PREP1 down-regulation changes the DNA replication timing of Lamin-associated DNA and induces DNA damage [Repli-Seq]

Down-regulation (DR) of PREP1 (aka PKNOX1) tumor suppressor induces H2Ax foci in human fibroblasts. Here we have analyzed the effect of PREP1 DR on DNA replication using cell cycle analysis, Repliseq, DNA combing, ChIP-seq, RNA-seq and immunofluorescence (IF). In human cells, PREP1 DR similarly affects both the rate of DNA replication and the progression of cells through the S phase. Genome wide, PREP1 DR induces late to early DNA replication shifts in normally late-replicated genomic regions amounting to 25% of the genome, in addition to unscheduled origins firing. A concomitant strong increase of unidirectional replication forks explains the appearance of DNA damage foci. The DNA target of PREP1 DR is the Lamin Associated DNA, in agreement with the simultaneous decrease of Lamin B1. Therefore PREP1 is a novel regulator of replication timing and Lamin B1 level, which ChIP-seq and RNA-seq data indicate as independent from its transcriptional activity. This activity must constitute the basis for its tumor suppression function. Repli-seq of HeLa cells transfected with siPrep1 and siLuc (control cells)