithelial cells. ANXA2-deficient (ANXA2-/-) mice treated with bleomycin exhibit reduced pulmonary fibrosis along with decreased cytokine production compared with bleomycin-challenged wild-type mice. Further, the surface ANXA2 inhibitor TM601 could ameliorate fibrotic and inflammatory response in bleomycin-treated mice. Taken together, our results indicated that, in addition to disturbing autophagic flux, ANXA2 can contribute to bleomycin-induced pulmonary fibrosis by mediating inflammatory response.

Multiple functions of S100A10, an important cancer promoter

The S100 group of calcium binding proteins is composed of 21 members that exhibit tissue/cell specific expressions. These S100 proteins bind a diverse range of targets and regulate multiple cellular processes, including proliferation, migration and differentiation. S100A10, also known as p11, binds mainly to annexin A2 and mediates the conversion of plasminogen to an active protease, plasmin. Higher S100A10 expression has been reported to link to worse outcome and/or chemoresistance in a number of cancer types in lung, breast, ovary, pancreas, gall bladder and colorectum and leukemia although some discrepancy was reported. In this review, we focused on the roles of the S100A10 in cancer. We summarized its biological functions, role in cancer progression, prognostic value and targeting of S100A10 for cancer therapy.

Annexin A2 extracellular translocation and virus interaction: A potential target for antivirus-drug discovery

Annexin A2 is a membrane scaffolding and binding protein, which mediated various cellular events. Its functions are generally affected by cellular localization. In the cytoplasm, they interacted with different phospholipid membranes in Ca²⁺ -dependent manner and play vital roles including actin binding, remodeling and dynamics, cytoskeletal rearrangement, and lipid-raft microdomain formation. However, upon cell exposure to certain stimuli, annexin A2 translocates to the external leaflets of the plasma membrane where annexin A2 was recently reported to serve as a virus receptor, play an important role in the formation of virus replication complex, or implicated in virus assembly and budding. Here, we review some of annexin A2 roles in virus infections and the potentiality of targeting annexin A2 in the design of novel and promising antivirus agent that may have a broader consequence in virus therapy.

IFIT1 and IFIT3 promote oral squamous cell carcinoma metastasis and contribute to the anti-tumor effect of gefitinib via enhancing p-EGFR recycling

IFIT1 and IFIT3 are abundant products of interferon-stimulating genes. While the importance of IFIT1 and IFIT3 in the prognosis of cancer has been reported, the molecular basis of IFIT1 and IFIT3 in cancer progression remains unexplored. In the present study, we investigated the modes of action and the clinical significance of IFIT1 and IFIT3 in oral squamous cell carcinoma (OSCC). Ectopic expression of IFIT1 or IFIT3 induced OSCC cell invasion by promoting the epithelial-mesenchymal transition, whereas IFIT1 or IFIT3 knockdown exhibited opposite effects. Overexpression of IFIT1 or IFIT3 promoted tumor growth, regional and distant metastasis in xenograft and orthotopic nude mice models. Most importantly, IFIT1 or IFIT3 overexpression increased the levels of p-EGFR^Y1068 and p-AKT^S473 in OSCC cells and also enhanced tumor inhibitory effect of gefitinib. By immunoprecipitation and LC-MS/MS analysis, we found that IFIT1 and IFIT3 interacted with ANXA2 that enhanced p-EGFR^Y1068 endosomal recycling. Depletion of ANXA2 using siRNA therefore abolished p-EGFR^Y1068 and p-AKT^S473 expression in IFIT1- or IFIT3-overexpressed cells. Furthermore, a significant positive association of increased IFIT1 and IFIT3 expression with advanced T-stage, lymph node metastasis, perineural invasion, lymphovascular invasion, extranodal extension, and poor overall survival rate was confirmed in OSCC patients. We also found a statistically positive correlation of p-EGFR^Y1068 expression with IFIT1 and IFIT3 in OSCC tumors and poor clinical outcome in patients. Collectively, we demonstrated a novel role of IFIT1 and IFIT3 in driving OSCC progression and metastasis by interacting with ANXA2 and hence enhancing p-EGFR recycling and its downstream signaling.

