Regulation of CD11b transcription by decreasing PRC2 and increased acH4 level during ATRA-induced HL-60 differentiation

Abstract

Polycomb repressive complex 2 (PRC2), which mediates trimethylation of lysine 27 on histone H3 (K27me3), plays an important role in many types of stem cell differentiation. Here, we try to reveal how PRC2, PRC2-mediated repressive histone marker H3K27me3, and active histone marker histone H4 acetylation (acH4) regulate the CD11b transcription during alltrans retinoic acid (ATRA)-induced HL-60 leukemia cell differentiation. By using quantitative real-time polymerase chain reaction (qPCR) and western blot analysis, we found that the mRNA and protein expression levels of two members of PRC2 were decreased during ATRA-induced HL-60 differentiation, respectively. When treated with ATRA for 72 h, the EZH2 and SUZ12 mRNA levels were decreased to 35% and 38% of the control group, respectively. At the same time, the granulocytic mature surface marker CD11b expression was increased significantly at mRNA level detected by qPCR and protein level detected by flow cytometry. By using chromatin immunoprecipitation assay, we compared the local changes in SUZ12 binding and PRC2-mediated H3K27me3 at the promoter of CD11b during ATRA-induced HL-60 differentiation. Both the levels of SUZ12 binding and PRC2-mediated H3K27me3 at the promoter of CD11b were decreased for 4.1 and 3.8 folds, respectively. And we also found the increase in the acH4 level up to 4 folds after 72 h of ATRA treatment. These results suggested that the histone modification including PRC2-mediated repressive histone marker H3K27me3 and active histone marker acH4 may involve in CD11b transcription during HL-60 leukemia cells reprogramming to terminal differentiation.