Zinc suppresses stem cell properties of lung cancer cells through protein kinase C-mediated ß-catenin degradation.

Highly tumorigenic cancer stem cells (CSCs) residing in most cancers are responsible for cancer progression and treatment failure. Zinc is an element regulator of several cell functions; however, its role in regulation of stem cell program in lung cancer has not been demonstrated. The present study reveals for the first time that zinc can suppress stem cell properties of lung cancer cells. Such findings were proved in different lung cancer cell lines (H460, H23, and H292) and it was found that CSC markers (CD133 and ALDH1A1), stem cell-associated transcription factors (Oct4, Nanog, and Sox-2), and the ability to form tumor spheroid were dramatically suppressed by zinc treatments. Zinc was found to activate protein kinase C-α (PKCα) that further phosphorylated and mediated ß-catenin degradation through the ubiquitin-proteasomal pathway. Zinc was found to increase the ß-catenin-ubiquitin complex, which can be inhibited by a specific PKC inhibitor, bisindolylmaleimide I. Using specific reactive oxygen species detection and antioxidants, we have demonstrated that superoxide anions generated by zinc are a key upstream mechanism for PKCα activation leading to the subsequent suppression of stem cell features of lung cancer. Zinc increased cellular superoxide anions and the addition of superoxide anion scavenger prevented the activation of PKCα and ß-catenin degradation. These findings indicate a novel role for zinc regulation in the PKCα/ß-catenin pathway and explain an important mechanism for controlling of stem cell program in lung cancer cells.

Benzophenone-3 increases metastasis potential in lung cancer cells via epithelial to mesenchymal transition.

Exposure to compounds with cancer-potentiating effects can contribute to the progression of cancer. Herein we have discovered for the first time that benzophenone-3 (BP-3), a chemical used as sunscreen in various cosmetic products, enhances the ability of lung cancer cells to undergo metastasis. The exposure of the lung cancer cells to BP-3 at non-toxic concentrations significantly increased the number of anoikis resistant cells in a dose-dependent manner. Also, BP-3 increased the growth rate as well as the number of colonies accessed by anchorage-independent growth assay. We found that the underlying mechanisms of such behaviors were the epithelial to mesenchymal transition (EMT) process of cancer cells, and the increase in caveolin-1 (Cav-1) expression. As both mechanistic events mediated anoikis resistance via augmentation of cellular survival signals, our results further revealed that the BP-3 treatment significantly up-regulated extracellular-signal-regulated kinase (ERK). Also, such compounds increased the cellular levels of anti-apoptotic Bcl-2 and Mcl-1 proteins. As the presence of a substantial level of BP-3 in plasma of the consumers has been reported, this finding may facilitate further investigations that lead to better understanding and evidence concerning the safety of use in cancer patients.

Zinc induces epithelial to mesenchymal transition in human lung cancer H460 cells via superoxide anion-dependent mechanism.

BACKGROUND: Epithelial to mesenchymal transition (EMT) has been shown to be a crucial enhancing mechanism in the process of cancer metastasis, as it increases cancer cell capabilities to migrate, invade and survive in circulating systems. This study aimed to investigate the effect of essential element zinc on EMT characteristics in lung cancer cells. METHODS: The effect of zinc on EMT was evaluated by determining the EMT behaviors using migration, invasion and colony formation assay. EMT markers were examined by western blot analysis. Reactive oxygen species (ROS) were detected by specific fluorescence dyes and flow cytometry. All results were analyzed by ANOVA, followed by individual comparisons with post hoc test. RESULTS: The present study has revealed for the first time that the zinc could induce EMT and related metastatic behaviors in lung cancer cells. Results showed that treatment of the cells with zinc resulted in the significant increase of EMT markers N-cadherin, vimentin, snail and slug and decrease of E-cadherin proteins. Zinc-treated cells exhibited the mesenchymal-like morphology and increased cancer cell motility with significant increase of activated FAK, Rac1, and RhoA. Also, tumorigenic abilities of lung cancer cells could be enhanced by zinc. Importantly, the underlying mechanism was found to be caused by the ability of zinc to generate intracellular superoxide anion. Zinc was shown to induce cellular superoxide anion generation and the up-regulation of EMT markers and the induced cell migration and invasion in zinc-treated cells could be attenuated by the treatment of MnTBAP, a specific superoxide anion inhibitor. CONCLUSION: Knowledge gains from this study may highlight the roles of this important element in the regulation of EMT and cancer metastasis and fulfill the understanding in the area of cancer cell biology.

Silymarin selectively protects human renal cells from cisplatin-induced cell death.

CONTEXT: Cisplatin-induced nephrotoxicity has been accepted as an important obstacle for efficient cisplatin-based chemotherapy. Silymarin from seeds of milk thistle [Silybum marianum L. (Asteraceae)] has been shown to possess various potential pharmacological properties; however, whether or not this agent selectively protects renal cells from cisplatin-induced cell death with no interfering effect on cancer cells is not clear. OBJECTIVE: Potential of silymarin in protection of cisplatin-induced renal cell death without compromising effect on anticancer activity of cisplatin was demonstrated in this study. MATERIALS AND METHODS: Cisplatin-induced cell death was evaluated in human proximal tubular HK-2, lung carcinoma H460, and melanoma G361 cells using MTT, Hoechst 33342, and propidium iodide assays. RESULTS: Cisplatin induced both apoptosis and necrosis in HK-2 cells and caused a decrease in cell viability by ~40% and 60% at the doses of 25 and 100 µM, respectively. Pretreatment with 25-200 µM of silymarin significantly protected against cisplatin-induced cell death in a dose-dependent manner. In contrast, pretreatment of silymarin (25-100 µM) caused no significant change on cisplatin-induced cell death in H460 cells but significantly potentiated cisplatin-induced apoptosis in G361 cells. DISCUSSION AND CONCLUSION: These findings reveal the selectivity of silymarin in protection of renal cells from cisplatin-induced cell death and could be beneficial for the development of this considerately safe compound as a renoprotective agent.

