Regulates Nucleotide Excision Repair Research Articles

Effect of ERCC1 polymorphisms on the response to platinum-based chemotherapy: A systematic review and meta-analysis based on Asian population.

Platinum-based chemotherapy is one of the most common treatments for many cancers; however, the effect of chemotherapy varies from individual to individual. Excision repair cross complementation group 1 (ERCC1) is widely recognized as a key gene regulating nucleotide excision repair (NER) and is closely associated with platinum response. Many studies have yielded conflicting results regarding whether ERCC1 polymorphisms can affect the response to platinum and overall survival (OS). Therefore, it is necessary to perform a meta-analysis of patients with specific races and cancer types. Eight databases (EMBASE, PubMed, Cochrane Library, Chinese National Knowledge Infrastructure, Scopus, VIP, China Biology Medicine disc and Wanfang databases) were searched. Results were expressed in terms of odds ratios (ORs), hazard ratios (HRs) and 95% CIs. In this study, rs11615, rs2298881 and rs3212986 SNPs were studied. In the comparison between CT and TT on the response to platinum, esophageal cancer [I2 = 0%, OR = 6.18, 95% CI(1.89,20.23), P = 0.003] and ovarian cancer [I2 = 0%, OR = 4.94, 95% CI(2.21,11.04), P<0.001] showed that the rs11615 CT genotype predicted a better response. In the comparison between CC and TT, ovarian cancer [I2 = 48.0%, OR = 6.15, 95% CI (2.56,14.29), P<0.001] indicated that the CC genotype predicted a better response. In the meta-analysis of OS, the CC genotype was related to longer OS than TT in ovarian cancer [TT vs CC: I2 = 57.7%, HR = 1.71, 95% CI (1.18, 2.49), P<0.001]. The ERCC1 rs11615 polymorphism was related to the response to platinum and OS, but the correlation is based on specific cancer types in the Asian population.

Metformin Sensitizes Cisplatin-induced Apoptosis Through Regulating Nucleotide Excision Repair Pathway In Cisplatin-resistant Human Lung Cancer Cells

Background: Lung cancer is a leading cause of cancer death globally. Platinum-based chemotherapeutic medications are essential for treating advanced NSCLC, despite that drug resistance severely limits its effectiveness. Objective: In this study, we investigated the cytotoxic effect of metformin on cisplatin-resistant NSCLC cells (A549/DDP) and its potential mechanisms. Methods: Anti-lung cancer efficacy of metformin, cisplatin, and metformin combined with cisplatin was examined in A549 and A549/DDP cells. The cell counting kit-8 (CCK-8) assay was applied for measuring cell proliferation. CalcuSyn software was used to calculate the combination index and estimate the synergistic effect of metformin and cisplatin on cell proliferation. The cell apoptosis was analyzed by flow cytometry and the expression of apoptosis-related proteins, Bcl-2, Bax and caspase-3 were analyzed using Western blot. Futhermore, the expression of key nucleotide excision repair (NER) proteins, ERCC1, XPF, and XPA, was also analyzed using Western blot. Results: We found that metformin had dose-dependent antiproliferative effects on A549/DDP and A549 cells. The combination of metformin and cisplatin had higher effectiveness in inhibiting A549/DDP and A549 cell growth than either of the two drugs alone. Flow cytometry analysis indicated that the combined treatment could cause more cell apoptosis than the single-drug treatment. Consistently, the combined treatment decreased the expression of Bcl-2 protein and elevated the expression of Bax, and cleaved caspase-3 proteins. The expression level of ERCC1, XPF, and XPA proteins were lower in the combined treatment than in either of metformin and cisplatin treatment alone. Conclusions: Our study suggested that metformin and cisplatin had synergistic antitumorigenic effects in A549/DDP cells. The combination of cisplatin and metformin could be promising drug candidates to sensitize cisplatin-induced apoptosis through regulating nucleotide excision repair pathways in lung cancer.

