Regulation of A + U-rich Element-directed mRNA Turnover Involving Reversible Phosphorylation of AUF1

Gerald M Wilson,Jiebo Lu,Kristina Sutphen,Yue Sun,Yung Huynh,Gary Brewer

doi:10.1074/jbc.m305772200

Gerald M Wilson, Jiebo Lu + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m305772200

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Abstract

Proteins binding A + U-rich elements (AREs) contribute to the rapid cytoplasmic turnover of mRNAs containing these sequences. However, this process is a regulated event and may be accelerated or inhibited by myriad signal transduction systems. For example, monocyte adherence at sites of inflammation or tissue injury is associated with inhibition of ARE-directed mRNA decay, which contributes to rapid increases in cytokine and inflammatory mediator production. Here, we show that acute exposure of THP-1 monocytic leukemia cells to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate mimics several features of monocyte adherence, including rapid induction and stabilization of ARE-containing mRNAs encoding interleukin-1 beta and tumor necrosis factor alpha. Additionally, TPA treatment alters the activity of cytoplasmic complexes that bind AREs, including complexes containing the ARE-specific, mRNA-destabilizing factor, AUF1. Analyses of AUF1 from control and TPA-treated cells indicated that post-translational modifications of the major cytoplasmic isoform, p40AUF1, are altered concomitant with changes in RNA binding activity and stabilization of ARE-containing mRNAs. In particular, p40AUF1 recovered from polysomes was phosphorylated on Ser83 and Ser87 in untreated cells but lost these modifications following TPA treatment. We propose that selected signal transduction pathways may regulate ARE-directed mRNA turnover by reversible phosphorylation of polysome-associated p40AUF1.

Highlights

Proteins binding A ؉ U-rich elements (AREs) contribute to the rapid cytoplasmic turnover of mRNAs containing these sequences
We have examined the stabilization of ARE-containing mRNAs encoding the cytokine IL-1␤ and the inflammatory mediator tumor necrosis factor ␣ (TNF␣), using a cultured cell model that mimics key features of monocyte adherence
To determine whether this acute TPA-induced adherence of THP-1 cells was accompanied by increased expression of cytokine and inflammatory mediator mRNAs, similar to that observed in adherent monocytes, the levels of IL-1␤ and TNF␣ mRNAs were measured across a time course of TPA treatment (Fig. 1)

Summary

Introduction

Proteins binding A ؉ U-rich elements (AREs) contribute to the rapid cytoplasmic turnover of mRNAs containing these sequences. Analyses of AUF1 from control and TPA-treated cells indicated that posttranslational modifications of the major cytoplasmic isoform, p40AUF1, are altered concomitant with changes in RNA binding activity and stabilization of ARE-containing mRNAs. In particular, p40AUF1 recovered from polysomes was phosphorylated on Ser83 and Ser87 in untreated cells but lost these modifications following TPA treatment.

Results

Conclusion