Suppression of Dominant-Negative Transcripts Escaping from Nonsense-Mediated mRNA Decay

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Abstract Nonsense-mediated mRNA decay (NMD) is a cellular RNA surveillance mechanism that plays a fundamental role in human health and disease. NMD selectively recognizes and degrades aberrant RNAs such as mutated transcripts and many viral RNAs. NMD misregulation is associated with disease onset and severity in various neurological disorders, cancers, and infectious diseases. Therefore, controlling NMD activity is an attractive approach to developing novel therapeutics for many human diseases. Although the suppression of NMD by premature termination codon (PTC) read-through strategies using aminoglycoside antibiotics or suppressor tRNAs has been widely studied, there are significant limitations to their efficacy and specificity. Conceptually, these PTC read-through strategies inhibit NMD and produce limited quantities of functional proteins. In contrast, the concept of NMD induction with the goal of selectively degrading NMD-insensitive targets has barely been studied. The method of NMD induction is critical for a subset of human diseases because about one-fourth of disease-causing PTCs are predicted to be insensitive to NMD. Although most of the NMD-insensitive transcripts are expected to produce truncated proteins and induce a gain-of-function or dominant-negative effect, the underlying molecular mechanisms are largely uncharacterized. Thus, there is no target-specific molecular therapy for NMD-insensitive disorders. Based on over ten years of experience in molecular studies of NMD mechanisms and using cutting-edge CRISPR-Cas13 technology, this proposal aims to establish a novel therapeutic approach, namely, the RNA-Programmed NMD Activation (RP-NMDA) system, to suppress NMD- insensitive dominant-negative transcripts. Aim 1 is a proof-of-concept experiment to develop the RP-NMDA methodology to trigger NMD of dominant-negative transcripts using a well-defined NMD reporter derived from the human beta-globin (HBB) gene. Aim 2 will extend the RP-NMDA approach to human colorectal cancer cell lines to selectively suppress both the expression of APC truncations and cancer progression. This application has high promise to specifically degrade aberrant transcripts derived from a mutated NMD-insensitive allele without any toxic effects on normal transcripts. If successful, my proposed innovative work will not only provide a disease- specific and efficient drug for dominant beta-thalassemia and colorectal cancers but also provide a potential therapeutic strategy for any NMD-insensitive disorders.