Abstract 3747: RPS3 positively regulates nucleotide excision repair with respect to XP-D and skin cancers

Abstract Ribosomal protein S3 (rpS3) is a multifunctional protein working in translation, DNA repair, cancer, apoptosis etc. UV induced DNA damage is repaired by the nucleotide excision repair (NER) pathways; defects in these pathways lead to a genetic instability known as xeroderma pigmentosum (XP) eventually developing skin cancers. We discovered that rpS3 associates with transcription factor IIH (TFIIH) via an interaction with the xeroderma pigmentosum complementation group D (XPD) protein and complements its function in the NER pathway. Here, we showed that XP-D cells overexpressing rpS3 showed markedly increased resistance to UV through XPD and rpS3 interaction thus augmenting the helicase activity of XPD protein. Additionally, the knockdown of rpS3 caused reduced NER efficiency and the subsequent addition of rpS3 restored the helicase activity of the TFIIH complex in cells. We present data suggesting that rpS3 is involved in post-excision processing in NER, assisting TFIIH in expediting the repair process by increasing its turnover rate when DNA is damaged. We also propose that rpS3 is a novel accessory protein of the NER pathway and its recruitment to the repair machinery upon UV damage augments repair efficiency by enhancing XPD helicase function and increasing its turnover rate, thus facilitating DNA repair. In addition to this, manipulations of rpS3 gene could complement XP-D phenotype and prevent UV damage and skin cancer occurrence. Animal studies strongly indicate that these result could be applied not only for the development of cancer drugs but also for cosmeceuticals. [1] FASEB J. (2020) 34: 8102 [2] Cell &amp; Mol Life Sci (2021) 78: 3591 Citation Format: Joon Kim, Yong-Joon Park, Tae Sung Kim, Woo Sung Ahn, Hag Dong Kim. RPS3 positively regulates nucleotide excision repair with respect to XP-D and skin cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3747.

Histone deacetylation regulates nucleotide excision repair through an interaction with the XPC protein

SummaryThe XPC protein complex plays a central role in DNA lesion recognition for global genome nucleotide excision repair (GG-NER). Lesion recognition can be accomplished in either a UV-DDB-dependent or -independent manner; however, it is unclear how these sub-pathways are regulated in chromatin. Here, we show that histone deacetylases 1 and 2 facilitate UV-DDB-independent recruitment of XPC to DNA damage by inducing histone deacetylation. XPC localizes to hypoacetylated chromatin domains in a DNA damage-independent manner, mediated by its structurally disordered middle (M) region. The M region interacts directly with the N-terminal tail of histone H3, an interaction compromised by H3 acetylation. Although the M region is dispensable for in vitro NER, it promotes DNA damage removal by GG-NER in vivo, particularly in the absence of UV-DDB. We propose that histone deacetylation around DNA damage facilitates the recruitment of XPC through the M region, contributing to efficient lesion recognition and initiation of GG-NER.

Timely upstream events regulating nucleotide excision repair by ubiquitin-proteasome system: ubiquitin guides the way

The ubiquitin–proteasome system (UPS) plays crucial roles in regulation of multiple DNA repair pathways, including nucleotide excision repair (NER), which eliminates a broad variety of helix-distorting DNA lesions that can otherwise cause deleterious mutations and genomic instability. In mammalian NER, DNA damage sensors, DDB and XPC acting in global genomic NER (GG-NER), and, CSB and RNAPII acting in transcription-coupled NER (TC-NER) sub-pathways, undergo an array of post-translational ubiquitination at the DNA lesion sites. Accumulating evidence indicates that ubiquitination orchestrates the productive assembly of NER preincision complex by driving well-timed compositional changes in DNA damage-assembled sensor complexes. Conversely, the deubiquitination is also intimately involved in regulating the damage sensing aftermath, via removal of degradative ubiquitin modification on XPC and CSB to prevent their proteolysis for the factor recycling. This review summaries the relevant research efforts and latest findings in our understanding of ubiquitin-mediated regulation of NER and active participation by new regulators of NER, e.g., Cullin-Ring ubiquitin ligases (CRLs), ubiquitin-specific proteases (USPs) and ubiquitin-dependent segregase, valosin-containing protein (VCP)/p97. We project hypothetical step-by-step models in which VCP/p97-mediated timely extraction of damage sensors is integral to overall productive NER. The USPs and proteasome subtly counteract in fine-tuning the vital stability and function of NER damage sensors.

