Extracellular export of sphingosine kinase-1a contributes to the vascular S1P gradient

• Published in: Biochemical journal Vol. 397; no. 3; pp. 461 - 471
• Main Authors: Venkataraman, Krishnan, Thangada, Shobha, Michaud, Jason, Oo, Myat Lin, Ai, Youxi, Lee, Yong-Moon, Wu, Mingtao, Parikh, Nehal S., Khan, Faraz, Proia, Richard L., Hla, Timothy
• Format: Journal Article
• Language: English
• Published: England Portland Press Ltd 01.08.2006
• Subjects: Animals; Cells, Cultured; Culture Media, Conditioned; Endothelium, Vascular - cytology; Extracellular Space - metabolism; Humans; Intracellular Space - metabolism; Isoenzymes - blood; Isoenzymes - metabolism; Isoenzymes - secretion; Lysophospholipids - biosynthesis; Lysophospholipids - blood; Mice; Mice, Inbred C57BL; Mice, Knockout; Phosphotransferases (Alcohol Group Acceptor) - blood; Phosphotransferases (Alcohol Group Acceptor) - metabolism; Phosphotransferases (Alcohol Group Acceptor) - secretion; Protein Transport; Receptors, Lysosphingolipid - metabolism; Sphingosine - analogs & derivatives; Sphingosine - biosynthesis; Sphingosine - blood
• ISSN: 0264-6021; 1470-8728; 1470-8728
• DOI: 10.1042/BJ20060251

Sphingosine 1-phosphate (S1P), produced by Sphks (sphingosine kinases), is a multifunctional lipid mediator that regulates immune cell trafficking and vascular development. Mammals maintain a large concentration gradient of S1P between vascular and extravascular compartments. Mechanisms by which S1P is released from cells and concentrated in the plasma are poorly understood. We recently demonstrated [Ancellin, Colmont, Su, Li, Mittereder, Chae, Stefansson, Liau and Hla (2002) J. Biol. Chem. 277, 6667–6675] that Sphk1 activity is constitutively secreted by vascular endothelial cells. In the present study, we show that among the five Sphk isoforms expressed in endothelial cells, the Sphk-1a isoform is selectively secreted in HEK-293 cells (human embryonic kidney cells) and human umbilical-vein endothelial cells. In sharp contrast, Sphk2 is not secreted. The exported Sphk-1a isoform is enzymatically active and produced sufficient S1P to induce S1P receptor internalization. Wild-type mouse plasma contains significant Sphk activity (179 pmol·min−1·g−1). In contrast, Sphk1−/− mouse plasma has undetectable Sphk activity and approx. 65% reduction in S1P levels. Moreover, human plasma contains enzymatically active Sphk1 (46 pmol·min−1·g−1). These results suggest that export of Sphk-1a occurs under physiological conditions and may contribute to the establishment of the vascular S1P gradient.