Annexin II up-regulates cellular levels of p11 protein by a post-translational mechanisms

BRD4L cooperates with MYC to block local tumor invasion via suppression of S100A10

Targeted therapy based on BRD4 and MYC shows promise due to their well-researched oncogenic functions in cancer, but their tumor-suppressive roles are less understood. In this study, we employ a systematic approach to delete exons that encode the low-complexity domain (LCD) of BRD4L in cells by using CRISPR-Cas9. In particular, the deletion of exon 14 (BRD4-E14) results in cellular morphological changes towards spindle-shaped and loosely packed. BRD4-E14 deficient cells show increased cell migration and reduced cell adhesion. The expression of S100A10 was significantly increased in cells lacking E14. BRD4L binds with MYC via the E14-encoded region of the LCD to inhibit the expression of S100A10. In cancer tissues, there is a positive correlation between BRD4 and MYC, while both of these proteins are negatively associated with S100A10 expression. Finally, knocking out the BRD4-E14 region or MYC promotes tumor growth in vivo. Together, these data support a tumor-suppressive role of BRD4L and MYC in some contexts. This discovery emphasizes the significance of a discreetly design and precise patient recruitment in clinical trials that testing cancer therapy based BRD4 and MYC.

Accumulation of annexin A2 and S100A10 prevents apoptosis of apically delaminated, transformed epithelial cells

In various epithelial tissues, the epithelial monolayer acts as a barrier. To fulfill its function, the structural integrity of the epithelium is tightly controlled. When normal epithelial cells detach from the basal substratum and delaminate into the apical lumen, the apically extruded cells undergo apoptosis, which is termed anoikis. In contrast, transformed cells often become resistant to anoikis and able to survive and grow in the apical luminal space, leading to the formation of multilayered structures, which can be observed at the early stage of carcinogenesis. However, the underlying molecular mechanisms still remain elusive. In this study, we first demonstrate that S100A10 and ANXA2 (Annexin A2) accumulate in apically extruded, transformed cells in both various cell culture systems and murine epithelial tissues in vivo. ANXA2 acts upstream of S100A10 accumulation. Knockdown of ANXA2 promotes apoptosis of apically extruded RasV12-transformed cells and suppresses the formation of multilayered epithelia. In addition, the intracellular reactive oxygen species (ROS) are elevated in apically extruded RasV12 cells. Treatment with ROS scavenger Trolox reduces the occurrence of apoptosis of apically extruded ANXA2-knockdown RasV12 cells and restores the formation of multilayered epithelia. Furthermore, ROS-mediated p38MAPK activation is observed in apically delaminated RasV12 cells, and ANXA2 knockdown further enhances the p38MAPK activity. Moreover, the p38MAPK inhibitor promotes the formation of multilayered epithelia of ANXA2-knockdown RasV12 cells. These results indicate that accumulated ANXA2 diminishes the ROS-mediated p38MAPK activation in apically extruded transformed cells, thereby blocking the induction of apoptosis. Hence, ANXA2 can be a potential therapeutic target to prevent multilayered, precancerous lesions.

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.

Advances in molecular mechanism of HPV16 E5 oncoprotein carcinogenesis

For a considerable duration, cervical cancer has posed a significant risk to the well-being and survival of women. The emergence and progression of cervical cancer have garnered extensive attention, with prolonged chronic infection of HPV serving as a crucial etiological factor. Consequently, investigating the molecular mechanism underlying HPV-induced cervical cancer has become a prominent research area. The HPV molecule is composed of a long control region (LCR), an early coding region and a late coding region.The early coding region encompasses E1, E2, E4, E5, E6, E7, while the late coding region comprises L1 and L2 ORF.The investigation into the molecular structure and function of HPV has garnered significant attention, with the aim of elucidating the carcinogenic mechanism of HPV and identifying potential targets for the treatment of cervical cancer. Research has demonstrated that the HPV gene and its encoded protein play a crucial role in the invasion and malignant transformation of host cells. Consequently, understanding the function of HPV oncoprotein is of paramount importance in comprehending the pathogenesis of cervical cancer. E6 and E7, the primary HPV oncogenic proteins, have been the subject of extensive study. Moreover, a number of contemporary investigations have demonstrated the significant involvement of HPV16 E5 oncoprotein in the malignant conversion of healthy cells through its regulation of cell proliferation, differentiation, and apoptosis via diverse pathways, albeit the precise molecular mechanism remains unclear. This manuscript aims to provide a comprehensive account of the molecular structure and life cycle of HPV.The HPV E5 oncoprotein mechanism modulates cellular processes such as proliferation, differentiation, apoptosis, and energy metabolism through its interaction with cell growth factor receptors and other cellular proteins. This mechanism is crucial for the survival, adhesion, migration, and invasion of tumor cells in the early stages of carcinogenesis. Recent studies have identified the HPV E5 oncoprotein as a promising therapeutic target for early-stage cervical cancer, thus offering a novel approach for treatment.

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.

Role of calcium-sensor proteins in cell membrane repair

Cell membrane repair is a critical process used to maintain cell integrity and survival from potentially lethal chemical, and mechanical membrane injury. Rapid increases in local calcium levels due to a membrane rupture have been widely accepted as a trigger for multiple membrane-resealing models that utilize exocytosis, endocytosis, patching, and shedding mechanisms. Calcium-sensor proteins, such as synaptotagmins (Syt), dysferlin, S100 proteins, and annexins, have all been identified to regulate, or participate in, multiple modes of membrane repair. Dysfunction of membrane repair from inefficiencies or genetic alterations in these proteins contributes to diseases such as muscular dystrophy (MD) and heart disease. The present review covers the role of some of the key calcium-sensor proteins and their involvement in membrane repair.

