Effect of Spindle Checkpoint on Akt2-mediated Paclitaxel-resistance in A2780 Ovarian Cancer Cells

Recent evidence has suggested that Akt2 plays an important role in the protection of cells from paclitaxel （PTX）-induced apoptosis and control of the cell cycle. In addition, some scholars suggested that the PTX sensitivity depends on a functional spindle assembly checkpoint. In the present study, we investigated the role of the Akt2/Bubl cross-talking in apoptosis and cell cycle after exposure of the A2780 ovarian cancer cells to paclitaxel （PTX）. Recombinant expression plasmid WT-Akt2 was transfected into A2780 cells by lipofectamine2000, and then the expression level of Akt2 gene was detected by using RT-PCR and Western blotting. Cell apoptosis and cell cycle were detected by flow cytometry and Hoechst 33342 staining after treatment with PTX. Moreover, we compared the expression level of Bubl in different groups by Western blotting. Our study showed that up-regulation of Akt2 contributed to A2780 ovarian cancer cells overriding PTX-induced G2/M arrest, and inhibited Bubl expression. Our findings might shed light on the molecular mechanism of PTX-induced resistance in ovarian cancer and help develop novel anti-neoplastic strategies.

A STUDY OF DECREASING DRUG-RESISTANCE OF HUMAN OVARIAN CANCER CELLS IN VITRO

A chemosensitivity test for ovarian cancer using tritiated thymidine incorporation assay was carried out. A dose-response relationship for cisplatin and potentiation of verapamil in increasing vincristine inhibition to ovarian cancer were investigated. A 5- fold increase of cisplatin density converted the tumors which were initially resistance to standard-dose cisplatin Into drug-sensitive ones. Vera-pamil was found to be able to overcome vincristine-resistance of some tumors in vitro. These results suggest that using high dose cisplatin therapy or increasing local drug concentration by using other administration way, we could expect some ovarian cancers that had failed to standard dose cisplatin therapy to be effective. Combination of vincristine with verapamll may be helpful in treating some vincristineresistant cases.

γ-Secretase Inhibitor, DAPT Inhibits Self-renewal and Stemness Maintenance of Ovarian Cancer Stem-like Cells In Vitro

Objective: The Notch signaling pathway plays an important role in the stem cell signaling network and contributes to tumorigenesis. However, the functions of Notch signaling in ovarian cancer stem cells (OCSCs) are not well understood. We aimed to investigate the effects of Notch blockade on self-renewal and stemness maintenance of OCSCs. Methods: Ovarian cancer stem-like cells were enriched from ovarian cancer cell lines in serum-free medium. A γ-secretase inhibitor, (DAPT), was used to block Notch signaling. MTT assays were performed to assess self-renewal and proliferation inhibition, flow cytometry was performed to analyze cell surface marker and immunofluorescence, Western Blot and Real-time RT-PCR assays were performed to detect Oct4 and Sox2 protein and mRNA expression of the Ovarian cancer stem-like cells treated with DAPT. Results: Notch blockade markedly inhibits self-renewal and proliferation of ovarian cancer stem-like cells, significantly downregulates the expression of OCSCs-specific surface markers, and reduces protein and mRNA expression of Oct4 and Sox2 in OCSC-like cells. Conclusion: Our results suggest that Notch signaling is not only critical for the self-renewal and proliferation of OCSCs, but also for the stemness maintenance of OCSCs. The γ-secretase inhibitor is a promising treatment targeting OCSCs.

