Translational inhibitors and other translation-interfering toxicants, termed ribotoxins, activate MAPKs via a process termed ribotoxic stress response (RSR). Deoxynivalenol (DON), a trichothecene mycotoxin produced by Fusarium spp., is a ribotoxin and commonly contaminates cereal-based foods and has the potential to adversely affect humans and animals. At low doses, DON induces immunostimulatory effects by upregulating expression of proinflammatory genes in macrophages, IL-8 in monocytes and IL-2 in T cells. In contrast, high doses of DON cause immunosuppression by inducing apoptosis and rRNA cleavage. While it is recognized that DON induces transcription and stability of inflammation-associated mRNAs in the macrophage, it is not known whether this toxin can selectively modulate translation of these mRNAs. Using a focused inflammation/autoimmunity PCR array, DON-induced changes in profiles of polysome-associated mRNA transcripts (translatome) was compared to total cellular mRNA transcripts (transcriptome) in the RAW 264.7 murine macrophage model. DON induced robust expression changes in inflammatory response genes including cytokines, cytokine receptors, chemokines, chemokine receptors, and transcription factors, which were remarkably similar in the translatome and transcriptome. Over 70 percent of DON-regulated genes in the translatome and transcriptome overlapped and most expression ratios in these pools are <2. Taken together, DON's capacity to alter translation expression of inflammation-associated genes is likely to be driven predominantly by selective transcription, however, a small subset of these genes might further be regulated at the translational level. The complete cleavage profile and exact signaling mechanism of DON-induced rRNA cleavage are unknown. PKR, Hck and p38 were found to be required for rRNA cleavage. Furthermore, rRNA fragmentation was suppressed by the p53 inhibitors pifithrin-α and pifithrin-μ as well as the pan caspase inhibitor Z-VAD-FMK. DON activated caspases 3, 8 and 9 thus suggesting the possible co-involvement of both extrinsic and intrinsic apoptotic pathways in rRNA cleavage. Notably, pan inhibitor for cathepsins also suppressed anisomycin-, SG-, ricin- and DON-induced rRNA cleavage. Accordingly, all four ribotoxins induced apoptosis-associated rRNA cleavage via activation of cathepsins and p53→caspase 8/9→caspase 3, the activation of which by DON and anisomycin involved PKR-and Hck-activated p38 whereas SG and ricin activated p53 by an alternative mechanism. Taken together, at low doses, DON selectively upregulates translation of inflammation-associated genes, which is likely to be driven predominantly by selective transcription of these genes. However, a small subset of these genes might further be regulated at the translational level. At high doses, DON induces apoptosis-associated rRNA cleavage via activation of cathepsins and PKR/Hck/p38/p53→caspase 8/9→caspase 3. Interestingly, DON and anisomycin share the same signaling pathways, whereas SG and ricin activate p53 by an alternative mechanism, indicating the downstream signalings are conserved for ribotoxins.
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