In response to DNA damage tissue homoeostasis is ensured by protein networks promoting DNA repair, cell cycle arrest or apoptosis. DNA damage response signaling pathways coordinate these processes, partly by propagating gene expression-modulating signals. DNA damage influences not only abundance of mRNAs, but also their coding information through alternative splicing. Here we show that transcription-blocking DNA lesions promote chromatin displacement of late-stage spliceosomes and initiate a positive feedback loop centered on the signaling kinase ATM. We propose that initial spliceosome displacement and subsequent R-loop formation is triggered by pausing of RNA polymerase at DNA lesions. In turn, R-loops activate ATM which signals to further impede spliceosome organization and augment UV-triggered alternative splicing at genome-wide level. Our findings define the R-loop-dependent ATM activation by transcription-blocking lesions as an important event in the DNA damage response of non-replicating cells and highlight a key role for spliceosome displacement in this process.

PARP1-mediated poly(ADP-ribosyl)ation of DDB2 prolongs its occupation on UV-damaged chromatin and promotes the recruitment of the chromatin remodeler ALC1.

In addition to its role in DNA lesion recognition, the damaged DNA-binding protein DDB2 elicits unfolding of large-scale chromatin structure independently of the CRL4 ubiquitin ligase complex.

No abstract

Cornelia de Lange syndrome (CdLS) is a rare dominantly inherited multisystem disorder affecting both physical and mental development. Heterozygous mutations in the NIPBL gene were found in about half of CdLS cases. Scc2, the fungal ortholog of the NIPBL gene product, is essential for establishing sister chromatid cohesion. In yeast, the absence of cohesion leads to chromosome mis-segregation and defective repair of DNA double-strand breaks. To evaluate possible DNA repair defects in CdLS cells, we characterized the cellular responses to DNA-damaging agents. We show that cells derived from CdLS patients, both with and without detectable NIPBL mutations, have an increased sensitivity for mitomycin C (MMC). Exposure of CdLS fibroblast and B-lymphoblastoid cells to MMC leads to enhanced cell killing and reduced proliferation and, in the case of primary fibroblasts, an increased number of chromosomal aberrations. After X-ray exposure increased numbers of chromosomal aberrations were also detected, but only in cells irradiated in the G(2)-phase of the cell cycle when repair of double-strand breaks is dependent on the establishment of sister chromatid cohesion. Repair at the G(1) stage is not affected in CdLS cells. Our studies indicate that CdLS cells have a reduced capacity to tolerate DNA damage, presumably as a result of reduced DNA repair through homologous recombination.