Differential regulation of the Wnt gene family during pregnancy and lactation suggests a role in postnatal development of the mammary gland

The pRb/RBL2-E2F1/4-GCN5 axis regulates cancer stem cell formation and G0 phase entry/exit by paracrine mechanisms

The lethality, chemoresistance and metastatic characteristics of cancers are associated with phenotypically plastic cancer stem cells (CSCs). How the non-cell autonomous signalling pathways and cell-autonomous transcriptional machinery orchestrate the stem cell-like characteristics of CSCs is still poorly understood. Here we use a quantitative proteomic approach for identifying secreted proteins of CSCs in pancreatic cancer. We uncover that the cell-autonomous E2F1/4-pRb/RBL2 axis balances non-cell-autonomous signalling in healthy ductal cells but becomes deregulated upon KRAS mutation. E2F1 and E2F4 induce whereas pRb/RBL2 reduce WNT ligand expression (e.g. WNT7A, WNT7B, WNT10A, WNT4) thereby regulating self-renewal, chemoresistance and invasiveness of CSCs in both PDAC and breast cancer, and fibroblast proliferation. Screening for epigenetic enzymes identifies GCN5 as a regulator of CSCs that deposits H3K9ac onto WNT promoters and enhancers. Collectively, paracrine signalling pathways are controlled by the E2F-GCN5-RB axis in diverse cancers and this could be a therapeutic target for eliminating CSCs.

WNT5B in Physiology and Disease

WNT5B, a member of the WNT family of proteins that is closely related to WNT5A, is required for cell migration, cell proliferation, or cell differentiation in many cell types. WNT5B signals through the non-canonical β-catenin-independent signaling pathway and often functions as an antagonist of canonical WNT signaling. Although WNT5B has a high amino acid identity with WNT5A and is often assumed to have similar activities, WNT5B often exhibits unique expression patterns and functions. Here, we describe the distinct effects and mechanisms of WNT5B on development, bone, adipose tissue, cardiac tissue, the nervous system, the mammary gland, the lung and hematopoietic cells, compared to WNT5A. We also highlight aberrances in non-canonical WNT5B signaling contributing to diseases such as osteoarthritis, osteoporosis, obesity, type 2 diabetes mellitus, neuropathology, and chronic diseases associated with aging, as well as various cancers.

Nuclear Dishevelled targets gene regulatory regions and promotes tumor growth

Dishevelled (DVL) critically regulates Wnt signaling and contributes to a wide spectrum of diseases and is important in normal and pathophysiological settings. However, how it mediates diverse cellular functions remains poorly understood. Recent discoveries have revealed that constitutive Wnt pathway activation contributes to breast cancer malignancy, but the mechanisms by which this occurs are unknown and very few studies have examined the nuclear role of DVL. Here, we have performed DVL3 ChIP-seq analyses and identify novel target genes bound by DVL3. We show that DVL3 depletion alters KMT2D binding to novel targets and changes their epigenetic marks and mRNA levels. We further demonstrate that DVL3 inhibition leads to decreased tumor growth in two different breast cancer models in vivo. Our data uncover new DVL3 functions through its regulation of multiple genes involved in developmental biology, antigen presentation, metabolism, chromatin remodeling, and tumorigenesis. Overall, our study provides unique insight into the function of nuclear DVL, which helps to define its role in mediating aberrant Wnt signaling.

Breast cancer development and progression: Risk factors, cancer stem cells, signaling pathways, genomics, and molecular pathogenesis

As the most commonly occurring cancer in women worldwide, breast cancer poses a formidable public health challenge on a global scale. Breast cancer consists of a group of biologically and molecularly heterogeneous diseases originated from the breast. While the risk factors associated with this cancer varies with respect to other cancers, genetic predisposition, most notably mutations in BRCA1 or BRCA2 gene, is an important causative factor for this malignancy. Breast cancers can begin in different areas of the breast, such as the ducts, the lobules, or the tissue in between. Within the large group of diverse breast carcinomas, there are various denoted types of breast cancer based on their invasiveness relative to the primary tumor sites. It is important to distinguish between the various subtypes because they have different prognoses and treatment implications. As there are remarkable parallels between normal development and breast cancer progression at the molecular level, it has been postulated that breast cancer may be derived from mammary cancer stem cells. Normal breast development and mammary stem cells are regulated by several signaling pathways, such as estrogen receptors (ERs), HER2, and Wnt/β-catenin signaling pathways, which control stem cell proliferation, cell death, cell differentiation, and cell motility. Furthermore, emerging evidence indicates that epigenetic regulations and noncoding RNAs may play important roles in breast cancer development and may contribute to the heterogeneity and metastatic aspects of breast cancer, especially for triple-negative breast cancer. This review provides a comprehensive survey of the molecular, cellular and genetic aspects of breast cancer.

Dishevelled: A masterful conductor of complex Wnt signals

The Dishevelled gene was first identified in Drosophila mutants with disoriented hair and bristle polarity [1-3]. The Dsh gene (Dsh/Dvl, in Drosophila and vertebrates respectively) gained popularity when it was discovered that it plays a key role in segment polarity during early embryonic development in Drosophila [4]. Subsequently, the vertebrate homolog of Dishevelled genes were identified in Xenopus (Xdsh), mice (Dvl1, Dvl2, Dvl3), and in humans (DVL1, DVL2, DVL3) [5-10]. Dishevelled functions as a principal component of Wnt signaling pathway and governs several cellular processes including cell proliferation, survival, migration, differentiation, polarity and stem cell renewal. This review will revisit seminal discoveries and also summarize recent advances in characterizing the role of Dishevelled in both normal and pathophysiological settings.

Signaling Networks in Epithelial Tube Formation

Epithelial tubes are crucial to the function of organ systems including the excretory, gastrointestinal, cardiovascular, and pulmonary. Studies in the last two decades using in vitro organotypic systems and a variety of animal models have substantiated a large number of the morphogenetic mechanisms required to form epithelial tubes in development and regeneration. Many of these mechanisms modulate the differentiation and proliferation events necessary for generating the cell movements and changes in cell shape to delineate the wide variety of epithelial tube sizes, lengths, and conformations. For instance, when coupled with oriented cell division, proliferation itself plays a role in changes in tube shape and their directed expansion. Most of these processes are regulated in response to signaling inputs from adjacent cells or soluble factors from the environment. Despite the great deal of recent investigation in this direction, the knowledge we have about the signaling pathways associated with all epithelial tubulogenesis in development and regeneration is still very limited.

