Noncanonical imprinting sustains embryonic development and restrains placental overgrowth.

Genomic imprinting regulates parental origin-dependent monoallelic gene expression. It is mediated by either germline differential methylation of DNA (canonical imprinting) or oocyte-derived H3K27me3 (noncanonical imprinting) in mice. Depletion of Eed, an essential component of Polycomb repressive complex 2, results in genome-wide loss of H3K27me3 in oocytes, which causes loss of noncanonical imprinting (LOI) in embryos. Although Eed maternal KO (matKO) embryos show partial lethality after implantation, it is unknown whether LOI itself contributes to the developmental phenotypes of these embryos, which makes it unclear whether noncanonical imprinting is developmentally relevant. Here, by combinatorial matKO of Xist, a noncanonical imprinted gene whose LOI causes aberrant transient maternal X-chromosome inactivation (XCI) at preimplantation, we show that prevention of the transient maternal XCI greatly restores the development of Eed matKO embryos. Moreover, we found that the placentae of Eed matKO embryos are remarkably enlarged in a manner independent of Xist LOI. Heterozygous deletion screening of individual autosomal noncanonical imprinted genes suggests that LOI of the Sfmbt2 miRNA cluster chromosome 2 miRNA cluster (C2MC), solute carrier family 38 member 4 (Slc38a4), and Gm32885 contributes to the placental enlargement. Taken together, our study provides evidence that Xist imprinting sustains embryonic development and that autosomal noncanonical imprinting restrains placental overgrowth.

APOBEC3B expression is promoted by lincNMR collaborating with TGF-ß-Smad pathway.

Long non-coding RNAs (lncRNAs) participate in carcinogenesis and cancer malignancies. Transforming growth factor-ß (TGF-ß) is involved in various cellular processes including cancer progression. We performed comprehensive RNA sequencing analyses to identify lncRNAs regulated by TGF-ß and found that lincNMR (long intergenic noncoding RNA-nucleotide metabolism regulator, also identified as MAP3K9-DT) was induced by TGF-ß in various cell lines. There are several variants of lincNMR (hereafter lincNMRs) in the lincNMR/MAP3K9-DT locus, and their expression was increased by TGF-ß. TGF-ß-mediated induction of lincNMRs was decreased by depletion of Smad2/3 in Huh7, suggesting that the TGF-ß-Smad pathway is involved in lincNMRs expression. We also found that APOBEC3B but not other APOBEC family members were a target gene of lincNMRs. APOBEC3B, a cytidine deaminase, promotes C to U mutation and highly expressed in various human cancers. Although it is associated with cancer progression, regulatory mechanisms of APOBEC3B expression have not been fully elucidated. We performed RNA immunoprecipitation assays and proved that lincNMRs bound to endogenous Smad2 in Huh7 cells. The increased activity of the promoter of APOBEC3B induced by overexpression of Smad2/3 was inhibited by depletion of lincNMRs. These data suggest that lincNMRs participate in APOBEC3B expression by collaborating with TGF-ß-Smad pathway. High expression of lincNMRs was positively correlated with high expression of APOBEC3B in various cancer cell lines. Overexpression of APOBEC3B as well as lincNMR was found in human cancers such as hepatic and lung cancers and was associated with their poor prognosis, suggesting that lincNMR may contribute to tumor malignancy via enhanced expression of APOBEC3B.

Homologous recombination is reduced in female embryonic stem cells by two active X chromosomes.

The reactivation of X-linked genes is observed in some primary breast tumors. Two active X chromosomes are also observed in female embryonic stem cells (ESCs), but whether double doses of X-linked genes affect DNA repair efficiency remains unclear. Here, we establish isogenic female/male ESCs and show that the female ESCs are more sensitive to camptothecin and have lower gene targeting efficiency than male ESCs, suggesting that homologous recombination (HR) efficiency is reduced in female ESCs. We also generate Xist-inducible female ESCs and show that the lower HR efficiency is restored when X chromosome inactivation is induced. Finally, we assess the X-linked genes with a role in DNA repair and find that Brcc3 is one of the genes involved in a network promoting proper HR. Our findings link the double doses of X-linked genes with lower DNA repair activity, and this may have relevance for common diseases in female patients, such as breast cancer.

