Class I Histone Deacetylase HDAC1 and WRN RECQ Helicase Contribute Additively to Protect Replication Forks upon Hydroxyurea-induced Arrest

Keffy Kehrli,Michael Phelps,Pavlo Lazarchuk,Eleanor Chen,Ray Monnat,Julia M Sidorova

doi:10.1074/jbc.m115.708594

Keffy Kehrli, Michael Phelps + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m115.708594

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Abstract

The WRN helicase/exonuclease is mutated in Werner syndrome of genomic instability and premature aging. WRN-depleted fibroblasts, although remaining largely viable, have a reduced capacity to maintain replication forks active during a transient hydroxyurea-induced arrest. A strand exchange protein, RAD51, is also required for replication fork maintenance, and here we show that recruitment of RAD51 to stalled forks is reduced in the absence of WRN. We performed a siRNA screen for genes that are required for viability of WRN-depleted cells after hydroxyurea treatment, and identified HDAC1, a member of the class I histone deacetylase family. One of the functions of HDAC1, which it performs together with a close homolog HDAC2, is deacetylation of new histone H4 deposited at replication forks. We show that HDAC1 depletion exacerbates defects in fork reactivation and progression after hydroxyurea treatment observed in WRN- or RAD51-deficient cells. The additive WRN, HDAC1 loss-of-function phenotype is also observed with a catalytic mutant of HDAC1; however, it does not correlate with changes in histone H4 deacetylation at replication forks. On the other hand, inhibition of histone deacetylation by an inhibitor specific to HDACs 1–3, CI-994, correlates with increased processing of newly synthesized DNA strands in hydroxyurea-stalled forks. WRN co-precipitates with HDAC1 and HDAC2. Taken together, our findings indicate that WRN interacts with HDACs 1 and 2 to facilitate activity of stalled replication forks under conditions of replication stress.

Highlights

Replication stress, defined as disturbances to normal progression rate, density, or distribution of replication forks, is a major driver of genomic instability and carcinogenesis [1,2,3]
As we previously showed that combined loss of WRN and RAD51 was not additive with respect to fork reactivation compared with the individual effects of these genes [15], our new results suggest that HDAC1 may facilitate fork recovery after HU-induced stress via a pathway parallel to the WRN/RAD51-dependent pathway
Consistent with previous work [36], our study has demonstrated that HDAC1 and -2 are both present at the replication fork

Summary

Edited by Patrick Sung

The WRN helicase/exonuclease is mutated in Werner syndrome of genomic instability and premature aging. Slowing or stalling of forks in HU and subsequent reactivation of normal fork progression after HU are highly regulated processes, which protect forks from inactivation and ensure faithful and complete replication of the genome This includes preserving the ability of forks to resume DNA synthesis after conditions normalize as well as preventing excessive truncation of nascent DNA strands at the fork and involves coordinated activities of many proteins, including checkpoint effectors and mediators, exonucleases, helicases, ATPases, low fidelity DNA polymerases, and proteins of homologous recombination machinery [4, 5]. Mutations in the BLM [16] and WRN [17] genes cause, respectively, Bloom syndrome (BS) and Werner syndrome, two heritable human genomic instability disorders characterized by developmental abnormalities (BLM) and premature aging (WRN), respectively [18, 19] Both syndromes are associated with increased predisposition to specific types of cancer [20, 21]. Our results highlight the importance of chromatin environment in mitigating disruptions to replication

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