We systematically verified the operation, usefulness, and specificity of our miRDREL system with miRNA-targeting cis-elements, including established oncomiRs [miR-21, let-7a, miR-7, miR-122, and miR-210 (data not shown)] and natural miRNA-targeting sites, such as those harbored in mRNAs encoding CDC34, PPP1R3B, SATB1, and GYS1 in various cancer cell lines and in animal tumor models. The gene discussed is PPP1R3B; the disease is cancer.