Aminoacyl tRNA synthetases and their connectionsto diseaseSang Gyu Park*, Paul Schimmel†‡, and Sunghoon Kim‡§

*Clinical Research Institute, Seoul National University Hospital, Seoul 110-744, Korea; †The Skaggs Institute for Chemical Biology,La Jolla, CA 92037; and §Center for Medicinal Protein Network and Systems Biology, College of Pharmacy, Seoul NationalUniversity, Seoul 151-742, Korea

Edited by Alan M. Lambowitz, University of Texas, Austin, TX, and approved May 19, 2008 (received for review March 31, 2008)

Aminoacylation of transfer RNAs establishes the rules of the genetic code. The reactions are catalyzed by an ancient group of 20enzymes (one for each amino acid) known as aminoacyl tRNA synthetases (AARSs). Surprisingly, the etiology of specific diseases—including cancer, neuronal pathologies, autoimmune disorders, and disrupted metabolic conditions—is connected to specific amino-acyl tRNA synthetases. These connections include heritable mutations in the genes for tRNA synthetases that are causally linked todisease, with both dominant and recessive disease-causing mutations being annotated. Because some disease-causing mutationsdo not affect aminoacylation activity or apparent enzyme stability, the mutations are believed to affect functions that are distinctfrom aminoacylation. Examples include enzymes that are secreted as procytokines that, after activation, operate in pathways con-nected to the immune system or angiogenesis. In addition, within cells, synthetases form multiprotein complexes with each other orwith other regulatory factors and in that way control diverse signaling pathways. Although much has been uncovered in recentyears, many novel functions, disease connections, and interpathway connections of tRNA synthetases have yet to be worked out.

AIMP � multifunctional protein

Aminoacyl tRNA synthetasescatalyze the ligation of aminoacids to their cognate tRNAs.Their catalytic activities deter-

mine the genetic code and for thatreason, they are essential for proteinsynthesis and cell viability. The basicreaction is:

AA � ATP � tRNA3 AA-tRNA

� AMP � PPi

Because the reactions require the capac-ity to recognize tRNAs as well as smallchemicals such as amino acids and ATP,the structures of AARSs are wellequipped for interacting with diversemolecules that may be associated withtheir functional versatility. Thus, thecatalytic activities for glycyl-, lysyl-, andtryptophanyl-tRNA synthetase havebeen adapted to synthesize diadenosinepolyphosphates (ApnA), which are be-lieved to regulate glucose metabolism(1, 2), cell proliferation, and death (3).Similarly, the tRNA recognition capacityof bacterial threonyl- and human glutamyl-prolyl-tRNA synthetases has beenadapted for regulating translation byinteracting with the 5� (4) and 3� UTRregions (5) of gene-specific transcripts.

In higher eukaryotes, AARSs formmacromolecular complexes via multiva-lent protein–protein interactions (6, 7).Fig. 1 depicts a single cell with many ofthe connections made by tRNA syn-thetases with each other and with othercell signaling molecules in the cytoplasm(light blue) and nucleus (white). Singleletter abbreviations are used for eachsynthetase, such as R for arginyl-tRNAsynthetase, and L for leucyl-tRNA syn-

thetase. As shown, some of the syn-thetases are tightly bound together in alarge multisynthetase complex, withthree tRNA-synthetase associated pro-teins at the core. These are known asaminoacyl tRNA synthetase-interactingmultifunctional protein (AIMP) 1, 2,and 3, and are simply designated as 1,2, and 3. Two of the enzymes in thecomplex are covalently fused together(glutamyl-prolyl-tRNA synthetase) andare designated as EP in Fig. 1. Thus, atleast nine synthetases and three syn-thetase-associated proteins are boundtogether. It is not known whether othersynthetases are more loosely bound withthe complex, and therefore not detectedas bound (with existing methods), orwhether they are not associatedwhatsoever.

Although these eukaryotic AARSsappear to get together to improve ami-noacylation efficiency by ‘‘channeling’’substrates to the ribosome (8), their pro-pensity to form complexes appears to berelated in part to the eukaryotic cell’sneed for a reservoir of regulatory fac-tors that are based on the alternativefunctions of these enzymes (9). Thecomplex-forming AARSs are involved inthe regulation of transcription, transla-tion, and various signaling pathways assummarized in Fig. 1 (7, 10). EukaryoticAARSs contain unique extensions anddomains, which endow them with func-tional diversity through the interactionswith various cellular partners (6, 11).The expanded functions of tRNA syn-thetases are not simply correlated withtheir being tightly associated with thecomplex. For example, tryptophanyl(WRS)- and tyrosyl (YRS)-tRNA syn-

thetases are well characterized procyto-kines (12–17), but are not generallyassociated with the complex. On theother hand, the unusual EP fusion pro-tein is associated with the multisyn-thetase complex and is released whencells are stimulated by �-IFN (the EPfusion enzyme then acts to regulatetranslation of mRNAs associated withthe inflammatory response) (5). In gen-eral, any specific synthetase may havemore than one subcellular location—including being bound to the multisyn-thetase complex, free in the cytosol, inthe nucleus, and mobilized for exocyto-sis (12, 18, 19). Considering the func-tional versatility of these enzymes, theirexpanded functions and expression maybe pathologically associated with varioushuman diseases. Here we describe spe-cific cases in which AARSs are impli-cated in human disease.

AARSs in Neuronal DiseasesCharcot–Marie–Tooth (CMT) Disease Causedby Heritable Mutations in GRS and YRS.CMT disease provides a clear exampleof heritable mutations in genes fortRNA synthetases being causally associ-ated with a specific pathological condi-tion. CMT disease has a frequency of�1 in 2,500, which makes it the mostcommon heritable disorder of the pe-ripheral nervous system. CMT disease is

Author contributions: S.G.P., P.S., and S.K. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

‡To whom correspondence may be addressed. E-mail:sungkim@snu.ac.kr or schimmel@scripps.edu.

© 2008 by The National Academy of Sciences of the USA

www.pnas.org�cgi�doi�10.1073�pnas.0802862105 PNAS � August 12, 2008 � vol. 105 � no. 32 � 11043–11049

PE

RS

PE

CT

IVE

Dow

nloa

ded

by g

uest

on

Oct

ober

23,

202

0

induced by axonal demyelination (typeI) or decreased amplitudes of evokedmotor and sensory nerve responses(type II), with no demyelination (20).Patients with CMT disease display mus-cular weakness and atrophy in the distalextremities, stoppage gait, high archedfoot (pes cavus), absent or diminisheddeep-tendon reflexes, and impairedsensation.

The genes coding for glycyl-tRNAsynthetase (GRS) and YRS are amongthe different genetic loci causally linkedto the disease (21, 22). The disease-causing mutations are dominant and themutant proteins have been shown inspecific instances to be fully active foraminoacylation (23). At least 11 distinctmutant alleles in the human populationhave been reported for GRS. These mu-tations cause CMT2D, a subtype of thedisease characterized by a slowly pro-gressing neuropathy affecting mostly thedistal extremities.

