Inhibition of ceramide pathway does not affect ability of TNF-alpha to activate nuclear factor-kappa B

TNF-alpha is a multifunctional cytokine that has been shown to activate a number of intracellular second messenger pathways. Recent studies demonstrate that the sphingomyelinase-ceramide pathway plays a potential role in the activation of nuclear factor-kappa B (NF-kappa B) by TNF-alpha. The following experiments both confirm that the addition of ceramide to cells can activate NF-kappa B and demonstrate that a 48-h pretreatment with phorbol 12-myristate (PMA) results in the loss of the ceramide-induced NF-kappa B response. In parallel experiments, in which SW480 cells were pretreated with PMA, TNF-alpha provided a signal resulting in the nuclear translocation of NF-kappa B that was similar to untreated cells. These data combined suggest that additional pathways exist that TNF-alpha can use for the activation of NF-kappa B. Supplementary data demonstrates that TNF-alpha, ceramide, and PMA activate a human cytomegalovirus-(HCMV) beta gal construct (promoter is responsive to NF-kappa B) that was stably transfected into the TNF receptor-bearing tumor cell line, SW480. PMA pretreatment of these cells resulted in a significant decrease in both the PMA and ceramide generated responses, 6% and 0% of controls, respectively. However, the response generated by TNF-alpha was not inhibited significantly (96% of control cells). This data suggests that although ceramide and 1,2-diacylglycerol (DAG) pathways may contribute to TNF-alpha activation of NF-kappa B, impedance of these pathways does not block TNF-alpha from activating NF-kappa B nor induction of the functional activation of the NF-kappa B responsive reporter construct, HCMV.