Rao L V, Tait J F, Hoang A D
Department of Medicine, University of California, San Diego 92093.
Thromb Res. 1992 Sep 1;67(5):517-31. doi: 10.1016/0049-3848(92)90013-z.
Proteins of the annexin/lipocortin family bind tightly to anionic phospholipids and platelets and act as in vitro anticoagulants. Annexins may be useful as tools to study the availability of anionic phospholipids on cell surfaces and their role in the regulation of blood coagulation. In the present study, we investigated the binding of annexin V (placental anticoagulant protein I) to a human ovarian carcinoma cell line, OC-2008, that constitutively expresses surface membrane tissue factor activity. Binding of annexin V to cell monolayers was calcium-dependent, specific, saturable and reversible; Scatchard analysis indicated a single class of binding sites with an apparent Kd of 9.4 +/- 3.1 nM and 5.2 +/- 1 x 10(6) sites per cell. Binding was completely inhibited by phospholipid vesicles containing phosphatidylserine, but was not inhibited by vesicles containing phosphatidylcholine. Annexin V inhibited the cell surface-dependent activity of prothrombinase complex, but did not inhibit the activity of the factor VIIa/tissue factor complex. In conclusion, these results suggest that anionic phospholipid is present on the extracellular face of OC-2008 cells; this anionic phospholipid is functionally important for the activity of the prothrombinase complex, but the importance of anionic phospholipid for the cell surface factor VIIa/tissue factor functional activity is unclear.
膜联蛋白/脂皮质蛋白家族的蛋白质与阴离子磷脂和血小板紧密结合，并在体外起到抗凝剂的作用。膜联蛋白可用作研究细胞表面阴离子磷脂的可利用性及其在血液凝固调节中作用的工具。在本研究中，我们研究了膜联蛋白V（胎盘抗凝蛋白I）与一种组成性表达表面膜组织因子活性的人卵巢癌细胞系OC - 2008的结合情况。膜联蛋白V与细胞单层的结合是钙依赖性的、特异性的、可饱和的且可逆的；Scatchard分析表明存在一类单一的结合位点，每个细胞的表观解离常数Kd为9.4±3.1 nM，结合位点数量为5.2±1×10(6)个。含有磷脂酰丝氨酸的磷脂囊泡可完全抑制结合，但含有磷脂酰胆碱的囊泡则不能抑制。膜联蛋白V抑制凝血酶原酶复合物的细胞表面依赖性活性，但不抑制因子VIIa/组织因子复合物的活性。总之，这些结果表明阴离子磷脂存在于OC - 2008细胞的细胞外表面；这种阴离子磷脂对凝血酶原酶复合物的活性具有重要功能意义，但阴离子磷脂对细胞表面因子VIIa/组织因子功能活性的重要性尚不清楚。
