The unfolded protein response affects readthrough of premature termination codons

Yifat S Oren,Steven M Rowe,Batsheva Kerem,Michelle L Mcclure,Eric J Sorscher,Joseph Rivlin,Tamar Geiger,Matthias Mann,Assaf C Bester,Miriam Manor,Fouad Zahdeh,Eitan Kerem

doi:10.1002/emmm.201303347

Abstract

One-third of monogenic inherited diseases result from premature termination codons (PTCs). Readthrough of in-frame PTCs enables synthesis of full-length functional proteins. However, extended variability in the response to readthrough treatment is found among patients, which correlates with the level of nonsense transcripts. Here, we aimed to reveal cellular pathways affecting this inter-patient variability. We show that activation of the unfolded protein response (UPR) governs the response to readthrough treatment by regulating the levels of transcripts carrying PTCs. Quantitative proteomic analyses showed substantial differences in UPR activation between patients carrying PTCs, correlating with their response. We further found a significant inverse correlation between the UPR and nonsense-mediated mRNA decay (NMD), suggesting a feedback loop between these homeostatic pathways. We uncovered and characterized the mechanism underlying this NMD-UPR feedback loop, which augments both UPR activation and NMD attenuation. Importantly, this feedback loop enhances the response to readthrough treatment, highlighting its clinical importance. Altogether, our study demonstrates the importance of the UPR and its regulatory network for genetic diseases caused by PTCs and for cell homeostasis under normal conditions.

Highlights

About 30% of inherited and acquired diseases are attributable to premature termination codon (PTC) through nonsense or frameshift mutations (Mendell & Dietz, 2001; Kuzmiak & Maquat, 2006)
nonsense-mediated mRNA decay (NMD) inhibition together with unfolded protein response (UPR) activation enhanced the response to readthrough treatment, highlighting the functional role of the NMD-UPR feedback loop
Both are homozygous for the CFTR W1282X allele, they differed in their response to the treatment, as measured by the normalization of the nasal potential difference (NPD), and in their CFTR transcript levels

Summary

Introduction

About 30% of inherited and acquired diseases are attributable to premature termination codon (PTC) through nonsense or frameshift mutations (Mendell & Dietz, 2001; Kuzmiak & Maquat, 2006). It is important to note that in the two disease models: CFTR and XLF, G418 alone did not have a significant effect on the protein function, indicating that upregulating the level of the PTC-bearing transcripts is required for a successful readthrough treatment. These results prove that UPR is a modifier of the response to readthrough treatment and show for the first time that UPR plays a role in modulating the response to a mutation-specific treatment. The readthrough agents inhibit the degradation of transcripts carrying PTCs

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