Abstract
Conflicts between replication and transcription are a common source of genomic instability, a characteristic of almost all human cancers. Aberrant R-loops can cause a block to replication fork progression. A growing number of factors are involved in the resolution of these harmful structures and many perhaps are still unknown. Here, we reveal that the Werner interacting protein 1 (WRNIP1)-mediated response is implicated in counteracting aberrant R-loop accumulation. Using human cellular models with compromised Ataxia-Telangiectasia and Rad3-Related (ATR)-dependent checkpoint activation, we show that WRNIP1 is stabilized in chromatin and is needed for maintaining genome integrity by mediating the Ataxia Telangiectasia Mutated (ATM)-dependent phosphorylation of Checkpoint kinase 1 (CHK1). Furthermore, we demonstrated that loss of Werner Syndrome protein (WRN) or ATR signaling leads to formation of R-loop-dependent parental ssDNA upon mild replication stress, which is covered by Radiorestistance protein 51 (RAD51). We prove that Werner helicase-interacting protein 1 (WRNIP1) chromatin retention is also required to stabilize the association of RAD51 with ssDNA in proximity of R-loops. Therefore, in these pathological contexts, ATM inhibition or WRNIP1 abrogation is accompanied by increased levels of genomic instability. Overall, our findings suggest a novel function for WRNIP1 in preventing R-loop-driven genome instability, providing new clues to understand the way replication–transcription conflicts are handled.
Highlights
DNA damage or unusual DNA structures may pose a serious impediment to DNA replication, threatening genome integrity
Werner interacting protein 1 (WRNIP1) was originally identified as a Werner Syndrome protein (WRN)-interacting protein [24], but there is no evidence that they cooperate in response to mild replication stress (MRS)
We first investigated if WRN and WRNIP1 interact in vivo by testing their coimmunoprecipitation
Summary
DNA damage or unusual DNA structures may pose a serious impediment to DNA replication, threatening genome integrity. The main transcription-associated structures that can be detrimental to fork movement are R-loops [3,4]. They are transient and reversible structures forming along the genome, consisting of a DNA–RNA hybrid and a displaced single-stranded DNA. Despite their beneficial function in a series of physiological processes, such as transcription termination, regulation of gene expression, and DNA repair [5], they can cause a head-on clash between the replisome and the RNA polymerase, leading to R-loop-driven replication stress if their turnover is deregulated [6,7]. Apart from direct regulators of Cancers 2020, 12, 389; doi:10.3390/cancers12020389 www.mdpi.com/journal/cancers
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