Transfection of the int-1 mammary oncogene in cuboidal RAC mammary cell line results in morphological transformation and tumorigenicity

S100A6 is a potential diagnostic and prognostic biomarker for human glioma

S100 calcium-binding protein A6 (S100A6) is a protein that belongs to the S100 family. The present study aimed to investigate the function of S100A6 in the diagnosis and survival prediction of glioma and elucidated the potential processes affecting glioma development. The Cancer Genome Atlas database was searched to identify the relationship among S100A6 expression, immune cell infiltration, clinicopathological parameters and glioma prognosis. Several clinical cases were used to verify these findings. S100A6 gene expression was high in glioma tissues, suggesting its diagnostic significance. In particular, S100A6 upregulation in glioma tissues exhibited a significant and positive correlation with the World Health Organization (WHO) grade, histological type, age, sex, primary treatment outcomes, 1p/19q codeletion, isocitrate dehydrogenase (IDH) status, overall survival (OS), progression-free interval and disease-specific survival. Kaplan-Meier and Cox regression analyses revealed that S100A6 gene expression can independently function as a risk factor affecting the prognosis of patients with glioma. Furthermore, Gene Ontology functional enrichment analysis revealed that S100A6 is implicated in immune responses and that the expression profiles of S100A6 are linked to the immune microenvironment. Furthermore, immunohistochemistry revealed that increased S100A6 protein levels are correlated with age, 1p/19q codeletion, IDH status, WHO grade and OS. The present findings suggest that increased S100A6 expression is an indicator of the dismal prognosis of patients with glioma and that it can be used as a potential diagnostic biomarker for this condition.

Prognostic and Predictive Biomarkers in the Era of Immunotherapy for Lung Cancer

The therapeutic algorithm of lung cancer has recently been revolutionized by the emergence of immune checkpoint inhibitors. However, an objective and durable response rate remains low with those recent therapies and some patients even experience severe adverse events. Prognostic and predictive biomarkers are therefore needed in order to select patients who will respond. Nowadays, the only validated biomarker is the PD-L1 expression, but its predictive value remains imperfect, and it does not offer any certainty of a sustained response to treatment. With recent progresses in molecular biology, genome sequencing techniques, and the understanding of the immune microenvironment of the tumor and its host, new molecular features have been highlighted. There are evidence in favor of the positive predictive value of the tumor mutational burden, as an example. From the expression of molecular interactions within tumor cells to biomarkers circulating in peripheral blood, many markers have been identified as associated with the response to immunotherapy. In this review, we would like to summarize the latest knowledge about predictive and prognostic biomarkers of immune checkpoint inhibitors efficacy in order to go further in the field of precision immuno-oncology.

Non-canonical WNT5A-ROR signaling: New perspectives on an ancient developmental pathway

Deciphering non-canonical WNT signaling has proven to be both fascinating and challenging. Discovered almost 30 years ago, non-canonical WNT ligands signal independently of the transcriptional co-activator β-catenin to regulate a wide range of morphogenetic processes during development. The molecular and cellular mechanisms that underlie non-canonical WNT function, however, remain nebulous. Recent results from various model systems have converged to define a core non-canonical WNT pathway consisting of the prototypic non-canonical WNT ligand, WNT5A, the receptor tyrosine kinase ROR, the seven transmembrane receptor Frizzled and the cytoplasmic scaffold protein Dishevelled. Importantly, mutations in each of these signaling components cause Robinow syndrome, a congenital disorder characterized by profound tissue morphogenetic abnormalities. Moreover, dysregulation of the pathway has also been linked to cancer metastasis. As new knowledge concerning the WNT5A-ROR pathway continues to grow, modeling these mutations will likely provide crucial insights into both the physiological regulation of the pathway and the etiology of WNT5A-ROR-driven diseases.

Wnt/β-Catenin Signaling and Resistance to Immune Checkpoint Inhibitors: From Non-Small-Cell Lung Cancer to Other Cancers

Lung cancer is the leading cause of cancer-related deaths worldwide. The standard of care for advanced non-small-cell lung cancer (NSCLC) without driver-gene mutations is a combination of an anti-PD-1/PD-L1 antibody and chemotherapy, or an anti-PD-1/PD-L1 antibody and an anti-CTLA-4 antibody with or without chemotherapy. Although there were fewer cases of disease progression in the early stages of combination treatment than with anti-PD-1/PD-L1 antibodies alone, only approximately half of the patients had a long-term response. Therefore, it is necessary to elucidate the mechanisms of resistance to immune checkpoint inhibitors. Recent reports of such mechanisms include reduced cancer-cell immunogenicity, loss of major histocompatibility complex, dysfunctional tumor-intrinsic interferon-γ signaling, and oncogenic signaling leading to immunoediting. Among these, the Wnt/β-catenin pathway is a notable potential mechanism of immune escape and resistance to immune checkpoint inhibitors. In this review, we will summarize findings on these resistance mechanisms in NSCLC and other cancers, focusing on Wnt/β-catenin signaling. First, we will review the molecular biology of Wnt/β-catenin signaling, then discuss how it can induce immunoediting and resistance to immune checkpoint inhibitors. We will also describe other various mechanisms of immune-checkpoint-inhibitor resistance. Finally, we will propose therapeutic approaches to overcome these mechanisms.

S100A6 Protein-Expression and Function in Norm and Pathology

S100A6, also known as calcyclin, is a calcium-binding protein belonging to the S100 protein family. It was first identified and purified more than 30 years ago. Initial structural studies, focused mostly on the mode and affinity of Ca²⁺ binding and resolution of the resultant conformational changes, were soon complemented by research on its expression, localization and identification of binding partners. With time, the use of biophysical methods helped to resolve the structure and versatility of S100A6 complexes with some of its ligands. Meanwhile, it became clear that S100A6 expression was altered in various pathological states and correlated with the stage/progression of many diseases, including cancers, indicative of its important, and possibly causative, role in some of these diseases. This, in turn, prompted researchers to look for the mechanism of S100A6 action and to identify the intermediary signaling pathways and effectors. After all these years, our knowledge on various aspects of S100A6 biology is robust but still incomplete. The list of S100A6 ligands is growing all the time, as is our understanding of the physiological importance of these interactions. The present review summarizes available data concerning S100A6 expression/localization, interaction with intracellular and extracellular targets, involvement in Ca²⁺-dependent cellular processes and association with various pathologies.

