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Abstract Background Circular RNAs (circRNAs) play a significant role in the tumorigenesis and progression of diverse human cancers, including lung adenocarcinoma. A previous study suggested that circ_0004140 expression was increased in lung adenocarcinoma cells. However, the molecular mechanism of circRNA circ_0004140 involved in lung adenocarcinoma is poorly defined. Methods Circ_0004140, microRNA‐330‐5p (miR‐330‐5p), and NOVA alternative splicing regulator 2 (NOVA2) expression were determined by real‐time quantitative polymerase chain reaction (RT‐qPCR). Cell proliferation, apoptosis, migration, invasion, and angiogenesis ability were assessed using 5‐ethynyl‐2’‐deoxyuridine (EdU), flow cytometry, wound healing, transwell, and capillary‐like network formation assays. Proliferating cell nuclear antigen (PCNA), cyclin D1, and NOVA2 protein levels were detected using Western blot assay. The interaction between miR‐330‐5p and circ_0004140 or NOVA2 was verified by dual‐luciferase reporter assay. Xenograft tumor model was utilized to assess the role of circ_0004140 in tumor growth in vivo. Results Circ_0004140 was upregulated in lung adenocarcinoma tissues and cell lines. Circ_0004140 silencing suppressed cell proliferation, migration, invasion and tube formation ability, and triggered the apoptosis of lung adenocarcinoma cells. Circ_0004140 acted as a molecular sponge for miR‐330‐5p, and miR‐330‐5p silencing largely reversed circ_0004140 knockdown‐induced effects in lung adenocarcinoma cells. NOVA2 was a target of miR‐330‐5p, and NOVA2 overexpression might largely overturn miR‐330‐5p overexpression‐induced influences in lung adenocarcinoma cells. Circ_0004140 upregulated NOVA2 expression via sponging miR‐330‐5p in lung adenocarcinoma cells. Circ_0004140 silencing restrained xenograft tumor growth in vivo. Conclusion Circ_0004140 knockdown might suppress the malignant biological behaviors of lung adenocarcinoma cells via miR‐330‐5p‐dependent regulation of NOVA2.

Background: Lung cancer is a common malignant tumor with high morbidity and mortality rate. Glucosamine 6-phosphate N-acetyltransferase (GNPNAT1), which serves as a critical enzyme in hexosamine biosynthetic pathway (HBP), has been identified as a metastasis-associated gene and is upregulated in lung adenocarcinoma (LUAD). However, the exact role and related mechanism of GNPNAT1 in LUAD metastasis remain unknown. Methods: We analyzed the expression of GNPNAT1 in the public databases and confirmed the results by immunohistochemistry (IHC). The biological functions of GNPNAT1 in LUAD were investigated based on The Cancer Genome Atlas (TCGA). Correlations between GNPNAT1 and cancer immune characteristics were analyzed via the Estimation of Stromal and Immune cells in Malignant Tumor tissues using Expression data (ESTIMATE) and Cell-type Identification by Estimating Relative Subsets of RNA Transcript (CIBERSORT) R package. The underlying mechanisms of altered GNPNAT1 expression on LUAD cell tumorigenesis, proliferation, migration, invasion, and metastasis were explored in vitro and in vivo. Results: We demonstrated that GNPNAT1 expression was significantly increased in LUAD and negatively associated with the overall survival (OS) of patients. hsa-miR-1-3p and hsa-miR-26a-5p were identified as upstream miRNA targets of GNPNAT1. GNPNAT1 was associated with the infiltration levels of CD8 T cells, memory-activated CD4 T cells, NK cells resting, macrophages M0, macrophages M1, neutrophils, gamma delta T cells, and eosinophils, while it was negatively correlated with memory-resting CD4 T cells, regulatory T cells (Tregs), resting NK cells, monocytes, resting dendritic cells, and resting mast cells. GNPNAT1 knockdown significantly inhibited proliferation, migration, invasion, epithelial–mesenchymal transition (EMT) process, and metastasis of LUAD cells, while overexpression of GNPNAT1 revealed the opposite effects. Rescue assay showed that Snai2 knockdown reversed GNPNAT1-induced LUAD cells migration, invasion, and EMT. Mechanistically, GNPNAT1 promoted cancer cell metastasis via repressing ubiquitination degradation of Snai2 in LUAD. Conclusions: Taken together, these data indicate that GNPNAT1 serves as a prognostic biomarker for LUAD patient. Additionally, GNPNAT1 is critical for promoting tumorigenesis and metastasis of LUAD cells and may be a potential therapeutic target for preventing LUAD metastasis.