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Purpose Gastric cancer (GC) is the second leading cause of cancer-related deaths worldwide. tRNA-derived fragments (tRFs) have been identified as potential biomarkers and cancer therapeutic targets. However, the influence of tRFs on GC remains unknown. The key tRFs were researched in vitro function and mechanism. Patients and Methods Here, differentially expressed tRFs between GC and paracancerous tissues were identified by small RNA sequencing, and the role of key tRF was evaluated in vitro. Results Eight tRFs were significantly differentially expressed between GC tissues and adjacent tissues: five were significantly upregulated and three were downregulated in GC tissues. The results of target gene prediction and functional enrichment analysis showed that tRFs with different expressions were mainly involved in cell adhesion and connection, cell migration, wingless-type (Wnt), mitogen-activated protein kinase (MAPK), and cancer signaling pathways. Quantitative real-time polymerase chain reaction (qRT-PCR) indicated that the expression of tRF-24-V29K9UV3IU and its target genes (CCND2, FZD3, and VANGL1) in GC tissues and cells was decreased compared with those in the control group. Importantly, overexpression of tRF-24-V29K9UV3IU inhibited cell proliferation, migration and invasion, while promoted cell apoptosis of GC cells. Conclusion This study suggests that tRF-24-V29K9UV3IU may hinder GC tumor progression by inhibiting cell proliferation, migration, invasion, while promoting cell apoptosis by regulating the Wnt signaling pathways.

Emerging studies have proved that tRNA-derived fragments (tRFs) play vital roles in tumor metastasis; however, the function of tRFs in gastric cancer (GC) remains largely unclear. We investigated the role of tRF-24-V29K9UV3IU in growth and metastasis of GC using a xenograft mouse model. Differential gene expression downstream of tRF-24-V29K9UV3IU was identified by transcriptome sequencing, and interaction was then verified by a dual luciferase reporter and RNA immunoprecipitation. MKN-45 cells were also used to explore the biological functions of tRF-24-V29K9UV3IU in vitro. Here, knockdown of tRF-24-V29K9UV3IU promoted tumor growth and metastasis of GC in vivo. The expression of tRF-24-V29K9UV3IU and E-cadherin (epithelial cell marker) was down-regulated in tumors of mice following tRF-24-V29K9UV3IU knockdown, whereas the mesenchymal cell markers N-cadherin and vimentin displayed an opposite trend. Transcriptome sequencing identified 87 differentially expressed genes (DEGs) down-regulated in the tRF-24-V29K9UV3IU-overexpressed groups compared with the control group. Among them, G-protein–coupled receptor 78 (GPR78), the most significantly down-regulated DEG, was also predicted to be a target of tRF-24-V29K9UV3IU. Moreover, tRF-24-V29K9UV3IU could function as a miRNA-like fragment and bind to AGO2 and directly silence GPR78 expression by complementing with the 3 ′ -untranslated region of the GPR78 mRNA. Functionally, overexpression of tRF-24-V29K9UV3IU significantly suppressed proliferation, migration, and invasion and promoted apoptosis of MKN-45 cells, whereas GPR78 attenuated these effects. Therefore, our data suggest that tRF-24-V29K9UV3IU functions as a miRNA-like fragment to suppress GPR78 expression and thus inhibit GC progression. These observations suggest that the tRF-24-V29K9UV3IU/GPR78 axis serves as a potential therapeutic target in GC.

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Background L-theanine, a non-protein amino acid was found principally in the green tea, has been previously shown to exhibit potent anti-obesity property and hepatoprotective effect. Herein, we investigated the effects of L-theanine on alleviating nonalcoholic hepatic steatosis in vitro and in vivo, and explored the underlying molecular mechanism. Methods In vitro, HepG2 and AML12 cells were treated with 500 μM oleic acid (OA) or treated with OA accompanied by L-theanine. In vivo, C57BL/6J mice were fed with normal control diet (NCD), high‐fat diet (HFD), or HFD along with L-theanine for 16 weeks. The levels of triglycerides (TG), accumulation of lipid droplets and the expression of genes related to hepatocyte lipid metabolic pathways were detected in vitro and in vivo. Results Our data indicated that, in vivo, L-theanine significantly reduced body weight, hepatic steatosis, serum levels of alanine transaminase (ALT), aspartate transaminase (AST), TG and LDL cholesterol (LDL-C) in HFD-induced nonalcoholic fatty liver disease (NAFLD) mice. In vitro, L-theanine also significantly alleviated OA induced hepatocytes steatosis. Mechanic studies showed that L-theanine significantly inhibited the nucleus translocation of sterol regulatory element binding protein 1c (SREBP-1c) through AMPK-mTOR signaling pathway, thereby contributing to the reduction of fatty acid synthesis. We also identified that L-theanine enhanced fatty acid β-oxidation by increasing the expression of peroxisome proliferator–activated receptor α (PPARα) and carnitine palmitoyltransferase-1 A (CPT1A) through AMP-activated protein kinase (AMPK). Furthermore, our study indicated that L-theanine can active AMPK through its upstream kinase Calmodulin-dependent protein kinase kinase-β (CaMKKβ). Conclusions Taken together, our findings suggested that L-theanine alleviates nonalcoholic hepatic steatosis by regulating hepatocyte lipid metabolic pathways via the CaMKKβ-AMPK signaling pathway.

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