Unknown,Transcriptomics,Genomics,Proteomics

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A POLD3/BLM dependent pathway handles DSBs in transcribed chromatin upon excessive RNA:DNA hybrids accumulation

ABSTRACT: Transcriptionally active loci are particularly prone to breakage and mounting evidence suggest that DNA Double-Strand Breaks arising in active genes are handled by a dedicated repair pathway, Transcription-Coupled DSB Repair (TC-DSBR), that entails R-loop accumulation and dissolution. Here, we uncovered a function for the Bloom RecQ DNA helicase (BLM) in TC-DSBR in human cells. BLM is recruited in a transcription dependent-manner at DSBs where it fosters resection, RAD51 binding and accurate Homologous Recombination repair. However, in an R-loop dissolution-deficient background, we found that BLM promotes cell death. We report that upon excessive R-loop accumulation, DNA synthesis is enhanced at DSBs, in a anner that depends on BLM and POLD3. Altogether our work unveils a role for BLM at DSBs in active chromatin, and highlights the toxic potential of RNA:DNA hybrids that accumulate at transcription-associated DSBs.

INSTRUMENT(S): NextSeq 500

ORGANISM(S): Homo sapiens

SUBMITTER: Vincent ROCHER

PROVIDER: E-MTAB-11592 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Missense mutations in the TP53 gene are frequent genetic alterations in human tumor tissue and cell lines. In contrast to wild-type p53, the mutant p53 (mutp53) protein has lost the transcriptional activity towards pro-apoptotic and growth arrest genes, but retained the property to interact with DNA in a structure-specific fashion. Expression of mutp53 is advantageous for tumor cells, however the molecular mechanism of mutp53 action is still not known. We used the glioblastoma-derived U-251 MG human cell line to analyze DNA binding of mutant p53 (R273H mutation) on a Nimblegen custom 135k tiling array and to correlate mutp53 binding regions with the epigenetic state and occupation by other transcription factors (ETS1 and SP1). We found that mutp53-binding regions are G/C-rich and are located around transcriptional start sites (TSS) of many protein-coding genes, which in most cases are active, but are not always regulated upon transient mutp53 depletion. We propose a model which does not only rely on interactions of mutp53 with diverse transcriptional regulators at active promoters, but primarily is based on a DNA binding activity of mutp53. We designed a Nimblegen custom 135k tiling array that covers a large set of putative and known p53 (wild-type and mutant) target genes in the human genome. For analysis of the epigenetic state of genes covered by the tiling array in control and mutant p53-depleted U251 cells we focused on changes in active histone marks, H3K4me3 and H3K9Ac, and RNA polymerase II recruitment and processivity. H3K4me3 and H3K9Ac marks are enriched in active promoter regions and the phosphorylation of serine 5 (S5-P) and serine 2 (S2-P) in the CTD of RNA polymerase II have been described to define initiated and elongating complexes, respectively. We performed the ChIP-chip experiments for H3K4me3, H3K9Ac, RNA polymerase II (S5-P) and RNA polymerase II (S2-P) from U251 cells transfected with p53-specific siRNA or control siRNA (2 biological replicates each). To analyze binding of mutant p53 to the genes covered by the tiling array we performed mutant p53 ChIP-chip experiments in 4 biological replicates of. In addition, we analyzed the distribution of SP1 and ETS1 binding sites in 3 biological replicates.

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A POLD3/BLM dependent pathway handles DSBs in transcribed chromatin upon excessive RNA:DNA hybrids accumulation

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