Tumor necrosis factor-α (TNF-α) signal transduction through ceramide: Dissociation of growth inhibitory effects of TNF-α from activation of nuclear factor-κB

Tumor necrosis factor-α (TNF-α) exerts pleiotropic biologic effects. Although TNF-α appears to activate a number of signal transduction pathways, the role of second messengers in mediating the different effects of TNF-α are not well defined. In this study, we investigated the role of ceramide as an intracellular mediator of TNF-α action. In Jurkat T cells, TNF-α caused early activation of the sphingomyelin cycle with peak hydrolysis of sphingomyelin observed at 30 min following addition of TNF-α. In this cell line, TNF-α caused potent activation of nuclear factor-κB (NF-κB) and exerted potent cytostatic/cytocidal activity. C₂-ceramide mimicked the effects of TNF-α on cell growth in a dose-dependent manner, but C₂-ceramide was unable to induce activation of NF-κB under multiple conditions investigated. C₂-ceramide, however, enhanced activation of NF-κB in response to TNF-α with peak effects observed at a concentration of C₂-ceramide of 5 μM. Thus, ceramide functions as a selective mediator of the cytostatic/cytotoxic effects of TNF-α and plays a positive feedback role in activation of NF-κB. TNF-α signaling, therefore, involves multiple second-messenger pathways that function independently or coordinately to transduce distinct functions of TNF-α.