A Tale of Two Signals: AR and WNT in Development and Tumorigenesis of Prostate and Mammary Gland

Prostate cancer (PCa) is one of the most common cancers and among the leading causes of cancer deaths for men in industrialized countries. It has long been recognized that the prostate is an androgen-dependent organ and PCa is an androgen-dependent disease. Androgen action is mediated by the androgen receptor (AR). Androgen deprivation therapy (ADT) is the standard treatment for metastatic PCa. However, almost all advanced PCa cases progress to castration-resistant prostate cancer (CRPC) after a period of ADT. A variety of mechanisms of progression from androgen-dependent PCa to CRPC under ADT have been postulated, but it remains largely unclear as to when and how castration resistance arises within prostate tumors. In addition, AR signaling may be modulated by extracellular factors among which are the cysteine-rich glycoproteins WNTs. The WNTs are capable of signaling through several pathways, the best-characterized being the canonical WNT/β-catenin/TCF-mediated canonical pathway. Recent studies from sequencing PCa genomes revealed that CRPC cells frequently harbor mutations in major components of the WNT/β-catenin pathway. Moreover, the finding of an interaction between β-catenin and AR suggests a possible mechanism of cross talk between WNT and androgen/AR signaling pathways. In this review, we discuss the current knowledge of both AR and WNT pathways in prostate development and tumorigenesis, and their interaction during development of CRPC. We also review the possible therapeutic application of drugs that target both AR and WNT/β-catenin pathways. Finally, we extend our review of AR and WNT signaling to the mammary gland system and breast cancer. We highlight that the role of AR signaling and its interaction with WNT signaling in these two hormone-related cancer types are highly context-dependent.

Multiple Roles of WNT5A in Breast Cancer

Breast cancer is one of the most common malignant tumors of women. Modern combinatorial therapeutic regimens can reduce patient tumor burdens to undetectable levels, yet in many cases these tumors will relapse. Understanding of breast cancer biology, developing more potent therapeutic approaches, and overcoming resistance are of great importance. WNT5A is a non-canonical signaling member of the WNT family. Its role in breast cancer still remains unclear. Most of the evidence shows that WNT5A is a suppressor in breast cancer and loss of its expression is associated with poor prognosis, while some evidence suggests the tumorigenicity of WNT5A. WNT signaling molecules are potent targets for treatment of cancer. Therefore, understanding the role of WNT5A in breast cancer may provide new ideas and methods for breast cancer treatment. We review the evidence concerning WNT5A and breast cancer involving the signaling pathways and the molecular-targeted therapy of WNT5A. Our results show that the role WNT5A plays depends on the availability of key receptors and intercellular interactions among different cell types.

Mammary Development and Breast Cancer: A Wnt Perspective

The Wnt pathway has emerged as a key signaling cascade participating in mammary organogenesis and breast oncogenesis. In this review, we will summarize the current knowledge of how the pathway regulates stem cells and normal development of the mammary gland, and discuss how its various components contribute to breast carcinoma pathology.

The mammary stem cell hierarchy: a looking glass into heterogeneous breast cancer landscapes

The mammary gland is a dynamic organ that undergoes extensive morphogenesis during the different stages of embryonic development, puberty, estrus, pregnancy, lactation and involution. Systemic and local cues underlie this constant tissue remodeling and act by eliciting an intricate pattern of responses in the mammary epithelial and stromal cells. Decades of studies utilizing methods such as transplantation and lineage-tracing have identified a complex hierarchy of mammary stem cells, progenitors and differentiated epithelial cells that fuel mammary epithelial development. Importantly, these studies have extended our understanding of the molecular crosstalk between cell types and the signaling pathways maintaining normal homeostasis that often are deregulated during tumorigenesis. While several questions remain, this research has many implications for breast cancer. Fundamental among these are the identification of the cells of origin for the multiple subtypes of breast cancer and the understanding of tumor heterogeneity. A deeper understanding of these critical questions will unveil novel breast cancer drug targets and treatment paradigms. In this review, we provide a current overview of normal mammary development and tumorigenesis from a stem cell perspective.

Recurrence and metastasis of breast cancer is influenced by ovarian hormone's effect on breast cancer stem cells

Cancer stem cells (CSCs) have recently attracted great interest because of their emerging role in initiation, progression and metastasis, combined with their intrinsic resistance to chemotherapy and radiation therapy. CSCs and its interaction with hormones in breast cancer are currently being investigated with the aim of uncovering the molecular mechanisms by which they evade conventional treatment regimens. In this review, we discuss recent experimental data and new perspectives in the area of steroid hormones and their cross-talk with breast CSCs. We have covered literature associated with biomarkers, hormone receptors and hormone responsive signaling pathways in breast CSC. In addition, we also discuss the role of miRNAs in hormone mediated regulation of breast CSCs.

Progesterone and Wnt4 control mammary stem cells via myoepithelial crosstalk

Ovarian hormones increase breast cancer risk by poorly understood mechanisms. We assess the role of progesterone on global stem cell function by serially transplanting mouse mammary epithelia. Progesterone receptor (PR) deletion severely reduces the regeneration capacity of the mammary epithelium. The PR target, receptor activator of Nf-κB ligand (RANKL), is not required for this function, and the deletion of Wnt4 reduces the mammary regeneration capacity even more than PR ablation. A fluorescent reporter reveals so far undetected perinatal Wnt4 expression that is independent of hormone signaling. Pubertal and adult Wnt4 expression is specific to PR+ luminal cells and requires intact PR signaling. Conditional deletion of Wnt4 reveals that this early, previously unappreciated, Wnt4 expression is functionally important. We provide genetic evidence that canonical Wnt signaling in the myoepithelium required PR and Wnt4, whereas the canonical Wnt signaling activities observed in the embryonic mammary bud and in the stroma around terminal end buds are independent of Wnt4. Thus, progesterone and Wnt4 control stem cell function through a luminal-myoepithelial crosstalk with Wnt4 acting independent of PR perinatally.

A Ror recruit to mammary gland development

Study shows how noncanonical Wnt signaling promotes differentiation and morphogenesis of mammary epithelia.

Ror2 regulates branching, differentiation, and actin-cytoskeletal dynamics within the mammary epithelium

Intricate cross-talk between classical and alternative Wnt signaling pathways includes an essential role for Ror2 in mammary epithelial development and differentiation.

Wnt signaling encompasses β-catenin–dependent and –independent networks. How receptor context provides Wnt specificity in vivo to assimilate multiple concurrent Wnt inputs throughout development remains unclear. Here, we identified a refined expression pattern of Wnt/receptor combinations associated with the Wnt/β-catenin–independent pathway in mammary epithelial subpopulations. Moreover, we elucidated the function of the alternative Wnt receptor Ror2 in mammary development and provided evidence for coordination of this pathway with Wnt/β-catenin–dependent signaling in the mammary epithelium. Lentiviral short hairpin RNA (shRNA)-mediated depletion of Ror2 in vivo increased branching and altered the differentiation of the mammary epithelium. Microarray analyses identified distinct gene level alterations within the epithelial compartments in the absence of Ror2, with marked changes observed in genes associated with the actin cytoskeleton. Modeling of branching morphogenesis in vitro defined specific defects in cytoskeletal dynamics accompanied by Rho pathway alterations downstream of Ror2 loss. The current study presents a model of Wnt signaling coordination in vivo and assigns an important role for Ror2 in mammary development.

Secreted frizzled-related protein 5 suppresses inflammatory response in rheumatoid arthritis fibroblast-like synoviocytes through down-regulation of c-Jun N-terminal kinase

OBJECTIVE

This study was performed to investigate the effect of secreted frizzled-related protein 5 (Sfrp5), a novel anti-inflammatory adipokine that competes with the frizzled proteins for Wnt binding, on inflammatory response and the c-Jun N-terminal kinase (JNK) signalling pathway in RA.