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.

Annexin A2 binds the internal ribosomal entry site of c-myc mRNA and regulates its translation

The expression and localization of the oncoprotein c-Myc is highly regulated at the level of transcription, mRNA transport, translation, as well as stability of the protein. We previously showed that Annexin A2 (AnxA2) binds to a specific localization element in the 3'untranslated region (UTR) of c-myc mRNA and is involved in its localization to the perinuclear region. In the present study, we demonstrate that AnxA2 binds in a Ca²⁺-dependent manner to the internal ribosomal entry site (IRES) containing two pseudo-knots in the 5´UTR of the c-myc mRNA. Here, we employ an in vitro rabbit reticulocyte lysate system with chimeric c-myc reporter mRNAs to demonstrate that binding of AnxA2 to the c-myc IRES modulates the expression of c-Myc. Notably, we show that low levels of AnxA2 appear to increase, while high levels of AnxA2 inhibits translation of the chimeric mRNA. However, when both the AnxA2-binding site and the ribosomal docking site in the c-myc IRES are deleted, AnxA2 has no effect on the translation of the reporter mRNA. Forskolin-treatment of PC12 cells results in upregulation of Ser25 phosphorylated AnxA2 expression while c-Myc expression is down-regulated. The effect of forskolin on c-Myc expression and the level of Ser25 phosphorylated AnxA2 was abolished in the presence of EGTA. These findings indicate that AnxA2 regulates both the transport and subsequent translation of the c-myc mRNA, possibly by silencing the mRNA during its transport. They also suggest that AnxA2 act as a switch to turn off the c-myc IRES activity in the presence of calcium.Abbreviations: AnxA2, Annexin A2; β₂--µglob, β₂-microglobulin; cpm, counts per minute; hnRNP, heterogenous nuclear ribonucleoprotein; IRES, internal ribosomal entry site; ITAF, IRES trans-acting factor; MM, multiple myeloma; PABP, poly(A)-binding protein; PCBP, poly(rC) binding protein; PSF, PTB-associated splicing factor; PTB, polypyrimidine tract binding protein; RRL, rabbit reticulocyte lysate; UTR, untranslated region; YB, Y-box binding protein.

High Migration and Invasion Ability of PGCCs and Their Daughter Cells Associated With the Nuclear Localization of S100A10 Modified by SUMOylation

Our previous studies have confirmed that cobalt chloride (CoCl₂) or chemoradiotherapy could induce the formation of polyploid tumor giant cells (PGCCs). Polyploid giant cancer cells are a special subpopulation of cancer cells that contribute to solid tumor heterogeneity. The size of PGCC was at least three times larger than regular diploid cancer cells. PGCCs have the properties of cancer stem cells (CSCs) and can express CSC markers CD44 and CD133. Daughter cells derived from PGCCs have strong proliferation, infiltration and migration abilities. However, the detailed molecular mechanism of daughter cells expressing mesenchymal phenotype and displaying strong abilities of proliferation and migration is unclear. As a plasminogen receptor, S100A10 which is closely associated with the invasion and metastasis of malignant tumors, was highly expressed in PGCCs with their daughter cells. In this study, CoCl₂ was used to induce the formation of PGCCs in LoVo and HCT116 CRC cells. Cell functional experiments, co-immunoprecipitation, MG132 and ginkgolic acid treatment, western blot, and ChIP-Seq were used to identify the mechanism of S100A10 nuclear location. The proliferation and migration abilities of PGCCs and their daughter cells decreased significantly after S100A10 knockdown. In the control cells, S100A10 was mainly ubiquitinated, while in PGCCs and daughter cells, S100A10 was mainly SUMOylated, which was associated with S100A10 nuclear location. After SUMO1 was inhibited, the nuclear S100A10 in PGCCs and daughter cells decreased, and their proliferation and migration abilities significantly decreased. ChIP-Seq combined with real-time fluorescent quantitative PCR showed that S100A10 regulated the expression of neutrophil defensin 3 (DEFA3), receptor-type tyrosine-protein phosphatase N2 (PTPRN2), and rho guanine nucleotide exchange factor 18 (ARHGEF18), which were associated with actin dynamics and cytoskeleton remodeling. The expression of S100A10 in the nuclei and cytoplasm of rectal cancer after neoadjuvant chemoradiation (nCRT) and liver metastases increased compared with that in rectal cancer without nCRT. Taken together, the expression and nuclear localization of S100A10 modified by SUMOylation were associated with the high proliferation and migration of PGCCs and their daughter cells, and the differentiation, metastases, and relapse of CRCs by regulating the expression of ARHGEF18, PTPRN2, and DEFA3.

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.

Molecular Mechanisms by Which S100A4 Regulates the Migration and Invasion of PGCCs With Their Daughter Cells in Human Colorectal Cancer

