Generation of reactive oxygen species by xanthine derivatives in MDA‐MB‐231 human breast cancer cells

Theophylline reduces cell number in MDAMB231 cells through mechanisms over and above phosphodiesterase inhibition. In the current study, we used an intracellular fluorescent dye to show that theophylline and, to a much greater extent, 3isobutyl1methylxanthine, evoke the generation of reactive oxygen species and also sensitize the cells to insult by other oxidants. Xanthine derivatives may therefore offer novel strategies for antitumor therapeutics.     

Estrogen and antiestrogens alter breast cancer invasiveness by modulating the transforming growth factor-β signaling pathway

In the later stages of breast cancer, estrogen receptor (ER)α-negative cancers typically have higher histological grades than ERα-positive cancers, and transforming growth factor (TGF)-β promotes invasion and metastasis. Our previous study indicated that ERα inhibited TGF-β signaling by inducing the degradation of Smad in an estrogen-dependent manner. In the present study, we report that the suppressive effects of ERα and estrogen on tumor progression are mediated by inhibiting TGF-β signaling. Furthermore, we investigated the effects of antiestrogens such as ICI182,780 (ICI) or tamoxifen (TAM) on TGF-β signaling and breast cancer invasiveness. The levels of total Smad and pSmad were reduced by estrogen, whereas ICI slightly increased them, and TAM had no effect. To investigate the effect of antiestrogens on breast cancer invasiveness, we generated highly migratory and invasive MCF-7-M5 cells. The migration and invasion of these cells were suppressed by the inhibitor of TGF-β receptor kinase, SB-505124, and estrogen. However, antiestrogens did not suppress the migration and invasion of these cells. In addition, we screened TGF-β target genes whose expression was reduced by estrogen treatment and identified four genes associated with breast cancer invasiveness and poor prognosis. The expression of these genes was not decreased by antiestrogens. These observations provide a new insight into estrogen function and the mechanisms underlying estrogen-mediated suppression of tumor progression.     

Estrogen receptor α is the major driving factor for growth in tamoxifen-resistant breast cancer and supported by HER/ERK signaling

Resistance to tamoxifen is a major clinical challenge in the treatment of breast cancer; however, it is still unclear which signaling pathways are the major drivers of tamoxifen-resistant growth. To characterize resistance mechanisms, we have generated different tamoxifen-resistant breast cancer cell lines from MCF-7. In this model, we investigated whether signaling from human epidermal growth factor receptors (HERs), their downstream kinases, or from the estrogen receptor α (ERα) was driving tamoxifen-resistant cell growth. Increased expression of EGFR and increased phosphorylation of HER3 were observed upon acquisition of tamoxifen resistance, and the extracellular activated kinase (ERK) signaling pathway was highly activated in the resistant cells. The EGFR inhibitor gefitinib and the ERK pathway inhibitor U0126 resulted in partial and preferential growth inhibition of tamoxifen-resistant cells. All the tamoxifen-resistant cell lines retained ERα expression but at a lower level compared to that in MCF-7. Importantly, we showed via ERα knockdown that the tamoxifen-resistant cells were dependent on functional ERα for growth and we observed a clear growth stimulation of resistant cell lines with clinically relevant concentrations of tamoxifen and 4-OH-tamoxifen, indicating that tamoxifen-resistant cells utilize agonistic ERα stimulation by tamoxifen for growth. The tamoxifen-resistant cells displayed high phosphorylation of ERα at Ser118 in the presence of tamoxifen; however, treatment with U0126 neither affected the level of Ser118 phosphorylation nor expression of the ERα target Bcl-2, suggesting that ERK contributes to cell growth independently of ERα in our cell model. In support of this, combined treatment against ERα and ERK signaling in resistant cells was superior to single-agent treatment and as effective as fulvestrant treatment of MCF-7 cells. Together, these findings demonstrate that ERα is a major driver of growth in tamoxifen-resistant cells supported by HER/ERK growth signaling, implying that combined targeting of these pathways may have a clinical potential for overcoming tamoxifen resistance.     