Expression of Tumor Suppressor FHIT Is Regulated by the LINC00173-SNAIL Axis in Human Lung Adenocarcinoma.

Long non-coding RNAs (lncRNAs) play a critical role in a variety of human diseases such as cancer. Here, to elucidate a novel function of a lncRNA called LINC00173, we investigated its binding partner, target gene, and its regulatory mechanism in lung adenocarcinoma, including the A549 cell line and patients. In the A549 cell line, RNA immunoprecipitation (RIP) assays revealed that LINC00173 efficiently binds to SNAIL. RNA-seq and RT-qPCR analyses revealed that the expression of FHIT was decreased upon LINC00173 depletion, indicating that FHIT is a target gene of LINC00173. Overexpression of SNAIL suppressed and depletion of SNAIL increased the expression of FHIT, indicating that SNAIL negatively regulates FHIT. The downregulation of FHIT expression upon LINC00173 depletion was restored by additional SNAIL depletion, revealing a LINC00173-SNAIL-FHIT axis for FHIT regulation. Data from 501 patients with lung adenocarcinoma also support the existence of a LINC00173-SNAIL-FHIT axis, as FHIT expression correlated positively with LINC00173 (p = 1.75 × 10-6) and negatively with SNAIL (p = 7.00 × 10-5). Taken together, we propose that LINC00173 positively regulates FHIT gene expression by binding to SNAIL and inhibiting its function in human lung adenocarcinoma. Thus, this study sheds light on the LINC00173-SNAIL-FHIT axis, which may be a key mechanism for carcinogenesis and progression in human lung adenocarcinoma.

Lineage-specific function of the noncoding Tsix RNA for Xist repression and Xi reactivation in mice.

The noncoding Tsix RNA is an antisense repressor of Xist and regulates X inactivation in mice. Tsix is essential for preventing the inactivation of the maternally inherited X chromosome in extraembryonic lineages where imprinted X-chromosome inactivation (XCI) occurs. Here we establish an inducible Tsix expression system for investigating Tsix function in development. We show that Tsix has a clear functional window in extraembryonic development. Within this window, Tsix can repress Xist, which is accompanied by DNA methylation of the Xist promoter. As a consequence of Xist repression, reactivation of the inactive X chromosome (Xi) is widely observed. In the parietal endoderm, Tsix represses Xist and causes reactivation of an Xi-linked GFP transgene throughout development, whereas Tsix progressively loses its Xist-repressing function from embryonic day 9.5 (E9.5) onward in trophoblast giant cells and spongiotrophoblast, suggesting that Tsix function depends on a lineage-specific environment. Our data also demonstrate that the maintenance of imprinted XCI requires Xist expression in specific extraembryonic tissues throughout development. This finding shows that reversible XCI is not exclusive to pluripotent cells, and that in some lineages cell differentiation is not accompanied by a stabilization of the Xi.

Inhibiting Skp2 E3 Ligase Suppresses Bleomycin-Induced Pulmonary Fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a progressive disease with poor prognosis and no curative therapies. SCF-Skp2 E3 ligase is a target for cancer therapy, but there have been no reports about Skp2 as a target for IPF. Here we demonstrate that Skp2 is a promising therapeutic target for IPF. We examined whether disrupting Skp2 suppressed pulmonary fibrosis in a bleomycin (BLM)-induced mouse model and found that pulmonary fibrosis was significantly suppressed in Skp2-deficient mice compared with controls. The pulmonary accumulation of fibrotic markers such as collagen type 1 and fibronectin in BLM-infused mice was decreased in Skp2-deficient mice. Moreover, the number of bronchoalveolar lavage fluid cells accompanied with pulmonary fibrosis was significantly diminished. Levels of the Skp2 target p27 were significantly decreased by BLM-administration in wild-type mice, but recovered in Skp2-/- mice. In vimentin-positive mesenchymal fibroblasts, the decrease of p27-positive cells and increase of Ki67-positive cells by BLM-administration was suppressed by Skp2-deficency. As these results suggested that inhibiting Skp2 might be effective for BLM-induced pulmonary fibrosis, we next performed a treatment experiment using the Skp2 inhibitor SZL-P1-41. As expected, BLM-induced pulmonary fibrosis was significantly inhibited by SZL-P1-41. Moreover, p27 levels were increased by the SZL-P1-41 treatment, suggesting p27 may be an important Skp2 target for BLM-induced pulmonary fibrosis. Our study suggests that Skp2 is a potential molecular target for human pulmonary fibrosis including IPF.

