Abstracts

Lysine specific-demethylase 1 (LSD1) is aberrantly expressed in acute myeloid leukemia (AML) and is emerging as a promising target for the epigenetic therapy of different AML subtypes. The Experimental Therapeutic Unit at the IFOM-IEO Campus optimized potent and specific LSD1 inhibitors, already characterized in vitro for their selectivity and in vivo for their anti-proliferative effects on self-renewing AML cells. In my thesis project, I studied the effects of these compounds on the pattern of histone post-translational modifications (PTMs) and on the LSD1 interaction network in NB4-APL cells (an AML subtype), using a panel of quantitative mass-spectrometry strategies. We discovered that a 24-hour treatment with the inhibitors alters the levels of histone modifications (increases H3K4me2, H3K27me2 and H3K27me3, and decreases H3K27me1). LSD1 knock-out NB4 cells display similar changes in histone PTMs, strongly suggesting a specific association with the cellular response to LSD1 inhibition. We also identified the complete set of LSD1 interactors in our model using SILAC-based proteomics, most of which are involved in chromatin remodelling and transcription regulation activities. The analysis of the LSD1-interactome after drug treatment identified two LSD1 interactors (GFI1 and GSE1) with decreased binding. Inhibition of the LSD1- GFI1 interaction promoted reduction of cell proliferation and differentiation of NB4 cells. Regarding the LSD1-GSE1 interaction, we found that GSE1 down-regulation and LSD1 inhibition up-regulated a common set of genes involved in “cytokine-mediated signalling” and “regulation of apoptosis”, thus suggesting the existence of a regulatory LSD1-GSE1 axis controlling the transcription of these genes. Collectively, these data provide novel insights into the molecular activity of LSD1 and its inhibitors in APL cells.