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Dominant-Negative Activator Protein 1 (TAM67) Targets Cyclooxygenase-2 and Osteopontin under Conditions in which It Specifically Inhibits Tumorigenesis

¹ Laboratory of Cancer Prevention, Center for Cancer Research, ² Science Applications International Corporation-Frederick, National Cancer Institute, Frederick, Maryland and ³ Emory University School of Medicine, Atlanta, Georgia

Requests for reprints: Connie P. Matthews, Laboratory of Cancer Prevention, Center for Cancer Research, National Cancer Institute-Frederick, Frederick, MD 21702. Phone: 301-846-6858; Fax: 301-846-6907; E-mail: cmatthews{at}mail.ncifcrf.gov.

Activation of activator protein 1 (AP-1) and nuclear factor B (NFB)–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 NFB activation by interacting with NFB 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 NFB-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 NFB sites important in the Cox-2 promoter and an AP-1 site important in the Opn promoter. [Cancer Res 2007;67(6):2430–8]

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