The peroxisome proliferator-activated reccptora (PPARa) is the mediator of the biological effects of pcroxisome proliferators through control of gene transcription. To determine if the toxic effects of di(2-ethylhexy1)phthalate (DEHP) are mediated by PPARa, we examined its effect in PPARa-null micc. Male Sv1129 mice. PPARa-null (-/-) or wild-typc (+I+) were fed nd libirirrn either a control diet or one containing 12.000 ppm DEHP for up to 24 wk. Significant body weight loss and high mortality was observcd in (+/+) mice fed DEHP. By 16 wk, all DEHP-fed (+I+) mice had died of cystic renal tubular disease. In contrast, the (-/-) mice fed DEHP had no changes in body weight until later in the study nor increased mortality. Histologically, (+/+) mice fed DEHP had typical toxic lesions in liver, kidney, and testis while (-/-) mice fed DEHP had no toxic liver lcsions but did show cvidence of toxicity in kidney and testis after 4-8 wk of feeding, which progressed into moderate lesions by 24 wk. Analysis of hepatic and renal mRNAs showed a typical pleiotropic response in gene expression in the DEHP-fed (+/+) mice that was absent in the DEHP-fed (-1 -) mice. These results provide evidence that PPARa mediates the subacute-chronic toxicity of DEHP in liver, kidney, and testis. However, because (-/-) mice did develop toxic lesions in kidney and testis. DEHP can also act through PPARa-independcnt pathways in mediating renal and testicular toxicity. Knockout mice; peroxisomal proliferator; liver; peroxisomal proliferator activated receptor; di(2-ethylhexy1)phthalate (DEHP); kidney; cystic kidneys Keywords.

Recent results suggest a paradigm shift from viewing inorganic phosphate as a passive requirement for basic cell functions to an active regulator of cell behavior. We have previously shown that elevated concentrations of phosphate increased cell proliferation and expression of protumorigenic genes such as Fra-1 and osteopontin in a preosteoblast cell line. Therefore, we hypothesized that elevated phosphate concentrations would promote cell transformation in vitro and tumorigenesis in vivo. Supplementation of medium with phosphate increased anchorage-independent transformation and proliferation of BALB/c mouse JB6 epidermal cells, activation of N-ras, ERK1/2, and activator protein-1, and increased gene expression of Fra-1, COX-2, and osteopontin in a dose-dependent manner. These in vitro results led to the hypothesis that varying the levels of dietary inorganic phosphate would alter tumorigenesis in the mouse model of skin carcinogenesis. Female FVB/N mice were treated with 7,12-dimethylbenz (a)anthracene/12-O-tetradecanoylphorbol-13-acetate and fed high-or low-phosphate diets (1.2% versus 0.2% of the diet) for 19 weeks. The high-phosphate diet increased skin papilloma number by ∼50% without changing feed intake and body weights. High dietary phosphate increased serum concentrations of phosphate, parathyroid hormone, and osteopontin and decreased serum concentrations of calcium. Thus, we conclude that elevated phosphate promotes cell transformation and skin tumorigenesis partly by increasing the availability of phosphate for activation of N-ras and its downstream targets, which defines reducing dietary phosphate as a novel target for chemoprevention. Cancer Prev Res; 3(3); 359-70. ©2010 AACR.

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]