Cell-Contact Dependent Epithelial-Stromal Cross Talk, Including A Modulation Of Stromal Pdgfr Expression, Drives The Progression Of Early-Stage Breast Cancer Lesions

We have investigated the distribution of PDGFR-a and -b in the stroma of normal breast tissue, ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) by immunohistochemistry. Both receptors were expressed by fibroblasts of normal breast tissue. While the PDGFRb remained high during cancer progression, the PDGFRa was lost in most of the DCIS samples and not detectable in IDC. The patient group with PDGFRa(low)/PDGFRb(high) fibroblasts had the highest risk for local recurrences or metastasis. The characteristic loss of stromal PDGFRa expression was also observed in the PyMT mouse breast cancer model. In vitro co-culture experiments confirmed a tumor cell-induced differentiation of fibroblasts, resulting in a fibroblast population marked by PDGFRa(low)/PDGFRb(high) expression. We could identify the interaction of Jagged-1 expressed by the tumor cells with Notch-2 expressed on the fibroblasts, as an essential activator of TGFb signaling in fibroblasts. Gene expression analysis and reporter-gene assays of sorted cells from co-cultures revealed, that fibroblasts switch from a more anti-tumorigenic signaling (expression of BMPs and Wnt antagonists) towards a pro-tumorigenic signaling (expression of BMP inhibitors, TGFb and Wnt ligands). Co-cultured tumor cells show an increased migratory activity and the induction of a mesenchymal phenotype. Inhibition of Notch or TGF signaling in fibroblasts could block these phenotypes. To investigate the impact of fibroblasts on the progression of DCIS to IDC, a DCIS xenograft model was used. Co-injection of MCF10.DCIS cells with human breast fibroblasts, expressing both PDGFRs, into the mouse mammary fat pad resulted in an earlier tumor take with faster tumor growth. The corresponding co-injection experiments with fibroblast and tumor cells, that were depleted of Notch2 respectively Jagged-1 expression by CRISPR/CAS technology is currently ongoing. Collectively the study identifies a potentially druggable paracrine cross-talk between epithelial and stromal cells, which promotes DCIS progression and involves a Notch mediated up-regulation of TGFb signaling. The study also suggests that loss of PDGFRa marks a subset of fibroblasts with specific tumor-promoting activities. Citation Format: Carina Strell, Janna Paulsson, Artur Mezheyeuski, Shao-Bo Jin, Pernilla Roswall, Johanna Andrea, Oliver Frings, Fredrick Warnberg, Hemming Johansson, Karin Jirstrom, Kristian Pietras, Per Hall, Urban Lendahl, Christer Betsholtz, Derek C. Radisky, Arne Ostman. Cell-contact dependent epithelial-stromal cross talk, including a modulation of stromal PDGFR expression, drives the progression of early-stage breast cancer lesions. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr B41.