Synthesis and discovery of the first potent proteolysis targeting chimaera (PROTAC) degrader of AIMP2-DX2 as a lung cancer drug.

ARS-interacting multifunctional proteins 2 (AIMP2) is known to be a powerful tumour suppressor. However, the target AIMP2-DX2, AIMP2-lacking exon 2, is often detected in many cancer patients and cells. The predominant approach for targeting AIMP-DX2 has been attempted via small molecule mediated inhibition, but due to the lack of satisfactory activity against AIMP2-DX2, new therapeutic strategies are needed to develop a novel drug for AIMP2-DX2. Here, we report the use of the PROTAC strategy that combines small-molecule AIMP2-DX2 inhibitors with selective E3-ligase ligands with optimised linkers. Consequently, candidate compound 45 was found to be a degrader of AIMP2-DX2. Together, these findings demonstrate that our PROTAC technology targeting AIMP2-DX2 would be a potential new strategy for future lung cancer treatment.

Targeting the interaction of AIMP2-DX2 with HSP70 suppresses cancer development.

A tumorigenic factor, AIMP2 lacking exon 2 (AIMP2-DX2), is often upregulated in many cancers. However, how its cellular level is determined is not understood. Here, we report heat-shock protein HSP70 as a critical determinant for the level of AIMP2-DX2. Interaction of the two factors was identified by interactome analysis and structurally determined by X-ray crystallography and NMR analyses. HSP70 recognizes the amino (N)-terminal flexible region, as well as the glutathione S-transferase domain of AIMP2-DX2, via its substrate-binding domain, thus blocking the Siah1-dependent ubiquitination of AIMP2-DX2. AIMP2-DX2-induced cell transformation and cancer progression in vivo was further augmented by HSP70. A positive correlation between HSP70 and AIMP2-DX2 levels was shown in various lung cancer cell lines and patient tissues. Chemical intervention in the AIMP2-DX2-HSP70 interaction suppressed cancer cell growth in vitro and in vivo. Thus, this work demonstrates the importance of the interaction between AIMP2-DX2 and HSP70 on tumor progression and its therapeutic potential against cancer.

Allosteric Inhibition of the Tumor-Promoting Interaction Between Exon 2-Depleted Splice Variant of Aminoacyl-Transfer RNA Synthetase-Interacting Multifunctional Protein 2 and Heat Shock Protein 70.

Although protein-protein interactions (PPIs) have emerged as an attractive therapeutic target space, the identification of chemicals that effectively inhibit PPIs remains challenging. Here, we identified through library screening a chemical probe (compound 1) that can inhibit the tumor-promoting interaction between the oncogenic factor exon 2-depleted splice variant of aminoacyl-transfer RNA synthetase-interacting multifunctional protein 2 (AIMP2-DX2) and heat shock protein 70 (HSP70). We found that compound 1 binds to the N-terminal subdomain of glutathione S-transferase (GST-N) of AIMP2-DX2, causing a direct steric clash with HSP70 and an intramolecular interaction between the N-terminal flexible region and the GST-N of AIMP2-DX2, which induces masking of the HSP70 binding region during molecular dynamics and mutation studies. Compound 1 thus interferes with the AIMP2-DX2 and HSP70 interaction and suppresses the growth of cancer cells that express high levels of AIMP2-DX2 in vitro and in preliminary in vivo experiment. This work provides an example showing that allosteric conformational changes induced by chemicals can be a way to control pathologic PPIs. SIGNIFICANCE STATEMENT: Compound 1 is a promising protein-protein interaction inhibitor between AIMP2-DX2 and HSP70 for cancer therapy by the mechanism with allosteric modulation as well as competitive binding. It seems to induce allosteric conformational change of AIMP2-DX2 proteins and direct binding clash between AIMP2-DX2 and HSP70. The compound reduced the level of AIMP2-DX2 in ubiquitin-dependent manner via suppression of binding between AIMP2-DX2 and HSP70 and suppressed the growth of cancer cells highly expressing AIMP2-DX2 in vitro and in preliminary in vivo experiment.

First Report of Colletotrichum siamense Causing Anthracnose of Chili Pepper Fruit in Korea.

