Transcriptional regulation of vascular endothelial growth factor expression in epithelial and stromal cells during mouse mammary gland development

A review concerning the breast cancer-related tumour microenvironment

Breast cancer (BC) is currently the most common malignant tumour in women and one of the leading causes of their death around the world. New and increasingly personalised diagnostic and therapeutic tools have been introduced over the last few decades, along with significant advances regarding the study and knowledge related to BC. The tumour microenvironment (TME) refers to the tumour cell-associated cellular and molecular environment which can influence conditions affecting tumour development and progression. The TME is composed of immune cells, stromal cells, extracellular matrix (ECM) and signalling molecules secreted by these different cell types. Ever deeper understanding of TME composition changes during tumour development and progression will enable new and more innovative therapeutic strategies to become developed for targeting tumours during specific stages of its evolution. This review summarises the role of BC-related TME components and their influence on tumour progression and the development of resistance to therapy. In addition, an account on the modifications in BC-related TME components associated with therapy is given, and the completed or ongoing clinical trials related to this topic are presented.

Interaction between Macrophages and Adipose Stromal Cells Increases the Angiogenic and Proliferative Potential of Pregnancy-Associated Breast Cancers

Pregnancy associated breast cancers (PABCs) exhibit increased aggressiveness and overall poorer survival. During lactation, changes take place in the breast tissue microenvironment that lead to increased macrophage recruitment and alterations in adipose stromal cells (ASC-Ls). The interaction of these cells in PABCs could play a role in the increased aggressiveness of these cancers. We utilized an in vitro co-culture model to recreate the interactions of ASC-Ls and macrophages in vivo. We performed qRT-PCR to observe changes in gene expression and cytokine arrays to identify transcriptional changes that result in an altered microenvironment. Additionally, functional assays were performed to further elicit how these changes affect tumorigenesis. The co-culture of ASC-Ls and macrophages altered both mRNA expression and cytokine secretion in a tumor promoting manner. Tumorigenic cytokines, such as IL-6, CXCL1, CXCL5, and MMP-9 secretion levels, were enhanced in the co-culture. Additionally, conditioned media from the co-culture elevated the tumor cell proliferation and angiogenic potential of endothelial cells. These finds indicate that the changes seen in the microenvironment of PABC, specifically the secretion of cytokines, play a role in the increased tumorigenesis of PABCs by altering the microenvironment to become more favorable to tumor progression.

Long-chain noncoding RNA sequencing analysis reveals the molecular profiles of chemically induced mammary epithelial cells

Long noncoding RNAs (lncRNAs) were important regulators affecting the cellular reprogramming process. Previous studies from our group have demonstrated that small molecule compounds can induce goat ear fibroblasts to reprogram into mammary epithelial cells with lactation function. In this study, we used lncRNA-Sequencing (lncRNA-seq) to analyze the lncRNA expression profile of cells before and after reprogramming (CK vs. 5i8 d). The results showed that a total of 3,970 candidate differential lncRNAs were detected, 1,170 annotated and 2,800 new lncRNAs. Compared to 0 d cells, 738 lncRNAs were significantly upregulated and 550 were significantly downregulated in 8 d cells. Heat maps of lncrnas and target genes with significant differences showed that the fate of cell lineages changed. Functional enrichment analysis revealed that these differently expressed (DE) lncRNAs target genes were mainly involved in signaling pathways related to reprogramming and mammary gland development, such as the Wnt signaling pathway, PI3K-Akt signaling pathway, arginine and proline metabolism, ECM-receptor interaction, and MAPK signaling pathway. The accuracy of sequencing was verified by real-time fluorescence quantification (RT-qPCR) of lncRNAs and key candidate genes, and it was also demonstrated that the phenotype and genes of the cells were changed. Therefore, this study offers a foundation for explaining the molecular mechanisms of lncRNAs in chemically induced mammary epithelial cells.

Changes in the mammary gland during aging and its links with breast diseases

The functional capacity of organisms declines in the process of aging. In the case of breast tissue, abnormal mammary gland development can lead to dysfunction in milk secretion, a primary function, as well as the onset of various diseases, such as breast cancer. In the process of aging, the terminal duct lobular units (TDLUs) within the breast undergo gradual degeneration, while the proportion of adipose tissue in the breast continues to increase and hormonal levels in the breast change accordingly. Here, we review changes in morphology, internal structure, and cellular composition that occur in the mammary gland during aging. We also explore the emerging mechanisms of breast aging and the relationship between changes during aging and breast-related diseases, as well as potential interventions for delaying mammary gland aging and preventing breast disease.

Lysophosphatidylinositol Promotes Chemotaxis and Cytokine Synthesis in Mast Cells with Differential Participation of GPR55 and CB2 Receptors

Mast cells (MCs) are the main participants in the control of immune reactions associated with inflammation, allergies, defense against pathogens, and tumor growth. Bioactive lipids are lipophilic compounds able to modulate MC activation. Here, we explored some of the effects of the bioactive lipid lysophosphatidylinositol (LPI) on MCs. Utilizing murine bone marrow-derived mast cells (BMMCs), we found that LPI did not cause degranulation, but slightly increased FcεRI-dependent β-hexosaminidase release. However, LPI induced strong chemotaxis together with changes in LIM kinase (LIMK) and cofilin phosphorylation. LPI also promoted modifications to actin cytoskeleton dynamics that were detected by an increase in cell size and interruptions in the continuity of the cortical actin ring. The chemotaxis and cortical actin ring changes were dependent on GPR55 receptor activation, since the specific agonist O1602 mimicked the effects of LPI and the selective antagonist ML193 prevented them. The LPI and O1602-dependent stimulation of BMMC also led to VEGF, TNF, IL-1α, and IL-1β mRNA accumulation, but, in contrast with chemotaxis-related processes, the effects on cytokine transcription were dependent on GPR55 and cannabinoid (CB) 2 receptors, since they were sensitive to ML193 and to the specific CB2 receptor antagonist AM630. Remarkably, GPR55-dependent BMMC chemotaxis was observed towards conditioned media from distinct mouse and human cancer cells. Our data suggest that LPI induces the chemotaxis of MCs and leads to cytokine production in MC in vitro with the differential participation of GPR55 and CB2 receptors. These effects could play a significant role in the recruitment of MCs to tumors and the production of MC-derived pro-angiogenic factors in the tumor microenvironment.

The level pro-inflammatory and anti-inflammatory biomarkers in patients with chronic mechanical low back pain under pulse radiofrequency therapy

Low back pain is a frequent and recurrent condition, often with a non-specific cause. Conventional treatment methods are generally insufficient in the treatment of chronic low back pain. The aim of the study was to estimate the level of IFN, IL-1, IL-6 (proinflammatory), IL-10, IL-4 (anti-inflammatory) and VEGF proteins in the serum of patients with chronic mechanical low back pain under Pulse radiofrequency (PRF) therapy. The study was carried out on 40 patients 20-60 years old, diagnosed with chronic low back pain for at least 4 months, primary complaint on lumbosacral low back pain, pain intensity VAS (visual analog scale) score of 5 and above, not responding well to conservative treatment (analgesic drugs, physiotherapy, etc.). Therapeutic Radiofrequency applications were carried out with an RF generator (RFG 3C Plus, Radionics). Blood samples were taken 1 day before interventional treatment (control), then 1 day (group1) and 15 days (group 2) after. The serum level of IFN, IL-1, IL-6, IL-10, IL-4 and VEGF l was analyzed with ELISA test. It was shown that as a result of PRF treatment the level of IL-1 was decreased while the levels of IL-4 and IL-6 were increased. It was concluded that the increase in serum levels of proinflammatory cytokines may be correlated with the severity of pain and that the increase in the level of anti-inflammatory cytokines reduces pain by reducing inflammation. Keywords: chronic low back pain, cytokines, radiofrequency therapy