S100A10 and Cancer Hallmarks: Structure, Functions, and its Emerging Role in Ovarian Cancer

S100A10, which is also known as p11, is located in the plasma membrane and forms a heterotetramer with annexin A2. The heterotetramer, comprising of two subunits of annexin A2 and S100A10, activates the plasminogen activation pathway, which is involved in cellular repair of normal tissues. Increased expression of annexin A2 and S100A10 in cancer cells leads to increased levels of plasmin—which promotes the degradation of the extracellular matrix—increased angiogenesis, and the invasion of the surrounding organs. Although many studies have investigated the functional role of annexin A2 in cancer cells, including ovarian cancer, S100A10 has been less studied. We recently demonstrated that high stromal annexin A2 and high cytoplasmic S100A10 expression is associated with a 3.4-fold increased risk of progression and 7.9-fold risk of death in ovarian cancer patients. Other studies have linked S100A10 with multidrug resistance in ovarian cancer; however, no functional studies to date have been performed in ovarian cancer cells. This article reviews the current understanding of S100A10 function in cancer with a particular focus on ovarian cancer.

Unconventional secretion of annexins and galectins

Eukaryotic cells have a highly evolved system of protein secretion, and dysfunction in this pathway is associated with many diseases including cancer, infection, metabolic disease and neurological disorders. Most proteins are secreted using the conventional endoplasmic reticulum (ER)/Golgi network and as such, this pathway is well-characterised. However, several cytosolic proteins have now been documented as secreted by unconventional transport pathways. This review focuses on two of these proteins families: annexins and galectins. The extracellular functions of these proteins are well documented, as are associations of their perturbed secretion with several diseases. However, the mechanisms and regulation of their secretion remain poorly characterised, and are discussed in this review. This review is part of a Special Issues of SCDB on 'unconventional protein secretion' edited by Walter Nickel and Catherine Rabouille.

Transbilayer phospholipid movement facilitates the translocation of annexin across membranes

Annexins are cytosolic phospholipid-binding proteins that can be found on the outer leaflet of the plasma membrane. The extracellular functions of annexin include modulating fibrinolysis activity and cell migration. Despite having well-described extracellular functions, the mechanism of annexin transport from the cytoplasmic inner leaflet to the extracellular outer leaflet of the plasma membrane remains unclear. Here, we show that the transbilayer movement of phospholipids facilitates the transport of annexins A2 and A5 across membranes in cells and in liposomes. We identified TMEM16F (also known as anoctamin-6, ANO6) as a lipid scramblase required for transport of these annexins to the outer leaflet of the plasma membrane. This work reveals a mechanism for annexin translocation across membranes which depends on plasma membrane phospholipid remodelling.

Exophagy of annexin A2 via RAB11, RAB8A and RAB27A in IFN-γ-stimulated lung epithelial cells

Annexin A2 (ANXA2), a phospholipid-binding protein, has multiple biological functions depending on its cellular localization. We previously demonstrated that IFN-γ-triggered ANXA2 secretion is associated with exosomal release. Here, we show that IFN-γ-induced autophagy is essential for the extracellular secretion of ANXA2 in lung epithelial cells. We observed colocalization of ANXA2-containing autophagosomes with multivesicular bodies (MVBs) after IFN-γ stimulation, followed by exosomal release. IFN-γ-induced exophagic release of ANXA2 could not be observed in ATG5-silenced or mutant RAB11-expressing cells. Furthermore, knockdown of RAB8A and RAB27A, but not RAB27B, reduced IFN-γ-triggered ANXA2 secretion. Surface translocation of ANXA2 enhanced efferocytosis by epithelial cells, and inhibition of different exophagic steps, including autophagosome formation, fusion of autophagosomes with MVBs, and fusion of amphisomes with plasma membrane, reduced ANXA2-mediated efferocytosis. Our data reveal a novel route of IFN-γ-induced exophagy of ANXA2.

