The RNA helicase Ddx5/p68 binds to hUpf3 and enhances NMD of Ddx17/p72 and Smg5 mRNA

Abstract

Non-sense-mediated mRNA decay (NMD) is a mechanism of translation-dependent mRNA surveillance in eukaryotes: it degrades mRNAs with premature termination codons (PTCs) and contributes to cellular homeostasis by downregulating a number of physiologically important mRNAs. In the NMD pathway, Upf proteins, a set of conserved factors of which Upf1 is the central regulator, recruit decay enzymes to promote RNA cleavage. In mammals, the degradation of PTC-containing mRNAs is triggered by the exon–junction complex (EJC) through binding of its constituents Upf2 and Upf3 to Upf1. The complex formed eventually induces translational repression and recruitment of decay enzymes. Mechanisms by which physiological mRNAs are targeted by the NMD machinery in the absence of an EJC have been described but still are discussed controversially. Here, we report that the DEAD box proteins Ddx5/p68 and its paralog Ddx17/p72 also bind the Upf complex by physical interaction with Upf3, thereby interfering with the binding of EJC. By activating the NMD machinery, Ddx5 is shown to regulate the expression of its own, Ddx17 and Smg5 mRNAs. For NMD triggering, the adenosine triphosphate-binding activity of Ddx5 and the 3′-untranslated region of substrate mRNAs are essential.

P68 RNA helicase promotes invasion of glioma cells through negatively regulating DUSP5

“…4,5 Because it is an ATPdependent RNA helicase, p68 can manipulate RNA structures, including pre-mRNA, rRNA, and microRNA. [6][7][8][9][10][11] P68 could also act as a transcriptional coactivator of several cancer-associated transcription factors, such as p53 tumor suppressor, 11 β-catenin, 12 and the androgen receptor, 13 which plays an essential role in cell proliferation, oncogenesis, and early stage organ development. 14 Indeed, p68 is aberrantly expressed or modified in different types of tumors, including breast, prostate, and colon cancer.…”

A Highly Conserved Region Essential for NMD in the Upf2 N-Terminal Domain

“…Dbp2, a DEAD-box helicase which, like Dbp6 is involved in ribosome biogenesis, manifests a two-hybrid interaction with Upf1 10 and functions in the NMD pathway 57 . Recently, p68/DDX5, the human Dbp2 orthologue, was shown to interact with human UPF3 and to enhance the NMD-dependent degradation of its own mRNA, as well as mRNAs encoding DDX17 (another DEAD-box helicase highly similar to DDX5) and SMG-5, which are all characterized by long 3′-UTR regions 58 . Furthermore, the C-terminal fragment from human UPF2 (encompassing the mIF4G-3 domain and the region involved in UPF1-CH binding) was shown to interact with eIF4AI in a yeast two-hybrid assay 59 .…”

Mechanism and regulation of the nonsense-mediated decay pathway

“…Thereby, a short motif of the core NMD factor UPF3b binds to the EJC core factors and serves as a platform to assemble an active NMD complex ( 52 , 77 ). Two other DEAD box proteins DDX5 and DDX17 have also recently been described to interact with UPF3b and this interaction seems crucial for the degradation of a limited subset of NMD substrates ( 78 ).…”