DMC-siERCC2 hybrid nanoparticle enhances TRAIL sensitivity by inducing cell cycle arrest for glioblastoma treatment.

ERCC2 plays a pivotal role in DNA damage repair, however, its specific function in cancer remains elusive. In this study, we made a significant breakthrough by discovering a substantial upregulation of ERCC2 expression in glioblastoma (GBM) tumor tissue. Moreover, elevated levels of ERCC2 expression were closely associated with poor prognosis. Further investigation into the effects of ERCC2 on GBM revealed that suppressing its expression significantly inhibited malignant growth and migration of GBM cells, while overexpression of ERCC2 promoted tumor cell growth. Through mechanistic studies, we elucidated that inhibiting ERCC2 led to cell cycle arrest in the G0/G1 phase by blocking the CDK2/CDK4/CDK6/Cyclin D1/Cyclin D3 pathway. Notably, we also discovered a direct link between ERCC2 and CDK4, a critical protein in cell cycle regulation. Additionally, we explored the potential of TRAIL, a low-toxicity death ligand cytokine with anticancer properties. Despite the typical resistance of GBM cells to TRAIL, tumor cells undergoing cell cycle arrest exhibited significantly enhanced sensitivity to TRAIL. Therefore, we devised a combination strategy, employing TRAIL with the nanoparticle DMC-siERCC2, which effectively suppressed the GBM cell proliferation and induced apoptosis. In summary, our study suggests that targeting ERCC2 holds promise as a therapeutic approach to GBM treatment.

KIAA1549 promotes the development and chemoresistance of colorectal cancer by upregulating ERCC2.

Colorectal cancer (CRC) is the third most commonly diagnosed cancer worldwide. Chemotherapy is the mainstay of treatment for patients with CRC in II-IV stages. Resistance to chemotherapy occurs commonly, which results in treatment failure. Therefore, the identification of novel functional biomarkers is essential for recognizing high-risk patients, predicting recurrence, and developing new therapeutic strategies. Herein, we assessed the roles of KIAA1549 in promoting tumor development and chemoresistance in colorectal cancer. As a result, we found that KIAA1549 expression is up-regulation in CRC. Public databases revealed a progressive up-regulation of KIAA1549 expression from adenomas to carcinomas. Functional characterization uncovered that KIAA1549 promotes tumor malignant phenotypes and boosts the chemoresistance of CRC cells in an ERCC2-dependent manner. Inhibition of KIAA1549 and ERCC2 effectively enhanced the sensitivity to chemotherapeutic drugs oxaliplatin and 5-fluorouracil. Our findings suggest that endogenous KIAA1549 might function as a tumor development-promoting role and trigger chemoresistance in colorectal cancer partly by upregulating DNA repair protein ERCC2. Hence, KIAA1549 could be an effective therapeutic target for CRC and inhibition of KIAA1549 combined with chemotherapy might be a potential therapeutic strategy in the future.

TFIIH central activity in nucleotide excision repair to prevent disease.

The heterodecameric transcription factor IIH (TFIIH) functions in multiple cellular processes, foremost in nucleotide excision repair (NER) and transcription initiation by RNA polymerase II. TFIIH is essential for life and hereditary mutations in TFIIH cause the devastating human syndromes xeroderma pigmentosum, Cockayne syndrome or trichothiodystrophy, or combinations of these. In NER, TFIIH binds to DNA after DNA damage is detected and, using its translocase and helicase subunits XPB and XPD, opens up the DNA and checks for the presence of DNA damage. This central activity leads to dual incision and removal of the DNA strand containing the damage, after which the resulting DNA gap is restored. In this review, we discuss new structural and mechanistic insights into the central function of TFIIH in NER. Moreover, we provide an elaborate overview of all currently known patients and diseases associated with inherited TFIIH mutations and describe how our understanding of TFIIH function in NER and transcription can explain the different disease features caused by TFIIH deficiency.

Investigation of XPD, miR-145 and miR-770 expression in patients with end-stage renal disease.

