Acetylation‐dependent nuclear arrangement and recruitment of BMI1 protein to UV‐damaged chromatin

Abstract

Polycomb group (PcG) proteins, organized into Polycomb bodies, are important regulatory components of epigenetic processes involved in the heritable transcriptional repression of target genes. Here, we asked whether acetylation can influence the nuclear arrangement and function of the BMI1 protein, a core component of the Polycomb group complex, PRC1. We used time-lapse confocal microscopy, micro-irradiation by UV laser (355 nm) and GFP technology to study the dynamics and function of the BMI1 protein. We observed that BMI1 was recruited to UV-damaged chromatin simultaneously with decreased lysine acetylation, followed by the recruitment of heterochromatin protein HP1β to micro-irradiated regions. Pronounced recruitment of BMI1 was rapid, with half-time τ = 15 sec; thus, BMI1 is likely involved in the initiation step leading to the recognition of UV-damaged sites. Histone hyperacetylation, stimulated by HDAC inhibitor TSA, suppression of transcription by actinomycin D, and ATP-depletion prevented increased accumulation of BMI1 to γH2AX-positive irradiated chromatin. Moreover, BMI1 had slight ability to recognize spontaneously occurring DNA breaks caused by other pathophysiological processes. Taken together, our data indicate that the dynamics of recognition of UV-damaged chromatin, and the nuclear arrangement of BMI1 protein can be influenced by acetylation and occur as an early event prior to the recruitment of HPβ to UV-irradiated chromatin.

Double strand breaks

“…The recruitment of Polycomb at DSBs and the methylation of H3K27me3 associated with Ezh2, a component of polycomb, were also reported by other groups. 27,[30][31][32][33] However, their role in RNAP II transcriptional arrest was not investigated. In addition to the polycomb complex, which marks facultative heterochromatin and is known to directly promote chromatin compaction, HP1 and Kap1 are also markers of constitutive heterochromatin associated with DSBs.…”

Polycomb repressive complex 2 contributes to DNA double-strand break repair

“…Some studies show increased H3K27me3 at DNA damage sites, 13,14 but others report no increase in H3K27me3. 16 PRC2 has been implicated in the methylation of various targets besides H3K27, 17,18 and thus it is possible there is a different methylation target at sites of DNA damage. EZH2 has been further implicated in cancer cells through regulation of the DNA damage checkpoint protein, Chk1, through unknown mechanisms.…”

Coilin is rapidly recruited to UVA-induced DNA lesions and γ-radiation affects localized movement of Cajal bodies

“…Hierarchical assembly of proteins, involved in DNA repair, occurs coordinately with the recruitment of additional chromatin-related factors, such as heterochromatin protein 1 (HP1) and the polycomb-group proteins BMI1 and Mel18. [20][21][22] Another interesting DNA repair-related event (associated with nucleotide excision repair) is linked to inhibition of RNA pol II-driven transcription elongation, when ionizing radiation induces DNA lesions, and is called transcription-coupled repair (TCR). 23 Moreover, double-strand breaks present a barrier for functioning of RNA polymerases, but inhibition of DNA protein kinase, for example, enables RNA pol II to bypass DNA breaks and continue in transcription elongation.…”