Sirt1 suppresses RNA synthesis after UV irradiation in combined xeroderma pigmentosum group D/Cockayne syndrome (XP-D/CS) cells
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Edited by Philip C. Hanawalt, Stanford University, Stanford, CA, and approved November 28, 2012 (received for review August 23, 2012)

Abstract
Specific mutations in the XPD subunit of transcription factor IIH result in combined xeroderma pigmentosum (XP)/Cockayne syndrome (CS), a severe DNA repair disorder characterized at the cellular level by a transcriptional arrest following UV irradiation. This transcriptional arrest has always been thought to be the result of faulty transcription-coupled repair. In the present study, we showed that, following UV irradiation, XP-D/CS cells displayed a gross transcriptional dysregulation compared with “pure” XP-D cells or WT cells. Furthermore, global RNA-sequencing analysis showed that XP-D/CS cells repressed the majority of genes after UV, whereas pure XP-D cells did not. By using housekeeping genes as a model, we demonstrated that XP-D/CS cells were unable to reassemble these gene promoters and thus to restart transcription after UV irradiation. Furthermore, we found that the repression of these promoters in XP-D/CS cells was not a simple consequence of deficient repair but rather an active heterochromatinization process mediated by the histone deacetylase Sirt1. Indeed, RNA-sequencing analysis showed that inhibition of and/or silencing of Sirt1 changed the chromatin environment at these promoters and restored the transcription of a large portion of the repressed genes in XP-D/CS cells after UV irradiation. Our work demonstrates that a significant part of the transcriptional arrest displayed by XP-D/CS cells arises as a result of an active repression process and not simply as a result of a DNA repair deficiency. This dysregulation of Sirt1 function that results in transcriptional repression may be the cause of various severe clinical features in patients with XP-D/CS that cannot be explained by a DNA repair defect.
Footnotes
↵1Present address: Department of Molecular Carcinogenesis, University of Texas MD Anderson Cancer Center, Science Park Research Division, Smithville, TX 78657.
↵2R.V.-C. and A.S.Z. contributed equally to this work.
- ↵3To whom correspondence should be addressed. E-mail: egly{at}igbmc.fr.
Author contributions: R.V.-C. and J.-M.E. designed research; R.V.-C. and A.S.Z. performed research; F.C. contributed new reagents/analytic tools and discussions; R.V.-C., A.S.Z., and J.-M.E. analyzed data; and R.V.-C. and J.-M.E. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
See Author Summary on page 814 (volume 110, number 3).
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1213076110/-/DCSupplemental.
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