title: Bidirectional interactions between the estrogen receptor and the cerbB-2 signaling pathways: heregulin inhibits estrogenic effects in breast cancer cells.
abstract: The responsiveness of estrogen receptor (ER)-positive breast cancer to endocrine therapy is frequently reduced in cells over-expressing c-erbB-2. Stimulation of ER suppresses c-erbB-2, indicating that estrogen controls the activity of c-erbB-2. Heregulin (HRG) has been described to bind to c-erbB-3/c-erbB-4 and to stimulate c-erbB-2. Here we describe the effects of HRG on cell growth and on ER and c-erbB-2 expression in breast cancer cell lines containing distinct levels of c-erbB-2 and ER (BT-474: c-erbB-2 , ER+; MDA-MB-361: c-erbB-2++, ER++; MCF-7: c-erbB-2+, ER ). Proliferation of estrogen-stimulated, c-erbB-2 and ER-positive cells is inhibited by HRG in a dose-dependent manner. In addition, HRG dose-dependently inhibits ER expression. Estrogen, however, inhibits c-erbB-2. Estrogen-mediated down-regulation of c-erbB-2 is most pronounced in MCF-7 but weaker in BT-474. In the latter cells HRG efficiently blocks the estrogenic effect on c-erbB-2. In MCF-7 cells, however, the inhibition of c-erbB-2 cannot be completely reverted by HRG. This modulation occurs in all 3 cell lines at protein, RNA and transcriptional levels, suggesting that the activity of the c-erbB-2 promoter, which contains an estrogen-responsive region, is affected by HRG. The intensity of the mutual inhibition between the HRG/c-erbB-2 and the estrogen/ER system depends on the relative levels of ER and c-erbB-2 expression in the respective cell lines.
authors.affiliation: Department of Internal Medicine I, University of Vienna, Austria.
authors.forename: T W
authors.initials: TW
authors.lastname: Grunt
authors.forename: M
authors.initials: M
authors.lastname: Saceda
authors.forename: M B
authors.initials: MB
authors.lastname: Martin
authors.forename: R
authors.initials: R
authors.lastname: Lupu
authors.forename: E
authors.initials: E
authors.lastname: Dittrich
authors.forename: G
authors.initials: G
authors.lastname: Krupitza
authors.forename: H
authors.initials: H
authors.lastname: Harant
authors.forename: H
authors.initials: H
authors.lastname: Huber
authors.forename: C
authors.initials: C
authors.lastname: Dittrich
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000648:ultrastructure; D002455:Cell Division / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D004347:Drug Interactions; D004958:Estradiol / Q000494:pharmacology*; D004965:Estrogen Antagonists / Q000494:pharmacology*; D006023:Glycoproteins / Q000494:pharmacology*; D006133:Growth Substances / Q000494:pharmacology*; D006801:Humans; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy / Q000378:metabolism* / Q000648:ultrastructure; D020880:Neuregulins; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology*; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D000970:Antineoplastic Agents; D004958:Estradiol; D004965:Estrogen Antagonists; D006023:Glycoproteins; D006133:Growth Substances; D020880:Neuregulins; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen