Staufen2, like Staufen1, functions in SMD by binding to itself and its paralog and promoting UPF1 helicase but not ATPase activity

Department of Biochemistry and Biophysics, School of Medicine and Dentistry, and Center for RNA Biology, University of Rochester, Rochester, NY 14642.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 12/2012; 110(2). DOI: 10.1073/pnas.1213508110
Source: PubMed

ABSTRACT Staufen (STAU)1-mediated mRNA decay (SMD) is a posttranscriptional regulatory mechanism in mammals that degrades mRNAs harboring a STAU1-binding site (SBS) in their 3'-untranslated regions (3' UTRs). We show that SMD involves not only STAU1 but also its paralog STAU2. STAU2, like STAU1, is a double-stranded RNA-binding protein that interacts directly with the ATP-dependent RNA helicase up-frameshift 1 (UPF1) to reduce the half-life of SMD targets that form an SBS by either intramolecular or intermolecular base-pairing. Compared with STAU1, STAU2 binds ∼10-fold more UPF1 and ∼two- to fivefold more of those SBS-containing mRNAs that were tested, and it comparably promotes UPF1 helicase activity, which is critical for SMD. STAU1- or STAU2-mediated augmentation of UPF1 helicase activity is not accompanied by enhanced ATP hydrolysis but does depend on ATP binding and a basal level of UPF1 ATPase activity. Studies of STAU2 demonstrate it changes the conformation of RNA-bound UPF1. These findings, and evidence for STAU1-STAU1, STAU2-STAU2, and STAU1-STAU2 formation in vitro and in cells, are consistent with results from tethering assays: the decrease in mRNA abundance brought about by tethering siRNA-resistant STAU2 or STAU1 to an mRNA 3' UTR is inhibited by downregulating the abundance of cellular STAU2, STAU1, or UPF1. It follows that the efficiency of SMD in different cell types reflects the cumulative abundance of STAU1 and STAU2. We propose that STAU paralogs contribute to SMD by "greasing the wheels" of RNA-bound UPF1 so as to enhance its unwinding capacity per molecule of ATP hydrolyzed.

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    • "Whereas all three UPF members are required for NMD, UPF2 and UPF3x are also dispensable for SMD and replication-dependent histone mRNA decay (Kaygun and Marzluff, 2005; Kim et al., 2005). Nevertheless, Staufen 1 and 2 are sensors for recognizing dsRNA sequences (Park et al., 2013), but do not have RNase activity. "
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    Cell 05/2015; 161(5):1058-1073. DOI:10.1016/j.cell.2015.04.029 · 33.12 Impact Factor
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    • "First, we have provided evidence for a role of Stau2 in the stabilization of mRNAs as Stau2 targets were predominantly downregulated in Stau2-deficient neurons. We note that the levels of a small fraction of Stau2 targets increase upon Stau2 downregulation, consistent with a recent study in human cell lines that implicates Stau2 in transcript destabilization (Park et al., 2013). Although no such role of transcript stabilization has been reported for Stau2 before, there is a recent publication for Stau1, together with the long noncoding RNA TINCR, showing a role in stabilizing differentiation mRNAs in human keratinocytes (Kretz et al., 2013). "
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    • "Two days after siRNA transfection, cells were re-transfected with a pmCMV-Gl (β-globin) test plasmid [22], either nonsense-free (Norm) or PTC-harboring (Ter), a pmCMV-GPx1 (glutathione peroxidase 1) test plasmid [23], and a phCMV-MUP (mouse major urinary protein) reference plasmid [24]. When specified, pCI-Neo–FLAG–UPF1 [25] was also transfected. Total-cell lysates were obtained by hypotonic solution containing 10 mM Tris–Cl pH 7.5, 10 mM NaCl, 10 mM EDTA, and 0.5% Triton X-100 followed by a 10-min incubation on ice as done in the previous report [26]. "
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