Cells In G1 Phase Research Articles

Repurposing of quinoline alkaloids identifies their ability to enhance doxorubicin‐induced sub‐G0/G1 phase cell cycle arrest and apoptosis in cervical and hepatocellular carcinoma cells

The ability of quinoline alkaloids (cinchonine, cinchonidine, quinine, and quinidine) to sensitize different human cancer cell lines to doxorubicin (DOX)-induced cell death was evaluated. Cell viability was analyzed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and the alkaloids ability to enhance DOX-induced apoptosis was explored using Western blotting analysis. Also, flow cytometry was applied to analyze cell fractions in the different cell cycle phases. All alkaloids showed a significant enhancement of DOX-induced cell death in HeLa and HepG2 cell lines. The chemosensitizing activity of the quinoline alkaloids was attributed to the induction of apoptosis as indicated by splitting of caspase-3 and its substrate poly (ADP-ribose) polymerase (PARP). In addition, there was an increase in the cell fractions in sub-G0/G1 phase in case of DOX combination with the alkaloids. This study proves the ability of the quinoline alkaloids to enhance DOX-induced apoptotic cell death in human cervical and hepatocellular carcinoma cells.

Cajal body dynamics in soybean root meristem cells under chilling stress and recovery

Cajal bodies (CBs) are nuclear domains widely present in eukaryotic cells. Their main functions include processing and modifications of small nuclear RNAs (snRNAs), including those participating in mRNA splicing. CBs are dynamic structures in terms of their mobility, fusion and split, which results in their variable number and size during cell cycle. CBs are supposed to play a role in response to various stresses or at least the cell reactions to these stressors is related with changing CB number and size. That is why the number and size of CBs were analyzed in primary root meristematic cells of soybean, a subtropical plant, whose seedlings were grown at 23 °C (the control), subjected to chilling stress (10 °C) and recovered at 23 °C after chilling. These parameters were examined in three classes of cell size which corresponded to the cells in G1, S and G2 phases. The general number of CBs in nuclei of the chilled plants was halved in comparison to the control cells, however this parameter returned to the control value during recovery. Such a result suggests that chilling may hinder formation of CBs or it may provoke their fusion. Moreover, the number of small CBs decreased and the number of large CBs increased during interphase progress, while the general number of CBs was constant in each treatment group. The constant number of CBs from G1 to G2 phase proves that in soybean cells they enlarge as a result of component accumulation rather than their fusion. The reasons of such a state of soybean CBs are discussed.

Abstract 4093: Drug combinations that can overcome resistance to PARP inhibitor therapy for BRCA1-associated breast cancer

Abstract Triple negative breast cancer (TNBC) represents approximately 10–15% of all breast cancers and has a poor outcome as it lacks a receptor target for therapy. Poly (ADP-ribose) polymerases inhibitors (PARPi) drugs have demonstrated some effectiveness in treating BRCA1 or BRCA2 mutated breast and ovarian cancers but resistance to PARPi is common. Published results found that resistance to Olaparib, a PARPi, can be due to downregulation of EMI1 and the consequent upregulation of the RAD51 recombinase. Using a tissue culture-based cell viability assay, we extended those observations to another PARPi and to other chemotherapy drugs that affect DNA repair or the cell cycle. As we expected, EMI1 downregulation resulted in resistance to another PARPi drug, Talazoparib. EMI1 downregulation also led to resistance to other cytotoxic drugs, Cisplatin and CHK1 inhibitor. Surprisingly, EMI1 downregulation also led to resistance to a MEK inhibitor, though this inhibitor blocks cells in G1 phase of the cell cycle and would not be expected to be sensitive to EMI1 levels. Notably, increasing the RAD51 protein expression can mimic the EMI1 downregulation and lead to resistance to different PARPis and the other cytotoxic drugs. This result suggests that the key downstream effect of EMI1 downregulation is increasing the concentration of RAD51 protein in the cell. We found that combining CHK1 inhibitor with Olaparib results in cell death in a dose specific manner. This combination therapy may be a means to overcome the PARPi resistance in BRCA1-deficient TNBC cells. Citation Format: Dina Mohamed Abd El Aziz Moustafa, Maha Abd Elwahed, Hanaa El Said, Jeffrey Parvin. Drug combinations that can overcome resistance to PARP inhibitor therapy for BRCA1-associated breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4093.

