Oncogenic functions of ARTEMIN in ER negative mammary carcinoma

Abstract

ARTEMIN (ARTN) is an estrogen regulated gene. The expression of ARTN promotes resistance to antiestrogen therapies; therefore, patients with estrogen receptor (ER) positive mammary carcinoma (ER+MC) treated with tamoxifen have poorer survival outcome. ARTN is also expressed in ER negative mammary carcinoma (ER-MC). Herein, I have demonstrated that ARTN promotes TWIST1 dependent epithelial to mesenchymal transition (EMT) of mammary carcinoma cells, which is associated with metastasis and poor survival outcome. ARTN modulates the expression of TWIST1 via AKT1 dependent signalling in ER-mammary carcinoma (ER-MC) cells. siRNA mediated depletion of TWIST1 abrogated ARTN stimulated cellular behavior associated with metastasis, and forced expression of TWIST1 abrogated the functional effects of ARTN depletion. Next, I also found ARTN mediated acquired resistance of mammary carcinoma cells to ionizing radiation (IR) or paclitaxel resistance by promoting TWIST1-BCL-2 dependent cancer stem cell-like (CSC) behavior. Herein, I have demonstrated that ARTN modulates the expression of CSC-like cells by increasing mammospheres, ALDH1+ populations. Furthermore, increased ARTN expression was significantly correlated with ALDH1 and BCL-2 expression in an ER-MC patient cohort. Forced expression of ARTN also dramatically enhanced tumour initiating capacity of mammary carcinoma cells in xenograft models at low inoculums. In addition, I have reported ARTN modulations of endothelial cell behavior and resultant increase of angiogenesis in ER-MC. ARTN promoted endothelial cell proliferation, migration, invasion and 3D matrigel tube formation. Angiogenic behavior promoted by ARTN was mediated by AKT1 with resultant increased TWIST1 and subsequently VEGF-A expression. In a patient cohort, ARTN was positively correlated with VEGF-A expression. In xenograft, ARTN produced tumours exhibited increased VEGF-A expression and microvessel density (CD31 and CD34) compared to tumours formed by control cells. Functional inhibition of VEGF-A by siRNA or bevacizumab (a humanized monoclonal anti-VEGF-A antibody) partially inhibited the ARTN mediated angiogenic effects of ER-MC cells. Thus, ARTN co-ordinates and regulates multiple aspects of tumour growth and metastasis in mammary carcinoma.