GPER-mediated proliferation and estradiol production in breast cancer-associated fibroblasts

• Published in: Endocrine-related cancer Vol. 21; no. 2; pp. 355 - 369
• Main Authors: Luo, Haojun, Yang, Guanglun, Yu, Tenghua, Luo, Shujuan, Wu, Chengyi, Sun, Yan, Liu, Manran, Tu, Gang
• Format: Journal Article
• Language: English
• Published: England Bioscientifica Ltd 01.04.2014
• Subjects: Breast Neoplasms - metabolism; Cell Cycle - drug effects; Cell Proliferation - drug effects; Cells, Cultured; Cyclopentanes - pharmacology; Estradiol - pharmacology; Female; Fibroblasts - drug effects; Fibroblasts - metabolism; Humans; Quinolines - pharmacology; Receptors, Estrogen - agonists; Receptors, Estrogen - metabolism; Receptors, G-Protein-Coupled - agonists; Receptors, G-Protein-Coupled - metabolism; Tamoxifen - pharmacology; CAF; breast cancer; tamoxifen resistance; GPER
• ISSN: 1351-0088; 1479-6821
• DOI: 10.1530/ERC-13-0237

Cancer-associated fibroblasts (CAFs) are crucial co-mediators of breast cancer progression. Estrogen is the predominant driving force in the cyclic regulation of the mammary extracellular matrix, thus potentially affecting the tumor-associated stroma. Recently, a third estrogen receptor, estrogen (G-protein-coupled) receptor (GPER), has been reported to be expressed in breast CAFs. In this study, GPER was detected by immunohistochemical analysis in stromal fibroblasts of 41.8% (59/141) of the primary breast cancer samples. GPER expression in CAFs isolated from primary breast cancer tissues was confirmed by immunostaining and RT-PCR analyses. Tamoxifen (TAM) in addition to 17β-estradiol (E2) and the GPER agonist G1 activated GPER, resulting in transient increases in cell index, intracellular calcium, and ERK1/2 phosphorylation. Furthermore, TAM, E2, and G1 promoted CAF proliferation and cell-cycle progression, both of which were blocked by GPER interference, the selective GPER antagonist G15, the epidermal growth factor receptor (EGFR) inhibitor AG1478, and the ERK1/2 inhibitor U0126. Importantly, TAM as well as G1 increased E2 production in breast CAFs via GPER/EGFR/ERK signaling when the substrate of E2, testosterone, was added to the medium. GPER-induced aromatase upregulation was probably responsible for this phenomenon, as TAM- and G1-induced CYP19A1 gene expression was reduced by GPER knockdown and G15, AG1478, and U0126 administration. Accordingly, GPER-mediated CAF-dependent estrogenic effects on the tumor-associated stroma are conceivable, and CAF is likely to contribute to breast cancer progression, especially TAM resistance, via a positive feedback loop involving GPER/EGFR/ERK signaling and E2 production.