Low Incidence Of Mammary Cancer Research Articles

MiRNA-214-3p stimulates carcinogen-induced mammary epithelial cell apoptosis in mammary cancer-resistant species

Mammary cancer incidence varies greatly across species and underlying mechanisms remain elusive. We previously showed that mammosphere-derived epithelial cells from species with low mammary cancer incidence, such as horses, respond to carcinogen 7, 12-Dimethylbenz(a)anthracene-induced DNA damage by undergoing apoptosis, a postulated anti-cancer mechanism. Additionally, we found that miR-214-3p expression in mammosphere-derived epithelial cells is lower in mammary cancer-resistant as compared to mammary cancer-susceptible species. Here we show that increasing miR-214 expression and decreasing expression of its target gene nuclear factor kappa B subunit 1 in mammosphere-derived epithelial cells from horses abolishes 7,12-Dimethylbenz(a)anthracene-induced apoptosis. A direct interaction of miR-214-3p with another target gene, unc-5 netrin receptor A, is also demonstrated. We propose that relatively low levels of miR-214 in mammosphere-derived epithelial cells from mammals with low mammary cancer incidence, allow for constitutive gene nuclear factor kappa B subunit 1 expression and apoptosis in response to 7, 12-Dimethylbenz(a)anthracene. Better understanding of the mechanisms regulating cellular responses to carcinogens improves our overall understanding of mammary cancer resistance mechanisms.

Dairy animals and breast cancer: reflections on a long-term study from the 1970s that was never done.

In this short commentary I recall a long-term experiment that was sketched out to determine if the low incidence of mammary cancer in dairy animals reflects a low incidence in these species generally or is the result of a protective effect of early pregnancy and long lactations. Although that experiment was never done, I discuss these questions in the light of developing knowledge on the incidence of cancer in ruminants generally and in the mammary gland in particular.

Development of mammary cancer in γ-irradiated F1 hybrids of susceptible Sprague-Dawley and resistant Copenhagen rats, with copy-number losses that pinpoint potential tumor suppressors.

Copenhagen rats are highly resistant to mammary carcinogenesis, even after treatment with chemical carcinogens and hormones; most studies indicate that this is a dominant genetic trait. To test whether this trait is also dominant after radiation exposure, we characterized the susceptibility of irradiated Copenhagen rats to mammary carcinogenesis, as well as its inheritance, and identified tumor-suppressor genes that, when inactivated or mutated, may contribute to carcinogenesis. To this end, mammary cancer-susceptible Sprague-Dawley rats, resistant Copenhagen rats, and their F1 hybrids were irradiated with 4 Gy of γ-rays, and tumor development was monitored. Copy-number variations and allelic imbalances of genomic DNA were studied using microarrays and PCR analysis of polymorphic markers. Gene expression was assessed by quantitative PCR in normal tissues and induced mammary cancers of F1 rats. Irradiated Copenhagen rats exhibited a very low incidence of mammary cancer. Unexpectedly, this resistance trait did not show dominant inheritance in F1 rats; rather, they exhibited intermediate susceptibility levels (i.e., between those of their parent strains). The susceptibility of irradiated F1 rats to the development of benign mammary tumors (i.e., fibroadenoma and adenoma) was also intermediate. Copy-number losses were frequently observed in chromosome regions 1q52-54 (24%), 2q12-15 (33%), and 3q31-42 (24%), as were focal (38%) and whole (29%) losses of chromosome 5. Some of these chromosomal regions exhibited allelic imbalances. Many cancer-related genes within these regions were downregulated in mammary tumors as compared with normal mammary tissue. Some of the chromosomal losses identified have not been reported previously in chemically induced models, implying a novel mechanism inherent to the irradiated model. Based on these findings, Sprague-Dawley × Copenhagen F1 rats offer a useful model for exploring genes responsible for radiation-induced mammary cancer, which apparently are mainly located in specific regions of chromosomes 1, 2, 3 and 5.

