Degli Esposti Mauro, Matarrese Paola, Tinari Antonella, Longo Agostina, Recalchi Serena, Khosravi-Far Roya, Malorni Walter, Misasi Roberta, Garofalo Tina, Sorice Maurizio
Italian Institute of Technology, Genoa, Italy.
Department of Drug Research and Evaluation, Istituto Superiore Sanita', Rome, Italy.
Apoptosis. 2017 May;22(5):681-695. doi: 10.1007/s10495-017-1362-6.
Once activated, some surface receptors promote membrane movements that open new portals of endocytosis, in part to facilitate the internalization of their activated complexes. The prototypic death receptor Fas (CD95/Apo1) promotes a wave of enhanced endocytosis that induces a transient intermixing of endosomes with mitochondria in cells that require mitochondria to amplify death signaling. This initiates a global alteration in membrane traffic that originates from changes in key membrane lipids occurring in the endoplasmic reticulum (ER). We have focused the current study on specific lipid changes occurring early after Fas ligation. We analyzed the interaction between endosomes and mitochondria in Jurkat T cells by nanospray-Time-of-flight (ToF) Mass Spectrometry. Immediately after Fas ligation, we found a transient wave of lipid changes that drives a subpopulation of early endosomes to merge with mitochondria. The earliest event appears to be a decrease of phosphatidylcholine (PC), linked to a metabolic switch enhancing phosphatidylinositol (PI) and phosphoinositides, which are crucial for the formation of vacuolar membranes and endocytosis. Lipid changes occur independently of caspase activation and appear to be exacerbated by caspase inhibition. Conversely, inhibition or compensation of PC deficiency attenuates endocytosis, endosome-mitochondria mixing and the induction of cell death. Deficiency of receptor interacting protein, RIP, also limits the specific changes in membrane lipids that are induced by Fas activation, with parallel reduction of endocytosis. Thus, Fas activation rapidly changes the interconversion of PC and PI, which then drives enhanced endocytosis, thus likely propagating death signaling from the cell surface to mitochondria and other organelles.
一旦被激活，一些表面受体可促进膜运动，从而打开新的内吞通道，部分是为了便于其激活复合物的内化。典型的死亡受体Fas（CD95/Apo1）会引发一波增强的内吞作用，在需要线粒体来放大死亡信号的细胞中，这种内吞作用会诱导内体与线粒体的短暂混合。这引发了膜运输的全局性改变，其起源于内质网（ER）中关键膜脂的变化。我们将当前的研究重点放在了Fas配体结合后早期发生的特定脂类变化上。我们通过纳米喷雾飞行时间（ToF）质谱分析了Jurkat T细胞中内体与线粒体之间的相互作用。在Fas配体结合后立即发现，有一波短暂的脂类变化，促使一部分早期内体与线粒体融合。最早的事件似乎是磷脂酰胆碱（PC）的减少，这与一种代谢转换有关，该转换增强了磷脂酰肌醇（PI）和磷酸肌醇，而它们对于液泡膜的形成和内吞作用至关重要。脂类变化独立于半胱天冬酶激活而发生，并且似乎会因半胱天冬酶抑制而加剧。相反，对PC缺乏的抑制或补偿会减弱内吞作用、内体 - 线粒体混合以及细胞死亡的诱导。受体相互作用蛋白RIP的缺乏也会限制Fas激活诱导的膜脂特异性变化，并同时减少内吞作用。因此，Fas激活会迅速改变PC和PI的相互转化，进而驱动增强的内吞作用，从而可能将死亡信号从细胞表面传播到线粒体和其他细胞器。
