Cyclin D1 silencing impairs DNA double strand break repair, sensitizes BRCA1 wildtype ovarian cancer cells to olaparib

Identification of potentially actionable genetic variants in epithelial ovarian cancer: a retrospective cohort study

Ovarian cancer is the most lethal gynecologic malignancy, mainly due to late-stage diagnosis, frequent recurrences, and eventually therapy resistance. To identify potentially actionable genetic variants, sequencing data of 351 Belgian ovarian cancer patients were retrospectively captured from electronic health records. The cohort included 286 (81%) patients with high-grade serous ovarian cancer, 17 (5%) with low-grade serous ovarian cancer, and 48 (14%) with other histotypes. Firstly, an overview of the prevalence and spectrum of the BRCA1/2 variants highlighted germline variants in 4% (11/250) and somatic variants in 11% (37/348) of patients. Secondly, application of a multi-gene panel in 168 tumors revealed a total of 214 variants in 28 genes beyond BRCA1/2 with a median of 1 (IQR, 1-2) genetic variant per patient. The ten most often altered genes were (in descending order): TP53, BRCA1, PIK3CA, BRCA2, KRAS, ERBB2 (HER2), TERT promotor, RB1, PIK3R1 and PTEN. Of note, the genetic landscape vastly differed between the studied histotypes. Finally, using ESCAT the clinical evidence of utility for every genetic variant was scored. Only BRCA1/2 pathogenic variants were classified as tier-I. Nearly all patients (151/168; 90%) had an ESCAT tier-II variant, most frequently in TP53 (74%), PIK3CA (9%) and KRAS (7%). In conclusion, our findings imply that although only a small proportion of genetic variants currently have direct impact on ovarian cancer treatment decisions, other variants could help to identify novel (personalized) treatment options to address the poor prognosis of ovarian cancer, particularly in rare histotypes.

Anticancer Effect of Active Component of Astragalus Membranaceus Combined with Olaparib on Ovarian Cancer Predicted by Network-Based Pharmacology

In China, a traditional Chinese medicine formulation called astragalus membranaceus (AM) has been utilised for more than 20 years to treat tumors with extraordinary effectiveness. The fundamental mechanisms, nevertheless, are still not well understood. The aim of this study is identifying its possible therapeutic targets and to evaluate the effects of AM in combination with a PARP inhibitor (olaparib) in the treatment of BRCA wild-type ovarian cancer. Significant genes were collected from Therapeutic Target Database and Database of Gene-Disease Associations. The components of AM were analyzed using the Traditional Chinese Medicine System Pharmacology (TCMSP) database to screen the active ingredients of AM based on their oral bioavailability and drug similarity index. In order to find intersection targets, Venn diagrams and STRING website diagrams were employed. STRING was also used to create a protein-protein interaction network. In order to create the ingredient-target network, Cytoscape 3.8.0 was used. DAVID database was utilized to carry out enrichment and pathway analyses. The binding ability of the active compounds of AM to the core targets of AM-OC was verified with molecular docking using AutoDock software. Experimental validations, including cell scratch, cell transwell, cloning experiment, were conducted to verify the effects of AM on OC cells. A total of 14 active ingredients of AM and 28 AM-OC-related targets were screened by network pharmacology analysis. The ten most significant Gene Ontology (GO) biological function analyses, as well as the 20 foremost Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment pathways were selected. Moreover, molecular docking results showed that bioactive compound (quercetin) demonstrated a good binding ability with tumor protein p53 (TP53), MYC, vascular endothelial growth factor A (VEGFA), phosphatase and tensin homolog (PTEN), AKT serine/threonine kinase 1 (AKT1) and cyclin D1 (CCND1) oncogenes. According to experimental methods, in vitro OC cell proliferation and migration appeared to be inhibited by quercetin, which also increased apoptosis. In addition, the combination with olaparib further enhanced the effect of quercetin on OC. Based on network pharmacology, molecular docking, and experimental validation, the combination of PARP inhibitor and quercetin enhanced the anti-proliferative activity in BRCA wild-type ovarian cancer cells, which supplies the theoretical groundwork for additional pharmacological investigation.

