Dominant-negative activator protein 1 (TAM67) targets cyclooxygenase-2 and osteopontin under conditions in which it specifically inhibits tumorigenesis.

Activation of activator protein 1 (AP-1) and nuclear factor kappaB (NFkappaB)-dependent transcription is required for tumor promotion in cell culture models and transgenic mice. Dominant-negative c-Jun (TAM67) blocks AP-1 activation by dimerizing with Jun or Fos family proteins and blocks NFkappaB activation by interacting with NFkappaB p65. Two-stage [7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)] skin carcinogenesis experiments in a model relevant to human cancer risk, transgenic mice expressing human papillomavirus 16 E7 oncogene (K14-HPV16-E7), show E7-enhanced tumor promotion. A cross to K14-TAM67-expressing mice results in dramatic inhibition of tumor promoter-induced AP-1 luciferase reporter activation and papillomagenesis. Epithelial specific TAM67 expression inhibits tumorigenesis without affecting TPA- or E7-induced hyperproliferation of the skin. Thus, the mouse model enriches for TAM67 targets relevant to tumorigenesis rather than to general cell proliferation or hyperplasia, implicating a subset of AP-1- and/or NFkappaB-dependent genes. The aim of the present study was to identify target genes responsible for TAM67 inhibition of DMBA-TPA-induced tumorigenesis. Microarray expression analysis of epidermal tissues revealed small sets of genes in which expression is both up-regulated by tumor promoter and down-regulated by TAM67. Among these, cyclooxygenase-2 (Cox-2/Ptgs2) and osteopontin (Opn/Spp1) are known to be functionally significant in driving carcinogenesis. Results identify both Cox-2 and Opn as transcriptional targets of TAM67 with CRE, but not NFkappaB sites important in the Cox-2 promoter and an AP-1 site important in the Opn promoter.