Regulation of the Equilibrium between Closed and Open Conformations of Annexin A2 by N-Terminal Phosphorylation and S100A4-Binding

Annexin A2 (ANXA2) has a versatile role in membrane-associated functions including membrane aggregation, endo- and exocytosis, and it is regulated by post-translational modifications and protein-protein interactions through the unstructured N-terminal domain (NTD). Our sequence analysis revealed a short motif responsible for clamping the NTD to the C-terminal core domain (CTD). Structural studies indicated that the flexibility of the NTD and CTD are interrelated and oppositely regulated by Tyr24 phosphorylation and Ser26Glu phosphomimicking mutation. The crystal structure of the ANXA2-S100A4 complex showed that asymmetric binding of S100A4 induces dislocation of the NTD from the CTD and, similar to the Ser26Glu mutation, unmasks the concave side of ANXA2. In contrast, pTyr24 anchors the NTD to the CTD and hampers the membrane-bridging function. This inhibition can be restored by S100A4 and S100A10 binding. Based on our results we provide a structural model for regulation of ANXA2-mediated membrane aggregation by NTD phosphorylation and S100 binding.

Annexin A2 contributes to lung injury and fibrosis by augmenting factor Xa fibrogenic activity

In lung injury and disease, including idiopathic pulmonary fibrosis (IPF), extravascular factor X is converted into factor Xa (FXa), a coagulant protease with fibrogenic actions. Extracellular annexin A2 binds to FXa, augmenting activation of the protease-activated receptor-1 (PAR-1). In this study, the contribution of annexin A2 in lung injury and fibrosis was investigated. Annexin A2 immunoreactivity was observed in regions of fibrosis, including those associated with fibroblasts in lung tissue of IPF patients. Furthermore, annexin A2 was detected in the conditioned media and an EGTA membrane wash of human lung fibroblast (LF) cultures. Incubation with human plasma (5% vol/vol) or purified FXa (15–50 nM) evoked fibrogenic responses in LF cultures, with FXa increasing interleukin-6 (IL-6) production and cell number by 270 and 46%, respectively ( P < 0.05, n = 5–8). The fibrogenic actions of plasma or FXa were attenuated by the selective FXa inhibitor apixaban (10 μM, or antibodies raised against annexin A2 or PAR-1 (2 μg/ml). FXa-stimulated LFs from IPF patients ( n = 6) produced twice as much IL-6 as controls ( n = 10) ( P < 0.05), corresponding with increased levels of extracellular annexin A2. Annexin A2 gene deletion in mice reduced bleomycin-induced increases in bronchoalveolar lavage fluid (BALF) IL-6 levels and cell number (* P < 0.05; n = 4–12). Lung fibrogenic gene expression and dry weight were reduced by annexin A2 gene deletion, but lung levels of collagen were not. Our data suggest that annexin A2 contributes to lung injury and fibrotic disease by mediating the fibrogenic actions of FXa. Extracellular annexin A2 is a potential target for the treatment of IPF.

S100A10 Regulates ULK1 Localization to ER-Mitochondria Contact Sites in IFN-γ-Triggered Autophagy

During the process of autophagy, the autophagy-related proteins are translocated to autophagosome formation sites. Here, we demonstrate that S100A10 is required for ULK1 localization to autophagosome formation sites. Silencing of S100A10 reduces IFN-γ-induced autophagosome formation. We also determined the role of annexin A2 (ANXA2), a binding partner of S100A10, which has been reported to promote phagophore assembly. Silencing of ANXA2 reduced S100A10 expression. However, overexpression of S100A10 in ANXA2-silenced cells was still able to enhance autophagosome formation, suggesting that ANXA2 regulates IFN-γ-induced autophagy through S100A10. We also observed that S100A10 interacted with ULK1 after IFN-γ stimulation, and S100A10 knockdown prevented ULK1 localization to autophagosome formation sites. Finally, the release of high mobility group protein B1, one of the functions mediated by IFN-γ-induced autophagy, was inhibited in S100A10 knockdown cells. These results elucidate the importance of S100A10 in autophagosome formation and reveal the relationship between S100A10 and ULK1 in IFN-γ-induced autophagy.

