Multiple drug resistance is a challenging issue in the clinic. There is growing evidence that the G-protein-coupled estrogen receptor (GPER) is a novel mediator in the development of multidrug resistance in both estrogen receptor (ER)-positive and -negative breast cancers, and that cancer-associated fibroblasts (CAFs) in the tumor microenvironment may be a new agent that promotes drug resistance in tumor cells. However, the role of cytoplasmic GPER of CAFs on tumor therapy remains unclear. Here we first show that the breast tumor cell-activated PI3K/AKT (phosphoinositide 3-kinase/AKT) signaling pathway induces the cytoplasmic GPER translocation of CAFs in a CRM1-dependent pattern, and leads to the activation of a novel estrogen/GPER/cAMP/PKA/CREB signaling axis that triggers the aerobic glycolysis switch in CAFs. The glycolytic CAFs feed the extra pyruvate and lactate to tumor cells for augmentation of mitochondrial activity, and this energy metabolically coupled in a ‘host–parasite relationship’ between catabolic CAFs and anabolic cancer cells confers the tumor cells with multiple drug resistance to several conventional clinical treatments including endocrine therapy (tamoxifen), Her-2-targeted therapy (herceptin) and chemotherapy (epirubicin). Moreover, the clinical data from 18F-fluorodeoxyglucose positron emission tomography/computed tomography further present a strong association between the GPER/cAMP/PKA/CREB pathway of stromal fibroblasts with tumor metabolic activity and clinical treatment, suggesting that targeting cytoplasmic GPER in CAFs may rescue the drug sensitivity in patients with breast cancer. Thus, our data define novel insights into the stromal GPER-mediated multiple drug resistance from the point of reprogramming of tumor energy metabolism and provide the rationale for CAFs as a promising target for clinical therapy.

The activation of cancer-associated fibroblasts (CAFs) is a key event in tumor progression, and alternative extracellular matrix (ECM) proteins derived from CAFs induce ECM remodeling and cancer cell invasion. Here we found that miR-200 s, which are generally downregulated in activated CAFs in breast cancer tissues and in normal fibroblasts (NFs) activated by breast cancer cells, are direct mediators of NF reprogramming into CAFs and of ECM remodeling. NFs with downregulated miR-200 s displayed the traits of activated CAFs, including accelerated migration and invasion. Ectopic expression of miR-200 s in CAFs at least partially restored the phenotypes of NFs. CAF activation may be governed by the targets of miR-200 s, Fli-1 and TCF12, which are responsible for cell development and differentiation; Fli-1 and TCF12 were obviously elevated in CAFs. Furthermore, miR-200 s and their targets influenced collagen contraction by CAFs. The upregulation of fibronectin and lysyl oxidase directly by miR-200 or indirectly through Fli-1 or TCF12 contributed to ECM remodeling, triggering the invasion and metastasis of breast cancer cells both in vitro and vivo. Thus, these data provide important and novel insights into breast CAF activation and ECM remodeling, which trigger tumor cell invasion.

Expression of Id-1 (inhibitors of DNA binding/differentiation protein 1) and TSP-1 (thrombospondin-1) in mucoepidermoid carcinoma and their relationship to pathological features and prognosis was studied. Moderately and poorly differentiated groups had significantly higher Id-1 positive expression rate (p<0.05) than well differentiated carcinoma. Stages III-IV showed significant increase of Id-1 positive expression rate (p<0.05) compared with stages I and II. Id-1 positive expression was significantly higher in patients with cervical lymph node metastasis or relapse at 5 years (p<0.05). After that, patients with negative Id-1 expression had significantly higher tumor-free survival than patients with positive expression (p<0.05). Correlation between the expression of Id-1 and TSP-1 in mucoepidermoid carcinoma was negative (p<0.05). Poorly differentiated groups show significantly lower TSP-1 positive expression rate than well differentiated groups (p<0.05). No significant differences of TSP-1 positive expression were detected with clinical stage. TSP-1 positive expression was significantly lower in patients with cervical lymph node metastasis or relapse at 5 years (p<0.05). After 5 years, patients with positive TSP-1 expression had significantly higher tumor-free survival than patients with negative TSP-1. Positive Id-1 expression is associated with high malignancy/poor prognosis; positive TSP-1 expression is associated with low malignancy/good prognosis. Protein expression status may help assess tumor malignancy and patient prognosis.