Mammary gland-specific regulation of GNRH and GNRH-receptor gene expression is likely part of a local autoregulatory system in female vizcachas (Rodentia: Chinchillidae)

In addition to key mammotrophic hormones such as the pituitary prolactin (PRL) and the ovarian steroids progesterone and estradiol, there are local factors that modulate the tissue dynamics of the mammary glands during pregnancy and lactation. By immunohistochemistry and RT-PCR, we found local transcription and translation of gonadotropin-releasing hormone (GNRH), GNRH receptor (GNRHR), PRL and PRL receptor (PRLR) in mammary glands of adult vizcachas during pregnancy and lactation. Both GNRH and GNRHR showed a lag between protein expression and gene transcription throughout the gestational period: while the highest transcription levels of these genes were recorded at early-pregnancy, the epithelial immunoexpressions of both showed their maximum during lactation. RIA results corroborated the presence of GNRH in mammary glands at all the analyzed stages and confirmed the maximum amount of this peptide in the lactating group. Significant amounts of GNRH were detected in milk samples as well. Conversely, PRL and PRLR shared similar protein and gene expression profiles, all exhibiting maximum values during lactation. GNRH peptide content in mammary glands of females with sulpiride-induced hyperprolactinemia (HP) was significantly lower than that of control females (CT). Although PRL mRNA levels remained unchanged, there was a marked increase in theα-lactalbumin (LALBA) transcription in mammary glands of HP- vs CT-females. These results suggest that after targeting mammary glands, PRL stimulates the expression of milk protein genes, but also, tempers the local expression of GNRH. Mammary gland-explantssupplemented with a GNRH analogue (GN-explants) had no differences in terms of PRLR orLALBA transcription levels compared to CT-explants, so the mammary PRLR signaling would not appear to be modulated by GNRH. Yet, mRNA expression levels of both GNRH and the GNRHR-downstream factor, EGR1, were significantly higher in GN-explants compared to that of CT which would point to a GNRH-positive feedback mechanism. In summary, the local coupled expression of GNRH, GNRHR and EGR1 in the mammary gland throughout pregnancy of vizcachas, the PRL-dependent mammary GNRH secretion as well as the GNRH positive feedback on its own transcription suggest an autocrine-paracrine regulatory mechanism and propose an active role for GNRH in mammary gland tissue remodeling.

Cross talk of vascular endothelial growth factor and neurotrophins in mammary gland development

During the period of lactation, there is extensive growth and development of the mammary gland in order to fulfil the increased demands of milk for the growing infant. Angiogenesis plays a key role in alveolar development and facilitates optimal milk production. Vascular endothelial growth factor (VEGF) is one of the key growth factors regulating angiogenesis in mammary gland. Apart from VEGF, neurotrophins are also known to regulate angiogenesis through direct or indirect mechanisms. Few studies have demonstrated mRNA levels of neurotrophins and their receptors in mammary gland both in humans and rodents. A cross talk between VEGF and neurotrophins has been described in placental development. The enteric and central nervous system are not fully developed at birth, making it imperative to have appropriate levels of angiogenic factors and neurotrophins during postnatal period. The current review summarises studies which describe the role of neurotrophins and angiogenic factors in the mammary gland development.

Adipocytes and microRNAs Crosstalk: A Key Tile in the Mosaic of Breast Cancer Microenvironment

Breast cancer (BC) is a disease characterized by a high grade of heterogeneity. Consequently, despite the great achievements obtained in the last decades, most of the current therapeutic regimens still fail. The identification of new molecular mechanisms that will increase the knowledge of all steps of tumor initiation and growth is mandatory in finding new clinical strategies. The BC microenvironment, consisting of endothelial cells, fibroblasts, immune cells and adipocytes, plays an essential role in regulating BC development, and recently it has gained great attention in the scientific community. In particular, adipose tissue is emerging as an important target to investigate among mammary gland components. The mechanisms underlying BC progression driven by adipocytes are predominantly unexplored, especially that involving the switch from normal adipocytes to the so-called cancer-associated adipocytes (CAAs). MicroRNAs (miRNAs), a class of gene expression modulators, have emerged as the regulators of key oncogenes and tumor suppressor genes that affect multiple pathways of the tumor microenvironment and adipose tissue. This review concerns a presentation of the role of adipocytes in breast tissue, and describes the most recent discoveries about the interplay between adipocytes and miRNAs, which collaborate in the arrangement of a pro-inflammatory and cancerous microenvironment, laying the foundations for new concepts in the prevention and treatment of BC.

Pink Adipocytes

Adipocytes are lipid-rich parenchymal cells contained in a very plastic organ, whose composition can undergo striking physiologic changes. In standard conditions the organ contains white and brown adipocytes which play opposite roles: lipid storage to meet metabolic requirements and lipid burning for thermogenesis, respectively. During chronic cold exposure, white adipocytes transdifferentiate to brown, to increase thermogenesis, whereas in conditions of chronic positive energy balance brown adipocytes transdifferentiate to white, to increase energy stores. During pregnancy, lactation, and post-lactation, subcutaneous white adipocytes convert to milk-producing glands formed by lipid-rich elements that can be defined as pink adipocytes. Recent fate-mapping data support the conversion of pink to brown adipocytes and the reversible conversion of brown adipocytes to myoepithelial cells of alveoli.

Reversible De-differentiation of Mature White Adipocytes into Preadipocyte-like Precursors during Lactation

Adipose tissue in the mammary gland undergoes dramatic remodeling during reproduction. Adipocytes are replaced by mammary alveolar structures during pregnancy and lactation, then reappear upon weaning. The fate of the original adipocytes during lactation and the developmental origin of the re-appearing adipocyte post involution are unclear. Here, we reveal that adipocytes in the mammary gland de-differentiate into Pdgfrα⁺ preadipocyte- and fibroblast-like cells during pregnancy and remain de-differentiated during lactation. Upon weaning, de-differentiated fibroblasts proliferate and re-differentiate into adipocytes. This cycle occurs over multiple pregnancies. These observations reveal the potential of terminally differentiated adipocytes to undergo repeated cycles of de-differentiation and re-differentiation in a physiological setting.

Stromal cells in breast cancer as a potential therapeutic target

Breast cancer in the United States is the second most commonly diagnosed cancer in women. About 1 in 8 women will develop invasive breast cancer over the course of her lifetime and breast cancer remains the second leading cause of cancer-related death. In pursuit of novel therapeutic strategies, researchers have examined the tumor microenvironment as a potential anti-cancer target. In addition to neoplastic cells, the tumor microenvironment is composed of several critical normal cell types, including fibroblasts, vascular and lymph endothelial cells, osteoclasts, adipocytes, and immune cells. These cells have important roles in healthy tissue stasis, which frequently are altered in tumors. Indeed, tumor-associated stromal cells often contribute to tumorigenesis, tumor progression, and metastasis. Consequently, these host cells may serve as a possible target in anti-tumor and anti-metastatic therapeutic strategies. Targeting the tumor associated host cells offers the benefit that such cells do not mutate and develop resistance in response to treatment, a major cause of failure in cancer therapeutics targeting neoplastic cells. This review discusses the role of host cells in the tumor microenvironment during tumorigenesis, progression, and metastasis, and provides an overview of recent developments in targeting these cell populations to enhance cancer therapy efficacy.

Inherited factors contribute to an inverse association between preeclampsia and breast cancer

Background

Preeclampsia is frequently linked to reduced breast cancer risk. However, little is known regarding the underlying genetic association and the association between preeclampsia and mammographic density.