METHODS

Expression of Sfrp5 mRNA in peripheral blood mononuclear cells (PBMCs) and fibroblast-like synoviocytes (FLSs) from patients with RA and OA was determined using real-time quantitative PCR (qPCR). Sfrp5 RNA interference (RNAi) plasmids were transfected to abrogate Sfrp5 expression in RA FLSs, and adenovirus containing the Sfrp5 transcript was delivered into RA FLSs to strengthen Sfrp5 expression. Levels of pro-inflammatory genes and their protein products were determined using real-time qPCR and ELISA in RA FLSs. Production of mitogen-activated protein kinase kinase 7 (MKK-7), JNK and c-Jun were assessed by Western blot analysis.

RESULTS

Expression of Sfrp5 mRNA was decreased in PMBCs and FLSs from patients with RA compared with patients with OA. Gene expression and production of IL-1β, IL-6, chemokine ligand 2 (CCL-2), CCL-7, cyclooxygenase 2 and MMP-9 were markedly increased in Sfrp5 RNAi plasmid-transfected RA FLSs, while transfection with adenoviral vectors encoding Sfrp5 induced reductions in those levels. Phosphorylated forms of MKK-7, JNK and c-Jun were increased by Sfrp5 RNAi plasmids and were decreased by adenoviral vectors encoding Sfrp5.

CONCLUSION

Sfrp5 suppressed the inflammatory response and down-regulated JNK signalling in RA FLSs. These findings provide evidence for the anti-inflammatory effect of Sfrp5 in RA.

Breaking the canon: indirect regulation of Wnt signaling in mammary stem cells by MMP3

Matrix metalloproteases promote tumor cell invasion, epithelial-to-mesenchymal transitions, and metastases, but whether they directly regulate stem cells is unknown. In this issue of Cell Stem Cell, Kessenbrock et al. (2013) now show that MMP3, independent of its proteolytic activity, regulates murine mammary stem cells by sequestering noncanonical Wnt signaling ligands, which has implications for breast cancer pathogenesis.

Repression of cathepsin E expression increases the risk of mammary carcinogenesis and links to poor prognosis in breast cancer

Despite advances in detection and treatment for breast cancer (BC), recurrence and death rates remain unacceptably high. Therefore, more convenient diagnostic and prognostic methods still required to optimize treatments among the patients. Here, we report the clinical significance of the serum cathepsin E (CatE) activity as a novel prognostic marker for BC. Correlation analysis between the serum levels of CatE expression and clinicopathological parameters revealed that the activity levels, but not the protein levels, were negatively associated with the stages and progression of BC. Univariate and multivariate analyses demonstrated that the serum CatE activity was significantly correlated with favorable prognostic outcomes of the patients. The functional link of CatE expression to BC progression was further corroborated by in vivo and in vitro studies with mice exhibiting different levels of CatE expression. Multiparous CatE (-) (/) (-) mice spontaneously developed mammary tumors concomitant with morphological transformation and altered growth characteristics of the mammary glands. These alterations were associated in part with the induction of epithelial-mesenchymal transition and the activation of β-catenin-dependent pathway in mammary cells. Loss of CatE strongly induced the translocation and accumulation of Wnt5a in the nuclei, thereby leading to the aberrant trafficking, maturation and secretion of Wnt5a and the impaired signaling. The interaction of CatE and Wnt5a was verified by proximity ligation assay and by knockdown or restoration of CatE expression in the mammary cells. Consequently, our data demonstrate that CatE contributes to normal growth and development of mammary glands through proper trafficking and secretion of Wnt5a.

A Common Docking Domain in Progesterone Receptor-B links DUSP6 and CK2 signaling to proliferative transcriptional programs in breast cancer cells

Progesterone receptors (PR) are transcription factors relevant to breast cancer biology. Herein, we describe an N-terminal common docking (CD) domain in PR-B, a motif first described in mitogen-activated protein kinases. Binding studies revealed PR-B interacts with dual-specificity phosphatase 6 (DUSP6) via the CD domain. Mutation of the PR-B CD domain (mCD) attenuated cell cycle progression and expression of PR-B target genes (including STAT5A and Wnt1); mCD PR-B failed to undergo phosphorylation on Ser81, a ck2-dependent site required for expression of these genes. PR-B Ser81 phosphorylation was dependent on binding with DUSP6 and required for recruitment of a transcriptional complex consisting of PR-B, DUSP6 and ck2 to an enhancer region upstream of the Wnt1 promoter. STAT5 was present at this site in the absence or presence of progestin. Furthermore, phospho-Ser81 PR-B was recruited to the STAT5A gene upon progestin treatment, suggestive of a feed-forward mechanism. Inhibition of JAK/STAT-signaling blocked progestin-induced STAT5A and Wnt1 expression. Our studies show that DUSP6 serves as a scaffold for ck2-dependent PR-B Ser81 phosphorylation and subsequent PR-B-specific gene selection in coordination with STAT5. Coregulation of select target genes by PR-B and STAT5 is likely a global mechanism required for growth promoting programs relevant to mammary stem cell biology and cancer.

An immunohistochemical evaluation of the proteins Wnt1 and glycogen synthase kinase (GSK)-3β in invasive breast carcinomas

AIMS

Our purpose was to investigate, in breast carcinomas, the prognostic importance of the proteins Wnt1 and glycogen synthasekinase (GSK)-3β, and their associations with classic clinicopathological indices.

METHODS AND RESULTS

Immunohistochemistry was performed on paraffin-embedded tissue specimens from 288 invasive breast carcinomas to detect the expression of the proteins Wnt1, GSK3β, oestrogen receptor (ER), progesterone receptor (PR), erbB2, p53, Ki67, caspase-3 and β-catenin. Both Wnt1 and GSK3β were detected predominantly in the cytoplasm of the invasive tumour cells and the in-situ component, while GSK3β was also detected in the stromal fibroblasts. Wnt1 immunoreactivity in the invasive tumour cells showed an inverse association with histological grade (P = 0.002), Ki67 (P = 0.008) and p53 (P = 0.031), while its relation with ER, erbB2 and caspase-3 was found to be positive (P = 0.007, P = 0.018 and P = 0.03, respectively). Cytoplasmic Wnt1 expression was related to a favourable prognosis within the subgroup of patients with stage II disease (P = 0.032).

CONCLUSIONS

Wnt1 expression in the invasive tumour cells seems to promote differentiation and apoptosis, while being related inversely to proliferation. Therefore, this suggests its participation in the primary stages of breast carcinogenesis. The latter is supported further by the immunodetection of Wnt1 in in-situ carcinomas.

The biology of progesterone receptor in the normal mammary gland and in breast cancer

This paper reviews work on progesterone and the progesterone receptor (PR) in the mouse mammary gland that has been used extensively as an experimental model. Studies have led to the concept that progesterone controls proliferation and morphogenesis of the luminal epithelium in a tightly orchestrated manner at distinct stages of development by paracrine signaling pathways, including receptor activator of nuclear factor κB ligand (RANKL) as a major paracrine factor. Progesterone also drives expansion of stem cells by paracrine signals to generate progenitors required for alveologenesis. During mid-to-late pregnancy, progesterone has another role to suppress secretory activation until parturition mediated in part by crosstalk between PR and prolactin/Stat5 signaling to inhibit induction of milk protein gene expression, and by inhibiting tight junction closure. In models of hormone-dependent mouse mammary tumors, the progesterone/PR signaling axis enhances pre-neoplastic progression by a switch from a paracrine to an autocrine mode of proliferation and dysregulation of the RANKL signaling pathway. Limited experiments with normal human breast show that progesterone/PR signaling also stimulates epithelial cell proliferation by a paracrine mechanism; however, the signaling pathways and whether RANKL is a major mediator remains unknown. Work with human breast cancer cell lines, patient tumor samples and clinical studies indicates that progesterone is a risk factor for breast cancer and that alteration in progesterone/PR signaling pathways contributes to early stage human breast cancer progression. However, loss of PR expression in primary tumors is associated with a less differentiated more invasive phenotype and worse prognosis, suggesting that PR may limit later stages of tumor progression.

