FENDRR represses Bladder Cancer Cell Proliferation, Stemness, Migration, Invasion, and EMT Process by Targeting miR-18a-5p/AFF4 Axis

Bladder cancer (BC) is the most prevalent malignancy of the urinary tract and ranks among the most common tumors globally due to its high recurrence and fatality rates. Evidence suggests that long noncoding RNAs (lncRNAs) may serve as novel biomarkers for cancer therapy. The study aimed to investigate the functions of lncRNA fetal-lethal non-coding developmental regulatory RNA (FENDRR) in regulating malignant phenotypes of BC cell lines (T24 and RT-4) and the underlying mechanism. RT-qPCR was used to measure FENDRR, miR-18a-5p, and AF4/FMR2 family member 4 (AFF4) expression in BC tissue samples and cell lines. Subcellular fractionation assay and fluorescence in situ hybridization were conducted to determine the localization of FENDRR in T24 and RT-4 cell. EdU, sphere formation, Transwell invasion, and wound healing assays were carried out to detect the changes in BC cell proliferation, stemness, invasion, and migration in response to FENDRR or AFF4 dysregulation. Protein levels of epithelial-mesenchymal transition (EMT) markers were quantified by western blotting. The interaction between miR-18a-5p and FENDRR (or AFF4) was verified by luciferase reporter assays. Experimental results revealed that FENDRR expression was downregulated in BC tissue samples and cell lines, with primary localization in cytoplasm of T24 and RT-4 cells. FENDRR overexpression inhibited BC cell proliferation, migration, invasion, stemness, and EMT process. FENDRR was shown to bind with miR-18a-5p, and AFF4 is a direct target of miR-18a-5p. In addition, AFF4 knockdown partially counteracted the effect of FENDRR on malignant phenotypes of BC cells. In summary, FENDRR represses BC cell proliferation, migration, invasion, stemness, and EMT process by targeting the miR-18a-5p/AFF4 axis.