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.

Influence of host factors on survival in dogs with malignant mammary gland tumors

The purpose of our study was to determine if specific host factors, such as age at diagnosis, obesity, and hormone status, influence the prognosis of canine mammary gland carcinomas and to confirm if previously reported risk factors (ie, histologic subtype, tumor size, and World Health Organization [WHO] stage) were important in a large series of affected dogs. Ninety-nine female dogs with mammary gland carcinomas, no previous therapy, an excisional biopsy, and known cause of death were studied. No significant association with survival was noted for age at diagnosis (chronologic or physiologic), obesity, or hormone status (ie, spayed versus intact, regardless of time of being spayed). Of the tumor factors analyzed, the histologic subtype anaplastic carcinoma (P = .02), WHO stage I (P = .01), evidence of metastasis at the time of diagnosis (P = .004), and tumor size of 3 cm or smaller (P = .005) all significantly influenced survival. Dogs that were classified as having tumor-related mortality had a shorter postoperative survival compared to dogs that died of other causes (14 months versus 23 months; P = .03). In conclusion, histologic subtype, WHO stage, and tumor size remain important prognostic factors in canine mammary gland tumors. Further study of other prognostic factors is needed to determine which tumors are adequately addressed with local therapy only and which dogs may require adjuvant treatment with chemotherapy.

[The mammary gland, an endocrine gland]

Features of acromegaly had developed in a 6-year-old crossbred Belgian shepherd dog (dog A) following treatment with medroxyprogesterone and an 8-year-old beagle dog (dog B) during the luteal phase of the oestrus cycle. Discontinuation of progesterone administration in dog A and ovariohysterectomy in both dogs was followed by a regression of the soft tissue changes and a normalisation of the initially high plasma growth hormone concentrations. These cases illustrate that the mammary gland is not just a gland which delivers milk in response to certain stimuli, but that it also transmits humoral signals, i.e., the mammary gland is an endocrine gland. Progestin-induced growth hormone is produced in areas of hyperplastic mammary epithelium and in mammary tumours. This suggests that locally-produced growth hormone is involved in the proliferation of unaffected and tumorous mammary tissue in an autocrine or paracrine manner. Now that the expression of the growth hormone gene has also been demonstrated in the human mammary gland, further studies are needed to answer questions such as (a) does mammary growth hormone also reach the systemic circulation in women?, (b) what is the role of local growth-hormone production in tumourigenesis?, and (c) does this phenomenon provide possibilities for therapeutic intervention in women with breast cancer?

Bcl-2 and androgen receptor gene expression in androgen-independent subclone derived from mouse androgen-dependent cells

We investigated bcl-2 and androgen receptor (AR) expression in an androgen-independent subline derived from mouse androgen-dependent mammary carcinoma cells. The androgen-independent SCAI cells were subcloned by cultivating androgen-dependent SC2G cells in serum-free, androgen-free conditions. The growth of the SCAI cells was not affected by testosterone. Western blot analysis showed greater expression of Bcl-2 protein in SCAI cells than in SC2G cells. A four-day culture with 4 microM antisense oligonucleotide complementary to mouse bcl-2 significantly decreased the viability of SCAI cells, when compared with sense control. The amount of the AR-mRNA expression in SCAI cells was slightly weaker. Direct sequence analysis showed no mutations in the AR of either androgen-dependent or -independent cells. These data indicate that the increased expression of Bcl-2 protein plays an important role in acquiring tolerance for the testosterone ablation, although it is not related to AR gene alteration.

ErbB-2-induced mammary tumor growth: the role of cyclin D1 and p27Kip1

The neu (c-erbB-2, HER2) proto-oncogene encodes a receptor tyrosine kinase that is a member of an important growth factor receptor family which includes the epidermal growth factor receptor (EGFR, ErbB1), ErbB3 and ErbB4. The neu is found over-expressed in 20-30% of human breast tumors. The c-erbB-2 is sufficient for the induction of mammary tumorigenesis in transgenic mice and the pathology of these mammary tumors strongly resembles human breast cancer. Murine transgenic models engineered to recapitulate human breast cancer provide an excellent and straightforward approach to dissect the molecular mechanisms governing the onset and progression of this disease. The molecular mechanisms by which ErbB-2 transforms cells involves direct effects on components of the cell-cycle regulatory apparatus. Recent studies have demonstrated a key role for components of the cell-cycle, in particular cyclin D1 and p27Kip1 (p27) in the onset and progression of ErbB-2-induced murine mammary tumorigenesis. Such studies have provided further impetus to therapeutics targeting these cell-cycle proteins.

