67 research outputs found
Proximity Enhanced Quantum Spin Hall State in Graphene
Graphene is the first model system of two-dimensional topological insulator
(TI), also known as quantum spin Hall (QSH) insulator. The QSH effect in
graphene, however, has eluded direct experimental detection because of its
extremely small energy gap due to the weak spin-orbit coupling. Here we predict
by ab initio calculations a giant (three orders of magnitude) proximity induced
enhancement of the TI energy gap in the graphene layer that is sandwiched
between thin slabs of Sb2Te3 (or MoTe2). This gap (1.5 meV) is accessible by
existing experimental techniques, and it can be further enhanced by tuning the
interlayer distance via compression. We reveal by a tight-binding study that
the QSH state in graphene is driven by the Kane-Mele interaction in competition
with Kekul\'e deformation and symmetry breaking. The present work identifies a
new family of graphene-based TIs with an observable and controllable bulk
energy gap in the graphene layer, thus opening a new avenue for direct
verification and exploration of the long-sought QSH effect in graphene.Comment: 4 figures in Carbon, 201
Simultaneously expressed miR-424 and miR-381 synergistically suppress the proliferation and survival of renal cancer cells---Cdc2 activity is up-regulated by targeting WEE1
OBJECTIVES: MiRNAs are intrinsic RNAs that interfere with protein translation. Few studies on the synergistic effects of miRNAs have been reported. Both miR-424 and miR-381 have been individually reported to be involved in carcinogenesis. They share a common putative target, WEE1, which is described as an inhibitor of G2/M progression. Here, we studied the synergistic effects of miR-424 and miR-381 on renal cancer cells. METHODS: The viability of 786-O cells was analyzed after transfection with either a combination of miR-424 and miR-381 or each miRNA alone. We investigated cell cycle progression and apoptosis with flow cytometry. To confirm apoptosis and the abrogation of G2/M arrest, we determined the level of pHH3, which is an indicator of mitosis, and caspase-3/7 activity. The expression levels of WEE1, Cdc25, ÎłH2AX, and Cdc2 were manipulated to investigate the roles of these proteins in the miRNA-induced anti-tumor effects. To verify that WEE1 was a direct target of both miR-424 and miR-381, we performed a dual luciferase reporter assay. RESULTS: We showed that the combination of these miRNAs synergistically inhibited proliferation, abrogated G2/M arrest, and induced apoptosis. This combination led to Cdc2 activation through WEE1 inhibition. This regulation was more effective when cells were treated with both miRNAs than with either miRNA alone, indicating synergy between these miRNAs. WEE1 was verified to be a direct target of each miRNA according to the luciferase reporter assay. CONCLUSIONS: These data clearly demonstrate that these two miRNAs might synergistically act as novel modulators of tumorigenesis by down-regulating WEE1 expression in renal cell cancer cells
Graphene-based topological insulator with an intrinsic bulk band gap above room temperature
Topological insulators (TIs) represent a new quantum state of matter
characterized by robust gapless states inside the insulating bulk gap. The
metallic edge states of a two-dimensional (2D) TI, known as quantum spin Hall
(QSH) effect, are immune to backscattering and carry fully spin-polarized
dissipationless currents. However, existing 2D TIs realized in HgTe and
InAs/GaSb suffer from small bulk gaps (<10 meV) well below room temperature,
thus limiting their application in electronic and spintronic devices. Here, we
report a new 2D TI comprising a graphene layer sandwiched between two Bi2Se3
slabs that exhibits a large intrinsic bulk band gap of 30 to 50 meV, making it
viable for room-temperature applications. Distinct from previous strategies for
enhancing the intrinsic spin-orbit coupling effect of the graphene lattice, the
present graphene-based TI operates on a new mechanism of strong inversion
between graphene Dirac bands and Bi2Se3 conduction bands. Strain engineering
leads to effective control and substantial enhancement of the bulk gap.