Methods

This study estimates the incidence rate ratios (IRRs) of breast cancer in patients with preeclampsia, when compared to women without preeclampsia, using Poisson regression models in two cohorts of pregnant women: a Swedish nationwide cohort (n = 1,337,934, 1973–2011) and the Karolinska Mammography Project for Risk Prediction of Breast Cancer (KARMA, n = 55,044, 1958–2015). To identify the genetic association between preeclampsia and breast cancer, we used logistic regression models to calculate the odds ratios (ORs) of preeclampsia in sisters of breast cancer patients, and in women with different percentiles of breast cancer polygenic risk scores (PRS). Linear regression models were used to estimate the mammographic density by preeclampsia status in the KARMA cohort.

Results

A decreased risk of breast cancer was observed among patients with preeclampsia in both the nationwide (IRR = 0.90, 95% CI = 0.85; 0.96) and KARMA cohorts (IRR = 0.75, 95% CI = 0.61; 0.93). Women with high breast cancer PRS and sisters of breast cancer patients had a lower risk of preeclampsia (OR = 0.89, 95% CI = 0.83; 0.96). Mammographic density was lower in women with preeclampsia compared to women without preeclampsia (-2.04%, 95% CI = -2.65; -1.43). Additionally, among sisters in the KARMA cohort (N = 3500), density was lower in sisters of patients with preeclampsia compared to sisters of women without preeclampsia (-2.76%, 95% CI = -4.96; -0.56).

Conclusion

Preeclampsia is associated with reduced risk of breast cancer and mammographic density. Inherited factors contribute to this inverse association.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-017-0930-6) contains supplementary material, which is available to authorized users.

RhoGTPase stimulation is associated with strontium chloride treatment to counter simulated microgravity-induced changes in multipotent cell commitment

Microgravity-related cytoskeletal disorganization is associated with an altered balance between osteoblastogenesis and adipogenesis of multipotent cells. Strontium chloride is known to increase osteoblastogenesis and repress adipogenesis, but its effects in microgravity-related conditions have not been established. Our goal was to investigate early events in this process, focusing on RhoGTPases as controllers of cytoskeletal organization leading to stem cell commitment. We cultivated C3H10T1/2 on microspheres using a rotating wall vessel bioreactor (NASA) in order to simulate microgravity-related conditions in adipogenesis and osteoblastogenesis conditions independently. We observed that rotating wall vessel cultures presented increased adipogenesis, while osteoblastogenesis was reduced. Strontium-treated multipotent cells presented a significant repression in adipogenesis (−90 %, p < 0.001 PPARyD8) and an activation of osteoblastogenesis (+95 %, p < 0.001 bone sialoprotein and osteopontin D8), even in gravity altered conditions. We established that concomitant RhoA/Rac1 activations were associated with osteoblastogenesis enhancement and adipogenesis limitation in uncommitted cells. As vascular endothelial growth factor splicing is mechanosensitive and its signaling is central to stem cell commitment, we investigated vascular endothelial growth factor production, isoforms and receptors expressions in our conditions. We observed that vascular endothelial growth factor and receptors expressions were not significantly affected, but we found that presence of soluble vascular endothelial growth factor was associated with RhoA/Rac1 activations, whereas sequestration of vascular endothelial growth factor by cells was associated with RhoA/Rac1 inhibitions. We propose that strontium triggers secretion of vascular endothelial growth factor and the subsequent Rac1 and RhoA activations leading to repression of adipogenesis and osteogenesis stimulation validating strontium as a counter measure for microgravity-induced alteration of cell commitment.

A chemical element naturally found for instance in seafood or grains, could counter bone loss from long-term spaceflight. Alain Guignandon and colleagues from the Université de Lyon à St-Etienne in France exposed multipotent embryonic fibroblasts to microgravity conditions similar to those found in space. They found the balance shifted in these stem cells from differentiating to bone-forming cells (osteoblasts) to differentiating to fatty-tissue forming cells (adipocytes). When the cells were treated with strontium, the shift toward osteoblastogenesis was regained. Strontium achieves this by sustaining the activity of two proteins that play a role in bone development but are suppressed in space. Strontium’s effect on the proteins could happen via release of vascular endothelial growth factor, which, under normal gravity conditions, plays a role in committing the cell to differentiation into osteoblasts rather than adipoyctes.

Regeneration of Bovine Mammary Gland in Immunodeficient Mice by Transplantation of Bovine Mammary Epithelial Cells Mixed with Matrigel

Background and Objectives

With the global demand for dairy protein for consumption growing annually, there has been increasing activity in the research field of dairy protein synthesis and production. From a manipulation perspective, it is more difficult to use live cattle for laboratory studies on the production of milk as well as of dairy protein such as casein, as compared with using laboratory animals like rodents. Therefore, we aimed to develop a mouse model of bovine mammary alveolar ducts for laboratory-scale studies. We studied the formation of the bovine mammary gland ductal structure by transplanting the MAC-T bovine alveolar cell line into mice.

Methods and Results

MAC-T cells (1×10⁷) were suspended in Matrigel and injected into the dorsal tissue of 8-week-old male BALB/C nude mice. Histological analysis of tissue dissected from the MAC-T cell-transplanted mice after 6 weeks showed the typical morphology of the tubuloalveolar female gland, as well as glands made up of branching ducts that were surrounded by smooth muscle with small alveoli budding off the ducts. In addition, the epithelial markers CK14 and CK18 were expressed within the duct-like structure. Prolactin was detected in the duct interior in these CK14+ and CK18+ cells but not in the non-transplanted MAC-T cells.

Conclusions

These results showed that duct-like tissue had been successfully formed after 6 weeks of transplantation of the CK14+ and CK18+ MAC-T cells into mice dorsal tissue. This mouse model will be a useful tool for further research on the bovine mammary gland.

Regulation and localization of vascular endothelial growth factor within the mammary glands during the transition from late gestation to lactation

The vascular network within the developing mammary gland (MG) grows in concert with the epithelium to prepare for lactation, although the mechanisms coordinating this vascular development are unresolved. Vascular endothelial growth factor A (VEGF-A) mediates angiogenesis and vascular permeability in the MG during pregnancy and lactation, where its expression is upregulated by prolactin. Given our previous finding that late-gestational hyperprolactinemia induced by domperidone (DOM) increased subsequent milk yield from gilts, we sought to establish changes in vascular development during late gestation and lactation in the MGs of these pigs and determine whether DOM altered MG angiogenesis and the factors regulating it. Gilts received either no treatment (n = 6) or DOM (n = 6) during late gestation, then had their MG biopsied from late gestation through lactation to assess microvessel density, VEGF-A distribution and messenger RNA expression, and aquaporin (AQP) gene expression. Microvessel density in the MG was unchanged during gestation then increased between days 2 and 21 of lactation (P < 0.05). The local expression of messenger RNA for VEGF-A120, VEGF-A147, VEGF-A164, VEGF-A164b, VEGF-A188, VEGF receptors-1 and -2, and AQP1 and AQP3 all generally increased during the transition from gestation to lactation (P < 0.05). Immunostaining localized VEGF-A to the apical cytoplasm of secretory epithelial cells, consistent with a far greater concentration of VEGF-A in colostrum and/or milk vs plasma (P < 0.0001). There was no effect of DOM on any of the variables analyzed. In summary, we found that vascular development in the MG increases during lactation in first-parity gilts and that VEGF-A is a part of the mammary secretome. Although late-gestational hyperprolactinemia increases milk yield, there was no evidence that it altered vascular development.

Autocrine effect of vascular endothelial growth factor-A is essential for mitochondrial function in brown adipocytes

OBJECTIVE

The obesity epidemic in the United States, as well as the accompanying condition of type 2 diabetes, puts a majority of the population at an increased risk of developing cardiovascular diseases including coronary artery disease, stroke, and myocardial infarction. In contrast to white adipose tissue (WAT), brown adipose tissue (BAT) is well vascularized, rich in mitochondria, and highly oxidative. While it is known that the angiogenic factor VEGF-A is required for brown adipocyte development, the functional consequences and exact mechanism remain to be elucidated. Here, we show that VEGF-A plays an essential autocrine role in the function of BAT.

