[Corrigendum] Nonsense-mediated mRNA decay factor Upf2 exists in both the nucleoplasm and the cytoplasm.

Following the publication of this article, after having re-examined our manuscript, an error was noted in the Acknowledgments section regarding the funding of our study. The Acknowledgments section should have appeared as follows: "This work was supported by grants from the Kanazawa Medical University (nos. C2014-3, C2015-1 and S2014-15), a grant from the Strategic Research Project (no. H2012-16 [S1201022]) from Kanazawa Medical University, Ministry of Education, Culture, Sports, Science and Technology, Japan (KAKENHI no. #25460376) and from the Sumitomo Science Foundation in Japan. We apologize to our funders for this error, and regret any confusion this may have caused. [the original article was published in the Molecular Medicine Reports 14: 655-660, 2016; DOI: 10.3892/mmr.2016.5331].

Nonsense-mediated mRNA decay factor Upf2 exists in both the nucleoplasm and the cytoplasm.

Upf2 protein predominantly localizes to the cytoplasmic fraction, and binds to the exon junction complex (EJC) on spliced mRNA. The present study aimed to determine the cellular site where the interaction between Upf2 and EJC occurs. First, the cell lysate was fractionated into the cytoplasm and nucleoplasm, and western blotting to detect levels of Upf2 protein was performed. Upf2 was clearly detected in the cytoplasm and in the nucleoplasm. Secondly, immunostaining was performed, and the majority of Upf2 was detected in the cytoplasmic perinuclear region; a small quantity of Upf2 was detected in the intranuclear region. RNase treatment of the cells reduced the Upf2 immunostained signal. The immunopurified fractions containing nuclear and cytoplasmic Upf2 also contained one of the EJC core factors, RBM8A. These results implied the existence of Upf2 in the nucleoplasm and the cytoplasm, and it appeared to be involved in the construction of the mRNA complex. In order to verify the construction of Upf2­binding EJC in the nucleoplasm, an in situ proximity ligation assay was performed with anti­Upf2 and anti­RBM8A antibodies. These results demonstrated that their interaction occurred not only in the cytoplasmic region, but also in the intranuclear region. Taken together, these results suggested that Upf2 combines with EJC in both the cytoplasmic and the intranuclear fractions, and that it is involved in mRNA metabolism in human cells.

Phosphorylation status of human RNA-binding protein 8A in cells and its inhibitory regulation by Magoh.

The RNA-binding protein 8A (RBM8A)-mago-nashi homolog, proliferation-associated (Magoh) complex is a component of the exon junction complex (EJC) required for mRNA metabolism involving nonsense-mediated mRNA decay (NMD). RBM8A is a phosphorylated protein that plays some roles in NMD. However, the detailed status and mechanism of the phosphorylation of RBM8A is not completely understood. Therefore, in this study, we analyzed in detail RBM8A phosphorylation in human cells. Accordingly, analysis of the phosphorylation status of RBM8A protein in whole-cell lysates by using Phos-tag gels revealed that the majority of endogenous RBM8A was phosphorylated throughout the cell-cycle progression. Nuclear and cytoplasmic RBM8A and RBM8A in the EJC were also found to be mostly phosphorylated. We also screened the phosphorylated serine by mutational analysis using Phos-tag gels to reveal modifications of serine residues 166 and 168. A single substitution at position 168 that concomitantly abolished the phosphorylation of serine 166 suggested the priority of kinase reaction between these sites. Furthermore, analysis of the role of the binding protein Magoh in RBM8A phosphorylation revealed its inhibitory effect in vitro and in vivo. Thus, we conclude that almost all synthesized RBM8A proteins are rapidly phosphorylated in cells and that phosphorylation occurs before the complex formation with Magoh.