Cell Density Dependent Inhibition of Dihydroceramide Desaturase

In our current work, we applied a metabolic approach to investigate the role of sphingolipids in cell density‐induced growth arrest. Our data revealed that sphingolipid metabolism significantly differs depending on the cells' population density. At high cell density cells exhibited G0/G1 cell cycle arrest and reduced ceramide, monohexosylceramide, and sphingomyelin, but dihydroceramide was increased. In addition, our data revealed that densely populated cells had increased message levels of both, anabolic and catabolic enzymes of the sphingolipid pathway, suggesting increased sphingolipid turnover at confluence. Moreover, our metabolic labeling experiments showed that at high cell density cells preferentially synthesized very‐long chain sphingolipids and dramatically decreased synthesis of sphingosine‐1‐phosphate. The metabolic labeling experiments also indicated an inhibition of dihydroceramide desaturase at confluence, which was confirmed by dihydroceramide desaturase activity in situ and in vitro . In conclusion, our data suggest a role of sphingolipids, dihydroceramides in particular, in confluence‐induced growth arrest.