A site-selective, irreversible inhibitor of the DNA replication auxiliary factor proliferating cell nuclear antigen (PCNA)

BLVRA exerts its biological effects to induce malignant properties of hepatocellular carcinoma cells via Wnt/β-catenin pathway

The function of Biliverdin Reductase A (BLVRA) in hepatocellular carcinoma (HCC) cells proliferation, invasion and migration remains unclear. Therefore, this research intends to explore the effect of BLVRA on HCC cells growth and metastasis. BLVRA expression was analyzed in public dataset and examined by using western blot. The malignant function of BLVRA in HCC cell lines and its effect on Wnt/β-catenin pathway were measured. Analysis from GEPIA website showed that BLVRA expression was significantly increased in HCC tissues, and high expression of BLVRA resulted in worse prognosis of HCC patients. Results from western blot showed that BLVRA expression was obviously increased in HCC cell lines. Moreover, HepG2 and Hep3B cells in si-BLVRA-1 or si-BLVRA-2 group displayed an obvious reduction in its proliferation, cell cycle, invasion and migration compared to those in the si-control group. Additionally, si-BLVRA-1 or si-BLVRA-2 transfection significantly reduced the protein levels of Vimentin, Snail1 and Snail2, as well as decreased Bcl-2 expression and increased Bax and cleaved-caspase 3 expression. Furthermore, si-BLVRA treatment inhibited the protein levels of c-MYC, β-catenin, and Cyclin D1. After IWP-4 (Wnt/β-catenin inhibitor) treatment, the proliferation ability of HCC cells was significantly reduced. BLVRA expression was significantly increased in HCC tissues and cell lines, and knocked down of BLVRA could suppress the proliferation, invasion and migration in HCC cell lines, as well as induce cell apoptosis. Moreover, si-BLVRA transfection blocked the activation of Wnt/β-catenin pathway.

A phenotypic screen with Trypanosoma brucei for discovering small molecules that target the SLiM-binding pocket of proliferating cell nuclear antigen orthologs

Proliferating cell nuclear antigen (PCNA) is a homo-trimeric protein complex that clamps around DNA to tether DNA polymerases to the template during replication and serves as a hub for many other interacting proteins. It regulates DNA metabolic processes and other vital cellar functions through the binding of proteins having short linear motifs (SLiMs) like the PIP-box (PCNA-interacting protein-box) or the APIM (AlkB homolog 2 PCNA-interacting motif) in the hydrophobic pocket where SLiMs bind. However, overproducing TbPCNA or human PCNA (hPCNA) in the pathogenic protist Trypanosoma brucei triggers a dominant-negative phenotype of arrested proliferation. The mechanism for arresting T. brucei proliferation requires the overproduced PCNA orthologs to have functional intact SLiM-binding pocket. Sight-directed mutagenesis studies showed that T. brucei overproducing PCNA variants with disrupted SLiM-binding pockets grew normally. We hypothesized that chemically disrupting the SLiM-binding pocket would restore proliferation in T. brucei, overproducing PCNA orthologs. Testing this hypothesis is the proof-of-concept for a T. brucei-based PCNA screening assay. The assay design is to discover bioactive small molecules that restore proliferation in T. brucei strains that overproduce PCNA orthologs, likely by disrupting interactions in the SLiM-binding pocket. The pilot screen for this assay discovered two hit compounds that linked to predetermined PCNA targets. Compound #1, a known hPCNA inhibitor, had selective bioactivity to hPCNA overproduced in T. brucei, validating the assay. Compound #6 had promiscuous bioactivity for hPCNA and TbPCNA but is the first compound discovered with bioactivity for inhibiting TbPCNA.

