Dual functions of Aire CARD multimerization in the transcriptional regulation of T cell tolerance

Aggregate-like biomolecular assemblies are emerging as new conformational states with functionality. Aire, a transcription factor essential for central T cell tolerance, is known to form large aggregate-like assemblies visualized as nuclear foci. We demonstrate that Aire utilizes Caspase Activation Recruitment Domain (CARD) to form filamentous homo-multimers in vitro, and this assembly mediates foci formation and transcriptional activity. However, CARD-mediated multimerization is a double-edged sword as it also makes Aire susceptible to interaction with PML bodies, sites of many nuclear processes including protein quality control of nuclear aggregates. Several loss-of-function Aire mutants, including those causing autoimmune polyendocrine syndrome type-1, form foci with increased PML body association. Directing Aire to PML bodies impairs Aires transcriptional activity, while dispersing PML bodies with a viral antagonist restores it. Thus, our study reveals a new regulatory role of PML bodies in Aire function and highlights the interplay between nuclear aggregate-like assemblies and PML-mediated quality control.