Interorganelle trafficking of ceramide is regulated by phosphorylation-dependent cooperativity between the PH and START domains of CERT.
The synthesis and transport of lipids are essential events for membrane biogenesis. However, little is known about how intracellular trafficking of lipids is regulated. Ceramide is synthesized at the endoplasmic reticulum (ER) and transported by the ceramide transfer protein CERT to the Golgi apparatus, where it is converted to sphingomyelin. CERT has a phosphoinositide-binding pleckstrin homology (PH) domain for Golgi-targeting and a lipid transfer START domain for intermembrane transfer of ceramide. We here show that CERT receives multiple phosphorylations at a serine-repeat motif, a possibe site for casein kinase I, and that the phosphorylation down-regulates the ER-to-Golgi transport of ceramide. In vitro assays show that the phosphorylation induces an autoinhibitory interaction between the PH and START domains and consequently inactivates both the phosphoinositide binding and ceramide transfer activities of CERT. Loss of sphingomyelin and cholesterol from cells causes dephosphorylation of CERT to activate it. The cooperative control of functionally distinct domains of CERT is a novel molecular event to regulate the intracellular trafficking of ceramide.
Kumagai
Keigo
K
Department of Biochemistry and Cell Biology, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8640, Japan.
Kawano
Miyuki
M
Shinkai-Ouchi
Fumiko
F
Nishijima
Masahiro
M
Hanada
Kentaro
K
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism*; D002518:Ceramides / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D021962:Membrane Microdomains / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D015388:Organelles / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D012694:Serine / Q000378:metabolism; D013912:Threonine / Q000378:metabolism
D002518:Ceramides; D013912:Threonine; D012694:Serine; C119090:CERT1 protein, human; D017346:Protein Serine-Threonine Kinases