Tumor β-catenin expression is associated with immune evasion in non-small cell lung cancer with high tumor mutation burden

β-catenin expression by tumor cells suppressed dendritic cell recruitment to the tumor microenvironment in a melanoma model, resulting in fewer tumor-infiltrating lymphocytes. Immunohistochemistry was used in the present study to examine the association between the expression of β-catenin and tumor infiltrating lymphocytes and CD11c⁺ cells in 122 patients with non-small cell lung cancer (NSCLC), who underwent radical surgery. β-catenin was positive in 24% of NSCLC tumors compared with 59% of squamous cell carcinomas and 11% of adenocarcinomas. There was no significant association between the expression of β-catenin and the frequency of CD8⁺ cell infiltration into tumor tissues, including the stroma. Conversely, the infiltration of CD8⁺ cells into tumor nests was significantly lower in β-catenin-positive cases compared with that in negative β-catenin cases. Similarly, CD11c⁺ cell infiltration was significantly lower in the β-catenin-positive group. The β-catenin-positive group had shorter overall survival and recurrence-free survival times compared with that in the negative group. Furthermore, β-catenin-positive NSCLC had a high tumor mutation burden, but tended to have a low expression of programmed death-ligand 1. In conclusion, the expression of β-catenin in NSCLC was negatively associated with CD11c⁺ cells and cytotoxic T cell infiltration at the tumor site and had a tendency towards a poor prognosis.

Regulation of Wnt Signaling through Ubiquitination and Deubiquitination in Cancers

The Wnt signaling pathway plays important roles in embryonic development, homeostatic processes, cell differentiation, cell polarity, cell proliferation, and cell migration via the β-catenin binding of Wnt target genes. Dysregulation of Wnt signaling is associated with various diseases such as cancer, aging, Alzheimer’s disease, metabolic disease, and pigmentation disorders. Numerous studies entailing the Wnt signaling pathway have been conducted for various cancers. Diverse signaling factors mediate the up- or down-regulation of Wnt signaling through post-translational modifications (PTMs), and aberrant regulation is associated with several different malignancies in humans. Of the numerous PTMs involved, most Wnt signaling factors are regulated by ubiquitination and deubiquitination. Ubiquitination by E3 ligase attaches ubiquitins to target proteins and usually induces proteasomal degradation of Wnt signaling factors such as β-catenin, Axin, GSK3, and Dvl. Conversely, deubiquitination induced by the deubiquitinating enzymes (DUBs) detaches the ubiquitins and modulates the stability of signaling factors. In this review, we discuss the effects of ubiquitination and deubiquitination on the Wnt signaling pathway, and the inhibitors of DUBs that can be applied for cancer therapeutic strategies.

A Review of the Role of Wnt in Cancer Immunomodulation

Alterations in the Wnt signaling pathway are associated with the advancement of cancers; however, the exact mechanisms responsible remain largely unknown. It has recently been established that heightened intratumoral Wnt signaling correlates with tumor immunomodulation and immune suppression, which likely contribute to the decreased efficacy of multiple cancer therapeutics. Here, we review available literature pertaining to connections between Wnt pathway activation in the tumor microenvironment and local immunomodulation. We focus specifically on preclinical and clinical data supporting the hypothesis that strategies targeting Wnt signaling could act as adjuncts for cancer therapy, either in combination with chemotherapy or immunotherapy, in a variety of tumor types.

WNT Signaling in Cancer Immunosurveillance

Deregulated WNT signaling has been shown to favor malignant transformation, tumor progression, and resistance to conventional cancer therapy in a variety of preclinical and clinical settings. Accumulating evidence suggests that aberrant WNT signaling may also subvert cancer immunosurveillance, hence promoting immunoevasion and resistance to multiple immunotherapeutics, including immune checkpoint blockers. Here, we discuss the molecular and cellular mechanisms through which WNT signaling influences cancer immunosurveillance and present potential therapeutic avenues to harness currently available WNT modulators for cancer immunotherapy.

microRNA regulation of Wnt signaling pathways in development and disease

Wnt signaling pathways and microRNAs (miRNAs) are critical regulators of development. Aberrant Wnt signaling pathways and miRNA levels lead to developmental defects and diverse human pathologies including but not limited to cancer. Wnt signaling pathways regulate a plethora of cellular processes during embryonic development and maintain homeostasis of adult tissues. A majority of Wnt signaling components are regulated by miRNAs which are small noncoding RNAs that are expressed in both animals and plants. In animal cells, miRNAs fine tune gene expression by pairing primarily to the 3'untranslated region of protein coding mRNAs to repress target mRNA translation and/or induce target degradation. miRNA-mediated regulation of signaling transduction pathways is important in modulating dose-sensitive response of cells to signaling molecules. This review discusses components of the Wnt signaling pathways that are regulated by miRNAs in the context of development and diseases. A fundamental understanding of miRNA functions in Wnt signaling transduction pathways may yield new insight into crosstalks of regulatory mechanisms essential for development and disease pathophysiology leading to novel therapeutics.

Beta-catenin versus the other armadillo catenins: assessing our current view of canonical Wnt signaling

The prevailing view of canonical Wnt signaling emphasizes the role of beta-catenin acting downstream of Wnt activation to regulate transcriptional activity. However, emerging evidence indicates that other armadillo catenins in vertebrates, such as members of the p120 subfamily, convey parallel signals to the nucleus downstream of canonical Wnt pathway activation. Their study is thus needed to appreciate the networked mechanisms of canonical Wnt pathway transduction, especially as they may assist in generating the diversity of Wnt effects observed in development and disease. In this chapter, we outline evidence of direct canonical Wnt effects on p120 subfamily members in vertebrates and speculate upon these catenins' roles in conjunction with or aside from beta-catenin.