MATERIALS AND METHODS

Mouse models were generated with an adipose-specific and macrophage-specific ablation of VEGF-A. Adipose tissue characteristics and thermogenic response were analyzed in vivo, and mitochondrial morphology and oxidative respiration were analyzed in vitro to assess effects of endogenous VEGF-A ablation.

RESULTS

VEGF-A expression levels are highest in adipocyte precursors compared to immune or endothelial cell populations within both WAT and BAT. Loss of VEGF-A in adipocytes, but not macrophages, results in decreased adipose tissue vascularization, with remarkably diminished thermogenic capacity in vivo. Complete ablation of endogenous VEGF-A decreases oxidative capacity of mitochondria in brown adipocytes. Further, acute ablation of VEGF-A in brown adipocytes in vitro impairs mitochondrial respiration, despite similar mitochondrial mass compared to controls.

CONCLUSION

These data demonstrate that VEGF-A serves to orchestrate the acquisition of thermogenic capacity of brown adipocytes through mitochondrial function in conjunction with the recruitment of blood vessels.

Mammary gland development: cell fate specification, stem cells and the microenvironment

The development of the mammary gland is unique: the final stages of development occur postnatally at puberty under the influence of hormonal cues. Furthermore, during the life of the female, the mammary gland can undergo many rounds of expansion and proliferation. The mammary gland thus provides an excellent model for studying the ‘stem/progenitor’ cells that allow this repeated expansion and renewal. In this Review, we provide an overview of the different cell types that constitute the mammary gland, and discuss how these cell types arise and differentiate. As cellular differentiation cannot occur without proper signals, we also describe how the tissue microenvironment influences mammary gland development.

STAT5 and prolactin participate in a positive autocrine feedback loop that promotes angiogenesis

We have shown previously that the murine prolactin/growth hormone family member proliferin plays a pivotal role in angiogenesis induced by the FGF2/STAT5 signaling cascade. To delineate the signaling pathway downstream of STAT5 in the human system, where proliferin does not exist, we expressed constitutively active (CA) or dominant-negative (DN) mutant STAT5A in hCMEC/D3 human brain endothelial cells. We found that conditioned medium from CA-STAT5A- but not from DN-STAT5A-overexpressing endothelial cells (EC) is sufficient to induce EC migration and tube formation but not proliferation, indicating that STAT5A regulates the secretion of autocrine proangiogenic factors. We identified prolactin (PRL) as a candidate autocrine factor. CA-STAT5A expression stimulates PRL production at the RNA and protein level, and STAT5A binds to the PRL promoter region, suggesting direct transcriptional regulation. Medium conditioned by CA-STAT5A-overexpressing EC induces phosphorylation of the PRL receptor and activates MAPK. Knockdown of PRL expression by shRNA or blocking of PRL activity with neutralizing antibodies removed the CA-STAT5A-dependent proangiogenic activity from the conditioned medium of EC. The addition of recombinant PRL restores this activity. STAT5A-induced PRL in the conditioned medium can activate STAT5, STAT1, and to a lesser extent STAT3 in hCMEC/D3 cells, suggesting the existence of a positive feedback loop between STAT5 and PRL that promotes angiogenesis. Furthermore, we find that VEGF, a potent proangiogenic factor, is induced by activation of STAT5A, and VEGF induction depends on PRL expression. These observations demonstrate a STAT5/PRL/VEGF signaling cascade in human brain EC and implicate PRL and VEGF as autocrine regulators of EC migration, invasion, and tube formation.

Mammary adipocytes bioactivate 25-hydroxyvitamin D₃ and signal via vitamin D₃ receptor, modulating mammary epithelial cell growth

The vitamin D(3) receptor (VDR) is present in all microenvironments of the breast, yet it is hypothesized to signal through the epithelium to regulate hormone induced growth and differentiation. However, the influence or contribution of the other microenvironments within the breast that express VDR, like the breast adipose tissue, are yet to be investigated. We hypothesized that the breast adipocytes express the signaling components necessary to participate in vitamin D(3) synthesis and signaling via VDR, modulating ductal epithelial cell growth and differentiation. We utilized human primary breast adipocytes and VDR wild type (WT) and knockout (KO) mice to address whether breast adipocytes participate in vitamin D(3) -induced growth regulation of the ductal epithelium. We report in this study that breast primary adipocytes express VDR, CYP27B1 (1α-hydroxylase, 1α-OHase), the enzyme that generates the biologically active VDR ligand, 1α,25-dihydroxyvitamin D(3) (1,25D(3) ), and CYP24 (24-hydroxylase, 24-OHase), a VDR-1,25D(3) induced target gene. Furthermore, the breast adipocytes participate in bioactivating 25-hydroxyvitamin D(3) (25D(3) ) to the active ligand, 1,25D(3) , and secreting it to the surrounding microenvironment. In support of this concept, we report that purified mammary ductal epithelial fragments (organoids) from VDR KO mice, co-cultured with WT breast adipocytes, were growth inhibited upon treatment with 25D(3) or 1,25D(3) compared to vehicle alone. Collectively, these results demonstrate that breast adipocytes bioactivate 25D(3) to 1,25D(3) , signal via VDR within the adipocytes, and release an inhibitory factor that regulates ductal epithelial cell growth, suggesting that breast adipose tissue contributes to vitamin D(3) -induced growth regulation of ductal epithelium.

16 kDa prolactin reduces angiogenesis, but not growth of human breast cancer tumors in vivo

Prolactin (PRL) is a peptide hormone necessary for normal growth and development of the human breast. In addition, high levels of PRL in plasma correlate with increased risk of breast cancer, especially among postmenopausal women. Several isoforms of PRL exist in human circulation, including a 16 kDa isoform that is an N-terminal fragment of the full-length 23 kDa PRL. 16 kDa PRL has been shown to be anti-angiogenic in vitro and in vivo, and to reduce formation of tumors from prostate, colon and melanoma cancer cell lines. Here we explore the effect of 16 kDa PRL expression in vitro and in vivo using two breast cancer cell line models (MCF-7 and MDA-MB-231) and also the HCT-116 colon cancer cell line. In all three cell lines, 16 kDa PRL expression inhibited cell proliferation in vitro compared to empty vector controls. In vivo results were markedly different between the two types of cell lines. HCT-116 cells expressing 16 kDa PRL exhibited reduced vascularization and tumor formation, consistent with published results. The breast cancer cell lines expressing 16 kDa PRL also exhibited inhibition of angiogenesis in vivo but no reduction in tumor size or formation. These results suggest that the effects of 16 kDa PRL on tumor formation may vary across tissue types. The unique sensitivity of breast cancer to PRL as a mitogen and/or additional factors in the mammary gland environment (e.g. local hormone/mitogen concentration) may play a dominant role in tumor formation in vivo, thus outweighing the anti-angiogenesis effects and in vitro reduction in cell proliferation induced by 16 kDa PRL.

Glucose transporter and hypoxia-associated gene expression in the mammary gland of transition dairy cattle

Glucose is an important energy substrate, especially needed by dairy cows postpartum to support the onset of lactation. The prioritization and regulation of glucose uptake is accomplished, in part, by changes in expression of cellular glucose transport molecules (GLUT) within the mammary gland. The objectives of this study were to (1) evaluate the expression and cell-type specific localization of GLUT and hypoxia-associated genes that may regulate GLUT expression over the transition period and through lactation in bovine mammary tissue and (2) determine functionality of GLUT on primary bovine mammary endothelial cells (BMEC). Mammary tissue biopsies were taken from cows at 15 d before calving and again at 1, 15, 30, 60, 120, and 240 d post-parturition for quantitative real-time PCR analysis of GLUT and hypoxia-associated genes. Additional mammary tissue samples were used to localize GLUT within the cells of the lobulo-alveolar system via fluorescence microscopy. Cultures of primary bovine mammary endothelial cells were used to confirm the functionality of GLUT with a fluorescent glucose analog uptake assay. Significant increases in GLUT1 gene expression were observed during early lactation, whereas both GLUT3 and GLUT4 gene expression increased during late lactation. The gene expression for 2 receptors of vascular endothelial growth factor increased significantly during early lactation and remained increased throughout lactation when compared with gene expression during the transition period. All GLUT were detected on cultured BMEC and were capable of internalizing glucose through GLUT-mediated mechanisms. These data suggest mammary vascular tissues express GLUT during lactation and BMEC express functional glucose transporters. A better understanding of glucose uptake at the endothelial level may prove to be critical to improve glucose absorption from the blood for utilization by mammary epithelial cells.

