AIMP1 regulates TCR signaling and induces differentiation of regulatory T cells by interfering with lipid raft association

The mARS complex: a critical mediator of immune regulation and homeostasis

Over the course of evolution, many proteins have undergone adaptive structural changes to meet the increasing homeostatic regulatory demands of multicellularity. Aminoacyl tRNA synthetases (aaRS), enzymes that catalyze the attachment of each amino acid to its cognate tRNA, are such proteins that have acquired new domains and motifs that enable non-canonical functions. Through these new domains and motifs, aaRS can assemble into large, multi-subunit complexes that enhance the efficiency of many biological functions. Moreover, because the complexity of multi-aminoacyl tRNA synthetase (mARS) complexes increases with the corresponding complexity of higher eukaryotes, a contribution to regulation of homeostatic functions in multicellular organisms is hypothesized. While mARS complexes in lower eukaryotes may enhance efficiency of aminoacylation, little evidence exists to support a similar role in chordates or other higher eukaryotes. Rather, mARS complexes are reported to regulate multiple and variegated cellular processes that include angiogenesis, apoptosis, inflammation, anaphylaxis, and metabolism. Because all such processes are critical components of immune homeostasis, it is important to understand the role of mARS complexes in immune regulation. Here we provide a conceptual analysis of the current understanding of mARS complex dynamics and emerging mARS complex roles in immune regulation, the increased understanding of which should reveal therapeutic targets in immunity and immune-mediated disease.

HIC1 interacts with FOXP3 multi protein complex: Novel pleiotropic mechanisms to regulate human regulatory T cell differentiation and function

Transcriptional repressor, hypermethylated in cancer 1 (HIC1) participates in a range of important biological processes, such as tumor repression, immune suppression, embryonic development and epigenetic gene regulation. Further to these, we previously demonstrated that HIC1 provides a significant contribution to the function and development of regulatory T (Treg) cells. However, the mechanism by which it regulates these processes was not apparent. To address this question, we used affinity-purification mass spectrometry to characterize the HIC1 interactome in human Treg cells. Altogether 61 high-confidence interactors were identified, including IKZF3, which is a key transcription factor in the development of Treg cells. The biological processes associated with these interacting proteins include protein transport, mRNA processing, non-coding (ncRNA) transcription and RNA metabolism. The results revealed that HIC1 is part of a FOXP3-RUNX1-CBFB protein complex that regulates Treg signature genes thus improving our understanding of HIC1 function during early Treg cell differentiation.

Secreted aminoacyl-tRNA synthetase-interacting multifunctional protein-1 (AIMP1) is a promising predictor for the severity of acute AQP4-IgG positive neuromyelitis optica spectrum disorder

BACKGROUND AND OBJECTIVES

Aminoacyl-tRNA synthetase complex interacting with multifunctional protein-1 (AIMP1) has been reported to carry pro-inflammatory properties and anti-angiogenesis effects. However, the exact role of AIMP1 in patients with NMOSD is not yet clear. Our objective was to investigate the relationship between plasma AIMP1 levels and disease severity in patients with AQP4-IgG⁺ NMOSD from North China based on the Expanded Disability Status Scale (EDSS) score.

METHODS

Plasma AIMP1 levels were measured using ELISA kits in 94 patients with AQP4-IgG⁺NMOSD (48 in the acute phase before high-dose intravenous methylprednisolone (IVMP) therapy, 21 in the acute phase after IVMP therapy, 25 in the clinical remission-phase)as well as 33 healthy controls (HCs). The disability function of NMOSD patients was evaluated using the EDSS score. Furthermore, the clinical characteristics of the patients were also evaluated, and laboratory tests were performed on blood samples.

RESULTS

The plasma AIMP1 levels in AQP4-IgG⁺NMOSD patients with acute phase before IVMP therapy were significantly higher as compared to those in patients after the IVMP therapy (p < 0.001) as well as those in the clinical remission phase (p = 0.021) or HCs (p < 0.001). Plasma AIMP1 levels were positively correlated with EDSS scores (r = 0.485, p < 0.001) and negatively correlated with serum complement 3 concentrations (r =-0.452, p = 0.001). AIMP1 exhibited the potential to distinguish NMOSD from HCs (AUROC 0.820, p < 0.0001) and could differentiate mild and moderate-severe NMOSD (AUROC 0.790, p = 0.0006). Furthermore, plasma AIMP1 levels of ≥49.55pg/mL were found to be an independent predictor of the risk for moderate-severe NMOSD (with OR 0.03, 95%CI 0.001-0.654, p = 0.026).

