title: Cathepsin-cleaved Bid promotes apoptosis in human neutrophils via oxidative stress-induced lysosomal membrane permeabilization.
abstract: Lysosomal membrane permeabilization (LMP) is emerging as an important regulator of cell apoptosis. Human neutrophils are highly granulated phagocytes, which respond to pathogens by exhibiting increased production of reactive oxygen species (ROS) and lysosomal degranulation. In a previous study, we observed that intracellular, nonphagosomal generation of ROS triggered by adherent bacteria induced ROS-dependent neutrophil apoptosis, whereas intraphagosomal production of ROS during phagocytosis had no effect. In the present study, we measured lysosomal membrane stability and leakage in human neutrophils and found that adherent, noningested, Type 1-fimbriated Escherichia coli bacteria induced LMP rapidly in neutrophils. Pretreatment with the NADPH oxidase inhibitor diphenylene iodonium markedly blocked the early LMP and apoptosis in neutrophils stimulated with Type 1-fimbriated bacteria but had no effect on the late LMP seen in spontaneously apoptotic neutrophils. The induced lysosomal destabilization triggered cleavage of the proapoptotic Bcl-2 protein Bid, followed by a decrease in the antiapoptotic protein Mcl-1. Involvement of LMP in initiation of apoptosis is supported by the following observations: Bid cleavage and the concomitant drop in mitochondrial membrane potential required activation of cysteine-cathepsins but not caspases, and the differential effects of inhibitors of cysteine-cathepsins and cathepsin D on apoptosis coincided with their ability to inhibit Bid cleavage in activated neutrophils. Together, these results indicate that in microbe-induced apoptosis in neutrophils, ROS-dependent LMP represents an early event in initiation of the intrinsic apoptotic pathway, which is followed by Bid cleavage, mitochondrial damage, and caspase activation.
authors.affiliation: Department of Molecular and Clinical Medicine, Faculty of Health Sciences, Linköping University, SE-581 85, Linköping, Sweden. robert.blomgran@imk.liu.se
authors.forename: Robert
authors.initials: R
authors.lastname: Blomgran
authors.forename: Limin
authors.initials: L
authors.lastname: Zheng
authors.forename: Olle
authors.initials: O
authors.lastname: Stendahl
mesh_terms: D017209:Apoptosis / Q000276:immunology*; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism*; D002403:Cathepsins / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000276:immunology*; D004926:Escherichia coli / Q000276:immunology; D010861:Fimbriae, Bacterial / Q000276:immunology; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000378:metabolism; D009504:Neutrophils / Q000201:enzymology* / Q000276:immunology; D018384:Oxidative Stress / Q000276:immunology*; D010100:Oxygen / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: C494826:BAX protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D051028:bcl-2-Associated X Protein; D002403:Cathepsins; D010100:Oxygen