Regulation of GATA-binding protein 2 levels via ubiquitin-dependent degradation by Fbw7: involvement of cyclin B-cyclin-dependent kinase 1-mediated phosphorylation of THR176 in GATA-binding protein 2.

A GATA family transcription factor, GATA-binding protein 2 (GATA2), participates in cell growth and differentiation of various cells, such as hematopoietic stem cells. Although its expression level is controlled by transcriptional induction and proteolytic degradation, the responsible E3 ligase has not been identified. Here, we demonstrate that F-box/WD repeat-containing protein 7 (Fbw7/Fbxw7), a component of Skp1, Cullin 1, F-box-containing complex (SCF)-type E3 ligase, is an E3 ligase for GATA2. GATA2 contains a cell division control protein 4 (Cdc4) phosphodegron (CPD), a consensus motif for ubiquitylation by Fbw7, which includes Thr(176). Ectopic expression of Fbw7 destabilized GATA2 and promoted its proteasomal degradation. Substitution of threonine 176 to alanine in GATA2 inhibited binding with Fbw7, and the ubiquitylation and degradation of GATA2 by Fbw7 was suppressed. The CPD kinase, which mediates the phosphorylation of Thr(176), was cyclin B-cyclin-dependent kinase 1 (CDK1). Moreover, depletion of endogenous Fbw7 stabilized endogenous GATA2 in K562 cells. Conditional Fbw7 depletion in mice increased GATA2 levels in hematopoietic stem cells and myeloid progenitors at the early stage. Increased GATA2 levels in Fbw7-conditional knock-out mice were correlated with a decrease in a c-Kit high expressing population of myeloid progenitor cells. Our results suggest that Fbw7 is a bona fide E3 ubiquitin ligase for GATA2 in vivo.

YB-1 promotes transcription of cyclin D1 in human non-small-cell lung cancers.

Cyclin D1, an oncogenic G1 cyclin, and YB-1, a transcription factor involved in cell growth, are both over-expressed in several human cancers. In human lung cancer, the functional association between YB-1 and cyclin D1 has never been elucidated. In this study, we show YB-1 is involved in the transcription of cyclin D1 in human lung cancer. Depletion of endogenous YB-1 by siRNA inhibited progression of G1 phase and down-regulated both the protein and mRNA levels of cyclin D1 in human lung cancer cells. Forced over-expression of YB-1 with a cyclin D1 reporter plasmid increased luciferase activity, and ChIP assay results showed YB-1 bound to the cyclin D1 promoter. Moreover, the amount of YB-1 mRNA positively correlated with cyclin D1 mRNA levels in clinical non-small-cell lung cancer (NSCLC) specimens. Immunohistochemical analysis also indicated YB-1 expression correlated with cyclin D1 expression in NSCLC specimens. In addition, most of the cases expressing both cyclin D1 and CDC6, another molecule controlled by YB-1, had co-existing YB-1 over-expression. Together, our results suggest that aberrant expression of both cyclin D1 and CDC6 by YB-1 over-expression may collaboratively participate in lung carcinogenesis.

Incomplete X-inactivation initiated by a hypomorphic Xist allele in the mouse.

X chromosome inactivation (X-inactivation) in female mammals is triggered by differential upregulation of the Xist gene on one of the two X chromosomes and subsequent coating of the X in cis with its non-coding transcripts. Although targeted mutation has clearly shown that Xist is essential for X-inactivation in cis, the molecular mechanism by which Xist RNA induces chromosome silencing is largely unknown. Here, we demonstrate that an Xist mutant generated previously in mouse by gene targeting, Xist(IVS), is unique in that it partially retains the capacity to silence the X chromosome. Although Xist(IVS) is differentially upregulated and its mutated transcript coats the X chromosome in cis in embryonic and extra-embryonic tissues, X-inactivation thus initiated does not seem to be fully established. The state of such incomplete inactivation is probably unstable and the mutated X is apparently reactivated in a subset of extra-embryonic tissues and, perhaps, early epiblastic cells. Xist(IVS), which can be referred to as a partial loss-of-function mutation, would provide an opportunity to dissect the molecular mechanism of Xist RNA-mediated chromosome silencing.

