Cripto-1 enhances migration and branching morphogenesis of mouse mammary epithelial cells

Pathological and Therapeutic Significance of Tumor-Derived Extracellular Vesicles in Cancer Cell Migration and Metastasis

The infiltration of primary tumors and metastasis formation at distant sites strongly impact the prognosis and the quality of life of cancer patients. Current therapies including surgery, radiotherapy, and chemotherapy are limited in targeting the complex cell migration mechanisms responsible for cancer cell invasiveness and metastasis. A better understanding of these mechanisms and the development of new therapies are urgently needed. Extracellular vesicles (EVs) are lipid-enveloped particles involved in inter-tissue and inter-cell communication. This review article focuses on the impact of EVs released by tumor cells, specifically on cancer cell migration and metastasis. We first introduce cell migration processes and EV subtypes, and we give an overview of how tumor-derived EVs (TDEVs) may impact cancer cell migration. Then, we discuss ongoing EV-based cancer therapeutic approaches, including the inhibition of general EV-related mechanisms as well as the use of EVs for anti-cancer drug delivery, focusing on the harnessing of TDEVs. We propose a protein-EV shuttle as a route alternative to secretion or cell membrane binding, influencing downstream signaling and the final effect on target cells, with strong implications in tumorigenesis. Finally, we highlight the pitfalls and limitations of therapeutic EV exploitation that must be overcome to realize the promise of EVs for cancer therapy.

A Novel Localization in Human Large Extracellular Vesicles for the EGF-CFC Founder Member CRIPTO and Its Biological and Therapeutic Implications

Tumor growth and metastasis strongly rely on cell–cell communication. One of the mechanisms by which tumor cells communicate involves the release and uptake of lipid membrane encapsulated particles full of bioactive molecules, called extracellular vesicles (EVs). EV exchange between cancer cells may induce phenotype changes in the recipient cells. Our work investigated the effect of EVs released by teratocarcinoma cells on glioblastoma (GBM) cells. EVs were isolated by differential centrifugation and analyzed through Western blot, nanoparticle tracking analysis, and electron microscopy. The effect of large EVs on GBM cells was tested through cell migration, proliferation, and drug-sensitivity assays, and resulted in a specific impairment in cell migration with no effects on proliferation and drug-sensitivity. Noticeably, we found the presence of the EGF-CFC founder member CRIPTO on both small and large EVs, in the latter case implicated in the EV-mediated negative regulation of GBM cell migration. Our data let us propose a novel route and function for CRIPTO during tumorigenesis, highlighting a complex scenario regulating its effect, and paving the way to novel strategies to control cell migration, to ultimately improve the prognosis and quality of life of GBM patients.

Whence CRIPTO: The Reemergence of an Oncofetal Factor in 'Wounds' That Fail to Heal

There exists a set of factors termed oncofetal proteins that play key roles in ontogeny before they decline or disappear as the organism's tissues achieve homeostasis, only to then re-emerge in cancer. Although the unique therapeutic potential presented by such factors has been recognized for more than a century, their clinical utility has yet to be fully realized1. This review highlights the small signaling protein CRIPTO encoded by the tumor derived growth factor 1 (TDGF1/Tdgf1) gene, an oft cited oncofetal protein whose presence in the cancer literature as a tumor promoter, diagnostic marker and viable therapeutic target continues to grow. We touch lightly on features well established and well-reviewed since its discovery more than 30 years ago, including CRIPTO's early developmental roles and modulation of SMAD2/3 activation by a selected set of transforming growth factor β (TGF-β) family ligands. We predominantly focus instead on more recent and less well understood additions to the CRIPTO signaling repertoire, on its potential upstream regulators and on new conceptual ground for understanding its mode of action in the multicellular and often stressful contexts of neoplastic transformation and progression. We ask whence it re-emerges in cancer and where it 'hides' between the time of its fetal activity and its oncogenic reemergence. In this regard, we examine CRIPTO's restriction to rare cells in the adult, its potential for paracrine crosstalk, and its emerging role in inflammation and tissue regeneration-roles it may reprise in tumorigenesis, acting on subsets of tumor cells to foster cancer initiation and progression. We also consider critical gaps in knowledge and resources that stand between the recent, exciting momentum in the CRIPTO field and highly actionable CRIPTO manipulation for cancer therapy and beyond.

Cripto-1 as a Key Factor in Tumor Progression, Epithelial to Mesenchymal Transition and Cancer Stem Cells

Cripto-1 is an essential protein for human development that plays a key role in the early phase of gastrulation in the differentiation of an embryo as well as assists with wound healing processes. Importantly, Cripto-1 induces epithelial to mesenchymal transition to turn fixed epithelial cells into a more mobile mesenchymal phenotype through the downregulation of epithelial adhesion molecules such as E-cadherin, occludins, and claudins, and the upregulation of mesenchymal, mobile proteins, such as N-cadherin, Snail, and Slug. Consequently, Cripto-1’s role in inducing EMT to promote cell motility is beneficial in embryogenesis, but detrimental in the formation, progression and metastasis of malignant tumors. Indeed, Cripto-1 is found to be upregulated in most cancers, such as breast, lung, gastrointestinal, hepatic, renal, cervical, ovarian, prostate, and skin cancers. Through its role in EMT, Cripto-1 can remodel cancer cells to enable them to travel through the extracellular matrix as well as blood and lymphatic vessels to metastasize to different organs. Additionally, Cripto-1 promotes the survival of cancer stem cells, which can lead to relapse in cancer patients.

CRIPTO antagonist ALK4L75A-Fc inhibits breast cancer cell plasticity and adaptation to stress

BACKGROUND

CRIPTO is a multi-functional signaling protein that promotes stemness and oncogenesis. We previously developed a CRIPTO antagonist, ALK4L75A-Fc, and showed that it causes loss of the stem cell phenotype in normal mammary epithelia suggesting it may similarly inhibit CRIPTO-dependent plasticity in breast cancer cells.

METHODS

We focused on two triple negative breast cancer cell lines (MDA-MB-231 and MDA-MB-468) to measure the effects of ALK4L75A-Fc on cancer cell behavior under nutrient deprivation and endoplasmic reticulum stress. We characterized the proliferation and migration of these cells in vitro using time-lapse microscopy and characterized stress-dependent changes in the levels and distribution of CRIPTO signaling mediators and cancer stem cell markers. We also assessed the effects of ALK4L75A-Fc on proliferation, EMT, and stem cell markers in vivo as well as on tumor growth and metastasis using inducible lentiviral delivery or systemic administration of purified ALK4L75A-Fc, which represents a candidate therapeutic approach.

RESULTS

ALK4L75A-Fc inhibited adaptive responses of breast cancer cells under conditions of nutrient and ER stress and reduced their proliferation, migration, clonogenicity, and expression of EMT and cancer stem cell markers. ALK4L75A-Fc also inhibited proliferation of human breast cancer cells in stressed tumor microenvironments in xenografts and reduced both primary tumor size and metastatic burden.

CONCLUSIONS

Cancer cell adaptation to stresses such as nutrient deprivation, hypoxia, and chemotherapy can critically contribute to dormancy, metastasis, therapy resistance, and recurrence. Identifying mechanisms that govern cellular adaptation, plasticity, and the emergence of stem-like cancer cells may be key to effective anticancer therapies. Results presented here indicate that targeting CRIPTO with ALK4L75A-Fc may have potential as such a therapy since it inhibits breast cancer cell adaptation to microenvironmental challenges and associated stem-like and EMT phenotypes.

