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

Abstract

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

Sulfiredoxin is an AP-1 target gene that is required for transformation and shows elevated expression in human skin malignancies

“…In an effort to identify genes that are stimulated by tumor promoter-induced AP-1 activation and inhibited by TAM67, comparative gene expression profiling of mouse epidermis from 12-dimethylbenz(a)anthracene (DMBA)-initiated wild-type or K14-TAM67 transgenic mice with or without exposure to TPA for 6 h was performed. As expected, only a small set of genes was shown to be significantly induced by a tumor promoter and blocked by TAM67 (9). Among them, Srx emerges as a unique target gene whose induction by TPA was blocked by TAM67.…”

“…JB6 cells were cultured in standard conditions with 4% FBS. DNA microarrays, transient transfections, and luciferase reporter assays were performed as previously reported (9). For cell growth and proliferation assay, 10 3 cells were plated in each well of 96-well plate.…”

“…Therefore, we hypothesize that TAM67 targets only a handful of AP-1-dependent genes that are critical for transformation and tumorigenesis. We previously identified a subset of genes whose expression was induced by TPA and inhibited by TAM67 using DNA microarray profiling of K14-TAM67 and wild-type mouse epidermis exposed to tumor promoter (9). Among these target genes are cyclooxygenase-2 (Cox-2), matrix metalloproteinase-10 (MMP-10), urokinase plasminogen activator (Plaur/uPAR), osteopontin (Spp1/Opn) and CD44 (9), which are known to play significant roles in driving tumor promotion and progression.…”

Suppressor role of activating transcription factor 2 (ATF2) in skin cancer

“…Specifically, c-Jun family members were shown to play an important role in skin cancer development because K14-driven expression of the TAM67 dominant-negative Jun family construct in the basal layer of the epidermis blocked phorbol 12-tetradecanoate 13-acetate (TPA) or UV-B induced tumors in a skin carcinogenesis model (18)(19)(20). In addition, mice in which c-Jun or JNK2 has been deleted exhibit marked reduction in skin cancer development (21)(22)(23).…”

Update on Cancer Prevention Research in the United States and China: The 2009 China—U.S. Forum on Frontiers of Cancer Research

“…The molecular events of AP-1 or NF-kB-dependent transcription and eIF4F-dependent translation in carcinogenesis have been a major focus of Dr. Nancy H. Colburn's (Laboratory of Cancer Prevention, Center for Cancer Research, National Cancer Institute, National Institutes of Health) laboratory for a number of years and these were highlighted by Dr. Colburn (77)(78)(79)(80). Activation of AP-1 and NF-kB is necessary to drive tumor promotion and tumor progression and Dr. Colburn's group has demonstrated that the preventive efficacy of the AP-1 blocker TAM67 now extends from skin to mammary and lung carcinogenesis.…”