EIF4A3 facilitates METTL3-mediated m6A methylation of circPCMTD1 to drive bladder cancer progression via miR-3681-5p/HPSE axis.
BACKGROUND Bladder cancer (BCa) is a common urological malignancy with high recurrence rates and limited treatment options for advanced disease. Circular RNAs (circRNAs) are emerging as key regulators of cancer progression, but the roles of most circRNAs in BCa remain poorly understood. OBJECTIVE To investigate the expression, function and mechanism of circPCMTD1 (hsa_circ_0001801) in BCa, focusing on its m6A methylation and its role as a ceRNA regulating the miR-3681-5p/HPSE/PI3K/AKT axis. METHODS circPCMTD1 expression was analyzed in GEO datasets, 30 paired BCa tissues and cell lines by qRT-PCR. Circular structure and stability were confirmed by RNase R and actinomycin D assays. Subcellular localisation was determined by fractionation and FISH. Gain- and loss-of-function experiments assessed circPCMTD1 effects on BCa cell malignancy. A subcutaneous xenograft model was used for in vivo validation. m6A sites were predicted by SRAMP, and circPCMTD1-EIF4A3 interaction validated by RIP. Protein-protein docking predicted EIF4A3-METTL3 binding. miRNA targets were screened by ENCORI and confirmed by qRT-PCR and RNA-FISH. miR-3681-5p targets were identified by transcriptome sequencing and database analysis. Western blotting assessed HPSE, PI3K, AKT and p-AKT. Rescue experiments verified the circPCMTD1/miR-3681-5p/HPSE axis. RESULTS circPCMTD1 was upregulated in BCa tissues and cells, stable and cytoplasmic. Knockdown suppressed BCa proliferation, migration, invasion and Tumor growth in vivo, while overexpression promoted these phenotypes. circPCMTD1 contained nine predicted m6A sites, interacted with EIF4A3, and EIF4A3 docked with METTL3. circPCMTD1 overexpression increased METTL3, METTL14, FTO and YTHDF2. circPCMTD1 directly sponged miR-3681-5p. miR-3681-5p acted as a tumor-suppressive miRNA. HPSE was a direct target of miR-3681-5p and overexpressed in BCa. circPCMTD1 positively regulated HPSE, PI3K and p-AKT, whereas miR-3681-5p had opposite effects. Rescue experiments confirmed that circPCMTD1 promoted BCa through sponging miR-3681-5p and activating HPSE/PI3K/AKT. CONCLUSIONS EIF4A3 facilitates METTL3-mediated m6A methylation of circPCMTD1. Methylated circPCMTD1 acts as a ceRNA sponging miR-3681-5p, derepressing HPSE and activating PI3K/AKT to drive BCa progression. This study identifies a novel EIF4A3/m6A-circPCMTD1/miR-3681-5p/HPSE/PI3K/AKT axis and suggests potential therapeutic targets for BCa.