title: Fulvestrant regulates epidermal growth factor (EGF) family ligands to activate EGF receptor (EGFR) signaling in breast cancer cells.
abstract: Estrogen receptor-α (ER) targeted therapies are routinely used to treat breast cancer. However, patient responses are limited by resistance to endocrine therapy. Breast cancer cells resistant to the pure steroidal ER antagonist fulvestrant (fulv) demonstrate increased activation of epidermal growth factor receptor (EGFR) family members and downstream ERK signaling. In this study, we investigated the effects of fulv on EGFR signaling and ligand regulation in several breast cancer cell lines. EGFR/HER2/HER3 phosphorylation and ERK1,2 activation were seen after 24-48 h after fulvestrant treatment in ER-positive breast cancer cell lines. 4-Hydroxy-tamoxifen and estradiol did not cause EGFR activation. Fulvestrant did not affect EGFR expression. Cycloheximide abolished the ability of fulv to activate EGFR suggesting the autocrine production of EGFR ligands might be responsible for fulvestrant induced EGFR signaling. qRT-PCR results showed fulv differentially regulated EGFR ligands; HB-EGF mRNA was increased, while amphiregulin and epiregulin mRNAs were decreased. Fulvestrant induced EGFR activation and upregulation of EGFR ligands were ER dependent since fulv treatment in C4-12, an ER-negative cell line derivative of MCF-7 cells, did not result in EGFR activation or change in ligand mRNA levels. ER downregulation by siRNA induced similar EGFR activation and regulation of EGFR ligands as fulvestrant. Neutralizing HB-EGF antibody blocked fulv-induced EGFR activation. Combination of fulv and EGFR family tyrosine kinase inhibitors (erlotinib and lapatinib) significantly decreased EGFR signaling and cell survival. In conclusion, fulvestrant-activated EGFR family members accompanied by ER dependent upregulation of HB-EGF within 48 h. EGF receptor or ligand inhibition might enhance or prolong the therapeutic effects of targeting ER by fulvestrant in breast cancer.
authors.affiliation: Department of Medicine, Masonic Cancer Center, University of Minnesota, Minneapolis, MN 55455, USA.
authors.forename: Xihong
authors.initials: X
authors.lastname: Zhang
authors.forename: Michael R
authors.initials: MR
authors.lastname: Diaz
authors.forename: Douglas
authors.initials: D
authors.lastname: Yee
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D005260:Female; D000077267:Fulvestrant; D015972:Gene Expression Regulation, Neoplastic; D066257:Heparin-binding EGF-like Growth Factor; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D008024:Ligands; D061986:MCF-7 Cells; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics; D011960:Receptors, Estrogen / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D018931:Antineoplastic Agents, Hormonal; C587883:HBEGF protein, human; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D008024:Ligands; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D000077267:Fulvestrant; D004958:Estradiol; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D048052:Mitogen-Activated Protein Kinase 3