Tumor necrosis factor (TNF) interferes with insulin signaling through the p55 TNF receptor death domain

Tumor necrosis factor (TNF) contributes to insulin resistance by binding to the 55kDa TNF receptor (TNF-R55), resulting in serine phosphorylation of proteins such as insulin receptor (IR) substrate (IRS)-1, followed by reduced tyrosine phosphorylation of IRS-1 through the IR and, thereby, diminished IR signal transduction. Through independent receptor domains, TNF-R55 activates a neutral (N-SMase) and an acid sphingomyelinase (A-SMase), that both generate the sphingolipid ceramide. Multiple candidate kinases have been identified that serine-phosphorylate IRS-1 in response to TNF or ceramide. However, due to the fact that the receptor domain of TNF-R55 mediating inhibition of the IR has not been mapped, it is currently unknown whether TNF exerts these effects with participation of N-SMase or A-SMase. Here, we identify the death domain of TNF-R55 as responsible for the inhibitory effects of TNF on tyrosine phosphorylation of IRS-1, implicating ceramide generated by A-SMase as a downstream mediator of inhibition of IR signaling.