Gene suppression by tristetraprolin and release by the p38 pathway

Abstract

Tristetraprolin (TTP) is a zinc finger protein that has been implicated in the control of tumor necrosis factor (TNF) mRNA stability. We show here that TTP protein has a suppressive effect on promoter elements from TNF-alpha and interleukin-8 and that lipopolysaccharide (LPS) stimulation can release this suppression. The release in LPS-stimulated cells was found to be primarily mediated by the p38 pathway because activation of p38 is sufficient to remove the suppressive effect of TTP. Indeed, TTP seems to be a direct substrate of p38 in vivo since it is an excellent substrate of p38 in vitro, and mutation of potential phosphorylation sites in TTP prevents release of the suppression imposed on TNF transcription. We found TTP protein to be present at low levels in the resting macrophage cell line RAW 264.7 and to be quickly induced after LPS stimulation. The kinetics of TTP induction suggests a potential role of TTP as an important player in switching off LPS-induced genes after induction. In conclusion, TTP plays an important role in maintaining gene quiescence, and this quenching effect on transcription can be released by p38 phosphorylation of TTP.

Tristetraprolin (TTP)-14-3-3 Complex Formation Protects TTP from Dephosphorylation by Protein Phosphatase 2a and Stabilizes Tumor Necrosis Factor-α mRNA

“…Other studies exploring this question have reported varying results (22)(23)(24)(25). Carballo et al reported that phosphorylated TTP bound less to a granulocyte macrophage-colony stimulating factor ARE probe than dephosphorylated TTP.…”

“…However, zinc fingers alone were not sufficient to mediate TNF-␣ mRNA degradation, because truncation of either the carboxyl or amino ends of TTP caused a loss TTP function (21). Both ends of the TTP zinc fingers contain a cluster of phosphorylation sites (22), yet the effects of phosphorylation on the mRNA binding and destabilizing activity of TTP remain controversial (22)(23)(24)(25).…”

Post‐transcriptional regulation of gene expression by degradation of messenger RNAs

“…As previously described, TTP promotes TNFa mRNA instability in mouse macrophages through direct interactions with its ARE (Taylor et al, 1996a;Carballo et al, 1997Carballo et al, , 1998Carballo et al, , 2000. It has recently been shown that TTP activation requires phosphorylation by p38 (Zhu et al, 2001). Although TTP is directly activated by p38, it exists in several phosphorylation states in cells, and the involvement of other kinases cannot be excluded (Zhu et al, 2001).…”

“…It has recently been shown that TTP activation requires phosphorylation by p38 (Zhu et al, 2001). Although TTP is directly activated by p38, it exists in several phosphorylation states in cells, and the involvement of other kinases cannot be excluded (Zhu et al, 2001).…”

Expression, Purification, and Biochemical Characterization of the Antiinflammatory Tristetraprolin: A Zinc-Dependent mRNA Binding Protein Affected by Posttranslational Modifications,

“…It is wellknown that TTP is a highly phosphorylated protein in mammalian cells (3,(20)(21)(22)(23)25). Phosphorylation of TTP in mammalian cells partially inhibits its binding to GM-CSF mRNA ARE and enhances its binding to the 14-3-3 protein (20,25).…”