Transcriptome of BAHD1 knock-down HEK293 cells with siRNA

Gene silencing via heterochromatin formation plays a major role in cell differentiation and maintenance of homeostasis. Here, we report the identification and characterization of a novel heterochromatinization factor in vertebrates, Bromo Adjacent Homology Domain-containing protein 1 (BAHD1). BAHD1 interacts with HP1, MBD1, HDAC5 and with several transcription factors. Through electron and immunofluorescence microscopy studies, we show that BAHD1 overexpression directs HP1 to specific nuclear sites and promotes formation of large heterochromatic domains, which lack acetyl histone H3 and are enriched in H3 trimethylated at lysine 27. Furthermore, ectopically expressed BAHD1 colocalizes with the heterochromatic X inactive chromosome. As highlighted by whole genome microarray analysis of BAHD1 knock down cells, BAHD1 represses several proliferation and survival genes and in particular, the insulin-like growth factor II gene (IGF2). BAHD1 specifically binds the CpG-rich P3 promoter of IGF2. This region contains DNA binding sequences for the transcription factor SP1, with which BAHD1 co-immunoprecipitates. Collectively, these findings provide evidence that BAHD1 acts as a silencer by recruiting proteins that coordinate heterochromatin assembly at specific sites in the genome.

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Bierne H, Tham TN, Batsche E, Dumay A, Leguillou M, Kernéis-Golsteyn S, Regnault B, Seeler JS, Muchardt C, Feunteun J, Cossart P