Subcellular localization of the autoimmune regulator protein - Characterization of nuclear targeting and transcriptional activation domain

The autoimmune regulator (AIRE) gene, defective in the hereditary autoimmun e disease APECED, encodes a transcriptional regulator protein. AIRE is expr essed in the medullary epithelial cells and monocyte-dendritic cells of the thymus with lower expression in the spleen, fetal liver, and lymph nodes. At the cellular level, AIRE is located in microtubular structures of the cy toskeleton and in discrete nuclear dots resembling ND10 nuclear bodies. We studied the determinants of the targeting of AIRE into these structures. We report here that the N-terminal HSR domain confers localization to the mic rotubular network whereas the C-terminal region contains a second nuclear l ocalization signal. We also demonstrate that the consensus nuclear localiza tion signal of AIRE is functional and that the HSR domain harbors a nuclear export signal. Accordingly, the nuclear export inhibitor leptomycin B part ially inhibits the nuclear export of AIRE, From a functional standpoint, we show that AIRE can activate the interferon P minimal promoter in a transfe ction assay and demonstrate that the transcriptional activating function of AIRE is mediated by its two plant homeodomain (PHD) zinc fingers.