Perturbation of sphingolipid metabolism induces endoplasmic reticulum stress‐mediated mitochondrial apoptosis in budding yeast

Abstract

Sphingolipids are a class of membrane lipids conserved from yeast to mammals which determine whether a cell dies or survives. Perturbations in sphingolipid metabolism cause apoptotic cell death. Recent studies indicate that reduced sphingolipid levels trigger the cell death, but little is known about the mechanisms. In the budding yeast Saccharomyces cerevisiae, we show that reduction in complex sphingolipid levels causes loss of viability, most likely due to the induction of mitochondria-dependent apoptotic cell death pathway, accompanied by changes in mitochondrial and endoplasmic reticulum morphology and endoplasmic reticulum stress. Elevated cytosolic free calcium is required for the loss of viability. These results indicate that complex sphingolipids are essential for maintaining endoplasmic reticulum homeostasis and suggest that perturbation in complex sphingolipid levels activates an endoplasmic reticulum stress-mediated and calcium-dependent pathway to propagate apoptotic signals to the mitochondria.

Osh proteins regulate COPII-mediated vesicular transport of ceramide from the endoplasmic reticulum in budding yeast

“…S1A). Because mutant strains that have abnormal sphingolipid metabolism exhibit altered sensitivity to inhibitors of sphingolipid synthesis, such as aureobasidin A (AbA) (Epstein et al, 2012;Kajiwara et al, 2012;Kajiwara et al, 2008;Malathi et al, 2004), we measured growth of oshD deletion strains on plates containing either AbA, which targets IPC synthase or myriocin (Myr), which targets serine palmitoyltransferase (Horvath et al, 1994;Nagiec et al, 1997). As reported previously, the osh3D strain was resistant to Myr (Yano et al, 2004), whereas it was hypersensitive to AbA (supplementary material Fig.…”

“…Drug and temperature sensitivity assays Drug and temperature sensitivity assays were performed as described previously (Kajiwara et al, 2012). Briefly, cells were grown to log phase at 25˚C in synthetic dextrose (SD) minimal medium (Funato et al, 2003).…”

“…Radiolabeled lipids were analyzed by thin layer chromatography (TLC) using solvent system I, chloroform:methanol:0.25% KCl (55:45:10,v/v) ]DHS were separated on TLC plates using solvent system II. Subsequently, fractions containing ceramides, which are ,2-3 cm from the top of the TLC plates (Funato and Riezman, 2001;Kajiwara et al, 2012), were collected by scraping and eluting with chloroform:methanol (1:1, v/v), and were analyzed by TLC using solvent system III: chloroform:methanol:acetc acid (190:9:1, v/v), as described previously (Cremesti and Fischl, 2000;Haak et al, 1997).…”

Loss of Ypk1, the Yeast Homolog to the Human Serum- and Glucocorticoid-induced Protein Kinase, Accelerates Phospholipase B1-mediated Phosphatidylcholine Deacylation

“…Consistent with our findings, a ypk1⌬ypk2⌬ strain bearing a YPK1 as allele displays increased expression of several genes, many that have Crz1 binding sites in their promoters, including PLB1 (10). Also, others have shown that disruption of sphingolipid synthesis leads to increased expression of PMC1, which is a calcineurin-dependent gene (77). Based on these and other data, a model was proposed (10) in which the TORC2 and calcineurin pathways act antagonistically to maintain the optimal cell growth and survival.…”

Activation of Checkpoint Kinase Chk1 by Reactive Oxygen Species Resulting from Disruption of wat1/pop3 in Schizosaccharomyces pombe

“…Nonmitochondrial sources such as endoplasmic reticulum stress, exposure to heavy metals, and other environmental factors are also responsible for ROS production (Halliwell and Cross 1994;Haynes et al 2004). More recently, ROS accumulation has also been observed due to the defects in vacuolar acidification, as well as reduced levels of sphingolipids (Milgrom et al 2007;Kajiwara et al 2012).…”