Effects of tamoxifen and soluble tumor-associated antigens on ovarian structure in mammary tumor-bearing rats

Previously, we showed that the 66 and 51 kDa soluble tumor-associated antigens (sTAAs) have distinct suppressive effects on chemically induced mammary cancer in rats, both alone and in combination with the hormone-related anticancer drug tamoxifen. Here, we describe the effects of both sTAA and tamoxifen on the histological structure of ovaries in mammary tumor-bearing 30- to 34-week-old rats. Central ovary sections were pooled, the number of the healthy and degenerated follicles were counted, and the size of the corpora lutea was estimated. In follicular development primordial, primary, preantral and antral stages were recognized. Only healthy follicles with visible nuclei were counted. Follicular degeneration was estimated as the number of atretic follicles with follicular remnants. Treatment with tamoxifen alone or in combination with sTAA significantly increased the number of primordial follicles and atretic follicles in the ovaries, and promoted the formation of small follicular cysts. Total area of the corpora lutea decreased. sTAA participated in this process by increasing apoptosis in degenerated follicles.

Dual role of AP-2gamma in ErbB-2-induced mammary tumorigenesis

A causative role of the membrane-bound tyrosine kinase ErbB-2 in breast tumorigenesis has been well established. MMTV/neu transgenic mice which overexpress ErbB-2 consistently develop mammary carcinomas with a high incidence. In human breast cancer, ErbB-2 is overexpressed in 25-30 of all cases and is representing a clinical marker of a poor prognosis. Besides to gene amplification, ErbB-2 overexpression has been attributed to transcription factors of the AP-2 family which were shown to control the ErbB-2 gene promoter in cell culture studies. Particularly AP-2alpha and gamma are often coexpressed in ErbB-2-positive breast carcinomas. However, LTRgamma transgenic mice which overexpress AP-2gamma in their mammary epithelium display only a very weak upregulation of the erbB-2 gene and do not develop mammary carcinoma. These findings therefore raise the possibility of functional cooperativity between both genes in breast cancer. To experimentally address the impact of AP-2gammaon ErbB-2-induced breast carcinogenesis we crossed MMTV/neu transgenic mice with LTRgamma transgenic mice and monitored tumor development in bitransgenic female progeny. AP-2gamma overexpression negatively influenced tumor incidence, as reflected by a reduced tumor number and a prolonged tumor latency. Histological analysis revealed three major types of tumors corresponding to different stages of tumor progression. Interestingly, an increased proportion of advanced stage carcinomas was observed in bitransgenic mice. Moreover, the AP-2gamma transgene differentially affected proliferation rates between the different progression stages: proliferation was enhanced at early stages but reduced in advanced stages in comparison to control tumors. Therefore, AP-2gamma while reducing the incidence of mammary tumors is promoting tumor progression.

Effect of perductal paclitaxel exposure on the development of MNU-induced mammary carcinoma in female S-D rats

BACKGROUND

Breast carcinoma and precancer are thought to start in the lining of the milk duct or lobule.

METHODS

At 5weeks of age, rats received a intraperitoneal (ip) injection of MNU for carcinogenesis. After mammary tumors were identified macroscopically using fiberscope, the rats were treated with perductal (pd) or ip injection of paclitaxel tri-weekly. At 36 weeks after MNU injection, tumor burden (No. of >1cm palpable mammary tumors/rat), total number of mammary carcinoma, apoptosis (AI), and microvessel density (MVD) were measured.

RESULTS

The administration of paclitaxel through the duct did not produce any toxic side effect. The tumor burden and total number of mammary carcinoma in the pd paclitaxel-treated group were significantly reduced compared to those seen in the ip paclitaxel-treated group. In addition, in the pd paclitaxel-treated group, AI was also increased and MVD was decreased, compared to those in the ip paclitaxel-treated group.

CONCLUSION

Local administration of paclitaxel may be useful for treatment of breast cancer.

