The radiotherapy-sensitization effect of cantharidin: Mechanisms involving cell cycle regulation, enhanced DNA damage, and inhibited DNA damage repair.

BACKGROUND: Cantharidin is an inhibitor of protein phosphatase 2 A (PP2A), and has been frequently used in clinical practice. In our previous study, we proved that cantharidin could arrest cell cycle in G2/M phase. Since cells at G2/M phase are sensitive to radiotherapy, in the present study, we investigated the radiotherapy-sesitization effect of cantharidin and the potential mechanisms involved. METHODS: Cell growth was determined by MTT assay. Cell cycle was evaluated by flow cytometry. DNA damage was visualized by phospho-Histone H2A.X staining. Expression of mRNA was tested by microarray assay and real-time PCR. Clinical information and RNA-Seq expression data were derived from The Cancer Genome Atlas (TCGA) pancreatic cancer cohort. Survival analysis was obtained by Kaplan-Meier estimates. RESULTS: Cantharidin strengthened the growth inhibition effect of irradiation. Cantharidin drove pancreatic cancer cells out of quiescent G0/G1 phase and arrested cell cycle in G2/M phase. As a result, cantharidin strengthened DNA damage which was induced by irradiation. Moreover, cantharidin repressed expressions of several genes participating in DNA damage repair, including UBE2T, RPA1, GTF2HH5, LIG1, POLD3, RMI2, XRCC1, PRKDC, FANC1, FAAP100, RAD50, RAD51D, RAD51B and DMC1, through JNK, ERK, PKC, p38 and/or NF-κB pathway dependent manners. Among these genes, worse overall survival for pancreatic cancer patients were associated with high mRNA expressions of POLD3, RMI2, PRKDC, FANC1, RAD50 and RAD51B, all of which could be down-regulated by cantharidin. CONCLUSION: Cantharidin can sensitize pancreatic cancer cells to radiotherapy. Multiple mechanisms, including cell cycle regulation, enhanced DNA damage, and inhibited DNA damage repair, may be involved.

High-throughput sequencing and degradome analysis reveal altered expression of miRNAs and their targets in a male-sterile cybrid pummelo (Citrus grandis).

BACKGROUND: G1 + HBP is a male sterile cybrid line with nuclear genome from Hirado Buntan pummelo (C. grandis Osbeck) (HBP) and mitochondrial genome from "Guoqing No.1" (G1, Satsuma mandarin), which provides a good opportunity to study male sterility and nuclear-cytoplasmic cross talk in citrus. High-throughput sRNA and degradome sequencing were applied to identify miRNAs and their targets in G1 + HBP and its fertile type HBP during reproductive development. RESULTS: A total of 184 known miRNAs, 22 novel miRNAs and 86 target genes were identified. Some of the targets are transcription factors involved in floral development, such as auxin response factors (ARFs), SQUAMOSA promoter binding protein box (SBP-box), MYB, basic region-leucine zipper (bZIP), APETALA2 (AP2) and transport inhibitor response 1 (TIR1). Eight target genes were confirmed to be sliced by corresponding miRNAs using 5' RACE technology. Based on the sequencing abundance, 42 differentially expressed miRNAs between sterile line G1 + HBP and fertile line HBP were identified. Differential expression of miRNAs and their target genes between two lines was validated by quantitative RT-PCR, and reciprocal expression patterns between some miRNAs and their targets were demonstrated. The regulatory mechanism of miR167a was investigated by yeast one-hybrid and dual-luciferase assays that one dehydrate responsive element binding (DREB) transcription factor binds to miR167a promoter and transcriptionally repress miR167 expression. CONCLUSION: Our study reveals the altered expression of miRNAs and their target genes in a male sterile line of pummelo and highlights that miRNA regulatory network may be involved in floral bud development and cytoplasmic male sterility in citrus.

Telekin suppresses human hepatocellular carcinoma cells in vitro by inducing G2/M phase arrest via the p38 MAPK signaling pathway.