BACKGROUND: The effective maintenance of genome integrity and fidelity is vital for the normal function of our tissues and organs, and the prevention of diseases. DNA repair pathways maintain genome stability, and the adequacy of genes acting in these pathways is essential for disease suppression and direct treatment responses. Chronic kidney disease is characterized by high levels of genomic damage. In this study, we examined the expression levels of the xeroderma pigmentosum group D (XPD) gene, which plays a role in the nucleotide excision repair (NER) repair mechanism, and the expression levels of miR-145 and miR-770 genes, which play a role in the regulation of the expression of the XPD gene, in hemodialysis patients with (n = 42) and without malignancy (n = 9) in pre- and post-dialysis conditions. We also evaluated these values with the clinical findings of the patients. METHODS & RESULTS: Gene expression analysis was performed by real-time polymerase chain reaction (qRT-PCR). Compared to the individuals with normal kidney function (2.06 ± 0.32), the XPD gene expression was lower in the pre-dialysis condition both in hemodialysis patients without cancer (1.24 ± 0.18; p = 0.02) and in hemodialysis patients with cancer (0.82 ± 0.114; p = 0.001). On the other hand, we found that miR-145 and miR-770 expression levels were high in both groups. We also found that expression levels were affected by dialysis processes. A statistically significant positive correlation was found between miR-145 and mir770 expression levels in the pre-dialysis group of patients with (r=-0.988. p = 0.0001) and without (r=-0.934. p = 0.0001) malignancy. CONCLUSIONS: Studies on DNA damage repair in the kidney will help develop strategies to protect kidney function against kidney diseases.

The Curcumin Analog PAC Is a Potential Solution for the Treatment of Triple-Negative Breast Cancer by Modulating the Gene Expression of DNA Repair Pathways.

Breast Cancer (BC) is one of the most common and challenging cancers among females worldwide. Conventional treatments for oral cancer rely on the use of radiology and surgery accompanied by chemotherapy. Chemotherapy presents many side effects, and the cells often develop resistance to this chemotherapy. It will be urgent to adopt alternative or complementary treatment strategies that are new and more effective without these negative effects to improve the well-being of patients. A substantial number of epidemiological and experimental studies reported that many compounds are derived from natural products such as curcumin and their analogs, which have a great deal of beneficial anti-BC activity by inducing apoptosis, inhibiting cell proliferation, migration, and metastasis, modulating cancer-related pathways, and sensitizing cells to radiotherapy and chemotherapy. In the present study, we investigated the effect of the curcumin-analog PAC on DNA repair pathways in MCF-7 and MDA-MB-231 human breast-cancer cell lines. These pathways are crucial for genome maintenance and cancer prevention. MCF-7 and MDA-MB-231 cells were exposed to PAC at 10 µM. MTT and LDH assays were conducted to evaluate the effects of PAC on cell proliferation and cytotoxicity. Apoptosis was assessed in breast cancer cell lines using flow cytometry with annexin/Pi assay. The expression of proapoptotic and antiapoptotic genes was determined by RT-PCR to see if PAC is active in programming cell death. Additionally, DNA repair signaling pathways were analyzed by PCR arrays focusing on genes being related and confirmed by quantitative PCR. PAC significantly inhibited breast-cancer cell proliferation in a time-dependent manner, more on MDA-MB-231 triple-negative breast cancer cells. The flow cytometry results showed an increase in apoptotic activity. These data have been established by the gene expression and indicate that PAC-induced apoptosis by an increased Bax and decreased Bcl-2 expression. Moreover, PAC affected multiple genes involved in the DNA repair pathways occurring in both cell lines (MCF-7 and MDA-MB231). In addition, our results suggest that PAC upregulated more than twice 16 genes (ERCC1, ERCC2, PNKP, POLL, MPG, NEIL2, NTHL1, SMUG1, RAD51D, RAD54L, RFC1, TOP3A, XRCC3, XRCC6BP1, FEN1, and TREX1) in MDA-MB-231, 6 genes (ERCC1, LIG1, PNKP, UNG, MPG, and RAD54L) in MCF-7, and 4 genes (ERCC1, PNKP, MPG, and RAD54L) in the two cell lines. In silico analysis of gene-gene interaction shows that there are common genes between MCF-7 and MDA-MB-321 having direct and indirect effects, among them via coexpression, genetic interactions, pathways, predicted and physical interactions, and shared protein domains with predicted associated genes indicating they are more likely to be functionally related. Our data show that PAC increases involvement of multiple genes in a DNA repair pathway, this certainly can open a new perspective in breast-cancer treatment.

