Identification of dominant negative AP-1 (TAM67) target genes important for inhibition of tumorigenesis but not cell proliferation or survival.

Fifth AACR International Conference on Frontiers in Cancer Prevention Research, Nov 12-15, 2006 A105 Activation of AP-1 and NFκB 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 NFκB activation by interacting with NFκB p65. Two-stage (DMBA/ 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 NFκB 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 whose 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. As predicted by the selective effects of TAM67 in the mouse model, transcription of cell proliferation genes (Cyclin D3/Ccnd3, Rb1) and cell survival genes (Bcl2l2/Bcl-w, Rela/p65) is not inhibited by TAM67. Interestingly, many of the TAM67 targets implicated after a single 6 hour dose of the tumor promoter TPA are genes known to be involved in invasion and metastasis. Many of these genes had not previously been established as important for earlier stages of carcinogenesis. This is a significant observation because these genes now emerge as promising treatment targets during early, middle, and late-stage carcinogenesis. Genes important for maintaining tumor phenotype and stimulating aggressive cancer development now emerge as important in tumor promotion and early tumorigenesis. Because the rate limiting steps in tumorigenesis occur during tumor promotion and progression, the functionally significant TAM67 targets implicated in tumorigenesis are important targets for cancer prevention. These observations raise the possibility that all of the epigenetic makings of cancer are present early in carcinogenesis during tumor promotion.