AIMP2 Controls Intestinal Stem Cell Compartments and Tumorigenesis by Modulating Wnt/β-Catenin Signaling

Identification and structure of AIMP2-DX2 for therapeutic perspectives

Regulation of cell fate and lung cell differentiation is associated with Aminoacyl-tRNA synthetases (ARS)-interacting multifunctional protein 2 (AIMP2), which acts as a non-enzymatic component required for the multi-tRNA synthetase complex. In response to DNA damage, a component of AIMP2 separates from the multi-tRNA synthetase complex, binds to p53, and prevents its degradation by MDM2, inducing apoptosis. Additionally, AIMP2 reduces proliferation in TGF-β and Wnt pathways, while enhancing apoptotic signaling induced by tumor necrosis factor-β. Given the crucial role of these pathways in tumorigenesis, AIMP2 is expected to function as a broad-spectrum tumor suppressor. The full-length AIMP2 transcript consists of four exons, with a small section of the pre-mRNA undergoing alternative splicing to produce a variant (AIMP2-DX2) lacking the second exon. AIMP2-DX2 binds to FBP, TRAF2, and p53 similarly to AIMP2, but competes with AIMP2 for binding to these target proteins, thereby impairing its tumor-suppressive activity. AIMP2-DX2 is specifically expressed in a diverse range of cancer cells, including breast cancer, liver cancer, bone cancer, and stomach cancer. There is growing interest in AIMP2-DX2 as a promising biomarker for prognosis and diagnosis, with AIMP2-DX2 inhibition attracting significant interest as a potentially effective therapeutic approach for the treatment of lung, ovarian, prostate, and nasopharyngeal cancers. [BMB Reports 2024; 57(7): 318-323].

The 'Not-So-Famous Five' in tumorigenesis: tRNAs, tRNA fragments, and tRNA epitranscriptome in concert with AARSs and AIMPs

RNA profiling studies have revealed that ∼75% of the human genome is transcribed to RNA but only a meagre fraction of it is translated to proteins. Majority of transcribed RNA constitute a specialized pool of non-coding RNAs. Human genome contains approximately 506 genes encoding a set of 51 different tRNAs, constituting a unique class of non-coding RNAs that not only have essential housekeeping functions as translator molecules during protein synthesis, but have numerous uncharted regulatory functions. Intriguing findings regarding a variety of non-canonical functions of tRNAs, tRNA derived fragments (tRFs), esoteric epitranscriptomic modifications of tRNAs, along with aminoacyl-tRNA synthetases (AARSs) and ARS-interacting multifunctional proteins (AIMPs), envision a 'peripheral dogma' controlling the flow of genetic information in the backdrop of qualitative information wrung out of the long-live central dogma of molecular biology, to drive cells towards either proliferation or differentiation programs. Our review will substantiate intriguing peculiarities of tRNA gene clusters, atypical tRNA-transcription from internal promoters catalysed by another distinct RNA polymerase enzyme, dynamically diverse tRNA epitranscriptome, intricate mechanism of tRNA-charging by AARSs governing translation fidelity, epigenetic regulation of gene expression by tRNA fragments, and the role of tRNAs and tRNA derived/associated molecules as quantitative determinants of the functional proteome, covertly orchestrating the process of tumorigenesis, through a deregulated tRNA-ome mediating selective codon-biased translation of cancer related gene transcripts.

AIMP2 restricts EV71 replication by recruiting SMURF2 to promote the degradation of 3D polymerase

Hand, foot and mouth disease (HFMD), mainly caused by enterovirus 71 (EV71), has frequently occurred in the Asia-Pacific region, posing a significant threat to the health of infants and young children. Therefore, research on the infection mechanism and pathogenicity of enteroviruses is increasingly becoming important. The 3D polymerase, as the most critical RNA-dependent RNA polymerase (RdRp) for EV71 replication, is widely targeted to inhibit EV71 infection. In this study, we identified a novel host protein, AIMP2, capable of binding to 3D polymerase and inhibiting EV71 infection. Subsequent investigations revealed that AIMP2 recruits the E3 ligase SMURF2, which mediates the polyubiquitination and degradation of 3D polymerase. Furthermore, the antiviral effect of AIMP2 extended to the CVA16 and CVB1 serotypes. Our research has uncovered the dynamic regulatory function of AIMP2 during EV71 infection, revealing a novel antiviral mechanism and providing new insights for the development of antienteroviral therapeutic strategies.

