Protein degradation is critical for cell cycle division, cell growth control, transcriptional regulation and metabolic control. Autophagy is a process whereby lysosomes degrade cytosolic proteins and organelles when cells are starved of nutrients. Defects or changes in autophagy have been linked to cancer development, neuromuscular dystrophies and aging. Multiple forms of autophagy exist, and a unique autophagy pathway has been identified in our lab. The gluconeogenic enzyme fructose-1,6-bisphosphatase (FBPase) is degraded when yeast cells are shifted from poor carbon sources to fresh glucose, and this degradation prevents energy futile cycles that are harmful to cells. FBPase can be degraded either in the proteasome or in the vacuole depending on the duration of starvation. For the vacuolar pathway, FBPase is first targeted to Vid vesicles and then to the vacuole. A number of VID genes function in both degradation pathways and they are evolutionary conserved. The Vid pathway is utilized for multiple cargo proteins including isocitrate lysase, phosphoenopyruvate carboxykinase and malate dehydrogenase. Our long-term goal is to understand the mechanisms underlying the vacuolar dependent pathway of FBPase degradation. The objective of this application is to understand why FBPase switches degradation from the proteasome to the vacuole. Our central hypothesis is that the switch is controlled by multiple protein complexes that can be activated or inactivated depending upon the duration of starvation. We plan to test this hypothesis by pursuing the following aims. 1. We will study why the Vid vesicle trafficking pathway is inactive in short termed starved cells. Is this because of an inactive cAMP signaling pathway, the absence of Vid vesicles, or incompetent Vid vesicles? 2. FBPase physically interacts with components of the Tori complex (TORC1). We will study how Tori regulates the vacuolar pathway. 3. Vid28p and VidSOp form a stable complex. We will study how this complex regulates both degradation pathways. The completion of the proposed experiments will enhance our understanding regarding how these two major proteolytic pathways are regulated. This may provide therapeutic advantages to eliminate abnormal proteins that accumulate in Parkinson's disease, Huntington's disease or other pathological conditions. ? ? ?
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