FIGURE 1.

MKK4 regulates Cx43 expression via JNK/c-Jun activation in cardiomyocytes. A, NRCMs were transfected with MKK4 siRNA or control siRNA for 72 h prior to immunoblotting for MKK4 expression. MKK7 protein expression was examined to determine the specificity of MKK4 knockdown. siMKK4-NRCMs were treated with PE (100 μm) for 30 min before detecting phosphorylation of JNK and c-Jun by immunoblotting. B, quantitative real-time PCR analyses of Cx43 transcript levels (upper panel) and immunoblot analysis of Cx43 protein expression (lower panel) in siMKK4-NRCMs following PE treatment (100 μm, 48 h). Tubulin expression is the protein loading control. C, siRNA-transfected NRCMs were infected with AdCx43APwt-Luc (multiplicity of infection, 25) for 24 h followed by PE treatment (100 μm, 24 h). The Cx43 promoter-dependent luciferase activity was measured by the luciferase reporter assay system. Data are mean ± S.E. (n = 3 per group). D, Ad-dnMKK4-NRCMs were treated with PE (100 μm) for 30 min before detecting activation of c-Jun and JNK by immunoblotting. Immunoblot analysis shows MKK4 expression in Ad-dnMKK4-NRCMs. E, quantitative real-time PCR analyses of Cx43 transcript levels (upper panel) and immunoblot analysis of Cx43 protein expression (lower panel) in Ad-dnMKK4-NRCMs. Ad-GFP is a control virus. Tubulin expression is the protein loading control. F, infection of Ad-dnMKK4 in cardiomyocytes decreased the PE-induced Cx43 promoter-dependent luciferase activity. Data are mean ± S.E. (n = 3 per group).