Targeting Nodal and Cripto-1: Perspectives Inside Dual Potential Theranostic Cancer Biomarkers

BACKGROUND

Elucidating the mechanisms of recurrence of embryonic signaling pathways in tumorigenesis has led to the discovery of onco-fetal players which have physiological roles during normal development but result aberrantly re-activated in tumors. In this context, Nodal and Cripto-1 are recognized as onco-developmental factors, which are absent in normal tissues but are overexpressed in several solid tumors where they can serve as theranostic agents.

OBJECTIVE

To collect, review and discuss the most relevant papers related to the involvement of Nodal and Cripto-1 in the development, progression, recurrence and metastasis of several tumors where they are over-expressed, with a particular attention to their occurrence on the surface of the corresponding sub-populations of cancer stem cells (CSC).

RESULTS

We have gathered, rationalized and discussed the most interesting findings extracted from some 370 papers related to the involvement of Cripto-1 and Nodal in all tumor types where they have been detected. Data demonstrate the clear connection between Nodal and Cripto-1 presence and their multiple oncogenic activities across different tumors. We have also reviewed and highlighted the potential of targeting Nodal, Cripto-1 and the complexes that they form on the surface of tumor cells, especially of CSC, as an innovative approach to detect and suppress tumors with molecules that block one or more mechanisms that they regulate.

CONCLUSION

Overall, Nodal and Cripto-1 represent two innovative and effective biomarkers for developing potential theranostic anti-tumor agents that target normal as well as CSC subpopulations and overcome both pharmacological resistance and tumor relapse.

Overexpression levels of cripto-1 predict poor prognosis in patients with prostate cancer following radical prostatectomy

Overexpression of cripto-1 (CR-1), an epidermal growth factor-cripto-1/FRL-1/Cryptic family protein, has been reported in multiple types of malignancy. However, the clinical functions of CR-1 in prostate cancer (PCa) remain largely unclear. The objective of the present study was to investigate the association between CR-1 expression and the clinicopathological features and prognosis of PCa. CR-1 expression was evaluated in 138 PCa tissues and 67 benign prostate hyperplasia (BPH) tissues using immunohistochemistry. The association between the clinicopathological features of patients with PCa and CR-1 expression was analyzed using a χ² test. Receiver operating characteristic (ROC) curve and Cox regression model were used to analyze the association between CR-1 expression and biochemical recurrence (BCR)-free survival. It was revealed that the protein expression of CR-1 was markedly higher in PCa tissues than in BPH tissues. The mRNA expression of CR-1 in PCa tissue and cells was also significantly higher than in BPH tissue and the normal RWPE-1 prostate cell line (P<0.05). In addition, high CR-1 expression was significantly associated with prostate-specific antigen level (P=0.008), Gleason score (P=0.011) and lymph node metastasis (P=0.025) in patients with PCa. ROC curve indicated that patients with elevated expression of CR-1 exhibited shorter BCR-free survival (P<0.001). Furthermore, multivariate statistical analysis demonstrated that overexpression of CR-1 may be a novel predictor for prognosis of patients with PCa. Accordingly, the present study considered CR-1 to be a valuable predictor of poor prognosis and progression in PCa, and a potential therapeutic target for patients with PCa.

Development of conformational antibodies targeting Cripto-1 with neutralizing effects in vitro

Human Cripto-1 (Cripto-1), the founding member of the EGF-CFC superfamily, is a key regulator of many processes during embryonic development and oncogenesis. Cripto-1 is barely present or even absent in normal adult tissues while it is aberrantly re-expressed in various tumors. Blockade of the CFC domain-mediated Cripto-1 functions is acknowledged as a promising therapeutic intervention point to inhibit the tumorigenic activity of the protein. In this work, we report the generation and characterization of murine monoclonal antibodies raised against the synthetic folded CFC [112-150] domain of the human protein. Through subtractive ELISA assays clones were screened for the ability to specifically recognize "hot spot" residues on the CFC domain, which are crucial for the interaction with Activin Type I receptor (ALK4) and GRP78. On selected antibodies, SPR and epitope mapping studies have confirmed their specificity and have revealed that recognition occurs only on a conformational epitope. Furthermore, FACS analyses have confirmed the ability of 1B4 antibody to recognize the membrane-anchored and soluble native Cripto-1 protein in a panel of human cancer cells. Finally, we have evaluated its functional effects through in vitro cellular signaling assays and cell cycle analysis. These findings suggest that the selected anti-CFC mAbs have the potential to neutralize the protein oncogenic activity and may be used as theranostic molecules suitable as tumor homing agents for Cripto-1-overexpressing cancer cells and tissues and to overcome drug-resistance in routine cancer therapies.

Cripto-1 Plasmid DNA Vaccination Targets Metastasis and Cancer Stem Cells in Murine Mammary Carcinoma

Metastatic breast cancer is a fatal disease that responds poorly to treatment. Cancer vaccines targeting antigens expressed by metastatic breast cancer cells and cancer stem cells could function as anticancer therapies. Cripto-1 is an oncofetal protein overexpressed in invasive breast cancer and cancer-initiating cells. In this study, we explored the potential of a Cripto-1-encoding DNA vaccine to target breast cancer in preclinical mouse models. BALB/c mice and BALB-neuT mice were treated with a DNA vaccine encoding mouse Cripto-1 (mCr-1). BALB/c mice were challenged with murine breast cancer 4T1 cells or TUBO spheres; BALB-neuT mice spontaneously developed breast cancer. Tumor growth was followed in all mouse models and lung metastases were evaluated. In vitro assays were performed to identify the immune response elicited by vaccination. Vaccination against mCr-1 reduced primary tumor growth in the 4T1 metastatic breast cancer model and reduced lung metastatic burden. In BALB-neuT mice, because the primary tumors are Cripto-1 negative, vaccination against mCr-1 did not affect primary tumors but did reduce lung metastatic burden. Spheroid-cultured TUBO cells, derived from a BALB/neuT primary tumor, develop a cancer stem cell-like phenotype and express mCr-1. We observed reduced tumor growth in vaccinated mice after challenge with TUBO spheres. Our data indicate that vaccination against Cripto-1 results in a protective immune response against mCr-1 expressing and metastasizing cells. Targeting Cripto-1 by vaccination holds promise as an immunotherapy for treatment of metastatic breast cancer. Cancer Immunol Res; 6(11); 1417-25. ©2018 AACR.

Cripto-1 promotes epithelial-mesenchymal transition in prostate cancer via Wnt/β-catenin signaling

The Cripto-1 (CR-1) derived EGF-CFC family was overexpressed in tumor development enhancing proliferation, epithelial-mesenchymal transition (EMT) and migration of tumor cells. However, correlation between CR-1 and prostate cancer (PCa) remains still unclear. In the present study, we proved that CR-1 was expressed in PCa and its function was in the progression of PCa. Compared with benign prostatic hyperplasia (BPH) tissues, we confirmed that PCa tissues had high expression of CR-1 by immunohistochemistry and statistical data showed that CR-1 promoted properties of EMT in PCa tissues, including the downregulation of the cell adhesion molecules β-catenin (membrane) and E-cadherin while upregulating transcription factors β-catenin. Overexpression of CR-1 had close relationship with PSA, Gleason, clinical staging and lymph node metastasis in PCa patients. Then, we found that PC-3 cells transfected with CR-1-shRNA inhibited EMT using RT-PCR, RT-qPCR, western blotting and immunofluorescence. Also, we evaluated cell invasive ability in vitro by transwell and wound-healing assay. Our data showed that transfected CR-1-shRNA altered EMT including β-catenin, E-cadherin, c-myc, GSK-3, p-GSK and Wnt/β-catenin pathway in PC-3. It also suppressed PC-3 cell migration. Additionally, our results displayed that Licl had antitumor activity against PC-3 through the inhibition of Wnt/β-catenin pathway. Inhibition of cell viability was dose-time dependent. The present study proved that CR-1 regulates EMT of PCa by Wnt/β-catenin pathway. Hence, CR-1 may provide a new biological marker, and possibly contributes to clinical treatment against PCa.

