A dozen years ago, the term 'S1P' (sphingosine 1-phosphate) was not in the lexicons of scientific literature databases. By early 2008, this query term retrieved well over 1,000 citations from PubMed -about 225 of these appeared in 2007. Indeed, S1P is arguably the most heavily studied lipid molecule at present. What happened to distinguish S1P among many other signaling lipids? We believe that the seminal event was the linking of the investigational drug, FTY720 (fingolimod), to S1P signaling. This realization profoundly altered understanding of S1P biology, revealing both that S1P is prominent in lymphocyte trafficking and that mimicking S1P signaling with an agonist drug can modulate the immune system to considerable therapeutic benefit. Neither fact was known prior to FTY720; indeed, this molecule is testament to the power of chemical biology. In this communication, we attempt to summarize progress to date in S1P chemical biology.
S1P biosynthesis and degradationIn mammals, the long chain base sphingosine is formed by amidase catalyzed hydrolysis of ceramides. Sphingosine is phosphorylated by sphingosine kinase types 1 or 2 (SPHK1, SPHK2) to form S1P, which is either converted back to sphingosine by lipid phosphatases or degraded irreversibly by S1P lyase [1]. S1P synthesis occurs in cells (but see reference [2]), thus the existence of S1P in plasma indicates some efflux system is responsible for S1P's appearance. A small fraction of long chain bases lack a double bond (sphinganine (dihydrosphingosine), which is the precursor to ceramide in mammalian sphingolipid anabolism) [3]. Sphinganine is a substrate of SPHK and the product, sphinganine 1-phosphate, is for the most part indistinguishable from S1P in its biologic effects (but see reference [4]). The S1P biosynthetic pathway is widespread among mammalian tissues. S1P concentrations in human and mouse plasma are 200-800 nanoM, where the molecule is nearly all protein-bound. S1P introduced into the mouse vasculature is degraded quickly (T1/2 15 min [5]), which indicates a rapid flux of sphingosine through the pathway outlined above. Mice lacking either SPHK1 or SPHK2 have decreased plasma S1P concentrations [6][7][8], but the reduction is more pronounced in SPHK1 null animals [6]. Disruption of both Sphk1 and Sphk2 gene loci is embryonic lethal in mice [9]. Characterization of the phosphatase(s) that hydrolyze the S1P phosphate monoester has been problematic. Leading candidates for this enzyme are the integral membrane lipid ectophosphatase LPP3 (lipid © 2008 Elsevier B.V. All rights reserved. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers tha...