Mammalian methionyl-tRNA synthetase (MRS) plays an essential role in initiating translation by transferring Met to initiator tRNA (tRNA i Met ). MRS also provides a cytosolic anchoring site for aminoacyl-tRNA synthetase-interacting multifunctional protein-3 (AIMP3)/ p18, a potent tumor suppressor that is translocated to the nucleus for DNA repair upon DNA damage. However, the mechanism by which this enzyme mediates these two seemingly unrelated functions is unknown. Here we demonstrate that AIMP3 is released from MRS by UV irradiation-induced stress. Dissociation was induced by phosphorylation of MRS at Ser662 by general control nonrepressed-2 (GCN2) following UV irradiation. Substitution of Ser662 to Asp (S662D) induced a conformational change in MRS and significantly reduced its interaction with AIMP3. This mutant possessed significantly reduced MRS catalytic activity because of loss of tRNA Met binding, resulting in down-regulation of global translation. According to the Met incorporation assay using stable HeLa cells expressing MRS S662A or eukaryotic initiation factor-2 subunit-α (eIF2α) S51A, inactivation of GCN2-induced phosphorylation at eIF2α or MRS augmented the role of the other, suggesting a cross-talk between MRS and eIF2α for efficient translational inhibition. This work reveals a unique mode of regulation of global translation as mediated by aminoacyl-tRNA synthetase, specifically MRS, which we herein identified as a previously unidentified GCN2 substrate. In addition, our research suggests a dual role for MRS: (i) as a coregulator with eIF2α for GCN2-mediated translational inhibition; and (ii) as a coupler of translational inhibition and DNA repair following DNA damage by releasing bound tumor suppressor AIMP3 for its nuclear translocation.T ranslational regulation is a mechanism by which genetic expression can be modulated to cope with various biological conditions. In diseases such as cancer, dysregulation of protein synthesis is frequently observed; therefore, accurate translational control appears to be important for the maintenance of normal growth and proliferation (1, 2). Under stress conditions, global translational control mainly occurs at the point of translational initiation through modification of eukaryotic initiation factors (eIFs). A key regulatory mechanism of this process is phosphorylation of eIF2 subunit-α (eIF2α), which prevents formation of a ternary complex (TC) comprising eIF2, GTP, and Metcharged initiator tRNA (Met-tRNA i Met ), thereby inhibiting further rounds of translation initiation (3).Aminoacyl-tRNA synthetases (ARSs) are essential enzymes for protein synthesis, linking codons to their corresponding amino acids (4, 5). A key factor in translation initiation, methionyltRNA synthetase (MRS) produces Met-tRNA i Met , which is indispensable for TC formation. MRS has been also found in the nucleus, where it may play a role in the biogenesis of rRNA (6). Under oxidative stress, MRS charges Met to noncognate tRNAs at a high frequency, resulting in reduced translational fi...
ObjectiveThe aim of the present study is to assess the prevalence of psychiatric symptoms and associated factors in North Korean Defectors (NKDs).MethodsOne hundred forty-four NKDs (male: 20; female: 124; average age: 40.4±11.7 yrs.) completed the Symptom Checklist-90-Revised (SCL-90-R) and the Center for Epidemiologic Studies Depression scale (CES-D). A stepwise logistic regression analysis was conducted to evaluate factors associated with the psychiatric symptoms of the participants.ResultsNKDs mainly reported somatization (42.4%) and depressive symptoms (38.9%). Female NKDs showed higher prevalence of somatization (p=0.001), anxiety (p=0.020), hostility (p=0.026) and psychoticism (p=0.022) than males. The presence of physical illness was strongly related to most psychiatric symptoms on the SCL-90-R including somatization (p<0.001), obsessive-compulsive symptoms (p=0.020), interpersonal sensitivity (p=0.031), depression (p<0.001), anxiety (p<0.001), hostility (p=0.011), paranoid ideation (p=0.015) and psychoticism (p<0.001). Younger age, unemployment, lower income, and longer duration of defection were found to be the risk factors of psychiatric symptoms. In regard to mental health service utilization, we found that most (83.3%) of the participants had not received any form of psychiatric help.ConclusionSomatization and depression were the most prevalent psychiatric symptoms in NKDs. Our results suggest that psychiatric symptoms accompany certain sociodemographic and clinical characteristics that are associated with susceptibility to acculturation stressors. An understanding of these factors will be helpful providing appropriate mental health services to NKDs.
Aminoacyl-tRNA synthetase-interacting multifunctional proteins (AIMPs) are nonenzymatic scaffolding proteins that comprise multisynthetase complex (MSC) with nine aminoacyl-tRNA synthetases in higher eukaryotes. Among the three AIMPs, AIMP3/p18 is strongly anchored to methionyl-tRNA synthetase (MRS) in the MSC. MRS attaches methionine (Met) to initiator tRNA (tRNA(i)(Met)) and plays an important role in translation initiation. It is known that AIMP3 is dispatched to nucleus or nuclear membrane to induce DNA damage response or senescence; however, the role of AIMP3 in translation as a component of MSC and the meaning of its interaction with MRS are still unclear. Herein, we observed that AIMP3 specifically interacted with Met-tRNA(i)(Met)in vitro, while it showed little or reduced interaction with unacylated or lysine-charged tRNA(i)(Met). In addition, AIMP3 discriminates Met-tRNA(i)(Met) from Met-charged elongator tRNA based on filter-binding assay. Pull-down assay revealed that AIMP3 and MRS had noncompetitive interaction with eukaryotic initiation factor 2 (eIF2) γ subunit (eIF2γ), which is in charge of binding with Met-tRNA(i)(Met) for the delivery of Met-tRNA(i)(Met) to ribosome. AIMP3 recruited active eIF2γ to the MRS-AIMP3 complex, and the level of Met-tRNA(i)(Met) bound to eIF2 complex was reduced by AIMP3 knockdown resulting in reduced protein synthesis. All these results suggested the novel function of AIMP3 as a critical mediator of Met-tRNA(i)(Met) transfer from MRS to eIF2 complex for the accurate and efficient translation initiation.
Glucose deposition in peripheral tissue is an important parameter for the treatment of type 2 diabetes mellitus. The aim of this study was to investigate the effects of Spatholobus suberectus (Ss) on glucose disposal in skeletal muscle cells and additionally explore its in vivo antidiabetic potential. Treatment of ethanolic extract of S. suberectus (EeSs) significantly enhanced the glucose uptake, mediated through the enhanced expression of GLUT4 in skeletal muscle via the stimulation of AKT and AMPK pathways in C2C12 cells. Moreover, EeSs have potential inhibitory action on α-glucosidase activity and significantly lowered the postprandial blood glucose levels in STZ-induced diabetic mice, associated with increased expression of GLUT4 and AKT and/or AMPK-mediated signaling cascade in skeletal muscle. Furthermore, administration of EeSs significantly boosted up the antioxidant enzyme expression and also mitigated the gluconeogenesis enzyme such as PEPCK and G-6-Pase enzyme expression in liver tissue of STZ-induced diabetic mice model. Collectively, these findings suggest that EeSs have a high potentiality to mitigate diabetic symptoms through stimulating glucose uptake in peripheral tissue via the activation of AKT and AMPK signaling cascade and augmenting antioxidant potentiality as well as blocking the gluconeogenesis process in diabetic mice.
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