Nutritional deprivation of cells plays an important role in human diseases ranging from stroke and ischemic heart disease to the cachexia of cancer and chronic infection. In addition to their ability to react to lack of specific nutrients, cells have evolved more general stress-response pathways that are activated by many forms of cellular malnutrition and other metabolic perturbations. The gene encoding the transcription factor CHOP/GADD153 is induced by a pathway that is activated when cells are deprived of oxygen, energy sources or essential amino-acids. Chop gene knock-out in mice and other experiments indicate that this pathway regulates adaptation to malnutrition in terms of changes in cell growth, differentiation and programmed cell death. Therefore, there is reason to believe that manipulating this response may impact on a broad range of medical conditions associated with cellular malnutrition. The goal of this study is to identify components of the signaling pathways that regulate Chop expression in starved cells and, utilizing genetic tools, to define their role in effecting cellular adaptation to this stressful state. Previous experiments implicate a stress-signal emanating from the endoplasmic reticulum (ER) in Chop induction in response to nutritional and metabolic stress. We have cloned two novel murine genes that are candidates for playing a role in regulating responses to ER stress in mammalian cells. The first, Ire1, encodes a murine homologue of the yeast protein Ire1p, implicated in activating gene expression in response to ER stress in that organism. The second, Perk, plays a role in attenuating translation in response to the accumulation of unfolded proteins in the ER and as such would be expected to play a role in reducing stress in that compartment. We will examine the hypothesis that Ire1 positively regulates Chop expression whereas Perk, by attenuating ER stress, negatively regulates it. We will examine the consequences of interfering with signaling by these two proteins in the context of mouse models of human diseases associated with ER stress. These will include a stroke model, models for renal acute tubular necrosis and mouse models for Pelizaeus-Merzbacher Leukodystrophy. A screen for other genes regulating Chop's response to malnutrition will also be carried out and these new components of the pathway will be examined functionally in cellular assays. If successful, these studies will shed light on basic biological principles that regulate the function of the secretory pathway in mammalian cells and on a poorly understood but broadly-utilized stress-response that is activated in many disease states. The anchoring of these studies in animal-based disease models will hopefully provide clues as to the likely outcome of interfering with the function of specific components of the pathway. This information will be invaluable for rational selection of targets for therapeutic interventions that rely on manipulating the cellular response to ER stress.
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