The AU-rich element mRNA decay-promoting activity of BRF1 is regulated by mitogen-activated protein kinase-activated protein kinase 2

Abstract

Regulated mRNA decay is a highly important process for the tight control of gene expression. Inherently unstable mRNAs contain AU-rich elements (AREs) in the 39 untranslated regions that direct rapid mRNA decay by interaction with decay-promoting AREbinding proteins (ARE-BPs). The decay of ARE-containing mRNAs is regulated by signaling pathways that are believed to directly target ARE-BPs. Here, we show that BRF1 involved in ARE-mediated mRNA decay (AMD) is phosphorylated by MAPK-activated protein kinase 2 (MK2). In vitro kinase assays using different BRF1 fragments suggest that MK2 phosphorylates BRF1 at four distinct sites, S54, S92, S203, and an unidentified site at the C terminus. Coexpression of an active form of MK2 inhibits ARE mRNA decay activity of BRF1. MK2-mediated inhibition of BRF1 requires phosphorylation at S54, S92, and S203. Phosphorylation of BRF1 by MK2 does not appear to alter its ability to interact with AREs or to associate with mRNA decay enzymes. Thus, MK2 inhibits BRF1-dependent AMD through direct phosphorylation. Although the mechanism underlying this inhibition is still unclear, it appears to target BRF1-dependent AMD at a level downstream from RNA binding and the recruitment of mRNA decay enzymes.

Activation and Function of the MAPKs and Their Substrates, the MAPK-Activated Protein Kinases

“…Several proteins bind ARE-containing mRNAs, many of which are specifically regulated by MK2/3 (248,401). Consistent with this, MK2 has been shown to bind and/or phosphorylate hnRNP A0 (297), tristetraprolin (TTP) (225), poly(A)-binding protein 1 (PABP1) (33), human R-antigen (HuR) (144,369), and butyrate response factor 1 (BRF1) (226). MK2-dependent phosphorylation of TTP creates functional 14-3-3-binding sites (61) that inhibit TTP-dependent degradation of ARE-containing transcripts and thereby contributes to LPS-induced TNF-␣ expression (38,154,345).…”

Phosphorylation of Tristetraprolin by MK2 Impairs AU-Rich Element mRNA Decay by Preventing Deadenylase Recruitment

“…Alternatively, different signaling pathways may affect TTP in different ways, whether by repression or activation of TTP. Other activators of ARE mRNA decay are inhibited by phosphorylation events, including the TTP paralogs BRF-1 and BRF-2, as well as the unrelated AUBPs AUF1 and KSRP (1,3,20,29,46,50,66). As with TTP, phosphorylation of these AUBPs leads to 14-3-3 recruitment, although the mechanistic consequences of this recruitment vary.…”

The role of the 3' untranslated region in post-transcriptional regulation of protein expression in mammalian cells.

“…The mechanism of inhibition is still unclear but it appears that MK2 phosphorylation occurs after the ARE binding and the recruitment of the mRNA decay machinery. 61 Ubiquitously expressed Hu-antigen R (HuR) is the most extensively studied TTR-RBP of the Hu protein family. HuR mostly ensures the stabilization of a wide variety of mRNAs, less frequently it regulates the translation or controls the nuclear export of related mRNAs.…”