Integrated morphodynamic signalling of the mammary gland

The mammary gland undergoes a spectacular series of changes as it develops, and maintains a remarkable capacity to remodel and regenerate for several decades. Mammary morphogenesis has been investigated for over 100 years, motivated by the dairy industry and cancer biologists. Over the past decade, the gland has emerged as a major model system in its own right for understanding the cell biology of tissue morphogenesis. Multiple signalling pathways from several cell types are orchestrated together with mechanical cues and cell rearrangements to establish the pattern of the mammary gland. The integrated mechanical and molecular pathways that control mammary morphogenesis have implications for the developmental regulation of other epithelial organs.

Characterization of ductal and lobular breast carcinomas using novel prolactin receptor isoform specific antibodies

BACKGROUND

Prolactin is a polypeptide hormone responsible for proliferation and differentiation of the mammary gland. More recently, prolactin's role in mammary carcinogenesis has been studied with greater interest. Studies from our laboratory and from others have demonstrated that three specific isoforms of the prolactin receptor (PRLR) are expressed in both normal and cancerous breast cells and tissues. Until now, reliable isoform specific antibodies have been lacking. We have prepared and characterized polyclonal antibodies against each of the human PRLR isoforms that can effectively be used to characterize human breast cancers.

METHODS

Rabbits were immunized with synthetic peptides of isoform unique regions and immune sera affinity purified prior to validation by Western blot and immunohistochemical analyses. Sections of ductal and lobular carcinomas were stained with each affinity purified isoform specific antibody to determine expression patterns in breast cancer subclasses.

RESULTS

We show that the rabbit antibodies have high titer and could specifically recognize each isoform of PRLR. Differences in PRLR isoform expression levels were observed and quantified using histosections from xenografts of established human breast cancer cells lines, and ductal and lobular carcinoma human biopsy specimens. In addition, these results were verified by real-time PCR with isoform specific primers. While nearly all tumors contained LF and SF1b, the majority (76%) of ductal carcinoma biopsies expressed SF1a while the majority of lobular carcinomas lacked SF1a staining (72%) and 27% had only low levels of expression.

CONCLUSIONS

Differences in the receptor isoform expression profiles may be critical to understanding the role of PRL in mammary tumorigenesis. Since these antibodies are specifically directed against each PRLR isoform, they are valuable tools for the evaluation of breast cancer PRLR content and have potential clinical importance in treatment of this disease by providing new reagents to study the protein expression of the human PRLR.

The role of estrogen receptors, erbB receptors, vascular endothelial growth factor and its receptors, and vascular endothelial growth inhibitor in the development of the rat mammary gland

We identified the localization and distribution of cell-specific epidermal growth factor receptors (EGFRs: erbB-1, erbB-2, erbB-3, erbB-4), vascular endothelial growth factor (VEGF), VEGF receptors [VEGFRs: VEGF-R1 (flt-1), VEGF-R2 (flk-1/KDR), VEGF-R3 (flt-4)], vascular endothelial growth inhibitor (VEGI), and estrogen receptor (ER), and determined whether or not these growth factors in rat mammary glands are functional. Thirty-five adult female Spraque-Dawley rats were randomly divided into five groups, each of which were at the 7th, 14th, and 21st day of pregnancy; 7th day post-delivery; and 7th day after weaning. It was determined that erbB, VEGF and its receptors, VEGI, and ER stained at different intensities. Intense staining was observed, in particular, in erbB receptors during pregnancy and involution, and also in VEGF and its receptors during lactation, while ER stained during the last periods of pregnancy and lactation. In conclusion, the expression of erbB, VEGF and its receptors, and ER were determined at varying intensities at different sites of the mammary gland during pregnancy, lactation, and involution periods.

The mammary gland vasculature revisited

Concomitant with the extensive growth and differentiation of the mammary epithelium during pregnancy and lactation, and epithelial involution after weaning, the vasculature of the mammary gland undergoes repeated cycles of expansion and regression. Vascular expansion is effected by sprouting angiogenesis, intussusception and conceivably also vasculogenesis. The capacity of the epithelial cells to stimulate vascular growth and differentiation is dependent on the constellation of systemic and local hormones and growth factors as well as the changing demands for oxygenation and nutrient supply. This results in the release of angiogenic factors which stimulate endothelial cell growth and regulate vascular architecture. In contrast to the angiogenic phase of the mammary gland cycle, little is known about the control of vascular regression although this would possibly offer new insights into therapeutic possibilities against breast cancer. In this review we summarize knowledge regarding the mechanisms regulating the vasculature of the mammary gland and delineate the importance of the vasculature in the attainment of organ function. In addition, we discuss the angiogenic mechanisms observed during mammary carcinogenesis and their consequences for breast cancer therapy.

Diverse and active roles for adipocytes during mammary gland growth and function

The mammary gland is unique in its requirement to develop in close association with a depot of adipose tissue that is commonly referred to as the mammary fat pad. As discussed throughout this issue, the mammary fat pad represents a complex stromal microenvironment that includes a variety of cell types. In this article we focus on adipocytes as local regulators of epithelial cell growth and their function during lactation. Several important considerations arise from such a discussion. There is a clear and close interrelationship between different stromal tissue types within the mammary fat pad and its adipocytes. Furthermore, these relationships are both stage- and species-dependent, although many questions remain unanswered regarding their roles in these different states. Several lines of evidence also suggest that adipocytes within the mammary fat pad may function differently from those in other fat depots. Finally, past and future technologies present a variety of opportunities to model these complexities in order to more precisely delineate the many potential functions of adipocytes within the mammary glands. A thorough understanding of the role for this cell type in the mammary glands could present numerous opportunities to modify both breast cancer risk and lactation performance.

Vascular Robo4 restricts proangiogenic VEGF signaling in breast

Formation of the vascular system within organs requires the balanced action of numerous positive and negative factors secreted by stromal and epithelial cells. Here, we used a genetic approach to determine the role of SLITs in regulating the growth and organization of blood vessels in the mammary gland. We demonstrate that vascularization of the gland is not affected by loss of Slit expression in the epithelial compartment. Instead, we identify a stromal source of SLIT, mural cells encircling blood vessels, and show that loss of Slit in the stroma leads to elevated blood vessel density and complexity. We examine candidate SLIT receptors, Robo1 and Robo4, and find that increased vessel angiogenesis is phenocopied by loss of endothelial-specific Robo4, as long as it is combined with the presence of an angiogenic stimulus such as preneoplasia or pregnancy. In contrast, loss of Robo1 does not affect blood vessel growth. The enhanced growth of blood vessels in Robo4(-/-) endothelium is due to activation of vascular endothelial growth factor (VEGF)-R2 signaling through the Src and FAK kinases. Thus, our studies present a genetic dissection of SLIT/ROBO signaling during organ development. We identify a stromal, rather than epithelial, source of SLITs that inhibits blood vessel growth by signaling through endothelial ROBO4 to down-regulate VEGF/VEGFR2 signaling.

