A 36 kDa monomeric protein and its complex with a 10 kDa protein both isolated from bovine aorta are calpactin-like proteins that differ in their Ca2+-dependent calmodulin-binding and actin-severing properties

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 2 has a dual role as regulator and effector of v-Src in cell transformation

Cell transformation by v-Src involves rearrangement of the actin cytoskeleton, disassembly of focal adhesions, and the development of anchorage-independent growth. Here, we report that this is dependent on annexin 2, a v-Src substrate and calcium-dependent regulator of actin dynamics. Using a thermoactivatable mutant of v-Src, we show that at the permissive temperature, annexin 2 becomes phosphorylated and colocalizes with activated v-Src and focal adhesion kinase both at the plasma membrane and in a Rab11-positive compartment of the endosomal pathway. In cells depleted of annexin 2 by small interfering RNA, v-Src becomes activated at the permissive temperature but does not target to the plasma membrane or to perinuclear vesicles, and cell transformation does not occur. Our findings reveal a dual role for annexin 2, first as a regulator of v-Src trafficking and targeting and second as a v-Src effector in the reorganization of actin.

Reorganization of cytoskeleton during surfactant secretion in lung type II cells: a role of annexin II

The secretion of lung surfactant requires the movement of lamellar bodies to the plasma membrane through cytoskeletal barrier at the cell cortex. We hypothesized that the cortical cytoskeleton undergoes a transient disassembly/reassembly in the stimulated type II cells, therefore allowing lamellar bodies access to the plasma membrane. Stabilization of cytoskeleton with Jasplakinolinde (JAS), a cell permeable actin microfilament stabilizer, caused a dose-dependent inhibition of lung surfactant secretion stimulated by terbutaline. This inhibition was also observed in ATP-, phorbol 12-myristate 13-acetate (PMA)- or Ca(2+) ionophore A23187-stimulated surfactant secretion. Stimulation of type II cells with terbutaline exhibited a transient disassembly of filamentous actin (F-actin) as determined by staining with Oregon Green 488 Phalloidin. The protein kinase A inhibitor, H89, abolished the terbutaline-induced F-actin disassembly. Western blot analysis using anti-actin and anti-annexin II antibodies showed a transient increase of G-actin and annexin II in the Triton X-100 soluble fraction of terbutaline-stimulated type II cells. Furthermore, introduction of exogenous annexin II tetramer (AIIt) into permeabilized type II cells caused a disruption in the cortical actin. Treatment of type II cells with N-ethylmaleimide (NEM) resulted in a disruption of the cortical actin. NEM also inhibited annexin II's abilities to bundle F-actin. The results suggest that cytoskeleton undergoes reorganization in the stimulated type II cells, and annexin II tetramer plays a role in this process.

Cholesterol enhances phospholipid binding and aggregation of annexins by their core domain

Annexins are Ca(2+)-dependent phospholipid-binding proteins composed of two domains: A conserved core that is responsible for Ca(2+)- and phospholipid-binding, and a variable N-terminal tail. A Ca(2+)-independent annexin 2-membrane association has been shown to be modulated by the presence of cholesterol in the membranes. Herein, the roles of the core and the N-terminal tail on the cholesterol-enhancement of annexin 2 membrane binding and aggregation were studied. The results show that (i) the cholesterol-mediated increase in membrane binding and in the Ca(2+) sensitivity for membrane aggregation were not modified by a N-terminal peptide (residues 15-26), and were conserved in mutants of the N-terminal end (S11 and S25 substitutions); (ii) cholesterol induced an increase in the Ca(2+)-dependent membrane binding and aggregation of the N-terminally truncated protein (Delta 1-29); and (iii) annexins 5 and 6, two proteins with unrelated N-terminal tails and homologous core domains showed a cholesterol-mediated enhancement of the Ca(2+)-dependent binding to membranes. These data indicate that the core domain is responsible for the cholesterol-mediated effects. A model for the cholesterol effect in membrane organisation, annexin binding and aggregation is discussed.

Characterization of the interaction between annexin I and profilin

Annexin I belongs to a family of calcium-dependent phospholipid-binding and membrane-binding proteins. Although many of the biochemical properties and the three-dimensional structure of this protein are known, its true physiological roles have yet to be thoroughly defined. Its putative functions include participation in the regulation of actin microfilaments dynamics, proposed after the discovery of an interaction with actin. In accordance with this hypothesis, we found that annexin I can also interact with profilin. We used different methods, overlay and surface plasmon resonance (BIAcore), to measure the parameters of the association equilibrium, i.e. k(on), k(off) and k(d). The affinity of annexin I for profilin was between 10(7) M and 10(8) M. High concentrations of KCl did not prevent the interaction, although a slight decrease in affinity was observed. Calcium, a modulator of annexin I functions interfered only marginally with the association, in a manner comparable to magnesium. Proteins or compounds known to interact with annexin I or profilin were found to inhibit the annexin-I--profilin interaction when added in the reaction medium. Recombinant profilin exhibited a slightly lower affinity than natural platelet protein when measured with BIAcore. Due to the submembrane localisation of annexin I and the regulatory activity of profilin on the cytoskeleton, an interaction between annexin I and profilin may therefore be implicated in the regulation of some cellular functions, particularly those governing membrane-cytoskeleton dynamic organization.

