title: SpliceArray profiling of breast cancer reveals a novel variant of NCOR2/SMRT that is associated with tamoxifen resistance and control of ERα transcriptional activity.
abstract: Gene expression profiling aimed at classifying and prognosing breast cancer has yielded signatures with little, if any, concordance. However, expression arrays used in these studies do not discriminate alternate RNA splice isoforms that vary widely in cancer and may resolve this problem. In this study, we profiled splice isoforms in a panel of tamoxifen-sensitive and -resistant cell lines, defining a novel variant (BQ323636.1) of the nuclear receptor corepressor 2 (NCOR2) that was associated with tamoxifen resistance. Overexpression of this variant in a tamoxifen-sensitive cell line induced its resistance to tamoxifen. We confirmed our initial findings from cell lines in 77 breast tumors from a Chinese cohort, where BQ323636.1 expression was higher in tamoxifen-resistant patients than tamoxifen-sensitive patients. For patients who were estrogen receptor (ER)-positive and had received tamoxifen treatment, higher BQ323636.1 expression level correlated with distant metastasis. High expression level of BQ323636.1 was found to be associated with poorer overall and disease-free survival for patients who had received tamoxifen treatment. Notably, higher BQ323636.1 versus NCOR2 wild-type ratio was also associated with negative ER and progesterone receptor (PR) status, and triple-negative status (ER-/PR-/HER2- receptor status). Mechanistic investigations showed that under conditions of tamoxifen exposure, BQ323636.1 suppressed the transcriptional activity of ERα, exhibiting promoter-regulating functions. Our findings highlight a novel splice variant of the ERα corepressor NCOR2 as a candidate biomarker in breast cancer that not only predicts tamoxifen response but may be targeted to overcome tamoxifen resistance.
authors.affiliation: Department of Pathology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Luduo
authors.initials: L
authors.lastname: Zhang
authors.forename: Chun
authors.initials: C
authors.lastname: Gong
authors.forename: Samantha L Y
authors.initials: SL
authors.lastname: Lau
authors.forename: Nan
authors.initials: N
authors.lastname: Yang
authors.forename: Oscar G W
authors.initials: OG
authors.lastname: Wong
authors.forename: Annie N Y
authors.initials: AN
authors.lastname: Cheung
authors.forename: Janice W H
authors.initials: JW
authors.lastname: Tsang
authors.forename: Kelvin Y K
authors.initials: KY
authors.lastname: Chan
authors.forename: Ui-Soon
authors.initials: US
authors.lastname: Khoo
mesh_terms: D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D047628:Estrogen Receptor alpha / Q000096:biosynthesis* / Q000235:genetics; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D056985:Nuclear Receptor Co-Repressor 2 / Q000235:genetics*; D020033:Protein Isoforms; D060888:Real-Time Polymerase Chain Reaction; D020845:Selective Estrogen Receptor Modulators / Q000627:therapeutic use; D013629:Tamoxifen / Q000627:therapeutic use; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D014408:Biomarkers, Tumor; D047628:Estrogen Receptor alpha; C539130:NCOR2 protein, human; D056985:Nuclear Receptor Co-Repressor 2; D020033:Protein Isoforms; D020845:Selective Estrogen Receptor Modulators; D013629:Tamoxifen