Tristetraprolin Impairs NF-κB/p65 Nuclear Translocation

Tristetraprolin (TTP) is a prototypic family member of CCCH-type tandem zinc-finger domain proteins that regulate mRNA destabilization in eukaryotic cells. TTP binds to AU-rich elements (AREs) in the 3'-untranslated region of certain mRNAs, including tumor necrosis factor alpha, granulocyte macrophage colony-stimulating factor, and immediate early response 3, thereby facilitating their ARE-mediated decay. Expression of TTP is up-regulated by a variety of agents, including inflammatory mediators such as tumor necrosis factor alpha, a prominent activator of the nuclear factor kappa B (NF-kappa B) family of transcription factors. Accordingly, TTP is involved in the negative feedback regulation of NF-kappa B through promoting mRNA degradation. We describe here a novel, ARE-mediated decay-independent function of TTP on the termination of NF-kappa B response: TTP suppresses the transcriptional activity of NF-kappa B-dependent promoters independent of its mRNA-destabilizing property. In TTP knockout mouse embryonic fibroblasts, lack of TTP leads to enhanced nuclear p65 levels, which is associated with the up-regulation of specific, ARE-less NF-kappa B target genes. We find that attenuation of NF-kappa B activity is at least in part due to an interference of TTP with the nuclear import of the p65 subunit of the transcription factor. This novel role of TTP may synergize with its mRNA-degrading function to contribute to the efficient regulation of proinflammatory gene expression.