Synergistic action of apoptosis induced by eicosapentaenoic acid and TNP‐470 on human breast cancer cells

The effects of eicosapentaenoic acid (EPA) and an angiogenesis inhibitor (TNP470) on the suppression of breast cancer cell growth were examined in five human breast cancer cell lines (MDAMB231, T47D, MCF7, KPL1, and MKLF). In all five cell lines, EPA and TNP470 alone both showed tumor growth inhibition in a time and dosedependent manner, and in combination, a synergistic effect was seen at high concentrations. EPA plus TNP470 treatment evoked apoptosis as confirmed by the appearance of sub G1 populations, by DNA fragmentation, and by cell morphology. With the combination, the expression of Bax and Bc1x_S, the apoptosisenhancing proteins, was more upregulated and that of Bcl2 and Bclx_L, the apoptosissuppressing proteins, was more downregulated compared to the use of EPA or TNP470 alone, suggesting that their synergistic effect was due to an acceleration of apoptosis.     

A novel β-catenin signaling pathway activated by IL-1β leads to the onset of epithelial–mesenchymal transition in breast cancer cells

Interleukin 1β has been associated with tumor development, invasiveness and metastasis in various types of cancer. However, the molecular mechanisms underlying this association have not been clearly elucidated. The present study is the first to show, in breast cancer cells, that an IL-1β/IL-1RI/β-catenin signaling pathway induces β-catenin accumulation due to GSK3β inactivation by Akt phosphorylation. Translocation to the nucleus of accumulated β-catenin and formation of the TCF/Lef/β-catenin complex induce sequential expression of c-MYC, CCDN1, SNAIL1 and MMP2, leading to up-regulation of proliferation, migration and invasion; all of the processes shown to be required, in cancerous cells, to initiate transition from a non-invading to an invasive phenotype.     

RETRACTED ARTICLE: Platelet-derived growth factor-D contributes to aggressiveness of breast cancer cells by up-regulating Notch and NF-κB signaling pathways

Platelet-derived growth factor-D (PDGF-D) has been linked with several human malignancies; however, its role in breast cancer progression is not known. We found that PDGF-D expressing breast cancer cell lines MDA-MB-231 and SUM-149 are more invasive compared to cell lines with little or no expression of PDGF-D such as MDA-MB-468 and MCF-7 cells. Over-expression of PDGF-D in PDGF-D low expressing MDA-MB-468 and MCF-7 cells by cDNA transfection showed increased cell proliferation while silencing the expression of PDGF-D by siRNA in PDGF-D high expressing MDA-MB-231 and SUM-149 cells showed decreased cell proliferation and increased apoptosis. Moreover, PDGF-D over-expression was positively correlated with the expression of Notch-1 and Jagged-1, and the expression of mesenchymal markers (Vimentin and ZEB-2) with concomitant decreased expression of epithelial marker E-cadherin. Since NF-κB activation plays a crucial role in Notch signaling as well as in epithelial–mesenchymal transition and tumor aggressiveness, we determined the DNA binding activity of NF-κB and our findings are consistent showing that PDGF-D over-expression led to increased DNA binding activity of NF-κB while it was found to be decreased by inactivation of PDGF-D. These results were also consistent with the expression and activity of MMP-9 and VEGF, as well as invasive characteristics. Further, forced expression of Notch-1/Jagged-1 by cDNA transfection de-repressed the effects of PDGF-D silencing on NF-κB activity and invasion. From these results, we conclude that PDGF-D plays an important role in breast tumor aggressiveness and this process is mechanistically linked with the activation of Notch and NF-κB signaling.     

