No abstract

Excessive weight gain during pregnancy increases breast cancer risk in women. To determine whether this may be caused by increased pregnancy leptin levels, leptin receptor (Ob-Rb) mutant (fa/fa) and wild-type (FA/FA) female Zucker rats and Sprague-Dawley rats were fed during pregnancy an obesity-inducing high-fat diet (OID) that increased pregnancy weight gain, or a control diet. Because mutant Zucker rats do not readily become pregnant, their pregnancy was mimicked by exposing the rats to subcutaneous silastic capsules containing 150 microg of estradiol and 30 mg of progesterone for 3 wk. Sprague-Dawley rats underwent normal pregnancy. An assessment of hormone levels on gestation d 17 indicated that an exposure to the OID significantly elevated serum leptin concentration but did not affect those of estradiol or insulin-like growth factor 1 (IGF-1). Insulin and adiponectin levels were higher in the obese than lean Zucker rats, but were not related to pregnancy weight gain. Exposure to the OID during pregnancy increased 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumorigenesis in all genetic backgrounds, including leptin receptor mutant Zucker rats. The results also indicated that obese Zucker rats that underwent mimicked pregnancy developed more palpable tumors and hyperplastic alveolar nodules that lean Zucker rats. Further, mammary epithelial cell proliferation assessed using PCNA staining was elevated in obese Zucker rats as was activation of mitogen-activated protein kinase (MAPK); however, neither of these 2 changes occurred in the context of excessive weight gain during pregnancy. It remains to be determined whether an increase in leptin levels was causally associated with an increase in the dams' mammary tumorigenesis, including in obese Zucker rats with dramatically reduced leptin signaling.

Flaxseed contains several dietary components that have been linked to low breast cancer risk; i.e., n-3 polyunsaturated fatty acids (PUFAs), lignans and fiber, but it also contains detectable levels of cadmium, a heavy metal that activates the estrogen receptor (ER). Since estrogenic exposures early in life modify susceptibility to develop breast cancer, we wondered whether maternal dietary intake of 5% or 10% flaxseed during pregnancy or lactation (between postpartum days 5 and 21) might affect 7,12-dimethylbenz[a]anthracene (DMBA) -induced mammary tumorigenesis in the rat offspring. Our data indicated that both in utero and postnatal 5% and 10% flaxseed exposures shortened mammary tumor latency, and 10% flaxseed exposure increased tumor multiplicity, compared to the controls. Further, when assessed in 8-week-old rats, in utero 10% flaxseed exposure increased lobular ER-α protein levels, and both in utero and postnatal flaxseed exposures dose-dependently reduced ER-β protein levels in the lobules and terminal end buds (TEBs). Exposures to flaxseed did not alter the number of TEBs or affect cell proliferation within the TEBs, lobules or ducts. In a separate group of immature rats that were fed 5% defatted flaxseed diet (flaxseed source different than in the diets fed to pregnant or lactating rats) for 7 days, cadmium exposure through the diet was 7-fold higher than allowed for humans by World Health Organization, and cadmium significantly accumulated in the liver and kidneys of the rats. It remains to be determined whether the increased mammary cancer in rats exposed to flaxseed through a maternal diet in utero or lactation was caused by cadmium present in flaxseed, and whether the reduced mammary ER-β content was causally linked to increased mammary cancer risk among the offspring.

Maternal diet during pregnancy has been proposed to modify female offspring's later susceptibility to develop breast cancer; however, most of the dietary factors identified thus far have led to increased risk. To identify dietary factors that might reduce offspring's breast cancer risk, pregnant rat dams were fed diets containing 6% fiber originating either from cellulose (control), or oat, whole wheat or defatted flax flour. At birth, dams were switched to the AIN93 semi-purified diet. Mammary tumor incidence and multiplicity, induced by administering the offspring 5 mg 7,12-dimethylbenz[a]anthracene (DMBA) at the age of 50 days, was reduced in the whole wheat flour-exposed offspring and increased in the defatted flax-exposed offspring. To identify the mechanisms mediating the effects of in utero dietary exposures, changes in mammary gland morphology and gene expression were assessed before puberty onset (3 weeks of age) and at the time rats are most susceptible to malignant transformation (8 weeks of age). The number of terminal end buds (TEBs), i.e., the targets of malignant transformation, was reduced in the mammary glands of whole wheat-and oat flour-exposed offspring, as compared to the controls. Further, the number of apoptotic epithelial cells (based on ISOL assay) was elevated in the whole wheat flour offspring, but no changes in cell proliferation (PCNA), estrogen receptor a (ERa) or cyclin D1 mRNA or protein levels were seen. The mRNA and/or protein levels of BRCA1 and p53 were significantly increased in the mammary glands of whole wheat flour offspring. Further, the levels of 8-hydroxy-2 0 -deoxyguanosine (8-OHdG), a marker of DNA damage, were significantly reduced in these rats, suggesting that maternal dietary exposure to whole wheat during pregnancy may reduce offspring's breast cancer risk by improving DNA damage repair mechanisms. ' 2006 Wiley-Liss, Inc.

Aberrations in BMP signaling have recently been implicated as a cause of human cancer. Here we demonstrate and define the tumor suppressive properties of BMP4. Consistent with its potential role in a tumor suppressor pathway, BMP4 treatment eliminated the tumorigenic potential of an undifferentiated human cancer cell line. This loss of tumorigenicity was accompanied by an increase in apoptosis, alterations in cell cycle profile, and an increase in cell size. Interestingly, human colon cancer cells were resistant to the growth-suppressive properties of BMP4. To identify putative downstream mediators of BMP4-mediated tumor suppression, Affymetrix Genechips were employed to identify BMP4-regulated genes. The human BMP4 transcriptome was characterized by the modulation of many genes well known to play important roles in differentiation and development, including the induction of numerous genes involved in Wnt signaling. Modulation of Wnt gene expression by BMP4 had several functional consequences--BMP4 treatment led to activation of TCF reporters; complete activation of at least one BMP4-responsive gene required TCF sites; and treatment with a Wnt ligand was sufficient to mimic several of the phenotypic effects of BMP4 treatment. These data demonstrate the tumor suppressive properties of BMP4 signaling, show that colon cancer cells are resistant to BMP4-induced differentiation and growth suppression, further define the BMP4 transcriptome, and raise the intriguing possibility that interactions between the Wnt and BMP signaling pathways may play an important role in differentiation and tumor suppression.