Patient mutation in AIRE disrupts P-TEFb binding and target gene transcription

Abstract

Autoimmune regulator (AIRE) is a transcription factor that induces the expression of a large subset of otherwise strictly tissue restricted antigens in medullary thymic epithelial cells, thereby enabling their presentation to developing T cells for negative selection. Mutations in AIRE lead to autoimmune-polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED), a rare monogenetic disease. Although it has been reported that AIRE interacts with proteins involved in nuclear transport, DNA-damage response, chromatin remodeling, transcription and pre-mRNA-splicing, the precise mechanism of AIRE-induced tissue restricted antigen expression has remained elusive. In this study, we investigated an APECED patient mutation that causes the loss of the extreme C-terminus of AIRE and found that this mutant protein is transcriptionaly inactive. When tethered heterologously to DNA, this domain could stimulate transcription and splicing by itself. Moreover, the loss of this C-terminus disrupted interactions with the positive transcription elongation factor b (P-TEFb). Via P-TEFb, AIRE increased levels of RNA polymerase II on and enhanced pre-mRNA splicing of heterologous and endogenous target genes. Indeed, the inhibition of CDK9, the kinase subunit of P-TEFb, inhibited AIRE-induced pre-mRNA splicing of these genes. Thus, AIRE requires P-TEFb to activate transcription elongation and co-transcriptional processing of target genes.

Induction de la tolérance centrale dans le thymus par le facteur de transcription Aire

“…Aire contient également un domaine riche en proline (PRR) caracté-ristique d'autres protéines impliquées dans le contrôle de la transcription. Enfin, à son extrémité carboxy-terminale, Aire possède un domaine TAD (transcriptionnal activation domain) qui est nécessaire à l'interaction avec le facteur d'élongation P-TEFb (positive transcription elongation factor) [29]. Les connaissances acquises sur la structure de Aire ainsi que l'identification de ses différents partenaires ont permis de proposer un modèle de régulation de l'expression des TRA.…”

An RNAi screen for Aire cofactors reveals a role for Hnrnpl in polymerase release and Aire-activated ectopic transcription

“…Several lines of investigation have shown that Aire primarily impacts the elongation steps of transcription, in particular by releasing promoter-bound polymerases that remain paused after abortive initiation (8,9). Correspondingly, Aire has been shown to interact with subunits of the key controller of polymerase release, the positive transcription elongation factor b (P-TEFb) (8,10,11). P-TEFb is recruited to stalled initiation complexes in many systems of regulated transcription.…”

The Mechanism of Tissue-Restricted Antigen Gene Expression by AIRE

“…These findings raise the conundrum of how AIRE can regulate such a large repertoire of divergent genes. Recent work from others and us has addressed this question and revealed the mechanisms of action of this enigmatic protein (26)(27)(28)(29)(30)(31).…”

“…1A), and this interaction is required for AIRE to activate transcription of genes in chromatin (26,30,37). The AIRE PHD2 sequence is divergent and does not interact with nucleosomes, but it contributes structurally to the activation of TRA genes by AIRE (27,31,43).…”

“…It serves as a transcriptional activation domain (TAD) (Fig. 1A) (27). It binds to P-TEFb and brings it to TRA genes (23,27).…”