The transgene contains a 2075-bp human keratin 14 promoter construct driving expression of a cDNA that encodes a fusion protein comprising a constitutively active mutant form of the catalytic domain of human RAF1, in which tyrosine is replaced by aspartic acid at amino acid positions 340 and 341 (Y340D/Y341D), joined at its carboxyl-terminal to the ligand-binding domain of human estrogen receptor 1. The fusion protein can be activated in the epidermis by topical application of 4-hydroxytamoxifen.