Abstract 92: Increasing TTFields treatment efficacy by targeting G2 cell cycle checkpoint

Abstract Introduction; Tumor Treating Fields (TTFields) is a novel non-invasive anticancer treatment modality utilizing alternating electric fields. TTFields is FDA approved for glioblastoma patients after demonstrating a 5 months increase in overall survival, and for unresectable mesothelioma patients after the STELLAR trial showed an overall survival of 18 months without increasing the toxicity. While the effectiveness of TTFields is initially attributed to the effects of TTFields during cell division, studies are ongoing analysing its interphase effects and impact on the tumor (micro)environment. Our aim is to further exploit the working mechanism of TTFields by analysing its effect on the cell cycle and identify targets to increase its efficacy. Material and Methods; To analyse the effect of TTFields on the cell cycle, A172 glioblastoma cells were synchronized in S-phase by double thymidine block. Six hours post-release, cells were subjected to TTFields treatment (200kHz; 4,5V/cm). Cell cycle analysis was performed by flow cytometry (PI, α-phospho-histone H3Ser10). Efficacy of combination strategies were tested in 3 different glioblastoma cells lines (A172, U251 and SNB-19). Efficacy was quantified by colony formation assay (CFA) testing the cell reproductive death after treatment (i.e. only viable cells after treatment are replated to analyse the colony forming capacity). Results: TTFields treatment of synchronized A172 cells showed that TTFields causes an accumulation of cells in G2 phase and delayed entry into mitosis with less than 1% of the cells in mitosis 4 hours after TTFields exposure (versus 5% of mitotic cells in the control arm, p<0.001). This arrest can be abrogated by Wee1 inhibition (AZD1775) increasing the mitotic population to more than 35% at 4 hours after TTFields exposure (p<0.001). To test the efficacy of targeting the G2 checkpoint during TTFields treatment, cells were treated with TTFields and a Wee1 (AZD1775, PD0166285) or Chk1 (AZD7762) inhibitor for 72 hours and then replated for CFA. We observed an impressive synergistic effect between TTFields and any of these G2 cell cycle interfering drugs in all three cell lines (p<0.001). Conclusion: The underlying mechanism of the G2 checkpoint activation and the synergistic effect of TTFields plus G2 checkpoint targeting agents is subject of ongoing research. By any means, the combination of TTFields and G2 checkpoint targeting agents causes a synergistic treatment effect and is a very promising strategy. Citation Format: Paul Slangen, Mariska van Geldorp, Mark de Gooijer, Olaf van Tellingen, Gerben Borst. Increasing TTFields treatment efficacy by targeting G2 cell cycle checkpoint [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 92.

Effect of circular RNA hsa_circ_0008898 on oral squamous cell carcinoma and its mechanism

Objective: To investigate the effect and molecular mechanism of hsa_circ_0008898 on the cell proliferation, migration, invasion and tumor formation of oral squamous cell carcinoma (OSCC). Methods: Quantitative real-time PCR (qPCR) and Western blotting were used to detect the expression of hsa_circ_0008898, miR-197-5p and ras homolog gene family member A (RHOA) in OSCC tissues, adjacent tissues, OSCC cells and human normal oral keratinocytes (NOK). CAL27 and SCC-25 cells were transfected with si-hsa_circ_0008898#1 (knockdown group 1), si-hsa_circ_0008898#2 (knockdown group 2), hsa_circ_0008898 (circ overexpression group) and blank plasmid (circ blank group), respectively. Then miR-197-5p inhibitor (inhibition group) and blank plasmid (inhibition control group) were transfected into hsa_circ_0008898 knockdown cells (knockdown group 1). CAL27 and SCC-25 cells were transfected with miR-197-5p mimics (miR overexpression group) and blank plasmid (miR blank group), and then transfected hsa_circ_0008898 vector (co-transfection group 1), RHOA vector (co-transfection group 2) and blank plasmid (co-transfection control group) in cells overexpressing miR-197-5p. Cell counting kit 8 (CCK-8), colony formation, Transwell and scratch test were used to detect cell proliferation, cloning ability, cell cycle distribution, cell invasion and migration ability. Ten nude mice were equally divided into two groups, with 5 mice in each group. SCC-25 cells transfected with blank plasmid (control group) and SCC-25 cells transfected with sh-hsa_circ_0008898 (knockout group) were subcutaneously injected into the armpit. The volume and mass of the tumor were measured. Results: The expressions of hsa_circ_0008898 (2.89±0.72) and RHOA (2.62±0.21) in OSCC tissues were significantly higher than those in para-carcinoma tissues (1.00±0.48, 1.00±0.11, respectively), while the expression of miR-197-5p in OSCC tissues （0.46±0.24） was significantly lower than that in para-carcinoma tissues (1.00±0.42) (P<0.05). Compared with NOK, the expression of hsa_circ_0008898 and RHOA in CAL27 and SCC-25 cells increased significantly, while the expression of miR-197-5p decreased (P<0.05). Compared with circ blank group, the cell viability, colony formation, scratch healing rate and invasive cell number of CAL27 and SCC-25 cells in knockdown group 1 and group 2 were significantly decreased, while the proportion of cells in G1 phase was significantly increased (P<0.05). Compared with inhibition control group, the cell viability, colony formation, scratch healing rate and invasive cell number of CAL27 and SCC-25 in inhibition group were significantly increased, while the proportion of cells in G1 phase was significantly decreased in inhibition group (P<0.05). Compared with miR blank group, the cell viability, colony formation, scratch healing rate and invasive cell number of CAL27 and SCC-25 in miR overexpression group were significantly decreased, while the proportion of cells in G1 phase was significantly increased in miR overexpression group (P<0.05). Compared with co-transfection control group, the cell viability, colony formation, migration area and invasive cell number of CAL27 and SCC-25 in co-transfection group2 were significantly increased, while the proportion of cells in G1 phase was significantly decreased in co-transfection group 2 (P<0.05). The volume and mass of transplanted tumor in knockout group ［(660.4±67.8) mm(3 )and (0.60±0.06) g, respectively］ were significantly lower than those in control group ［(1 210.4±198.9) mm(3) and (1.00±0.12) g, respectively］. Conclusions: Knockdown of hsa_circ_0008898 inhibited OSCC cells proliferation, cloning, migration and invasion and induced cell cycle arrest in vitro by regulating the miR-197-5p/RHOA. Additionally, Knockdown of hsa_circ_0008898 also inhibited tumor formation of OSCC cells in vivo.

