title: Antiestrogen Resistant Cell Lines Expressing Estrogen Receptor α Mutations Upregulate the Unfolded Protein Response and are Killed by BHPI.
abstract: Outgrowth of metastases expressing ERα mutations Y537S and D538G is common after endocrine therapy for estrogen receptor α (ERα) positive breast cancer. The effect of replacing wild type ERα in breast cancer cells with these mutations was unclear. We used the CRISPR-Cas9 genome editing system and homology directed repair to isolate and characterize 14 T47D cell lines in which ERαY537S or ERαD538G replace one or both wild-type ERα genes. In 2-dimensional, and in quantitative anchorage-independent 3-dimensional cell culture, ERαY537S and ERαD538G cells exhibited estrogen-independent growth. A progestin further increased their already substantial proliferation in micromolar 4-hydroxytamoxifen and fulvestrant/ICI 182,780 (ICI). Our recently described ERα biomodulator, BHPI, which hyperactivates the unfolded protein response (UPR), completely blocked proliferation. In ERαY537S and ERαD538G cells, estrogen-ERα target genes were constitutively active and partially antiestrogen resistant. The UPR marker sp-XBP1 was constitutively activated in ERαY537S cells and further induced by progesterone in both cell lines. UPR-regulated genes associated with tamoxifen resistance, including the oncogenic chaperone BiP/GRP78, were upregulated. ICI displayed a greater than 2 fold reduction in its ability to induce ERαY537S and ERαD538G degradation. Progestins, UPR activation and perhaps reduced ICI-stimulated ERα degradation likely contribute to antiestrogen resistance seen in ERαY537S and ERαD538G cells.
authors.affiliation: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Chengjian
authors.initials: C
authors.lastname: Mao
authors.affiliation: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Mara
authors.initials: M
authors.lastname: Livezey
authors.affiliation: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Ji Eun
authors.initials: JE
authors.lastname: Kim
authors.affiliation: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Shapiro
mesh_terms: D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000037:antagonists & inhibitors / Q000235:genetics*; D005260:Female; D000077267:Fulvestrant; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D009154:Mutation; D011372:Progestins / Q000494:pharmacology; D013629:Tamoxifen / Q000031:analogs & derivatives / Q000494:pharmacology; D056811:Unfolded Protein Response
chemical_list: C000599673:3,3-bis(4-hydroxyphenyl)-7-methyl-1,3-dihydro-2H-indol-2-one; C506487:ESR1 protein, human; D000091342:Endoplasmic Reticulum Chaperone BiP; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; C000717247:HSPA5 protein, human; D007211:Indoles; D011372:Progestins; D013629:Tamoxifen; C016601:afimoxifene; D000077267:Fulvestrant; D004958:Estradiol