PPP1R13L and skin neoplasm: AP1 was first identified as a TPA-activated transcription factor (Angel et al., 1987) and is also an important regulator of epidermal differentiation and skin tumor development (Eckert et al., 2013), consistent with iASPP being an inhibitor of AP1 and a suppressor of DMBA/TPA-induced tumorigenesis in mouse skin (Figure 7B).