title: Phosphatidic acid mediates the targeting of tBid to induce lysosomal membrane permeabilization and apoptosis.
abstract: Upon apoptotic stimuli, lysosomal proteases, including cathepsins and chymotrypsin, are released into cytosol due to lysosomal membrane permeabilization (LMP), where they trigger apoptosis via the lysosomal-mitochondrial pathway of apoptosis. Herein, the mechanism of LMP was investigated. We found that caspase 8-cleaved Bid (tBid) could result in LMP directly. Although Bax or Bak might modestly enhance tBid-triggered LMP, they are not necessary for LMP. To study this further, large unilamellar vesicles (LUVs), model membranes mimicking the lipid constitution of lysosomes, were used to reconstitute the membrane permeabilization process in vitro. We found that phosphatidic acid (PA), one of the major acidic phospholipids found in lysosome membrane, is essential for tBid-induced LMP. PA facilitates the insertion of tBid deeply into lipid bilayers, where it undergoes homo-oligomerization and triggers the formation of highly curved nonbilayer lipid phases. These events induce LMP via pore formation mechanisms because encapsulated fluorescein-conjugated dextran (FD)-20 was released more significantly than FD-70 or FD-250 from LUVs due to its smaller molecular size. On the basis of these data, we proposed tBid-PA interactions in the lysosomal membranes form lipidic pores and result in LMP. We further noted that chymotrypsin-cleaved Bid is more potent than tBid at binding to PA, inserting into the lipid bilayer, and promoting LMP. This amplification mechanism likely contributes to the culmination of apoptotic signaling.
authors: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China.
authors: Kai
authors: K
authors: Zhao
authors: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China; Graduate University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China.
authors: Hejiang
authors: H
authors: Zhou
authors: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China.
authors: Xingyu
authors: X
authors: Zhao
authors: Department of Pharmacology, Creighton University School of Medicine, Omaha, NE 68178; and.
authors: Dennis W
authors: DW
authors: Wolff
authors: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China; Department of Pharmacology, Creighton University School of Medicine, Omaha, NE 68178; and.
authors: Yaping
authors: Y
authors: Tu
authors: State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China.
authors: Huili
authors: H
authors: Liu
authors: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China. Electronic address: weitt@moon.ibp.ac.cn.
authors: Taotao
authors: T
authors: Wei
authors: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Chaoyang District, Beijing 100101, China. Electronic address: yangfy@sun5.ibp.ac.cn.
authors: Fuyu
authors: F
authors: Yang
mesh_terms: D000818:Animals; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D010539:Permeability; D010712:Phosphatidic Acids / Q000378:metabolism*; D051381:Rats; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D051023:BH3 Interacting Domain Death Agonist Protein; D010712:Phosphatidic Acids; D051028:bcl-2-Associated X Protein