A novel design of thermal anomaly for mammary gland tumor phantom for microwave radiometer

Microwave radiometry is the spectral measurement technique of resolving electromagnetic radiation of all matters which temperature is above absolute zero. This technique utilizes the electromagnetic noise field generated by a thermal volume similar to a mechanism existing in biological tissues. One particular application of microwave radiometry is for analyzing temperature differentials of inside of human body to detect and diagnose some crucial pathological conditions. For the general evaluation of a microwave radiometer, we propose a new type of phantom containing a mammary gland tumor imitator by considering biological heat diffusion effects propagated by a real tumor. Theoretical researches of human tumor revealed the fact that temperature distribution of tissues around a tumor formed a Gaussian statistics. To comply with the physiological property of the real tumor, we built a mammary gland tumor imitator composed of two parts (pseudotumor and thermal anomaly) and observed its temperature distribution when it was placed inside a phantom. Our results showed that the thermal properties of tumor imitator well agreed with heat-transfer properties of a real tumor and the proportional linear relationship existed between the location of tumor imitator and the intensity of radiometer measurements. From this relationship, we could also estimate several parameters related with our phantom, such as the minimum detectable size and maximum detectable depth of a tumor imitator.

Stromal effects on mammary gland development and breast cancer

Breast cancer manifests itself in the mammary epithelium, yet there is a growing recognition that mammary stromal cells also play an important role in tumorigenesis. During its developmental cycle, the mammary gland displays many of the properties associated with breast cancer, and many of the stromal factors necessary for mammary development also promote or protect against breast cancer. Here we review our present knowledge of the specific factors and cell types that contribute to epithelial-stromal crosstalk during mammary development. To find cures for diseases like breast cancer that rely on epithelial-stromal crosstalk, we must understand how these different cell types communicate with each other.

Biological relevance of oxytocin and oxytocin receptors in cancer cells and primary tumors

For a long time, the hypothalamic nonapeptide oxytocin (OT) is known to play a crucial role in many reproductive and behavioral functions. In recent years, a new biological effect of OT has been identified in neoplastic pathology. In this context, OT acts as a growth regulator. through the activation of specific G-coupled transmembrane receptors (OTR). In vitro, an antiproliferative effect of OT was demonstrated in neoplastic cells of either epithelial (mammary and endometrial) or nervous or bone origin, all expressing OTR. Furthermore, the growth-inhibiting effect of OT was also tested and confirmed in mouse and rat mammary carcinomas in vivo. In neoplastic cells from another OT target tissue, trophoblast, the OT effect was to promote proliferation, the opposite of what previously observed in all the other neoplastic OT responsive cells. The signal transduction involved in the OT biological effect was different in OT growth-inhibited or growth-stimulated cells. In the former, the OT effect was mediated by the activation of the cAMP-PKA pathway, a non-conventional OT signaling, whereas in the latter by the increase of intracellular calcium and tyrosine phosphorylation, which are the 'classical' OT transducers. The unexpected role of OT (and OT analogues) in regulating cell proliferation, as well as the diffuse expression of OTR in neoplastic tissue of different origin, open new perspectives on the biological role of the OT-OTR system in cancer.