In October 2015, typical anthracnose symptoms were observed on approximately 15 to 20% of the chili fruits (cv. Manita) growing in Goesan County, Chungcheong Province, South Korea. Infection of fruits were characterized by the presence of circular, sunken lesions with concentric rings of orange conidial acervuli. Fresh samples were collected from the infected fruits and lesions from seven symptomatic fruits were cut into small pieces (5 mm2) and surface sterilized by soaking them in 1% sodium hypochlorite for 3 min, followed by rinsing thrice using sterilized water, and drying on sterilized filter paper. The tissue pieces were then placed on potato dextrose agar (PDA) and incubated at 25 ± 2°C with 12hrs photoperiod. After 2 to 3 days, single hyphal tips were transferred to fresh PDA and a total of seven isolates were selected from typical single hyphae. The upper surfaces of the colonies formed on PDA were white to gray in color with cottony mycelia, in which salmon-colored acervuli were clearly visible (Supplementary 1). Thirty conidia were examined; all were hyaline, smooth-walled, aseptate, straight, mainly cylindrical with round ends, 12 to 17 µm long, and 3 to 4.5 µm wide. Appressoria were oval to irregular inshape, dark brown in color, and range from 9.5 to 11.5 µm × 6.5 to 7.5 µm in sizes. Morphological characteristics of the seven isolates were identical and resembled those of C. siamense (Weir et al. 2012). To confirm the identification of the fungal isolates, DNA from seven isolates were extracted (Cenis et al. 1992) and the genes encoding glyceraldehyde-3-phosphate dehydrogenase (GAPDH), internal transcribed spacer (ITS) rDNA regions, and ß-Tublin-2 (TUB2) were partially amplified and sequenced. Sequences from all seven isolates were identical each other. Nucleotide sequences of ITS, GAPDH, and TUB2 from representative isolates CNU180002 and CNU180012 were deposited in GenBank under accession numbers MH085103, MH085105, and MH085107 for CNU180002 and MK033503, MK033504, and MK033505 for CNU180012, respectively. The sequences for all three genes exhibited 99 to 100% identity with C. siamense, GenBank accession nos. FJ972613 (ITS), FJ972575 (GAPDH), and FJ907438 (TUB2) for both isolates. A multi-locus phylogenetic tree with closely related reference sequences downloaded from the GenBank database demonstrated that these two isolates were aligned with C. siamense. Pathogenicity of isolates CNU180002 and CNU180012 was confirmed on healthy fruits (Manita) by using a pin-pricked wound/drop (1 mm depth) and non-wound/drop inoculation method (Oo et al. 2017) and control fruits were mock-inoculated with sterilized distilled water. Three fruits were inoculated for each isolate and pathogenicity test were repeated thrice. After inoculation, the fruits were placed on a sterilized paper tissue in moistened clean boxes with a relative humidity of approximately 90% and incubated for 7 days at 25°C in the dark. Disease symptoms were appeared 5 to 7 days after inoculation on wounded fruits whereas non-wounded fruits were observed after 10 days. The two isolates showed identical symptoms and control fruits remained symptomless. Both isolates were re-isolated from infected fruits and were identical to the original isolates in morphology characteristics as well as on molecular sequences of ITS, GAPDH and TUB2 genes. To our knowledge, this is the first report of anthracnose caused by C. siamense on chili pepper fruit in Korea.

Anticancer Activity of Pyrimethamine via Ubiquitin Mediated Degradation of AIMP2-DX2.

While aminoacyl-tRNA synthetase-interacting multifunctional protein 2 (AIMP2) is a tumor suppressor, its exon 2-depleted splice variant (AIMP2-DX2 or shortly DX2) is highly expressed in human lung cancer, and the ratio of DX2 to AIMP2 increases according to the progression of lung cancer. In this study, pyrimethamine inhibited the level of DX2 (IC50 = 0.73 µM) in A549 cells expressing nanoluciferase-tagged DX2. In a panel of 5 lung cancer cell lines with various DX2 levels, pyrimethamine most potently suppressed the growth of H460 cells, which express high levels of DX2 (GI50 = 0.01 µM). An immunoblot assay in H460 cells showed that pyrimethamine decreased the DX2 level dose-dependently but did not affect the AIMP2 level. Further experiments confirmed that pyrimethamine resulted in ubiquitination-mediated DX2 degradation. In an in vivo mouse xenograft assay using H460 cells, intraperitoneal administration of pyrimethamine significantly reduced the tumor size and weight, comparable with the effects of taxol, without affecting body weight. Analysis of tumor tissue showed a considerably high concentration of pyrimethamine with a decreased levels of DX2. These results suggest that pyrimethamine, currently used as anti-parasite drug, could be repurposed to treat lung cancer patients expressing high level of DX2.

Purification and biophysical characterization of the AIMP2-DX2 protein.

