While evidence in both sporadic and inherited human colorectal cancer and MIN mice implicate the tumor suppressor gene, APC, in the causation of colorectal carcinogenesis, this gene has not been confirmed to be involved in rodent chemically-induced colon cancer models (RCCM). These experimental models are widely used to elucidate mechanisms involved in colon carcinogenesis (initiation, promotion and progression) as well as studies on chemoprevention (dietary and other) and intervention. To validate the RCCM as relevant models for sporadic human colorectal cancer, and to facilitate research on the role of the APC gene in colon carcinogenesis, we investigated the role of APC in azoxymethane (AOM)-induced colorectal tumors in mice. Using an antibody that recognizes the carboxy terminus of APC, we have characterized the pattern of staining observed in normal mouse intestinal tissue, in MIN mouse intestinal adenomas and in AOM-induced mouse colon tumors. The APC protein was localized in the cytoplasm of normal colonic epithelial cells. In the small intestine there was APC immunoreactivity along the villous and staining of the Paneth cells at the base of the glands. In the proximal and distal colonic crypts there appeared to be a gradient of staining which increased towards the luminal surface. This gradient was not as apparent in the small intestinal villi. Nuclei and mucus in the goblet cells showed no immunoreactivity. MIN mouse small bowel and colonic adenomas, known to have lost APC, stained negatively for APC. AOM-induced adenomas and carcinomas also consistently stained negatively using this antibody. This study demonstrates for the first time the loss of wild-type APC protein in AOM-induced mouse colon tumors and suggests that alterations in expression of this tumor suppressor gene, which is so commonly mutated in human colon cancer, is also involved in this animal model of colon cancer.

Nonsteroidal anti-inflammatory drugs (NSAIDs) including sulindac have shown potent chemopreventive and tumor regressive effects against colorectal cancer, the second leading cause of cancer death in the United States. However, the mechanisms by which sulindac inhibits tumor cell growth are not completely understood. We previously reported that sulindac metabolites inhibit the mitogen-activated protein/extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase (MEK/ ERK) signaling cascade in colorectal cancer cell lines at doses that induce apoptosis, and inhibition of MEK/ERK activity with U0126 is sufficient to induce apoptotic cell death. To determine whether inhibition of MEK/ ERK activity is necessary for sulindac-induced apoptosis of human colon cancer cells, stable transfectants were created that express an activated MEK1 gene in HT29 cells. HT29-MEK1(R4F) clones displayed a 10-to 20-fold increase in MEK1 activity compared with control HT29-pCEP4 clones. When compared with control HT29-pCEP4 clones, HT29-MEK1(R4F) clones were resistant to both apoptosis and inhibition of ERK1/2 phosphorylation induced by sulindac metabolites. These results suggest that inhibition of MEK/ERK signaling is necessary for the induction of apoptosis by sulindac metabolites.

SUMMARYBacteriophage-like particles were induced from 6 of 21 strains of stalked bacteria, using mitomycin C or ultraviolet irradiation as the inducing agents. The phage inductions were observed in strains of Caulobacter crescentus, C. vibrioides and C. bacteroides. The phage-like particles were observed, using electron microscopy. Two of the phage-like entities, tentatively designated defective phages, could not be propagated on any of 2I potential host strains tested, nor did they possess bacteriocin activity. Host strains which permitted lyric cycles of phage replication were found for four induced phages .These bacteriophages contained double-stranded DNA. The bacterial strains from which they were induced were iresistant to infection by their respective phage. Four bacterial strains were treated with specific antiphage serum, but clones so treated retained their capacity to produce the phages. The inefficacy of antiphage serum in curing the bacteria of phage suggested that these Caulobacter strains were lysogenic.

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