title: Aryl hydrocarbon receptor modulation of tumor necrosis factor-alpha-induced apoptosis and lysosomal disruption in a hepatoma model that is caspase-8-independent.
abstract: Recent studies suggest that the aryl hydrocarbon receptor (AhR) modulates susceptibilities to some pro-apoptotic agents. AhR-containing murine hepatoma 1c1c7 cultures underwent apoptosis following exposure to tumor necrosis factor-alpha (TNFalpha) + cycloheximide (CHX). In contrast, Tao cells, an AhR-deficient variant of the 1c1c7 line, were refractory to this treatment. AhR sense/antisense transfection studies demonstrated that AhR contents influenced susceptibility to the pro-apoptotic effects of TNFalpha + CHX. 1c1c7 cells and all variants expressed comparable amounts of TNF receptor-1 and TRADD. However, no cell line expressed FADD, and consequently pro-caspase-8 was not activated. AhR content did not influence JNK and NF-kappaB activation. However, Bid and pro-caspase-9, -3, and -12 processing occurred only in AhR-containing cells. Analyses of cathepsin B and D activities in digitonin-permeabilized cultures and the monitoring of cathepsin B/D co-localization with Lamp-1 indicated that TNFalpha + CHX disrupted late endosomes/lysosomes in only AhR-containing cells. Stabilization of acidic organelles with 3-O-methylsphingomyelin inhibited TNFalpha + CHX-induced apoptosis. The cathepsin D inhibitor pepstatin A suppressed in vitro cleavage of Bid by 1c1c7 lysosomal extracts. It also delayed the induction of apoptosis and partially prevented Bid cleavage and the activation of pro-caspases-3/7 in cultures treated with TNFalpha + CHX. Similar suppressive effects occurred in cultures transfected with murine Bid antisense oligonucleotides. These studies showed that in cells where pro-caspase-8 is not activated, TNFalpha + CHX can initiate apoptosis through lysosomal disruption. Released proteases such as cathepsin D trigger the apoptotic program by activating Bid. Furthermore, in the absence of exogenous ligand, the AhR modulates lysosomal disruption/permeability.
authors.affiliation: Institute of Environmental Health Sciences, Wayne State University, Detroit, Michigan 48201, USA.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Caruso
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Mathieu
authors.forename: Aby
authors.initials: A
authors.lastname: Joiakim
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
authors.forename: John J
authors.initials: JJ
authors.lastname: Reiners
mesh_terms: D000818:Animals; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism*; D002401:Cathepsin B / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism; D045744:Cell Line, Tumor; D003513:Cycloheximide / Q000378:metabolism / Q000494:pharmacology; D004072:Digitonin / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D011992:Endosomes / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D007930:Leucine / Q000737:chemistry; D008247:Lysosomes / Q000201:enzymology / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D015233:Models, Statistical; D009841:Oligonucleotides / Q000737:chemistry; D010447:Peptide Hydrolases / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*; D013109:Sphingomyelins / Q000494:pharmacology; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: C508074:3-O-methylsphingomyelin; D051023:BH3 Interacting Domain Death Agonist Protein; D009841:Oligonucleotides; D011500:Protein Synthesis Inhibitors; D018336:Receptors, Aryl Hydrocarbon; D013109:Sphingomyelins; D014409:Tumor Necrosis Factor-alpha; D003513:Cycloheximide; D007770:L-Lactate Dehydrogenase; D010447:Peptide Hydrolases; C505526:Casp8 protein, mouse; D053181:Caspase 8; D020169:Caspases; D002401:Cathepsin B; D002402:Cathepsin D; D007930:Leucine; D004072:Digitonin