Mechanism of Fibronectin Binding to Human Trabecular Meshwork Exosomes and Its Modulation by Dexamethasone

Exosomes are emerging as important mediators of cell-matrix interactions by means of specific adhesion proteins. Changes in the tissue-specific exosomal protein expression may underlie pathological conditions whereby extracellular matrix turnover and homeostasis is disrupted. Ocular hypertension due to extracellular matrix accumulation in the trabecular meshwork is a hallmark of glucocorticoid-induced glaucoma. In the trabecular meshwork, exosomal fibronectin mediates cell matrix interactions at cellular structures called “invadosomes”. Trabecular meshwork cells use invadosomes to turn over their surrounding matrix and maintain passageways for flow of aqueous humor. In this study, we observed that human trabecular meshwork explants treated with dexamethasone released exosomes with significantly reduced amounts of fibronectin bound per exosome. Further, we found that exosome-fibronectin binding is heparan sulfate-dependent, consistent with our observation that trabecular meshwork exosomes are enriched in the heparin/heparan sulfate binding annexins A2 and A6. In this way, dexamethasone-treated explants released exosomes with a significant reduction in annexin A2 and A6 per exosome. Interestingly, we did not detect exosomal matrix metalloproteinases, but we identified abundant dipeptidyl peptidase 4, a serine protease whose activity was reduced on exosomes isolated from dexamethasone-treated explants. Together, our findings demonstrate mechanistically how corticosteroid-induced alterations in exosomal adhesion cargo and properties can account for the pathological matrix accumulation seen in many glaucoma patients.

The Coagulant Factor Xa Induces Protease-Activated Receptor-1 and Annexin A2-Dependent Airway Smooth Muscle Cytokine Production and Cell Proliferation

During asthma exacerbation, plasma circulating coagulant factor X (FX) enters the inflamed airways and is activated (FXa). FXa may have an important role in asthma, being involved in thrombin activation and an agonist of protease-activated receptor-1 (PAR-1). Extracellular annexin A2 and integrins are also implicated in PAR-1 signaling. In this study, the potential role of PAR-1 in mediating the effects of FXa on human airway smooth muscle (ASM) cell cytokine production and proliferation was investigated. FXa (5-50 nM), but not FX, stimulated increases in ASM IL-6 production and cell number after 24- and 48-hour incubation, respectively (P < 0.05; n = 5). FXa (15 nM) also stimulated increases in the levels of mRNA for cytokines (IL-6), cell cycle-related protein (cyclin D1), and proremodeling proteins (FGF-2, PDGF-B, CTGF, SM22, and PAI-1) after 3-hour incubation (P < 0.05; n = 4). The actions of FXa were insensitive to inhibition by hirudin (1 U/ml), a selective thrombin inhibitor, but were attenuated by SCH79797 (100 nM), a PAR-1 antagonist, or Cpd 22 (1 μM), an inhibitor of integrin-linked kinase. The selective targeting of PAR-1, annexin A2, or β1-integrin by small interfering RNA and/or by functional blocking antibodies also attenuated FXa-evoked responses. In contrast, the targeting of annexin A2 did not inhibit thrombin-stimulated ASM function. In airway biopsies of patients with asthma, FXa and annexin A2 were detected in the ASM bundle by immunohistochemistry. These findings establish FXa as a potentially important asthma mediator, stimulating ASM function through actions requiring PAR-1 and annexin A2 and involving integrin coactivation.

Chronic Infection and Severe Asthma

Chronic bacterial infection is implicated in both the development and severity of asthma. The atypical bacteria Mycoplasma pneumoniae and Chlamydophila pneumoniae have been identified in the airways of asthmatics and correlated with clinical features such as adult onset, exacerbation risks, steroid sensitivity, and symptom control. Asthmatic patients with evidence of bacterial infection may benefit from antibiotic treatment directed towards these atypical organisms. Examination of the airway microbiome may identify microbial communities that confer risk for or protection from severe asthma.

