ROLE OF DIHYDROCERAMIDE IN CELL SIGNALING

Sphingolipids are a class of bioactive lipids. Ceramide is the hub molecule of the intricate sphingolipid biosynthetic pathway. It is a bioactive lipid, regulating a number of physiological functions such as apoptosis, cell growth arrest, differentiation, senescence, migration and adhesion. The dihydroceramide is the precursor of ceramide along the de novo biosynthetic pathway. Several groups considered the dihydroceramide an inactive molecule. Recent studies associated dihydroceramide with the induction of cellular processes such as cell cycle arrest and programmed cell death. On the other hand this molecule also showed antiapoptotic properties. The goal of my doctorate project is to demonstrate the dihydroceramide implication in the regulation of a pro-survival cell response to stress. Hence, the human gastric carcinoma HGC-27 cells were treated with resveratrol, a molecule that induces dihydroceramide accumulation. Resveratrol is a polyphenol with well known anti-oxidant and anti-tumoral properties. On the other hand it is a calorie restriction mimetic, thus it activates sirtuins, promoting cell survival. A number of studies demonstrated that resveratrol modulates the biosynthetic de novo pathway of ceramide. Here we demonstrated that resveratrol, similarly to the specific inhibitor XM462, inhibits DEGS-1 desaturase activity, inducing dihydroceramide accumulation. This accumulation results in autophagy induction without affecting cell viability. We also obtained this response treating different cell lines with several drugs or conditions known to induce dihydroceramide accumulation. Although autophagy did not affect cell viability, however it causes a delay in cell proliferation. In fact we demonstrated that dihydroceramide accumulation in HGC-27 cells induces a temporary arrest in G0/G1 phase resulting in the delayed cell cycle phases progression. Moreover, we demonstrated that both autophagy activation and cell cycle arrest are temporally subsequent to the unfolded protein response (UPR) which is due to the dihydroceramide accumulation-mediated ER stress. All these results give an important contribute to the understanding of the metabolic role of sphingolipid mediators and their targeting in the anti-tumoral therapy.