Gamma-tocotrienol inhibits neoplastic mammary epithelial cell proliferation by decreasing Akt and nuclear factor kappaB activity

Tocotrienols, a subgroup within the vitamin E family of compounds, have been shown to display potent anticancer activity and inhibit preneoplastic and neoplastic mammary epithelial cell proliferation at treatment doses that have little or no effect on normal cell growth and function. However, the specific intracellular mechanisms mediating the antiproliferative effects of tocotrienols are presently unknown. Because Akt and nuclear factor kappaB (NFkappaB) are intimately involved in mammary tumor cell proliferation and survival, studies were conducted to determine the effects of gamma-tocotrienol on Akt and NFkappaB activity in neoplastic +SA mammary epithelial cells in vitro. Treatment with 0-8 microM gamma-tocotrienol for 0-3 days caused a dose-responsive inhibition in +SA cell growth and mitotic activity, as determined by MTT colorimetric assay and proliferating cell nuclear antigen immunocytochemical staining, respectively. Studies also showed that treatment with 4 microM gamma-tocotrienol, a dose that inhibited +SA cell growth by more than 50% compared with that of untreated control cells, decreased intracellular levels of activated phosphotidylinositol 3-kinase-dependent kinase (PI3K)-dependent kinase 1 (phospho-PDK-1) and Akt, and reduced phospho-Akt kinase activity. Furthermore, these effects were not found to be associated with an increase in either phosphatase and tensin homologue deleted from chromosome 10 (PTEN) or protein phosphatase type 2A phosphatase activity. In addition, gamma-tocotrienol treatment was shown to decrease NFkappaB transcriptional activity, apparently by suppressing the activation of IkappaB-kinase-alpha/beta, an enzyme associated with inducing NFkappaB activation. In summary, these findings demonstrate that the antiproliferative effects of gamma-tocotrienol result, at least in part, from a reduction in Akt and NFkappaB activity in neoplastic +SA mammary epithelial cells.

Rnd3/RhoE induces tight junction formation in mammary epithelial tumor cells

Glucocorticoid hormones stimulate adherens and tight junction formation in Con8 mammary epithelial tumor cells through a multistep process in which the membrane organization of structural apical junction proteins and tight junction sealing is controlled by specific signal transduction components. We have previously shown that dexamethasone stimulation of apical junction formation requires down-regulation of the small GTPase RhoA. Here we identified Rnd3/RhoE, a GTPase-deficient Rho family member and RhoA antagonist, as a key regulator of apical junction dynamics. Exogenously expressed Rnd3/RhoE co-localized with actin at the cell periphery and induced the localization of the adherens junction protein beta-catenin and the tight junction protein ZO-1 to sites of cell-cell contact, and led to the formation of highly sealed tight junctions. Treatment with glucocorticoids was not required to achieve complete apical junction remodeling. Consistent with Rnd3/RhoE acting as an antagonist of RhoA, expression of Rnd3/RhoE rescued the disruptive effects of constitutively active RhoA on apical junction organization. Our results demonstrate a new role for the Rho family member Rnd3/RhoE in regulating the assembly of the apical junction complex and tight junction sealing.

Alterations of DNA Copy Number and Expression in Genes Involved in Cell Cycle Regulation and Apoptosis Signal Pathways in γ-Radiation-Sensitive SX9 Cells and -Resistant SR-1 Cells

In the present study, genomic differences related to sensitivity to radiation were examined by comparative genomic hybridization and GeneChip 45K microarray in SX9 cells (radiation-sensitive) and their parental line, SR-1 (radiation-resistant). SX9 cells have defective DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity. DNA-PKcs is a DNA double-strand break repair protein that maintains chromosomal stability through nonhomologous end joining. However, the molecular basis of the radiation sensitivity of SX9 cells is unclear. Flow cytometry analysis showed that SR-1 and SX9 cells had a larger G2/M-phase population at 12 h after 4 Gy gamma irradiation, while only SR-1 cells progressed to G1/S at 24-36 h. SX9 and SR-1 cells had similar patterns of DNA copy number alteration, but the gains were observed on chromosome 9 (cent-E2), 11 (cent-A3), and 12 (C1-E) only in SX9 cells. Expression of genes located on those regions is higher in SX-9 cells than in SR1 cells, and the regions include genes associated with apoptosis and cell cycle regulation. Time-course data for gene expression at 0, 1, 3, 6 and 12 h after 4 Gy gamma irradiation revealed that the genes whose expression was altered in SX9 cells but not in SR-1 cells are in 16 clusters. Three of these clusters included genes for cell cycle regulation: JNK, PKC (PRKC) and ceramide cascade protein. These results suggest that amplification and altered expression of genes associated with cell cycle and apoptosis regulators in DNA-PK-deficient SX9 cells affect the differences in response to gamma radiation between SX9 and SR-1 cells.

