Article

Inactivation of the C-elegans lipin homolog leads to ER disorganization and to defects in the breakdown and reassembly of the nuclear envelope

The Laboratory of Biochemistry and Genetics and National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 8 Center Drive, Bethesda, MD 20892, USA.
Journal of Cell Science (Impact Factor: 5.33). 07/2009; 122(Pt 12):1970-8. DOI: 10.1242/jcs.044743
Source: PubMed

ABSTRACT The nuclear envelope (NE) is a dynamic structure, undergoing periods of growth, breakdown and reassembly during the cell cycle. In yeast, altering lipid synthesis by inactivating the yeast homolog of lipin, a phosphatidic acid phosphohydrolase, leads to disorganization of the peripheral ER and abnormal nuclear shape. These results suggest that lipid metabolism contributes to NE dynamics; however, since yeast undergo closed mitosis, the relevance of these observations to higher eukaryotes is unclear. In mammals, lipin has been implicated in adipose tissue differentiation, insulin resistance, lipid storage and obesity, but the underlying cellular defects caused by altering lipin levels are not known. Here, we identify the Caenorhabditis elegans lipin homolog (LPIN-1) and examine its affect on NE dynamics. We find that downregulating LPIN-1 by RNAi results in the appearance of membrane sheets and other abnormal structures in the peripheral ER. Moreover, lpin-1 RNAi causes defects in NE breakdown, abnormal chromosome segregation and irregular nuclear morphology. These results uncover cellular processes affected by lipin in metazoa, and suggest that lipid synthesis has a role in NE dynamics.

0 Followers
 · 
83 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Pah1 is the phosphatidate phosphatase in the yeast Saccharomyces cerevisiae that produces diacylglycerol for triacylglycerol synthesis and concurrently controls the levels of phosphatidate used for phospholipid synthesis. Phosphorylation and dephosphorylation of Pah1 regulate its subcellular location and phosphatidate phosphatase activity. Compared with its phosphorylation by multiple protein kinases, Pah1 is dephosphorylated by a protein phosphatase complex consisting of Nem1 (catalytic subunit) and Spo7 (regulatory subunit). In this work, we characterized the Nem1-Spo7 phosphatase complex for its enzymological, kinetic, and regulatory properties with phosphorylated Pah1. The dephosphorylation of Pah1 by Nem1-Spo7 phosphatase resulted in the stimulation (6-fold) of phosphatidate phosphatase activity. For Pah1 phosphorylated by the Pho85-Pho80 kinase complex, maximum Nem1-Spo7 phosphatase activity required Mg(2+) ions (8 mM) and Triton X-100 (0.25 mM) at pH 5.0. The energy of activation for the reaction was 8.4 kcal/mol, and the enzyme was thermally labile at temperatures above 40 °C. The enzyme activity was inhibited by sodium vanadate, sodium fluoride, N-ethylmaleimide, and phenylglyoxal, but was not significantly affected by lipids or nucleotides. Nem1-Spo7 phosphatase activity was dependent on the concentrations of Pah1 phosphorylated by Pho85-Pho80, Cdc28-cyclin B, PKA, and PKC with kcat and Km values of 0.29 s(-1) and 81 nM, 0.11 s(-1) and 127 nM, 0.10 s(-1) and 46 nM, and 0.02 s(-1) and 38 nM, respectively. Its specificity constant (kcat/Km) for Pah1 phosphorylated by Pho85-Pho80 was 1.6-, 4-, and 6-fold higher, respectively, than that phosphorylated by PKA, Cdc28-cyclin B, and PKC.
    Journal of Biological Chemistry 10/2014; DOI:10.1074/jbc.M114.614883 · 4.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Proteins in the lipin family play a key role in lipid synthesis due to their phosphatidate phosphatase activity, and they also act as transcriptional coactivators to regulate the expression of genes involved in lipid metabolism. The lipin family includes three members, lipin1, lipin2, and lipin3, which exhibit tissue-specific expression, indicating that they may have distinct roles in mediating disease. To date, most studies have focused on lipin1, whereas the roles of lipin2 and lipin3 are less understood. This review introduces the structural characteristics, physiological functions, relationship to lipid metabolism, and patterns of expression of the lipin family proteins, highlighting their roles in lipid metabolic homeostasis. © 2014 S. Karger AG, Basel.
    Annals of Nutrition and Metabolism 01/2015; 66(1):10-8. DOI:10.1159/000368661 · 2.75 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Triacylglycerol (TAG) metabolism is a key aspect of intracellular lipid homeostasis in yeast and mammals, but its role in vegetative tissues of plants remains poorly defined. We previously reported that PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE1 (PDAT1) is crucial for diverting fatty acids (FAs) from membrane lipid synthesis to TAG and thereby protecting against FA-induced cell death in leaves. Here, we show that overexpression of PDAT1 enhances the turnover of FAs in leaf lipids. Using the trigalactosyldiacylglycerol1-1 (tgd1-1) mutant, which displays substantially enhanced PDAT1-mediated TAG synthesis, we demonstrate that disruption of SUGAR-DEPENDENT1 (SDP1) TAG lipase or PEROXISOMAL TRANSPORTER1 (PXA1) severely decreases FA turnover, leading to increases in leaf TAG accumulation, to 9% of dry weight, and in total leaf lipid, by 3-fold. The membrane lipid composition of tgd1-1 sdp1-4 and tgd1-1 pxa1-2 double mutants is altered, and their growth and development are compromised. We also show that two Arabidopsis thaliana lipin homologs provide most of the diacylglycerol for TAG synthesis and that loss of their functions markedly reduces TAG content, but with only minor impact on eukaryotic galactolipid synthesis. Collectively, these results show that Arabidopsis lipins, along with PDAT1 and SDP1, function synergistically in directing FAs toward peroxisomal β-oxidation via TAG intermediates, thereby maintaining membrane lipid homeostasis in leaves.
    The Plant Cell 10/2014; 26(10). DOI:10.1105/tpc.114.130377 · 9.58 Impact Factor