Besides their primary role in protein synthesis, aminoacyl-tRNA synthetases (AARSs) are involved in several non-canonical processes such as apoptosis, inflammation and angiogenesis through their interactions with various cellular proteins. Nine of these AARSs interact with three aminoacyl-tRNA synthetase interacting multifunctional proteins (AIMPs), forming a multi-synthetase complex (MSC) in eukaryotes. Among the three AIMPs, AIMP2 is involved in controlling cell proliferation and apoptosis. However, a splicing variant of AIMP2 lacking exon 2, referred to as AIMP2-DX2, is oncogenic and compromises the pro-apoptotic activity of AIMP2 by competing with it for p53 and TRAF2. AIMP2-DX2 is also an inhibitor of p14arf activity. Thus, there is a pressing need for structural insight into the oncogenic role of AIMP2-DX2. In this study, we expressed and purified human AIMP2-DX2 using a SUMO tag to more than 95% purity and a yield of 10 mg/L. We have used size exclusion chromatography, glutaraldehyde cross-linking, dynamic light scattering and nuclear magnetic resonance spectroscopy to characterize its biophysical properties. These data indicate monomer-dimer equilibrium of AIMP2-DX2 in solution. These results form the basis for the structure-function study of oncogenic AIMP2-DX2.

Promiscuous methionyl-tRNA synthetase mediates adaptive mistranslation to protect cells against oxidative stress.

Aminoacyl-tRNA synthetases (ARSs) acylate transfer (t)RNAs with amino acids. Charging tRNAs with the right amino acids is the first step in translation; therefore, the accurate and error-free functioning of ARSs is an essential prerequisite for translational fidelity. A recent study found that methionine (Met) can be incorporated into non-Met residues of proteins through methionylation of non-cognate tRNAs under conditions of oxidative stress. However, it was not understood how this mis-methionylation is achieved. Here, we report that methionyl-tRNA synthetase (MRS) is phosphorylated at Ser209 and Ser825 by extracellular signal-related kinase (ERK1/2) under conditions of stress caused by reactive oxygen species (ROS), and that this phosphorylated MRS shows increased affinity for non-cognate tRNAs with lower affinity for tRNA(Met), leading to an increase in Met residues in cellular proteins. The expression of a mutant MRS containing the substitutions S209D and S825D, mimicking dual phosphorylation, reduced ROS levels and cell death. This controlled inaccuracy of MRS seems to serve as a defense mechanism against ROS-mediated damage at the cost of translational fidelity.

Chemical inhibition of prometastatic lysyl-tRNA synthetase-laminin receptor interaction.

Lysyl-tRNA synthetase (KRS), a protein synthesis enzyme in the cytosol, relocates to the plasma membrane after a laminin signal and stabilizes a 67-kDa laminin receptor (67LR) that is implicated in cancer metastasis; however, its potential as an antimetastatic therapeutic target has not been explored. We found that the small compound BC-K-YH16899, which binds KRS, impinged on the interaction of KRS with 67LR and suppressed metastasis in three different mouse models. The compound inhibited the KRS-67LR interaction in two ways. First, it directly blocked the association between KRS and 67LR. Second, it suppressed the dynamic movement of the N-terminal extension of KRS and reduced membrane localization of KRS. However, it did not affect the catalytic activity of KRS. Our results suggest that specific modulation of a cancer-related KRS-67LR interaction may offer a way to control metastasis while avoiding the toxicities associated with inhibition of the normal functions of KRS.

Identification of CD23 as a functional receptor for the proinflammatory cytokine AIMP1/p43.

Aminoacyl-tRNA-synthetase-interacting multifunctional protein 1 (AIMP1/p43) can be secreted to trigger proinflammatory molecules while it is predominantly bound to a cytoplasmic macromolecular protein complex that contains several different aminoacyl-tRNA synthetases. Although its activities as a secreted signaling factor have been well characterized, the functional receptor for its proinflammatory activity has not yet identified. In this study, we have identified the receptor molecule for AIMP1 that mediates the secretion of TNF-α from THP-1 monocytic cells and primary human peripheral blood mononuclear cells (PBMCs). In a screen of 499 soluble receptors we identified CD23, a known low-affinity receptor for IgE, as a high affinity binding partner of AIMP1. We found that downregulation of CD23 attenuated AIMP1-induced TNF-α secretion and AIMP1 binding to THP-1 and PBMCs. We also observed that in THP-1 and PBMCs, AIMP1-induced TNF-α secretion, mediated by CD23, involved activation of ERK1/2. Interestingly, endothelial monocyte activating polypeptide II (EMAP II), the C-terminal fragment of AIMP1 that is also known to work as a proinflammatory cytokine, was incapable of binding to CD23 and of activating ERK1/2. Therefore, identification of CD23 not only explains the inflammatory function of AIMP1 but also provides the first evidence by which the mode of action of AIMP1 can be distinguished from that of its C-terminal domain, EMAP II.

