23,047 research outputs found
Regulation of 92-kD gelatinase release in HL-60 leukemia cells
Matrix metalloproteinase 9 (MMP-9), also known as 92-kD type IV collagenase/gelatinase, is believed to play a critical role in tumor invasion and metastasis. Here, we report that MMP-9 was constitutively released from the human promyelocytic cell line HL-60 as determined by zymographic analysis. Tumor necrosis factor-alpha (TNF-alpha) enhanced the enzyme release threefold to fourfold and the protein kinase C (PKC) activator and differentiation inducer 12-O-tetradecanoylphorbol-13- acetate (TPA) eightfold to ninefold. Gelatinase induction by TNF-alpha and TPA was inhibited by actinomycin D or cycloheximide, indicating that de novo protein synthesis was required. Neutralizing monoclonal antibodies to TNF-alpha (anti-TNF-alpha) decreased the basal MMP-9 release of these cells. In addition, these antibodies also significantly interfered with the TPA-induced enzyme release. Agents that inhibit TNF-alpha expression in HL-60 cells, such as pentoxifylline and dexamethasone, completely abrogated both the constitutive and TPA-evoked MMP-9 release. Diethyldithiocarbamate, which is known to stimulate TNF-alpha production in HL-60 cells, exerted a positive effect on MMP-9 release in untreated cells but was inhibitory in TPA-treated HL-60 cells. The PKC inhibitor staurosporine at low concentrations (100 ng/mL) caused a significant augmentation of MMP-9 release in untreated cultures that was blocked by the addition of anti-TNF-alpha. High concentrations (2 mumol/L) of staurosporine completely abolished the extracellular enzyme activity both in untreated and TPA-stimulated cells. These results suggest, that TNF- alpha is required for basal and PKC-mediated MMP-9 release in HL-60 leukemia cells. Thus, MMP-9 secretion may be regulated by TNF-alpha not only in a paracrine but also in an autocrine fashion. This may potentiate the matrix degradative capacity of immature leukemic cells in the processes of bone marrow egress and the evasion of these cells into peripheral tissue
Einselection without pointer states
We consider small subsystems of large, closed quantum systems that evolve
according to the von Neumann equation. Without approximations and without
making any special assumptions on the form of the interaction we prove that,
for almost all initial states and almost all times, the off-diagonal elements
of the density matrix of the subsystem in the eigenbasis of its local
Hamiltonian must be small, whenever the energy difference of the corresponding
eigenstates is larger than the interaction energy. This proves that decoherence
with respect to the local energy eigenbasis is a natural property of weakly
interacting quantum systems.Comment: published in Phys. Rev. E, 4 pages, no figures, revised introduction
and conclusions, references revised and new references added, editorial
change
Small eigenvalues of large Hankel matrices:The indeterminate case
In this paper we characterise the indeterminate case by the eigenvalues of
the Hankel matrices being bounded below by a strictly positive constant. An
explicit lower bound is given in terms of the orthonormal polynomials and we
find expresions for this lower bound in a number of indeterminate moment
problems.Comment: 14 pages, 1 figur
Competition of mixing and segregation in rotating cylinders
Using discrete element methods, we study numerically the dynamics of the size
segregation process of binary particle mixtures in three-dimensional rotating
drums, operated in the continuous flow regime. Particle rotations are included
and we focus on different volume filling fractions of the drum to study the
interplay between the competing phenomena of mixing and segregation. It is
found that segregation is best for a more than half-filled drum due to the
non-zero width of the fluidized layer. For different particle size ratios, it
is found that radial segregation occurs for any arbitrary small particle size
difference and the final amount of segregation shows a linear dependence on the
size ratio of the two particle species. To quantify the interplay between
segregation and mixing, we investigate the dynamics of the center of mass
positions for each particle component. Starting with initially separated
particle groups we find that no mixing of the component is necessary in order
to obtain a radially segregated core.Comment: 9 pages, 12 figures (EPIC/EEPIC & EPS, macros included), submitted to
Physics of Fluid
Stability borders of feedback control of delayed measured systems
When stabilization of unstable periodic orbits or fixed points by the method
given by Ott, Grebogi and Yorke (OGY) has to be based on a measurement delayed
by orbit lengths, the performance of unmodified OGY method is expected
to decline. For experimental considerations, it is desired to know the range of
stability with minimal knowledge of the system. We find that unmodified OGY
control fails beyond a maximal Ljapunov number of
. In this paper the area of stability is
investigated both for OGY control of known fixed points and for difference
control of unknown or inaccurately known fixed points. An estimated value of
the control gain is given. Finally we outline what extensions have to be
considered if one wants to stabilize fixed points with Ljapunov numbers above
.Comment: 5 pages LaTeX using revtex and epsfig (4 figs included). Revised
versio
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