In JoVE (1)

Other Publications (16)

Articles by Nikki Cheng in JoVE

Other articles by Nikki Cheng on PubMed

Blockade of EphA Receptor Tyrosine Kinase Activation Inhibits Vascular Endothelial Cell Growth Factor-induced Angiogenesis

Molecular Cancer Research : MCR. Nov, 2002  |  Pubmed ID: 12496364

Angiogenesis is a multistep process involving a diverse array of molecular signals. Ligands for receptor tyrosine kinases (RTKs) have emerged as critical mediators of angiogenesis. Three families of ligands, vascular endothelial cell growth factors (VEGFs), angiopoietins, and ephrins, act via RTKs expressed in endothelial cells. Recent evidence indicates that VEGF cooperates with angiopoietins to regulate vascular remodeling and angiogenesis in both embryogenesis and tumor neovascularization. However, the relationship between VEGF and ephrins remains unclear. Here we show that interaction between EphA RTKs and ephrinA ligands is necessary for induction of maximal neovascularization by VEGF. EphA2 RTK is activated by VEGF through induction of ephrinA1 ligand. A soluble EphA2-Fc receptor inhibits VEGF-, but not basic fibroblast growth factor-induced endothelial cell survival, migration, sprouting, and corneal angiogenesis. As an independent, but complementary approach, EphA2 antisense oligonucleotides inhibited endothelial expression of EphA2 receptor and suppressed ephrinA1- and VEGF-induced cell migration. Taken together, these data indicate an essential role for EphA receptor activation in VEGF-dependent angiogenesis and suggest a potential new target for therapeutic intervention in pathogenic angiogenesis.

Soluble Eph A Receptors Inhibit Tumor Angiogenesis and Progression in Vivo

Oncogene. Oct, 2002  |  Pubmed ID: 12370823

The Eph family of receptor tyrosine kinases and their ligands, known as ephrins, play a crucial role in vascular development during embryogenesis. The function of these molecules in adult angiogenesis has not been well characterized. Here, we report that blocking Eph A class receptor activation inhibits angiogenesis in two independent tumor types, the RIP-Tag transgenic model of angiogenesis-dependent pancreatic islet cell carcinoma and the 4T1 model of metastatic mammary adenocarcinoma. Ephrin-A1 ligand was expressed in both tumor and endothelial cells, and EphA2 receptor was localized primarily in tumor-associated vascular endothelial cells. Soluble EphA2-Fc or EphA3-Fc receptors inhibited tumor angiogenesis in cutaneous window assays, and tumor growth in vivo. EphA2-Fc or EphA3-Fc treatment resulted in decreased tumor vascular density, tumor volume, and cell proliferation, but increased cell apoptosis. However, EphA2-Fc had no direct effect on tumor cell growth or apoptosis in culture, yet inhibited migration of endothelial cells in response to tumor cells, suggesting that the soluble receptor inhibited blood vessel recruitment by the tumor. These data provide the first functional evidence for Eph A class receptor regulation of pathogenic angiogenesis induced by tumors and support the function of A class Eph receptors in tumor progression.

The Ephrins and Eph Receptors in Angiogenesis

Cytokine & Growth Factor Reviews. Feb, 2002  |  Pubmed ID: 11750881

Eph receptors are a unique family of receptor tyrosine kinases that play critical roles in embryonic patterning, neuronal targeting, vascular development and adult neovascularization. Engagement of Eph receptors by ephrin ligands mediates critical steps of angiogenesis, including juxtacrine cell-cell contacts, cell adhesion to extracellular matrix, and cell migration. Recent evidence from in vitro angiogenesis assays and analysis of mice deficient for one or more members of the Eph family establishes the role of Eph signaling in sprouting angiogenesis and blood vessel remodeling during vascular development. Furthermore, elevated expression of Eph receptors and ephrin ligands is associated with tumors and associated tumor vasculature, suggesting that Eph receptors and their ephrin ligands also play critical roles in tumor angiogenesis and tumor growth. This review will focus on the relevance of Eph receptor signaling in embryonic and adult neovascularization, and possible contributions to tumor growth and metastasis.