Paracrine signaling by progesterone

Steroid hormones coordinate and control the development and function of many organs and are implicated in many pathological processes. Progesterone signaling, in particular, is essential for several important female reproductive functions. Physiological effects of progesterone are mediated by its cognate receptor, expressed in a subset of cells in target tissues. Experimental evidence has accumulated that progesterone acts through both cell intrinsic as well as paracrine signaling mechanisms. By relegating the hormonal stimulus to paracrine signaling cascades the systemic signal gets amplified locally and signaling reaches different cell types that are devoid of hormone receptors. Interestingly, distinct biological responses to progesterone in different target tissues rely on several tissue-specific and some common paracrine factors that coordinate biological responses in different cell types. Evidence is forthcoming that the intercellular signaling pathways that control development and physiological functions are important in tumorigenesis.

Conditional Wwox deletion in mouse mammary gland by means of two Cre recombinase approaches

Loss of WWOX expression has been reported in many different cancers including breast cancer. Elucidating the function of this gene in adult tissues has not been possible with full Wwox knockout models. Here we characterize the first conditional models of Wwox ablation in mouse mammary epithelium utilizing two transgenic lines expressing Cre recombinase, keratin 5-Cre (BK5-Cre) and MMTV-Cre. In the BK5-Cre model we observed very efficient Wwox ablation in KO mammary glands. However, BK5-Cre Wwox KO animals die prematurely for unknown reasons. In the MMTV-Cre model we observed significant ablation of Wwox in mammary epithelium with no effect on survival. In both of these models we found that Wwox deletion resulted in impaired mammary branching morphogenesis. We demonstrate that loss of Wwox is not carcinogenic in our KO models. Furthermore, no evidence of increase proliferation or development of premalignant lesions was observed. In none of the models did loss of a single Wwox allele (i.e. haploinsufficiency) have any observable phenotypic effect in mammary gland. To better understand the function of Wwox in the mammary gland, transcriptome profiling was performed. We observed that Wwox ablation results in the deregulation of genes involved in various cellular processes. We found that expression of the non-canonical Wnt ligand, Wnt5a, was significantly upregulated in Wwox KO mammary epithelium. Interestingly, we also determined that components of the Jak/Stat3 signaling pathway were upregulated in KO mice and this correlated with a very robust increase in phospho-Stat3 signaling, which warrants further testing. Even though the loss of Wwox expression in breast and other cancers is very well documented, our findings suggest that Wwox does not act as a classical tumor suppressor as previously thought.

Modulation of Wnt5a expression by periodontopathic bacteria

Wingless proteins, termed Wnt, are involved in embryonic development, blood cell differentiation, and tumorigenesis. In mammalian hematopoiesis, Wnt signaling is essential for stem-cell homeostasis and lymphocyte differentiation. Recent studies have suggested that these molecules are associated with cardiovascular diseases, rheumatoid arthritis, and osteoarthritis. Furthermore, Wnt5a signaling is essential for the general inflammatory response of human macrophages. Periodontitis is a chronic inflammatory disease caused by gram-negative periodontopathic bacteria and the resultant host immune response. Periodontitis is characterized by loss of tooth-supporting structures and alveolar bone resorption. There have been no previous reports on Wnt5a expression in periodontitis tissue, and only few study reported the molecular mechanisms of Wnt5a expression in LPS-stimulated monocytic cells. Using RT-PCR, we demonstrated that Wnt5a mRNA expression was up-regulated in chronic periodontitis tissue as compared to healthy control tissue. P. gingivalis LPS induced Wnt5a mRNA in the human monocytic cell line THP-1 with a peak at 4 hrs after stimulation. P. gingivalis LPS induced higher up-regulation of Wnt5a mRNA than E. coli LPS. The LPS receptors TLR2 and TLR4 were equally expressed on the surface of THP-1 cells. P. gingivalis LPS induced IκBα degradation and was able to increase the NF-κB binding activity to DNA. P. gingivalis LPS-induced Wnt5a expression was inhibited by NF-κB inhibitors, suggesting NF-κB involvement. Furthermore, IFN-γ synergistically enhanced the P. gingivalis LPS-induced production of Wnt5a. Pharmacological investigation and siRNA experiments showed that STAT1 was important for P. gingivalis LPS-induced Wnt5a expression. These results suggest that the modulation of Wnt5a expression by P. gingivalis may play an important role in the periodontal inflammatory process and serve a target for the development of new therapies.

Wnt signalling in murine postnatal mammary gland development

The mammary gland undergoes numerous developmental processes postnatally, from the elongation of the ductal tree-like structure to pregnancy-induced lobulo-alveolar development. Mammary epithelial stem cells have been suggested to be central to the control of enormous tissue expansion and remodelling during phases of mammary development. The Wnt signalling pathway plays a critical role in these biological steps and is suggested to be involved in the maintenance of the stem cell population. This review provides insight into recent findings on the activity of Wnt signalling during ductal and lobular mammary development and discusses the potential interplay between Wnt signals and mammary stem cells in mice.

Misexpression of wingless-related MMTV integration site 5A in mouse mammary gland inhibits the milk ejection response and regulates connexin43 phosphorylation

Wingless-related MMTV integration site 5A (Wnt5a) is a noncanonical signaling WNT that is expressed in every stage of mouse mammary gland development except lactation. Using slow release pellets containing WNT5A as well as Wnt5a-null tissue, we previously showed that WNT5A acts to limit mammary development. Here, we generated transgenic mice that overexpress WNT5A in the mammary epithelium using the mouse mammary tumor virus promoter (M5a mice). Lactation was impaired in two high WNT5A-expressing lines. Lactation defects could not be explained by differences in apoptosis, lineage differentiation, milk synthesis, or secretion. Instead, misexpression of WNT5A led to a failure in oxytocin response and milk ejection. Noting the similarity between the M5a phenotype and that of mice with a mutation in connexin43 (Cx43; official gene symbol Gja1), we examined Cx43 phosphorylation and localization in M5a mice. In wild-type mice, Cx43 switched from a phosphorylated to a more hypophosphorylated form after parturition. In contrast, the phosphorylated form of Cx43 was maintained after parturition in M5a mice. Using a nontumorigenic breast cell line, MCF10A, we showed that, in addition to increasing the levels of phosphorylation of Cx43 on serine-368, ectopic expression of WNT5A reduced or blocked the amount of dye transferred between cells. In summary, we propose that WNT5A inhibits the response to oxytocin and prevents milk ejection through regulation of Cx43 function.

