miRNA profiling of biliary intraepithelial neoplasia reveals stepwise tumorigenesis in distal cholangiocarcinoma via the miR-451a/ATF2 axis.

Distal cholangiocarcinoma (dCCA) is a biliary tract cancer with a dismal prognosis and is often preceded by biliary intraepithelial neoplasia (BilIN), representing the most common biliary non-invasive precursor lesion. BilIN are histologically well defined but have not so far been characterised systematically at the molecular level. The aim of this study was to determine miRNA-regulated genes in cholangiocarcinogenesis via BilIN. We used a clinicopathologically well-characterised cohort of 12 dCCA patients. Matched samples of non-neoplastic biliary epithelia, BilIN and invasive tumour epithelia of each patient were isolated from formalin-fixed paraffin-embedded tissue sections by laser microdissection. The resulting 36 samples were subjected to total RNA extraction and the expression of 798 miRNAs was assessed using the Nanostring® technology. Candidate miRNAs were validated by RT-qPCR and functionally investigated following lentiviral overexpression in dCCA-derived cell lines. Potential direct miRNA target genes were identified by microarray and prediction algorithms and were confirmed by luciferase assay. We identified 49 deregulated miRNAs comparing non-neoplastic and tumour tissue. Clustering of these miRNAs corresponded to the three stages of cholangiocarcinogenesis, supporting the concept of BilIN as a tumour precursor. Two downregulated miRNAs, i.e. miR-451a (-10.9-fold down) and miR-144-3p (-6.3-fold down), stood out by relative decrease. Functional analyses of these candidates revealed a migration inhibitory effect in dCCA cell lines. Activating transcription factor 2 (ATF2) and A disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) were identified as direct miR-451a target genes. Specific ATF2 inhibition by pooled siRNAs reproduced the inhibitory impact of miR-451a on cancer cell migration. Thus, our data support the concept of BilIN as a direct precursor of invasive dCCA at the molecular level. In addition, we identified miR-451a and miR-144-3p as putative tumour suppressors attenuating cell migration by inhibiting ATF2 in the process of dCCA tumorigenesis. © The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.