Screening of the Metastasis-Associated Genes by Gene Chip in High Metastatic Human Ovarian Cancer Cell Lines

Affymetrix U133A oligonucleotide microarrays were used to study the differences of gene expressions between high （H） metastatic ovarian cancer cell line, HO-8910PM, and normal ovarian tissues （C）. Bioinformatics was used to identify their chromosomal localizations. A total of 1,237 genes were found to have a difference in expression levels more than eight times. Among them 597 were upregulated [Signal Log Ratio （SLR） ≥3], and 640 genes were downregulated （SLR≤-3）. Except one gene, whose location was unknown, all these genes were randomly distributed on all the chromosomes. However, chromosome 1 contained the most differentially expressed genes （115 genes, 9.3%）, followed by chromosome 2 （94 genes, 7.6%）, chromosome 12 （88 genes, 7.1%）, chromosome 11 （76 genes, 6.1%）, chromosomes X （71 genes, 5.7%）, and chromosomes l7 （69 genes, 5.6%）. These genes were localized on short-arm of chromosome （q）, which had 805 （65.1%） genes, and the short arms of No.13, 14, 15, 21, and 22 chromosomes were the only parts of the chromosomes where the differentially expressed genes were localized. Functional classification showed that most of the genes （306 genes, 24.7%） belonged to the enzymes and their regulator groups. The subsequent group was the nucleic acid binding genes （144 genes, 11.6%）. The rest of the top two groups were signal transduction genes （137 genes, 11.1%） and proteins binding genes （116 genes, 9.4%）. These comprised 56.8% of all the differentially expressed genes. There were also 207 genes whose functions were unknown （16.7 %）. Therefore it was concluded that differentially expressed genes in high metastatic ovarian cancer cell were supposed to be randomly distributed across the genome, but the majority were found on chromosomes 1, 2, 12, 11, 17, and X. Abnormality in four groups of genes, including in enzyme and its regulator, nucleic acid binding, signal transduction and protein binding associated genes, might play important roles in ovarian cancer metastasis. Those genes need to be further studied.

Reversal of Multidrug Resistance and Inhibition of Phosphorylation of AKT in Human Ovarian Cancer Cell Line by Wild-type PTEN Gene

The reversing effect of wild-type PTEN gene on resistance of C 13K cells to cisplatin and its inhibitory effect on the phosphorylation of protein kinase B （AKT） were studied. The expression of PTEN mRNA and protein in OV2008 cells and C13K cells were semi-quantitatively detected by using RT-PCR and Western blotting. Recombinant eukaryotic expression plasmid containing human wild-type PTEN gene was transfected into C13K cells by lipofectamine2000. The expression of PTEN mRNA was monitored by RT-PCR and the expression of PTEN, Akt, p-Akt protein were ana- lyzed by Western blotting in PTEN-transfected and non-transfected C13K cells. Proliferation and chemosensitivity of cells to DDP were measured by MTT, and cell apoptosis was detected by flow cytometry after treatment with cisplatin. The expression of PTEN mRNA and protein in OV2008 cells were significantly higher than those in C13K cells. After transfection with PTEN gene for 48 h, the expression of PTEN mRNA and protein in C 13K cells were 2.04 ± 0.10, 0.94± 0.04 respectively and the expression of p-Akt protein （ 0.94± 0.07） was lower than those in control groups （1.68 ±0.14, 1.66± 0.10） （P〈 0.05）. The IC50 of DDP to C 13 K cells transfected with PTEN （7.2± 0.3 la mol/L） was obviously lower than those of empty-vector transfected cells and non-transfected cells （12.7±0.4 lamol/1, 13.0±0.3 lamol/L） （P〈0.05）. The apopototis ratio of wild-type PTEN-transfected, empty vector transfected and non-transfected C13K cells were （41.65___0.87）%, （18.61 ±0.70）% and （15.28±0.80）% respectively, and the difference was statistically significant （P〈0.05）. PTEN gene plays an important role in ovarian cancer multidrug resistance. Transfection of PTEN could increase the expression of PTEN and restore drug sensitivity to cisplatin in human ovarian cancer cell line C 13K with multidrug-resistance by decreasing the expression of p-Akt.

