Protein misfolding in the early secretory pathway exerts it pathological affects by two distinct mechanisms: Retention and degradation of misfolded mutant proteins by the endoplasmic reticulum's (ER) quality control machinery leads to loss-of-function phenotypes (exemplified by lysosomal storage diseases). Production and accumulation of the misfolded protein threatens the integrity of the organelle by causing ER stress, leading to cell dysfunction and death, which is believed to contribute to neurodegenerative disorders, diabetes mellitus and other diseases of aging. The protein folding environment in the ER is controlled by a small number of signal transduction pathways and these respond to ER stress in a stereotyped fashion, mediating the unfolded protein response (UPR). Recent evidence suggests that the level of signaling in the UPR is defined by global parameters and by the averaged needs of the ER's diverse protein clientele. It is unlikely therefore that the UPR is finely tuned to the specific exigencies of any one mutation-causing disease. Evidence for this has recently presented itself as circumstances in which knockout of normal genes that function in the UPR improved survival under conditions of ER stress. Such examples of failure of homeostasis indicate that the UPR can be manipulated therapeutically in pathophysiological conditions. Regulated phosphorylation and dephosphorylation of translation initiation factor 2a (elF2a) is a well understood and potentially malleable arm of the UPR, referred to as the integrated stress response (ISR). We propose to identify drug like small molecules that will enhance and others that will reduce the ISR's activity. Transient inhibition of the ISR might overwhelm the quality control mechanism of the ER and promote trafficking of enzymatically active mutant proteins to their functional compartment, alleviating the associated loss of function phenotypes. ISR inactivation might also prove beneficial in the cell culture based production of biotherapeutics used to treat diseases caused by misfolding by enzyme replacement therapy. Activators of the ISR are likely to protect cells and organs against the lethal consequences of ER stress and may prove useful in treating diseases of aging. To accomplish these goals we will develop high throughput screens (HTS) for compounds that inhibit the ER stress inducible elF2a kinase PERK and secondary screens to evaluate the potency, specificity, bioavailability and off-target effects of the compounds. In a parallel strand we will develop HTS assays for inhibitors of elF2a dephosphorylation and others for activators of elF2a kinases, which function by non-canonical mechanisms and activate the ISR without causing stress. The long-term goal of this proposal is therefore to create a pharmacological platform for manipulating the cellular response to misfolded proteins. Given the pervasive role of protein misfolding in human diseases, such agents are likely to become part of the therapeutic armamentarium of future physicians.