A bioactive calcium silicate nanowire-containing hydrogel for organoid formation and functionalization

Organoids, which are 3D multicellular constructs, have garnered significant attention in recent years. Existing organoid culture methods predominantly utilize natural and synthetic polymeric hydrogels. This study explored the potential of a composite hydrogel mainly consisting of calcium silicate (CS) nanowires and methacrylated gelatin (GelMA) as a substrate for organoid formation and functionalization, specifically for intestinal and liver organoids. Furthermore, the research delved into the mechanisms by which CS nanowires promote the structure formation and development of organoids. It was discovered that CS nanowires can influence the stiffness of the hydrogel, thereby regulating the expression of the mechanosensory factor yes-associated protein (YAP). Additionally, the bioactive ions released by CS nanowires in the culture medium could accelerate Wnt/β-catenin signaling, further stimulating organoid development. Moreover, bioactive ions were found to enhance the nutrient absorption and ATP metabolic activity of intestinal organoids. Overall, the CS/GelMA composite hydrogel proves to be a promising substrate for organoid formation and development. This research suggested that inorganic biomaterials hold significant potential in organoid research, offering bioactivities, biosafety, and cost-effectiveness.

Pan-cancer Analysis Identifies AIMP2 as a Potential Biomarker for Breast Cancer

Introduction

Aminoacyl tRNA synthetase complex interacting with multifunctional protein 2 (AIMP2) is a significant regulator of cell proliferation and apoptosis. Despite its abnormal expression in various tumor types, the specific functions and effects of AIMP2 on tumor immune cell infiltration, proliferation, and migration remain unclear.

Materials and Methods

To assess AIMP2's role in tumor immunity, we conducted a pan-cancer multi-database analysis using the Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), and Cancer Cell Lines Encyclopedia (CCLE) datasets, examining expression levels, prognosis, tumor progression, and immune microenvironment. Additionally, we investigated AIMP2's impact on breast cancer (BRCA) proliferation and migration using cell counting kit 8 (CCK-8) assay, transwell assays, and western blot analysis.

Results

Our findings revealed that AIMP2 was overexpressed in 24 tumor tissue types compared to normal tissue and was associated with four tumor stages. Survival analysis indicated that AIMP2 expression was strongly correlated with overall survival (OS) in certain cancer patients, with high AIMP2 expression linked to poorer prognosis in five cancer types.

Conclusion

Finally, siRNA-mediated AIMP2 knockdown inhibited BRCA cell proliferation and migration in vitro. In conclusion, our pan-cancer analysis suggests that AIMP2 may play a crucial role in tumor immunity and could serve as a potential prognostic marker, particularly in BRCA.

Molecular regulation after mucosal injury and regeneration in ulcerative colitis

Ulcerative colitis (UC) is a chronic nonspecific inflammatory disease with a complex etiology. Intestinal mucosal injury is an important pathological change in individuals with UC. Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5+) intestinal stem cells (ISCs) exhibit self-renewal and high differentiation potential and play important roles in the repair of intestinal mucosal injury. Moreover, LGR5+ ISCs are intricately regulated by both the Wnt/β-catenin and Notch signaling pathways, which jointly maintain the function of LGR5+ ISCs. Combination therapy targeting multiple signaling pathways and transplantation of LGR5+ ISCs may lead to the development of new clinical therapies for UC.

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.

Direct targeting of oncogenic KRAS activity is a challenge. Here the authors report that a splice variant of AIMP2, AIMP2-DX2, enhances KRAS stability by blocking ubiquitin-mediated degradation of KRAS via the E3 ligase, Smurf2, and identify a chemical that can hinder AIMP2-DX2 from interacting with KRAS.