Cytotoxic effects of a triterpene‐enriched fraction of Cecropia pachystachya on the human hormone-refractory prostate cancer PC3 cell line

BackgroundProstate cancer (PCa) is the most diagnosed invasive cancer and a leading cause of death in men in western countries. Most patients initially respond to androgen deprivation but finally develop hormone-refractory disease, which results in advanced clinical failure and death. Since hormone-refractory disease is highly radiotherapy and chemotherapy resistant, increasing interest has been placed on finding novel therapies for this advanced type of Pca. PurposeThe potential cytotoxic effects of the crude extract and fractions obtained from the leaves of Cecropia pachystachya Trécul on different human cancer cell lines were investigated. Additionally, the mechanism of cell death induction of the most active sample (triterpene-enriched fraction, TEF) on the human hormone-refractory prostate PC3 cell line was examined. MethodsSulforhodamine B assay was used to measure the viability of human tumor and non-tumor cell lines. To elucidate the mechanism of PC3 cells death induced by TEF, different methodological approaches were used: cell cycle analysis and annexin V/PI staining, nuclear morphological analysis, and senescence-associated-β-galactosidase assay. Moreover, the mitochondrial membrane potential was measured, and the long-term effects of TEF on PC3 cells were evaluated. ResultsTEF exerted cytotoxic effects on PC3 cells but not on human non-tumor cells. The analysis of nuclear morphology of PC3 cells treated with TEF increased the number of cells with large and regular nuclei suggesting senescence induction, which was supported by β-galactosidase overexpression. Regarding PC3 cells cycle, TEF reduced the number of cells in G1 phase and increased that in sub G0/G1. Apoptosis was not involved in PC3 cell death. However, there was a decrease in mitochondrial membrane potential without the participation of reactive oxygen species (ROS) in the cytotoxic effects detected. Furthermore, there was a decrease in the number of viable cells able to duplicate after long-term TEF treatment. ConclusionsThe results showed the in vitro cytotoxic potential of the triterpene-enriched fraction obtained from the leaves of C. pachystachya on human prostate cancer PC3 cell line.

G1/S transcription factors assemble in increasing numbers of discrete clusters through G1 phase.

In budding yeast, the transcription factors SBF and MBF activate a large program of gene expression in late G1 phase that underlies commitment to cell division, termed Start. SBF/MBF are limiting with respect to target promoters in small G1 phase cells and accumulate as cells grow, raising the questions of how SBF/MBF are dynamically distributed across the G1/S regulon and how this impacts the Start transition. Super-resolution Photo-Activatable Localization Microscopy (PALM) mapping of the static positions of SBF/MBF subunits in fixed cells revealed each transcription factor was organized into discrete clusters containing approximately eight copies regardless of cell size and that the total number of clusters increased as cells grew through G1 phase. Stochastic modeling using reasonable biophysical parameters recapitulated growth-dependent SBF/MBF clustering and predicted TF dynamics that were confirmed in live cell PALM experiments. This spatio-temporal organization of SBF/MBF may help coordinate activation of G1/S regulon and the Start transition.

