Antisense targeting of decoy exons can reduce intron retention and increase protein expression in human erythroblasts

The decoy exon model has been proposed to regulate a subset of intron retention (IR) events involving predominantly larger introns (>1kb). Splicing reporter studies have shown that decoy splice sites are essential for activity, suggesting that decoys act by engaging intron-terminal splice sites and competing with cross-intron interactions required for intron excision. The decoy model predicts that antisense oligonucleotides blocking decoy splice sites in endogenous pre-mRNA should increase productive gene expression by reducing IR. Indeed, we now demonstrate that targeting a decoy 5' splice site in the O-GlcNAc transferase (OGT) gene reduced IR from [~]80% to [~]20% in primary human erythroblasts, accompanied by increases in spliced OGT RNA and OGT protein expression. The remaining OGT IR was refractory to antisense treatment and might be mediated by independent mechanism(s). In contrast, other retained introns were strongly dependent on decoy function, since IR was nearly eliminated by antisense targeting of 5' splice sites. Genes in the latter group encode the widely expressed splicing factor (SF3B1), and the erythroid-specific structural protein, alpha-spectrin (SPTA1). These results show that modulating decoy exon function can dramatically alter IR, and suggest that dynamic regulation of decoy exons could be a mechanism to fine tune gene expression post-transcriptionally in many cell types.