Coupling of UPR Induction with Aminoglycosides: A Potential Therapeutic Strategy for Genetic Disorders Caused by Nonsense Mutations. N.A. Sharifi, H.C. Dietz. Inst of Genet Med, Johns Hopkins Univ Sch of Med and HHMI, Baltimore, MD.
   It is estimated that nonsense mutations are seen in up to 20% of all human disease alleles. The presence of a PTC does not usually lead to production of truncated peptides since the majority of nonsense transcripts are recognized and degraded by a translation-coupled and highly efficient process known as nonsense-mediated mRNA decay (NMD). Recent attempts to treat diseases caused by nonsense mutations with readthrough-promoting agents (e.g. aminoglycosides) have shown limited and highly variable success in model systems and in people. A near uniform finding is that these agents do not increase the amount of nonsense transcripts. Thus, despite high readthrough potency for selected drugs, the opportunity is simply lacking in the face of ongoing NMD. While simultaneous inhibition of NMD and promotion of readthrough represents a potentially potent strategy, the toxicity of known drugs that inhibit NMD precludes their use in both animal models and people. Our microarray analysis of physiologic mRNA substrates for mammalian NMD revealed significant overlap with transcripts that are upregulated by the unfolded protein response (UPR). Initiation of the UPR in response to diverse forms of cellular stress induces phosporylation of eIF2 and the subsequent inhibition of bulk translation, while maintaining selective translation of proteins that would promote cellular survival (e.g. ATF3). It seemed possible that either inhibition of NMD leads to the production of truncated proteins that then initiate the UPR, or that the induction of UPR and subsequent relative inhibition of translation inhibits NMD. We provide definitive experimental evidence that only the latter is true. Furthermore, the inhibition of NMD was both potent and observed in all tested nonsense transcripts. Furthermore, we show that geldanamycin and its less toxic derivative 17AAG, which are in phase II clinical trials for anti-tumor activity in people, both induce the UPR and inhibit NMD. These agents maintain sufficient residual translation to support readthrough protein production in the presence of aminoglycoside, constituting a complete strategy for the treatment of diseases caused by PTCs.