Muscarinic receptors participation in angiogenic response induced by macrophages from mammary adenocarcinoma-bearing mice

Introduction

The role of macrophages in tumor progression has generated contradictory evidence. We had previously demonstrated the ability of peritoneal macrophages from LMM3 murine mammary adenocarcinoma-bearing mice (TMps) to increase the angiogenicity of LMM3 tumor cells, mainly through polyamine synthesis. Here we investigate the ability of the parasympathetic nervous system to modulate angiogenesis induced by TMps through the activation of the muscarinic acetylcholine receptor (mAchR).

Methods

Peritoneal macrophages from female BALB/c mice bearing a 7-day LMM3 tumor were inoculated intradermally (3 × 10⁵ cells per site) into syngeneic mice. Before inoculation, TMps were stimulated with the muscarinic agonist carbachol in the absence or presence of different muscarinic antagonists or enzyme inhibitors. Angiogenesis was evaluated by counting vessels per square millimeter of skin. The expression of mAchR, arginase and cyclo-oxygenase (COX) isoforms was analyzed by Western blotting. Arginase and COX activities were evaluated by urea and prostaglandin E₂ (PGE₂) production, respectively.

Results

TMps, which stimulate neovascularization, express functional mAchR, because carbachol-treated TMps potently increased new blood vessels formation. This response was completely blocked by preincubating TMps with pirenzepine and 4-diphenylacetoxy-N-methylpiperidine (4-DAMP), M₁ and M₃ receptor antagonists, and partly by the M₂ receptor antagonist methoctramine. M₁ receptor activation by carbachol in TMps triggers neovascularization through arginase products because N^ω-hydroxy-L-arginine reversed the agonist action. Preincubation of TMps with methoctramine partly prevented carbachol-stimulated urea formation. In addition, COX-derived liberation of PGE₂ is responsible for the promotion of TMps angiogenic activity by M₃ receptor. We also detected a higher expression of vascular endothelial growth factor (VEGF) in TMps than in macrophages from normal mice. Carbachol significantly increased VEGF expression in TMps, and this effect was totally reversed by methoctramine and pirenzepine. Arginase and COX inhibitors partly decreased VEGF derived from TMps.

Conclusion

TMps themselves induce a potent angiogenic response that is augmented by carbachol action. mAchR activation triggers arginine metabolism, PGE₂ synthesis and VEGF production, promoting neovascularization.

Salicylate inhibition of rat mammary carcinogenesis and angiogenesis in female rat compatible with misoprostol administration

Epidemiological data suggest that non-steroidal anti-inflammatory drugs prevent colon cancer. The evidence for other types of tumour is less conclusive, though animal and in vitro studies indicate that they may be effective against mammary cancer cells. We assessed the effect of dietary acetylsalicylic and salicylic acid against dimethylbenzanthracene-induced rat tumours. Tumour angiogenesis was also investigated to explore the mechanism responsible for salicylate effect. Mammary tumours were induced in female Sprague-Dawley rats fed with different amounts of acetylsalicylic and salicylic acid. Serum vascular endothelial growth factor concentrations were measured and vascularization of basement membrane proteins injected in vivo (Matrigel) was determined by evaluation of haemoglobin content to assess the extent to which angiogenesis was inhibited. Dimethylbenzanthracene-induced carcinogenesis was inhibited by both acids and there was a log-dose/response correlation between the tumour diameter and salicylate concentration. Salicylic acid seems more effective than acetylsalicylic acid. Vascular endothelial growth factor was less concentrated in treated animals than in the controls and so was Matrigel haemoglobin. The mechanism involved, however, is still uncertain, though concomitant inhibition of tumour angiogenesis may be an important component. The documented salicylate serum VEGF modulation is interesting also for presence of the flk-1 receptor in mammary tumour cells of our model. Although misoprostol is a prostaglandin analogous its concomitant administration did not compromise the salicylate anti-tumour effect.