Ribosomal protein S3 associates with the TFIIH complex and positively regulates nucleotide excision repair.

In mammalian cells, the bulky DNA adducts caused by ultraviolet radiation are mainly repaired via the nucleotide excision repair (NER) pathway; some defects in this pathway lead to a genetic disorder known as xeroderma pigmentosum (XP). Ribosomal protein S3 (rpS3), a constituent of the 40S ribosomal subunit, is a multi-functional protein with various extra-ribosomal functions, including a role in the cellular stress response and DNA repair-related activities. We report that rpS3 associates with transcription factor IIH (TFIIH) via an interaction with the xeroderma pigmentosum complementation group D (XPD) protein and complements its function in the NER pathway. For optimal repair of UV-induced duplex DNA lesions, the strong helicase activity of the TFIIH complex is required for unwinding damaged DNA around the lesion. Here, we show that XP-D cells overexpressing rpS3 showed markedly increased resistance to UV radiation through XPD and rpS3 interaction. Additionally, the knockdown of rpS3 caused reduced NER efficiency in HeLa cells and the overexpression of rpS3 partially restored helicase activity of the TFIIH complex of XP-D cells in vitro. We also present data suggesting that rpS3 is involved in post-excision processing in NER, assisting TFIIH in expediting the repair process by increasing its turnover rate when DNA is damaged. We propose that rpS3 is an accessory protein of the NER pathway and its recruitment to the repair machinery augments repair efficiency upon UV damage by enhancing XPD helicase function and increasing its turnover rate.

EIF3a Regulation of NHEJ Repair Protein Synthesis and Cellular Response to Ionizing Radiation.

Translation initiation in protein synthesis regulated by eukaryotic initiation factors (eIFs) is a crucial step in controlling gene expression. eIF3a has been shown to regulate protein synthesis and cellular response to treatments by anticancer agents including cisplatin by regulating nucleotide excision repair. In this study, we tested the hypothesis that eIF3a regulates the synthesis of proteins important for the repair of double-strand DNA breaks induced by ionizing radiation (IR). We found that eIF3a upregulation sensitized cellular response to IR while its downregulation caused resistance to IR. eIF3a increases IR-induced DNA damages and decreases non-homologous end joining (NHEJ) activity by suppressing the synthesis of NHEJ repair proteins. Furthermore, analysis of existing patient database shows that eIF3a expression associates with better overall survival of breast, gastric, lung, and ovarian cancer patients. These findings together suggest that eIF3a plays an important role in cellular response to DNA-damaging treatments by regulating the synthesis of DNA repair proteins and, thus, eIIF3a likely contributes to the outcome of cancer patients treated with DNA-damaging strategies including IR.

The deacetylase SIRT6 promotes the repair of UV-induced DNA damage by targeting DDB2.

The NAD+-dependent deacetylase and mono-ADP-ribosyl transferase SIRT6 stabilizes the genome by promoting DNA double strand break repair, thereby acting as a tumor suppressor. However, whether SIRT6 regulates nucleotide excision repair (NER) remains unknown. Here, we showed that SIRT6 was recruited to sites of UV-induced DNA damage and stimulated the repair of UV-induced DNA damage. Mechanistic studies further indicated that SIRT6 interacted with DDB2, the major sensor initiating global genome NER (GG-NER), and that the interaction was enhanced upon UV irradiation. SIRT6 deacetylated DDB2 at two lysine residues, K35 and K77, upon UV stress and then promoted DDB2 ubiquitination and segregation from chromatin, thereby facilitating downstream signaling. In addition, we characterized several SIRT6 mutations derived from melanoma patients. These SIRT6 mutants ablated the stimulatory effect of SIRT6 on NER and destabilized the genome due to (i) partial loss of enzymatic activity (P27S or H50Y), (ii) a nonsense mutation (R150*) or (iii) high turnover rates (G134W). Overall, we demonstrate that SIRT6 promotes NER by deacetylating DDB2, thereby preventing the onset of melanomagenesis.