Effect of miR-34a on the expression of clock and clock-controlled genes in DLD1 and Lovo human cancer cells with different backgrounds with respect to p53 functionality and 17β-estradiol-mediated regulation

The small non-coding RNA miR-34a is a p53-regulated miRNA that acts as a tumour suppressor of colorectal cancer (CRC). Oncogenesis is also negatively influenced by deregulation of the circadian system in many types of tumours with various genetic backgrounds. As the clock gene per2 was recently recognized as one of the target genes of miR-34a, we focused on the miR-34a-mediated influence on the circadian oscillator in CRC cell lines DLD1 and LoVo, which differ in their p53 status. Previously, a sex-dependent association between the expression of per2 and that of miR-34a was demonstrated in CRC patients. Therefore, we also investigated the effect of 17β-estradiol (E2) on miR-34a oncostatic functions. miR-34a mimic caused a pronounced inhibition of per2 expression in both cell lines. Moreover, miR-34a mimic significantly inhibited bmal1 expression in LoVo and rev-erbα expression in DLD1 cells and induced clock gene expression in both cell lines. miR-34a mimic caused a pronounced decrease in sirt1 and cyclin D1 expression, which may be related to the inhibition of proliferation observed after mir-34a administration in DLD1 cells. E2 administration inhibited the migration and proliferation of DLD1 cells. E2 and miR-34a, when administered simultaneously, did not potentiate each other's effects. To conclude, miR-34a strongly influences the expression of components of the circadian oscillator without respect to p53 status and exerts its oncostatic effects via inhibition of sirt1 and cyclin D1 mRNA expression. E2 administration inhibits the growth of DLD1 cells; however, this effect seems to be independent of miR-34a-mediated action. With respect to the possible use of miR-34a in cancer treatment, clock genes can be considered as off-target genes, as changes in their expression induced by miR-34a treatment do not contribute to the oncostatic functions of miR-34a. Possible ambiguous oncogenic characteristics should be taken into consideration in future clinical studies focused on miR-34a.

CCND1-associated ceRNA network reveal the critical pathway of TPRG1-AS1-hsa-miR-363-3p-MYO1B as a prognostic marker for head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSC) is one of the leading causes of cancer death globally, yet there are few useful biomarkers for early identification and prognostic prediction. Previous studies have confirmed that CCND1 amplification is closely associated with head and neck oncogenesis, and the present study explored the ceRNA network associated with CCND1. Gene expression profiling of the Head and Neck Squamous Cell Carcinoma (HNSC) project of The Cancer Genome Atlas (TCGA) program identified the TPRG1-AS1-hsa-miR-363-3P-MYO1B gene regulatory axis associated with CCND1. Further analysis of the database showed that MYOB was regulated by methylation in head and neck tumors, and functional enrichment analysis showed that MYO1B was involved in "actin filament organization" and "cadherin binding ". Immune infiltration analysis suggested that MYO1B may influence tumorigenesis and prognosis by regulating the immune microenvironment of HNSC. MYO1B enhanced tumor spread through the EMT approach, according to epithelial mesenchymal transition (EMT) characterisation. We analyzed both herbal and GSCALite databases and found that CCND1 and MYO1B have the potential as predictive biomarkers for the treatment of HNSC patients. RT-qPCR validated bioinformatic predictions of gene expression in vitro cell lines. In conclusion, we found a CCND1-related ceRNA network and identified the novel TPRG1-AS1-hsa-miR-363-3p-MYO1B pathway as a possible HNSC diagnostic biomarker and therapeutic target.