Inhibition of myc-dependent breast tumor formation in transgenic mice

One of the most promising approaches for cancer gene therapy is the use of the so-called suicide genes, which encode prodrug-activating enzymes and render transduced cells more sensitive to prodrugs. The enzyme nitroreductase (NTR) converts prodrug CB1954 into a cytotoxic DNA interstrand cross-linking agent. We have established transgenic mice in which the pro-oncogene c-myc and NTR were fused to the internal ribosome entry site and coexpressed in luminal cells of the mammary gland under the control of mouse whey acidic protein (WAP) promoter to evaluate NTR mediated ablation of mammary tumors. More than 78% of transgenic females developed in situ or infiltrating carcinomas after three to four pregnancies. By contrast, if the transgenic female mice were given the prodrug CB1954 during their third lactation, the incidence of tumors decreased to less than 40% (P < 0.05). The total number of carcinomas was even more striking with 117 carcinomas identified in 14 non-ablated transgenics compared with only five in 15 treated animals (p < 0.05, student t test). C-myc induced pleomorphic nuclei and mitotic figures were seen as a field change in over 70% of the untreated transgenics compared to 20% in the treated group. Our results suggest that the enzyme pro-drug system NTR-CB1954 efficiently inhibit myc-dependent tumor formation and malignant progression in the mammary gland.

Polyunsaturated fatty acids and epidermal growth factor receptor/mitogen-activated protein kinase signaling in mammary cancer

Mammary cancer is the second leading cause of cancer death in women, the second most common neoplasm in dogs and the third leading neoplasm in cats. Mammary tumors are similar in morphology and progression in these species, so cats and dogs are good models for determining treatment or prevention modalities for the human population. Epidemiological, in vitro and rodent studies have demonstrated that polyunsaturated fatty acids (PUFA) can influence the growth, progression and metastasis of mammary cancer. Although a role of PUFA in modulating mammary cancer growth has been shown, the mechanisms by which this occurs remain unclear. Recent studies have demonstrated that PUFA may influence the activity of the epidermal growth factor receptor/mitogen-activated protein kinase pathway, which is involved in regulating several oncogenes (c-myc, c-fos, neu/c-erb-b2) involved in the progression of cancer. We review the potential mechanism by which PUFA may modulate the growth of mammary cancer through regulation of the epidermal growth factor receptor/mitogen-activated protein kinase signal transduction cascade.

Colony-stimulating factor 1 promotes progression of mammary tumors to malignancy

In human breast carcinomas, overexpression of the macrophage colony-stimulating factor (CSF-1) and its receptor (CSF-1R) correlates with poor prognosis. To establish if there is a causal relationship between CSF-1 and breast cancer progression, we crossed a transgenic mouse susceptible to mammary cancer with mice containing a recessive null mutation in the CSF-1 gene (Csf1(op)) and followed tumor progression in wild-type and null mutant mice. The absence of CSF-1 affects neither the incidence nor the growth of the primary tumors but delayed their development to invasive, metastatic carcinomas. Transgenic expression of CSF-1 in the mammary epithelium of both Csf1(op)/Csf1(op) and wild-type tumor-prone mice led to an acceleration to the late stages of carcinoma and to a significant increase in pulmonary metastasis. This was associated with an enhanced infiltration of macrophages into the primary tumor. These studies demonstrate that the growth of mammary tumors and the development to malignancy are separate processes and that CSF-1 selectively promotes the latter process. CSF-1 may promote metastatic potential by regulating the infiltration and function of tumor-associated macrophages as, at the tumor site, CSF-1R expression was restricted to macrophages. Our data suggest that agents directed at CSF-1/CSF-1R activity could have important therapeutic effects.

Progestin-induced mammary growth hormone (GH) production

Toxicity studies using beagle dogs revealed in the 1980s that synthetic progestins may induce a syndrome of growth hormone (GH) excess, known as acromegaly, and the development of predominantly benign mammary hyperplasia. In the early 1990s is was discovered that progestin-induced GH excess in the dog originates within the mammary gland. This mammary-derived GH may have endocrine, para/autocrine as well as exocrine effects. The expression of GH mRNA is also found in cats and humans indicating that mammary GH expression is not unique for the dog. The mammary gene is identical to the pituitary-expressed gene and uses the same promoter. Nevertheless a striking difference exists in the mammary gland. Pit-1, which is a prerequisite factor for pituitary GH mRNA expression, is likely not involved in the mammary gene expression. These studies shed new light on the mechanism of progesterone-induced mammary hyperplasia and urges for further research on potential adverse effects of synthetic progestins.

