ADAR2 suppresses bladder cancer metastasis by binding and destabilizing FASN mRNA in an RNA editing-independent manner

Bladder cancer (BCa) metastasis remains a major challenge to patient survival, and the underlying mechanisms have not been fully elucidated. Although the ADAR family has been implicated in tumor biology, the role of ADAR2 in BCa metastasis remains unclear. ADAR2 expression in BCa was analyzed using TCGA datasets and validated by quantitative real-time PCR (RT-qPCR) in 40 pairs of BCa and adjacent normal tissues. Functional effects were investigated using in vitro migration and invasion assays and in vivo mouse models of popliteal lymph node and lung metastasis. Mechanistic studies included mRNA sequencing, gas chromatography-mass spectrometry (GC-MS), Nile Red staining, free fatty acid (FFA) quantification, RNA immunoprecipitation (RIP), rescue assays using editing-domain mutants, and actinomycin D chase assays to investigate the regulation of fatty acid synthase (FASN) and fatty acid synthesis. ADAR2 was downregulated in BCa tissues, and its expression was positively associated with an improved patient prognosis. Functionally, ADAR2 inhibited BCa cell migration and invasion in vitro, as demonstrated by Transwell migration, Matrigel invasion, and wound-healing assays, and in vivo, as demonstrated using popliteal lymph node and lung metastasis models. Integrated analysis of mRNA-sequencing data, together with Nile Red staining, Oil Red O staining, and FFA quantification, revealed that ADAR2 reduced cytoplasmic FFA accumulation by downregulating FASN. Mechanistically, the absence of detectable A-to-I editing in FASN exons and the inability of the catalytically inactive ADAR2 E396A mutant to rescue FASN expression indicated an editing-independent mechanism. Actinomycin D chase, dual-luciferase reporter, and RIP assays demonstrated that ADAR2 acted as an RNA-binding protein (RBP) that bound to the FASN mRNA 3′ UTR, destabilized the transcript, and thereby downregulated FASN expression. ADAR2 inhibited BCa cell migration and invasion by downregulating FASN-mediated fatty acid synthesis through an RNA editing-independent pathway.