Secreted sphingomyelins modulate low mammary cancer incidence observed in certain mammals

Determining mechanisms that naturally protect species from developing cancer is critical in order to prevent and treat cancer. Here, we describe a novel cancer-suppressing mechanism, via the secretion of bioactive factors by mammary cells, that is present in domesticated mammals with a low mammary cancer incidence. Specifically, these bioactive factors induced triple-negative breast cancer cell (TNBC) death in vitro and reduced tumorigenicity in a xenograft TNBC mouse model in vivo. RNA deep sequencing showed significant downregulation of genes associated with breast cancer progression in secretome-cultured TNBC cells. Further in-depth multi-omics analysis identified sphingomyelins as key secreted factors, and their role was confirmed via inhibition of the sphingomyelin signaling pathway. We speculate that secreted sphingomyelins in the mammary gland of mammals with a naturally low incidence of mammary cancer mediate the elimination of cancer cells. This study contributes to the growing list of protective mechanisms identified in cancer-proof species.

The epigenetic role of breastfeeding in mammary differentiation.

Maternal milk consumption can cause changes in the mammary epithelium of the offspring that result in the expression of molecules involved in the induction of differentiation, reducing the risk of developing mammary cancer later in life. We previously showed that animals that maintained a higher intake of maternal milk had a lower incidence of mammary cancer. In the present study, we evaluated one of the possible mechanisms by which the consumption of maternal milk could modify the susceptibility to mammary carcinogenesis. We used Sprague Dawley rats reared in litters of 3 (L3), 8 (L8), or 12 (L12) pups per mother in order to generate a differential consumption of milk. Whole mounts of mammary glands were performed to analyze the changes in morphology. Using real-time polymerase chain reaction (PCR), we analyzed the expression of mammary Pinc, Tbx3, Stat6, and Gata3 genes. We use the real-time methylation-specific polymerase chain reaction method to assess the methylation status of Stat6 and Gata3 CpG sites. Our findings show an increase in the size of the epithelial tree and a smaller number of ducts called terminal end buds in L3 vs. L12. We observed an increased expression of mRNA of Stat6, Gata3, Tbx3, and a lower expression of Pinc in L3 with respect to L12. Stat6 and Gata3 are more methylated in the CpG islands of the promoter analyzed in L12 vs. L3. In conclusion, the increased consumption of maternal milk during the postnatal stage generates epigenetic and morphological changes associated with the differentiation of the mammary gland.

Differential signaling pathway activation in 7,12-dimethylbenz[a] anthracene (DMBA)-treated mammary stem/progenitor cells from species with varying mammary cancer incidence.

A natural variation exists in the susceptibility to mammary cancer among wild and domestic mammalian species. Mammary stem/progenitor cells (MaSC) represent a primary target cell for transformation; however, little is known about the intrinsic response of these cells to carcinogenic insults. Polycyclic aromatic hydrocarbons (PAH), such as 7,12-dimethylbenz[a]anthracene (DMBA), are abundantly present in the environment and have been linked to the development of mammary cancer in humans and rodents. We treated MaSC from equine (mammary cancer-resistant) and canine (mammary cancer-susceptible) species with DMBA and assessed cytochrome P450 metabolic activity, DNA damage and viability. Our notable findings were that MaSC from both species showed DNA damage following DMBA treatment; however, equine MaSC initiated cell death whereas canine MaSC repaired this DNA damage. Follow-up studies, based on genome-wide transcriptome analyses, revealed that DMBA induced activation of both the intrinsic and extrinsic apoptotic pathways in equine, but not canine, MaSC. Based on these findings, we propose a hypothetical model in which undergoing apoptosis in response to an oncogenic event might contribute to a lower incidence of mammary cancer in certain mammalian species. Such a mechanism would allow for the elimination of DNA-damaged MaSC, and hence, reduce the risk of potential tumor-initiating mutations in these cells.

Comparative breast cancer research, lessons from companion animals.

Comparative breast cancer research, lessons from companion animals.

