Dynamics of polycomb proteins-mediated histone modifications during UV irradiation-induced DNA damage.

Polycomb group (PcG) complexes are known to be chromatin modifiers and transcriptional repressors. In this work, we reported that the histone-modifying PcG complexes are able to participate in the repair process of ultraviolet (UV)-induced DNA lesions in the silkworm, Bombyx mori. The silkworm cells with depletion of PcG genes showed hypersensitive to UV-C irradiation and increased inhibition of cell proliferation. Interestingly, an SQ site in the silkworm-human chimeric H2A protein synthesized here was phosphorylated rapidly upon UV-C exposure, which could be used as a marker for monitoring the response to DNA damage in silkworm cells. Under these UV-C irradiated conditions, we found that PRC1-mediated ubiquitylation of H2AX, but not of H2AZ, were decreased and this deubiquitylation was independent of its phosphorylation event. In contrast, UV-C irradiation induced the increase of trimethylation of lysine 27 on histone H3 (H3K27me3), a mark of transcriptionally silent chromatin catalyzed by another PcG subcomplex, PRC2. Collectively, we provided the first evidence on chromatin remodeling in response to UV-C lesion in silkworm and revealed another layer role for PcG complexes-mediated histone modifications in contributing to creating an open chromatin structure for the efficient repair of DNA damages.
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