title: Subcellular targeting domains of sphingomyelin synthase 1 and 2.
abstract: Sphingomyelin synthase (SMS) sits at the crossroads of sphingomyelin (SM), ceramide, diacylglycerol (DAG) metabolism. It utilizes ceramide and phosphatidylcholine as substrates to produce SM and DAG, thereby regulating lipid messengers which play a role in cell survival and apoptosis. Furthermore, its product SM has been implicated in atherogenic processes such as retention of lipoproteins in the blood vessel intima. There are two mammalian sphingomyelin synthases: SMS1 and SMS2. SMS1 is found exclusively in the Golgi at steady state, whereas SMS2 exists in the Golgi and plasma membrane. Conventional motifs responsible for protein targeting to the plasma membrane or Golgi are either not present in, or unique to, SMS1 and SMS2. In this study, we examined how SMS1 and SMS2 achieve their respective subcellular localization patterns. Brefeldin A treatment prevented SMS1 and SMS2 from exiting the ER, demonstrating that they transit through the classical secretory pathway. We created truncations and chimeras of SMS1 and SMS2 to define their targeting signals. We found that SMS1 contains a C-terminal Golgi targeting signal and that SMS2 contains a C-terminal plasma membrane targeting signal.
authors.affiliation: Department of Cell Biology, State University of New York Downstate Medical Center, 450 Clarkson Ave,, Brooklyn, New York, 11203 USA. XJiang@downstate.edu.
authors.forename: Calvin
authors.initials: C
authors.lastname: Yeang
authors.forename: Tingbo
authors.initials: T
authors.lastname: Ding
authors.forename: William J
authors.initials: WJ
authors.lastname: Chirico
authors.forename: Xian-Cheng
authors.initials: XC
authors.lastname: Jiang