Clinical significance of cripto-1 expression in lung adenocarcinoma

Cripto-1 can promote tumourigenesis and may be a potential prognostic biomarker in several malignancies, yet little is known about this protein in lung adenocarcinoma (LAC). The aim of this study was to evaluate the prognostic value of cripto-1 expression in a cohort of patients with LAC. Tumours from 290 patients with pathologically confirmed LAC were used for an immunohistochemical analysis of cripto-1 expression. The correlation between cripto-1 expression and the clinicopathological parameters of patients, EGFR-TKI sensitivity was analysed. Significant associations between cripto-1 expression and pT status, pN status, pTNM status, E-cadherin expression and EGFR-TKI sensitivity were identified. Compared with patients with low cripto-1 expression, patients with high cripto-1 expression exhibited significantly poorer progression-free survival (PFS) and overall survival (OS). Moreover, multivariate analyses showed that high cripto-1 expression was an independent predictor of worse survival of patients with LAC. The combination of cripto-1 expression and serum CEA level was correlated with both PFS and OS. In conclusion, cripto-1 may be a potential prognostic biomarker of survival in patients with LAC.

CRIPTO overexpression promotes mesenchymal differentiation in prostate carcinoma cells through parallel regulation of AKT and FGFR activities

Members of the EGF-CFC (Cripto, FRL-1, Cryptic) protein family are increasingly recognized as key mediators of cell movement and cell differentiation during vertebrate embryogenesis. The founding member of this protein family, CRIPTO, is overexpressed in various human carcinomas. Yet, the biological role of CRIPTO in this setting remains unclear. Here, we find CRIPTO expression as especially high in a subgroup of primary prostate carcinomas with poorer outcome, wherein resides cancer cell clones with mesenchymal traits. Experimental studies in PCa models showed that one notable function of CRIPTO expression in prostate carcinoma cells may be to augment PI3K/AKT and FGFR1 signaling, which promotes epithelial-mesenchymal transition and sustains a mesenchymal state. In the observed signaling events, FGFR1 appears to function parallel to AKT, and the two pathways act cooperatively to enhance migratory, invasive and transformation properties specifically in the CRIPTO overexpressing cells. Collectively, these findings suggest a novel molecular network, involving CRIPTO, AKT, and FGFR signaling, in favor of the emergence of mesenchymal-like cancer cells during the development of aggressive prostate tumors.

Serum Cripto-1 is a novel biomarker for non-small cell lung cancer diagnosis and prognosis

INTRODUCTION

Cripto-1 (CR-1) is highly expressed in several different types of human tumors. However, the clinical significance of CR-1 expression in serum specimens from non-small cell lung cancer (NSCLC) patients has not yet been determined.

OBJECTIVES

The aim of this study was to explore the diagnostic and prognostic value of serum CR-1 levels in patients with NSCLC.

METHODS

Serum specimens from 592 NSCLC patients, 180 benign lung disease patients and 240 healthy controls were collected. The concentrations of CR-1 were measured by sandwich enzyme-linked immunosorbent assay.

RESULTS

Patients with NSCLC had higher serum CR-1 levels than the controls (P < 0.01) and patients with benign lung diseases (P < 0.01). When a cutoff point of 1.8 ng/mL was selected (diagnostic specificity 95%), the diagnostic sensitivity for NSCLC is 56.8%. About 37.5% of carcinoembryonic antigen (CEA)-negative lung cancer patients were CR-1 positive at 95% specificity. In patients with stage I/II lung cancer, use of these two markers in combination results in almost 21% increase in sensitivity, at 95% specificity, compared with CEA alone. Uni-variate analysis revealed that NSCLC patients with positive CR-1 had a shorter overall survival (OS) and progression-free survival (PFS) than those with negative CR-1 [hazard ratio (HR) of 2.93, P = 0.005; HR of 2.12, P = 0.005]. Cox multi-variate analysis indicated that CR-1 was an independent prognostic indicator of PFS and OS (HR of 1.91, P = 0.006; HR of 1.82, P = 0.007). Kaplan-Meier survival curves further confirmed that patients with negative CR-1 had longer PFS and OS (P = 0.026 and P = 0.011, respectively).

CONCLUSIONS

In conclusion, measurement of serum CR-1 is a useful diagnostic and prognostic marker for NSCLC patients.

Cripto-1 vaccination elicits protective immunity against metastatic melanoma

Metastatic melanoma is a fatal disease that responds poorly to classical treatments but can be targeted by T cell-based immunotherapy. Cancer vaccines have the potential to generate long-lasting cytotoxic CD8⁺ T cell responses able to eradicate established and disseminated tumors. Vaccination against antigens expressed by tumor cells with enhanced metastatic potential represents a highly attractive strategy to efficiently target deadly metastatic disease. Cripto-1 is frequently over-expressed in human carcinomas and melanomas, but is expressed only at low levels on normal differentiated tissues. Cripto-1 is particularly upregulated in cancer-initiating cells and is involved in cellular processes such as cell migration, invasion and epithelial–mesenchymal transition, which are hallmarks of aggressive cancer cells able to initiate metastatic disease. Here, we explored the potential of Cripto-1 vaccination to target metastatic melanoma in a preclinical model. Cripto-1 was overexpressed in highly metastatic B16F10 cells as compared to poorly metastatic B16F1 cells. Moreover, B16F10 cells grown in sphere conditions to enrich for cancer stem cells (CSC) progressively upregulated cripto1 expression. Vaccination of C57Bl/6 mice with a DNA vaccine encoding mouse Cripto-1 elicited a readily detectable/strong cytotoxic CD8⁺ T cell response specific for a H-2 Kb-restricted epitope identified based on its ability to bind H-2^b molecules. Remarkably, Cripto-1 vaccination elicited a protective response against lung metastasis and subcutaneous challenges with highly metastatic B16F10 melanoma cells. Our data indicate that vaccination against Cripto-1 represents a novel strategy to be tested in the clinic.

Cripto-1 ablation disrupts alveolar development in the mouse mammary gland through a progesterone receptor-mediated pathway

Cripto-1, a member of the epidermal growth factor-Cripto-1/FRL-1/Cryptic family, is critical for early embryonic development. Together with its ligand Nodal, Cripto-1 has been found to be associated with the undifferentiated status of mouse and human embryonic stem cells. Several studies have clearly shown that Cripto-1 is involved in regulating branching morphogenesis and epithelial-mesenchymal transition of the mammary gland both in vitro and in vivo and together with the cofactor GRP78 is critical for the maintenance of mammary stem cells ex vivo. Our previous studies showed that mammary-specific overexpression of human Cripto-1 exhibited dramatic morphological alterations in nulliparous mice mammary glands. The present study shows a novel mechanism for Cripto-1 regulation of mammary gland development through direct effects on progesterone receptor expression and pathways regulated by progesterone in the mammary gland. We demonstrate a strict temporal regulation of mouse Cripto-1 (mCripto-1) expression that occurs during mammary gland development and a stage-specific function of mCripto-1 signaling during mammary gland development. Our data suggest that Cripto-1, like the progesterone receptor, is not required for the initial ductal growth but is essential for subsequent side branching and alveologenesis during the initial stages of pregnancy. Dissection of the mechanism by which this occurs indicates that mCripto-1 activates receptor activator NF-κB/receptor activator NF-κB ligand, and NF-κB signaling pathways.