TFIIH stabilization recovers the DNA repair and transcription dysfunctions in thermo-sensitive trichothiodystrophy.

Trichothiodystrophy (TTD) is a rare hereditary disease whose prominent feature is brittle hair. Additional clinical signs are physical and neurodevelopmental abnormalities and in about half of the cases hypersensitivity to UV radiation. The photosensitive form of TTD (PS-TTD) is most commonly caused by mutations in the ERCC2/XPD gene encoding a subunit of the transcription/DNA repair complex TFIIH. Here we report novel ERCC2/XPD mutations affecting proper protein folding, which generate thermo-labile forms of XPD associated with thermo-sensitive phenotypes characterized by reversible aggravation of TTD clinical signs during episodes of fever. In patient cells, the newly identified XPD variants result in thermo-instability of the whole TFIIH complex and consequent temperature-dependent defects in DNA repair and transcription. Improving the protein folding process by exposing patient cells to low temperature or to the chemical chaperone glycerol allowed rescue of TFIIH thermo-instability and a concomitant recovery of the complex activities. Besides providing a rationale for the peculiar thermo-sensitive clinical features of these new cases, the present findings demonstrate how variations in the cellular concentration of mutated TFIIH impact the cellular functions of the complex and underlie how both quantitative and qualitative TFIIH alterations contribute to TTD clinical features.

Phosphorylation of XPD drives its mitotic role independently of its DNA repair and transcription functions.

The helicase XPD is known as a key subunit of the DNA repair/transcription factor TFIIH. However, here, we report that XPD, independently to other TFIIH subunits, can localize with the motor kinesin Eg5 to mitotic spindles and the midbodies of human cells. The XPD/Eg5 partnership is promoted upon phosphorylation of Eg5/T926 by the kinase CDK1, and conversely, it is reduced once Eg5/S1033 is phosphorylated by NEK6, a mitotic kinase that also targets XPD at T425. The phosphorylation of XPD does not affect its DNA repair and transcription functions, but it is required for Eg5 localization, checkpoint activation, and chromosome segregation in mitosis. In XPD-mutated cells derived from a patient with xeroderma pigmentosum, the phosphomimetic form XPD/T425D or even the nonphosphorylatable form Eg5/S1033A specifically restores mitotic chromosome segregation errors. These results thus highlight the phospho-dependent mitotic function of XPD and reveal how mitotic defects might contribute to XPD-related disorders.

Adult-Onset Neurodegeneration in Nucleotide Excision Repair Disorders (NERDND ): Time to Move Beyond the Skin.

BACKGROUND: Variants in genes of the nucleotide excision repair (NER) pathway have been associated with heterogeneous clinical presentations ranging from xeroderma pigmentosum to Cockayne syndrome and trichothiodystrophy. NER deficiencies manifest with photosensitivity and skin cancer, but also developmental delay and early-onset neurological degeneration. Adult-onset neurological features have been reported in only a few xeroderma pigmentosum cases, all showing at least mild skin manifestations. OBJECTIVE: The aim of this multicenter study was to investigate the frequency and clinical features of patients with biallelic variants in NER genes who are predominantly presenting with neurological signs. METHODS: In-house exome and genome datasets of 14,303 patients, including 3543 neurological cases, were screened for deleterious variants in NER-related genes. Clinical workup included in-depth neurological and dermatological assessments. RESULTS: We identified 13 patients with variants in ERCC4 (n = 8), ERCC2 (n = 4), or XPA (n = 1), mostly proven biallelic, including five different recurrent and six novel variants. All individuals had adult-onset progressive neurological deterioration with ataxia, dementia, and frequently chorea, neuropathy, and spasticity. Brain magnetic resonance imaging showed profound global brain atrophy in all patients. Dermatological examination did not show any skin cancer or pronounced ultraviolet damage. CONCLUSIONS: We introduce NERDND as adult-onset neurodegeneration (ND ) within the spectrum of autosomal recessive NER disorders (NERD). Our study demonstrates that NERDND is probably an underdiagnosed cause of neurodegeneration in adulthood and should be considered in patients with overlapping cognitive and movement abnormalities. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Trichothiodystrophy hair shafts display distinct ultrastructural features.