Aminoacyl-tRNA synthetases of the multi-tRNA synthetase complex and their role in tumorigenesis

In mammalian cells, 20 aminoacyl-tRNA synthetases (AARS) catalyze the ligation of amino acids to their cognate tRNAs to generate aminoacylated-tRNAs. In higher eukaryotes, 9 of the 20 AARSs, along with 3 auxiliary proteins, join to form the cytoplasmic multi-tRNA synthetase complex (MSC). The complex is absent in prokaryotes, but evolutionary expansion of MSC constituents, primarily by addition of novel interacting domains, facilitates formation of subcomplexes that join to establish the holo-MSC. In some cases, environmental cues direct the release of constituents from the MSC which enables the execution of non-canonical, i.e., "moonlighting", functions distinct from their essential activities in protein translation. These activities are generally beneficial, but can also be deleterious to the cell. Elucidation of the non-canonical activities of several AARSs residing in the MSC suggest they are potential therapeutic targets for cancer, as well as metabolic and neurologic diseases. Here, we describe the role of MSC-resident AARSs in cancer progression, and the factors that regulate their release from the MSC. Also, we highlight recent developments in therapeutic modalities that target MSC AARSs for cancer prevention and treatment.

tRNA Metabolism and Lung Cancer: Beyond Translation

Lung cancer, one of the most malignant tumors, has extremely high morbidity and mortality, posing a serious threat to global health. It is an urgent need to fully understand the pathogenesis of lung cancer and provide new ideas for its treatment. Interestingly, accumulating evidence has identified that transfer RNAs (tRNAs) and tRNA metabolism–associated enzymes not only participate in the protein translation but also play an important role in the occurrence and development of lung cancer. In this review, we summarize the different aspects of tRNA metabolism in lung cancer, such as tRNA transcription and mutation, tRNA molecules and derivatives, tRNA-modifying enzymes, and aminoacyl-tRNA synthetases (ARSs), aiming at a better understanding of the pathogenesis of lung cancer and providing new therapeutic strategies for it.

Allosteric Inhibition of the Tumor-Promoting Interaction between AIMP2-DX2 and HSP70

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 AIMP2-DX2 and 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 (NFR) 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.

Biology of the mRNA Splicing Machinery and Its Dysregulation in Cancer Providing Therapeutic Opportunities

Dysregulation of messenger RNA (mRNA) processing—in particular mRNA splicing—is a hallmark of cancer. Compared to normal cells, cancer cells frequently present aberrant mRNA splicing, which promotes cancer progression and treatment resistance. This hallmark provides opportunities for developing new targeted cancer treatments. Splicing of precursor mRNA into mature mRNA is executed by a dynamic complex of proteins and small RNAs called the spliceosome. Spliceosomes are part of the supraspliceosome, a macromolecular structure where all co-transcriptional mRNA processing activities in the cell nucleus are coordinated. Here we review the biology of the mRNA splicing machinery in the context of other mRNA processing activities in the supraspliceosome and present current knowledge of its dysregulation in lung cancer. In addition, we review investigations to discover therapeutic targets in the spliceosome and give an overview of inhibitors and modulators of the mRNA splicing process identified so far. Together, this provides insight into the value of targeting the spliceosome as a possible new treatment for lung cancer.

TRIP13 promotes metastasis of colorectal cancer regardless of p53 and microsatellite instability status

