Immune recognition of lysyl-tRNA synthetase and isoleucyl-tRNA synthetase by anti-OJ antibody-positive sera.

OBJECTIVE: Anti-aminoacyl-tRNA synthetase (anti-ARS) antibodies are useful for identifying a clinical subset of patients with idiopathic inflammatory myopathies (IIMs). Anti-OJ antibodies, which recognize multi-enzyme synthetase complexes including isoleucyl-tRNA synthetase (IARS) and lysyl-tRNA synthetase (KARS), are among the anti-ARS antibodies. Although testing antibodies to other ARSs have been used clinically, no validated immunoassays for detecting anti-OJ antibodies are available. We aimed to establish an anti-OJ ELISA. METHODS: Serum samples were collected from 279 patients with IIMs and 22 patients with idiopathic interstitial pneumonia. Sixty-four of the samples that had been confirmed to be negative for anti-OJ by standard immunoprecipitation were used as the negative control, and 12 anti-OJ-positive reference sera were used as the positive control. Antibodies to IARS and KARS were assayed by ELISA using biotinylated recombinant proteins generated by in vitro transcription/translation. RESULTS: The anti-OJ-positive sera strongly reacted with the KARS and IARS recombinant proteins in ELISA. Although all 12 reference sera were positive in the anti-KARS ELISA, 4 of the 64 anti-OJ-negative sera were also weakly positive. The sensitivity and the specificity were 100% and 93.8%, respectively. Since our anti-KARS ELISA performed well, showing a high agreement with the results for immunoprecipitation (Cohen's κ > 0.8), the remaining 237 samples were also tested. Thirteen anti-KARS-positive sera were newly found by ELISA, all of which were anti-OJ positive by immunoprecipitation. CONCLUSION: Immunoassays for detecting anti-OJ antibodies using KARS and IARS recombinant proteins were developed. Our ELISAs performed well, with very high agreement of the results by immunoprecipitation and can be applied to the first reliable, easy-to-use measurement assays for anti-OJ antibodies.

Mutation in KARS: A novel mechanism for severe anaphylaxis.

BACKGROUND: Anaphylaxis is a severe allergic reaction that can be lethal if not treated adequately. The underlying molecular mechanisms responsible for the severity are mostly unknown. OBJECTIVE: This study is based on a clinical case of a patient with extremely severe anaphylaxis to paper wasp venom. This patient has a mutation in the KARS gene, which encodes lysyl-tRNA synthetase (LysRS), a moonlight protein with a canonical function in protein synthesis and a noncanonical function in antigen dependent-FcεRI activation in mast cells. In this study, the objective was to characterize the mutation at the molecular level. METHODS: Analysis of the KARS mutation was carried out using biochemical and functional approaches, cell transfection, Western blot, confocal microscopy, cell degranulation, prostaglandin D2 secretion, and proteases gene transcription. Structural analysis using molecular dynamics simulations and well-tempered metadynamics was also performed. RESULTS: The mutation found, P542R (proline was replaced by arginine at aminoacid 542), affects the location of the protein as we show in biochemical and structural analyses. The mutation resembles active LysRS and causes a constitutive activation of the microphthalmia transcription factor, which is involved in critical mast cell functions such as synthesis of mediators and granule biogenesis. Moreover, the structural analysis provides insights into how LysRS works in mast cell activation. CONCLUSIONS: A link between the aberrant LysRS-P542R function and mast cell-exacerbated activation with increase in proinflammatory mediator release after antigen-IgE-dependent response could be established.

Lysyl-Transfer RNA Synthetase Induces the Maturation of Dendritic Cells through MAPK and NF-κB Pathways, Strongly Contributing to Enhanced Th1 Cell Responses.

In addition to essential roles in protein synthesis, lysyl-tRNA synthetase (KRS) is secreted to trigger a proinflammatory function that induces macrophage activation and TNF-α secretion. KRS has been associated with autoimmune diseases such as polymyositis and dermatomyositis. In this study, we investigated the immunomodulatory effects of KRS on bone marrow-derived dendritic cells (DCs) of C57BL/6 mice and subsequent polarization of Th cells and analyzed the underlying mechanisms. KRS-treated DCs increased the expression of cell surface molecules and proinflammatory cytokines associated with DC maturation and activation. Especially, KRS treatment significantly increased production of IL-12, a Th1-polarizing cytokine, in DCs. KRS triggered the nuclear translocation of the NF-κB p65 subunit along with the degradation of IκB proteins and the phosphorylation of MAPKs in DCs. Additionally, JNK, p38, and ERK inhibitors markedly recovered the degradation of IκB proteins, suggesting the involvement of MAPKs as the upstream regulators of NF-κB in the KRS-induced DC maturation and activation. Importantly, KRS-treated DCs strongly increased the differentiation of Th1 cells when cocultured with CD4+ T cells. The addition of anti-IL-12-neutralizing Ab abolished the secretion of IFN-γ in the coculture, indicating that KRS induces Th1 cell response via DC-derived IL-12. Moreover, KRS enhanced the OVA-specific Th1 cell polarization in vivo following the adoptive transfer of OVA-pulsed DCs. Taken together, these results indicated that KRS effectively induced the maturation and activation of DCs through MAPKs/NF-κB-signaling pathways and favored DC-mediated Th1 cell response.

The function of lysyl-tRNA synthetase and Ap4A as signaling regulators of MITF activity in FcepsilonRI-activated mast cells.

The involvement of microphthalmia transcription factor (MITF) in the function of mast cells, melanocytes, and osteoclasts has recently started to be investigated in depth. In a previous study, we found Hint to be associated with MITF in mast cells and showed that it suppresses MITF's transcriptional activity. Here, we have found that lysyl-tRNA synthetase (LysRS) is also associated with MITF and forms a multicomplex with MITF and Hint. We have also shown that Ap4A, an endogenous molecule consisting of two adenosine linked by four phosphate which is known to be synthesized by LysRS, is accumulated intracellularily above 700 microM in IgE-Ag-activated mast cells, binds to Hint, liberates MITF, and thus leads to the activation of MITF-dependent gene expression. This implies that LysRS plays a key role via Ap4A as an important signaling molecule in MITF transcriptional activity.

Metabolites influence control of lysine transfer ribonucleic acid synthetase formation in Escherichia coli K-12.

A mutant of E. coli K-12 has been isolated which has only 1-3% of the wild-type lysyl-tRNA synthetase activity [L-lysine:tRNA ligase (AMP forming), EC 6.1.1.6]. Additions of 20 mM L-alanine or 6 mM leucine dipeptides to the culture medium can restore the activity of lysyl-tRNA synthetase in the mutant strain to the wild-type level. Experiments on the in vivo charging of lysine tRNA in the mutant show that in the absence of the metabolites lysine tRNA is charged 15-23%. Upon the addition of 3 mM L-leucyl-L-alanine to the medium the lysyl tRNA synthetase activity increases 25-fold and the in vivo charging of lysine tRNA returns to the wild-type level. Experiments with antibody against lysyl-tRNA synthetase show that the stimulation of lysyl-tRNA synthetase activity by the metabolites is the result of new protein synthesis.