Abstract
Autophagy is a conserved process that recycles cellular contents to promote survival. Although nitrogen limitation is the canonical inducer of autophagy, recent studies have revealed several other nutrients important to this process. In this study, we used a quantitative, high-throughput assay to identify potassium starvation as a new and potent inducer of autophagy in the yeast Saccharomyces cerevisiae We found that potassium-dependent autophagy requires the core pathway kinases Atg1, Atg5, and Vps34, and other components of the phosphatidylinositol 3-kinase complex. Transmission EM revealed abundant autophagosome formation in response to both stimuli. RNA-Seq indicated distinct transcriptional responses: nitrogen affects transport of ions such as copper, whereas potassium targets the organization of other cellular components. Thus, nitrogen and potassium share the ability to influence molecular supply and demand but do so in different ways. Both inputs promote catabolism through bulk autophagy, but result in distinct mechanisms of cellular remodeling and synthesis.
Highlights
Many eukaryotic organisms experience nutrient starvation, and their ability to adapt is important for their survival
In addition to removing cytoplasmic proteins, autophagy helps to replenish the cellular pool of biologically important metals, which are required in large abundance or in trace amounts to maintain physiological parameters such as cell volume, pH, and protein synthesis [27,28,29]
Using RNA-Seq, we demonstrate that nitrogen limitation and potassium starvation result in substantially different transcriptional profiles
Summary
Many eukaryotic organisms experience nutrient starvation, and their ability to adapt is important for their survival. To further compare potassium starvation and nitrogen limitation, we examined the accumulation of autophagosomes in individual cells using transmission EM (TEM). To test the role of the effector complexes in potassium-dependent autophagy, we analyzed individual gene deletions using the GFP-Atg8 immunoblotting assay.
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