Circ_CIT Promotes Nasopharyngeal Carcinoma Progression and Macrophage M2 Polarization Through miR-409-3p/ZEB1 Axis

Circular RNAs (circRNAs) play a crucial role in the progression of various cancers, including nasopharyngeal carcinoma (NPC). However, the mechanism of circRNA in the progression of NPC remains to be elucidated.

The expression levels of circ_CIT, microRNA-409-3p and ZEB1 in NPC tissues were detected by Real-time quantitative PCR (qRT-PCR). Nuclear separation and fluorescence in situ hybridization (FISH) assays were used to determine the localization of circ_CIT. Dual luciferase reporter was performed to confirm the binding of circ_CIT with micro (miR)-409-3p. Cellular behaviors were determined using Cell Counting Kit-8 (CCK-8), colony formation, wound healing, transwell and macrophage chemotaxis assays. Enzyme Linked Immunosorbent Assay (ELISA) and immunofluorescence Assays was used to evaluated macrophage markers.

We identified that circ_CIT was mainly located in the cytoplasm. Circ_CIT expression was increased in NPC tissues and cell lines. Knockdown of circ_CIT inhibited cell proliferation, invasion and migration. Circ_CIT-mediated NPC tumorigenesis by sponging miR-409-3p and promoting ZEB1 expression. The inhibitors of miR-409-3p could reverse the effects of circ_CIT knockdown on NPC cells. The expression of circ_CIT and ZEB1 was found to be positively correlated with NPC tumor stage. Downregulation of expression of circ_CIT could promote macrophage M2 polarization through NPC cells. Overexpression of ZEB1 could reverse the inhibitory effect of circ_CIT knockdown on the polarization of macrophages to M2 phenotype.

Highly expressed circ_CIT adsorbs miR-409-3p to upregulate ZEB1 expression, thereby promoting the proliferation and metastatic ability of NPC cells and activating macrophage M2 polarization. Therefore, circ_CIT may be a potential therapeutic target for NPC patients.