The GARP complex is required for cellular sphingolipid homeostasis

Abstract

Sphingolipids are abundant membrane components and important signaling molecules in eukaryotic cells. Their levels and localization are tightly regulated. However, the mechanisms underlying this regulation remain largely unknown. In this study, we identify the Golgi-associated retrograde protein (GARP) complex, which functions in endosome-to-Golgi retrograde vesicular transport, as a critical player in sphingolipid homeostasis. GARP deficiency leads to accumulation of sphingolipid synthesis intermediates, changes in sterol distribution, and lysosomal dysfunction. A GARP complex mutation analogous to a VPS53 allele causing progressive cerebello-cerebral atrophy type 2 (PCCA2) in humans exhibits similar, albeit weaker, phenotypes in yeast, providing mechanistic insights into disease pathogenesis. Inhibition of the first step of de novo sphingolipid synthesis is sufficient to mitigate many of the phenotypes of GARP-deficient yeast or mammalian cells. Together, these data show that GARP is essential for cellular sphingolipid homeostasis and suggest a therapeutic strategy for the treatment of PCCA2.DOI: http://dx.doi.org/10.7554/eLife.08712.001

TOR Complex 2-Regulated Protein Kinase Fpk1 Stimulates Endocytosis via Inhibition of Ark1/Prk1-Related Protein Kinase Akl1 in Saccharomyces cerevisiae

“…For example, Vps54 is a component of the GARP complex, which has recently been shown to be required for sphingolipid homeostasis (73); Lcb5 is a long-chain (sphingoid) base kinase (74), and Erg1 is the squalene monooxygenase that generates the squalene epoxide required for ergosterol biosynthesis (75). Further study of such putative Fpk1 substrates could deepen our understanding of how the TORC2-Ypk1-Fpk1 signaling circuit controls PM homeostasis.…”

Vaccinia Virus Uses Retromer-Independent Cellular Retrograde Transport Pathways To Facilitate the Wrapping of Intracellular Mature Virions during Virus Morphogenesis

“…GARP is localized to the TGN, where it facilitates tethering and, ultimately, the fusion of transport vesicles traveling in a retrograde direction from endosomes to the TGN (40). Cargoes which require GARP for transport to the TGN include receptors for lysosomal hydrolase precursors, such as the mannose 6-phosphate receptors, the TGN-resident protein TGN46 (17), and sphingolipids (18). Our work supports a model whereby the GARP complex tethers transport vesicles containing viral membrane proteins as they are recycled back from the plasma membrane to the TGN via retrograde transport pathways for reuse.…”

“…Different cargoes use different combinations of cargo sorters, SNAREs, tethers, and GTPases (16). Well-characterized endogenous cargoes that are transported along retrograde pathways include mannose 6-phosphate receptor, TGN-46 (17), sphingolipids (18), and β1 integrin (19). In addition to cellular proteins, toxins also transit along retrograde vesicle pathways to access their site of action, including Shiga toxin, Shiga-like toxins 1 and 2, ricin, and cholera toxin (16).…”

Taming the sphinx: Mechanisms of cellular sphingolipid homeostasis

“…Mutants in GARP appear to re-route sphingolipids to the vacuole, where they are degraded. Lack of recycling decreases sphingolipid levels in the plasma membrane, triggering up-regulation of the sphingolipid synthesis machinery (101). The current model posits that the massive mis-sorting of sphingolipids from the plasma membrane to the vacuole/lysosome apparently overwhelms the degradation recycling machinery, leading to defects in cell growth in yeast.…”