Sperm protein (sp50) binds to acrosome and plasma membranes in a Ca(2+)-dependent manner: possible role in acrosome reaction

Annexins are a family of Ca(2+)-binding proteins involved in the exocytotic process. The presence and the role of annexins in mammalian spermatozoa have not been well established. Two annexin-like proteins were obtained from guinea pig testis, a doublet of Mr 31-33 kD (p31/33) and a protein of Mr 50 kD (p50). Both proteins were able to bind to erythrocyte ghosts in a Ca(2+)-dependent fashion. Polyclonal antibodies against p31/33 reacted with two major proteins, Mrs 50 kD (sp50) and 42 kD (sp42), from mature and immature guinea pig spermatozoa. p50 and sp50 are likely the native proteins from testis and spermatozoa, respectively, and they are seemingly related. By immunofluorescence, sp50 was only found in the acrosome region of immature and capacitated and noncapacitated spermatozoa, and its location was intracellular. In spermatozoa undergoing acrosome reaction, sp50 was detected in the whole acrosome, while in spermatozoa that had undergone acrosome reaction sp50 was not detected. However, in the protein pattern of acrosome reaction vesicles, anti-p31/33 antibody revealed diffuse bands of Mr 35-38 kD. sp50 was able to bind to plasma membrane fragments and acrosome outer membrane from demembranated sperm in a Ca(2+)-dependent fashion. The presence of sp50 in the acrosome region, its distribution throughout the acrosome membrane just before the acrosome reaction, and its ability to bind both plasma and outer acrosome membranes in a Ca(2+)-dependent manner suggest that sp50 may participate in the acrosome reaction mechanism in guinea pig spermatozoa.

In vivo and in vitro phosphorylation of annexin II in T cells: potential regulation by annexin V

In order to understand how signal transduction occurs during T cell activation, it is necessary to identify the key regulatory molecules whose function is influenced by phosphorylation. Annexins II (A-II) and V (A-V) belong to a large family of Ca(2+)-dependent phospholipid-binding proteins. Among many putative functions, annexins may be involved in signal transduction during cellular proliferation and differentiation. In the present study we show that A-II is phosphorylated in vivo in the Jurkat human T cell line. Indeed, A-II is phosphorylated after stimulation by phorbol myristate acetate and on serine residues after T cell antigen receptor (TcR) stimulation. In cytosol from Jurkat cells, A-II is phosphorylated only by Ca2+/phospholipid-stimulated kinases such as Ca(2+)-dependent protein kinases C (cPKCs). A-V inhibits the phosphorylation of A-II and other substrates of cPKCs and has no effect on kinases activated only by phospholipids. In conclusion, A-II is phosphorylated both in vitro and in vivo in Jurkat cells, and may play a role as a substrate during signal transduction in lymphocytes via the TcR through the PKC pathway. On the other hand, A-V could act as a potent modulator of cPKCs in Jurkat cells.

Annexin II tetramer: structure and function

The annexins are a family of proteins that bind acidic phospholipids in the presence of Ca2+. The interaction of these proteins with biological membranes has led to the suggestion that these proteins may play a role in membrane trafficking events such as exocytosis, endocytosis and cell-cell adhesion. One member of the annexin family, annexin II, has been shown to exist as a monomer, heterodimer or heterotetramer. The ability of annexin II tetramer to bridge secretory granules to plasma membrane has suggested that this protein may play a role in Ca(2+)-dependent exocytosis. Annexin II tetramer has also been demonstrated on the extracellular face of some metastatic cells where it mediates the binding of certain metastatic cells to normal cells. Annexin II tetramer is a major cellular substrate of protein kinase C and pp60src. Phosphorylation of annexin II tetramer is a negative modulator of protein function.

Purification of cardiac annexin V from the beagle dog heart and changes in its localization in the ischemic rat heart

We isolated and purified 35 kDa protein from the myocardium of the beagle dog and identified it to be annexin V from partial amino acid sequence determination. It was confirmed that anticanine cardiac annexin V rabbit polyclonal antibody, which was produced using the 35 kDa protein, cross-reacts with annexin V of the myocardium, lung, liver, kidney, and brain of the rat. The localization of cardiac annexin V and the effect of ischemia for 30-180 min in the rat were immunohistochemically studied with the use of the Langendorff perfusion heart. In the normal myocardium, annexin V, accompanied by cross-striation, was observed throughout the cell. In ischemia of 30 min, extracellular leakage of annexin V was observed with uneven staining in the cytoplasm. When the ischemic time exceeded 60 min, annexin V was observed in the cell membrane with a decrease of annexin V in the cytoplasm. Also, extracellular leakage of annexin V was observed prominently. In ischemia for 180 min, almost all the annexin V in the cytoplasm disappeared. These results suggest that the level of ischemia can be estimated from the changes in localization of annexin V.