Downregulation of RIF1 Enhances Sensitivity to Platinum-Based Chemotherapy in Epithelial Ovarian Cancer (EOC) by Regulating Nucleotide Excision Repair (NER) Pathway

Background/Aims: Rap1 interacting factor 1 (RIF1) was deemed to be involved in replication timing regulation and DNA damage response. However, little is known about the role of RIF1 in malignancies. Thus, this study aimed to investigate whether the expression of RIF1 is relevant to the response of epithelial ovarian cancer (EOC) patients to cisplatin chemotherapy and its underlying mechanism. Methods: Immunohistochemistry was used for detecting the expression of RIF1 in 72 human ovarian cancer tissues followed by association analysis of RIF1 expression with patients’ responses to platinum-based chemotherapy. The survival analysis of ovarian patients based on platinum chemotherapy was analyzed using online databases. RNA interference of RIF1 was carried out in OVCAR3 and A2780 cell lines, to determine the effect of lacking RIF1 expression on cellular responses to cisplatin by using MTS assay. The nucleotide excision repair (NER) capacity of these cells was assessed by using host-cell reactivation and UV sensitivity assay. Western Blot analysis was carried out to determine the effect of RIF1 on the proteins of NER and apoptosis signaling pathway by using RIF1 knockdown cells. BALB/c nude mice model was used for detection of response to cisplatin in vivo. Results: RIF1 expression was significantly associated with the response of ovarian patients to platinum-based chemotherapy (P< 0.01). In cohorts from online databases, high expression of RIF1 was associated with higher mortality of EOC patients based on platinum chemotherapy (P < 0.01). RIF1 knockdown increased sensitivity to cisplatin in EOC in vitro and in vivo. Deletion of RIF1 impaired the NER activity by inhibiting the NER proteins in ovarian cancer cells. Besides, knockdown of RIF1 enhanced cisplatin-induced apoptosis. Conclusions: RIF1 plays an important role in regulating the expression of NER proteins, which in turn contributes to cellular response to cisplatin and EOC patients’ response to platinum-based chemotherapy. RIF1 knockdown also promotes cisplatin-induced apoptosis. RIF1 may serve as a novel biomarker for predicting platinum-based chemosensitivity and the prognosis of EOC patients.

UV radiation-induced SUMOylation of DDB2 regulates nucleotide excision repair.

Subunit 2 of DNA damage-binding protein complex (DDB2) is an early sensor of nucleotide excision repair (NER) pathway for eliminating DNA damage induced by UV radiation (UVR) and cisplatin treatments of mammalian cells. DDB2 is modified by ubiquitin and poly(ADP-ribose) (PAR) in response to UVR, and these modifications play a crucial role in regulating NER. Here, using immuno-analysis of irradiated cell extracts, we have identified multiple post-irradiation modifications of DDB2 protein. Interestingly, although the DNA lesions induced by both UVR and cisplatin are corrected by NER, only the UV irradiation, but not the cisplatin treatment, induces any discernable DDB2 modifications. We, for the first time, show that the appearance of UVR-induced DDB2 modifications depend on the binding of DDB2 to the damaged chromatin and the participation of functionally active 26S proteasome. The in vitro and in vivo analysis revealed that SUMO-1 conjugations comprise a significant portion of these UVR-induced DDB2 modifications. Mapping of SUMO-modified sites demonstrated that UVR-induced SUMOylation occurs on Lys-309 residue of DDB2 protein. Mutation of Lys-309 to Arg-309 diminished the DDB2 SUMOylation observable both in vitro and in vivo. Moreover, K309R mutated DDB2 lost its function of recruiting XPC to the DNA damage sites, as well as the ability to repair cyclobutane pyrimidine dimers following cellular UV irradiation. Taken together, our results indicate that DDB2 is modified by SUMOylation upon UV irradiation, and this post-translational modification plays an important role in the initial recognition and processing of UVR-induced DNA damage occurring within the context of chromatin.

