Mario Mancino

The ErbB receptors and their ligands in cancer: an overview.

This review article provides an overview on the most recent advances on the role of ErbB receptors and growth factors of the epidermal growth factor (EGF)-family of peptides in cancer pathogenesis and progression. The ErbB tyrosine kinases and the EGF-like peptides form a complex system. In fact, the interactions occurring between receptors and ligands of these families affect the type and the duration of the intracellular signals that derive from receptor activation. Interestingly, activation of ErbB receptors is also driven by different classes of membrane receptor, suggesting that ErbB kinases can amplify growth promoting signals carried by different pathways. The importance of ErbB receptors and EGF-like peptides in development of organs and tissues has been demonstrated by using different mouse models. In vitro and in vivo studies have also shown that ErbB receptors and their ligands can act as transforming genes. However, evidence suggests that cooperation of different receptors and ligands is necessary to induce a fully transformed phenotype. Indeed, co-expression of different ErbB receptors and EGF-like growth factors is a common phenomenon in human primary carcinomas. This observation suggests that the growth and the survival of carcinoma cells is sustained by a network of receptors/ligands of the ErbB family. In this respect, the contemporary expression of different ErbB tyrosine kinases and/or EGF-like growth factors in human carcinomas might also affect tumor response to target based agents directed against the ErbB receptor/ligand system.

The MEK/MAPK pathway is involved in the resistance of breast cancer cells to the EGFR tyrosine kinase inhibitor gefitinib.

We investigated the role of the MEK/MAPK pathway in the sensitivity/resistance of breast carcinoma cells to the EGFR tyrosine kinase inhibitor gefitinib (IRESSA). We assessed the effects of gefitinib on the growth of three breast cancer cell lines that showed high (SK‐Br‐3; IC50 4 µM), intermediate (MDA‐MB‐361; IC50 5.3 µM), and low (MDA‐MB‐468; IC50 6.8 µM) sensitivity to the drug. Although treatment with gefitinib inhibited EGFR activation in the three cell lines in a similar fashion, significant reduction of both p42/p44‐MAPK and AKT phosphorylation was observed in SK‐Br‐3 and MDA‐MB‐361, but not in MDA‐MB‐468 cells. The growth of MDA‐MB‐468 cells was significantly inhibited by treatment with either the PI3K‐inhibitor LY294002 or the MEK‐inhibitor PD98059. In agreement with these findings, treatment of MDA‐MB‐468 cells with a combination of PD98059 and gefitinib produced a synergistic anti‐tumor effect, whereas this combination was only additive in SK‐Br‐3 and MDA‐MB‐361 cells. The combination of gefitinib and PD98059 also produced a significant increase in the levels of apoptosis in MDA‐MB‐468 cells as compared with treatment with a single agent. This phenomenon was associated with a profound decrease in MAPK activation, reduction of BAD (ser112) phosphorylation and a paradoxical increase in the levels of AKT activation. Finally, overexpression of a constitutively activated form of p42‐MAPK in MCF‐10A non‐transformed human mammary epithelial cells resulted in a two‐ to three‐fold increase in the IC50 to gefitinib. Taken together, these data strongly support the role of the MEK/MAPK pathway in the resistance to gefitinib, and provide the rationale for novel therapeutic approaches based on combinations of signal transduction inhibitors. J. Cell. Physiol. 207: 420–427, 2006.

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.

Cripto-1 Is Required for Hypoxia to Induce Cardiac Differentiation of Mouse Embryonic Stem Cells

Cripto-1 is a membrane-bound protein that is highly expressed in embryonic stem cells and in human tumors. In the present study, we investigated the effect of low levels of oxygen, which occurs naturally in rapidly growing tissues, on Cripto-1 expression in mouse embryonic stem (mES) cells and in human embryonal carcinoma cells. During hypoxia, Cripto-1 expression levels were significantly elevated in mES cells and in Ntera-2 or NCCIT human embryonal carcinoma cells, as compared with cells growing with normal oxygen levels. The transcription factor hypoxia-inducible factor-1alpha directly regulated Cripto-1 expression by binding to hypoxia-responsive elements within the promoter of mouse and human Cripto-1 genes in mES and NCCIT cells, respectively. Furthermore, hypoxia modulated differentiation of mES cells by enhancing formation of beating cardiomyocytes as compared with mES cells that were differentiated under normoxia. However, hypoxia failed to induce differentiation of mES cells into cardiomyocytes in the absence of Cripto-1 expression, demonstrating that Cripto-1 is required for hypoxia to fully differentiate mES cells into cardiomyocytes. Finally, cardiac tissue samples derived from patients who had suffered ischemic heart disease showed a dramatic increase in Cripto-1 expression as compared with nonischemic heart tissue samples, suggesting that hypoxia may also regulate Cripto-1 in vivo.

