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ER activity in the colon prevents tumorigenesis by suppressing inflammation, regulating cytokine, Wnt and Ihh availability and providing maintenance of the ISC microenvironment through modulation of crosstalk in the ECM.Adenomatous polyposis coli (APC)-regulated Wnt and transforming growth factor-β (TGFβ) signaling cooperate in the intestine to maintain normal enterocyte functions. Human clinical trials showed that estrogen [17β-estradiol (E2)], the ligand of nuclear receptors estrogen receptor α (ERα) and ERβ, inhibited colorectal cancer (CRC) in women. Consistent with this finding, we reported that E2, ERα and ERβ suppressed intestinal tumorigenesis in the C57BL/6J-Min/+ (Min/+) mouse, a CRC model. Here, we extended our results with further comparisons of colon and small intestine from intact female Apc+/+ (WT), Min/+ and ER-deficient Min/+ mice. In the colon of ER-deficient Min/+ mice, ER loss reduced TGFβ signaling in crypt base cells as evidenced by minimal expression of the effectors Smad 2, 3 and 4 in these strains. We also found reduced expression of Indian hedgehog (Ihh), bone morphogenetic protein 4 and hepatocyte nuclear factor 3β or FoxA2, factors needed for paracrine signaling between enterocytes and mesenchyme. In proximal colon, ER loss produced a >10-fold increased incidence of crypt fission, a marker for wound healing and tumor promotion. These data, combined with our previous work detailing the specific roles of E2, ERα and ERβ in the colon, suggest that ER activity helps to maintain the intestinal stem cell (ISC) microenvironment by modulating epithelial–stromal crosstalk in ways that regulate cytokine, Wnt and Ihh availability in the extracellular matrix (ECM). [ABSTRACT FROM AUTHOR]

Epidemiological studies consistently indicate that consumption of fruits and vegetables lowers cancer risk in humans and suggest that certain dietary constituents may be effective in preventing colon cancer. Plant-derived phenolic compounds manifest many beneficial effects and can potentially inhibit several stages of carcinogenesis in vivo. In this study, we investigated the efficacy of several plant-derived phenolics, including caffeic acid phenethyl ester (CAPE), curcumin, quercetin and rutin, for the prevention of tumors in C57BL/6J-Min/+ (Min/+) mice. These animals bear a germline mutation in the Apc gene and spontaneously develop numerous intestinal adenomas by 15 weeks of age. At a dietary level of 0.15%, CAPE decreased tumor formation in Min/+ mice by 63%. Curcumin induced a similar tumor inhibition. Quercetin and rutin, however, both failed to alter tumor formation at dietary levels of 2%. Examination of intestinal tissue from the treated animals showed that tumor prevention by CAPE and curcumin was associated with increased enterocyte apoptosis and proliferation. CAPE and curcumin also decreased expression of the oncoprotein β-catenin in the enterocytes of the Min/+ mouse, an observation previously associated with an antitumor effect. These data place the plant phenolics CAPE and curcumin among a growing list of anti-inflammatory agents that suppress Apc-associated intestinal carcinogenesis. [ABSTRACT FROM PUBLISHER]

