Iakhiaev A, Pendurthi U R, Voigt J, Ezban M, Vijaya Mohan Rao L
Department of Biochemistry, The University of Texas Health Center, Tyler, Texas 75708, USA.
J Biol Chem. 1999 Dec 24;274(52):36995-7003. doi: 10.1074/jbc.274.52.36995.
Vascular injury leads to the exposure of blood to fibroblasts and smooth muscle cells within the vessel wall. These cells constitutively express tissue factor (TF), the cellular receptor for plasma clotting factor VIIa (FVIIa). Formation of TF.FVIIa complexes on cell surfaces triggers the blood coagulation cascade. In the present study, we have investigated the fate of TF.FVIIa complexes formed on the cell surface of fibroblasts in the presence and absence of plasma inhibitor, tissue factor pathway inhibitor (TFPI). FVIIa bound to TF on the cell surface was internalized and degraded without depleting the cell surface TF antigen and activity. TFPI significantly enhanced the TF-specific internalization and degradation of FVIIa. TFPI-enhanced internalization and degradation of FVIIa requires the C-terminal domain of TFPI and factor Xa. TFPI. Xa-mediated internalization of FVIIa was associated with the depletion of TF from the cell surface. A majority of the internalized FVIIa was degraded, but a small portion of the internalized FVIIa recycles back to the cell surface as an intact protein. In addition to TF, other cell surface components, such as low density lipoprotein receptor-related protein (LRP) and heparan sulfates, are essential for TFPI.Xa-induced internalization of FVIIa. Acidification of cytosol, which selectively inhibits the endocytotic pathway via coated pits, inhibited TFPI.Xa-mediated internalization but not the basal internalization of FVIIa. Overall, our data support the concept that FVIIa bound to cell surface TF was endocytosed by two different pathways. FVIIa complexed with TF in the absence of the inhibitor was internalized via a LRP-independent and probably noncoated pit pathway, whereas FVIIa complexed with TF along with the inhibitor was internalized via LRP-dependent coated pit pathway.
血管损伤会导致血液与血管壁内的成纤维细胞和平滑肌细胞接触。这些细胞组成性地表达组织因子（TF），它是血浆凝血因子VIIa（FVIIa）的细胞受体。细胞表面TF.FVIIa复合物的形成会触发血液凝固级联反应。在本研究中，我们研究了在存在和不存在血浆抑制剂组织因子途径抑制剂（TFPI）的情况下，成纤维细胞表面形成的TF.FVIIa复合物的命运。与细胞表面TF结合的FVIIa被内化并降解，而不会耗尽细胞表面的TF抗原和活性。TFPI显著增强了FVIIa的TF特异性内化和降解。TFPI增强的FVIIa内化和降解需要TFPI的C末端结构域和因子Xa。TFPI.Xa介导的FVIIa内化与细胞表面TF的消耗有关。大部分内化的FVIIa被降解，但一小部分内化的FVIIa作为完整蛋白质循环回到细胞表面。除了TF，其他细胞表面成分，如低密度脂蛋白受体相关蛋白（LRP）和硫酸乙酰肝素，对于TFPI.Xa诱导的FVIIa内化也是必不可少的。细胞质酸化选择性地抑制通过被膜小窝的内吞途径，抑制了TFPI.Xa介导的内化，但不抑制FVIIa的基础内化。总体而言，我们的数据支持这样的概念，即与细胞表面TF结合的FVIIa通过两种不同途径被内吞。在没有抑制剂的情况下与TF复合的FVIIa通过不依赖LRP且可能是非被膜小窝的途径内化，而与TF复合且同时有抑制剂的FVIIa通过依赖LRP的被膜小窝途径内化。