A mouse model developed by Seburnet al. encodes a mutant GRS that is fullyactive for aminoacylation (24). The mu-tant mice have the CMT2D phenotypeof reduced nerve conduction velocities,a loss of axons with large diameters, andhave no defects in myelination. Consis-tent with a deficit of aminoacylationfunction per se not being the cause ofCMT, a mouse harboring a loss-of-function (aminoacylation) allele createdby a gene trap insertion was normal.

The x-ray crystallographic structuresof the homodimeric human YRS (25)and GRS (26) proteins and a disease-causing G526 mutant allele of GRS havebeen solved (27). Placing 11 disease-causing mutations onto the structure ofhuman GRS showed them within a bandencompassing both sides of the dimerinterface (23). Strikingly, two CMT-causing mutations are complementarypartners of a ‘‘kissing’’ contact across

the dimer interface. Thus, mutation ofeither of these two residues causesCMT. Further analyses showed thatmost mutations affect dimer formation(i.e. either enhance or weaken it). Asubset of seven mutant proteins and thewild-type protein were expressed intransfected neuroblastoma cells thatsprout primitive neurites. Whereas thewild-type protein distributed into thenascent neurites and was associated withnormal sprouting, all mutant proteinswere distribution-defective. Thus, theCMT-causing mutations of GRS have acommon defect that may be connectedin some way to a change in the surfacesat the dimer interface (23).

Significantly, YRS is located promi-nently at axonal termini of differentiatingprimary motor neurons (22). CMT-associated missense or deletion muta-tions of YRS were transported totermini of differentiating neuronal cellsand induced axonal degeneration. Theseresults are consistent with both GRSand YRS having a specific role in thedevelopment or homeostasis (or both)of the peripheral nervous system. Thisrole appears to be in addition to itsfunction in protein synthesis.

Editing-Defective tRNA Synthetase CausallyAssociated with Ataxia in the Mouse. Asubset of synthetases sometimes catalyzethe linkage of noncognate amino acidsto tRNAs by mistake. For enzymes thatmake occasional errors, they have a sec-ond active site that clears the mis-charged tRNA (28–31). An example isalanyl-tRNA synthetase ARS, whichdeacylates Ser-tRNAAla and Gly-tRNAAla. If these mischarged tRNAsare not cleared, then the wrong aminoacid is inserted at the codons for alanine.Even a small amount of mischargingthat is not corrected can, in principle,lead to the synthesis of proteins witherrors that cause local or global misfold-ing. Over time, mistranslation leads tothe gradual accumulation of these mis-folded proteins (32–34). The sti/stimouse harbors a mutation in the editingdomain of ARS, which results in a ap-proximately two-fold decrease in theactivity to clear Ser-tRNAAla (35). Theaminoacylation activity of the mutantenzyme is normal. Despite the smallreduction in editing activity, the sti/stimouse shows a marked loss of Purkinjecells in the cerebellum, and developssevere ataxia. Significantly, intracellularunfolded proteins accumulate in neu-rons, accompanied by up-regulation ofcytoplasmic protein chaperones and in-duction of the unfolded proteinresponse.

Unlike the dominant CMT-causingmutations in GRS and YRS, the sti mu-

Fig. 1. Signaling network mediated by mammalian AARSs. Nine different AARSs (EP: glutamyl-prolyl-, I:isoleucyl-, L: leucyl-, M: methionyl-, Q: glutaminyl-, R: arginyl-, K: lysyl-, and D: aspartyl-tRNA synthetase) forma macromolecular complex with three nonenzymatic factors, AIMP1/p43, AIMP2/p38 and AIMP3/p18 (10).Among the components of the complex, EPRS is activated by IFN-� and dissociates from the complex to forma new complex named GAIT (IFN-gamma-activated inhibitor of translation) that binds to the 3�UTR of theceruloplasmin transcript for translational silencing (5). KRS is secreted to induce the inflammatory process (18),and QRS binds to apoptosis signal-regulating kinase 1 (ASK1) to regulate apoptosis in a glutamine-dependentmanner (89). MRS is translocated to nucleoli to stimulate rRNA synthesis on growth stimuli (90). Among thenonenzyme factors, AIMP2 is translocated to the nucleus to suppress c-Myc via ubiquitin-dependent degra-dation of far upstream element binding protein (FBP) (64), whereas AIMP3 is mobilized by DNA damage (66)or an oncogenic stimulus (67) to activate p53 via ATM/ATR. AIMP1 is secreted as an extracellular multifunc-tional ligand active in inflammation (91–93), angiogenesis (61, 62), wound healing (94, 95), and glucosemetabolism (83), and it influences the autoimmune response via its association with gp96 (78). AIMP1 alsodown-regulates the signal mediated by TGF-� through the stabilization of SMAD specific E3 ubiquitin proteinligase2(Smurf2) (96).KRS-generatedAp4Areleasesmicrophthalmia-associatedtranscriptionfactor (MITF)andupstream stimulatory factor (USF2) from their bound complexes for transcriptional control of target genes(97). KRS is packaged into the HIV virion via its interaction with the gag protein (98). Among noncomplexforming AARSs, WRS (tryptophanyl-tRNA synthetase) is secreted and its N-terminal truncation results in theformation of an active angiostatic cytokine that works via VE-cadherin (13, 14, 25, 99–102). The activefragment of WRS also inhibits the response of endothelial cells to shear stress (100). YRS (tyrosyl-tRNAsynthetase) is also secreted and cleaved into two distinct cytokines that work in angiogenesis as well as in theimmune response (14, 15, 25, 103).

11044 � www.pnas.org�cgi�doi�10.1073�pnas.0802862105 Park et al.

Dow

nloa

ded

by g

uest

on

Oct

ober

23,

202

0

tation in the gene for ARS is recessive.Most likely, stronger editing-defectivemutations would be lethal and possiblydominant. On this point, it is worthnoting that a dominant phenotype(apoptosis-like response) was observedwhen a stronger editing-defective muta-tion (in the case of VRS) was intro-duced into mammalian cells. In thisinstance, the unfolded protein responsewas also triggered (36).

Possible Connection of KRS to AmyotrophicLateral Sclerosis. In some patients, a mu-tation in Cu/Zn superoxide dismutase 1(SOD1) is causally associated withamyotrophic lateral sclerosis 1 (ALS1)(37–41). Interestingly, lysyl-tRNA syn-thetase (KRS) associates with mutantbut not wild-type SOD1 (42). TheSOD1 mutation enhances oligomeriza-tion of SOD1 to form aggregates withother proteins, which induces apoptosisof motor neurons, thus leading to theonset of neurodegeneration that is thehallmark of ALS. Whether the oli-gomerization or aggregation of SOD1with KRS contributes to the inhibitionof the normal activity of KRS is notknown. If so, then the neuronal degen-eration seen in patients with a SOD1mutation might be caused or enhancedby a defect in protein synthesis.

