Sphingosine and other long-chain bases have diverse effects on cell function. They inhibit protein kinase C, activate the tyrosine kinase activity of the epidermal growth factor receptor, and affect a number of other regulatory systems at relatively low (micromolar) concentrations. These effects, and the associated possibility that long-chain bases may serve as another class of """"""""lipid second messenger,"""""""" has rekindled interest in how these compounds are made and turned over, as well as in the structural requirements for their behavior. Over the last several years, we have developed a stereoselective synthesis for sphingosine and structurally related compounds that will allow us to conduct such analyses. Thus far, we have made over two dozen analogs and determined their potency as inhibitors of protein kinase C and representative cell functions thought to be mediated via this enzyme. We have also identified some of the relevant physical properties of these compounds (e.g., the pKa of the amino group, the critical micelle concentration of sphingosine, the ability of sphingosine to move rapidly between membranes but to tend to associate with negatively charged lipids). In this grant, we plan to: 1) refine further the structural features that result in inhibition of protein kinase C, stimulation of cell growth, and other cellular effects of these compounds; 2) gain a more complete picture of the physical state of sphingosine in membranes (such as the degree of protonation, which will be determined by C-13 NMR), and to relate these observations to their cellular effects; and 3) determine the metabolic fate of the stereoisomers of sphingosine and related compounds. These investigations will provide fundamental information about the biochemistry and cell biology of sphingosine, and could provide valuable tools and insight into long-chain bases as modulators of cell behavior.
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