Chemical suppression of an oncogenic splicing variant of AIMP2 induces tumour regression.

AIMP2 (aminoacyl-tRNA synthetase-interacting multifunctional protein 2) is a potent tumour suppressor that induces apoptosis in response to various oncogenic signals. AIMP2-DX2, an exon2-deleted splicing variant of AIMP2, is up-regulated in lung cancer and competitively suppresses the pro-apoptotic activity of AIMP2, resulting in tumorigenesis. In the present study we report that BC-DXI01, a synthetic compound, specifically reduces the cellular levels of AIMP2-DX2 through selective degradation of the AIMP2-DX2 mRNA transcript. We found that BC-DXI01-mediated cell death positively correlates with AIMP2-DX2 expression in the lung cancer cell lines tested. Administration of BC-DXI01 in a AIMP2-DX2-driven tumour xenograft mice model led to reduced tumour sizes and volumes of up to 60% in comparison with vehicle-treated mice group, consistent with decreases in AIMP2-DX2 transcript and protein levels. Taken together, our findings suggest that tumorigenic activity of AIMP2-DX2 can be controlled by the small chemical BC-DXI01, which can selectively suppress the AIMP2-DX2 mRNA transcript.

Cancer-associated splicing variant of tumor suppressor AIMP2/p38: pathological implication in tumorigenesis.

Although ARS-interacting multifunctional protein 2 (AIMP2, also named as MSC p38) was first found as a component for a macromolecular tRNA synthetase complex, it was recently discovered to dissociate from the complex and work as a potent tumor suppressor. Upon DNA damage, AIMP2 promotes apoptosis through the protective interaction with p53. However, it was not demonstrated whether AIMP2 was indeed pathologically linked to human cancer. In this work, we found that a splicing variant of AIMP2 lacking exon 2 (AIMP2-DX2) is highly expressed by alternative splicing in human lung cancer cells and patient's tissues. AIMP2-DX2 compromised pro-apoptotic activity of normal AIMP2 through the competitive binding to p53. The cells with higher level of AIMP2-DX2 showed higher propensity to form anchorage-independent colonies and increased resistance to cell death. Mice constitutively expressing this variant showed increased susceptibility to carcinogen-induced lung tumorigenesis. The expression ratio of AIMP2-DX2 to normal AIMP2 was increased according to lung cancer stage and showed a positive correlation with the survival of patients. Thus, this work identified an oncogenic splicing variant of a tumor suppressor, AIMP2/p38, and suggests its potential for anti-cancer target.

Crystal structure of human cytosolic aspartyl-tRNA synthetase, a component of multi-tRNA synthetase complex.

Human cytosolic aspartyl-tRNA synthetase (DRS) catalyzes the attachment of the amino acid aspartic acid to its cognate tRNA and it is a component of the multi-tRNA synthetase complex (MSC) which has been known to be involved in unexpected signaling pathways. Here, we report the crystal structure of DRS at a resolution of 2.25 Å. DRS is a homodimer with a dimer interface of 3750.5 Å(2) which comprises 16.6% of the monomeric surface area. Our structure reveals the C-terminal end of the N-helix which is considered as a unique addition in DRS, and its conformation further supports the switching model of the N-helix for the transfer of tRNA(Asp) to elongation factor 1α. From our analyses of the crystal structure and post-translational modification of DRS, we suggest that the phosphorylation of Ser146 provokes the separation of DRS from the MSC and provides the binding site for an interaction partner with unforeseen functions.

Interaction of two translational components, lysyl-tRNA synthetase and p40/37LRP, in plasma membrane promotes laminin-dependent cell migration.

Although human lysyl-tRNA synthetase (KRS), an enzyme for protein synthesis, is often highly expressed in various cancer cells, its pathophysiological implications have not been understood. Here we found that KRS induces cancer cell migration through interaction with the 67-kDa laminin receptor (67LR) that is converted from ribosomal subunit p40. On laminin signal, KRS was phosphorylated at the T52 residue by p38MAPK and dissociated from the cytosolic multi-tRNA synthetase complex for membrane translocation. The importance of T52 phosphorylation for membrane translocation of KRS was confirmed by site-directed mutagenesis. In the membrane, turnover of 67LR was controlled by Nedd4-mediated ubiquitination, and KRS inhibited ubiquitin-dependent degradation of 67LR, thereby enhancing laminin-induced cell migration. This work thus unveiled a unique function of KRS in the control of cell migration and its pathological implication in metastasis.