Role of steroid hormones and prolactin in canine mammary cancer

In several animal studies, prolactin has been found to be essential for mammary epithelial development, and its administration has been consistently shown to increase the rate of mammary tumours. High levels of steroid hormones have also been suggested to enhance mammary cancer development. The present study investigates the levels of the following hormones in serum and in tissue homogenates in dogs bearing canine mammary tumours: prolactin (PRL), progesterone (P4), dehydroepiandrosterone (DHEA), androstenedione (A4), testosterone (T), 17beta-estradiol (17beta-E2) and estrone sulfate (S04E1). Eighty mammary tumours (40 dysplasias and benign and 40 malignant tumours) from 32 female dogs, and 10 normal mammary glands from eight female dogs without history of mammary tumours, were analysed. Prolactin and steroid hormones in serum and tissue homogenates, were analysed by enzyme immunoassays (EIA) techniques, previously validated for this animal species. Levels of prolactin in tissue homogenates were significantly different between malignant and benign mammary tumours (p<0.01). Serum prolactin concentrations were lower in the control group as compared with the group of dogs with benign tumours and in dogs with malignant tumours (p=0.01). Serum prolactin levels in dogs with benign lesions were not significantly different than those obtained from dogs with malignant tumours. Levels of steroid hormones were significantly higher in malignant tumours compared with the benign tumours and normal mammary glands (p<0.01) both in serum and homogenate determinations. Our results suggest that the canine neoplastic mammary gland could be a source of prolactin. Our hypothesis is that both prolactin and steroid hormones are involved in the growth of canine mammary cancer, and that they might have an autocrine/paracrine role in the maintenance of this disease.

Atm heterozygous deficiency enhances development of mammary carcinomas in p53 heterozygous knockout mice

Introduction

Ataxia-telangiectasia is an autosomal-recessive disease that affects neuro-immunological functions, associated with increased susceptibility to malignancy, chromosomal instability and hypersensitivity to ionizing radiation. Although ataxia-telangiectasia mutated (ATM) heterozygous deficiency has been proposed to increase susceptibility to breast cancer, some studies have not found excess risk. In experimental animals, increased susceptibility to breast cancer is not observed in the Atm heterozygous deficient mice (Atm^+/-) carrying a knockout null allele. In order to determine the effect of Atm heterozygous deficiency on mammary tumourigenesis, we generated a series of Atm^+/- mice on the p53^+/- background with a certain predisposition to spontaneous development of mammary carcinomas, and we examined the development of the tumours after X-irradiation.

Methods

BALB/cHeA-p53^+/- mice were crossed with MSM/Ms-Atm^+/- mice, and females of the F₁ progeny ([BALB/cHeA × MSM/Ms]F₁) with four genotypes were used in the experiments. The mice were exposed to X-rays (5 Gy; 0.5 Gy/min) at age 5 weeks.

Results

We tested the effect of haploinsufficiency of the Atm gene on mammary tumourigenesis after X-irradiation in the p53^+/- mice of the BALB/cHeA × MSM/Ms background. The singly heterozygous p53^+/- mice subjected to X-irradiation developed mammary carcinomas at around 25 weeks of age, and the final incidence of mammary carcinomas at 39 weeks was 31% (19 out of 61). The introduction of the heterozygous Atm knockout alleles into the background of the p53^+/- genotype significantly increased the incidence of mammary carcinoma to 58% (32 out of 55) and increased the average number of mammary carcinomas per mouse. However, introduction of Atm alleles did not change the latency of development of mammary carcinoma.

Conclusion

Our results indicate a strong enhancement in mammary carcinogenesis by Atm heterozygous deficiency in p53^+/- mice. Thus, doubly heterozygous mice represent a useful model system with which to analyze the interaction of heterozygous genotypes for p53, Atm and other genes, and their effects on mammary carcinogenesis.

Deregulation of Stat5 expression and activation causes mammary tumors in transgenic mice

Members of the signal transducers and activators of transcription (Stat) family regulate essential cellular growth and survival functions in normal cells and have also been implicated in tumorigenesis. We have studied the potential role of Stat5 in mammary tumorigenesis by targeting Stat5 variants to the mammary gland of transgenic mice using regulatory sequences of the beta-lactoglobulin gene. Mammary-directed expression of the wild-type Stat5, constitutively activated Stat5 and carboxyl-terminally truncated dominant negative Stat5 forms resulted in mammary tumors with incidence rates of up to 22% and latency periods of 8-12 months. Undifferentiated carcinomas most frequently occurred in mice expressing the carboxyl-terminally truncated Stat5. The more differentiated papillary and micropapillary adenocarcinomas were primarily found in mice overexpressing the native and constitutively active transgenes. Higher levels of translation initiation factor 4E (eIF4E) and cyclin D1 expression but lower levels of activated Stat3 were found in tumors of mice expressing the constitutively active Stat5 when compared to mice expressing the wild-type or truncated forms. A higher expression of the estrogen receptor (ERalpha) was observed in carcinomas compared to other phenotypes. The ability of both forms of Stat5, the transactivating form and the dominant negative form, to participate in oncogenesis indicates that there is more than one mechanism by which Stat5 contributes to this process. The transactivation function of Stat5 is involved in the determination of tumors with a more differentiated phenotype.

