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  • 1
    Publication Date: 2010-02-26
    Description: Despite the essential roles of sphingolipids both as structural components of membranes and critical signalling molecules, we have a limited understanding of how cells sense and regulate their levels. Here we reveal the function in sphingolipid metabolism of the ORM genes (known as ORMDL genes in humans)-a conserved gene family that includes ORMDL3, which has recently been identified as a potential risk factor for childhood asthma. Starting from an unbiased functional genomic approach in Saccharomyces cerevisiae, we identify Orm proteins as negative regulators of sphingolipid synthesis that form a conserved complex with serine palmitoyltransferase, the first and rate-limiting enzyme in sphingolipid production. We also define a regulatory pathway in which phosphorylation of Orm proteins relieves their inhibitory activity when sphingolipid production is disrupted. Changes in ORM gene expression or mutations to their phosphorylation sites cause dysregulation of sphingolipid metabolism. Our work identifies the Orm proteins as critical mediators of sphingolipid homeostasis and raises the possibility that sphingolipid misregulation contributes to the development of childhood asthma.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2877384/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2877384/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Breslow, David K -- Collins, Sean R -- Bodenmiller, Bernd -- Aebersold, Ruedi -- Simons, Kai -- Shevchenko, Andrej -- Ejsing, Christer S -- Weissman, Jonathan S -- N01-HV-28179/HV/NHLBI NIH HHS/ -- P50 GM073210/GM/NIGMS NIH HHS/ -- P50 GM073210-06/GM/NIGMS NIH HHS/ -- Howard Hughes Medical Institute/ -- England -- Nature. 2010 Feb 25;463(7284):1048-53. doi: 10.1038/nature08787.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Cellular and Molecular Pharmacology, University of California, San Francisco, 1700 4th Street, San Francisco, California 94158, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20182505" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Asthma/metabolism ; Cell Line ; Conserved Sequence ; Fatty Acids, Monounsaturated/pharmacology ; HeLa Cells ; *Homeostasis ; Humans ; Molecular Sequence Data ; *Multigene Family ; Multiprotein Complexes/chemistry/metabolism ; Phosphoric Monoester Hydrolases/genetics/metabolism ; Phosphorylation ; Protein Binding ; Saccharomyces cerevisiae/drug effects/enzymology/genetics/*metabolism ; Saccharomyces cerevisiae Proteins/classification/genetics/*metabolism ; Serine C-Palmitoyltransferase/genetics/metabolism ; Sphingolipids/biosynthesis/*metabolism
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
  • 3
    Publication Date: 2011-11-30
    Description: The Orm family proteins are conserved integral membrane proteins of the endoplasmic reticulum that are key homeostatic regulators of sphingolipid biosynthesis. Orm proteins bind to and inhibit serine:palmitoyl-coenzyme A transferase, the first enzyme in sphingolipid biosynthesis. In Saccharomyces cerevisiae, Orm1 and Orm2 are inactivated by phosphorylation in response to compromised sphingolipid synthesis (e.g., upon addition of inhibitor myriocin), thereby restoring sphingolipid production. We show here that protein kinase Ypk1, one of an essential pair of protein kinases, is responsible for this regulatory modification. Myriocin-induced hyperphosphorylation of Orm1 and Orm2 does not occur in ypk1∆ cells, and immunopurified Ypk1 phosphorylates Orm1 and Orm2 robustly in vitro exclusively on three residues that are known myriocin-induced sites. Furthermore, the temperature-sensitive growth of ypk1ts ypk2∆ cells is substantially ameliorated by deletion of ORM genes, confirming that a primary physiological role of Ypk1-mediated phosphorylation is to negatively regulate Orm function. Ypk1 immunoprecipitated from myriocin-treated cells displays a higher specific activity for Orm phosphorylation than Ypk1 from untreated cells. To identify the mechanism underlying Ypk1 activation, we systematically tested several candidate factors and found that the target of rapamycin complex 2 (TORC2) kinase plays a key role. In agreement with prior evidence that a TORC2-dependent site in Ypk1(T662) is necessary for cells to exhibit a wild-type level of myriocin resistance, a Ypk1(T662A) mutant displays only weak Orm phosphorylation in vivo and only weak activation in vitro in response to sphingolipid depletion. Additionally, sphingolipid depletion increases phosphorylation of Ypk1 at T662. Thus, Ypk1 is both a sensor and effector of sphingolipid level, and reduction in sphingolipids stimulates Ypk1, at least in part, via TORC2-dependent phosphorylation.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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