Phosphorylation of SRSF1 is modulated by replicational stress.

DNA ligase I-deficient 46BR.1G1 cells show a
delay in the maturation of replicative intermediates
resulting in the accumulation of single- and doublestranded
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 replicationdependent
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.