AIM: Telekin, isolated from the Chinese herb Carpesium divaricatum, has shown anti-proliferation effects against various cancer cells, including hepatocellular carcinoma cells. In this study, we investigated the anti-proliferation mechanisms of telekin in human hepatocellular carcinoma HepG2 cells in vitro. METHODS: HepG2 cells were treated with telekin. Cell viability was evaluated using MTT assay. Flow cytometry was used to measure cell cycle profiles, ROS level and apoptosis. The protein expression levels were analyzed with Western blotting. RESULTS: Telekin (3.75-30 µmol/L) dose-dependently inhibited the viability of HepG2 cells and induced l apoptosis. Furthermore, the treatment induced cell cycle arrest at G2/M phase, accompanied by significantly increased the phosphorylation of Cdc25A and Cdc2, and decreased Cyclin B1 level. Moreover, the treatment significantly stimulated ROS production, and increased the phosphorylation of p38 and MAPKAPK-2 in the cells. Pretreatment with the antioxidant NAC (2.5, 5, and 10 mmol/L), or the p38 MAPK inhibitor SB203580 (2.5 and 5 µmol/L) dose-dependently attenuated these telekin-induced effects in the cells. CONCLUSION: Telekin suppresses hepatocellular carcinoma cells in vitro by inducing G2/M phase arrest via activating the p38 MAPK pathway.

iTRAQ-based quantitative proteomics analysis revealed alterations of carbohydrate metabolism pathways and mitochondrial proteins in a male sterile cybrid pummelo.

Comprehensive and quantitative proteomic information on citrus floral bud is significant for understanding male sterility of the cybrid pummelo (G1+HBP) with nuclear genome of HBP and foreign mitochondrial genome of G1. Scanning electron microscopy and transmission electron microscopy analyses of the anthers showed that the development of pollen wall in G1+HBP was severely defective with a lack of exine and sporopollenin formation. Proteomic analysis was used to identify the differentially expressed proteins between male sterile G1+HBP and fertile type (HBP) with the aim to clarify their potential roles in anther development and male sterility. On the basis of iTRAQ quantitative proteomics, we identified 2235 high-confidence protein groups, 666 of which showed differentially expressed profiles in one or more stages. Proteins up- or down-regulated in G1+HBP were mainly involved in carbohydrate and energy metabolism (e.g., pyruvate dehydrogenase, isocitrate dehydrogenase, ATP synthase, and malate dehydrogenase), nucleotide binding (RNA-binding proteins), protein synthesis and degradation (e.g., ribosome proteins and proteasome subunits). Additionally, the proteins located in mitochondria also showed changed expression patterns. These findings provide a valuable inventory of proteins involved in floral bud development and contribute to elucidate the mechanism of cytoplasmic male sterility in the cybrid pummelo.

DLJ14, a novel chemo-sensitization agent, enhances therapeutic effects of adriamycin against MCF-7/A cells both in vitro and in vivo.

OBJECTIVES: We investigated the chemo-sensitization of a ligustrazine derivate, (E)-2-(2, 4-dimethoxystyryl)-3, 5, 6-trimethylpyrazine (DLJ14) on Adriamycin (Adr, Wanle, Shenzhen, China)-resistant human breast cancer (MCF-7/A) cells both in vivo and in vitro. METHODS: The antitumour effects of DLJ14 and Adr was observed in MCF-7/A cells by 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay in vitro and was evaluated by MCF-7/A xenografts in nude mice. The intracellular Adr accumulation was assessed by mean fluorescence intensity of Adr. The messenger RNA level of glutathione (GSH) S-transferase (GST)π in MCF-7/A cells was determined by real-time reverse transcription PCR assay. The expression of GSTπ, c-jun NH2 -terminal kinase (JNK) and phosphor-JNK (p-JNK) was detected by Western blotting method. KEY FINDINGS: The MTT results showed that DLJ14 exhibited a weak inhibition on proliferation of both MCF-7 and MCF-7/A cells, in contrast with the strong inhibition of verapamil. When DLJ14 is combined with Adr, the inhibitory effect on MCF-7/A cells and MCF-7/A xenografts was enhanced significantly through increasing intracellular accumulation of Adr by inhibition of GSH level and the activity of GSH peroxidase and GST. Moreover, DLJ14 could downregulate the expression of GSTπ and increase the expression of JNK and p-JNK in MCF-7/A cells or in xenografts. CONCLUSION: DLJ14 is a promising chemo-sensitization candidate for the reversal of multidrug resistance in cancers.

Fluopsin C induces oncosis of human breast adenocarcinoma cells.