Glucose transporters: Important regulators of endometrial cancer therapy sensitivity

Glucose is of great importance in cancer cellular metabolism. Working together with several glucose transporters (GLUTs), it provides enough energy for biological growth. The main glucose transporters in endometrial cancer (EC) are Class 1 (GLUTs 1–4) and Class 3 (GLUTs 6 and 8), and the overexpression of these GLUTs has been observed. Apart from providing abundant glucose uptake, these highly expressed GLUTs also participate in the activation of many crucial signaling pathways concerning the proliferation, angiogenesis, and metastasis of EC. In addition, overexpressed GLUTs may also cause endometrial cancer cells (ECCs) to be insensitive to hormone therapy or even resistant to radiotherapy and chemoradiotherapy. Therefore, GLUT inhibitors may hopefully become a sensitizer for EC precision-targeted therapies. This review aims to summarize the expression regulation, function, and therapy sensitivity of GLUTs in ECCs, aiming to provide a new clue for better diagnosis and treatment of EC.

The long non-coding RNA UPAT promotes gastric cancer cell progression via UHRF1

BACKGROUND

LncRNA ubiquitin-like with PHD and RING finger domains 1 (UHRF1) protein associated transcript (UPAT) regulates the progression of many cancers. However, its role in gastric cancer (GC) is less frequently reported.

OBJECTIVE

In the context of the promoting effect of lncRNA on modulating GC progression, detailed insights into the role and underlying mechanism of UPAT in GC are the foothold in this study.

METHODS

Overall survival was calculated. The mRNA expressions of UPAT and UHRF1 were measured by qRT-PCR, and the protein expressions of UHRF1, Cyclin D1 and cleaved caspase-3 were determined by western blot. Cell viability, growth, migration and invasion were assessed by CCK-8, colony formation, wound healing and Transwell assays, respectively. Apoptosis rate and cell cycle were assayed by flow cytometry.

RESULTS

UPAT was overexpressed in GC tissue and cell lines. Decreased UPAT level was associated with higher overall survival. Down-regulation of UPAT diminished cell proliferation, Cyclin D1 expression, and migration and invasion rates, increased apoptosis rate and cleaved caspase-3 expression, and blocked cell cycle in AGS and NCI-N87 cells. UPAT expression in GC was positively correlated with UHRF1 expression. UHRF1 overexpression offset the inhibitory effects of UPAT down-regulation on cell proliferation, migration, invasion and cell cycle, and partially reversed the positive effect of UPAT down-regulation on apoptosis.

CONCLUSION

UPAT might positively regulate the progression of GC via interacting with UHRF1. The UHRF1/UPAT axis revealed in the present study may provide a promising approach to intervene in the progression of GC.

MicroRNA‑532‑5p regulates oxidative stress and insulin secretion damage in high glucose‑induced pancreatic β cells by downregulating the expression levels of CCND1

Diabetes mellitus is a metabolic disorder caused by insufficient insulin secretion. The expression of microRNA (miR)-532-5P is downregulated in diabetes, but its specific role in diabetes has not yet been elucidated. The present study aimed to investigate the specific mechanism underlying the effects of miR-532-5p on diabetes. Cell viability was determined using an MTT assay. The expression levels of miR-532-5P, cyclin D1 (CCND1), Insulin1 and Insulin2 were detected using reverse transcription-quantitative PCR. The expression of miR-532-5p and CCND1 were overexpressed in cells by cell transfection. ELISA was used to detect insulin secretion. 2′,7′-dichlorodihydrofluorescein diacetate was used to quantify reactive oxygen species levels in cells. Apoptosis was detected using a TUNEL assay. Western blotting was performed to detect the expression of apoptosis-related proteins, CCND1 and p53. A dual-luciferase reporter assay was conducted, and verified the targeted binding of miR-532-5p and CCND1. The expression of miR-532-5p was downregulated in high glucose (HG)-induced MIN6 cells. Overexpression of miR-532-5p could improve the HG-induced decline in insulin secretion and inhibit HG-induced oxidative stress and apoptosis in cells. miR-532-5p can target and regulate the expression of CCND1. Overexpression of miR-532-5p downregulated HG-induced cell insulin secretion, oxidative stress and apoptosis by downregulating CCND1, which is involved in regulating the expression of p53. To conclude, miR-532-5p regulated oxidative stress and insulin secretion damage in HG-induced pancreatic β cells by downregulating the expression of CCND1, which is involved in the upregulation of the expression of p53.

