Margarethe Geiger, Center of Physiology and Pharmacology, Department of Vascular Biology and Thrombosis Research, Medical University of Vienna, Schwarzspanierstraße 17, A-1090 Vienna, Austria, Tel.: +43 1 40160 31106, Fax: +43 1 40160 931129, E-mail:
Thromb Haemost. 2014 Jan;111(1):41-52. doi: 10.1160/TH13-06-0478. Epub 2013 Oct 17.
Protein C inhibitor (PCI, SerpinA5) is a heparin-binding serpin which can penetrate through cellular membranes. Selected negatively charged phospholipids like unsaturated phosphatidylserine and oxidised phosphatidylethanolamine bind to PCI and stimulate its inhibitory activity towards different proteases. The interaction of phospholipids with PCI might also alter the lipid distribution pattern of blood cells and influence the remodelling of cellular membranes. Here we showed that PCI is an additional binding partner of phosphatidic acid (PA), cardiolipin (CL), and phosphoinositides (PIPs). Protein lipid overlay assays exhibited a unique binding pattern of PCI towards different lipid species. In addition PA, CL, and unsaturated, monophosphorylated PIPs stimulated the inhibitory property of PCI towards activated protein C in a heparin like manner. As shown for kallistatin (SerpinA4) and vaspin (SerpinA12), the incubation of cells with PCI led to the activation of protein kinase B (AKT), which could be achieved through direct interaction of PCI with PIPs. This model is supported by the fact that PCI stimulated the PIP-dependent 5-phosphatase SHIP2 in vitro, which would result in AKT activation. Hence the interaction of PCI with different lipids might not only stimulate the inhibition of potential target protease by PCI, but could also alter intracellular lipid signalling.
蛋白 C 抑制剂（PCI，SerpinA5）是一种肝素结合丝氨酸蛋白酶抑制剂，能够穿透细胞膜。一些带负电荷的磷脂，如不饱和磷脂酰丝氨酸和氧化型磷脂酰乙醇胺，与 PCI 结合并刺激其对不同蛋白酶的抑制活性。磷脂与 PCI 的相互作用还可能改变血细胞的脂质分布模式，并影响细胞膜的重塑。在这里，我们发现 PCI 是磷脂酸（PA）、心磷脂（CL）和磷酸肌醇（PIPs）的另一个结合伴侣。蛋白脂质覆盖实验显示 PCI 与不同脂质种类具有独特的结合模式。此外，PA、CL 和不饱和单磷酸化 PIPs 以肝素样方式刺激 PCI 对活化蛋白 C 的抑制特性。与 kallistatin（SerpinA4）和 vaspin（SerpinA12）一样，将 PCI 孵育细胞会导致蛋白激酶 B（AKT）的激活，这可以通过 PCI 与 PIPs 的直接相互作用来实现。这一模型得到了以下事实的支持：PCI 刺激了体外依赖 PIP 的 5-磷酸酶 SHIP2，这将导致 AKT 的激活。因此，PCI 与不同脂质的相互作用不仅可以刺激 PCI 对潜在靶蛋白酶的抑制作用，还可以改变细胞内脂质信号。
