Signal Transduction VDR Status Arbitrates the Prometastatic Effects of Tumor- Associated Macrophages

The relationship between tumor-associated macrophages (TAM) and epithelial-to-mesenchymal transition (EMT) during the initiation and progression of metastasis is still unclear. Here, a role for the vitamin D receptor (VDR) in metastasis was identified, as well as a role in the relationship between TAMs and EMT. First, the expression level of VDRwas examined in clinical tissue fromhuman patients with breast cancer or amousemodel of breast cancer with differential metastasis. These results revealed that VDR expression negatively correlates with metastasis in breast cancer. Second, coculture of VDR-overexpressing breast cancer cells with amacrophage cell line demonstrated that overexpression of VDR alleviated the prometastatic effect of cocultured macrophages on breast cancer cells. Furthermore, VDRoverexpression abrogated the induction of EMT in breast cancer cells by cocultured macrophage cells, as measured by a loss of E-cadherin (CDH1) and induction ofa-smooth muscle actin (a-SMA). TNFa in macrophage conditioned media inhibited VDR expression, whereas downregulation of VDR further mediated the promotion of TGFb-induced EMT by TNFa. In addition, b-catenin expression was inhibited in VDR-overexpressing breast cancer cells and tumor xenografts. Finally, administration of calcitriol [1,25-(OH) 2D3], an active vitaminDmetabolite, exerted similar antimetastatic effects in breast cancer cells in vitro and amouse model of breast cancer in vivo with preservation of VDR and suppression of b-catenin. Implications:VDR suppression byTNFamediates the prometastatic effect of TAMs through enhancement of the b-catenin pathway. Mol Cancer Res; 12(8); 1–11. 2014 AACR. Introduction Metastasis has emerged as the primary cause of poor prognosis for patients with breast cancer, in part, as a result of significant progress in the early diagnosis and therapy during recent years. Accumulating evidence suggests that the derangement of the tumor microenvironment is one of the critical factors in the malignant progression of tumor. The tumormicroenvironment includes a wide variety of cells that are involved in the acquisition of malignant tumor hallmark traits (1). It is currently believed that macrophages are the most abundant cells in the tumor microenvironment, playing active roles in almost all aspects of tumor growth and development (2, 3). Antitumor strategies targeting tumorassociated macrophages (TAM) have achieved encouraging results in impairing the metastasis of solid tumors (4, 5). Several factors have been found to be involved in macrophage-stimulated invasiveness, such as an EGF—colonystimulating factor 1 (CSF1) paracrine interaction, the Wnt5a noncanonical pathway, and the induction of TNFa by theNF-kBpathway (6–8).However, the precisemechanisms underlying the prometastatic role of macrophages remain to be fully elucidated. The vitamin D receptor (VDR) belongs to the nuclear hormone receptor superfamily and mediates the major biologic effects of vitamin D. Upon ligand binding, VDR recruits and forms complexes with cofactors such as the retinoid X receptor. The complex then binds to the VDR element in the promoter region of target genes to regulate gene transcription. Previous studies have shown that VDR gene polymorphism alters the risk of breast cancer (9–11). Comparative genome analysis identified VDR as a direct transcriptional target of p53 and that VDR plays a role in p53-mediated suppression of tumor growth (12). More recently, a positive association between VDR expression level and a prolonged progression-free and overall survival of patients with breast cancer have been reported (13). However, the mechanisms behind the loss of VDR and its subsequent influence on tumor metastasis remain poorly understood. Authors' Affiliations: Departments of Immunology and Pathology, Medical School of Nankai University, Tianjin; and State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu, China Note: Supplementary data for this article are available at Molecular Cancer Research Online (http://mcr.aacrjournals.org/). Corresponding Authors: Xiaoyue Tan, Department of Pathology, Medical School of Nankai University, 94 Weijin Road, Tianjin 300071, China. Phone: 86-22-23504447; Fax: 86-22-23502554; E-mail: [email protected]; and Rong Xiang. Phone: 86-22-23509505; Fax: 86-22-23502554; E-mail: [email protected] doi: 10.1158/1541-7786.MCR-14-0036 2014 American Association for Cancer Research. Molecular Cancer Research www.aacrjournals.org OF1 on June 24, 2017. © 2014 American Association for Cancer Research. mcr.aacrjournals.org Downloaded from Published OnlineFirst May 12, 2014; DOI: 10.1158/1541-7786.MCR-14-0036