Localization of the APECED protein in distinct nuclear structures

Autoimmune-polyendocrinopathy-candidiasis-ecodermal dystrophy (APECED) is t he only systemic autoimmune disease with a monogenic background known so fa r revealing no association with the major histocompatibility complex region . We have recently isolated the gene defective in this syndrome and charact erized several different mutations in individuals with the disorder, The no vel gene, AIRE, contains a putative bipartite nuclear targeting signal pred icting a nuclear location of the corresponding protein. The presence of two PHD-type zinc finger domains as well as the newly described putative DNA-b inding domain, SAND, in the amino acid sequence of the APECED protein impli es that it may be involved in the regulation of gene expression. Using tran sient expression of AIRE cDNA in mammalian cells we demonstrate here the nu clear location of the APECED protein, Immunohistochemical staining of trans fected cells revealed that most of the recombinant 58 kDa APECED protein is present in the form of nuclear dots. By double immunofluorescence labellin g we further show that these APECED-containing structures and the previousl y described PML nuclear bodies are largely nonoverlapping. The AIRE protein was also visualized in multiple human tissues: a subset of the cells in th ymus, in spleen and in lymph node showed nuclear staining with APECED antis erum. Immunofluorescence labelling of peripheral blood mononuclear leukocyt es also revealed a nuclear body-like staining pattern in a fraction of thes e cells, These data from both in vitro and ex vivo systems, together with t he predicted structural features of the APECED protein, suggest that this p rotein is most probably involved in the regulation of gene expression.