Mutations in Mitochondrial DRS Associatedwith Leukoencephalopathy. Specific muta-tions in the gene for mitochondrial as-partyl-tRNA synthetase (DRS) causeleukoencephalopathy, which has brain-stem and spinal cord involvement andlactate elevation (LBSL) (43). LBSL isdiagnosed by a characteristic constella-tion of abnormalities that can be ob-served by magnetic resonance imagingand spectroscopy. The disease is causedby autosomal recessive mutations thatinduce progressive cerebella ataxia.Most of the disease-causing mitochon-drial DRS mutations are located withinexons three and five. These mutationscan alter normal splicing and lead toframe shifts, premature termination oftranslation, or exon skipping. Althoughmutant mitochondrial DRSs have re-duced aminoacylation activity, the mito-chondrial complex, critical for electrontransport, is not affected. Thus, develop-ment of LBSL appears to be caused bya defect in mitochondrial DRS that isrelated to subtle effects on metabolicevents within mitochondria.

Possible Connection of AIMP2 to Parkinson’sDisease. The aminoacyl-tRNA syn-thetase-interacting factor, AIMP2 (alsoknown as p38), was shown to be thesubstrate of Parkin, an E3 ubiquitin–protein ligase (44, 45). Parkin promotes

ubiquitination and proteasome degrada-tion of specific protein substrates. Thecontrol of expression of Parkin sub-strates through ubiquitination and deg-radation is critical for dopaminergic cellsurvival (45). Loss of Parkin function bymutation results in the accumulation ofabnormal or toxic proteins, leading toParkinson’s disease (PD). In Parkin nullmice, AIMP2 is overexpressed in theventral midbrain/hindbrain and over-expression of AIMP2 induces apoptosisin neuronal cells and the formation ofaggresome-like inclusions (45). Theseobservations raise the possibility of apathological connection of AIMP2 toneurodegenerative disease.

AARSs in CancerPossible Role for MRS. Several compo-nents of the translation apparatus showabnormal up- or down-regulation inhepatomas, colon cancer, Burkett’s lym-phoma, prostate adenocarcinoma, breastcancer, sarcoma, colorectal adenocarci-noma and pituitary adenoma (46). Thisabnormal regulation could be partly be-cause of differences in the quantity andquality of cellular protein synthesis intumors. The aminoacylation activity ofmethionyl-tRNA synthetase (MRS),which is required for translation initia-tion, is increased in human colon cancer(47). Coincidently, the 3� untranslatedregion (UTR) of MRS contains a 56base pair complementary sequence tothat of the 3� UTR of C/EBP homolo-gous protein (CHOP) that is criticallyconnected to the onset of specific tu-mors (48–51). Thus, the transcripts forMRS and CHOP have at least the po-tential to associate via 56 base pairs.Whether this complementary relation-ship has any connection to the etiologyof cancer is still to be determined.

Potential Involvement of Other tRNA Syn-thetases in the Etiology of Cancer. In an-other vein, genes encoding differentAARSs have been highly expressed ormodified in association with a variety ofcancers. For example, cysteinyl-tRNAsynthetase (CRS) is expressed as fusionproteins to anaplastic lymphoma kinase(ALK) (52, 53). As another example,the promoter region of mitochondrialisoleucyl-tRNA synthetase (IRS), en-coded by nuclear DNA, was mutated tomodify its expression in hereditary non-polyposis colorectal cancer (HNPCC)and Turcot syndrome (54). Because ex-pression of glutamyl-prolyl-tRNA syn-thetase (EPRS) and IRS is controlled bythe c-myc proto-oncogene (55), abnor-mal expression of EPRS and IRS underoncogenic conditions is not surprising.Preferential expression of the �-subunitof phenylalanyl-tRNA synthetase (FRS)

was observed in lung solid tumors andacute phase chronic myeloid leukemia(56, 57). GRS up-regulation was alsoreported in papillary thyroid carcinoma(PTC) (58, 59), and KRS is overex-pressed in breast cancer (18). It wouldbe interesting to see whether cancer-specific overexpression of these enzymesis also observed in other cancers.Whereas YRS and tryptophanyl-tRNAsynthetase (WRS) directly regulate an-giogenesis as pro- and antiangiogeniccytokines (Fig. 1), EPRS negatively reg-ulates this process via translational sup-pression of vascular endothelial growthfactor-A (VEGF-A) (60). Because an-giogenesis is associated with cancer de-velopment, the unique roles of theseenzymes in the control of angiogenesismay have some implications intumorigenesis.

Involvement of Aminoacyl-tRNA Synthetase-Interacting Factors. Three AARS-interacting factors associated with themultisynthetase complex (AIMPs) haveeach been linked to signaling pathwaysrelevant to cancers. For example,AIMP1/p43 enhances phosphorylationof Jun N-terminal kinase (JNK) andsequentially induces activation ofcaspase 3 to stimulate apoptosis of en-dothelial cells that are linked to tumorangiogenesis (61). As expected, systemicadministration of AIMP1 suppressescancer progression (62).

AIMP2/p38 is essential for the stabil-ity of the multisynthetase complex(63). Interestingly, transforming growthfactor-� (TGF-�) induces nuclear local-ization of AIMP2, where it binds toFUSE-binding protein (FBP), which isthe transcriptional activator of the c-mycproto-oncogene (64). AIMP2 enhancesubiquitin-dependent degradation ofFBP, which results in down-regulation ofc-Myc. Consistent with this observation,genetic depletion of mouse AIMP2 re-sulted in overexpression of c-Myc andcaused neonatal lethality for the hyper-plasia of lung epithelial cells. Becausemembers of the Myc family of proteinsare overexpressed in the majority ofcancers, and TGF-� is a critical tumorsuppressive signal, the role of AIMP2 inlinking c-Myc to TGF-� implies its po-tential role as a tumor suppressor.

AIMP3/p18 harbors the glutathioneS-transferase (GST) homology domainand associates with MRS within themultisynthetase complex (65). AIMP3 isactivated by DNA damage (66) and on-cogenic stresses (67), and translocatesto the nucleus to interact with ataxia-telangiectasia mutated (ATM) andataxia-telangiectasia and Rad-3 related(ATR) kinases, thereby leading to theactivation of p53. Based on these activi-

Park et al. PNAS � August 12, 2008 � vol. 105 � no. 32 � 11045

Dow

nloa

ded

by g

uest

on

Oct

ober

23,

202

0

ties, AIMP3 was thought to be a novelhaploinsufficient tumor suppressor. Ho-mozygous depletion of AIMP3 causedembryonic lethality in the mouse,whereas mice with a single allelic loss ofAIMP3 developed breast adenocarci-noma, a sarcoma of unknown origin,adenocarcinoma in seminal vesicles,hepatocarcinoma, and lymphoma (66).A few mutations of AIMP3 that affectits interaction with ATM and ability toactivate p53 have been found in humanchronic myeloid leukemia patients (68),further supporting its relationship to theinitiation or progression of humanleukemia.

