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Biochim Biophys Acta. 2015 Nov;1851(11):1450-64. doi: 10.1016/j.bbalip.2015.08.003. Epub 2015 Aug 12.

Seipin is involved in the regulation of phosphatidic acid metabolism at a subdomain of the nuclear envelope in yeast.

Author information

1
Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Austria. Electronic address: heimo.wolinski@uni-graz.at.
2
Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Austria.
3
Institute of Cell Biology, Histology and Embryology, and ZMF, Center for Medical Research, Medical University of Graz, Austria.
4
Institute of Molecular Biosciences, BioTechMed Graz, University of Graz, Austria; OMICS-Center Graz, Austria.

Abstract

Yeast Fld1 and Ldb16 resemble mammalian seipin, implicated in neutral lipid storage. Both proteins form a complex at the endoplasmic reticulum-lipid droplet (LD) interface. Malfunction of this complex either leads to LD clustering or to the generation of supersized LD (SLD) in close vicinity to the nuclear envelope, in response to altered phospholipid (PL) composition. We show that similar to mutants lacking Fld1, deletion of LDB16 leads to abnormal proliferation of a subdomain of the nuclear envelope, which is tightly associated with clustered LD. The human lipin-1 ortholog, the PAH1 encoded phosphatidic acid (PA) phosphatase, and its activator Nem1 are highly enriched at this site. The specific accumulation of PA-binding marker proteins indicates a local enrichment of PA in the fld1 and ldb16 mutants. Furthermore, we demonstrate that clustered LD in fld1 or ldb16 mutants are transformed to SLD if phosphatidylcholine synthesis is compromised by additional deletion of the phosphatidylethanolamine methyltransferase, Cho2. Notably, treatment of wild-type cells with oleate induced a similar LD clustering and nuclear membrane proliferation phenotype as observed in fld1 and ldb16 mutants. These data suggest that the Fld1-Ldb16 complex affects PA homeostasis at an LD-forming subdomain of the nuclear envelope. Lack of Fld1-Ldb16 leads to locally elevated PA levels that induce an abnormal proliferation of nER membrane structures and the clustering of associated LD. We suggest that the formation of SLD is a consequence of locally altered PL metabolism at this site.

KEYWORDS:

Diacylglycerol; Lipid droplet; Nuclear envelope; Phosphatidate phosphatase; Phosphatidic acid; Saccharomyces cerevisiae; Seipin; Yeast

PMID:
26275961
DOI:
10.1016/j.bbalip.2015.08.003
[Indexed for MEDLINE]
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