Drug‐induced readthrough of premature stop codons leads to the stabilization of laminin α2 chain mRNA in CMD myotubes

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Abstract
Background The most common form of congenital muscular dystrophy is caused by a deficiency in the α2 chain of laminin‐211, a protein of the extracellular matrix. A wide variety of mutations, including 20 to 30% of nonsense mutations, have been identified in the corresponding gene, LAMA2. A promising approach for the treatment of genetic disorders due to premature termination codons (PTCs) is the use of drugs to force stop codon readthrough. Methods Here, we analyzed the effects of two compounds on a PTC in the LAMA2 gene that targets the mRNA to nonsense‐mediated RNA decay, in vitro using a dual reporter assay, as well as ex vivo in patient‐derived myotubes. Results We first showed that both gentamicin and negamycin promote significant readthrough of this PTC. We then demonstrated that the mutant mRNAs were strongly stabilized in patient‐derived myotubes after administration of negamycin, but not gentamicin. Nevertheless, neither treatment allowed re‐expression of the laminin α2‐chain protein, pointing to problems that may have arisen at the translational or post‐translational levels. Conclusions Taken together, our results emphasize that achievement of a clinical benefit upon treatment with novel readthrough‐inducing agents would require several favourable conditions including PTC nucleotide context, intrinsic and induced stability of mRNA and correct synthesis of a full‐length active protein. Copyright © 2007 John Wiley & Sons, Ltd.