circ_0075829 regulates ferroptosis and immune escape in colon cancer cells through the miR-330-5p/TCF4 axis

Many lines of evidence suggest that circular RNAs (circRNAs) are closely associated with the occurrence and progression of colon cancer. The objective of this study was to investigate the regulatory effects and mechanisms of circ_0075829 on ferroptosis and immune escape in colon cancer. We utilized colon cancer cell lines and a xenograft mouse model to analyze the function of circ_0075829 in vitro and in vivo. The gene expression level was assessed by qRT-PCR and western blotting. Cell proliferation was evaluated using the CCK-8 assay. The targeting relationships between circ_0075829, miR-330-5p, and TCF4 were analyzed through a dual-luciferase reporter experiment and RNA pull-down experiment. Cytokine levels were measured using the ELISA assay. Fe2+, MDA, and SOD levels were tested using appropriate kits, and the ROS level was detected by immunofluorescence. Knockdown of circ_0075829 resulted in increased levels of Fe2+, ROS, and MDA and decreased levels of GPX4 and xCT proteins in cells. Furthermore, silencing of circ_0075829 increased the cell proliferation rates of CD8+T cells co-cultured with colon cells. Moreover, it also enhanced IFN-γ, IL-2, and TNF-α concentration in the supernatants of the co-culturing system and reduced PD-L1 protein expression levels. Subsequently, silencing of circ_0075829 induced ferroptosis and inhibited immune escape in vivo. Meaningfully, we certified that circ_0075829 functions as a sponge for miR-330-5p, leading to the upregulation of TCF4 expression. TCF4 was identified as a downstream target of miR-330-5p. Additionally, co-transfection with anti-miR-330-5p or TCF4 overexpression plasmid reversed the effects observed following the knockout of circ_0075829. Collectively, our research indicates that the circ_0075829 plays a significant role in regulating ferroptosis and immune escape in colon cancer by sponging miR-330-5p to modulate TCF4 expression.