Bax regulates c-Myc-induced mammary tumour apoptosis but not proliferation in MMTV-c-myc transgenic mice

The expression of the proto-oncogene c-myc is frequently deregulated, via multiple mechanisms, in human breast cancers. Deregulated expression of c-myc contributes to mammary epithelial cell transformation and is causally involved in mammary tumorigenesis in MMTV-c-myc transgenic mice. c-Myc is known to promote cellular proliferation, apoptosis, genomic instability and tumorigenesis in several distinct tissues, both in vivo and in vitro. Expression of the proapoptotic regulatory gene bax is reduced or absent in human breast cancers, and c-Myc has been shown to regulate the expression of Bax, as well as cooperate with Bax in controlling apoptosis in a fibroblast model. Additionally, loss of bax reduces c-Myc-induced apoptosis in lymphoid cells and increases c-Myc-mediated lymphomagenesis in vivo. In order to assess whether loss of bax could influence c-Myc-induced apoptosis and tumorigenesis in the mammary gland in vivo, we generated MMTV-c-myc transgenic mice in which neither, one, or both wild-type alleles of bax were eliminated. Haploid loss of bax in MMTV-c-myc transgenic mice resulted in significantly reduced mammary tumour apoptosis. As anticipated for an apoptosis-regulatory gene, loss of the wild-type bax alleles did not significantly alter cellular proliferation in either mammary adenocarcinomas or dysplastic mammary tissues. However, in contrast to c-Myc-mediated lymphomagenesis, loss of one or both alleles of bax in MMTV-c-myc transgenic mice did not significantly enhance mammary tumorigenesis, despite evidence that haploid loss of bax might modestly increase mammary tumour multiplicity. Our results demonstrate that Bax contributes significantly to c-Myc-induced apoptosis in mammary tumours. In addition, they suggest that in contrast to c-Myc-induced lymphomagenesis, mammary tumorigenesis induced by deregulated c-myc expression requires some amount of Bax expression.

High-Fat Corn Oil Diet Promotes the Development of High Histologic Grade Rat DMBA-Induced Mammary Adenocarcinomas, While High Olive Oil Diet Does Not

Effects of a high corn oil and a high olive oil diet on the histopathologic characteristics of rat dimethylbenz(alpha)anthracene-induced mammary adenocarcinomas were investigated in comparison with those of a control low-fat diet. Two experimental series (A and B) studied the influence of a high corn oil diet on the initiation and the promotion of mammary carcinogenesis, while another one (C) assessed the effects of the two dietary lipids on the promotion. Nine parameters have been analyzed and a new histologic grading method, adapted to rat tumors, has been applied in each carcinoma. High corn oil diets, particularly when acting as promoters, associated with higher-grade carcinomas than control (p < 0.05) and high olive oil groups. Stromal invasion and tumoral necrosis were more prominent and a prevailing cribriform pattern was observed (p < 0.05). High olive oil diet adenocarcinomas exhibited a predominantly low histologic grade and few necrotic and invasive areas, similar to the control, and they presented the highest percentage of papillary areas. Lymphoplasmacytic and mast cell infiltration were also influenced by the dietary lipids. Thus, high corn oil diet adenocarcinomas presented a higher degree of morphological malignancy than control and high olive oil tumors, which is in line with the greater clinical malignancy described in rats from the former group and the non-promoting effect of the high olive oil diet. As far as we are concerned, a similar histopathologic approach of the effects of the dietary lipids on experimental breast cancer has not been carried out up to now.

