Expression of the ORMDLS, modulators of serine palmitoyltransferase, is regulated by sphingolipids in mammalian cells.
The relationship between serine palmitoyltransferase (SPT) activity and ORMDL regulation of sphingolipid biosynthesis was investigated in mammalian HEK293 cells. Each of the three human ORMDLs reduced the increase in long-chain base synthesis seen after overexpression of wild-type SPT or SPT containing the C133W mutation in hLCB1, which produces the non-catabolizable sphingoid base, 1-deoxySa. ORMDL-dependent repression of sphingoid base synthesis occurred whether SPT was expressed as individual subunits or as a heterotrimeric single-chain SPT fusion protein. Overexpression of the single-chain SPT fusion protein under the control of a tetracycline-inducible promoter in stably transfected cells resulted in increased endogenous ORMDL expression. This increase was not transcriptional; there was no significant increase in any of the ORMDL mRNAs. Increased ORMDL protein expression required SPT activity since overexpression of a catalytically inactive SPT with a mutation in hLCB2a had little effect. Significantly, increased ORMDL expression was also blocked by myriocin inhibition of SPT as well as fumonisin inhibition of the ceramide synthases, suggesting that increased expression is a response to a metabolic signal. Moreover, blocking ORMDL induction with fumonisin treatment resulted in significantly greater increases in in vivo SPT activity than was seen when ORMDLs were allowed to increase, demonstrating the physiological significance of this response.
From the Departments of Biochemistry and Molecular Biology and.
Sita D
SD
Gupta
From the Departments of Biochemistry and Molecular Biology and.
Kenneth
K
Gable
Genetics of Development and Disease Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
Aikaterini
A
Alexaki
Genetics of Development and Disease Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
Panagiotis
P
Chandris
Genetics of Development and Disease Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
Richard L
RL
Proia
From the Departments of Biochemistry and Molecular Biology and.
Teresa M
TM
Dunn
Pharmacology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799 and jeffrey.harmon@usuhs.edu.
Jeffrey M
JM
Harmon
D005229:Fatty Acids, Monounsaturated / Q000494:pharmacology; D037341:Fumonisins / Q000494:pharmacology; D005786:Gene Expression Regulation; D057809:HEK293 Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D021122:Protein Subunits / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D051102:Serine C-Palmitoyltransferase / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D013107:Sphingolipids / Q000378:metabolism* / Q000494:pharmacology; D013379:Substrate Specificity
D005229:Fatty Acids, Monounsaturated; D037341:Fumonisins; D008565:Membrane Proteins; C464259:ORMDL1 protein, human; C464279:ORMDL2 protein, human; C464399:ORMDL3 protein, human; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D013107:Sphingolipids; D010088:Oxidoreductases; C108138:dihydroceramide desaturase; D051102:Serine C-Palmitoyltransferase; C001996:thermozymocidin
Enzyme; Lipid Metabolism; Metabolic Regulation; Serine Palmitoyltransferase; Sphingolipid