Reactivation of the inactive X chromosome in development and reprogramming.

In mammals, one of the two X chromosomes of female cells is inactivated for dosage compensation between the sexes. X chromosome inactivation is initiated in early embryos by the noncoding Xist RNA. Subsequent chromatin modifications on the inactive X chromosome (Xi) lead to a remarkable stability of gene repression in somatic cell lineages. In mice, reactivation of genes on the Xi accompanies the establishment of pluripotent cells of the female blastocyst and the development of primordial germ cells. Xi reactivation also occurs when pluripotency is established during the reprogramming of somatic cells to induced pluripotent stem cells. The mechanism of Xi reactivation has attracted increasing interest for studying changes in epigenetic patterns and for improving methods of cell reprogramming. Here, we review recent advances in the understanding of Xi reactivation during development and reprogramming and illustrate potential clinical applications.

Cell cycle regulation by long non-coding RNAs.

The mammalian cell cycle is precisely controlled by cyclin-dependent kinases (CDKs) and related pathways such as the RB and p53 pathways. Recent research on long non-coding RNAs (lncRNAs) indicates that many lncRNAs are involved in the regulation of critical cell cycle regulators such as the cyclins, CDKs, CDK inhibitors, pRB, and p53. These lncRNAs act as epigenetic regulators, transcription factor regulators, post-transcription regulators, and protein scaffolds. These cell cycle-regulated lncRNAs mainly control cellular levels of cell cycle regulators via various mechanisms, and may provide diversity and reliability to the general cell cycle. Interestingly, several lncRNAs are induced by DNA damage and participate in cell cycle arrest or induction of apoptosis as DNA damage responses. Therefore, deregulations of these cell cycle regulatory lncRNAs may be involved in tumorigenesis, and they are novel candidate molecular targets for cancer therapy and diagnosis.

p130RB2 positively contributes to ATR activation in response to replication stress via the RPA32-ETAA1 axis.

Ataxia-telangiectasia mutated and Rad3-related (ATR) kinase is a crucial regulator of the cell cycle checkpoint and activated in response to DNA replication stress by two independent pathways via RPA32-ETAA1 and TopBP1. However, the precise activation mechanism of ATR by the RPA32-ETAA1 pathway remains unclear. Here, we show that p130RB2, a member of the retinoblastoma protein family, participates in the pathway under hydroxyurea-induced DNA replication stress. p130RB2 binds to ETAA1, but not TopBP1, and depletion of p130RB2 inhibits the RPA32-ETAA1 interaction under replication stress. Moreover, p130RB2 depletion reduces ATR activation accompanied by phosphorylation of its targets RPA32, Chk1, and ATR itself. It also causes improper re-progression of S phase with retaining single-stranded DNA after cancelation of the stress, which leads to an increase in the anaphase bridge phenotype and a decrease in cell survival. Importantly, restoration of p130RB2 rescued the disrupted phenotypes of p130RB2 knockdown cells. These results suggest positive involvement of p130RB2 in the RPA32-ETAA1-ATR axis and proper re-progression of the cell cycle to maintain genome integrity.

CCIVR2 facilitates comprehensive identification of both overlapping and non-overlapping antisense transcripts within specified regions.

Pairs of sense and antisense transcriptions that are adjacent at their 5' and 3' regions are called divergent and convergent transcription, respectively. However, the structural properties of divergent/convergent transcription in different species or RNA biotypes are poorly characterized. Here, we developed CCIVR2, a program that facilitates identification of both overlapping and non-overlapping antisense transcripts produced from divergent/convergent transcription whose transcription start sites (TSS) or transcript end sites (TES) are located within a specified region. We used CCIVR2 to analyze antisense transcripts starting around the sense TSS (from divergent transcription) or ending around the sense TES (from convergent transcription) in 11 different species and found species- and RNA biotype-specific features of divergent/convergent transcription. Furthermore, we confirmed that CCIVR2 enables the identification of multiple sense/antisense transcript pairs from divergent transcription, including those with known functions in processes such as embryonic stem cell differentiation and TGFß stimulation. CCIVR2 is therefore a valuable bioinformatics tool that facilitates the characterization of divergent/convergent transcription in different species and aids the identification of functional sense/antisense transcript pairs from divergent transcription in specified biological processes.

