Trichothecene Toxicity and the Ribotoxic Stress Response

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DESCRIPTION (provided by applicant): The trichothecenes, a group of sesquiterpenoid mycotoxins commonly encountered as food contaminants worldwide, have been etiologically linked to human and animal illnesses with the immune system being a major target. In experimental animals, these mycotoxins and other natural toxins that bind with high affinity to eukaryotic ribosomes (eg. ricin, Shiga toxin, anisomycin) induce proinflammatory gene expression and apoptosis in lymphoid tissues. Because of their potential for use in chemical terrorism, trichothecenes and other ribotoxins are now included on the CDC Select Agents list. Although ribosome-directed agents are known to exert toxicity by activating mitogen-activated protein kinases, the underlying mechanisms for this "ribotoxic stress response" (RSR) remain largely undefined. Thus, a critical gap exists in our knowledge of the signal transduction mechanisms by which ribotoxins modulate gene expression and apoptosis. The objective of this proposal is to test the guiding hypothesis that the ribosome plays a central role in the initiation and integration of protein kinase-mediated stress responses to trichothecenes and other ribotoxic agents. This hypothesis is based on observations in the macrophage that: 1)deoxynivalenol (DON), a common foodborne trichothecene, mediates cleavage of 18S and 28S ribosomal (r)RNA, 2) double-stranded RNA-activated protein kinase (PKR), a ribosome-associated serine-threonine kinase, is essential for DON-induced protein kinase activation and 3) DON induces mobilization of several protein kinases to the ribosome whereupon they are phosphorylated. To test our hypothesis, three Specific Aims are proposed. In Aim 1, we will characterize DON-induced rRNA cleavage relative to targets, kinetics and mechanisms in the macrophage. In Aim 2, we will use both macrophage and cell-free models to characterize the role of PKR as an early sensor of DON-induced rRNA damage. In Aim 3, we will track DON-induced changes in ribosome-associated proteins in the macrophage relative to composition, kinetics and kinase activites. From these studies, we expect to understand how the ribosome mediates the induction and integration of multiple intracellular signaling cascades that drive altered gene expression and apoptosis in mononuclear phagocytes in response to ribotoxic agents. Anticipated outcomes include: 1) improved understanding of the molecular basis by which trichothecenes and other ribotoxins disrupt immunity, 2) enhanced capacity to assess and manage risks associated with exposure to trichothecenes and other ribotoxins, and 3) mechanism-based strategies for preventing and/or treating persons exposed to trichothecenes and ribotoxic chemicals via natural contamination or chemical terrorism. Collectively, these outcomes will positively impact public health by providing a scientific basis for generating sound recommendations relative to this important class of toxins and appropriate remedial actions should exposure occur. PUBLIC HEALTH RELEVANCE: We propose to learn how a class of potent biological toxins interferes with the function and survival of cells that are essential to the immune system. This research will enhance our capacity to assess and manage risks associated with exposure to these toxins as well as yield mechanism-based strategies for preventing and/or treating persons exposed to these agents via inadvertent food contamination or deliberate chemical terrorism. Collectively, these outcomes will positively impact public health by providing a scientific basis for generating sound recommendations relative to these important toxins and appropriate remedial actions should exposures occur.