Altering Sphingolipid Metabolism in Saccharomyces cerevisiae Cells Lacking the Amphiphysin Ortholog Rvs161 Reinitiates Sugar Transporter Endocytosis

Abstract

ABSTRACT Amphiphysins are proteins thought to be involved in synaptic vesicle endocytosis. Amphiphysins share a common BAR domain, which can sense and/or bend membranes, and this function is believed to be essential for endocytosis. Saccharomyces cerevisiae cells lacking the amphiphysin ortholog Rvs161 are inviable when starved for glucose. Altering sphingolipid levels in rvs161 cells remediates this defect, but how lipid changes suppress remains to be elucidated. Here, we show that the sugar starvation-induced death of rvs161 cells extends to other fermentable sugar carbon sources, and the loss of sphingolipid metabolism suppresses these defects. In all cases, rvs161 cells respond to the starvation signal, elicit the appropriate transcriptional response, and properly localize the requisite sugar transporter(s). However, Rvs161 is required for transporter endocytosis. rvs161 cells accumulate transporters at the plasma membrane under conditions normally resulting in their endocytosis and degradation. Transporter endocytosis requires the endocytosis ( endo ) domain of Rvs161. Altering sphingolipid metabolism by deleting the very-long-chain fatty acid elongase SUR4 reinitiates transporter endocytosis in rvs161 and rvs161 endo − cells. The sphingolipid-dependent reinitiation of endocytosis requires the ubiquitin-regulating factors Doa1, Doa4, and Rsp5. In the case of Doa1, the phospholipase A 2 family ubiquitin binding motif is dispensable. Moreover, the conserved AAA-ATPase Cdc48 and its accessory proteins Shp1 and Ufd1 are required. Finally, rvs161 cells accumulate monoubiquitin, and this defect is remediated by the loss of SUR4 . These results show that defects in sphingolipid metabolism result in the reinitiation of ubiquitin-dependent sugar transporter endocytosis and suggest that this event is necessary for suppressing the nutrient starvation-induced death of rvs161 cells.