Induction of RelB participates in endotoxin tolerance

Using a THP-1 human promonocyte model of endotoxin tolerance that simulates the sepsis leukocyte phenotype, we previously showed that tolerant cells remain responsive to LPS endotoxin with degradation of I kappa B in the cytosol and nuclear translocation and accumulation of p50 and p65 NF-kappa B transcription factors. Despite this, endotoxin-inducible NF-kappa B-dependent innate immunity genes, like IL-1 beta, remained transcriptionally unresponsive in the tolerant phenotype, similar to the endotoxin tolerance observed in sepsis patients. In this study, we examined this paradox and found that ROB, another member of the NF-kappa B family, is induced during the establishment of tolerance. ReIB expression correlated with IL-1 beta repression, and sepsis patients showed increased ROB when compared with normal controls. Transient expression of ROB inhibited IL-1 beta in endotoxin-responsive cells. In the inverse experiment, small inhibitory RNAs decreased ROB expression in tolerant cells and restored endotoxin induction of IL-1 beta. When we examined tolerant cell extracts, we found transcriptionally inactive NF-kappa B p65/ReIB heterodimers. Taken together, our findings demonstrate that ROB can repress proinflammatory gene expression, and suggest that ReIB expression in sepsis patient blood leukocytes may play a role in the endotoxin-tolerant phenotype.