title: Identification and characterization of RPK118, a novel sphingosine kinase-1-binding protein.
abstract: Sphingosine kinase (SPHK) is a key enzyme catalyzing the formation of sphingosine 1 phosphate (SPP), a lipid messenger that is implicated in the regulation of a wide variety of important cellular events through intracellular as well as extracellular mechanisms. However, the molecular mechanism of the intracellular actions of SPP remains unclear. Here we have cloned a novel sphingosine kinase-1 (SPHK1)-binding protein, RPK118, by yeast two-hybrid screening. RPK118 contains several functional domains whose sequences are homologous to other known proteins including the phox homology domain and pseudokinase 1 and 2 domains and is shown to be a member of an evolutionarily highly conserved gene family. The pseudokinase 2 domain of RPK118 is responsible for SPHK1 binding as judged by yeast two-hybrid screening and immunoprecipitation studies. RPK118 is also shown to co-localize with SPHK1 on early endosomes in COS7 cells expressing both recombinant proteins. Furthermore, RPK118 specifically binds to phosphatidylinositol 3-phosphate. These results strongly suggest that RPK118 is a novel SPHK1-binding protein that may be involved in transmitting SPP-mediated signaling into the cell.
authors.affiliation: Division of Biochemistry, Department of Molecular and Cellular Biology, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan.
authors.forename: Shun
authors.initials: S
authors.lastname: Hayashi
authors.forename: Taro
authors.initials: T
authors.lastname: Okada
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Igarashi
authors.forename: Toshitada
authors.initials: T
authors.lastname: Fujita
authors.forename: Saleem
authors.initials: S
authors.lastname: Jahangeer
authors.forename: Shun-Ichi
authors.initials: S
authors.lastname: Nakamura
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015152:Blotting, Northern; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D005822:Genetic Vectors; D006801:Humans; D015151:Immunoblotting; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D019893:Ribosomal Protein S6 Kinases; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014018:Tissue Distribution; D014162:Transfection; D020798:Two-Hybrid System Techniques; D000099157:Sphingosine Kinase
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; D047908:Intracellular Signaling Peptides and Proteins; D018129:Phosphatidylinositol Phosphates; D017853:Phosphotransferases (Alcohol Group Acceptor); D019893:Ribosomal Protein S6 Kinases; D000099157:Sphingosine Kinase; C055525:phosphatidylinositol 3-phosphate; C467003:RPS6KC1 protein, human