Autophagy positively regulates DNA damage recognition by nucleotide excision repair

ABSTRACTMacroautophagy (hereafter autophagy) is a cellular catabolic process that is essential for maintaining tissue homeostasis and regulating various normal and pathologic processes in human diseases including cancer. One cancer-driving process is accumulation of genetic mutations due to impaired DNA damage repair, including nucleotide excision repair. Here we show that autophagy positively regulates nucleotide excision repair through enhancing DNA damage recognition by the DNA damage sensor proteins XPC and DDB2 via 2 pathways. First, autophagy deficiency downregulates the transcription of XPC through TWIST1-dependent activation of the transcription repressor complex E2F4-RBL2. Second, autophagy deficiency impairs the recruitment of DDB2 to ultraviolet radiation (UV)-induced DNA damage sites through TWIST1-mediated inhibition of EP300. In mice, the pharmacological autophagy inhibitor Spautin-1 promotes UVB-induced tumorigenesis, whereas the autophagy inducer rapamycin reduces UVB-induced tumorigenesis. These findings demonstrate the crucial role of autophagy in maintaining proper nucleotide excision repair in mammalian cells and suggest a previously unrecognized tumor-suppressive mechanism of autophagy in cancer.

Mitotic regulator Nlp interacts with XPA/ERCC1 complexes and regulates nucleotide excision repair (NER) in response to UV radiation

Cellular response to DNA damage, including ionizing radiation (IR) and UV radiation, is critical for the maintenance of genomic fidelity. Defects of DNA repair often result in genomic instability and malignant cell transformation. Centrosomal protein Nlp (ninein-like protein) has been characterized as an important cell cycle regulator that is required for proper mitotic progression. In this study, we demonstrate that Nlp is able to improve nucleotide excision repair (NER) activity and protects cells against UV radiation. Upon exposure of cells to UVC, Nlp is translocated into the nucleus. The C-terminus (1030–1382) of Nlp is necessary and sufficient for its nuclear import. Upon UVC radiation, Nlp interacts with XPA and ERCC1, and enhances their association. Interestingly, down-regulated expression of Nlp is found to be associated with human skin cancers, indicating that dysregulated Nlp might be related to the development of human skin cancers. Taken together, this study identifies mitotic protein Nlp as a new and important member of NER pathway and thus provides novel insights into understanding of regulatory machinery involved in NER.

Molecular regulation of UV-induced DNA repair.

Ultraviolet (UV) radiation from sunlight is a major etiologic factor for skin cancer, the most prevalent cancer in the United States, as well as premature skin aging. In particular, UVB radiation causes formation of specific DNA damage photoproducts between pyrimidine bases. These DNA damage photoproducts are repaired by a process called nucleotide excision repair, also known as UV-induced DNA repair. When left unrepaired, UVB-induced DNA damage leads to accumulation of mutations, predisposing people to carcinogenesis as well as to premature aging. Genetic loss of nucleotide excision repair leads to severe disorders, namely, xeroderma pigmentosum (XP), trichothiodystrophy (TTD) and Cockayne syndrome (CS), which are associated with predisposition to skin carcinogenesis at a young age as well as developmental and neurological conditions. Regulation of nucleotide excision repair is an attractive avenue to preventing or reversing these detrimental consequences of impaired nucleotide excision repair. Here, we review recent studies on molecular mechanisms regulating nucleotide excision repair by extracellular cues and intracellular signaling pathways, with a special focus on the molecular regulation of individual repair factors.

