Mechanism of degradation of the proteasome through autophagy



 DESCRIPTION (provided by applicant): Two cellular components, the lysosome (vacuole in yeast and plants) and the proteasome degrade the majority of proteins in eukaryotic cells. They display a partial overlap in substrates and crosstalk between them has been observed. Therefore, to understand the cells ability to degrade proteins it is important to know how the cellular level of the proteasome is controlled. While transcriptional regulation of proteasomes has been studied in yeast and mammalian cells, little is known concerning the mechanism or physiological conditions that target proteasomes for degradation. Reducing proteasome levels through degradation can impact many cellular processes and increase a cell's sensitivity to drugs. This can be therapeutically relevant, because cells can become more sensitive to proteasome inhibitors, like the FDA approved drugs Bortezomib and Carfizomib used in the treatment of multiple myelomas and mantle cell lymphomas. The objective of the research proposed here is to elucidate at the molecular level the signal pathways and biological processes that lead to the degradation of proteasomes by using biochemical and cell biological assays. Since many proteasome related processes are highly conserved amongst eukaryotes and little is known about this process, yeast will be used as a model organism. This will provide a wider array of techniques and screening abilities to determine the basic mechanism involved. Based on our preliminary data, two distinct processes are proposed to lead to proteasome degradation. Aim 1 will determine how overall proteasome levels are reduced upon nitrogen starvation. The goal is to identify proteins, post- translational modifications, and other signals involved in the process of nuclear export and autophagic packaging upon nitrogen starvation. Aim 2 will test the hypothesis that proteasomes that fail quality control are specifically removed via autophagy. The goal is to determine how factors that recognize faulty proteasomes link these complexes to the autophagy pathway that targets them for lysosomal degradation. The expected outcomes from these aims are the identification and a molecular understanding of the process that leads to targeting of proteasomes for autophagy. Understanding of these pathways will be important for future characterization of the impact these processes have on conditions that are relevant for human health. This can include conditions like nutrient starved cancer cells, increased oxidative stress, aging, or neurodegenerative diseases, which all have been shown to be impacted by the ubiquitin- proteasome system.