A FRET-Based Assay for the Identification of PCNA Inhibitors

Proliferating cell nuclear antigen (PCNA) is the key regulator of human DNA metabolism. One important interaction partner is p15, involved in DNA replication and repair. Targeting the PCNA-p15 interaction is a promising therapeutic strategy against cancer. Here, a Förster resonance energy transfer (FRET)-based assay for the analysis of the PCNA-p15 interaction was developed. Next to the application as screening tool for the identification and characterization of PCNA-p15 interaction inhibitors, the assay is also suitable for the investigation of mutation-induced changes in their affinity. This is particularly useful for analyzing disease associated PCNA or p15 variants at the molecular level. Recently, the PCNA variant C148S has been associated with Ataxia-telangiectasia-like disorder type 2 (ATLD2). ATLD2 is a neurodegenerative disease based on defects in DNA repair due to an impaired PCNA. Incubation time dependent FRET measurements indicated no effect on PCNA^C148S-p15 affinity, but on PCNA stability. The impaired stability and increased aggregation behavior of PCNA^C148S was confirmed by intrinsic tryptophan fluorescence, differential scanning fluorimetry (DSF) and asymmetrical flow field-flow fractionation (AF4) measurements. The analysis of the disease associated PCNA variant demonstrated the versatility of the interaction assay as developed.

Replacement of Less-Preferred Dipolar Aprotic and Ethereal Solvents in Synthetic Organic Chemistry with More Sustainable Alternatives

Dipolar aprotic and ethereal solvents comprise just over 40% of all organic solvents utilized in synthetic organic, medicinal, and process chemistry. Unfortunately, many of the common "go-to" solvents are considered to be "less-preferable" for a number of environmental, health, and safety (EHS) reasons such as toxicity, mutagenicity, carcinogenicity, or for practical handling reasons such as flammability and volatility. Recent legislative changes have initiated the implementation of restrictions on the use of many of the commonly employed dipolar aprotic solvents such as dimethylformamide (DMF) and N-methyl-2-pyrrolidinone (NMP), and for ethers such as 1,4-dioxane. Thus, with growing legislative, EHS, and societal pressures, the need to identify and implement the use of alternative solvents that are greener, safer, and more sustainable has never been greater. Within this review, the ubiquitous nature of dipolar aprotic and ethereal solvents is discussed with respect to the physicochemical properties that have made them so appealing to synthetic chemists. An overview of the current legislative restrictions being imposed on the use of dipolar aprotic and ethereal solvents is discussed. A variety of alternative, safer, and more sustainable solvents that have garnered attention over the past decade are then examined, and case studies and examples where less-preferable solvents have been successfully replaced with a safer and more sustainable alternative are highlighted. Finally, a general overview and guidance for solvent selection and replacement are included in the Supporting Information of this review.

Betaine Supplementation Attenuates S-Adenosylhomocysteine Hydrolase-Deficiency-Accelerated Atherosclerosis in Apolipoprotein E-Deficient Mice

S-adenosylhomocysteine (SAH) is a risk factor of cardiovascular diseases and atherosclerosis. However, the causal association between SAH and atherosclerosis is still uncertain. In the present study, heterozygous SAH hydrolase (SAHH^+/−) knockout mice were bred with apolipoprotein E-deficient mice to produce ApoE^−/−/SAHH^+/− mice. At 8 weeks of age, these mice were fed on AIN-93G diets added with or without betaine (4 g betaine/100 g diet) for 8 weeks. Compared with ApoE^−/−/SAHH^WT mice, SAHH deficiency caused an accumulation of plasma SAH concentration and a decrease in S-adenosylmethionine (SAM)/SAH ratio as well as plasma homocysteine levels. Betaine supplementation lowered SAH levels and increased SAM/SAH ratio and homocysteine levels in ApoE^−/−/SAHH^+/− mice. Furthermore, SAHH deficiency promoted the development of atherosclerosis, which was reduced by betaine supplementation. The atheroprotective effects of betaine on SAHH-deficiency-promoted atherosclerosis were associated with inhibition of NFκB inflammation signaling pathway and inhibition of proliferation and migration of smooth muscle cells. In conclusion, our results suggest that betaine supplementation lowered plasma SAH levels and protected against SAHH-deficiency-promoted atherosclerosis through repressing inflammation and proliferation and migration of smooth muscle cells.

