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. 2000 Feb;66(2):378-92.
doi: 10.1086/302765.

Mutations in the AIRE gene: effects on subcellular location and transactivation function of the autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy protein

P Björses  1 , M Halonen, J J Palvimo, M Kolmer, J Aaltonen, P Ellonen, J Perheentupa, I Ulmanen, L Peltonen
Affiliations

Mutations in the AIRE gene: effects on subcellular location and transactivation function of the autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy protein

P Björses et al. Am J Hum Genet. 2000 Feb.

Abstract

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a monogenic autosomal disease with recessive inheritance. It is characterized by multiple autoimmune endocrinopathies, chronic mucocutaneous candidiasis, and ectodermal dystrophies. The defective gene responsible for this disease was recently isolated, and several different mutations in the novel gene, AIRE, have been identified, by us and by others, in patients with APECED. We have shown that the APECED protein is mainly localized, both in vitro and in vivo, to the cell nucleus, where it forms distinct speckles. This accords with the predicted structural features of the protein, which suggest involvement of AIRE in the regulation of gene transcription. Here, we report the results of mutational analyses of a series of 112 patients with APECED who were from various ethnic backgrounds. A total of 16 different mutations, covering 91% of disease alleles, were observed; of these, 8 were novel. The mutations are spread throughout the coding region of AIRE, yet four evident mutational hotspots were observed. In vitro expression of four different naturally occurring nonsense and missense mutations revealed a dramatically altered subcellular location of the protein in cultured cells. Interestingly, the wild-type APECED protein tethered to the Gal4 DNA-binding domain acted as a strong transcriptional activator of reporter genes in mammalian cells, whereas most of the analyzed mutant polypeptides had lost this capacity.

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Figures

Figure 1
Figure 1
Schematic presentation of the APECED gene and protein structure, with the locations of all of the mutations characterized in the present study indicated. The dark gray–shaded box indicates the highly conserved N-terminal HSR domain; blackened boxes, the LXXLL nuclear receptor–binding domains; horizontally striped boxes, the putative nuclear targeting signal; the vertically striped box, the putative DNA-binding SAND domain; hatched boxes, the PHD zinc fingers; and the light gray–shaded box, the proline-rich region. The arrow indicates a single-nucleotide substitution; the triangle, a small deletion; and the inverted triangle, a small insertion.
Figure 2
Figure 2
A, Western blot analyses of cell extracts from COS-1 cells transiently expressing the wild-type and mutated forms of the APECED protein. The cells were transfected with the plasmids indicated in the figure. All of the polypeptides were resolved by means of 11% SDS-PAGE. The blot was probed with the rabbit antiserum against the APECED peptide. The molecular masses of the specific polypeptides are in conformity with their calculated values. Cells transfected with the empty SV-poly vector were used as controls. B, Metabolic labeling and immunoprecipitation of the wild-type APECED polypeptide and the polypeptide carrying the common Iranian Jewish mutation. The COS-1 cells were transfected with the constructs indicated in the figure. After 1 h of metabolic labeling with 200 μCi of [35S]-Cys, the cell-culture medium was collected and the cells were lysed. The antibody against the N-terminal half of the APECED protein with Protein A Sepharose was used to immunoprecipitate the polypeptides. The immunoprecipitated samples were electrophoresed on 11% SDS-PAGE, and the polypeptides were visualized by autoradiography. The molecular masses of the low-range marker (Bio-Rad) are indicated on the right side of both figures.
Figure 3
Figure 3
Subcellular locations of the wild-type and mutated APECED polypeptides. The proteins were visualized by indirect immunofluorescent analysis of COS-1 cells transiently transfected with different AIRE expression constructs. The cells were fixed, permeabilized, and incubated with the polyclonal antibody raised against the APECED peptide. A, The wild-type APECED protein is localized mainly in the cell nucleus, where it forms distinct speckles. B, The protein carrying the common Iranian Jewish missense mutation was mainly transported to the nucleus, where it was observed as speckles similar to those formed by the wild-type protein. C, The bulk of the 256-amino-acid–long truncated APECED protein mimicking the common Finnish mutant was found in the cytoplasm, where the staining pattern was mainly filamentous. In addition, some large cytoplasmic granules were detected in a fraction of cells. No staining could be observed in the nucleus. D, A point mutation disrupting the first PHD finger of the APECED protein was mainly located in the cytoplasm. E, In a small fraction of the cells transfected with this mutant form, some nuclear staining could also be detected, but the mutant protein failed to form any distinct structures. F, The APECED protein lacking the second PHD finger, as a consequence of a single-nucleotide deletion, was detected, only in the cytoplasm, as small granules. A filamentous staining pattern was observed in very few transfected cells.
Figure 4
Figure 4
A, Schematic diagram of the wild-type and different mutant Gal4 DBD-APECED constructs. The dark gray–shaded boxes indicate the GAL4 DBD domains; the light gray–shaded boxes, the HSR domains; the striped boxes, the SAND domains; and the hatched boxes, PHD zinc fingers 1 and 2. B, Comparison of the transcription-activation function of the constructs shown in panel A. The wild-type APECED tethered to the GAL4 DBD strongly activates the pG5LUC reporter target, and this activation level is taken as 100% transcription activation. The mutation A374G, which is the major Iranian Jewish mutation, disrupts the HSR domain of the protein. This disruption has no major effect on the transcription-activation level, which is 115% of the wild-type activity. The Finnish major C889T mutation, which deletes both PHD zinc fingers, has no transactivation function. Similarly, the mutant protein carrying the C1313 deletion and, thus, lacking the second PHD zinc finger fails to cause any transcription activation. The G1052A substitution disrupts the first PHD finger, which in turn decreases the transactivation function of the protein to 30%.
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References

Electronic-Database Information

    1. CEPH, http://www.cephb.fr/
    1. GenBank, http://www.ncbi.nlm.nih.gov/Genbank/index.html (for AIRE cDNA [accession number Z97990] and the AIRE genomic sequence [accession number AJ009610])
    1. European Molecular Biology Laboratory Database, http://www.ebi.ac.uk/embl/index.html (for the AIRE genomic sequence [accession number AJ009610])
    1. Online Mendelian Inheritance in Man (OMIM), http://www.ncbi.nlm.nih.gov/Omim/ (for APECED [MIM 240300])

References

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