Daidzein–Estrogen Interaction in the Rat Uterus and Its Effect on Human Breast Cancer Cell Growth

Sex hormone replacement therapy provides several advantages in the quality of life for climacteric women. However, estrogen-induced cell proliferation in the uterus and mammary gland increases the risk of cancer development in these organs. The lower incidence of mammary cancer in Asian women as compared with Western women has been attributed to high intake of soy isoflavones, including genistein. We have previously shown that genistein induces an estradiol-like hypertrophy of uterine cells, but does not induce cell proliferation, uterine eosinophilia, or endometrial edema. It also inhibits estradiol-induced mitosis in uterine cells and hormone-induced uterine eosinophilia and endometrial edema. Nevertheless, genistein stimulates growth of human breast cancer cells in culture; therefore, it is not an ideal estrogen for use in hormone replacement therapy (HRD). The present study investigated the effect of another soy isoflavone, daidzein (subcutaneous, 0.066 mg/kg body weight), in the same animal model, and its effect on responses induced by subsequent treatment (1 h later) with estradiol-17β (E(2); subcutaneous, 0.33 mg/kg body weight). In addition, we investigated the effects of daidzein (1 μg/mL) or E(2) on the growth of human breast cancer cells in culture. Results indicate that daidzein stimulates growth of breast cancer cells and potentiates estrogen-induced cell proliferation in the uterus. We suggest caution for the use of daidzein or formulas containing this compound in HRD. Future research strategies should be addressed in the search for new phytoestrogens that selectively inhibit cell proliferation in the uterus and breast.

Genistein Selectively Inhibits Estrogen-Induced Cell Proliferation and Other Responses to Hormone Stimulation in the Prepubertal Rat Uterus

Sex hormone replacement therapy helps improve quality of life in climacteric women. However, estrogen-induced cell proliferation in the uterus and mammary gland increases the risk for cancer in these organs. The lower incidence of mammary cancer in Asian women than in western women has been attributed to high intake of soy isoflavones, including genistein. Our previous work in the prepubertal rat uterus model showed that genistein (0.5 mg/kg body weight subcutaneously) caused an estradiol-like hypertrophy in myometrial and uterine luminal epithelial cells and an increase in RNA content in luminal epithelium; however, it did not induce cell proliferation, uterine eosinophilia, or endometrial edema. The present study investigated, in the same animal model, the effect of genistein administration (0.5 mg/kg body weight subcutaneously) before treatment with estradiol-17β (0.33 mg/kg body weight subcutaneously) on uterine responses that were not induced by genistein. Pretreatment with this phytoestrogen completely inhibited estradiol-induced mitoses in uterine luminal epithelium, endometrial stroma, and myometrium and partially inhibited estradiol-induced uterine eosinophilia and endometrial edema. These findings indicate that genistein protects against estrogen-induced cell proliferation in the uterus and suggest that future studies should investigate the possibility of using this agent to decrease the risk for uterine cancer after hormone replacement therapy in climacteric women.

Long-term hormonal promotion overcomes genetic resistance to mammary cancer

It is well known that ovarian steroids estradiol and progesterone play a vital role in the development of mammary cancer. Here, using the genetically highly resistant Copenhagen rats we demonstrate that sustained exogenous treatment with estradiol and progesterone overcomes genetic resistance to mammary cancer. It has been demonstrated that Copenhagen rats develop preneoplastic lesions upon exposure to carcinogens. However, these preneoplastic lesions fail to progress to ductal carcinomas in situ or overt mammary carcinomas. The preneoplastic lesions eventually decrease in number and are absent by 60 days post-carcinogen treatment. In the present study, we exposed 7-week-old female Copenhagen rats to N-methyl-N-nitrosourea (MNU; 50 mg/kg BW). Immediately after MNU treatment the rats were divided into the following groups: (1) control; (2) 30 mg estradiol 17β; (3) 30 mg progesterone; and (4) 30 mg estradiol 17β plus 30 mg progesterone. All hormone treatments were administered via individual silastic pellets for a period of 9 months post-carcinogen treatment. The control animals displayed a low incidence of mammary cancer (10%). Hormone treatments produced significantly higher incidences of mammary cancer, with estradiol at 50%, progesterone at 65% and estradiol plus progesterone at 90%. Hormone treatment sustained the growth of the lesions induced by MNU by increasing expression of Areg, Bcl-2, Ccnd-1 and Vegf genes, while decreasing expression of Bad, Bax, Casp 3, 8, 9 and p53 genes. Furthermore, hormone treatment increased CCND-1 and PARP proteins levels. The data clearly demonstrates that hormonal environment supports mammary cancer progression by increasing cell proliferation, and angiogenesis while inhibiting apoptosis.

