Jian Kang

Artemin is oncogenic for human mammary carcinoma cells.

We report that artemin, a member of the glial cell line-derived neurotrophic factor family of ligands, is oncogenic for human mammary carcinoma. Artemin is expressed in numerous human mammary carcinoma cell lines. Forced expression of artemin in mammary carcinoma cells results in increased anchorage-independent growth, increased colony formation in soft agar and in three-dimensional Matrigel, and also promotes a scattered cell phenotype with enhanced migration and invasion. Moreover, forced expression of artemin increases tumor size in xenograft models and leads to highly proliferative, poorly differentiated and invasive tumors. Expression data in Oncomine indicate that high artemin expression is significantly associated with residual disease after chemotherapy, metastasis, relapse and death. Artemin protein is detectable in 65% of mammary carcinoma and its expression correlates to decreased overall survival in the cohort of patients. Depletion of endogenous artemin with small interfering RNA, or antibody inhibition of artemin, decreases the oncogenicity and invasiveness of mammary carcinoma cells. Artemin is therefore oncogenic for human mammary carcinoma, and targeted therapeutic approaches to inhibit artemin function in mammary carcinoma warrant consideration.

Cyclin E2 Overexpression Is Associated with Endocrine Resistance but not Insensitivity to CDK2 Inhibition in Human Breast Cancer Cells

Cyclin E2, but not cyclin E1, is included in several gene signatures that predict disease progression in either tamoxifen-resistant or metastatic breast cancer. We therefore examined the role of cyclin E2 in antiestrogen resistance in vitro and its potential for therapeutic targeting through cyclin-dependent kinase (CDK) inhibition. High expression of CCNE2, but not CCNE1, was characteristic of the luminal B and HER2 subtypes of breast cancer and was strongly predictive of shorter distant metastasis-free survival following endocrine therapy. After antiestrogen treatment of MCF-7 breast cancer cells, cyclin E2 mRNA and protein were downregulated and cyclin E2–CDK2 activity decreased. However, this regulation was lost in tamoxifen-resistant (MCF-7 TAMR) cells, which overexpressed cyclin E2. Expression of either cyclin E1 or E2 in T-47D breast cancer cells conferred acute antiestrogen resistance, suggesting that cyclin E overexpression contributes to the antiestrogen resistance of tamoxifen-resistant cells. Ectopic expression of cyclin E1 or E2 also reduced sensitivity to CDK4, but not CDK2, inhibition. Proliferation of tamoxifen-resistant cells was inhibited by RNAi-mediated knockdown of cyclin E1, cyclin E2, or CDK2. Furthermore, CDK2 inhibition of E-cyclin overexpressing cells and tamoxifen-resistant cells restored sensitivity to tamoxifen or CDK4 inhibition. Cyclin E2 overexpression is therefore a potential mechanism of resistance to both endocrine therapy and CDK4 inhibition. CDK2 inhibitors hold promise as a component of combination therapies in endocrine-resistant disease as they effectively inhibit cyclin E1 and E2 overexpressing cells and enhance the efficacy of other therapeutics. Mol Cancer Ther; 11(7); 1488–99. ©2012 AACR.

Artemin Stimulates Oncogenicity and Invasiveness of Human Endometrial Carcinoma Cells

Here, we provide evidence for a functional role of artemin (ARTN) in progression of endometrial carcinoma (EC). Increased ARTN protein expression was observed in EC compared with normal endometrial tissue, and ARTN protein expression in EC was significantly associated with higher tumor grade and invasiveness. Forced expression of ARTN in EC cells significantly increased total cell number as a result of enhanced cell cycle progression and cell survival. In addition, forced expression of ARTN significantly enhanced anchorage-independent growth and invasiveness of EC cells. Moreover, forced expression of ARTN increased tumor size in xenograft models and produced highly proliferative, poorly differentiated, and invasive tumors. The ARTN-stimulated increases in oncogenicity and invasion were mediated by increased expression and activity of AKT1. Small interfering RNA-mediated depletion or antibody inhibition of ARTN significantly reduced oncogenicity and invasion of EC cells. Thus, inhibition of ARTN may be considered as a potential therapeutic strategy to retard progression of EC.

Artemin is estrogen regulated and mediates antiestrogen resistance in mammary carcinoma

We have previously identified an oncogenic role of artemin (ARTN), a member of glial cell derived neurotrophic factor family of ligands, in mammary carcinoma. We herein report that ARTN is an estrogen-inducible gene. Meta-analysis of gene expression data sets showed that ARTN expression is positively correlated to estrogen receptor (ER) status in human mammary carcinoma. Furthermore, in patients with ER-positive mammary carcinoma treated with tamoxifen, high ARTN expression is significantly correlated with decreased survival. Forced expression of ARTN in ER-positive human mammary carcinoma cells increased ER transcriptional activity, promoted estrogen-independent growth and produced resistance to tamoxifen and fulvestrant in vitro and to tamoxifen in xenograft models. ARTN-stimulated resistance to tamoxifen and fulvestrant is mediated by increased BCL-2 expression. Conversely, depletion of endogenous ARTN by small-interfering RNA or functional antagonism of ARTN by antibody enhanced the efficacy of antiestrogens. Tamoxifen decreased ARTN expression in tamoxifen-sensitive mammary carcinoma cells whereas ARTN expression was increased in tamoxifen-resistant cells and not affected by tamoxifen treatment. Antibody inhibition of ARTN in tamoxifen-resistant cells improved tamoxifen sensitivity. Functional antagonism of ARTN therefore warrants consideration as an adjuvant therapy to enhance antiestrogen efficacy in ER-positive mammary carcinoma.

