Repair of CFTR mRNA by spliceosome-mediated RNA trans-splicing

Most messenger RNA precursors (pre-mRNA) undergo cis-splicing in which intr ons are excised and the adjoining exons from a single pre-mRNA are ligated together to form mature messenger RNA. This reaction is driven by a complex known as the spliceosome. Spliceosomes can also combine sequences from two independently transcribed pre-mRNAs in a process known as trans-splicing. Spliceosome-mediated RNA trans-splicing (SMaRT) is an emerging technology i n which RNA pre-therapeutic molecules (PTMs) are designed to recode a speci fic pre-mRNA by suppressing cis-splicing while enhancing trans-splicing bet ween the PTM and its pre-mRNA target. This study examined the feasibility o f SMaRT as a potential therapy for genetic diseases to correct mutations us ing cystic fibrosis (CF) as an example. We used several versions of a cysti c fibrosis transmembrane conductance regulator (CFTR) mini-gene expressing mutant (Delta F508) pre-mRNA targets and tested this against a number of PT Ms capable of binding to the CFTR target intron 9 and trans-splicing in the normal coding sequences for exons 10-24 (containing F508). When 293T cells were cotransfected with both constructs, they produced a trans-spliced mRN A in which normal exon 10-24 replaced mutant exon 10. To test whether SMaRT produced mature CFTR protein, proteins were immunoprecipitated from lysate s of cotransfected cells and detected by Western blotting and PKA-phosphory lation. Tryptic phosphopeptide mapping confirmed the identity of CFTR. This proof-of-concept study demonstrates that exon replacement by SMaRT can rep air an abnormal pre-mRNA associated with a genetic disease.