AIM: Fluopsin C, an antibiotic isolated from Pseudomonas jinanesis, has shown antitumor effects on several cancer cell lines. In the current study, the oncotic cell death induced by fluopsin C was investigated in human breast adenocarcinoma cells in vitro. METHODS: Human breast adenocarcinoma cell lines MCF-7 and MD-MBA-231 were used. The cytotoxicity was evaluated using MTT assay. Time-lapse microscopy and transmission electron microscopy were used to observe the morphological changes. Cell membrane integrity was assessed with propidium iodide (PI) uptake and lactate dehydrogenase (LDH) assay. Flow cytometry was used to measure reactive oxygen species (ROS) level and mitochondrial membrane potential (Δψm). A multimode microplate reader was used to analyze the intracellular ATP level. The changes in cytoskeletal system were investigated with Western blotting and immunostaining. RESULTS: Fluopsin C (0.5-8 µmol/L) reduced the cell viability in dose- and time-dependent manners. Its IC50 values in MCF-7 and MD-MBA-231 cells at 24 h were 0.9 and 1.03 µmol/L, respectively. Fluopsin C (2 µmol/L) induced oncosis in both the breast adenocarcinoma cells characterized by membrane blebbing and swelling, which was blocked by pretreatment with the pan-caspase inhibitor Z-VAD-fmk. In MCF-7 cells, fluopsin C caused PI uptake into the cells, significantly increased LDH release, induced cytoskeletal system degradation and ROS accumulation, decreased the intracellular ATP level and Δψm. Noticeably, fluopsin C exerted comparable cytotoxicity against the normal human hepatocytes (HL7702) and human mammary epithelial cells with the IC50 values at 24 h of 2.7 and 2.4 µmol/L, respectively. CONCLUSION: Oncotic cell death was involved in the anticancer effects of fluopsin C on human breast adenocarcinoma cells in vitro. The hepatoxicity of fluopsin C should not be ignored.

1-Oxoeudesm-11(13)-eno-12,8a-lactone induces G2/M arrest and apoptosis of human glioblastoma cells in vitro.

AIM: To investigate the effects of 1-oxoeudesm-11(13)eno-12,8a-lactone (OEL), a novel eudesmane-type sesquiterpene isolated from Aster himalaicus, on the cell cycle and apoptosis in human glioblastoma cells in vitro. METHODS: Human malignant glioblastoma cell lines U87 and A172 were used. The cytotoxicity of OEL was examined using the MTT assay. Cell apoptosis was assessed with DAPI staining and flow cytometry. DNA damage was determined by measuring the phosphorylation of H2AX using immunofluorescence staining and Western blotting. Cell cycle profiles were measured with flow cytometry. The mRNA expression of p53 and p21Waf1/Cip1 was investigated using real-time PCR. The protein expression of γ-H2AX, caspase-9, caspase-3, p53, p21Waf1/Cip1, cyclin B1, and cdc2 was analyzed with Western blotting. RESULTS: Treatment of the malignant glioblastoma cells with OEL inhibited the cell growth in dose- and time-dependent manners (the values of IC(50) at 48 and 72 h were 29.5 and 16.99 µmol/L, respectively, in U87 cells; 7.2 and 9.5 µmol/L, respectively, in A172 cells). OEL (10-30 µmol/L) induced apoptosis and G(2)/M phase arrest in both U87 and A172 cells. OEL induced the phosphorylation of cdc2, a G(2)/M phase cyclin-dependent kinase, and decreased the expression of cyclin B1 required for progression through the G(2)/M phase in U87 cells. The compound remarkably increased the phosphorylation of H2AX in U87 cells. Moreover, OEL increased the mRNA and protein levels of p53 and its target gene p21(Waf1/Cip1) in U87 cells. The compound also induced p53 phosphorylation. Pretreatment with PFT-α, a specific inhibitor of p53 transcriptional activity, could partially reverse the inhibition of OEL on the viability of U87 and A172 cells. CONCLUSION: OEL suppresses the growth of human glioblastoma cells in vitro via inducing DNA damage, p53-mediated cell cycle arrest and apoptosis, thus warrants further studies as a lead compound of anti-glioblastoma drug.

Comparative transcript profiling of a male sterile cybrid pummelo and its fertile type revealed altered gene expression related to flower development.