DTYMK promote hepatocellular carcinoma proliferation by regulating cell cycle

Overexpression of DTYMK is related with tumorigenesis and progression in several human tumors. However, the role of upregulated DTYMK in hepatocellular carcinoma (HCC) patients still remains unclear. In this study, the DTYMK expression in HCC tumors was evaluated in three GEO series (GSE14520, GSE54236, GSE63898), TCGA-LIHC, and ICGC-IRLR-JP cohorts. Survival analysis of DTYMK based on TCGA-LIHC and ICGC-LIRI-JP cohorts was conducted. We found that DTYMK was dramatically upregulated in tumor tissue compared with that in adjacent liver tissue. Kaplan-Meier analysis revealed that high expression of DTYMK in HCC patients' tumor tissue was significantly corresponded to worse overall survival (OS) (P < 0.05). Further analysis showed that overexpressing DTYMK led to poor relapse free survival (RFS) and disease-specific survival (DSS) (all P < 0.05). In conclusion, DTYMK is upregulated in tumors and correlated with poor prognosis in HCC patients. In our report, DTYMK is higher expression in HCC cancer tissue and cell line than tumor adjacent tissue and normal liver cell line. Knocking down DTYMK can inhabit tumor cell proliferation by interfering cell cycle, whereas overexpression of DTYMK can promote tumor cell proliferation. These findings indicate that upregulation of DTYMK enhances tumor growth and proliferation by promoting cell cycle.

Translesion synthesis inhibitors as a new class of cancer chemotherapeutics

Introduction: Translesion synthesis (TLS) is a DNA damage tolerance mechanism that replaces the replicative DNA polymerase with a specialized, low-fidelity TLS DNA polymerase that can copy past DNA lesions during active replication. Recent studies have demonstrated a primary role for TLS in replicating past DNA lesions induced by first-line genotoxic agents, resulting in decreased efficacy and acquired chemoresistance. With this in mind, targeting TLS as a combination strategy with first-line genotoxic agents has emerged as a promising approach to develop a new class of anti-cancer adjuvant agents. Areas covered: In this review, we provide a brief background on TLS and its role in cancer. We also discuss the identification and development of inhibitors that target various TLS DNA polymerases or key protein-protein interactions (PPIs) in the TLS machinery. Expert opinion: TLS inhibitors have demonstrated initial promise; however, their continued study is essential to more fully understand the clinical potential of this emerging class of anti-cancer chemotherapeutics. It will be important to determine whether a specific protein involved in TLS is an optimal target. In addition, an expanded understanding of what current genotoxic chemotherapies synergize with TLS inhibitors will guide the clinical strategies for devising combination therapies.

The inhibitory effect of (-)-Epicatechin gallate on the proliferation and migration of vascular smooth muscle cells weakens and stabilizes atherosclerosis

Vascular smooth muscle cells (VSMCs) lesions play an important role in atherosclerosis. The latest findings indicate that green tea extract has potential benefits for patients with atherosclerosis, but the components and mechanisms of action are unknown. (-)-Epicatechin gallate (ECG) is the main active ingredient extracted from green tea and has significant biological functions. However, the mechanism of ECG in atherosclerosis remains unclear. Therefore, we investigated the intervention of ECG on VSMCs induced by oxidized low-density lipoprotein (ox-LDL). The results show that ECG reduces the inflammatory response by preventing the overproduction of inflammatory mediators in VSMCs. ECG regulates the cell cycle and down-regulates the expression of proliferating cell nuclear antigen (PCNA) and cyclinD1, and then exerts an anti-proliferative effect. Furthermore, inhibition of the expression of matrix metalloproteinase 2 (MMP-2) and intercellular adhesion molecule 1 (ICAM-1) may be the mechanism by which ECG inhibits the migration of ox-LDL-induced VSMCs. Oil red O staining results show that ECG can improve cell foaming and reduce the content of total cholesterol (TC). In addition, ECG significantly reduces reactive oxygen species activity and also reduces the expression of p-p38, p-JNK, p-ERK1/2, p-IκBα, p-NF-κBp65, and TLR4. These results indicate that ECG has potential clinical applications for preventing atherosclerosis.

Targeting Proliferating Cell Nuclear Antigen (PCNA) as an Effective Strategy to Inhibit Tumor Cell Proliferation

Targeting highly proliferating cells is an important issue for many types of aggressive tumors. Proliferating Cell Nuclear Antigen (PCNA) is an essential protein that participates in a variety of processes of DNA metabolism, including DNA replication and repair, chromatin organization and transcription and sister chromatid cohesion. In addition, PCNA is involved in cell survival, and possibly in pathways of energy metabolism, such as glycolysis. Thus, the possibility of targeting this protein for chemotherapy against highly proliferating malignancies is under active investigation. Currently, approaches to treat cells with agents targeting PCNA rely on the use of small molecules or on peptides that either bind to PCNA, or act as a competitor of interacting partners. Here, we describe the status of the art in the development of agents targeting PCNA and discuss their application in different types of tumor cell lines and in animal model systems.

