Caspase regulation of autophagy in Drosophila melanogaster

Autophagy is an evolutionary conserved process whereby intracellular components are sequestered and delivered to lysosomes for degradation. Autophagy acts as a cell survival mechanism in response to stress, such as starvation, and also engages in a complex relationship with apoptosis. Understanding the crosstalk between autophagy and apoptosis is important, as it plays a critical role in the balance between survival and death, and has important implications in both normal development and human diseases. To better understand the crosstalk between autophagy and apoptosis, I examined the role of the Drosophila melanogaster effector caspase Dcp-1 in starvation-induced autophagy during mid-oogenesis. I confirmed that Dcp-1 positively regulates starvation-induced autophagic flux in degenerating mid-stage egg chambers, and does so in a catalytically dependent manner. Dcp-1 candidate interactors/substrates, identified previously, were analyzed using in vitro autophagy assays to elucidate potential mechanisms related to Dcp-1-mediated autophagy. I identified 13 novel Dcp-1-associated regulators of starvation-induced autophagy, including the chloride intracellular channel protein Clic, the heat shock protein Hsp83, and the mitochondrial protein SesB. In vivo analyses revealed that Clic and Hsp83 act as negative regulators of autophagic flux following starvation during Drosophila oogenesis. Further investigation into the possible mitochondrial-related role of Dcp-1 in autophagy revealed that Dcp-1 partially localizes within the mitochondria where it functions to regulate mitochondrial network morphology and ATP levels, demonstrated both in vitro and in vivo during mid-oogenesis. Moreover, I found that the pro-form of Dcp-1 interacts with the adenine nucleotide translocase SesB, and as such, Dcp-1 does not cleave SesB but rather affects its stability. In addition, I identified SesB as a novel negative regulator of autophagic flux during mid-oogenesis. Depletion of ATP or reduction of SesB levels rescued the autophagic defect in Dcp-1 loss-of-function flies, and genetic interaction studies revealed that SesB acts downstream of Dcp-1 in the regulation of autophagy. In conclusion, I found that non-apoptotic caspase activity is an important molecular mechanism underlying autophagy regulation and mitochondrial physiology in vivo, and have provided a foundation for further analyses involving Dcp-1-associated regulators of starvation-induced autophagy.