Overexpression of TRIP13, a member of the AAA-ATPase family, is linked with various cancers, but its role in metastasis is unknown in colorectal cancer (CRC). In the current study, we investigated the role TRIP13 in experimental metastasis and its involvement in regulation of WNT/β-catenin and EGFR signaling pathways. Evaluation of formalin-fixed paraffin-embedded (FFPE) and frozen tissues of adenomas and CRCs, along with their corresponding normal samples, showed that TRIP13 was gradually increased in its phenotypic expression from adenoma to carcinoma and that its overexpression in CRCs was independent of patient's gender, age, race/ethnicity, pathologic stage, and p53 and microsatellite instability (MSI) status. Moreover, liver metastases of CRCs showed TRIP13 overexpression as compared to matched adjacent liver tissues, indicating the biological relevance of TRIP13 in CRC progression and metastasis. TRIP13 knockdown impeded colony formation, invasion, motility, and spheroid-forming capacity of CRC cells irrespective of their p53 and MSI status. Furthermore, xenograft studies demonstrated high expression of TRIP13 contributed to tumor growth and metastasis. Depletion of TRIP13 in CRC cells decreased metastasis and it was independent of the p53 and MSI status. Furthermore, TRIP13 interacted with a tyrosine kinase, FGFR4; this interaction could be essential for activation of the EGFR-AKT pathway. In addition, we demonstrated the involvement of TRIP13 in the Wnt signaling pathway and in the epithelial-mesenchymal transition. Cell-based assays revealed that miR-192 and PNPT1 regulate TRIP13 expression in CRC. Additionally, RNA sequencing of CRC cells with TRIP13 knockdown identified COL6A3, TREM2, SHC3, and KLK7 as downstream targets that may have functional relevance in TRIP13-mediated tumor growth and metastasis. In summary, our results demonstrated that TRIP13 promotes tumor growth and metastasis regardless of p53 and MSI status, and indicated that it is a target for therapy of CRC.

Recent Development of Aminoacyl-tRNA Synthetase Inhibitors for Human Diseases: A Future Perspective

Aminoacyl-tRNA synthetases (ARSs) are essential enzymes that ligate amino acids to tRNAs and translate the genetic code during protein synthesis. Their function in pathogen-derived infectious diseases has been well established, which has led to the development of small molecule therapeutics. The applicability of ARS inhibitors for other human diseases, such as fibrosis, has recently been explored in the clinical setting. There are active studies to find small molecule therapeutics for cancers. Studies on central nervous system (CNS) disorders are burgeoning as well. In this regard, we present a concise analysis of the recent development of ARS inhibitors based on small molecules from the discovery research stage to clinical studies as well as a recent patent analysis from the medicinal chemistry point of view.

Roles of Aminoacyl-tRNA Synthetases in Cancer

Aminoacyl-tRNA synthetases (ARSs) catalyze the ligation of amino acids to their cognate transfer RNAs (tRNAs), thus playing an important role in protein synthesis. In eukaryotic cells, these enzymes exist in free form or in the form of multi-tRNA synthetase complex (MSC). The latter contains nine cytoplasmic ARSs and three ARS-interacting multifunctional proteins (AIMPs). Normally, ARSs and AIMPs are regarded as housekeeping molecules without additional functions. However, a growing number of studies indicate that ARSs are involved in a variety of physiological and pathological processes, especially tumorigenesis. Here, we introduce the roles of ARSs and AIMPs in certain cancers, such as colon cancer, lung cancer, breast cancer, gastric cancer and pancreatic cancer. Furthermore, we particularly focus on their potential clinical applications in cancer, aiming at providing new insights into the pathogenesis and treatment of cancer.

Single-cell analysis of AIMP2 splice variants informs on drug sensitivity and prognosis in hematologic cancer

Aminoacyl-tRNA synthetase-interacting multifunctional protein 2 (AIMP2) is a non-enzymatic component required for the multi-tRNA synthetase complex. While exon 2 skipping alternatively spliced variant of AIMP2 (AIMP2-DX2) compromises AIMP2 activity and is associated with carcinogenesis, its clinical potential awaits further validation. Here, we found that AIMP2-DX2/AIMP2 expression ratio is strongly correlated with major cancer signaling pathways and poor prognosis, particularly in acute myeloid leukemia (AML). Analysis of a clinical patient cohort revealed that AIMP2-DX2 positive AML patients show decreased overall survival and progression-free survival. We also developed targeted RNA-sequencing and single-molecule RNA-FISH tools to quantitatively analyze AIMP2-DX2/AIMP2 ratios at the single-cell level. By subclassifying hematologic cancer cells based on their AIMP2-DX2/AIMP2 ratios, we found that downregulating AIMP2-DX2 sensitizes cells to anticancer drugs only for a subgroup of cells while it has adverse effects on others. Collectively, our study establishes AIMP2-DX2 as a potential biomarker and a therapeutic target for hematologic cancer.