The Rev1-Polζ translesion synthesis mutasome: Structure, interactions and inhibition

DNA contains information that must be safeguarded, but also accessed for transcription and replication. To perform replication, eukaryotic cells use the B-family DNA polymerase enzymes Polδ and Polɛ, which are optimized for accuracy, speed, and processivity. The molecular basis of these high-performance characteristics causes these replicative polymerases to fail at sites of DNA damage (lesions), which would lead to genomic instability and cell death. To avoid this, cells possess additional DNA polymerases such as the Y-family of polymerases and the B-family member Polζ that can replicate over sites of DNA damage in a process called translesion synthesis (TLS). While able to replicate over DNA lesions, the TLS polymerases exhibit low-fidelity on undamaged DNA and, consequently, must be prevented from replicating DNA under normal circumstances and recruited only when necessary. The replicative bypass of most types of DNA lesions requires the consecutive action of these specialized TLS polymerases assembled into a dynamic multiprotein complex called the Rev1/Polζ mutasome. To this end, posttranslational modifications and a network of protein-protein interactions mediated by accessory domains/subunits of the TLS polymerases control the assembly and rearrangements of the Rev1/Polζ mutasome and recruitment of TLS proteins to sites of DNA damage. This chapter focuses on the structures and interactions that control these processes underlying the function of the Rev1/Polζ mutasome, as well as the development of small molecule inhibitors of the Rev1/Polζ-dependent TLS holding promise as a potential anticancer therapy.

Post-replication repair: Rad5/HLTF regulation, activity on undamaged templates, and relationship to cancer

The eukaryotic post-replication repair (PRR) pathway allows completion of DNA replication when replication forks encounter lesions on the DNA template and are mediated by post-translational ubiquitination of the DNA sliding clamp proliferating cell nuclear antigen (PCNA). Monoubiquitinated PCNA recruits translesion synthesis (TLS) polymerases to replicate past DNA lesions in an error-prone manner while addition of K63-linked polyubiquitin chains signals for error-free template switching to the sister chromatid. Central to both branches is the E3 ubiquitin ligase and DNA helicase Rad5/helicase-like transcription factor (HLTF). Mutations in PRR pathway components lead to genomic rearrangements, cancer predisposition, and cancer progression. Recent studies have challenged the notion that the PRR pathway is involved only in DNA lesion tolerance and have shed new light on its roles in cancer progression. Molecular details of Rad5/HLTF recruitment and function at replication forks have emerged. Mounting evidence indicates that PRR is required during lesion-less replication stress, leading to TLS polymerase activity on undamaged templates. Analysis of PRR mutation status in human cancers and PRR function in cancer models indicates that down regulation of PRR activity is a viable strategy to inhibit cancer cell growth and reduce chemoresistance. Here, we review these findings, discuss how they change our views of current PRR models, and look forward to targeting the PRR pathway in the clinic.

Profiling analysis of 17β-estradiol-regulated lncRNAs in mouse thymic epithelial cells

Thymus is the primary organ for T cell differentiation and maturation. Many studies have demonstrated that estrogen plays a crucial role in thymic epithelial cell (TEC) proliferation during thymic involution. LncRNAs are involved in various biological processes; however, estrogen-mediated lncRNA expression in TECs has not been yet reported. To address this question, the mouse medullary thymic epithelial cell line 1 (MTEC1) was treated with 17β-estradiol (E2). By using CCK8 assay and flow cytometry, we found that E2 was able to inhibit viability and proliferation of MTEC1 cells. The expression profiles of lncRNAs in MTEC1 cells with or without E2 treatment were then measured by RNA-Seq, and a total of 962 lncRNAs and 2,469 mRNAs were shown to be differentially expressed. The reliability of RNA-Seq was confirmed by quantitative RT-PCR. Correlation analysis was conducted to investigate the potential function of lncRNAs. According to gene ontology (GO) analysis, differentially expressed lncRNAs were mainly related to cell proliferation, cell cycle and cell apoptosis. KEGG pathway analysis indicated that these lncRNAs were associated with several pathways, namely immunological activity, metabolism and cytokine-cytokine receptor interaction. In conclusion, our study provided a novel direction for studying the relationship between lncRNAs and E2 in the thymus.

