Mir-21 and ANF Promoter activity assays. 8A. Mir-21 promoter is regulated by SRF and its cofactors, myocardin and p49/Strap. In vitro transfection assay indicates that both SRF and p49/Strap repressed the mir-21-luciferase reporter activity, respectively (p < 0.05, n = 3). Myocardin (MYOCD) strongly activated the mir-21 promoter activity (p < 0.05). p49 also repressed mir-21-luciferase reporter activity induced by myocardin in a dose-dependent manner (p < 0.01 **, n = 3). 8B. The mir-21 microRNA up-regulates ANF expression. The microRNA mir-21 up-regulated ANF gene promoter (p < 0.05*, n = 3). P49/Strap (p49), SRF isoform Δ3, SRF, Zipzap (zip) and Nkx2.5 all down-regulated the ANF gene promoter activity that was induced by mir-21 microRNA (p < 0.05, n = 3).