Dysregulation of the TGF-β Postreceptor Signaling Pathway in Cell Lines Derived from Primary or Metastatic Ovarian Cancer

Transforming growth factor beta (TGF β) may cause cell cycle arrest, terminal differentiation, or apoptosis in most normal epithelial cells, whereas most malignant cell lines are resistant to TGF β. Mechanisms of resistance to TGF β caused by modulation of cell cycle regulators and/or inactivation of components of the TGF β signaling transduction pathway such as C myc and Smad4 are not well understood. To investigate the potential association between loss of sensitivity to TGF β and expression status of transforming growth factor receptor Ⅱ (TβRⅡ), Smad4, CDC25A and C myc in 14 cell lines derived from ovarian cancer, the expression levels of these genes were detected by semi quantitative RT PCR. Normal ovarian surface tissues were used as controls. The expression of TβRⅡ was detectable in all of 14 cell lines. The expression of Smad4 was decreased in 10 cell lines and 9 cell lines overexpressed CDC25A, as compared to normal controls. CDC25A gene was overexpressed with 88 % (8/9) in tumorigenic cell lines as determined by xenografts in nude mice, and only in 20 % (1/5) of non tumorigenic cell lines ( P <0.05). C myc was not overexpressed in any of these cell lines. The loss of sensitivity to TGF β of cell lines derived from ovarian cancers may be related to a decreased expression of Smad4, which mediates TGF β induced growth inhibition, and/or an overexpression of CDC25A. This overexpression of CDC25A correlates with increased tumorigenicity of ovarian cancer cell lines. The loss of sensitivity to TGF β is not associated with a lack of TβRⅡ.

Antisense oligonucleotide to insulin-like growth factorⅡ induces apoptosis in human ovarian cancer AO cellline

The effects of antisense oligonucleotide to insulin-like growth factor 11 (IGFII) to induce apoptosis in human ovarian cancer cells were evaluated. Antiproliferation effects of antisense to IGFII in ovarian cancer AO cells were determined by 3H-thymidine incorporation. Apoptosis of the IGFll antisense-treated cells was quantitated by both nuclear condensation and flow cytometry after cells were stained with propidium iodide. IGFII antisense (4.5μM)treatment of 48 h maximally inhibited proliferation of AO cells. More than 25% of IGFII antisense-treated cells (4.5PM for 24 h) had undergone apoptosis, whereas less than 3% of the cells were apoptotic in either IGFII sense-treatedcells or untreated cells. Antisense oligonucleotide to IGFII significantly inhibited cell proliferation and induced apoptosis in human ovarian cancer AO cell. These data suggest that IGFII may be a potential target in treatment of ovarian cancer and antisense oligonucleotide to IGFⅡmay serve as a therapeutic approach.

Gene expression profile differences in high and low metastatic human ovarian cancer cell lines by gene chip

Objectives To study the difference between gene expressions of high (H0-8910PM) and low (HO-8910) metastatic human ovarian carcinoma cell lines and screen novel associated genes by cDNA microarray. Methods cDNA retro-transcribed from equal quantities of mRNA derived from high and low metastatic tumor cells or normal ovarian tissues were labeled with Cy5 and Cy3 fluorescein as probes. The mixed probe was hybridized with two pieces of BioDoor 4096 double dot human whole gene chip and scanned with a ScanArray 3000 laser scanner. The acquired image was analyzed by ImaGene 3.0 software. Results A total of 355 genes with expression levels more than 3 times larger were found by comparing the HO-8910 cell with normal ovarian epithelial cells. A total of 323 genes with expression levels more than 3 times larger in HO-8910PM cells compared to normal ovarian epithelium cells were also detected. A total of 165 genes whose expression levels were more than two times those of HO-8910PM cells compared to their mother cell line (HO-8910) were detected. Twenty-one genes with expression levels 】3 times were found from comparison of these two tumor cell lines.Conclusions cDNA microarray techniques are effective in screening differential gene expression between two human ovarian cancer cell lines (H0-8910PM; HO-8910) and normal ovarian epithelial cells. These genes may be related to the genesis and development of ovarian carcinoma. Analysis of the human ovarian cancer gene expression profile with cDNA microarray may help in gene diagnosis, treatment and prevention.