JUN and papilloma: For example A-C/EBP (a dominant negative of C/EBP family of bZIPs) when expressed as transgene in the mouse skin, regress pre-formed papilloma13 whereas expression of A-Fos, a dominant negative that inhibits the functions of Fos and Jun family of bZIPs, transdifferentiate papilloma into benign sebaceous adenomas11.