Three decades of Wnts: a personal perspective on how a scientific field developed

Wnt genes and components of Wnt signalling pathways have been implicated in a wide spectrum of important biological phenomena, ranging from early organismal development to cell behaviours to several diseases, especially cancers. Emergence of the field of Wnt signalling can be largely traced back to the discovery of the first mammalian Wnt gene in 1982. In this essay, we mark the thirtieth anniversary of that discovery by describing some of the critical scientific developments that led to the flowering of this field of research.

Striking the target in Wnt-y conditions: intervening in Wnt signaling during cancer progression

Wnt signaling can be divided into three pathways, namely the canonical Wnt/beta-catenin pathway, and the non-canonical (or heretical) Wnt/Ca(2+) and planar cell polarity (PCP) pathways. Although the canonical Wnt/beta-catenin pathway is the best described in cancer, increasing data points to the importance of the heretical Wnt pathways in several aspects of tumor progression. The recent advances in understanding the players and mechanisms by which these Wnt pathways contribute to cancer progression have led to the identification of numerous molecules that are already, or could be considered, targets for cancer therapy.

Transgenic mice and host cell mutants resistant to transformation as model systems for identifying multiple components in oncogenesis

Tumorigenesis appears to be a multistep process involving mutations of conventional, dominantly acting proto-oncogenes, mutations of other genes that may act in a recessive manner, and interactions (or a lack of interactions) between the products of mutant and wild-type genes. Our laboratory is using a few well-established, dominant oncogenes to pose experimental questions that could lead to a better understanding of the more elusive genetic interactions which occur during tumour development. Two such situations are described: (1) We have created a line of transgenic mice that carry the int-1 proto-oncogene under the control of the enhancer element in the mouse mammary tumour virus long terminal repeat. Such mice express the transgene in mammary glands, salivary glands and male reproductive tract; mammary glands from both male and female animals are grossly hyperplastic, yet tumours arise rarely in the males and sporadically in the females (80% of female mice have one or a few tumours by six months of age). Thus expression of int-1 in these mice appears to place a large number of mammary cells at risk for secondary events that lead to carcinogenesis, providing a provocative experimental context for identifying such secondary events. (2) We have isolated a rat cell line that lacks most of the characteristics of transformed cells, despite the expression of two wild-type copies of the v-src gene of Rous sarcoma virus. This line harbours what appears to be a dominant mutation in an unidentified gene that renders the cell resistant to transformation by v-src and several other oncogenes. Isolation of the mutant gene responsible for suppressing transformation in this line should provide new insights into the interactions between oncoproteins and other cellular proteins.

The int genes in mouse mammary tumorigenesis and in normal development

In mice, the mouse mammary tumour virus causes tumours by insertional activation of host cell oncogenes. By the application of transposon tagging techniques, several cellular oncogenes, called int, have been discovered. The int-1 gene encodes a cysteine-rich protein with a signal peptide, suggesting that it may act as an extracellular growth or differentiation factor. Normally, the int-1 gene is expressed in early embryogenesis of the mouse, in particular in the developing nervous system. The essential role of int-1 in embryogenesis is underscored by its high degree of homology with the Drosophila segment polarity gene wingless, a gene involved in pattern formation in segments of the developing fly. In Drosophila, the int-1/wingless gene appears to encode a secreted factor, as concluded from antibody staining experiments. The int-4 gene is not yet fully characterized at the molecular level. From its expression pattern, however, we have concluded that int-4 may also act in the control of embryogenesis: the gene is expressed only during specific time intervals in mouse embryos and it is highly conserved in evolution.

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.

FGFs, Wnts and BMPs mediate induction of VEGFR-2 (Quek-1) expression during avian somite development

Regulation of VEGFR-2 (Quek1) is an important mechanism during blood vessel formation. In the paraxial mesoderm, Quek1 expression is restricted to the lateral portion of the somite and later to sclerotomal cells surrounding the neural tube. By implanting FGF 8b/8c or SU 5402 beads into the paraxial mesoderm, we show that FGF8 in addition to BMP4 from the intermediate mesoderm (IM) is a positive regulator of VEGFR-2 (Quek1) expression in the quail embryo. The expression of Quek1 in the medial somite half is normally repressed by the notochord and Sfrps-expression in the neural tube. Over-expression of Wnt 1/3a also results in an up-regulation of Quek1 expression in the somites. We also show that up-regulation of FGF8/Wnt 1/3a leads to an increase in the number of endothelial cells, whereas inhibition of FGF and Wnt signaling by SU 5402 and Sfrp-2 results in a loss of endothelial cells. Our results demonstrate that the regulation of Quek1 expression in the somites is mediated by the cooperative actions of BMP4, FGF8 and Wnt-signaling pathways.

Cell polarity and epithelial oncogenesis

Pathologists have long recognized that tumour formation in epithelia leads to disruption of normal epithelial cell polarity. Despite this, few studies have taken advantage of new information on the biogenesis of cell polarity to analyse the process of epithelial oncogenesis. Recent studies of epithelial cell lines now indicate that the pattern of breakdown of polarity during oncogenesis may reflect the way in which normal epithelial cells achieve polarity. These results suggest not only a novel way to study the development of polarity in vitro, but also new ideas for the early detection of cancer.

