NuclearDrosophilaCerS Schlank regulates lipid homeostasis via the homeodomain, independent of the lag1p motif

Abstract

Edited by Laszlo NagyDrosophila Ceramide Synthase (CerS) Schlank regulates both ceramide synthesis and fat metabolism. Schlank contains a catalytic lag1p motif and, like many CerS in other species, a homeodomain of unknown function. Here, we show that the Drosophila CerS Schlank is imported into the nucleus and requires two nuclear localization signals (NLSs) within its homeodomain and functional Importin-b import machinery. Expression of Schlank variants containing the homeodomain without functional lag1p motif rescued the fat metabolism phenotype of schlank mutants whereas a variant with a mutated NLS site did not rescue. Thus, the homeodomain of Schlank is involved in the regulation of lipid metabolism independent of the catalytic lag1p motif.Keywords: ceramide synthase; Drosophila; homeodomain; importin; lipid homeostasis; nuclear function Ceramides and sphingolipids are key intermediates in diverse cellular processes for growth, stress resistance, apoptosis, neurodegeneration, insulin function, and lipid homeostasis [1][2][3][4][5].In synthesis of ceramide, Ceramide Synthases (CerSs) acylate a sphingoid long-chain base (LCB) with a fatty acyl-CoA of distinct length to generate (dihydro) ceramide, the backbone of all complex sphAbbreviations aa, amino acid; ASAH1, acid ceramidase; ATF2, activating transcription factor 2; cDNA, complementary DNA; CerSs, ceramide synthases; dsRNA, double-stranded RNA; ER, endoplasmic reticulum; Gal4, galactose-responsive transcription factor; GFP, green fluorescent protein; GlcT-1, glucosylceramide synthase; H215D, change in a histidine at position 215 of schlank into glutamate; INM, inner nuclear membrane;

The ceramide synthase 2b gene mediates genomic sensing and regulation of sphingosine levels during zebrafish embryogenesis

“…The single Drosophila Cers ortholog, Schlank, also has a homeodomain, in addition to the Lag motif. Interestingly, schlank mutants could be rescued by expression of variant proteins lacking a functional Lag motif, as long as they contained the homeodomain and a nuclear localization signal ( Voelzmann et al, 2016 ). While the mechanism for Cers2b action during zebrafish embryogenesis remains unclear, our results suggest the critical role played by this ER/nuclear membrane-localized enzyme is in autoregulation of sphingolipid metabolism.…”

Dietary rescue of lipotoxicity-induced mitochondrial damage in Peroxin19 mutants

“…Of note, upon addition of 5% coconut oil to the diet, Schlank indeed regained its localization to the nuclear membrane ( Fig 5D, 5F, 5H and 5I ) in the Pex2 , Pex3 , and Pex19 mutants we analyzed and would thus be enabled to repress lip3 , explaining the observed decrease in lip3 expression, reduced free fatty acid levels, ameliorated mitochondrial morphology, and rescue to adulthood. To further prove this hypothesis, we overexpressed a shortened version of Schlank (Schlank aa1–138 ) [ 38 , 27 ], which is constitutively nuclear (supplemental file S3 Fig ), in the Pex19 mutant background. We found that forcing Schlank into the nucleus in this manner rescues the lethality of Pex19 mutants ( Fig 5J ).…”

Characterization of Drosophila saposin-related mutants as a model for lysosomal sphingolipid storage diseases

“…In recent years, Drosophila has gained traction as an efficient model to study lipid metabolism in general (for a review, see Kühnlein, 2012) and sphingolipids in particular (Acharya and Acharya, 2005; Kraut, 2011; Bauer et al, 2009; Voelzmann et al, 2016). However, there is still a lack of knowledge concerning the degradation of membranes and in particular sphingolipids in Drosophila .…”