A shift in sphingolipid composition from C24 to C16 increases susceptibility to apoptosis in HeLa cells

Sphingolipids, major lipid components of the eukaryotic plasma membrane, have a variety of physiological functions and have been associated with many diseases. They have also been implicated in apoptosis. Sphingolipids are heterogeneous in their acyl chain length, with long-chain (C16) and very long-chain (C24) sphingolipids being predominant in most mammalian tissues. We demonstrate that knockdown of ELOVL1 or CERS2, which catalyze synthesis of C24 acyl-CoAs and C24 ceramide, respectively, drastically reduced C24 sphingolipid levels with a complementary increase in C16 sphingolipids. Under ELOVL1 or CERS2 knockdown conditions, cisplatin-induced apoptosis significantly increased. Enhanced sensitivity to cisplatin-induced apoptosis exhibited close correlation with increases in caspase-3/7 activity. No significant alterations in sphingolipid metabolism such as ceramide generation were apparent with the cisplatin-induced apoptosis, and inhibitors of ceramide generation had no effect on the apoptosis. Apoptosis induced by UV radiation or C6 ceramides also increased in ELOVL1 or CERS2 knockdown cells. Changes in the composition of sphingolipid chain length may affect susceptibility to stimuli-induced apoptosis by affecting the properties of cell membranes, such as lipid microdomain/raft formation.