Vascular expression of annexin A2 in lupus nephritis

AIMS

To evaluate vascular expression of annexin A2 (ANXA2) and its subunit S100A10 in lupus nephritis (LN).

METHODS

The present histological study included 14 patients with LN and 11 controls (patients with non-lupus kidney diseases). Kidney biopsies from patients with lupus were scored for lupus glomerulonephritis (according to the International Society of Nephrology/Renal Pathology Society 2003 classification) and vascular lesions (such as microthrombi and antiphospholipid syndrome nephropathy (APSN)). ANXA2 and S100A10 expression in glomerular and peritubular capillaries was evaluated by immunohistochemistry on tissue sections. The staining intensity score ranged from 0 (no expression) to 4 (intense expression).

RESULTS

In patients with LN, the median age (range) at first kidney biopsy was 36 (18-49). Vascular lesions were observed in six patients (including two with APSN). We observed intense expression of ANXA2 in glomerular and peritubular capillaries while expression of S100A10 was weaker. However, one of the patients with APSN showed strong S100A10 expression. Patients with LN and controls differed significantly in terms of S100A10 expression in peritubular capillaries. We also observed a statistical difference between patients who had LN with renal vascular lesions and those without renal vascular lesions in terms of ANXA2 expression in peritubular capillaries.

CONCLUSIONS

The presence of vascular lesions in LN appears to be associated with significant differences in the vascular expression of ANXA2. Vascular expression of ANXA2 was somewhat higher in LN. Vascular expression of S100A10 was somewhat lower in LN (except one of the two patients with APSN). Further studies of ANXA2's putative value as a biomarker of active LN or of vascular lesions in LN are required.

A functional proteomics approach to the comprehension of sarcoidosis

Pulmonary sarcoidosis (Sar) is an idiopathic disease histologically typified by non-caseating epitheliod cell sarcoid granulomas. A cohort of 37 Sar patients with chronic persistent pulmonary disease was described in this study. BAL protein profiles from 9 of these Sar patients were compared with those from 8 smoker (SC) and 10 no-smoker controls (NSC) by proteomic approach. Principal Component Analysis was performed to clusterize the samples in the corresponding conditions highlighting a differential pattern profiles primarily in Sar than SC. Spot identification reveals thirty-four unique proteins involved in lipid, mineral, and vitamin Dmetabolism, and immuneregulation of macrophage function. Enrichment analysis has been elaborated by MetaCore, revealing 14-3-3ε, α1-antitrypsin, GSTP1, and ApoA1 as "central hubs". Process Network as well as Pathway Maps underline proteins involved in immune response and inflammation induced by complement system, innate inflammatory response and IL-6signalling. Disease Biomarker Network highlights Tuberculosis and COPD as pathologies that share biomarkers with sarcoidosis. In conclusion, Sar protein expression profile seems more similar to that of NSC than SC, conversely to other ILDs. Moreover, Disease Biomarker Network revealed several common features between Sar and TB, exhorting to orientate the future proteomics investigations also in comparative BALF analysis of Sar and TB.

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.

Annexin A2 mediates Mycoplasma pneumoniae community-acquired respiratory distress syndrome toxin binding to eukaryotic cells