Inositol hexakisphosphate kinase-1 mediates assembly/disassembly of the CRL4-signalosome complex to regulate DNA repair and cell death.

Inositol polyphosphates containing an energetic pyrophosphate bond are formed primarily by a family of three inositol hexakisphosphate (IP6) kinases (IP6K1-3). The Cullin-RING ubiquitin ligases (CRLs) regulate diverse biological processes through substrate ubiquitylation. CRL4, comprising the scaffold Cullin 4A/B, the E2-interacting Roc1/2, and the adaptor protein damage-specific DNA-binding protein 1, is activated by DNA damage. Basal CRL4 activity is inhibited by binding to the COP9 signalosome (CSN). UV radiation and other stressors dissociate the complex, leading to E3 ligase activation, but signaling events that trigger signalosome dissociation from CRL4 have been unclear. In the present study, we show that, under basal conditions, IP6K1 forms a ternary complex with CSN and CRL4 in which IP6K1 and CRL4 are inactive. UV dissociates IP6K1 to generate IP7, which then dissociates CSN-CRL4 to activate CRL4. Thus, IP6K1 is a novel CRL4 subunit that transduces UV signals to mediate disassembly of the CRL4-CSN complex, thereby regulating nucleotide excision repair and cell death.

Ubiquitin-specific Protease 7 Regulates Nucleotide Excision Repair through Deubiquitinating XPC Protein and Preventing XPC Protein from Undergoing Ultraviolet Light-induced and VCP/p97 Protein-regulated Proteolysis

Ubiquitin specific protease 7 (USP7) is a known deubiquitinating enzyme for tumor suppressor p53 and its downstream regulator, E3 ubiquitin ligase Mdm2. Here we report that USP7 regulates nucleotide excision repair (NER) via deubiquitinating xeroderma pigmentosum complementation group C (XPC) protein, a critical damage recognition factor that binds to helix-distorting DNA lesions and initiates NER. XPC is ubiquitinated during the early stage of NER of UV light-induced DNA lesions. We demonstrate that transiently compromising cellular USP7 by siRNA and chemical inhibition leads to accumulation of ubiquitinated forms of XPC, whereas complete USP7 deficiency leads to rapid ubiquitin-mediated XPC degradation upon UV irradiation. We show that USP7 physically interacts with XPC in vitro and in vivo. Overexpression of wild-type USP7, but not its catalytically inactive or interaction-defective mutants, reduces the ubiquitinated forms of XPC. Importantly, USP7 efficiently deubiquitinates XPC-ubiquitin conjugates in deubiquitination assays in vitro. We further show that valosin-containing protein (VCP)/p97 is involved in UV light-induced XPC degradation in USP7-deficient cells. VCP/p97 is readily recruited to DNA damage sites and colocalizes with XPC. Chemical inhibition of the activity of VCP/p97 ATPase causes an increase in ubiquitinated XPC on DNA-damaged chromatin. Moreover, USP7 deficiency severely impairs the repair of cyclobutane pyrimidine dimers and, to a lesser extent, affects the repair of 6-4 photoproducts. Taken together, our findings uncovered an important role of USP7 in regulating NER via deubiquitinating XPC and by preventing its VCP/p97-regulated proteolysis.

Abstract 1786: UV damage-induced histone H3 lysine 56 deacetylation regulates nucleotide excision repair and checkpoint signaling.

