Faucette K J, Fitzgerald L A, Liu L, Parker C J, Rodgers G M
Department of Pediatrics, University of Utah Medical Center, Salt Lake City 84132.
Blood. 1993 Nov 1;82(9):2684-92.
Normal human plasma contains procoagulant albumin (PC-Al), an anionic form of albumin that induces tissue factor (TF) activity in human umbilical vein endothelial cells (HUVEC) and monocytes. In this study, we investigated both the interactions between HUVEC and PC-Al and the mechanism by which PC-Al induces TF activity. Binding of PC-Al to HUVEC was specific and reversible. Further studies indicated that membrane-bound PC-Al was not internalized by HUVEC. A potential receptor on HUVEC was suggested by studies in which the capacity of a variety of reagents to inhibit the activity of PC-Al was quantitated. Induction of TF activity by PC-Al was antagonized by dextran sulfate, heparin, fucoidan, and concanavalin A but not by ovalbumin, polyglutamic acid, or polyvinyl sulfate. This competition profile bears similarities to those reported for scavenger receptors that have been identified on both HUVEC and monocytes. Involvement of protein kinase C (PKC) in the PC-Al-induced enhancement of TF activity was suggested by experiments in which staurosporine, an inhibitor of PKC, suppressed the activity of PC-Al. The induction of TF activity by PC-Al was further characterized by using a quantitative polymerase chain reaction assay. Increased TF mRNA was first seen after 1 hour of incubation with PC-Al. Maximal observed expression occurred at 2 hours, but at 5 hours, expression had significantly decreased. Monocytes could also be induced to express TF mRNA after a 2-hour incubation with PC-Al. These results suggest that the functionally relevant binding of PC-Al to HUVEC may be mediated through interactions with a membrane constituent that has some of the properties of a scavenger receptor and that this interaction augments TF activity by enhancing transcription of TF mRNA, at least in part, by a mechanism that is dependent on activation of PKC.
正常人体血浆中含有促凝血白蛋白（PC-Al），它是白蛋白的一种阴离子形式，可诱导人脐静脉内皮细胞（HUVEC）和单核细胞中的组织因子（TF）活性。在本研究中，我们调查了HUVEC与PC-Al之间的相互作用以及PC-Al诱导TF活性的机制。PC-Al与HUVEC的结合是特异性且可逆的。进一步研究表明，膜结合的PC-Al不会被HUVEC内化。通过定量各种试剂抑制PC-Al活性的能力的研究，提示了HUVEC上可能存在一种潜在受体。硫酸葡聚糖、肝素、岩藻依聚糖和伴刀豆球蛋白A可拮抗PC-Al诱导的TF活性，但卵清蛋白、聚谷氨酸或聚硫酸乙烯酯则不能。这种竞争模式与在HUVEC和单核细胞上已鉴定出的清道夫受体的报道相似。蛋白激酶C（PKC）参与PC-Al诱导的TF活性增强，这一推测来自实验，即PKC抑制剂星形孢菌素可抑制PC-Al的活性。通过定量聚合酶链反应分析进一步表征了PC-Al诱导的TF活性。与PC-Al孵育1小时后首次观察到TF mRNA增加。最大观察到的表达在2小时出现，但在5小时时，表达已显著下降。与PC-Al孵育2小时后，单核细胞也可被诱导表达TF mRNA。这些结果表明，PC-Al与HUVEC的功能相关结合可能通过与具有清道夫受体某些特性的膜成分相互作用介导，并且这种相互作用至少部分地通过依赖PKC激活的机制增强TF mRNA转录来增强TF活性。
