MAPK8 and epidermolysis bullosa simplex: An interesting point in this regard is the ability of retinoic acid to act as an antagonist of Jun N-terminal kinase (JNK)-signaling, mediated by activating protein 1 (AP1) [30], since JNK/mitogen activated protein kinase (MAPK) signal transduction has previously been shown to be dysregulated in EBS-DM model keratinocytes [9, 31, 32].