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  4. The Ubiquitin-mediated Regulation of AMPK in Chronological Aging
 
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The Ubiquitin-mediated Regulation of AMPK in Chronological Aging

Date Issued
2014
Date
2014
Author(s)
Liu, Tzu-Ning
URI
http://ntur.lib.ntu.edu.tw//handle/246246/262466
Abstract
Ubiquitin is a small regulatory protein that is expressed ubiquitously in eukaryoticorganisms. Conjugation of ubiquitins to proteins directs them to compartments in the cell, including the proteasome, which destroys and recycles proteins. Based on the genetic interaction analysis, I purposed that Snf1, highly conserved yeast AMPK, may be a target by both of Ubp8 and Ubp10, two highly conserved ubiquitin-specific proteases (DUBs). Snf1 plays an important role in modulating energy status in the cell, which is usually inactive. Only when glucose depleted can Snf1 be activated by its upstream kinases. Via changing chromatin structures, activating transcription factors and modulating transcription, Snf1 enhances the abilities of the cell to use alternative carbon sources and resist stresses. In this study, I aimed to reveal the pathway of the ubiquitin-mediated Snf1 regulation. Western blot analyses demonstrated that the level of Snf1 was dramatically decreased in ubp8∆ubp10∆ cells, but the mRNA level detection did not change significantly. Snf1 has been shown to be involved in aging processes; I first examined the possible roles of Ubp8 and Ubp10 in yeast aging. The deletion of UBP8 and UBP10 affected the cellular resistance to oxidative stresses and chronological life span (CLS) phenotype, possibly due to the decreased Snf1 protein level; while there was no significant change in replicative life span (RLS). In addition, the ubp8∆ubp10∆ cells exhibited regrowth phenotype which is known to be induce accumulated ROS and mutagenesis; however, in those cells I found no evidence of ROS-mediated genome instabilities. Further investigation revealed that despite the protein level was decreased, Snf1 was hyperphosphorylated in ubp8∆ubp10∆ cells. The ubp8∆ubp10∆ cells was able to grow on non-fermentable carbon sources but was not the SNF1 deleted cells. Taken together, my results suggest that Snf1 is likely protected by both Ubp8 and Ubp10 from proteasome-mediated degradation, which diminishes thecellular level of Snf1. Interestingly, the remaining Snf1 in in ubp8∆ubp10∆ cells is hyperphosphorylated via an unknown mechanism. I propose that the hyperphosphorylated Snf1 in ubp8∆ubp10∆ cells are able to activate the stress-responsive (STRE) transcription to maintain the cellular resistance to stresses. The potential pathways that may participate in the hyperphosphorylaiton of Snf1 are discussed.
Subjects
Snf1
AMPK
複製存活壽命
繼代存活壽命
去泛素化酵素
壓力力反應序列
Type
thesis
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