AARSs in Autoimmune DiseasesAutoantibodies Directed Against a Subsetof Synthetases in Autoimmune Disorders.Autoantibodies against different AARSsincluding histidyl-tRNA synthetase (HRS),threonyl-tRNA synthetase (TRS), ARS,IRS, FRS, GRS and asparaginyl-tRNAsynthetase (NRS) have been found in�30% of all autoimmune patients (69,70). The ‘‘antisynthetase syndrome’’ in-cludes, among others, idiopathic inflam-matory myopathies (IIM), interstitiallung diseases (ILD), rheumatoid anderosive arthritis, and Reynaud’s phe-nomenon. IIM is a group of systemicdiseases characterized by chronic muscleinflammation and can be classified intothree distinct clinicopathologic sub-groups – polymyositis (PM), dermato-myositis (DM) and inclusion bodymyositis (IBM). Both PM and DM pa-tients slowly develop proximal and oftensymmetrical muscle weakness overweeks to months. The frequent diseasetypes correlated with anti-synthetaseantibodies are PM and DM. HRS (Jo-1)is the most frequently targeted autoanti-gen in PM. Anti-HRS autoantibodiesare produced in 15 to 25% of all pa-tients with PM. The patients identifiedwith anti-NRS antibodies have ILD (71).

Rationale for Autoantibodies DirectedAgainst AARSs. The reason why AARSsare targeted as autoantigens is not un-derstood. Because there is a generalsimilarity in conformation between cer-tain tRNA synthetases, common struc-tural motifs are speculated as importantfor autoantibody generation. In thatconnection, AARSs can be divided intotwo classes—class I and class II–basedon their characteristic motifs and con-formational architecture. Except forIRS, most autoantigenic AARSs belongto class II. However, the epitope ofHRS for autoantibody generation inmost patients is found at the N-terminusof the protein (72), spanning �60 aminoacids that make up a coiled-coil struc-ture. An N-terminal deletion mutant is

not recognized by the HRS autoantibod-ies that are found in patients (72). It isworth noting that the peptides that arehomologous to this antigenic N-terminalpeptide of HRS are also present in theN-terminal extension of EPRS andGRS, which are other autoantigenicAARSs. The N-terminal extension is notpart of the structure that is conservedand shared by all class II enzymes. Thiscoiled-coil structure is commonly foundin �40% of autoantigens associatedwith a variety of autoimmune diseases,including non-tRNA synthetase autoan-tigens. For example, autoantibodies di-rected against NRS recognize a similarcoiled-coil structure.

Many autoantigens redistribute to andcluster on the surface of cells undergo-ing apoptosis (73). Because autoantigensare commonly generated by apoptoticproteases (during apoptosis) to generateantigenic fragments (74, 75), the nativesynthetases are not likely to be the au-toantigen responsible for the autoim-mune response. Recent studies suggestthat most autoantigens targeted in sys-temic autoimmune diseases are sub-strates of granzyme B, a serine proteasethat is involved in the induction of apo-ptosis during lymphocyte cytotoxicity(76). IRS, HRS and ARS are efficientlycleaved by granzyme B, releasing thefragments that contain the epitopes forthe autoantibodies. Interestingly, HRSand NRS induce migration of CD4� andCD8� T cells, monocytes, and immaturedendritic cells (iDC) via the CCR5 andCCR3 receptors, respectively (77). iDCsexpress these receptors on their surface,and infiltrate muscle tissue in patientsburdened with myositis. Thus, AARSsmight be cleaved by granzyme B togenerate autoantigenic fragments withchemokine activity. Uptake and presen-tation of antigenic fragments by antigenpresenting cells (APCs) initiates the pri-mary immune response against the self-antigen. Self-reactive CD8� T cellsmight further generate additional frag-ments, thereby amplifying both chemo-attraction and immune responses.

AIMP1/p43 Involvement in the AutoimmuneResponse. AIMP1 is also implicated inthe control of the autoimmune response.A portion of the protein is located inthe endoplasmic reticulum (ER) whereit can hold the ER-resident chaperonegp96, which belongs to the hsp90 family(78). Surface translocation or extracellu-lar release of gp96 induces activation ormaturation of dendritic cells (DCs) viaits interaction with CD91 and Toll-likereceptor 2/4 of DCs. Thus, chronic sur-face presentation of gp96 could result inabnormal activation of DCs, leading to alupus-like autoimmune condition (79).

Aberrant surface presentation of gp96hyperactivates DCs that then secreteTNF-�, IL-1�, and IL-12, resulting insystemic immune activation (78). Be-cause AIMP1 prevents surface presenta-tion of gp96, genetic depletion ofAIMP1 in antigen-presenting cells suchas splenocytes, fibroblasts, and macro-phages enhances surface localization ofgp96, thereby leading to the phenotypesthat are similar to the chronic surfacepresentation of gp96 (78). In summary,AIMP1 may act as a regulator for theER retention of gp96 and provide aregulatory mechanism for immuneresponses.

Potential Connections of AARSswith DiabetesMitochondrial leucyl-tRNA synthetase(Mito-LRS), like all mitochondrial tRNAsynthetases in humans, is encoded bythe nuclear genome. In diabetes, bothhyperglycemia and hyperinsulinemiastimulate accumulation of mitochondrialtRNA mutations by inducing oxidativestress. In addition, a single nucleotidepolymorphism of mito-LRS leading toan amino acid substitution (H324Q) wasfound in patients aff licted with type 2diabetes mellitus (80). Because H324Qmito-LRS has normal aminoacylationand editing activities, the causal rela-tionship between the mito-LRS H324Qmutation and type 2 diabetes is not yetunderstood. Likewise, mutations in mi-tochondrial tRNAs, the substrates ofAARSs, appear to have a causal rela-tionship to multiple diseases includingdiabetes (81, 82).

In another vein, AIMP1 works as reg-ulator of glucose homeostasis (83). Ge-netic depletion of AIMP1 in the mouseleads to hypoglycemic phenotypes. Yetto be determined is whether this patho-logical phenotype can also be applied tohumans.

Implications and PerspectivesThe tRNA synthetases arose early inevolution, being essential for establish-ing the genetic code that relates nucleo-tide triplets to specific amino acids. Inan RNA world, the aminoacylation reac-tion is thought to have been catalyzedby ribozymes. Because the aminoacyllinkage is higher in energy than the pep-tide bond, the production of aminoacylRNAs provided a straightforward pathto peptides (for example, the side-by-side docking of two aminoacyl tRNAsleads to spontaneous peptide bond for-mation) (84, 85). The present-day ge-netic code proved so robust that itoverwhelmed all other alternatives, andover the eons, gave birth to the tree oflife with its three great kingdoms—archae, bacteria, and eukarya. The two

11046 � www.pnas.org�cgi�doi�10.1073�pnas.0802862105 Park et al.

Dow

nloa

ded

by g

uest

on

Oct

ober

23,

202

0

classes of tRNA synthetases are presentat the root, or base, of this tree and areintimately tied to the historical develop-ment of the universal code.