CCIVR facilitates comprehensive identification of cis-natural antisense transcripts with their structural characteristics and expression profiles.

Cis-natural antisense transcripts (cis-NATs) are transcribed from the same genomic locus as their partner gene but from the opposite DNA strand and overlap with the partner gene transcript. Here, we developed a simple and convenient program termed CCIVR (comprehensive cis-NATs identifier via RNA-seq data) that comprehensively identifies all kinds of cis-NATs based on genome annotation with expression data obtained from RNA-seq. Using CCIVR with genome databases, we demonstrated total cis-NAT pairs from 11 model organisms. CCIVR analysis with RNA-seq data from parthenogenetic and androgenetic embryonic stem cells identified well-known imprinted cis-NAT pair, KCNQ1/KCNQ1OT1, ensuring the availability of CCIVR. Finally, CCIVR identified cis-NAT pairs that demonstrate inversely correlated expression upon TGFß stimulation including cis-NATs that functionally repress their partner genes by introducing epigenetic alteration in the promoters of partner genes. Thus, CCIVR facilitates the investigation of structural characteristics and functions of cis-NATs in numerous processes in various species.

Chromatin-remodeling factor BAZ1A/ACF1 targets UV damage sites in an MLL1-dependent manner to facilitate nucleotide excision repair.

Ultraviolet (UV) light irradiation generates pyrimidine dimers on DNA, such as cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts. Such dimers distort the high-order DNA structure and prevent transcription and replication. The nucleotide excision repair (NER) system contributes to resolving this type of DNA lesion. There are two pathways that recognize pyrimidine dimers. One acts on transcribed strands of DNA (transcription-coupled NER), and the other acts on the whole genome (global genome-NER; GG-NER). In the latter case, DNA damage-binding protein 2 (DDB2) senses pyrimidine dimers with several histone modification enzymes. We previously reported that histone acetyltransferase binding to ORC1 (HBO1) interacts with DDB2 and facilitates recruitment of the imitation switch chromatin remodeler at UV-irradiated sites via an unknown methyltransferase. Here, we found that the phosphorylated histone methyltransferase mixed lineage leukemia 1 (MLL1) was maintained at UV-irradiated sites in an HBO1-dependent manner. Furthermore, MLL1 catalyzed histone H3K4 methylation and recruited the chromatin remodeler bromodomain adjacent to zinc finger domain 1A (BAZ1A)/ATP-utilizing chromatin assembly and remodeling factor 1 (ACF1). Depletion of MLL1 suppressed BAZ1A accumulation at UV-irradiated sites and inhibited the removal of CPDs. These data indicate that the DDB2-HBO1-MLL1 axis is essential for the recruitment of BAZ1A to facilitate GG-NER.

Dynamics of transcription-mediated conversion from euchromatin to facultative heterochromatin at the Xist promoter by Tsix.

The fine-scale dynamics from euchromatin (EC) to facultative heterochromatin (fHC) has remained largely unclear. Here, we focus on Xist and its silencing initiator Tsix as a paradigm of transcription-mediated conversion from EC to fHC. In mouse epiblast stem cells, induction of Tsix recapitulates the conversion at the Xist promoter. Investigating the dynamics reveals that the conversion proceeds in a stepwise manner. Initially, a transient opened chromatin structure is observed. In the second step, gene silencing is initiated and dependent on Tsix, which is reversible and accompanied by simultaneous changes in multiple histone modifications. At the last step, maintenance of silencing becomes independent of Tsix and irreversible, which correlates with occupation of the -1 position of the transcription start site by a nucleosome and initiation of DNA methylation introduction. This study highlights the hierarchy of multiple chromatin events upon stepwise gene silencing establishment.

HDAC3 Is Required for XPC Recruitment and Nucleotide Excision Repair of DNA Damage Induced by UV Irradiation.

