A translational silencing function of MCPIP1/Regnase-1 specified by the target site context.

The expression of proteins during inflammatory and immune reactions is coordinated by post-transcriptional mechanisms. A particularly strong suppression of protein expression is exerted by a conserved translational silencing element (TSE) identified in the 3' UTR of NFKBIZ mRNA, which is among the targets of the RNA-binding proteins Roquin-1/2 and MCPIP1/Regnase-1. We present evidence that in the context of the TSE MCPIP1, so far known for its endonuclease activity toward mRNAs specified by distinct stem-loop (SL) structures, also suppresses translation.

Interleukin-17 (IL-17) and IL-1 activate translation of overlapping sets of mRNAs, including that of the negative regulator of inflammation, MCPIP1.

Changes in gene expression during inflammation are in part caused by post-transcriptional mechanisms. A transcriptome-wide screen for changes in ribosome occupancy indicated that the inflammatory cytokine IL-17 activates translation of a group of mRNAs that overlaps partially with those affected similarly by IL-1. Included are mRNAs of IκBζ and of MCPIP1, important regulators of the quality and course of immune and inflammatory responses.

Interleukin-1 activates synthesis of interleukin-6 by interfering with a KH-type splicing regulatory protein (KSRP)-dependent translational silencing mechanism.

Post-transcriptional mechanisms play an important role in the control of inflammatory gene expression. The heterogeneous nuclear ribonucleoprotein K homology (KH)-type splicing regulatory protein (KSRP) triggers rapid degradation of mRNAs for various cytokines, chemokines, and other inflammation-related proteins by interacting with AU-rich elements (AREs) in the 3'-untranslated mRNA regions. In addition to destabilizing mRNAs, AU-rich elements can restrict their translation.

IL-1-induced post-transcriptional mechanisms target overlapping translational silencing and destabilizing elements in IκBζ mRNA.

The inflammatory cytokine IL-1 induces profound changes in gene expression. This is contributed in part by activating translation of a distinct set of mRNAs, including IκBζ, as indicated by genome-wide analysis of changes in ribosomal occupancy in IL-1α-treated HeLa cells. Polysome profiling of IκBζ mRNA and reporter mRNAs carrying its 3' UTR indicated poor translation in unstimulated cells.

Functional analysis of KSRP interaction with the AU-rich element of interleukin-8 and identification of inflammatory mRNA targets.

mRNA stability is a major determinant of inflammatory gene expression. Rapid degradation of interleukin-8 (IL-8) mRNA is imposed by a bipartite AU-rich element (ARE) in the 3' untranslated region (R. Winzen et al.

Inhibition of mRNA deadenylation and degradation by different types of cell stress.

We have previously observed rapid and strong inhibition of mRNA deadenylation and degradation in response to UV-B light [Gowrishankar et al., Biol. Chem.

Inhibition of mRNA deadenylation and degradation by ultraviolet light.

Post-transcriptional mechanisms contribute to the changes in gene expression induced by cell stress. The effect of UV-B light on mRNA degradation in HeLa cells was investigated using a transcriptional chase system to determine the decay kinetics of tet-off vector-derived mRNAs containing or lacking a destabilizing AU-rich element. Degradation of both mRNAs was strongly inhibited in cells exposed to UV-B light.

Distinct domains of AU-rich elements exert different functions in mRNA destabilization and stabilization by p38 mitogen-activated protein kinase or HuR.

AU-rich elements (AREs) control the expression of numerous genes by accelerating the decay of their mRNAs. Rapid decay and deadenylation of beta-globin mRNA containing AU-rich 3' untranslated regions of the chemoattractant cytokine interleukin-8 (IL-8) are strongly attenuated by activating the p38 mitogen-activated protein (MAP) kinase/MAP kinase-activated protein kinase 2 (MK2) pathway. Further evidence for a crucial role of the poly(A) tail is provided by the loss of destabilization and kinase-induced stabilization in ARE RNAs expressed as nonadenylated forms by introducing a histone stem-loop sequence.

Affinity purification of ARE-binding proteins identifies polyA-binding protein 1 as a potential substrate in MK2-induced mRNA stabilization.

An important determinant for the expression level of cytokines and proto-oncogenes is the rate of degradation of their mRNAs. AU-rich sequence elements (AREs) in the 3(') untranslated regions have been found to impose rapid decay of these mRNAs. ARE-containing mRNAs can be stabilized in response to external signals which activate the p38 MAP kinase cascade including the p38 MAP kinase substrate MAPKAP kinase 2 (MK2).

Evidence for general stabilization of mRNAs in response to UV light.

mRNA stabilization plays an important role in the changes in protein expression initiated by inducers of inflammation or direct cell stress such as UV light. This study provides evidence that stabilization in response to UV light differs from that induced by proinflammatory stimuli such as bacterial lipopolysaccharide or interleukin (IL)-1. Firstly, UV-induced stabilization is independent of the p38 MAP kinase pathway, which has previously been shown to mediate stabilization induced by IL-1 or lipopolysaccharide.

MK2 targets AU-rich elements and regulates biosynthesis of tumor necrosis factor and interleukin-6 independently at different post-transcriptional levels.

We demonstrate that lipopolysaccharide-induced tumor necrosis factor (TNF) biosynthesis becomes independent of MAPKAP kinase 2 (MK2) when the AU-rich element (ARE) of the TNF gene is deleted. In spleen cells and macrophages where TNF biosynthesis is restored as a result of this deletion, interleukin (IL)-6 biosynthesis is still dependent on MK2. In MK2-deficient macrophages the half-life of IL-6 mRNA is reduced more than 10-fold, whereas the half-life of TNF mRNA is only weakly decreased.