N6-methyladenosine (m6A) represents the most prevalent and dynamic post-transcriptional alteration on messenger RNAs in eukaryotic organisms, exerting a critical influence on the initiation and advancement of breast cancer (BC). Circular RNAs (circRNAs) have the capacity to function as oncogenic drivers or inhibitors through their role as microRNA (miRNA) decoys in BC. Nevertheless, the precise pathways by which circRNAs contribute to BC development by modulating m6A regulators are not fully elucidated. m6A regulators associated with prognosis were pinpointed among 1065 BC cases drawn from The Cancer Genome Atlas (TCGA) database. Differentially expressed miRNAs and circRNAs were detected in comparisons between tumor and healthy tissues using data from TCGA and the GSE101123 dataset, respectively. Interactions between miRNAs and target mRNAs, as well as between circRNAs and miRNAs, were validated employing MiRDIP and the Circular RNA Interactome databases. Functional enrichment analyses via GSEA, KEGG pathways, and ssGSEA were performed to investigate potential biological roles and immune-related characteristics in groups stratified by high versus low HNRNPC levels. Expression levels of HNRNPC and circBACH2 in MCF-7 and MDA-MB-231 cell lines were measured using qRT-PCR and Western blotting. Cell proliferation in BC was evaluated through CCK-8 and EdU incorporation assays. Two prognostic m6A regulators, namely HNRNPC and YTHDF3, were detected in individuals with BC. Subsequently, an interaction network involving circRNAs, miRNAs, and m6A regulators was established, incorporating 2 differentially expressed m6A factors (HNRNPC and YTHDF3), 12 differentially expressed miRNAs, and 11 differentially expressed circRNAs. Of particular interest, elevated HNRNPC alongside reduced hsa-miR-944 levels in BC cases were linked to advanced disease stages and reduced overall survival. KEGG analysis further indicated that differentially expressed HNRNPC is linked to the MAPK pathway in BC. Additionally, circBACH2 (identified as hsa_circ_0001625) was validated to function as a decoy for hsa-miR-944, thereby enhancing HNRNPC levels and driving BC cell growth through the MAPK pathway, establishing a circBACH2/hsa-miR-944/HNRNPC regulatory pathway in BC. This research uncovers a distinctive m6A modulation mechanism mediated by circRNAs that contributes to BC advancement, offering promising avenues for improved diagnosis and treatment approaches in BC management.