Coactivation of Rac and Rho by Wnt/Frizzled signaling is required for vertebrate gastrulation

Wnt/Frizzled (Fz) signaling controls cell polarity/movements during vertebrate gastrulation via incompletely defined mechanisms. We demonstrated previously that Wnt/Fz activation of Rho, a GTPase and regulator of cytoskeletal architecture, is essential for vertebrate gastrulation. Here we report that in mammalian cells and Xenopus embryos, Wnt/Fz signaling coactivates Rho and Rac, another GTPase and distinct regulator of cytoskeletal architecture. Wnt/Fz activation of Rac is independent of Rho and mediates Wnt/Fz activation of Jun N-terminal kinase (JNK). Dishevelled (Dvl), a cytoplasmic protein downstream of Fz, forms a Wnt-induced complex with Rac independent of the Wnt-induced Dvl-Rho complex. Depletion or inhibition of Rac function perturbs Xenopus gastrulation without affecting Wnt/Fz activation of the Rho or beta-catenin pathway. We propose that parallel activation of Rac and Rho pathways by Wnt/Fz signaling is required for cell polarity and movements during vertebrate gastrulation.

Wnt/beta-catenin signaling suppresses apoptosis in low serum medium and induces morphologic change in rodent fibroblasts

Wnt/beta-catenin signaling plays important roles in tumorigenesis in certain tumors as well as during development. However, the mechanism of tumorigenesis mediated by this signaling remains to be elucidated. We investigated the response of rodent fibroblasts to activation of Wnt/beta-catenin signaling by treatment with conditioned medium containing soluble Wnt-3a protein (W3a-CM) and by expression of a constitutive active beta-catenin gene harbored by an adenovirus vector. W3a-CM induced transcriptional activation of a beta-catenin/T-cell factor (Tcf)-responsive promoter in rodent fibroblasts such as NIH3T3, Rat-1, Swiss3T3 and Balb3T3 cells. In these cells, an increase in saturation density and an inhibition of apoptosis and/or promotion of growth in low-serum medium were induced by treatment with W3a-CM. In Rat-1 cells, morphologic changes were also induced. All these alterations were reversible. Moreover, the inhibition of apoptosis of NIH3T3 cells in low-serum medium and the morphologic changes in Rat-1 cells, but not the increase in saturation density, were also induced by ectopic expression of a constitutive active beta-catenin gene. These results suggested that activation of Wnt/beta-catenin signaling induces inhibition of apoptosis and morphologic changes in these cells.

A possible role for the WNT-1 pathway in oral carcinogenesis

Reductions in cell-cell adhesion and stromal and vascular invasion are essential steps in the progression from localized malignancy to metastatic disease for all cancers. Proteins involved in intercellular adhesion, such as E-cadherin and catenin, probably play an important role in metastatic processes and cellular differentiation. While E-cadherin and beta-catenin expression has been extensively studied in many forms of human cancers, less is known about the role of the Wingless-Type-1 (WNT-1) pathway in human tumors. A large body of genetic and biochemical evidence has identified beta-catenin as a key downstream component of the WNT signaling pathway, and recent studies of colorectal tumors have shown a functional link among beta-catenin, adenomatous polyposis coli gene product (APC), and other components of the WNT-1 pathway. WNT-1 pathway signaling is thought to be mediated via interactions between beta-catenin and members of the LEF-1/TCF family of transcription factors. The WNT signal stabilizes beta-catenin protein and promotes its accumulation in the cytoplasm and nucleus. In the nucleus, beta-catenin associates with TCF to form a functional transcription factor which mediates the transactivation of target genes involved in the promotion of tumor progression, invasion, and metastasis, such as C-Myc, cyclin D1, c-jun, fra-1, and u-PAR. There is a strong correlation between the ability of the WNT-1 gene to induce beta-catenin accumulation and its transforming potential in vivo, suggesting that the WNT-1 gene activates an intracellular signaling pathway that can induce the morphological transformation of cells. For these reasons, data obtained from the study of the WNT-1 pathway could be important in our understanding of the mechanisms of epithelial tumors, in general, and probably also of oral squamous cell carcinoma, in particular.

Expression of an activated Notch4(int-3) oncoprotein disrupts morphogenesis and induces an invasive phenotype in mammary epithelial cells in vitro

The protein encoded by the Notch4 gene is a member of the Notch/lin-12 family of transmembrane receptor proteins, which have been shown to control cell fate determination and cell differentiation in a wide variety of organisms. Expression of Notch4(int-3), a truncated form of Notch4 having most of its extracellular domain deleted, as a transgene in mice induces the formation of poorly differentiated mammary carcinomas. To establish whether Notch4(int-3) has the capacity of subverting normal epithelial architecture, we assessed the effect of Notch4(int-3) expression on the in vitro morphogenetic properties of TAC-2 mammary epithelial cells. When grown in three-dimensional collagen gels in the presence of hydrocortisone, both wild-type and LacZ-transfected TAC-2 cells formed alveolar-like structures composed of polarized epithelial cells surrounding a central lumen. In contrast, TAC-2 cells programmed to express Notch4(int-3) formed compact cell aggregates devoid of tissue-specific organization. In addition, when grown on the surface of a collagen gel, Notch4(int-3)-expressing TAC-2 cells invaded the underlying matrix, whereas TAC-2 LacZ cells remained strictly confined to the gel surface. Expression of Notch4(int-3) in TAC-2 cells also disrupted contact-inhibition of cell proliferation, resulting in cell multilayering. Our results suggest that the ability of Notch4(int-3) to subvert normal epithelial morphogenesis and to promote invasion of the extracellular matrix contributes significantly to its tumorigenic potential.

Mechanism and function of signal transduction by the Wnt/beta-catenin and Wnt/Ca2+ pathways

Communication between cells is often mediated by secreted signaling molecules that bind cell surface receptors and modulate the activity of specific intracellular effectors. The Wnt family of secreted glycoproteins is one group of signaling molecules that has been shown to control a variety of developmental processes including cell fate specification, cell proliferation, cell polarity and cell migration. In addition, mis-regulation of Wnt signaling can cause developmental defects and is implicated in the genesis of several human cancers. The importance of Wnt signaling in development and in clinical pathologies is underscored by the large number of primary research papers examining various aspects of Wnt signaling that have been published in the past several years. In this review, we will present a synopsis of current research with particular attention paid to molecular mechanism of Wnt signal transduction and how the mis-regulation of Wnt signaling leads to cancer.