Recent studies have demonstrated that lysine acetylation of histones is crucial for nucleotide excision repair (NER) by relaxing the chromatin structure, which facilitates the recruitment of repair factors. However, few studies have focused on the contribution of histone deacetylases (HDAC) to NER. Here, we found that histone H3 Lys14 (H3K14) was deacetylated by HDAC3 after UV irradiation. Depletion of HDAC3 caused defects in cyclobutene pyrimidine dimer excision and sensitized cells to UV irradiation. HDAC3-depleted cells had impaired unscheduled DNA synthesis, but not recovery of RNA synthesis, which indicates that HDAC3 was required for global genome NER. Moreover, xeroderma pigmentosum, complementation group C (XPC) accumulation at the local UV-irradiated area was attenuated in HDAC3-depleted cells. In addition to the delay of XPC accumulation at DNA damage sites, XPC ubiquitylation was inhibited in HDAC3-depleted cells. These results suggest that the deacetylation of histone H3K14 by HDAC3 after UV irradiation contributes to XPC recruitment to DNA lesions to promote global genome NER. IMPLICATIONS: Involvement of histone deacetylation for XPC accumulation after UV irradiation indicates conversion of chromatin structure is essential for nucleotide excision repair in human cancer cells.

Substitution of Thr572 to Ala in mouse c-Myb attenuates progression of early erythroid differentiation.

The expression level of transcription factor c-Myb oscillates during hematopoiesis. Fbw7 promotes ubiquitin-mediated degradation of c-Myb, which is dependent on phosphorylation of Thr572. To investigate the physiological relevance of Fbw7-mediated c-Myb degradation, we generated mutant mice carrying c-Myb-T572A (TA). Homozygous mutant (TA/TA) mice exhibited a reduction in the number of peripheral red blood cells and diminished erythroblasts in bone marrow, presumably as a result of failure during erythroblast differentiation. We found that c-Myb high-expressing cells converged in the Lin-CD71+ fraction, and the expression of c-Myb was higher in TA/TA mice than in wild-type mice. Moreover, TA/TA mice had an increased proportion of the CD71+ subset in Lin- cells. The c-Myb level in the Lin-CD71+ subset showed three peaks, and the individual c-Myb level was positively correlated with that of c-Kit, a marker of undifferentiated cells. Ultimately, the proportion of c-Mybhi subgroup was significantly increased in TA/TA mice compared with wild-type mice. These results indicate that a delay in reduction of c-Myb protein during an early stage of erythroid differentiation creates its obstacle in TA/TA mice. In this study, we showed the T572-dependent downregulation of c-Myb protein is required for proper differentiation in early-stage erythroblasts, suggesting the in vivo significance of Fbw7-mediated c-Myb degradation.

Long Noncoding RNA ELIT-1 Acts as a Smad3 Cofactor to Facilitate TGFß/Smad Signaling and Promote Epithelial-Mesenchymal Transition.

TGFß is involved in various biological processes, including development, differentiation, growth regulation, and epithelial-mesenchymal transition (EMT). In TGFß/Smad signaling, receptor-activated Smad complexes activate or repress their target gene promoters. Smad cofactors are a group of Smad-binding proteins that promote recruitment of Smad complexes to these promoters. Long noncoding RNAs (lncRNA), which behave as Smad cofactors, have thus far not been identified. Here, we characterize a novel lncRNA EMT-associated lncRNA induced by TGFß1 (ELIT-1). ELIT-1 was induced by TGFß stimulation via the TGFß/Smad pathway in TGFß-responsive cell lines. ELIT-1 depletion abrogated TGFß-mediated EMT progression and expression of TGFß target genes including Snail, a transcription factor critical for EMT. A positive correlation between high expression of ELIT-1 and poor prognosis in patients with lung adenocarcinoma and gastric cancer suggests that ELIT-1 may be useful as a prognostic and therapeutic target. RIP assays revealed that ELIT-1 bound to Smad3, but not Smad2. In conjunction with Smad3, ELIT-1 enhanced Smad-responsive promoter activities by recruiting Smad3 to the promoters of its target genes including Snail, other TGFß target genes, and ELIT-1 itself. Collectively, these data show that ELIT-1 is a novel trans-acting lncRNA that forms a positive feedback loop to enhance TGFß/Smad3 signaling and promote EMT progression. SIGNIFICANCE: This study identifies a novel lncRNA ELIT-1 and characterizes its role as a positive regulator of TGFß/Smad3 signaling and EMT.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/11/2821/F1.large.jpg.

Author Correction: Phosphorylated HBO1 at UV irradiated sites is essential for nucleotide excision repair.

This corrects the article DOI: 10.1038/ncomms16102.