Abstract 3848: Abrogation of TGF-β signaling promotes mammary carcinoma progression by enhanced Th17 response
Authors: Novitskiy Sergey V. , Pickup Michael W. , Gorska Agnieszka E. , Harold Moses L. 
Published: February 2011

We have shown that TGF-β signaling in carcinoma cells can suppress the expression of chemokines that are responsible for the expansion and recruitment of myeloid derived suppressor cells (MDSCs) in tumor bearing mice. Using mice with conditional deletion of the type II TGF-β receptor gene (Tgfbr2) in mammary epithelial cells we have shown that derivative MMTV-PyMT induced carcinomas were better able to recruit tumor-promoting MDSCs than carcinomas with intact TGF-β signaling. This recruitment correlated with higher levels of Cxcl1/5 expression in tumors lacking intact TGF-β signaling. Cxcl1/5 signal through the CXCR2 receptor and it has been shown that CXCR2 signaling in vitro was able to promote migration and invasion of MDSC. IL-17 can up-regulate secretion of Cxc chemokines by epithelial cells. Differentiation of Th17 cells in the tumor microenvironment depends on the balance of cytokines such as TGF-β, IL-6 and IL-23, which are primarily produced by tumor infiltrating myeloid cells. Based on this information, we hypothesize that loss of TGF-β signaling in carcinoma cells results in increased tumor volume through an enhanced Th17 response.

In vivo studies were performed using a spontaneous tumor model MMTV-PyMT and MMTV-PyMT/Tgfbr2 KO. On 7-9 days after tumor formation we isolated tumor tissue and prepared single cell suspensions which were used for flow cytometry analysis and for FACS sorting. CD4+ cells were isolated by CD4 Microbeads from Miltenyi Biotec. For in vitro studies we used immortalized epithelial cell lines which were prepared from PyMT tumors of MMTV-WT and MMTV-KO mice. Levels of cytokines were measured by ELISA.

We found that MDSCs don't express CXCR2 in the lung and tumor tissue compared with MDSCs from the spleen and bone marrow. Carcinoma cells without Tgbr2 produce more CXCL1/5 and ELISA data showed that release of these two chemokines is upregulated by IL-17. Also, we have found increased expression of IL-17r on knockout epithelial cells and these cells are 4 times more sensitive to low concentrations of IL-17. In parallel, we found that TGF-β decreases secretion of CXCL1/5 from normal epithelial cells but not from cells without Tgbr2. Levels of TGF-β and IL-6, which are important for differentiation of Th17 cells, are increased in tumor tissue without Tgbr2. These data are paralleled with an increased number of Th-17 cells and level of IL-17. In addition, we discovered a secondary effect of IL-17 in increasing the suppressive function of MDSC's on T cells through the upregulation of Arg, IDO and COX2.

We conclude that the tumor microenvironment of mammary carcinomas with defective TGF-β signaling in epithelial cells have increased levels of IL-17 which enhance tumor progression thru increased MDSCs migration and enhanced suppressive function.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3848.