(A-E) SKOV3 cells were transfected with 5 nM siRNA for control-2, CerS2, CerS5, or CerS6 for 48 h and then lipids were extracted. Lipid contents (ceramide, sphingomyelin, hexosylceramide, sphingosine-1-phosphate, and sphingosine) were determined by mass spectrometry (n = 4). (F) Lipids were extracted from CRISPR control (C14) and CerS KO (3-6) cells and then ceramide contents were determined by mass spectrometry (n = 3).