ARMC8α promotes proliferation and invasion of non-small cell lung cancer cells by activating the canonical Wnt signaling pathway

ARMC8 proteins are novel armadillo repeat containing proteins, which are well conserved in eukaryotes and are involved in a variety of processes such as cell migration, proliferation, tissue maintenance, signal transduction, and tumorigenesis. Armadillo repeat proteins include well-known proteins such as β-catenin and p120ctn. Our current knowledge of ARMC8, especially its role in cancer, is limited. In this study, we quantified ARMC8 expression in 112 non-small cell lung cancer (NSCLC) tissues and adjacent non-cancerous tissues, and seven lung cancer cell lines using immunohistochemistry staining and Western blotting. ARMC8 level was significantly higher in NSCLC tissues than in the adjacent normal tissues (67.9 % versus 5.4 %, p?p?=?0.022), lymph node metastasis (p?=?0.001), and poor prognosis (p?NSCLC patients. Cox regression analysis demonstrated that ARMC8 was an independent prognostic factor for NSCLC. Consistent with this, ARMC8α downregulation by siRNA knockdown inhibited growth, colony formation, and invasion in A549 lung cancer cells, while ARMC8α overexpression promoted growth, colony formation, and invasion in H1299 lung cancer cells. In addition, ARMC8α knockdown downregulated canonical Wnt-signaling pathway activity and cyclin D1 and matrix metalloproteinase (MMP)-7 expression. Consistent with this, ARMC8α overexpression upregulated canonical Wnt-signaling pathway activity and cyclin D1 and MMP-7 expression. These results indicate that ARMC8α upregulates cyclin D1 and MMP7 expression by activating the canonical Wnt-signaling pathway and thereby promoting lung cancer cell proliferation and invasion. Therefore, ARMC8 might serve as a novel therapeutic target in NSCLC.     

CD133+ cells from medulloblastoma and PNET cell lines are more resistant to cyclopamine inhibition of the sonic hedgehog signaling pathway than CD133− cells

CD133 has recently been used as a reliable marker for brain tumor stem cells isolation. Sonic hedgehog (SHH) is implicated in medulloblastoma and central primitive neuroectodermal tumor (cPNET) formation. It has recently been suggested a role for the EWS/FLI1 fusion protein—typical of pPNET—in the upregulation of GLI1 and PTCH1 genes. Cyclopamine inhibits the SHH pathway in medulloblastoma cell lines, but its effect on cPNET and pPNET cell lines has not been well established yet. Our purpose was to study the effect of cyclopamine on medulloblastoma and PNET cell lines and to analyze whether CD133 expression might be able to modify this effect. We analyzed gene expression, cell viability, apoptosis, and tumorigenic capability before and after cyclopamine treatment in CD133 high-expressing and CD133 low-expressing cell lines. All medulloblastoma and PNET cell lines displayed an inhibitory effect on the expression of SHH pathway genes, on viability, and on tumorigenic potential after treatment. Nevertheless, CD133 expression made the cells more resistant to cyclopamine inhibition. These results open new doors to the understanding of CD133+ cancer stem cells as residual cells that might be responsible for treatment resistance.     

Ca2+ influx-mediated dilation of the endoplasmic reticulum and c-FLIPL downregulation trigger CDDO-Me–induced apoptosis in breast cancer cells

The synthetic triterpenoid 2-cyano-3, 12-dioxooleana-1, 9(11)-dien-C28-methyl ester (CDDO-Me) is considered a promising anti-tumorigenic compound. In this study, we show that treatment with CDDO-Me induces progressive endoplasmic reticulum (ER)-derived vacuolation in various breast cancer cells and ultimately kills these cells by inducing apoptosis. We found that CDDO-Me–induced increases in intracellular Ca²⁺ levels, reflecting influx from the extracellular milieu, make a critical contribution to ER-derived vacuolation and subsequent cell death. In parallel with increasing Ca²⁺ levels, CDDO-Me markedly increased the generation of reactive oxygen species (ROS). Interestingly, there exists a reciprocal positive-regulatory loop between Ca²⁺ influx and ROS generation that triggers ER stress and ER dilation in response to CDDO-Me. In addition, CDDO-Me rapidly reduced the protein levels of c-FLIP_L (cellular FLICE-inhibitory protein) and overexpression of c-FLIP_L blocked CDDO-Me–induced cell death, but not vacuolation. These results suggest that c-FLIP_L downregulation is a key contributor to CDDO-Me–induced apoptotic cell death, independent of ER-derived vacuolation. Taken together, our results show that ER-derived vacuolation via Ca²⁺ influx and ROS generation as well as caspase activation via c-FLIP_L downregulation are responsible for the potent anticancer effects of CDDO-Me on breast cancer cells.     

