Autophagy is a catabolic pathway utilized by cells to maintain homeostasis. Dysregulation of this pathway often leads to various diseases, such as cancers and neurodegeneration. Therefore, autophagy must be tightly regulated by the extracellular environment or signaling pathways. The class III PI3 kinase complex, a lipid kinase complex functioning in converting phosphatidylinositol to phosphatidylinositol-3-phosphate, is a key regulator of autophagy that functions as a signaling hub where multiple regulatory signals converge. Here, we demonstrate that the class III PI3 kinase complex is negatively regulated by cyclin-dependent kinases (Cdks). The catalytic subunit of the kinase complex, Vps34, is phosphorylated by Cdk1 in mitotic cells and by Cdk5 in postmitotic cells. Phosphorylation on Vps34 results in its dissociation from a regulatory subunit Beclin 1, leading to decreased lipid kinase activity. As a result, autophagy is inhibited in dividing cells and postmitotic neuronal cells with elevated Cdk5 activity. Since dysfunction of autophagy has been shown to be implicated in cancers and neurodegeneration, which are characterized by abnormal activity of Cdk1 and Cdk5, respectively, our study provides a mechanism by which autophagy is modulated in those diseases. To further discover the regulatory mechanisms of autophagy, we used a novel autophagy inhibitor, spautin-1, identified in a small molecule screening. Spautin-1 inhibits autophagy by inhibiting Usp10/Usp13, which deubiquitinate and stabilize the class III PI3 kinase complex. Interestingly, Usp10/Usp13 are also stabilized by the class III PI3 kinase complex, suggesting that they are reciprocally regulated. These results led us to the observation that p53, a substrate of Usp10 is regulated by the class III PI3 kinase complex and spautin-1. We also report that A70, a more potent derivative of spautin-1, leads to the degradation of mutant p53 through the chaperone-mediated autophagy, whereas the wild-type p53 is degraded by the ubiquitin-proteasome system. Our study demonstrates an important regulatory interaction between the class III PI3 kinase complex and p53, suggesting a novel tumor suppressive function of the class III PI3 kinase complex.
| Identifer | oai:union.ndltd.org:harvard.edu/oai:dash.harvard.edu:1/9797300 |
| Date | 23 October 2012 |
| Creators | Kim, Minsu |
| Contributors | Yuan, Junying |
| Publisher | Harvard University |
| Source Sets | Harvard University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Rights | open |
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