Investigation of the relationship between sphingolipid and insulin signaling pathways

Abstract

Sphingolipids are the membrane lipids which have significant roles in signal transduction as second messengers and in regulatory pathways including cell cycle arrest, apoptosis, senescence and differentiation. Ceramide functioning in sphingolipid metabolism is known to inhibit Akt/ protein kinase B (PKB) which is one of the core proteins of insulin signaling pathway. However, the mechanism of crosstalk between sphingolipid signaling pathway and insulin signaling pathway has not been elucidated completely. In this study, we investigated the proteins which play important roles in the association of sphingolipid and insulin signaling pathways. The deletion mutants of PKH1, YPK1 and YPK2 of Saccharomyces cerevisiae at 30g/l initial glucose concentration had reduced IPC percentages compared to wild type strain in agreement with the literature information. However, at 40 g/l initial glucose concentration, the deletion mutants resulted in higher percentages of lipid composition compared to wild type strain as well as higher amounts of remaining glucose in the medium as expected. When the initial glucose concentration in the medium was increased, the effect of other proteins having roles in glucose signal reception and transduction might be dominant. Nevertheless, the experimental results on the relation between glucose consumption and complex sphingolipid production were found to be in agreement with the literature. Then, Akt2 protein was further investigated from the aspect of drug discovery since Akt/PKB is the most significant protein that affects GLUT4 translocation, and it is also a critical target protein for anticancer drug discovery. Therefore, the pockets of Akt2 were identified by using both geometric and energetic approaches. SplitPocket (geometry-based program) identified all the residues whereas Q-SiteFinder (energetic-based program) detected only one residue that was reported as an inhibitor binding site in literature. Furthermore, solvation energy, electrostatics and druggability index of binding pockets were also estimated. These results can be used as a starting point for docking suitable ligands.