Date of Award

August 2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Sergei Kuchin

Committee Members

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

Keywords

AMPK, mitochondria, nutrient stress, Snf1, yeast

Abstract

The AMP-activated protein kinase (AMPK) family is involved in responses to energy stress and is highly conserved among eukaryotes. In mammals, AMPK remains inactive when ATP levels are high. However, AMPK becomes catalytically active in response to low ATP levels (and thus a high AMP: ATP ratio). When the AMP: ATP ratio is high, AMP binds to AMPK, causing its phosphorylation (catalytic activation) by upstream kinases. Catalytic activation causes AMPK to upregulate processes related to ATP generation (such as mitochondrial respiration) and to downregulate processes related to ATP consumption (such as growth). AMPK therefore acts as a direct sensor of energy levels. It comes as no surprise then that in mammals, AMPK forms a negative feedback loop with the mitochondria: activated AMPK stimulates mitochondrial respiration, which produces more ATP, which in turn returns AMPK to its inactive state.In the yeast Saccharomyces cerevisiae, we have found that the mitochondria actually positively regulate the yeast AMPK ortholog known as Snf1 (sucrose non-fermenting 1). For example, our lab has previously shown that cells lacking the mitochondrial voltage-dependent anion channel (VDAC) genes POR1 and POR2 experience a defect in Snf1 activation. We therefore asked if there were any other pathways by which the mitochondria regulate Snf1. It was found that respiratory-null yeast cells lacking the mitochondrial genome (rho0) also experience a defect in Snf1 regulation, but in a manner independent of Por1 and Por2. Here, we present evidence that the rho0 mutation alters the regulation, composition, and nucleocytoplasmic distribution of the yeast Snf1 protein kinase complex. Yeast Snf1/AMPK has been implicated in the pathogenesis of Candida albicans. Understanding how yeast AMPK is regulated by mitochondria could further the research toward developing new antifungal compounds. Furthermore, mammalian AMPK is also a clinically significant drug target. In humans, its dysregulation is associated with conditions such as diabetes and cancer, and has additionally been implicated in cellular aging. Since AMPK is highly conserved among eukaryotes (including humans), further insights into the regulation of yeast Snf1/AMPK may help better understand how human AMPK is also regulated.

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