AIMP2-DX2 provides therapeutic interface to control KRAS-driven tumorigenesis.

Recent development of the chemical inhibitors specific to oncogenic KRAS (Kirsten Rat Sarcoma 2 Viral Oncogene Homolog) mutants revives much interest to control KRAS-driven cancers. Here, we report that AIMP2-DX2, a variant of the tumor suppressor AIMP2 (aminoacyl-tRNA synthetase-interacting multi-functional protein 2), acts as a cancer-specific regulator of KRAS stability, augmenting KRAS-driven tumorigenesis. AIMP2-DX2 specifically binds to the hypervariable region and G-domain of KRAS in the cytosol prior to farnesylation. Then, AIMP2-DX2 competitively blocks the access of Smurf2 (SMAD Ubiquitination Regulatory Factor 2) to KRAS, thus preventing ubiquitin-mediated degradation. Moreover, AIMP2-DX2 levels are positively correlated with KRAS levels in colon and lung cancer cell lines and tissues. We also identified a small molecule that specifically bound to the KRAS-binding region of AIMP2-DX2 and inhibited the interaction between these two factors. Treatment with this compound reduces the cellular levels of KRAS, leading to the suppression of KRAS-dependent cancer cell growth in vitro and in vivo. These results suggest the interface of AIMP2-DX2 and KRAS as a route to control KRAS-driven cancers.

2-Aminophenylpyrimidines as Novel Inhibitors of Aminoacyl-tRNA Synthetase Interacting Multifunctional Protein 2 (AIMP2)-DX2 for Lung Cancer Treatment.

Aminoacyl-tRNA synthetase interacting multifunctional proteins (AIMPs) have recently been considered novel therapeutic targets in several cancers. In this publication we report the development of novel 2-aminophenylpyrimidines as new AIMP2-DX2 inhibitors. In particular, aminophenylpyrimidine 3 not only exhibited promising in vitro and in vivo potency but also exerted selective inhibition of H460 and A549 cells and AIMP2-DX2 rather than WI-26 cells and AIMP2. Aminophenylpyrimidine 3 offers possible therapeutic potential in the treatment of lung cancer.

Synthesis and Structure-Activity Relationships of Arylsulfonamides as AIMP2-DX2 Inhibitors for the Development of a Novel Anticancer Therapy.

AIMP2-DX2, a splicing variant of AIMP2, is up-regulated in lung cancer, possesses oncogenic activity, and results in tumorigenesis. Specifically inhibiting the interaction between AIMP2-DX2 and HSP70 to suppress AIMP2-DX2-dependent cancers with small molecules is considered a promising avenue for cancer therapeutics. Optimization of hit BC-DXI-04 (IC50 = 40.1 µM) provided new potent sulfonamide based AIMP2-DX2 inhibitors. Among these, BC-DXI-843 showed improved inhibition against AIMP2-DX2 (IC50 = 0.92 µM) with more than 100-fold selectivity over AIMP2 in a luciferase assay. Several binding assays indicated that this compound effectively induces cancer cell apoptosis by specifically interrupting the interaction between DX2 and HSP70, which leads to the degradation of DX2 via Siah1-mediated ubiquitination. More importantly, BC-DXI-843 demonstrated in vivo efficacy in a tumor xenograft mouse model (H460 cells) at a dosage of 50 mg/kg, suggesting it as a promising lead for development of novel therapeutics targeting AIMP2-DX2 in lung cancer.

An Isoform of the Oncogenic Splice Variant AIMP2-DX2 Detected by a Novel Monoclonal Antibody.

