Abstract
BackgroundRadiation-induced alterations in posttranslational histone modifications (PTMs) may affect the cellular response to radiation damage in the DNA. If not reverted appropriately, altered PTM patterns may cause long-term alterations in gene expression regulation and thus lead to cancer. It is therefore important to characterize radiation-induced alterations in PTM patterns and the factors affecting them.MethodsA lymphoblastoid cell line established from a normal donor was used to screen for alterations in methylation levels at H3K4, H3K9, H3K27, and H4K20, as well as acetylation at H3K9, H3K56, H4K5, and H4K16, by quantitative Western Blot analysis at 15 min, 1 h and 24 h after irradiation with 2 Gy and 10 Gy. The variability of alterations in acetylation marks was in addition investigated in a panel of lymphoblastoid cell lines with differing radiosensitivity established from lung cancer patients.ResultsThe screening procedure demonstrated consistent hypomethylation at H3K4me3 and hypoacetylation at all acetylation marks tested. In the panel of lymphoblastoid cell lines, however, a high degree of inter-individual variability became apparent. Radiosensitive cell lines showed more pronounced and longer lasting H4K16 hypoacetylation than radioresistant lines, which correlates with higher levels of residual γ-H2AX foci after 24 h.ConclusionSo far, the factors affecting extent and duration of radiation-induced histone alterations are poorly defined. The present work hints at a high degree of inter-individual variability and a potential correlation of DNA damage repair capacity and alterations in PTM levels.
Highlights
Radiation-induced alterations in posttranslational histone modifications (PTMs) may affect the cellular response to radiation damage in the DNA
Estimating conservatively that 10 Gy of γ-irradiation induce about 400 Double-strand break (DSB), each resulting in a γ-H2AX domain of about 2 Mbp [7], a complete loss of a given PTM within these domains would result in a reduction of the total nuclear signal by about 13%
H4K20 methylation is involved in chromatin compaction and DNA damage response
Summary
Radiation-induced alterations in posttranslational histone modifications (PTMs) may affect the cellular response to radiation damage in the DNA. DNA double-strand breaks (DSBs) elicit a response in an Mbp-large chromatin region surrounding the break that involves alterations in several. Immunofluorescence detection of PTMs demonstrated alterations in several modifications in the γ-H2AX domain following DSB induction that are associated with regulation of chromatin accessibility, recruitment of DNA damage response factors, and regulation of DNA metabolism and transcription [4]. We decided to conduct a screen to identify PTMs that alter in response to irradiation. We here report that histone methylation marks exhibit little alteration, except for tri-methylation of H3K4 the levels of which were consistently reduced after irradiation. All acetylation marks tested exhibited a rather longlasting, globally detectable hypoacetylation after irradiation. Longterm hypoacetylation of H4K16 was strongest in cell lines exhibiting increased radiosensitivity and enhanced levels of residual γ-H2AX foci
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