CONCLUSION

AIMP1 may be involved in the pathogenesis of AQP4-IgG⁺NMOSD disease and predict the disease activity, severity, or effect of treatment in patients with NMOSD. Further studies should be performed to reveal the precise mechanisms of AQP4-IgG⁺NMOSD.

Aminoacyl transfer ribonucleic acid synthetase complex-interacting multifunctional protein 1 induces microglial activation and M1 polarization via the mitogen-activated protein kinase/nuclear factor-kappa B signaling pathway

Activation of microglia, which is the primary immune cell of the central nervous system, plays an important role in neuroinflammation associated with several neuronal diseases. Aminoacyl tRNA synthetase (ARS) complex-interacting multifunctional protein 1 (AIMP1), a structural component of the multienzyme ARS complex, is secreted to trigger a pro-inflammatory function and has been associated with several inflammatory diseases. However, the effect of AIMP1 on microglial activation remains unknown. AIMP1 elevated the expression levels of activation-related cell surface markers and pro-inflammatory cytokines in primary and BV-2 microglial cells. In addition to the AIMP1-mediated increase in the expression levels of M1 markers [interleukin (IL)-6, tumor necrosis factor-α, and IL-1β], the expression levels of CD68, an M1 cell surface molecule, were also increased in AIMP-1-treated microglial cells, while those of CD206, an M2 cell surface molecule, were not, indicating that AIMP1 triggers the polarization of microglial cells into the M1 state but not the M2 state. AIMP1 treatment induced the phosphorylation of mitogen-activated protein kinases (MAPKs), while MAPK inhibitors suppressed the AIMP1-induced microglial cell activation. AIMP1 also induced the phosphorylation of the nuclear factor-kappa B (NF-κB) components and nuclear translocation of the NF-κB p65 subunit in microglial cells. Furthermore, c-Jun N-terminal kinase (JNK) and p38 inhibitors markedly suppressed the AIMP1-induced phosphorylation of NF-κB components as well as the nuclear translocation of NF-κB p65 subunit, suggesting the involvement of JNK and p38 as upstream regulators of NF-κB in AIMP1-induced microglial cell activation. The NF-κB inhibitor suppressed the AIMP1-induced M1 polarization of the microglial cells. Taken together, AIMP1 effectively induces M1 microglial activation via the JNK and p38/NF-κB-dependent pathways. These results suggest that AIMP1 released under stress conditions may be a pathological factor that induces neuroinflammation.

Erythroid Differentiation Regulator 1 Strengthens TCR Signaling by Enhancing PLCγ1 Signal Transduction Pathway

Erythroid differentiation regulator 1 (Erdr1) has previously been reported to control thymocyte selection via TCR signal regulation, but the effect of Erdr1 as a TCR signaling modulator was not studied in peripheral T cells. In this report, it was determined whether Erdr1 affected TCR signaling strength in CD4 T cells. Results revealed that Erdr1 significantly enhanced the anti-TCR antibody-mediated activation and proliferation of T cells while failing to activate T cells in the absence of TCR stimulation. In addition, Erdr1 amplified Ca²⁺ influx and the phosphorylation of PLCγ1 in CD4 T cells with the TCR stimuli. Furthermore, NFAT1 translocation into nuclei in CD4 T cells was also significantly promoted by Erdr1 in the presence of TCR stimulation. Taken together, our results indicate that Erdr1 positively modulates TCR signaling strength via enhancing the PLCγ1/Ca²⁺/NFAT1 signal transduction pathway.

Threonyl-tRNA Synthetase Promotes T Helper Type 1 Cell Responses by Inducing Dendritic Cell Maturation and IL-12 Production via an NF-κB Pathway

