The p11 subunit of the annexin II tetramer plays a key role in the stimulation of t-PA-dependent plasminogen activation

Liver-derived plasminogen mediates muscle stem cell expansion during caloric restriction through the plasminogen receptor Plg-RKT

An intriguing effect of short-term caloric restriction (CR) is the expansion of certain stem cell populations, including muscle stem cells (satellite cells), which facilitate an accelerated regenerative program after injury. Here, we utilized the MetRSL274G (MetRS) transgenic mouse to identify liver-secreted plasminogen as a candidate for regulating satellite cell expansion during short-term CR. Knockdown of circulating plasminogen prevents satellite cell expansion during short-term CR. Furthermore, loss of the plasminogen receptor KT (Plg-RKT) is also sufficient to prevent CR-related satellite cell expansion, consistent with direct signaling of plasminogen through the plasminogen receptor Plg-RKT/ERK kinase to promote proliferation of satellite cells. Importantly, we are able to replicate many of these findings in human participants from the CALERIE trial. Our results demonstrate that CR enhances liver protein secretion of plasminogen, which signals directly to the muscle satellite cell through Plg-RKT to promote proliferation and subsequent muscle resilience during CR.

Identification and characterization of calreticulin as a novel plasminogen receptor

Calreticulin (CRT) was originally identified as a key calcium-binding protein of the endoplasmic reticulum. Subsequently, CRT was shown to possess multiple intracellular functions, including roles in calcium homeostasis and protein folding. Recently, several extracellular functions have been identified for CRT, including roles in cancer cell invasion and phagocytosis of apoptotic and cancer cells by macrophages. In the current report, we uncover a novel function for extracellular CRT and report that CRT functions as a plasminogen-binding receptor that regulates the conversion of plasminogen to plasmin. We show that human recombinant or bovine tissue-derived CRT dramatically stimulated the conversion of plasminogen to plasmin by tissue plasminogen activator or urokinase-type plasminogen activator. Surface plasmon resonance analysis revealed that CRT-bound plasminogen (KD = 1.8 μM) with moderate affinity. Plasminogen binding and activation by CRT were inhibited by ε-aminocaproic acid, suggesting that an internal lysine residue of CRT interacts with plasminogen. We subsequently show that clinically relevant CRT variants (lacking four or eight lysines in carboxyl-terminal region) exhibited decreased plasminogen activation. Furthermore, CRT-deficient fibroblasts generated 90% less plasmin and CRT-depleted MDA MB 231 cells also demonstrated a significant reduction in plasmin generation. Moreover, treatment of fibroblasts with mitoxantrone dramatically stimulated plasmin generation by WT but not CRT-deficient fibroblasts. Our results suggest that CRT is an important cellular plasminogen regulatory protein. Given that CRT can empower cells with plasmin proteolytic activity, this discovery may provide new mechanistic insight into the established role of CRT in cancer.

Recent Advances in Molecular and Cellular Functions of S100A10

S100A10 (p11, annexin II light chain, calpactin light chain) is a multifunctional protein with a wide range of physiological activity. S100A10 is unique among the S100 family members of proteins since it does not bind to Ca2+, despite its sequence and structural similarity. This review focuses on studies highlighting the structure, regulation, and binding partners of S100A10. The binding partners of S100A10 were collated and summarized.

Plasminogen Binding and Activation at the Mesothelial Cell Surface Promotes Invasion through a Collagen Matrix

Plasminogen (Plg) activation to the serine protease plasmin (Pla) plays a key role in regulating wound healing and fibrotic responses, particularly when bound to cell surface receptors. Our previous work suggested that mesothelial cells bind Plg at the cell surface, though no Plg receptors were described for these cells. Since mesothelial cells contribute to injury responses, including cellular differentiation to a mesenchymal-like phenotype and extracellular matrix remodeling, we hypothesized that Plg binding would promote these responses. Here, we confirm that Plg binds to both pleural and peritoneal mesothelial cells via the lysine-binding domain present in Plg, and we demonstrate the presence of three Plg receptors on the mesothelial cell surface: α-Enolase, Annexin A2, and Plg-R_KT. We further show that bound-Plg is activated to Pla on the cell surface and that activation is blocked by an inhibitor of urokinase plasminogen activator or by the presence of animal-derived FBS. Lastly, we demonstrate that Plg promotes mesothelial cell invasion through a type I collagen matrix but does not promote cellular differentiation or proliferation. These data demonstrate for the first time that mesothelial cells bind and activate Plg at the cell surface and that active Pla is involved in mesothelial cell invasion without cell differentiation.

The Urokinase Plasminogen Activation System in Pancreatic Cancer: Prospective Diagnostic and Therapeutic Targets

Pancreatic cancer is a highly aggressive malignancy that features high recurrence rates and the poorest prognosis of all solid cancers. The urokinase plasminogen activation system (uPAS) is strongly implicated in the pathophysiology and clinical outcomes of patients with pancreatic ductal adenocarcinoma (PDAC), which accounts for more than 90% of all pancreatic cancers. Overexpression of the urokinase-type plasminogen activator (uPA) or its cell surface receptor uPAR is a key step in the acquisition of a metastatic phenotype via multiple mechanisms, including the increased activation of cell surface localised plasminogen which generates the serine protease plasmin. This triggers multiple downstream processes that promote tumour cell migration and invasion. Increasing clinical evidence shows that the overexpression of uPA, uPAR, or of both is strongly associated with worse clinicopathological features and poor prognosis in PDAC patients. This review provides an overview of the current understanding of the uPAS in the pathogenesis and progression of pancreatic cancer, with a focus on PDAC, and summarises the substantial body of evidence that supports the role of uPAS components, including plasminogen receptors, in this disease. The review further outlines the clinical utility of uPAS components as prospective diagnostic and prognostic biomarkers for PDAC, as well as a rationale for the development of novel uPAS-targeted therapeutics.

The Annexin A2/S100A10 Complex: The Mutualistic Symbiosis of Two Distinct Proteins

Mutualistic symbiosis refers to the symbiotic relationship between individuals of different species in which both individuals benefit from the association. S100A10, a member of the S100 family of Ca²⁺-binding proteins, exists as a tight dimer and binds two annexin A2 molecules. This association forms the annexin A2/S100A10 complex known as AIIt, and modifies the distinct functions of both proteins. Annexin A2 is a Ca²⁺-binding protein that binds F-actin, phospholipid, RNA, and specific polysaccharides such as heparin. S100A10 does not bind Ca²⁺, but binds tPA, plasminogen, certain plasma membrane ion channels, neurotransmitter receptors, and the structural scaffold protein, AHNAK. S100A10 relies on annexin A2 for its intracellular survival: in the absence of annexin A2, it is rapidly destroyed by ubiquitin-dependent and independent proteasomal degradation. Annexin A2 requires S100A10 to increase its affinity for Ca²⁺, facilitating its participation in Ca²⁺-dependent processes such as membrane binding. S100A10 binds tissue plasminogen activator and plasminogen, and promotes plasminogen activation to plasmin, which is a process stimulated by annexin A2. In contrast, annexin A2 acts as a plasmin reductase and facilitates the autoproteolytic destruction of plasmin. This review examines the relationship between annexin A2 and S100A10, and how their mutualistic symbiosis affects the function of both proteins.