Hair shafts from three trichothiodystrophy (TTD) patients with mutations in the ERCC2 (XPD) gene were examined by transmission electron microscopy. TTD is a rare, recessive disorder with mutations in several genes in the DNA repair/transcription pathway, including ERCC2. Unlike previous studies, the hair shafts were examined after relaxation of their structure by partial disulphide bond reduction in the presence of sodium dodecyl sulphate, permitting improved visualization. Compared with hair shafts of normal phenotype, TTD cuticle cells displayed aberrant marginal bands and exocuticle layers. Clusters of cells stained differently (light versus dark) in the cortex of aberrant shafts, and the keratin macrofibrils appeared much shorter in the cytoplasm. Considerable heterogeneity in these properties was evident among samples and even along the length of single hair shafts. The results are consistent with not only a paucity of high sulphur components, such as keratin-associated proteins, but also a profound imbalance in protein content and organization.

Role of Xeroderma pigmentosum D (XPD) protein in genome maintenance in human cells under oxidative stress.

Xeroderma pigmentosum D (XPD) protein plays a pivotal role in the nucleotide excision repair pathway. XPD unwinds the local area of the damaged DNA by virtue of constituting transcription factor II H (TFIIH) and is important not only for repair but also for basal transcription. Although cells deficient in XPD have shown to be defective in oxidative base-lesion repair, the effects of the oxidative assault on primary fibroblasts from patients suffering from Xeroderma Pigmentosum D have not been fully explored. Therefore, we sought to investigate the role of XPD in oxidative DNA damage-repair by treating primary fibroblasts derived from a patient suffering from Xeroderma Pigmentosum D, with hydrogen peroxide. Our results show dose-dependent increase in genotoxicity with minimal effect on cytotoxicity with H2O2 in XPD deficient cells compared to control cells. XPD deficient cells displayed increased susceptibility and reduced repair capacity when subjected to DNA damage induced by oxidative stress. XPD deficient fibroblasts exhibited increased telomeric loss after H2O2 treatment. In addition, we demonstrated that chronic oxidative stress induced accelerated premature senescence characteristics. Gene expression profiling revealed alterations in genes involved in transcription and nucleotide metabolisms, as well as in cellular and cell cycle processes in a more significant way than in other pathways. This study highlights the role of XPD in the repair of oxidative stress and telomere maintenance. Lack of functional XPD seems to increase the susceptibility of oxidative stress-induced genotoxicity while retaining cell viability posing as a potential cancer risk factor of Xeroderma Pigmentosum D patients.

Radiation-induced DNA Damage and Repair in Lens Epithelial Cells of both Ptch1(+/-) and Ercc2(+/-) Mutated Mice.

Epidemiological studies suggest an increased incidence and risk of cataract after low-dose (<2 Gy) ionizing radiation exposures. However, the biological mechanism(s) of this process are not fully understood. DNA damage and repair are thought to have a contributing role in radiation-induced cataractogenesis. Recently we have reported an inverse dose-rate effect, as well as the low-dose response, of DNA damage and repair in lens epithelial cells (LECs). Here, we present further initial findings from two mutated strains (Ercc2+/- and Ptch1+/-) of mice, both reportedly susceptible to radiation-induced cataract, and their DNA damage and repair response to low-dose and low-dose-rate gamma rays. Our results support the hypothesis that the lens epithelium responds differently to radiation than other tissues, with reported radiation susceptibility to DNA damage not necessarily translating to the LECs. Genetic predisposition and strain(s) of mice have a significant role in radiation-induced cataract susceptibility.

Radiation-Induced Lens Opacity and Cataractogenesis: A Lifetime Study Using Mice of Varying Genetic Backgrounds.

