Lingfeng He

OGG1 is essential in oxidative stress induced DNA demethylation.

DNA demethylation is an essential cellular activity to regulate gene expression; however, the mechanism that triggers DNA demethylation remains unknown. Furthermore, DNA demethylation was recently demonstrated to be induced by oxidative stress without a clear molecular mechanism. In this manuscript, we demonstrated that 8-oxoguanine DNA glycosylase-1 (OGG1) is the essential protein involved in oxidative stress-induced DNA demethylation. Oxidative stress induced the formation of 8-oxoguanine (8-oxoG). We found that OGG1, the 8-oxoG binding protein, promotes DNA demethylation by interacting and recruiting TET1 to the 8-oxoG lesion. Downregulation of OGG1 makes cells resistant to oxidative stress-induced DNA demethylation, while over-expression of OGG1 renders cells susceptible to DNA demethylation by oxidative stress. These data not only illustrate the importance of base excision repair (BER) in DNA demethylation but also reveal how the DNA demethylation signal is transferred to downstream DNA demethylation enzymes.

Targeting DNA Flap Endonuclease 1 to Impede Breast Cancer Progression

DNA flap endonuclease 1 (FEN1) plays critical roles in maintaining genome stability and integrity by participating in both DNA replication and repair. Suppression of FEN1 in cells leads to the retardation of DNA replication and accumulation of unrepaired DNA intermediates, resulting in DNA double strand breaks (DSBs) and apoptosis. Therefore, targeting FEN1 could serve as a potent strategy for cancer therapy. In this study, we demonstrated that FEN1 is overexpressed in breast cancers and is essential for rapid proliferation of cancer cells. We showed that manipulating FEN1 levels in cells alters the response of cancer cells to chemotherapeutic drugs. Furthermore, we identified a small molecular compound, SC13 that specifically inhibits FEN1 activity, thereby interfering with DNA replication and repair in vitro and in cells. SC13 suppresses cancer cell proliferation and induces chromosome instability and cytotoxicity in cells. Importantly, SC13 sensitizes cancer cells to DNA damage-inducing therapeutic modalities and impedes cancer progression in a mouse model. These findings could establish a paradigm for the treatment of breast cancer and other cancers as well.

FEN1 promotes tumor progression and confers cisplatin resistance in non‐small‐cell lung cancer

Lung cancer is one of the leading causes of cancer mortality worldwide. The therapeutic effect of chemotherapy is limited due to the resistance of cancer cells, which remains a challenge in cancer therapeutics. In this work, we found that flap endonuclease 1 (FEN1) is overexpressed in lung cancer cells. FEN1 is a major component of the base excision repair pathway for DNA repair systems and plays important roles in maintaining genomic stability through DNA replication and repair. We showed that FEN1 is critical for the rapid proliferation of lung cancer cells. Suppression of FEN1 resulted in decreased DNA replication and accumulation of DNA damage, which subsequently induced apoptosis. Manipulating the amount of FEN1 altered the response of lung cancer cells to chemotherapeutic drugs. A small-molecule inhibitor (C20) was used to target FEN1 and this enhanced the therapeutic effect of cisplatin. The FEN1 inhibitor significantly suppressed cell proliferation and induced DNA damage in lung cancer cells. In mouse models, the FEN1 inhibitor sensitized lung cancer cells to a DNA damage-inducing agent and efficiently suppressed cancer progression in combination with cisplatin treatment. Our study suggests that targeting FEN1 may be a novel and efficient strategy for a tumor-targeting therapy for lung cancer.

Mutation of DNA Polymerase β R137Q Results in Retarded Embryo Development Due to Impaired DNA Base Excision Repair in Mice

DNA polymerase β (Pol β), a key enzyme in the DNA base excision repair (BER) pathway, is pivotal in maintaining the integrity and stability of genomes. One Pol β mutation that has been identified in tumors, R137Q (arginine to glutamine substitution), has been shown to lower polymerase activity, and impair its DNA repair capacity. However, the exact functional deficiency associated with this polymorphism in living organisms is still unknown. Here, we constructed Pol β R137Q knock-in mice, and found that homozygous knock-in mouse embryos were typically small in size and had a high mortality rate (21%). These embryonic abnormalities were caused by slow cell proliferation and increased apoptosis. In R137Q knock-in mouse embryos, the BER efficiency was severely impaired, which subsequently resulted in double-strand breaks (DSBs) and chromosomal aberrations. Furthermore, R137Q mouse embryo fibroblasts (MEFs) were more sensitive to DNA-damaging reagents, such as methyl methanesulfonate (MMS) and H2O2. They displayed a higher percentage of DSBs, and were more likely to undergo apoptosis. Our results indicate that R137 is a key amino acid site that is essential for proper Pol β functioning in maintaining genomic stability and embryo development.