PSMC2/CCND1 axis promotes development of ovarian cancer through regulating cell growth, apoptosis and migration

Ovarian cancer is known as one of the most common malignancies of the gynecological system, whose treatment is still not satisfactory because of the unclear understanding of molecular mechanism. PSMC2 is an essential component of 19 S regulatory granules in 26 S proteasome and its relationship with ovarian cancer is still not clear. In this study, we found that PSMC2 was upregulated in ovarian cancer tissues, associated with tumor grade and could probably predict poor prognosis. Knocking down the endogenous PSMC2 expression in ovarian cancer cells could decrease colony formation ability, cell motility and cell proliferation rate, along with increasing cell apoptosis rate. Cells models or xenografts formed by cells with relatively lower expression of PSMC2 exhibited weaker oncogenicity and slower growth rate in vivo. Moreover, gene microarray was used to analyze the alteration of gene expression profiling of ovarian cancer induced by PSMC2 knockdown and identify CCND1 as a potential downstream of PSMC2. Further study revealed the mutual regulation between PSMC2 and CCND1, and demonstrated that knockdown of CCND1 could enhance the regulatory effects induced by PSMC2 knockdown and overexpression of CCND1 reverses it. In summary, PSMC2 may promote the development of ovarian cancer through CCND1, which may predict poor prognosis of ovarian cancer patients.

Enhancing the sensitivity of ovarian cancer cells to olaparib via microRNA-20b-mediated cyclin D1 targeting

We previously reported that cyclin D1 silencing interferes with RAD51 accumulation and increases the sensitivity of BRCA1 wild-type ovarian cancer cells to olaparib. However, the mechanisms associated with cyclin D1 overexpression in ovarian cancer are not fully understood. TargetScan predicted the potential binding sites for microRNA-20b (miR-20b) and the 3'-untranslated region of cyclin D1 mRNA; thus, we used luciferase reporter assay to verify those binding sites. The Kaplan-Meier method and log-rank test were used to examine the relationship between miR-20b and progression-free survival of ovarian cancer patients in The Cancer Genome Atlas (n = 367) dataset. In vitro experiments were performed to evaluate the effects of miR-20b on cyclin D1 expression, cell cycle and response to olaparib. A peritoneal cavity metastasis model of ovarian cancer was established to determine the effect of miR-20b on the sensitivity of olaparib. Immunohistochemistry was performed to evaluate molecular mechanisms. In this work, we demonstrated that miR-20b down-regulates cyclin D1, increases the sensitivity of ovarian cancer cells to olaparib, reduces the expression of RAD51, and induces cell cycle arrest in G0/G1 phase. Ovarian cancer patients with higher expression of miR-20b had significantly longer progression-free survival. These results indicate that miR-20b may be a potential clinical indicator for the sensitivity of ovarian cancer to olaparib and the survival of ovarian cancer patients. Our findings suggest that miR-20b may have therapeutic value in combination with olaparib treatment for ovarian cancer.

