Studio delle modificazioni post-traduzionali della proteina AIRE e dell’effetto sulla sua attività trascrizionale, stabilità e localizzazione cellulare

The AIRE protein plays a remarkable role as a regulator of central tolerance by controlling the promiscuous expression of tissue-specific antigens in thymic medullary epithelial cells. Defects in the AIRE gene cause the autoimmune polyendocrinopathy- candidiasis-ectodermal dystrophy, a rare disease frequent in Iranian Jews, Finns, and Sardinian population. AIRE protein has functional domains shared by others transcriptional factors thus suggesting that AIRE plays an important role in the regulation of the transcriptional process. AIRE protein is primarily known as a transcriptional regulator which functions as activator or repressor, depending on the cellular context in which the protein is functionally active. However, the exact mechanism has not yet completely clarified. It is widely accepted that its proper functioning is critical for the organization and maintenance of immunological tolerance. AIRE is capable of interacting with numerous proteins. The first characterized partner of AIRE is the ubiquitous transcription factor CREB-binding protein (CBP), which regulates DNA transcription through the acetylation and deacetylation of histones. Several evidences have shown that AIRE-CBP interaction occurs in nuclear bodies and increases the expression of its target genes (Akiyoshi H et al 2004), (Pitkänen J. et al 2005), (Ferguson BJ et al 2008). More recently, the role of p300 in AIRE acetylation, which could influence the selection of AIRE activated genes (Saare et al 2012) has been described. In the acetylation process, the lysines are the residues target and their position in the side chain is very important for protein function. In this study, we have precisely mapped, by mass spectrometry experiments, the sites of protein acetylation and, by mutagenesis assays, we have described a set of acetylated lysines as being crucial in influencing the subcellular localization of AIRE. On the basis of our results and those reported in literature, we propose a model in which lysines acetylation increases the stability of AIRE in the nucleus, where it assembles in aggregates called Nuclear Bodies. We have explored the role of acetyltransferase enzymes, beside p300, involved in the lysine acetylation of AIRE. Furthermore, since acetylation is a reversible process, once assessed that AIRE is deacetylated, we have also explored the possible role of the deacetylase complex in the biological function of AIRE protein.