Perhaps because of their presencefrom the beginning, the synthetases havealways been available for adaptation andrecruitment to emerging cell signalingpathways. Insertions of new motifs, thecarving out of novel fragments by alter-native splicing or proteolysis, and post-translational modifications were allpossible and provided a way to linktranslation to cell signaling pathwaysand biological networks. Viewed fromthis perspective, the synthetases mayhave been among the earliest cytokinesand cell signaling molecules. Later de-velopments, such as the formation ofthe multisynthetase complex in eu-karyotes, gathered together many of thetRNA synthetase cytokines in an orga-nized way that, among other features,enabled them to be mobilized by specific

cues (such as IFN-� stimulation) fortheir expanded functions.

In the future, the major advances inunderstanding how synthetases arelinked to cell signaling pathways willcome from elucidation of the many in-teracting protein partners of tRNA syn-thetases. Annotation of these interactingpartners, and the structural elucidationof the motifs needed for these interac-tions, will provide some of the mostfundamental understanding of how syn-thetases became so tightly connectedwith a vast array of cell signaling path-ways. These investigations will undoubt-edly lead back to the catalytic site itself,and the pockets and determinants forbinding the amino acid ligand, ATP, andtRNA. Adaptations of these pockets anddeterminants for protein–protein andprotein–nucleic acid interactions concep-tually provide at least one route to ex-panding the world of the synthetases.These enzymes also have attachments

and insertions of peptides that are capa-ble of interacting with diverse partners.These additional domains might havepaved another way for functional diver-sification. Initially, as proteins present inevery cell type, they constantly were ex-posed to many other cellular compo-nents with which they had serendipitousand ‘‘nonphysiological’’ contacts. Thesecontacts, over time, could have engen-dered new activities that eventually be-came highly specific and even essentialfor cell growth and development.

The diverse connections of AARSswith various human diseases make themattractive as targets for the developmentof therapeutics (Fig. 2). Two of the syn-thetases—WRS and EPRS—have beenstudied in detail for their alternativefunctions in cell signaling pathways buthave not yet been linked to a specificdisease. Regardless of such disease con-nections, however, therapeutics based onthe potent cytokine fragments of thesynthetases like WRS are of great inter-est. In addition, because the enzymesare essential, their active sites in patho-genic microorganisms are obvious tar-gets for antiinfectives (86, 87). Here,specificity for the pathogen synthetase ispossible because of the variations in theevolution of the active site residues, sothat a drug targeted to the pathogendoes not cross-bind to the human coun-terpart. Many of the synthetases have asecond active site designed for clearingerrors of aminoacylation. This site offersyet another target for antiinfectives. In-terestingly, a novel antifungal trapstRNALeu in the editing site of yeast cy-toplasmic LRS (88). As a consequence,tRNALeu cannot be aminoacylated.Thus, as therapeutic agents in and ofthemselves, and as targets for drugs, thetRNA synthetases will yield many op-portunities for disease intervention.

ACKNOWLEDGMENTS. This work was supportedby the Korea Science and Engineering Founda-tion through Acceleration Research Grant R17-2007-020-01000-0, Seoul Research and Develop-ment Program 11125, by National Institutes ofHealth Grants GM15539, 23562, and CA92577,and by a fellowship from the National Founda-tion for Cancer Research.

1. Edgecombe M, Craddock HS, Smith DC, McLennanAG, Fisher MJ (1997) Diadenosine polyphosphate-stimulated gluconeogenesis in isolated rat proximaltubules. Biochem J 323:451–456.

2. Verspohl EJ, Hohmeier N, Lempka M (2003) Diade-nosine tetraphosphate (Ap4A) induces a diabetogenicsituation: Its impact on blood glucose, plasma insulin,gluconeogenesis, glucose uptake and GLUT-4 trans-porters. Pharmazie 58:910–915.

3. Nishimura A, et al. (1997) Diadenosine 5�, 5�-P1, P4-tetraphosphate (Ap4A) controls the timing of cell divi-sion in Escherichia coli. Genes Cells 2:401–413.

4. Romby P, Springer M (2003) Bacterial translationalcontrol at atomic resolution. Trends Genet 19:155–161.

5. Sampath P, et al. (2004) Noncanonical function ofglutamyl-prolyl-tRNA synthetase: Gene-specific si-lencing of translation. Cell 119:195–208.

6. Rho SB, et al. (1999) Genetic dissection of protein–protein interactions in multi-tRNA synthetase complex.Proc Natl Acad Sci USA 96:4488–4493.

7. Lee SW, Cho BH, Park SG, Kim S (2004) Aminoacyl-tRNA synthetase complexes: Beyond translation. J CellSci 117:3725–3734.

8. Kyriacou SV, Deutscher MP (2008) An important rolefor the multienzyme aminoacyl-tRNA synthetasecomplex in mammalian translation and cell growth.Mol Cell 29:419–427.

9. Ray PS, Arif A, Fox PL (2007) Macromolecular com-plexes as depots for releasable regulatory proteins.

Trends Biochem Sci 32:158–164.10. Park SG, Ewalt KL, Kim S (2005) Functional expansion

of aminoacyl-tRNA synthetases and their interactingfactors: New perspectives on housekeepers. TrendsBiochem Sci 30:569–574.

11. Jia J, Arif A, Ray PS, Fox PL (2008) WHEP domains directnoncanonical function of glutamyl-prolyl tRNAsynthetase in translational control of gene expres-sion. Mol Cell 29:679–690.

12. Wakasugi K, Schimmel P (1999) Two distinct cytokinesreleased from a human aminoacyl-tRNA synthetase.Science 284:147–151.

13. Wakasugi K, et al. (2002) A human aminoacyl-tRNAsynthetase as a regulator of angiogenesis. Proc NatlAcad Sci USA 99:173–177.

Fig. 2. Linkage map of AARSs with various human diseases. Mutants of G/Y/ARS, mitochondrial DRSand AIMP2 are implicated in CMT, leukoencephalopathy and Parkinson’s disease, respectively. The M,C, I, EP, F and KRSs are overexpressed in various human cancers, although the potential cause for theoverexpression is probably idiosyncratic. AIMP3/p18 is a haploinsufficient tumor suppressor acting onATM/ATR, thereby leading to activation of p53. The H, T, A, I, F, G, S and NRSs are implicated in theautoimmune diseases collectively designated ‘‘antisynthetase syndrome.’’ AIMP1 controls a lupus-likeautoimmune disease via its interaction with gp96. The C-terminal domains of YRS and KRS work asinflammatory cytokines. The secretion of the N-terminal domain of YRS, N-terminal truncated WRS,and full-length AIMP1/p43 regulate angiogenesis. EPRS represses angiogenesis via translationalsilencing of VEGF-A (60). A mutation of mitochondrial LRS is associated with type 2 diabetes, eventhough the mutation does not affect its catalytic activity. Reduced activity of mitochondrial DRS isassociated with leukoencephalopathy and lactate elevation. Mutations in mitochondrial tRNALys (104,105), tRNALeu (106), and tRNASer (107) were shown to be associated with diabetes. AIMP1 works ashormone for glucose homeostasis.

