Transgenic and knockout experiments demonstrated that SERPINB2 (plasminogen activator inhibitor-2) promotes HRASQ61L-driven skin papilloma formation in mice treated with 7,12-Dimethylbenz[a]anthracene (DMBA) and 12-O-Tetradecanoylphorbol-13-acetate (TPA) [37, 38] and we demonstrated that ERK-mediated SerpinB2 up-regulation was responsible for the elevated levels of DMBA/TPA-induced skin carcinogenesis observed in mice lacking DUSP5 [14]. Here, MAPK1 is linked to skin papilloma.