Evaluation of genetic variation in tumor suppressor miRNA encoding and their target genes in breast cancer; focus on miRNA interaction and expression analysis

Background: Genetic variations in tumor suppressor miRNAs and the 3'UTR of their target genes influence tumor biology and breast cancer (BC) risk. Objective: This study investigated genetic variations in tumor suppressor miRNAs (hsa-let-7c, hsa-miR-34a, hsa-miR-145a) and their target genes (KRAS, IGFBP6, IGF1R), and their functional significance in BC patients. Methods: The miRNA encoding regions and 3'UTRs of the selected target genes were sequenced in 208 BC patients. Functional analyses were performed using luciferase assay, RT-PCR, IHC, and Western blotting. RNAfold, TNM plot, Kaplan-Meier Plotter, and ROC Plotter were used for structural predictions, survival, and therapy response analysis. Results: Two variants, rs712 and rs9266, were found in the 3'UTR of KRAS. Luciferase assay confirmed that rs9266 disrupts the binding of hsa-let-7c and hsa-miR-181c, leading to increased KRAS expression. KRAS expression was highest in heterozygous, followed by homozygous mutant, and lowest in wild-type genotypes. Higher hsa-let-7c and hsa-miR-181c expression correlated with better survival. ROC analysis identified KRAS as a potential predictive biomarker for chemotherapy response. Conclusion: Variants rs712 and rs9266 in the KRAS 3'UTR impair miRNA binding, enhancing KRAS expression and tumorigenesis, while elevated hsa-let-7c and hsa-miR-181c levels predict favourable survival outcomes in BC patients.