Electrical switching of ferro-rotational order in nanometre-thick 1T-TaS2 crystals.

Hysteretic switching of domain states is a salient characteristic of all ferroic materials and the foundation for their multifunctional applications. Ferro-rotational order is emerging as a type of ferroic order that features structural rotations, but control over state switching remains elusive due to its invariance under both time reversal and spatial inversion. Here we demonstrate electrical switching of ferro-rotational domain states in the charge-density-wave phases of nanometre-thick 1T-TaS2 crystals. Cooling from the high-symmetry phase to the ferro-rotational phase under an external electric field induces domain state switching and domain wall formation, which is realized in a simple two-terminal configuration using a volt-scale bias. Although the electric field does not couple with the order due to symmetry mismatch, it drives domain wall propagation to give rise to reversible, durable and non-volatile isothermal state switching at room temperature. These results offer a route to the manipulation of ferro-rotational order and its nanoelectronic applications.

Axial-Bonding-Driven Dimensionality Effect on the Charge-Density Wave in NbSe2.

2H-NbSe2 is a prototypical charge-density-wave (CDW) system, exhibiting such a symmetry-breaking quantum ground state in its bulk and down to a single-atomic-layer limit. However, how this state depends on dimensionality and what governs the dimensionality effect remain controversial. Here, we experimentally demonstrate a robust 3 × 3 CDW phase in both freestanding and substrate-supported bilayer NbSe2, far above the bulk transition temperature. We exclude environmental effects and reveal a strong temperature and thickness dependence of Raman intensity from an axially vibrating A1g phonon mode, involving Se ions. Using first-principles calculations, we show that these result from a delicate but profound competition between the intra- and interlayer bonding formed between Se-pz orbitals. Our results suggest the crucial role of Se out-of-plane displacement in driving the CDW distortion, revealing the Se-dominated dimensionality effect and establishing a new perspective on the chemical bonding and mechanical stability in layered CDW materials.

Patterns and driving forces of dimensionality-dependent charge density waves in 2H-type transition metal dichalcogenides.

Charge density wave (CDW) is a startling quantum phenomenon, distorting a metallic lattice into an insulating state with a periodically modulated charge distribution. Astonishingly, such modulations appear in various patterns even within the same family of materials. Moreover, this phenomenon features a puzzling diversity in its dimensional evolution. Here, we propose a general framework, unifying distinct trends of CDW ordering in an isoelectronic group of materials, 2H-MX2 (M = Nb, Ta and X = S, Se). We show that while NbSe2 exhibits a strongly enhanced CDW order in two dimensions, TaSe2 and TaS2 behave oppositely, with CDW being absent in NbS2 entirely. Such a disparity is demonstrated to arise from a competition of ionic charge transfer, electron-phonon coupling, and electron correlation. Despite its simplicity, our approach can, in principle, explain dimensional dependence of CDW in any material, thereby shedding new light on this intriguing quantum phenomenon and its underlying mechanisms.

Proton-assisted growth of ultra-flat graphene films.

Graphene films grown by chemical vapour deposition have unusual physical and chemical properties that offer promise for applications such as flexible electronics and high-frequency transistors1-10. However, wrinkles invariably form during growth because of the strong coupling to the substrate, and these limit the large-scale homogeneity of the film1-4,11,12. Here we develop a proton-assisted method of chemical vapour deposition to grow ultra-flat graphene films that are wrinkle-free. Our method of proton penetration13-17 and recombination to form hydrogen can also reduce the wrinkles formed during traditional chemical vapour deposition of graphene. Some of the wrinkles disappear entirely, owing to the decoupling of van der Waals interactions and possibly an increase in distance from the growth surface. The electronic band structure of the as-grown graphene films shows a V-shaped Dirac cone and a linear dispersion relation within the atomic plane or across an atomic step, confirming the decoupling from the substrate. The ultra-flat nature of the graphene films ensures that their surfaces are easy to clean after a wet transfer process. A robust quantum Hall effect appears even at room temperature in a device with a linewidth of 100 micrometres. Graphene films grown by proton-assisted chemical vapour deposition should largely retain their intrinsic performance, and our method should be easily generalizable to other nanomaterials for strain and doping engineering.