Transient overexpression of murine dishevelled genes results in apoptotic cell death

The Dishevelled (Dvl) gene family encodes cytoplasmic proteins that are implicated in Wnt signal transduction. In mammals, the manner in which Wnt signals are transduced remains unclear. The biochemical and molecular mechanisms defining the Wnt-1 pathway are of great interest because of its important role in development and its activation in murine breast tumors. In order to elucidate Dvl's role in Wnt signaling, we attempted to overexpress Dvl in cells, but were unable to obtain stable cell lines. We show here that the overexpression of Dvl genes alters nuclear and cellular morphology of COS-1 and C57MG cells and causes cell death due to the induction of apoptosis. Deletion studies demonstrate that all three conserved domains of Dvl (DIX, PDZ, and DEP) are required for Dvl-mediated cell death. Coexpression of protein phosphatase 2Calpha, a Dvl-interacting protein identified in yeast two-hybrid studies, protects cells from the cell death observed in cells overexpressing Dvl alone. Furthermore, the adenomatous polyposis coli (APC) gene product appears to be required for Dvl-mediated cell death. The relevance of these findings to Wnt signal transduction, as well as to developmental processes and disease, are discussed.

Antisense downregulation of a mouse mammary tumor virus activated protooncogene in mouse mammary tumor cells reverses the malignant phenotype

Activation of the protooncogene Wnt-1 by insertion of the mouse mammary tumor virus (MMTV) is known to cause mammary tumors in mice. Wnt-1 expression in mammary glands has been postulated to confer direct local growth stimulation of mammary epithelial cells leading to their acquisition of a preneoplastic state. Wnt-1 expression also induces morphological alterations in cultured normal mammary cells. However, it has not been determined whether or not transformed mammary cells require continuous Wnt-1 expression for their ability to form tumors in vivo. To address this question, we constructed antisense and sense Wnt-1 expression vectors containing a synthetic promoter composed of five high-affinity glucocorticoid response elements (GRE5). This promoter is at least 50-fold more inducible by dexamethasone than the promoter contained in the long terminal repeats of MMTV. The vectors were introduced into a mouse mammary tumor cell line (R/Sa-MT) that expresses high levels of endogenous Wnt-1 mRNA and forms rapidly growing tumors when transplanted into syngeneic hosts. Of the 12 stably transfected cell lines established (9 with antisense and 3 with sense constructs), 2 antisense cell lines (R/Sa-MT/antisense) and 1 sense cell line (R/Sa-MT/sense) were examined for inducibility by dexamethasone of antisense and sense Wnt-1 RNAs, changes in endogenous Wnt-1 RNA expression, and changes in cell morphology. The growth patterns of the cells in vitro and in vivo were also examined. Our results show that (1) the levels of the expression of endogenous Wnt-1 mRNA and protein were reduced significantly (>80%) in those cells (R/Sa-MT/antisense) that expressed antisense Wnt-1 RNA at high levels following exposure to dexamethasone, compared to the R/Sa-MT/sense and R/Sa-MT control cells and (2) transplantation of the R/Sa-MT/antisense cells produced smaller tumors ( approximately 0.2 cm in 16 weeks) compared to the tumors ( approximately 2.0 cm in 8 weeks) that were produced by the R/Sa-MT/sense and R/Sa-MT cells. We therefore suggest that Wnt-1 expression is required not only for the transformation of normal mammary cells into tumor cells, but also for the maintenance of their tumorigenicity.

Chimeric Wnt proteins define the amino-terminus of Wnt-1 as a transformation-specific determinant

Wnt-1 induces morphological transformation of C57MG mammary epithelial cells and accumulation of cytosolic beta-catenin whereas Wnt-5a has no effect. To identify regions within the 370 amino acid Wnt-1 protein required for these functions we tested eleven chimeric genes that contained variable amounts of Wnt-1 and Wnt-5a sequence. Transformation and beta-catenin regulation in C57MG cells is controlled by amino acids that lie within 186 residues of the amino terminus of Wnt-1. Small substitutions between residues 186 and 292 reduced Wnt-1 activity. Replacement of the carboxy terminal 79 amino acids of Wnt-1 by Wnt-5a did not affect function. These results were supported by transient expression assays in 293 cells wherein beta-catenin accumulated in the cytoplasm in response to ectopic Wnt-1 expression. In 293 cells, a larger region of the amino-terminus of Wnt-1 was found to be required for beta-catenin regulation. Nonfunctional chimeras that contained at least 99 amino terminal Wnt-1 residues inhibited Wnt-1 stimulation of 293 cells. One of these chimeras inhibited both Wnt-1 and Wnt-3 activity suggesting that Wnt-1 and Wnt-3 interact with a common signaling component.

Wnt signaling from the dorsal neural tube is required for the formation of the medial dermomyotome

Signals originating from tissues surrounding somites are involved in mediolateral and dorsoventral patterning of somites and in the differentiation of the myotome. Wnt-1 and Wnt-3a, which encode members of the Wnt family of cystein-rich secreted signaling molecules, are coexpressed at the dorsal midline of the developing neural tube, an area adjacent to the dorsomedial portion of the somite. Several lines of evidence indicate that Wnt-1 and Wnt-3a have the ability to induce the development of the medial and dorsal portion of somites, as well as to induce myogenesis. To address whether these Wnt signalings are really essential for the development of somites during normal embryogenesis, we investigated the development of somites in mouse embryos lacking both Wnt-1 and Wnt-3a. Here we demonstrate that the medial compartment of the dermomyotome is not formed and the expression of a lateral dermomyotome marker gene, Sim-1, is expanded more medially in the absence of these Wnt signalings. In addition, the expression of a myogenic gene, Myf-5, is decreased at 9.5 days post coitum whereas the level of expression of a number of myogenic genes in the later stage appeared normal. These results indicate that Wnt-1 and Wnt-3a signalings actually regulate the formation of the medial compartment of the dermomyotome and the early part of myogenesis.

