METTL3-mediated circ_0003998 serves as oncogene in non-small cell lung cancer through regulating miR-330-5p/CXCL3 axis.

Circular RNA (circRNA) is involved in the occurrence of many cancers. Nonetheless, the mechanism of circ_0003998 in non-small cell lung cancer (NSCLC) needs to be studied in depth. Real-time quantitative PCR (RT-qPCR) was carried out to check the expression of circ_0003998, microRNA-330-5p (miR-330-5p), chemokine (C-X-C motif) ligand 3 (CXCL3) and methyltransferase-3 (METTL3) in NSCLC tissues and cells. CXCL3, Vimentin and E-cadherin protein levels were measured by western blot. The functions of circ_0003998 in NSCLC cell proliferation, apoptosis, angiogenesis, migration and invasion were tested by clone formation assay, flow cytometry, tube formation assay, wound healing assay, and transwell assay in vitro. The dual-luciferase reporter assay was made to verify the relationship between miR-330-5p and circ_0003998 or CXCL3. Finally, animal experiment was made to further research the function of circ_0003998 on tumor formation in vivo. The interaction between circ_0003998 and METTL3 was analyzed by RNA Immunoprecipitation (RIP) assay, methylated RNA Immunoprecipitation (MeRIP) assay and dual-luciferase reporter assay. In NSCLC tissue and cells, circ_0003998 was markedly overexpressed. Circ_0003998 suppression inhibited NSCLC cell growth, angiogenesis, migration and invasion. Circ_0003998 sponged miR-330-5p, and miR-330-5p inhibitor could reverse the suppression effect of circ_0003998 knockdown on NSCLC cell behaviors. CXCL3 was a downstream target gene of miR-330-5p, and CXCL3 overexpression also reversed the suppressive effect of miR-330-5p on NSCLC cell behaviors. Interference of circ_0003998 reduced NSCLC tumorigenesis by regulating miR-330-5p/CXCL3 axis. Also, METTL3 promoted the expression of circ_0003998 by m6A modification. METTL3-modified circ_0003998 promoted NSCLC cell malignancy through miR-330-5p/CXCL3 axis, suggesting that circ_0003998 might be a new treatment strategy for NSCLC.