Cripto-1: an extracellular protein - connecting the sequestered biological dots

Cripto-1 (CR-1) is a multifunctional embryonic protein that is re-expressed during inflammation, wound repair, and malignant transformation. CR-1 can function either as a tethered co-receptor or shed as a free ligand underpinning its flexible role in cell physiology. CR-1 has been shown to mediate cell growth, migration, invasion, and induce epithelial to mesenchymal transition (EMT). The main signaling pathways mediating CR-1 effects include Nodal-dependent (Smad2/3) and Nodal-independent (Src/p44/42/Akt) signaling transduction pathways. In addition, there are several naturally occurring binding partner proteins (BPPs) for CR-1 that can either agonize or antagonize its bioactivity. We will review the collective role of CR-1 as an extracellular protein, discuss caveats to consider in developing a quantitation assay, define possible mechanistic avenues applicable for drug discovery, and report on our experimental approaches to overcome these problematic issues.

Genetic variants modulating CRIPTO serum levels identified by genome-wide association study in Cilento isolates

Cripto, the founding member of the EGF-CFC genes, plays an essential role in embryo development and is involved in cancer progression. Cripto is a GPI-anchored protein that can interact with various components of multiple signaling pathways, such as TGF-β, Wnt and MAPK, driving different processes, among them epithelial-mesenchymal transition, cell proliferation, and stem cell renewal. Cripto protein can also be cleaved and released outside the cell in a soluble and still active form. Cripto is not significantly expressed in adult somatic tissues and its re-expression has been observed associated to pathological conditions, mainly cancer. Accordingly, CRIPTO has been detected at very low levels in the plasma of healthy volunteers, whereas its levels are significantly higher in patients with breast, colon or glioblastoma tumors. These data suggest that CRIPTO levels in human plasma or serum may have clinical significance. However, very little is known about the variability of serum levels of CRIPTO at a population level and the genetic contribution underlying this variability remains unknown. Here, we report the first genome-wide association study of CRIPTO serum levels in isolated populations (n = 1,054) from Cilento area in South Italy. The most associated SNPs (p-value<5*10-8) were all located on chromosome 3p22.1-3p21.3, in the CRIPTO gene region. Overall six CRIPTO associated loci were replicated in an independent sample (n = 535). Pathway analysis identified a main network including two other genes, besides CRIPTO, in the associated regions, involved in cell movement and proliferation. The replicated loci explain more than 87% of the CRIPTO variance, with 85% explained by the most associated SNP. Moreover, the functional analysis of the main associated locus identified a causal variant in the 5’UTR of CRIPTO gene which is able to strongly modulate CRIPTO expression through an AP-1-mediate transcriptional regulation.

Cripto gene has a fundamental role in embryo development and is also involved in cancer. The protein is bound to the cell membrane through an anchor, that can be cleaved, causing the secretion of the protein, in a still active form. In the adult, CRIPTO is detected at very low levels in normal tissues and in the blood, while its increase in both tissues and blood is associated to pathological conditions, mainly cancer. As other GPI linked proteins such as the carcinoembryonic antigen (CEA), one of the most used tumor markers, CRIPTO is able to reach the bloodstream. Therefore, CRIPTO represents a new promising biomarker and potential therapeutic target, and blood CRIPTO levels might be associated to clinical features. Here we examined the variability of blood CRIPTO levels at a population level (population isolates from the Cilento region in South Italy) and we investigated the genetic architecture underlying this variability. We reported the association of common genetic variants with the levels of CRIPTO protein in the blood and we identified a main locus on chromosome 3 and additional five associated loci. Moreover, through functional analyses, we were able to uncover the mechanism responsible for the variation in CRIPTO levels, which is a regulation mediated by the transcriptional factor AP-1.

The multifaceted role of the embryonic gene Cripto-1 in cancer, stem cells and epithelial-mesenchymal transition

Cripto-1 (CR-1)/Teratocarcinoma-derived growth factor1 (TDGF-1) is a cell surface glycosylphosphatidylinositol (GPI)-linked glycoprotein that can function either in cis (autocrine) or in trans (paracrine). The cell membrane cis form is found in lipid rafts and endosomes while the trans acting form lacking the GPI anchor is soluble. As a member of the epidermal growth factor (EGF)/Cripto-1-FRL-1-Cryptic (CFC) family, CR-1 functions as an obligatory co-receptor for the transforming growth factor-β (TGF-β) family members, Nodal and growth and differentiation factors 1 and 3 (GDF1/3) by activating Alk4/Alk7 signaling pathways that involve Smads 2, 3 and 4. In addition, CR-1 can activate non-Smad-dependent signaling elements such as PI3K, Akt and MAPK. Both of these pathways depend upon the 78kDa glucose regulated protein (GRP78). Finally, CR-1 can facilitate signaling through the canonical Wnt/β-catenin and Notch/Cbf-1 pathways by functioning as a chaperone protein for LRP5/6 and Notch, respectively. CR-1 is essential for early embryonic development and maintains embryonic stem cell pluripotentiality. CR-1 performs an essential role in the etiology and progression of several types of human tumors where it is expressed in a population of cancer stem cells (CSCs) and facilitates epithelial-mesenchymal transition (EMT). In this context, CR-1 can significantly enhance tumor cell migration, invasion and angiogenesis. Collectively, these facts suggest that CR-1 may be an attractive target in the diagnosis, prognosis and therapy of several types of human cancer.

Cripto-1 expression in glioblastoma multiforme

Human glioblastoma multiforme (GBM) is an aggressive cancer with a very poor prognosis. Cripto-1 (CR-1) has a key regulatory role in embryogenesis, while in adult tissue re-expression of CR-1 has been correlated to malignant progression in solid cancers of non-neuronal origin. As CR-1 expression has yet to be described in cerebral cancer and CR-1 is regulated by signaling pathways dysregulated in GBM, we aimed to investigate CR-1 in the context of expression in GBM. The study was performed using enzyme-linked immunosorbent assay (ELISA), Western blotting, polymerase chain reaction (PCR) and immunohistochemistry to analyze the blood and tissue from 28 GBM and 4 low-grade glioma patients. Within the patient cohort, we found high CR-1 protein levels in blood plasma to significantly correlate with a shorter overall survival. We identified CR-1 in different areas of GBM tissue, including perivascular tumor cells, and in endothelial cells. Collectively, our data suggest that CR-1 could be a prognostic biomarker for GBM with the potential of being a therapeutic target.

Cripto-1 enhances the canonical Wnt/β-catenin signaling pathway by binding to LRP5 and LRP6 co-receptors

Cripto-1 is implicated in multiple cellular events, including cell proliferation, motility and angiogenesis, through the activation of an intricate network of signaling pathways. A crosstalk between Cripto-1 and the canonical Wnt/β-catenin signaling pathway has been previously described. In fact, Cripto-1 is a downstream target gene of the canonical Wnt/β-catenin signaling pathway in the embryo and in colon cancer cells and T-cell factor (Tcf)/lymphoid enhancer factor binding sites have been identified in the promoter and the first intronic region of the mouse and human Cripto-1 genes. We now demonstrate that Cripto-1 modulates signaling through the canonical Wnt/β-catenin/Tcf pathway by binding to the Wnt co-receptors low-density lipoprotein receptor-related protein (LRP) 5 and LRP6, which facilitates Wnt3a binding to LRP5 and LRP6. Cripto-1 functionally enhances Wnt3a signaling through cytoplasmic stabilization of β-catenin and elevated β-catenin/Tcf transcriptional activation. Conversely, Wnt3a further increases Cripto-1 stimulation of migration, invasion and colony formation in soft agar of HC11 mouse mammary epithelial cells, indicating that Cripto-1 and the canonical Wnt/β-catenin signaling co-operate in regulating motility and in vitro transformation of mammary epithelial cells.