Cyclin D1 in Cancer: A Molecular Connection for Cell Cycle Control, Adhesion and Invasion in Tumor and Stroma

Cyclin D1, an important regulator of cell cycle, carries out a central role in the pathogenesis of cancer determining uncontrolled cellular proliferation. In normal cells, Cyclin D1 expression levels are strictly regulated, conversely, in cancer, its activity is intensified in various manners. Different studies demonstrate that CCDN1 gene is amplified in several tumor types considering it as a negative prognostic marker of this pathology. Cyclin D1 is known for its role in the nucleus, but recent clinical studies associate the amount located in the cytoplasmic membrane with tumor invasion and metastasis. Cyclin D1 has also other functions: it governs the expression of specific miRNAs and it plays a crucial role in the tumor-stroma interactions potentiating most of the cancer hallmarks. In the present review, we will summarize the current scientific evidences that highlight the involvement of Cyclin D1 in the pathogenesis of different types of cancer, best of all in breast cancer. We will also focus on recent insights regarding the Cyclin D1 as molecular bridge between cell cycle control, adhesion, invasion, and tumor/stroma/immune-system interplay in cancer.

Human La Protein: An RNA-Binding Protein Involved in Ovarian Cancer Development and Multidrug Resistance

Multidrug resistance is the main cause of chemotherapy failure and death in patients with advanced ovarian cancer. Drug resistance is a problem that must be solved to improve the survival rate of patients with advanced ovarian cancer. The RNA-binding protein La and the La-related protein family are highly expressed in various malignant tumors, including ovarian cancer. This article reviews the mechanisms of La protein in tumorigenesis, development, and drug resistance. High La protein expression in tumor cells promotes tumor proliferation, invasion, and migration; disrupts cell cycle; and inhibits tumor cell apoptosis caused by chemotherapeutic drugs through various pathways, resulting in chemotherapy resistance in ovarian cancer. Further study of the role of La protein in ovarian cancer multidrug resistance may be conducive to the development of human La protein-specific inhibitors that suppress ovarian cancer drug resistance.

An olaparib window-of-opportunity trial in patients with early-stage endometrial carcinoma: POLEN study

OBJECTIVE

Olaparib is a potent inhibitor of poly(ADP-ribose) polymerase (PARP)-1, 2, and 3 with potential activity in endometrial cancer (EC).

METHODS

In this window-of-opportunity trial, women with operable type 1 EC received olaparib oral tablets (300mg) twice daily for 28days before surgery. The primary objective was to evaluate the effects of olaparib on EC in tissue samples taken at baseline and at treatment completion. Signal of activity was defined as significant changes in the expression of the cell cycle-related proteins cyclin D1, Ki67, and cleaved caspase-3.

RESULTS

A total of 31 patients were included in the biomarker analysis. The median time of olaparib exposure was 24 days (1-39). Significant inhibition was found for cyclin D1 (p < 0.01), but not for Ki67 and active caspase 3 immunostaining. PARP-1 levels positively correlated with cyclin D1 levels (rho = 0.661, p = 0.0001). Both PARP-1 and cyclin D1 levels were significantly lower (p = 0.022 and p = 0.004, respectively) in patients with ARID1A[-] tumors than ARID1A[+] tumors. A significant relationship between plasma olaparib concentrations and decreased GLUT1 activity was observed (r = -0.5885; p < 0.05). Drug-related toxicity consisted mostly of gastrointestinal and grade 1 or 2 adverse events.

CONCLUSIONS

Olaparib reduced expression of cyclin D1, which positively correlated with PARP-1 levels. This effect was more evident in ARID1A-deficient tumors. Olaparib further induced inhibition of GLUT1 plasma activity. Our findings could have noteworthy implications in predicting which patients with EC would benefit from olaparib-based strategies.

A first-in-class CDK4 inhibitor demonstrates in vitro, ex-vivo and in vivo efficacy against ovarian cancer

INTRODUCTION

Cyclin-dependent kinases 4 and 6 (CDK4/6) are fundamental drivers of the cell cycle and are involved in the initiation and progression of various cancers. Deregulation of the CDK4/6-cyclin D-retinoblastoma (Rb) pathway is common in ovarian cancer and is associated with an aggressive phenotype and poor prognosis. Patients with advanced ovarian cancer whose tumor demonstrates Rb-positivity, a low expression of p16 and overexpression of cyclin D1 are most likely to benefit from CDK4/6 inhibition.