Structure of proliferating cell nuclear antigen (PCNA) bound to an APIM peptide reveals the universality of PCNA interaction

Proliferating cell nuclear antigen (PCNA) provides a molecular platform for numerous protein-protein interactions in DNA metabolism. A large number of proteins associated with PCNA have a well characterized sequence termed the PCNA-interacting protein box motif (PIPM). Another PCNA-interacting sequence termed the AlkB homologue 2 PCNA-interacting motif (APIM), comprising the five consensus residues (K/R)-(F/Y/W)-(L/I/V/A)-(L/I/V/A)-(K/R), has also been identified in various proteins. In contrast to that with PIPM, the PCNA-APIM interaction is less well understood. Here, the crystal structure of PCNA bound to a peptide carrying an APIM consensus sequence, RFLVK, was determined and structure-based interaction analysis was performed. The APIM peptide binds to the PIPM-binding pocket on PCNA in a similar way to PIPM. The phenylalanine and leucine residues within the APIM consensus sequence and a hydrophobic residue that precedes the APIM consensus sequence are crucially involved in interactions with the hydrophobic pocket of PCNA. This interaction is essential for overall binding. These results provide a structural basis for regulation of the PCNA interaction and might aid in the development of specific inhibitors of this interaction.

Modulation of human melanoma cell proliferation and apoptosis by hydatid cyst fluid of Echinococcus granulosus

Objective

The objective of this paper was to assess the effects of hydatid cyst fluid (HCF) of Echinococcus granulosus on melanoma A375 cell proliferation and apoptosis.

Methods

A375 cells were classified into five groups by in vitro culture: normal group, control group, 10% HCF group, 20% HCF group and 30% HCF group. Trypan blue staining method was employed to detect the toxicity of HCF. Effects of different concentrations of HCF on melanoma A375 cell proliferation at different time points were evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Flow cytometry and propidium iodide (PI) staining were used to detect cell cycle, and Annexin-V/PI double staining method was used to determine A375 cell apoptotic rate. Western blotting was applied to detect the expression of phosphorylated extracellular regulated protein kinases, proliferating cell nuclear antigen (PCNA), cell-cycle-related proteins (cyclin A, cyclin B1, cyclin D1 and cyclin E) and apoptosis-related proteins (Bcl-2, Bax and caspase-3).

Results

HCF with a high concentration was considered as atoxic to A375 cells. HCF promoted A375 cell proliferation, and the effects got stronger with an increase in concentrations but was retarded after reaching a certain range of concentrations. HCF increased phosphorylation level and expression of extracellular regulated protein kinase, as well as PCNA expression. HCF also promoted the transferring progression of A375 cells from the G0/G1 phase to the S phase to increase the cell number in S phase and increased the expression of cyclin A, cyclin D1 and cyclin E. HCF increased the expression of procaspase-3 (the precursor of apoptosis-related protein caspase-3) and antiapoptotic protein-Bcl-2, and decreased the expression of proapoptotic factor Bax, thereby inhibiting cell apoptosis.

Conclusion

As a result, this study confirmed that HCF promotes proliferation and inhibits apoptosis of melanoma A375 cells.

Targeting the Translesion Synthesis Pathway for the Development of Anti-Cancer Chemotherapeutics

Human cells possess tightly controlled mechanisms to rescue DNA replication following DNA damage caused by environmental and endogenous carcinogens using a set of low-fidelity translesion synthesis (TLS) DNA polymerases. These polymerases can copy over replication blocking DNA lesions while temporarily leaving them unrepaired, preventing cell death at the expense of increasing mutation rates and contributing to the onset and progression of cancer. In addition, TLS has been implicated as a major cellular mechanism promoting acquired resistance to genotoxic chemotherapy. Owing to its central role in mutagenesis and cell survival after DNA damage, inhibition of the TLS pathway has emerged as a potential target for the development of anticancer agents. This review will recap our current understanding of the structure and regulation of DNA polymerase complexes that mediate TLS and describe how this knowledge is beginning to translate into the development of small molecule TLS inhibitors.

