Figure 2: Compounds 1–4 improve translational defects caused by r(CUG)^exp.

Improvement of translational could occur if a compound binds to r(CUG)^exp (compound 2) or MBNL1 (compound 1), as both modes of action disrupt the r(CUG)^exp–MBNL1 complex and could allow for more efficient nucleocytoplasmic export. (a, top) A schematic of the luciferase reporter system that models the DM1 translational defect. The presence of r(CUG)^exp in the 3′-UTR of firefly luciferase reduces nucleocytoplasmic transport and thereby suppresses luciferase expression. However, if a small molecule binds r(CUG)^exp and displaces proteins, nucleocytoplasmic transport is improved and luciferase activity increases. Likewise, if a small molecule binds proteins and displaces them from r(CUG)^exp, nucleocytoplasmic transport is also improved and luciferase activity increases. (a, bottom) Effects on luciferase activity when cells are dosed with 20 μM compound of interest. ‘+r(CUG)^exp’ indicates that the cell line expresses luciferase with r(CUG)^exp in the 3′-UTR, ‘-r(CUG)^exp’ indicates that the cell line expresses luciferase without r(CUG)^exp. Results are expressed as the percentage increase of luciferase activity relative to untreated cells, where a value of ‘0’ denotes no change in activity. Experiments were completed in triplicate. Values shown in the plot are the averages of those experiments, and the errors reported are the s.d. values. (b) Competition dialysis data for binding of 1 to BSA, MBNL1 and r(CUG)₁₂. The data clearly show that the preferred target is MBNL1 as there is no measureable binding to r(CUG)₁₂ or to BSA. Experiments were completed in duplicate. The values reported are the averages of those experiments, and the errors reported are the s.d. values.