Fibroblast growth factor signalling and cyclin D1 function are necessary for normal mammary gland development during pregnancy. A transgenic mouse approach

A number of growth factors, growth factor receptors and cell cycle regulatory proteins have been implicated in the genesis of mammary carcinomas both in animal models as well as in human breast tumour samples. Studies on the development of the mammary gland has revealed that several of the proto-oncogenes, or their closely related gene-family members, have a function in the normal growth and differentiation of the gland. In this review the role of fibroblast growth factor signalling and the critical requirement for the cell cycle regulator, cyclin D1 is discussed with respect to their normal function in mammary gland development and abnormal role in mammary carcinogenesis.

Somatostatin and opioid receptors in mammary tissue. Role in cancer cell growth

Somatostatin and opioid systems, are the two main inhibitory systems in mammals. Both classes of substances have been identified in normal and malignant mammary gland, as well as their cognitive receptors. They have been implied in the inhibition of cell growth of cancer cells and cell lines, in a dose-dependent and reversible manner. Somatostatin acts through homologous receptors (SSTRs), belonging to five distinct classes (SSTR1-5). We, and others have identified SSTR2 and 3 as been the only SSTRs present in the breast. Furthermore, opioids act through the three classes of opioid receptors (mu, delta,kappa). In the breast, kappa opioid receptor subtypes (kappa 1-kappa 3) are the most widely expressed. We further have shown that opioids, in addition to their binding to opioid receptors, compete for binding to SSTRs. This functional interaction, together with other identified modes of opioid action in the breast (modulation of steroid receptors, proteases' secretion, interaction with cytoskeletal elements), will be discussed, taking into consideration also the possible local production of casomorphins (casein-derived opioids), which are very potent antiproliferative agents.

Inducible transgenics. New lessons on events governing the induction and commitment in mammary tumorigenesis

Breast cancer arises from multiple genetic events that together contribute to the established, irreversible malignant phenotype. The development of inducible tissue-specific transgenics has allowed a careful dissection of the events required for induction and subsequent maintenance of tumorigenesis. Mammary gland targeted expression of oncogenic Ras or c-Myc is sufficient for the induction of mammary gland tumorigenesis in the rodent, and when overexpressed together the rate of tumor onset is substantially enhanced. In an exciting recent finding, D'Cruz et al discovered tetracycline-regulated c-Myc overexpression in the mammary gland induced invasive mammary tumors that regressed upon withdrawal of c-Myc expression. Almost one-half of the c-Myc-induced tumors harbored K-ras or N-ras gene point mutations, correlating with tumor persistence on withdrawal of c-Myc transgene expression. These findings suggest maintenance of tumorigenesis may involve a second mutation within the Ras pathway.

Tamoxifen suppresses histologic progression to atypia and DCIS in MCFIOAT xenografts, a model of early human breast cancer

We evaluated the effects of tamoxifen on the growth and progression of MCFIOAT xenografts, an estrogen responsive model of human breast tumor progression, in which cells are injected orthotopically into the mammary fat pad of female nude mice. At 10 weeks following implantation, histologic sections of each graft were evaluated microscopically for histologic lesions analogous to human breast tumor progression, graded as simple hyperplasia, complex hyperplasia, atypical hyperplasia, ductal carcinoma in situ and invasive carcinoma. Three out of five xenografts in (endocrine intact) control animals progressed to atypical hyperplasia, one progressed to ductal carcinoma in situ and one to invasive carcinoma. The latter two control grafts also contained foci of putative precursor lesions (i.e. atypical hyperplasia and in situ carcinoma, respectively). Tamoxifen supplemented xenografts (N= 17) were uniformly smaller than controls, but contained invasive carcinoma in a similar proportion (4/17, 24%). However, none of these grafts exhibited ductal carcinoma in situ and only one contained atypical hyperplasia. Most grafts in tamoxifen supplemented animals (10/17, including all four with carcinomas) showed complex hyperplasia, which typically dominated the graft. We conclude that tamoxifen selectively inhibits the appearance or growth of preinvasive index lesions. Development of malignancy in the absence of such precursors, though, implies selection for alternative histogenetic pathways as a result of endocrine manipulation.

