2,6-Diaminopurine Induces ACTN3 Premature Termination Codon Readthrough

The ACTN3 gene encodes a sarcomeric α-actinin-3 protein, which forms an anti-parallel dimer and constitutes the Z-lines in human skeletal muscle fast-twitch fibers. In human ACTN3, a nonsense mutation that replaces a CGA codon for the 577th arginine (R) residue with a TGA premature termination codon (PTC; specified as X) produces the R577X polymorphism. Since ACTN3 577X mRNA is targeted and degraded by a cellular nonsense-mediated mRNA decay (NMD) system, individuals with the homozygous ACTN3 577XX genotype do not express α-actinin-3 protein in the muscles, resulting in a decrease in speed-oriented athletic performance and muscle mass. The PTC has been a target for translational readthrough using aminoglycoside antibiotics, which enable the full-length α-actinin-3 protein to be produced from the ACTN3 577X gene. However, this effect requires a supraphysiological dose (mM levels) and supportive NMD inhibition. Using expression plasmids and HEK293 cultured cells, in this paper I show that 2,6-diaminopurine (DAP), a recently identified natural compound with translational readthrough activity, can produce a full-length α-actinin-3 protein from the ACTN3 577X gene even when used alone and at a relatively low concentration (µM levels). Most ACTN3 577X alleles likely contain three missense mutations (Q523R, R628C, and R776Q). Full-length α-actinin-3 proteins derived from the ACTN3 577X gene formed more homodimers than α-actinin-3 proteins derived from the ACTN3 577R gene. These results indicate that DAP-induced translational readthrough has the potential to restore function to the lost gene ACTN3 577X in humans.