Wnt signaling stabilizes the dual-function protein beta-catenin in diverse cell types

The Wnt proteins constitute a large family of secreted signaling factors that performed a wide variety of inductive and regulatory functions in embryonic and postnatal development. In mammals, these include crucial roles in morphogenesis of the central nervous system, kidneys, limbs, and mammary glands. In recent years, much progress has been made in identifying components of the intracellular Wnt-1 signal transduction pathway through studies in Drosophila, C. elegans, Xenopus, and mammalian systems. Several features of this pathway are remarkably well conserved in evolution. A key component of the Wnt pathway is the cytoplasmic protein beta-catenin, whose stability is increased as a result of Wnt signaling. Although morphological effects of Wnt-1 in cell culture are seen in only a limited number of cell lines, we show here that responsiveness to Wnt-1 at the biochemical level is a common property of both epithelial and mesenchymal cells. The increased abundance of beta-catenin may have at least two functional consequences, depending on the subcellular localization of the protein. In some cell lines that respond to Wnt-1, there is a significant increase in the beta-catenin fraction associated with the plasma membrane, where the protein acts as a component of cell-cell adhesive junctions. In other cell types, the major effect of Wnt signaling is an increase in the cytosolic pool of beta-catenin. Increased abundance of this pool has recently been correlated with entry of beta-catenin into the nucleus, where the protein forms complexes with Tcf transcription factors and is thought to modulate the expression of specific genes. The dual consequences of Wnt signaling on cell adhesion and/or gene expression provide at least two potential mechanisms by which this key pathway can function in the regulation of morphogenesis.

Wnt-1 induces growth, cytosolic beta-catenin, and Tcf/Lef transcriptional activation in Rat-1 fibroblasts

Genetic evidence suggests that regulation of beta-catenin and regulation of Tcf/Lef family transcription factors are downstream events of the Wnt signal transduction pathway. However, a direct link between Wnt activity and Tcf/Lef transcriptional activation has yet to be established. In this study, we show that Wnt-1 induces a growth response in a cultured mammalian cell line, Rat-1 fibroblasts. Wnt-1 induces serum-independent cellular proliferation of Rat-1 fibroblasts and changes in morphology. Rat-1 cells stably expressing Wnt-1 (Rat-1/Wnt-1) show a constitutive up-regulation of cytosolic beta-catenin, while membrane-associated beta-catenin remains unaffected. Induction of cytosolic beta-catenin in Rat-1/Wnt-1 cells is correlated with activation of a Tcf-responsive transcriptional element. We thus provide evidence that Wnt-1 induces Tcf/Lef transcriptional activation in a mammalian system. Expression of a mutant beta-catenin (beta-CatS37A) in Rat-1 cells does not result in a proliferative response or a detectable change in the cytosolic beta-catenin protein level. However, beta-CatS37A expression in Rat-1 cells results in strong Tcf/Lef transcriptional activation, comparable to that seen in Wnt-1-expressing cells. These results suggest that Wnt-1 induction of cytosolic beta-catenin may have functions in addition to Tcf/Lef transcriptional activation.

The effects of the neuN and neuT genes on differentiation and transformation of mammary epithelial cells

Overexpression of the proto-oncogene product, p185neuN, in a non-tumorigenic mammary epithelial line (31E) facilitates aspects of lactogenic differentiation. Formation of branching cords and induction of beta-casein synthesis by 31E cells normally require co-culture of these cells with fibroblasts, or the presence of collagen or fibronectin. In contrast, 31E cells expressing p185neuN spontaneously form branching cords when grown on tissue culture plastic and can synthesize beta-casein in the absence of exogenous substrates or feeder layers. Under these conditions, the cells deposit laminin and fibronectin, indicating a possible role for p185neuN in the deposition of extracellular matrix proteins. Overexpression of the corresponding oncogene product, p185neuT, has markedly different effects. Expression of p185neuT does not facilitate the formation of branching cords or the synthesis of beta-casein when grown on tissue culture plastic, although these cells do deposit laminin and fibronectin. Confocal microscopy indicates a significant difference in the distribution of laminin and fibronectin in 31E cells expressing p185neuT compared to those expressing p185neuN. The effects of p185neuN and p185neuT expression on cell transformation depend on cell type. Expression of both p185neuN and p185neuT increases anchorage-independent growth of 31E cells, but only p185neuT induces anchorage-independent growth of NIH 3T3 fibroblasts. This lineage specificity in the action of p185neuN may be related to observations that overexpression of p185c-erbB-2 (the human homologue of p185neuN) is only associated with the development of human epithelial cancers. The effects of p185neuN on laminin deposition by 31E cells may be relevant to the transforming ability of p185neuN, since laminin can induce anchorage-independent growth of mouse mammary cells. These results suggest that p185neuN and p185neuT could exert their effects on differentiation and transformation of mammary epithelial cells in part by promoting the deposition of extracellular matrix proteins.

Wnt-1-dependent regulation of local E-cadherin and alpha N-catenin expression in the embryonic mouse brain

E-cadherin is transiently expressed in local regions of the embryonic mouse brain, which include several patchy areas on the mesencephalon and diencephalon and their roof plate and part of cerebellar rudiments. In the present study, we compared this E-cadherin expression with that of Wnt-1, which occurs in specific zones in the embryonic brain, and found certain spatiotemporal relations between them: Wnt-1 expression tended to run parallel or overlap with peripheries of the E-cadherin-positive areas. For example, in the dorsal midline, Wnt-1 was expressed at the middle of the roof plate, while E-cadherin was absent in the middle zone but detected in two arrays of marginal roof plate cells. Furthermore, alpha N-catenin, a cadherin-associated protein, was found to occur at the roof plate of the mesencephalon and diencephalon, coinciding with Wnt-1 expression. The expression of these molecules was then studied in two alleles of the Wnt-1 mutation, Wnt-1sw and Wnt-1neo. In mice homozygous for these mutant genes, E-cadherin expression in the roof plate was up-regulated; the middle E-cadherin-negative zone disappeared. Moreover, E-cadherin expression in the roof plate began earlier in the mutant mice than in wild-type mice. On the contrary, alpha N-catenin expression in the dorsal midline was suppressed in these mutants. These changes in cadherin and catenin expression occurred at the level of mRNA expression. These results suggest that the Wnt-1 signal is, either directly or indirectly, involved in the regulation of expression of E-cadherin and alpha N-catenin in restricted regions of the embryonic brain. This mechanism may contribute to the patterning of the expression of these adhesion-related proteins in the embryonic brain.

