150 research outputs found
Novel diffusion mechanism on the GaAs(001) surface: the role of adatom-dimer interaction
Employing first principles total energy calculations we have studied the
behavior of Ga and Al adatoms on the GaAs(001)-beta2 surface. The adsorption
site and two relevant diffusion channels are identified. The channels are
characterized by different adatom-surface dimer interaction. Both affect in a
novel way the adatom migration: in one channel the diffusing adatom jumps
across the surface dimers and leaves the dimer bonds intact, in the other one
the surface dimer bonds are broken. The two channels are taken into account to
derive effective adatom diffusion barriers. From the diffusion barriers we
conclude a strong diffusion anisotropy for both Al and Ga adatoms with the
direction of fastest diffusion parallel to the surface dimers. In agreement
with experimental observations we find higher diffusion barriers for Al than
for Ga.Comment: 4 pages, 2 figures, Phys. Rev. Lett. 79 (1997). Other related
publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm
Atorvastatin attenuation of ABCB1 expression is mediated by microRNA miR-491-3p in Caco-2 cells
AimAtorvastatin, a HMG-CoA reductase inhibitor, used in the treatment of hypercholesterolemia, has been previously shown to regulate ABCB1 expression in vivo and in vitro. We hypothesized that the statin could regulate gene expression of ABCB1 transporter via microRNAs.MethodsExpression of microRNAs and ABCB1 mRNA was examined in atorvastatin-treated and control cells using real-time PCR. miR-491-3P mimic and inhibitor were transfected in Caco-2 and ABCB1 expression was monitored by western blot and real-time PCR.ResultsIn HepG2 cells, none of the microRNAs predicted to target ABCB1 3'UTR was regulated by atorvastatin treatment. In agreement with this, ABCB1 3'UTR activity was not modulated in HepG-2 cells after 48h-treatment as measured by luciferase assay. In Caco-2 cells, atorvastatin treatment provoked a decrease in luciferase activity and, accordingly, miR-491-3p was upregulated about 2.7 times after 48h-statin treatment. Luciferase analysis of miR-491-3p with a mimetic or inhibitor of miR-491-3p revealed that this microRNA could target ABCB1 3'UTR, as after miR-491-3p inhibition, ABCB1 levels were increased by two-fold, and miR-491-3p superexpression decreased ABCB1 3'UTR activity. Finally, functional analysis revealed that treatment with miR-491-3p inhibitor could reverses atorvastatin attenuation of ABCB1 (Pg-p) protein levels.ConclusionOur results suggest atorvastatin control ABCB1 expression via miR-491-3p in Caco-2 cells. This finding may be an important mechanism of statin drug-drug interaction, since common concomitant drugs used in the prevention of cardiovascular diseases are ABCB1 substrates
FoxP3+ T regulatory cells in cancer : prognostic biomarkers and therapeutic targets
T Regulatory cells (Tregs) can have both protective and pathological roles. They maintain immune homeostasis and inhibit immune responses in various diseases, including cancer. Proportions of Tregs in the peripheral blood of some cancer patients increase by five-to ten-folds, compared to those in healthy individuals. Tregs contribute to cancer development and progression by suppressing T effector cell functions, thereby compromising tumor killing and promoting tumor growth. Highly immunosuppressive Tregs express upregulated levels of the transcription factor, Forkhead box protein P3 (FoxP3). Elevated levels of FoxP3+ Tregs within the tumor microenvironment (TME) showed a positive correlation with poor prognosis in various cancer patients. Despite the success of immunotherapy, including the use of immune checkpoint inhibitors, a significant proportion of patients show low response rates as a result of primary or acquired resistance against therapy. Some of the mechanisms which underlie the development of therapy resistance are associated with Treg suppressive function. In this review, we describe Treg contribution to cancer development/progression, and the mechanisms of Treg-mediated immunosuppression. We discuss the prognostic significance of FoxP3+ Tregs in different cancers and their potential use as prognostic biomarkers. We also describe potential therapeutic strategies to target Tregs in combination with other types of immunotherapies aiming to overcome tumor resistance and improve clinical outcomes in cancer patients. Overall, understanding the prognostic significance of FoxP3+ Tregs in various cancers and their contribution to therapeutic resistance could help in the development of more effective targeted therapeutic strategies to enhance the clinical outcomes in cancer patients
Modified f(R) gravity from scalar-tensor theory and inhomogeneous EoS dark energy
The reconstruction of f(R)-gravity is showed by using an auxiliary scalar
field in the context of cosmological evolution, this development provide a way
of reconstruct the form of the function f (R) for a given evolution of the
Hubble parameter. In analogy, f(R)-gravity may be expressed by a perfect fluid
with an inhomogeneous equation of state that depends on the Hubble parameter
and its derivatives. This mathematical equivalence that may confuse about the
origin of the mechanism that produces the current acceleration, and possibly
the whole evolution of the Hubble parameter, is shown here.Comment: 8 page
Growth of nanostructures by cluster deposition : a review
This paper presents a comprehensive analysis of simple models useful to
analyze the growth of nanostructures obtained by cluster deposition. After
detailing the potential interest of nanostructures, I extensively study the
first stages of growth (the submonolayer regime) by kinetic Monte-Carlo
simulations. These simulations are performed in a wide variety of experimental
situations : complete condensation, growth with reevaporation, nucleation on
defects, total or null cluster-cluster coalescence... The main scope of the
paper is to help experimentalists analyzing their data to deduce which of those
processes are important and to quantify them. A software including all these
simulation programs is available at no cost on request to the author. I
carefully discuss experiments of growth from cluster beams and show how the
mobility of the clusters on the surface can be measured : surprisingly high
values are found. An important issue for future technological applications of
cluster deposition is the relation between the size of the incident clusters
and the size of the islands obtained on the substrate. An approximate formula
which gives the ratio of the two sizes as a function of the melting temperature
of the material deposited is given. Finally, I study the atomic mechanisms
which can explain the diffusion of the clusters on a substrate and the result
of their mutual interaction (simple juxtaposition, partial or total
coalescence...)Comment: To be published Rev Mod Phys, Oct 99, RevTeX, 37 figure
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