Shankaranarayanan Pattabhiraman, Nigam Santosh
Eicosanoid and Lipid Research Division, Department of Gynecology, University Medical Center Benjamin Franklin, Free University Berlin, Germany.
J Immunol. 2003 Jan 15;170(2):887-94. doi: 10.4049/jimmunol.170.2.887.
The proinflammatory cytokine IL-4 is secreted in large amounts during allergic inflammatory response in asthma and plays a pivotal role in the airway inflammation. IL-4 has been shown to up-regulate 15-lipoxygenase and produce 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE) in A549 cells via the Janus kinase/STAT6 pathway under coactivation of CREB binding protein/p300. IL-4 has also been shown to up-regulate peroxisome proliferator-activated receptor gamma (PPARgamma) nuclear receptors in macrophages and A549 cells. In this study we demonstrate that 15(S)-HETE binds to PPARgamma nuclear receptors and induces apoptosis in A549 cells. Moreover, pretreatment of cells with nordihydroguaiaretic acid, a 15-lipoxygenase inhibitor, prevented PPARgamma activation and apoptosis. The latter was accomplished by the interaction of the 15(S)-HETE/PPARgamma complex with the adapter protein Fas-associating protein with death domain and caspase-8, as shown by transfection of Fas-associating protein with death domain dominant negative vector and cleavage of caspase 8 to active subunits p41/42 and p18. Whereas IL-4 and PPARgamma ligands failed to induce cleavage of Bid and release of cytochrome c from mitochondria, they caused translocation of the proapoptotic protein Bax from cytoplasm to mitochondria with a concomitant decrease in the Bcl-x(L) level. We therefore believe that in unstimulated cells Bcl-x(L) and Bax form a heterodimer, in which Bcl-x(L) dominates and prevents the induction of apoptosis, whereas in IL-4-stimulated cells the 15(S)-HETE/PPARgamma complex down-regulates Bcl-x(L), and the resulting overweight of Bax commits the cell to apoptosis via caspase-3. However, this pathway does not rule out the direct caspase-8-mediated activation of caspase-3. In conclusion, IL-4-induced apoptosis may contribute to severe loss of alveolar structures and infiltration of eosinophils, mononuclear phagocytes, etc., into the lung tissue of chronic asthma patients.
促炎细胞因子白细胞介素-4（IL-4）在哮喘的过敏性炎症反应中大量分泌，在气道炎症中起关键作用。研究表明，在CREB结合蛋白/p300的共同激活下，IL-4通过Janus激酶/信号转导子和转录激活子6（STAT6）途径上调A549细胞中的15-脂氧合酶并产生15（S）-羟基二十碳四烯酸（15（S）-HETE）。IL-4还被证明可上调巨噬细胞和A549细胞中的过氧化物酶体增殖物激活受体γ（PPARγ）核受体。在本研究中，我们证明15（S）-HETE与PPARγ核受体结合并诱导A549细胞凋亡。此外，用15-脂氧合酶抑制剂去甲二氢愈创木酸预处理细胞可防止PPARγ激活和细胞凋亡。如通过转染死亡结构域显性负性载体的Fas相关蛋白以及将半胱天冬酶8切割成活性亚基p41/42和p18所示，后者是通过15（S）-HETE/PPARγ复合物与接头蛋白死亡结构域相关蛋白Fas结合蛋白和半胱天冬酶8的相互作用实现的。虽然IL-4和PPARγ配体未能诱导Bid的切割和细胞色素c从线粒体的释放，但它们导致促凋亡蛋白Bax从细胞质易位至线粒体，同时Bcl-x（L）水平降低。因此，我们认为在未受刺激的细胞中，Bcl-x（L）和Bax形成异二聚体，其中Bcl-x（L）占主导并阻止细胞凋亡的诱导，而在IL-4刺激的细胞中，15（S）-HETE/PPARγ复合物下调Bcl-x（L），导致Bax过量，使细胞通过半胱天冬酶3发生凋亡。然而，该途径并不排除半胱天冬酶8直接介导的半胱天冬酶3激活。总之，IL-4诱导的细胞凋亡可能导致慢性哮喘患者肺泡结构的严重丧失以及嗜酸性粒细胞、单核吞噬细胞等浸润到肺组织中。