Inhibition of VEGF-dependent Multistage Carcinogenesis by Soluble EphA Receptors

Neoplasia (New York, N.Y.). Sep-Oct, 2003  |  Pubmed ID: 14670182

Elevated expression of Eph receptors has long been correlated with the growth of solid tumors. However, the functional role of this family of receptor tyrosine kinases in carcinogenesis and tumor angiogenesis has not been well characterized. Here we report that soluble EphA receptors inhibit tumor angiogenesis and tumor progression in vivo in the RIP-Tag transgenic model of vascular endothelial growth factor (VEGF)-dependent multistage pancreatic islet cell carcinoma. Soluble EphA receptors delivered either by a transgene or an osmotic minipump inhibited the formation of angiogenic islet, a premalignant lesion, and reduced tumor volume of solid islet cell carcinoma. EphA2-Fc or EphA3-Fc treatment resulted in decreased tumor volume but increased tumor and endothelial cell apoptosis in vivo. In addition, soluble EphA receptors inhibited VEGF and betaTC tumor cell-conditioned medium-induced endothelial cell migration in vitro and VEGF-induced cornea angiogenesis in vivo. A dominant negative EphA2 mutant inhibited--whereas a gain-of-function EphA2 mutant enhanced--tumor cell-induced endothelial cell migration, suggesting that EphA2 receptor activation is required for tumor cell-endothelial cell interaction. These data provide functional evidence for EphA class receptor regulation of VEGF-dependent tumor angiogenesis, suggesting that the EphA signaling pathway may represent an attractive novel target for antiangiogenic therapy in cancer.

Genomic and Proteomic Analysis of Mammary Tumors Arising in Transgenic Mice

Journal of Proteome Research. Nov-Dec, 2005  |  Pubmed ID: 16335954

Transforming growth factor-beta (TGF-beta) is the prototype of a large family of signaling molecules. TGF-beta signaling profoundly influences tumor development as demonstrated in several engineered mouse models. The present study was designed to identify differences by cDNA microarray and MALDI-TOF MS analyses in mammary carcinomas with and without TGF-beta signaling. The results demonstrate a significant potential for combination of profiling technologies to further understand the molecular mechanisms of breast cancer.

Loss of TGF-beta Type II Receptor in Fibroblasts Promotes Mammary Carcinoma Growth and Invasion Through Upregulation of TGF-alpha-, MSP- and HGF-mediated Signaling Networks

Oncogene. Jul, 2005  |  Pubmed ID: 15856015

Stromal fibroblasts regulate epithelial cell behavior through direct and indirect cell-cell interactions. To clarify the role of TGF-beta signaling in stromal fibroblasts during mammary development and tumorigenesis, we conditionally knocked out the TGF-beta type II receptor gene in mouse mammary fibroblasts (Tgfbr2(fspKO)). Tgfbr2(fspKO) mice exhibit defective mammary ductal development, characterized in part by increased ductal epithelial cell turnover associated with an increase in stromal fibroblast abundance. Tgfbr2(fspKO) mammary fibroblasts transplanted with mammary carcinoma cells promote growth and invasion, which is associated with increased activating phosphorylation of the receptors: erbB1, erbB2, RON, and c-Met. Furthermore, the increased receptor phosphorylation correlates with increased secretion of the cognate ligands by Tgfbr2(fspKO) fibroblasts. Treatment of tumor cells with fibroblast-conditioned medium leads to increased tumor cell proliferation and motility, which are blocked by addition of pharmacologic inhibitors of TGF-alpha signaling or neutralizing antibodies to macrophage-stimulating protein (MSP), HGF, or c-Met. These studies characterize a significant role for stromal TGF-beta signaling in mammary tissue homeostasis and mammary tumor progression via regulation of TGF-alpha, MSP, and HGF signaling pathways.