Growth factor induction of cripto-1 shedding by glycosylphosphatidylinositol-phospholipase D and enhancement of endothelial cell migration

Cripto-1 (CR-1) is a glycosylphosphatidylinositol (GPI)-anchored membrane glycoprotein that has been shown to play an important role in embryogenesis and cellular transformation. CR-1 is reported to function as a membrane-bound co-receptor and as a soluble ligand. Although a number of studies implicate the role of CR-1 as a soluble ligand in tumor progression, it is unclear how transition from the membrane-bound to the soluble form is physiologically regulated and whether differences in biological activity exist between these forms. Here, we demonstrate that CR-1 protein is secreted from tumor cells into the conditioned medium after treatment with serum, epidermal growth factor, or lysophosphatidic acid, and this soluble form of CR-1 exhibits the ability to promote endothelial cell migration as a paracrine chemoattractant. On the other hand, membrane-bound CR-1 can stimulate endothelial cell sprouting through direct cell-cell interaction. Shedding of CR-1 occurs at the GPI-anchorage site by the activity of GPI-phospholipase D (GPI-PLD), because CR-1 shedding was suppressed by siRNA knockdown of GPI-PLD and enhanced by overexpression of GPI-PLD. These findings describe a novel molecular mechanism of CR-1 shedding, which may contribute to endothelial cell migration and possibly tumor angiogenesis.

Requirement of Glycosylphosphatidylinositol Anchor of Cripto-1 for trans Activity as a Nodal Co-receptor

Cripto-1 (CR-1) has an indispensable role as a Nodal co-receptor for patterning of body axis in embryonic development. CR-1 is reported to have a paracrine activity as a Nodal co-receptor, although CR-1 is primarily produced as a glycosylphosphatidylinositol (GPI)-anchored membrane protein. Regulation of cis and trans function of CR-1 should be important to establish the precise body patterning. However, the mechanism by which GPI-anchored CR-1 can act in trans is not well known. Here we confirmed the paracrine activity of CR-1 by fluorescent cell-labeling and immunofluorescent staining. We generated COOH-terminal-truncated soluble forms of CR-1 based on the attachment site for the GPI moiety (ω-site), which we identified in the present study. GPI-anchored CR-1 has a significantly higher activity than COOH-terminal-truncated soluble forms to induce Nodal signal in trans as well as in cis. Moreover, transmembrane forms of CR-1 partially retained their ability to induce Nodal signaling only when type I receptor Activin-like kinase 4 was overexpressed. NTERA2/D1 cells, which express endogenous CR-1, lost the cell-surface expression of CR-1 after phosphatidylinositol-phospholipase C treatment and became refractory to stimulation of Nodal. These observations suggest that GPI attachment of CR-1 is required for the paracrine activity as a Nodal co-receptor.

Smad2 functions as a co-activator of canonical Wnt/β-catenin signaling pathway independent of Smad4 through histone acetyltransferase activity of p300

Both canonical Wnt/beta-catenin and TGFbeta/Smad signaling pathways coordinately regulate pattern formation during embryogenesis as well as tumor progression. Evidence of cross-talk between these two pathways has been reported. Here we demonstrated that the Activin-like kinase 4 (Alk4)/Smad2 pathway facilitates the transcriptional activity of the oncogenic Wnt/beta-catenin/Tcf4 pathway through a novel Smad4-independent mechanism. Upon activation, Smad2 physically interacted with Tcf4, beta-catenin and the co-activator p300 to enhance transcriptional activity of beta-catenin/Tcf4 through the histone acetyltransferase activity of p300. Transactivation by Smad2 was independent of a Smad-binding element (SBE) and Smad4. Indeed, the enhancement of beta-catenin/Tcf4 transcriptional activity by activated Smad2 was negatively regulated by the presence of Smad4. Moreover, a tumor-derived missense mutant of Smad2, lacking the ability to bind to Smad4 was still able to enhance the Tcf4 transcriptional reporter in the presence of beta-catenin and Tcf4. Our findings suggest that Smad2 may function as an activator of canonical Wnt/beta-catenin/Tcf4 signaling through a SBE/Smad4-independent pathway.