Differential expression of integrin mRNAs and proteins during normal rat mammary gland development and in carcinogenesis

A rat model was used to address the roles of integrins in the regulation of normal mammary epithelial cell (MEC) growth and differentiation and in mammary carcinogenesis. The expression of integrins alpha5, alpha6, beta1, and beta4 was examined via Northern and Western blotting analyses in freshly isolated MEC from various postnatal developmental stages. mRNAs for all four integrins were detectable at puberty and were increased during pregnancy. During lactation, the expression of alpha5, alpha6, and beta1 integrin mRNAs reached a peak, whereas that of beta4 integrin decreased dramatically. At day 7 of involution, the levels of all four integrin mRNAs were similar to or slightly higher than that of the pubertal mammary gland. Although alpha5 integrin protein decreased during pregnancy and lactation, beta1 and beta4 integrin proteins had similar profiles as the expression of their respective mRNAs, suggesting that integrin gene expression is regulated at both transcriptional and post-transcriptional levels. All four integrins were heterogeneously expressed in 7,12-dimethylbenz[a]anthracene- and N-nitroso-N-methyl-urea-induced mammary tumors and in RBA and NMU rat mammary tumor cell lines. Adhesion assays showed that isolated MEC interacted with fibronectin to a greater extent than with laminin and collagen I in vitro, and that tumor cells with altered integrin expression exhibited greater adhesive ability to various substrata. Together, our results indicate that alpha5, alpha6, beta1, and beta4 integrins are differentially expressed during normal MEC development and in mammary tumors, supporting the hypothesis that these integrins play important yet complex roles in the mammary gland.

Loss of p21WAF1/CIP1 accelerates Ras oncogenesis in a transgenic/knockout mammary cancer model

Upregulation of the cyclin-dependent kinase inhibitor p21WAF1/CIP1 and subsequent cell growth arrest or senescence is one mechanism by which normal cells are believed to respond to stress induced by the constitutively activated GTPase Ras. We hypothesize that in the absence of p21, the onset of Ras-dependent oncogenesis is accelerated. To test this hypothesis, we crossed MMTV/v-Ha-ras transgenic mice into a p21-deficient background. By 63 days of age, all 8 ras/p21-/- mice developed either malignant (mammary and/or salivary adenocarcinomas) or benign (Harderian hyperplasia) tumors. In contrast, by the same age, only one out of nine of the ras/p21+/+ mice developed a tumor. Furthermore, by 94 days of age, half of the ras/p21-/- mice, but none of the ras/p21+/+ mice, developed mammary tumors. p21-deficiency also accelerated the development of salivary (T50=66 days for ras/p21-/- vs T50=136 days for ras/p21+/+) and Harderian (T50=52 days for ras/p21-/- vs T50>221 days for ras/p21+/+) tumors. Furthermore, two out of the eight ras/p21-/- mice had metastatic lesions, one in its lungs, the other in its abdomen. None of the nine ras/p21+/+ mice had metastatic lesions. By 4 months of age, the mammary tumor multiplicity was 10-fold greater in ras/p21-/- (average 3.40 tumors/mouse) than in ras/p21+/+ (average 0.33 tumor/mouse) mice. However, once the tumors appeared, their growth rate, apoptosis level, and mitotic index were not affected by the loss of p21, suggesting that loss of p21 is critical in early but not late events of Ras oncogenesis. Altogether, the results show that tumor onset in MMTV/v-Ha-ras mice is p21-dependent with loss of p21 associated with earlier tumor appearance and increased tumor multiplicity and aggressiveness.

