dna repair 7 ( 2 0 0 8 ) 1659–1669 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/dnarepair Cell-type-specific consequences of nucleotide excision repair deficiencies: Embryonic stem cells versus fibroblasts Harm de Waard a,1 , Edwin Sonneveld b , Jan de Wit a , Rebecca Esveldt-van Lange b , Jan H.J. Hoeijmakers a , Harry Vrieling b , Gijsbertus T.J. van der Horst a,∗ a MGC, Department of Genetics, Erasmus University Medical Center, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands b MGC, Department of Toxicogenetics, Leiden University Medical Center, Einthovenweg 20, 2333 ZC Leiden, The Netherlands article info Article history: Received 4 February 2008 Received in revised form 13 June 2008 Accepted 14 June 2008 Published on line 26 July 2008 Keywords: DNA repair Nucleotide excision repair UV-sensitivity Embryonic stem cells Mutagenesis abstract Pluripotent embryonic stem cells (ES cells) are the precursors of all different cell types com- prising the organism. Since persistent DNA damage in this cell type might lead to mutations that cause huge malformations in the developing organism, genome caretaking is of prime importance. We first compared the sensitivity of wild type mouse embryonic fibroblasts (MEFs) and ES cells for various genotoxic agents and show that ES cells are more sensi- tive to treatment with UV-light, -rays and mitomycin C than MEFs. We next investigated the contribution of the transcription-coupled (TC-NER) and global genome (GG-NER) sub- pathways of nucleotide excision repair (NER) in protection of ES cells, using cells from mouse models for the NER disorders xeroderma pigmentosum (XP) and Cockayne syndrome (CS). TC-NER-deficient Csb -/- and GG-NER/TC-NER-defective Xpa -/- MEFs are hypersensi- tive to UV, whereas GG-NER-deficient Xpc -/- MEFs attribute intermediate UV sensitivity. The observed UV-hypersensitivity in Csb -/- and Xpa -/- MEFs correlates with increased apopto- sis. In contrast, Xpa -/- and Xpc -/- ES cells are highly UV-sensitive, while a Csb deficiency only causes a mild increase in UV-sensitivity. Surprisingly, a UV-induced hyperapoptotic response is mainly observed in Xpa -/- ES cells, suggesting a different mechanism of apop- tosis induction in ES cells, mainly triggered by damage in the global genome rather than in transcribed genes (as in MEFs). Moreover, we show a pronounced S-phase delay in Xpa -/- and Xpc -/- ES cells, which might well function as a safeguard mechanism for heavily dam- aged ES cells in case the apoptotic response fails. Although Xpa -/- and Xpc -/- ES cells are totally NER-defective or GG-NER-deficient respectively, mutation induction upon UV is sim- ilar compared to wild type ES cells indicating that the observed apoptotic and cell cycle responses are indeed sufficient to protect against proliferation of damaged cells. In con- clusion, we show a double safeguard mechanism in ES cells against NER-type of damages, which mainly relies on damage detection in the global genome. © 2008 Elsevier B.V. All rights reserved. ∗ Corresponding author. Tel.: +31 10 7043455; fax: +31 10 7044743. E-mail address: g.vanderhorst@erasmusmc.nl (G.T.J. van der Horst). 1 Current address: Laboratory of Clinical Chemistry and Hematology, Jeroen Bosch Hospital, POB 90153, 5200 ME ‘s-Hertogenbosch, The Netherlands. 1568-7864/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.dnarep.2008.06.009