MATERIALS AND METHOD

Anti-proliferative activity and mechanistic investigations for CDDD2-94, employing palbociclib as comparator, were evaluated by MTT assay, cell cycle and apoptosis analysis, western blotting as well as senescence and colony formation assay. In vivo safety and efficacy studies were done in A2780 tumor-bearing nude mice. Combinations of CDDD2-94 with mTOR, MEK, PI3K or PARP inhibitors were evaluated in A2780 and OVCAR5 ovarian cancer cells.

RESULTS

Consistent with a CDK4-targeted mechanism, CDDD2-94 arrested the G1/G0 cell cycle, induced senescence and inhibited the proliferation of Rb-proficient ovarian cancer cells. CDDD2-94 exhibited synergistic anti-proliferative activities with mTOR, MEK, PI3K or PARP inhibitors. Importantly, unlike palbociclib which caused significant reductions in the number of lymphocytes and neutrophils, CDDD2-94 had little effect. CDDD2-94, as single agent and in combination with everolimus, delayed tumor growth and significantly increased survival of mice.

CONCLUSION

Given its high specificity in targeting CDK4 and excellent anti-tumor efficacy with low toxicity, CDDD2-94 has potential to be developed as a standalone agent or in combination with targeted therapeutics for the treatment of ovarian cancer.

Knockdown of ALPK2 inhibits the development and progression of Ovarian Cancer

Background

Alpha protein kinase 2 (ALPK2) was known to play a vital role in cancer by regulating cell cycle and DNA repair. Ovarian cancer (OC) is one of the most lethal malignancies in the female reproductive system. The emphasis of this study is to explore the role of ALPK2 in OC.

Methods

Firstly, tumor and normal tissues were collected for detecting expression of ALPK2 in OC. Lentivirus-mediated shRNA knockdown of ALPK2 was used to construct OC cell model, which was verified by qRT-PCR and Western blot. The cell proliferation was detected by MTT, cell cycle and apoptosis were measured through flow cytometry. Wound-healing assay was conducted to detect the migration of OC cells.

Results

It was proved that the expression of ALPK2 in OC tissues was significantly higher than that in normal ovarian tissues. Moreover, knockdown of ALPK2 could inhibit proliferation, migration and promote apoptosis, arrested cell cycle of OC cells. It was also found that ALPK2 knockdown inhibited tumor growth in xenograft mice in vivo. Furthermore, ALPK2 was involved in OC cells via regulating EMT-related proteins (N-cadherin, Vimentin and Snail), inhibiting apoptosis-related proteins (Bcl-2, Bcl-w, HSP27, HSP60, IGF-I, IGF-1sR, Survivin and XIAP), as well as the regulation of downstream pathways (Akt, p-Akt, Cyclin D1, CDK6 and PIK3CA).

Conclusions

In conclusion, ALPK2 might serve as an optional target for prognosis and therapeutic of OC patients.

Clinical Implications of DNA Repair Defects in High-Grade Serous Ovarian Carcinomas

Despite significant improvements in surgical and medical management, high grade serous ovarian cancer (HGSOC) still represents the deadliest gynecologic malignancy and the fifth most frequent cause of cancer-related mortality in women in the USA. Since DNA repair alterations are regarded as the “the Achille’s heel” of HGSOC, both DNA homologous recombination and DNA mismatch repair deficiencies have been explored and targeted in epithelial ovarian cancers in the latest years. In this review, we aim at focusing on the therapeutic issues deriving from a faulty DNA repair machinery in epithelial ovarian cancers, starting from existing and well-established treatments and investigating new therapeutic approaches which could possibly improve ovarian cancer patients’ survival outcomes in the near future. In particular, we concentrate on the role of both Poly (ADP-ribose) Polymerase (PARP) inhibitors (PARPis) and immune checkpoint inhibitors in HGSOC, highlighting their activity in relation to BRCA1/2 mutational status and homologous recombination deficiency (HRD). We investigate the biological rationale supporting their use in the clinical setting, pointing at tracking their route from the laboratory bench to the patient’s bedside. Finally, we deal with the onset of mechanisms of primary and acquired resistance to PARPis, reporting the pioneering strategies aimed at converting homologous-recombination (HR) proficient tumors into homologous recombination (HR)-deficient HGSOC.

