Monocyte/Macrophage - like cell differentiation induced by TPA in HL60 cells leads to loss of Histone H4 Lysine 16 Acetylation

Abstract

12-O-Tetradecanoylphorbol-13-acetate (TPA) is a phorbol ester and induces monocyte/macrophage like cell differentiation in HL60 cells. The levels and patterns of gene expression differ greatly between differentiated and undifferentiated HL60 cells. Epigenetic histone modifications play a crucial role in transcriptional activation and alterations in the modification levels greatly affect the gene expression pattern. Acetylation of Histone H4 Lysine 16 (H4K16ac) is one such modification and has a significant role in transcriptional activation. Changes in its acetylation level either due to a physiological or pathological effect will have a dramatic effect on cellular gene expression. Here, a study was done to see the effect of TPA induced differentiation on H4K16ac levels in HL60 cells. Results obtained from flow cytometric analysis showed expression of macrophage cell surface marker CD11b on TPA differentiated HL60 cells and the western blots revealed a drastic downregulation of H4K16ac in differentiated cells. Immunoblotting and co-immunoprecipitation assay revealed DNA damage dependent enhancement of H4K16 acetylation and its co-localization with γH2AX in undifferentiated cells. Whereas, TPA differentiated cells (CD11B+ve) didn’t show any such enhancement in H4K16acetylation levels in the presence of DNA damage. The present study shows that TPA induced differentiation of HL60 cells into macrophages leads to the downregulation of H4K16 acetylation.