Inhibition of Retinal Neovascularization by Soluble EphA2 Receptor

Experimental Eye Research. Apr, 2006  |  Pubmed ID: 16359662

Eph receptor tyrosine kinases (RTKs) and their ligands, known as ephrins, play an important role in vascular remodeling during embryogenesis, but their functions in adult angiogenesis are just beginning to be investigated. In this report, we investigated the effect of blocking EphA receptor activation on VEGF-induced angiogenic responses of cultured retinal endothelial cells and on retinal neovascularization in a rodent model of retinopathy of prematurity (ROP). Soluble EphA2-Fc receptors inhibited ephrin-A1 ligand or VEGF-induced BRMEC migration and tube formation without affecting proliferation in vitro. Since EphA2-Fc receptors can inhibit activation of multiple EphA receptors, the specific role of EphA2 receptor in angiogenesis was further investigated in EphA2-deficient endothelial cells. Loss of EphA2 in endothelial cells leads to defective cell migration and assembly in response to either ephrin-A1 or VEGF. Finally, a significant reduction in the severity of abnormal retinal neovascularization was observed in the eyes treated with soluble EphA2-Fc receptors, yet the normal total retinal vascular area was not significantly changed. Because soluble Eph receptor significantly inhibited pathologic retinal angiogenesis without affecting normal intraretinal vessels, it may be a promising agent for treatment of retinal angiogenesis in a number of human ocular diseases.

Epidermal Growth Factor Receptor Plays a Significant Role in Hepatocyte Growth Factor Mediated Biological Responses in Mammary Epithelial Cells

Cancer Biology & Therapy. Apr, 2007  |  Pubmed ID: 17495520

Breast cancers often have deregulated hepatocyte growth factor (HGF) and c-Met signaling that results in increased tumor growth and invasion. Elucidating the mechanism responsible for HGF/c-Met action in breast cancer progression has been difficult as c-Met communicates with a number of secondary receptors that can lead to various pathological outcomes. Understanding how these secondary receptors facilitate HGF/c-Met cellular responses will aid in the development of better therapeutic treatment options for breast cancer patients with elevated HGF signaling. In the present study it was shown that the epidermal growth factor receptor (EGFR) plays a significant role in HGF/c-Met mediated biological activities indicative of advanced tumor pathology, including enhanced proliferation and invasion. The clinically relevant EGFR inhibitor gefitinib was used to determine the role of EGFR in HGF-induced proliferation and motility in several mammary carcinoma cells including PyVmT, MDA-MB-231 and 4T1. Our analyses indicated that EGFR inhibition significantly blocked HGF activation of c-Met and EGFR and that inhibition of these pathways mitigated HGF induced proliferation and motility. The data indicate that this inhibition was not through a direct effect of gefitinib on c-Met, but that EGFR is necessary for c-Met activation in the assays performed. These results provide a novel mechanism of action for EGFR as a mediator of HGF signaling thereby linking EGFR to the oncogenic potential of c-Met in mammary carcinomas cells.

Enhanced Hepatocyte Growth Factor Signaling by Type II Transforming Growth Factor-beta Receptor Knockout Fibroblasts Promotes Mammary Tumorigenesis

Cancer Research. May, 2007  |  Pubmed ID: 17495323

Transforming growth factor-beta (TGF-beta) plays complex dual roles as an inhibitor and promoter of tumor progression. Although the influence of the stromal microenvironment on tumor progression is well recognized, little is known about the functions of TGF-beta signaling in the stroma during tumor progression. Using cre-lox technology, expression of the type II TGF-beta receptor was selectively knocked out in fibroblasts (Tgfbr2(FspKO)). In a co-xenograft model, we show that Tgfbr2(FspKO) fibroblasts enhance mammary carcinoma growth and metastasis in mice while increasing hepatocyte growth factor (HGF) expression and c-Met signaling downstream pathways including signal transducers and activators of transcription 3 (Stat3) and p42/44 mitogen-activated protein kinase (MAPK). Treatment of tumor-bearing mice with a pharmacologic inhibitor (EXEL-7592) of c-Met blocks tumor progression and reduces levels of phospho-Stat3 and phospho-p42/44 MAPK. Similarly, small interfering RNA knockdown of c-Met expression in mammary tumor cells reduces metastasis and c-Met signaling caused by Tgfbr2(FspKO) fibroblasts. The results show that TGF-beta signaling in fibroblasts suppresses tumor metastasis by antagonizing HGF/c-Met signaling within tumor epithelial cells. Furthermore, this co-xenograft model represents a unique context to study stromal TGF-beta and HGF signaling in mammary tumorigenesis.

