A ROS may result in ER-stress. ROS or/and ER-stress incurs JNK activation. The activated JNK leads to pancreatic β cell apoptosis via mitochondria-dependent or independent pathways. B Acute ROS or ER-stress results in the expression of NR4A1, which in turn enhances the expression of MKP7, while MKP7 is able to abolish partial JNK activation by exerting its phosphatase activity, therefore, largely reduces pancreatic β cell apoptosis. The fate of pancreatic β cells depends on the balance between the availability of NR4A1 or MKP7 and the severity of ROS or ER-stress.