CRISPR/Cas9-mediated Knockout of SIRT6 Imparts Remarkable Antiproliferative Response in Human Melanoma Cells in vitro and in vivo.

Melanoma is one of the most aggressive, potentially fatal forms of skin cancer and has been shown to be associated with solar ultraviolet radiation-dependent initiation and progression. Despite remarkable recent advances with targeted and immune therapeutics, lasting and recurrence-free survival remain significant concerns. Therefore, additional novel mechanism-based approaches are needed for effective melanoma management. The sirtuin SIRT6 appears to have a pro-proliferative function in melanocytic cells. In this study, we determined the effects of genetic manipulation of SIRT6 in human melanoma cells, in vitro and in vivo. Our data demonstrated that CRISPR/Cas9-mediated knockout (KO) of SIRT6 in A375 melanoma cells resulted in a significant (1) decrease in growth, viability and clonogenic survival and (2) induction of G1-phase cell cycle arrest. Further, employing a RT2 Profiler PCR array containing 84 key transformation and tumorigenesis genes, we found that SIRT6 KO resulted in modulation of genes involved in angiogenesis, apoptosis, cellular senescence, epithelial-to-mesenchymal transition, hypoxia signaling and telomere maintenance. Finally, we found significantly decreased tumorigenicity of SIRT6 KO A375 cells in athymic nude mice. Our data provide strong evidence that SIRT6 promotes melanoma cell survival, both in vitro and in vivo, and could be exploited as a target for melanoma management.

In Vitro and In Vivo Antitumor Efficacy of Hizikia fusiforme Celluclast Extract against Bladder Cancer

Various physiological benefits have been linked to Hizikia fusiforme (HF), an edible brown seaweed. Here, fucose-containing sulfated polysaccharides were extracted from celluclast-processed HF (SPHF) and their antitumor efficacy against bladder cancer was evaluated in vitro and in vivo. SPHF possesses high sulfated polysaccharide and fucose contents and free radical scavenging activities compared to those of celluclast-processed HF extracts (CHF). SPHF inhibited bladder cancer EJ cell proliferation via G1-phase cell cycle arrest. This was due to the induction of p21WAF1 expression associated with the downregulation of CDKs and cyclins. Moreover, JNK phosphorylation was identified as an SPHF-mediated signaling molecule. SPHF treatment also hindered the migration and invasion of EJ cells by inhibiting MMP-9 expression, which was attributed to the repression of transcriptional binding to NF-κB, AP-1, and Sp-1 in the MMP-9 promoter region. In an animal study, SPHF treatment suppressed EJ tumor growth in xenograft mice similarly to cisplatin. Furthermore, no toxicity signs were found after weight loss assessment, biochemical tests, and organ tissue immunostaining during oral administration of 20–200 mg/kg SPHF for 20 days. Therefore, our study demonstrates the antitumor efficacy of SPHF in vitro and in vivo, thus highlighting its potential for bladder cancer treatment development.

Nuclear accumulation of ZFP36L1 is cell cycle-dependent and determined by a C-terminal serine-rich cluster.

ZFP36L1 is an RNA-binding protein responsible for mRNA decay in the cytoplasm. ZFP36L1 has also been suggested as a nuclear-cytoplasmic shuttling protein because it contains a potential nuclear localization signal and a nuclear export signal. However, it remains unclear how the nuclear localization of ZFP36L1 is controlled. In this study, we provide evidence that the nuclear accumulation of ZFP36L1 protein is modulated in a cell cycle-dependent manner. ZFP36L1 protein accumulation in fractionated nuclei was particularly prominent in cellsarrested at G1-/S-phase boundary, while it was downregulated in S-phase cells, and eventually disappeared in G2-phase nuclei. Moreover, forced nuclear targeting of ZFP36L1 revealed marked downregulation of this proteinin S- and G2-phase cells, suggesting that ZFP36L1 can be eliminated in the nucleus. The C-terminal serine-rich cluster of ZFP36L1 is critical for the regulation of its nuclear accumulation because truncation of this probable disordered region enhanced the nuclear localization of ZFP36L1, increased its stability and abolished its cell cycle-dependent fluctuations. These findings provide the first hints to the question of how ZFP36L1 nuclear accumulation is controlled during the course of the cell cycle.