The ANXA2/S100A10 Complex—Regulation of the Oncogenic Plasminogen Receptor

The generation of the serine protease plasmin is initiated by the binding of its zymogenic precursor, plasminogen, to cell surface receptors. The proteolytic activity of plasmin, generated at the cell surface, plays a crucial role in several physiological processes, including fibrinolysis, angiogenesis, wound healing, and the invasion of cells through both the basement membrane and extracellular matrix. The seminal observation by Albert Fischer that cancer cells, but not normal cells in culture, produce large amounts of plasmin formed the basis of current-day observations that plasmin generation can be hijacked by cancer cells to allow tumor development, progression, and metastasis. Thus, the cell surface plasminogen-binding receptor proteins are critical to generating plasmin proteolytic activity at the cell surface. This review focuses on one of the twelve well-described plasminogen receptors, S100A10, which, when in complex with its regulatory partner, annexin A2 (ANXA2), forms the ANXA2/S100A10 heterotetrameric complex referred to as AIIt. We present the theme that AIIt is the quintessential cellular plasminogen receptor since it regulates the formation and the destruction of plasmin. We also introduce the term oncogenic plasminogen receptor to define those plasminogen receptors directly activated during cancer progression. We then discuss the research establishing AIIt as an oncogenic plasminogen receptor-regulated during EMT and activated by oncogenes such as SRC, RAS, HIF1α, and PML-RAR and epigenetically by DNA methylation. We further discuss the evidence derived from animal models supporting the role of S100A10 in tumor progression and oncogenesis. Lastly, we describe the potential of S100A10 as a biomarker for cancer diagnosis and prognosis.

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.

Plasminogen Receptors and Fibrinolysis

The ability of cells to promote plasminogen activation on their surfaces is now well recognized, and several distinct cell surface proteins have been demonstrated to function as plasminogen receptors. Here, we review studies demonstrating that plasminogen bound to cells, in addition to plasminogen directly bound to fibrin, plays a major role in regulating fibrin surveillance. We focus on the ability of specific plasminogen receptors on eukaryotic cells to promote fibrinolysis in the in vivo setting by reviewing data obtained predominantly in murine models. Roles for distinct plasminogen receptors in fibrin surveillance in intravascular fibrinolysis, immune cell recruitment in the inflammatory response, wound healing, and lactational development are discussed.

S100A10 Has a Critical Regulatory Function in Mammary Tumor Growth and Metastasis: Insights Using MMTV-PyMT Oncomice and Clinical Patient Sample Analysis

Simple Summary

The key challenges that face patients during breast cancer therapy is the metastatic spread and aggressiveness of the disease. Thus, the goal of current breast cancer research is to discover new therapeutic and diagnostic targets that limit the aggressive spread of the cancer. In this study, we investigated the role of protein S100A10 (p11) in breast tumor growth, progression, and metastasis using mouse cancer models and patient tumor sample analysis. We have demonstrated in our previous studies that p11 is critical for the function of a proteolytic enzyme–plasmin, which aids in the digestion of the tissues surrounding the tumor and allows the escape of the cancer cells from the breast tissue to organs such as the lungs and bone. Here, we present evidence that genetic deletion of p11 results in smaller and less aggressive mammary tumors in mice. We also observed that the cancer spread to the lungs is dramatically reduced in the absence of p11 gene in mice. Subsequent analysis of breast cancer patient tissues showed a correlation between higher p11 expression and both poor survival and aggressive cancer.

Abstract

S100A10 (p11) is a plasminogen receptor that regulates cellular plasmin generation by cancer cells. In the current study, we used the MMTV-PyMT mouse breast cancer model, patient tumor microarray, and immunohistochemical (IHC) analysis to investigate the role of p11 in oncogenesis. The genetic deletion of p11 resulted in significantly decreased tumor onset, growth rate, and spontaneous pulmonary metastatic burden in the PyMT/p11-KO (knock-out) mice. This phenotype was accompanied by substantial reduction in Ki67 positivity, macrophage infiltration, decreased vascular density in the primary tumors, and decrease in invasive carcinoma and pulmonary metastasis. Surprisingly, IHC analysis of wild-type MMTV-PyMT mice failed to detect p11 expression in the tumors or metastatic tumor cells and loss of p11 did not decrease plasmin generation in the PyMT tumors and cells. Furthermore, tumor cells expressing p11 displayed dramatically reduced lung metastasis when injected into p11-depleted mice, further strengthening the stromal role of p11 in tumor growth and metastasis. Transcriptome analysis of the PyMT tumors from p11-KO mice showed marked reduction in genes such as Areg, Muc1, and S100a8 involved in breast cancer development, progression, and inflammation. The PyMT/p11-KO tumors displayed a remarkable increase in inflammatory cytokines such as interleukin (Il)-6, Il-10, and interferon (Ifn)-γ. Gene expression profiling and IHC of primary breast cancer samples showed that p11 mRNA and protein levels were significantly higher in tumor tissues compared to normal mammary tissue. P11 mRNA expression was significantly associated with poor patient prognosis and significantly elevated in high grade, triple negative (TN) tumors, and tumors with high proliferative index. This is the first study examining the crucial role of p11 in breast tumor development and metastasis, thus emphasizing its potential as a diagnostic and prognostic biomarker in breast cancer.

Membranous S100A10 involvement in the tumor budding of colorectal cancer during oncogenesis: report of two cases with immunohistochemical analysis

Background

Tumor budding (TB) and poorly differentiated clusters (PDCs) are a sequence of histologic findings that predict worse prognosis and node metastasis in colorectal cancer (CRC). TB and PDC (TB/PDC) are caused by cancer cell detachment and are distinguished by the number of cancer cells that constitute a cell cluster. In short, PDC is regarded as the previous step of TB. TB/PDC and epithelial-mesenchymal transition (EMT) are closely linked, but its pathogenic mechanisms are still unclear. S100A10, a member of the S100 protein family, forms a heterocomplex with annexin A2 (ANX A2) and then translocates to cell membrane from the cytoplasm and plays various roles in cell dynamics, including plasminogen activation. S100A10 is the activation modulator of the heterocomplex and promotes cell invasion. S100A10 is involved in the remodeling of both actin and extracellular matrix (ECM), which is also associated with EMT.

