Genome-wide Screen To Identify Regulators Of Autophagy Activity In C. Elegans

Autophagy is an evolutionarily conserved lysosome-mediated degradation process from yeast to mammals. This unique biological process is always divided into several sequential steps:Isolation membrane formation (initiation or PAS formation), membrane nucleation and expansion until complete autophagosome formation, autophagosome maturation, auto-lysosomal degradation and utilization of degradation products. Autophagy plays a very important role in protein or organelle quality control by eliminating unneeded cytoplasmic contents or damaged organelles. Defective autophagy will cause accumulation of ectopic protein aggregates which may disrupt the normal physiological function of the cells or organisms. Thus, defective autophagy is linked with all kinds of human diseases, especially neuron-neurodegenerative diseases such as Huntington’s or Alzheimer’s diseases. Autophagy can be activated by many kinds of stress, including nutrient starvation, energy deprivation, reactive oxygen species and so on. Up to now, multiple signaling pathways have been suggested be involved in regulation of autophagy activity, such as mTOR pathway, Ras/PKA pathway, Insulin/IGF-1signaling pathway and AMPK pathway.Although numerous factors have been uncovered that regulate autophagy activity, the mechanisms which coordinate regulation of autophagy with developmental signaling during multicellular organism development remain largely unknown. In this study, we showed that impaired function of ribosomal protein RPL-43causes accumulation of SQST-1(homolog of mammalian p62) aggregates in the larval intestine and these aggregates are removed upon autophagy induction. So basing on this model, we perform genome-wide RNAi screen to find those genes inactivation of which can up-regulate autophagy activity. After several rounds of confirmation, finally we identified139genes which, when inactivated, effectively up-regulate autophagy activity and thus promote degradation of SQST-1aggregates in rpl-43mutant. Further studies demonstrated that a variety of developmental signaling pathways, including Sma/Mab TGF-β signaling, LIN-35/Rb signaling, the XBP-1-mediated ER stress response and the ATFS-1-mediated mitochondrial stress response, transcriptionally regulate the expression of autophagy genes.People’s understanding of autophagy regulation all comes from cell biology studies in vitro in the past. However, in vitro studies always are not the truth. This study used rpl-43mutant from the classical model organism—C. elegans to perform RNAi screen and found many genes involved in autophagy regulation. Further studies suggested that different signaling pathways can mediate autophagy activity on transcriptional level. Therefore, this study has great significance for people to understand the role of signaling pathways in regulation of autophagy under physiological conditions.