Abstract
Fibroblasts are the principal cellular component of connective tissue and are associated with cancer cells at all stages of tumor progression. Structural and functional contributions of fibroblasts to the growth, survival, and invasive capacity of cancer cells are beginning to emerge. In breast carcinoma, approximately 80% of stromal fibroblasts termed cancer-associated fibroblasts (CAF) are thought to manifest an activated phenotype that promotes cancer cell proliferation tumor growth at metastatic sites similar to the primary tumor. In this report, we show that CAFs respond to physiologic concentrations of 17beta-estradiol (E2) by rapidly inducing extracellular signal-regulated kinase phosphorylation and immediate early gene expression, including c-fos and connective tissue growth factor, and cyclin D1. Notably, the E2 response is mediated by the alternate estrogen receptor GPR30, which interfaces with the epidermal growth factor receptor (EGFR) signaling pathway. In particular, E2 stimulates a physical interaction between GPR30 and phosphorylated EGFR, recruiting them to the cyclin D1 gene promoter. Nuclear localization induced by E2 was confirmed by cellular immunofluorescence methods. GPR30 was required for CAF proliferation and migration induced by E2. Our results provide important new mechanistic insights into how CAFs are stimulated by estrogen through a GPR30-mediated nuclear signaling pathway. More generally, they define estrogenic GPR30 signaling as a functionally important component of the tumor microenvironment.