title: Phosphatidylinositol 4-kinase IIIbeta regulates the transport of ceramide between the endoplasmic reticulum and Golgi.
abstract: The recently identified ceramide transfer protein, CERT, is responsible for the bulk of ceramide transport from the endoplasmic reticulum (ER) to the Golgi. CERT has a C-terminal START domain for ceramide binding and an N-terminal pleck-strin homology domain that binds phosphatidylinositol 4-phosphate suggesting that phosphatidylinositol (PI) 4-kinases are involved in the regulation of CERT-mediated ceramide transport. In the present study fluorescent analogues were used to follow the ER to Golgi transport of ceramide to determine which of the four mammalian PI 4-kinases are involved in this process. Overexpression of pleckstrin homology domains that bind phosphatidylinositol 4-phosphate strongly inhibited the transport of C5-BODIPY-ceramide to the Golgi. A newly identified PI 3-kinase inhibitor, PIK93 that selectively inhibits the type III PI 4-kinase beta enzyme, and small interfering RNA-mediated down-regulation of the individual PI 4-kinase enzymes, revealed that PI 4-kinase beta has a dominant role in ceramide transport between the ER and Golgi. Accordingly, inhibition of PI 4-kinase III beta either by wortmannin or PIK93 inhibited the conversion of [3H]serine-labeled endogenous ceramide to sphingomyelin. Therefore, PI 4-kinase beta is a key enzyme in the control of spingomyelin synthesis by controlling the flow of ceramide from the ER to the Golgi compartment.
authors.affiliation: Section on Molecular Signal Transduction, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Balázs
authors.initials: B
authors.lastname: Tóth
authors.forename: András
authors.initials: A
authors.lastname: Balla
authors.forename: Hui
authors.initials: H
authors.lastname: Ma
authors.forename: Zachary A
authors.initials: ZA
authors.lastname: Knight
authors.forename: Kevan M
authors.initials: KM
authors.lastname: Shokat
authors.forename: Tamas
authors.initials: T
authors.lastname: Balla
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001692:Biological Transport; D001896:Boron Compounds / Q000494:pharmacology; D019556:COS Cells; D002518:Ceramides / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020224:Expressed Sequence Tags; D005456:Fluorescent Dyes / Q000494:pharmacology; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D008956:Models, Chemical; D017434:Protein Structure, Tertiary
chemical_list: C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D002518:Ceramides; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D019870:1-Phosphatidylinositol 4-Kinase