Recently, an increasing number of evidences have shown that polyploid giant cancer cells (PGCCs) could generate daughter cells with a strong migration and invasion ability, which have been implicated in cancer recurrence and metastasis. However, the underlying molecular mechanisms of PGCCs with their daughter cells remain largely unclear. In vitro and in vivo experiments combined with 222 cases of human colorectal cancer (CRC) samples were used to identify the molecular mechanisms of S100A4-related proteins regulating the invasion and metastasis of PGCCs with their daughter cells. PGCCs with their daughter cells had high migration, invasion, and proliferation abilities compared to control cells; these were significantly inhibited after S100A4 knockdown. The high expression of cathepsin B, cyclin B1, TRIM21, and Annexin A2 were significantly downregulated after S100A4 knockdown, while the overexpression of S100A4, cathepsin B, cyclin B1, and S100A10 were significantly downregulated after TRIM21 knockdown in PGCCs with their daughter cells. The tumorigenic and metastatic ability of PGCCs with their daughter cells in vivo was significantly stronger compared to the untreated cells, which was significantly decreased after S100A4 knockdown. Moreover, the expression of S100A4-related proteins was positively correlated with the malignancy degree of human CRC, and maintained a high level in lymph node metastasis. S100A4 and TRIM21 may regulate each other to affect the expression and subcellular localization of cyclin B1, and participate in regulating the structure and function of Annexin A2/S100A10 complex, affecting downstream cathepsin B, resulting in the invasion and metastasis of PGCCs with their daughter cells. Besides, 14-3-3 ζ/δ and Ezrin may be involved in the motility and invasion of PGCCs with their daughter cells via cytoskeletal constructions with S100A4.

Long non-coding RNA LUCAT1 promotes tumourigenesis by inhibiting ANXA2 phosphorylation in hepatocellular carcinoma

Long non‐coding RNAs (lncRNAs) play essential roles in diverse biological processes; however, current understanding of the mechanism underlying the regulation of tumour proliferation and metastasis is limited. Lung cancer‐associated transcript 1 (LUCAT1) has been reported in a variety of human cancers, while its role in hepatocellular carcinoma (HCC) remains unclear. This study aimed to determine the biological role and underlying mechanism of LUCAT1 on progression and metastasis in HCC cells and clinical specimens. Our results demonstrated that LUCAT1 was up‐regulated in HCC tissues and cells. Loss‐ and gain‐of‐function studies revealed that LUCAT1 promotes the proliferation and metastasis of HCC cells in vitro and in vivo. Furthermore, RNA pulldown and Western blot assays indicated that LUCAT1 inhibited the phosphorylation of Annexin A2 (ANXA2) to reduce the degradation of ANXA2‐S100A10 heterotetramer (AIIt), which in turn accelerated the secretion of plasminogen into plasmin, thereby resulting in the activation of metalloprotease proteins. In conclusion, we propose that LUCAT1 serves as a novel diagnostic and therapeutic target for HCC.

Regulation of cell surface protease receptor S100A10 by retinoic acid therapy in acute promyelocytic leukemia (APL)☆

S100A10 (p11), a member of the S100 family of small dimeric EF-hand-type Ca²⁺-binding proteins, plays a role in a variety of both intracellular and extracellular processes. Previous studies have suggested that p11 is intrinsically unstable and requires binding to annexin A2 (p36) to prevent its rapid ubiquitylation and degradation. Our laboratory has shown that p11 levels are stimulated by the expression of the oncoprotein, PML/RARα. Furthermore, treatment of the APL cell line, NB4 with all-trans retinoic acid (ATRA) causes the rapid loss of p36 and p11 protein. However, the mechanism by which ATRA regulates p11 levels has not been established. Here, we show that the proteasomal inhibitor, lactacystin reversed the ATRA-dependent loss of p11, but did not cause an accumulation of ubiquitylated forms of p11, suggesting that ATRA promotes the proteasomal degradation of p11 in an ubiquitin-independent manner. ATRA treatment of MCF-7 breast cancer cells reduced p11 but not p36 transcript and protein levels, thus indicating that ATRA can regulate p11 levels independently of PML/RARα and p36. Overexpression of p36 upregulated p11 protein but not mRNA levels, indicating that p36 affects p11 post translationally. The forced expression of ubiquitin and p11 in 293 T cells resulted in ubiquitylation of p11 that was blocked by mutagenesis of lysine 57. This study highlights the complex regulation of p11 by retinoid signaling and challenges the hypothesis that ubiquitin-mediated proteasomal degradation of p11 represents a universal mechanism of regulation of this protein.

Heterotetrameric annexin A2/S100A10 (A2t) is essential for oncogenic human papillomavirus trafficking and capsid disassembly, and protects virions from lysosomal degradation

Human papillomavirus (HPV) entry into epithelial cells is independent of canonical endocytic pathways. Upon interaction with host cells, HPV establishes infection by traversing through an endocytic pathway that is clathrin- and caveolin-independent, but dependent on the annexin A2/S100A10 heterotetramer (A2t). We examined the contribution of monomeric annexin A2 (AnxA2) vs. A2t in HPV infection and endocytosis, and further characterized the role of these molecules in protein trafficking. We specifically show that cell surface A2t is not required for HPV attachment, and in the absence of A2t virion internalization remains clathrin-independent. Without A2t, viral progression from early endosomes to multivesicular endosomes is significantly inhibited, capsid uncoating is dramatically reduced, and lysosomal degradation of HPV is accelerated. Furthermore, we present evidence that AnxA2 forms a complex with CD63, a known mediator of HPV trafficking. Overall, the observed reduction in infection is less significant in the absence of S100A10 alone compared to full A2t, supporting an independent role for monomeric AnxA2. More broadly, we show that successful infection by multiple oncogenic HPV types is dependent on A2t. These findings suggest that A2t is a central mediator of high-risk HPV intracellular trafficking post-entry and pre-viral uncoating.

Annexin A2 plays a critical role in epithelial ovarian cancer

PURPOSE

This study aimed at investigating the potential role and prognostic significance of Annexin A2 in human epithelial ovarian cancer (EOC).

METHODS

Western blot was used to evaluate the expression of Annexin A2 in nine fresh EOC tissues, and immunohistochemical analysis was performed on formalin-fixed paraffin-embedded sections of 119 cases of ovarian cancers. Then, we used Fisher exact test to analyze the correlation between Annexin A2 and clinicopathological parameters. Starvation refeeding was used to detect the alteration of Annexin A2 in HO8910 cell cycle.

