Pin-Chao Liao, a , † Enrique J. Garcia, a , † Gary Tan, a Catherine A. Tsang, a and Liza A. Pon a ,*
"aDepartment of Pathology and Cell Biology, Columbia University, New York, NY 10032
Competing interests: The authors declare no competing interests.
†P-CL and EJG contributed equally to these studies.
Author contributions: conceptualization: L.A.P., P.-C.L., and E.J.G.; methodology: P.-C.L. and E.J.G.; formal analysis: P.-C.L., E.J.G., and G.T.; investigation: P.-C.L., E.J.G., G.T., and C.A.T.; writing: L.A.P., P-C.L., and E.J.G.; supervision: L.A.P., P.-C.L., and E.J.G.; funding acquisition: L.A.P. and E.J.G.
*Address correspondence to: Liza A. Pon ([email protected])."
"Microlipophagy (µLP), degradation of lipid droplets (LDs) by microautophagy, occurs by autophagosome-independent direct uptake of LDs at lysosomes/vacuoles in response to nutrient limitations and ER stressors in Saccharomyces cerevisiae. In nutrient-limited yeast, liquid-ordered (Lo) microdomains, sterol-rich raftlike regions in vacuolar membranes, are sites of membrane invagination during LD uptake. The endosome sorting complex required for transport (ESCRT) is required for sterol transport during Lo formation under these conditions. However, ESCRT has been implicated in mediating membrane invagination during µLP induced by ER stressors or the diauxic shift from glycolysis- to respiration-driven growth. Here we report that ER stress induced by lipid imbalance and other stressors induces Lo microdomain formation. This process is ESCRT independent and dependent on Niemann-Pick type C sterol transfer proteins. Inhibition of ESCRT or Lo microdomain formation partially inhibits lipid imbalance-induced µLP, while inhibition of both blocks this µLP. Finally, although the ER stressors dithiothreitol or tunicamycin induce Lo microdomains, µLP in response to these stressors is ESCRT dependent and Lo microdomain independent. Our findings reveal that Lo microdomain formation is a yeast stress response, and stress-induced Lo microdomain formation occurs by stressor-specific mechanisms. Moreover, ESCRT and Lo microdomains play functionally distinct roles in LD uptake during stress-induced µLP.
DOI: https://dx.doi.org/ 10.1091/mbc.E21-04-0179
Images were acquired with an Axioskop 2 microscope equipped with a 100×/1.4 Plan-Apochromat objective (Zeiss) and an Orca-ER cooled CCD camera (Hamamatsu) and a pE-4000 LED illumination system (coolLED, Andover, UK) controlled by NIS Elements 4.60 Lambda software (Nikon, Melville, NY).
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The pE-4000 Universal Illumination System offers 16 selectable wavelengths from 365 - 770 nm, making it a highly flexible illuminator covering a wide variety of fluorophores
Molecular Biology of the Cell
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