Abstract Nucleotide excision repair (NER) is the major pathway in cells for the removal of bulky photoproducts and ensuring integrity of the genome. NER constitutes lesion recognition, excision of damaged DNA, synthesis of a DNA fragment, and ligation of the repair patch. Nonetheless, DNA within the cells is compacted into chromatin and lesion recognition requires chromatin to be remodeled to permit access of repair and checkpoint machinery to the damage site. Consequent to repair of the lesions, chromatin structure is restored to its original state so that cells resume cell cycle progression. Although several reports have demonstrated the role of chromatin remodelers, histone modifications and histone chaperones in DNA damage response (DDR), knowledge of how these epigenetic mechanisms control the DDR is largely in its infancy. We and others have recently observed that histone H3 is deacetylated on lysine 56 immediately in response to UV-induced DNA damage. Acetylation is promptly restored upon completion of repair and is necessary for recovery from DNA damage induced cell cycle arrest. However, the function of H3K56 deacetylation in the DDR remains to be determined. We found that UV-induced deacetylation of H3K56 is abrogated in the presence of TSA and sodium butyrate, both of which inhibit class I histone deacetylases (HDACs). Knockdown of either HDAC1 or HDAC2 alone did not affect UV-induced deacetylation of H3K56. However, simultaneous knockdown of both HDAC1 and 2 resulted in retention of H3K56 acetylation after UV irradiation. Consistently, both HDAC1 and HDAC2 localized to sites of UV damage. These observations are consistent with that reported by Miller et. al., indicating that HDAC1 and HDAC2 are responsible for the deacetylation of H3K56 in response to DNA damage. Since the deacetylation of H3K56 is one of the most immediate responses to UV-irradiation, we assumed it to play a crucial role in NER. Accordingly, we observed that CPD removal was affected in H1299 cells with histone H3K56Q mutation that mimics constitutive acetylation. Furthermore, we found that localization of the checkpoint kinase ATM to UV damage sites was affected in these cells. Consequently, ATM-mediated H2AX phosphorylation was also found to be defective in the mutant cells. Based on our observations, we speculate that HDAC1 and 2 mediated H3K56 deacetylation regulates NER and checkpoint signaling cascade in response to UV damage. This work was supported by PHS grants ES2388, ES12991 and CA93413 and Pelotonia postdoctoral fellowship to AB. Citation Format: Aruna Battu, Altaf Ahmad Wani. UV damage-induced histone H3 lysine 56 deacetylation regulates nucleotide excision repair and checkpoint signaling. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1786. doi:10.1158/1538-7445.AM2013-1786

Hemifacial Hypertrophy: A Rare Case Report

Xeroderma pigmentosum, or XP, is an autosomal recessive genetic disorder in which the ability to repair DNA damage caused by ultraviolet (UV) light is deficient. In extreme cases, all exposure to sunlight must be forbidden, no matter how small. As such, individuals with the disease are often colloquially referred to as 'Children of the Night'. Mutations in XP genes that regulate nucleotide excision repair, not only predispose persons with xeroderma pigmentosum to multiple malignancies, but also promote premature cutaneous and ocular ageing, and in some cases promote progressive neurodegenerative changes. There is a great involvement of many parts of the body, especially head and neck. The oral manifestations are mainly related to the occurrence of malignant tumors in the lips, tongue and buccal mucosa. This paper reports a rare case of XP in a 40-year-old female presenting with dermatological, oral and ophthalmological involvement.

Abstract 2538: HIF1α regulated expression of XPA contributes to cisplatin resistance in lung cancer

Abstract Factors regulating nucleotide excision repair (NER) likely contribute to the heterogenous response of advanced stage lung cancer patients to drugs such as cisplatin. Studies to identify the genes in the NER pathway most closely associated with resistance to cisplatin have not been conclusive. We hypothesized that Xeroderma pigmentosum complementation group A (XPA) because of its dual role in sensing and recruiting other DNA repair proteins to the damage template would be critical in defining sensitivity to cisplatin. Studies were conducted to identify factors regulating transcription of XPA, to assess its role in modulating sensitivity to cisplatin, and its expression in primary lung tumors. HIF1α was found to bind with strong affinity to a hypoxia response element sequence in the promoter of XPA. Modulating expression of HIF1α by siRNA or cobalt chloride markedly reduced or increased transcription of XPA in lung cancer cell lines, respectively. Protein levels of XPA were strongly correlated with sensitivity to cisplatin (r = 0.868; p &amp;lt; 0.001) in cell lines and sensitivity could be increased by siRNA depletion of XPA. Expression of XPA determined in 54 primary lung tumors was increased on average 5.2-fold when compared to normal bronchial epithelial cells and correlated with levels of HIF1α (r = 0.58; p &amp;lt; 0.01). Together, these studies identify XPA as a novel target for regulation by HIF1α whose modulation could impact lung cancer therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2538. doi:1538-7445.AM2012-2538