Involvement of TGF-beta(s)/T(beta)Rs system in tumor progression of murine mammary adenocarcinomas

We studied the expression of TGF-beta/T(beta)R system and its biological role in tumor development, in M3 and MM3 murine mammary adenocarcinomas with different metastasizing capability and in LM3 and LMM3 derived cell lines. All the studied cells secreted TGF-beta(s) and expressed T(beta)Rs. While the proliferation of the poorly metastatic M3 cells was significantly inhibited by 4 ng/ml TGF-beta(s), the highly metastatic MM3 cells were only slightly inhibited in response to the highest dose used. LM3 and LMM3 cells, highly invasive and metastatic, were totally refractory to TGF-beta antiproliferative effect. The role of TGF-beta in modulating key proteolytic cascades in tumor progression was also studied. TGF-beta(s) enhanced metalloproteinases production in all the studied cells while induced a stimulatory net effect on plasmin system activity only in the more metastatic cells. Our results in this murine mammary tumor lineage support the concept that dissociation of TGF-beta regulated growth control versus proteolytic enzyme pathways promotes tumor dissemination.

Role of CXCR4 and SDF-1 in mammary tumor metastasis in the cat

It has recently been suggested that the chemokine receptor CXCR4 and its ligand SDF-1 (CXCL12) promote metastasis of various cancers in humans. Since feline mammary tumors also metastasize to distant organs frequently, we used real-time quantitative PCR to examine the expression of feline CXCR4 (fCXCR4) in ten feline mammary tumor cell lines and seven feline mammary tumor tissues, and also the expression of feline SDF-1 (fSDF-1) in various organs. Cell lines derived from metastatic regions expressed more fCXCR4 than those derived from primary tumors. Mammary tumor tissues overexpressed more fCXCR4 than normal mammary tissues. Organs with high levels of fSDF-1 expression represent common sites of metastasis. Migration assays using the feline mammary tumor cell line NAC were also performed to test the activity of TN14003 and TC14012, antagonists of human CXCR4, to antagonize fCXCR4 expressed on NAC cells. TN14003 and TC14012 inhibited migration of NAC cells. We conclude that fCXCR4 may be a therapeutic target for feline mammary tumors.

Role of the CDK inhibitor p27 (Kip1) in mammary development and carcinogenesis: insights from knockout mice

The cyclin-dependent kinase inhibitor p27 (Kip1) is an important cell cycle regulatory gene in breast cancer, and decreased p27 expression is associated with poor prognosis. Some investigations of its role in mammary development have demonstrated reduced cyclin D1 expression and consequent lack of lobuloalveolar development, but others have found increased cyclin E-Cdk2 activity and increased proliferation balanced by increased apoptosis. It is unclear at present why these apparently divergent results have been obtained. Mice with reduced p27 gene dosage alone do not develop mammary carcinomas but do display substantially shorter tumor latency upon overexpression of erbB2, consistent with a role for p27 as a mammary tumor suppressor gene. In this review we summarize these and other data addressing the role of p27 in normal mammary epithelium and experimental models of mammary carcinogenesis.

Cell cycle genes in a mouse mammary hyperplasia model

Human mammary epithelial cells emerge spontaneously from senescence, exhibiting eroding telomeric sequences, and ultimately enter crisis to generate the type of chromosomal abnormalities seen in early stages of breast cancer. In a mouse mammary tumor model, the spontaneous escape of senescence can be observed as an increase in DNA synthesis that is reflected by alterations in the cell cycle profile and increases in the expression levels and activities of cell cycle molecular components. This review provides an overview of gene alterations in the cell cycle components in mouse mammary hyperplasia.

Cyclins and breast cancer

The D-type and E-type cyclins control the G(1) to S phase transition during normal cell cycle progression and are critical components of steroid- and growth factor-induced mitogenesis in breast epithelial cells. Mammary epithelial cell-specific overexpression of these genes leads to mammary carcinoma, while in cyclin D1-deficient mice mammary gland development is arrested prior to lobuloalveolar development. Cyclin D1 null mice are resistant to mammary carcinoma induced by the neu and ras oncogenes, indicating an essential role for cyclin D1 in the development of some mammary cancers. Cyclin D1 and E1 are commonly overexpressed in primary breast cancer, with some evidence of an association with an adverse patient outcome. This observation may result in part from their ability to confer resistance to endocrine therapies. The functional consequences of cyclin E overexpression in breast cancer are likely related to its role in cell cycle progression, whereas that of cyclin D1 may also be a consequence of a more recently defined role in transcriptional regulation.

