title: Sphingosine enhances phosphatidylinositol 4-kinase activity in rabbit platelets.
abstract: The modulating effect of sphingosine on the metabolism of inositol phospholipids was investigated using rabbit platelets. When [3H]arachidonic acid- or [3H]inositol-labeled platelets were incubated at 37 degrees C with sphingosine, the radioactivity of the phosphatidylinositol (PI) fraction obtained on TLC decreased time-dependently up to 5 min, and phosphatidylinositol monophosphate (PIP) and phosphatidylinositol bisphosphate (PIP2) increased concomitantly, though neither arachidonic acid nor 1,2-diacylglycerol was formed. The effect of sphingosine was dose-dependent, the maximum effect being observed at 20 microM. Treatment with a sphingosine derivative, sphingosine-1-phosphate (Sph-1-P) or N-hexanoyl-sphingosine (C6-ceramide), did not result in an increase in PIP. The increased radioactivity of PIP with sphingosine was attributable to an increase in phosphatidylinositol 4-phosphate, but not phosphatidylinositol 3-phosphate. Furthermore, wortmannin, an inhibitor of PI 3-kinase, did not affect the modulating effect of sphingosine at 100 nM, at which the enzyme is known to be completely inhibited. The activity of PI 4-kinase in the platelet lysate was increased by sphingosine but not by Sph-1-P. These results suggest that sphingosine enhances the activity of PI 4-kinase and thereby contributes to the regulation of inositol phospholipid metabolism.
authors.affiliation: Department of Pathological Biochemistry, Kyoto Pharmaceutical University.
authors.forename: T
authors.initials: T
authors.lastname: Hashizume
authors.forename: M
authors.initials: M
authors.lastname: Nakao
authors.forename: T
authors.initials: T
authors.lastname: Sato
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D019870:1-Phosphatidylinositol 4-Kinase; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000097:blood; D001792:Blood Platelets / Q000201:enzymology*; D002518:Ceramides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008246:Lysophospholipids; D019869:Phosphatidylinositol 3-Kinases; D010716:Phosphatidylinositols / Q000097:blood; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000097:blood*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology; D011817:Rabbits; D013110:Sphingosine / Q000031:analogs & derivatives / Q000494:pharmacology*; D019311:Staurosporine / Q000494:pharmacology; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002518:Ceramides; D004791:Enzyme Inhibitors; D008246:Lysophospholipids; D010716:Phosphatidylinositols; C060506:sphingosine 1-phosphate; D016718:Arachidonic Acid; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D019870:1-Phosphatidylinositol 4-Kinase; D011493:Protein Kinase C; D019311:Staurosporine; D013110:Sphingosine; D000077191:Wortmannin