Reduction in mammary tumorigenesis in the rat by cabbage and cabbage residue

Mammary cancer was induced in female Sprague-Dawley rats by a single injection of N-methyl-N-nitrosourea (MNU) and rats were randomized to control fat (5%) and high fat (24.6%) diets. In addition, dried cabbage (5 and 10%) and collards (5%) were included in the diets of some animals. No statistically significant differences were observed in food consumption, body wt gain and caloric intake between the MNU-treated and control groups in the rats fed the low-fat diet. However, the groups fed the high-fat diet consumed more than the rats maintained on the control diet. The rats on the control fat diet containing cabbage exhibited a significantly lower incidence of mammary cancer than rats that were fed the control-fat diet without cabbage. This effect was not observed in comparable rats on the high-fat diet. The inhibitory effect on mammary tumorigenesis was demonstrated using a residue obtained from cabbage by exhaustive extraction with methanol, methylene chloride and petroleum ether. These studies reinforce the efficacy of cabbage as a 'suppressor' of cancer in experimental model systems under control-fat dietary conditions.

The effect of bromocriptine on the lactotroph cells in two inbred strains of mice [formula omitted] and [formula omitted

This paper deals with the effect of bromocriptine on the morphology and the number of lactotrophs in two inbred strains of mice, one with a high and the other with a low mammary cancer incidence. Bromocriptine decreases the number of lactotrophs in C 3H mice while their number in AKR is not affected. These observations suggest that bromocriptine affects the two strains in a different way, probably due to their different prolactin levels in the pituitary. The above treatment resulted also in a shrinking of the RER and a reduction in size of prolactin granules, probably due to a decline in the secretory activity of lactotrophs. Of special interest was the appearance of a ‘new’ cell type with mixed characteristics of somatotrophs and lactotrophs. These findings, along with an increase in the number of chromophobes, suggest that bromocriptine can induce cell regression. Probably the ‘new’ cell is an intermediate form between chromophobes and lactotrophs and somatotrophs.

Levels of mammary tumor virus proteins (MTVp27 AND MTVgp52) in the milk of low and high mammary cancer mouse strains of japanese origin compared with european and American strains

AbstractA competition radioimmunoassay for purified MTV proteins, MTVp27gag and MTVgp52env, was applied to measure the amounts of these proteins in the milk of various mice of Japanese origin. The results were compared to those from European and American strains of high and low mammary cancer incidence. The sensitivity of detection for the assay was less than 1 ng viral protein per mg milk protein. The SL/NiA strain was positive for MTVp27 in the milk (10–100 ng/mg). Foster‐nursing of this strain on BALB/c mice did not lead to the disappearance of MTVp27 antigen expression, indicating that MTV in this strain is genetically transmitted. This strain was negative for MTVgp52. Various high mammary cancer strains had large amounts of MTV, invariably transmitted in milk, e.g. (1) FM/JmsA, (2) C57BL/6MsMtA, a strain selected for high mammary cancer incidence in Japan and maintained at the Aichi Cancer Center, (3) DD/Tbr. Levels of MTVp27 and MTVgp52 in the milk of these strains were comparable to those of the C3H/HeA, A/BrA and RIII/SeA. They were generally somewhat lower than in the BALB/cHeA strain foster‐nursed on high mammary cancer strain mice, such as A/BrA, RIII/SeA and FM/JmsA. Weight ratios of MTVp27 to MTVgp52 were usually 1:1 with the exception of the BALB/c foster A strain whose levels of MTVgp52 were comparatively high. BALB/cHeA strain milk itself showed some positivity for both MTV proteins at the borderline of detection (around 0.1 ng/mg protein). Mice of the C3H/HeA strain, foster‐nursed on C57BL/LiA mice, have much lower levels of MTVp27 (10–40 ng/mg) and MTVgp52 (8–50 ng/mg) than all the high mammary cancer strains. (C57BL × C3Hf)F1 hybrid mice had even less MTVp27 and gp52 in their milk than the C3Hf strain mice, permitting genetic analysis of the gene(s) for this suppression by the C57BL genotype.

