Site-specific DNA methylation by a complex of PU.1 and Dnmt3a/b

The Ets transcription factor PU.1 is a hematopoietic master regulator essential for the development of myeloid and B-cell lineages. As we previously reported, PU.1 sometimes represses transcription on forming a complex with mSin3A-histone deacetyl transferase-MeCP2. Here, we show an interaction between PU.1 and DNA methyltransferases, DNA methyltransferase (Dnmt)3a and Dnmt3b (Dnmt3s). Glutathione-S-transferase pull-down assay revealed that PU.1 directly interacted with the ATRX domain of Dnmt3s through the ETS domain. Dnmt3s repressed the transcriptional activity of PU.1 on a reporter construct with trimerized PU.1-binding sites. The repression was recovered by addition of 5-aza-deoxycitidine, a DNA methyltransferase inhibitor, but not trichostatin A, a histone deacetylase inhibitor. Bisulfite sequence analysis revealed that several CpG sites in the promoter region neighboring the PU.1-binding sites were methylated when Dnmt3s were coexpressed with PU.1. We also showed that the CpG sites in the p16 INK4A promoter were methylated by overexpression of PU.1 in NIH3T3 cells, accompanied by a downregulation of p16 INK4A gene expression. These results suggest that PU.1 may down-regulate its target genes through an epigenetic modification such as DNA methylation.