Mutations in the segment polarity genes wingless and porcupine impair secretion of the wingless protein

We have characterized the molecular nature of mutations in wingless (wg), a segment polarity gene acting during various stages of Drosophila development. Embryo-lethal alleles have undergone mutations in the protein-encoding domain of the gene, including deletions and point mutations of conserved residues. In a temperature sensitive mutation, a conserved cysteine residue is replaced by a serine. In embryo-viable alleles, the wg transcriptional unit is not affected. Immunostaining of mutant embryos shows that the embryo-lethal alleles produce either no wg antigen or a form of the protein that is retained within cells. Interestingly, embryos mutant for the segment polarity gene porcupine show a similar retention of the wg antigen. We have also transfected wild type wg alleles into Drosophila tissue culture cells, which then display wg protein on the cell surface and in the extracellular matrix. In similar experiments with mutant alleles, the proteins are retained in intracellular compartments and appear not to be secreted. These data provide further evidence that wg acts as a secreted factor and suggest that porcupine provides an accessory function for wg protein secretion or transport.

The Wnt-1 proto-oncogene induces changes in morphology, gene expression, and growth factor responsiveness in PC12 cells

The product of the Wnt-1 proto-oncogene is a secreted glycoprotein that is normally produced in regions of the embryonic neural tube. We show here that expression of mouse Wnt-1 cDNA in the rat PC12 pheochromocytoma cell line causes a dramatic conversion from a round to a flat cell morphology. In addition, PC12 cells expressing Wnt-1 (PC12/Wnt-1) fail to extend neurites after treatment with NGF, despite the presence and activation of high affinity NGF receptors encoded by the trk gene and the induction of early response genes. Furthermore, PC12/Wnt-1 cells fail to express several neuron- and chromaffin-specific genes, indicating that PC12/Wnt-1 cells have assumed a new phenotype. Although NGF and FGF utilize similar signal transduction pathways in PC12 cells, only FGF is capable of inducing a morphological response and synthesis of transin mRNA in PC12/Wnt-1 cells.

Activity of Wnt-1 as a transmembrane protein

The product of the Wnt-1 proto-oncogene is a cysteine-rich glycoprotein that plays a crucial role in the development of the vertebrate central nervous system. Wnt-1 protein is secreted but remains associated with the cell surface and extracellular matrix. The function of Wnt-1 in several different biological settings can be carried out by cells that receive the Wnt signal from adjacent cells. Ectopic expression of Wnt-1 in certain mammary gland cell lines, such as C57MG, causes morphological transformation; C57MG cells can also be transformed by a paracrine mechanism when mixed with other cell types secreting Wnt-1 protein. To ask whether Wnt-1 protein can function while bound to the cell of origin, a variety of cell types were programmed to produce chimeric proteins containing the complete sequence of mature Wnt-1 protein fused to part or all of the transmembrane protein CD4 or CD8. The chimeras were found at the cell surface of transfected cells and did not appear to be proteolytically processed. In autocrine and paracrine transformation assays with C57MG cells and in an axis induction assay in Xenopus laevis embryos, the Wnt-1/CD4 or CD8 fusions retained significant activity, as did a secreted chimera containing the CD8 extracellular domain but lacking the transmembrane domain. However, a chimera lacking a spacer between the Wnt-1 and the transmembrane domains was weakly active and only in autocrine transformation. These results show that tethering Wnt-1 to the cell surface still allows Wnt-1-mediated cell-to-cell signaling.

Role of the gene on trisomic and pentasomic chromosome 13 in murine mammary tumorigenesis

To study a possible role(s) played by the trisomy and pentasomy of chromosome 13 in murine mammary tumors, we examined, in eight cloned established cell lines derived from a single BALB/c mammary tumor induced by MTV, a correlation between the presence of trisomy or pentasomy 13 and transformation parameters and in vivo tumorigenicity in syngeneic mice. We found that cell lines with a higher incidence of trisomy or pentasomy 13 in cells of diploid and tetraploid chromosome numbers, respectively, grew to a much higher cell density in flasks than did those with low incidence, and they formed tumors in syngeneic BALB/c mice, whereas those with a low incidence of trisomy or pentasomy 13 were poorly tumorigenic. The presence in the tumorigenic cells of trisomy or pentasomy 13 was not correlated with their growth in soft agar. Furthermore, other chromosomes manifested a wide range of copy numbers in the presence of trisomy or pentasomy 13, indicating that no chromosomes counteracted chromosome 13 to prevent the tumorigenicity. In light of the tumorigenic growth of the cells that maintain gene dosage of chromosome 13 at different ploidy levels, the possibility of the yeast G1 cyclin-like roles played by the gene(s) residing on chromosome 13 in murine mammary tumorigenesis is discussed.

