All ETDs from UAB

Advisory Committee Chair

Steven M Rowe

Advisory Committee Members

David M Bedwell

Alecia Gross

Maaike Everts

Zsuzsanna Bebok

Document Type

Dissertation

Date of Award

2019

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Cystic fibrosis (CF) is a monogenic autosomal recessive disease caused by over 1,900 naturally occurring variants in the CF transmembrane conductance regulator (CFTR). CFTR is an epithelial anion channel which regulates the movement of chloride and bicarbonate ions. Mutations in the CFTR causes diminished CFTR protein and/or reduced CFTR function that lead to clinical manifestations. These include severe epithelial dysfunction of multiple tissues, including the lungs, intestine, pancreas, and reproductive organs. Premature termination codons (PTC), or nonsense mutations, are among the most severe CFTR variants and occur in ~11% of the CF population. PTCs are caused by the presence of an in-frame stop codon that leads to synthesis of a truncated protein. Furthermore unstable, aberrant mRNA is degraded by the cellular surveillance mechanism nonsense-mediated decay (NMD), reducing transcript levels available for translation. Translation termination is a highly efficient and multi-step process, involves number of proteins to work together, which represents several potential therapeutic targets to induce nonsense suppression. Suppression of translation termination at PTCs by insertion of near-cognate amino acids at the stop codon (i.e. translational readthrough) has demonstrated modest, physiologically relevant rescue of CFTR activity. Unfortunately, use of single readthrough treatments currently available are not sufficient to restore CFTR function to clinically relevant levels (~15-30% of wild-type CFTR). An overarching goal of our work is to elucidate if two mechanistically/structurally distinct readthrough agents can contribute to the enhanced readthrough efficacy than the single agent therapy and to identify the molecular targets of these synergistic readthrough agents. To this end, high-throughput analysis revealed several compounds that induces translational readthrough. Here, we investigated the effects of a combination of readthrough treatments and their mechanistic basis. Findings demonstrated that the novel readthrough agent SRI-37240/SRI-41315 enhanced CFTR expression and function in various FRT and HBE cell based systems through eRF1 mediated protein degradation, indicating a first in its class eRF1 chemical inhibitor and its synergistic readthrough potential with aminoglycosides. CFTR function could be further enhanced by addition of a CFTR corrector, VX-809, to augment CFTR processing and folding in addition to a CFTR potentiator, VX-770, to enhance channel function. To ultimately evaluate the agents in vivo, we generated and chacterized a novel NMD sensitive CFTR-G542X, homozygous rat model that recapitulates the respiratory and gastrointestinal characteristics of the CF clinical phenotype. Keywords: CFTR, PTC, eRF1, readthrough, combinations treatment, NMD, CFTR- G542X rat.

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