[Show abstract][Hide abstract] ABSTRACT: Aminoacyl-tRNA synthetases (ARSs) recognize a specific sequence or structural characteristics of their cognate tRNAs. To contribute to the understanding how these recognition sites were selected, we generated two different RNA libraries containing either 42mer or 70mer random sequence and used them to select RNA aptamers that specifically bound to methionyl-tRNA synthetase (MRS) of Mycobacterium tuberculosis. The aptamer pools selected from the two RNA libraries showed strong binding affinity and selectivity to M. tuberculosis MRS compared to that of the homologous Escherichia coli MRS. The RNA aptamers selected from the two completely unrelated RNA pools shared the octamer sequence including CAU and the anticodon sequence of tRNA(Met). The secondary structure prediction suggested that the octamer motif in the selected aptamers would form a loop similar to the anticodon loop of tRNA(Met). The results suggest that the RNA loop containing CAU triplet could selected as a major recognition site for MRS during evolution more or less regarding, and also showed that species-specific ARS inhibitors can be obtained by in vitro evolution.
Biochemical and Biophysical Research Communications 02/2013; 432(2). DOI:10.1016/j.bbrc.2013.01.116 · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Amino acids are required for activation of the mammalian target of rapamycin (mTOR) kinase, which regulates protein translation, cell size, and autophagy. However, the amino acid sensor that directly couples intracellular amino acid-mediated signaling to mTORC1 is unknown. Here we show that leucyl-tRNA synthetase (LRS) plays a critical role in amino acid-induced mTORC1 activation by sensing intracellular leucine concentration and initiating molecular events leading to mTORC1 activation. Mutation of LRS amino acid residues important for leucine binding renders the mTORC1 pathway insensitive to intracellular levels of amino acids. We show that LRS directly binds to Rag GTPase, the mediator of amino acid signaling to mTORC1, in an amino acid-dependent manner and functions as a GTPase-activating protein (GAP) for Rag GTPase to activate mTORC1. This work demonstrates that LRS is a key mediator for amino acid signaling to mTORC1.
[Show abstract][Hide abstract] ABSTRACT: Although AIMP3/p18 is normally associated with the macromolecular tRNA synthetase complex, recent reports have revealed a new role of AIMP3 in tumor suppression. In this study, we generated a transgenic mouse that overexpresses AIMP3 and characterized the associated phenotype in vivo and in vitro. Surprisingly, the AIMP3 transgenic mouse exhibited a progeroid phenotype, and the cells that overexpressed AIMP3 showed accelerated senescence and defects in nuclear morphology. We found that overexpression of AIMP3 resulted in proteasome-dependent degradation of mature lamin A, but not of lamin C, prelamin A, or progerin. The resulting imbalance in the protein levels of lamin A isoforms, namely altered stoichiometry of prelamin A and progerin to lamin A, appeared to be responsible for a phenotype that resembled progeria. An increase in the level of endogenous AIMP3 has been observed in aged human tissues and cells. The findings in this report suggest that AIMP3 is a specific regulator of mature lamin A and imply that enhanced expression of AIMP3 might be a factor driving cellular and/or organismal aging.
[Show abstract][Hide abstract] ABSTRACT: The presentation of the endoplasmic reticulum resident chaperone protein, gp96 on the cell surface have been considered as a phenomenon of the immunogenic process activation. Previously, we showed aminoacyl-tRNA synthetase-interacting multifunctional protein 1 (AIMP1) can form a molecular complex with gp96, regulate the ER retention of gp96 through KDEL receptor, and suppress its cell surface expression. However, the physiological conditions that modulate AIMP1-gp96 interaction and cell surface expression of gp96 are not known. In this study, we investigated the process that which can modulate dissociation of AIMP1 and gp96 by using Toll-like receptor (TLR) activation. MyD88 pathway by LPS-mediated TLR4 activation induced the cell surface presentation of gp96 through c-Jun N-terminal kinase (JNK). AIMP1 was phosphorylated by JNK upon LPS stimulation and gp96 was dissociated from phosphorylated AIMP1. We further demonstrated that serine-140 residue of AIMP1 was phosphorylated by JNK and alanine mutation of serine-140 suppressed LPS-induced cell surface expression of gp96. Altogether, these results suggest that AIMP1 is phosphorylated by JNK through TLR-MyD88 pathway and lose the regulatory activity for ER retention of gp96, resulting in the increase of cell surface expression of gp96, and provide a new molecular mechanism underlying TLR-mediated gp96 regulation.
Biochemical and Biophysical Research Communications 06/2010; 397(1):100-5. DOI:10.1016/j.bbrc.2010.05.075 · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background: Drug discovery programs are based on the presumption of one drug-one action-one disease, which is frustrated by the complexity of biological systems. Because the aberration of a single gene often leads to multiple pathological symptoms, we should understand the functional network of the disease-related proteins to develop effective therapy. Objectives: To describe how activities of proteins are reflected in phenotypes and their pathological implications using aminoacyl-tRNA synthetase-interacting multi-functional protein 1 (AIMP1). Methods: The physiological activities of AIMP1 are unveiled through in vitro approaches and in vivo phenotyptic investigation. Bioinformatics tool was used to combine all AIMP1-target proteins. Conclusion: Although a cytosolic protein, AIMP1 can be secreted as a cytokine to control immune response, angiogenesis and wound healing, and as a glucagon-like hormone for glucose homeostasis. It is involved in the regulation of autoimmune control and TGF-β signaling within the cells. AIMP1-deficient mice developed multiple phenotypes in immune systems, metabolism and body growth. The therapeutic potential of this multi-functional protein with associated biological activities are discussed.
Expert Opinion on Drug Discovery 08/2008; 3(8):945-57. DOI:10.1517/174604188.8.131.525 · 3.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An aminoacyl-tRNA synthetase-associated factor, p43, was recently shown to be secreted to induce a proinflammatory response. Because a proinflammatory response involves the cell-cell adhesion between endothelial and immune cells, we first examined the mechanism of p43-induced cell-cell adhesion of myelomonocytic leukemia cells. Intercellular adhesion molecule-1 (ICAM-1) was up-regulated by p43 and mediated p43-induced cell-cell adhesion via the interaction with LFA-1 or Mac-1. We also investigated p43-stimulated signaling pathways involved in the homotypic THP-1 cell adhesion. Because the specific inhibitors for PI3-K (phosphatidylinositol 3-kinase), ERK (extracellular signal-regulating kinase), and p38 MAPK (mitogen-activated protein kinase) blocked p43-stimulated ICAM-1 expression and homotypic THP-1 cell adhesion, these kinases were responsible for p43-induced cell-cell adhesion. p43-Dependent activation of ERK was inhibited by PI3-K inhibitors, and the activation of p38 MAPK was not. Thus, the results of this work suggest that p43 should induce cell-cell adhesion via the PI3-K/ERK- and p38 MAPK-dependent up-regulation of ICAM-1.
Journal of Leukocyte Biology 03/2002; 71(2):223-30. · 4.30 Impact Factor