Case presentation

In two representative cases of conventional advanced CRC, we immunohistochemically examined S100A10 and ANX A2 expressions in which both TB and PDC were prominent. Both CRCs metastasized to multiple regional lymph nodes. In both cases, a membranous positivity for S100A10 was diffusely found in both tumor buds and PDCs and was observed in the tumor cells protruding toward the stroma, giving rise to TB/PDC. However, even in tumor glands with TB/PDC, the tumor cells with a smooth border around the stroma showed either cytoplasmic fine-granular expression or no positivity. The immunoreactivity for ANX A2 was almost the same as that for S100A10. In the main tumor components without TB/PDC, no distinct positivity was detected at their smooth borders.

Conclusions

During oncogenesis, membranous S100A10 has the potential to be related to TB of CRC. This may be due to plasminogen activation, actin remodeling, and interaction with an altered ECM. However, further study is required to confirm this hypothesis.

Functions of the plasminogen receptor Plg-RKT

Plg-RKT is a structurally unique transmembrane plasminogen receptor with both N- and C-terminal domains exposed on the extracellular face of the cell. Its C-terminal lysine functions to tether plasminogen to cell surfaces. Overexpression of Plg-RKT increases cell surface plasminogen binding capacity while genetic deletion of Plg-RKT decreases plasminogen binding. Plasminogen binding to Plg-RKT results in promotion of plasminogen activation to the broad spectrum serine protease plasmin. This function is promoted by the physical association of Plg-RKT with the urokinase receptor (uPAR). Plg-RKT is broadly expressed in cells and tissues throughout the organism and its sequence is remarkably conserved phylogenetically. Plg-RKT also is required for lactation and, thus, is necessary for survival of the species. This review provides an overview of established and emerging functions of Plg-RKT and highlights major roles for Plg-RKT in both the initiation and resolution of inflammation. While the roles for Plg-RKT in the inflammatory response are predominantly plasmin(ogen)-dependent, its role in lactation requires both plasminogen-dependent and plasminogen-independent mechanisms. Furthermore, the functions of Plg-RKT are dependent on sex. In view of the broad tissue distribution of Plg-RKT , its role in a broad array of physiological and pathological processes should provide a fruitful area for future investigation.

Critical role and its underlying molecular events of the plasminogen receptor, S100A10 in malignant tumor and non-tumor diseases

S100A10 is a small molecular weight protein expressed in the cytoplasm of many cells and one of the members of the S100 protein family that binds calcium and forms the largest subgroup of EF-hand proteins. The regulatory processes of S100A10 are complicated. S100A10 participates in the regulation of a variety of tumor and non-tumor diseases through cascade reactions with multitudinous signaling molecules. In malignant tumors, such as acute promyelocytic leukemia (APL) and lung cancer, S100A10 is likely involved in their progression, including invasion and metastasis through the regulation of plasmin production and subsequent plasmin-dependent stimulation of other proteases, such as matrix metalloproteinase (MMP)-2 and -9. Both the plasmin and MMPs are capable of inducing degradation of the extracellular matrix (ECM) and basement membrane, which is a critical step for tumor progression. In non-tumor diseases, the distribution of S100A10 in the brain and its interaction with 5-hydroxytryptamine 1B (5-HT1B) receptor, an important mediator in the central nervous system that maintains a dynamic balance of the neurotransmitters, correlates with depression-like behavior. S100A10 also participates in inflammatory responses through the regulation of peripheral macrophage migration to the inflammatory sites, which depends on the generation of plasmin and other proteinases at the surface of macrophages. Considerable attention should be paid to understand the significant role of S100A10 in the modulation of malignant tumor and non-tumor diseases.

P11 Loss-of-Function is Associated with Decreased Cell Proliferation and Neurobehavioral Disorders in Mice

Although depression is associated with anxiety and memory deficit in humans, the molecular mechanisms of the complication remain largely unknown. In this study, we generated P11 knockout mice using CRISPR/Cas9 technology, as well as P11 knockout MEF cell lines, and confirmed depression-like phenotype. We observed that knockout of P11 in MEFs led to a decreased cell proliferation compared with P11+/+ MEFs. Moreover, P11 knockout resulted in a larger cell size, which resulted probably from accumulated F-actin stress fibers. The number of proliferating cells was decreased in the hippocampus of P11 KO mice. We observed anxiety-like disorder in addition to depression phenotype in the knockout mice. In addition, knockout of P11 led to memory deficit in female mice, but not in males. These data indicated that P11 is involved in regulating cell proliferation and cell size. The molecular associations of depression behavior with anxiety and memory deficit suggested a potential approach to improve therapeutic intervention through P11 in these disorders.

Cell surface protease activation during RAS transformation: Critical role of the plasminogen receptor, S100A10

The link between oncogenic RAS expression and the acquisition of the invasive phenotype has been attributed to alterations in cellular activities that control degradation of the extracellular matrix. Oncogenic RAS-mediated upregulation of matrix metalloproteinase 2 (MMP-2), MMP-9 and urokinase-type plasminogen activator (uPA) is critical for invasion through the basement membrane and extracellular matrix. The uPA converts cell surface-bound plasminogen to plasmin, a process that is regulated by the binding of plasminogen to specific receptors on the cell surface, however, the identity of the plasminogen receptors that function in this capacity is unclear. We have observed that transformation of cancer cells with oncogenic forms of RAS increases plasmin proteolytic activity by 2- to 4-fold concomitant with a 3-fold increase in cell invasion. Plasminogen receptor profiling revealed RAS-dependent increases in both S100A10 and cytokeratin 8. Oncogenic RAS expression increased S100A10 gene expression which resulted in an increase in S100A10 protein levels. Analysis with the RAS effector-loop mutants that interact specifically with Raf, Ral GDS pathways highlighted the importance of the RalGDS pathways in the regulation of S100A10 gene expression. Depletion of S100A10 from RAS-transformed cells resulted in a loss of both cellular plasmin generation and invasiveness. These results strongly suggest that increases in cell surface levels of S100A10, by oncogenic RAS, plays a critical role in RAS-stimulated plasmin generation, and subsequently, in the invasiveness of oncogenic RAS expressing cancer cells.

Genetic variations in the p11/tPA/BDNF pathway are associated with post stroke depression

BACKGROUND

The effects of BDNF on post stroke depression (PSD) may be influenced by genetic variations in intracellular signal transduction pathways, such as the p11/tPA/BDNF pathway. In this study, we aimed to determine the association of polymorphisms in candidate genes of the gene transduction pathway with PSD, as well as the effects of the interactions between genes in our Chinese sample.

