Wang Xue, Wang Yong, Kim Hong Pyo, Choi Augustine M K, Ryter Stefan W
Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, University of Pittsburgh Medical Center, 3459 Fifth Avenue, MUH 628NW, Pittsburgh, PA 15213, USA.
Free Radic Biol Med. 2007 May 15;42(10):1599-609. doi: 10.1016/j.freeradbiomed.2007.02.020. Epub 2007 Feb 28.
High oxygen tension (hyperoxia) causes pulmonary cell death, involving apoptosis, necrosis, or mixed death phenotypes, though the underlying mechanisms remain unclear. In mouse lung endothelial cells (MLEC) hyperoxia activates both extrinsic (Fas-dependent) and intrinsic (mitochondria-dependent) apoptotic pathways. We examined the hypothesis that FLIP, an inhibitor of caspase-8, can protect endothelial cells against the lethal effects of hyperoxia. Hyperoxia caused the time-dependent downregulation of FLIP in MLEC. Overexpression of FLIP attenuated intracellular reactive oxygen species generation during hyperoxia exposure, by downregulating extracellular-regulated kinase-1/2 activation and p47(phox) expression. FLIP prevented hyperoxia-induced trafficking of the death-inducing signal complex from the Golgi apparatus to the plasma membrane. Furthermore, FLIP blocked the activations of caspase-8/Bid, caspases -3/-9, and inhibited the mitochondrial translocation and activation of Bax, resulting in protection against hyperoxia-induced cell death. Under normoxic conditions, FLIP expression increased the phosphorylation of p38 mitogen-activated protein kinase leading to increased phosphorylation of Bax during hyperoxic stress. Furthermore, FLIP expression markedly inhibited protein kinase C activation and expression of distinct protein kinase C isoforms (alpha, eta, and zeta), and stabilized an interaction of PKC with Bax. In conclusion, FLIP exerted novel inhibitory effects on extrinsic and intrinsic apoptotic pathways, which significantly protected endothelial cells from the lethal effects of hyperoxia.
高氧张力（高氧）会导致肺细胞死亡，包括凋亡、坏死或混合性死亡表型，但其潜在机制仍不清楚。在小鼠肺内皮细胞（MLEC）中，高氧会激活外源性（Fas依赖）和内源性（线粒体依赖）凋亡途径。我们检验了一种假设，即半胱天冬酶-8的抑制剂FLIP可以保护内皮细胞免受高氧的致死作用。高氧导致MLEC中FLIP随时间下调。FLIP的过表达通过下调细胞外调节激酶-1/2的激活和p47（phox）的表达，减弱了高氧暴露期间细胞内活性氧的产生。FLIP阻止了高氧诱导的死亡诱导信号复合物从高尔基体向质膜的转运。此外，FLIP阻断了半胱天冬酶-8/ Bid、半胱天冬酶-3/ -9的激活，并抑制了Bax的线粒体易位和激活，从而防止高氧诱导的细胞死亡。在常氧条件下，FLIP的表达增加了p38丝裂原活化蛋白激酶的磷酸化，导致高氧应激期间Bax的磷酸化增加。此外，FLIP的表达显著抑制了蛋白激酶C的激活和不同蛋白激酶C亚型（α、η和ζ）的表达，并稳定了蛋白激酶C与Bax的相互作用。总之，FLIP对外源性和内源性凋亡途径发挥了新的抑制作用，显著保护内皮细胞免受高氧的致死作用。
