Ypt4andlvs1regulate vacuolar size and function inSchizosaccharomyces pombe

Abstract

The yeast vacuole plays key roles in cellular stress responses. Here, we show that deletion of lvs1, the fission yeast homolog of the Chediak-Higashi Syndrome CHS1/LYST gene, increases vacuolar size, similar to deletion of the Rab4 homolog ypt4. Overexpression of lvs1-YFP rescued vacuolar size in ypt4Δ cells, but ypt4-YFP did not rescue lvs1Δ, suggesting that lvs1 may act downstream of ypt4. Vacuoles were capable of hypotonic shock-induced fusion and recovery in both ypt4Δ and lvs1Δ cells, although recovery may be slightly delayed in ypt4Δ. Endocytic and secretory trafficking were not affected, but ypt4Δ and lvs1Δ strains were sensitive to neutral pH and CaCl2, consistent with vacuolar dysfunction. In addition to changes in vacuolar size, deletion of ypt4 also dramatically increased cell size, similar to tor1 mutants. These results implicate ypt4 and lvs1 in maintenance of vacuolar size and suggest that ypt4 may link vacuolar homeostasis to cell cycle progression.

Complex Rab4-Mediated Regulation of Endosomal Size and EGFR Activation

“…Herein, we have demonstrated that Rab4A is a modulator of endocytic volume because Rab4A overexpression leads to increased endosomal size in both MCF10A and MDA-MB-231, whereas knockdown of Rab4A results in increased endosomal size in MCF10A but not in MDA-MB-231 cells. Previously, similar results have been shown in other cell types (59)(60)(61), suggesting that precise control of Rab4 expression regulates EE volume in a cell-specific manner. Considering that Rab4 has been shown to be involved in both membrane fusion and fission events (58,62), changes in Rab4 expression could result in increased EE size.…”

The yeast LYST homolog Bph1 is a Rab5 effector and prevents Atg8 lipidation at endosomes

“…Here, we find that Ypt52 has an exclusive function in binding Bph1. Ypt52 might be equivalent to the Rab4 homolog Ypt4 in S. pombe, as deletions in the LYST homolog Lvs1 and Ypt4 lead to similar phenotypes (Rains et al, 2017). Bph1 is, however, more critical than Ypt52, because bph1Δ cells, but not ypt52Δ cells, sort Atg8 into the 9 vacuole lumen (Fig.…”

“…Interestingly, these studies have not found significant defects in the transport of biosynthetic proteins to lysosomes, nor in endocytosis. Similarly, loss of Lvs1, the LYST homolog in Schizosaccharomyces pombe, results in large vacuoles (Rains et al, 2017).…”

“…The bar graphs in A and B correspond to the mean±s. analyzed to determine possible defects in endocytosis (Holland et al, 2014;Sepulveda et al, 2015;Rains et al, 2017;Falkenstein and Lozanne, 2014). In this regard, vacuolar proteomics provides a decisive advantage because it uncovers global changes in the endogenous protein levels of purified vacuoles that occur due to the deletion of interest, and therefore it is far more sensitive than other approaches (Eising et al, 2019).…”