Annexin A5

Template:PBB Annexin A5 (or annexin V) is a cellular protein in the annexin group. The function of the protein is unknown; however, annexin A5 has been proposed to play a role in the inhibition of blood coagulation by competing for phosphatidylserine binding sites with prothrombin and also to inhibit the activity of phospholipase A1. These properties have been found by in vitro experiments.

Annexin A5 in pathology

Antibodies directed against annexin A5 are found in patients with a disease called the antiphospholipid syndrome (APS), a thrombophilic disease associated with autoantibodies against phospholipid compounds.

Annexin A5 forms a shield around negatively-charged phospholipid molecules. The formation of an annexin A5 shield blocks the entry of phospholipids into coagulation (clotting) reactions. In the antiphospholipid antibody syndrome, the formation of the shield is disrupted by antibodies. Without the shield, there is an increased quantity of phospholipid molecules on cell membranes, speeding up coagulation reactions and causing the blood-clotting characteristic of the antiphospholipid antibody syndrome.
Annexin A5 showed upregulation in papillary thyroid carcinoma.^[1]

Laboratory use of annexin A5

Annexin A5 is used as a probe to detect cells that have expressed phosphatidylserine (PS) and phosphatidylethanolamine (PE) on the cell surface, an event found in apoptosis as well as other forms of cell death.^[2]^[3] Platelets also expose PS on their surface when activated, which serves as binding site for various coagulation factors.

The annexin A5 affinity assay typically uses a conjugate of annexin V and a fluorescent or enzymatic label, biotin or other tags, or a radioelement, in a suitable buffer (annexin V binding to aminophospholipids is Ca²⁺ dependent). The assay combines annexin V staining of PS and PE membrane events with the staining of cell nucleus with PI or AAD-7 distinguish viable cells from apoptotic cells and necrotic cells.^[4] Detection occurs by flow cytometry or a fluorescence microscope.

Interactions

Annexin A5 has been shown to interact with Kinase insert domain receptor^[5] and Integrin, beta 5.^[6]

References

^ Sofiadis A, Becker S, Hellman U, Hultin-Rosenberg L, Dinets A, Hulchiy M, Zedenius J, Wallin G, Foukakis T, Höög A, Auer G, Lehtiö J, Larsson C. (April 2012). "Proteomic profiling of follicular and papillary thyroid tumors". Eur J Endocrinol.. 166 (4): 657–67. doi:10.1530/EJE-11-0856. PMID 22275472.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Koopman G, Reutelingsperger CP, Kuijten GAM; et al. (1994). "Annexin V for flow cytometric detection of phosphatidylserine expression on B cells undergoing apoptosis". Blood. 84 (5): 1415–20. PMID 8068938. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)
^ Vermes I, Haanen C, Steffens-Nakken H, Reutelingsperger C (1995). "A novel assay for apoptosis—flow cytometric detection of phosphatidylserine expression on early apoptotic cells using fluorescein labelled Annexin V". Journal of Immunology Methods. 184 (1): 39–51. doi:10.1016/0022-1759(95)00072-I. PMID 7622868.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Annexin-FP488 fluorescent staining protocol at Interchim
^ Wen, Y (May 1999). "Lipocortin V may function as a signaling protein for vascular endothelial growth factor receptor-2/Flk-1". Biochem. Biophys. Res. Commun. 258 (3). UNITED STATES: 713–21. doi:10.1006/bbrc.1999.0678. ISSN 0006-291X. PMID 10329451. {{cite journal}}: Cite has empty unknown parameters: |laydate=, |laysummary=, and |laysource= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
^ Cardó-Vila, Marina (May 2003). "Alpha v beta 5 integrin-dependent programmed cell death triggered by a peptide mimic of annexin V". Mol. Cell. 11 (5). United States: 1151–62. doi:10.1016/S1097-2765(03)00138-2. ISSN 1097-2765. PMID 12769841. {{cite journal}}: Cite has empty unknown parameters: |laydate=, |laysummary=, and |laysource= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)