Chu Arthur J, Lin Shi-Hua, Piasentin Evano
Department of Surgery, School of Medicine, Wayne State University, 416 Lande Medical Research Building, 550 E. Canfield, Detroit, MI 48201, USA.
Br J Haematol. 2002 Aug;118(2):569-76. doi: 10.1046/j.1365-2141.2002.03611.x.
The enhanced extrinsic tissue factor (TF)-initiated coagulation, often resulting from sepsis, could lead to disseminated intravascular coagulation presenting cardiovascular complications. Using model human leukaemia THP-1 monocytes, we studied monocytic TF (mTF) hypercoagulation and its regulation. After an 8 h exposure to bacterial endotoxin [lipopolysaccharide (LPS); 100 ng/ml], mTF activity was significantly upregulated as the result of the enhanced mTF synthesis. Thereafter, LPS induction declined, exhibiting a "quiescent-desensitizing' phenomenon. Such diminished LPS induction was,however,associated with sustained LPS-enhanced mTF synthesis, revealing the possible occurrence of a post-translational downregulation. It was noted that LPS desensitization was accompanied by the increased expression of myristoylated alanine-rich C kinase substrate (Marcks). In contrast, A23187 (20 micromol/l) or Quin-2AM (20 micromol/l) drastically activated mTF activity without detectable effect on mTF synthesis; both of which showed that sustained functional upregulation during 24 h culture did not enhance Marcks expression. These inverse correlations between mTF activity upregulation and Marcks expression suggested that Marcks could be inhibitory. Marcks phosphorylation site domain (151-175) (Marcks PSD) readily inhibited mTF-dependent FVII activation and diminished FVIIa formation in LPS-challenged cells. As a result, Marcks PSD offset LPS-induced mTF hypercoagulation upon inclusion in the single-stage clotting assays. The anticoagulant activity was confirmed by showing that Marcks PSD significantly blocked rabbit brain thromboplastin (rbTF) procoagulation and inhibited rbTF-dependent FVII activation as well as FVIIa formation. Our study suggests that Marcks expression plays a role in a novel cellular modulation to downregulate mTF hypercoagulation.
败血症常导致外源性组织因子（TF）启动的凝血增强，进而引发弥散性血管内凝血并出现心血管并发症。我们使用人白血病THP - 1单核细胞模型，研究了单核细胞TF（mTF）的高凝状态及其调控机制。在暴露于细菌内毒素[脂多糖（LPS）；100 ng/ml] 8小时后，由于mTF合成增强，mTF活性显著上调。此后，LPS诱导作用下降，呈现出“静止 - 脱敏”现象。然而，这种LPS诱导作用的减弱与LPS增强的mTF合成持续存在相关，提示可能发生了翻译后下调。值得注意的是，LPS脱敏伴随着富含豆蔻酰化丙氨酸的C激酶底物（Marcks）表达增加。相比之下，A23187（20 μmol/l）或喹吖因 - 2AM（20 μmol/l）可显著激活mTF活性，但对mTF合成无明显影响；这两者均表明在24小时培养过程中持续的功能上调并未增强Marcks表达。mTF活性上调与Marcks表达之间的这些负相关表明Marcks可能具有抑制作用。Marcks磷酸化位点结构域（151 - 175）（Marcks PSD）可轻易抑制mTF依赖的FVII激活，并减少LPS刺激细胞中FVIIa的形成。结果，在单阶段凝血试验中加入Marcks PSD可抵消LPS诱导的mTF高凝状态。通过显示Marcks PSD可显著阻断兔脑凝血活酶（rbTF）的促凝作用，并抑制rbTF依赖的FVII激活以及FVIIa形成，证实了其抗凝活性。我们的研究表明，Marcks表达在一种新型细胞调节中发挥作用，以下调mTF高凝状态。