CDK4/6 inhibitor palbociclib overcomes acquired resistance to third-generation EGFR inhibitor osimertinib in non-small cell lung cancer (NSCLC).

BackgroundThe third‐generation EGFR‐TKI, represented by osimertinib, has been widely used in clinical practice; however, resistance eventually emerges. At present, it remains unclear whether an abnormal cell cycle is involved in acquired resistance, and whether the combination of palbociclib (CDK4/6 inhibitor) and osimertinib can overcome the third‐generation TKI resistance.MethodsWe established osimertinib‐resistant cells (H1975 OR) derived from EGFR‐mutant NSCLC cells H1975. Drug effects on cells were assessed with Cell Counting Kit‐8 (CCK8). Protein alterations were detected with western blot analysis. RT‐PCR was used to evaluate the differences of gene mRNA. Cell cycle distribution of H1975 S and H1975 OR cells was compared using flow cytometry.ResultsCompared with H1975, the sensitivity of H1975OR to the CDK4/6 inhibitor was increased and the proportion of cells in G1 phase was decreased. The mRNA level of CDK4, CDK 6 and the protein level of CDK4, pRB were increased in H1975OR. In the H1975OR cells, palbociclib significantly increased the proportion of G1 phase cells. The combination of osimertinib and palbociclib synergistically decreased the survival of H1975OR by cell cycle arrest. Combined treatment was found to inhibit the initial phosphorylation of RB by inhibiting the function of CDK4/6, significantly reducing the level of p‐RB, and blocking cell proliferation.ConclusionsAn osimertinib acquired resistance cell line (H1975 OR) was successfully established. The expression of cell cycle related genes was altered in H1975OR. The expression of CDK4 and the phosphorylation of Rb, the downstream molecule of CDK4/6, was increased in H1975OR cells. The combination of CDK4/6 inhibitor palbociclib and osimertinib could overcome the acquired resistance of osimertinib.

Abstract A53: Synergistic interaction of HDACi and PLK1i in Group 3 MYC-amplified medulloblastoma

Abstract Medulloblastoma (MB) is one of the common malignant brain tumors in children. Patients with MYC-amplified Group 3 MBs exhibit particularly poor survival rates even after intensive therapy. Surviving patients often suffer from long-term side effects. This calls for new therapeutic strategies, such as targeted therapy options. The sensitivity of MYC-amplified MBs to class I histone deacetylase (HDAC) inhibition was previously shown. In order to elucidate potential combination partners, we have identified PLK1 as one of the top regulated genes following treatment of MYC-amplified Group 3 MB cells with class I HDACi entinostat. Our aim here is to investigate possible combination treatments with entinostat and several PLK1i (volasertib, GSK461364, onvansertib). The cell metabolic activity was evaluated using MYC-amplified and nonamplified MB, high-grade glioma (HGG) and neuroblastoma (NB) cell lines after single and combination treatments. The interaction effect was determined by combination index (CI) (Chou-Talalay CI calculation method). Results were validated assessing cell viability, cell cycle profile, and caspase activity upon treatment with single agents or combination. On-target activity was examined using immunoblotting for pTCTP and H3K27ac. We have confirmed our findings in an inducible MYC cell line. The gene expression profile was analyzed in HD-MB03 cell line after entinostat, volasertib, or combination treatment. We demonstrate that the MYC target gene PLK1 is significantly downregulated upon HDACi treatment. Based on this, we hypothesized that inhibition of both class I HDACs and PLK1 could have synergistic effects. MYC-amplified cell lines were more sensitive than nonamplified cell lines to treatment with all PLK1i investigated, showing 3 to 10 times lower IC50. PLK1i and entinostat interacted synergistically (CI below 0.9) at lower concentrations in MYC-amplified compared to non-amplified MB cell lines. Similar results were obtained for MYC or N-MYC-amplified HGG and NB cell lines. We also observed the loss of viability and loss of fraction of cells in G1 phase in MYC-amplified MB cells after treatment with entinostat and PLK1i. MYC target genes were significantly downregulated in the MYC-amplified MB cell line HD-MB03 after treatment with PLK1i and entinostat. Moreover, we demonstrated reduction of MYC levels and faster MYC degradation upon volasertib treatment. Our data suggest that MYC-amplification might serve as a predictive biomarker for PLK1i treatment in MB and other entities. The combination of entinostat and PLKi could be a candidate therapy for future clinical trials for MYC-amplified Group 3 MB, and possibly other tumors harboring MYC amplification. Citation Format: Gintvile Valinciute, Jonas Ecker, Thomas Hielscher, Christin Schmidt, Marc Remke, Gianluca Sigismondo, Jeroen Krijgsveld, Stefan M. Pfister, Olaf Witt, Till Milde. Synergistic interaction of HDACi and PLK1i in Group 3 MYC-amplified medulloblastoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A53.