Ku, Kim et al develop a method to analyse the ratio of the alternatively spliced variant of AIMP2 to full length AIMP via single-molecule RNA-FISH. They can subclassify hematologic cancer based on AIMP2-DX2/AIMP2 ratio and find that cells with high AIMP2-DX2 ratio can be sensitized to chemotherapy drugs by depleting AIMP2-DX2.

Aminoacyl-tRNA synthetases

The aminoacyl-tRNA synthetases are an essential and universally distributed family of enzymes that plays a critical role in protein synthesis, pairing tRNAs with their cognate amino acids for decoding mRNAs according to the genetic code. Synthetases help to ensure accurate translation of the genetic code by using both highly accurate cognate substrate recognition and stringent proofreading of noncognate products. While alterations in the quality control mechanisms of synthetases are generally detrimental to cellular viability, recent studies suggest that in some instances such changes facilitate adaption to stress conditions. Beyond their central role in translation, synthetases are also emerging as key players in an increasing number of other cellular processes, with far-reaching consequences in health and disease. The biochemical versatility of the synthetases has also proven pivotal in efforts to expand the genetic code, further emphasizing the wide-ranging roles of the aminoacyl-tRNA synthetase family in synthetic and natural biology.

Roles of aminoacyl-tRNA synthetase-interacting multi-functional proteins in physiology and cancer

Aminoacyl-tRNA synthetases (ARSs) are an important class of enzymes with an evolutionarily conserved mechanism for protein synthesis. In higher eukaryotic systems, eight ARSs and three ARS-interacting multi-functional proteins (AIMPs) form a multi-tRNA synthetase complex (MSC), which seems to contribute to cellular homeostasis. Of these, AIMPs are generally considered as non-enzyme factors, playing a scaffolding role during MSC assembly. Although the functions of AIMPs are not fully understood, increasing evidence indicates that these scaffold proteins usually exert tumor-suppressive activities. In addition, endothelial monocyte-activating polypeptide II (EMAP II), as a cleavage product of AIMP1, and AIMP2-DX2, as a splice variant of AIMP2 lacking exon 2, also have a pivotal role in regulating tumorigenesis. In this review, we summarize the biological functions of AIMP1, EMAP II, AIMP2, AIMP2-DX2, and AIMP3. Also, we systematically introduce their emerging roles in cancer, aiming to provide new ideas for the treatment of 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.

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.

Structures and functions of multi-tRNA synthetase complexes

Human body is a finely-tuned machine that requires homeostatic balance based on systemically controlled biological processes involving DNA replication, transcription, translation, and energy metabolism. Ubiquitously expressed aminoacyl-tRNA synthetases have been investigated for many decades, and they act as cross-over mediators of important biological processes. In particular, a cytoplasmic multi-tRNA synthetase complex (MSC) appears to be a central machinery controlling the complexity of biological systems. The structural integrity of MSC determined by the associated components is correlated with increasing biological complexity that links to system development in higher organisms. Although the role of the MSCs is still unclear, this chapter describes the current knowledge on MSC components that are associated with and regulate functions beyond their catalytic activities with focus on human MSC.

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.