Growth of environmentally stable transition metal selenide films.

Two-dimensional transition metal selenides (TMSs) possess fascinating physical properties. However, many as-prepared TMSs are environmentally unstable and limited in sample size, which greatly hinder their wide applications in high-performance electrical devices. Here we develop a general two-step vapour deposition method and successfully grow different TMS films with controllable thickness, wafer size and high quality. The superconductivity of the grown NbSe2 film is comparable with sheets exfoliated from bulk materials, and can maintain stability after a variety of harsh treatments, which are ascribed to the absence of oxygen during the whole growth process. Such environmental stability can greatly simplify the fabrication procedure for device applications, and should be of both fundamental and technological significance in developing TMS-based devices.

CLDN6 enhances chemoresistance to ADM via AF-6/ERKs pathway in TNBC cell line MDAMB231.

Claudin-6 (CLDN6), a critical tight junction protein acting as a tumor suppressor in breast cancer, is also considered to be a stem cell marker. Triple-negative breast cancer (TNBC) is a subtype of claudin-low and stem cell-like breast cancer which is chemoresistant to multiple anti-cancer drugs. The aim of our study was to determine whether CLDN6 plays a role in chemoresistance of TNBC. We found that overexpression of CLDN6 in TNBC cell line MDAMB231 significantly inhibited cell growth, migration, and invasion. The expression of CLDN6 increased the IC50 of adriamycin (ADM) and promoted the clonogenic survival. CLDN6 inhibited ADM-induced apoptosis and senescence in MDAMB231 cells. However, P-gp, a resistance-related protein highly associated with chemoresistance, was downregulated by CLDN6 overexpression in MDAMB231 cells. Epithelial mesenchymal transition (EMT) marker E-cadherin was increased, and vimentin was decreased by CLDN6. In addition, stem cell markers OCT4, SOX2, and Nanog were dramatically increased. CLDN6 colocalized and interacted with AF-6. Overexpression of CLDN6 increased the expression of afadin (AF-6) and hampered the activation of ERK signaling. PMA, a specific ERK activator, reversed the expression of EMT and stem cell markers, and decreased chemoresistance of MDAMB231 cells to ADM with a decreased IC50 and an increased apoptosis resulting from CLDN6. Together, we conclude that CLDN6 enhances the chemoresistance to ADM via activating the AF-6/ERK signaling pathway and up-regulating cancer stem cell characters in MDAMB231 cells.

SMAD2 Inactivation Inhibits CLDN6 Methylation to Suppress Migration and Invasion of Breast Cancer Cells.

The downregulation of tight junction protein CLDN6 promotes breast cancer cell migration and invasion; however, the exact mechanism underlying CLDN6 downregulation remains unclear. CLDN6 silence is associated with DNA methyltransferase 1 (DNMT1) mediated DNA methylation, and DNMT1 is regulated by the transforming growth factor beta (TGFß)/SMAD pathway. Therefore, we hypothesized that TGFß/SMAD pathway, specifically SMAD2, may play a critical role for CLDN6 downregulation through DNA methyltransferase 1 (DNMT1) mediated DNA methylation. To test this hypothesis, we blocked the SMAD2 pathway with SB431542 in two human breast cancer cell lines (MCF-7 and SKBR-3). Our results showed that treatment with SB431542 led to a decrease of DNMT1 expression and the binding activity for CLDN6 promoter. The methylation level of CLDN6 promoter was decreased, and simultaneously CLDN6 protein expression increased. Upregulation of CLDN6 inhibited epithelial to mesenchymal transition (EMT) and reduced the migration and invasion ability of both MCF-7 and SKBR-3 cells. Furthermore, knocked down of CLDN6 abolished SB431542 effects on suppression of EMT associated gene expression and inhibition of migration and invasion. Thus, we demonstrated that the downregulation of CLDN6 is regulated through promoter methylation by DNMT1, which depends on the SMAD2 pathway, and that CLDN6 is a key regulator in the SMAD2/DNMT1/CLDN6 pathway to inhibit EMT, migration and invasion of breast cancer cells.