Role of Cripto-1 during epithelial-to-mesenchymal transition in development and cancer

Epithelial-to-mesenchymal transition (EMT) is a critical multistep process that converts epithelial cells to more motile and invasive mesenchymal cells, contributing to body patterning and morphogenesis during embryonic development. In addition, both epithelial plasticity and increased motility and invasiveness are essential for the branching morphogenesis that occurs during development of the mammary gland and during tumor formation, allowing cancer cells to escape from the primary tumor. Cripto-1, a member of the epidermal growth factor-Cripto-1/FRL-1/Cryptic (EGF/CFC) gene family, together with the transforming growth factor (TGF)-β family ligand Nodal, regulates both cell movement and EMT during embryonic development. During postnatal development, Cripto-1 regulates the branching morphogenesis of the mouse mammary gland and enhances both the invasive and migratory properties of mammary epithelial cells in vitro. Furthermore, transgenic mouse models have shown that Cripto-1 promotes the formation of mammary tumors that display properties of EMT, including the down-regulation of the cell surface adherens junctional protein E-cadherin and the up-regulation of mesenchymal markers, such as vimentin, N-cadherin, and Snail. Interestingly, Cripto-1 is enriched in a subpopulation of embryonal, melanoma, prostate, and pancreatic cancer cells that possess stem-like characteristics. Therefore, Cripto-1 may play a role during developmental EMT, and it may also be involved in the reprogramming of differentiated tumor cells into cancer stem cells through the induction of an EMT program.

Tension, free space, and cell damage in a microfluidic wound healing assay

We use a novel, microfluidics-based technique to deconstruct the classical wound healing scratch assay, decoupling the contribution of free space and cell damage on the migratory dynamics of an epithelial sheet. This method utilizes multiple laminar flows to selectively cleave cells enzymatically, and allows us to present a 'damage free' denudation. We therefore isolate the influence of free space on the onset of sheet migration. First, we observe denudation directly to measure the retraction in the cell sheet that occurs after cell-cell contact is broken, providing direct and quantitative evidence of strong tension within the sheet. We further probe the mechanical integrity of the sheet without denudation, instead using laminar flows to selectively inactivate actomyosin contractility. In both cases, retraction is observed over many cell diameters. We then extend this method and complement the enzymatic denudation with analogies to wounding, including gradients in signals associated with cell damage, such as reactive oxygen species, suspected to play a role in the induction of movement after wounding. These chemical factors are evaluated in combination with the enzymatic cleavage of cells, and are assessed for their influence on the collective migration of a non-abrasively denuded epithelial sheet. We conclude that free space alone is sufficient to induce movement, but this movement is predominantly limited to the leading edge, leaving cells further from the edge less able to move towards the wound. Surprisingly, when coupled with a gradient in ROS to simulate the chemical effects of abrasion however, motility was not restored, but further inhibited.

The role of Cripto-1 in the tumorigenesis and progression of oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC), the most common malignancy of the oral cavity, remains a lethal disease in over 50% of cases diagnosed annually, due mostly to late detection of this cancer in its advanced stages despite the easy accessibility of the oral cavity for regular examinations. Cripto-1 is a member of the epidermal growth factor (EGF)-CFC protein family and is involved in the activation of several different signaling pathways during embryonic development and cellular transformation. Although the Cripto-1 protein is overexpressed in several human cancers including breast, colon, cervix, gastric, and pancreatic cancer, no prior study has evaluated Cripto-1 expression in OSCC. Therefore, our aims in this study were to examine Cripto-1 expression in clinical samples of OSCC patients using immunohistochemistry, to analyze the correlation between Cripto-1 expression and clinicopathologic parameters, and to identify the oncogenic roles of Cripto-1 in OSCC cell lines. Both epithelial dysplasia (73.3%) and OSCC (55.5%) tissue samples showed significantly higher expression of Cripto-1 than normal mucosa (20%) (p=0.031). In the OSCC samples, there was a significant correlation between Cripto-1 expression and the histological differentiation of OSCC (p=0.015) and a high PCNA index (p=0.011). The in vitro cell proliferation assays demonstrated that recombinant human Cripto-1 (rhCripto-1) induced both SCC-4 and SCC-25 cells to proliferate as compared with control cells (p<0.05 and p<0.01, respectively). In in vitro migration assays, treatment of SCC-4 and SCC-25 cells with rhCripto-1 protein induced a 2.4-fold and 1.7-fold-increase in cell migration, respectively (p=0.000 and p=0.008, respectively). Taken together, our data suggest that Cripto-1 plays a role in the malignant transformation of the oral mucosa and is involved in the tumorigenesis and progression of OSCC by promoting the growth and migration of malignant cells.

An antibody-cytotoxic conjugate, BIIB015, is a new targeted therapy for Cripto positive tumours

BIIB015 is an immunoconjugate created for the treatment of solid tumours and is currently in Phase I of clinical evaluation. BIIB015 consists of a humanised monoclonal antibody against the Cripto protein carrying a payload, via a hindered disulphide linker, of the maytansinoid derivative, DM4. Cripto is a GPI-linked protein required for signal transduction of the TGF-beta ligand, Nodal. Cripto has been previously described as an oncogene and fits the classic pattern of an embryonic gene that is re-expressed in a transformed tumour cell. Cripto expression is highly prevalent on a number of solid tumours, including greater than 75% of breast, lung, and colorectal tumours. Our report documents for the first time that targeting the cell surface Cripto protein with an anti-Cripto antibody-cytotoxic conjugate is an effective means of inhibiting or regressing growth of Cripto positive tumours. BIIB015 which utilises a 'cleavable' linker containing a disulphide bond exhibits superior activity when compared to huB3F6 mAb conjugates with different linker systems, including one with a 'non-cleavable' linker. BIIB015 displays specificity for Cripto in both in vitro and in vivo experiments. In human xenograft models originating from lung (Calu-6), colon (CT-3), testicular (NCCIT) and breast (MDA-MB-231) tumour samples, BIIB015 shows robust activity with results ranging from >50% tumour inhibition to complete tumour regression. The efficacy seen in the MDA-MB-231 model, a triple negative (-HER2, -ER, and -PR) tumour, is particularly exciting since there is currently no approved therapy for this indication. In addition, BIIB015 can be combined with standard of care chemotherapeutics for enhanced efficacy.

Targeting the embryonic gene Cripto-1 in cancer and beyond

IMPORTANCE OF THE FIELD

Emerging evidence has clearly implicated an inappropriate activation of embryonic regulatory genes during cell transformation in adult tissues. An example of such a case is the embryonic gene Cripto-1. Cripto-1 is critical for embryonic development and is considered a marker of undifferentiated embryonic stem cells. Critpo-1 is expressed at low levels in adult tissues, but is re-expressed at a high frequency in a number of different types of human carcinomas, therefore, representing an attractive therapeutic target in cancer.