Novel Poly(ADP-ribose) Polymerase-1 Inhibitor DDHCB Inhibits Proliferation of BRCA Mutant Breast Cancer Cell In Vitro and In Vivo through a Synthetic Lethal Mechanism

Poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors are drugs that are effectively used to treat breast cancer. We synthesized a novel bromophenol derivative ethyl (E)-4-(2-(2,3-dibromo-4,5-dimethoxybenzylidene)hydrazine-1-carbothioamido)benzoate (DDHCB) as a novel PARP-1 inhibitor. Our study found that DDHCB could inhibit PARP-1 activity with an IC₅₀ value of 58.3 nM. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphe-nyltetrazolium bromide (MTT) assay indicated that DDHCB could selectively inhibit proliferation of BRCA mutant cells and demonstrate the ability of synthetic lethality. DDHCB could also induce DNA double-strand breaks with the ability to increase the foci quantitation of γ-H2AX. Moreover, DDHCB could increase PARP-1-DNA trapping and inhibit PAR formation in HCC-1937 cells. Further investigation showed that DDHCB induced apoptosis and G2/M cycle arrest. Finally, we found that DDHCB inhibited the growth of HCC-1937 xenografts with low toxicity. In vivo mechanisms showed that the level of γ-H2AX was increased in the DDHCB-treated tumors, indicating the PARP-1 inhibition ability of DDHCB in vivo. Our study results indicated that the future development of DDHCB for the treatment of breast cancer is promising.

DUSP3 maintains genomic stability and cell proliferation by modulating NER pathway and cell cycle regulatory proteins

The DUSP3 phosphatase regulates cell cycle, proliferation, apoptosis and senescence of different cell types, lately shown as a mediator of DNA repair processes. This work evaluated the impact of DUSP3 loss of function (lof) on DNA repair-proficient fibroblasts (MRC-5), NER-deficient cell lines (XPA and XPC) and translesion DNA synthesis (TLS)-deficient cells (XPV), after UV-radiation stress. The levels of DNA strand breaks, CPDs and 6-4-PPs have accumulated over time in all cells under DUSP3 lof, with a significant increase in NER-deficient lines. The inefficient repair of these lesions increased sub-G1 population of XPA and XPC cells 24 hours after UV treatment, notably marked by DUSP3 lof, which is associated with a reduced cell population in G1, S and G2/M phases. It was also detected an increase in S and G2/M populations of XPV and MRC-5 cells after UV-radiation exposure, which was slightly attenuated by DUSP3 lof due to a discrete increase in sub-G1 cells. The cell cycle progression was accompanied by changes in the levels of the main Cyclins (A1, B1, D1 or E1), CDKs (1, 2, 4 or 6), and the p21 ^Cip1 inhibitor, in a DUSP3-dependent manner. DUSP3 lof affected the proliferation of MRC-5 and XPA cells, with marked worsening of the XP phenotype after UV radiation. This work highlights the roles of DUSP3 in DNA repair fitness and in the fine control of regulatory proteins of cell cycle, essential mechanisms to maintenance of genomic stability.

