# Polyamines enhance repeat-associated non-AUG translation from CCUG repeats by stabilizing the tertiary structure of RNA

## TL;DR

Polyamines like spermine help CCUG repeat RNA form stable structures, which increases non-AUG translation, a process linked to certain genetic disorders.

## Contribution

This study reveals that polyamines, especially spermine, enhance CCUG repeat-associated non-AUG translation by stabilizing RNA structure.

## Key findings

- Polyamines promote CCUG repeat-dependent RAN translation in cell-free and cell-based systems.
- Depletion of polyamines suppresses RAN translation, which can be restored by adding polyamines.
- Spermine most effectively stabilizes CCUG RNA structure and enhances RAN translation.

## Abstract

Repeat expansion disorders are caused by abnormal expansion of microsatellite repeats. Repeat-associated non-AUG (RAN) translation is one of the pathogenic mechanisms underlying repeat expansion disorders, but the exact molecular mechanism underlying RAN translation remains unclear. Polyamines are ubiquitous biogenic amines that are essential for cell proliferation and cellular functions. They are predominantly found in cells in complexes with RNA and influence many cellular events, but the relationship between polyamines and RAN translation is yet to be explored. Here, we show that, in both a cell-free protein synthesis system and cell culture, polyamines promote RAN translation of RNA-containing CCUG repeats. The CCUG-dependent RAN translation is suppressed when cells are depleted of polyamines but can be recovered by the addition of polyamines. Thermal stability analysis revealed that the tertiary structure of the CCUG-repeat RNA is stabilized by the polyamines. Spermine was the most effective polyamine for stabilizing CCUG-repeat RNA and enhancing RAN translation. These results suggest that polyamines, particularly spermine, modulate RAN translation of CCUG-repeat RNA by stabilizing the tertiary structure of the repeat RNA.