The miR-106b-25 Polycistron, Activated by Genomic Amplification, Functions as an Oncogene by Suppressing p21 and Bim

Abstract

Background & Aims Barrett’s esophagus (BE) is a highly premalignant disease that predisposes to the development of esophageal adenocarcinoma (EAC); however, the involvement of microRNAs (miRs) in BE-EAC carcinogenic progression is not known. Methods Esophageal cultured cells (HEEpiC, QhTRT, ChTRT, GihTRT and OE-33) and esophageal tissues (22 normal epithelia, 24 BE and 22 EAC) were studied. MiR microarrays and quantitative RT-PCR were employed to explore and verify differentially expressed miRs. Quantitative genomic PCR was performed to study genomic copy number variation at the miR-106b-25 polycistron and MCM7 gene locus on chromosome 7q22.1. In vitro cell proliferation, cell cycle, and apoptosis assays and in vivo tumorigenesis experiments were performed to elucidate biological effects of the miR-106b-25 polycistron. Western blotting and luciferase assays were performed to confirm direct mRNA targeting by miR-106b-25 polycistron. Results The miR-106b-25 polycistron exerted potential proliferative, anti-apoptotic, cell cycle-promoting effects in vitro and tumorigenic activity in vivo. MiRs -93 and -106b targeted and inhibited p21, while miR-25 targeted and inhibited Bim. This polycistron was upregulated progressively at successive stages of neoplasia, in association with genomic amplification and overexpression of MCM7. In addition, miRs -93 and -106b decreased p21 mRNA, while miR-25 did not alter Bim mRNA, suggesting the following discrete miR effector mechanisms: 1) for p21, mRNA degradation; 2) for Bim, translational inhibition. Conclusions The miR-106b-25 polycistron is activated by genomic amplification and is potentially involved in esophageal neoplastic progression and proliferation via suppression of two target genes, p21 and Bim.