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

Abstract

AIRE is a transcriptional activator that directs the ectopic expression of many tissue-specific genes in medullary thymic epithelial cells, which plays an important role in the negative selection of autoreactive T cells. However, its mechanism of action remains poorly understood. In this study, we found that AIRE regulates the step of elongation rather than initiation of RNA polymerase II. For these effects, AIRE bound and recruited P-TEFb to target promoters in medullary thymic epithelial cells. In these cells, AIRE activated the ectopic transcription of insulin and salivary protein 1 genes. Indeed, by chromatin immunoprecipitation, we found that RNA polymerase II was already engaged on these promoters but was unable to elongate in the absence of AIRE. Moreover, the genetic inactivation of cyclin T1 from P-TEFb abolished the transcription of AIRE-responsive genes and led to lymphocytic infiltration of lacrimal and salivary glands in the CycT1 ؊/؊ mouse. Our findings reveal critical steps by which AIRE regulates the transcription of genes that control central tolerance in the thymus.

Aire employs a histone-binding module to mediate immunological tolerance, linking chromatin regulation with organ-specific autoimmunity

“…Aire displays punctate subnuclear localization adjacent to nuclear speckles in MECs (13), structures often close to highly active transcription sites and enriched in phosphorylated Pol II, transcription elongation factors (e.g., P-TEFb), and pre-mRNA splicing factors (14,15). Concordant with this localization, a study on trichostatin A-induced cell lines suggested that Aire physically interacts with and recruits P-TEFb to promoters of tissue-specific genes (41). Moreover, native Aire coimmunoprecipitation assays reveal direct interactions with RNA splicing/processing factors that are required for the Airedependent up-regulation of PTAs in 293T cells (J.A., C.B., and D.M., unpublished results).…”

Brd4 bridges the transcriptional regulators, Aire and P-TEFb, to promote elongation of peripheral-tissue antigen transcripts in thymic stromal cells

“…At the outset of this study, diverse lines of evidence had argued that Aire's primary mechanism of action is to promote elongation of Pol-II stalled just downstream of the TSS (11)(12)(13). The present study furnishes molecular insight into the mechanisms by which Aire releases polymerase pausing: Brd4 serves as a critical bridge between Aire and P-TEFb, thereby mobilizing the transcriptional elongation and splicing machineries.…”

“…However, the large number of genes whose expression Aire affects and the vast geographic, temporal, and quantitative variety of these genes' expression in nonthymic cells suggest that it may not operate as a classical transcription factor, binding to a promoter or enhancer element and simply turning transcription up or down. Indeed, recent data derived from a variety of experimental approaches argue that Aire's major modus operandi is to release promoter-proximal RNA polymerase II (Pol-II) pausing (11)(12)(13).…”

Ovarian autoimmune disease: clinical concepts and animal models

“…[75][76][77] However, AIRE also contains two PHD (Plant HomeoDomain)-type zinc fingers that confer its ability to associate with numerous protein partners and that are essential for regulation of gene expression. [78][79][80] These PHD domains associate with histone 3 at unmethylated lysine 4 residues (H3K4me0), which are typically within transcriptionally inactive chromatin regions, and in combination with DNA-dependent protein kinase, appear to promote subsequent transcription. [81][82][83] Consistent with this model of transcriptional regulation, AIREregulated genes are chromosomally clustered and stochastically expressed.…”