High incidence of breast and endometrial neoplasia resembling human Cowden syndrome in pten+/- mice

PTEN is one of the most commonly mutated tumor suppressor genes in human cancer. PTEN mutations have been implicated in the development of a variety of human neoplasia, including high-grade glioblastoma, prostate, breast, endometrial, and thyroid carcinoma. Germ-line mutations of PTEN cause Cowden's syndrome (CS), a multiple hamartoma condition resulting in increased susceptibility for the development of cancer. When more than 6 months old, pten+/- mice develop a range of tumors, partially resembling the spectrum of neoplasia observed in CS patients. One-half (32 of 65) of pten+/- females developed breast tumors, whereas all (65 of 65) of the females had endometrial hyperplasia, and there was a high incidence (14 of 65) of endometrial cancer. Hamartoamous tumors of the gastrointestinal tract, as well as prostate and adrenal neoplasia, were also frequently observed. Significantly, the spectrum of neoplasia observed in pten+/- mice partially overlaps with the types of tumors frequently detected in CS patients. The majority of tumors in pten+/- mice exhibit loss of heterozygosity at the pten locus, which indicates the importance for loss of PTEN function in tumor formation. Consistent with the role of PTEN in negative regulation of PKB/Akt phosphorylation and activity, pten loss of heterozygosity is accompanied by hyperphosphorylation of PKB/Akt in tumors. Taken together, our results establish pten+/- mice as an excellent animal model system for the investigation of PTEN-related hamartoma syndromes, as well as the role of PTEN in breast and endometrial carcinogenesis.

Openings between defective endothelial cells explain tumor vessel leakiness

Leakiness of blood vessels in tumors may contribute to disease progression and is key to certain forms of cancer therapy, but the structural basis of the leakiness is unclear. We sought to determine whether endothelial gaps or transcellular holes, similar to those found in leaky vessels in inflammation, could explain the leakiness of tumor vessels. Blood vessels in MCa-IV mouse mammary carcinomas, which are known to be unusually leaky (functional pore size 1.2-2 microm), were compared to vessels in three less leaky tumors and normal mammary glands. Vessels were identified by their binding of intravascularly injected fluorescent cationic liposomes and Lycopersicon esculentum lectin and by CD31 (PECAM) immunoreactivity. The luminal surface of vessels in all four tumors had a defective endothelial monolayer as revealed by scanning electron microscopy. In MCa-IV tumors, 14% of the vessel surface was lined by poorly connected, overlapping cells. The most superficial lining cells, like endothelial cells, had CD31 immunoreactivity and fenestrae with diaphragms, but they had a branched phenotype with cytoplasmic projections as long as 50 microm. Some branched cells were separated by intercellular openings (mean diameter 1.7 microm; range, 0.3-4.7 microm). Transcellular holes (mean diameter 0.6 microm) were also present but were only 8% as numerous as intercellular openings. Some CD31-positive cells protruded into the vessel lumen; others sprouted into perivascular tumor tissue. Tumors in RIP-Tag2 mice had, in addition, tumor cell-lined lakes of extravasated erythrocytes. We conclude that some tumor vessels have a defective cellular lining composed of disorganized, loosely connected, branched, overlapping or sprouting endothelial cells. Openings between these cells contribute to tumor vessel leakiness and may permit access of macromolecular therapeutic agents to tumor cells.

Sigma-2 receptors as a biomarker of proliferation in solid tumours

Over the past several years, our group has provided considerable evidence that the expression of sigma-2 (sigma2) receptors may serve as a biomarker of tumour cell proliferation. In these in vitro studies, sigma2 receptors were expressed 8-10 times more in proliferative (P) tumour cells than in quiescent (Q) tumour cells, and the extent and kinetics of their expression were independent of a number of biological, physiological and environmental factors often found in solid tumours. Moreover, the expression of sigma2 receptors followed both the population growth kinetics when Q-cells were recruited into the P-cell compartment and the proliferative status of human breast tumour cells treated with cytostatic concentrations of tamoxifen. However, these in vitro studies may or may not be indicative of what might occur in solid tumours. In the present study, the sigma2 receptor P:Q ratio was determined for the cells from subcutaneous 66 (diploid) and 67 (aneuploid) tumours grown in female nude mice. The sigma2 receptor P:Q ratio of the 66 tumours was 10.6 compared to the sigma2 receptor P:Q ratio of 9.5 measured for the 66 tissue culture model. The sigma2 receptor P:Q ratio of the 67 tumours was 4.5 compared to the sigma2 receptor P:Q ratio of approximately equal 8 measured for the 67 tissue culture model. The agreement between the solid tumour and tissue culture data indicates that: (1) the expression of sigma2 receptors may be a reliable biomarker of the proliferative status of solid tumours and (2) radioligands with both high affinity and high selectivity for sigma2 receptors may have the potential to non-invasively assess the proliferative status of human solid tumours using imaging techniques such as positron emission tomography or single-photon emission computerized tomography.

