The role of a small transforming growth factor beta (TGF-β)-induced TIAF1 (TGF-β1-induced antiapoptotic factor) in the pathogenesis of Alzheimer's disease (AD) was investigated. TIAF1 physically interacts with mothers against DPP homolog 4 (Smad4), and blocks SMAD-dependent promoter activation when overexpressed. Accordingly, knockdown of TIAF1 by small interfering RNA resulted in spontaneous accumulation of Smad proteins in the nucleus and activation of the promoter governed by the SMAD complex. TGF-β1 and environmental stress (e.g., alterations in pericellular environment) may induce TIAF1 self-aggregation in a type II TGF-β receptor-independent manner in cells, and Smad4 interrupts the aggregation. Aggregated TIAF1 induces apoptosis in a caspase-dependent manner. By filter retardation assay, TIAF1 aggregates were found in the hippocampi of nondemented humans and AD patients. Total TIAF1-positive samples containing amyloid β (Aβ) aggregates are 17 and 48%, respectively, in the nondemented and AD groups, suggesting that TIAF1 aggregation occurs preceding formation of Aβ. To test this hypothesis, in vitro analysis showed that TGF-β-regulated TIAF1 aggregation leads to dephosphorylation of amyloid precursor protein (APP) at Thr668, followed by degradation and generation of APP intracellular domain (AICD), Aβ and amyloid fibrils. Polymerized TIAF1 physically interacts with amyloid fibrils, which would favorably support plaque formation in vivo.

Self-aggregation of transforming growth factor β (TGF-β)1-induced antiapoptotic factor (TIAF1) is known in the nondemented human hippocampus, and the aggregating process may lead to generation of amyloid β (Aβ) for causing neurodegeneration. Here, we determined that overexpressed TIAF1 exhibits as aggregates together with Smad4 and Aβ in the cancer stroma and peritumor capsules of solid tumors. Also, TIAF1/Aβ aggregates are shown on the interface between brain neural cells and the metastatic cancer cell mass. TIAF1 is upregulated in developing tumors, but may disappear in established metastatic cancer cells. Growing neuroblastoma cells on the extracellular matrices from other cancer cell types induced production of aggregated TIAF1 and Aβ. In vitro induction of TIAF1 self-association upregulated the expression of tumor suppressors Smad4 and WW domain-containing oxidoreductase (WOX1 or WWOX), and WOX1 in turn increased the TIAF1 expression. TIAF1/Smad4 interaction further enhanced Aβ formation. TIAF1 is known to suppress SMAD-regulated promoter activation. Intriguingly, without p53, self-aggregating TIAF1 spontaneously activated the SMAD-regulated promoter. TIAF1 was essential for p53-, WOX1- and dominant-negative JNK1-induced cell death. TIAF1, p53 and WOX1 acted synergistically in suppressing anchorage-independent growth, blocking cell migration and causing apoptosis. Together, TIAF1 shows an aggregation-dependent control of tumor progression and metastasis, and regulation of cell death.

Optical selection rules for one-dimensional graphene nanoribbons are explored based on the tight-binding model. A theoretical explanation, through analyzing the velocity matrix elements and the features of the wavefunctions, can account for the selection rules, which depend on the edge structure of the nanoribbon, i.e., armchair or zigzag edges. The selection rule of armchair nanoribbons is ΔJ = Jc - Jv = 0, and the optical transitions occur from the conduction to the valence subbands of the same index. Such a selection rule originates in the relationships between two sublattices and between the conduction and valence subbands. On the other hand, zigzag nanoribbons exhibit the selection rule |ΔJ| = odd, which results from the alternatively changing symmetry property as the subband index increases. Furthermore, an efficient theoretical prediction on transition energies is obtained by the application of selection rules, and the energies of the band-edge states become experimentally attainable via optical measurements.

Magneto-electronic properties of asymmetric bilayer nanographene ribbons are enriched by geometric structures, interlayer atomic interactions, magnetic quantization and finite-size confinement. There are drastic changes on the band symmetry, the degeneracy of the partial flat bands, the number of band-edge states, the energy dispersion, the carrier density, and the spatial symmetry of the wave function. Quasi-Landau levels might be converted into oscillating bands where extra band-edge states are created. When the upper ribbon is located at the ribbon centre, the Landau wave functions are completely destroyed. Meanwhile, a charge transfer between different layers or different sublattices in the same layer occurs. Furthermore, the density of states, reflecting the band structure, is also severely altered in terms of the number, structure, energy, and height of the prominent peaks.

We develop the tight-binding model to study electronic and optical properties of graphane. The strong sp3 chemical bondings among the carbon and hydrogen atoms induce a special band structure and thus lead to the rich optical excitations. The absorption spectrum hardly depends on the direction of electric polarization. It ex- hibits a lot of shoulder structures and absorption peaks, which arise from the extreme points and the saddle points of the parabolic bands, respectively. The threshold op- tical excitations, only associated with the 2px and 2py orbitals of the carbon atoms, are revealed in a shoulder structure at ?3.5 eV. The first symmetric absorption peak, appearing at ~11 eV, corresponds to energy bands due to the considerable hybridiza- tion of carbon 2pz orbitals and H 1s orbitals. Also, some absorption peaks at higher frequencies indicate the bonding of 2s and 1s orbitals. These results are in sharp contrast to those of the sp2 graphene systems.Comment: 16 pages, 5 figure

The band anticrossing (BAC) model is introduced to describe the influence of the incorporated nitrogen on the band structure of dilute nitrides. An isolated N introduces highly localized states in these nitrides, which interact with the extended conduction‐band states of the host semiconductor. The interaction splits the conduction band into an upper and a lower subband. There are reports of the band‐gap reduction in InGaPN, but no experimental observations of the upper subband have been reported. In this work, temperature‐dependent photoreflectance (PR) and photoluminescence (PL) spectra are employed to examine the band structure of InGaPN/GaAs heterostructures. Besides the band gap, the upper subband predicted by the BAC model is observed in the PR spectra. By eliminating the contributions of the strain and ordering effects in InGaPN, and assigning the localized state energy EN introduced by an isolated N to be 2.04 eV at 293 K, the interaction potential is determined as 1.449±0.170 eV. With N incorporation, the PL peak energy exhibits a particular behavior with temperature, which is not observed in the PR spectra. This is attributed to carrier localization at low temperatures occurring in N‐diluted semiconductors. Additionally, the temperature dependence of the band gap is described by the BAC model incorporating two different EN levels, either constant or temperature‐dependent. In our hands, the assumption of the temperature‐dependent EN level results in a better fit with the experimental data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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