RESULTS

Annexin A2 was overexpressed in carcinoma tissues compared with normal tissue, and the expression levels gradually increased from G1 to G3. Moreover, the staining of tissue microarray was consistent with the result we got from western blot, increasing from G1 to G3 gradually, and it was related to the Figo stage (P = 0.005), histologic grade (P = 0.002), ascite (P < 0.001), malignant tumor cells (P < 0.001), residual tumor size (P = 0.044), Ki-67 (P = 0.003). Kaplan-Meier analysis revealed that high Annexin A2 expression was significantly associated with poor prognoses of the patients (P < 0.001). Multivariate analysis demonstrated that Annexin A2 was an independent prognostic indicator for overall survival. Starvation refeeding indicated that Annexin A2 was related to EOC cell proliferation.

CONCLUSIONS

We could hypothesize that Annexin A2 acted a critical role in EOC cell proliferation, and may be used as a potential and novel therapeutic target for EOC. These data suggest that Annexin A2 may promote the progression of EOC and be a therapeutic target for EOC therapy.

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

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

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.

Dynamic reciprocity: the role of annexin A2 in tissue integrity

Interactions between cells and the extracellular matrix are integral to tissue development, remodelling and pathogenesis. This is underlined by bi-directional flow of information signalling, referred to as dynamic reciprocity. Annexin A2 is a complex and multifunctional protein that belongs to a large family of Ca(2+)-dependent anionic phospholipid and membrane-binding proteins. It has been implicated in diverse cellular processes at the nuclear, cytoplasmic and extracellular compartments including Ca(2+)-dependent regulation of endocytosis and exocytosis, focal adhesion dynamics, transcription and translation, cell proliferation, oxidative stress and apoptosis. Most of these functions are mediated by the annexin A2-S100A10 heterotetramer (AIIt) via its ability to simultaneously interact with cytoskeletal, membrane and extracellular matrix components, thereby mediating regulatory effects of extracellular matrix adhesion on cell behaviour and vice versa. While Src kinase-mediated phosphorylation of filamentous actin-bound AIIt results in membrane-cytoskeletal remodelling events which control cell polarity, cell morphology and cell migration, AIIt at the cell surface can bind to a number of extracellular matrix proteins and catalyse the activation of serine and cysteine proteases which are important in facilitating tissue remodelling during tissue repair, neoangiogenesis and pathological situations. This review will focus on the role of annexin A2 in regulating tissue integrity through intercellular and cell-extracellular matrix interaction. Annexin A2 is differentially expressed in various tissue types as well as in many pathologies, particularly in several types of cancer. These together suggest that annexin A2 acts as a central player during dynamic reciprocity in tissue homeostasis.

Forced expression of S100A10 reduces sensitivity to oxaliplatin in colorectal cancer cells

Background

Individual responses to oxaliplatin (L-OHP)-based chemotherapy remain unpredictable. Our recent proteomics studies have demonstrated that intracellular protein expression levels of S100A10 are significantly correlated with the sensitivity of colorectal cancer (CRC) cells to L-OHP, but not 5-FU, suggesting that S100A10 is a candidate predictive marker for the response to L-OHP. In this study, we investigated whether S100A10 is involved in L-OHP sensitivity or not.

Results

Forced expression of S100A10 in COLO-320 CRC cells significantly increased the 50% inhibitory concentration (IC₅₀) for L-OHP (P = 0.003), but did not change that for 5-FU, indicating that S100A10 is more specific to L-OHP than 5-FU. Silencing of the S100A10 gene showed no apparent effect on sensitivity to L-OHP in HT29 cells. Silencing of the annexin A2 (a binding partner of S100A10) gene alone downregulated both annexin A2 and S100A10 protein levels, with no change in S100A10 gene expression. However, original levels of intact S100A10 protein in CRC cells positively correlated with S100A10 mRNA levels (P = 0.002, R = 0.91).

Conclusions

The present results have shown that protein expression of S100A10 was associated with resistance to L-OHP, but not 5-FU, supporting the hypothesis that S100A10 expression may predict L-OHP sensitivity. Thus, our present study provides basic findings to support that S100A10 expression can be used as a predictive marker for tumor sensitivity to L-OHP.

Inhibition of Langerhans cell maturation by human papillomavirus type 16: a novel role for the annexin A2 heterotetramer in immune suppression

High-risk human papillomaviruses (HPVs) are sexually transmitted viruses causally associated with several cancers. During its natural life cycle, HPV16, the most common high-risk genotype, infects the epithelial basal cells in a process facilitated through a recently identified receptor, the annexin A2 heterotetramer (A2t). During infection, HPV16 also interacts with Langerhans cells (LC), the APC of the epithelium, inducing immune suppression, which is mediated by the HPV16 L2 minor capsid protein. Despite the importance of these virus-immune cell interactions, the specific mechanisms of HPV16 entry into LC and HPV16-induced immune suppression remain undefined. An N-terminal peptide of HPV16 L2 (aa 108-126) has been shown to specifically interact with A2t. In this study, we show that incubation of human LC with this peptide blocks binding of HPV16. Inhibiting this interaction with an A2t ligand or by small interfering RNA downregulation of A2t significantly decreases HPV16 internalization into LC in an L2-dependent manner. A2t is associated with suppression of LC maturation as demonstrated through attenuated secretion of Th1-associated cytokines and decreased surface expression of MHC class II on LC exposed to A2t. Conversely, small molecule inhibition of A2t prevents HPV16-induced suppression of LC immune function as indicated by significantly increased secretion of inflammatory cytokines and surface expression of CD86 in HPV16 treated LC pre-exposed to A2t inhibitors. These results demonstrate that HPV16 suppresses LC maturation through an interaction with A2t, revealing a novel role for this protein.