Of mice and Myc: c-Myc and mammary tumorigenesis

The proto-oncogene c- myc is involved in regulating proliferation and apoptosis, and its deregulation via genomic and postgenomic mechanisms, contributes to the development and progression of multiple human cancers, including those of the breast. Deregulated expression of c-Myc also contributes to neoplastic transformation by altering cellular differentiation pathways and by facilitating mutagenesis through induction of genomic instability. Transgenic and gene-knockout mice are frequently utilized to resolve the mechanisms through which specific genes influence the development and progression of malignancies. In this review, we discuss how research findings obtained from various c- myc transgenic mammary tumor models help to improve our resolution of c-Myc's role both in tumorigenesis of the murine mammary gland and cancer of the human breast.

Lymphatic drainage on healthy and neoplasic mammary glands in female dogs: can it really be altered?

The purpose of this research was to study the mammary lymphatic drainage under a macroscopic and mesoscopic view, comparing the vascular pattern of healthy and neoplasic mammary glands injected with drawing ink alcoholic and fluorescein solutions, in 46 mongrel female dogs. The results pointed out that the thoracic gland is drained by the axillary lymph centre, but in mammary neoplasia either superficial cervical or ventral thoracic lymph centres can be involved. Cranial and caudal abdominal glands may be drained by the axillary, inguinofemoral and popliteal lymph centres. However, the popliteal drainage is specific for the healthy caudal abdominal mammary gland. The inguinal gland can be drained by both inguinofemoral and popliteal lymph centres in both neoplasic and healthy conditions. Regarding the mammary lymphatic communications, this research demonstrated that neoplasic glands present more types of anastomosis (40.9%), than healthy glands (33.33%), and an increase in contralateral anastomosis (50%) compared with healthy ones (33%). Given the data, the mammary neoplasia can change the lymphatic drainage pattern in terms of lymph centres and vascular arborization, thus forming new drainage channels and recruiting a larger number of lymph nodes. Lastly, some comments were made about the severity of a specific neoplasic mammary gland and conditions to be considered before making a decision in terms of the most adequate operative procedure, and suggestions for further investigations.

Transcriptional regulators in mammary gland development and cancer

The mammary gland represents a remarkable developmental system for the study of genetic programs underlying proliferation, differentiation and inductive tissue interactions. Mammary gland ontogeny occurs predominantly in the adult and involves a complex cycle of morphogenesis, with the continuous production, differentiation and apoptosis of mammary epithelial cells occurring with each pregnancy. Perturbations in pathways controlling any of these processes may lead to neoplasia. Substantial progress has been made in defining signaling pathways important for mammopoiesis, in particular those that mediate the effects of peptide and steroid hormones. However, much less is known about the transcriptional regulators that dictate cell specificity, proliferation and differentiation within the mammary gland. This review will discuss recent insights into the transcriptional networks important for mammary gland development and consider how deregulation of specific transcription factors contributes to the pathogenesis of breast cancer.

Long term inhibition by estradiol or progesterone of melatonin secretion after administration of a mammary carcinogen, the dimethyl benz(a)anthracene, in Sprague-Dawley female rat; inhibitory effect of Melatonin on mammary carcinogenesis