ARTEMIN synergizes with TWIST1 to promote metastasis and poor survival outcome in patients with ER negative mammary carcinoma

IntroductionARTEMIN (ARTN) is an estrogen regulated growth factor, the expression of which promotes resistance to antiestrogen therapies and predicts poorer survival outcome of patients with estrogen receptor (ER) positive mammary carcinoma (ER+MC) treated with tamoxifen. ARTN is also expressed in ER negative mammary carcinoma (ER-MC). Herein, we determined the role of ARTN in ER-MC and defined the mechanism of action producing poor patient prognosis.MethodsWe modulated the expression of ARTN in two ER- (mesenchymal/claudin-low) mammary carcinoma cell lines (BT549 and MDA-MB-231) by forced expression or small interfering RNA (siRNA) mediated depletion. The effects of modulation of ARTN expression were examined by various in vitro measures of oncogenicity, including the expression of TWIST1 messenger RNA (mRNA) and protein. In vitro results were correlated to xenograft studies in immunodeficient mice. Co-expression of ARTN and TWIST1 and their association to poor survival outcome were examined in a cohort of patients with ER-MC. Pathway analysis was performed by pharmacological inhibition of phosphorylation of AKT (pAKT-Ser 473) or modulation of TWIST1 expression.ResultsARTN expression resulted in ER-MC cells with enhanced mesenchymal characteristics, including increased invasion and a gene expression profile consistent with enhanced mesenchymal phenotype. ARTN stimulated ER-MC cell anchorage independent and 3D matrigel growth, endothelial cell adhesion and transmigration of ER-MC cells through an endothelial cell barrier. Forced expression of ARTN produced a larger, locally invasive tumour mass with tumour emboli that produced distant metastasis. ARTN regulated TWIST1 expression in ER-MC cells and ARTN expression was significantly correlated to TWIST1 expression in a panel of mammary carcinoma cell lines and in a cohort of patients with ER-MC. Low expression of both ARTN and TWIST1 predicted 100% relapse free and overall survival in patients with ER-MC, whereas high expression of both ARTN and TWIST1 was associated with a poor survival outcome. ARTN stimulated an increase in TWIST1 expression via increased AKT activity. siRNA mediated depletion of TWIST1 abrogated ARTN stimulated cellular behaviour associated with metastasis, and forced expression of TWIST1 abrogated the functional effects of ARTN depletion.ConclusionsARTN and TWIST1 synergize to produce a worse outcome in ER-MC and combined inhibition of ARTN and phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) may therefore provide a novel therapeutic strategy in this subtype of mammary carcinoma.

Artemin-stimulated progression of human non-small cell lung carcinoma is mediated by BCL2

We herein show that Artemin (ARTN), one of the glial cell line–derived neurotrophic factor family of ligands, promotes progression of human non–small cell lung carcinoma (NSCLC). Oncomine data indicate that expression of components of the ARTN signaling pathway (ARTN, GFRA3, and RET) is increased in neoplastic compared with normal lung tissues; increased expression of ARTN in NSCLC also predicted metastasis to lymph nodes and a higher grade in certain NSCLC subtypes. Forced expression of ARTN stimulated survival, anchorage-independent, and three-dimensional Matrigel growth of NSCLC cell lines. ARTN increased BCL2 expression by transcriptional upregulation, and inhibition of BCL2 abrogated the oncogenic properties of ARTN in NSCLC cells. Forced expression of ARTN also enhanced migration and invasion of NSCLC cells. Forced expression of ARTN in H1299 cells additionally resulted in larger xenograft tumors, which were highly proliferative, invasive, and metastatic. Concordantly, either small interfering RNA–mediated depletion or functional inhibition of endogenous ARTN with antibodies reduced oncogenicity and invasiveness of NSCLC cells. ARTN therefore mediates progression of NSCLC and may be a potential therapeutic target for NSCLC. Mol Cancer Ther; 9(6); 1697–708. ©2010 AACR.

ARTEMIN Promotes De Novo Angiogenesis in ER Negative Mammary Carcinoma through Activation of TWIST1-VEGF-A Signalling

The neurotrophic factor ARTEMIN (ARTN) has been reported to possess a role in mammary carcinoma progression and metastasis. Herein, we report that ARTN modulates endothelial cell behaviour and promotes angiogenesis in ER-mammary carcinoma (ER-MC). Human microvascular endothelial cells (HMEC-1) do not express ARTN but respond to exogenously added, and paracrine ARTN secreted by ER-MC cells. ARTN promoted endothelial cell proliferation, migration, invasion and 3D matrigel tube formation. Angiogenic behaviour promoted by ARTN secreted by ER-MC cells was mediated by AKT with resultant increased TWIST1 and subsequently VEGF-A expression. In a patient cohort of ER-MC, ARTN positively correlated with VEGF-A expression as measured by Spearman’s rank correlation analysis. In xenograft experiments, ER-MC cells with forced expression of ARTN produced tumors with increased VEGF-A expression and increased microvessel density (CD31 and CD34) compared to tumors formed by control cells. Functional inhibition of ARTN by siRNA decreased the angiogenic effects of ER-MC cells. Bevacizumab (a humanized monoclonal anti-VEGF-A antibody) partially inhibited the ARTN mediated angiogenic effects of ER-MC cells and combined inhibition of ARTN and VEGF-A by the same resulted in further significant decrease in the angiogenic effects of ER-MC cells. Thus, ARTN stimulates de novo tumor angiogenesis mediated in part by VEGF-A. ARTN therefore co-ordinately regulates multiple aspects of tumor growth and metastasis.