Male sterile and seedless characters are highly desired for citrus cultivar improvement. In our breeding program, a male sterile cybrid pummelo, which could be considered as a variant of male fertile pummelo, was produced by protoplast fusion. Herein, ecotopic stamen primordia initiation and development were detected in this male sterile cybrid pummelo. Histological studies revealed that the cybrid showed reduced petal development in size and width, and retarded stamen primordia development. Additionally, disorganized cell proliferation was also detected in stamen-like structures (fused to petals and/or carpel). To gain new insight into the underlying mechanism, we compared, by RNA-Seq analysis, the nuclear gene expression profiles of floral buds of the cybrid with that of fertile pummelo. Gene expression profiles which identified a large number of differentially expressed genes (DEGs) between the two lines were captured at both petal primordia and stamen primordia distinguishable stages. For example, nuclear genes involved in nucleic acid binding and response to hormone synthesis and metabolism, genes required for floral bud identification and expressed in particular floral whorls. Furthermore, in accordance with flower morphology of the cybrid, expression of PISTILLATA (PI) was reduced in stamen-like structures, even though it was restricted to correct floral whorls. Down-regulated expression of APETALA3 (AP3) coincided with that of PI. These finding indicated that, due to their whorl specific effects in flower development, citrus class-B MADS-box genes likely constituted 'perfect targets' for CMS retrograde signaling, and that dysfunctional mitochondria seemed to cause male sterile phenotype in the cybrid pummelo.

Ligustrazine derivate DLJ14 reduces multidrug resistance of K562/A02 cells by modulating GSTπ activity.

Multidrug resistance (MDR) of tumor cells is a major obstacle in chemotherapeutic cancer treatment. Over-expression of glutathione S-transferase π (GSTπ) is one of the mechanisms contributing to MDR. In this study, we investigated the reversal of MDR by DLJ14, a ligustrazine derivate, in adriamycin (Adr) resistant human myelogenous leukemia (K562/A02) cells by modulating the expression of GSTπ and the activity of GST-related enzymes. In the MTT test, DLJ14 showed a weak inhibition on proliferation of both K562/A02 and K562 cells, while verapamil at the same concentration showed a much stronger inhibition. The sensitivity of K562/A02 cells to cytotoxic killing by Adr was enhanced by incubation with DLJ14 as a result of the increased intracellular accumulation of Adr. The accumulation of Adr induced by DLJ14 may due to down regulation of GST-related enzyme activity. Western blot analysis and RT-PCR showed that DLJ14 was able to inhibit the protein expression and mRNA expression of GSTπ in K562/A02 cells. Moreover, DLJ14 increased the expression of cellular c-Jun NH(2)-terminal kinase (JNK) in K562/A02 cells exposure to Adr. This is consistent with the inhibition of GSTπ. These results demonstrate that DLJ14 may be an attractive new agent for the chemosensitization of cancer cells.

A novel Ta.AGP.S.1b transcript in Chinese common wheat (Triticum aestivum L.).

ADP-glucose pyrophosphorylase (AGPase), the key enzyme of starch synthesis in plants, is composed of two small and two large subunits, and has plastidial and cytosolic isoforms. In kernels of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.), transcripts for cytosolic (Ta.AGP.S1a) and plastidial (Ta.AGP.S1b) small subunits of AGPase were encoded by the same gene (Ta.AGP.S.1) by use of the alternative first exons. In this study, a cDNA sequence (1631 bp) [NCBI: EU586278] encoding a novel Ta.AGP.S1b transcript was isolated in kernels of Chinese common wheat cultivars. Compared with another Ta.AGP.S1b transcript [NCBI: FJ643609] isolated in kernels of non-Chinese wheat cultivars, EU586278 lacked a long fragment (117 bp) at its 5'terminal, resulting in a shorten transit peptide. The lacked fragments of Ta.AGP.S1b (EU586278) were universally found in surveyed 22 Chinese common wheat cultivars. Partial genomic DNA sequence [NCBI: FJ907395] of Ta.AGP.S.1 gene, which was corresponded to 5'terminal of EU586278 transcript, was also isolated in Chinese common cultivars and sequencing indicated that FJ907395 contained the corresponding lacked fragment of EU586278 transcript, inferring the lacked fragment in EU586278 transcript was not present in the genome, but possibly occurred at transcription level. Using TargetP software, the predicated transit peptide of putative plastidial SSU encoded by EU586278 contained merely 25 amino acids, considerably shorter than those of other plant AGP. S.1bs (54-70 amino acids). Phylogenetic tree analysis indicated that the amino acid sequence of EU586278 transit peptide was not clustered together with those of other wheat Ta.AGP.S1bs [NCBI: AF536819 and FJ643609] and barley AGP.S1b [NCBI: Z48563]. These implied that EU586278 could be a novel Ta.AGP.S1b transcript. Semi-quantitative PCR analysis indicated that transcripts of EU586278 were abundantly expressed in leaf, moderately in endosperm and stem, and weakly in root.