Knockdown of E2F5 induces cell death via the TP53­dependent pathway in breast cancer cells carrying wild­type TP53.

E2F transcription factor 5 (E2F5) is a member of the E2F family of transcription factors, which are involved in regulation of various cellular processes, including cellular proliferation, apoptosis, differentiation and DNA damage response. Previously, we reported that E2F5 was aberrantly overexpressed in estrogen receptor (ER)­negative breast cancer, especially in triple­negative breast cancer (TNBC). In the present study, it was revealed that E2F5 gene silencing caused a significant reduction in the proliferation rate of breast cancer MCF7 (ER­positive luminal­type) and MDA­MB­231 (TNBC­type) cells. Additional experiments demonstrated that E2F5 knockdown triggered cell death of MCF7 cells but not MDA­MB­231 cells. As MCF7 and MDA­MB­231 cells carry wild­type and mutant TP53, respectively, and BT474 (ER­negative, HER2­positive type) carrying mutant TP53 exhibited similar results to MDA­MB­231, the possible effects of E2F5 gene depletion on cell death­related TP53­target gene expression were examined. Real­time RT­qPCR analysis revealed that knockdown of E2F5 in MCF7 cells stimulated cell death­related transcription of TP53­target genes such as BAX, NOXA and PUMA. For MDA­MB­231 and BT474 cells, E2F5 gene silencing revealed marginal effects on the expression of TP53 target genes. In addition, silencing of TP53 abrogated the effect of E2F5 silencing in MCF7 cells. Collectively, the present results indicated that E2F5 participated in the carcinogenesis of breast cancer carrying wild­type TP53 through suppression of TP53, while E2F5 had a pro­proliferative but not anti­apoptotic effect on breast cancer with TP53 mutation.

Silencing of EPHB2 promotes the epithelial-mesenchymal transition of skin squamous cell carcinoma-derived A431 cells.

Erythropoietin-producing hepatocellular (Eph) receptors and their ligand ephrins serve crucial roles in the interactions among epithelial cells. Eph receptor/ephrin signaling regulates cell functions, including proliferation, differentiation and migration, via these cell-cell interactions. We reported previously that EPHB2, a member of the Eph receptor family, was highly expressed in chemically induced cutaneous squamous cell carcinoma (cSCC) tissues in mice. Although the higher expression level of EPHB2 has been observed in various human cancers, its roles in the development and progression of cancers are still unclear. In the present study, the functional implications of EPHB2 in the acquisition of malignant phenotypes of cSCC cells was investigated. Silencing of EPHB2 in the human cSCC cell line A431 induced epithelial-mesenchymal transition (EMT)-like morphological changes accompanied by a significant upregulation of epithelial-mesenchymal transition-associated genes such as zinc finger E-box binding homeobox 1/2. In addition, silencing of EPHB2 suppressed anchorage-independent cell growth under 3D culture conditions. Consistent with these observations, EPHB2 exhibited higher levels of expression in tumor spheres formed under 3D culture conditions than in cells cultured in adherent form, and the expression pattern of EMT markers indicated that EMT was suppressed in tumor spheres. The results of the present study indicated that EPHB2 serves a pivotal role in promoting the anchorage-independent growth of A431 cells through the suppression of EMT.

Cold PSM, but not TRAIL, triggers autophagic cell death: A therapeutic advantage of PSM over TRAIL.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and cold plasma-stimulated medium (PSM) are promising novel anticancer tools due to their strong anticancer activities and high tumor-selectivity. The present study demonstrated that PSM and TRAIL may trigger autophagy in human malignant melanoma and osteosarcoma cells. Live-cell imaging revealed that even under nutritional and stress-free conditions, these cells possessed a substantial level of autophagosomes, which were localized in the cytoplasm separately from tubular mitochondria. In response to cytotoxic levels of PSM, the mitochondria became highly fragmented, and aggregated and colocalized with the autophagosomes. The cytotoxic effects of PSM were suppressed in response to various pharmacological autophagy inhibitors, including 3-methyladenine (3-MA) and bafilomycin A1, thus indicating the induction of autophagic cell death (ACD). Lethal levels of PSM also resulted in non-apoptotic, non-autophagic cell death in a reactive oxygen species-dependent manner under certain circumstances. Furthermore, TRAIL exhibited only a modest cytotoxicity toward these tumor cells, and did not induce ACD and mitochondrial aberration. The combined use of TRAIL and subtoxic concentrations of 3-MA resulted in decreased basal autophagy, increased mitochondrial aberration, colocalization with autophagosomes and apoptosis. These results indicated that PSM may induce ACD, whereas TRAIL may trigger cytoprotective autophagy that compromises apoptosis. To the best of our knowledge, the present study is the first to demonstrate that PSM can induce ACD in human cancer cells. These findings provide a rationale for the advantage of PSM over TRAIL in the destruction of apoptosis-resistant melanoma and osteosarcoma cells.

Plasma-stimulated medium kills TRAIL-resistant human malignant cells by promoting caspase-independent cell death via membrane potential and calcium dynamics modulation.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and cold plasma-stimulated medium (PSM) have been shown to exhibit tumor-selective cytotoxicity and have emerged as promising new tools for cancer treatment. However, to date, at least to the best of our knowledge, no data are available as to which substance is more potent in killing cancer cells. Thus, in this study, we systematically compared their abilities to kill human malignant cells from different origins. We found that PSM dose-dependently killed TRAIL-resistant melanoma, osteosarcoma and neuroblastoma cells. Moreover, PSM had little cytotoxicity toward osteoblasts. PSM was more potent than TRAIL in inducing caspase-3/7 activation, mitochondrial network aberration and caspase-independent cell death. We also found that PSM was more potent in inducing plasma membrane depolarization (PMD) and disrupting endoplasmic-mitochondrial Ca2+ homeostasis. Moreover, persistent PMD was caused by different membrane-depolarizing agents; the use of the anti-type II diabetes drug, glibenclamide, alone caused mitochondrial fragmentation and enhanced TRAIL-induced Ca2+ modulation, mitochondrial network abnormalities and caspase-independent cell killing. These results demonstrate that PSM has a therapeutic advantage over TRAIL owing to its greater capacity to evoke caspase-independent cell death via mitochondrial network aberration by disrupting membrane potential and Ca2+ homeostasis. These findings may provide a strong rationale for developing PSM as a novel approach for the treatment of TRAIL-resistant malignant cells.