PRMT1 regulates the tumour-initiating properties of esophageal squamous cell carcinoma through histone H4 arginine methylation coupled with transcriptional activation

Esophageal squamous cell carcinoma (ESCC) is the most difficult subtype of esophageal cancer to treat due to a paucity of effective targeted therapy. ESCC is believed to arise from tumour initiating cells (TICs), which contribute to metastasis and chemoresistance. In this study, we found that Protein arginine methyltransferase 1(PRMT1) was highly expressed in ESCCs and associated with aberrant clinicopathological characteristics of ESCC patients. In ESCC specimens, the elevated expression of PRMT1 and OV6 was significantly associated with histologic grade, TNM stage and poor patient prognosis. Moreover, overexpression of PRMT1 was observed in esophageal TICs purified by magnetic sorting of adherent and spheroid ECA109/TE1 cells. The increased level of PRMT1 in TICs facilitated the expression of TIC markers, stem cell-like properties, resistance to chemotherapy, tumorigenicity and increased their percentages in ECSS samples. Conversely, knockdown of PRMT1 significantly diminished the self-renewal properties of ESCC. Moreover, we show that PRMT1 can catalyse histone H4R3 asymmetric dimethylation and promote transcription activation of down-stream genes. Further RNA-Seq transcriptome analysis reveals that overexpression of PRMT1 in ESCC cell lines activates Wnt/β-catenin and Notch signaling pathway. Together, our studies highlight that PRMT1 activates and maintains esophageal TICs by mediating transcription alteration through histone H4 arginine methylation.

Evolution of the multi-tRNA synthetase complex and its role in cancer

Aminoacyl-tRNA synthetases (ARSs) are enzymes that ligate their cognate amino acids to tRNAs for protein synthesis. However, recent studies have shown that their functions are expanded beyond protein synthesis through the interactions with diverse cellular factors. In this review, we discuss how ARSs have evolved to expand and control their functions by forming protein assemblies. We particularly focus on a macromolecular ARS complex in eukaryotes, named multi-tRNA synthetase complex (MSC), which is proposed to provide a channel through which tRNAs reach bound ARSs to receive their cognate amino acid and transit further to the translation machinery. Approximately half of the ARSs assemble into the MSC through cis-acting noncatalytic domains attached to their catalytic domains and trans-acting factors. Evolution of the MSC included its functional expansion, during which the MSC interaction network was augmented by additional cellular pathways present in higher eukaryotes. We also discuss MSC components that could be functionally involved in the pathophysiology of tumorigenesis. For example, the activities of some trans-acting factors have tumor-suppressing effects or maintain DNA integrity and are functionally compromised in cancer. On the basis of Gene Ontology analyses, we propose that the regulatory activities of the MSC-associated ARSs mainly converge on five biological processes, including mammalian target of rapamycin (mTOR) and DNA repair pathways. Future studies are needed to investigate how the MSC-associated and free-ARSs interact with each other and other factors in the control of multiple cellular pathways, and how aberrant or disrupted interactions in the MSC can cause disease.

Jade family PHD finger 3 (JADE3) increases cancer stem cell-like properties and tumorigenicity in colon cancer

Jade family PHD finger 3 (JADE3) plays a role in inducing histone acetylation during transcription, and is involved in the progression of several human cancers; however, its role in colon cancer remains unclear. Herein, we found that JADE3 was markedly upregulated in colon cancer tissues and significantly correlated with cancer progression, and predicted shorter patient survival. Further, JADE3 was expressed much higher in colon cancer cell lines that are enriched with a stem-like signature. Overexpression of JADE3 increased, while silencing JADE3 reduced cancer stem cell-like traits in colon cancer cells in vitro and in vivo. Importantly, silencing of JADE3 strongly impaired the tumor initiating capacity of colon cancer cells in vivo. Furthermore, JADE3 interacted with the promoters of colon stem cell marker LGR5 and activated its transcription, by increasing the occupancy of p300 acetyltransferase and histone acetylation on the promoters. Finally, we found that JADE3 expression was substantially induced by Wnt/β-catenin signaling. These findings suggest an oncogenic role of JADE3 by regulating cancer stem cell-like traits in the colon cancer, and therefore JADE3 might be a potential therapeutic target for the treatment of colon cancer.