VHL deletion impairs mammary alveologenesis but is not sufficient for mammary tumorigenesis

Overexpression of hypoxia inducible factor-1 (HIF-1)alpha, which is common in most solid tumors, correlates with poor prognosis and high metastatic risk in breast cancer patients. Because HIF-1alpha protein stability is tightly controlled by the tumor suppressor von Hippel-Lindau (VHL), deletion of VHL results in constitutive HIF-1alpha expression. To determine whether VHL plays a role in normal mammary gland development, and if HIF-1alpha overexpression is sufficient to initiate breast cancer, Vhl was conditionally deleted in the mammary epithelium using the Cre/loxP system. During first pregnancy, loss of Vhl resulted in decreased mammary epithelial cell proliferation and impaired alveolar differentiation; despite these phenotypes, lactation was sufficient to support pup growth. In contrast, in multiparous dams, Vhl(-/-) mammary glands exhibited a progressive loss of alveolar epithelium, culminating in lactation failure. Deletion of Vhl in the epithelium also impacted the mammary stroma, as there was increased microvessel density accompanied by hemorrhage and increased immune cell infiltration. However, deletion of Vhl was not sufficient to induce mammary tumorigenesis in dams bred continuously for up to 24 months of age. Moreover, co-deletion of Hif1a could not rescue the Vhl(-/-)-dependent phenotype as dams were unable to successfully lactate during the first lactation. These results suggest that additional VHL-regulated genes besides HIF1A function to maintain the proliferative and regenerative potential of the breast epithelium.

Mast cells contribute to the stromal microenvironment in mammary gland branching morphogenesis

The stromal microenvironment regulates mammary gland branching morphogenesis. We have observed that mast cells are present in the mammary gland throughout its postnatal development and, in particular, are found around the terminal end buds and ductal epithelium of the pubertal gland. Mast cells contribute to allergy, inflammatory diseases, and cancer development but have not been implicated in normal development. Genetic and pharmacological disruption of mast cell function in the mammary gland revealed that mast cells are involved in rapid proliferation and normal duct branching during puberty, and this effect is independent of macrophage recruitment, which also regulates mammary gland development. For mast cells to exert their effects on normal morphogenesis required activation of their serine proteases and degranulation. Our observations reveal a novel role for mast cells during normal pubertal development in the mammary gland.

Inactivation of VEGF in mammary gland epithelium severely compromises mammary gland development and function

To investigate the role of the angiogenic cytokine vascular endothelial growth factor (VEGF) during pregnancy and lactation, we used mice in which VEGF had been inactivated in mammary gland epithelial cells. Pups born to mutant mothers failed to thrive, displaying little milk in their stomachs. However, when they were transferred to control mothers they developed normally. Investigation of the mammary gland morphology revealed that lobulo-alveolar expansion into the fat pad was not complete in lactating mutant glands, and an accumulation of fat globules was evident in their secretory epithelium. In contrast to control glands, lactating mutant glands failed to up-regulate mRNAs for genes involved in milk secretion. Blood vessel density was comparable in pregnant mice of both groups but was only half that of controls in lactating mutant mice. FITC-labeled albumin injected intravenously (i.v.) into lactating mice extravasated rapidly and accumulated in the mammary gland epithelial cells in control animals, but was almost completely retained within the vessels in the mutants. Injection of recombinant VEGF i.v. reversed this effect. These findings demonstrate that mammary epithelium-derived VEGF is partially dispensable for angiogenesis during pregnancy and lactation, and by regulating vascular function during lactation, this factor is crucial to mammary gland differentiation and milk production.

Effect of a Biological Response Modifier on Expression of Growth Factors and Cellular Proliferation at Drying Off

Agents that increase natural protective mechanisms have been proposed for the prevention and treatment of intramammary infections. Staphylococcus aureus is a major pathogen causing primarily subclinical chronic mastitis that responds poorly to antibiotic therapy. The objectives of this study were to describe the effects of a single intramammary infusion of a lipopolysaccharide-based biological response modifier (BRM) on mammary epithelial cellular proliferation and expression of insulin-like growth factor-I (IGF-I) and vascular endothelial growth factor (VEGF) in uninfected and Staph. aureus-infected bovine mammary glands during involution. Three groups of 12 cows, 6 Staph. aureus-infected and 6 uninfected, were infused with BRM or placebo in 2 mammary quarters and killed at 7, 14, and 21 d of involution. The proportion of infected quarters, mammary cell proliferation, and IGF-I and VEGF expression were evaluated. Biological response modifier treatment decreased the proportion of Staph. aureus-infected mammary quarters at 7 d of involution, but a similar number of isolations were observed at 14 and 21 d of involution in either treated or control quarters. The percentage of proliferating mammary epithelial cells was higher in infected than uninfected quarters at every observation period, irrespective of the treatment administered, whereas uninfected BRM-treated quarters showed increased cell proliferation at 7 d of involution. Insulin-like growth factor-I expression in uninfected quarters was not affected by treatment and showed a decrease at 21 d of involution. Expression of IGF-I was greater in infected than uninfected quarters at every observation period, irrespective of the treatment received. Expression of VEGF was greater in BRM-treated uninfected quarters at 7 d of involution compared with controls. In infected quarters, VEGF expression was lowest in BRM-treated quarters at 7 d of involution and increased throughout the observation period. Conversely, untreated infected quarters showed the highest VEGF expression at 7 d and decreased at 21 d of involution. Mammary cell proliferation and expression of IGF-I and VEGF were increased in Staph. aureus-infected quarters. Increased mammary cell proliferation and VEGF expression were observed in BRM-treated quarters during the first week of involution.

Unique vascular phenotypes following over-expression of individual VEGFA isoforms from the developing lens

Formation of a correctly organised vasculature and subsequently embryonic survival is critically dependent on the dosage and site-specific expression of VEGF. Murine VEGF exists in three common isoforms (viz. 120, 164 and 188 amino acids) having different organ specific distribution levels. Gene knock-in studies show that expression of any of the individual isoforms of VEGF extends survival until birth, although each is associated with distinct organ-specific abnormalities. Comparison of the effects of VEGF isoform expression is complicated by the general lethality of mis-expression, in addition to cumulative effects of adjacent tissues from the inappropriately patterned vasculature. Here we investigate the effects of over-expression of individual VEGFA isoforms from the lens-specific alphaA-Crystallin promoter and characterise their effects on the vessel morphology of the hyaloid and developing retinal vasculature. Since the hyaloid vasculature is an anatomically distinct, transient vasculature of the eye, comprising 3 cell types (endothelium, pericytes and macrophages) it is possible to more readily interpret the role of individual VEGF-A isoforms in vascular pattern formation in this model. The severity of the vascular phenotype, characterised by a hyperplastic hyaloid at E13.5 and subsequently retinal vascular patterning and ocular defects, is most severe in transgenics over-expressing the more diffusible forms of VEGFA (120 and 164), whereas in VEGFA(188) transgenics the hyaloid vascular defects partially resolve post-natally. The results of this study indicate that individual isoforms of VEGFA induce distinct vascular phenotypes in the eye during embryonic development and that their relative doses provide instructive cues for vascular patterning.