A Novel Combination Treatment with Honokiol and Rapamycin Effectively Restricts c-Met-Induced Growth of Renal Cancer Cells, and also Inhibits the Expression of Tumor Cell PD-L1 Involved in Immune Escape.

The mTOR inhibitor Rapamycin has tumor inhibitory properties; and it is also used as an immunosuppressive agent after organ transplantation. However, prolonged Rapamycin treatment re-activates Akt and can promote cancer growth. Honokiol is a natural compound with both anti-tumorigenic and anti-inflammatory properties. Here, we assessed the anti-tumor effects of Rapamycin and Honokiol combination in renal cell carcinoma (RCC). Receptor tyrosine kinase c-Met-mediated signaling plays a major role in RCC growth. We observed that compared with Rapamycin alone, Rapamycin + Honokiol combination can effectively down-regulate c-Met-induced Akt phosphorylation in renal cancer cells; and it markedly inhibited Ras activation and cell proliferation and promoted G1 phase cell cycle arrest. The combination treatment significantly induced ROS generation and cancer cell apoptosis even when c-Met is activated. Importantly, Honokiol, but not Rapamycin, decreased c-Met-induced expression of the co-inhibitory molecule PD-L1, implied in the immune escape of renal cancer cells. In mouse renal cancer cells and Balb/c splenocytes co-culture assay, Rapamycin + Honokiol markedly potentiated immune-cell-mediated killing of cancer cells, possibly through the down-regulation of PD-L1. Together, Honokiol can effectively overcome the limitation of Rapamycin treatment alone; and the combination treatment can markedly restrict the growth of RCC, with particular importance to post-transplantation renal cancer.

The MRE11 nuclease promotes homologous recombination not only in DNA double-strand break resection but also in post-resection in human TK6 cells

Homologous recombination (HR) repairs double-strand breaks (DSBs) occurring in sister chromatids using the intact sisters as the repair template. HR is initiated by DSB resection, which generates 3′ single-strand DNA (ssDNA). RAD51 recombinase polymerizes on the ssDNA and undergoes strand exchange with intact sister chromatids, generating junction molecules (JMs). The separation of JMs completes HR-dependent DSB repair. Defective resolution of JMs not only leaves DSBs unrepaired but also has the broken sisters remain entangled with the intact sisters, leading to the formation of isochromatid-type breaks, where both sister chromatids are broken at the same sites, in mitotic chromosome spreads. The MRE11 nuclease plays a key role in HR, and it is generally believed that MRE11 does so by initiating DSB resection. We here showed that the loss of MRE11 reduced the efficiency of HR in human TK6 cells without affecting DSB resection, indicating a role for MRE11 in HR also at a post-resection step. MRE11-deficient TK6 cells showed proficient induction of RAD51 foci by ionizing-radiation (IR) and olaparib but significantly delayed their resolution. Although exposure of G2-phase cells to IR cleaves only one of two sister chromatids, the loss of the MRE11-nuclease activity increased the number of isochromosome-type breaks in subsequent M phase. The overexpression of GEN1 resolvase suppressed the formation of IR-induced isochromatid-type breaks in MRE11-nuclease-deficient TK6 cells. These data indicate that MRE11 plays an important role in HR by processing JMs. We propose the dual roles of MRE11 in HR at DSB resection and post-resection steps.

Dexmedetomidine Attenuates High Glucose-induced HK-2 Epithelial-mesenchymal Transition by Inhibiting AKT and ERK

ObjectiveTo explore the protective effects of dexmedetomidine (Dex) against high glucose-induced epithelial-mesenchymal transition in HK-2 cells and relevant mechanisms. MethodsHK-2 cells were exposed to either glucose or glucose+Dex for 6 h. The production of ROS, morphology of HK-2 cells, and cell cycle were detected. Moreover, the expression of AKT, p-AKT, ERK, p-ERK, PI3K, E-Cadherin, Claudin-1, and α-SMA were determined and compared between HK-2 cells exposed to glucose and those exposed to both glucose and Dex with or without PI3K/AKT pathway inhibitor LY294002 and ERK pathway inhibitor U0126. ResultsCompared with HK-2 cells exposed to high level of glucose, the HK-2 cells exposed to both high level of glucose and Dex showed: (1) lower level of ROS production; (2) cell morphology was complete; (3) more cells in G1 phase; (4) lower expression of p-AKT, p-ERK and α-SMA, higher expression of E-Cadherin and Claudin-1. PI3K/AKT inhibitor LY294002 and ERK inhibitor U0126 decreased the expression of p-AKT, p-ERK and α-SMA, and increased the expression of E-Cadherin and Claudin-1. ConclusionDex can attenuate high glucose-induced HK-2 epithelial-mesenchymal transition by inhibiting AKT and ERK.

