Mechanisms of TOR-dependent control of autophagy in Drosophila

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PROJECT SUMMARY The long term goal of this project is to understand the regulation and physiological roles of autophagy, a process by which proteins, organelles and bulk cytoplasm are sequestered within autophagic vesicles and delivered to the lysosome for degradation. This process plays several distinct, vital roles in the cell, acting to recycle aged or damaged components, to provide a source of nutrients in response to starvation, and in some cases to initiate cell death. These cellular functions underlie a growing appreciation for the impact of autophagy on a broad range of human illnesses and on normal physiological processes such as aging. Fundamental questions regarding autophagy remain to be addressed, including how autophagy initiation is regulated by nutrients and other signals, how autophagic vesicles mature to become competent for degradation, and how rates of autophagy are maintained at homeostatic levels optimal for cell survival. The exciting prospect of harnessing autophagy as a therapeutic tool awaits better understanding of these basic principals. The proposed studies will use genetic, biochemical and imaging-based approaches in the Drosophila system to help define mechanisms of autophagy regulation in the context of in an intact organism. Our previous studies identified a number of key targets and mechanisms through which the Target of Rapamycin (TOR) pathway inhibits autophagy in response to favorable nutrient conditions. The current proposal seeks to understand 1) how TOR signaling is integrated with other nutrient and developmental cues such as cAMP- dependent protein kinase A to control the initial steps of autophagy induction; 2) to test hypotheses that describe potential mechanisms by which TOR signaling controls the fusion of autophagosomes with lysosomes and the subsequent acidification of the autolysosome; and 3) to decipher the feedback mechanisms that provide homeostatic control limiting the rates and levels of autophagic activity. Experiments in this proposal were selected for their likelihood of having a high impact on key questions important to the field of autophagy. This proposal makes use of recently developed reagents including knockouts of several autophagy-related (Atg) genes, in vivo markers of autophagic activity, and novel methods of genetic manipulation in cell clones. Information gained from studies of autophagy in Drosophila will provide an important whole-animal complement to mammalian cell culture-based studies.