METHODS

Two-hundred-fifty-four Chinese samples with acute ischaemic stroke included 122 PSD patients and 132 nonPSD patients. Sixty-five single nucleotide polymorphisms (SNPs) in six genes (p11, tPA, PAI-1, BDNF, TrkB and p75NTR) of the p11/tPA/BDNF pathway with minor allele frequencies > 5% were successfully genotyped from an initial series of 76 SNPs. The severity of depressive symptoms was assessed by the 17-item Hamilton Depression Rating scale score. Environmental factors were measured with the life events scale and social support rating scale for all patients. SNP and haplotype associations were analysed using gPLINK software. Gene-gene interactions were evaluated with generalized multifactor dimensionality reduction software.

RESULTS

The results showed that TrkB polymorphisms (rs11140793AC genotype, rs7047042CG genotype, rs1221CT genotype, rs2277193TC genotype and rs2277192AG genotype) were significantly associated with PSD. Three haplotypes (AT, GG, and AAT) of TrkB were significantly associated with PSD. Seven haplotypes (GC, AG, ACG, CGC, GCT, ACGC and ACAT) of BDNF were significantly correlated with PSD. We identified significant gene-gene interactions between the p11 (rs11204922 SNP), tPA (rs8178895, rs2020918 SNPs) and BDNF (rs6265, rs2049046, rs16917271, rs727155 SNPs) genes in the PSD group. We also identified significant gene-gene interactions between the BDNF (rs2049046, rs7931247 SNPs) and TrkB (rs7816 SNP) genes with increased occurrence of PSD and sig gene-gene interactions between the BDNF gene (rs6265, rs56164415, rs2049046, rs4923468, rs2883187, rs16917271, rs1491850, rs727155, rs2049048 SNPs) and p75NTR gene (rs2072446, rs11466155) in the PSD group.

CONCLUSION

These findings provides evidence that the TrkB gene, BDNF and TrkB haplotypes, and gene-gene interactions between p11, tPA and BDNF are all associated with PSD, which suggests that genetic variations in the p11/tPA/BDNF pathway may play a central role in regulating the underlying mechanism of PSD.

Activation of tissue plasminogen activator by metastasis-inducing S100P protein

S100P protein in human breast cancer cells is associated with reduced patient survival and, in a model system of metastasis, it confers a metastatic phenotype upon benign mammary tumour cells. S100P protein possesses a C-terminal lysine residue. Using a multiwell in vitro assay, S100P is now shown for the first time to exhibit a strong, C-terminal lysine-dependent activation of tissue plasminogen activator (tPA), but not of urokinase-catalysed plasminogen activation. The presence of 10 μM calcium ions stimulates tPA activation of plasminogen 2-fold in an S100P-dependent manner. S100P physically interacts with both plasminogen and tPA in vitro, but not with urokinase. Cells constitutively expressing S100P exhibit detectable S100P protein on the cell surface, and S100P-containing cells show enhanced activation of plasminogen compared with S100P-negative control cells. S100P shows C-terminal lysine-dependent enhancement of cell invasion. An S100P antibody, when added to the culture medium, reduced the rate of invasion of wild-type S100P-expressing cells, but not of cells expressing mutant S100P proteins lacking the C-terminal lysine, suggesting that S100P functions outside the cell. The protease inhibitors, aprotinin or α-2-antiplasmin, reduced the invasion of S100P-expressing cells, but not of S100P-negative control cells, nor cells expressing S100P protein lacking the C-terminal lysine. It is proposed that activation of tPA via the C-terminal lysine of S100P contributes to the enhancement of cell invasion by S100P and thus potentially to its metastasis-promoting activity.

Mechanism of plasmin generation by S100A10

Plasminogen (Pg) is cleaved to form plasmin by the action of specific plasminogen activators such as the tissue plasminogen activator (tPA). Although the interaction of tPA and Pg with the surface of the fibrin clot has been well characterised, their interaction with cell surface Pg receptors is poorly understood. S100A10 is a cell surface Pg receptor that plays a key role in cellular plasmin generation. In the present report, we have utilised domain-switched/deleted variants of tPA, truncated plasminogen variants and S100A10 site-directed mutant proteins to define the regions responsible for S100A10-dependent plasmin generation. In contrast to the established role of the finger domain of tPA in fibrin-stimulated plasmin generation, we show that the kringle-2 domain of tPA plays a key role in S100A10-dependent plasmin generation. The kringle-1 domain of plasminogen, indispensable for fibrin-binding, is also critical for S100A10-dependent plasmin generation. S100A10 retains activity after substitution or deletion of the carboxyl-terminal lysine suggesting that internal lysine residues contribute to its plasmin generating activity. These studies define a new paradigm for plasminogen activation by the plasminogen receptor, S100A10.

Plasminogen-receptor KT : plasminogen activation and beyond

The cell surface orchestrates plasminogen activation through the concomitant binding of plasminogen and plasminogen activators to specific receptors. In this issue, Miles and colleagues describe their detailed phenotypic characterization of mice deficient in Plg-RKT, a key plasminogen receptor expressed in numerous tissues, but highly expressed by proinflammatory macrophages. The analysis provides critical and surprising new insights into the biology of this receptor.

WOMEN IN CANCER THEMATIC REVIEW: Ovarian cancer-peritoneal cell interactions promote extracellular matrix processing

Ovarian cancer has a distinct tendency for metastasising via shedding of cancerous cells into the peritoneal cavity and implanting onto the peritoneum that lines the pelvic organs. Once ovarian cancer cells adhere to the peritoneal cells, they migrate through the peritoneal layer and invade the local organs. Alterations in the extracellular environment are critical for tumour initiation, progression and intra-peritoneal dissemination. To increase our understanding of the molecular mechanisms involved in ovarian cancer metastasis and to identify novel therapeutic targets, we recently studied the interaction of ovarian cancer and peritoneal cells using a proteomic approach. We identified several extracellular matrix (ECM) proteins including, fibronectin, TGFBI, periostin, annexin A2 and PAI-1 that were processed as a result of the ovarian cancer-peritoneal cell interaction. This review focuses on the functional role of these proteins in ovarian cancer metastasis. Our findings together with published literature support the notion that ECM processing via the plasminogen-plasmin pathway promotes the colonisation and attachment of ovarian cancer cells to the peritoneum and actively contributes to the early steps of ovarian cancer metastasis.

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.

