title: Low extracellular pH augments TRAIL-induced apoptotic death through the mitochondria-mediated caspase signal transduction pathway.
abstract: Tumor necrosis factor-related apoptosis inducing ligand (TRAIL/APO-2L), a member of the tumor necrosis factor (TNF) gene family, is considered as one of the most promising cancer therapeutic agents due to its ability to selectively kill tumor cells. Although microenvironments of solid tumors (hypoxia, nutrient deprivation, and low pH) often affect the effectiveness of chemotherapy, few studies have been reported on the relationship between tumor microenvironments and TRAIL. In this study, we investigated whether low extracellular pH affects TRAIL-induced apoptotic death. When human prostate carcinoma DU145 cells were treated with 200 ng/ml His-tagged TRAIL for 4 h, the survival was approximately 10% at pH 6.3-6.6 and 61.3% at pH 7.4. Similar results were observed in human colorectal carcinoma CX-1 cell line. The TRAIL-mediated activation of caspase, cytochrome c release, and poly (ADP-ribose) polymerase (PARP) cleavage was promoted at low extracellular pH. Immunoprecipitation followed by western blot analysis shows that low extracellular pH enhances the association of truncated Bid with Bax during treatment with TRAIL. Western blot analysis also shows that the low extracellular pH-enhanced TRAIL cytotoxicity does not involve modulation of the levels of TRAIL receptors (DR4, DR5, and DcR2), FLIP, inhibitor of apoptosis (IAP), and Bcl-2. Overexpression of Bcl-2 effectively prevented low extracellular pH-augmented TRAIL cytotoxicity. Taken together, we propose that TRAIL-mediated cytotoxicity is greatly enhanced in low pH environments by promoting caspase activation.
authors.affiliation: Department of Surgery and Cancer Institute, School of Medicine, University of Pittsburgh, PA 15213, USA. leeyj@msx.upmc.edu
authors.forename: Yong J
authors.initials: YJ
authors.lastname: Lee
authors.forename: Jae J
authors.initials: JJ
authors.lastname: Song
authors.forename: Jin H
authors.initials: JH
authors.lastname: Kim
authors.forename: Hyeong-Reh Choi
authors.initials: HR
authors.lastname: Kim
authors.forename: Young K
authors.initials: YK
authors.lastname: Song
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins; D051023:BH3 Interacting Domain Death Agonist Protein; D002277:Carcinoma / Q000188:drug therapy; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000188:drug therapy; D045304:Cytochromes c / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D008954:Models, Biological; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D011471:Prostatic Neoplasms / Q000188:drug therapy; D011506:Proteins / Q000187:drug effects / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein
chemical_list: D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D020169:Caspases