IGF and insulin action in the mammary gland: lessons from transgenic and knockout models

Transgenic and knockout mice have become valuable experimental systems with which to study specific molecular events within the mammary gland of an intact animal. These models have provided a wealth of information about the effects of a number of oncogenes and growth factors. This review focuses on results obtained from the application of transgenic and knockout models to determine the roles of insulin and insulin-like growth factors (IGF) in the regulation of mammary gland development, lactation and tumorigenesis. Transgenic models which overexpress IGF-I or -II display specific alterations in mammary gland development and an increased incidence of mammary tumors. Analysis of mammary gland development in knockout mice which are deficient in IGF-I or the IGF-I receptor supports the conclusion that the IGF system is important for normal mammary gland development. This review discusses these observations in detail and attempts to fit them into a larger picture of IGF and insulin action in the mammary gland.

Mammary growth hormone and tumorigenesis--lessons from the dog

The discovery in the early 1990s that progestin-induced growth hormone (GH) excess in the dog originates in the mammary gland can be seen as a hallmark in the research on the pathogenesis of mammary cancer in the dog. The local biosynthesis and release of GH may provide a highly proliferative environment in the mammary gland, which contributes to the development and/or progression of mammary tumours. Before final goals such as prevention of tumour formation or inhibition of tumour promotion can be achieved it is of eminent importance to elucidate the mechanism of progesterone-induced mammary GH production and the mechanism of local autocrine/paracrine action of GH. These local GH effects may be achieved through direct growth stimulating effects of GH as well as by indirect effects mediated by the stimulation of the biosynthesis of insulin-like growth factor-I (IGF-I). The biological effects of the IGFs largely depend on the presence of IGF binding proteins (IGFBPs) which may both enhance or inhibit the activity of the IGFs. This review concentrates on recent advances in the understanding of the local mammary GH-IGF axis and the lessons which can be drawn from the dog for mammary cancer research in other species.

Breast cancer cells interact with osteoblasts to support osteoclast formation

Breast cancers commonly cause osteolytic metastases in bone, a process that is dependent upon osteoclast-mediated bone resorption. Recently the osteoclast differentiation factor (ODF), better termed RANKL (receptor activator of NF-kappaB ligand), expressed by osteoblasts has been cloned as well as its cognate signaling receptor, receptor activator of NFkappaB (RANK), and a secreted decoy receptor osteoprotegerin (OPG) that limits RANKL's biological action. We determined that the breast cancer cell lines MDA-MB-231, MCF-7, and T47D as well as primary breast cancers do not express RANKL but express OPG and RANK. MCF-7, MDA-MB-231, and T47D cells did not act as surrogate osteoblasts to support osteoclast formation in coculture experiments, a result consistent with the fact that they do not express RANKL. When MCF-7 cells overexpressing PTH-related protein (PTHrP) were added to cocultures of murine osteoblasts and hematopoietic cells, osteoclast formation resulted without the addition of any osteotropic agents; cocultures with MCF-7 or MCF-7 cells transfected with pcDNAIneo required exogenous agents for osteoclast formation. When MCF-7 cells overexpressing PTHrP were cultured with murine osteoblasts, osteoblastic RANKL messenger RNA (mRNA) levels were enhanced and osteoblastic OPG mRNA levels diminished; MCF-7 parental cells had no effect on RANKL or OPG mRNA levels when cultured with osteoblastic cells. Using a murine model of breast cancer metastasis to bone, we established that MCF-7 cells that overexpress PTHrP caused significantly more bone metastases, which were associated with increased osteoclast formation, elevated plasma PTHrP concentrations and hypercalcaemia compared with parental or empty vector controls.