Targeting androgen receptor in estrogen receptor-negative breast cancer

Endocrine therapies for breast cancer that target the estrogen receptor (ER) are ineffective in the 25%-30% of cases that are ER negative (ER-). Androgen receptor (AR) is expressed in 60%-70% of breast tumors, independent of ER status. How androgens and AR regulate breast cancer growth remains largely unknown. We find that AR is enriched in ER- breast tumors that overexpress HER2. Through analysis of the AR cistrome and androgen-regulated gene expression in ER-/HER2+ breast cancers we find that AR mediates ligand-dependent activation of Wnt and HER2 signaling pathways through direct transcriptional induction of WNT7B and HER3. Specific targeting of AR, Wnt or HER2 signaling impairs androgen-stimulated tumor cell growth suggesting potential therapeutic approaches for ER-/HER2+ breast cancers.

Wnt5a as an effector of TGFβ in mammary development and cancer

Wnt5a is a member of the Wingless-related/MMTV-integration family of secreted growth factors, which are involved in a wide range of cellular processes. Wnt signaling can be broadly divided into two categories the canonical, ß-catenin-dependent pathway and the non-canonical ß-catenin-independent pathway. Wnt5a is a non-canonical signaling member of the Wnt family. Loss of Wnt5a is associated with early relapse of invasive breast cancer, increased metastasis, and poor survival in humans. It has been shown that TGF-ß directly regulates expression of Wnt5a in mammary gland and that Wnt5a mediates the effects of TGF-ß on branching during mammary gland development. Here we review the evidence suggesting Wnt5a acts as an effector of TGF-ß actions in breast cancer. It is suggested that the tumor suppressive functions of TGF-ß involve Wnt5a-mediated antagonism of Wnt/ß-catenin signaling and limiting the stem cell population. Interactions between TGF-ß and Wnt5a in metastasis appear to be more complex, and may depend on specific cues from the microenvironment as well as activation of specific intracellular signaling pathways.

Activation of the canonical Wnt/β-catenin pathway in ATF3-induced mammary tumors

Female transgenic mice that constitutively overexpress the transcription factor ATF3 in the basal epithelium of the mammary gland develop mammary carcinomas with high frequency, but only if allowed to mate and raise pups early in life. This transgenic mouse model system reproduces some features of human breast cancer in that about 20% of human breast tumor specimens exhibit overexpression of ATF3 in the tumor cells. The ATF3-induced mouse tumors are phenotypically similar to mammary tumors induced by overexpression of activating Wnt/β-catenin pathway genes. We now show that the Wnt/β-catenin pathway is indeed activated in ATF3-induced tumors. β-catenin is transcriptionally up-regulated in the tumors, and high levels of nuclear β-catenin are seen in tumor cells. A reporter gene for Wnt/β-catenin pathway activity, TOPGAL, is up-regulated in the tumors and several downstream targets of Wnt signaling, including Ccnd1, Jun, Axin2 and Dkk4, are also expressed at higher levels in ATF3-induced tumors compared to mammary glands of transgenic females. Several positive-acting ligands for this pathway, including Wnt3, Wnt3a, Wnt7b, and Wnt5a, are significantly overexpressed in tumor tissue, and mRNA for Wnt3 is about 5-fold more abundant in transgenic mammary tissue than in non-transgenic mammary tissue. Two known transcriptional targets of ATF3, Snai1 and Snai2, are also overexpressed in the tumors, and Snail and Slug proteins are found to be located primarily in the nuclei of tumor cells. In vitro knockdown of Atf3 expression results in significant decreases in expression of Wnt7b, Tcf7, Snai2 and Jun, suggesting that these genes may be direct transcriptional targets of ATF3 protein. By chromatin immunoprecipitation analysis, both ATF3 and JUN proteins appear to bind to a particular subclass of AP-1 sites upstream of the transcriptional start sites of each of these genes.

Wnt proteins are self-renewal factors for mammary stem cells and promote their long-term expansion in culture

Adult stem cells have the ability to self-renew and to generate specialized cells. Self-renewal is dependent on extrinsic niche factors but few of those signals have been identified. In addition, stem cells tend to differentiate in the absence of the proper signals and are therefore difficult to maintain in cell culture. The mammary gland provides an excellent system to study self-renewal signals, because the organ develops postnatally, arises from stem cells, and is readily generated from transplanted cells. We show here that adult mammary glands contain a Wnt-responsive cell population that is enriched for stem cells. In addition, stem cells mutant for the negative-feedback regulator Axin2 and therefore sensitized to Wnt signals have a competitive advantage in mammary gland reconstitution assays. In cell culture experiments, exposure to purified Wnt protein clonally expands mammary stem cells for many generations and maintains their ability to generate functional glands in transplantation assays. We conclude that Wnt proteins serve as rate-limiting self-renewal signals acting directly on mammary stem cells.

The expression of Wnt4 is regulated by estrogen via an estrogen receptor alpha-dependent pathway in rat pituitary growth hormone-producing cells

Wnt signaling is important in many aspects of cell biology and development. In the mouse female reproductive tract, Wnt4, Wnt5a, and Wnt7a show differential expression during the estrus cycle, suggesting that they participate in female reproductive physiology. Although the pituitary is a major gland regulating reproduction, the molecular mechanism of Wnt signaling here is unclear. We elucidated the subcellular distribution of Wnt4 in the pituitary of estrogen-treated ovariectomized female rats. Expression of Wnt4 mRNA increased dramatically, particularly in proestrus compared with estrus and metestrus. Wnt4 protein was observed in the cytoplasm of almost all growth hormone (GH)-producing cells and in only a few thyroid-stimulating hormone β (TSHβ)-producing cells. In rat GH-producing pituitary tumor (MtT/S) cells, estrogen-induced expression of Wnt4 mRNA was completely inhibited by estrogen receptor antagonist ICI 182,780 in vitro. Thus, rat pituitary GH cells synthesize Wnt4 and this is induced by estrogen mediated via an estrogen receptor alpha-dependent pathway.

Wnt4 is not sufficient to induce lobuloalveolar mammary development

BACKGROUND

Brisken et al (2000) showed that Wnt4 null mammary glands were deficient in early lobuloalveolar mammary outgrowth during pregnancy, and implicated Wnt4 as an effector for the progesterone-induced mammary growth program. Though ectopic Wnt1 signaling is known to be mitogenic and oncogenic, no endogenously expressed Wnt ligands have ever been directly implicated in mammary growth and morphogenesis. Therefore, we generated conditional transgenic mice to test whether Wnt4 can stimulate mammary epithelial cell growth.

RESULTS

We found that despite pregnancy-associated expression levels of Wnt4, mammary glands did not display the side-branching typical of early pregnancy. Control experiments designed to test the Wnt4 construct in zebrafish reproduced other studies that demonstrated Wnt4-specific phenotypes distinct from Wnt1-induced phenotypes. Indeed, using qPCR-based array analyses, we found that a specific transcriptional target of Wnt4, namely Wnt16, was induced in Wnt4-expressing transgenic glands, to levels equivalent to that of early pregnant glands.

CONCLUSION

Taken together, we propose that Wnt4 is necessary, but not sufficient, to induce side-branch development.

