No abstract

bMolecular chaperones monitor the proper folding of misfolded proteins and function as the first line of defense against mutant protein aggregation in neurodegenerative diseases. The eukaryotic chaperonin TRiC is a potent suppressor of mutant protein aggregation and toxicity in early stages of disease progression. Elucidation of TRiC functional regulation will enable us to better understand the pathological mechanisms of neurodegeneration. We have previously shown that vaccinia-related kinase 2 (VRK2) downregulates TRiC protein levels through the ubiquitin-proteasome system by recruiting the E3 ligase COP1. However, although VRK2 activity was necessary in TRiC downregulation, the phosphorylated substrate was not determined. Here, we report that USP25 is a novel TRiC interacting protein that is also phosphorylated by VRK2. USP25 catalyzed deubiquitination of the TRiC protein and stabilized the chaperonin, thereby reducing accumulation of misfolded polyglutamine protein aggregates. Notably, USP25 deubiquitinating activity was suppressed when VRK2 phosphorylated the Thr 680 , Thr 727 , and Ser 745 residues. Impaired USP25 deubiquitinating activity after VRK2-mediated phosphorylation may be a critical pathway in TRiC protein destabilization.

e Misfolding of proteins containing abnormal expansions of polyglutamine (polyQ) repeats is associated with cytotoxicity in several neurodegenerative disorders, including Huntington's disease. Recently, the eukaryotic chaperonin TRiC hetero-oligomeric complex has been shown to play an important role in protecting cells against the accumulation of misfolded polyQ protein aggregates. It is essential to elucidate how TRiC function is regulated to better understand the pathological mechanism of polyQ aggregation. Here, we propose that vaccinia-related kinase 2 (VRK2) is a critical enzyme that negatively regulates TRiC. In mammalian cells, overexpression of wild-type VRK2 decreased endogenous TRiC protein levels by promoting TRiC ubiquitination, but a VRK2 kinase-dead mutant did not. Interestingly, VRK2-mediated downregulation of TRiC increased aggregate formation of a polyQ-expanded huntingtin fragment. This effect was ameliorated by rescue of TRiC protein levels. Notably, small interference RNA-mediated knockdown of VRK2 enhanced TRiC protein stability and decreased polyQ aggregation. The VRK2-mediated reduction of TRiC protein levels was subsequent to the recruitment of COP1 E3 ligase. Among the members of the COP1 E3 ligase complex, VRK2 interacted with RBX1 and increased E3 ligase activity on TRiC in vitro. Taken together, these results demonstrate that VRK2 is crucial to regulate the ubiquitination-proteosomal degradation of TRiC, which controls folding of polyglutamine proteins involved in Huntington's disease.

The growth of hexagonal Gd disilicide nanowires on Si(100) is studied by scanning tunneling microscopy. Gd disilicide nanowires are grown on Si(100) by submonolayer Gd deposition on the substrate at 600 °C. The formation of nanowires is shown to be due to anisotropic lattice mismatches between hexagonal Gd disilicide and Si. The nanowires have widths of several nanometers and lengths up to micrometer length scales. The top of the nanowires has a c(2×2) structure, indicating that the crystalline structure is Si-deficient Gd disilicide. The nanowires were shown to have metallic properties using scanning tunneling spectroscopy.

We investigated the formation of Pt silicide nanowires on a Si(100) surface using scanning tunnelling microscopy and high-resolution photoemission spectroscopy. Pt silicide nanowires with a tetragonal Pt2Si structure are formed along the step edges of Si(100). Pt-induced c(4 × 2) reconstructions also appear adjacent to the tetragonal Pt2Si nanowires. Formation of the Pt2Si nanowires is attributed to the anisotropic lattice mismatches between the tetragonal Pt2Si structure and Si(100). Scanning tunnelling spectroscopy data show that the nanowires are metallic. The stoichiometry of Pt silicide is confirmed by high-resolution photoemission spectroscopy.