title: Cholesterol biosynthesis pathway as a novel mechanism of resistance to estrogen deprivation in estrogen receptor-positive breast cancer.
abstract: Therapies targeting estrogenic stimulation in estrogen receptor-positive (ER+) breast cancer (BC) reduce mortality, but resistance remains a major clinical problem. Molecular studies have shown few high-frequency mutations to be associated with endocrine resistance. In contrast, expression profiling of primary ER+ BC samples has identified several promising signatures/networks for targeting.
  
  
  
  To identify common adaptive mechanisms associated with resistance to aromatase inhibitors (AIs), we assessed changes in global gene expression during adaptation to long-term estrogen deprivation (LTED) in a panel of ER+ BC cell lines cultured in 2D on plastic (MCF7, T47D, HCC1428, SUM44 and ZR75.1) or in 3D on collagen (MCF7) to model the stromal compartment. Furthermore, dimethyl labelling followed by LC-MS/MS was used to assess global changes in protein abundance. The role of target genes/proteins on proliferation, ER-mediated transcription and recruitment of ER to target gene promoters was analysed.
  
  
  
  The cholesterol biosynthesis pathway was the common upregulated pathway in the ER+ LTED but not the ER- LTED cell lines, suggesting a potential mechanism dependent on continued ER expression. Targeting the individual genes of the cholesterol biosynthesis pathway with siRNAs caused a 30-50 % drop in proliferation. Further analysis showed increased expression of 25-hydroxycholesterol (HC) in the MCF7 LTED cells. Exogenous 25-HC or 27-HC increased ER-mediated transcription and expression of the endogenous estrogen-regulated gene TFF1 in ER+ LTED cells but not in the ER- LTED cells. Additionally, recruitment of the ER and CREB-binding protein (CBP) to the TFF1 and GREB1 promoters was increased upon treatment with 25-HC and 27-HC. In-silico analysis of two independent studies of primary ER+ BC patients treated with neoadjuvant AIs showed that increased expression of MSMO1, EBP, LBR and SQLE enzymes, required for cholesterol synthesis and increased in our in-vitro models, was significantly associated with poor response to endocrine therapy.
  
  
  
  Taken together, these data provide support for the role of cholesterol biosynthesis enzymes and the cholesterol metabolites, 25-HC and 27-HC, in a novel mechanism of resistance to endocrine therapy in ER+ BC that has potential as a therapeutic target.
authors.affiliation: The Breast Cancer Now Toby Robins Research Centre, The Institute of Cancer Research, London, SW3 6JB, UK.
authors.forename: Nikiana
authors.initials: N
authors.lastname: Simigdala
authors.affiliation: The Breast Cancer Now Toby Robins Research Centre, The Institute of Cancer Research, London, SW3 6JB, UK.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Gao
authors.affiliation: The Breast Cancer Now Toby Robins Research Centre, The Institute of Cancer Research, London, SW3 6JB, UK.
authors.forename: Sunil
authors.initials: S
authors.lastname: Pancholi
authors.affiliation: Department of Chemistry, University of Oslo, 0371, Oslo, Norway.
authors.forename: Hanne
authors.initials: H
authors.lastname: Roberg-Larsen
authors.affiliation: The Breast Cancer Now Toby Robins Research Centre, The Institute of Cancer Research, London, SW3 6JB, UK.
authors.forename: Marketa
authors.initials: M
authors.lastname: Zvelebil
authors.affiliation: The Breast Cancer Now Toby Robins Research Centre, The Institute of Cancer Research, London, SW3 6JB, UK.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Ribas
authors.affiliation: The Breast Cancer Now Toby Robins Research Centre, The Institute of Cancer Research, London, SW3 6JB, UK.|Academic Department of Biochemistry, Royal Marsden Hospital, London, SW3 6JJ, UK.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Folkerd
authors.affiliation: Proteomics Core Facility, Institute of Cancer Research, London, SW3 6JB, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Thompson
authors.affiliation: Proteomics Core Facility, Institute of Cancer Research, London, SW3 6JB, UK.
authors.forename: Amandeep
authors.initials: A
authors.lastname: Bhamra
authors.affiliation: The Breast Cancer Now Toby Robins Research Centre, The Institute of Cancer Research, London, SW3 6JB, UK.|Academic Department of Biochemistry, Royal Marsden Hospital, London, SW3 6JJ, UK.
authors.forename: Mitch
authors.initials: M
authors.lastname: Dowsett
authors.affiliation: The Breast Cancer Now Toby Robins Research Centre, The Institute of Cancer Research, London, SW3 6JB, UK. lesley-ann.martin@icr.ac.uk.
authors.forename: Lesley-Ann
authors.initials: LA
authors.lastname: Martin
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology* / Q000627:therapeutic use; D015415:Biomarkers; D053898:Biosynthetic Pathways; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000401:mortality; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002784:Cholesterol / Q000096:biosynthesis*; D002788:Cholesterol Esters / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D004967:Estrogens / Q000378:metabolism*; D005260:Female; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D010641:Phenotype; D011379:Prognosis; D020543:Proteome; D040901:Proteomics / Q000379:methods; D034622:RNA Interference; D011960:Receptors, Estrogen / Q000378:metabolism*; D059467:Transcriptome; D016896:Treatment Outcome
chemical_list: D018931:Antineoplastic Agents, Hormonal; D015415:Biomarkers; D002788:Cholesterol Esters; D004967:Estrogens; D020543:Proteome; D011960:Receptors, Estrogen; D002784:Cholesterol
keywords: Breast cancer; Cholesterol biosynthesis; Estrogen receptor; Oxysterol; Proteomics; Transcriptomics