title: Reversal of an antiestrogen-mediated cell cycle arrest of MCF-7 cells by viral tumor antigens requires the retinoblastoma protein-binding domain.
abstract: Proliferation of MCF-7 cells is estrogen dependent and antiestrogen sensitive. In the absence of estrogens or presence of antiestrogens MCF-7 cells arrest in the G1 phase of the cell cycle, and this arrest is associated with an accumulation of the active, hypophosphorylated form of the retinoblastoma protein (pRb). Because active pRb negatively regulates passage from G1 to S phase, this suggests that pRb is a crucial target of estrogen action, and that its inactivation might lead to antiestrogen resistance. We tested this hypothesis by expressing viral tumor antigens (T antigens), which bind and inactivate pRb, in MCF-7 cells, and determining the effects on cell proliferation in the presence of antiestrogens. The results of these experiments demonstrate that T antigen expression confers antiestrogen resistance to MCF-7 cells. Using a panel of mutant T antigens, we further demonstrate that the pRb-binding, but not the p53 binding domain is required to confer antiestrogen resistance. Thus, pRb is an important target of estrogen action, and its inactivation can contribute to the development of antiestrogen resistance.
authors.affiliation: Department of Biochemistry, Michigan State University, East Lansing 48824-1101, USA.
authors.forename: H
authors.initials: H
authors.lastname: Varma
authors.forename: S E
authors.initials: SE
authors.lastname: Conrad
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology*; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism / Q000502:physiology*; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000473:pathology*; D019938:Cyclin D1 / Q000502:physiology; D019008:Drug Resistance, Neoplasm; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology*; D004967:Estrogens; D005260:Female; D000077267:Fulvestrant; D016193:G1 Phase / Q000187:drug effects; D006801:Humans; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D009376:Neoplasms, Hormone-Dependent / Q000473:pathology*; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000502:physiology; D016160:Retinoblastoma Protein / Q000037:antagonists & inhibitors / Q000502:physiology*; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000952:Antigens, Polyomavirus Transforming; D018931:Antineoplastic Agents, Hormonal; D020847:Estrogen Receptor Modulators; D004967:Estrogens; D009363:Neoplasm Proteins; D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein; D013629:Tamoxifen; D019938:Cyclin D1; C016601:afimoxifene; D000077267:Fulvestrant; D004958:Estradiol