No abstract

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.

No abstract

Circadian gene expression is defined by the gene-specific phase and amplitude of daily oscillations in mRNA and protein levels. D site-binding protein mRNA (Dbp mRNA) shows high-amplitude oscillation; however, the underlying mechanism remains elusive. Here, we demonstrate that heterogeneous nuclear ribonucleoprotein K (hnRNP K) is a key regulator that activates Dbp transcription via the poly(C) motif within its proximal promoter. Biochemical analyses identified hnRNP K as a specific protein that directly associates with the poly(C) motif in vitro. Interestingly, we further confirmed the rhythmic binding of endogenous hnRNP K within the Dbp promoter through chromatin immunoprecipitation as well as the cycling expression of hnRNP K. Finally, knockdown of hnRNP K decreased mRNA oscillation in both Dbp and Dbp-dependent clock genes. Taken together, our results show rhythmic protein expression of hnRNP K and provide new insights into its function as a transcriptional amplifier of Dbp.

No abstract

Fragile X syndrome (FXS) caused by loss of fragile X mental retardation protein (FMRP), is the most common cause of inherited intellectual disability. Numerous studies show that FMRP is an RNA binding protein that regulates translation of its binding targets and plays key roles in neuronal functions. However, the regulatory mechanism for FMRP expression is incompletely understood. Conflicting results regarding internal ribosome entry site (IRES)-mediated fmr1 translation have been reported. Here, we unambiguously demonstrate that the fmr1 gene, which encodes FMRP, exploits both IRES-mediated translation and canonical cap-dependent translation. Furthermore, we find that heterogeneous nuclear ribonucleoprotein Q (hnRNP Q) acts as an IRES-transacting factor (ITAF) for IRES-mediated fmr1 translation in neurons. We also show that semaphorin 3A (Sema3A)-induced axonal growth cone collapse is due to upregulation of hnRNP Q and subsequent IRES-mediated expression of FMRP. These data elucidate the regulatory mechanism of FMRP expression and its role in axonal growth cone collapse.

Huntington’s disease (HD) is a neurodegenerative disorder caused by an abnormal expansion of polyglutamine repeats in the N-terminal of huntingtin. The amount of aggregate-prone protein is controlled by various mechanisms, including molecular chaperones. Vaccinia-related kinase 2 (VRK2) is known to negatively regulate chaperonin TRiC, and VRK2-facilitated degradation of TRiC increases polyQ protein aggregation, which is involved in HD. We found that VRK2 activity was negatively controlled by glycogen synthase kinase 3β (GSK3β). GSK3β directly bound to VRK2 and inhibited the catalytic activity of VRK2 in a kinase activity-independent manner. Furthermore, GSK3β increased the stability of TRiC and decreased the formation of HttQ103-GFP aggregates by inhibiting VRK2. These results indicate that GSK3β signaling may be a regulatory mechanism of HD progression and suggest targets for further therapeutic trials for HD.

Lead‐free (Na0.53K0.45Li0.02)(Nb0.8Ta0.2)O3 (NKLNT) was prepared using a conventional cold‐pressing method. A commercial piezoresponse force microscope (PFM) was applied to observe the domain structures of NKLNT ceramics. The typical configuration of the ferroelectric domain was analyzed in abnormal grains with grain sizes that exceeded 40 μm, where tetragonal 90° domains are predominant. The local piezoresponse hysteresis loops were characterized and studied as a function of the domain width (dw) in the range 300–1000 nm. It was found that the amplitude signals increased and the coercive field reduced significantly with a decrease in the domain size. Finally, the local longitudinal piezoelectric coefficient (d33) increased as the domain size decreased.