Mammalian UPF3A and UPF3B can activate nonsense-mediated mRNA decay independently of their exon junction complex binding (2022)
Figure 6

Fig 6. CASC3 promote EJC association of UPF3 paralogs to enhance NMD.

A, B. Western blots showing levels of EJC proteins or HNRNPA1 (control) in input, IgG IP or EIF4A3 IP following overexpression (OE) of CASC3 wild-type (WT) and EJC binding deficient (HDAA) mutant proteins in (A) HeLa Tet-off cells, and (B) 3BKO#3 HeLa Tet-off cells. Ramps above lanes indicate expression levels of the CASC3 proteins. The asterisk (*) represents p<0.05 in t-test with null hypothesis of true mean less or equal than 1.

C. Western blots showing levels of EJC/UPF proteins and HNRNPA1 in input and FLAG followed by EIF4A3 tandem IP from HCT116 cells expressing the FLAG-tagged endogenous protein indicated above each lane. Quantifications of UPF3B and CASC3 protein enrichment from two replicates are shown at the bottom.

D. Meta-exon plot showing read distributions within the 100 nucleotide (nt) window from the exon 3′ end in RIPiT-Seq replicates of MAGOH:EIF4A3, UPF3B:EIF4A3, and CASC3:EIF4A3. The black vertical line indicates the -24 nt position.

E. Venn diagram showing the degree of overlap between genes significantly enriched in CASC3:EIF4A3 EJC and UPF3B:EIF4A3 EJC occupancy as compared to MAGOH:EIF4A3 EJC occupancy.

F. Scatter plot comparing log2-transformed fold change in occupancy of CASC3:EIF4A3 EJC as compared to MAGOH:EIF4A3 EJC (x-axis) and UPF3B:EIF4A3 EJC compared to MAGOH:EIF4A3 EJC. Each dot represents a gene where gene-level occupancy of each EJC composition was quantified at the canonical position for EJC footprints. Pearson correlation coefficient is shown on the top left. The black dotted line indicates the x=y diagonal and the red dashed line indicates the total least square regression fit for the data points.

G. Box plots comparing occupancy of a specific EJC composition on mRNA (indicated on y-axis; normalized by gene expression from RNA-Seq) between genes of different NMD efficiency. Up, no, and down stands for upregulation, no obvious change or downregulation of a representative PTC+ isoform for each gene (see material and methods) that is used to reflect overall NMD efficiency for each gene. In the box plots, central band represents the median, boxes represent the interquartile range (IQR), whiskers indicate maximum (top) and minimum (bottom) values (1.5-times the highest or lowest IQR values, respectively), and circles represent the outliers. p-values are from Wilcoxon signed-rank test comparing the two indicated distributions.

H. Box plots as in G comparing specific EJC composition occupancy relative to EJC core occupancy (normalized by MAGOH:EIF4A3 RIPiT-Seq) between genes of different NMD efficiency. Up, no, down, central band, boxes, and whiskers are as in G.

I. Bar plots showing fold changes measured by isoform specific RT-qPCR of PTC+ and PTC- isoform from genes indicated on the bottom in WT and CASC3-KO HCT116 cells. Relative levels from each replicate are shown by white circles. Error bars indicate standard error of means. The asterisk (*) represents p<0.05 in t-test with null hypothesis of true mean being 1 (n=3 biological replicates).