Protein misfolding is linked to the development and pathology of many neurodegenerative diseases. The endoplasmic reticulum (ER) is a membrane-bound organelle essential for the folding of virtually all secreted and membrane proteins in eukaryotic cells. Pathologic events that interfere with ER protein folding cause ER stress. Cells activate the Unfolded Protein Response (UPR) when they are confronted with protein misfolding and ER stress. UPR signaling and chronic ER stress are seen in many neurodegenerative diseases. UPR signaling promotes cell death and pathology by mechanisms that are poorly understood. Studies from many labs have demonstrated that the UPR signal transduction pathway controlled by PRK-like ER Kinase (PERK) plays an important role in driving ER stress-induced cell death. PERK encodes an ER-resident transmembrane kinase with a luminal domain that detects misfolded proteins coupled to a cytosolic kinase domain and initiates a powerful translational and transcriptional program in response to ER stress. PERK activation leads to global translational attenuation. PERK activation concomitantly induces synthesis of transcription factors, including ATF4 and CHOP. Chronic PERK activation or forced over-expression of ATF4 and CHOP trigger cell death. Conversely, Chop-/- mice are partially resistant to ER stress-induced cell death. The mechanisms by which PERK, ATF4, and CHOP trigger apoptosis are poorly understood. We have recently discovered that chronic ER stress down-regulates the Inhibitor of Apoptosis (IAP) protein family through activity of the PERK-ATF4 signaling axis. Loss of IAPs sensitizes cells to ER stress-induced cell death. Based on these findings, we hypothesize that PERK-ATF4 regulation of IAPs determines whether cells succumb to apoptosis in response to chronic ER stress. To test this model and to further decipher the mechanisms by which PERK-ATF4 regulates XIAP and cell death, we propose the following Specific Aims: 1. Determine the mechanisms that regulate IAP proteins during ER stress. 2. Test the roles of IAP-domain family proteins in ER stress-induced neuronal cell death. 3. Determine the roles of PERK-induced miRNAs in regulating Iaps and cell survival in response to ER stress and protein misfolding. In summary, we propose experiments to decipher how PERK and ATF4 regulate the IAP protein family in response to protein misfolding and ER stress. The significance of our studies is that we will decipher molecular mechanisms that directly trigger apoptosis when cells are confronted with chronic ER stress and protein misfolding. These studies will positively impact society and patient care by identifying fundamental mechanisms governing the pathogenesis and progression of neuronal diseases arising from protein misfolding and ER stress, and these mechanisms can then be targeted to prevent cell death and thereby ameliorate disease.
Protein misfolding leads to cell death and underlies the pathogenesis of many neurodegenerative disorders. The mechanisms that trigger apoptosis in response to protein misfolding are poorly understood. This project investigates the role of Unfolded Protein Response signaling in triggering neuronal cell death.
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