phalloidine and 2-hexadecenal

The bioactive signaling molecule D-erythro-sphingosine-1-phosphate (S1P) is irreversibly degraded by the enzyme S1P lyase (SPL). The reaction of SPL with C18-S1P generates ethanolamine phosphate and a long-chain fatty aldehyde, trans-2-hexadecenal. Modulation of SPL expression in cells and organisms produces significant phenotypes, most of which have been attributed to corresponding changes in S1P-dependent signaling. However, the physiological functions of SPL products are not well understood. In the present study, we explored the biological activities of trans-2-hexadecenal in human and murine cells. We demonstrate that trans-2-hexadecenal causes cytoskeletal reorganization leading to cell rounding, detachment and eventual cell death by apoptosis in multiple cell types, including HEK293T, NIH3T3 and HeLa cells. Trans-2-hexadecenal stimulated a signaling pathway involving MLK3 and the respective phosphorylation of MKK4/7 and JNK, whereas ERK, AKT and p38 were unaffected. Trans-2-hexadecenal-induced apoptosis was accompanied by activation of downstream targets of JNK including c-Jun phosphorylation, cytochrome c release, Bax activation, Bid cleavage and increased translocation of Bim into mitochondria. The antioxidant N-acetylcysteine prevented JNK activation by trans-2-hexadecenal. Further, inhibition of JNK abrogated the cytoskeletal changes and apoptosis caused by trans-2-hexadecenal, whereas Rac1 and RhoA were not involved. In conclusion, our studies provide a new paradigm of sphingolipid signaling by demonstrating for the first time that S1P metabolism generates a bioactive product that induces cellular effects through oxidant stress-dependent MAP kinase cell signaling.

Topics: Acetylcysteine; Aldehydes; Animals; Apoptosis; Apoptosis Regulatory Proteins; bcl-2-Associated X Protein; Bcl-2-Like Protein 11; BH3 Interacting Domain Death Agonist Protein; cdc42 GTP-Binding Protein; Cytoskeleton; Enzyme Activation; Free Radical Scavengers; HEK293 Cells; Humans; JNK Mitogen-Activated Protein Kinases; MAP Kinase Kinase Kinases; Membrane Proteins; Mice; Mitogen-Activated Protein Kinase Kinase Kinase 11; Mitogen-Activated Protein Kinase Kinases; NIH 3T3 Cells; Phalloidine; Phosphorylation; Protein Processing, Post-Translational; Protein Transport; Proto-Oncogene Proteins; rac1 GTP-Binding Protein; Reactive Oxygen Species; Signal Transduction; Sphingolipids