Date of Award

8-1-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Sergei Kuchin

Committee Members

Sonia Bardy, Daad Saffarini, Mark McBride, Ching-Hong Yang

Abstract

In eukaryotes, members of the conserved AMP-activated protein kinase (AMPK) family play a pivotal role in sensing and responding to energy stress. Mammalian AMPK becomes activated when the AMP:ATP ratio is too high, and functions to prevent unnecessary ATP spending and to increase ATP production. Due to their role in ATP production through aerobic respiration, mitochondria are known to play an indirect role in the negative control of AMPK. The conserved voltage-dependent anion channel (VDAC) proteins, also known as mitochondrial porins, mediate the passage of small metabolites between the mitochondria and cytoplasm, including the release of ATP. One would therefore expect VDACs to play a role in the negative regulation of AMPK. Contrary to this expectation, our results in budding yeast (Saccharomyces cerevisiae) provide evidence that mitochondria and VDACs play a role in the positive control of Snf1, the yeast homolog of AMPK.

In yeast, Snf1 protein kinase stimulates the utilization of alternate carbon/energy sources when the preferred source – glucose – becomes limiting. Under carbon/energy stress conditions, Snf1 is activated and enriches in the nucleus to elicit various transcriptional responses.

Our results indicate that Snf1 physically interacts with the yeast VDAC proteins Por1 and Por2. Interestingly, Por1 and Por2 contribute to the positive - rather than negative - control of Snf1. We present evidence indicating that Por1 and Por2 function redundantly to promote Snf1 catalytic activation, presumably as receptors of an intracellular glucose/energy signal. We also present evidence for novel mechanisms by which mitochondria positively regulate Snf1 nuclear localization.

In summary, our experiments in yeast reveal an array of mechanisms by which mitochondria positively regulate Snf1/AMPK, i.e. in a way that would be entirely counter-intuitive to researchers in the mammalian field. Due to the evolutionary conservation of the players involved, further studies of these novel mechanisms in the yeast model could provide invaluable insights into the etiology and therapy of AMPK- ,VDAC-, and mitochondria-associated diseases including cancer, diabetes, obesity, and cardiac disorders.

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