Recent epidemiological findings and reanalysis of historical data suggest lens opacities resulting from ionizing radiation exposures are likely induced at lower doses than previously thought. These observations have led to ICRP recommendations for a reduction in the occupational dose limits for the eye lens, as well as subsequent implementation in EU member states. The EU CONCERT LDLensRad project was initiated to further understand the effects of ionizing radiation on the lens and identify the mechanism(s) involved in radiation-induced cataract, as well as the impact of dose and dose-rate. Here, we present the results of a long-term study of changes to lens opacity in male and female adult mice from a variety of different genetic (radiosensitive or radioresistant) backgrounds, including mutant strains Ercc2 and Ptch1, which were assumed to be susceptible to radiation-induced lens opacities. Mice received 0.5, 1 and 2 Gy 60Co gamma-ray irradiation at dose rates of 0.063 and 0.3 Gy min-1. Scheimpflug imaging was used to quantify lens opacification as an early indicator of cataract, with monthly observations taken postirradiation for an 18-month period in all strains apart from 129S2, which were observed for 12 months. Opacification of the lens was found to increase with time postirradiation (with age) for most mouse models, with ionizing radiation exposure increasing opacities further. Sex, dose, dose rate and genetic background were all found to be significant contributors to opacification; however, significant interactions were identified, which meant that the impact of these factors was strain dependent. Mean lens density increased with higher dose and dose rate in the presence of Ercc2 and Ptch1 mutations. This project was the first to focus on low (<1 Gy) dose, multiple dose rate, sex and strain effects in lens opacification, and clearly demonstrates the importance of these experimental factors in radiobiological investigations on the lens. The results provide insight into the effects of ionizing radiation on the lens as well as the need for further work in this area to underpin appropriate radiation protection legislation and guidance.

The DNA Repair Enzyme XPD Is Partially Regulated by PI3K/AKT Signaling in the Context of Bupivacaine-Mediated Neuronal DNA Damage.

Bupivacaine, a local anesthetic widely used for regional anesthesia and pain management, has been reported to induce neuronal injury, especially DNA damage. Neurons employ different pathways to repair DNA damage. However, the mechanism underlying bupivacaine-mediated DNA damage repair is unclear. A rat neuronal injury model was established by intrathecal injection of (3%) bupivacaine. An in vitro neuronal injury model was generated by exposing SH-SY5Y cells to bupivacaine (1.5 mmol/L). Then, a cDNA plate array was used to identify the DNA repair genes after bupivacaine exposure. The results showed that xeroderma pigmentosum complementary group D (XPD) of the nuclear excision repair (NER) pathway was closely associated with the repair of DNA damage induced by bupivacaine. Subsequently, Western blot assay and immunohistochemistry indicated that the expression of the repair enzyme XPD was upregulated after DNA damage. Downregulation of XPD expression by a lentivirus aggravated the DNA damage induced by bupivacaine. In addition, phosphatidyl-3-kinase (PI3K)/AKT signaling in neurons was inhibited after exposure to bupivacaine. After PI3K/AKT signaling was inhibited, bupivacaine-mediated DNA damage was further aggravated, and the expression of XPD was further upregulated. However, knockdown of XPD aggravated bupivacaine-mediated neuronal injury but did not affect PI3K/AKT signaling. In conclusion, the repair enzyme XPD, which was partially regulated by PI3K/AKT signaling, responded to bupivacaine-mediated neuronal DNA damage. These results can be used as a reference for the treatment of bupivacaine-induced neurotoxicity.

Association between Molecular Genetic Markers of DNA Repair and Cell Cycle Control Genes and Response to Platinum-Based Chemotherapy in Ovarian Cancer Patients.