Wnt5a is required for proper mammary gland development and TGF-beta-mediated inhibition of ductal growth

Transforming growth factor-beta (TGF-beta) plays an essential role in growth and patterning of the mammary gland, and alterations in its signaling have been shown to illicit biphasic effects on tumor progression and metastasis. We demonstrate in mice that TGF-beta (Tgfbeta) regulates the expression of a non-canonical signaling member of the wingless-related protein family, Wnt5a. Loss of Wnt5a expression has been associated with poor prognosis in breast cancer patients; however, data are lacking with regard to a functional role for Wnt5a in mammary gland development. We show that Wnt5a is capable of inhibiting ductal extension and lateral branching in the mammary gland. Furthermore, Wnt5a(-/-) mammary tissue exhibits an accelerated developmental capacity compared with wild-type tissue, marked by larger terminal end buds, rapid ductal elongation, increased lateral branching and increased proliferation. Additionally, dominant-negative interference of TGF-beta signaling impacts not only the expression of Wnt5a, but also the phosphorylation of discoidin domain receptor 1 (Ddr1), a receptor for collagen and downstream target of Wnt5a implicated in cell adhesion/migration. Lastly, we show that Wnt5a is required for TGF-beta-mediated inhibition of ductal extension in vivo and branching in culture. This study is the first to show a requirement for Wnt5a in normal mammary development and its functional connection to TGF-beta.

The pattern of beta-catenin responsiveness within the mammary gland is regulated by progesterone receptor

Experiments involving beta-catenin loss- and gain-of-function in the mammary gland have decisively demonstrated the role of this protein in normal alveologenesis. However, the relationship between hormonal and beta-catenin signaling has not been investigated. In this study, we demonstrate that activated beta-catenin rescues alveologenesis in progesterone receptor (PR; Pgr)-null mice during pregnancy. Two distinct subsets of mammary cells respond to expression of DeltaN89beta-catenin. Cells at ductal tips are inherently beta-catenin-responsive and form alveoli in the absence of PR. However, PR activity confers beta-catenin responsiveness to progenitor cells along the lateral ductal borders in the virgin gland. Once activated by beta-catenin, responding cells switch on an alveolar differentiation program that is indistinguishable from that observed in pregnancy and is curtailed by PR signaling.

WNT10B functional dualism: beta-catenin/Tcf-dependent growth promotion or independent suppression with deregulated expression in cancer

We found aberrant DNA methylation of the WNT10B promoter region in 46% of primary hepatocellular carcinoma (HCC) and 15% of colon cancer samples. Three of 10 HCC and one of two colon cancer cell lines demonstrated low or no expression, and 5-aza-2'deoxycytidine reactivated WNT10B expression with the induction of demethylation, indicating that WNT10B is silenced by DNA methylation in some cancers, whereas WNT10B expression is up-regulated in seven of the 10 HCC cell lines and a colon cancer cell line. These results indicate that WNT10B can be deregulated by either overexpression or silencing in cancer. We found that WNT10B up-regulated beta-catenin/Tcf activity. However, WNT10B-overexpressing cells demonstrated a reduced growth rate and anchorage-independent growth that is independent of the beta-catenin/Tcf activation, because mutant beta-catenin-transduced cells did not suppress growth, and dominant-negative hTcf-4 failed to alleviate the growth suppression by WNT10B. Although WNT10B expression alone inhibits cell growth, it acts synergistically with the fibroblast growth factor (FGF) to stimulate cell growth. WNT10B is bifunctional, one function of which is involved in beta-catenin/Tcf activation, and the other function is related to the down-regulation of cell growth through a different mechanism. We suggest that FGF switches WNT10B from a negative to a positive cell growth regulator.

Human chorionic gonadotropin (hCG) up-regulates wnt5b and wnt7b in the mammary gland, and hCGbeta transgenic female mice present with mammary Gland tumors exhibiting characteristics of the Wnt/beta-catenin pathway activation

Transgenic (TG) mice expressing human chorionic gonadotropin (hCG) beta-subunit under the ubiquitin C promoter, presenting with a moderately elevated level of LH/hCG bioactivity develop multiple neoplasms secondary to the endocrine abnormalities, including mammary gland tumors after the age of 9 months. The increased levels of circulating estradiol, progesterone, and prolactin of the TG females after puberty boost the lobuloalveolar development in the mammary gland resulting ultimately in the formation of estrogen and progesterone receptor-negative, malignant tumors. These tumors have a similar histopathology with those observed in TG mice with activated wnt/beta-catenin pathway, showing increased expression of beta-catenin, also a common finding in human breast tumors. Transdifferentiation is observed in mammary tumors of the hCGbeta TG mice, accompanied by abnormal expression of the Wnt genes in the tumorous and nontumorous mammary gland tissue. Specifically we found increased expression of Wnt5b in the TG mammary glands at the age of 3 months and up-regulation of Wnt7b and -5b in the subsequently appearing tumors. Importantly, hCG was found to up-regulate these wnt ligands in mouse mammary gland, independent of the changes in ovarian steroidogenesis. Thus, the hCGbeta-overexpressing TG mice represent a novel model that links enhanced hCG action to dysregulated wnt signaling in the mammary gland, resulting in beta-catenin-stabilizing mammary tumorigenesis. The novel finding of hCG up-regulating wnt7b and wnt5b could contribute to pregnancy-induced breast cancer in humans.

Comparative analysis of gene sequence of goat CSN1S1 F and N alleles and characterization of CSN1S1 transcript variants in mammary gland

In this paper, we report the full characterization, at DNA and RNA level, of the defective goat CSN1S1 F and N alleles and an extensive comparison with the A allele counterpart. By utilizing genomic DNA as template, we amplified the whole CSN1S1 gene plus 1972/3 nucleotides of the 5' region plus 610 nucleotides of the 3' region of the goat CSN1S1 N and CSN1S1 F alleles. Comparison of sequences of the N, F and A CSN1S1 alleles showed a total of 118 polymorphic sites. In particular, both the N and the F alleles are characterized by a deletion of the cytosine at the 23rd nucleotide of the 9th exon. The resulting one-nucleotide frameshift determines a premature stop codon (TGA, nucleotides 17-19 of the 12th exon). On the basis of the information so far available, it seems reasonable to hypothesize that the CSN1S1 N allele might be originated by interallelic recombination events. Comparison of transcripts produced by the N and F alleles shows a remarkable variability in alternative splicing events which concern, even though with different percentage ratios, mainly the lack of the 9th exon, the deletion of the last 5 nucleotides of the 9th exon and the contemporary deletion of exons 10 and 11.

Human breast epithelial stem cells and their regulation

This review summarizes the current evidence for the existence of human breast stem cells and the pathways involved in their regulation, and discusses how the disruption of these pathways may result in the generation of a population of cells with the capacity for unlimited self-renewal. Relevant data from mouse model systems are also discussed where appropriate. By understanding the molecular pathways that regulate self-renewal of normal mammary stem cells, it may be possible to target the activation of these pathways in breast tumours.