Park et al. PNAS � August 12, 2008 � vol. 105 � no. 32 � 11047

Dow

nloa

ded

by g

uest

on

Oct

ober

23,

202

0

14. Yang XL, Schimmel P, Ewalt KL (2004) Relationship oftwo human tRNA synthetases used in cell signaling.Trends Biochem Sci 29:250–256.

15. Wakasugi K, et al. (2002) Induction of angiogenesis bya fragment of human tyrosyl-tRNA synthetase. J BiolChem 277:20124–20126.

16. Otani A, et al. (2002) Bone marrow-derived stem cellstarget retinal astrocytes and can promote or inhibitretinal angiogenesis. Nat Med 8:1004–1010.

17. Kise Y, et al. (2004) A short peptide insertion crucialfor angiostatic activity of human tryptophanyl-tRNAsynthetase. Nat Struct Mol Biol 11:149–156.

18. Park SG, et al. (2005) Human lysyl-tRNA synthetase issecreted to trigger pro-inflammatory response. ProcNatl Acad Sci USA 102:6356–6361.

19. Kapoor M, et al. (2008) Evidence for annexin II-S100A10 complex and plasmin in mobilization of cy-tokine activity of human TrpRS. J Biol Chem283:2070–2077.

20. Dyck PJ, Lambert EH (1968) Lower motor and primarysensory neuron diseases with peroneal muscular at-rophy. II. Neurologic, genetic, and electrophysiologicfindings in various neuronal degenerations. ArchNeurol 18:619–625.

21. Antonellis A, et al. (2003) Glycyl-tRNA synthetase mu-tations in Charcot-Marie-Tooth disease type 2D anddistal spinal muscular atrophy type V. Am J HumGenet 72:1293–1299.

22. Jordanova A, et al. (2006) Disrupted function andaxonal distribution of mutant tyrosyl-tRNA syn-thetase in dominant intermediate Charcot-Marie-Tooth neuropathy. Nat Genet 38:197–202.

23. Nangle LA, Zhang W, Xie W, Yang XL, Schimmel P(2007) Charcot-Marie-Tooth disease-associated mu-tant tRNA synthetases linked to altered dimer inter-face and neurite distribution defect. Proc Natl AcadSci USA 104:11239–11244.

24. Seburn KL, Nangle LA, Cox GA, Schimmel P, BurgessRW (2006) An active dominant mutation of glycyl-tRNA synthetase causes neuropathy in a Charcot-Marie-Tooth 2D mouse model. Neuron 51:715–726.

25. Yang XL, Skene RJ, McRee DE, Schimmel P (2002)Crystal structure of a human aminoacyl-tRNA syn-thetase cytokine. Proc Natl Acad Sci USA 99:15369–15374.

26. Xie W, Schimmel P, Yang XL (2006) Crystallization andpreliminary X-ray analysis of a native human tRNAsynthetase whose allelic variants are associated withCharcot-Marie-Tooth disease. Acta Crystallogr F62:1243–1246.

27. Cader MZ, et al. (2007) Crystal structure of human wildtype and S581L-mutant glycyl-tRNA synthetase, anenzyme underlying distal spinal muscular atrophy.FEBS Lett 581:2959–2964.

28. Eldred EW, Schimmel PR (1972) Rapid deacylation byisoleucyl transfer ribonucleic acid synthetase of isole-ucine-specific transfer ribonucleic acid aminoacylatedwith valine. J Biol Chem 247:2961–2964.

29. Schreier AA, Schimmel PR (1972) Transfer ribonucleicacid synthetase catalyzed deacylation of aminoacyltransfer ribonucleic acid in the absence of adenosinemonophosphate and pyrophosphate. Biochemistry11:1582–1589.

30. Yarus M (1972) Phenylalanyl-tRNA synthetase and iso-leucyl-tRNAPhe: A possible verification mechanism foraminoacyl-tRNA. Proc Natl Acad Sci USA 69:1915–1919.

31. Fersht A (1985) Enzyme Structure and Mechanism(Freeman, New York).

32. Doring V, et al. (2001) Enlarging the amino acid set ofEscherichia coli by infiltration of the valine codingpathway. Science 292:501–504.

33. Nangle LA, Motta CM, Schimmel P (2006) Global ef-fects of mistranslation from an editing defect in mam-malian cells. Chem Biol 13:1091–1100.

34. Williams AM, Martinis SA (2006) Mutational unmask-ing of a tRNA-dependent pathway for preventinggenetic code ambiguity. Proc Natl Acad Sci USA103:3586–3591.

35. Lee JW, et al. (2006) Editing-defective tRNA syn-thetase causes protein misfolding and neurodegen-eration. Nature 443:50–55.

36. Nangle LA, De Crecy Lagard V, Doring V, Schimmel P(2002) Genetic code ambiguity. Cell viability relatedto the severity of editing defects in mutant tRNAsynthetases. J Biol Chem 277:45729–45733.

37. Banci L, et al. (2007) Metal-free superoxide dismutaseforms soluble oligomers under physiological condi-tions: A possible general mechanism for familial ALS.Proc Natl Acad Sci USA 104:11263–11267.

38. Kim YJ, Nakatomi R, Akagi T, Hashikawa T, TakahashiR (2005) Unsaturated fatty acids induce cytotoxic ag-gregate formation of amyotrophic lateral sclerosis-linked superoxide dismutase 1 mutants. J Biol Chem280:21515–21521.

39. Khare SD, Caplow M, Dokholyan NV (2004) The rateand equilibrium constants for a multistep reactionsequence for the aggregation of superoxide dis-mutase in amyotrophic lateral sclerosis. Proc NatlAcad Sci USA 101:15094–15099.

40. Andrekopoulos C, Zhang H, Joseph J, Kalivendi S,Kalyanaraman B (2004) Bicarbonate enhances alpha-synuclein oligomerization and nitration: Intermedi-acy of carbonate radical anion and nitrogen dioxideradical. Biochem J 378:435–447.

41. Valentine JS, Hart PJ (2003) Misfolded CuZnSOD andamyotrophic lateral sclerosis. Proc Natl Acad Sci USA100:3617–3622.

42. Kunst CB, Mezey E, Brownstein MJ, Patterson D (1997)Mutations in SOD1 associated with amyotrophic lat-eral sclerosis cause novel protein interactions. NatGenet 15:91–94.

43. Scheper GC, et al. (2007) Mitochondrial aspartyl-tRNAsynthetase deficiency causes leukoencephalopathywith brain stem and spinal cord involvement andlactate elevation. Nat Genet 39:534–539.

44. Corti O, et al. (2003) The p38 subunit of the aminoacyl-tRNA synthetase complex is a Parkin substrate: Link-ing protein biosynthesis and neurodegeneration.Hum Mol Genet 12:1427–1437.