Transforming Growth Factor-beta Signaling-deficient Fibroblasts Enhance Hepatocyte Growth Factor Signaling in Mammary Carcinoma Cells to Promote Scattering and Invasion

Molecular Cancer Research : MCR. Oct, 2008  |  Pubmed ID: 18922968

Fibroblasts are major cellular components of the tumor microenvironment, regulating tumor cell behavior in part through secretion of extracellular matrix proteins, growth factors, and angiogenic factors. In previous studies, conditional deletion of the type II transforming growth factor-beta (TGF-beta) receptor in fibroblasts (Tgfbr2FspKO) was shown to promote mammary tumor metastasis in fibroblast-epithelial cell cotransplantation studies in mice, correlating with increased expression of hepatocyte growth factor (HGF). Here, we advance our findings to show that Tgfbr2(FspKO) fibroblasts enhance HGF/c-Met and HGF/Ron signaling to promote scattering and invasion of mammary carcinoma cells. Blockade of c-Met and Ron by small interfering RNA silencing and pharmacologic inhibitors significantly reduced mammary carcinoma cell scattering and invasion caused by Tgfbr2FspKO fibroblasts. Moreover, neutralizing antibodies to c-Met and Ron significantly inhibited HGF-induced cell scattering and invasion, correlating with reduced Stat3 and p42/44MAPK phosphorylation. Investigation of the signal transducer and activator of transcription 3 (Stat3) and mitogen-activated protein kinase (MAPK) signaling pathways by pharmacologic inhibition and small interfering RNA silencing revealed a cooperative interaction between the two pathways to regulate HGF-induced invasion, scattering, and motility of mammary tumor cells. Furthermore, whereas c-Met was found to regulate both the Stat3 and MAPK signaling pathways, Ron was found to regulate Stat3 but not MAPK signaling in mammary carcinoma cells. These studies show a tumor-suppressive role for TGF-beta signaling in fibroblasts, in part by suppressing HGF signaling between mammary fibroblasts and epithelial cells. These studies characterize complex functional roles for HGF and TGF-beta signaling in mediating tumor-stromal interactions during mammary tumor cell scattering and invasion, with important implications in the metastatic process.

Identification of Novel Smad2 and Smad3 Associated Proteins in Response to TGF-beta1

Journal of Cellular Biochemistry. Oct, 2008  |  Pubmed ID: 18729074

Transforming growth factor-beta 1 (TGF-beta1) is an important growth inhibitor of epithelial cells and insensitivity to this cytokine results in uncontrolled cell proliferation and can contribute to tumorigenesis. TGF-beta1 signals through the TGF-beta type I and type II receptors, and activates the Smad pathway via phosphorylation of Smad2 and Smad3. Since little is known about the selective activation of Smad2 versus Smad3, we set out to identify novel Smad2 and Smad3 interacting proteins in epithelial cells. A non-transformed human cell line was transduced with Myc-His(6)-Smad2 or Myc-His(6)-Smad3-expressing retrovirus and was treated with TGF-beta1. Myc-His(6)-Smad2 or Myc-His(6)-Smad3 was purified by tandem affinity purification, eluates were subject to SDS-PAGE and Colloidal Blue staining, and select protein bands were digested with trypsin. The resulting tryptic peptides were analyzed by liquid chromatography (LC) and tandem mass spectrometry (MS/MS) and the SEQUEST algorithm was employed to identify proteins in the bands. A number of proteins that are known to interact with Smad2 or Smad3 were detected in the eluates. In addition, a number of putative novel Smad2 and Smad3 associated proteins were identified that have functions in cell proliferation, apoptosis, actin cytoskeleton regulation, cell motility, transcription, and Ras or insulin signaling. Specifically, the interaction between Smad2/3 and the Cdc42 guanine nucleotide exchange factor, Zizimin1, was validated by co-immunoprecipitation. The discovery of these novel Smad2 and/or Smad3 associated proteins may reveal how Smad2 and Smad3 are regulated and/or uncover new functions of Smad2 and Smad3 in TGF-beta1 signaling.