We analyzed associations of polymorphic markers of DNA repair genes (XRCC1, ERCC2), cell cycle control genes (TP53, MDM2, and CDKN1A), methylation of promoter region, and mutation 5382insC of BRCA1 gene in ovarian cancer with effectiveness of platinumbased chemotherapy assessed by the median of progression-free survival time for markers of DNA repair genes and by relapse risk for all studied markers. An increase in the median of progression-free survival time for carriers of the Gln allele (р=0.025) and Gln/Gln genotype (р=0.022) of the Gln399Arg XRCC1 was observed during the 19-months period after chemotherapy. In carriers of C/C genotype of 5382insC mutation of BRCA1 gene (n=6), no relapses were observed (р=0.035), while 17 of 49 patients without this mutation developed relapses. Of 14 patients with BRCA1 gene function inactivation due to promoter methylation or the presence of the C/C genotype of 5382insC, one relapse was observed (p=0.033). Multivariate analysis revealed an association of markers of the XRCC1, TP53, MDM2 genes, BRCA1 gene inactivation, and type of surgery with the risk of relapse during the follow-up period up to 19 months after the end of chemotherapy (р≤0.0007).

Three targets in one complex: A molecular perspective of TFIIH in cancer therapy.

The general transcription factor II H (TFIIH) plays an essential role in transcription and nucleotide excision DNA repair (NER). TFIIH is a complex 10 subunit containing molecular machine that harbors three enzymatic activities while the remaining subunits assume regulatory and/or structural functions. Intriguingly, the three enzymatic activities of the CDK7 kinase, the XPB translocase, and the XPD helicase exert different impacts on the overall activities of TFIIH. While the enzymatic function of the XPD helicase is exclusively required in NER, the CDK7 kinase is deeply involved in transcription, whereas XPB is essential to both processes. Recent structural and biochemical endeavors enabled unprecedented details towards the molecular basis of these different TFIIH functions and how the enzymatic activities are regulated within the entire complex. Due to its involvement in two fundamental processes, TFIIH has become increasingly important as a target in cancer therapy and two of the three enzymes have already been addressed successfully. Here we explore the possibilities of recent high resolution structures in the context of TFIIH druggability and shed light on the functional consequences of the different approaches towards TFIIH inhibition.

Structural characterisation of the Chaetomium thermophilum Chl1 helicase.

Chl1 is a member of the XPD family of 5'-3' DNA helicases, which perform a variety of roles in genome maintenance and transmission. They possess a variety of unique structural features, including the presence of a highly variable, partially-ordered insertion in the helicase domain 1. Chl1 has been shown to be required for chromosome segregation in yeast due to its role in the formation of persistent chromosome cohesion during S-phase. Here we present structural and biochemical data to show that Chl1 has the same overall domain organisation as other members of the XPD family, but with some conformational alterations. We also present data suggesting the insert domain in Chl1 regulates its DNA binding.

Xeroderma Pigmentosum group D suppresses proliferation and promotes apoptosis of HepG2 cells by downregulating ERG expression via the PPARγ pathway.

Xeroderma Pigmentosum group D (XPD) gene has been shown to suppress hepatocellular carcinoma (HCC) progression, but its mechanism remains not fully understood. ETS-related gene (ERG) is generally known as an oncogenic gene. This study aimed to explore whether XPD regulated HCC cell proliferation, apoptosis and cell cycle by inhibiting ERG expression via the PPARγ pathway. The human hepatoma cells (HepG2) were transfected with the XPD overexpression vector (pEGFP-N2/XPD) or empty vector (pEGFP-N2). The PPARγ inhibitor GW9662 was used to determine whether XPD effects were mediated by activation of PPARγ pathway. Cell cycle and apoptosis were ascertained by flow cytometry, and cell viability was measured by MTT assay. Reverse transcription-polymerase chain reaction and Western blot were performed to determine the mRNA and protein levels. Overexpression of XPD significantly enhanced the expression of PPARγ and p-PPARγ, whereas it downregulated that of ERG and cdk7. Furthermore, XPD overexpression notably inhibited proliferation, promoted apoptosis and decreased the percentage of cells in the S + G2 phase of HepG2 cells. However, these effects of XPD overexpression were abrogated by GW9662. Collectively, XPD suppresses proliferation and promotes apoptosis of HepG2 cells by downregulating ERG expression via activation of the PPARγ pathway.

COL4A1, negatively regulated by XPD and miR-29a-3p, promotes cell proliferation, migration, invasion and epithelial-mesenchymal transition in liver cancer cells.