Breast cancer cells with acquired resistance to the EGFR tyrosine kinase inhibitor gefitinib show persistent activation of MAPK signaling

Although the epidermal growth factor receptor (EGFR) is frequently expressed in human primary breast carcinoma, the majority of breast cancer patients do not respond to treatment with EGFR tyrosine-kinase inhibitors such as gefitinib. We isolated through a stepwise dose escalation of the drug two gefitinib-resistant SK-Br-3 clones, ZD6 and ZD10 (ZD) cells, which showed, respectively, a three- to five-fold increase in the IC50 for gefitinib as compared with parental cells. The levels of expression of EGFR were increased in ZD cells as compared with wild-type SK-Br-3 cells. The phosphorylation of EGFR, ErbB-2, ErbB-3 and Akt was significantly reduced in gefitinib-resistant cells. In contrast, ZD cells showed levels of MAPK phosphorylation similar to untreated wild-type cells when cultured in presence of gefitinib. Persistent activation of MAPK was also observed in gefitinib-resistant clones isolated from MDA-MB-175 and MDA-MB-361 breast cancer cell lines. ZD cells showed an increased sensitivity to the MEK inhibitor PD98059 as compared with SK-Br-3 cells, and a synergistic anti-tumor effect was observed when ZD cells were treated with a combination of gefitinib and PD98059. Overexpression of a constitutively activated form of p42-MAPK in SK-Br-3 cells resulted in an approximately 50% increase in the IC50 to gefitinib. Finally, culture of ZD10 resistant cells in absence of gefitinib led to reversion of the resistant phenotype. These observations suggest that MAPK signaling might play a role in the resistance that develops in breast cancer cells after long-term exposure to gefitinib.

Regulation of human cripto-1 gene expression by TGF-β1 and BMP-4 in embryonal and colon cancer cells

Human Cripto‐1 (CR‐1) is a cell membrane protein that is overexpressed in several different types of human carcinomas. In the present study we investigated the mechanisms that regulate the expression of CR‐1 gene in cancer cells. We cloned a 2,481 bp 5′‐flanking region of the human CR‐1 gene into a luciferase reporter vector and transfected NTERA‐2 human embryonal carcinoma cells and LS174‐T colon cancer cells to test for promoter activity. Activity of CR‐1 promoter in both cell lines was modulated by two TGF‐β family members, TGF‐β1 and BMP‐4. In particular, TGF‐β1 significantly up‐regulated CR‐1 promoter activity, whereas a dramatic reduction in CR‐1 promoter activity was observed with BMP‐4 in NTERA‐2 and LS174‐T cells. Changes in the CR‐1 promoter activity following TGF‐β1 and BMP‐4 treatments correlated with changes in CR‐1 mRNA and protein expression in NTERA‐2 and LS174‐T cells. We also identified three Smad binding elements (SBEs) within the CR‐1 promoter and point mutation of SBE1 (−2,197/−2,189) significantly reduced response of the CR‐1 promoter to both TGF‐β1 and BMP‐4 in NTERA‐2 and LS174‐T cells. Chromatin immunoprecipitation assay also demonstrated binding of Smad‐4 to a CR‐1 promoter DNA sequence containing SBE1 in LS174‐T cells. Finally, BMP‐4 inhibited migration of LS174‐T cells and F9 mouse embryonal carcinoma cells by downregulation of CR‐1 protein. In conclusion, these results suggest a differential modulation of CR‐1 gene expression in embryonal and colon cancer cells by two different members of the TGF‐β family. J. Cell. Physiol. 215: 192–203, 2008.

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.