AIMP2-DX2, an exon 2-deleted splice variant of AIMP2 (aminoacyl-tRNA synthetase-interacting multifunctional protein 2), is highly expressed in lung cancer and involved in tumor progression in vivo. Oncogenic function of AIMP2-DX2 and its correlation with poor prognosis of cancer patients have been well established; however, the application of this potentially important biomarker to cancer research and diagnosis has been hampered by a lack of antibodies specific for the splice variant, possibly due to the poor immunogenicity and/or stability of AIMP2-DX2. In this study a monoclonal antibody, H5, that specifically recognizes AIMP2-DX2 and its isoforms was generated via rabbit immunization and phage display techniques, using a short peptide corresponding to the exon 1/3 junction sequence as an antigen. Furthermore, based on mutagenesis, limited cleavage, and mass spectrometry studies, it is also suggested that the endogenous isoform of AIMP2-DX2 recognized by H5 is produced by proteolytic cleavage of 33 amino acids from N-terminus and is capable of inducing cell proliferation similarly to the uncleaved protein. H5 monoclonal antibody is applicable to enzyme-linked immunosorbent assay, immunoblot, immunofluorescence, and immunohistochemistry, and expected to be a valuable tool for detecting AIMP2-DX2 with high sensitivity and specificity for research and diagnostic purposes.

ERK-dependent phosphorylation of the linker and substrate-binding domain of HSP70 increases folding activity and cell proliferation.

The enhanced productive folding of translated polypeptides by heat shock protein 70 (HSP70) is often required for the survival of cancer cells. Although the folding activity of HSP70 is considered a significant determinant of the progression of cancer cells, it is still unknown how this activity could be regulated. Here, we report that the phosphorylation of HSP70 facilitates its folding activity, enhancing cell proliferation. Mass spectrometry identified the serine residues at positions 385 and 400 in the linker and substrate-binding domains of HSP70, respectively, as sites of phosphorylation mediated by EGF signaling, and this result was further confirmed by site-directed mutagenesis. ERK is known to be a specific kinase. The phosphorylation of the two sites induces the extended conformation of HSP70 via the regulation of the binding of the linker to the nucleotide- and substrate-binding domains, augmenting the binding affinity of HSP70 to substrates and enhancing its folding activity; this ultimately results in pro-proliferative effects. Cell lines harboring activated ERK showed increased phosphorylation of HSP70, and a positive correlation between the phosphorylation of HSP70 and the activity of ERK was observed. Thus, this study demonstrated that the ERK-dependent phosphorylation of HSP70 facilitated its folding activity and cellular proliferative function.

Data on optimization of expression and purification of AIMP2-DX2 protein in Escherichia coli.

AIMP2-DX2 is a splicing variant of AIMP2 protein which has been implicated in human lung cancer and chemoresistance of ovarian cancer (J.W. Choi, D.G. Kim, A.E. Lee, H.R. Kim, J.Y. Lee, N.H. Kwon, et al., 2011; J.W. Choi, J.W. Lee, J.K. Kim, H.K. Jeon, J.J. Choi, D.G. Kim, et al., 2012) [1,2]. We have shown, here, the data for the expression of AIMP2-DX2 protein in Escherichia coli and optimization of the critical steps in purification of AIMP2-DX2. The data described here has been successfully used to get a maximum yield of highly pure AIMP2-DX2 for subsequent characterization of its biophysical property in: "Purification and biophysical characterization of the AIMP2-DX2 protein" (R. Jha, H.Y. Cho, A. Ul Mushtaq, K. Lee, D.G. Kim, S. Kim, et al., 2017) [3].

Suppression of lysyl-tRNA synthetase, KRS, causes incomplete epithelial-mesenchymal transition and ineffective cell­extracellular matrix adhesion for migration.

The cell-adhesion properties of cancer cells can be targeted to block cancer metastasis. Although cytosolic lysyl-tRNA synthetase (KRS) functions in protein synthesis, KRS on the plasma membrane is involved in cancer metastasis. We hypothesized that KRS is involved in cell adhesion-related signal transduction for cellular migration. To test this hypothesis, colon cancer cells with modulated KRS protein levels were analyzed for cell-cell contact and cell-substrate adhesion properties and cellular behavior. Although KRS suppression decreased expression of cell-cell adhesion molecules, cells still formed colonies without being scattered, supporting an incomplete epithelial mesenchymal transition. Noteworthy, KRS-suppressed cells still exhibited focal adhesions on laminin, with Tyr397-phopshorylated focal adhesion kinase (FAK), but they lacked laminin-adhesion-mediated extracellular signal-regulated kinase (ERK) and paxillin activation. KRS, p67LR and integrin α6ß1 were found to interact, presumably to activate ERK for paxillin expression and Tyr118 phosphorylation even without involvement of FAK, so that specific inhibition of ERK or KRS in parental HCT116 cells blocked cell-cell adhesion and cell-substrate properties for focal adhesion formation and signaling activity. Together, these results indicate that KRS can promote cell-cell and cell-ECM adhesion for migration.