Abrogation of TGF-beta Signaling Enhances Chemokine Production and Correlates with Prognosis in Human Breast Cancer

The Journal of Clinical Investigation. Jun, 2009  |  Pubmed ID: 19451693

In human breast cancer, loss of carcinoma cell-specific response to TGF-beta signaling has been linked to poor patient prognosis. However, the mechanisms through which TGF-beta regulates these processes remain largely unknown. In an effort to address this issue, we have now identified gene expression signatures associated with the TGF-beta signaling pathway in human mammary carcinoma cells. The results strongly suggest that TGF-beta signaling mediates intrinsic, stromal-epithelial, and host-tumor interactions during breast cancer progression, at least in part, by regulating basal and oncostatin M-induced CXCL1, CXCL5, and CCL20 chemokine expression. To determine the clinical relevance of our results, we queried our TGF-beta-associated gene expression signatures in 4 human breast cancer data sets containing a total of 1,319 gene expression profiles and associated clinical outcome data. The signature representing complete abrogation of TGF-beta signaling correlated with reduced relapse-free survival in all patients; however, the strongest association was observed in patients with estrogen receptor-positive (ER-positive) tumors, specifically within the luminal A subtype. Together, the results suggest that assessment of TGF-beta signaling pathway status may further stratify the prognosis of ER-positive patients and provide novel therapeutic approaches in the management of breast cancer.

Chemokine Signaling in Cancer: Implications on the Tumor Microenvironment and Therapeutic Targeting

Cancer Therapy. Apr, 2009  |  Pubmed ID: 20651940

Chemokines are soluble factors shown to play important roles in regulating immune cell recruitment during inflammatory responses and defense against foreign pathogens. De-regulated expression and activity of several chemokine signaling pathways have been implicated in cancer progression, including: CCL2, CCL5, CXCL1 and CXCL12. While studies in the past have focused the role of these chemokine signaling pathways in regulating immune responses, emerging studies show that these molecules regulate diverse cellular processes including angiogenesis, and regulation of epithelial cell growth and survival. New evidence indicates that chemokines are critical for cancer progression and indicate complex and diverse functions in the tumor microenvironment. This review will focus on the contributions of chemokine signaling in regulating cancer microvironment and discuss the utility of targeting or delivering chemokines in cancer therapeutics.

Loss of Transforming Growth Factor-beta Signaling in Mammary Fibroblasts Enhances CCL2 Secretion to Promote Mammary Tumor Progression Through Macrophage-dependent and -independent Mechanisms

Neoplasia (New York, N.Y.). May, 2010  |  Pubmed ID: 20454514

Whereas the accumulation of fibroblasts and macrophages in breast cancer is a well-documented phenomenon and correlates with metastatic disease, the functional contributions of these stromal cells on breast cancer progression still remain largely unclear. Previous studies have uncovered a potentially important role for CCL2 inflammatory chemokine signaling in regulating metastatic disease through a macrophage-dependent mechanism. In these studies, we demonstrate a significant regulatory mechanism for CCL2 expression in fibroblasts in mediating mammary tumor progression and characterize multiple functions for CCL2 in regulating stromal-epithelial interactions. Targeted ablation of the transforming growth factor-beta (TGF-beta) type 2 receptor in fibroblasts (Tgfbr2(FspKO)) results in a high level of secretion of CCL2, and cografts of Tgfbr2(FspKO) fibroblasts with 4T1 mammary carcinoma cells enhanced tumor progression associated with recruitment of tumor-associated macrophages (TAMs). Antibody neutralization of CCL2 in tumor-bearing mice inhibits primary tumor growth and liver metastases as evidenced by reduced cell proliferation, survival, and TAM recruitment. Both high and low stable expressions of small interfering RNA to CCL2 in Tgfbr2(FspKO) fibroblasts significantly reduce liver metastases without significantly affecting primary tumor growth, cell proliferation, or TAM recruitment. High but not low knockdown of CCL2 enhances tumor cell apoptosis. These data indicate that CCL2 enhances primary tumor growth, survival, and metastases in a dose-dependent manner, through TAM-dependent and -independent mechanisms, with important implications on the potential effects of targeting CCL2 chemokine signaling in the metastatic disease.

