Epigenetic role of CCAAT box‐binding transcription factor NF‐Y on ID gene family in human embryonic carcinoma cells

Abstract

Nuclear factor Y (NF-Y) is a histone substitute protein that specifically binds to the CCAAT box of the target genes and thereby promotes their regulation. NF-Y transcription factor, with defined CCAAT element-binding activities, target a gene family that encodes a group of basic helix-loop-helix ID factors (ID1-ID4), with or without CCAAT box at their promoter region. In this study, the expressions of NF-Y in mRNA and protein level were evaluated in a human embryonic carcinoma cell line, named NTera2, before and after 7 days induction of differentiation. We also looked into expression levels of ID genes in NTera2 cells during differentiation because of their critical role in development. By using chromatin immunoprecipitation coupled with real-time polymerase chain reaction, NF-Y incorporation and acetylation/dimethylation of histone H3 at lysine 9 (H3K9ac/me2) was quantitatively evaluated on the regulatory regions of considered genes to monitor the changes in epigenetic markers at ID gene promoters throughout differentiation. The results demonstrated a marked down-regulation of ID1, ID2, and ID3 genes, parallel to a loss of NF-Y binding to the promoters of these genes. The data show that although the genes encoding NF-Y complex remained expressed at mRNA level, NF-YC is lost at the protein level onset of differentiation. Additionally, the epigenetic marks of H3K9ac and H3K9me2 at the target gene promoters decreased and increased, respectively, after 1 day of differentiation. It is suggested that, in the absence of NF-Y binding, the corresponding regions adopt a heterochromatic nature, whereas when NF-Y comes back after 7 days of differentiation, the ID1-3 promoters become again converted into active chromatin. The ID4 gene, lacking a CCAAT box, behaves differently and does not show any incorporation. This experiment implies for the first time that the presence of NF-Y transcription factor plays a pivotal role in transcriptional regulation of ID genes in development.