Sinoporphyrin sodium triggered sono-photodynamic effects on breast cancer both in vitro and in vivo

Sono-photodynamic therapy (SPDT) is a promising anti-cancer strategy. Briefly, SPDT combines ultrasound and light to activate sensitizers that produce mechanical, sonochemical and photochemical activities. Sinoporphyrin sodium (DVDMS) is a newly identified sensitizer that shows great potential in both sonodynamic therapy (SDT) and photodynamic therapy (PDT). In this study, we primarily evaluated the combined effects of SDT and PDT by using DVDMS on breast cancer both in vitro and in vivo. In vitro, DVDMS-SPDT elicits much serious cytotoxicity compared with either SDT or PDT alone by MTT and colony formation assays. 2',7'-Dichlorodihydrofluo-rescein-diacetate (DCFH-DA) and dihydroethidium (DHE) staining revealed that intracellular reactive oxygen species (ROS) were significantly increased in groups given combined therapy. Terephthalic acid (TA) method and FD500-uptake assay reflected that cavitational effects and cell membrane permeability changes after ultrasound irradiation were also involved in the enhancement of combination therapy. In vivo, DVDMS-SPDT markedly inhibits the tumor volume and tumor weight growth. Hematoxylin-eosin staining and immunohistochemistry analysis show DVDMS-SPDT greatly suppressed tumor proliferation. Further, DVDMS-SPDT significantly inhibits tumor lung metastasis in the highly metastatic 4T1 mouse xenograft model, which is consistent well with the in vitro findings evaluated by transwell assay. Moreover, DVDMS-SPDT did not produces obvious effect on body weight and major organs in 4T1 xenograft model. The results suggest that by combination SDT and PDT, the sensitizer DVDMS would produce much better therapeutic effects, and DVDMS-SPDT may be a potential strategy against highly metastatic breast cancer.

Evaluation of the protective effects of hesperetin against cisplatin-induced ototoxicity in a rat animal model

OBJECTIVES

We aimed to investigate the effects of hesperetin as a flavanon both histopathologically and immunohistochemically on cochlear apoptosis in a rat model of cisplatin-induced ototoxicity (CIO). The evaluation of the effects of hesperetin on cisplatin-induced hearing loss was performed using distortion product otoacoustic emission (DPOAE).

METHODS

Twenty-eight wistar albino rats were used in the current study. The rats were randomly divided into four groups with seven rats in each group. Group C was exposed to a single dose of cisplatin (12mg/kg) by intraperitoneal injection. Group CH received intraperitoneally cisplatin (12mg/kg) and hesperetin (20mg/kg). Group H was exposed to hesperetin (20mg/kg) intraperitoneally. The sham group (group S) received normal saline (6cc) intraperitoneally. The measurements of DPOAE and signal-noise ratios (SNR) were performed before the treatment and again on the first and 6 days after administration of the drugs. Rats were sacrificed and cochleae were dissected 10 days after drug administration. The cochlear tissue was assessed in all groups by histopathologic, immunohistochemical and TUNEL assay. In addition, serum oxidative stress markers and antioxidant parameters were analyzed.

RESULTS

There was a significant difference between the basal value and the sixth day at frequencies 8.4, 9.6 and 9.96 for group C. We also found a significant difference between the first and sixth day at frequencies 7.2, 8.4, 9.6 and 9.96. On the 6th day, there were significant differences between C and S groups at all frequencies except 2.4. We showed a significant difference between C and H groups at frequencies 4.8, 6.0, 8.4, 9.6 and 9.96. There was also a significant difference between C and CH groups at frequencies 2.4, and 3.6. We found lower levels of oxidants and higher levels of antioxidants in CH group as compared to C group. C group had a significantly greater number of TUNEL-positive cells than did S, H and CH groups. The number of TUNEL-positive cells in CH group was higher than in S and H groups. There was a significant difference between the positive PCNA cells of CH group compared to S and H groups in spiral ganglion and stria vascularis. In addition, there were no positive PCNA cells in C group.

CONCLUSIONS

Hesperetin may prevent ototoxicity by increased antioxidant enzymes and reduced oxidant parameters and protected against apoptosis resulting from a proliferation of cochlear cells in CIO.