Threonyl-tRNA synthetase (TRS) is an aminoacyl-tRNA synthetase that catalyzes the aminoacylation of tRNA by transferring threonine. In addition to an essential role in translation, TRS was extracellularly detected in autoimmune diseases and also exhibited pro-angiogenetic activity. TRS is reported to be secreted into the extracellular space when vascular endothelial cells encounter tumor necrosis factor-α. As T helper (Th) type 1 response and IFN-γ levels are associated with autoimmunity and angiogenesis, in this study, we investigated the effects of TRS on dendritic cell (DC) activation and CD4 T cell polarization. TRS-treated DCs exhibited up-regulated expression of activation-related cell-surface molecules, including CD40, CD80, CD86, and MHC class II. Treatment of DCs with TRS resulted in a significant increase of IL-12 production. TRS triggered nuclear translocation of the NF-κB p65 subunit along with the degradation of IκB proteins and the phosphorylation of MAPKs in DCs. Additionally, MAPK inhibitors markedly recovered the degradation of IκB proteins and the increased IL-12 production in TRS-treated DCs, suggesting the involvement of MAPKs as the upstream regulators of NF-κB in TRS-induced DC maturation and activation. Importantly, TRS-stimulated DCs significantly increased the populations of IFN-γ⁺CD4 T cells, and the levels of IFN-γ when co-cultured with CD4⁺ T cells. The addition of a neutralizing anti-IL-12 mAb to the cell cultures of TRS-treated DCs and CD4⁺ T cells resulted in decreased IFN-γ production, indicating that TRS-stimulated DCs may enhance the Th1 response through DC-derived IL-12. Injection of OT-II mice with OVA-pulsed, TRS-treated DCs also enhanced Ag-specific Th1 responses in vivo. Importantly, injection with TRS-treated DC exhibited increased populations of IFN-γ⁺-CD4⁺ and -CD8⁺ T cells as well as secretion level of IFN-γ, resulting in viral clearance and increased survival periods in mice infected with influenza A virus (IAV), as the Th1 response is associated with the enhanced cellular immunity, including anti-viral activity. Taken together, these results indicate that TRS promotes the maturation and activation of DCs, DC-mediated Th1 responses, and anti-viral effect on IAV infection.

Novel functions of cytoplasmic aminoacyl-tRNA synthetases shaping the hallmarks of cancer

With the intense protein synthesis demands of cancer, the classical enzymatic role of aminoacyl-tRNA synthetases (aaRSs) is required to sustain tumor growth. However, many if not all aaRSs also possess regulatory functions outside of the domain of catalytic tRNA aminoacylation, which can further contribute to or even antagonize cancers in non-translational ways. These regulatory functions of aaRS are likely to be manipulated in cancer to ensure uncontrolled growth and survival. This review will largely focus on the unique capacities of individual and sometimes collaborating synthetases to influence the hallmarks of cancer, which represent the principles and characteristics of tumorigenesis. An interesting feature of cytoplasmic aaRSs in higher eukaryotes is the formation of a large multi-synthetase complex (MSC) with nine aaRSs held together by three non-enzymatic scaffolding proteins (AIMPs). The MSC-associated aaRSs, when released from the complex in response to certain stimulations, often participate in pathways that promote tumorigenesis. In contrast, the freestanding aaRSs are associated with activities in both directions-some promoting while others inhibiting cancer. The AIMPs have emerged as potent tumor suppressors through their own distinct mechanisms. We propose that the tumor-suppressive roles of AIMPs may also be a consequence of keeping the cancer-promoting aaRSs within the MSC. The rich connections between cancer and the synthetases have inspired the development of innovative cancer treatments that target or take advantage of these novel functions of aaRSs.

Molecular Markers of Regulatory T Cells in Cancer Immunotherapy with Special Focus on Acute Myeloid Leukemia (AML) - A Systematic Review

The next-generation immunotherapy can only be effective if researchers have an in-depth understanding of the function and regulation of Treg cells in antitumor immunity combined with the discovery of new immunity targets. This can enhance clinical efficacy of future and novel therapies and reduces any adverse reactions arising from the latter. This review discusses tumor treatment strategies using regulatory T (Treg) cell therapy in a Tumor Microenvironment (TME). It also discusses factors affecting TME instability as well as relevant treatments to prevent future immune disorders. It is prognosticated that PD-1 inhibitors are risky and their adverse effects should be taken into account when they are administered to treat Acute Myeloid Leukemia (AML), lung adenocarcinoma, and prostate adenocarcinoma. In contrast, Treg molecular markers FoxP3 and CD25 analyzed here have stronger expression in almost all kinds of cancers compared with normal people. However, CD25 inhibitors are more effective compared to FoxP3 inhibitors, especially in combination with TGF-β blockade, in predicting patient survival. According to the data obtained from the Cancer Genome Atlas, we then concentrate on AML immunotherapy and discuss different therapeutic strategies including anti-CD25/IL-2, anti-CTLA-4, anti-IDO, antityrosine kinase receptor, and anti-PI3K therapies and highlight the recent advances and clinical achievements in AML immunotherapy. In order to prognosticate the risk and adverse effects of key target inhibitors (namely against CTLA-4, FoxP3, CD25, and PD-1), we finally analyzed and compared the Cancer Genome Atlas derived from ten common cancers. This review shows that Treg cells are strongly increased in AML and the comparative review of key markers shows that Tregbased immunotherapy is not effective for all kinds of cancer. Therefore, blocking CD25(+)FoxP3(+) Treg cells is suggested in AML more than other kinds of cancer; meanwhile, Treg markers studied in other cancers have also great lessons for AML immunotherapy.

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.