Long noncoding RNA MEG3 suppresses liver cancer cells growth through inhibiting β-catenin by activating PKM2 and inactivating PTEN

Maternally expressed gene 3 (MEG3) encodes an lncRNA which is suggested to function as a tumor suppressor and has been showed to involve in a variety of cancers. Herein, our findings demonstrate that MEG3 inhibits the malignant progression of liver cancer cells in vitro and in vivo. Mechanistically, MEG3 promotes the expression and maturition of miR122 which targets PKM2. Therefore, MEG3 decreases the expression and nuclear location of PKM2 dependent on miR122. Furthermore, MEG3 also inhibits CyclinD1 and C-Myc via PKM2 in liver cancer cells. On the other hand, MEG3 promotes β-catenin degradation through ubiquitin-proteasome system dependent on PTEN. Strikingly, MEG3 inhibits β-catenin activity through PKM2 reduction and PTEN increase. Significantly, we also found that excessive β-catenin abrogated the effect of MEG3 in liver cancer. In conclusion, our study for the first time demonstrates that MEG3 acts as a tumor suppressor by negatively regulating the activity of the PKM2 and β-catenin signaling pathway in hepatocarcinogenesis and could provide potential therapeutic targets for the treatment of liver cancer.

Ratio of Autoantibodies of Tumor Suppressor AIMP2 and Its Oncogenic Variant Is Associated with Clinical Outcome in Lung Cancer

Aminoacyl-tRNA synthetase-interacting multi-functional protein 2 (AIMP2) works as potent tumor suppressor, while its splicing variant lacking exon 2 (AIMP2-DX2) competes with AIMP2 for binding to target proteins and compromises its anti-tumor activity. Assuming that AIMP2 and its variant AIMP2-DX2 could be released out to human sera in pathological condition, we investigated the diagnostic and prognostic usefulness of autoantibodies against AIMP2 and AIMP2-DX2 by measuring their serum levels in 80 normal and lung cancer samples that were matched in age, gender and smoking status. The area under the curve of AIMP2-DX2, AIMP2, and AIMP2-DX2/AIMP2 autoantibody ratio was low (0.416, 0.579, and 0.357, respectively), suggesting limited diagnostic value. A total of 165 lung cancer patients were classified into low and high AIMP2-DX2, AIMP2, and AIMP2-DX2/AIMP2 based on the median expression of each parameter. The high AIMP2-DX2 group was older and had larger tumors (>3 cm) than the low AIMP2-DX2 group. The high AIMP2-DX2/AIMP2 group had higher CYFRA-21 levels and significantly shorter overall survival than the low AIMP2-DX2/AIMP2 group (18.6 vs. 48.9 months, P = 0.021, Log Rank Test). Taken together, autoantibodies against AIMP2-DX2 and AIMP2 are detectable in the human blood and the increased ratio of AIMP2-DX2/AIMP2 is related to poor clinical outcome of lung cancer.

Retinol Promotes In Vitro Growth of Proximal Colon Organoids through a Retinoic Acid-Independent Mechanism

Retinol (ROL), the alcohol form of vitamin A, is known to control cell fate decision of various types of stem cells in the form of its active metabolite, retinoic acid (RA). However, little is known about whether ROL has regulatory effects on colonic stem cells. We examined in this study the effect of ROL on the growth of murine normal colonic cells cultured as organoids. As genes involved in RA synthesis from ROL were differentially expressed along the length of the colon, we tested the effect of ROL on proximal and distal colon organoids separately. We found that organoid forming efficiency and the expression level of Lgr5, a marker gene for colonic stem cells were significantly enhanced by ROL in the proximal colon organoids, but not in the distal ones. Interestingly, neither retinaldehyde (RAL), an intermediate product of the ROL-RA pathway, nor RA exhibited growth promoting effects on the proximal colon organoids, suggesting that ROL-dependent growth enhancement in organoids involves an RA-independent mechanism. This was confirmed by the observation that an inhibitor for RA-mediated gene transcription did not abrogate the effect of ROL on organoids. This novel role of ROL in stem cell maintenance in the proximal colon provides insights into the mechanism of region-specific regulation for colonic stem cell maintenance.