LAUSR

Simple Summary MicroRNAs (miRNAs) are a class of highly conserved small, non-protein coding RNAs with often-deregulated expression in cancer. miR-21 is a well-studied cancer-associated microRNA which is able to regulate proliferation, apoptosis, and invasion. The aim of this study was to investigate the molecular pathways which govern miR-21 expression in gastric cancer (GC), and to assess the therapeutic benefit of targeting miR-21 function with a small, synthetic miR-21 antagomir. We confirmed that miR-21 expression in a preclinical model of early gastric cancer is dependent on Stat3 downstream of the IL-6 family cytokine-mediated activation of gp130 receptor signaling. Antagomir therapy curbed gastric tumor growth, and restricted epithelial-to-mesenchymal transition and matrix remodeling. Our study established miR-21 as a promising anti-cancer target in GC. Abstract MicroRNA-21 (miR-21) is a small, non-coding RNA overexpressed in gastric cancer and many other solid malignancies, where it exhibits both pro-and anti-tumourigenic properties. However, the pathways regulating miR-21 and the consequences of its inhibition in gastric cancer remain incompletely understood. By exploiting the spontaneous Stat3-dependent formation of inflammation-associated gastric tumors in Gp130F/F mice, we functionally established miR-21 as a Stat3-controlled driver of tumor growth and progression. We reconciled our discoveries by identifying several conserved Stat3 binding motifs upstream of the miR-21 gene promoter, and showed that the systemic administration of a miR-21-specific antisense oligonucleotide antagomir reduced the established gastric tumor burden in Gp130F/F mice. We molecularly delineated the therapeutic benefits of miR-21 inhibition with the functional restoration of PTEN in vitro and in vivo, alongside an attenuated epithelial-to-mesenchymal transition and the extracellular matrix remodeling phenotype of tumors. We corroborated our preclinical findings by correlating high STAT3 and miR-21 expression with the reduced survival probability of gastric cancer patients. Collectively, our results provide a molecular framework by which miR-21 mediates inflammation-associated gastric cancer progression, and establish miR-21 as a robust therapeutic target for solid malignancies characterized by excessive Stat3 activity.