MAPK8 and pulmonary fibrosis: Supporting a role for JNK in stromal tissues, JNK1 has been shown to promote lung fibrosis in vivo, and to control ROS production through NADPH oxidase 4 (NOX4) thus inducing myofibroblast differentiation and upregulation of alpha-smooth muscle actin (α-SMA) in human breast stromal cells [18, 19].