Targeted activation of beta-catenin signaling in basal mammary epithelial cells affects mammary development and leads to hyperplasia

Wnt/beta-catenin signaling pathway is involved in the maintenance of the progenitor cell population in the skin, intestine and other tissues, and its aberrant activation caused by stabilization of beta-catenin contributes to tumorigenesis. In the mammary gland, constitutive activation of Wnt/beta-catenin signaling in luminal secretory cells results in precocious lobuloalveolar differentiation and induces adenocarcinomas, whereas the impact of this signaling pathway on the function of the second major mammary epithelial cell lineage, the basal myoepithelial cells, has not been analyzed. We have used the keratin (K) 5 promoter to target the expression of stabilized N-terminally truncated beta-catenin to the basal cell layer of mouse mammary epithelium. The transgenic mice presented an abnormal mammary phenotype: precocious lateral bud formation, increased proliferation and premature differentiation of luminal epithelium in pregnancy, persistent proliferation in lactation and accelerated involution. Precocious development in pregnancy was accompanied by increased Myc and cyclin D1 transcript levels, and a shift in p63 variant expression towards the DeltaNp63 form. The expression of ECM-degrading proteinases and their inhibitors was altered in pregnancy and involution. Nulliparous transgenic females developed mammary hyperplasia that comprised undifferentiated basal (K5/14-positive, K8- and alpha-smooth muscle-actin-negative) cells. Multiparous mice, in addition, developed invasive basal-type carcinomas. Thus, activation of beta-catenin signaling in basal mammary epithelial cells affects the entire process of mammary gland development and induces amplification of basal-type cells that lack lineage markers, presumably, a subpopulation of mammary progenitors able to give rise to tumors.

Characterization and expression of the human WNT4; lack of associated germline mutations in high--to moderate--risk breast and ovarian cancer

Wnt4 is needed for correct development of several tissues in the mouse, and WNT4 is found here to be expressed in a temporal manner in human embryonic tissues. In addition, WNT4 mRNA is seen in several adult tissues. The 1.5 kb transcript is dominant in adult tissues, whereas the 2.4 kb transcript is the major one in embryonic tissues. The involvement of WNT4 in normal mammary gland and ovary development suggests that WNT4 germline mutations may be associated with the human cancer predisposition. Their absence in cancer families, however, implies lack of involvement of WNT4 mutations in the etiology of hereditary susceptibility to breast and ovarian cancer. Finally, the chromosomal location of WNT4 is narrowed to 1p36.12.

Canonical Wnt signaling is critical to estrogen-mediated uterine growth

Major biological effects of estrogen in the uterus are thought to be primarily mediated by nuclear estrogen receptors, ERalpha and ERbeta. We show here that estrogen in an ER-independent manner rapidly up-regulates the expression of Wnt4 and Wnt5a of the Wnt family and frizzled-2 of the Wnt receptor family in the mouse uterus. One of the mechanisms by which Wnts mediate canonical signaling involves stabilization of intracellular beta-catenin. We observed that estrogen treatment prompts nuclear localization of active beta-catenin in the uterine epithelium. We also found that adenovirus mediated in vivo delivery of SFRP-2, a Wnt antagonist, down-regulates estrogen-dependent beta-catenin activity without affecting some of the early effects (water imbibition and angiogenic markers) and inhibits uterine epithelial cell growth, suggesting that canonical Wnt signaling is critical to estrogen-induced uterine growth. Our present results provide evidence for a novel role of estrogen that targets early Wnt/beta-catenin signaling in an ER-independent manner to regulate the late uterine growth response that is ER dependent.

Wnt7a Is a Suppressor of Cell Death in the Female Reproductive Tract and Is Required for Postnatal and Estrogen-Mediated Growth1

The murine female reproductive tract is undifferentiated at birth and undergoes pronounced growth and cytodifferentiation during postnatal life. Postnatal reproductive tract development proceeds in the absence of high levels of circulating estrogens and is disrupted by precocious exposure to estrogens. The WNT gene family is critical in guiding the epithelial-mesenchymal interactions that direct postnatal uterine development. We have previously described a role for Wnt7a in controlling morphogenesis in the uterus. In addition to patterning defects, Wnt7a mutant uteri are atrophic in adults and do not show robust postnatal growth. In the present study, we examine immature female Wnt7a mutant and wild-type uteri to assess the cellular processes that underlie this failure in postnatal uterine growth. Levels of proliferation are higher in wild-type versus Wnt7a mutant uteri. Exposure to the potent estrogen-agonist diethylstilbestrol (DES) leads to an increase in cell proliferation in the uterus in wild-type as well as in mutant uteri, indicating that Wnt7a is not required in mediating cell proliferation. In contrast, we observe that Wnt7a mutant uteri display high levels of cell death in response to DES, whereas wild-type uteri display almost no cell death, revealing that Wnt7a plays a key role as a cell death suppressor. The expression pattern of other key regulatory genes that guide uterine development, including estrogen receptor (alpha), Hox, and other WNT genes, reveals either abnormal spatial distribution of transcripts or abnormal regulation in response to DES exposure. Taken together, the results of the present study demonstrate that Wnt7a coordinates a variety of cell and developmental pathways that guide postnatal uterine growth and hormonal responses and that disruption of these pathways leads to aberrant cell death.

Wnt proteins in mammary development and cancer

Secreted proteins of the Wnt family play widespread roles in the regulation of embryonic development, and aberrant activation of the canonical Wnt/beta-catenin pathway is one of the most frequent signaling abnormalities known in human cancer. While the consequences of Wnt signaling in development are diverse at the cellular level, they are often concerned with cell fate determination. Recent data also indicate that Wnt proteins influence the self-renewal of stem cells in certain tissues. In the mammary gland, Wnt signals are strongly implicated in initial development of the mammary rudiments, and in the ductal branching and alveolar morphogenesis that occurs during pregnancy. Transgenic expression of Wnt1 or Wnt10b in the mouse mammary gland leads to lobuloalveolar hyperplasia with a major risk of progression to carcinoma. Recent evidence suggests that this phenotype is associated with expansion of a multipotent progenitor cell population. In human breast cancer, evidence of beta-catenin accumulation implies that the canonical Wnt signaling pathway is active in over 50% of carcinomas. However, specific mutations that might account for this activation of signaling have not yet been identified.

The Wnt signaling pathway in solid childhood tumors

The Wnt signaling pathway has long been known to direct growth and patterning during embryonic development. Recent evidence also implicates this pathway in the development of childhood tumors of the liver, the kidney, the brain, and the pancreas. Here, we review the current evidence on how constitutive activation of the Wnt signaling pathway may occur in hepato-, nephro-, medullo- and pancreatoblastomas. With particular emphasis the mutational activation of CTNNB1, an emerging major oncogene in solid childhood tumors, is discussed.

Amplification, up-regulation and over-expression of DVL-1, the human counterpart of the Drosophila disheveled gene, in primary breast cancers

Wnt proteins form a family of highly conserved, secreted signaling molecules that regulate cell-to-cell interactions during embryogenesis. Wnt genes and Wnt signaling are also implicated in cancer. It has been shown that Wnt proteins bind to receptors of the frizzled family on the cell surface. Through several cytoplasmic relay components including DVL-1, the human counterpart of the Drosophila disheveled gene, the signal is transduced to beta-catenin, which then enters the nucleus and forms a complex with T-cell factor (TCF) to activate transcription of Wnt target genes. We describe here the amplification of DVL-1 in 13 of 24 primary breast cancers examined, and increased expression of this gene in 11 of those tumors in comparison to corresponding non-cancerous breast tissues. Immunohistochemical staining demonstrated that DVL-1 protein was prominent in the cytoplasm of cancer cells, but not in normal epithelial cells of the mammary duct or in myoepithelial cells. These data indicate that amplification and increased expression of the DVL-1 gene may play some role in human breast carcinogenesis through derangement of the Wnt signaling pathway.