45. Ko HS, et al. (2005) Accumulation of the authenticparkin substrate aminoacyl-tRNA synthetase cofac-tor, p38/JTV-1, leads to catecholaminergic cell death.J Neurosci 25:7968–7978.

46. Lee SW, Kang YS, Kim S (2006) Multi-functional pro-teins in tumorigenesis: Aminoacyl-tRNA synthetasesand translational components. Curr Proteomics3:233–247.

47. Kushner JP, Boll D, Quagliana J, Dickman S (1976)Elevated methionine-tRNA synthetase activity in hu-man colon cancer. Proc Soc Exp Biol Med 153:273–276.

48. Forus A, Florenes VA, Maelandsmo GM, Fodstad O,Myklebost O (1994) The protooncogene CHOP/GADD153, involved in growth arrest and DNA dam-age response, is amplified in a subset of human sar-comas. Cancer Genet Cytogenet 78:165–171.

49. Nilbert M, Rydholm A, Mitelman F, Meltzer PS, Man-dahl N (1995) Characterization of the 12q13–15 am-plicon in soft tissue tumors. Cancer Genet Cytogenet83:32–36.

50. Palmer JL, Masui S, Pritchard S, Kalousek DK, SorensenPH (1997) Cytogenetic and molecular genetic analysisof a pediatric pleomorphic sarcoma reveals similari-ties to adult malignant fibrous histiocytoma. CancerGenet Cytogenet 95:141–147.

51. Reifenberger G, et al. (1996) Refined mapping of12q13–q15 amplicons in human malignant gliomassuggests CDK4/SAS and MDM2 as independent am-plification targets. Cancer Res 56:5141–5145.

52. Cools J, et al. (2002) Identification of novel fusionpartners of ALK, the anaplastic lymphoma kinase, inanaplastic large-cell lymphoma and inflammatorymyofibroblastic tumor. Genes Chromosomes Cancer34:354–362.

53. Debelenko LV, et al. (2003) Identification of CARS-ALK fusion in primary and metastatic lesions of aninflammatory myofibroblastic tumor. Lab Invest83:1255–1265.

54. Miyaki M, et al. (2001) Alterations of repeated se-quences in 5� upstream and coding regions in colo-rectal tumors from patients with hereditary nonpol-yposis colorectal cancer and Turcot syndrome.Oncogene 20:5215–5218.

55. Coller HA, et al. (2000) Expression analysis with oligo-nucleotide microarrays reveals that MYC regulatesgenes involved in growth, cell cycle, signaling, andadhesion. Proc Natl Acad Sci USA 97:3260–3265.

56. Lieber M, Smith B, Szakal A, Nelson-Rees W, Todaro G(1976) A continuous tumor-cell line from a humanlung carcinoma with properties of type II alveolarepithelial cells. Int J Cancer 17:62–70.

57. Rodova M, Ankilova V, Safro MG (1999) Human phe-nylalanyl-tRNA synthetase: Cloning, characterizationof the deduced amino acid sequences in terms of thestructural domains and coordinately regulated ex-pression of the alpha and beta subunits in chronicmyeloid leukemia cells. Biochem Biophys Res Com-mun 255:765–773.

58. Wasenius VM, et al. (2003) Hepatocyte growth factorreceptor, matrix metalloproteinase-11, tissue inhibi-tor of metalloproteinase-1, and fibronectin are up-regulated in papillary thyroid carcinoma: A cDNA andtissue microarray study. Clin Cancer Res 9:68–75.

59. Scandurro AB, Weldon CW, Figueroa YG, Alam J,Beckman BS (2001) Gene microarray analysis reveals anovel hypoxia signal transduction pathway in humanhepatocellular carcinoma cells. Int J Oncol 19:129–135.

60. Ray PS, Fox PL (2007) A post-transcriptional pathwayrepresses monocyte VEGF-A expression and angio-genic activity. EMBO J 26:3360–3372.

61. Park SG, et al. (2002) Dose-dependent biphasic activityof tRNA synthetase-associating factor, p43, in angio-genesis. J Biol Chem 277:45243–45248.

62. Lee YS, et al. (2006) Antitumor activity of the novelhuman cytokine AIMP1 in an in vivo tumor model.Mol Cells 21:213–217.

63. Kim JY, et al. (2002) p38 is essential for the assemblyand stability of macromolecular tRNA synthetasecomplex: Implications for its physiological signifi-cance. Proc Natl Acad Sci USA 99:7912–7916.

64. Kim MJ, et al. (2003) Downregulation of fuse-bindingprotein and c-myc by tRNA synthetase cofactor, p38, isrequired for lung differentiation. Nat Genet 34:330–336.

65. Quevillon S, Mirande M (1996) The p18 component ofthe multisynthetase complex shares a protein motifwith the beta and gamma subunits of eukaryoticelongation factor 1. FEBS Lett 395:63–67.

66. Park BJ, et al. (2005) The haploinsufficient tumorsuppressor p18 upregulates p53 via interactions withATM/ATR. Cell 120:209–221.

67. Park BJ, et al. (2006) AIMP3 haploinsufficiency dis-rupts oncogene-induced p53 activation and genomicstability. Cancer Res 66:6913–6918.

68. Kim KJ, et al. (2008) Determination of three dimen-sional structure and residues of novel tumor suppres-sor, AIMP3/p18, required for the interaction withATM. J Biol Chem 283:14032–14040.

69. Mathews MB, Bernstein RM (1983) Myositis autoanti-body inhibits histidyl-tRNA synthetase: A model forautoimmunity. Nature 304:177–179.

70. Mathews MB, Reichlin M, Hughes GR, Bernstein RM(1984) Anti-threonyl-tRNA synthetase, a second myo-sitis-related autoantibody. J Exp Med 160:420–434.

71. Hirakata M, et al. (1999) Anti-KS: Identification ofautoantibodies to asparaginyl-transfer RNA syn-thetase associated with interstitial lung disease. J Im-munol 162:2315–2320.

72. Raben N, et al. (1994) A motif in human histidyl-tRNAsynthetase which is shared among several aminoacyl-tRNA synthetases is a coiled-coil that is essential forenzymatic activity and contains the major autoanti-genic epitope. J Biol Chem 269:24277–24283.

73. Casciola-Rosen LA, Anhalt G, Rosen A (1994) Autoan-tigens targeted in systemic lupus erythematosus areclustered in two populations of surface structures onapoptotic keratinocytes. J Exp Med 179:1317–1330.

74. Andrade F, et al. (1998) Granzyme B directly andefficiently cleaves several downstream caspase sub-strates: Implications for CTL-induced apoptosis. Im-munity 8:451–460.

75. Casciola-Rosen L, Rosen A (1997) Ultraviolet light-induced keratinocyte apoptosis: A potential mecha-nism for the induction of skin lesions and autoanti-body production in LE. Lupus 6:175–180.

76. Casciola-Rosen L, Andrade F, Ulanet D, Wong WB,Rosen A (1999) Cleavage by granzyme B is stronglypredictive of autoantigen status: Implications for ini-tiation of autoimmunity. J Exp Med 190:815–826.

