Activation of ceramide synthase 6 by celecoxib leads to a selective induction of C16:0-ceramide

Ceramides serve as bioactive molecules with important roles in cell proliferation and apoptosis Ceramides (Cer) with different N-acyl side chains (C-14:0-Cer-C-26:0-Cer) possess distinctive roles in cell signaling and are differentially expressed in HIT-116 colon cancer cells Celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, exhibiting antiproliferative effects, activates the sphingolipid pathway. To elucidate the mechanism, HCT-116 cells were treated with 50 mu M celecoxib leading to a significant increase of C-16:0-Cer. Interestingly, 50 mu M celecoxib resulted in a 2 8-fold increase of ceramide synthase (CerS) activity as measured by a cell-based activity assay siRNA against several CerSs revealed that CerS6 was predominantly responsible for the increase of C-16:0-Cer in HCT-116 cells Moreover, the silencing of CerS6 partially protected HIT-116 cells from the toxic effects induced by celecoxib Treatment of cells with celecoxib and fumonisin B1 (inhibitor of CerSs) or myriocin (Inhibitor oft-serine palmitoyl transferase) or desipramine (inhibitor of acid sphingomyelinase and acid ceramidase) revealed that the increase of C-16:0-Cer results predominantly from activation of the salvage pathway Using the nude mouse model we demonstrated that celecoxib Induces also in vivo a significant Increase of C-16:0-Cer in stomach, small intestine and tumor tissue In conclusion, celecoxib causes a specific Increase of C-16:0-Cer by activating CerS6 and the salvage pathway, which contribute to the toxic effects of celecoxib. (C) 2010 Elsevier Inc All rights reserved