Ρύθμιση της δράσης μεταγραφικών παραγόντων μέσω μεθυλίωσης σε κατάλοιπα λυσίνης

Abstract

Recent studies revealed that histone lysine-methyltransferases, in addition to their function on chromatin, can also regulate specific gene expression programs through methylation of transcription factors. The emerging field of lysine methylation encouraged us to extend our studies on identifying new substrates for Set9, Smyd2 and Smyd3, which is presented in the first part of my thesis. It was found that Set9 efficiently methylates E2F1. Both Set9 and Smyd2 methylate the tumor-suppressor protein Rb, the transcription factor HNF4 and the linker histone H1o. Smyd2 also methylates the heat shock protein HSP90 and Set9 methylates the methyltransferase Smyd2. Histone modifying enzymes can regulate various cellular processes through the methylation of transcription factors. The most characteristic example is the regulation of DNA damage-induced apoptosis through modulation of p53 function. In particular, the studies identified a pro-apoptotic function of the histone methyltransferase Set9 and an anti-apoptotic role of the histone demethylase LSD1, through mechanisms that involve methylation and demethylation of two different residues of p53, respectively. In the second part of my thesis we study the role of Set9 and LSD1 in DNA damage-induced cell death in the p53-deficient cell line H1299 (human lung carcinoma cell line). The two enzymes regulate DNA damage-induced cell death in a manner opposite to that observed in p53+/+ cells (U2OS). The anti-apoptotic role of Set9 and the pro-apoptotic role of LSD1 emerges through modulation of E2F1. The Set9-mediated methylation of E2F1 at lysine-185 destabilizes the protein and negatively influences E2F1-mediated cell death, as opposed to its stabilizing function on p53, which promotes apoptosis. LSD1 is required for DNA damage induced accumulation of E2F1 and activation of pro-apoptotic targets, while its enzymatic action inhibits p53 transcriptional activity. In the third part of my thesis we aimed to characterize the genomic locations bound by the methyltransferase Set9, the demethylase LSD1 and the transcription factor E2F1. The processing of the results provided information regarding their distribution profile on their target genes. Furthermore, we performed comparative analysis preparative to locate co-recruitment of these factors on common sites.