RESUMO
The molecular basis of TNF tolerance is poorly understood. In human monocytes we detected two forms of TNF refractoriness, as follows: absolute tolerance was selective, dose dependently affecting a small group of powerful effector molecules; induction tolerance represented a more general phenomenon. Preincubation with a high TNF dose induces both absolute and induction tolerance, whereas low-dose preincubation predominantly mediates absolute tolerance. In cells preincubated with the high TNF dose, we observed blockade of IκBα phosphorylation/proteolysis and nuclear p65 translocation. More prominent in cells preincubated with the high dose, reduced basal IκBα levels were found, accompanied by increased IκBα degradation, suggesting an increased IκBα turnover. In addition, a nuclear elevation of p50 was detected in tolerant cells, which was more visible following high-dose preincubation. TNF-induced phosphorylation of p65-Ser(536), p38, and c-jun was inhibited, and basal inhibitory p65-Ser(468) phosphorylation was increased in tolerant cells. TNF tolerance induced by the low preincubation dose is mediated by glycogen synthesis kinase-3, whereas high-dose preincubation-mediated tolerance is regulated by A20/glycogen synthesis kinase-3 and protein phosphatase 1-dependent mechanisms. To our knowledge, we present the first genome-wide analysis of TNF tolerance in monocytic cells, which differentially inhibits NF-κB/AP-1-associated signaling and shifts the kinase/phosphatase balance. These forms of refractoriness may provide a cellular paradigm for resolution of inflammation and may be involved in immune paralysis.
