The Role of Annexin II Tetramer in the Activation of Plasminogen

Abstract

One of the major physiological functions of the proteolytic enzyme plasmin is the degradation and solubilization of fibrin, the major constituent of blood clots. Plasmin has a broad trypsin-like specificity and the production of plasmin from its precursor plasminogen is precisely regulated (reviewed in Refs. 1-5). One way in which plasmin activity is localized to the fibrin clot involves a fibrin-specific mechanism for the conversion of plasminogen to plasmin by tissue-type plasminogen activator (t-PA).1 For example, recent studies have shown that by virtue of its ability to bind both t-PA and plasminogen, fibrin acts as a template that promotes the formation of a t-PA⅐fibrin⅐plasminogen ternary complex. The catalytic efficiency of t-PA-dependent conversion of plasminogen to plasmin is determined by the stability of the ternary complex (6). Thus, fibrin is both a substrate of plasmin and a template for plasmin production. Fibrin also plays a role in the plasmin-dependent stimulation of plasmin formation. For example, the partial proteolysis of fibrin results in the transient generation of new carboxyl-terminal lysine residues that act as high affinity binding sites for the lysine-binding sites of plasminogen (7, Recently, the endothelial cell-surface Ca 2ϩ -binding protein, annexin II, has also been shown to stimulate the t-PA-dependent formation of plasmin from plasminogen (13,14). Annexin II was originally identified as an intracellular Ca 2ϩ -and phospholipid-binding protein and subsequent studies suggested that this protein was potentially involved in the regulation of membrane trafficking events such as exocytosis or endocytosis (reviewed in Ref. 15). Annexin II can exist in cells as both a monomer or as a heterotetramer. The heterotetramer, called annexin II tetramer (AIIt) consists of two annexin II molecules and two molecules of an 11-kDa regulatory subunit referred to as the p11 light chain. The binding of the p11 light chain regulates many of the in vitro activities of annexin II and the biochemical properties of AIIt are distinct from the annexin II monomer (16,17). In many cells such as Madin-Darby canine kidney cells, bovine intestinal epithelial cells, and calf pulmonary arterial endothelial cells, 90 -95% of the total cellular annexin II is present in the heterotetrameric form (18,19). Annexin II and AIIt have been shown to exist on the extracellular surface of many cells although the relative extracellular distribution of the two forms of the protein has not been quantified (13, 20 -23).In the present report, we have compared the kinetics of annexin II and AIIt-dependent activation of t-PA-mediated plasminogen activation. These experiments establish the presence of AIIt on the HUVEC surface and that AIIt is a potent in vitro activator of t-PA-mediated plasminogen activation. EXPERIMENTAL PROCEDURESMaterials-Fibrinogen was obtained from Sigma and further purified by gel permeation chromatography on Superose 12 to remove

Expression of annexin A2 in GABAergic interneurons in the normal rat brain

“…While still in an early stage, several possibilities based on previously acquired knowledge may direct the future research: First, given ANX2 is a potent co-activator of tPA/ plaminogen (Cesarman et al 1994;Kassam et al 1998), it is of great interest to investigate whether ANX2 is complexed with and required for neuronal tPA/plasminogen activation that has been shown to play an important role in synaptic plasticity and memory formation (Huang et al 1996;Frey et al 1996;Calabresi et al 2000;Baranes et al 1998;Pang et al 2004). Second, global activation of tPA/plasminogen can also be harmful to the brain and has been shown to trigger neuronal death (Gingrich and Traynelis 2000;Tsirka 2002;Siao and Tsirka 2002), which may involve in the activation of glial cells.…”

“…Formation of ANX2 heterotetramer enables its association with lipid rafts on the plasma membrane, where it is proposed to be involved in regulation of protein and membrane trafficking (Waisman 1995;Oliferenko et al 1999;Babiychuk and Draeger 2000;Zobiack et al 2002;Jacob et al 2004). Moreover, the ANX2 heterotetramer functions as a co-activator of plasminogen on the membrane surface, where it works with tissue-plasminogen activator (tPA) markedly increasing the tPA-mediated conversion of plasminogen to plasmin (Cesarman et al 1994;Kassam et al 1998). In doing so, the ANX2 tetramer plays a role in cell surface fibrinolysis (Hajjar 1995;Choi et al 2001;Kim and Hajjar 2002), angiogenesis (Kwon et al 2002;Tuszynski et al 2002), cancer metastasis (Mai et al 2000), and neurite outgrowth (Fox et al 1991;Jacovina et al 2001).…”

RNA Interference-mediated Silencing of the S100A10 Gene Attenuates Plasmin Generation and Invasiveness of Colo 222 Colorectal Cancer Cells

“…Thus, both immunofluorescence microscopy and surface biotinylation suggested that annexin A2 was not present on the surface of the colorectal cells. The absence of annexin A2 from the extracellular surface was unexpected, because typically both S100A10 and its binding partner, annexin A2, are found on the extracellular surface as the heterotetrameric complex, AIIt (26,31,32,34). The absence of annexin A2 from the extracellular surface presented the opportunity to examine the role of S100A10 in plasminogen regulation in the absence of its annexin A2 binding partner.…”

Feedback Regulation of Endothelial Cell Surface Plasmin Generation by PKC-dependent Phosphorylation of Annexin A2

“…Complex formation with p11 increases the affinity of A2 for calcium and phospholipids, thereby directing it to cellular membranes (4). Components of the (A2⅐p11) 2 tetramer, moreover, specifically bind tissue plasminogen activator (t-PA) and plasminogen and strongly enhance plasmin generation (5)(6)(7)(8)52).…”