MAPKAP kinase 2 blocks tristetraprolin-directed mRNA decay by inhibiting CAF1 deadenylase recruitment.
ABSTRACT Tristetraprolin (TTP) directs its target AU-rich element (ARE)-containing mRNAs for degradation by promoting removal of the poly(A) tail. The p38 MAPK pathway regulates mRNA stability via the downstream kinase MAPK-activated protein kinase 2 (MAPKAP kinase 2 or MK2), which phosphorylates and prevents the mRNA-destabilizing function of TTP. We show that deadenylation of endogenous ARE-containing tumor necrosis factor mRNA is inhibited by p38 MAPK. To investigate whether phosphorylation of TTP by MK2 regulates TTP-directed deadenylation of ARE-containing mRNAs, we used a cell-free assay that reconstitutes the mechanism in vitro. We find that phosphorylation of Ser-52 and Ser-178 of TTP by MK2 results in inhibition of TTP-directed deadenylation of ARE-containing RNA. The use of 14-3-3 protein antagonists showed that regulation of TTP-directed deadenylation by MK2 is independent of 14-3-3 binding to TTP. To investigate the mechanism whereby TTP promotes deadenylation, it was necessary to identify the deadenylases involved. The carbon catabolite repressor protein (CCR)4.CCR4-associated factor (CAF)1 complex was identified as the major source of deadenylase activity in HeLa cells responsible for TTP-directed deadenylation. CAF1a and CAF1b were found to interact with TTP in an RNA-independent fashion. We find that MK2 phosphorylation reduces the ability of TTP to promote deadenylation by inhibiting the recruitment of CAF1 deadenylase in a mechanism that does not involve sequestration of TTP by 14-3-3. Cyclooxygenase-2 mRNA stability is increased in CAF1-depleted cells in which it is no longer p38 MAPK/MK2-regulated.
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ABSTRACT: The mitogen-activated protein kinases (MAPKs) regulate diverse cellular programs by relaying extracellular signals to intracellular responses. In mammals, there are more than a dozen MAPK enzymes that coordinately regulate cell proliferation, differentiation, motility, and survival. The best known are the conventional MAPKs, which include the extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun amino-terminal kinases 1 to 3 (JNK1 to -3), p38 (α, β, γ, and δ), and ERK5 families. There are additional, atypical MAPK enzymes, including ERK3/4, ERK7/8, and Nemo-like kinase (NLK), which have distinct regulation and functions. Together, the MAPKs regulate a large number of substrates, including members of a family of protein Ser/Thr kinases termed MAPK-activated protein kinases (MAPKAPKs). The MAPKAPKs are related enzymes that respond to extracellular stimulation through direct MAPK-dependent activation loop phosphorylation and kinase activation. There are five MAPKAPK subfamilies: the p90 ribosomal S6 kinase (RSK), the mitogen- and stress-activated kinase (MSK), the MAPK-interacting kinase (MNK), the MAPK-activated protein kinase 2/3 (MK2/3), and MK5 (also known as p38-regulated/activated protein kinase [PRAK]). These enzymes have diverse biological functions, including regulation of nucleosome and gene expression, mRNA stability and translation, and cell proliferation and survival. Here we review the mechanisms of MAPKAPK activation by the different MAPKs and discuss their physiological roles based on established substrates and recent discoveries.Microbiology and molecular biology reviews: MMBR 03/2011; 75(1):50-83. · 12.59 Impact Factor
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ABSTRACT: Messenger RNA decay is a critical mechanism to control the expression of many inflammation- and cancer-associated genes. These transcripts are targeted for rapid degradation through AU-rich element (ARE) motifs present in the mRNA 3' untranslated region (3'UTR). Tristetraprolin (TTP) is an RNA-binding protein that plays a significant role in regulating the expression of ARE-containing mRNAs. Through its ability to bind AREs and target the bound mRNA for rapid degradation, TTP can limit the expression of a number of critical genes frequently overexpressed in inflammation and cancer. Regulation of TTP occurs on multiple levels through cellular signaling events to control transcription, mRNA turnover, phosphorylation status, cellular localization, association with other proteins, and proteosomal degradation, all of which impact TTP's ability to promote ARE-mediated mRNA decay along with decay-independent functions of TTP. This review summarizes the current understanding of post-transcriptional regulation of ARE-containing gene expression by TTP and discusses its role in maintaining homeostasis and the pathological consequences of losing TTP expression.Frontiers in Bioscience 01/2012; 17:174-88. · 3.29 Impact Factor
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ABSTRACT: The function of cytoplasmic PABPs [poly(A)-binding proteins] in promoting mRNA translation has been intensively studied. However, PABPs also have less clearly defined functions in mRNA turnover including roles in default deadenylation, a major rate-limiting step in mRNA decay, as well as roles in the regulation of mRNA turnover by cis-acting control elements and in the detection of aberrant mRNA transcripts. In the present paper, we review our current understanding of the complex roles of PABP1 in mRNA turnover, focusing on recent progress in mammals and highlighting some of the major questions that remain to be addressed.Biochemical Society Transactions 08/2012; 40(4):856-64. · 2.59 Impact Factor