CircHSPB6 Promotes Tumor-Associated Macrophages M2 Polarization and Infiltration to Accelerate Cell Malignant Properties in Lung Adenocarcinoma by CCL2

Circular RNAs (circRNAs) are reported to be involved in the tumorigenesis of lung adenocarcinoma (LUAD). Here, this study focused on studying the function and mechanism of circHSPB6 in LUAD progression. Levels of genes and proteins were tested using qRT-PCR and western blotting analyses. The 5-ethynyl-2'-deoxyuridine (EdU), colony formation, flow cytometry, and transwell assays were adopted for in vitro assays. In vivo assay was conducted using mouse xenograft models. The binding between let-7a-2-3p and circHSPB6 or CCL2 was validated using RIP and dual-luciferase reporter assays. The M2 polarization of tumor-associated macrophages (TAMs) was analyzed by flow cytometry. LUAD tissues and cells showed high circHSPB6 expression, knockdown of circHSPB6-suppressed LUAD cell proliferation, migration, invasion, and induced cell apoptosis in vitro, as well as hindered tumor growth in vivo. Mechanistically, circHSPB6/let-7a-2-3p/CCL2 forms a feedback loop. CircHSPB6 could regulate CCL2 expression via sponging let-7a-2-3p. Further rescue assays showed that the effects of circHSPB6 silencing on LUAD cells were reversed by let-7a-2-3p inhibition or CCL2 overexpression. Moreover, circHSPB6 promoted the M2 polarization and infiltration of TAMs by CCL2. Functionally, circHSPB6 knockdown in A549 and H1299 cells inhibited TAM M2 polarization and then suppressed cell proliferation, migration, invasion, and emergency medical technicians (EMT) progression, while these effects were reversed by CCL2 up-regulation CircHSPB6 induced TAM M2 polarization to promote LUAD cell proliferation, migration, invasion, and EMT progression through let-7a-2-3p/CCL2 axis.