Microautophagy in the yeast vacuole depends on the activities of phosphatidylinositol 4-kinases, Stt4p and Pik1p

• Published in: Biochimica et biophysica acta. Biomembranes Vol. 1862; no. 11; p. 183416
• Main Authors: Kurokawa, Yuna, Konishi, Rikako, Yoshida, Akane, Tomioku, Kanna, Tanabe, Kenji, Fujita, Akikazu
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-11-2020
• Subjects: 1-Phosphatidylinositol 4-Kinase - genetics; 1-Phosphatidylinositol 4-Kinase - metabolism; Autophagy; Mutation; Protein Domains; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - genetics; Saccharomyces cerevisiae Proteins - metabolism; Vacuoles - genetics; Vacuoles - metabolism; NPC; QF-FRL; ATG; ESCRT; Osh; PLC; OSBP; LD; ORP
• ISSN: 0005-2736; 1879-2642
• DOI: 10.1016/j.bbamem.2020.183416

Morphologically, the lipophagy in yeast cell mimics microautophagy, which includes a direct amendment of the vacuolar membrane that engulfs lipid droplets (LDs). The molecular mechanism of the membrane modifications that elicits microautophagy still remains elusive. In this study, an analysis of membrane lipid distribution at a nanoscale level showed that PtdIns(4)P is localized in the cytoplasmic leaflet of microautophagic vesicles, which are derived when the vacuole's membrane domains engulfed LDs both in the stationary phase and in acute nitrogen starvation. Furthermore, the PtdIns(4)P-positive raft-like domains engulf LDs through a microautophagic mechanism. When single temperature-conditional mutants of STT4 or PIK1 PtdIns 4-kinases were used, in the vacuole of STT4 and PIK1 mutant cells, microautophagic vesicles drastically decreased at restrictive temperatures, and the labeling density of PtdIns(4)P on the microautophagic vesicles and the sizes of the mutants' microautophagic vesicles also decreased. These results suggest that both Stt4p and Pik1p have important roles in the microautophagy of the vacuole in the stationary phase and under nitrogen starvation conditions.
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•PtdIns(4)P is located on the cytoplasmic leaflets of the microautophagic vesicles.•PtdIns(4)P is localized on the vacuolar membrane contacting with lipid droplet.•Both Stt4p and Pik1p have essential roles in the microautophagy of the vacuole.