Biology subjects

Hanaoka, K.

Publications and source records attributed to Hanaoka, K..

5 recordsLinked to original sources

bioRxiv2026

Ire1 membrane stress responses support cell growth upon disruptions in inter-organelle contacts

Disruptions in inter-organelle contacts result in membrane lipid homeostasis defects that ultimately impair cellular function and viability. Yet, essential responses to membrane lipid imbalances remain poorly understood. In this study, we demonstrate that Ire1-dependent Membrane Stress Responses (MSR), distinct from the canonical Unfolded Protein Response (UPR), sustain the growth of yeast cells lacking inter-organelle contacts. Comprehensive lipidomics reveal that the Ire1-mediated MSR compensates for glycerophospholipid synthesis defects by modulating sphingolipid metabolism. Quantitative imaging further indicates that Ire1 mediates these effects, at least in part, by elevating cytoplasmic Ca2+ which in turn stimulates calcineurin activity necessary for cellular homeostasis. Accordingly, inhibition of calcineurin results in severe endoplasmic reticulum stress in yeast cells depleted of inter-organelle contacts. Thus, the Ire1 MSR directs Ca2+-dependent calcineurin activity and lipid metabolism upon disruptions in membrane contact sites to maintain cellular homeostasis. Alterations in inter-organelle contacts are associated with several diseases, including neurodegenerative disorders. Our findings in yeast suggest that evoking the MSR may be a means to ameliorate neuronal degeneration and delay the progression of neurodegenerative disorders.

cell biology↗

bioRxiv2026

The revised three-step detour pathway in dolichol biosynthesis is evolutionarily conserved in budding yeast

The identification of SRD5A3, a causative gene for congenital disorders of glycosylation (CDGs), together with its yeast ortholog DFG10, established the prevailing model that dolichol is synthesized from polyprenol in a single step. Subsequently, a recent discovery of DHRSX in CDG patients revised this view and led to the proposal of a three-step detour pathway for dolichol biosynthesis. However, it remains unclear whether this pathway represents a conserved mechanism or reflects evolutionary diversity in eukaryotes. Here, we identified TDA5 as a yeast ortholog of DHRSX. Deletion of TDA5 caused glycosylation defects, reduced dolichol levels, and accumulated polyprenol. All these phenotypes were rescued by expression of DHRSX, but not by DFG10 or SRD5A3. These findings show that Tda5 serves the same function as DHRSX in yeast, thereby demonstrating conservation of the three-step detour pathway in yeast and supporting a broader eukaryotic framework for dolichol biosynthesis.

cell biology↗

bioRxiv2026

GPI lipid remodeling regulates lipophagy by forming lipid domains in response to glucose deprivation

Lipophagy is an important microautophagic process that degrades lipid droplets (LDs) to mobilize stored lipids as an energy source during nutrient starvation. However, the molecular mechanisms regulating lipophagy in response to nutrient starvation remain poorly understood. We found that budding yeast mutants defective in glycosylphosphatidylinositol (GPI) lipid remodeling exhibited aberrant accumulation of lipid droplets (LDs) and neutral lipids under glucose starvation. Our data suggest that the accumulation results from a failure of vacuolar liquid-ordered (Lo) domain-mediated lipophagy. Furthermore, we demonstrated that glycosylphosphatidylinositol-anchored proteins (GPI-APs) localize to vacuoles in response to glucose depletion and that a mutant defective in endocytosis has defects in both vacuolar Lo domain formation and lipophagy. These results imply that GPI lipid remodeling is required for Lo domain-mediated lipophagy upon glucose starvation. We propose that endocytosis functions to supply the lipid portion of GPI-APs, remodeled to C26 diacylglycerol, to the vacuolar membrane for Lo domain formation. Summary StatementOur data suggest that the endocytic transport of GPI-APs remodeled with C26 diacylglycerol to the vacuole is required for vacuolar Lo domain formation and subsequent lipophagy in response to glucose deprivation. This reveals the essential role of GPI lipid remodeling in ensuring lipophagy to adapt to changes in nutrient availability.

cell biology↗

bioRxiv2024

ER sensing of lipid metabolism drives PRA family-dependent regulation of COPII vesicle transport

Newly synthesized secretory proteins and many lipids are transported from the endoplasmic reticulum (ER) to the Golgi prior to their ultimate destinations. The ER-to-Golgi transport must be tightly regulated during adaptation to environmental stress. However, the sensing mechanism and regulatory pathways governing the consecutive formation, budding and transportation of COPII vesicles from the ER remain insufficiently explored. Here, we present evidence indicating that COPII-mediated vesicle transport is transcriptionally controlled through the phosphatidic acid-dependent Opi1-Ino2/Ino4 regulatory circuit. Our analysis indicates that YIP3, a target gene of Ino2/Ino4, exerts a negative regulatory impact on COPII-mediated vesicle transport. Furthermore, we demonstrated that Ino2/Ino4 but not Yip3 modulates Sar1 activation, the initial step in COPII vesicle formation, whereas Yip3 hinders Sec16 assembly on the ER membrane, thereby implying that Ino2/Ino4 governs COPII-mediated trafficking at multiple steps. Thus, this study provides the first evidence for an ER sensing system that transcriptionally fine-tunes multiple steps of anterograde vesicular transport in response to alterations in lipid composition of the ER membrane.

cell biology↗

bioRxiv2023

Membrane contact sites regulate vacuolar fission via sphingolipid metabolism

Membrane contact sites (MCSs) are junctures that perform important roles including coordinating lipid metabolism. Previous studies have indicated that vacuolar fission/fusion processes are coupled with modifications in the membrane lipid composition. However, it has been still unclear whether MCS-mediated lipid metabolism controls the vacuolar morphology. Here we report that deletion of tricalbins (Tcb1, Tcb2, Tcb3), tethering proteins at endoplasmic reticulum (ER)-plasma membrane (PM) and ER-Golgi contact sites, alters fusion/fission dynamics and causes vacuolar fragmentation in the yeast Saccharomyces cerevisiae. In addition, we show that the sphingolipid precursor phytosphingosine accumulates in tricalbin-deleted cells, triggering the vacuolar division. Detachment of the nucleus vacuole junction (NVJ), an important contact site between the vacuole and the perinuclear ER, restored vacuolar morphology in both cells subjected to high exogenous phytosphingosine and Tcb3-deleted cells, supporting that phytosphingosine transport across the NVJ induces vacuole division. Thus, our results suggest that vacuolar morphology is maintained by MCSs through the metabolism of sphingolipids.

cell biology↗