Biological characteristics of a novel giant cell tumor cell line derived from spine

Giant cell tumor of bone(GCTB) is a special bone tumor for it consists of various cell types, and its biological characteristics is different from common benign or malignant neoplasm. In the present study, we report the biological features of a primary Asian GCTB cell line named GCTB28. We analyzed extensive properties of the GCTB28 cells including morphological observations, growth, cell cycle, karyotype, proliferation, proteins expression, surface biomarker verification, and tumorigenicity in nude mice. We found that the stromal cells of GCTB were endowed with self-renewal capacity and played dominant roles in GCTB development. Moreover, we confirmed that GCTB cells can be CD33(-)CD14(-) phenotype which was not in accord with previous study. This study provides an in vitro model system to investigate pathogenic mechanisms and molecular characteristics of GCTB and also provides a useful tool for researching the therapeutic targeting of GCTB.

Cell surface interaction of annexin A2 and galectin-3 modulates epidermal growth factor receptor signaling in Her-2 negative breast cancer cells

Overexpression and activation of tyrosine kinase receptors like EGFR and Src regulate the progression and metastasis of Her-2 negative breast cancer. Recently we have reported the role of cell membrane interaction of phospholipid-binding protein annexin A2 (AnxA2) and EGFR in regulating cellular signaling in the activation of angiogenesis, matrix degradation, invasion, and cancer metastasis. Beta-galactoside-specific animal lectin galectin-3 is an apoptosis inhibitor, and cell surface-associated extracellular galectin-3 also has a role in cell migration, cancer progression, and metastasis. Similar expression pattern and membrane co-localization of these two proteins made us to hypothesize in the current study that galectin-3 and AnxA2 interaction is critical for Her-2 negative breast cancer progression. By various experimental analyses, we confirm that glycosylated AnxA2 at the membrane surface interacts with galectin-3. N-linked glycosylation inhibitor tunicamycin treatment convincingly blocked AnxA2 membrane translocation and its association with galectin-3. To analyze whether this interaction has any functional relevance, we tried to dissociate this interaction with purified plant lectin from chickpea (Cicer arietinum agglutinin). This highly specific 30 kDa plant lectin could dissociate AnxA2 from endogenous lectin galectin-3 interaction at the cell surface. This dissociation could down-regulate Bcl-2 family proteins, cell proliferation, and migration simultaneously triggering cell apoptosis. Targeting this interaction of membrane surface glycoprotein and its animal lectin in Her-2 negative breast cancer may be of therapeutic value.

Exploitation of plasmin(ogen) by bacterial pathogens of veterinary significance

The plasminogen (Plg) system plays an important homeostatic role in the degradation of fibrin clots, extracellular matrices and tissue barriers important for cellular migration, as well as the promotion of neurotransmitter release. Plg circulates in plasma at physiologically high concentrations (150-200μg ml(-1)) as an inactive proenzyme. Proteins enriched in lysine and other positively charged residues (histidine and arginine) as well as glycosaminoglycans and gangliosides bind Plg. The binding interaction initiates a structural adjustment to the bound Plg that facilitates cleavage by proteases (plasminogen activators tPA and uPA) that activate Plg to the active serine protease plasmin. Both pathogenic and commensal bacteria capture Plg onto their cell surface and promote its conversion to plasmin. Many microbial Plg-binding proteins have been described underpinning the importance this process plays in how bacteria interact with their hosts. Bacteria exploit the proteolytic capabilities of plasmin by (i) targeting the mammalian fibrinolytic system and degrading fibrin clots, (ii) remodeling the extracellular matrix and generating bioactive cleavage fragments of the ECM that influence signaling pathways, (iii) activating matrix metalloproteinases that assist in the destruction of tissue barriers and promote microbial metastasis and (iv) destroying immune effector molecules. There has been little focus on the exploitation of the fibrinolytic system by veterinary pathogens. Here we describe several pathogens of veterinary significance that possess adhesins that bind plasmin(ogen) onto their cell surface and promote its activation to plasmin. Cumulative data suggests that these attributes provide pathogenic and commensal bacteria with a means to colonize and persist within the host environment.

Acute Administration of Branched-Chain Amino Acids Increases the Pro-BDNF/Total-BDNF Ratio in the Rat Brain

Maple syrup urine disease (MSUD) is caused by an inborn error in metabolism resulting from a deficiency in the branched-chain α-keto acid dehydrogenase complex activity. This blockage leads to accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine and valine, as well as their corresponding α-keto acids and α-hydroxy acids. High levels of BCAAs are associated with neurological dysfunction and the role of pro- and mature brain-derived neurotrophic factor (BDNF) in the neurological dysfunction of MSUD is still unclear. Thus, in the present study we investigated the effect of an acute BCAA pool administration on BDNF levels and on the pro-BDNF cleavage-related proteins S100A10 and tissue plasminogen activator (tPA) in rat brains. Our results demonstrated that acute Hyper-BCAA (H-BCAA) exposure during the early postnatal period increases pro-BDNF and total-BDNF levels in the hippocampus and striatum. Moreover, tPA levels were significantly decreased, without modifications in the tPA transcript levels in the hippocampus and striatum. On the other hand, the S100A10 mRNA and S100A10 protein levels were not changed in the hippocampus and striatum. In the 30-day-old rats, we observed increased pro-BDNF, total-BDNF and tPA levels only in the striatum, whereas the tPA and S100A10 mRNA expression and the immunocontent of S100A10 were not altered. In conclusion, we demonstrated that acute H-BCAA administration increases the pro-BDNF/total-BDNF ratio and decreases the tPA levels in animals, suggesting that the BCAA effect may depend, at least in part, on changes in BDNF post-translational processing.

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.

On the contribution of S100A10 and annexin A2 to plasminogen activation and oncogenesis: an enduring ambiguity

ABSTRACT 

Plasminogen receptors are becoming increasingly relevant in regulating many diseases such as cancer, stroke and inflammation. However, controversy has emerged concerning the putative role of some receptors, in particular annexin A2, in binding plasminogen. Several reports failed to account for the effects of annexin A2 on the stability and conformation of its binding partner S100A10. This has created an enduring ambiguity as to the actual function of annexin A2 in plasmin regulation. Supported by a long line of evidence, we conclude that S100A10, and not annexin A2, is the primary plasminogen receptor within the annexin A2-S100A10 complex and contributes to the plasmin-mediated effects that were originally ascribed to annexin A2.

