Estrogen receptor (ER)-negative breast cancer cells are probably more aggressive with larger metastatic potential than ER-positive cells. Loss of ER in recurrent breast cancer is associated with poor response to endocrine therapy. G protein-coupled receptor 30 (GPR30) is expressed in half of ER-negative breast cancers. Tumor cell-derived heregulin-beta 1 (HRG-beta 1) is also found mainly in ER-negative cancer. In SkBr3 breast cancer cells that lack ER but express GPR30, HRG-beta 1 upregulates mRNA and protein levels of GPR30 by promoting ErbB2-ErbB3 heterodimerization and activating the downstream MAPK-ERK signaling pathway. Moreover, GPR30 boosts HRG-beta 1 -induced migration and invasion of SkBr3 cells after combinative treatment with E2, 4-hydroxy-tamoxifen or the specific GPR30 agonist G-1, which are blocked by the specific GPR30 antagonist G-15 or the transfection with the small interfering RNA for GPR30. The ErbB2 inhibitor AG825 and the MEK1/2 inhibitor U0126 also partly inhibit the enhanced migration and invasion. Therefore, HRG-beta 1 -induced migration and invasion partly depend on the upregulation of GPR30 expression through activation of the ErbB2-ERK pathway in SkBr3 cells. The results of this study indicate that the crosstalk between GPR30 and HRGs signaling is important for endocrine therapy resistance and may provide a new therapeutic way to treat breast cancer. (C) 2012 Elsevier Inc. All rights reserved.