title: Genetic screen identifies insulin-like growth factor binding protein 5 as a modulator of tamoxifen resistance in breast cancer.
abstract: Tamoxifen resistance is one of the overarching challenges in the treatment of patients with estrogen receptor (ER)-positive breast cancer. Through a genome-wide RNA interference screen to discover genes responsible for tamoxifen resistance in vitro, we identified insulin-like growth factor binding protein 5 (IGFBP5) as a determinant of drug sensitivity. Specific knockdown of IGFBP5 by retroviral infection with short hairpin RNA-expressing cassette in MCF7 human breast cancer cells (pRS-shIGFBP5) conferred tamoxifen resistance in vitro due to concomitant loss of ERalpha expression and signaling. IGFBP5 expression was also reduced in MCF7 cells selected for tamoxifen resistance in culture (TAMR). Both tamoxifen-resistant MCF7-TAMR and MCF7-pRS-shIGFBP5 cells could be resensitized to drug by treatment with exogenous recombinant IGFBP5 (rIGFBP5) protein. Treatment with rIGFBP5 protein in mouse tumor xenografts reversed the in vivo tamoxifen resistance of MCF7-pRS-shIGFBP5 cell-derived tumors by reducing tumor cell proliferation. IGFBP5 immunohistochemical staining in a cohort of 153 breast cancer patients showed that low IGFBP5 expression was associated with shorter overall survival after tamoxifen therapy. Thus, IGFBP5 warrants investigation as an agent to reverse tamoxifen resistance.
authors.affiliation: Department of Biochemistry and Molecular Biology, Laboratory Medicine, Clark H Smith Brain Tumour Centre, and Southern Alberta Cancer Research Institute, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Bo Young
authors.initials: BY
authors.lastname: Ahn
authors.forename: Adam N
authors.initials: AN
authors.lastname: Elwi
authors.forename: Byoungchun
authors.initials: B
authors.lastname: Lee
authors.forename: Diane L N
authors.initials: DL
authors.lastname: Trinh
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Klimowicz
authors.forename: Annie
authors.initials: A
authors.lastname: Yau
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Chan
authors.forename: Anthony
authors.initials: A
authors.lastname: Magliocco
authors.forename: Sung-Woo
authors.initials: SW
authors.lastname: Kim
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D015331:Cohort Studies; D019008:Drug Resistance, Neoplasm; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000378:metabolism*; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D013629:Tamoxifen / Q000494:pharmacology*
chemical_list: D018975:Insulin-Like Growth Factor Binding Protein 5; D013629:Tamoxifen