Upregulation of functional Kv11.1 isoform expression by inhibition of intronic polyadenylation with antisense morpholino oligonucleotides.

The KCNH2 gene encodes the Kv11.1 potassium channel that conducts the rapidly activating delayed rectifier current in the heart. KCNH2 pre-mRNA undergoes alternative processing; intron 9 splicing leads to the formation of a functional, full-length Kv11.1a isoform, while polyadenylation within intron 9 generates a non-functional, C-terminally truncated Kv11.1a-USO isoform. The relative expression of Kv11.1 isoforms plays an important role in the regulation of Kv11.1 channel function and the pathogenesis of long QT syndrome. In this study, we identified cis-acting elements that are required for KCNH2 intron 9 poly(A) signal activity. Mutation of these elements decreased Kv11.1a-USO expression and increased the expression of Kv11.1a mRNA, protein and channel current. More importantly, blocking these elements by antisense morpholino oligonucleotides shifted the alternative processing of KCNH2 intron 9 from the polyadenylation to the splicing pathway, leading to the predominant production of Kv11.1a and a significant increase in Kv11.1 current. Our findings indicate that the expression of the Kv11.1a isoform can be upregulated by an antisense approach. Antisense inhibition of KCNH2 intronic polyadenylation represents a novel approach to increase Kv11.1 channel function.