Sirvi Kuupäev , alustades "2010-03-12T10:49:55Z" järgi

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Molecular function of the first PHD finger domain of Autoimmune Regulator protein
(2010-03-12T10:49:55Z) Org, Tõnis
Negative selection of self-reactive T-cells in the thymus is the fundamental process that ensures proper central self-tolerance. The basis for negative selection is the presentation of self peptides to developing thymocytes which relies on the availability of different self proteins in the thymus. The AIRE protein has a unique role in this process as it promotes the expression of large number of tissue-specific antigens in medullary thymic epithelial cells thus making them available for presentation to thymocytes. In our studies, we focused on the molecular mechanisms of AIRE mediated promiscuous gene expression of tissue-specific genes. More specifically, we studied the function of the first PHD finger domain of AIRE since this domain was recently shown to interact with histone H3 N-terminal tails. We identified that similar to other proteins with PHD fingers, AIRE can directly interact with histone H3 through its first PHD zinc finger domain, and that several histone H3 N-terminal modifications interfere with this interaction. We also showed that AIRE can bind to mononucleosomes in vitro and that it selectively interacts with histones in vivo. Furthermore, using a model system, HEK293 cell-lines stably expressing AIRE, we showed that AIRE preferentially activates genes that are tissue-specific and characterized by low levels of initial expression. We also identified that AIRE regulated genes lack active chromatin marks H3K4me3 and AcH3 on their promoters. During the activation by AIRE, some of the target genes acquire histone H3 posttranslational modifications associated with transcription and RNA polymerase II, suggesting that AIRE mediated increase in mRNA levels is mediated, at least in part, at the transcriptional level. Finally, we confirmed our current model of AIRE function by showing that AIRE target genes have low levels of H3K4me3 on their promoters in vivo by studying histone posttranslational modifications in mouse thymus and peripheral tissues. In summary, our studies have led to the identification of novel molecular mechanism how AIRE can be recruited to certain regions in chromatin. This recruitment results in preferential activation of tissue-specific genes, which is needed for the establishment of proper central tolerance.