NHERF1 and NHERF2 regulation of SR-B1 stability via ubiquitination and proteasome degradation

Scavenger receptor class B type 1 (SR-B1), an HDL receptor plays a crucial role in cholesterol metabolism in the liver, steroidogenic tissues, and vascular cells including macrophages. SR-B1 is subject to regulation at the transcription, posttranscription and posttranslational levels. We previously provided evidence that PDZ domain containing NHERF1 and NHERF2 regulate SR-B1 protein levels post-transcriptionally, although the underlying mechanism(s) by which NHERF1 and NHERF2 regulate SR-B1 protein levels is not well understood. In this study, we demonstrate that SR-B1 is degraded intracellularly via ubiquitin-proteasome pathway and that SR-B1 can be ubiquitinated at K500 and K508 residues. Overexpression of NHERF1 or NHERF2 enhanced SR-B1 ubiquitination and degradation. NHERF1 and NHERF2 promote SR-B1 ubiquitination at sites K508 and K500, respectively. These results suggest that NHERF1 and NHERF2 down-regulated SR-B1 at least in part via the ubiquitin/proteasome pathway.

Prominent role of histone lysine demethylases in cancer epigenetics and therapy

Protein methylation has an important role in the regulation of chromatin, gene expression and regulation. The protein methyl transferases are genetically altered in various human cancers. The enzymes that remove histone methylation have led to increased awareness of protein interactions as potential drug targets. Specifically, Lysine Specific Demethylases (LSD) removes methylated histone H3 lysine 4 (H3K4) and H3 lysine 9 (H3K9) through formaldehyde-generating oxidation. It has been reported that LSD1 and its downstream targets are involved in tumor-cell growth and metastasis. Functional studies of LSD1 indicate that it regulates activation and inhibition of gene transcription in the nucleus. Here we made a discussion about the summary of histone lysine demethylase and their functions in various human cancers.

Wnt pathway is involved in 5-FU drug resistance of colorectal cancer cells.

Colorectal cancer (CRC) is one of the leading causes of cancer-related death worldwide. 5-Fluorouracil (5-FU) is widely used in the treatment of cancers, but its antineoplastic activity is limited in drug-resistant cancer cells. To investigate the detailed mechanism of 5-FU resistance, we developed a model of 5-FU-resistant cells from HCT-8 cells, a well-established colorectal cancer cell line. We found that the drug-resistant cells demonstrated high expression of TCF4 and β-catenin, indicating an upregulated Wnt pathway. A microarray analysis revealed that the suppression of the checkpoint kinase 1 (CHK1) pathway explained the resistance to 5-FU, especially in p53 wild-type cancer cells such as HCT-8. Our data also demonstrated that the CHK1 pathway is suppressed by the Wnt pathway in 5-FU-resistant cells. In summary, we have discovered a novel mechanism for 5-FU resistance mediated by histone deacetylation, which also revealed the crosstalk between the Wnt pathway and CHK1 pathway.Colorectal cancer: pathways to drug resistanceThe interaction between two signaling pathways may be related to resistance to a leading cancer drug in colorectal cancer cells. The drug 5-fluorouracil (5-FU) is widely used to limit malignant cell proliferation, but some cancers, including colorectal cancers, are resistant to 5-FU. Zhigang Guo at Nanjing Normal University, China, and co-workers have uncovered the signaling pathways behind 5-FU resistance in colorectal cancer cell lines. They found that 5-FU-resistant cells expressed high levels of two proteins indicative of an over-active Wnt signaling pathway, a crucial pathway in healthy development, the disruption of which is implicated in many diseases. This upregulated pathway suppressed another signaling pathway, leading to reduced cancer cell death. This interaction between the pathways could prove to be a valuable therapeutic target to limit resistance to 5-FU.

Synergistic antitumor effect of combined paclitaxel with FEN1 inhibitor in cervical cancer cells

Studies on cervical cancer are urgently required to improve clinical outcomes. As a major anticancer drug for cervical cancer, paclitaxel has been used for many years in clinical therapy but its therapeutic efficacy is limited by common obstacle from cancer cells. The enhanced DNA repair pathways of cancer cells have been proved to survive DNA damage induced by chemotherapeutic drug. Inhibitors of specific DNA repair pathway can sensitize cancer cells to the treatment of chemotherapeutic drugs. In this paper we found that the effect of paclitaxel can be significantly improved when used in combination with FEN1 inhibitor SC13, suggesting a synergistic mechanism between the two compounds. Our studies suggest that FEN1 inhibition could be a novel strategy of tumor-targeting therapy for cervical cancer. Our work also revealed that paclitaxel demonstrates stronger synergistic effect with SC13 than other common used chemical drugs such as doxorubicin, carboplatin or camptothecin on cervical cancer cells.

Interacting partners of FEN1 and its role in the development of anticancer therapeutics

Protein-protein interaction (PPI) plays a key role in cellular communication, Protein-protein interaction connected with each other with hubs and nods involved in signaling pathways. These interactions used to develop network based biomarkers for early diagnosis of cancer. FEN1(Flap endonuclease 1) is a central component in cellular metabolism, over expression and decrease of FEN1 levels may cause cancer, these regulation changes of Flap endonuclease 1reported in many cancer cells, to consider this data may needs to develop a network based biomarker. The current review focused on types of PPI, based on nature, detection methods and its role in cancer. Interacting partners of Flap endonuclease 1 role in DNA replication repair and development of anticancer therapeutics based on Protein-protein interaction data.