title: Mechanisms for ribotoxin-induced ribosomal RNA cleavage.
abstract: The Type B trichothecene deoxynivalenol (DON), a ribotoxic mycotoxin known to contaminate cereal-based foods, induces ribosomal RNA (rRNA) cleavage in the macrophage via p38-directed activation of caspases. Here we employed the RAW 264.7 murine macrophage model to test the hypothesis that this rRNA cleavage pathway is similarly induced by other ribotoxins. Capillary electrophoresis confirmed that the antibiotic anisomycin (≥25ng/ml), the macrocylic trichothecene satratoxin G (SG) (≥10ng/ml) and ribosome-inactivating protein ricin (≥300ng/ml) induced 18s and 28s rRNA fragmentation patterns identical to that observed for DON. Also, as found for DON, inhibition of p38, double-stranded RNA-activated kinase (PKR) and hematopoietic cell kinase (Hck) suppressed MAPK anisomycin-induced rRNA cleavage, while, in contrast, their inhibition did not affect SG- and ricin-induced rRNA fragmentation. The p53 inhibitor pifithrin-μ and pan caspase inhibitor Z-VAD-FMK suppressed rRNA cleavage induced by anisomycin, SG and ricin, indicating that these ribotoxins shared with DON a conserved downstream pathway. Activation of caspases 8, 9 and 3 concurrently with apoptosis further suggested that rRNA cleavage occurred in parallel with both extrinsic and intrinsic pathways of programmed cell death. When specific inhibitors of cathepsins L and B (lysosomal cysteine cathepsins active at cytosolic neutral pH) were tested, only the former impaired anisomycin-, SG-, ricin- and DON-induced rRNA cleavage. Taken together, the data suggest that (1) all four ribotoxins induced p53-dependent rRNA cleavage via activation of cathepsin L and caspase 3, and (2) activation of p53 by DON and anisomycin involved p38 whereas SG and ricin activated p53 by an alternative mechanism.
authors.affiliation: Department of Microbiology and Molecular Genetics, USA.
authors.forename: Kaiyu
authors.initials: K
authors.lastname: He
authors.forename: Hui-Ren
authors.initials: HR
authors.lastname: Zhou
authors.forename: James J
authors.initials: JJ
authors.lastname: Pestka
mesh_terms: D000818:Animals; D000841:Anisomycin / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D053181:Caspase 8 / Q000187:drug effects; D056668:Cathepsin L / Q000494:pharmacology; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019384:Nucleic Acid Synthesis Inhibitors / Q000633:toxicity; D051572:Proto-Oncogene Proteins c-hck / Q000378:metabolism; D059367:RNA Cleavage / Q000187:drug effects*; D012335:RNA, Ribosomal / Q000187:drug effects* / Q000302:isolation & purification; D012276:Ricin / Q000633:toxicity; D014255:Trichothecenes / Q000494:pharmacology / Q000633:toxicity*; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D019384:Nucleic Acid Synthesis Inhibitors; D012335:RNA, Ribosomal; D014255:Trichothecenes; D016159:Tumor Suppressor Protein p53; C028268:satratoxin G; D000841:Anisomycin; D012276:Ricin; C496632:Hck protein, mouse; D051572:Proto-Oncogene Proteins c-hck; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D053181:Caspase 8; D056668:Cathepsin L; C007262:deoxynivalenol