Lag1p and Lac1p Are Essential for the Acyl-CoA–dependent Ceramide Synthase Reaction inSaccharomyces cerevisae

Abstract

Lag1p and Lac1p are two homologous transmembrane proteins of the endoplasmic reticulum in Saccharomyces cerevisiae. Homologous genes have been found in a wide variety of eukaryotes. In yeast, both genes, LAC1 and LAG1, are required for efficient endoplasmic reticulum-to-Golgi transport of glycosylphosphatidylinositol-anchored proteins. In this study, we show that lag1⌬lac1⌬ cells have reduced sphingolipid levels due to a block of the fumonisin B1-sensitive and acyl-CoA-dependent ceramide synthase reaction. The sphingolipid synthesis defect in lag1⌬lac1⌬ cells can be partially corrected by overexpression of YPC1 or YDC1, encoding ceramidases that have been reported to have acyl-CoA-independent ceramide synthesis activity. Quadruple mutant cells (lag1⌬lac1⌬ypc1⌬ydc1⌬) do not make any sphingolipids, but are still viable probably because they produce novel lipids. Moreover, lag1⌬lac1⌬ cells are resistant to aureobasidin A, an inhibitor of the inositolphosphorylceramide synthase, suggesting that aureobasidin A may be toxic because it leads to increased ceramide levels. Based on these data, LAG1 and LAC1 are the first genes to be identified that are required for the fumonisin B1-sensitive and acyl-CoAdependent ceramide synthase reaction.

Aging in rat causes hepatic hyperresposiveness to interleukin-1β which is mediated by neutral sphingomyelinase-2

“…47 And lastly, but most importantly, convincing evidence for ceramide's involvement in the process of aging comes from studies in yeast, where the longevity assurance genes, LAG1 and LAC1, in yeast that participate in de novo ceramide biosynthesis, have been shown to determine yeast lifespan. 48 In summary, we present evidence that NSMase-2 plays a crucial role in the regulation of hepatic functions during aging and mediates aging-associated hyperresponsiveness to IL-1␤ (Fig. 7).…”

Sphingolipid Homeostasis in the Endoplasmic Reticulum and Beyond

“…Conversely, an excess of sphingolipids is also toxic, leading to ER stress and disruption of calcium homeostasis (LloydEvans et al 2008;Han et al 2010). Increased levels of ceramides or LCB-Ps cause lethality in yeast (Schorling et al 2001;Zhang et al 2001), and a number of human lysosomal storage diseases, including Tay-Sachs disease, Niemann-Pick disease, and Gaucher disease, are attributable to mutations that block sphingolipid breakdown (Schulze and Sandhoff 2011). Additionally, a heredity sensory neuropathy has recently been shown to be caused by accumulation of nondegradable sphingolipid metabolites (Gable et al 2010;Penno et al 2010).…”

Role of human longevity assurance gene 1 and C18-ceramide in chemotherapy-induced cell death in human head and neck squamous cell carcinomas

“…It has been shown previously that endogenous ceramide can be generated by various mechanisms, including de novo synthesis of ceramide, or activation of sphingomyelinases (11 -13). One of the key enzymes of the de novo pathway is (dihydro)ceramide synthase, and it has been shown that in Saccharomyces cerevisiae, longevity assurance gene (LAG) members (LAG1p and Lac1p) play a role in the regulation of life span (14) and are also required for ceramide synthase activity (15,16). Recent studies also revealed that one of the mouse homologues of these proteins, known as upstream of growth and differentiation factor 1 (mUOG1 or mouse LASS1) specifically regulates the synthesis of stearoyl (C 18 )-containing sphingolipids, including C 18 -ceramide (17,18).…”