AREA COVERED IN THIS REVIEW

This review surveys different approaches that have been used to target Cripto-1 in cancer as reflected by the relevant patent literature as well as peer-reviewed publications. Potential involvement and targeting of Cripto-1 in neurodegenerative and degenerative muscle diseases are also discussed.

WHAT THE READER WILL GAIN

The reader will gain an overview of different mAbs, vaccines or oligonucleotides antisense targeting Cripto-1. A humanized anti-Cripto-1 antibody is currently being tested in a Phase I clinical trial in cancer patients.

TAKE HOME MESSAGE

Targeting Cripto-1 in human tumors has the potential to eliminate not only differentiated cancer cells but also destroy an undifferentiated subpopulation of cancer cells with stem-like characteristics that support tumor initiation and self-renewal.

Cripto-1: an embryonic gene that promotes tumorigenesis

Several studies have shown that cell fate regulation during embryonic development and oncogenic transformation share common regulatory mechanisms and signaling pathways. Indeed, an embryonic gene member of the EGF–Cripto-1/FRL1/Cryptic family, Cripto-1, has been implicated in embryogenesis and in carcinogenesis. Cripto-1 together with the TGF-β ligand Nodal is a key regulator of embryonic development and is a marker of undifferentiated human and mouse embryonic stem cells. While Cripto-1 expression is very low in normal adult tissues, Cripto-1 is re-expressed at high levels in several different human tumors, modulating cancer cell proliferation, migration, epithelial-to-mesenchymal transition and stimulating tumor angiogenesis. Therefore, inhibition of Cripto-1 expression using blocking antibodies or antisense expression vectors might be a useful modality not only to target fully differentiated cancer cells but also to target a subpopulation of tumor cells with stem-like characteristics.

Epithelial-mesenchymal transition in cancer: parallels between normal development and tumor progression

From the earliest stages of embryonic development, cells of epithelial and mesenchymal origin contribute to the structure and function of developing organs. However, these phenotypes are not always permanent, and instead, under the appropriate conditions, epithelial and mesenchymal cells convert between these two phenotypes. These processes, termed Epithelial-Mesenchymal Transition (EMT), or the reverse Mesenchymal-Epithelial Transition (MET), are required for complex body patterning and morphogenesis. In addition, epithelial plasticity and the acquisition of invasive properties without the full commitment to a mesenchymal phenotype are critical in development, particularly during branching morphogenesis in the mammary gland. Recent work in cancer has identified an analogous plasticity of cellular phenotypes whereby epithelial cancer cells acquire mesenchymal features that permit escape from the primary tumor. Because local invasion is thought to be a necessary first step in metastatic dissemination, EMT and epithelial plasticity are hypothesized to contribute to tumor progression. Similarities between developmental and oncogenic EMT have led to the identification of common contributing pathways, suggesting that the reactivation of developmental pathways in breast and other cancers contributes to tumor progression. For example, developmental EMT regulators including Snail/Slug, Twist, Six1, and Cripto, along with developmental signaling pathways including TGF-beta and Wnt/beta-catenin, are misexpressed in breast cancer and correlate with poor clinical outcomes. This review focuses on the parallels between epithelial plasticity/EMT in the mammary gland and other organs during development, and on a selection of developmental EMT regulators that are misexpressed specifically during breast cancer.

Msx2 induces epithelial-mesenchymal transition in mouse mammary epithelial cells through upregulation of Cripto-1

Epithelial-mesenchymal transition (EMT) is a process occurring during both embryogenesis and early stages of invasive cancer. Epithelial cells that undergo EMT become more migratory and invasive with a mesenchymal morphology. Herein we assess EMT induction in a mouse mammary epithelial cell line driven by Msx2, a homeobox-containing transcription factor important during mammary gland development. NMuMG cells, a normal mouse mammary epithelial cell line, stably transfected with a Msx2 cDNA showed downregulation of an epithelial marker E-cadherin and upregulation of the mesenchymal markers vimentin and N-cadherin. Furthermore, overexpression of Cripto-1, a member of the epidermal growth factor-CFC protein family already known to be involved in EMT, was detected in Msx2-transfected cells. The expression of Cripto-1 was accompanied by activation of the tyrosine kinase c-Src pathway and an increase in the invasive ability of the cells. Functional assays also demonstrated inhibition of the invasive behavior of the Msx2-transfected cells by a c-Src specific inhibitor. Moreover, immunohistochemistry of human infiltrating breast carcinomas showed positive staining for Msx2 only in the infiltrating tumor cells while the non-infiltrating tumor cells were negative. These results suggest that Msx2 may play a significant role in promoting EMT in epithelial cells that acquire properties involved in tumor invasion. J. Cell. Physiol. 219: 659-666, 2009. Published 2009 Wiley-Liss, Inc.

Emerging roles of nodal and Cripto-1: from embryogenesis to breast cancer progression

Breast carcinoma cells and embryonic progenitors similarly implement stem cell-associated signaling pathways to sustain continued growth and plasticity. Indeed, recent studies have implicated signaling pathways, including those associated with the Notch, and Transforming Growth Factor-Beta (TGF-beta) superfamilies, as instrumental to both embryological development and breast cancer progression. In particular, Nodal, an embryonic morphogen belonging to the TGF-beta superfamily, and its co-receptor, Cripto-1, are requisite to both embryogenesis and mammary gland maturation. Moreover, these developmental proteins have been shown to promote breast cancer progression. Here, we review the role of Nodal and its co-receptor Cripto-1 during development and we describe how this signaling pathway may be involved in breast cancer tumorigenesis. Moreover, we emphasize the potential utility of this signaling pathway as a novel target for the treatment and diagnosis of breast cancer.

Activation of a Nodal-independent signaling pathway by Cripto-1 mutants with impaired activation of a Nodal-dependent signaling pathway

Cripto-1, a co-receptor for Nodal, can activate Nodal-dependent and Nodal-independent signaling pathways. In this study we have investigated whether Cripto-1 mutants, that fail to activate a Nodal-dependent signaling pathway, are capable to activate a Nodal-independent signaling pathway in mammary epithelial cells. Cripto-1 mutants expressed in EpH4 mouse mammary epithelial cells are fully functional in regard to activation of a Nodal-independent signaling pathway, leading to phosphorylation of mitogen-activated protein kinase (MAPK) and Akt and to enhanced proliferation and motility of these cells, suggesting that Cripto-1 mutants with impaired Nodal signaling are still active in a Nodal-independent signaling pathway.

Cripto-1 alters keratinocyte differentiation via blockade of transforming growth factor-beta1 signaling: role in skin carcinogenesis

Cripto-1 is an epidermal growth factor-Cripto/FRL1/Cryptic family member that plays a role in early embryogenesis as a coreceptor for Nodal and is overexpressed in human tumors. Here we report that in the two-stage mouse skin carcinogenesis model, Cripto-1 is highly up-regulated in tumor promoter-treated normal skin and in benign papillomas. Treatment of primary mouse keratinocytes with Cripto-1 stimulated proliferation and induced expression of keratin 8 but blocked induction of the normal epidermal differentiation marker keratin 1, changes that are hallmarks of tumor progression in squamous cancer. Chemical or genetic blockade of the transforming growth factor (TGF)-beta1 signaling pathway using the ALK5 kinase inhibitor SB431542 and dominant negative TGF-beta type II receptor, respectively, had similar effects on keratinocyte differentiation. Our results show that Cripto-1 could block TGF-beta1 receptor binding, phosphorylation of Smad2 and Smad3, TGF-beta-responsive luciferase reporter activity, and TGF-beta1-mediated senescence of keratinocytes. We suggest that inhibition of TGF-beta1 by Cripto-1 may play an important role in altering the differentiation state of keratinocytes and promoting outgrowth of squamous tumors in the mouse epidermis.