Combination of curcumin and bicalutamide enhanced the growth inhibition of androgen-independent prostate cancer cells through SAPK/JNK and MEK/ERK1/2-mediated targeting NF-κB/p65 and MUC1-C

Background

Prostate cancer is one of the most common malignancies in men. The mucin 1 (MUC1) heterodimeric oncoprotein is overexpressed in human prostate cancers with aggressive pathologic and clinical features, resulting in a poor outcome. However, the functional role for MUC1 C-terminal domain (MUC1-C) in androgen-independent prostate cancer occurrence and development has remained unclear.

Methods

Cell viability was measured by MTT assays. Western blot analysis was performed to measure the phosphorylation and protein expression of SAPK/JNK and ERK1/2, and MUC1-C, NF-κB subunit p65 and p50. Exogenous expression of MUC1-C, NF-κB subunit p65 was carried out by transient and electroporated transfection assays.

Results

We showed that curcumin inhibited the growth of androgen-independent prostate cancer cells and a synergy was observed in the presence of curcumin and bicalutamide, the androgen receptor antagonist. To further explore the potential mechanism underlining this, we found that curcumin increased the phosphorylation of ERK1/2 and SAPK/JNK, which was enhanced by bicalutamide. In addition, curcumin reduced the protein expression of MUC1-C and NF-κB subunit p65, which were abrogated in the presence of the inhibitors of MEK/ERK1/2 (PD98059) and SAPK/JNK (SP60015). A further reduction was observed in the combination of curcumin with bicalutamide. Moreover, while exogenous expression of MUC1-C had little effect on curcumin-reduced p65, the overexpression of p65 reversed the effect of curcumin on MUC1-C protein expression suggesting that p65 is upstream of MUC1-C. Intriguingly, we showed that exogenous expression of MUC1-C feedback diminished the effect of curcumin on phosphorylation of ERK1/2 and SAPK/JNK, and antagonized the effect of curcumin on cell growth.

Conclusion

Our results show that curcumin inhibits the growth of androgen-independent prostate cancer cells through ERK1/2- and SAPK/JNK-mediated inhibition of p65, followed by reducing expression of MUC1-C protein. More importantly, there are synergistic effects of curcumin and bicalutamide. The negative feedback regulatory loop of MUC1-C to ERK1/2 and SAPK/JNK further demonstrates the role of MUC1-C that contributes to the overall responses of curcumin. This study unveils the potential molecular mechanism by which combination of curcumin with bicalutamide enhances the growth inhibition of androgen-independent prostate cancer cells.     

Gene expression profiling and pathway analysis identify the integrin signaling pathway to be altered by IL-1β in human pancreatic cancer cells: role of JNK

CYR61 over-expression promotes cell proliferation by inhibiting carboplatin-induced apoptosis, decreasing Bax expression, and increasing Bcl-xL, Mcl-1, and Bcl-2. At the same time, down-regulating p53 expression, while up-regulated NF-κB expression. Additionally, p21 and p53 promoter activities were reduced, while NF-κB and Bcl-2 activities increased. In parallel, CYR61-expressing cells, during carboplatin-induced apoptosis, resulted in an increase of Akt phosphorylation, while rapamycin-treated cells were not affected. Carboplatin effectively inhibited the activation of mTOR signaling cascade, which includes mTOR, 4E-BP1, p70S6K, HIF-1α, and VEGF. These results provide evidence that CYR61 promotes cell proliferation and inhibits apoptosis.