Casein kinase I{gamma}2 down-regulates trafficking of ceramide in the synthesis of sphingomyelin.
Intracellullar trafficking of lipids is fundamental to membrane biogenesis. For the synthesis of sphingomyelin, ceramide is transported from the endoplasmic reticulum to the Golgi apparatus by the ceramide transfer protein CERT. CERT is phosphorylated by protein kinase D at S132 and subsequently multiple times in a serine-repeat motif, resulting in its inactivation. However, the kinase involved in the multiple phosphorylation remains unclear. Here, we identify the gamma2 isoform of casein kinase I (CKIgamma2) as a kinase whose overexpression confers sphingomyelin-directed toxin-resistance to Chinese hamster ovary cells. In a transformant stably expressing CKIgamma2, CERT was hyperphosphorylated, and the intracellular trafficking of ceramide was retarded, thereby reducing de novo sphingomyelin synthesis. The reduction in the synthesis of sphingomyelin caused by CKIgamma2 was reversed by the expression of CERT mutants that are not hyperphosphorylated. Furthermore, CKIgamma2 directly phosphorylated CERT in vitro. Among three gamma isoforms, only knockdown of gamma2 isoform caused drastic changes in the ratio of hypo- to hyperphosphorylated form of CERT in HeLa cells. These results indicate that CKIgamma2 hyperphosphorylates the serine-repeat motif of CERT, thereby inactivating CERT and down-regulating the synthesis of sphingomyelin.
Tomishige
Nario
N
Department of Biochemistry and Cell Biology, National Institute of Infectious Diseases, Tokyo, Japan.
Kumagai
Keigo
K
Kusuda
Jun
J
Nishijima
Masahiro
M
Hanada
Kentaro
K
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D047389:Casein Kinase I / Q000235:genetics / Q000378:metabolism*; D002518:Ceramides / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D004721:Endoplasmic Reticulum / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013109:Sphingomyelins / Q000096:biosynthesis*; D014118:Toxins, Biological / Q000378:metabolism
D002518:Ceramides; D007527:Isoenzymes; D011993:Recombinant Fusion Proteins; D013109:Sphingomyelins; D014118:Toxins, Biological; C107040:lysenin; C119090:CERT1 protein, human; D047389:Casein Kinase I; D017346:Protein Serine-Threonine Kinases