EPIGENETIC MODIFICATIONS IN A T(8;21) ACUTE MYELOID LEUKEMIA CELL LINE CAUSED BY ADMINISTRATION OF THE HDAC INHIBITOR D1

The acute myeloid leukemia (AML) cell line Kasumi- 1 is characterized by the translocation t(8;21), manifested with the expression of AML1/ETO fusion protein, responsible for HDAC recruitment, determining transcriptional repression of target genes involved in myeloid maturation. We recently demonstrated that sodium butyrate and the stable prodrug xylitol butyrate derivative (D1) are able as single agents to restore histone acetylation and granulocytic maturation in Kasumi-1 cell line, as well as in primary AML blasts. D1 differentiative effects were confirmed by increased membrane expression of CD11b and CD15, decrease of CD34 and reduction of blasts absolute number. These effects were paralleled by massive induction of apoptosis as well as reduction of cell number. Acetylation and methylation of specific lysine residues on histone H4 and H3 has been associated with transcriptional regulation. The acetylation pattern of lysine residues of histone H4 was investigated. K5 and K16 residues were not acetylated in the absence of D1 and their acetylation strongly increased after 6 h D1 administration. K8 and K12 residues showed a basal acetylation which was further increased although not markedly. Lysine methylation of histone H3 was evaluated. D1 determined a reduction of di-methylated K9 H3, related to gene silencing. Di-methylated K4 H3, related to both gene silencing and transcriptional activation, was unmodified after D1 administration. These histone modifications paralleled D1-induced transcriptional activation of AML1/ETO target genes. The cyclindependent kinase inhibitors (CDKi) belonging to the Cip/Kip family are known to be involved in cell cycle as well as apoptosis and cancer. D1 determined an increase of p21/cip1 expression and a decrease of p27/kip1.Appearance of a conspicuous amount of p57/kip2, an as yet uncharacterised oncosuppressor, after 72-96 h treatment with D1 was observed. The maturation effects of D1 were further investigated at molecular level. D1 was found to modulate the expression of transcription factors important for terminal cell differentiation. In particular, C/EBPepsilon, PU. 1, c-jun, AML1/ETO as well as C/EBPa expression was modified after exposure to D1.These results suggest that HDAC inhibition determines profound gene remodelling trough specific epigenetic modifications.