Song Jin H, Bellail Anita, Tse Margaret C L, Yong V Wee, Hao Chunhai
Department of Pathology and Laboratory Medicine, Center of Neurodegenerative Disease, Winship Cancer Institute, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
J Neurosci. 2006 Mar 22;26(12):3299-308. doi: 10.1523/JNEUROSCI.5572-05.2006.
Human astrocytes express Fas yet are resistant to Fas-induced apoptosis. Here, we report that calcium/calmodulin-dependent protein kinase II (CaMKII) is constitutively activated in human astrocytes and protects the cells from apoptotic stimulation by Fas agonist. Once stimulated, Fas recruits Fas-associated death domain and caspase-8 for the assembly of the death-inducing signaling complex (DISC); however, caspase-8 cleavage is inhibited in the DISC. Inhibition of CaMKII kinase activity inhibits the expression of phosphoprotein enriched astrocytes-15 kDa/phosphoprotein enriched in diabetes (PEA-15/PED) and cellular Fas-associated death domain-like interleukin-1beta-converting enzyme-inhibitory protein (c-FLIP), thus releasing their inhibition of caspase-8 cleavage. Inhibition of PEA-15/PED or c-FLIP by small interfering RNA sensitizes human astrocytes to Fas-induced apoptosis. In contrast, inhibition of CaMKII, PEA-15, or c-FLIP does not affect the sensitivity of human astrocytes to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). TRAIL death receptors (DR4, DR5) are weakly expressed at mRNA, protein, and cell surface levels and thus fail to mediate the assembly of the DISC in human astrocytes. Overexpression of DR5 restores TRAIL signaling pathways and sensitizes the human astrocytes to TRAIL-induced apoptosis if CaMKII kinase activity or expression of PEA-15 and c-FLIP is inhibited; the results suggest that CaMKII-mediated pathways prevent TRAIL-induced apoptosis in human astrocytes under conditions in which TRAIL death receptors are upregulated. This study has therefore identified the molecular mechanisms that protect normal human astrocytes from apoptosis induced by Fas ligand and TRAIL.
人类星形胶质细胞表达Fas，但对Fas诱导的凋亡具有抗性。在此，我们报告钙/钙调蛋白依赖性蛋白激酶II（CaMKII）在人类星形胶质细胞中持续激活，并保护细胞免受Fas激动剂的凋亡刺激。一旦受到刺激，Fas招募Fas相关死亡结构域和半胱天冬酶-8以组装死亡诱导信号复合物（DISC）；然而，半胱天冬酶-8的切割在DISC中受到抑制。抑制CaMKII激酶活性会抑制富含磷酸蛋白的星形胶质细胞-15 kDa/糖尿病中富含磷酸蛋白（PEA-15/PED）和细胞Fas相关死亡结构域样白细胞介素-1β转换酶抑制蛋白（c-FLIP）的表达，从而解除它们对半胱天冬酶-8切割的抑制。用小干扰RNA抑制PEA-15/PED或c-FLIP会使人类星形胶质细胞对Fas诱导的凋亡敏感。相反，抑制CaMKII、PEA-15或c-FLIP不会影响人类星形胶质细胞对肿瘤坏死因子相关凋亡诱导配体（TRAIL）的敏感性。TRAIL死亡受体（DR4、DR5）在mRNA、蛋白质和细胞表面水平上弱表达，因此无法介导人类星形胶质细胞中DISC的组装。如果抑制CaMKII激酶活性或PEA-15和c-FLIP的表达，DR5的过表达可恢复TRAIL信号通路并使人类星形胶质细胞对TRAIL诱导的凋亡敏感；结果表明，在TRAIL死亡受体上调的条件下，CaMKII介导的通路可防止TRAIL诱导人类星形胶质细胞凋亡。因此，本研究确定了保护正常人类星形胶质细胞免受Fas配体和TRAIL诱导凋亡的分子机制。