Deleting valine-125 and cysteine-126 in glycoprotein gI of pseudorabies virus strain NIA-3 decreases plaque size and reduces virulence in mice

We investigated the function of antigenic domains on gI in virulence and immunogenicity. Three PRV gI mutants were constructed by deleting nucleotides coding for the following amino acids: valine-125 and cysteine-126, located in a discontinuous antigenic domain (M 303); glycine-59 and aspartic acid-60 located in a continuous antigenic domain (M304); and arginine-67 and alanine-68, located in a discontinuous antigenic domain (M305). Mismatch primers in the polymerase chain reaction were used to introduce the deletions. Anti-gI monoclonal antibodies were used in an immunoperoxidase monolayer assay to distinguish PRV gI mutants from wild-type PRV. The gI mutant viruses were tested for their growth in vitro and for their virulence in mice. The growth properties of PRV gI mutant virus M303 were comparable to the growth properties of a PRV gI-negative mutant (M301): both mutants produced small plaques in various cells, and when grown on swine kidney cells and chicken embryo fibroblasts, their growth was disadvantaged compared to wild-type PRV. However, in embryonal Balb/c mouse cells expressing gI, gI mutant viruses and wild-type PRV produced plaques of the same size, confirming that the mutations in gI are responsible for the small plaque phenotype. The growth properties of PRV gI mutant viruses M 304 and M 305 were comparable to the growth properties of wild-type PRV. When the mean time to death was used as the criterion, the gI mutant viruses M 301 and M 303 were significantly less virulent in mice than wild-type PRV. Four other, independently obtained, PRV mutants all carrying the valine-125 and cysteine-126 deletion (M 308, M 309, M 310 and M 311 respectively) exhibit the same phenotype. Our results show that deleting valine-125 and cysteine-126 in gI decreases plaque size and reduces virulence in mice to the same degree as deleting the gI protein.

Activated oncogenes and putative tumor suppressor genes involved in human breast cancers

Cytogeneticists first proposed that the karyotypic abnormalities identified on chromosomes 1, 3, 6, 11, 13, 16, 17, and 18 supported a genetic basis for breast cancer. Such abnormal banding patterns, however, may represent either loss-of-function or gain-of-function molecular events. RFLP analyses have since confirmed that 20-60% of primary and spontaneous human breast tumors exhibit allelic losses on these same chromosomes, although the exact genes involved at these chromosomal sites remain largely unknown. Knowledge gained about the Rb-1 and p53 tumor suppressor genes at 13q14 and 17p13 in breast and other human tumors supports the paradigm that for any chromosomal locus, allelic loss associated with a mutation in the remaining tumor allele signifies an involved tumor suppressor gene. Given this paradigm, there are nearly a dozen putative breast tumor suppressor genes under active investigation, with most investigators now focusing on various chromosome 17 loci. Among the known proto-oncogenes found activated in breast cancer, amplification of c-erbB-2 at 17q21 is the most widely studied and clinically significant gain-of-function event uncovered to date, occurring in about 20% of all primary breast tumors. The involvement of this overexpressed membrane receptor has engendered interest in related tyrosine kinase receptors, such as EGFR, IR, and IGF-I-R, as well as their respective ligands, which may be overexpressed in a greater fraction of tumors, contributing to the autocrine and paracrine regulation of breast cancer growth and metastasis. New attention is being given to the potentially oncogenic function of structurally altered nuclear transactivating steroid hormone receptors, such as ER, whose overexpression has long been used to determine endocrine therapy and prognosis for individual breast cancer patients. While c-myc was one of the first known proto-oncogenes to be found amplified and overexpressed in human breast cancers, the actual incidence and clinical significance of its activation remain disputed and in need of further study. Lastly, we can expect greater clarification about the importance of various 11q13 genes found coamplified in nearly 20% of primary breast cancers, and pursuit into the intriguing possibility that a cyclin-encoding gene represents the overexpressed locus of real interest in this amplicon. Virtually all of these important genetic abnormalities identified thus far are associated with but not restricted to human breast cancers. The absence of identifiable molecular defects relating to the tissue specificity of this malignancy must be considered a substantial gap in our basic understanding of breast carcinogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

The Wnt gene family in tumorigenesis and in normal development

Various members of the Wnt gene family have been identified as activated oncogenes in mouse mammary tumors. We show that some tumors are oligoclonal for activation of a Wnt gene, and clonal variation when those tumors are transplanted to become hormone-independent. The normal function of many Wnt genes is to control pattern formation in early embryos, as shown by expression profiles and by mutant analysis.

Isolation of cDNAs partially encoding four Xenopus Wnt-1/int-1-related proteins and characterization of their transient expression during embryonic development

To begin to study the functions of the Wnt-1/int-1 gene family during vertebrate development, we have isolated four Xenopus laevis cDNAs encoding the partial sequence of proteins homologous to Wnt-1/int-1. Xwnt-3, Xwnt-4, Xwnt-5A, and Xwnt-8 demonstrate between 35 and 50% amino acid identity with X. laevis Wnt-1/int-1 and most cysteine residues are conserved. Xwnt-4 and Xwnt-3 transcripts are detected only during the neurula through tadpole stages of development. Expression of Xwnt-8 is observable during gastrulation, declines during neurulation, and is undetectable by the tadpole stage of development. Xwnt-5A transcripts are most prevalent in RNA from oocytes and tadpoles, although low level expression is detected at all stages examined. The temporal changes in expression of these transcripts imply a unique role for each Xwnt during embryogenesis.

The proto-oncogene int-1 encodes a secreted protein associated with the extracellular matrix

The proto-oncogene int-1 plays an important role in mammary tumorigenesis when activated by proviral insertions of the mouse mammary tumor virus. In normal mouse tissues the gene is expressed in the embryonic neural tube, suggesting a developmental function, while in Drosophila the homolog of int-1 is the segment polarity gene wingless. In order to study the protein products of int-1 we have derived fibroblast cell lines infected with multiple copies of a retroviral vector expressing int-1 cDNA. By Western blot analysis and immunoprecipitation we have identified a 44 kd form of int-1 protein which is secreted from these cells. The 44 kd species is distinct from the major intracellular forms of int-1 protein as judged by its slower mobility in SDS-polyacrylamide gels and by its longer half-life in pulse-chase experiments. Under normal growth conditions, little or none of the 44 kd protein is detectable in the cell culture medium but instead the majority is found associated with the extracellular matrix (ECM). The protein appears to bind heparin in vitro, suggesting that it might bind glycosaminoglycans in the ECM. These data support the view that int-1 protein may play a role in cell-cell communication over short distances.