HIC1 (hypermethylated in cancer 1) SUMOylation is dispensable for DNA repair but is essential for the apoptotic DNA damage response (DDR) to irreparable DNA double-strand breaks (DSBs).

Sonia Paget,Brennan T Harmon,Corinne Abbadie,Joe Nassour,Nathalie Spruyt,Dominique Leprince,Brian R Rood,Marion Dubuissez,Vanessa Dehennaut,Ingrid Loison

doi:10.18632/oncotarget.13807

Abstract

The tumor suppressor gene HIC1 (Hypermethylated In Cancer 1) encodes a transcriptional repressor mediating the p53-dependent apoptotic response to irreparable DNA double-strand breaks (DSBs) through direct transcriptional repression of SIRT1. HIC1 is also essential for DSB repair as silencing of endogenous HIC1 in BJ-hTERT fibroblasts significantly delays DNA repair in functional Comet assays. HIC1 SUMOylation favours its interaction with MTA1, a component of NuRD complexes. In contrast with irreparable DSBs induced by 16-hours of etoposide treatment, we show that repairable DSBs induced by 1 h etoposide treatment do not increase HIC1 SUMOylation or its interaction with MTA1. Furthermore, HIC1 SUMOylation is dispensable for DNA repair since the non-SUMOylatable E316A mutant is as efficient as wt HIC1 in Comet assays. Upon induction of irreparable DSBs, the ATM-mediated increase of HIC1 SUMOylation is independent of its effector kinase Chk2. Moreover, irreparable DSBs strongly increase both the interaction of HIC1 with MTA1 and MTA3 and their binding to the SIRT1 promoter. To characterize the molecular mechanisms sustained by this increased repression potential, we established global expression profiles of BJ-hTERT fibroblasts transfected with HIC1-siRNA or control siRNA and treated or not with etoposide. We identified 475 genes potentially repressed by HIC1 with cell death and cell cycle as the main cellular functions identified by pathway analysis. Among them, CXCL12, EPHA4, TGFβR3 and TRIB2, also known as MTA1 target-genes, were validated by qRT-PCR analyses. Thus, our data demonstrate that HIC1 SUMOylation is important for the transcriptional response to non-repairable DSBs but dispensable for DNA repair.

Highlights

The genomic integrity of all living organisms is constantly challenged by deleterious attacks due to endogenous or exogenous genotoxic stress
HEK293T cells were transfected with the empty FLAG or FLAG-HIC1 expression vectors with or without an expression vector for His-SUMO2 and/or the de-SUMOylase SENP2. 48 hours after transfection, cells were treated with 20 μM etoposide for 16 hours to induce non-repairable DNA damage and immediately lysed under denaturing conditions
Since endogenous HIC1 activates the kinetics and/or efficiency of double-strand breaks (DSBs) repair in BJ-hTERT fibroblasts, we wanted to address the importance of HIC1 SUMOylation in the repair process [8]

Summary

Introduction

The genomic integrity of all living organisms is constantly challenged by deleterious attacks due to endogenous or exogenous genotoxic stress. DNA damage and in particular DNA double-strand breaks (DSBs) are highly deleterious since they can be lethal if unrepaired or predispose to oncogenic transformation if misrepaired. To cope with these lesions, cells have developed multiple interacting pathways called the DNA damage response (DDR) that lead either to damage repair or to programmed cell death depending on the extent of the damage [1]. Re-expression of HIC1 in MCF-7 cells through adenoviral infection restores their sensitivity to P53-induced apoptosis [6] This effect relies mainly on the HIC1-mediated direct transcriptional repression of SIRT1, which deacetylates and inactivates P53 allowing cells to by-pass P53 induced apoptosis and survive DNA damage [6]. Down-regulation of endogenous HIC1 expression through RNA interference in normal human fibroblasts treated for 1 hour with Etoposide delays DNA repair, as shown by functional comet assays [8]

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