Wnt1 and Wnt5a induce cyclin D1 expression through ErbB1 transactivation in HC11 mammary epithelial cells

Constitutive expression of Wnt1 and Wnt5a in HC11 mammary cells led to elevated TCF transcriptional activity. Intriguingly, Wnt-expressing cells also displayed activation of ErbB1 and mitogen-activated protein kinase (MAPK), in contrast to control HC11 cells, which did not. Furthermore, conditioned media harvested from Wnt-expressing cells stimulated ErbB1 and the MAPK cascade when added to control cells. This process was rapid and could be blocked by an ErbB1 antibody that interferes with ligand binding and by matrix metalloproteinase (MMP) inhibitors. These results suggest that in mammary cells Wnt binding to its receptor, Frizzled (Fz), transactivates ErbB1, probably by MMP-mediated release of soluble ErbB1 ligands. Importantly, Wnt-transactivated ErbB1 was responsible for MAPK activation and the increased levels of cyclin D1 present in the Wnt-expressing HC11 cells. Our finding that Wnts transactivate ErbB1 in addition to stimulating the prototypic beta-catenin/TCF pathway may help to explain why wnt1 is a potent oncogene in the mammary gland.

Ligand-dependent inhibition of beta-catenin/TCF signaling by androgen receptor

Beta-catenin signaling may contribute to prostate cancer (CaP) progression. Although beta-catenin is known to upregulate T cell factor (TCF) target gene expression in CaP cells, recent evidence demonstrates its capacity to enhance ligand-dependent androgen receptor (AR) function. Thus, we wished to further understand the interaction between these two pathways. We find in both CaP cells (CWR22-Rv1, LAPC-4, DU145) and non-CaP cells (HEK-293, TSU, SW480, HCT-116) that beta-catenin/TCF-related transcription (CRT), as measured by activation of a synthetic promoter and that of cyclin D1, is inhibited by androgen treatment. This inhibition is AR-dependent, as it only occurs in cells expressing AR endogenously or transiently, and is abrogated by AR antagonists. Additional analyses convey that the ligand-dependent nature of CRT suppression depends on transactivation-competent AR in the nucleus, but not on indirect effects stemming from AR target gene expression. Given the recent work identifying an AR/beta-catenin interaction, and from our finding that liganded AR does not prompt gross changes in the constitutive nuclear localization of TCF4 or mutant beta-catenin, we hypothesized that transcription factor (i.e. AR and TCF) competition for beta-catenin recruitment may explain, in part, androgen-induced suppression of CRT. To address this idea, we expressed an AR mutant lacking its DNA-binding domain (DBD). This receptor could not orchestrate ligand-dependent CRT repression, thereby providing support for those recent data implicating the AR DBD/LBD as necessary for beta-catenin interaction. Further supporting this hypothesis, TCF/LEF over-expression counteracts androgen-induced suppression of CRT, and requires beta-catenin binding activity to do so. Interestingly, TCF4 over-expression potently antagonizes AR function; however, this inhibition may occur independently of beta-catenin/TCF4 interaction. These results from TCF4 over-expression analyses, taken together, provide further evidence that AR-mediated suppression of CRT is a consequence of limiting amounts of beta-catenin, and not AR target gene expression. Our analyses point to a reciprocal balance between AR and CRT function that may shape critical processes during normal prostate development and tumor progression.

Altered mammary epithelial development, pattern formation and involution in transgenic mice expressing the EphB4 receptor tyrosine kinase

We have previously documented the cell-type-specific and hormone-dependent expression of the EphB4 receptor in the mouse mammary gland. To investigate its role in the biology of the mammary gland, we have established transgenic mice bearing the EphB4 receptor under the control of the MMTV-LTR promoter, which represents the first transgenic mouse model to investigate the effect(s) of unscheduled expression of EphB4 in adult organisms. Transgene expression in the mammary epithelium was induced at puberty, increased during pregnancy, culminated at early lactation and persisted until day three of post-lactational involution. In contrast, expression of the endogenous EphB4 gene is downregulated during pregnancy, is essentially absent during lactation and is re-induced after day three of post-lactational involution. The unscheduled expression of EphB4 led to a delayed development of the mammary epithelium at puberty and during pregnancy. During pregnancy, less lobules were formed, these however exhibited more numerous but smaller alveolar units. Transgenic mammary glands were characterized by a fragile, irregular morphology at lactation; however, sufficient functionality was maintained to nourish the young. Transgenic mammary glands exhibited untimely epithelial apoptotic cell death during pregnancy and abnormal epithelial DNA synthesis at early post-lactational involution, indicating a disturbed response to proliferative/apoptotic signals. Mammary tumours were not observed in the EphB4 transgenic animals; however, in double transgenic animals expressing both EphB4 and the neuT genes, tumour appearance was significantly accelerated and, in contrast to neuT-only animals, metastases were observed in the lung. These results implicate EphB4 in the regulation of tissue architecture, cellular growth response and establishment of the invasive phenotype in the adult mammary gland.

Wnt-1 and int-2 mammary oncogene effects on the beta-catenin pathway in immortalized mouse mammary epithelial cells are not sufficient for tumorigenesis

Development of strategies for prevention of breast cancer development requires an understanding of the effects of mammary oncogenes on mammary cells at early stages in neoplastic transformation. As mammary oncogenes wnt-1 and int-2 affect different signal transduction pathways, we investigated their effects on established mouse mammary epithelial cell lines (MMECLs) reflecting early stages in tumorigenesis. Normal interactions between beta-catenin and E-cadherin were abrogated in all three immortalized MMECLs and the cells lacked beta-catenin-mediated transactivation activity, detectable using a reporter assay, suggesting that alterations in cell adhesion may be very early events in mammary tumorigenesis. Immortalized FSK4 and EL12 cells and hyperplastic TM3 cells were stably transfected with expression vectors encoding wnt-1 or int-2 or the control vector, and drug-selected pooled cells from each line were confirmed by reverse transcription-polymerase chain reaction to express the transfected oncogene; this expression persisted in the cells analysed in vitro and in vivo. Resultant phenotypic changes depended both on the oncogene and the target mammary cell line. In FSK4 cells, expression of wnt-1 or int-2 resulted in proliferative changes in vitro, including reduced contact inhibition, increased beta-catenin expression, and decreased p53 transcriptional activity, but neither oncogene conferred upon those cells the ability to produce tumors in vivo. EL12 cells were highly refractory to the effects of both oncogenes, with the only measurable changes being increased E-cadherin levels induced by both oncogenes and increased proliferation of the int-2-transfected cells in the absence of serum. Parental TM3 cells were phenotypically similar to wnt-1- or int-2-transfected FSK4 cells and displayed an increased rate of proliferation in vitro and markedly increased tumorigenicity in vivo following transfection with int-2 but not with wnt-1. These results suggest that wnt-1 signaling is redundant in the hyperplastic TM3 cells and indicate that wnt-1-induced effects in the immortalized FSK4 and EL12 cells were not sufficient to mediate a tumorigenic phenotype. This study showed that the wnt-1 and int-2 oncogenes have similar but distinguishable effects on immortalized MMECLs and that the genetic background of the mammary cells greatly influences the consequences of oncogene expression at early stages of cell transformation.