Molecular Insights into Determinants of Translational Readthrough and Implications for Nonsense Suppression Approaches

Abstract

The fidelity of protein synthesis, a process shaped by several mechanisms involving specialized ribosome regions and external factors, ensures the precise reading of sense and stop codons. However, premature termination codons (PTCs) arising from mutations may, at low frequency, be misrecognized and result in PTC suppression, named ribosome readthrough, with production of full-length proteins through the insertion of a subset of amino acids. Since some drugs have been identified as readthrough inducers, this fidelity drawback has been explored as a therapeutic approach in several models of human diseases caused by nonsense mutations. Here, we focus on the mechanisms driving translation in normal and aberrant conditions, the potential fates of mRNA in the presence of a PTC, as well as on the results obtained in the research of efficient readthrough-inducing compounds. In particular, we describe the molecular determinants shaping the outcome of readthrough, namely the nucleotide and protein context, with the latter being pivotal to produce functional full-length proteins. Through the interpretation of experimental and mechanistic findings, mainly obtained in lysosomal and coagulation disorders, we also propose a scenario of potential readthrough-favorable features to achieve relevant rescue profiles, representing the main issue for the potential translatability of readthrough as a therapeutic strategy.

Translational readthrough as a potential therapeutic for AIPL1-associated Leber Congenital Amaurosis in a patient-derived iPSC-retinal organoid model

“…TRID molecules allow for the incorporation of cognate/near-cognate amino acids at PTC sites and the translation of full-length protein via a mechanism involving tight ribosomal binding. 54 However there is evidence that PTC124 acts through a different mechanism whereupon it inhibits release factor (eRF1/eRF3) activity at the ribosomal complex to promote readthrough of PTCs (Figure 5A). 33…”

“…TRID molecules allow for the incorporation of cognate/near-cognate amino acids at PTC sites and the translation of full-length protein via a mechanism involving tight ribosomal binding. 54 However there is evidence that PTC124 acts through a different mechanism whereupon it inhibits release factor (eRF1/eRF3) activity at the ribosomal complex to promote readthrough of PTCs (Figure 5A). 33 In order to generate optimal controls for the investigation of the effect of PTC124 on LCA4-1 ROs homozygous for the c.834G>A, p.W278X nonsense mutation, CRISPR-Cas9 homology directed repair (HDR) was carried out to generate isogenic repair lines (Figure 5B).…”

Promoting translational readthrough to augment fibrillin-1 (FBN1) deposition in Marfan syndrome fibroblasts: A proof-of-concept study

“…Because PTCs are read through at a higher level (up to 1%) compared to normal stop codons (0.001 – 0.1%), further promoting translational readthrough with small molecules with or without NMD inhibition represents a potential strategy to augment the amount of functional full-length protein in patients with genetic disorders caused by PTCs [6, 7]. Since the mid-1980s, several drugs were identified that promoted translational readthrough in vitro, in patient-derived cells and in mouse models, some of which have entered clinical trials [8, 9]. It has been shown that aminoglycoside antibiotics such as G418 or gentamicin can promote translational readthrough of PTCs resulting in increased amounts of full-length protein without substantially altering the efficiency of the natural termination codon [10].…”

SMG9 Serves as an Oncogene to Promote the Tumor Progression via EMT and Wnt/β-Catenin Signaling Pathway in Hepatocellular Carcinoma

“…However, their sensitivity and specificity remain limited. Recently, increasing evidences indicate that posttranscriptional modifications and remodeling also play key roles in regulating tumor progression, as cancers often exhibit abnormal transcription and mRNA processing (Lombardi et al, 2020). Nonsense-mediated decay (NMD) is a post-transcriptional surveillance mechanism that recognizes and degrades mRNAs containing premature translation termination codons (PTCs) to ensure the fidelity and accuracy of process from transcription of genetic information to protein synthesis (Yamashita et al, 2009).…”