HIF1α regulated expression of XPA contributes to cisplatin resistance in lung cancer

Factors regulating nucleotide excision repair probably contribute to the heterogenous response of advanced stage lung cancer patients to drugs such as cisplatin. Studies to identify the genes in the nucleotide excision repair pathway most closely associated with resistance to cisplatin have not been conclusive. We hypothesized that Xeroderma pigmentosum complementation group A (XPA), because of its dual role in sensing and recruiting other DNA repair proteins to the damaged template, would be critical in defining sensitivity to cisplatin. Studies were conducted to identify factors regulating transcription of XPA, to assess its role in modulating sensitivity to cisplatin and its expression in primary lung tumors. Hypoxia-inducible factor 1 alpha (HIF1α) subunit was found to bind with strong affinity to a hypoxia response element sequence in the promoter of XPA. Modulating expression of HIF1α by small interfering RNA or cobalt chloride markedly reduced or increased transcription of XPA in lung cancer cell lines, respectively. Protein levels of XPA were strongly correlated with sensitivity to cisplatin (r = 0.88; P < 0.001) in cell lines and sensitivity could be increased by small interfering RNA depletion of XPA. Expression of XPA determined in 54 primary lung tumors was elevated on average 5.2-fold when compared with normal bronchial epithelial cells and correlated with levels of HIF1α (r = 0.58; P < 0.01). Together, these studies identify XPA as a novel target for regulation by HIF1α whose modulation could impact lung cancer therapy.

The oncogenic phosphatase WIP1 negatively regulates nucleotide excision repair

Nucleotide excision repair (NER) is the only mechanism in humans to repair UV-induced DNA lesions such as pyrimidine (6-4) pyrimidone photoproducts and cyclobutane pyrimidine dimers (CPDs). In response to UV damage, the ataxia telangiectasia mutated and Rad3-related (ATR) kinase phosphorylates and activates several downstream effector proteins, such as p53 and XPA, to arrest cell cycle progression, stimulate DNA repair, or initiate apoptosis. However, following the completion of DNA repair, there must be active mechanisms that restore the cell to a prestressed homeostatic state. An important part of this recovery must include a process to reduce p53 and NER activity as well as to remove repair protein complexes from the DNA damage sites. Since activation of the damage response occurs in part through phosphorylation, phosphatases are obvious candidates as homeostatic regulators of the DNA damage and repair responses. Therefore, we investigated whether the serine/threonine wild-type p53-induced phosphatase 1 (WIP1/PPM1D) might regulate NER. WIP1 overexpression inhibits the kinetics of NER and CPD repair, whereas WIP1 depletion enhances NER kinetics and CPD repair. This NER suppression is dependent on WIP1 phosphatase activity, as phosphatase-dead WIP1 mutants failed to inhibit NER. Moreover, WIP1 suppresses the kinetics of UV-induced damage repair largely through effects on NER, as XPD-deficient cells are not further suppressed in repairing UV damage by overexpressed WIP1. Wip1 null mice quickly repair their CPD and undergo less UV-induced apoptosis than their wild-type counterparts. In vitro phosphatase assays identify XPA and XPC as two potential WIP1 targets in the NER pathway. Thus WIP1 may suppress NER kinetics by dephosphorylating and inactivating XPA and XPC and other NER proteins and regulators after UV-induced DNA damage is repaired.