Regulation of Cripto-1 signaling and biological activity by caveolin-1 in mammary epithelial cells

Human and mouse Cripto-1 (CR-1/Cr-1) proteins play an important role in mammary gland development and tumorigenesis. In this study, we examined the relationship between Cripto-1 and caveolin-1 (Cav-1), a membrane protein that acts as a tumor suppressor in the mammary gland. Cripto-1 was found to interact with Cav-1 in COS7 cells and mammary epithelial cells. Using EpH4 mouse mammary epithelial cells expressing Cr-1 (EpH4 Cr-1) or Cr-1 and Cav-1 (EpH4 Cr-1/Cav-1), we demonstrate that Cav-1 expression markedly reduced the ability of Cr-1 to enhance migration, invasion, and formation of branching structures in EpH4 Cr-1/Cav-1 cells as compared to EpH4 Cr-1 cells. Furthermore, coexpression of Cav-1 together with Cr-1 in EpH4 Cr-1/Cav-1 cells inhibited Cr-1-mediated activation of c-src and mitogen-activated protein kinase signaling pathways. Conversely, primary mammary epithelial cells isolated from Cav-1 null(-/-)/mouse mammary tumor virus-CR-1 transgenic animals showed enhanced motility and activation of mitogen-activated protein kinase and c-src as compared to Cav-1(+/-)/CR-1 mammary cells. Finally, mammary tumors derived from mouse mammary tumor virus-CR-1 mice showed a dramatic reduction of Cav-1 expression as compared to mammary tissue from normal FVB/N mice, suggesting that in vivo Cav-1 is down-regulated during the process of CR-1-mediated mammary tumorigenesis.

In vitro and ex vivo green fluorescent protein expression in alveolar mammary epithelial cells and mammary glands driven by the distal 5'-regulative sequence and intron 1 of the goat beta-casein gene

The 5'-regulative sequence and intron 1 of the goat beta-casein gene from -4044 to +2123 bp was cloned and fused with the reporter gene of green fluorescent protein (GFP) to create a plasmid termed pGB562/GFP. To detect GFP expression, pGB562/GFP was transfected in vitro via liposomes into the mammary epithelial cell line NMuMG. Cells could not express GFP unless the transfected NMuMG cells lined up to create functional alveoli. These functional cells were cultured with lactogenic hormones, including insulin, dexamethasone and prolactin, and were grown on a layer of the extracellular matrix Matrigel. Green fluorescent protein expression levels in NMuMG cells were 25-, 55- and 42-fold those in the control group at 24, 48, and 72 h after pGB562/GFP transfection respectively. In addition, pGB562/GFP was transfected ex vivo by electroporation into mammary gland fragments and cells were then cultured in vitro with a supplement of lactogenic hormones. Strong GFP expression localized in fragments of the mammary gland was observed 24 h after gene transfer. The novel strategy of ex vivo gene transfer into mammary tissue using GFP as a reporter gene to detect the function of a tissue-specific promoter is efficient and convenient. The data obtained herein reveal that the 5'-regulative sequence and intron 1 of the 6.2 kb goat beta-casein gene can enhance the efficiency of transgene expression. Thus, the GB562 sequence may act as a good promoter and effectively elevate the production of exogenous protein in mammary glands.

Prion protein facilitates hormone-induced differentiation of mammary gland epithelial cells

Expression of prion protein has been reported for a variety of cell types including neuronal cells, haematopoietic stem cells, lymphocytes, fibroblasts, and epithelial cells. However, the characterization of the physiological roles exhibited by this protein is still in progress and multiple biological functions have been described to date. In this study we have characterized the contribution of prion protein during hormone-induced differentiation of mouse mammary gland epithelial cells. We present evidence that prion expression enhances the differentiation-capabilities of these cells indicating novel physiological roles during mammary gland development. In addition we were able to demonstrate the presence of prion molecules resistant to mild proteinase digestion in differentiated mammary gland epithelial cells. This represents the first report of proteinase-resistant prion proteins in a physiological, non-pathogenic context.

Progesterone enhances branching morphogenesis in the mouse mammary gland by increased expression of Msx2

Branching morphogenesis within the peripubertal mouse mammary gland is directed by progesterone (P). A role for the homeobox-containing transcription factor, Msx2, during branching morphogenesis is suggested from its ontogenic expression profile and hormonal regulation. Herein, we define the spatio-temporal control of Msx2 expression, the regulation of its expression by P and its direct role in ductal branching morphogenesis. P induces Msx2 in the presence of estrogen (E) both in vitro and in vivo while absence of the P receptor (PR) decreased Msx2 expression. Stable transfection of PR into mouse mammary epithelial cells increased the endogenous expression of Msx2 and their ability to undergo branching morphogenesis in vitro. Furthermore, normal mammary cells stably-transfected with Msx2 demonstrated increased branching morphogenesis in vitro while transgenic mice expressing Msx2 in their mammary glands demonstrated enhanced lateral branching during early development. The action of P on branching morphogenesis appears to involve Bmp2/4. Together, these data demonstrate that P, acting through PR-A and the Bmp2/4 pathway, induces Msx2 to enhance ductal branching in the mammary glands.

Prion protein resides in membrane microclusters of the immunological synapse during lymphocyte activation

Expression of prion protein (PrP) has been reported for a variety of cell types including neuronal cells, haematopoietic stem cells, antigen-presenting cells, as well as lymphocytes. However, besides this widespread occurrence little is known about the physiological roles exhibited by this enigmatic protein. In this study, the contribution of PrP to the classical T-lymphocyte activation process was characterized by clustering the T-cell receptor component CD3epsilon as well as PrP with soluble and surface-immobilized antibodies, respectively. We present evidence that PrP is a component of signaling structures recently described as plasma membrane microclusters established during T-lymphocyte activation. The formation of immunological synapses, however, did not depend on the presence of PrP as proven by siRNA knockdown experiments, indicating very subtle physiological roles of PrP in vivo within the immune system.

Cripto binds transforming growth factor beta (TGF-beta) and inhibits TGF-beta signaling

Cripto is a developmental oncoprotein and a member of the epidermal growth factor-Cripto, FRL-1, Cryptic family of extracellular signaling molecules. In addition to having essential functions during embryogenesis, Cripto is highly expressed in tumors and promotes tumorigenesis. During development, Cripto acts as an obligate coreceptor for transforming growth factor beta (TGF-beta) ligands, including nodals, growth and differentiation factor 1 (GDF1), and GDF3. As an oncogene, Cripto is thought to promote tumor growth via mechanisms including activation of mitogenic signaling pathways and antagonism of activin signaling. Here, we provide evidence supporting a novel mechanism in which Cripto inhibits the tumor suppressor function of TGF-beta. Cripto bound TGF-beta and reduced the association of TGF-beta with its type I receptor, TbetaRI. Consistent with its ability to block receptor assembly, Cripto suppressed TGF-beta signaling in multiple cell types and diminished the cytostatic effects of TGF-beta in mammary epithelial cells. Furthermore, targeted disruption of Cripto expression by use of small inhibitory RNA enhanced TGF-beta signaling, indicating that endogenous Cripto plays a role in restraining TGF-beta responses.

