Annexin A2 may not play a role as a plasminogen receptor

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

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

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.

Yeast two-hybrid screening of proteins interacting with plasmin receptor subunit: C-terminal fragment of annexin A2

AIM

To identify proteins that interact with the C-terminal fragment of annexin A2 (A2IC), generated by plasmin cleavage of the plasmin receptor, a heterotetramer (AA2t) containing annexin A2.

METHODS

The gene that encodes the A2IC fragment was obtained from PCR-amplified cDNA isolated from human monocytes, and was ligated into the pBTM116 vector using a DNA ligation kit. The resultant plasmid (pBTM116-A2IC) was sequenced with an ABI PRISM 310 Genetic Analyzer. The expression of an A2IC bait protein fused with a LexA-DNA binding domain (BD) was determined using Western blot analysis. The identification of proteins that interact with A2IC and are encoded in a human monocyte cDNA library was performed using yeast two-hybrid screening. The DNA sequences of the relevant cDNAs were determined using an ABI PRISM BigDye terminator cycle sequencing ready reaction kit. Nucleotide sequence databases were searched for homologous sequences using BLAST search analysis (http://www.ncbi.nlm.nih.gov). Confirmation of the interaction between the protein LexA-A2IC and each of cathepsin S and SNX17 was conducted using a small-scale yeast transformation and X-gal assay.

RESULTS

The yeast transformed with plasmids encoding the bait proteins were screened with a human monocyte cDNA library by reconstituting full-length transcription factors containing the GAL4-active domain (GAL4-AD) as the prey in a yeast two-hybrid approach. After screening 1×10(7) clones, 23 independent β-Gal-positive clones were identified. Sequence analysis and a database search revealed that 15 of these positive clones matched eight different proteins (SNX17, ProCathepsin S, RPS2, ZBTB4, OGDH, CCDC32, PAPD4, and actin which was already known to interact with annexin A2).

CONCLUSION

A2IC A2IC interacts with various proteins to form protein complexes, which may contribute to the molecular mechanism of monocyte activation induced by plasmin. The yeast two-hybrid system is an efficient approach for investigating protein interactions.

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.

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.

New insights into the molecular mechanisms of the fibrinolytic system

Fibrinolysis is regulated by specific molecular interactions between its main components. Activation of plasminogen by tissue-type plasminogen activator (t-PA) is enhanced in the presence of fibrin or at the endothelial cell surface. Urokinase-type plasminogen activator (u-PA) binds to a specific cellular u-PA receptor (u-PAR), resulting in enhanced activation of cell-bound plasminogen. Inhibition of fibrinolysis occurs at the level of plasminogen activation or at the level of plasmin. Assembly of fibrinolytic components at the surface of fibrin results in fibrin degradation. Assembly at the surface of cells provides a mechanism for generation of localized cell-associated proteolytic activity. This review includes novel proteins such a thrombin-activatable fibrinolysis inhibitor (TAFI) and discusses new insights into molecular mechanisms obtained from the rapidly growing knowledge of crystal structures of proteins.

Annexin A2 regulates the levels of plasmin, S100A10 and Fascin in L5178Y cells

Annexin A2 (ANXA2) was reported as the receptor, activator, expression enhancer, or cooperator for plasmin, S100A10, and others. To delineate the effect of ANXA2 on the proteins that are probably associated with tumor development and metastasis by a credible experimental method, we generated an ANXA2 gene knockout tumor cell line, ANXA2(-/-) L5178Y, and compared the expression levels of plasmin, S100A10 and fascin in the generated cell line with in wild type of L5178Y at mRNA and protein levels. The results showed that the mRNA level of plasminogen (PLG) was not substantially changed in cultured ANXA2(-/-) cells, but the protein level of plasmin was significantly lower in the cultured ANXA2(-/-) cells than in cultured ANXA2(+/+) cells. For S100A10 and fascin, their mRNA and protein levels were significantly lower in the cultured ANXA2(-/-) cells than in cultured ANXA2(+/+) cells. Results indicate that ANXA2 introduces the generation or expression of plasmin, S100A10, and fascin in tumor cells. ANXA2 affects PLG/plasmin level by a way post transcription and may be an inducer or enhancer to fascin expression at transcription level. By the regulations, ANXA2 enhances the development, invasion, and metastasis of tumor. The detailed mechanism for the regulations above remains to be further investigated, but our results show the potential of ANXA2 as a new target molecule for the strategies of tumor biotherapy or tumor gene therapy.

S100-annexin complexes--biology of conditional association

S100 proteins and annexins both constitute groups of Ca2+-binding proteins, each of which comprises more than 10 members. S100 proteins are small, dimeric, EF-hand-type Ca2+-binding proteins that exert both intracellular and extracellular functions. Within the cells, S100 proteins regulate various reactions, including phosphorylation, in response to changes in the intracellular Ca2+ concentration. Although S100 proteins are known to be associated with many diseases, exact pathological contributions have not been proven in detail. Annexins are non-EF-hand-type Ca2+-binding proteins that exhibit Ca2+-dependent binding to phospholipids and membranes in various tissues. Annexins bring different membranes into proximity and assist them to fuse, and therefore are believed to play a role in membrane trafficking and organization. Several S100 proteins and annexins are known to interact with each other in either a Ca2+-dependent or Ca2+-independent manner, and form complexes that exhibit biological activities. This review focuses on the interaction between S100 proteins and annexins, and the possible biological roles of these complexes. Recent studies have shown that S100-annexin complexes have a role in the differentiation of gonad cells and neurological disorders, such as depression. These complexes regulate the organization of membranes and vesicles, and thereby may participate in the appropriate disposition of membrane-associated proteins, including ion channels and/or receptors.

Histone H2B as a functionally important plasminogen receptor on macrophages

Plasminogen (Plg) facilitates inflammatory cell recruitment, a function that depends upon its binding to Plg receptors (Plg-Rs). However, the Plg-Rs that are critical for cell migration are not well defined. Three previously characterized Plg-Rs (alpha-enolase, annexin 2, and p11) and a recently identified Plg-R (histone H2B [H2B]) were assessed for their contribution to Plg binding and function on macrophages. Two murine macrophage cell lines (RAW 264.7 and J774A.1) and mouse peritoneal macrophages induced by thioglycollate were analyzed. All 4 Plg-Rs were present on the surface of these cells and showed enhanced expression on the thioglycollate-induced macrophages compared with peripheral blood monocytes. Using blocking Fab fragments to each Plg-R, H2B supported approximately 50% of the Plg binding capacity, whereas the other Plg-Rs contributed less than 25%. Anti-H2B Fab also demonstrated a major role of this Plg-R in plasmin generation and matrix invasion. When mice were treated intravenously with anti-H2B Fab, peritoneal macrophage recruitment in response to thioglycollate was reduced by approximately 45% at 24, 48, and 72 hours, with no effect on blood monocyte levels. Taken together, these data suggest that multiple Plg-Rs do contribute to Plg binding to macrophages, and among these, H2B plays a very prominent and functionally important role.

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.