Mammary Tumorigenesis through Irradiation of Mice

RAP mice, possibly harboring mammary tumor virus (MTV), of representative ages were exposed to limited or lifetime whole-body continuous gamma and to fractionated x-irradiation. Doses varied from 30-2100 R and dose rates from 0.062-121 R/day in the two series GA and PN in which mammary cancer incidence was elevated. Induction of mammary cancer was found to be related to the dose range for ovarian tumorigenesis, 30-500 R, but unrelated to age when exposed. There was no statistically significant correlation between mammary cancer and ovarian tumors. Active MTV infection was suggested by cancer-prone litters in one irradiated (PN U + SR) and one unirradiated series (OCB). Unirradiated descendents of perinatally irradiated mice with an inherited hormonal disorder had a lower incidence of mammary cancer than stock virgin mice. The balance of evidence pointed to induction of mammary cancer through systemic change set in motion by irradiation.

Electron Microscopic and Bioassay Studies of Milk From Mice of High and Low Mammary-Cancer and High and Low Leukemia Strains<xref ref-type="fn" rid="FN2">2</xref><xref ref-type="fn" rid="FN3">3</xref>

High-speed centrifugal pellets were prepared from defatted and decaseinated milk obtained from mice of 33 substrains of 15 different strains, 3 stocks, 2 germfree strains, and 2 hybrid lines with high or low incidence of mammary cancer and high or low incidence of leukemia. Electron microscopic studies were carried out on sections of these pellets, some of which were tested for tumor-inducing and hyperplastic nodule-inducing activity. Type-B virus particles were found in the milk of mice of high and of some low cancer strains. In addition, type-C virus particles and “signet-ring” particles were observed in some strains. A high degree of correlation was noted between the presence of type-B particles and tumor-inducing as well as nodule-inducing activity in RIII and A, high mammary-cancer strains, and to a lesser extent in Af and C3Hf, low cancer strains, and (C57 × Af)F1mice. A high degree of correlation was found in the milk of BALB/c and CBA mice, low mammary-cancer strains, between the absence of type-B particles and lack of tumor-inducing and nodule-inducing activity. Although no type-B particles could be found in C57BL milk, it showed high nodule-inducing activity. Milk from a substrain of AKR mice with medium leukemia incidence showed presence of type-B particles and tumor-inducing activity. Structures resembling lactic dehydrogenase (LDH) virus were found in several low cancer strains. Bioassays of milk samples from 2 of these strains failed, however, to reveal LDH virus activity.

Mammary cancer in fostered CBA mice and CBA hybrids.

In the absence of the mammary-tumor agent (MTA), breeding females of the CBA stock, observed since 1951, have remained free of spontaneous mammary cancer. After CBA young had been nursed by females of the cancerous Z (C3H) stock, to obtain the MTA, CBA breeders of the fostered and succeeding 3 generations had an incidence of 99 percent, with an average cancer age of 252 days. Because gonadectomized mice of the CBA stock developed adrenal cortical lesions, CBA males were mated with females of the A strain, which have a low incidence of mammary cancer in nonbreeders. The F1 females, maintained as virgins, showed a high incidence. These observations demonstrate that mice of the inbred CBA stock are susceptible to spontaneous mammary cancer and, in addition, transmit the mammary-cancer-inducing inherited hormonal pattern associated with postcastrational adrenal alterations.

A Comparative Study of the Life History of the Female Mammary Gland in Two Strains of Albino Mice

In searching the literature nothing could be found concerning the life history of the mammary gland in mice, although much work has been done on other rodents. Since the mouse is used so extensively in cancer research as an experimental animal, and since cancer of the mammary gland is a well recognized entity in certain strains of mice, it was thought that it would be interesting to make a comparative study. To do this, two strains of mice were necessary, one showing a low incidence of mammary cancer in the females, and the other showing a high incidence. The material presented here represents an attempt to work out the development and distribution of mammary tissue in two such strains of mice. The study is a preliminary one, and the material is limited, but it was decided that should the two strains exhibit any remarkable differences, a more extensive survey might prove both interesting and profitable. The high tumor incident strain has been designated throughout as SPTM, and the low tumor incident strain as Loomis 1. Bagg strain was abandoned because of lack of material. Data concerning the animals used in this study are found preceding the plan of work. Purpose. By gross and microscopic study (1) to trace the development and distribution of mammary tissue in female mice; (2) to compare two strains: (a) one having a low mammary carcinoma incidence (no strain that has been studied earefully has been known to be tumor free) and (b) a high spontaneous mammary tumor strain; (3) to find, if possible, when deviations from the normal begin to occur, and to trace these deviations to the developed neoplasm.