O. E. Petukhova

Extra‐cellular matrix proteins induce re‐distribution of α‐actinin‐1 and α‐actinin‐4 in A431 cells

Alpha‐actinins are actin‐binding proteins of non‐muscle cells, which can participate in the regulation of transcription factor activity. We describe the distribution of α‐actinin‐1 and −4 depending on different actin cytoskeleton formed as a result of cell adhesion to extracellular matrix proteins, such as fibronectin and laminin 2/4. Immunofluorescent studies show a difference in the distribution of α‐actinin and −4. Both isoforms localise along stress‐fibres, but α‐actinin‐1 localises in the perinuclear region more abundantly than α‐actinin‐4. Western blot analysis demonstrated existence of truncated forms of both isoforms. Truncated α‐actinin‐1 appears in cells spread on fibronectin or laminin. Cell spreading also correlated with more tight association of α‐actinin‐4 with chromatin. Basing on our previous finding of an interaction of α‐actinin‐4 with p65 subunit of the NF‐κB, we checked the possible influence of immobilised ligands on its redistribution in nuclear complexes containing p65. α‐Actinin‐4 seems to be present in some but not all nuclear complexes containing p65. Immobilised ligands may affect the interaction of α‐actinin‐4/p65 complexes with chromatin. The data suggest that adhesion to extra‐cellular matrix may interfere in cellular reactions mediated by α‐actinin‐1 and −4.

Resistivity tensor correlations in the mixed state of electron-doped superconductor Nd2−xCexCuO4+δ

Abstract The magnetic-field dependencies of the longitudinal and Hall resistance of the electron-doped compounds Nd 2 − x Ce x CuO 4 + δ in underdoped region with x = 0.14 and with varying degrees of disorder ( δ ) were investigated. It was established experimentally that the correlation between the longitudinal electrical resistivity and the Hall resistivity can be analyzed on the basis of scaling relationships: ρ xy ( B ) ∼ [ ρ xx ( B )] β . For the totality of the investigated single-crystal films of Nd 2 − x Ce x CuO 4 + δ /SrTiO 3 the values of β from 0.8 to 1.55 is found. The observed feature in the electron-doped two-dimensional systems can be associated both with a displaying of anisotropic s - wave or d - wave pairing symmetry and with a pinning due to an essential degree of disorder in the samples under study.

Functional compartmentalisation of NF-κB-associated proteins in A431 cells

NF‐κB proteins belong to a family of ubiquitous transcription factors involved in a number of cellular responses. While the pathways of NF‐κB activation and input into the regulation of gene activity have been comprehensively investigated, its cytoplasmic functions are poorly understood. In this study we addressed effects of the compartmentalisation of NF‐κB proteins RelA/p65 and p50 in relation to the inhibitor IκB‐α, using fibronectin (FN) and epidermal growth factor (EGF) for environmental stimulation of epidermoid carcinoma A431 cells. We thus assessed the presence of NF‐κB family proteins in the cytosol, membrane, nuclear and cytoskeletal fractions with a special attention to the cytoskeletal fraction to define whether NF‐κB was active or not. Sub‐cellular fractionation demonstrated that the proportion of RelA/p65 differed in diverse sub‐cellular fractions, and that the cytoskeleton harboured about 7% thereof. Neither the nuclear nor the cytoskeleton fraction did contain IκB‐α. The cytoskeleton binding of RelA/p65 and p50 was further confirmed by co‐localisation and electron microscopy data. During 30‐min EGF stimulation similar dynamics were found for RelA/p65 and IκB‐α in the cytosol, RelA/p65 and p50 in the nucleus and p50 and IκB‐α in the membrane. Furthermore, EGF stimulation for 30 min resulted in a threefold accumulation of RelA/p65 in cytoskeletal fraction. Our results suggest that nuclear‐, membrane‐ and cytoskeleton‐associated NF‐κB are dynamic and comprise active pools, whereas the cytoplasmic is more constant and likely non‐active due to the presence of IκB‐α. Moreover, we discovered the existence of a dynamic, IκB‐α‐free pool of RelA/p65 associated with cytoskeletal fraction, what argues for a special regulatory role of the cytoskeleton in NF‐κB stimulation.

