Poster abstracts
Poster number 60 submitted by Zhongxia Yi
Investigating UPF3B-independent nonsense-mediated mRNA decay
Zhongxia Yi (Department of Molecular Genetics), Lauren A. Woodward (Department of Molecular Genetics), Justin W. Mabin (Department of Molecular Genetics)
Abstract:
Nonsense-mediated mRNA decay (NMD) rapidly degrades aberrant transcripts with premature termination codon (PTC) to limit the production of truncated polypeptides. NMD also regulates around 10-20% of the normal transcripts, and is essential for development, differentiation and stress response [1]. Intriguingly, while in yeast all three NMD factors, Upf1p, Upf2p and Upf3p, are essential for NMD, several NMD substrates can still undergo efficient NMD after depleting UPF3B in human cells [2]. In human, recognition of NMD substrates is largely assisted by exon junction complexes (EJCs), while yeasts do not contain EJCs. EJCs are deposited at exon-exon junctions by spliceosome after splicing and they facilitate the mRNA export to the cytoplasm, where EJCs will be removed by the first translating ribosome. An EJC downstream of a terminated ribosome signals a premature termination event in which this EJC recruits NMD factors UPF3B, UPF2 and UPF1 sequentially that finally leads to the degradation of the transcript [3]. Recently, our lab has discovered the heterogenous EJC compositions and we have identified at least two mutually exclusive EJCs. We hypothesize that the alternative EJC composition might help bypass the UPF3B need. Here, our work shows that EJCs with distinct compositions preferentially associate with different NMD factors. An alternative EJC, characterized by containing EJC component RNPS1, preferentially associates with UPF2 over UPF3B. We are creating knockout cell lines using CRISPR-Cas9 to test the effect of RNPS1 and UPF3B on the association between UPF1 and EJCs. We also plan to characterize transcriptome-wide substrates of UPF3B-independent NMD. The parallel NMD branches could help explain how NMD regulates subsets of transcripts differentially in biological processes.
References:
[1] Karousis ED, Nasif S, Mühlemann O. Nonsense-mediated mRNA decay: novel mechanistic insights and biological impact. Wiley Interdiscip Rev RNA, 2016, 7: 661-682.
[2] Chan WK, Huang L, Gudikote JP, Chang YF, Imam JS, MacLean JA et al. An alternative branch of the nonsense-mediated decay pathway. EMBO J, 2007, 26: 1820-1830.
[3] Woodward LA, Mabin JW, Gangras P, Singh G. The exon junction complex: a lifelong guardian of mRNA fate. Wiley Interdiscip Rev RNA, 2017, 8: e1411.
Keywords: Nonsense-mediated mRNA decay, Exon junction complexes, UPF3B