Circ_0000437 promotes proliferation,invasion,migration and epithelial-mesenchymal transition of breast cancer cells by targeting the let-7b-5p/CTPS1 axis

MA Siyuan; ZHANG Bochao; PU Chun

doi:10.12122/j.issn.1673-4254.2025.08.13

Abstract：Objective To investigate the role of circular RNA circ_0000437 in regulating biological behaviors of breast cancer cells and the molecular mechanism.Methods Breast cancer MCF-7 and MDA-MB-231 cells were transfected with sh-circ_0000437,mimics,inhibitor,si-CTPS1,or their respective negative controls.qRT-PCR was used to detect the expression levels of circ_0000437,let-7b-5p,CTPS1,Notch1,Hes1,and Numb in breast cancer cell lines and tissues.RNase R digestion was used to confirm the circular structure of circ_0000437 and its subcellular localization in the breast cancer cells was determined by cellular distribution analysis.The changes in proliferation,invasion and migration of the transfected cells were assessed using CCK-8 assay,Transwell assay and scratch assay.Dual-luciferase reporter gene and RNA immunoprecipitation assays were employed to validate binding interactions among circ_0000437,let-7b-5p,and CTPS1.The cellular expressions of CTPS1,E-cadherin,N-cadherin,and vimentin proteins were detected with Western blotting.A tumor-bearing mouse model was used to verify the oncogenic mechanism of circ_0000437 and CTPS1.Results Circ_0000437 and CTPS1 were upregulated while let-7b-5p was downregulated in breast cancer tissues and cell lines.Circ_0000437 or CTPS1 knockdown obviously suppressed breast cancer cell proliferation,invasion,migration and epithelial-mesenchymal transition(EMT).Overexpression of let-7b-5p produced similar inhibitory effects,whereas inhibition of let-7b-5p significantly enhanced malignant behaviors of the cells.In the tumor-bearing mouse models,circ_0000437 knockdown significantly suppressed tumor growth,but co-transfection of the cells with pcDNA-CTPS1 accelerated tumor growth.Binding sites were identified between circ_0000437 and let-7b-5p and between let-7b-5p and CTPS1,and circ_0000437,let-7b-5p,and CTPS1 showed functional interactions in breast cancer cells.Conclusion Circ_0000437 is upregulated in breast cancer tissues and cells,and its high expression promotes proliferation,invasion,migration and EMT of breast cancer cells through the let-7b-5p/CTPS1 axis.