MiR-128 and miR-125 regulate expression of coagulation Factor IX gene with nonsense mutation by repressing nonsense-mediated mRNA decay

Hemophilia could be caused by a nonsense mutation of the Factor IX gene, leading to a deficiency of Factor IX (F9). The nonsense mutation frequency of F9 is more than 10% according to the database. Nonsense-mediated mRNA decay (NMD) is a defined cellular response that can potentially prevent the production of such deleterious C-terminal truncated proteins from aberrant mRNA. Here, we constructed a mini-gene of Factor IX (Mini-hF9) and some nonsense mutants and characterized the mini-gene splicing pattern. We discovered that NMD regulated mini-hF9 expression in two nonsense mutants: E7a (nt 34 G > T in exon 7) and E7b (nt 52 G > T in exon 7), but not in another nonsense mutants: E7c (nt 85 G > T in exon 7) and E8 (nt 42 C > T in exon 8). In addition, mini-hF9 transcripts were accumulated after transfection with miR-128 or miR-125 mimics in E7a and E7b. Our results suggest that PTC (premature termination codon) location is a key determination for triggering NMD; miR-128 and miR-125 could help to increase the nonsense-mutant F9 levels by repressing NMD.