Quantitative Analysis of the Secretome of TGF-beta Signaling-deficient Mammary Fibroblasts

Proteomics. Jul, 2010  |  Pubmed ID: 20405477

Transforming growth factor beta (TGF-beta) is a master regulator of autocrine and paracrine signaling pathways between a tumor and its microenvironment. Decreased expression of TGF-beta type II receptor (TbetaRII) in stromal cells is associated with increased tumor metastasis and shorter patient survival. In this study, SILAC quantitative proteomics was used to identify differentially externalized proteins in the conditioned media from the mammary fibroblasts with or without intact TbetaRII. Over 1000 proteins were identified and their relative differential levels were quantified. Immunoassays were used to further validate identification and quantification of the proteomic results. Differential expression was detected for various extracellular proteins, including proteases and their inhibitors, growth factors, cytokines, and extracellular matrix proteins. CXCL10, a cytokine found to be up-regulated in the TbetaRII knockout mammary fibroblasts, is shown to directly stimulate breast tumor cell proliferation and migration. Overall, this study revealed hundreds of specific extracellular protein changes modulated by deletion of TbetaRII in mammary fibroblasts, which may play important roles in the tumor microenvironment. These results warrant further investigation into the effects of inhibiting the TGF-beta signaling pathway in fibroblasts because systemic inhibition of TGF-beta signaling pathways is being considered as a potential cancer therapy.

Loss of One Tgfbr2 Allele in Fibroblasts Promotes Metastasis in MMTV: Polyoma Middle T Transgenic and Transplant Mouse Models of Mammary Tumor Progression

Clinical & Experimental Metastasis. Apr, 2011  |  Pubmed ID: 21374085

Accumulation of fibroblasts is a phenomenon that significantly correlates with formation of aggressive cancers. While studies have shown that the TGF-β signaling pathway is an important regulator of fibroblast activation, the functional contribution of TGF-β signaling in fibroblasts during multi-step tumor progression remains largely unclear. In previous studies, we used a sub-renal capsule transplantation model to demonstrate that homozygous knockout of the Tgfbr2 gene (Tgbr2(FspKO)) enhanced mammary tumor growth and metastasis. Here, we show for the first time a significant role for loss of one Tgfbr2 allele during multi-step mammary tumor progression. Heterozygous deletion of Tgfbr2 in stromal cells in MMTV-PyVmT transgenic mice (PyVmT/Tgfbr2(hetFspKO) mice) resulted in earlier tumor formation and increased stromal cell accumulation. In contrast to previous studies of Tgbr2(FspKO) fibroblasts, Tgfbr2(hetFspKO) fibroblasts did not significantly increase tumor growth, but enhanced lung metastasis in PyVmT transgenic mice and in co-transplantation studies with PyVmT mammary carcinoma cells. Furthermore, Tgfbr2(hetFspKO) fibroblasts enhanced mammary carcinoma cell invasiveness associated with expression of inflammatory cytokines including CXCL12 and CCL2. Analyses of Tgbr2(FspKO) and Tgfbr2(hetFspKO) fibroblasts revealed differences in the expression of factors associated with metastatic spread, indicating potential differences in the mechanism of action between homozygous and heterozygous deletion of Tgfbr2 in stromal cells. In summary, these studies demonstrate for the first time that loss of one Tgfbr2 allele in fibroblasts enhances mammary metastases in a multi-step model of tumor progression, and demonstrate the importance of clarifying the functional contribution of genetic alterations in stromal cells in breast cancer progression.

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