The papillomavirus major capsid protein L1

The elegant icosahedral surface of the papillomavirus virion is formed by a single protein called L1. Recombinant L1 proteins can spontaneously self-assemble into a highly immunogenic structure that closely mimics the natural surface of native papillomavirus virions. This has served as the basis for two highly successful vaccines against cancer-causing human papillomaviruses (HPVs). During the viral life cycle, the capsid must undergo a variety of conformational changes, allowing key functions including the encapsidation of the ~8 kb viral genomic DNA, maturation into a more stable state to survive transit between hosts, mediating attachment to new host cells, and finally releasing the viral DNA into the newly infected host cell. This brief review focuses on conserved sequence and structural features that underlie the functions of this remarkable protein.

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.

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.

The S100A10 subunit of the annexin A2 heterotetramer facilitates L2-mediated human papillomavirus infection

Mucosotropic, high-risk human papillomaviruses (HPV) are sexually transmitted viruses that are causally associated with the development of cervical cancer. The most common high-risk genotype, HPV16, is an obligatory intracellular virus that must gain entry into host epithelial cells and deliver its double stranded DNA to the nucleus. HPV capsid proteins play a vital role in these steps. Despite the critical nature of these capsid protein-host cell interactions, the precise cellular components necessary for HPV16 infection of epithelial cells remains unknown. Several neutralizing epitopes have been identified for the HPV16 L2 minor capsid protein that can inhibit infection after initial attachment of the virus to the cell surface, which suggests an L2-specific secondary receptor or cofactor is required for infection, but so far no specific L2-receptor has been identified. Here, we demonstrate that the annexin A2 heterotetramer (A2t) contributes to HPV16 infection and co-immunoprecipitates with HPV16 particles on the surface of epithelial cells in an L2-dependent manner. Inhibiting A2t with an endogenous annexin A2 ligand, secretory leukocyte protease inhibitor (SLPI), or with an annexin A2 antibody significantly reduces HPV16 infection. With electron paramagnetic resonance, we demonstrate that a previously identified neutralizing epitope of L2 (aa 108-120) specifically interacts with the S100A10 subunit of A2t. Additionally, mutation of this L2 region significantly reduces binding to A2t and HPV16 pseudovirus infection. Furthermore, downregulation of A2t with shRNA significantly decreases capsid internalization and infection by HPV16. Taken together, these findings indicate that A2t contributes to HPV16 internalization and infection of epithelial cells and this interaction is dependent on the presence of the L2 minor capsid protein.

Upregulated expression of annexin II is a prognostic marker for patients with gastric cancer

Background

The role of annexin II in the development and progression of gastric cancer was explored.

Methods

Real-time PCR was conducted to detect annexin II and S100A6 mRNA expression. Protein expressions of annexin II and S100A6 were also examined by immunohistochemistry in 436 clinicopathologically characterized gastric cancer cases.

Results

The expression of annexin II and S100A6 mRNA differ significantly among gastric tumor tissue and matched non-cancerous gastric mucosa. Protein levels of annexin II and S100A6 were up-regulated in gastric cancer compared with adjacent non-cancerous tissues. High expression of annexin II correlated with age, location of tumor, size of tumor, differentiation, histological type, depth of invasion, vessel invasion, lymph node metastasis, distant metastasis and Tumor, Node, Metastasis (TNM) stage, and also with expression of S100A6. Further multivariate analysis suggested that expression of annexin II and S100A6 were independent prognostic indicators for gastric cancer.

Cumulative five-year survival rates of patients with high expression of both annexin II and S100A6 was significantly lower than those with low expression of both.

Conclusion

Expression of annexin II in gastric cancer was significantly associated with depth of invasion, lymph node metastasis and distant metastasis, TNM stage, high S100A6 expression, and poor prognosis. Annexin II and S100A6 proteins could be useful prognostic marker to predict tumor progression and prognosis in gastric cancer.

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.

Annexin II binds to capsid protein VP1 of enterovirus 71 and enhances viral infectivity

Enterovirus type 71 (EV71) causes hand, foot, and mouth disease (HFMD), which is mostly self-limited but may be complicated with a severe to fatal neurological syndrome in some children. Understanding the molecular basis of virus-host interactions might help clarify the largely unknown neuropathogenic mechanisms of EV71. In this study, we showed that human annexin II (Anx2) protein could bind to the EV71 virion via the capsid protein VP1. Either pretreatment of EV71 with soluble recombinant Anx2 or pretreatment of host cells with an anti-Anx2 antibody could result in reduced viral attachment to the cell surface and a reduction of the subsequent virus yield in vitro. HepG2 cells, which do not express Anx2, remained permissive to EV71 infection, though the virus yield was lower than that for a cognate lineage expressing Anx2. Stable transfection of plasmids expressing Anx2 protein into HepG2 cells (HepG2-Anx2 cells) could enhance EV71 infectivity, with an increased virus yield, especially at a low infective dose, and the enhanced infectivity could be reversed by pretreating HepG2-Anx2 cells with an anti-Anx2 antibody. The Anx2-interacting domain was mapped by yeast two-hybrid analysis to VP1 amino acids 40 to 100, a region different from the known receptor binding domain on the surface of the picornavirus virion. Our data suggest that binding of EV71 to Anx2 on the cell surface can enhance viral entry and infectivity, especially at a low infective dose.

