LysRS Serves as a Key Signaling Molecule in the Immune Response by Regulating Gene Expression

Department of Biochemistry, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
Molecular cell (Impact Factor: 14.02). 07/2009; 34(5):603-11. DOI: 10.1016/j.molcel.2009.05.019
Source: PubMed


Lysyl-tRNA synthetase (LysRS) was found to produce diadenosine tetraphosphate (Ap(4)A) in vitro more than two decades ago. Here, we used LysRS silencing in mast cells in combination with transfected normal and mutated LysRS to demonstrate in vivo the critical role played by LysRS in the production of Ap(4)A in response to immunological challenge. Upon such challenge, LysRS was phosphorylated on serine 207 in a MAPK-dependent manner, released from the multisynthetase complex, and translocated into the nucleus. We previously demonstrated that LysRS forms a complex with MITF and its repressor Hint-1, which is released from the complex by its binding to Ap(4)A, enabling MITF to transcribe its target genes. Here, silencing LysRS led to reduced Ap(4)A production in immunologically activated cells, which resulted in a lower level of MITF inducible genes. Our data demonstrate that specific LysRS serine 207 phosphorylation regulates Ap(4)A production in immunologically stimulated mast cells, thus implying that LysRS is a key mediator in gene regulation.

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    • "KRS is secreted from intact human cells in response to tumor necrosis factor a (TNF-a) stimulation and enhances macrophage migration [17], and KRS expression and its association with the assembly mechanism of human immunodeficiency virus type 1 (HIV-1) is responsible for HIV-1 infectivity [18]. Furthermore, KRS is a major source of diadenosine tetraphosphate (Ap4A) in immunologically activated mast cells, and via translocation into the nucleus, KRS controls the expression of microphthalmia-associated transcription factor (MITF)inducible genes in allergic responses [12]. KRS was recently shown to induce cancer cell migration through its interaction with the 67-kDa laminin receptor (67LR) 0014-5793/Ó 2014 The Authors. "
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    • "One such effect is removal of repressor Hint-1 (histidine triad nucleotide binding protein 1) from MITF (microphthalmia-associated transcription factor), enabling it to transcribe its target genes. Consequently, KARS has a signal transduction role besides its other well-defined roles in immunologically activated cells [13]. "
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    • "In contrast, overexpression of recombinant LysRS WT augmented Ap 4 A production only in activated mast cells, whereas overexpression of LysRS S207D increased Ap 4 A levels in both quiescent and activated cells (Figure 6A). Further, expression of LysRS WT does not increase Ap 4 A levels when mast cells were treated with a MAPK kinase inhibitor to inhibit Ser207 phosphorylation of LysRS (Yannay-Cohen et al., 2009). Because S207D and G540Y open up the structure of the enzyme, these results indicate that the open conformer directs this new function of LysRS. "
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    ABSTRACT: Lysyl-tRNA synthetase (LysRS), a component of the translation apparatus, is released from the cytoplasmic multi-tRNA synthetase complex (MSC) to activate the transcription factor MITF in stimulated mast cells through undefined mechanisms. Here we show that Ser207 phosphorylation provokes a new conformer of LysRS that inactivates its translational function but activates its transcriptional function. The crystal structure of an MSC subcomplex established that LysRS is held in the MSC by binding to the N terminus of the scaffold protein p38/AIMP2. Phosphorylation-created steric clashes at the LysRS domain interface disrupt its binding grooves for p38/AIMP2, releasing LysRS and provoking its nuclear translocation. This alteration also exposes the C-terminal domain of LysRS to bind to MITF and triggers LysRS-directed production of the second messenger Ap(4)A that activates MITF. Thus our results establish that a single conformational change triggered by phosphorylation leads to multiple effects driving an exclusive switch of LysRS function from translation to transcription.
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