Transcriptional repression of DNA repair genes is a hallmark and a cause of cellular senescence

Guillaume Collin,Marine Warnier,Anda Huna,David Bernard,Jean-Michel Flaman

doi:10.1038/s41419-018-0300-z

Abstract

Cellular senescence response is (i) activated by numerous stresses, (ii) is characterized by a stable proliferation arrest, and (iii) by a set of specific features. Timely regulated senescence is thought to be beneficial, whereas chronic senescence such as during normal or premature aging is deleterious as it favors most, if not all, age-related diseases. In this study, using in-house or publicly available microarray analyses of transcriptomes of senescent cells, as well as analyses of the level of expression of several DNA repair genes by RT-qPCR and immunoblot, we show that repression of DNA repair gene expression is associated with cellular senescence. This repression is mediated by the RB/E2F pathway and it may play a causal role in senescence induction, as single DNA repair gene repression by siRNA induced features of premature senescence. Importantly, activating RB independently of direct DNA damage also results in repression of DNA repair genes and in the subsequent induction of DNA damage and senescence. The dogma is that DNA damage observed during cellular senescence is directly provoked by DNA lesions following genotoxic attack (UV, IR, and ROS) or by induction of replicative stress upon oncogenic activation. Our in vitro results support a largely unsuspected contribution of the loss of DNA repair gene expression in the induction and the accumulation of the DNA damage observed in most, if not all, kinds of cellular senescence, and thus in the induction of cellular senescence. Further demonstration using in vivo models will help to generalize our findings.

Highlights

The state of cellular senescence is characterized by a stable proliferation arrest and the acquisition of specific features such as morphological, metabolic and transcriptional changes
To gain some insight into the mechanisms regulating cellular senescence in epithelial cells, which are at the origin of most cancers, we characterized the transcriptome of immortalized human mammary epithelial cells expressing a fused inducible MEK:ER oncogene (HMEC-MEK), a model of oncogene-induced senescence (OIS) that we have described previously[17,18,19]
To perform further functional analysis, 12 genes, involved in several DNA repair pathways, commonly and strongly down-regulated in the 4 different “senescence transcriptomes” were selected (Fig. 1b). Negative regulation of these 12 DNA repair genes was further confirmed by RT-qPCR in three different models of senescence, in MRC5 normal human fibroblasts (i) overexpressing a fused inducible oncogene RAF:ER (MRC5RAF) (Supplementary Figure S1), (ii) exposed to H2O2 (MRC5-H2O2) (Supplementary Figure S2) (iii) expressing a non-functional TRF2 leading to telomere dysfunction (MRC5-ΔTRF2) (Supplementary Figure S3) (Fig. 1c)

Summary

Introduction

The state of cellular senescence is characterized by a stable proliferation arrest and the acquisition of specific features such as morphological, metabolic and transcriptional changes. Cellular senescence can be activated by numerous cellular stresses such as replicative exhaustion, radiation, genotoxicity, oncogenic signals, as well as oxidative stress. They induce senescence, at least in part, through induction of DNA damage and DNA damage signaling. Increased DNA damage observed in senescent cells is thought to be due to physical attacks of the DNA, such as by reactive oxygen species (ROS) or ionizing radiation (IR), and/or to replicative stress after oncogene activation[13,14,15,16]

Methods

Results

Conclusion