Phosphorylation of SRSF1 is modulated by replicational stress

Abstract

DNA ligase I-deficient 46BR.1G1 cells show a delay in the maturation of replicative intermediates resulting in the accumulation of single- and double-stranded DNA breaks. As a consequence the ataxia telangiectasia mutated protein kinase (ATM) is constitutively phosphorylated at a basal level. Here, we use 46BR.1G1 cells as a model system to study the cell response to chronic replication-dependent DNA damage. Starting from a proteomic approach, we demonstrate that the phosphorylation level of factors controlling constitutive and alternative splicing is affected by the damage elicited by DNA ligase I deficiency. In particular, we show that SRSF1 is hyperphosphorylated in 46BR.1G1 cells compared to control fibroblasts. This hyperphosphorylation can be partially prevented by inhibiting ATM activity with caffeine. Notably, hyperphosphorylation of SRSF1 affects the subnuclear distribution of the protein and the alternative splicing pattern of target genes. We also unveil a modulation of SRSF1 phosphorylation after exposure of MRC-5V1 control fibroblasts to different exogenous sources of DNA damage. Altogether, our observations indicate that a relevant aspect of the cell response to DNA damage involves the post-translational regulation of splicing factor SRSF1 which is associated with a shift in the alternative splicing program of target genes to control cell survival or cell death.

Pre-mRNA processing factors meet the DNA damage response

“…Notably, both the level of SRSF1 phosphorylation and splicing programs can revert to those observed in normal cells by inhibiting ATM activity, indicating that SRSF1 phosphorylation could be part of a regulatory circuit through which cells cope with DNA damage. In agreement with this interpretation, SRSF1 phosphorylation is modulated in response to a wide set of DNA-damaging insults (Leva et al, 2012) and SRSF1 is involved in the choice between pro- and anti-apoptotic pathways (Moore et al, 2010). …”

“…The LigI defect hampers the maturation of Okazaki fragments and results in the accumulation of single-stranded DNA breaks (SSBs) and DSBs and in the constitutive activation of the ATM checkpoint pathway (Soza et al, 2009). By applying a proteomic approach, we have shown that the entire set of SR splicing factors, particularly SRSF1, is hyper-phosphorylated in LigI-deficient cells and this modification is accompanied by a shift in the alternative splicing program of apoptotic genes such as caspase 9 (Leva et al, 2012). Notably, both the level of SRSF1 phosphorylation and splicing programs can revert to those observed in normal cells by inhibiting ATM activity, indicating that SRSF1 phosphorylation could be part of a regulatory circuit through which cells cope with DNA damage.…”

RNA Splicing: A New Player in the DNA Damage Response

“…It was recently shown that genotoxic stress can induce the phosphorylation and the relocalization of these kinases to the nucleus where they in turn hyperphosphorylate SR proteins leading to changes in pre-mRNA splicing [22, 23]. Moreover, chronic replication-dependent DNA damage was shown to induce the hyperphosphorylation of ASF/SF2 (SRSF1) [24]. …”

Single Cell Analysis of Human RAD18-Dependent DNA Post-Replication Repair by Alkaline Bromodeoxyuridine Comet Assay

“…During an undisturbed replication process, when the elongating DNA ends synthesized from neighbouring replicons abut, DNA ligase seals the gaps of DNA fragments and the nascent DNA becomes continuous [40]. This process is also referred to as DNA maturation of replicative intermediates for both the nascent leading strand DNA and Okazaki fragments [41], [42] (Figure 1B). Before the DNA maturation is completed the nascent DNA fragments can be unwound under alkaline conditions, indicating incomplete replication and the presence of single-stranded gaps in the newly replicated DNA (Figure 1C, left panel).…”