CCND1 silencing suppresses liver cancer stem cell differentiation and overcomes 5-Fluorouracil resistance in hepatocellular carcinoma

OBJECTIVE

Chemoresistance is one of the major barriers in chemotherapy-based hepatocellular carcinoma (HCC) intervention. 5-Fluorouracil (5-Fu) is a widely used as an anticancer drug. Liver cancer stem cells (LCSCs) are considered the origin of tumor recurrence and resistance. CCND1 (Cyclin D1) plays an important role in tumorigenesis and metastasis in multiple cancers including HCC. Herein, this study was designed to explore the role of CCND1 in regulating LCSCs differentiation and 5-Fu resistance in HCC cells.

METHODS

The CCND1 mRNA level was examined by qRT-PCR. The protein levels of γ-H2AX (a DNA damage marker) and RAD51 (a DNA repair protein) were examined by Western blot. CD133 was used as a LCSC marker and CD133+ cell percentage in HCC cells was detected by flow cytometry.

RESULTS

CCND1 silencing decreased CD133+ cell percentage in HepG2 and SMMC-7721 cells. Furthermore, CCND1 silencing significantly increased protein level of γ-H2AX and decreased that of RAD51 under 5-Fu exposure. Moreover, CCND1 silencing enhanced the sensitivity of HepG2 and SMMC-7721 cells to 5-Fu, which was effectively abrogated by RAD51 upregulation.

CONCLUSION

Collectively, CCND1 silencing suppresses LCSCs differentiation and overcomes 5-Fu resistance in HCC.

Therapeutic Strategies and Biomarkers to Modulate PARP Activity for Targeted Cancer Therapy

Poly-(ADP-ribose) polymerase 1 (PARP1) is commonly known for its vital role in DNA damage response and repair. However, its enzymatic activity has been linked to a plethora of physiological and pathophysiological transactions ranging from cellular proliferation, survival and death. For instance, malignancies with BRCA1/2 mutations heavily rely on PARP activity for survival. Thus, the use of PARP inhibitors is a well-established intervention in these types of tumors. However, recent studies indicate that the therapeutic potential of attenuating PARP1 activity in recalcitrant tumors, especially where PARP1 is aberrantly overexpressed and hyperactivated, may extend its therapeutic utility in wider cancer types beyond BRCA-deficiency. Here, we discuss treatment strategies to expand the tumor-selective therapeutic application of PARP inhibitors and novel approaches with predictive biomarkers to perturb NAD⁺ levels and hyperPARylation that inactivate PARP in recalcitrant tumors. We also provide an overview of genetic alterations that transform non-BRCA mutant cancers to a state of "BRCAness" as potential biomarkers for synthetic lethality with PARP inhibitors. Finally, we discuss a paradigm shift for the use of novel PARP inhibitors outside of cancer treatment, where it has the potential to rescue normal cells from severe oxidative damage during ischemia-reperfusion injury induced by surgery and radiotherapy.

WIP1 Promotes Homologous Recombination and Modulates Sensitivity to PARP Inhibitors

Genotoxic stress triggers a combined action of DNA repair and cell cycle checkpoint pathways. Protein phosphatase 2C delta (referred to as WIP1) is involved in timely inactivation of DNA damage response by suppressing function of p53 and other targets at chromatin. Here we show that WIP1 promotes DNA repair through homologous recombination. Loss or inhibition of WIP1 delayed disappearance of the ionizing radiation-induced 53BP1 foci in S/G2 cells and promoted cell death. We identify breast cancer associated protein 1 (BRCA1) as interactor and substrate of WIP1 and demonstrate that WIP1 activity is needed for correct dynamics of BRCA1 recruitment to chromatin flanking the DNA lesion. In addition, WIP1 dephosphorylates 53BP1 at Threonine 543 that was previously implicated in mediating interaction with RIF1. Finally, we report that inhibition of WIP1 allowed accumulation of DNA damage in S/G2 cells and increased sensitivity of cancer cells to a poly-(ADP-ribose) polymerase inhibitor olaparib. We propose that inhibition of WIP1 may increase sensitivity of BRCA1-proficient cancer cells to olaparib.