Sir2 regulates selective autophagy in stationary-phase yeast cells

Jan 26, 2026Microbial cell (Graz, Austria)

Sir2 controls selective cell cleanup in resting yeast cells

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Abstract

Deletion of Sir2 led to sustained autophagy activation, particularly affecting selective autophagy pathways.

Sir2 was identified as a key suppressor of autophagy during the stationary phase in nutrient-rich complex media.
Selective autophagy processes, such as mitophagy and pexophagy, were inhibited by Sir2, while non-selective autophagy remained largely unaffected.
Transcriptomic analysis showed that Sir2 regulates pathways involved in ribosome biogenesis and nutrient responses during the stationary phase.
Sir2 stabilizes Ume6, a transcription repressor, which limits autophagic activity.
Deletion of Sir2 increased phosphorylation and stabilization of the mitochondrial receptor Atg32, leading to enhanced mitophagy.
Reactive oxygen species (ROS) generated by mitophagy may enhance autophagy through a positive feedback loop.

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Autophagy contributes to cellular homeostasis by degrading and recycling intracellular components, especially under nutrient-limited conditions. While autophagy is well characterized under acute starvation in synthetic media in, its regulation during the stationary phase of prolonged growth in nutrient-rich complex media, when cells experience gradual metabolic shifts and sustained stress, remains poorly understood. In this study, we identified Sir2, an NAD-dependent histone deacetylase, as a key suppressor of autophagy during the stationary phase in YPD complex medium. Using GFP-Atg8 processing as a readout of autophagic flux, we demonstrated thatdeletion led to sustained autophagy activation. Notably, Sir2 selectively inhibited mitophagy, pexophagy, and the Cvt pathway, while non-selective autophagy remained largely unaffected. Transcriptomic analysis revealed that Sir2 facilitates a coordinated entry into quiescence, in part by regulating ribosome biogenesis and nutrient-responsive pathways during the stationary phase. Mechanistically, Sir2 stabilized Ume6, a repressor oftranscription, thereby limiting autophagic activity. Deletion ofdrastically increased the phosphorylation and stabilization of the mitochondrial receptor Atg32 during the stationary phase, leading to enhanced mitophagy. Additionally, we found that ROS generated by mitophagy enhanced autophagy through a positive feedback loop. Collectively, our findings establish Sir2 as a previously unrecognized regulator of selective autophagy during the stationary phase in complex medium and highlight how cells dynamically control organelle degradation to maintain viability under extended metabolic stress. Saccharomyces cerevisiae SIR2ATG8SIR2 +

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Sir2 regulates selective autophagy in stationary-phase yeast cells

Abstract

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