Abstract
Cellular heat stress can cause damage, and significant changes, to a variety of cellular structures. When exposed to chronically high temperatures, yeast cells invaginate vacuolar membranes. In this study, we found that the expression of Atg8, an essential autophagy factor, is induced after chronic heat stress. In addition, without Atg8, vacuolar invaginations are induced conspicuously, beginning earlier and invaginating vacuoles more frequently after heat stress. Our results indicate that Atg8’s invagination-suppressing functions do not require Atg8 lipidation, in contrast with autophagy, which requires Atg8 lipidation. Genetic analyses of vps24 and vps23 further suggest that full ESCRT machinery is necessary to form vacuolar invaginations irrespective of Atg8. In contrast, through a combined mutation with the vacuole BAR domain protein Ivy1, vacuoles show constitutively enhanced invaginated structures. Finally, we found that the atg8Δivy1Δ mutant is sensitive against agents targeting functions of the vacuole and/or plasma membrane (cell wall). Collectively, our findings revealed that Atg8 maintains vacuolar membrane homeostasis in an autophagy-independent function by coordinating with other cellular factors.
Highlights
Environmental changes and stress can damage organisms and the cells that constitute them
Our previous study showed that vacuolar invagination occurs during chronic heat stress without Atg[1] or Atg[9], indicating that autophagic events are not involved in this process[13]
Using super-resolution confocal live imaging microscopy (SCLIM), additional three-dimensional observation of these cells after 3 h at 40.5 °C showed that more invaginated structures from the vacuolar membrane were created in the atg8Δ mutants than in wild-type cells, and confirmed that invaginated structures were continuous with the cytosol around the vacuole (Fig. 1c,d, Videos 1 and 2)
Summary
Environmental changes and stress can damage organisms and the cells that constitute them. Hsp104Δ, but not ubi4Δ, mutants can survive chronic heat stress from sub-lethal elevated temperatures, such as at 38.5 °C–41 °C for hours to a day. These conditions may be similar to environmental changes typically experienced on a hot summer day. These findings indicate that many copies of ubiquitins, but not Hsp[104], are required for survival under conditions of chronic heat stress. The reasons for varying requirements for different types of heat stresses are not well understood; at lethal temperatures, protein unfolding damage is so severe that the disaggregation of partially-unfolded proteins by Hsp[104] may be the most important factor for the rescue of the cell[6,7]. As several plasma membranes proteins degrade more rapidly after heat stress, and with more multivesicular bodies (MVBs) being expected to be delivered and fused with vacuoles under such conditions, the vacuolar invaginations may represent a cellular strategy for coping with increased vacuolar membranes without a massive increase in vacuole volume
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