OBJECTIVE: Collagen type IV alpha 1 (COL4A1) exerts tumor-promoting functions in several tumors. However, its role in liver cancer remains not fully understood. Hence, this study aims to investigate the role of COL4A1 in regulating liver cancer cell behaviors and to validate its upstream regulatory mechanism. METHODS: Expression of xeroderma pigmentosum D (XPD) and COL4A1 was examined by qRT-PCR and western blot. Cell proliferation, migration, and invasion were evaluated. The protein levels of N-cadherin, vimentin, and E-cadherin were determined by western blot to evaluate epithelial-mesenchymal transition (EMT). The interaction between miR-29a-3p and COL4A1 was analyzed by luciferase reporter assay. RESULTS: COL4A1 overexpression significantly promoted cell proliferation, migration, invasion, and EMT in Hep3B cells. In contrast, COL4A1 silencing yielded the opposite effects in HepG2 cells. Expression of COL4A1 was increased, whereas expression of XPD and miR-29a-3p was decreased in HCC tissues compared to controls. COL4A1 mRNA level was negatively correlated with expression of XPD and miR-29a-3p in HCC tissues. Furthermore, XPD silencing-mediated up-regulation of COL4A1 expression was attenuated by miR-29a-3p mimic. Moreover, miR-29a-3p mimic inhibited Hep3B cell proliferation, migration, and invasion by directly targeting COL4A1. CONCLUSION: COL4A1 is negatively regulated by XPD-miR-29a-3p axis and promotes liver cancer progression in vitro.

Switch-like control of helicase processivity by single-stranded DNA binding protein.

Helicases utilize nucleotide triphosphate (NTP) hydrolysis to translocate along single-stranded nucleic acids (NA) and unwind the duplex. In the cell, helicases function in the context of other NA-associated proteins such as single-stranded DNA binding proteins. Such encounters regulate helicase function, although the underlying mechanisms remain largely unknown. Ferroplasma acidarmanus xeroderma pigmentosum group D (XPD) helicase serves as a model for understanding the molecular mechanisms of superfamily 2B helicases, and its activity is enhanced by the cognate single-stranded DNA binding protein replication protein A 2 (RPA2). Here, optical trap measurements of the unwinding activity of a single XPD helicase in the presence of RPA2 reveal a mechanism in which XPD interconverts between two states with different processivities and transient RPA2 interactions stabilize the more processive state, activating a latent 'processivity switch' in XPD. A point mutation at a regulatory DNA binding site on XPD similarly activates this switch. These findings provide new insights on mechanisms of helicase regulation by accessory proteins.

The roles of PARP-1 and XPD and their potential interplay in repairing bupivacaine-induced neuron oxidative DNA damage.

Bupivacaine has been widely used in clinical Anesthesia, but its neurotoxicity has been frequently reported, implicating cellular oxidative DNA damage as the major underlying mechanism. However, the mechanism underlying bupivacaine-induced oxidative DNA damage is unknown. We, thus, exposed SH-SY5Y cells to 1.5mM bupivacaine to induce neurotoxicity. Then, iTRAQ proteomic analysis was used to explore the repair of neuronal oxidative DNA damage. By analyzing the STRING version 11.0 database, the bioinformatics relationship between key repair enzymes was tracked. Subsequently, immunofluorescence co-localization and immunoprecipitation were used to investigate the interaction between key repair enzymes. The iTRAQ showed that Poly [ADP-ribose] polymerase 1 (PARP-1) from the base excision repair pathway participated closely in the repair of oxidative DNA damage induced by bupivacaine, and inhibition of PARP-1 expression significantly aggravated bupivacaine-induced DNA damage and apoptosis. Interestingly, this study showed that there were interactions and co-expression between PARP-1 and XPD (xeroderma pigmentosum D), another key protein of the nucleic acid excision repair pathway. After inhibiting XPD, PARP-1 expression was significantly reduced. However, simultaneous inhibition of both XPD and PARP-1 did not further increase DNA damage. It is concluded that PARP-1 may repair bupivacaine-induced oxidative DNA damage through XPD-mediated interactions.