Bioinformatic analysis reveals potential properties of human Claudin-6 regulation and functions.

Claudin-6 (CLDN6) is an integral component of the tight junction proteins in polarized epithelial and endothelial cells and plays a crucial role in maintaining cell integrity. Deregulation of CLDN6 expression and distribution in tumor tissues have been widely documented and correlated with cancer progression and metastasis. However, a complete mechanistic understanding of CLDN6 regulation and function remains to be studied. Herein, we show new potential properties of CLDN6 regulation and functions from bioinformatics analysis. Using numerous algorithms to characterize the CLDN6 gene promoter elements and the CLDN6 protein structure, physio-chemical and localization properties, and its evolutionary relationships. CLDN6 is regulated by a diverse set of transcription factors (SP1, SPR, AML-1a, CdxA, CRE-BP and CREB) and associated with the levels of methylation of CpG islands in promoters. The structural properties of CLDN6 indicate that it promotes cancer cell behavior via the ASK1-p38/JNK MAPK secretory signaling pathway. In conclusion, this information from bioinformatics analysis will help future attempts to better understand CLDN6 regulation and functions.

TTF1, in the Form of Nanoparticles, Inhibits Angiogenesis, Cell Migration and Cell Invasion In Vitro and In Vivo in Human Hepatoma through STAT3 Regulation.

TTF1-NP (5,2',4'-trihydroxy-6,7,5'-trimethoxyflavone nanoparticles), derived from the traditional Changbai Mountain medicinal plant Sorbaria sorbifolia (SS), has been showed its anti-cancer effect in various liver cancer cell types and tissues. The present study was designed to evaluate the antitumor mechanism of the TTF1-NP against HepG2 hepatoma cells and HepG2 cells-induced hepatocarcinoma (HCC) in nude mouse model. Here we demonstrated that TTF1-NP inhibits tube formation of HUVECs and HepG2 cell migration and invasion, and inhibits tumor growth in nude mice implanted with HepG2 cells through the downregulation of STAT3 protein and activation, along with VEGF, KDR, bFGF, MMP2 and MMP9 levels. We further revealed that TTF1-NP decreased the DNA-binding capacity of STAT3. Together our results provide a mechanism by which TTF1-NP suppresses cancer cell migration, invasion and angiogenesis through the action of STAT3 and suggests TTF1-NP as a potential therapy for hepatocellular cancer treatment.

DNA methylation of claudin-6 promotes breast cancer cell migration and invasion by recruiting MeCP2 and deacetylating H3Ac and H4Ac.

BACKGROUND: Claudin-6 (CLDN6), a member of claudin transmembrane protein family, has recently been reported to be undetectable or at low levels in human breast cancer cell lines and tissues and plays a role in suppression of migration and invasion in breast cancer cells. In addition, it is reported that CLDN6 expression is regulated by DNA methylation in various human cancers and cell lines. However, it is unclear how DNA methylation regulates CLDN6 expression. Here we show the mechanism by which DNA methylation regulates CLDN6 expression in human breast cancer cell line MCF-7. METHODS: RT-PCR, Western blot and immunofluorescent staining were utilized to investigate CLDN6 expression in breast cancer tissues and MCF-7 cells. Methylation-Specific PCR (MSP) was applied to determine DNA methylation status in CLDN6 gene promoter region. Wound-healing assay and invasion assay were utilized to test mobility of MCF-7 cells treated with 5-aza-dC (DNA methyltransferase inhibitor). MeCP2 binding, H3Ac and H4Ac in CLDN6 promoter region were analyzed by ChIP assay. Nuclease accessibility assay was performed for analysis of the chromatin conformation of CLDN6 gene. To study the role of CLDN6 in malignant progression, we used RNAi to knockdown CLDN6 expression in MCF-7 cells treated with 5-aza-dC, and examined the mobility of MCF-7 cells by wound-healing assay and invasion assay. RESULTS: 5-aza-dC and TSA (histone deacetylase inhibitor) application induced CLDN6 expression in MCF-7 cells respectively and synergistically. 5-aza-dC treatment induced CLDN6 demethylation, inhibited MeCP2 binding to CLDN6 promoter and increased H3Ac and H4Ac in the promoter. In addition, TSA increased H4Ac, not H3Ac in the promoter. The chromatin structure of CLDN6 gene became looser than the control group after treating with 5-aza-dC in MCF-7 cells. 5-aza-dC up-regulated CLDN6 expression and suppressed migration and invasion in MCF-7 cells, whereas CLDN6 silence restored tumor malignance in MCF-7 cells. CONCLUSIONS: DNA methylation down-regulates CLDN6 expression through MeCP2 binding to the CLDN6 promoter, deacetylating H3 and H4, and altering chromatin structure, consequently promoting migratory and invasive phenotype in MCF-7 cells.