Vascular Endothelial Growth Factor (VEGF) Production by the Monkey Corpus Luteum During the Menstrual Cycle: Isoform-Selective Messenger RNA Expression In Vivo and Hypoxia-Regulated Protein Secretion In Vitro1

Experiments were designed to investigate the expression and regulation of vascular endothelial growth factor (VEGF) in the primate corpus luteum (CL) throughout the luteal life span in the natural menstrual cycle. Corpora lutea were collected during the early (ECL; Days 3-5 post-LH surge), mid (MCL; Day 6-8 post-LH surge), mid-late (MLCL; Days 10-12 post-LH surge), late (LCL; Days 14-16 post-LH surge), and very late (Days 17- 18 post-LH surge) luteal phase. Specific primers were designed to amplify mRNAs encoding VEGF isoforms 206, 189, 183, 165, 145, and 121. Only two cDNA products were obtained by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends; cloning and sequencing confirmed their 98% homology to the corresponding human VEGF 165 and 121 sequences. Semiquantitative RT-PCR assays indicated that VEGF 165 mRNA levels increased (P < 0.05) from ECL to MLCL but then declined (P < 0.05) by LCL. Although VEGF 121 mRNA levels were limited in ECL, they increased significantly in MCL (P < 0.05). Levels of VEGF protein, as measured by Western blot analysis, were two- to fourfold higher for VEGF 165 versus VEGF 121. Also, VEGF 165 levels were higher (P < 0.05) in ECL and MCL compared to those at later stages. During 2-day culture, preparations of dispersed luteal cells secreted VEGF into the media; the highest levels were observed in ECL and declined (P < 0.05) by LCL. Regardless of luteal stage, hypoxic conditions increased (P < 0.05) VEGF levels, whereas LH exposure increased (P < 0.05) progesterone, but not VEGF, in the media. These results are consistent with a dynamic, local regulation of VEGF production during the life span of the primate CL that is not directly controlled by LH.

Coupling of COX-1 to mPGES1 for prostaglandin E2 biosynthesis in the murine mammary gland

The mammary gland, like most tissues, produces measurable amounts of prostaglandin E2 (PGE2), a metabolite of arachidonic acid produced by sequential actions of two cyclooxygenases (COX-1 and COX-2) and three terminal PGE synthases: microsomal prostaglandin E2 synthase-1 (mPGES1), mPGES2, and cytosolic prostaglandin E2 synthase (cPGES). High PGE2 levels and COX-2 overexpression are frequently detected in mammary tumors and cell lines. However, less is known about PGE2 metabolic enzymes in the context of normal mammary development. Additionally, the primary COX partnerships of terminal PGE synthases and their contribution to normal mammary PGE2 biosynthesis are poorly understood. We demonstrate that expression of COX-1, generally considered constitutive, increases dramatically with lactogenic differentiation of the murine mammary gland. Concordantly, total PGE2 levels increase throughout mammary development, with highest levels measured in lactating tissue and breast milk. In contrast, COX-2 expression is extremely low, with only a modest increase detected during mammary involution. Expression of the G(s)-coupled PGE2 receptors, EP2 and EP4, is also temporally regulated, with highest levels detected at stages of maximal proliferation. PGE2 production is dependent on COX-1, as PGE2 levels are nearly undetectable in COX-1-deficient mammary glands. Interestingly, PGE2 levels are similarly reduced in lactating glands of mPGES1-deficient mice, indicating that PGE2 biosynthesis results from the coordinated activity of COX-1 and mPGES1. We thus provide evidence for the first time of functional coupling between COX-1 and mPGES1 in the murine mammary gland in vivo.

22-Oxa-1alpha,25-dihydroxyvitamin D3 inhibits metastasis and angiogenesis in lung cancer

1alpha,25-Dihydroxyvitamin D(3) (1alpha,25-D(3)) has potent antiproliferative and anti-invasive properties in vitro in cancer cells. However, its calcemic effect in vivo limits its therapeutic applications. Here, we report the efficacy of 22-oxa-1alpha,25-dihydroxyvitamin D(3) (22-oxa-1alpha,25-D(3)), a low calcemic analog of vitamin D, against the development of metastatic lung carcinoma after an intravenous injection of green fluorescent protein-transfected Lewis lung carcinoma (LLC-GFP) cells in C57BL/6 mice. The mice injected with tumor cells were implanted simultaneously with osmotic minipumps containing either 1alpha,25-D(3), 22-oxa-1alpha,25-D(3) or vehicle. The 1alpha,25-D(3) treatment group had been hypercalcemic, but the 22-oxa-1alpha,25-D(3) and vehicle treatment groups remained normocalcemic for the duration of the experiment. The total number of lung metastases, lung weight and the expression of GFP mRNA in the lung were markedly decreased in 1alpha,25-D(3) and 22-oxa-1alpha,25-D(3)-treated mice. In the in vitro experiment, 1alpha,25-D(3) and 22-oxa-1alpha,25-D(3) reduced the expression of matrix metalloproteinase (MMP)-2, MMP-9, vascular endothelial growth factor and parathyroid hormone-related protein in LLC-GFP cells. Furthermore, in the angiogenesis assay, the number of tumor cells or basic fibroblast growth factor-induced angiogenesis was reduced in 1alpha,25-D(3) and 22-oxa-1alpha,25-D(3)-treated mice. Moreover, using a new experimental model of vitamin D receptor (VDR) null mutant (VDR(-/-)) mice with corrected hypocalcemia and hypervitaminosis D, we examine the anti-cancer effect of 22-oxa-1alpha,25-D(3) without other functions induced by 22-oxa-1alpha,25-D(3) in the host. In the VDR(-/-) mice, 22-oxa-1alpha,25-D(3) directly inhibited the metastatic activity of LLC-GFP cells in a dose-dependent manner without exerting a direct influence on the calcemic activity or other actions regulated by 22-oxa-1alpha,25-D(3) in the host. These results indicate that the inhibition of metastasis and angiogenesis-inducing activity in cancer cells seemed to be a major mechanism responsible for the anti-cancer effects of 22-oxa-1alpha,25-D(3). Our findings show that 22-oxa-1alpha,25-D(3) is beneficial for the prevention of metastasis in lung carcinoma.

Re-expression of detachment-inducible chloride channel mCLCA5 suppresses growth of metastatic breast cancer cells

The calcium-activated chloride channel hCLCA2 has been identified as a candidate tumor suppressor in human breast cancer. It is greatly down-regulated in breast cancer, and its re-expression suppresses tumorigenesis by an unknown mechanism. To establish a mouse model, we identified the mouse ortholog of hCLCA2, termed mCLCA5, and investigated its behavior in mammary epithelial cell lines and tissues. Expression in the immortalized cell line HC11 correlated with slow or arrested growth. Although rapidly dividing, sparsely plated cells had low levels of expression, mCLCA5 was induced by 10-fold when cells became confluent and 30-fold when cells were deprived of growth factors or anchorage. The apoptosis effector Bax was induced in parallel. Like hCLCA2, mCLCA5 was down-regulated in metastatic mammary tumor cell lines such as 4T1 and CSML-100. Ectopic re-expression in 4T1 cells caused a 20-fold reduction in colony survival relative to vector control. High mCLCA5 expression in stable clones inhibited proliferation and enhanced sensitivity to detachment. Moreover, mCLCA5 was induced in lactating and involuting mammary gland, correlating with differentiation and onset of apoptosis. Together, these results establish mCLCA5 as the mouse ortholog of hCLCA2, demonstrate that mCLCA5 is a detachment-sensitive growth inhibitor, and suggest a mechanism whereby these channels may antagonize mammary tumor progression.