Doping effect on the evolution of the pairing symmetry in n-type superconductor near antiferromagnetic phase boundary

We present the investigation results of the in-plane \{rho}(T) resistivity tensor at the temperature range 0.4-40 K in magnetic fields up to 90kOe (H||c, J||ab) for electron-doped Nd{2-x}Ce{x}CuO{4+{\delta}} with different degree of disorder near antiferromagnetic - superconducting phase boundary. We have experimentally found that for optimally doped compound both the upper critical field slope and the critical temperature decrease with increasing of the disorder parameter (d-wave pairing) while in the case of the underdoped system the critical temperature remains constant and (dHc2/dT)|Tc increases with increasing of the disorder (s-wave pairing). These features suggest a possible implementation of the complex mixture state as the (s+id)-pairing.

Pairing type change upon an increase in the cerium doping level in the Nd2 − xCexCuO4 + δ electronic superconductor

We report on the results of analyzing the temperature dependences of the resistivity of the Nd2 − xCexCuO4 + δ electronic superconductor with x = 0.14 (underdoped range), x = 0.15 (optimal doping), and x = 0.18 (overdoped range) and with various degrees of annealing in an oxygen-free atmosphere in magnetic fields up to H = 90 kOe (H ‖ c, J ‖ ab) in the temperature range T = (0.4–300) K. It is shown that the observed differences in the dependences of the slope of the upper critical field

Incoherent interlayer transport in single-crystal films of Nd2-xCexCuO4/SrTiO3

(dH_{c2} /dT)|_{T_c }

Correlation between the Hall Resistance and Magnetoresistance in the Mixed State of an Nd2 − xCexCuO4 + δ Electronic Superconductor

on the degree of disorder in the Nd2 − xCexCuO4 + δ system upon a change in the cerium doping level indicate a change in the symmetry of d-type pairing to anisotropic s pairing.

The mixed-state Hall conductivity of single-crystal films Nd2–xCexCuO4+δ (x = 0.14)

The conductivity in Nd2-xCexCuO4/SrTiO3 single-crystal films with the c-axis perpendicular or parallel to the substrate plane was studied. A comparison of the results for two types of films reveals the quasi-two-dimensional character of transport processes in stoichiometric (optimally annealed) single crystal films with 0.135 ≤ x ≤ 0.15 at the antiferromagnetic - superconducting phase transition.

Anomalous Temperature Dependence of the Upper Critical Magnetic Field in Electron-Doped High-Temperature Superconductor

The Hall resistance and the magnetoresistance in the mixed state of the Nd2 − xCexCuO4 + δ quasi-two-dimensional system near the antiferromagnetic-superconductor (AF-SC) phase transition have been measured at doping levels x = 0.14 and 0.15, and a correlation has been established. This correlation can be analyzed using the following power relationship: ρxy(B) ~ [ρxx (B)]β. It was found that index β varied from 0.94 ± 0.03 in the region of AF and SC coexistence (x = 0.14) to 0.6 ± 0.1 in the SC region with the maximum critical temperature (x = 0.15) at low temperatures and weak magnetic fields. This reduction suggests that the symmetry of carrier pairing changes at the boundary of the transition from the phase of antiferromagnetic ordering and spin density waves to the superconducting phase in the presence of antiferromagnetic spin fluctuations.

Upper critical field in electron-Doped Nd1.86Ce0.14CuO4 superconductor

The magnetic-field dependencies of the longitudinal and Hall resistivity of the electron-doped compounds Nd2–xCexCuO4+δ in underdoped region (x = 0.14) were investigated. It was established experimentally a strong magnetic field dependence of the Hall conductivity, σxy(B) = C – b/B, in the region of magnetic fields corresponding to a transition from superconducting to resistive state. The observed feature can be explained with the sum of contributions of the quasiparticles and moving Abrikosov vortices into Hall effect in a mixed state of type-II superconductor.