Ceramides are key intermediates in sphingolipid biosynthesis and potent signaling molecules. However, excess ceramide is toxic, causing growth arrest and apoptosis. In this study, we identify a novel mechanism by which cells prevent the toxic accumulation of ceramides; they facilitate nonvesicular ceramide transfer from the endoplasmic reticulum (ER) to the Golgi complex, where ceramides are converted to complex sphingolipids. We find that the yeast protein Nvj2p promotes the nonvesicular transfer of ceramides from the ER to the Golgi complex. The protein is a tether that generates close contacts between these compartments and may directly transport ceramide. Nvj2p normally resides at contacts between the ER and other organelles, but during ER stress, it relocalizes to and increases ER-Golgi contacts. ER-Golgi contacts fail to form during ER stress in cells lacking Nvj2p. Our findings demonstrate that cells regulate ER-Golgi contacts in response to stress and reveal that nonvesicular ceramide transfer out of the ER prevents the buildup of toxic amounts of ceramides.

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Journal Article

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Liu LK, Choudhary V, Toulmay A, Prinz WA

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