Abstract
BackgroundExocytosis is a process by which vesicles are transported to and fused with specific areas of the plasma membrane. Although several studies have shown that sphingolipids are the main components of exocytic compartments, whether they control exocytosis process is unclear.ResultsHere, we have investigated the role of sphingolipids in exocytosis by reducing the activity of the serine palmitoyl-transferase (SPT), which catalyzes the first step in sphingolipid synthesis in endoplasmic reticulum. We found that the exocyst polarity and exocytic secretion were impaired in lcb1-100 mutant cells and in wild type cells treated with myriocin, a chemical which can specifically inhibit SPT enzyme activity, suggesting that sphingolipids controls exocytic secretion. This speculation was further confirmed by immuno-fluorescence and electron microscopy results that small secretory vesicles were accumulated in lcb1-100 mutant cells.ConclusionsTaken together, our results suggest that sphingolipids are required for exocytosis. Mammals may use similar regulatory mechanisms because components of the exocytic secretion apparatus and signaling pathways are conserved.
Highlights
Exocytosis is a process by which vesicles are transported to and fused with specific areas of the plasma membrane
We found that polarized localization of exocyst complex at the bud and the exocytic secretion of Bgl2 and invertase rely on the activity of serine palmitoyl transferase, the initial enzyme in sphingolipid synthesis, but not the enzymes required for ceramides
The LCB1 gene encodes a subunit of the serine palmitoyltransferase, which catalyzes the first step in sphingolipid synthesis [2, 7]. lcb1-100 mutant is unable to produce sphingoid bases, ceramides, and sphingolipids at restrictive temperature [17, 27, 30, 46]
Summary
Exocytosis is a process by which vesicles are transported to and fused with specific areas of the plasma membrane. Cell surface growth is performed through exocytic secretion, in which post-Golgi secretory vesicles carrying proteins and lipids are docked to and fused with the plasma membrane [15]. It was reported that cell surface delivery of Fus-Mid-GFP is blocked in lcb100 mutant, in which the activity of serine palmitoyl-transferase, an enzyme in the first step of sphingolipids synthesis, is dramatically reduced at a restrictive temperature [37]. These facts suggest that sphingolipids may be involved in exocytic secretion. There is no direct evidence to confirm this speculation yet
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