Pivotal role of tissue plasminogen activator in the mechanism of action of electroconvulsive therapy

Electroconvulsive therapy is an important treatment option for major depressive disorders, acute mania, mood disorders with psychotic features, and catatonia. Several hypotheses have been proposed as electroconvulsive therapy's mechanism of action. Our hypothesis involves many converging pathways facilitated by increased synthesis and release of tissue-plasminogen activator. Human and animal experiments have shown that tissue-plasminogen activator participates in many mechanisms of action of electroconvulsive therapy or its animal variant, electroconvulsive stimulus, including improved N-methyl-D-aspartate receptor-mediated signaling, activation of both brain-derived neurotrophic factor and vascular endothelial growth factor, increased bioavailability of zinc, purinergic release, and increased mobility of dendritic spines. As a result, tissue-plasminogen activator helps promote neurogenesis in limbic structures, modulates synaptic transmission and plasticity, improves cognitive function, and mediates antidepressant effects. Notably, electroconvulsive therapy seems to influence tissue-plasminogen activator metabolism. For example, electroconvulsive stimulus increases the expression of glutamate decarboxylase 65 isoform in γ-aminobutyric acid-releasing neurons, which enhances the release of tissue-plasminogen activator, and the expression of p11, a protein involved in plasminogen and tissue-plasminogen activator assembling. This paper reviews how electroconvulsive therapy correlates with tissue-plasminogen activator. We suggest that interventions aiming at increasing tissue-plasminogen activator levels or its bioavailability - such as daily aerobic exercises together with a carbohydrate-restricted diet, or normalization of homocysteine levels - be evaluated in controlled studies assessing response and remission duration in patients who undergo electroconvulsive therapy.

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

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

New insights into the role of Plg-RKT in macrophage recruitment

Plasminogen (PLG) is the zymogen of plasmin, the major enzyme that degrades fibrin clots. In addition to its binding and activation on fibrin clots, PLG also specifically interacts with cell surfaces where it is more efficiently activated by PLG activators, compared with the reaction in solution. This results in association of the broad-spectrum proteolytic activity of plasmin with cell surfaces that functions to promote cell migration. Here, we review emerging data establishing a role for PLG, plasminogen receptors and the newly discovered plasminogen receptor, Plg-RKT, in macrophage recruitment in the inflammatory response, and we address mechanisms by which the interplay between PLG and its receptors regulates inflammation.

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.

Ceramide 1-phosphate mediates endothelial cell invasion via the annexin a2-p11 heterotetrameric protein complex

The bioactive sphingolipid, ceramide 1-phosphate (C-1-P), has been implicated as an extracellular chemotactic agent directing cellular migration in hematopoietic stem/progenitor cells and macrophages. However, interacting proteins that could mediate these actions of C-1-P have, thus far, eluded identification. We have now identified and characterized interactions between ceramide 1-phosphate and the annexin a2-p11 heterotetramer constituents. This C-1-P-receptor complex is capable of facilitating cellular invasion. Herein, we demonstrate in both coronary artery macrovascular endothelial cells and retinal microvascular endothelial cells that C-1-P induces invasion through an extracellular matrix barrier. By employing surface plasmon resonance, lipid-binding ELISA, and mass spectrometry technologies, we have demonstrated that the heterotetramer constituents bind to C-1-P. Although the annexin a2-p11 heterotetramer constituents do not bind the lipid C-1-P exclusively, other structurally similar lipids, such as phosphatidylserine, sphingosine 1-phosphate, and phosphatidic acid, could not elicit the potent chemotactic stimulation observed with C-1-P. Further, we show that siRNA-mediated knockdown of either annexin a2 or p11 protein significantly inhibits C-1-P-directed invasion, indicating that the heterotetrameric complex is required for C-1-P-mediated chemotaxis. These results imply that extracellular C-1-P, acting through the extracellular annexin a2-p11 heterotetrameric protein, can mediate vascular endothelial cell invasion.

Plasminogen receptors: the first quarter century

The interaction of plasminogen with cell surfaces results in promotion of plasmin formation and retention on the cell surface. This results in arming cell surfaces with the broad-spectrum proteolytic activity of plasmin. Over the past quarter century, key functional consequences of the association of plasmin with the cell surface have been elucidated. Physiologic and pathophysiologic processes with plasmin-dependent cell migration as a central feature include inflammation, wound healing, oncogenesis, metastasis, myogenesis, and muscle regeneration. Cell surface plasmin also participates in neurite outgrowth and prohormone processing. Furthermore, plasmin-induced cell signaling also affects the functions of inflammatory cells, via production of cytokines, reactive oxygen species, and other mediators. Finally, plasminogen receptors regulate fibrinolysis. In this review, we highlight emerging data that shed light on longstanding controversies and raise new issues in the field. We focus on (1) the impact of the recent X-ray crystal structures of plasminogen and the development of antibodies that recognize cell-induced conformational changes in plasminogen on our understanding of the interaction of plasminogen with cells; (2) the relationship between apoptosis and plasminogen binding to cells; (3) the current status of our understanding of the molecular identity of plasminogen receptors and the discovery of a structurally unique novel plasminogen receptor, Plg-RKT; (4) the determinants of the interplay between distinct plasminogen receptors and cellular functions; and (5) new insights into the role of colocalization of plasminogen and plasminogen activator receptors on the cell surface.

Annexin A2 is a discriminative serological candidate in early hepatocellular carcinoma

To date, the useful markers of hepatocellular carcinoma (HCC) remains incompletely developed. Here, we show that annexin A2 complement alpha-fetoprotein (AFP), a widely used liver cancer marker, in the serologically surveillance and early detection of HCC. First, differentially expressed proteins in HCC were identified using a subcellular proteomic approach. Annexin A2 was then selected for further verification. It was found to be overexpressed in HCC tissues (60.7%, 136/224). Using a self-estabished sandwich enzyme-linked immunosorbent assay, we found that annexin A2 significantly increased in the sera of HCC (n = 175, median, 24.75ng/µl) compared with the healthy (n = 49, median, 16.69ng/µl), benign tumors (n = 19, median, 19.92ng/µl), hepatitis (n = 23, median, 6.48ng/µl) and cirrhosis (n = 51, median, 7.39ng/µl) controls and other malignant tumors (n = 87). Importantly, raised concentrations of annexin A2 were observed in 83.2% (79/95) of early stage (median, 24.32ng/µl) and 78.4% (58/74) of AFP-negative (median, 24.09ng/µl) patients. Annexin A2 alone had a better area under the receiver-operating characteristic curve (AUC = 0.79, 95% confidence interval: 0.73–0.85) in comparison with AFP (AUC = 0.73, 95% confidence interval: 0.66–0.80) in detecting of early stage HCC. Combining both markers notably improved the diagnostic efficiency of early HCC with an achieved sensitivity of 87.4%. Additionally, the expression characteristics of annexin A2 during hepatocarcinogenesis were detected in p21-HBx gene knockin transgenic mice model. The results showed that annexin A2 expression was substantially elevated in HCC-bearing mice, in accordance with the finding in human samples. In conclusion, annexin A2 may be an independent serological candidate for hepatitis B virus–related HCC, especially in the early stage cases with normal serum AFP.