A single intragastric administration of 7,12-dimethylbenz(a)anthracene (DMBA) has been shown to induce mammary tumors in young cycling female Sprague-Dawley rats. The appearance of the tumors is preceded by a series of neuroendocrine disturbances, including attenuation of the preovulatory Luteinizing Hormone surge and Gonadotropin-Releasing Hormone release and amplification of the preovulatory 17beta-Estradiol (E2) surge. In this study, we examined the hypothesis that a single administration of DMBA increases the E2 and Progesterone inhibition of the spontaneous and Isoproterenol-induced Melatonin (MT) secretion from the pineal gland, during the latency phase. Also, the incidence of mammary tumors, as well as the possible preventive effect of various doses of Melatonin, were recorded up to 6 months after daily administration. For all studies, Sprague-Dawley rats, 55-60 days of age, received, on the Estrous day of the Estrous cycle, a single dose of 15 mg DMBA delivered by intragastric intubation. For the study on ovarian steroids, they were ovariectomized 5 days later and then sacrificed by decapitation at 10 a.m., one month later. Pineal glands were removed and placed in perifusion chambers containing Hanks 199 medium. The medium was saturated with O2/CO2 (95%/5%) and its pH was 7.4. Ten independent chambers were immersed in a water bath at 37 degrees C. Each pineal gland received medium (flow rate: 0.16 ml/min) through a system of input lines. The fractions were collected every 10 min, and immediately frozen at -20 degrees C until Melatonin RIA. Experiments were repeated to obtain up to five experimental points for each treatment. E2 (10(-11)-10(-9) M) and Progesterone (10(-9)-10(-7) M) were applied during the entire perifusion period (7 h). Isoproterenol (10(-6) M) was applied for 20 min after 2.5 h in perifusion. Melatonin concentrations and Areas Under the Curves were compared using two-factor ANOVA as well as parametric or nonparametric two-sample methods after testing sample normality. For the study on the possible preventive effect of Melatonin, they were daily treated, by the intragastric route, with increasing doses of Melatonin for 6 months. The percentage of female rats having at least one mammary carcinoma were compared using the Fischer exact t-test. During the latency phase, in vehicle-treated rats, E2 and Progesterone treatments lead an almost significant inhibition of the Isoproterenol-induced stimulation of Melatonin secretion. In DMBA-treated rats, E2 treatment leads to a complete blunting of the Isoproterenol-induced stimulation of Melatonin and Progesterone treatment leads to a cyclic inhibition of the Isoproterenol-induced Melatonin secretion. During the promotion phase, there was a dose-dependent inhibitory effect (up to 65% inhibition) of the daily administration of Melatonin, on mammary tumors occurrence. In conclusion, the long term inhibition of DMBA upon Melatonin secretion from the pineal gland might accelerate the promotion of mammary tumors induced by the mammary carcinogen. Inversely, the daily administration of Melatonin for 6 months induces a long lasting protective effect against the formation of mammary tumors.

An expression study of hormone receptors in spontaneously developed, carcinogen-induced and hormone-induced mammary tumors in female Noble rats

The Noble (Nb) rat model has been used in the study of hormonal carcinogenesis of mammary and prostate glands, as this rat strain is susceptible to tumor induction in these glands by hormonal treatments. Recently, we demonstrated that this rat strain can develop spontaneously mammary tumors at high incidence in aged animals and also show high sensitivity to chemical carcinogens (DMBA and MNU) and combined treatments with sex hormones in mammary tumor induction. In the present study, we examined and compared the expression of hormone receptors [including estrogen receptors (ERalpha and ERbeta), androgen receptor (AR), progesterone receptor (PR), prolactin receptor (PRLR)] and prolactin (PRL) by immunohistochemistry, Western blotting and RT-PCR in spontaneous mammary tumors, and mammary tumors induced by sex hormones (T+E2 and T+DES for 8-10 months) and DMBA in Nb rat model. Immunohistochemistry and Western blotting showed that both the spontaneously developed and hormone-induced carcinomas exhibited strong immunoreactivity of ERalpha, ERbeta, AR, PR and PRLR, while the spontaneous fibroadenomas showed weak to moderate immunoreactivity of ERalpha and PRLR, whereas the DMBA-induced carcinomas exhibited weak to moderate immunoreactivity of ERalpha, AR, PR and PRLR, and sporadic weak ERbeta immunoreactivity. RT-PCR analyses showed that mRNA expression pattern of these markers resembled that of proteins. In addition, weak mRNA expression of PRL was detected in spontaneous carcinomas and carcinomas induced by DMBA and hormones, suggesting that PRL could be produced locally within the tumors. The results showed that the expression status of hormone receptors and PRL was different in spontaneous mammary tumors and tumors induced by carcinogen or hormones, suggesting that the extent of involvement of steroid hormones and their receptors in the spontaneous, carcinogen- or hormone-induced mammary carcinogenesis might be different.

The role of prolactin in mammary carcinoma

The contribution of prolactin (PRL) to the pathogenesis and progression of human breast cancer at the cellular, transgenic, and epidemiological levels is increasingly appreciated. Acting at the endocrine and autocrine/paracrine levels, PRL functions to stimulate the growth and motility of human breast cancer cells. The actions of this ligand are mediated by at least six recognized PRL receptor isoforms found on, or secreted by, human breast epithelium. The PRL/PRL receptor complex associates with and activates several signaling networks that are shared with other members of the cytokine receptor superfamily. Coupled with the recently identified intranuclear function of PRL, these networks are integrated into the in vitro and in vivo actions induced by ligand. These findings indicate that antagonists of PRL/PRL receptor interaction or PRL receptor-associated signal transduction may be of considerable utility in the treatment of human breast cancer.