We found that HBO1 was notably increased in breast cancer. E2-upregulated HBO1 expression could be inhibited by ICI 182,780 or ERα RNAi in breast cancer cells. Furthermore, we also showed that ERK1/2 signaling pathway was involved in the expression of HBO1 increased by E2. Methods Materials Dulbecco’s modified Eagle’s medium (DMEM), phenol red-free DMEM (PR-free DMEM), U0126 and

17β-estradiol (E2) were purchased from Sigma. Lipofectamine 2000, Trizol Reagent and fetal bovine serum (FBS) were purchased from Invitrogen. Charcoal-stripped fetal bovine serum (CS-FBS) was purchased from Biowest. PVDF membrane, leupeptin, aprotinin, phenylmethylsulfonyl fluoride (PMSF) and X-tremeGENE siRNA Transfection Reagent were purchased from Roche. RNA PCR Kit (AMV) Ver.3.0 was purchased from TaKaRa. Polinl-2-plus kit was a product of GBI. Anti-phospho-ERK1/2 (Thr202/Tyr204) and find more anti-ERK1/2 antibodies were purchased from Cell Signaling Technology. ERα siRNA, mouse monoclonal anti-ERα, anti-GAPDH, SC75741 horseradish peroxidase (HRP)-conjugated goat anti-rabbit and HRP-conjugated goat anti-mouse IgG secondary antibodies were from Santa Cruz Biotechnology. Rabbit polyclonal

anti-HBO1 antibody (Catalog No: 13751-1-AP) was purchased from Protein Tech Group, Inc. The enhanced chemiluminescence (ECL) assay kit was purchased from Tiangen. Dual-luciferase reporter assay system was bought from Promega. ICI 182,780 was purchased from Tocris Bioscience. Cell culture and transfection Human MCF-7, T47 D, MDA-MB-453 and MDA-MB-435 breast cancer cells were obtained from the Cell Bank of Type Culture Collection of Chinese Academy of Sciences. MCF-7 cells were cultured in DMEM supplemented with 10% fetal calf serum (FBS), 10 ug/ml of insulin, 100 U/ml of penicillin and 50 ug/ml of streptomycin. T47 D cells were maintained in DMEM supplemented with 10% FBS, 100 U/ml of penicillin and 50 ug/ml streptomycin. SiRNA was transfected with X-tremeGENE siRNA Transfection Reagent according to the manufacture’s instructions. Western blot analyses Proteins were detected

by western blot analysis as described previously [10]. The cells were for lysed by lysis buffer, separated in 10% SDS-PAGE and then transferred to a PVDF membrane. The membrane was incubated with primary antibody followed by incubation with horseradish peroxidase-conjugated secondary antibody. Then the membrane was developed using the ECL detection system. Tissue samples 112 primary breast cancer specimens were consecutively obtained from pathological XAV-939 archives of Huashan Hospital, Fudan University from 2005 to 2008. There was no any bias for selection. Tissues were formalin-fixed and paraffin-embedded for histopathologic diagnosis and immunohistochemical study. The malignancy degree of tumor was scored according to the Scarff-Bloom-Richardson system. Immunohistochemistry (IHC) Serial sections (5 μm thick) were mounted on glass slides coated with 10% polylysine.