Effects of annexin V on the activity of the anticoagulant proteins C and S

New Insights into the Occurrence of Matrix Metalloproteases -2 and -9 in a Cohort of Breast Cancer Patients and Proteomic Correlations

Matrix metalloproteases (MMPs) are a family of well-known enzymes which operate prevalently in the extracellular domain, where they fulfil the function of remodeling the extracellular matrix (ECM). Within the 26 family members, encoded by 24 genes in humans, MMP-2 and MMP-9 have been regarded as primarily responsible for the basement membrane and peri-cellular ECM rearrangement. In cases of infiltrating carcinomas, which arise from the epithelial tissues of a gland or of an internal organ, a marked alteration of the expression and the activity levels of both MMPs is known to occur. The present investigation represents the continuation and upgrading of our previous studies, now focusing on the occurrence and intensity levels of MMP-2 and -9 and their proteomic correlations in a cohort of 80 breast cancer surgical tissues.

New insights into the tPA-annexin A2 interaction. Is annexin A2 CYS8 the sole requirement for this association?

Annexin A2 has been described as an important receptor for tissue-type plasminogen activator in endothelium and other cell types. Interaction between tissue-type plasminogen activator and its cellular receptor is critical for many of the functions of this protease. The annexin A2 motif that mediates tissue plasminogen activator interaction has been assigned to the hexapeptide LCKLSL in the amino-terminal domain of the protein, and it has been proposed that Cys(8) of this sequence is essential for tPA binding. In an attempt to identify other amino acids critical for tPA-annexin A2 interaction, we have analyzed a set of peptides containing several modifications of the original hexapeptide, including glycine scans, alanine scans, d-amino acid scans, conservative mutations, cysteine blocking, and enantiomer and retroenantiomer sequences. Using a non-radioactive competitive binding assay, we have found that all cysteine-containing peptides, independently of their sequence, compete the interaction between tPA and annexin A2. Cysteine-containing peptides also inhibit tPA binding to the surface of cultured human umbilical vein endothelial cells (HUVEC). Mass spectrometry demonstrates that the peptides bind through a disulfide bond to a cysteine residue of annexin A2, the same mechanism that has been suggested for the inhibition mediated by homocysteine. These data call for a revision of the role of the LCKLSL sequence as the sole annexin A2 structural region required to bind tPA and indicate that further studies are necessary to better define the annexin A2-tPA interaction.

Ligand-regulated secretion of recombinant annexin V from cultured thyroid epithelial cells

The exposure of anionic phospholipids on the external surface of injured endothelial cells and activated platelets is a primary biological signal to initiate blood coagulation. Disease conditions that promote the formation of ectopic thrombi result in tissue ischemia. Annexins, Ca2+-dependent anionic phospholipid binding proteins, are potential therapeutic agents for the inhibition of coagulation. We have designed a transgene that targets secretion of annexin V from cultured thyroid cells under the control of doxycycline. Our results indicate that annexin V in the endoplasmic reticulum (ER)/Golgi lumen does not affect the synthesis, processing, and secretion of thyroglobulin. ER luminal Ca2+ was moderately increased and can be released by inositol 1,4,5-trisphosphate. Our study demonstrates that targeting and secretion of annexin V through the secretory pathway of mammalian cells does not adversely affect cellular function. Regulated synthesis and release of annexin V may exert anticoagulatory and anti-inflammatory effects systemically and may prove useful in further developing therapeutic strategies for conditions including antiphospholipid syndrome.

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.

Anti-annexin V antibody in systemic lupus erythematosus patients with lupus anticoagulant and/or anticardiolipin antibody

We investigated anti-annexin V antibody (aANX) in patients with systemic lupus erythematosus (SLE), and correlated to positivity with lupus anticoagulant (LA)/anticardiolipin antibody (aCL). aANX was positive in 12/47 SLE patients (26%), including 7 with beta 2-glycoprotein 1 (GPI)-dependent aANX. The positivity of aANX was higher in patients with aCL (19%) and LA/aCL (50%) than in those without LA/aCL (10%). From these results, it is concluded that aANX is an autoantibody closely related to LA/aCL, and can be a possible new risk marker for thrombosis.

Interaction of annexin V and platelets: effects on platelet function and protein S binding

Intact annexin V but not its fragments bound specifically to platelets in the presence of calcium. Maximal binding observed was 0.87 pmole annexin V per 10(8) platelets with an apparent dissociation constant of 2.13 x 10(-11) M. This represents approximately 5000 binding sites per platelet. Platelet stimulation by thrombin increased the binding of annexin V by 40-fold. Addition of phospholipid vesicles or treatment with phospholipase C inhibited annexin V binding to platelets, suggesting that phospholipid is the binding site for annexin V and that phosphatidylcholine forms at least part of this site. Binding of annexin V did not cause platelet aggregation and did not affect thrombin or collagen induced aggregation. However annexin V significantly inhibited the binding of protein S to the platelet surface.