Prion protein modifies TGF-β induced signal transduction

Members of the transforming growth factor-beta (TGF-beta) superfamily regulate a multitude of cellular processes as well as the expression of various proteins such as, e.g., matrix metalloproteinases (MMPs). These endopeptidases selectively degrade components of the extracellular matrix as well as non-matrix substrates like growth factors and cell surface receptors. MMPs are activated during embryonic development, morphogenesis, and tissue resorption/remodeling as well as in pathological conditions such as deranged wound healing and cancer metastasis. In this report we demonstrate that over-expression of cellular prion protein in mouse mammary gland epithelial cells is able to modulate TGF-beta induced signal transduction leading to a synergistic increase of secreted MMP-2 activity. This correlates with elevated substrate detachment of cells grown as an epithelial monolayer as well as interfering with morphogenesis of cells cultured in a three-dimensional collagen type I matrix.

Identification of Cripto-1 as a Novel Serologic Marker for Breast and Colon Cancer

PURPOSE

Human Cripto-1 (CR-1), a cell membrane glycosylphosphatidylinositol-anchored glycoprotein that can also be cleaved from the membrane, is expressed at high levels in several different types of human tumors. We evaluated whether CR-1 is present in the plasma of patients with breast and colon cancer, and if it can represent a new biomarker for these malignancies.

EXPERIMENTAL DESIGN

We determined CR-1 plasma levels using a sandwich-type ELISA in 21 healthy volunteers, 54 patients with breast cancer, 33 patients with colon carcinoma, and 21 patients with benign breast lesions. Immunohistochemical analysis was also used to assess CR-1 expression in cancerous tissues.

RESULTS

Very low levels of CR-1 (mean+/-SD) were detected in the plasma of healthy volunteers (0.32+/-0.19 ng/mL). A statistically significant increase in the levels of plasma CR-1 was found in patients with colon carcinoma (4.68+/-3.5 ng/mL) and in patients with breast carcinoma (2.97+/-1.48 ng/mL; P<0.001). Although moderate levels of plasma CR-1 were found in women with benign lesions of the breast (1.7+/-0.99 ng/mL), these levels were significantly lower than in patients with breast cancer (P<0.001). Finally, immunohistochemical analysis and real-time reverse transcription-PCR confirmed strong positivity for CR-1 in colon and/or breast tumor tissues.

CONCLUSION

This study suggests that plasma CR-1 might represent a novel biomarker for the detection of breast and colon carcinomas.

Epithelial-to-mesenchymal transition confers resistance to apoptosis in three murine mammary epithelial cell lines

Epithelial-to-mesenchymal transition (EMT) is an essential embryogenic and developmental process, characterized by altered cellular morphology, loss of cell adhesion, and gain of migratory ability. Dysregulation of this process has been implicated in tumorigenesis, mediating the acquisition of migratory and invasive phenotypes by tumor cells. Mammary epithelial cells provide an excellent model in which to study the process, being derived from mammary gland tissue that utilizes EMT to facilitate branching morphogenesis through which the developing gland migrates into and invades the fat pad. Inappropriate EMT has been heavily implicated in the progression of ductal hyperplasia and mammary tumor metastasis. We examined the morphological and molecular changes of three murine mammary epithelial cell lines following EMT induction. EMT was induced in the EpH-4 and NMuMG cell lines by transforming growth factor (TGF)-beta1 but not by ethanol, while the KIM-2 cell line was partially resistant to TGF-beta1 but responded fully to ethanol. The response to EMT-inducing reagent was shown to be critically dependent on the time of treatment, with confluent cells failing to respond. Timelapse photography identified increased motility during wound healing in cells pre-treated with EMT-inducing reagent compared with untreated controls. Furthermore, EMT conferred resistance to UV-induced apoptosis. Our data indicate that evaluation of characteristics other than loss and gain of phenotypic markers may be of benefit when assessing EMT, and contribute to the evidence suggesting that inappropriate EMT facilitates the acquisition of resistance to apoptosis, a key characteristic required for tumor survival.

Modulation of TGF-β signaling by EGF-CFC proteins

Members of the transforming growth factor-beta (TGF-beta) family of ligands exhibit potent growth-suppressive and/or apoptosis-inducing effects on different types of cells. They perform essential roles in the elimination of damaged or abnormal cells from healthy tissues. On the other hand, TGF-betas have also been shown to act as tumor-promoting cytokines in a number of malignancies that are capable of stimulating extracellular matrix production, cell migration, invasion, angiogenesis, and immune suppression. Dissecting the complex, multifaceted roles of different TGF-beta-related peptides especially during the development of pathological conditions and in carcinogenesis is an area of continuous research and development. The characterization of EGF-CFC proteins as essential co-receptors that contribute to the modulation of the physiological activities of some of the TGF-beta ligands will be beneficial for future medical research and the adaptation and possible readjustment of currently applied therapeutic regimes.

Netrin-1 regulates invasion and migration of mouse mammary epithelial cells overexpressing Cripto-1 in vitro and in vivo

The neuronal guidance molecule, Netrin-1, has been suggested to play a role in the adhesion and migration of the mammary gland epithelium. Human and mouse Cripto-1 induce proliferation, migration, invasion and colony formation by epithelial cells in 3D matrices. Here we investigate whether Netrin-1 affects these Cripto-1-dependent activities in mouse mammary epithelial cells. Overexpression of Cripto-1 in EpH4 and HC-11 cells (EpH4/Cripto-1 or HC-11/Cripto-1) was associated with low expression of Netrin-1 and increased expression of its receptor Neogenin compared to that of wild-type cells. No change was observed in the expression of the other Netrin-1 receptor, UNC5H1. Treating EpH4/Cripto-1 or HC-11/Cripto-1 mammary cells with exogenous soluble Netrin-1 resulted in increased expression of E-cadherin and UNC5H1, decreased expression of vimentin and decreased activation of Akt as determined by western blotting. Colony formation by Eph4/Cripto-1 cells in 3D gels was significantly reduced in proximity to a Netrin-1 source, and mammary glands of transgenic mice overexpressing human Cripto-1 showed altered ductal growth in proximity to implanted Netrin-1-releasing pellets. Terminal end buds in the treated transgenic mice mammary glands also showed increased expression of E-cadherin and UNC5H1 and decreased expression of active Akt determined by immunohistochemistry. Together, these results suggest that regulation of Netrin-1 expression is important in regulating Cripto-1-dependent invasion and migration of mammary epithelial cells.

Overexpression of human Cripto-1 in transgenic mice delays mammary gland development and differentiation and induces mammary tumorigenesis

Overexpression of Cripto-1 has been reported in several types of human cancers including breast cancer. To investigate the role of human Cripto-1 (CR-1) in mammary gland development and tumorigenesis, we developed transgenic mice that express the human CR-1 transgene under the regulation of the whey acidic protein (WAP) promoter in the FVB/N mouse background. The CR-1 transgene was detected in the mammary gland of 15-week-old virgin WAP-CR-1 female mice that eventually developed hyperplastic lesions. From mid-pregnancy to early lactation, mammary lobulo-alveolar structures in WAP-CR-1 mice were less differentiated and delayed in their development due to decreased cell proliferation as compared to FVB/N mice. Early involution, due to increased apoptosis, was observed in the mammary glands of WAP-CR-1 mice. Higher levels of phosphorylated AKT and MAPK were detected in mammary glands of multiparous WAP-CR-1 mice as compared to multiparous FVB/N mice suggesting increased cell proliferation and survival of the transgenic mammary gland. In addition, more than half (15 of 29) of the WAP-CR-1 multiparous female mice developed multifocal mammary tumors of mixed histological subtypes. These results demonstrate that overexpression of CR-1 during pregnancy and lactation can lead to alterations in mammary gland development and to production of mammary tumors in multiparous mice.