The human papillomavirus type 16 E5 oncoprotein translocates calpactin I to the perinuclear region

The human papillomavirus type 16 (HPV-16) E5 oncoprotein is embedded in membranes of the endoplasmic reticulum and nuclear envelope with its C terminus exposed to the cytoplasm. Among other activities, E5 cooperates with the HPV E6 oncoprotein to induce koilocytosis in human cervical cells and keratinocytes in vitro. The effect of E5 on infected cells may rely on its interactions with various cellular proteins. In this study we identify calpactin I, a heterotetrameric, Ca(2+)- and phospholipid-binding protein complex that regulates membrane fusion, as a new cellular target for E5. Both the annexin A2 and p11 subunits of calpactin I coimmunoprecipitate with E5 in COS cells and in human epithelial cell lines, and an intact E5 C terminus is required for binding. Moreover, E5-expressing cells exhibit a perinuclear redistribution of annexin A2 and p11 and show increased fusion of perinuclear membrane vesicles. The C terminus of E5 is required for both the perinuclear redistribution of calpactin I and increased formation of perinuclear vacuoles. These results support the hypothesis that the E5-induced relocalization of calpactin I to the perinuclear region promotes perinuclear membrane fusion, which may underlie the development of koilocytotic vacuoles.

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.

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.

Proteomic analysis of human umbilical vein endothelial cells incubated with Cryptococcus neoformans var. neoformans

Cryptococcus neoformans is a medically important fungus and can infect all the organs of the body. As vascular endothelial cell is an important target for C. neoformans to penetrate any organs, the differential protein expression of human umbilical vascular endothelial cell (HUVEC) after incubating with C. neoformans may be the key to penetration. The proteins of HUVECs incubated with C. neoformans and normal HUVECs were collected and purified. After two-dimensional electrophoresis, the differential protein expression was identified by matrix-assisted laser desorption/ionisation mass spectrometry. The mRNA levels of some proteins were measured by real-time PCR. Three proteins were found significantly overexpressed in HUVECs incubated with C. neoformans, and nine other proteins were downregulated. The mRNA levels of S100A10 and peroxiredoxin I fluctuated with the protein levels. These results suggested that the expressions of peroxiredoxin I and S100A10 were regulated during the process of invasion of HUVECs by C. neoformans. We hypothesise that these proteins take part in the modifications of HUVEC cytoskeleton and the tolerance to oxidative stress, which may affect the process of invasion by C. neoformans.

S100A10 regulates plasminogen-dependent macrophage invasion

The plasminogen activation system plays an integral role in the migration of macrophages in response to an inflammatory stimulus, and the binding of plasminogen to its cell-surface receptor initiates this process. Although previous studies from our laboratory have shown the importance of the plasminogen receptor S100A10 in cancer cell plasmin production, the potential role of this protein in macrophage migration has not been investigated. Using thioglycollate to induce a peritoneal inflammatory response, we demonstrate, for the first time, that compared with wild-type (WT) mice, macrophage migration across the peritoneal membrane into the peritoneal cavity in S100A10-deficient (S100A10(-/-)) mice was decreased by up to 53% at 24, 48, and 72 hours. Furthermore, the number of S100A10-deficient macrophages that infiltrated Matrigel plugs was reduced by 8-fold compared with their WT counterpart in vivo. Compared with WT macrophages, macrophages from S100A10(-/-) mice demonstrated a 50% reduction in plasmin-dependent invasion across a Matrigel barrier and a 45% reduction in plasmin generation in vitro. This loss in plasmin-dependent invasion was in part the result of a decreased generation of plasmin and a decreased activation of pro-MMP-9 by S100A10-deficient macrophages. This study establishes a direct involvement of S100A10 in macrophage recruitment in response to inflammatory stimuli.

Host cell entry by apicomplexa parasites requires actin polymerization in the host cell

Apicomplexa are obligate intracellular parasites that actively invade host cells using their membrane-associated, actin-myosin motor. The current view is that host cell invasion by Apicomplexa requires the formation of a parasite-host cell junction, which has been termed the moving junction, but does not require the active participation of host actin. Using Toxoplasma gondii tachyzoites and Plasmodium berghei sporozoites, we show that host actin participates in parasite entry. Parasites induce the formation of a ring-shaped F-actin structure in the host cell at the parasite-cell junction, which remains stable during parasite entry. The Arp2/3 complex, an actin-nucleating factor, is recruited at the ring structure and is important for parasite entry. We propose that Apicomplexa invasion of host cells requires not only the parasite motor but also de novo polymerization of host actin at the entry site for anchoring the junction on which the parasite pulls to penetrate the host cell.

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

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

Endothelial cell annexin A2 regulates polyubiquitination and degradation of its binding partner S100A10/p11

The annexin A2 (A2) heterotetramer, consisting of two copies of A2 and two copies of S100A10/p11, promotes fibrinolytic activity on the surface of vascular endothelial cells by assembling plasminogen and tissue plasminogen activator (tPA) and accelerating the generation of plasmin. In humans, overexpression of A2 by acute promyelocytic leukemia cells is associated with excessive fibrinolysis and hemorrhage, whereas anti-A2 autoantibodies appear to accentuate the risk of thrombosis in patients with anti-phospholipid syndrome. Complete deficiency of A2 in mice leads to a lack of tPA cofactor activity, accumulation of intravascular fibrin, and failure to clear arterial thrombi. Within the endothelial cell, p11 is required for Src kinase-mediated tyrosine phosphorylation of A2, which signals translocation of both proteins to the cell surface. Here we show that p11 is expressed at very low levels in the absence of A2 both in vitro and in vivo. We demonstrate further that unpartnered p11 becomes polyubiquitinated and degraded via a proteasome-dependent mechanism. A2 stabilizes intracellular p11 through direct binding, thus masking an autonomous p11 polyubiquitination signal that triggers proteasomal degradation. This interaction requires both the p11-binding N-terminal domain of A2 and the C-terminal domain of p11. This mechanism prevents accumulation of free p11 in the endothelial cell and suggests that regulation of tPA-dependent cell surface fibrinolytic activity is precisely tuned to the intracellular level of p11.