11048 � www.pnas.org�cgi�doi�10.1073�pnas.0802862105 Park et al.

Dow

nloa

ded

by g

uest

on

Oct

ober

23,

202

0

77. Howard OM, et al. (2002) Histidyl-tRNA synthetaseand asparaginyl-tRNA synthetase, autoantigens inmyositis, activate chemokine receptors on T lympho-cytes and immature dendritic cells. J Exp Med196:781–791.

78. Han JM, et al. (2007) Aminoacyl-tRNA synthetase-interacting multifunctional protein 1/p43 controls en-doplasmic reticulum retention of heat shock proteingp96: Its pathological implications in lupus-like auto-immune diseases. Am J Pathol 170:2042–2054.

79. Liu B, et al. (2003) Cell surface expression of an endo-plasmic reticulum resident heat shock protein gp96triggers MyD88-dependent systemic autoimmune dis-eases. Proc Natl Acad Sci USA 100:15824–15829.

80. t Hart LM, et al. (2005) Evidence that the mitochon-drial leucyl tRNA synthetase (LARS2) gene representsa novel type 2 diabetes susceptibility gene. Diabetes54:1892–1895.

81. Florentz C (2002) Molecular investigations on tRNAsinvolved in human mitochondrial disorders. BiosciRep 22:81–98.

82. Florentz C, Sohm B, Tryoen-Toth P, Putz J, Sissler M(2003) Human mitochondrial tRNAs in health anddisease. Cell Mol Life Sci 60:1356–1375.

83. Park SG, et al. (2006) Hormonal activity of AIMP1/p43for glucose homeostasis. Proc Natl Acad Sci USA103:14913–14918.

84. Tamura K, Schimmel P (2001) Oligonucleotide-directed peptide synthesis in a ribosome- and ri-bozyme-free system. Proc Natl Acad Sci USA 98:1393–1397.

85. Tamura K, Schimmel P (2003) Peptide synthesis with atemplate-like RNA guide and aminoacyl phosphateadaptors. Proc Natl Acad Sci USA 200:8666–8669.

86. Kim S, Lee SW, Choi EC, Choi SY (2003) Aminoacyl-tRNA synthetases and their inhibitors as a novel familyof antibiotics. Appl Microbiol Biotechnol 61:278–288.

87. Pohlmann J, Brotz-Oesterhelt H (2004) New amino-acyl-tRNA synthetase inhibitors as antibacterialagents. Curr Drug Targets Infect Disord 4:261–272.

88. Rock FL, et al. (2007) An antifungal agent inhibits anaminoacyl-tRNA synthetase by trapping tRNA in theediting site. Science 316:1759–1761.

89. Ko YG, et al. (2001) Glutamine-dependent anti-apo-ptotic interaction of human glutaminyl-tRNA syn-thetase with apoptosis signal-regulating kinase 1.J Biol Chem 276:6030–6036.

90. Ko YG, Kang YS, Kim EK, Park SG, Kim S (2000) Nucle-olar localization of human methionyl-tRNA syn-thetase and its role in ribosomal RNA synthesis. J CellBiol 149:567–574.

91. Ko YG, et al. (2001) A cofactor of tRNA synthetase,p43, is secreted to up-regulate proinflammatorygenes. J Biol Chem 276:23028–32303.

92. Park H, et al. (2002) Monocyte cell adhesion inducedby a human aminoacyl-tRNA synthetase associatedfactor, p43: Identification of the related adhesionmolecules and signal pathways. J Leukoc Biol 71:223–230.

93. Park H, Park SG, Kim J, Ko YG, Kim S (2002) Signalingpathways for TNF production induced by human ami-noacyl-tRNA synthetase-associating factor, p43. Cyto-kine 20:148–153.

94. Park SG, et al. (2005) The novel cytokine p43 stimu-lates dermal fibroblast proliferation and wound re-pair. Am J Pathol 166:387–398.

95. Han JM, Park SG, Lee Y, Kim S (2006) Structural sepa-ration of different extracellular activities in amino-acyl-tRNA synthetase-interacting multi-functionalprotein, p43/AIMP1. Biochem Biophys Res Commun342:113–118.

96. Lee YS, et al. (2008) AIMP1/p43 downregulates TGF-�signaling via stabilization of smurf2. Biochem BiophysRes Commun 371:395–400.

97. Yannay-Cohen N, Razin E (2006) Translation and tran-scription: The dual functionality of KRS in mast cells.Mol Cells 22:127–132.

98. Halwani R, et al. (2004) Cellular distribution of lysyl-tRNA synthetase and its interaction with Gag duringhuman immunodeficiency virus type 1 assembly. J Vi-rol 78:7553–7564.

99. Liu J, Shue E, Ewalt KL, Schimmel P (2004) A newgamma-interferon-inducible promoter and splicevariants of an anti-angiogenic human tRNA syn-thetase. Nucl Acids Res 32:719–727.

100. Tzima E, et al. (2003) Biologically active fragment of ahuman tRNA synthetase inhibits fluid shear stress-activated responses of endothelial cells. Proc NatlAcad Sci USA 100:14903–14907.

101. Tzima E, et al. (2005) VE-cadherin links tRNA syn-thetase cytokine to anti-angiogenic function. J BiolChem 280:2405–2408.

102. Banin E, et al. (2006) T2-WRS inhibits preretinal neo-vascularization and enhances physiological vascularregrowth in OIR as assessed by a new method ofquantification. Invest Ophthalmol Vis Sci 47:2125–2134.

103. Ivakhno SS, Kornelyuk AI (2004) Cytokine-like activi-ties of some aminoacyl-tRNA synthetases and auxil-iary p43 cofactor of aminoacylation reaction and theirrole in oncogenesis. Exp Oncol 26:250–255.

104. Kameoka K, et al. (1998) Novel mitochondrial DNAmutation in tRNA(Lys) (8296A–�G) associated withdiabetes. Biochem Biophys Res Commun 245:523–527.

105. Kameoka K, Isotani H, Tanaka K, Kitaoka H, Ohsawa N(1998) Impaired insulin secretion in Japanese diabeticsubjects with an A-to-G mutation at nucleotide 8296of the mitochondrial DNA in tRNA (Lys). Diabetes Care21:2034–2035.

106. Janssen GM, Maassen JA, van Den Ouweland JM(1999) The diabetes-associated 3243 mutation in themitochondrial tRNA (Leu(UUR)) gene causes severemitochondrial dysfunction without a strong decreasein protein synthesis rate. J Biol Chem 274:29744–29748.

107. Choo-Kang AT, et al. (2002) Defining the importanceof mitochondrial gene defects in maternally inheriteddiabetes by sequencing the entire mitochondrial ge-nome. Diabetes 51:2317–2320.

Park et al. PNAS � August 12, 2008 � vol. 105 � no. 32 � 11049

Dow

nloa

ded

by g

uest

on

Oct

ober

23,

202

0