Polycyclic aromatic hydrocarbons (PAHs) with sterically hindered fjord region diol epoxides are interesting with respect to their potency as carcinogens, interactions with DNA and mutagenic specificities. Unlike the bay region PAH derivative, -7,8-dihydroxy--9,10-epoxy-7,8,9,10-tetrahydroxybenzo[a]pyrene (BPDE), reactive metabolites of two fjord region PAH, -3,4-dihydroxy--1,2-epoxy-1,2,3,4-tetrahydrobenzo[]-Phenanthrene [(±)--BPHDE] and -11,12-dihydroxy--13,14-epoxy-11,12,13,14-tetrabenzo[g]chrysene [(±)--BgCDE], react with DNA to yield high levels of adenine adducts. We previously found that forward mutations induced by (±)--BPHDE in the dihydrofolate reductase () gene of Chinese hamster ovary (CHO) cells preferentially targeted mRNA splice acceptor sites. (±)--BPHDE and (±)--BgCDE are structurally similar; they differ only by the presence of an additional benzene ring. Thus we used (±)--BgCDE to learn if the mutational target bias reflects aspects of the mutagen structure or its capacity to efficiently modify deoxyadenosine (dA) . mutants were induced after treatment of hemizygous UA21 cells with a 0.75 μM dose of (±)--BgCDE. Cell survival after carcinogen exposure was 40%. The induced mutation frequency was 9×10, nearly 10-fold higher than the spontaneous one, but ∼19-fold lower than formerly observed using (±)--BPHDE. In the 26 confirmed null mutants 27 mutations were identified by DNA sequencing. The types of (±)--BCDE-induced mutations were very similar to those formerly induced by (±)--BPHDE. Consistent with the binding specificity, both chemicals induced transversion base substitutions at purines (R→T). The most prevalent type of mutation was A→T, which represented 59% of the induced changes, compared with 42% for (±)--BPHDE. (±)--BCDE mutated mostly novel targets in the gene, sites not found mutated with any of the several other mutagens we have used in former studies. Whereas the 25 kb gene contains six coding exons, the majority (16/27) of (±)--BCDE-induced mutations were located in a single one (exon 4). A random distribution of mutations affecting splice acceptor sites (22%) was induced by (±)--BCDE. Hence, preferential mutation of these sites by (±)--BPHDE may reflect aspects of chromatin structure which make these sequences better targets for modification. Alternatively, the sequence context of these sites may dictate an adduct conformation which is poorer for damage recognition and/or efficient repair. [ABSTRACT FROM PUBLISHER]

This study presents the physical characterization of mutants induced in mammalian cells by high linear energy transfer α-Particle radiation that simulates exposure to radon daughters. α-Particles from accelerated He at 150 keV/μm were used to induce 20 Chinese hamster ovary mutants that are deficient in dihydrofolate reductase (DHFR) activity. Parental cells were the hemizygous UA21 line. Cell survival decreased exponentially in response to radiation dose from 0.25 to 1.75 Gy. Mutants were obtained at 1.0 (17/20) and 1.25 Gy (3/20); treatments at 1.50 Gy failed to yield mutants. The induced frequency of mutation was 2.3×10 at the 1.0 Gy dose, ∼18-fold greater than the spontaneous mutation rate at this locus. DNA of the 20 confirmed null mutants were examined for alterations in the 25 kb gene by Southern blotting using a mixed probe that scans a continuous 34 kb of sequence. Deletions were the most prevalent induced change (18/20). Of the two point mutants, DNA sequencing showed that one carries a T:A→G:C base substitution that changed Vall35 to Gly in exon 5; carcinogen-induced reversion to a DHFR phenotype at a frequency of 3×10 confirmed that the other also carried a single base change. The distribution of deletion break sites in the locus was non-random. In half of the mutants deletion break sites were clustered within a single 9.4 kb intron. Fine mapping within the gene of 14 mutants by Southern blotting localized 10 distinct break sites to small restriction fragments (<2 kb). Results of this mapping indicated that three unequivocally independent mutants apparently arose by the same deletion and that others shared single break sites. Deletion sizes in these mutants were determined by Southern analysis using six cosmids and two plasmid probes that together span ∼500 kb of sequence in the region of the locus. Probing blots with the cosmids defined a maximal deletion size in 15/17 mutants and confirmed that deletions extended <150 kb in 11, a qualitatively different result from that previously obtained after a similar analysis of γ-ray-induced mutants. Since deletions were non-randomly distributed, typically less than replicon size and spared regions containing matrix attachment sites, the results suggest a model whereby α-particles induce double-strand breaks in accessible chromatin loops. [ABSTRACT FROM PUBLISHER]

Eighteen mutants deficient in dihydrofolate reductase (DHFR) activity were induced with 0.5 μM -hydroxy-aminofluorene in four separate experiments. This carcinogen dose killed ∼80% of the treated cells and resulted in a mutational frequency ∼3×10. The nature of the induced changes in each of the mutants was determined by direct sequencing following polymerase chain reaction amplification, or in one instance, by Southern blot analysis. Nearly all (15/17) of the mutations were single base changes. Consistent with the binding specificity of this chemical, all mutations were targeted to guanine bases. The predominant change was G:C → T:A transversion which was evident in 11/15 mutants. A single dG-AF mutational hotspot was noted at a site in the DHFR coding sequence of exon 4; one-third of the induced point mutations arose at this position. These results are compared with our previous analyses of mutants induced with the related aromatic amine, -2-acetoxy-2-acetyl-aminofluorene. [ABSTRACT FROM PUBLISHER]