CLDN6-induced apoptosis via regulating ASK1-p38/JNK signaling in breast cancer MCF-7 cells.

Claudin 6 (CLDN6), a member of tight junction protein claudin (CLDN) family, inhibits proliferation and induces apoptosis of MCF-7 breast cancer cells. However, these molecular mechanisms of CLDN6-induced apoptosis remain largely elusive. We previously found that restoration of human CLDN6 gene expression was correlated with the expression level of apoptosis signal-regulating kinase 1 (ASK1) using cDNA array and bioinformatics analysis. ASK1, a mitogen-activated protein kinase kinase kinase, is involved in environmental stress-activation of the c-jun N-terminal kinase (JNK) and p38 pathways, which contribute to apoptosis-associated tumor cell death. In the present study, we show that the restoration of CLDN6 gene expression in MCF-7 cells marhedly decreased ASK1 phosphorylation at Ser967. Activated ASK1ser967 further induced the activation of downstream targets, JNK and p38 kinase. MCF-7/CLDN6 stable transfection cell clone treated with TRX1, an ASK1 inhibitor, showed suppressed JNK and p38 activation, and showed substantially increased survival and colony formation and reduced percent of apoptotic cells using TUNEL staining and DNA ladder. Furthermore, TRX1 treatment increased Bcl-2/Bax ratio and reduced caspase-3 cleavage in MCF-7/CLDN6 stable transfection cell clone. Therefore, these data show that CLDN6 mediates ASK1-p38/JNK apoptotic signaling in MCF-7 cells, and it is correlated with constitutive deregulation of the balance of Bcl-2 family proteins and activation of caspase-3.

Expression of apoptosis signal-regulating kinase 1 is associated with tight junction protein claudin-6 in cervical carcinoma.

In our previous work, apoptosis signal-regulating kinase 1 (ASK1), a member of the mitogen-activated protein kinase (MAPK) kinase family has been proved to be associated with the pro-apoptosis effect of tight junction protein claudin-6 in breast cancer. However, its expression in cervical carcinoma has not been reported. The ASK1 and claudin-6 expression in cervical carcinoma tissues and adjacent non-neoplastic tissues was examined by immunohistochemistry. The mRNA and protein expression of ASK1 and claudin-6 in cervical cancer carcinoma cells was detected by reverse transcription (RT)-PCR and western blot. The expression level of ASK1 was down-regulated in cervical carcinoma tissues compared with the adjacent non-neoplastic tissues and positively correlated with the level of claudin-6 in cervical carcinoma cells and tissues. Our present study reveals that ASK1 protein expression altered between human cervical carcinoma and adjacent non-neoplastic tissues. The expression of ASK1 is correlated with the level of claudin-6 in cervical carcinoma cells and tissues.

Tight junction protein claudin-6 inhibits growth and induces the apoptosis of cervical carcinoma cells in vitro and in vivo.

