Tetraarsenic oxide-mediated apoptosis in a cervical cancer cell line, SiHa

Tetraarsenic oxide affects non-coding RNA transcriptome through deregulating polycomb complexes in MCF7 cells

Non-coding RNAs (ncRNAs) play important and diverse roles in mammalian cell biology and pathology. Although the functions of an increasing number of ncRNAs have been identified, the mechanisms underlying ncRNA gene expression remain elusive and are incompletely understood. Here, we investigated ncRNA gene expression in Michigan cancer foundation 7 (MCF7), a malignant breast cancer cell line, on treatment of tetraarsenic oxide (TAO), a potential anti-cancer drug. Our genomic analyses found that TAO up- or down-regulated ncRNA genes genome-wide. A subset of identified ncRNAs with critical biological and clinical functions were validated by real-time quantitative polymerase chain reaction. Intriguingly, these TAO-regulated genes included CDKN2B-AS, HOXA11-AS, SHH, and DUSP5 that are known to interact with or be targeted by polycomb repressive complexes (PRCs). In addition, the PRC subunits were enriched in these TAO-regulated ncRNA genes and TAO treatment deregulated the expression of PRC subunits. Strikingly, TAO decreased the cellular and gene-specific levels of EZH2 expression and H3K27me3. In particular, TAO reduced EZH2 and H3K27me3 and increased transcription at MALAT1 gene. Inhibiting the catalytic activity of EZH2 using GSK343 increased representative TAO-inducible ncRNA genes. Together, our findings suggest that the expression of a subset of ncRNA genes is regulated by PRC2 and that TAO could be a potent epigenetic regulator through PRCs to modulate the ncRNA gene expression in MCF7 cells.

Tetraarsenic oxide and cisplatin induce apoptotic synergism in cervical cancer

Tetraarsenic oxide (As4O6, TAO) is a new arsenic compound that inhibits cell growth and induces apoptosis in human cervical cancer cell lines. In the present study, we report that the growth of tumor cells (CaSki) was inhibited by treatment with TAO alone or in combination with cisplatin or paclitaxel in vitro and in vivo. Proliferation was assessed by WST-1 assay, and apoptosis was assessed by Annexin-V/PI FACS analysis in the CaSki cell line treated with a single agent or with the combinations of two agents. Expression of apoptosis-related proteins was analyzed by western blot analysis. A mouse xenograft model using CaSki cells was used to determine the in vivo activity of tetraarsenic oxide alone and in combination with cisplatin or paclitaxel by estimation of tumor size. At the end of the experiment, tumor tissue from each mouse was removed and processed for TUNEL analysis for confirmation of apoptotic cells. TAO was able to inhibit cell proliferation in a time- and dose-dependent manner. A combination of TAO and cisplatin effectively induced apoptosis by activating caspase-3. Using a mouse xenograft model, the sizes of tumors which were treated with a single agent and with a combination of agents decreased in a time-dependent manner. A combination of TAO and cisplatin resulted in a significantly reduced tumor size (P<0.05). The data for the histochemical staining of TUNEL-positive cells showed that the number of apoptotic cells was significantly increased by the combination of TAO and cisplatin. Thus, TAO is a good candidate for use in a combined regimen with cisplatin for patients with cervical cancer.