Mycoplasma pneumoniae synthesizes a novel human surfactant protein A (SP-A)-binding cytotoxin, designated community-acquired respiratory distress syndrome (CARDS) toxin, that exhibits ADP-ribosylating and vacuolating activities in mammalian cells and is directly linked to a range of acute and chronic airway diseases, including asthma. In our attempt to detect additional CARDS toxin-binding proteins, we subjected the membrane fraction of human A549 airway cells to affinity chromatography using recombinant CARDS toxin as bait. A 36-kDa A549 cell membrane protein bound to CARDS toxin and was identified by time of flight (TOF) mass spectroscopy as annexin A2 (AnxA2) and verified by immunoblotting with anti-AnxA2 monoclonal antibody. Dose-dependent binding of CARDS toxin to recombinant AnxA2 reinforced the specificity of the interaction, and further studies revealed that the carboxy terminus of CARDS toxin mediated binding to AnxA2. In addition, pretreatment of viable A549 cells with anti-AnxA2 monoclonal antibody or AnxA2 small interfering RNA (siRNA) reduced toxin binding and internalization. Immunofluorescence analysis of CARDS toxin-treated A549 cells demonstrated the colocalization of CARDS toxin with cell surface-associated AnxA2 upon initial binding and with intracellular AnxA2 following toxin internalization. HepG2 cells, which express low levels of AnxA2, were transfected with a plasmid expressing AnxA2 protein, resulting in enhanced binding of CARDS toxin and increased vacuolization. In addition, NCI-H441 cells, which express both AnxA2 and SP-A, upon AnxA2 siRNA transfection, showed decreased binding and subsequent vacuolization. These results indicate that CARDS toxin recognizes AnxA2 as a functional receptor, leading to CARDS toxin-induced changes in mammalian cells.

Host cell susceptibility to bacterial toxins is usually determined by the presence and abundance of appropriate receptors, which provides a molecular basis for toxin target cell specificities. To perform its ADP-ribosylating and vacuolating activities, community-acquired respiratory distress syndrome (CARDS) toxin must bind to host cell surfaces via receptor-mediated events in order to be internalized and trafficked effectively. Earlier, we reported the binding of CARDS toxin to surfactant protein A (SP-A), and here we show how CARDS toxin uses an alternative receptor to execute its pathogenic properties. CARDS toxin binds selectively to annexin A2 (AnxA2), which exists both on the cell surface and intracellularly. Since AnxA2 regulates membrane dynamics at early stages of endocytosis and trafficking, it serves as a distinct receptor for CARDS toxin binding and internalization and enhances CARDS toxin-induced vacuolization in mammalian cells.

Protein interactions between surface annexin A2 and S100A10 mediate adhesion of breast cancer cells to microvascular endothelial cells

Annexin A2 (AnxA2) and S100A10 are known to form a molecular complex. Using fluorescence-based binding assays, we show that both proteins are localised on the cell surface, in a molecular form that allows mutual interaction. We hypothesized that binding between these proteins could facilitate cell-cell interactions. For cells that express surface S100A10 and surface annexin A2, cell-cell interactions can be blocked by competing with the interaction between these proteins. Thus an annexin A2-S100A10 molecular bridge participates in cell-cell interactions, revealing a hitherto unexplored function of this protein interaction.

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.

The biochemistry and regulation of S100A10: a multifunctional plasminogen receptor involved in oncogenesis

The plasminogen receptors mediate the production and localization to the cell surface of the broad spectrum proteinase, plasmin. S100A10 is a key regulator of cellular plasmin production and may account for as much as 50% of cellular plasmin generation. In parallel to plasminogen, the plasminogen-binding site on S100A10 is highly conserved from mammals to fish. S100A10 is constitutively expressed in many cells and is also induced by many diverse factors and physiological stimuli including dexamethasone, epidermal growth factor, transforming growth factor-α, interferon-γ, nerve growth factor, keratinocyte growth factor, retinoic acid, and thrombin. Therefore, S100A10 is utilized by cells to regulate plasmin proteolytic activity in response to a wide diversity of physiological stimuli. The expression of the oncogenes, PML-RARα and KRas, also stimulates the levels of S100A10, suggesting a role for S100A10 in pathophysiological processes such as in the oncogenic-mediated increases in plasmin production. The S100A10-null mouse model system has established the critical role that S100A10 plays as a regulator of fibrinolysis and oncogenesis. S100A10 plays two major roles in oncogenesis, first as a regulator of cancer cell invasion and metastasis and secondly as a regulator of the recruitment of tumor-associated cells, such as macrophages, to the tumor site.