Cytoplasmic p21 Mediates 5-Fluorouracil Resistance by Inhibiting Pro-Apoptotic Chk2.

The oncogenic cytoplasmic p21 contributes to cancer aggressiveness and chemotherapeutic failure. However, the molecular mechanisms remain obscure. Here, we show for the first time that cytoplasmic p21 mediates 5-Fluorouracil (5FU) resistance by shuttling p-Chk2 out of the nucleus to protect the tumor cells from its pro-apoptotic functions. We observed that cytoplasmic p21 levels were up-regulated in 5FU-resistant colorectal cancer cells in vitro and the in vivo Chorioallantoic membrane (CAM) model. Kinase array analysis revealed that p-Chk2 is a key target of cytoplasmic p21. Importantly, cytoplasmic form of p21 mediated by p21T145D transfection diminished p-Chk2-mediated activation of E2F1 and apoptosis induction. Co-immunoprecipitation, immunofluorescence, and proximity ligation assay showed that p21 forms a complex with p-Chk2 under 5FU exposure. Using in silico computer modeling, we suggest that the p21/p-Chk2 interaction hindered the nuclear localization signal of p-Chk2, and therefore, the complex is exported out of the nucleus. These findings unravel a novel mechanism regarding an oncogenic role of p21 in regulation of resistance to 5FU-based chemotherapy. We suggest a possible value of cytoplasmic p21 as a prognosis marker and a therapeutic target in colorectal cancer patients.

Potential Anti-metastasis Natural Compounds for Lung Cancer.

As lung cancer is the most common malignancy worldwide and high mortalities are the result of metastasis, novel information surpassing the treatment strategies and therapeutic agents focusing on cancer dissemination are of interest. Lung cancer metastasis involves increased motility, survival in circulation and ability to form new tumors. Metastatic cells increase their aggressive features by utilizing several mechanisms to overcome hindrances of metastasis, including epithelial to mesenchymal transition (EMT), increased in cellular survival and migratory signals. Sufficient amounts of natural product-derived compounds have been shown to have promising anti-metastasis activities by suppressing key molecular features upholding such cell aggressiveness. The knowledge regarding molecular mechanisms rendering cell dissemination together with the anti-metastasis information of natural product-derived compounds may lead to development of novel therapeutic strategies.

Angiotensin II Increases Cancer Stem Cell-like Phenotype in Lung Cancer Cells.

BACKGROUND: Cancer stem cells (CSCs) have been proposed as important players in cancer progression, metastasis, and chemotherapeutic resistance in many cancers, including lung cancer. However, effects of the endogenous substance angiotensin II (ANG II) on cancer stem cell-like phenotype in lung cancer are largely unknown. MATERIALS AND METHODS: Human lung cancer cells were treated with non-cytotoxic concentrations of ANG II. The CSC phenotype was evaluated by spheroid formation, 3D culture, and anchorage-independent growth assays. The expression levels of CSC makers were determined by western blot analysis. RESULTS: ANG II significantly increased the ability of lung cancer cells to form spheroids. ANG II also increased the growth of cancer cells in a 3D culture Matrigel-based assay and facilitated cancer cell survival in an anchorage-independent condition. Western blot analysis revealed that cell treatment with ANG II significantly up-regulated CD133 levels. CONCLUSION: The present study revealed that the endogenous substance ANG II enhances CSC-like phenotype in lung cancer cells.

Ouabain mediates integrin switch in human lung cancer cells.

BACKGROUND: Physiological effects of ouabain, an endogenous human hormone, are being intensively investigated. However, its role in regulation of integrin pattern in lung cancer is largely unknown. The switching in the expression pattern of integrins is recognized as an important factor facilitating metastasis of several cancers. MATERIALS AND METHODS: Cytotoxicity and proliferative effects of ouabain on H460 lung cancer cells were evaluated by the MTT assay. The levels of integrin proteins in response to ouabain were determined by western blotting. Anchorage-independent growth and migration behaviors were performed by the wound healing assay and colony formation assay, respectively. RESULTS: Herein, the results suggested that exposure of the lung cancer cells to physiological concentrations of ouabain significantly altered the level of integrins. Ouabain suppressed integrin α4, α5, αv, ß3 and ß4, whereas it had no significant effect on integrin ß1 and ß4. According to the switch patterns of integrins, ouabain treatment resulted in a dramatic reduction of cell colony size and inhibition of cancer cell migration. However, ouabain-induced integrin switch had only a slight effect on chemotherapeutic drug susceptibility. CONCLUSION: Ouabain may have a role in suppressing cancer metastasis via integrin regulation.