APECED-causing mutations in AIRE reveal the functional domains of the protein

Abstract

A defective form of the AIRE protein causes autoimmune destruction of target organs by disturbing the immunological tolerance of patients with a rare monogenic disease, autoimmune polyendocrinopathy (APE)-candidiasis (C)-ectodermal dystrophy (ED), APECED. Recently, experiments on knockout mice revealed that AIRE controls autoimmunity by regulating the transcription of peripheral tissue-restricted antigens in thymic medullary epithelial cells. Thus, AIRE provides a unique model for molecular studies of organ-specific autoimmunity. In order to analyze the molecular and cellular consequences of 16 disease-causing mutations in vitro, we studied the subcellular localization, transactivation capacity, homomultimerization, and complex formation of several mutant AIRE polypeptides. Most of the mutations altered the nucleus-cytoplasm distribution of AIRE and disturbed its association with nuclear dots and cytoplasmic filaments. While the PHD zinc fingers were necessary for the transactivation capacity of AIRE, other regions of AIRE also modulated this function. Consequently, most of the mutations decreased transactivation. The HSR domain was responsible for the homomultimerization activity of AIRE; all the missense mutations of the HSR and the SAND domains decreased this activity, but those in other domains did not. The AIRE protein was present in soluble high-molecular-weight complexes. Mutations in the HSR domain and deletion of PHD zinc fingers disturbed the formation of these complexes. In conclusion, we propose an in vitro model in which AIRE transactivates transcription through heteromeric molecular interactions that are regulated by homomultimerization and conditional localization of AIRE in the nucleus or in the cytoplasm.

AIRE Recruits P-TEFb for Transcriptional Elongation of Target Genes in Medullary Thymic Epithelial Cells

“…Previously, AIRE was found to activate transcription via heterologous DNA tethering using the Gal.AIRE fusion proteins (14,37,38). In our study, we demonstrated that the free AIRE protein also acted synergistically with GalDBD or Sp1 to activate transcription.…”

“…They migrate as a 670-kDa complex, which could contain up to 12 AIRE proteins (14). Monomers of AIRE neither bind DNA in vitro (24,39) nor activate transcription in cells (14).…”

“…Monomers of AIRE neither bind DNA in vitro (24,39) nor activate transcription in cells (14). Of interest, most mutations in patients disrupt this oligomerization of AIRE (14,32).…”

“…Monomers of AIRE neither bind DNA in vitro (24,39) nor activate transcription in cells (14). Of interest, most mutations in patients disrupt this oligomerization of AIRE (14,32). Moreover, the homogenously staining region, SAND, and two PHD motifs are necessary for the formation of oligomers as well as the transcriptional activity of AIRE (5,48).…”

Aire’s plant homeodomain(PHD)-2 is critical for induction of immunological tolerance

“…It seems not to operate like a traditional transcription factor, binding to a promoter and/or enhancer element and inducing transcript initiation, but instead to somehow release RNA polymerase (RNA-Pol)II pausing and promote transcript elongation (9,10). Aire targets and regulates genes as a component of one or more large multiprotein complexes (11)(12)(13). Its numerous associates include sets of proteins involved in nuclear transport, chromatin binding/structure, transcription, and pre-mRNA processing (12).…”