Granulocyte-macrophage colony-stimulating factor enhances effect of temozolomide on high-grade glioma cells.

In the present study, to delve into the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) combined with temozolomide (TMZ) on high-grade glioma cells and related mechanism, six cases of high-grade glioma cells from patient's tumor tissues were cultured. 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide (MTT) assay was performed to detect cell proliferation and toxicity. Flow cytometry was performed to ascertain cell cycle and apoptosis rate. To detect the expressions of O6-methylguanine-DNA methyltransferase (MGMT) methylation status and MGMT protein, respectively, specific PCR and immunofluorescence were performed. According to the results of MTT assay, compared with the results of control group, GM-CSF group exhibited enhanced cell viability in varying degrees. In three cases of cells (MGMT gene methylation), the combination group [(67.67 ± 1.16), (68.13 ± 1.06), (68.42 ± 1.73)] had noticeably lower cell viability than the corresponding TMZ group [(90.00 ± 1.73), (82.33 ± 1.53), (82.67 ± 2.11)] (P < 0.01). Nevertheless, the two groups showed no significant difference in another three cases (MGMT gene unmethylated) (P > 0.05). In combination group, the apoptosis rate of the MGMT methylation cells was higher than that in the corresponding TMZ group (P < 0.01), which is consistent with MTT assay results. In all six cases of primary glioma cells, the fraction of cells in G1 phase of GM-CSF-treated group was noticeably down-regulated and was up-regulated in S phase (P < 0.01). GM-CSF could induce high-grade glioma cells to rapidly enter the cell cycle, thereby enhancing the lethal effect of TMZ on glioma cells with MGMT gene promoter methylation. However, this effect is not ideal on glioma cells with MGMT unmethylation.

Purification, Characterization, Identification, and Anticancer Activity of a Circular Bacteriocin From Enterococcus thailandicus.

New anticancer agents are continually needed because cancerous cells continue to evolve resistance to the currently available chemotherapeutic agents. The aim of the present study was to screen, purify and characterize a hepatotoxic bacteriocin from Enterococcus species. The production of bacteriocin from the Enterococcus isolates was achieved based on their antibacterial activity against indicator reference strains. Enterococcus isolates showed a broad spectrum of antibacterial activity by forming inhibition zones with diameters ranged between 12 and 29 mm. The most potent bacteriocin producing strain was molecularly identified as Enterococcus thailandicus. The crude extracted bacteriocin was purified by cation exchange and size exclusion chromatography that resulted in 83 fractions. Among them, 18 factions were considered as bacteriocins based on their positive antibacterial effects. The anticancer effects of the purified bacteriocins were tested against HepG2 cell line. The most promising enterocin (LNS18) showed the highest anticancer effects against HepG2 cells (with 75.24% cellular inhibition percentages), with IC50 value 15.643 μM and without any significant cytotoxic effects on normal fibroblast cells (BJ ATCC® CRL-2522™). The mode of anticancer action of enterocin LNS18 against HepG2 cells could be explained by its efficacy to induce cellular ROS, decrease HepG2 CD markers and arrest cells in G0 phase. Amino acid sequence of enterocin LNS18 was determined and the deduced peptide of the structural gene showed 86 amino acids that shared 94.7% identity with enterocin NKR-5-3B from E. faecium. Enterocin LNS18 consisted of 6 α-helices; 5 circular and one linear. Model-template alignment constructed between enterocin LNS18 and NKR-5-3B revealed 95.31% identity. The predicted 3D homology model of LNS18, after circularization and release of 22 amino acids, showed the formation of a bond between Leu23 and Trp86 amino acid residues at the site of circularization. Furthermore, areas of positive charges were due to the presence of 6 lysine residues resulting in a net positive charge of +4 on the bacteriocin surface. Based on the above mentioned results, our characterized bacteriocin is a promising agent to target liver cancer without any significant toxic effects on normal cell lines.

Alisol A is potentially therapeutic in human breast cancer cells.

