Over the last few years, extensive studies have linked the activity of the transcription factor EB (TFEB) to lysosomal function. These observations proposed an intriguing integration of cellular catabolism, sustained by lysosomes, with anabolic processes largely controlled by the mechanistic target of rapamycin complex 1 (mTORC1) signaling. Interestingly, lysosomal function directly affects mTORC1 activity and is regulated by TFEB, a transcription factor and direct substrate of mTORC1. Thus, the lysosomal-mTOR signaling complex represents a hub of cellular energy metabolism, and its dysregulation underlies the onset of several multifaceted disorders including neurodegeneration, cancer, and Type 2 diabetes. Recent evidence has suggested that under nutrient-deficient conditions TFEB controls mTORC1 reactivation and induction of anabolic processes upon nutrient replenishment by modulating the transcriptional levels of small GTPases to re-tether mTORC1 to lysosomal membranes. Although very significant, these studies did not address the subsequent intracellular mechanisms that lead to the stimulation of mTORC1 kinase activity and autophagy during starvation. Here, I demonstrated that TFEB promotes assembly of a mTORC1-containing nutrient sensing complex through the formation of endosomes carrying activated phosphoinositide-dependent kinase 1 (p-PDK1), its activated substrate, protein kinase B (p-AKT), and the mTORC1-tethering factor RagD. Therefore, TFEB-induced signaling endosomes en route to lysosomes are required to dissociate lysosomal-mTORC1 inhibitor, Tuberous Sclerosis complex (TSC), and re-tether mTORC1 to endolysosomal membranes. Chromatin immunoprecipitation assays identified 623 endocytic genes regulated by TFEB, of which 46 were core endocytic genes including Clathrin, Caveolin, early and the late endosomal markers, Rab5 and Rab7, respectively. Validation of expression of these endocytic proteins in blots and endocytosis assays using Dextran-Rhodamine and EGF-Rhodamine showed that TFEB stimulates endocytosis. Pharmacological and genetic inhibition of endocytosis or retrograde trafficking abolished mTORC1 activity without affecting total levels of pT308-Akt and despite the presence of active TFEB in the nucleus. These TFEB-induced endosomes are required to assemble the so-called lysosomal nutrient sensing complex (LYNUS), composed of vATPase, Ragulator and the small GTPases RagA/B and C/D. LYNUS tethers mTORC1 to lysosomal membranes. I show that during starvation, TFEB-triggered endocytosis reactivates mTORC1 and is required for autophagy. I found that TFEB-triggered endocytosis is required for delivery of mTORC1 activators, lysosome biogenesis, and autophagy flux. This study identifies TFEB-mediated endocytosis as a critical process driving lysosome biogenesis and mTORC1 activation and emphasizes the role of the endolysosomal system in molecular clearance.
Subject (authority = RUETD)
Topic
Biology
RelatedItem (type = host)
TitleInfo
Title
Rutgers University Electronic Theses and Dissertations
Identifier (type = RULIB)
ETD
Identifier
ETD_8607
PhysicalDescription
Form (authority = gmd)
electronic resource
InternetMediaType
application/pdf
InternetMediaType
text/xml
Extent
1 online resource (xii, 195 p. : ill.)
Note (type = degree)
Ph.D.
Note (type = bibliography)
Includes bibliographical references
Note (type = vita)
Includes vita
Note (type = statement of responsibility)
by Israel Chukwudi Nnah
RelatedItem (type = host)
TitleInfo
Title
Graduate School - Newark Electronic Theses and Dissertations
Identifier (type = local)
rucore10002600001
Location
PhysicalLocation (authority = marcorg); (displayLabel = Rutgers, The State University of New Jersey)
I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.