circKLHL24 Blocks Breast Cancer Development by Regulating the miR-1204/ALX4 Network

Background: Breast cancer is a major challenge affecting women's survival. Circular RNAs have been demonstrated to be vital regulators in the pathogenesis of human cancers. The authors' objective was to determine the functional role and mechanism of circKLHL24 in breast cancer development. Materials and Methods: The expression of circKLHL24, miR-1204, and aristaless-like 4 (ALX4) mRNA was measured using quantitative real-time polymerase chain reaction. The effects on cell viability, proliferation, migration/invasion, and glycolysis were identified using the Cell Counting Kit-8 (CCK-8) assay, colony formation assay, Transwell assay, and glycolysis stress test, respectively. For glycolysis progression analysis, glucose consumption and lactate production were assessed using corresponding kits, and the expression of glycolysis-related proteins was detected by western blot. The putative interactions between miR-1204 and circKLHL24 or ALX4 were validated by dual-luciferase reporter assay or RNA pull-down assay. The expression of ALX4 at the protein level was detected by western blot. Animal study was performed to clarify the role of circKLHL24 in vivo. Results: circKLHL24 and ALX4 were downregulated, while miR-1204 was upregulated in breast cancer tissues and cells. circKLHL24 overexpression blocked cell viability, colony formation, migration/invasion, and glycolysis progression. circKLHL24 competitively targeted miR-1204, and miR-1204 reintroduction reversed the effects of circKLHL24 restoration. miR-1204 bound to ALX4, and circKLHL24 sponged miR-1204 to upregulate ALX4. Cell viability, colony formation, migration/invasion, and glycolysis progression suppressed by miR-1204 deficiency were recovered by ALX4 knockdown. Besides, circKLHL24 blocked tumor growth in vivo by regulating miR-1204 and ALX4. Conclusions: circKLHL24 blocked the progression of breast cancer by activating ALX4 through targeting miR-1204, which might be a novel perspective to understand the pathogenesis of breast cancer.