Recent developments in breast cancer therapy have significantly improved patient survival rate; however, recurrence remains a major problem. Systemic treatment of breast cancer with available therapies is not curative. Natural products can be potentially used for treating cancer. Recently, a wide range of pharmacological activities has been reported for Alismatis Rhizoma, a popular traditional Chinese medicine. However, the mechanisms via which its compounds act on breast cancer remain unclear. The present study aimed to investigate the potential of natural therapeutic agents from Alismatis Rhizoma for treating breast cancer. Human breast cancer MDA‑MB‑231 cells were treated with four main protostane triterpenes from Alismatis Rhizoma, including alisol A, alisol A 24‑acetate, alisol B and alisol B 23‑acetate. Among these, alisol A significantly inhibited cell viability. AlisolA induced cell apoptosis, G1 phase cell cycle arrest, autophagy, and intracellular reactive oxygen species (ROS) generation in MDA‑MB‑231 cells. The number of APE1‑/γH2AX‑/LC3‑II positive cells was also significantly higher compared with that of negative control cells. All these results were dose‑dependent. Cleaved caspase‑3, cleaved caspase 9, Bcl‑2, and p‑p38 expression indicated cell apoptosis after alisol A treatment. The changes in cyclin A and cyclin D1 expression was associated with cell cycle arrest upon alisol A treatment. Furthermore, LC3‑II expression upon alisol A treatment was indicative of autophagy. Alisol A treatment can induce autophagy‑dependent apoptosis in human breast cancer cells via induction of ROS and DNA damage. Thus, Alisol A might serve as a new therapeutic agent against breast cancer.

PD173074 blocks G1/S transition via CUL3-mediated ubiquitin protease in HepG2 and Hep3B cells.

Fibroblast growth factor receptors (FGFRs) are frequently altered in a variety of human cancer cells and are overexpressed in hepatocellular carcinoma (HCC). Several literatures have proven that they are efficacious for HCC therapy, however, the underlying mechanism remains unclear. Here, we found FGFR4 was overexpressed in HCC cell lines HepG2 and Hep3B and we used PD173074, an FGFR4 inhibitor, to explore the role of FGFR4 and its underlying mechanism in these cell lines. The results showed that PD173074 significantly arrested HepG2 and Hep3B cells in G1 phase and inhibited cell proliferation. Furthermore, Western blot analysis revealed that PD173074 decreased the levels of P-FRS2α, P-ERK, CDK2, cyclin E and NF-κB (p65) in the nucleus while it increased the levels of ubiquitin and CUL3, an E3 ubiquitin ligase which involves in cyclin E degradation. Meanwhile, the data from RT-qPCR showed that PD173074 also decreased miR-141 level. In conclusion, these results suggest that FGFR4 is involved in HCC by ERK/CUL3/cyclin E signaling pathway, and the finding may provide a potential theoretical basis for treatment by targeting FGFR4 in HCC.

Chaetocin Abrogates the Self-Renewal of Bladder Cancer Stem Cells via the Suppression of the KMT1A-GATA3-STAT3 Circuit.

Bladder cancer stem cells (BCSCs) have the abilities of self-renewal, differentiation, and metastasis; confer drug resistance; and exhibit high tumorigenicity. We previously identified that the KMT1A–GATA3–STAT3 axis drives the self-renewal of BCSCs. However, the therapeutic effect of targeting KMT1A in BCSCs remains unknown. In this study, we confirmed that the expression of KMT1A was remarkably higher in BCSCs (3–5-fold) than those in bladder cancer non-stem cells or normal bladder epithelial cells. Among the six KMT1A inhibitors, chaetocin significantly suppressed the cell propagation (inhibition ratio: 65%–88%, IC50 = 24.4–32.5 nM), induced apoptosis (2–5-fold), and caused G1 phase cell cycle arrest (68.9 vs 55.5%) of bladder cancer (BC) cells, without influencing normal bladder epithelial cells. More importantly, chaetocin abrogated the self-renewal of BCSCs (inhibition ratio: 80.1%) via the suppression of the KMT1A–GATA3–STAT3 circuit and other stemness-related pathways. Finally, intravesical instillation of chaetocin remarkably inhibited the growth of xenograft tumors (inhibition ratio: 71–82%) and prolonged the survival of tumor-bearing mice (70 vs 53 days). In sum, chaetocin abrogated the stemness maintenance and tumor growth of BCSCs via the suppression of the KMT1A–GATA3–STAT3 circuit. Chaetocin is an effective inhibitor targeting KMT1A in BCSCs and could be a promising therapeutic strategy for BC.