The mechanisms that initiate liver regeneration after resection of liver tissue are not known. To determine whether cytokines are involved in the initiation of liver growth, we studied the regeneration of the liver after partial hepatectomy (PH) in mice lacking type I tumor necrosis factor receptor (TNFR-I). DNA synthesis after PH was severely impaired in these animals, and the expected increases in the binding of the NF-B and STAT3 transcription factors shortly after PH failed to occur. Binding of AP-1 after PH was decreased in TNFR-I knockout mice compared with animals with the intact receptor whereas C͞EBP binding was not modified. Injection of interleukin 6 in TNFR-I-deficient animals 30 min before PH corrected the defect in DNA synthesis and restored STAT3 and AP-1 binding to normal levels but had no effect on NF-B binding in the regenerating liver. The results indicate that TNF, signaling through the TNFR-I, can initiate liver regeneration and acts by activating an interleukin 6-dependent pathway that involves the STAT3 transcription factor.

The POU-domain transcription factor Oct-4 is normally expressed in pluripotent cells of the mammalian embryo. In addition, germ-cell tumors and a few somatic tumors show detectable expression of Oct-4. While Oct-4's role during preimplantation development is to maintain embryonic cells in a pluripotent state, little is known about its potential oncogenic properties. Here we investigate the effect of ectopic Oct-4 expression on somatic tissues of adult mice using a doxycycline-dependent expression system. Activation of Oct-4 results in dysplastic growths in epithelial tissues that are dependent on continuous Oct-4 expression. Dysplastic lesions show an expansion of progenitor cells and increased beta-catenin transcriptional activity. In the intestine, Oct-4 expression causes dysplasia by inhibiting cellular differentiation in a manner similar to that in embryonic cells. These data show that certain adult progenitors remain competent to interpret key embryonic signals and support the notion that progenitor cells are a driving force in tumorigenesis.

To develop an efficient animal model for colitis-related carcinogenesis, male Crj: CD-1 (ICR) mice were given a single intraperitoneal administration (10 mg/kg body weight) of a genotoxic colonic carcinogen, azoxymethane (AOM), and a 1-week oral exposure (2% in drinking water) to a non-genotoxic carcinogen, dextran sodium sulfate (DSS), under various protocols. At week 20, colonic neoplasms (adenocarcinomas, 100% incidence with 5.60 ± ± ± ±2.42 multiplicity; and adenomas, 38% incidence with 0.20 ± ± ± ±0.40 multiplicity) with dysplastic lesions developed in mice treated with AOM followed by DSS. Protocols in which AOM was given during or after DSS administration induced a few tubular adenomas or no tumors in the colon. Immunohistochemical investigation of such dysplasias and neoplasms revealed that all lesions were positive for β β β β-catenin, cyclooxygenase-2 and inducible nitric oxide synthase, but did not show p53 immunoreactivity. The results indicate that 1-week administration of 2% DSS after initiation with a low dose of AOM exerts a powerful tumor-promoting activity in colon carcinogenesis in male ICR mice, and may provide a novel mouse model for investigating colitis-related colon carcinogenesis and for identifying xenobiotics with modifying effects. (Cancer Sci 2003; 94: 965-973) n the developed world, colorectal cancer (CRC) is one of the commonest non-smoking related cancers. This malignancy is one of the most serious complications of inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), 1,2) and the risk of CRC increases with increasing extent and duration of the disease.Animal experiments are assumed to simulate or at least provide plausible pathophysiological mechanisms in various diseases including cancer and inflammatory disorders. For IBD and IBD-related CRC, several animal models have been reported. The most widely used is a mouse model with dextran sodium sulfate (DSS).3) There are a number of reports on modifying effects of xenobiotics on CRC-related colon carcinogenesis in this model 4,5) : folic acid, short chain fatty acid (butyrate), ursodeoxycholic acid, nonsteroidal anti-inflammatory drugs (NSAIDs)/cyclooxygenase (COX)-2 inhibitors, and 5-aminosalicylic acid (5-ASA) were found to inhibit the occurrence of UC-related CRC. However, this colitis model using DSS with or without carcinogen needs a long period or repeated administration of DSS to induce colitis and colitis-related CRC, and the incidence and/or multiplicity of induced tumors are relatively low.6) Many studies have suggested that chronic or repeated mucosal inflammation may result in carcinogenesis through mechanisms such as induction of genetic mutations, increased cryptal cell proliferation, changes in crypt cell metabolism, changes in bile acid enterohepatic circulation, and alterations in bacteria flora. 7,8) These ideas are consistent with the hypothesis that chronic inflammation could be associated with epithelial malignant neoplasia in the large bowel. 8) We recently reported c...