Shen L, Dahlbäck B
Department of Clinical Chemistry, University of Lund, Malmö General Hospital, Sweden.
J Biol Chem. 1994 Jul 22;269(29):18735-8.
Inherited resistance to activated protein C (APC) is a recently identified major cause of thrombosis. It is associated with a mutation in the factor V gene affecting one of the cleavage sites for APC. APC resistance was recently found to be corrected by factor V, suggesting that factor V may have anticoagulant properties as a cofactor to APC. To elucidate this further, we have studied the effect of factor V and protein S, which is a known cofactor to APC, on APC-mediated degradation of factor VIIIa in a purified system. The APC-mediated degradation of factor VIIIa was monitored by a factor X activation reaction using purified factor IXa, phospholipid, and calcium. In the presence of both factor V and protein S, APC was found to inhibit factor VIIIa activity efficiently. APC alone or together with factor V was ineffective, whereas APC in combination with protein S was less efficient than when factor V was also included in the reaction. Two monoclonal antibodies, one against protein S and the other directed toward factor V, were found to inhibit the APC cofactor activity of the factor V-protein S mixture. Factor Va did not express APC cofactor activity, and addition of excess factor Va over factor V did not inhibit the APC cofactor function of a factor V-protein S mixture. In conclusion, the results suggest that factor V and protein S work in synergy as phospholipid-bound cofactors to APC.
遗传性活化蛋白C（APC）抵抗是最近发现的血栓形成的主要原因。它与影响APC一个裂解位点的凝血因子V基因突变有关。最近发现APC抵抗可被凝血因子V纠正，这表明凝血因子V作为APC的辅因子可能具有抗凝特性。为进一步阐明这一点，我们在一个纯化系统中研究了凝血因子V和蛋白S（已知的APC辅因子）对APC介导的凝血因子VIIIa降解的影响。通过使用纯化的凝血因子IXa、磷脂和钙的凝血因子X激活反应来监测APC介导的凝血因子VIIIa降解。在同时存在凝血因子V和蛋白S的情况下，发现APC能有效抑制凝血因子VIIIa的活性。单独的APC或与凝血因子V一起都无效，而APC与蛋白S联合时比反应中也包含凝血因子V时效率更低。发现两种单克隆抗体，一种针对蛋白S，另一种针对凝血因子V，可抑制凝血因子V - 蛋白S混合物的APC辅因子活性。凝血因子Va不表达APC辅因子活性，并且在凝血因子V之上添加过量的凝血因子Va不会抑制凝血因子V - 蛋白S混合物的APC辅因子功能。总之，结果表明凝血因子V和蛋白S作为与磷脂结合的APC辅因子协同发挥作用。
