Rotolo Jimmy A, Zhang Jianjun, Donepudi Manjula, Lee Hyunmi, Fuks Zvi, Kolesnick Richard
Laboratory of Signal Transduction and Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
J Biol Chem. 2005 Jul 15;280(28):26425-34. doi: 10.1074/jbc.M414569200. Epub 2005 Apr 22.
Recent evidence suggests clustering of plasma membrane rafts into ceramide-enriched platforms serves as a transmembrane signaling mechanism for a subset of cell surface receptors and environmental stresses (Grassme, H., Jekle, A., Riehle, A., Schwarz, H., Berger, J., Sandhoff, K., Kolesnick, R., and Gulbins, E. (2001) J. Biol. Chem. 276, 20589-20596; Cremesti, A., Paris, F., Grassme, H., Holler, N., Tschopp, J., Fuks, Z., Gulbins, E., and Kolesnick, R. (2001) J. Biol. Chem. 276, 23954-23961). Translocation of the secretory form of acid sphingomyelinase (ASMase) into microscopic rafts generates therein the ceramide that drives raft coalescence. This process serves to feed forward Fas activation, with approximately 2% of full caspase 8 activation sufficient for maximal ASMase translocation, leading to death-inducing signaling complex formation within ceramide-rich platforms, and apoptosis. Here we report that treatment of Jurkat T cells with UV-C also induces ASMase translocation into rafts within 1 min, catalyzing sphingomyelin hydrolysis to ceramide and raft clustering. In contrast to Fas, UV-induced ASMase translocation and activation were caspase-independent. Nonetheless, ceramide-rich platforms promoted UV-C-induced death signaling, because ASMase inhibition or raft disruption inhibited apoptosis, improving clonogenic cell survival. These studies thus define two distinct mechanisms for biologically relevant ASMase activation within rafts; a Fas-mediated mechanism dependent upon caspase 8 and FADD, and a UV-induced mechanism independent of caspase activation. Consistent with this notion, genetic depletion or pharmacologic inhibition of caspase 8 or FADD, which render Jurkat cells incapable of sphingolipid signaling and apoptosis upon Fas ligation, did not impair these events upon UV-C stimulation.
最近的证据表明，质膜筏聚集成富含神经酰胺的平台是细胞表面受体和环境应激的一个子集的跨膜信号传导机制（格拉斯梅，H.，杰克勒，A.，里尔，A.，施瓦茨，H.，伯杰，J.，桑德霍夫，K.，科尔斯尼克，R.，和古尔宾斯，E.（2001年）《生物化学杂志》276，20589 - 20596；克雷梅斯蒂，A.，帕里斯，F.，格拉斯梅，H.，霍勒，N.，茨科普，J.，富克斯，Z.，古尔宾斯，E.，和科尔斯尼克，R.（2001年）《生物化学杂志》276，23954 - 23961）。酸性鞘磷脂酶（ASMase）分泌形式转位到微小筏中会在其中产生驱动筏聚结的神经酰胺。这个过程有助于前馈激活Fas，大约2%的完全半胱天冬酶8激活就足以实现最大程度的ASMase转位，导致在富含神经酰胺的平台内形成死亡诱导信号复合物，并引发细胞凋亡。在这里我们报告，用UV - C处理Jurkat T细胞也会在1分钟内诱导ASMase转位到筏中，催化鞘磷脂水解为神经酰胺并使筏聚集。与Fas不同，UV诱导的ASMase转位和激活不依赖于半胱天冬酶。尽管如此，富含神经酰胺的平台促进了UV - C诱导的死亡信号传导，因为ASMase抑制或筏破坏会抑制细胞凋亡，提高克隆形成细胞的存活率。因此，这些研究确定了筏内生物学相关的ASMase激活的两种不同机制；一种是依赖于半胱天冬酶8和FADD的Fas介导机制，以及一种不依赖于半胱天冬酶激活的UV诱导机制。与此观点一致的是，半胱天冬酶8或FADD的基因缺失或药物抑制会使Jurkat细胞在Fas连接时无法进行鞘脂信号传导和细胞凋亡，但在UV - C刺激时不会损害这些事件。