Claudin-6, a member of claudin family integral membrane proteins, has recently been reported to be a tumor suppressor for breast cancer. However, whether it plays a role in other types of cancer remains unclear. In the present study, we showed that the expression of claudin-6 is down-regulated in cervical carcinoma tissues as revealed by immunohistochemistry. Through over-expressing claudin-6 in HeLa and C33A cervical carcinoma cells, we found that claudin-6 is localized at plasma membrane and it increases transepithelial electrical resistance of the cells. Gain of claudin-6 expression suppresses cell proliferation, colony formation in vitro, and tumor growth in vivo. The effects are accompanied and potentially caused by promotion of tumor cell apoptosis. Taken together, these results suggest that claudin-6 may function as a tumor suppressor and loss of claudin-6 contributes to enhanced tumorigenic properties of cervical carcinoma cells.

The effects of shRNA-mediated gene silencing of transcription factor SNAI1 on the biological phenotypes of breast cancer cell line MCF-7.

To research the effects of silencing transcription factor SNAI1 on the in vitro biological phenotypes of breast cancer cell line MCF-7, based on the gene sequence of SNAI1, we linked shRNA with the green fluorescent protein-expressing eukaryotic expression vector pGCsilencer™ U6/Neo/GFP, and transfected it into MCF-7 cells. The SNAI1 gene-silencing effect was authenticated by RT-PCR and immunofluorescence. We then examined the effect of gene silencing on the expression of epithelial and mesenchymal markers and on their biological phenotypes of the target cells. Finally, we explained that SNAI1 was bound to E-cadherin in MCF-7 cells by ChIP. Silencing SNAI1 upregulated the expression of epithelial markers claudin-4, claudin-7, and E-cadherin, while expression of the mesenchymal marker matrix metalloproteinase-2 was downregulated. The capacity for proliferation, migration, and invasion was diminished. SNAI1 binds to the E-cadherin gene promoter and inhibits its transcription. We can conclude that silencing gene SNAI1 inhibits expression of properties that are associated with the malignant phenotype of MCF-7 cells and reverses the epithelial-mesenchymal transition process by regulating relevant target gene E-cadherin.

Clinicopathologic significance of claudin-6, occludin, and matrix metalloproteinases -2 expression in ovarian carcinoma.

BACKGROUND: Tight junctions (TJs) are mainly composed of claudins, occludin, and tight junction adhesion molecules (JAM). The invasive and metastatic phenotype of highly invasive cancer cells has been related to abnormal structure and function of TJs, and with expression of activated matrix metalloproteinases (MMPs). The relevance of these mechanisms responsible for the invasion and metastasis of ovarian carcinoma is unclear. Similarly, it is not known if the expression of claudin-6, occludin and MMP2 is related with the clinical properties of these tumors. METHODS: Expression of claudin-6, occludin, and MMP2 was detected in samples of human ovarian cancer tissues by immunohistochemistry and correlated with the clinical properties of the tumors. RESULTS: The positive expression rates of claudin-6 and MMP-2 were higher in ovarian papillary serous carcinomas than n ovarian serous adenomas (P < 0.05). There were no differences in the expression of occludin (P > 0.05). The expression of claudin-6 and occludin in ovarian cancer was not correlated with patient age, pathological grade, clinical stage, and metastasis (P > 0.05). MMP-2 expression was enhanced with increased clinical stage and metastasis (P < 0.05), but was unrelated to patient age or tumor grade (P > 0.05). There were no apparent correlations between expression of claudin-6, occludin and MMP-2 in ovarian cancer tissue (P > 0.05). CONCLUSIONS: Our data suggest, for the first time, that the claudin-6 and MMP-2 are up-regulated in ovarian papillary serous carcinomas, MMP-2 expression was enhanced with increased clinical stage and metastasis. Claudin-6 and MMP-2 may play a positive role in the invasion and metastasis of ovarian cancer. VIRTUAL SLIDES: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1775628454106511.