Recently reported synthesis of smooth graphene/Bi2Se3 interfaces demonstrates
feasibility of experimental realization of this new 2D TI structure, which
holds great promise for nanoscale device applications.Comment: 3 figures, 1 tabl
Opening Band Gap without Breaking Lattice Symmetry: A New Route toward Robust Graphene-Based Nanoelectronics
Developing graphene-based nanoelectronics hinges on opening a band gap in the
electronic structure of graphene, which is commonly achieved by breaking the
inversion symmetry of the graphene lattice via an electric field (gate bias) or
asymmetric doping of graphene layers. Here we introduce a new design strategy
that places a bilayer graphene sheet sandwiched between two cladding layers of
materials that possess strong spin-orbit coupling (e.g., Bi2Te3). Our ab initio
and tight-binding calculations show that proximity enhanced spin-orbit coupling
effect opens a large (44 meV) band gap in bilayer graphene without breaking its
lattice symmetry, and the band gap can be effectively tuned by interlayer
stacking pattern and significantly enhanced by interlayer compression. The
feasibility of this quantum-well structure is demonstrated by recent
experimental realization of high-quality heterojunctions between graphene and
Bi2Te3, and this design also conforms to existing fabrication techniques in the
semiconductor industry. The proposed quantum-well structure is expected to be
especially robust since it does not require an external power supply to open
and maintain a band gap, and the cladding layers provide protection against
environmental degradation of the graphene layer in its device applications
Impurity screening and stability of Fermi arcs against Coulomband magnetic scattering in a Weyl monopnictide
We present a quasiparticle interference study of clean and Mn surface-doped
TaAs, a prototypical Weyl semimetal, to test the screening properties as well
as the stability of Fermi arcs against Coulomb and magnetic scattering.
Contrary to topological insulators, the impurities are effectively screened in
Weyl semimetals. The adatoms significantly enhance the strength of the signal
such that theoretical predictions on the potential impact of Fermi arcs can be
unambiguously scrutinized. Our analysis reveals the existence of three
extremely short, previously unknown scattering vectors. Comparison with theory
traces them back to scattering events between large parallel segments of
spin-split trivial states, strongly limiting their coherence. In sharp contrast
to previous work [R. Batabyal et al., Sci. Adv. 2, e1600709 (2016)], where
similar but weaker subtle modulations were interpreted as evidence of
quasiparticle interference originating from Femi arcs, we can safely exclude
this being the case. Overall, our results indicate that intra- as well as
inter-Fermi arc scattering are strongly suppressed and may explain why-in spite
of their complex multiband structure-transport measurements show signatures of
topological states in Weyl monopnictides
Long Non-Coding RNAs As Prognostic Markers In Human Breast Cancer
Long non-coding RNAs (lncRNAs) have been recently shown to play an important role in gene regulation and normal cellular functions, and disease processes. However, despite the overwhelming number of lncRNAs identified to date, little is known about their role in cancer for vast majority of them. The present study aims to determine whether lncRNAs can serve as prognostic markers in human breast cancer. We interrogated the breast invasive carcinoma dataset of the Cancer Genome Atlas (TCGA) at the cBioPortal consisting of ~ 1,000 cases. Among 2,730 lncRNAs analyzed, 577 lncRNAs had alterations ranging from 1% to 32% frequency, which include mutations, alterations of copy number and RNA expression. We found that deregulation of 11 lncRNAs, primarily due to copy number alteration, is associated with poor overall survival. At RNA expression level, upregulation of 4 lncRNAs (LINC00657, LINC00346, LINC00654 and HCG11) was associated with poor overall survival. A third signature consists of 9 lncRNAs (LINC00705, LINC00310, LINC00704, LINC00574, FAM74A3, UMODL1-AS1, ARRDC1-AS1, HAR1A, and LINC00323) and their upregulation can predict recurrence. Finally, we selected LINC00657 to determine their role in breast cancer, and found that LINC00657 knockout significantly suppresses tumor cell growth and proliferation, suggesting that it plays an oncogenic role. Together, these results highlight the clinical significance of lncRNAs, and thus, these lncRNAs may serve as prognostic markers for breast cancer
Identification of RNA silencing suppressor encoded by citrus chlorotic dwarf-associated virus
IntroductionCitrus chlorotic dwarf-associated virus (CCDaV) is an economically important citrus virus associated with leaf curling, deformation, and chlorosis found in China. Plants have evolved RNA silencing to defend against viral infections; however, the mechanism by which CCDaV suppresses RNA silencing in citrus remains unknown.MethodsSix proteins encoded by CCDaV were ectopically expressed in Nicotiana benthamiana 16c using the pCHF3 vector to identify RNA-silencing suppression activities.ResultsV2 protein encoded by CCDaV suppressed local RNA silencing and systemic RNA silencing triggered by GFP RNA, but did not impede short-distance movement of the RNA silencing signal in N. benthamiana 16c. GFP fluorescence observations showed that the ability of V2 protein to suppress RNA silencing was weaker than tomato bushy stunt virus P19. Deletion analysis showed that the putative nuclear localization signal (NLS, 25–54 aa) was involved in the RNA silencing suppression activity of V2 protein. Furthermore, V2 protein cannot block dsRNA-triggered RNA silencing. The subcellular localization assay suggested that V2 protein was localized to nucleus of N. benthamiana.ConclusionOverall, the results of this study demonstrate that CCDaV-V2 acts as an activity of silencing suppression. This is the first reported RNA-silencing suppressor encoded by Citlodavirus and will be valuable in revealing the molecular mechanism of CCDaV infection
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