Molecular mapping of human hepatocellular carcinoma provides deeper biological insight from genomic data

DNA microarray analysis of human cancer has resulted in considerable accumulation of global gene profiles. However, extraction and understanding the underlying biology of cancer progression remains a significant challenge. This study applied a novel integrative computational and analytical approach to this challenge in human hepatocellular carcinoma (HCC) with the aim of identifying potential molecular markers or novel therapeutic targets. We analysed 100 HCC tissue samples by human 30K DNA microarray. The gene expression data were uploaded into the network analysis tool, and the biological networks were displayed graphically. We identified several activated 'hotspot' regions harbouring a concentration of upregulated genes. Several 'hotspot' regions revealed integrin and Akt/NF-kappaB signalling. We identified key members linked to these signalling pathways including osteopontin (SPP1), glypican-3 (GPC3), annexin 2 (ANXA2), S100A10 and vimentin (VIM). Our integrative approach should significantly enhance the power of microarray data in identifying novel potential targets in human cancer.

Annexins sense changes in intracellular pH during hypoxia

The pH(i) (intracellular pH) is an important physiological parameter which is altered during hypoxia and ischaemia, pathological conditions accompanied by a dramatic decrease in pH(i). Sensors of pH(i) include ion transport systems which control intracellular Ca2+ gradients and link changes in pH(i) to functions as diverse as proliferation and apoptosis. The annexins are a protein family characterized by Ca2+-dependent interactions with cellular membranes. Additionally, in vitro evidence points to the existence of pH-dependent, Ca(2+)-independent membrane association of several annexins. We show that hypoxia promotes the interaction of the recombinant annexin A2-S100A10 (p11) and annexin A6 with the plasma membrane. We have investigated in vivo the influence of the pH(i) on the membrane association of human annexins A1, A2, A4, A5 and A6 tagged with fluorescent proteins, and characterized this interaction for endogenous annexins present in smooth muscle and HEK (human embryonic kidney)-293 cells biochemically and by immunofluorescence microscopy. Our results show that annexin A6 and the heterotetramer A2-S100A10 (but not annexins A1, A4 and A5) interact independently of Ca2+ with the plasma membrane at pH 6.2 and 6.6. The dimerization of annexin A2 within the annexin A2-S100A10 complex is essential for the pH-dependent membrane interaction at this pH range. The pH-induced membrane binding of annexins A6 and A2-S100A10 might have consequences for their functions as membrane organizers and channel modulators.

S100A10/p11: family, friends and functions

S100A10, also known as p11 or annexin 2 light chain, is a member of the S100 family of small, dimeric EF hand-type Ca(2+)-binding proteins that generally modulate cellular target proteins in response to intracellular Ca(2+) signals. In contrast to all other S100 proteins, S100A10 is Ca(2+) insensitive because of amino acid replacements in its Ca(2+)-binding loops that lock the protein in a permanently active state. Within cells, the majority of S100A10 resides in a tight heterotetrameric complex with the peripheral membrane-binding protein annexin A2 that directs the complex to specific target membranes, in particular the plasma membrane and the membrane of early endosomes. Several other Ca(2+)-independent interaction partners of S100A10 have been described in the recent past. Many of these interactions, which have been shown to be of functional significance for the respective partner, involve plasma membrane-resident proteins. In most of these cases, S100A10, probably residing in a complex with annexin A2, appears to regulate the intracellular trafficking of the respective target protein and thus its functional expression at the cell surface. In this paper, we review the current information on S100A10 protein interactions placing a particular emphasis on data that contribute to an understanding of the mechanistic basis of the S100A10 action. Based on these data, we propose that S100A10 functions as a linker tethering certain transmembrane proteins to annexin A2 thereby assisting their traffic to the plasma membrane and/or their firm anchorage at certain membrane sites.

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

Introduction

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

Methods

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

Results

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

Conclusion

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

PTEN-mediated apical segregation of phosphoinositides controls epithelial morphogenesis through Cdc42

Formation of the apical surface and lumen is a fundamental, yet poorly understood, step in epithelial organ development. We show that PTEN localizes to the apical plasma membrane during epithelial morphogenesis to mediate the enrichment of PtdIns(4,5)P2 at this domain during cyst development in three-dimensional culture. Ectopic PtdIns(4,5)P2 at the basolateral surface causes apical proteins to relocalize to the basolateral surface. Annexin 2 (Anx2) binds PtdIns(4,5)P2 and is recruited to the apical surface. Anx2 binds Cdc42, recruiting it to the apical surface. Cdc42 recruits aPKC to the apical surface. Loss of function of PTEN, Anx2, Cdc42, or aPKC prevents normal development of the apical surface and lumen. We conclude that the mechanism of PTEN, PtdIns(4,5)P2, Anx2, Cdc42, and aPKC controls apical plasma membrane and lumen formation.