α-Enolase, a multifunctional protein: its role on pathophysiological situations

α-Enolase is a key glycolytic enzyme in the cytoplasm of prokaryotic and eukaryotic cells and is considered a multifunctional protein. α-enolase is expressed on the surface of several cell types, where it acts as a plasminogen receptor, concentrating proteolytic plasmin activity on the cell surface. In addition to glycolytic enzyme and plasminogen receptor functions, α-Enolase appears to have other cellular functions and subcellular localizations that are distinct from its well-established function in glycolysis. Furthermore, differential expression of α-enolase has been related to several pathologies, such as cancer, Alzheimer's disease, and rheumatoid arthritis, among others. We have identified α-enolase as a plasminogen receptor in several cell types. In particular, we have analyzed its role in myogenesis, as an example of extracellular remodelling process. We have shown that α-enolase is expressed on the cell surface of differentiating myocytes, and that inhibitors of α-enolase/plasminogen binding block myogenic fusion in vitro and skeletal muscle regeneration in mice. α-Enolase could be considered as a marker of pathological stress in a high number of diseases, performing several of its multiple functions, mainly as plasminogen receptor. This paper is focused on the multiple roles of the α-enolase/plasminogen axis, related to several pathologies.

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.

Bacterial plasminogen receptors utilize host plasminogen system for effective invasion and dissemination

In order for invasive pathogens to migrate beyond the site of infection, host physiological barriers such as the extracellular matrix, the basement membrane, and encapsulating fibrin network must be degraded. To circumvent these impediments, proteolytic enzymes facilitate the dissemination of the microorganism. Recruitment of host proteases to the bacterial surface represents a particularly effective mechanism for enhancing invasiveness. Plasmin is a broad spectrum serine protease that degrades fibrin, extracellular matrices, and connective tissue. A large number of pathogens express plasminogen receptors which immobilize plasmin(ogen) on the bacterial surface. Surface-bound plasminogen is then activated by plasminogen activators to plasmin through limited proteolysis thus triggering the development of a proteolytic surface on the bacteria and eventually assisting the spread of bacteria. The host hemostatic system plays an important role in systemic infection. The interplay between hemostatic processes such as coagulation and fibrinolysis and the inflammatory response constitutes essential components of host defense and bacterial invasion. The goal of this paper is to highlight mechanisms whereby pathogenic bacteria, by engaging surface receptors, utilize and exploit the host plasminogen and fibrinolytic system for the successful dissemination within the host.

The plasminogen activation system and the regulation of catecholaminergic function

The local environment of neurosecretory cells contains the major components of the plasminogen activation system, including the plasminogen activators, tissue plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA), as well as binding sites for t-PA, the receptor for u-PA (uPAR), and also the plasminogen activator inhibitor, PAI-1. Furthermore, these cells express specific binding sites for plasminogen, which is available in the circulation and in interstitial fluid. Colocalization of plasminogen and its activators on cell surfaces provides a mechanism for promoting local plasminogen activation. Plasmin is retained on the cell surface where it is protected from its inhibitor, α₂-antiplasmin. In neurosecretory cells, localized plasmin activity provides a mechanism for extracellular processing of secreted hormones. Neurotransmitter release from catecholaminergic cells is negatively regulated by cleavage products formed by plasmin-mediated proteolysis. Recently, we have identified a major plasminogen receptor, Plg-R_KT. We have found that Plg-R_KT is highly expressed in chromaffin cells of the adrenal medulla as well as in other catecholaminergic cells and tissues. Plg-R_KT-dependent plasminogen activation plays a key role in regulating catecholaminergic neurosecretory cell function.

Reciprocal regulation of annexin A2 and EGFR with Her-2 in Her-2 negative and herceptin-resistant breast cancer

Alternative survival pathways are commonly seen to be upregulated upon inhibition of receptor tyrosine kinases (RTK), including Her-2. It is established that treatment with Herceptin leads to selective overexpression and activation of epidermal growth factor receptor (EGFR) and Src which further contributes to oncogenesis in Herceptin resistant and triple negative breast cancer (TNBC) patients. Here, we show a co-regulated upregulation in the expression of Annexin A2 (AnxA2), a known substrate of Src and one of the regulators of EGFR receptor endocytosis, in Herceptin resistant and Her-2 negative breast cancer. Immunohistochemical expression analysis revealed a reciprocal regulation between Her-2 and AnxA2 in breast cancer clinical samples as well as in cell lines as confirmed by protein and RNA analysis. The siRNA and Herceptin mediated downregulation/inhibition of Her-2 in Her-2 amplified cells induced AnxA2 expression and membrane translocation. In this study we report a possible involvement of AnxA2 in maintaining constitutively activated EGFR downstream signaling intermediates and hence in cell proliferation, migration and viability. This effect was consistent in Herceptin resistant JIMT-1 cells as well as in Her-2 negative breast cancer. The siRNA mediated AnxA2 downregulation leads to increased apoptosis, decreased cell viability and migration. Our studies further indicate the role of AnxA2 in EGFR-Src membrane bound signaling complex and ligand induced activation of downstream signaling pathways. Targeting this AnxA2 dependent positive regulation of EGFR signaling cascade may be of therapeutic value in Her-2 negative breast cancer.

Recruitment and membrane interactions of host cell proteins during attachment of enteropathogenic and enterohaemorrhagic Escherichia coli

EPEC (enteropathogenic Escherichia coli) and EHEC (enterohaemorrhagic Escherichia coli) are attaching and effacing pathogens frequently associated with infectious diarrhoea. EPEC and EHEC use a T3SS (type III secretion system) to translocate effectors that subvert different cellular processes to sustain colonization and multiplication. The eukaryotic proteins NHERF2 (Na(+)/H(+) exchanger regulatory factor 2) and AnxA2 (annexin A2), which are involved in regulation of intestinal ion channels, are recruited to the bacterial attachment sites. Using a stable HeLa-NHERF2 cell line, we found partial co-localization of AnxA2 and NHERF2; in EPEC-infected cells, AnxA2 and NHERF2 were extensively recruited to the site of bacterial attachment. We confirmed that NHERF2 dimerizes and found that NHERF2 interacts with AnxA2. Moreover, we found that AnxA2 also binds both the N- and C-terminal domains of the bacterial effector Tir through its C-terminal domain. Immunofluorescence of HeLa cells infected with EPEC showed that AnxA2 is recruited to the site of bacterial attachment in a Tir-dependent manner, but independently of Tir-induced actin polymerization. Our results suggest that AnxA2 and NHERF2 form a scaffold complex that links adjacent Tir molecules at the plasma membrane forming a lattice that could be involved in retention and dissemination of other effectors at the bacterial attachment site.

