How autophagy is induced under stress or starvation remains poorly understood. The lack of knowledge represents an important problem for cell biology and human health because it prevents understanding of the cellular abnormalities associated with de-regulation of autophagy, which contribute to aging and cancer. The long-term goal is to understand how mammalian target of rapamycin (mTOR) regulates autophagy induction and how knowledge of this regulation can be utilized to improve prevention and therapy. The objective of the current application is to determine how the protein kinase ULK1 (C. elegans UNC51-like kinase 1, mammalian homologue of Atg1) mediates mTOR signaling to the autophagy induction machinery. The central hypothesis is that mTOR negatively regulates autophagy induction by phosphorylating ULK1 and inhibiting the function of ULK1 in activation of the Atg14L-containing PI 3- kinase class III (PI3KC3) complex. Our hypothesis has been formulated based on our preliminary data demonstrating a protein complex consisting of ULK1 and Atg13. We identified this protein complex as a target of mTOR and the mediator of mTOR activity to the autophagy machinery, defining the long-sought molecular link between mTOR and autophagy. The rationale for the proposed research is that understanding how mTOR regulates the function of ULK1 will advance the fundamental knowledge on the mechanism of autophagy induction and assist in the development of molecular tools that are currently lacking to monitor and modulate a specific autophagy event. Guided by strong preliminary data, the hypothesis will be tested and accomplished by pursing the following three specific aims: 1) Determine how mTOR negatively regulates the ULK1-Atg13 complex;2) Determine the role of Atg13 in autophagy induction;3) Determine how ULK1 regulates the Atg14L-containing PI3KC3 complex. Under the first aim, phosphorylation sites of ULK1 that is a target of mTOR will be identified and their function in the regulation of autophagy will be characterized. Under the second aim, the protein-protein interaction mediated by Atg13 and the role of the interaction in the regulation of the Atg14L-containing PI3KC3 complex will be studied. Under the third aim, phosphorylation sites of Atg14L that is a substrate of ULK1 will be identified and the function of the phosphorylation in autophagy induction will be determined. The research proposed in this application is highly innovative, because it focuses on a previously unexplored pathway that fills in the current existing gap that links mTOR with the autophagy machinery. The proposed research is significant, because it will transform understanding of the mechanism of autophagy induction to an unprecedented detailed level. This is the essential first step in a continuum of research that is expected to enable development of strategies that specifically monitor and manipulate autophagy activity.
The proposed research is relevant to public health because the identified mechanism will ultimately advance knowledge on the regulation of autophagy, the evolutionarily-conserved cellular degradation process that is often deregulated in cancer, aging and aging-related diseases. The project is relevant to NIH's mission that pertains to developing fundamental knowledge that will enhance our ability to treat or prevent the human diseases associated with deregulation of autophagy.
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