Angiostatin receptor annexin II in vascular tumors including angiosarcoma

Inhibitors of angiogenesis, such as angiostatin, are increasingly used for targeting the tumor neovasculature and have had mixed success. Annexin II (ANX2), a 36KDa calcium and phospholipid binding protein, is a cell surface receptor for angiostatin. We hypothesized that, like normal vascular endothelium, vascular neoplasms would express ANX2, implying the potential usefulness of angiostatins in the therapy of this family of soft tissue tumors. Thirty-eight (38) vascular tumors tested included: hemangiomas - capillary [4], cavernous [6], lobular capillary [6], intramuscular hemangioma [3], spindle cell [1], and epithelioid hemangioma [4]; epithelioid hemangioendothelioma [3]; angiosarcoma [7], 4 of which were epithelioid; and angiolipomas [4]. ANX2 antibody (Zymed) was used (1/50 dilution, Ventana ES autostainer). Reactivity location (cytoplasmic, nuclear, membrane), intensity (1+/2+/3+), and quantity (focal, diffuse) was recorded. ANX2 was expressed in 97% of cases (37/38); mostly diffuse [35/37] and focal in 2 cases. Staining was strong (2+ or 3+) in 87%, and 1+ in 5/37 (14%), all benign tumors. Location was mostly cytoplasmic and membranous; no nuclear staining was seen. Both endothelium and pericytes were positive. Epithelioid angiosarcomas showed predominantly membranous staining. To our knowledge this is the first demonstration of an angiostatin receptor (ANX2) in vascular endothelial tumors including angiosarcoma. Diffuse and strong reactivity signified the absence of any down-regulation of ANX2 in both benign and malignant tumors. ANX2 reactivity may be the basis of treatment for a variety of benign tumors, especially in pediatric patients, and may offer a new and potentially less toxic therapy for angiosarcoma.

Annexin 2-mediated enhancement of cytomegalovirus infection opposes inhibition by annexin 1 or annexin 5

Biochemical studies have suggested that annexin 2 (A2) may participate in cytomegalovirus (CMV) infection. In the current work, effects of A2 monomer (p36) and heterotetramer (A2t; p36(2)p11(2)) were investigated. Demonstrating a role for endogenous A2, the four stages of infection that were followed were each inhibited by anti-p36 or anti-p11 at 37 degrees C. Immuno-inhibition was attenuated when the virus and cells were pre-incubated at 4 degrees C to coordinate virus entry initiated afterwards at 37 degrees C, reconciling controversy in the literature. As an explanation, CMV-induced phosphorylation of p36 was prevented by the 4 degrees C treatment. Supporting these immuno-inhibition data, purified A2t or p11 increased CMV infectious-progeny generation and CMV gene expression. A specific role for A2t was indicated by purified p36 having no effect. Unlike other steps, primary plaque formation was not enhanced by purified A2t or p11, possibly because of undetectable phosphorylation. As annexins 1 (A1) and 5 (A5) interact with A2, their effect on CMV was also tested. Both purified proteins inhibited CMV infection. In each experiment, the concentration of A1 required for half-maximal inhibition was five- to 10-fold lower than that of A5. Addition of A2 opposed A1- or A5-mediated inhibition of CMV, as did certain A2-specific antibodies that had no effect in the absence of added A1 or A5. Transfection of the p36-deficient cell line HepG2 increased CMV infection and was required for inhibition by the other annexins. These data suggest that CMV exploits A2t at physiological temperature to oppose the protection of cells conferred by A1 or A5.

Regulation of actin dynamics by annexin 2

Annexin 2 is a ubiquitous Ca(2+)-binding protein that is essential for actin-dependent vesicle transport. Here, we show that in spontaneously motile cells annexin 2 is concentrated in dynamic actin-rich protrusions, and that depletion of annexin 2 using siRNA leads to the accumulation of stress fibres and loss of protrusive and retractile activity. Cells co-expressing annexin 2-CFP and actin-YFP exhibit Ca(2+)-dependent fluorescense resonance energy transfer throughout the cytoplasm and in membrane ruffles and protrusions, suggesting that annexin 2 may directly interact with actin. This notion was supported by biochemical studies, in which we show that annexin 2 reduces the polymerisation rate of actin monomers in a dose-dependent manner. By measuring actin polymerisation rates in the presence of barbed-end and pointed-end cappers, we further demonstrate that annexin 2 specifically inhibits filament elongation at the barbed ends. These results show that annexin 2 has an essential role in maintaining the plasticity of the dynamic membrane-associated actin cytoskeleton, and that its activity in this context may be at least partly explained through direct interactions with polymerised and monomeric actin.

Identification of the annexin A2 heterotetramer as a receptor for the plasmin-induced signaling in human peripheral monocytes

We have previously demonstrated that plasmin acts as a potent proinflammatory activator of human peripheral monocytes. Here we identify the annexin A2 heterotetramer, composed of annexin A2 and S100A10, as a receptor for the plasmin-induced signaling in human monocytes. Monocytes express the annexin A2 heterotetramer on the cell surface as shown by flow cytometry, fluorescence microscopy, and coimmunoprecipitation of biotinylated cell surface proteins. Binding of plasmin to annexin A2 and S100A10 on monocytes was verified by biotin transfer from plasmin labeled with a trifunctional cross-linker. Antibodies directed against annexin A2 or S100A10 inhibited the chemotaxis elicited by plasmin, but not that induced by fMLP. Further, down-regulation of annexin A2 or S100A10 in monocytes by antisense oligodeoxynucleotides impaired the chemotactic response to plasmin, but not that to fMLP. Antisense oligodeoxynucleotides similarly decreased the TNF-alpha release by plasmin-stimulated, but not by LPS-stimulated, monocytes. At the molecular level, stimulation with plasmin, but not with catalytically inactivated plasmin, induced cleavage of annexin A2 and dissociation of the heterotetramer complex. Substitution of lysine to alanine in position 27 abolished the cleavage of recombinant annexin A2 in vitro. Together, these data identify the annexin A2 heterotetramer as a signaling receptor activated by plasmin via proteolysis.

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

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