Gene expression profile of coronary artery cells treated with nonsteroidal anti-inflammatory drugs reveals off-target effects

Nonsteroidal anti-inflammatory drugs (NSAIDs) have come under scrutiny because of the gastrointestinal, renal, and cardiovascular toxicity associated with prolonged use of these drugs. The purpose of this study was to identify molecular targets for NSAIDs related to cellular toxicity with a view to optimize drug efficacy in the clinic. Coronary artery smooth muscle cells and endothelial cells were treated with low (clinically achievable) and high (typically used in preclinical studies) concentrations of celecoxib, NS398, and ibuprofen for 24 hours. NSAIDs-induced gene expression changes were evaluated by microarray analysis and validated by real-time reverse-transcription polymerase chain reaction and western blotting. The functional significance of differentially expressed genes was evaluated by Ingenuity Pathway Analysis. At high concentrations, NSAIDs altered the expression of genes regulating cell proliferation and cell death. NSAIDs also altered genes associated with cardiovascular functions including inflammation, thrombosis, fibrinolysis, coronary artery disease, and hypertension. The gene expression was most impacted by ibuprofen, celecoxib, and NS398, in that order. This study revealed that NSAIDs altered expression of an array of genes associated with cardiovascular events and emphasizes the potential for fingerprinting drugs in preclinical studies to assess the potential drug toxicity and to optimize the drug efficacy in clinical settings.

The role of the annexin A2 heterotetramer in vascular fibrinolysis

The vascular endothelial cells line the inner surface of blood vessels and function to maintain blood fluidity by producing the protease plasmin that removes blood clots from the vasculature, a process called fibrinolysis. Plasminogen receptors play a central role in the regulation of plasmin activity. The protein complex annexin A2 heterotetramer (AIIt) is an important plasminogen receptor at the surface of the endothelial cell. AIIt is composed of 2 molecules of annexin A2 (ANXA2) bound together by a dimer of the protein S100A10. Recent work performed by our laboratory allowed us to clarify the specific roles played by ANXA2 and S100A10 subunits within the AIIt complex, which has been the subject of debate for many years. The ANXA2 subunit of AIIt functions to stabilize and anchor S100A10 to the plasma membrane, whereas the S100A10 subunit initiates the fibrinolytic cascade by colocalizing with the urokinase type plasminogen activator and receptor complex and also providing a common binding site for both tissue-type plasminogen activator and plasminogen via its C-terminal lysine residue. The AIIt mediated colocalization of the plasminogen activators with plasminogen results in the rapid and localized generation of plasmin to the endothelial cell surface, thereby regulating fibrinolysis.

Regulation of fibrinolysis by S100A10 in vivo

Endothelial cells form the inner lining of vascular networks and maintain blood fluidity by inhibiting blood coagulation and promoting blood clot dissolution (fibrinolysis). Plasmin, the primary fibrinolytic enzyme, is generated by the cleavage of the plasma protein, plasminogen, by its activator, tissue plasminogen activator. This reaction is regulated by plasminogen receptors at the surface of the vascular endothelial cells. Previous studies have identified the plasminogen receptor protein S100A10 as a key regulator of plasmin generation by cancer cells and macrophages. Here we examine the role of S100A10 and its annexin A2 binding partner in endothelial cell function using a homozygous S100A10-null mouse. Compared with wild-type mice, S100A10-null mice displayed increased deposition of fibrin in the vasculature and reduced clearance of batroxobin-induced vascular thrombi, suggesting a role for S100A10 in fibrinolysis in vivo. Compared with wild-type cells, endothelial cells from S100A10-null mice demonstrated a 40% reduction in plasminogen binding and plasmin generation in vitro. Furthermore, S100A10-deficient endothelial cells demonstrated impaired neovascularization of Matrigel plugs in vivo, suggesting a role for S100A10 in angiogenesis. These results establish an important role for S100A10 in the regulation of fibrinolysis and angiogenesis in vivo, suggesting S100A10 plays a critical role in endothelial cell function.

Regulation of S100A10 by the PML-RAR-α oncoprotein

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia that results from the expression of the promyelocytic leukemia–retinoic acid receptor α (PML-RAR-α) oncoprotein. It is characterized by severe hemorrhagic complications due in part to excessive fibrinolysis, resulting from the excessive generation of the fibrinolytic enzyme, plasmin, at the cell surface of the PML cells. The treatment of patients with all-trans retinoic acid (ATRA) effectively ameliorates the disease by promoting the destruction of the PML-RAR-α oncoprotein. In the present study we show for the first time that the plasminogen receptor, S100A10, is present on the extracellular surface of APL cells and is rapidly down-regulated in response to all-trans retinoic acid. The loss of S100A10 is concomitant with a loss in fibrinolytic activity. Furthermore, the induced expression of the PML-RAR-α oncoprotein increased the expression of cell surface S100A10 and also caused a dramatic increase in fibrinolytic activity. Depletion of S100A10 by RNA interference effectively blocked the enhanced fibrinolytic activity observed after induction of the PML-RAR-α oncoprotein. These experiments show that S100A10 plays a crucial role in the generation of plasmin leading to fibrinolysis, thus providing a link to the clinical hemorrhagic phenotype of APL.

The role of annexin A2 in tumorigenesis and cancer progression

Annexin A2 is a calcium-dependent, phospholipid-binding protein found on various cell types. It is up-regulated in various tumor types and plays multiple roles in regulating cellular functions, including angiogenesis, proliferation, apoptosis, cell migration, invasion and adhesion. Annexin A2 binds with plasminogen and tissue plasminogen activator on the cell surface, which leads to the conversion of plasminogen to plasmin. Plasmin is a serine protease which plays a key role in the activation of metalloproteinases and degradation of extracellular matrix components essential for metastatic progression. We have recently found that both annexin A2 and plasmin are increased in conditioned media of co cultured ovarian cancer and peritoneal cells. Our studies suggest that annexin A2 is part of a tumor-host signal pathway between ovarian cancer and peritoneal cells which promotes ovarian cancer metastasis. Accumulating evidence suggest that interactions between annexin A2 and its binding proteins play an important role in the tumor microenvironment and act together to enhance cancer metastasis. This article reviews the current knowledge on the biological role of annexin A2 and its binding proteins in solid malignancies including ovarian cancer.