Transforming growth factor-beta1 stimulates vascular endothelial growth factor 164 via mitogen-activated protein kinase kinase 3-p38alpha and p38delta mitogen-activated protein kinase-dependent pathway in murine mesangial cells

Transforming growth factor-beta1 (TGF-beta1) is a potent inducer of extracellular matrix synthesis leading to progressive glomerular fibrosis. The intracellular signaling mechanisms involved in this process remain incompletely understood. The p38 mitogen-activated protein kinase (MAPK) is a major stress signal transducing pathway that is rapidly activated by TGF-beta1 in mesangial cells. We have previously demonstrated MKK3 as the immediate upstream MAPK kinase required for selective activation of p38 MAPK isoforms, p38alpha and p38delta, and stimulation of pro-alpha1(I) collagen by TGF-beta1 in murine mesangial cells. In this study, we further sought to determine MAPK kinase 3 (MKK3)-dependent TGF-beta1 responses by gene expression profiling analysis utilizing mesangial cells isolated from Mkk3-/- mice compared with Mkk3+/+ controls. Interestingly, vascular endothelial growth factor (VEGF) was identified as a TGF-beta1-induced gene affected by deletion of Mkk3. VEGF is a well known endothelial mitogen, whose actions in nonendothelial cell types are still not well understood. We confirmed that TGF-beta1 increased VEGF mRNA and protein synthesis of VEGF164 and VEGF188 isoforms in wild-type mesangial cells. However, in the Mkk3-/- mesangial cells, both TGF-beta1-induced VEGF mRNA and VEGF164 protein expression were inhibited, whereas TGF-beta1-induced VEGF188 protein expression was unaffected. Furthermore, transfection of dominant negative mutants of p38alpha and p38delta resulted in marked inhibition of TGF-beta1-induced VEGF164 expression but not VEGF188, and treatment with recombinant mouse VEGF164 increased collagen and fibronectin mRNA expression in mesangial cells. Taken together, our findings suggest a critical role for the MKK3-p38alpha and p38delta MAPK pathway in mediating VEGF164 isoform-specific stimulation by TGF-beta1 in mesangial cells. Further, VEGF164 stimulates collagen and fibronectin expression in mesangial cells and thus in turn enhances TGF-beta1-induced extracellular matrix and may play an important role in progressive glomerular fibrosis.

Role of prostaglandin E2-dependent angiogenic switch in cyclooxygenase 2-induced breast cancer progression

Overexpression of human cyclooxygenase 2 (COX-2) in the mammary glands of transgenic mice induces tissue-specific tumorigenic transformation. However, the molecular mechanisms involved are not yet defined. Here we show that COX-2 expressed in the epithelial cell compartment regulates angiogenesis in the stromal tissues of the mammary gland. Microvessel density increased before visible tumor growth and exponentially during tumor progression. Inhibition of prostanoid synthesis with indomethacin strongly decreased microvessel density and inhibited tumor progression. Up-regulation of angiogenic regulatory genes in COX-2 transgenic mammary tissue was also potently inhibited by indomethacin treatment, suggesting that prostanoids released from COX-2-expressing mammary epithelial cells induce angiogenesis. G protein-coupled receptors for the major product, prostaglandin E(2) (PGE(2)) EP(1-4), are expressed during mammary gland development, and EP(1,2,4) receptors were up-regulated in tumor tissue. PGE(2) stimulated the expression angiogenic regulatory genes in mammary tumor cells isolated from COX-2 transgenic mice. Such cells are tumorigenic in nude mice; however, treatment with Celecoxib, a COX-2-specific inhibitor, reduced tumor growth and microvessel density. These results define COX-2-derived PGE(2) as a potent inducer of angiogenic switch during mammary cancer progression.

Lipoteichoic acid up-regulates VEGF expression in macrophages and pulp cells

Vascular endothelial growth factor (VEGF) is a potent inducer of angiogenesis, vascular permeability, and edema. Up-regulation of VEGF expression in the dental pulp may result in increased intra-pulpal pressure, and contribute to pain and irreversible tissue damage. Lipoteichoic acid (LTA) is an amphiphilic molecule from Gram-positive bacteria that has been associated with the pathogenesis of pulpitis. To investigate if LTA regulates expression of VEGF, we exposed mouse odontoblast-like cells (MDPC-23), undifferentiated pulp cells (OD-21), fibroblasts, or macrophages to streptococcal LTA, and evaluated VEGF expression by ELISA and RT-PCR. LTA induced up to a nine-fold increase in VEGF protein expression in macrophages, a 2.4-fold increase in MDPC-23, and a 1.6-fold increase in OD-21 as compared with controls. In contrast, LTA did not induce VEGF expression in fibroblasts. VEGF mRNA expression remained constant upon exposure to LTA, which suggests that VEGF regulation in these cells is primarily post-transcriptional. This work constitutes the first demonstration that lipoteichoic acid is sufficient to induce expression of a pro-angiogenic factor.

Effect of lipopolysaccharides on vascular endothelial growth factor expression in mouse pulp cells and macrophages

Vascular endothelial growth factor (VEGF), a potent pro-angiogenic factor, might regulate the neovascularization observed in the pulp of teeth with deep caries. The purpose of this in vitro study was to evaluate the effect of bacterial lipopolysaccharides (LPS) on VEGF expression in dental pulp cells. Mouse odontoblast-like cells (MDPC-23) or undifferentiated pulp cells (OD-21) were exposed to 0-20 microg ml-1Escherichia coli LPS or 0-80 microg ml-1Prevotella intermedia LPS. As controls, mouse macrophages or gingival fibroblasts were exposed to LPS, since these cells are known to secrete VEGF. The VEGF expression was evaluated by reverse transcriptase polymerase chain reaction or enzyme-linked immunosorbent assay. The baseline expression levels of VEGF protein were higher in MDPC-23 and OD-21 than in fibroblasts or macrophages. Vascular endothelial growth factor protein expression was upregulated in MDPC-23 and macrophages exposed to E. coli LPS, but not in OD-21 cells or fibroblasts. Higher concentrations of P. intermedia LPS were required to induce VEGF expression in MDPC-23 cells. Treatment with LPS did not affect VEGF expression at the mRNA level in any of the cells evaluated. These results demonstrate that bacterial LPS upregulates VEGF expression in odontoblast-like cells and macrophages, and suggest that the regulation of VEGF expression occurs primarily at a post-transcriptional level.

Differential expression of VEGF receptors in adrenal atrophy induced by dexamethasone: a protective role of ACTH

Although ACTH is important to adrenal growth and steroidogenesis, its role in vascular development and function has not been established in vivo. In the present study, we demonstrate the expression of mRNA for all four VEGF isoforms (mVEGF(120,144,164,188)) and for Flk-1/KDR and Flt-1 receptors in the mouse adrenal in vivo. Suppression of the pituitary adrenocortical axis by dexamethasone (0.5 mg x 100 g body wt(-1) x day(-1) during 6 days) induced a decrease in corticosterone levels, adrenal weights by 50% (P < 0.001), VEGF(188) mRNA, and Flk-1/KDR mRNA, whereas Flt-1 remained consistent during steroid treatment. A daily injection of ACTH-(1-39) restored the transcript for Flk-1/KDR and both VEGF(188) and plasma corticosterone to control levels. To gain further insights into the effects of ACTH, cultured endothelial cells (ECs) were treated with forskolin, which increases cAMP, the second messenger in ACTH action. We demonstrate that Flk-1/KDR protein expression was markedly increased by forskolin within 24-48 h of treatment in a dose-dependent manner (0.1-10 microM). The biological effect of ACTH on ECs was then tested by use of coincubations of fasciculata cells and ECs in 3D-collagen assay. Within 5-7 days of culture, ECs organized into multicellular structures that resemble networks of microvasculature, which characterize angiogenesis in vitro.

Increased expression of vascular endothelial growth factor in placentas of p57(Kip2) null embryos

Placentas of mice lacking p57(Kip2) expression have trophoblastic hyperplasia. To elucidate the mechanism underlying this phenomenon, we studied expression of two angiogenic factors, vascular endothelial growth factor (VEGF) and placenta growth factor (PlGF). Immunohistochemical analysis with anti-VEGF antibodies indicated that VEGF expression was stronger and more clearly detectable in placentas of p57(Kip2) null embryos compared to wild-type placentas. PlGF showed no significant differences between placentas of p57(Kip2) null and wild-type embryos. In quantitative analysis, placentas of p57(Kip2) null embryos showed higher VEGF messenger (m)RNA and protein levels than did wild-type placentas. PlGF mRNA and protein levels were not significantly different. These findings suggest that VEGF is involved in the hyperplasia that occurs in placentas of p57(Kip2) null embryos.